A high-performance polyethylene flat filament product and its preparation and application

Abstract

The present invention relates to a high-performance polyethylene flat filament product and its preparation and application. The specific preparation process is as follows: (1) A mixed material of polyethylene raw material, color powder, and processing aids is fed into a screw extruder to extrude high-temperature polyethylene unstretched filaments; (2) The polyethylene unstretched filaments are kept at a high temperature and subjected to biaxial stretching in a molten state; (3) The filaments biaxially stretched in step (2) are subjected to secondary unidirectional multi-fold stretching through a hot runner; (4) The filaments after secondary unidirectional multi-fold stretching are subjected to hot stretching, and finally cut and wound up to obtain a high-performance polyethylene flat filament product. Compared with the prior art, the present invention can overcome the problems of the need for weaving of ultra-high molecular weight polyethylene flat medical suture, uneven surface, and complex production process of the fiber matrix used.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and relates to a high-performance polyethylene flat filament product and its preparation and application. Background Art

[0002] The cross-section of a medical suture is generally circular. The cross-sectional area of this type of suture is small, and the area in direct contact with human tissue is very small. When the tissue that the suture needs to fix is under great stress, such as in the application fields of rotator cuff injury, tendon injury, orthopedics, etc., it will cause a relatively large pressure of the surgical suture on the tissue per unit area. If the elasticity of the suture is insufficient, it will make the human tissue in a cutting state, easily causing secondary injury and being unfavorable for the postoperative recovery of the patient. A suture with a larger surface area in contact with human tissue (such as a flat shape) and having a certain elasticity is beneficial to reducing secondary injury and is also beneficial to the patient's recovery. In addition, during the surgical process, a colored suture has an obvious contrast with blood or the tissue in the operation area, which is beneficial for doctors to identify.

[0003] Most sutures with non-circular cross-sections are obtained by weaving. Chinese Patent CN107334502 B and US Patent US2005 / 0192631A1 prepared flat ribbon sutures including materials such as ultra-high molecular weight polyethylene (UHMWPE) by a weaving process.

[0004] Currently, it is reported that ultra-high molecular weight polyethylene sutures have higher tensile strength compared to other non-absorbable sutures, and ultra-high molecular weight polyethylene flat ribbon sutures are more suitable for high-strength suturing.

[0005] Although the flat ribbon suture prepared by the weaving process increases the contact area between the suture and the tissue, the surface of the weaving structure is not smooth, which is more difficult during the process of passing through the surgical needle hole and the surgical wound, easily causing tissue injury. At the same time, bacteria will be hidden in the pores, increasing the infection probability, and also increasing the process steps.

[0006] The ultra-high molecular weight polyethylene fiber used for weaving in the ultra-high molecular weight polyethylene suture flat ribbon suture is prepared by a solvent spinning process, with solvent residues, and is generally fine denier fiber, which is extremely easy to adsorb bacteria. At the same time, the ultra-high molecular weight polyethylene fiber product has an extremely low elongation at break and almost no elasticity, and is also easy to cause secondary injury to the tissue.

[0007] Therefore, in view of the above problems, it is necessary to develop a fiber matrix for manufacturing a colored non-absorbable medical suture with high strength, high elasticity, smooth surface, and large contact area, and its preparation method, which has a simple preparation process and is applied to the suturing work of damaged parts with higher requirements for suture strength. Summary of the Invention

[0008] The object of the present invention is to provide a high-performance polyethylene flat filament product and its preparation and application, which can be used in fields such as medical sutures, etc., so as to overcome the problems of the ultra-high molecular weight polyethylene flat medical suture that needs to be braided, has a non-smooth surface, and the production process of the fiber matrix used is complex.

[0009] The object of the present invention can be achieved by the following technical solutions:

[0010] One of the technical solutions of the present invention provides a preparation method of a high-performance polyethylene flat filament product, including the following steps:

[0011] (1) Feed the mixed material of polyethylene raw material, color powder, and processing aid into a screw extruder and extrude high-temperature polyethylene unstretched raw filaments.

[0012] (2) Keep the polyethylene unstretched raw filaments at a high temperature and perform biaxial stretching in a molten state.

[0013] (3) Subject the raw filaments after biaxial stretching in step (2) to secondary unidirectional multi-fold stretching through a hot runner.

[0014] (4) Subject the raw filaments after secondary unidirectional multi-fold stretching to hot stretching, and finally perform cutting and winding to obtain a high-performance polyethylene flat filament product.

[0015] Further, in step (1), during the high-temperature extrusion process, the temperature of the extrusion section of the screw extruder is 145 - 200 °C, preferably 150 °C - 180 °C, and the temperature from the melt pump to the die head is 145 - 220 °C, preferably 150 °C - 180 °C.

[0016] Further, in step (2), the high-temperature insulation is controlled at 60 - 150 °C, preferably 100 - 135 °C, and during the biaxial stretching process, the transverse stretching ratio is 1 - 5 times, and the longitudinal stretching ratio is 4 - 20 times.

[0017] Further, in step (3), the multiple of the secondary unidirectional multi-fold stretching is 5 - 25 times.

[0018] Further, in step (3), the temperature of the hot runner during the secondary unidirectional multi-fold stretching is 60 - 130 °C, preferably 100 - 120 °C.

