A raw material and spinning process for preparing medium-high strength polyethylene fiber by melt spinning

Abstract

The present invention relates to a raw material for preparing medium-high strength polyethylene fiber by melt spinning, which is mainly composed of polyethylene with an intrinsic viscosity of 4-12 dl / g, the content of polyethylene in the raw material is not less than 99%, and its melt index is 0.1-1.0 g / 10min (190°C, weight of 5kg). The polyethylene includes two components, one is polyethylene A material with an intrinsic viscosity of 5-12 dl / g and a molecular weight distribution index of ≤4, and the other is polyethylene B material with an intrinsic viscosity of 4-7 dl / g and a molecular weight distribution index of ≥20. The raw material may also contain an antioxidant, and the mass fractions of polyethylene A material, polyethylene B material, and antioxidant in the raw material are 50-95%, 5-50%, and 0-1%, respectively. Compared with the prior art, the present invention can prepare a spinning raw material with a controllable melt index by combining polyethylene raw materials with different intrinsic viscosities and different molecular weight distribution indexes without adding diluents or various additives.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength fiber materials, and specifically relates to a raw material and a spinning process for preparing medium- and high-strength polyethylene fibers by melt spinning. Background Art

[0002] Ultra-high molecular weight polyethylene fiber is the third high-performance fiber after carbon fiber and aramid. It has the advantages of light weight, high strength, high modulus, and impact resistance. It is an indispensable strategic material in the national defense and military industry and high-tech fields, and is also a basic material urgently needed for the development of the national economy.

[0003] At present, the UHMWPE fiber manufacturing methods that have entered the industrial production stage in the world mainly include gel spinning and melt spinning. In the gel spinning process, a large amount of organic solvents are used, the UHMWPE content is low, and the equipment is complex, which easily leads to high energy consumption and environmental problems, and high production costs. The main product specifications are 100D-1600D multifilament fibers, with a breaking strength of generally above 25cN / dtex, which are suitable for high-end application scenarios.

[0004] The melt spinning process does not require solvents or extractants, and does not require corresponding dissolution and extraction processes, so the equipment is compact, the production process is shortened, the cost is reduced, and the production process is pollution-free, which complies with national environmental protection policies. Therefore, studying the melt spinning process to prepare UHMWPE fibers can achieve low-cost production of medium and high-strength UHMWPE fibers, thereby broadening the application range of UHMWPE fibers in the civilian field.

[0005] In previous studies on ultra-high molecular weight polyethylene melt spinning, a single ultra-high molecular weight polyethylene raw material is often used for melt extrusion. Due to the poor fluidity of the melt, only ultra-high pressure spinning can be carried out, and industrial production cannot be achieved. When low molecular weight polyethylene is used for melt spinning, due to the large number of entanglement points between molecular chains in the molten polymer, the degree of crystal orientation is low, and high-strength fibers cannot be obtained.

[0006] In view of the disadvantages of ultra-high molecular weight polyethylene (UHMWPE) of extremely high melt viscosity and extremely poor fluidity, when preparing polyethylene fibers by melt spinning, the prior art usually adds diluents or additives during the spinning process to improve the fluidity of polyethylene. Adding diluents can easily cause the volatilization of diluents in subsequent processing steps, which is not friendly to the environment, and the solvent needs to be recovered, which greatly increases the cost; adding additives (fluorine, silicone, metal, polymer macromolecules, etc.) will affect the spinnability of the fiber due to the problems of smoke and broken fibers during the extrusion process. Summary of the invention

[0007] In view of the problems of poor melt fluidity and low stretching multiple of primary filaments in the process of preparing medium- and high-strength polyethylene fibers from ultra-high molecular weight polyethylene by melt spinning, the present invention provides a raw material and a spinning method for preparing medium- and high-strength polyethylene fibers by melt spinning, and polyethylene fibers with a strength of 20-25 cN / dtex are prepared, and the production cost is low, the process is simple, and the fibers are energy-saving and environmentally friendly, which can meet the needs of low-end civilian fields.

[0008] The purpose of the present invention can be achieved by the following technical solutions: A raw material for preparing medium-high strength polyethylene fiber by melt spinning, mainly composed of polyethylene with an intrinsic viscosity of 4-12 dl / g, the content of polyethylene in the raw material is not less than 99%, and its melt index is 0.1-1.0 g / 10min (190°C, weight of 5kg). The polyethylene includes two components, one is polyethylene A material with an intrinsic viscosity of 5-12 dl / g and a molecular weight distribution index of ≤4, and the other is polyethylene B material with an intrinsic viscosity of 4-7 dl / g and a molecular weight distribution index of ≥20. The raw material may also contain an antioxidant, and the mass fractions of polyethylene A material, polyethylene B material, and antioxidant in the raw material are 50-95%, 5-50%, and 0-1%, respectively.

