Polypropylene industrial silk production process!

Raw material preparation

Raw material selection: The production of Polypropylene industrial silk mainly uses isotactic polypropylene resin as raw material. This resin has a high isotropy, and the isotropy is generally required to be above 95% to ensure that the fiber has good crystallization properties and strength. In order to meet the performance requirements of different products, a small number of additives are also added, such as antioxidants to prevent the oxidative degradation of polypropylene during processing, light stabilizers to improve the fiber's UV resistance, and color masterbatches added as needed to give the fiber color.

Raw material drying: polypropylene raw materials are easy to absorb water during storage and transportation, and water melting at high temperature will lead to the hydrolysis of polypropylene molecular chain, reducing the quality of the fiber. Therefore, raw materials need to be dried before production. Usually using hot air circulation drying equipment, the polypropylene slice is dried at a temperature of 80-100 °C for 2-4 hours, so that the moisture content is reduced to less than 0.03%.

Melt extrusion

Screw extruder: The dried polypropylene slices go into the screw extruder. The screw extruder pushes the raw material forward through the rotation of the screw, while the heater outside the screw heats the raw material. With the rotation of the screw, the raw material is gradually compacted and melted in the screw groove. The structural design of the screw is crucial to the conveying, melting and mixing effect of the material, generally using a gradual type of screw, the depth of the screw groove gradually becomes shallow from the feeding section to the homogenization section, and the compression ratio is usually between 3-5 to ensure that the polypropylene slice is fully melted and evenly mixed.

Temperature control: The temperature of each stage of the extruder needs to be precisely controlled. The general feeding section temperature is slightly lower than the melting point of polypropylene, about 160-180 °C, so that the raw material is initially softened; The temperature of the compression section is gradually increased to 200-220 °C to promote the complete melting of the raw material; The temperature of the homogenization section is controlled at 210-230 °C to ensure uniform melt temperature and good fluidity. The residence time of melt in the extruder is generally controlled at 3-5 minutes to avoid degradation caused by too long residence time.

spinning

Spinning assembly: After the molten polypropylene melt is extruded from the extruder, it passes through the melt pipe into the spinning assembly. The spinning assembly mainly comprises a filter device and a spinneret. The filter device usually uses a multi-layer metal filter screen with a mesh number of 100-500 mesh to remove impurities and unmelted particles in the melt and prevent blockage of the spinners. The shape and size of the spinneret hole on the spinneret determines the cross-section shape and monofilament size of the polypropylene industrial yarn. The common spinneret holes are round, and special shaped spinneret holes are used for the production of special-shaped fibers, such as triangles and trilobes. The diameter of the spinneret hole is generally between 0.2 and 0.8 mm.

Spinning temperature and pressure: The spinning temperature is generally controlled at 230-250 °C to ensure that the melt has the right flow and can be successfully extruded from the spinneret hole. The spinning pressure is adjusted according to the resistance of the spinneret and the flow rate of the melt, generally between 10-20MPa. Higher spinning pressure helps to improve the melt extrusion speed, thereby improving the production efficiency, but too high pressure may lead to instability of the melt and affect the quality of the filament.

Cooling molding: The thin stream of melt extruded from the spinneret hole is rapidly cooled and solidified in the air to form the primary fiber. The cooling method generally adopts side-blowing cooling, and the cooling speed and uniformity of the fiber are controlled by adjusting the wind temperature, wind speed and air volume. The wind temperature is generally 18-25 °C, the wind speed is 0.3-0.8 m/s, and the air volume is adjusted according to the number of spinning points and the specifications of the strips. Suitable cooling conditions can make the fiber form a good crystalline structure, which has an important effect on the subsequent properties of the fiber.

stretch

Tensile equipment: the strength of the primary fiber is low, the crystallinity is low, and the performance of the fiber needs to be improved by stretching. Drawing is usually carried out on multistage drawing equipment, which generally includes two stages: preheat drawing and main drawing. The preheating and stretching equipment mostly uses hot plates or hot rollers to heat the fiber to a glass transition temperature close to the polypropylene (about 100-120 °C), so that the fiber has good plasticity and is easy to stretch. The main drawing equipment stretches the fiber through multiple sets of drawing rollers, and the drawing multiple is generally between 3-8 times. The speed difference of the stretch roller determines the stretch ratio of the fiber. The stability of the stretch ratio can be ensured by accurately controlling the speed of the stretch roller.

Drawing process parameters: drawing temperature, drawing speed and drawing multiple are the key parameters of drawing process. The tensile temperature has an important effect on the tensile property and structure of the fiber, and the appropriate tensile temperature can make the molecular chain of the fiber better orientation and crystallization. The stretching speed is generally between 500-1500 m/min, too fast stretching speed may lead to fiber fracture, too slow will affect the production efficiency. The choice of tensile multiple depends on the final performance requirements of the product, a higher tensile multiple can improve the strength and modulus of the fiber, but at the same time it will reduce the elongation of the fiber.

Heat setting

Purpose of heat setting: There is a certain internal stress in the stretched fiber, and the crystalline structure is not perfect. The purpose of heat setting is to eliminate the internal stress of the fiber, stabilize the size and structure of the fiber, and further improve the crystallinity and thermal stability of the fiber. Heat setting is generally carried out on heat setting equipment, such as hot boxes, hot rollers, etc

Heat setting process: The heat setting temperature is generally between 140-180 °C, slightly lower than the melting point of polypropylene. The fibers remain in the heat setting equipment for a certain amount of time, usually 5-15 seconds, so that the molecular chain segments inside the fibers can be fully adjusted and crystallized. During the heat setting process, the fiber needs to maintain a certain tension to prevent fiber shrinkage and deformation. The dimensional stability, strength retention rate and fatigue resistance of industrial polypropylene fibers can be significantly improved by appropriate heat setting process.

wind

Winding equipment: The heat-shaped polypropylene industrial wire is wound into bobbin through the winding equipment. The winding equipment generally uses a precision winding head, which can accurately control the winding speed, tension and winding Angle to ensure that the winding formed bobbin has a good appearance and internal quality. The winding speed is adjusted according to the fiber specification and production efficiency, generally between 800-2000 m/min.

Winding tension control: Winding tension has an important effect on the quality of the fiber and the stability of the packaging. If the winding tension is too large, the fiber is easy to be pulled off or produce internal stress, which affects the subsequent processing performance of the fiber. The winding tension is too small, the winding is loose, and it is easy to have problems such as collapsing edge and dropping ring. During the winding process, the tension of the fiber is monitored by the tension sensor in real time, and the winding speed is automatically adjusted by the control system or the brake device is applied to keep the winding tension stable. The wrapped bobbin can be packed and stored after it passes the quality inspection.

Each link of the production process of polypropylene industrial silk is related to each other and affects each other. Only by accurately controlling the process parameters can we produce high-quality and high-performance polypropylene industrial silk products to meet the application needs of different industrial fields.

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