[0019] Further, in step (4), the temperature of the hot stretching is 40 - 80 °C, and the amplitude is 1% - 5%.

[0020] Further, in step (1), the polyethylene raw material is polymerized using a single-site catalyst, with a weight-average molecular weight of 100,000 - 600,000, a molecular weight distribution less than 3 (i.e., the ratio of weight-average molecular weight to number-average molecular weight Mw / Mn < 3.0), the number of methyl groups per thousand carbons < 10, and a density > 0.93 g / cm 3. Further, the single-site catalyst is selected from metallocene catalysts or late transition metal catalysts, preferably a supported catalyst system.

[0021] Further, in step (1), the additive includes a mixture of an antioxidant and a surface lubricant, and the mass ratio of the antioxidant to the surface lubricant is 1:0.2 to 1:5.

[0022] Furthermore, the antioxidant is one or more of 2,6-di-tert-butyl-p-cresol, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];

[0023] The surface lubricant is one or more of titanate compounds, fluororubber compounds, stearate compounds, or aluminate compounds.

[0024] Further, in step (1), the die of the screw extruder is a rectangular wire outlet or an oval wire outlet. Among them, the thickness of the rectangular wire outlet is 0.1 mm - 20 mm, and the minimum diameter of the oval wire outlet is 1 - 30 mm.

[0025] The polyethylene obtained by polymerization with a single-site catalyst has a narrow molecular weight distribution. In the spinning process, polyethylene with a narrow molecular weight distribution has processability, and its mechanical properties are comparable to those of ultra-high molecular weight polyethylene. The present invention uses high molecular weight polyethylene with a molecular weight of 100,000 - 600,000 and polymerized with a single-site catalyst as a raw material to develop a high-performance polyethylene flat yarn product, which can be applied to fields such as medical sutures and is suitable for manufacturing the fiber matrix of flat colored medical sutures with high strength, smooth surface, and large contact area.

[0026] Generally speaking, polyethylene flat yarn products with a wide molecular weight distribution have low melt strength. When melt stretching is carried out at too high an extrusion temperature, problems such as uneven film thickness and film breakage will occur. Therefore, during the process of extruding the flat yarn or film into a film, biaxial stretching is first carried out at a lower temperature. However, due to the strong molecular chain movement ability and fast crystallization rate of polyethylene resin molecules, biaxial orientation of molecular chains will inevitably occur during the biaxial stretching process. During the process of forming flat yarn products by subjecting the film with biaxial molecular chain orientation to unidirectional hot stretching again, reorientation of molecular chains will form an uneven orientation structure, which greatly affects the tensile properties of the final flat yarn products. Innovatively, the present invention aims at the characteristic of high melt viscosity of narrow molecular weight distribution polyethylene obtained by single-site polymerization, and discovers that during the flat yarn extrusion process, by using a preheating device to perform biaxial stretching on the extruded flat yarn at a high temperature above 100°C, even higher than the melting temperature of polyethylene, the thickness of the flat yarn can be controlled without affecting the molecular chain structure of the polyethylene melt, and flat yarns or films can be formed, while no molecular chain orientation structure will be formed. The flat yarn products only form a uniform unidirectional orientation structure of molecular chains during subsequent high-ratio stretching, ensuring the mechanical properties of the flat yarn products. Since the present invention adopts a melt extrusion process and does not use solvents to swell and dissolve polyethylene, it is impossible to obtain a structure with completely disentangled molecular chains by the methods of swelling and dissolution like the solvent spinning process. The present invention uses single-site polyethylene as the raw material, and after extrusion, a high-temperature heat preservation device is adopted to ensure uniform temperature of the flat yarn during the stretching process in the molten state. At the same time, the molecular chain structure of the resin with high molecular weight and narrow molecular weight distribution is initially disentangled. The low entanglement state is conducive to the stretching of molecular chains. Biaxial stretching in the molten state is conducive to uniform stretching to obtain a uniform thickness, and the thickness of the flat yarn can be controlled. At the same time, the problem of surface breakage of the flat yarn caused by uneven temperature is overcome. The present invention discovers that the flat yarns obtained by biaxial stretching in the molten state have a higher draw ratio, better mechanical properties, and the obtained fibers have a higher melting point and a shorter melting range, which also proves that the obtained fibers have more uniform crystallization and more complete orientation.

[0027] The second technical solution of the present invention provides a high-performance polyethylene flat yarn product, which is prepared by using the preparation method described in any one of the above. The tensile strength of this polyethylene flat yarn product is greater than 15 cN / dtex, and the elongation at break reaches more than 5%.

[0028] The third technical solution of the present invention provides an application of a high-performance polyethylene flat yarn product, and this polyethylene flat yarn product is used for preparing medical sutures.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1) The high-performance polyethylene flat yarn uses polyethylene obtained by polymerization with a single-site catalyst as the raw material and is prepared by a melt extrusion process. The production process is simple, environmentally friendly, and has no solvent residue, meeting the conditions of the medical field.

[0031] 2) The tensile strength of the high-performance polyethylene flat yarn can reach over 15 cN / dtex. High strength, high elasticity, and non-absorbency ensure the stability of surgical suturing with medical sutures, reducing the probability of suture breakage during and after surgery.