[0009] A spinning process for preparing medium-high strength polyethylene fibers by melt spinning, comprising the following steps: mixing the raw materials of the medium-high strength polyethylene fibers, and then melt spinning them with a screw extruder, cooling them in a water bath to obtain spun fibers; and subjecting the spun fibers to three-stage hot drawing to obtain medium-high strength polyethylene fibers. The aspect ratio of the screw extruder is ≥15, the spinneret aperture is ≥2mm, the spinneret stretching multiple is 9-11 times, the water bath temperature is 30-50°C, and the spun fibers are stretched 18-23 times.

[0010] Beneficial effects: Compared with the prior art, the present invention can prepare spinning raw materials with controllable melt index by combining polyethylene raw materials with different intrinsic viscosities and different molecular weight distribution indexes without adding diluents or various additives, while taking into account the tensile properties of the primary yarn and the performance of the final product, avoiding the potential harm to the environment and products caused by the introduction of diluents or various additives (fluorine, silicone, metal, polymer macromolecules, etc.). In addition, the production cost is low, the process is simple, and it is energy-saving and environmentally friendly. The strength of the polyethylene fiber prepared by melt spinning is between 20 and 25 cN / dtex, which can meet the needs of low-end civilian fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a comparative data table of the embodiments of the present invention. DETAILED DESCRIPTION Example

[0012] The weight ratio of each component of the medium-high strength polyethylene fiber melt spinning raw material is: polyethylene A 90%, polyethylene B 10%. The IV value (intrinsic viscosity) of polyethylene A is 5.2, the MDI value (molecular weight distribution index) is 2.3, and the IV value of polyethylene B is 6.9, and the MDI value is 28.6. After being mixed evenly in a high-speed mixer, the spinning raw material is obtained. The MI value (melt index) of the raw material at 190°C and a weight of 5kg is 0.72g / 10min.

[0013] The spinning process is as follows: melt spinning the spinning raw materials, the spinning temperature is 300°C, the spinneret stretching multiple is 10.2 times, the primary yarn stretching multiple is 22.5 times, and the obtained polyethylene fiber strength is 20.1 cN / dtex.

[0014] For details of embodiments 2 to 6, see the attached Figure 1 .

[0015] Comparative Example 1 The weight ratio of each component of the medium-high strength polyethylene fiber melt spinning raw material is: polyethylene A 99%, antioxidant B2251%, polyethylene A IV value 8.1, MDI value 2.9. After being mixed evenly in a high-speed mixer, the spinning raw material is obtained, and the MI value of the raw material at 190°C and a weight of 5kg is less than 0.1g / 10min.

[0016] The spinning process is to melt-spin the spinning raw materials. However, since the raw materials have poor fluidity in the molten state, spinning is not possible.

[0017] Comparative Example 2 The weight ratio of each component of the medium-high strength polyethylene fiber melt spinning raw material is: polyethylene B 99%, antioxidant B2251%, polyethylene B IV value 4.8, MDI value 26.5. After being mixed evenly in a high-speed mixer, the spinning raw material is obtained, and the MI value of the raw material at 190°C and a weight of 5kg is 1.8g / 10min.

[0018] The spinning process is as follows: melt spinning the spinning raw materials, the spinning temperature is 315°C, the spinneret stretching multiple is 9.2 times, the primary yarn stretching multiple is 18.2 times, and the obtained polyethylene fiber strength is 7.8 cN / dtex.

Claims

1. A raw material for preparing medium- and high-strength polyethylene fibers by melt spinning, mainly composed of polyethylene with an intrinsic viscosity of 4 to 12 dl / g, characterized in that: The content of polyethylene in the raw material is not less than 99%, and its melt index is 0.1-1.0 g / 10min; the polyethylene comprises two components, one is polyethylene A material with an intrinsic viscosity of 5-12 dl / g and a molecular weight distribution index of ≤4, and the other is polyethylene B material with an intrinsic viscosity of 4-7 dl / g and a molecular weight distribution index of ≥20; the raw material may also contain an antioxidant; the mass fractions of polyethylene A material, polyethylene B material and antioxidant in the raw material are 50-95%, 5-50% and 0-1% respectively.

2. A spinning process for preparing medium- and high-strength polyethylene fibers by melt spinning, characterized in that: The method comprises the following steps: mixing the raw materials of the medium-high strength polyethylene fibers as claimed in claims 1 to 4, melt spinning them with a screw extruder, cooling them in a water bath to obtain spun fibers; and subjecting the spun fibers to three-stage hot drawing to obtain medium-high strength polyethylene fibers.

3. The spinning process for preparing medium- and high-strength polyethylene fibers by melt spinning according to claim 2, characterized in that: The aspect ratio of the screw extruder is ≥15, the spinneret aperture is ≥2mm, the spinneret stretching multiple is 9~11 times, the water bath temperature is 30~50℃, and the primary yarn stretching multiple is 18~23 times.

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