[0032] 3) The high-performance polyethylene flat yarn can be used to prepare smooth-surfaced flat medical sutures without weaving, with fewer process steps; the suture surface is smooth, with small friction, causing less damage to the wound during suturing, and the smooth surface is conducive to reducing the hiding of bacteria, making it more suitable for suturing contaminated wounds. The flat cross-section is conducive to increasing the contact area between the suture and the tissue, reducing damage during suturing.

[0033] 4) The high-performance polyethylene flat yarn is a colored fiber, and the colored medical sutures prepared from the high-performance polyethylene flat yarn have an obvious color difference from tissues and blood, which is conducive to doctors' identification. Detailed implementation mode

[0034] The present invention will be described in detail below in conjunction with specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0035] In the following embodiments, the polyethylene resin can be obtained by ethylene polymerization using single-site polyethylene catalysts, including supported and unsupported metallocene-based catalysts or late transition metal catalysts, and the catalysts described in Patent CN109306029A can be used. Specifically, the preparation process of the polyethylene raw material in this embodiment is as follows:

[0036] Add n(methanol):n(original carrier Mg(OH)) = 5:1 to the reaction flask, heat up to 100 °C, add diisobutyl phthalate, stir at high speed, with a stirring speed of 500 revolutions per minute, react for 4 h, and after the reaction is completed, quickly press the obtained mixture into a large amount of -15 °C n-hexane for shaping to obtain a solid. Place the obtained solid in a nitrogen protection atmosphere and heat it to 60 °C, keep it for 5 h, to obtain the required carrier Mg1, with an average particle size of 150 μm and a specific surface area of 450 m / g. Dissolve the metal catalyst in toluene, add triethylaluminum, stir evenly to obtain a catalyst solution; add carrier Mg1 and stir evenly to obtain the supported catalyst C1. The ethylene pressurized polymerization reaction device is a 2 L stainless steel reaction kettle equipped with a water circulation temperature control system. Fill it with nitrogen, add 1 L of n-hexane, catalyst C1, and co-catalyst triethylaluminum under a nitrogen atmosphere, then replace the nitrogen with ethylene three times, adjust the ethylene inlet valve to keep the ethylene pressure constant at 1 Mpa, and carry out the polymerization reaction at 60 °C to 80 °C. After the reaction is completed, dry it to a constant weight and weigh it to obtain the polyethylene product.

[0037] The rest of the raw materials or processing techniques, unless otherwise specified, are conventional commercially available raw materials or conventional processing techniques in the art.

[0038] A method for preparing a high-performance polyethylene flat wire product, the process flow is as follows:

[0039] (1) A polyethylene raw material with a weight average molecular weight of 100,000-600,000 obtained by polymerization with a single active center catalyst is mixed with a color powder, a processing aid, etc., and the polyethylene unstretched raw yarn is extruded through a screw extruder at high temperature. The single active center catalyst is, for example, a metallocene catalyst or a late transition metal catalyst; the polyethylene raw material has a weight average molecular weight of 100,000-600,000, a weight average molecular weight to number average molecular weight ratio Mw / Mn <3.0, a thousand carbon methyl number <10, and a density >0.93 g / cm 3 The temperature of the extrusion section is 145°C-200°C, the temperature of the melt pump to the die is 145°C-220°C, and the die head of the screw extruder has a rectangular wire hole with a thickness of 0.1-20mm, or an elliptical wire hole with a minimum diameter of 1-30mm.

[0040] (2) After extrusion, the polyethylene passes through a high-temperature insulation device and is biaxially stretched in the molten state. The transverse stretching ratio is 1-5 times, and the longitudinal stretching ratio is 4-20 times. The temperature of the biaxial stretching hot channel is controlled at 100-135°C.

[0041] (3) After high-multiple stretching, the flat yarn or film is stretched again in one direction at high temperature through a hot tunnel, with the stretching multiple being 5-25 times. The temperature of the hot tunnel is controlled at 100-120°C.

[0042] (4) subjecting the highly drawn flat yarn or film to 1-5% heat stretching in a heat box at a stretching temperature of 40-80°C;

[0043] (5) Cutting and winding the high-temperature stretched polyethylene fibers to obtain high-performance polyethylene flat yarn products that can be used in high-strength medical sutures and other fields. The tensile strength of the single yarn can be greater than 15 cN / dtex, and the elongation at break can reach more than 5%.

[0044] The following are more detailed implementation cases, which further illustrate the technical solutions of the present invention and the technical effects that can be obtained.

[0045] The characterization data of the polyethylene fibers in the examples are obtained by the following method:

[0046] Tensile properties

[0047] The tensile strength and elongation at break of the finished yarn were tested using the method and equipment of ASTM D885M.

[0048] Example 1

[0049] The polyethylene raw material obtained by polymerization using a metallocene catalyst, the weight-average molecular weight of the polyethylene raw material is 150,000, Mw / Mn is 2.8, the number of methyl groups per thousand carbons < 10, and the density is 0.945 g / cm 3 . The polyethylene raw material, phthalocyanine, antioxidant 1010, and fluororubber are fed into a twin-screw extruder for melt extrusion. The dosages of phthalocyanine, antioxidant 1010, and fluororubber are 0.5%, 0.2%, and 0.05% of the mass of polyethylene respectively. The temperatures of the twin-screw from the feeding section to the discharging section are 145°C, 160°C, 170°C, 180°C, 185°C respectively, the rotation speed is 90 revolutions / min, and the minimum diameter of the elliptical extrusion die is 1 mm.

[0050] The extruded raw filaments pass through a high-temperature heat preservation device, are subjected to biaxial stretching at 100°C and then wound up. The transverse stretching is 2 times, and the longitudinal stretching multiple is 4. The wound flat filaments or films pass through a hot channel and are subjected to unidirectional multi-fold stretching again at a high temperature, the stretching multiple is 15 times, and the temperature of the hot channel is 100°C. The flat filaments or films after high-fold drawing are subjected to 1% hot stretching in a hot box, and the stretching temperature is 40°C.

[0051] The fibers after high-temperature stretching are cut and wound up. The fibers are tested to obtain high-performance polyethylene flat filaments with a tensile strength of 15.9 cN / dtex and an elongation at break of 15%. The contact area of the flat filaments as the suture fiber matrix is 0.8 mm per 1 mm unit length 2 .

[0052] Example 2

[0053] The polyethylene raw material obtained by polymerization using a late transition metal catalyst, the weight-average molecular weight of the polyethylene raw material is 200,000, Mw / Mn is 2.9, the number of methyl groups per thousand carbons < 10, and the density is 0.943 g / cm 3 . The polyethylene raw material, titanium dioxide, antioxidant 2,6-di-tert-butyl-p-cresol, and fluororubber are fed into a twin-screw extruder for melt extrusion. The dosages of titanium dioxide, antioxidant 2,6-di-tert-butyl-p-cresol, and fluororubber are 0.5%, 0.2%, and 0.05% of the mass of polyethylene respectively. The temperatures of the twin-screw from the feeding section to the discharging section are 145°C, 160°C, 170°C, 180°C, 190°C respectively, the rotation speed is 90 revolutions / min, and the minimum diameter of the elliptical extrusion die is 30 mm.

[0054] The extruded raw filaments pass through a high-temperature heat preservation device, are subjected to biaxial stretching at 110°C and then wound up. The transverse stretching is 5 times, and the longitudinal stretching multiple is 10. The wound flat filaments or films pass through a hot channel and are subjected to unidirectional multi-fold stretching again at a high temperature, the stretching multiple is 10 times, and the temperature of the hot channel is 110°C. The flat filaments or films after high-fold drawing are subjected to 3% hot stretching in a hot box, and the stretching temperature is 60°C.

[0055] The fibers after high-temperature stretching are cut and wound. The fibers are tested to obtain high-performance polyethylene flat filaments with a tensile strength of 16.13 cN / dtex and an elongation at break of 20%. The contact area of the flat filaments as the suture fiber matrix is 4.5 mm per 1 mm unit length. 2 。

[0056] Example 3

[0057] A polyethylene raw material polymerized with a late transition metal catalyst, the polyethylene raw material having a weight average molecular weight of 400,000, Mw / Mn of 2.9, less than 10 methyl groups per thousand carbons, and a density of 0.941 g / cm 3 . The polyethylene raw material, iron oxide pigment, antioxidant 1010, and calcium stearate are fed into a screw extruder for melt extrusion. The dosages of the iron oxide pigment, antioxidant 1010, and calcium stearate are 0.2%, 0.2%, and 0.4% of the polyethylene mass respectively. The temperature of the twin-screw from the feeding section to the discharging section is 145°C, 160°C, 170°C, 180°C, 190°C respectively, the rotation speed is 110 revolutions / min, and the minimum diameter of the oval extrusion die is 20 mm.

[0058] The extruded raw filaments pass through a high-temperature heat preservation device, are biaxially stretched at 125°C and then wound. The transverse stretch is 5 times and the longitudinal stretch is 20 times. The wound flat filaments or films are passed through a hot channel and uniaxially multi-fold stretched again at a high temperature, the stretch ratio is 10 times, and the temperature of the hot channel is 120°C. The flat filaments or films after high-fold drawing are thermally stretched by 5% in a hot box, and the stretching temperature is 70°C.

[0059] The fibers after high-temperature stretching are cut and wound. The fibers are tested to obtain high-performance polyethylene flat filaments with a tensile strength of 19.32 cN / dtex and an elongation at break of 18%. The contact area of the flat filaments as the suture fiber matrix is 2.5 mm per 1 mm unit length. 2 。

[0060] Example 4

[0061] A polyethylene raw material polymerized with a metallocene catalyst, the polyethylene raw material having a weight average molecular weight of 200,000, Mw / Mn of 2.7, less than 10 methyl groups per thousand carbons, and a density of 0.943 g / cm 3 . The polyethylene raw material, phthalocyanine, antioxidant 1076, and zinc stearate are fed into a screw extruder for melt extrusion. The dosages of the phthalocyanine, antioxidant 1076, and zinc stearate are 0.2%, 0.2%, and 0.4% of the polyethylene mass respectively. The temperature of the twin-screw from the feeding section to the discharging section is 145°C, 160°C, 180°C, 190°C, 200°C respectively, the rotation speed is 200 revolutions / min, and the minimum diameter of the oval extrusion die is 10 mm.

[0062] The as-extruded raw filaments pass through a high-temperature heat preservation device, are subjected to biaxial stretching at 115 °C and then wound up. The transverse stretch is 3 times and the longitudinal stretch is 10 times. The wound flat filaments or films are passed through a hot runner and are unidirectionally stretched multiple times at high temperature again. The stretching multiple is 10 times and the temperature of the hot runner is 120 °C. The flat filaments or films after high-ratio drawing are subjected to 2% hot stretching in a hot box, and the stretching temperature is 60 °C.

[0063] The fibers after high-temperature stretching are cut and wound up. The fibers are tested to obtain high-performance polyethylene flat filaments with a tensile strength of 16.31 cN / dtex and an elongation at break of 17%. The contact area of the flat filaments as the suture fiber matrix per 1 mm unit length is 1.5 mm 2 。

[0064] Example 5

[0065] A polyethylene raw material polymerized with a metallocene catalyst, the polyethylene raw material has a weight-average molecular weight of 600,000, Mw / Mn is 2.4, the number of methyl groups per thousand carbons < 10, and the density is 0.933 g / cm 3 The polyethylene raw material, titanium dioxide, antioxidant 1076, zinc stearate, and calcium stearate are fed into a screw extruder for melt extrusion. The dosages of titanium dioxide, antioxidant 1076, zinc stearate, and calcium stearate are 0.5%, 0.2%, 0.5%, and 0.5% of the mass of polyethylene respectively. The temperature of the twin-screw from the feeding section to the discharging section is 145 °C, 160 °C, 180 °C, 190 °C, 200 °C, the rotation speed is 220 revolutions / min, and the thickness of the rectangular extrusion die is 0.1 mm.

[0066] The as-extruded raw filaments pass through a high-temperature heat preservation device, are subjected to biaxial stretching at 135 °C and then wound up. The transverse stretch is 5 times and the longitudinal stretch is 15 times. The wound flat filaments or films are passed through a hot runner and are unidirectionally stretched multiple times at high temperature again. The stretching multiple is 6 times and the temperature of the hot runner is 120 °C. The flat filaments or films after high-ratio drawing are subjected to 5% hot stretching in a hot box, and the stretching temperature is 80 °C.

[0067] The fibers after high-temperature stretching are cut and wound up. The fibers are tested to obtain high-performance polyethylene flat filaments with a tensile strength of 20.01 cN / dtex and an elongation at break of 5%. The contact area of the flat filaments as the suture fiber matrix per 1 mm unit length is 0.5 mm 2 。

[0068] Example 6

[0069] A polyethylene raw material polymerized with a late transition metal catalyst, the polyethylene raw material has a weight-average molecular weight of 300,000, Mw / Mn is 2.0, the number of methyl groups per thousand carbons < 10, and the density is 0.95 g / cm 3The polyethylene raw material, titanium dioxide, antioxidant 1076, and fluororubber are fed into a screw extruder for melt extrusion. The dosages of titanium dioxide, antioxidant 1076, and fluororubber are 0.5%, 0.25%, and 0.05% of the mass of the polyethylene respectively. The temperature of the twin-screw from the feeding section to the discharging section is 145°C, 160°C, 180°C, 190°C, 200°C, the rotation speed is 220 revolutions / min, the temperature from the melt pump to the die head is 145°C - 220°C, and the thickness of the rectangular extrusion die is 1 mm.

[0070] The extruded raw filaments pass through a high-temperature heat preservation device, are subjected to biaxial stretching at 125°C and then wound up. The transverse stretching ratio is 1 time, and the longitudinal stretching ratio is 4 times. The wound flat filaments or films are passed through a hot runner and are unidirectionally stretched multiple times at high temperature again. The stretching ratio is 10 times, and the temperature of the hot runner is 110°C. The flat filaments or films after high-stretch drawing are subjected to 1% hot stretching in a hot box, and the stretching temperature is 80°C.

[0071] The fibers after high-temperature stretching are cut and wound up. The fibers are tested to obtain high-performance polyethylene flat filaments with a tensile strength of 16.11 cN / dtex and an elongation at break of 10%. The contact area of the flat filaments as the suture fiber matrix per 1 mm unit length is 3.5 mm 2 。

[0072] Example 7

[0073] The polyethylene raw material obtained by polymerization using a late transition metal catalyst, the weight-average molecular weight of the polyethylene raw material is 150,000, Mw / Mn is 2.5, the number of methyl groups per thousand carbons < 10, and the density is 0.942 g / cm 3 The polyethylene raw material, phthalocyanine, antioxidant 1010, calcium stearate, and titanate are fed into a screw extruder for melt extrusion. The dosages of phthalocyanine, antioxidant 1010, calcium stearate, and titanate are 0.5%, 0.2%, 0.2%, and 0.2% of the mass of the polyethylene respectively. The temperature of the twin-screw from the feeding section to the discharging section is 145°C, 160°C, 180°C, 180°C, 180°C respectively, the rotation speed is 200 revolutions / min, the temperature from the melt pump to the die head is 150°C - 180°C, and the thickness of the rectangular extrusion die is 20 mm.

[0074] The extruded raw filaments pass through a high-temperature heat preservation device, are subjected to biaxial stretching at 110°C and then wound up. The transverse stretching ratio is 4 times, and the longitudinal stretching ratio is 10 times. The wound flat filaments or films are passed through a hot runner and are unidirectionally stretched multiple times at high temperature again. The stretching ratio is 15 times, and the temperature of the hot runner is 105°C. The flat filaments or films after high-stretch drawing are subjected to 3% hot stretching in a hot box, and the stretching temperature is 60°C.

[0075] The fibers after high-temperature stretching are cut and wound, and the fibers are tested to obtain high-performance polyethylene flat filaments with a tensile strength of 17.11 cN / dtex and an elongation at break of 17%. The flat filaments, as the suture fiber matrix, have a contact area of 2.5 mm per 1 mm unit length 2 。

[0076] Comparative Example 1

[0077] Take polyethylene with a weight-average molecular weight of 400,000 and Mw / Mn = 13.5, the number of methyl groups per thousand carbons < 10, and a density of 0.95 g / cm 3 , and the polyethylene raw material, iron oxide pigment, antioxidant 1010, and calcium stearate are fed into a screw extruder for melt extrusion. The dosages of the iron oxide pigment, antioxidant 1010, and calcium stearate are 0.2%, 0.2%, and 0.4% of the polyethylene mass respectively. The temperature of the twin-screw from the feeding section to the discharging section is 145 °C, 160 °C, 170 °C, 180 °C, 190 °C, the rotation speed is 110 revolutions / min, and the minimum diameter of the oval extrusion die is 20 mm

[0078] The extruded raw filaments are prepared into film castings by die extrusion and casting. The castings are preheated and then biaxially stretched at 95 °C below the melting point and wound. The transverse stretch is 5 times and the longitudinal stretch is 20 times. The wound flat filaments or films are passed through a hot runner and unidirectionally multi-fold stretched again at a high temperature, with a stretch ratio of 10 times and a hot runner temperature of 120 °C. The flat filaments or films after high-fold drawing are thermally stretched by 5% in a hot box at a stretching temperature of 70 °C. The fibers are cut and wound to obtain polyethylene flat filaments with a tensile strength of 7.5 cN / dtex and an elongation at break of 8%. The flat filaments, as the suture fiber matrix, have a contact area of 2.2 mm per 1 mm unit length 2 。

[0079] Comparative Example 2

[0080] Except that the extruded raw filaments are prepared into film castings by die extrusion and casting, and the castings are preheated and then biaxially stretched at 95 °C below the melting point and wound, other steps are used to prepare polyethylene flat filaments by the same method as in Example 3, with a tensile strength of 10.39 cN / dtex and an elongation at break of 9%. The flat filaments, as the suture fiber matrix, have a contact area of 2.0 mm per 1 mm unit length 2 。

[0081] Comparative Example 3

[0082] Use a high-density polyethylene raw material with a wide molecular weight distribution. The weight-average molecular weight of the polyethylene raw material is 400,000, Mw / Mn is 13.5, the number of methyl groups per thousand carbons < 10, and the density is 0.95 g / cm 3The polyethylene raw material, iron oxide pigment, antioxidant 1010, and calcium stearate are fed into a screw extruder for melt extrusion. The dosages of the iron oxide pigment, antioxidant 1010, and calcium stearate are 0.2%, 0.2%, and 0.4% of the mass of the polyethylene respectively. The temperature of the twin-screw from the feeding section to the discharging section is 145°C, 160°C, 170°C, 180°C, 190°C, the rotation speed is 110 revolutions per minute, and the minimum diameter of the oval extrusion die is 20 mm.

[0083] The extruded raw filaments pass through a high-temperature heat preservation device, are biaxially stretched at 125°C and then wound up. The transverse stretch is 5 times and the longitudinal stretch is 20 times. Melt fracture occurs during the stretching process, and the molten state cannot be biaxially stretched.

[0084] Comparative Example 4

[0085] Except that the extruded raw filaments are extruded through a die and cast into a film sheet, and the cast sheet is preheated and then biaxially stretched at 125°C and wound up, other steps are the same as those in Example 3 to prepare polyethylene flat filaments. The tensile strength is 11.88 cN / dtex, the elongation at break is 8%, and the contact area of the flat filaments as the suture fiber matrix per 1 mm unit length is 1.8 mm 2 。

[0086] Comparative Example 5

[0087] Except that the extruded raw filaments are directly biaxially stretched and wound up under the condition that the die exit temperature is below 95°C, other steps are the same as those in Example 3 to prepare polyethylene flat filaments. The tensile strength is 9.12 cN / dtex, the elongation at break is 10%, and the contact area of the flat filaments as the suture fiber matrix per 1 mm unit length is 2.5 mm 2 。

[0088] Comparative Example 6

[0089] Select ultra-high molecular weight polyethylene powder resin with a weight average molecular weight of 1.5 - 2 million as the raw material, add 3% - 8% (weight ratio) of polyethylene modified masterbatch, and obtain high-strength polyethylene flat filaments through melt extrusion with a screw with a length-diameter ratio of 1:40 and super-ratio stretching. The fiber strength is 10 cN / dtex - 15 cN / dtex, and the elongation at break is less than 5%.

[0090] The specific production process implementation steps are as follows:

[0091] The first step: Preparation of polyethylene modified masterbatch:

[0092] 1. Select LDPE low-density polyethylene or LLDPE linear low-density polyethylene as the raw material, add 11% (weight ratio) of POE polyolefin elastomer, 4% of PE foaming agent, and 8% of ethylene-propylene rubber EPDM for uniform mixing;

[0093] 2. Granulate the above-mentioned polymer that has been uniformly blended through twin-screw compounding: The temperatures of each section of the twin-screw are 145°C, 160°C, 170°C, 180°C, and 180°C respectively. The rotation speed of the twin-screw is controlled at 200 - 250 revolutions per minute to prepare a polyethylene modified masterbatch.

[0094] Its compounded polyethylene modified masterbatch has excellent functions such as low melting point, low viscosity, lubricity, good fluidity, and easy dispersion.

[0095] The second step: Preparation of ultra-high molecular weight polyethylene by melt extrusion:

[0096] 1. Select ultra-high molecular weight polyethylene resin with a molecular weight of 1.8 million, and uniformly mix it with 5% (by weight) of the compounded polyethylene modified masterbatch.

[0097] 2. Convey the above mixture into a screw extruder for melt extrusion: The length-diameter ratio of the screw is 1:40. The temperatures of each section of the screw are 145°C, 190°C, 240°C, 250°C, and 250°C respectively. The extrusion speed of the screw is 200 - 250 revolutions per minute. The thickness of the rectangular extrusion die is 10 mm. The temperature of the extruded melt is controlled at about 210°C. After the polyethylene is extruded, it passes through a high-temperature heat preservation device and is subjected to biaxial stretching in a molten state, with a transverse stretch ratio of 5 times and a longitudinal stretch ratio of 10 times. After biaxial stretching, it is cooled by a water bath, and the temperature of the water bath is controlled at 22°C; after water bath cooling, it is wound into a roll.

[0098] 3. Then, the film that has been wound into a roll is subjected to two passes of unidirectional ultra-multiple stretching, drying, shaping, and cutting, and finally finished fibers are made: For the first pass of ultra-multiple stretching, water bath stretching is used, and the water bath temperature is 85°C, with a stretch ratio of 8 times; for the second pass, overheated steam stretching is used, and the steam temperature is 120°C, with a stretch ratio of 4 times; after ultra-multiple stretching, it is dried using hot air circulation drying, and the drying temperature is 125°C, with a tension of about 1.15 times; then it is shaped, and the shaping temperature is 135°C, and the shaping linear speed is 30 meters per minute; the film is cut and wound to make ultra-high molecular weight polyethylene finished fibers. The fiber strength of the made ultra-high molecular weight polyethylene fibers is 10 cN / dtex - 15 cN / dtex, the elongation at break is less than 5%, and the contact area of the flat filament as the suture fiber matrix per 1 mm unit length is 1.0 mm 2 。

[0099] Comparative Example 7

[0100] Take polyethylene with a weight-average molecular weight of 150,000 and an Mw / Mn of 5.1, and extrude it at 270°C through an elliptical wire outlet with a minimum diameter of 1 mm. The extruded polyethylene passes through high-temperature heat preservation and is subjected to double stretching in a molten state, with a transverse stretch ratio of 2 times and a longitudinal stretch ratio of 4 times, and then quenched and cooled at 20°C and wound.

[0101] The polyethylene film is unidirectionally stretched by multiple times at a stretching temperature of 100 °C and a stretching multiple of 7 times. The film with high draw ratio is thermally stretched by 1% in a hot box at a stretching temperature of 40 °C, cut and wound up. The obtained polyethylene fiber has a strength of 9.5 cN / dtex, an elongation at break of 5%, and the contact area of the flat yarn as the suture fiber matrix per 1 mm unit length is 2.5 mm 2 .

[0102] Comparative Example 8

[0103] Take high-density polyethylene with a weight-average molecular weight of 300,000 and a ratio of weight-average molecular weight to number-average molecular weight of 4.5, add antioxidant and carry out melt extrusion. The temperature of the screw extrusion section is 230 °C, the temperature of the extrusion die head is 290 °C, the extrusion die is a rectangular wire outlet hole with a thickness of 1 mm, and it is impossible to directly carry out biaxial stretching after extrusion. The high-temperature flat yarn is cooled by water cooling and wound up, and then biaxially stretched again, with a transverse stretch of 2 times and a longitudinal stretch of 6 times, cut and wound up. The tensile strength of the obtained fiber is 7 cN / dtex, and the contact area of the flat yarn as the suture fiber matrix per 1 mm unit length is 1.5 mm 2 .

[0104] Comparative Example 9:

[0105] Compared with Example 3, most of them are the same, except that the flat yarn or film after high draw ratio is thermally stretched by 10% in a hot box at 80 °C, and film breakage occurs.

[0106] Table 1

[0107]

[0108] The results of Example 3, Comparative Example 2, and Comparative Example 4 show that for the preparation of single-site polyethylene flat filaments, compared with biaxially stretching the extruded raw filaments after cooling and heating them to a temperature below the melting point or a partially molten temperature, directly biaxially stretching the extruded raw filaments under a temperature higher than the melting temperature after heat preservation avoids the biaxial orientation of molecular chains and at the same time provides a lower degree of entanglement. The flat filaments prepared after uniaxial stretching obtained better properties. The results of Example 3 and Comparative Example 5 show that for the preparation of single-site polyethylene flat filaments, directly cooling and stretching the extruded raw filaments below 95°C without heat preservation results in poor properties of the prepared flat filaments. This is also because biaxial orientation of molecular chains occurs during stretching and at the same time, the degree of molecular chain entanglement is relatively high, and uneven stretching temperature causes surface cracking of the flat filaments, ultimately affecting the properties. The results of Example 3 and Comparative Example 3 show that due to the relatively low melt viscosity of the wide molecular weight distribution high-density polyethylene raw material, melt fracture occurs when the extruded raw filaments are stretched above the melting point. Therefore, biaxial stretching cannot be carried out above the melting point. For the preparation of wide molecular weight distribution high-density polyethylene flat filaments, the method in Comparative Example 1 is adopted, and the raw filaments are cooled and then heated to a temperature below the melting point for biaxial stretching. At this temperature, its melt viscosity can meet the requirements of biaxial stretching and no melt fracture occurs, but the properties of the finally prepared flat filaments are not high.

[0109] As can be seen from the above table, the polyethylene raw material used in this method is polymerized by a single-site catalyst with a weight-average molecular weight of 100,000 - 600,000 and a density higher than 0.93 g / cm 3 ³. Through the process of melt extrusion, a high-performance polyethylene flat filament product is prepared, which can be applied to fields such as medical sutures, and meets the requirements of fiber matrices used in fields such as high-strength medical sutures in terms of mechanical properties. Moreover, the mechanical properties are significantly better than those of polyethylene flat filament products prepared from wide molecular weight distribution polyethylene raw materials and ultra-high molecular weight polyethylene / low molecular weight polyethylene blend raw materials in the comparative examples. The use of a high-temperature heat preservation device further improves the mechanical properties of the flat filament products. At the same time, it is far superior to the fiber matrices used in fields such as high-strength medical sutures prepared by solution dissolution and the current melt extrusion method in terms of cost, process complexity, and environmental protection. In addition, as a suture fiber matrix, the contact area of the high-performance polyethylene flat filament is equivalent to that of a braided flat medical suture. It has a large contact area and can prepare a flat medical suture without braiding. Compared with the braided medical suture, it has the advantage of a smooth surface.

[0110] In the description of this specification, the description referring to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0111] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and use the invention. Obviously, those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should fall within the protection scope of the present invention.

Claims

1. A preparation method of a high-performance polyethylene flat filament product, characterized in that, The steps include the following: (1) Feed the mixed material of polyethylene raw material, color powder and processing aids into a screw extruder and extrude high-temperature polyethylene undrawn filaments; (2) Keep the polyethylene undrawn filaments at a high temperature and conduct biaxial stretching in a molten state; (3) Conduct secondary unidirectional multi-fold stretching on the filaments biaxially stretched in step (2) through a hot runner; (4) Conduct hot stretching on the filaments after secondary unidirectional multi-fold stretching, and finally conduct cutting and winding to obtain high-performance polyethylene flat filaments; In step (1), the polyethylene raw material is polymerized using a single-site catalyst, with a weight-average molecular weight of 100,000 - 600,000, a ratio of weight-average molecular weight to number-average molecular weight Mw / Mn < 3.0, less than 10 per thousand carbon methyl groups, and a density > 0.93 g / cm 3 .

2. The preparation method of a high-performance polyethylene flat yarn product according to claim 1, characterized in that, In step (1), during the high-temperature extrusion process, the temperature of the extrusion section of the screw extruder is 145 - 200 °C, and the temperature from the melt pump to the die head is 145 - 220 °C.

3. The preparation method of a high-performance polyethylene flat filament product according to claim 1, characterized in that, In step (2), the high-temperature heat preservation is controlled at 60 - 150 °C, and during the biaxial stretching process, the transverse stretching ratio is 1 - 5 times, and the longitudinal stretching ratio is 4 - 20 times.

4. The preparation method of a high-performance polyethylene flat filament product according to claim 1, characterized in that, In step (3), the multiple of secondary unidirectional multi-fold stretching is 5 - 25 times.

5. The preparation method of a high-performance polyethylene flat yarn product according to claim 1, characterized in that, In step (3), the temperature of the hot runner during secondary unidirectional multi-fold stretching is 60 - 130 °C.

6. The preparation method of a high-performance polyethylene flat yarn product according to claim 1, characterized in that, In step (4), the temperature of hot stretching is 40 - 80 °C, and the amplitude is 1% - 5%.

7. The preparation method of a high-performance polyethylene flat yarn product according to claim 1, characterized in that, In step (1), the die head of the screw extruder is a rectangular wire outlet hole or an oval wire outlet hole. Among them, the thickness of the rectangular wire outlet hole is 0.1 mm - 20 mm, and the minimum diameter of the oval wire outlet hole is 1 - 30 mm.

8. A high-performance polyethylene flat yarn product, which is prepared by using the preparation method described in any one of claims 1-7, characterized in that, The tensile strength of the polyethylene flat filament product is greater than 15 cN / dtex, and the elongation at break reaches more than 5%.

9. The application of a high-performance polyethylene flat filament product as described in claim 8, characterized in that, The polyethylene flat filament product is used for preparing medical suture threads.

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