Polyvinylidene fluoride fiber for filter fabric and method for producing the same

Abstract

This invention discloses a polyvinylidene fluoride (PVDF) fiber for filter fabrics and its preparation method. The method includes mixing 0.2–3 wt.% of a perfluorinated polymer compound, 0.5–4 wt.% of an oleophilic-hydrophobic nucleating agent, and 93–99 wt.% of PVDF resin, and adding the mixture to a twin-screw extruder to form a PVDF composite masterbatch; feeding the masterbatch into a single-screw extruder to form a melt; extruding the melt through a screw extrusion spinning machine to obtain a molten extrudate; passing the molten extrudate through an air bath, a second air bath, an oil bath, a first stretching roller, a second stretching roller, a third stretching roller, a heat-setting roller, and a networker, and then winding it to obtain the PVDF fiber. The obtained fiber has a smooth, non-porous surface, good fineness uniformity, high crystallinity, good macromolecular chain orientation, good mechanical properties, excellent aging resistance, and can be used continuously in a temperature range of -40–150°C, exhibiting good chemical stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fiber preparation, in particular to a polyvinylidene fluoride fiber for filter fabric and a preparation method thereof. BACKGROUND

[0002] Liquid filter is an indispensable device on the pipeline conveying medium. From the market demand, it is widely used in the fields of semiconductor, chemical industry, medicine, food, metal processing, water treatment, automobile, etc. In the commonly used plate filter and cylinder filter devices, according to the working condition of liquid, polypropylene filament and polytetrafluoroethylene monofilament are mostly used. However, the former cannot adapt to the filtering environment of special working conditions due to poor material corrosion resistance and aging resistance. Although polytetrafluoroethylene has excellent chemical stability and temperature resistance, it cannot be used to manufacture fibers by melt spinning technology due to its "insoluble and infusible" characteristics, and it is difficult to produce monofilament and multifilament products below 100D, which cannot meet the demand of high-efficiency liquid filtering working condition. In addition, the uniformity of the polytetrafluoroethylene fiber prepared by paste extrusion method or film splitting method needs to be improved. Polyvinylidene fluoride (PVDF) has thermoplasticity, and does not need any organic reagent in the melt spinning process, which is environmentally friendly. The prepared fiber has good uniformity and can be adjusted. For the preparation of high-end liquid filter fabric, PVDF fiber is indispensable, and the industrialization of PVDF fiber will help to improve the filtering level in the fields of medicine, food, water treatment, chemical industry, etc. Therefore, the development of PVDF fiber for filter fabric has important research and application value.

[0003] Unlike other conventional thermoplastic polymers, PVDF (polyvinylidene fluoride) is a fluoropolymer with high melt viscosity, which is prone to "melt fracture" phenomenon in the spinning process. In addition, PVDF has hydrophobicity, and the fiber has high elongation at break, which is difficult to hold during the stretching and winding process, and is prone to produce lint, broken filament and other phenomena, so the spinning is difficult. Therefore, at present, most of the reports about PVDF fiber are mainly research, and there is still a big gap in industrial production. Further, there are fewer reports about PVDF fiber for filter fabric. Most of the literature and patents are only limited to the study of the influence of spinning process parameters on the crystalline structure of PVDF fiber, mainly aiming at medical sutures, artificial stents, pressure sensors, flame-retardant fabrics, fishing lines, fishing nets, etc. Patent CN106350879A discloses a method for preparing PVDF fiber by solution spinning technology, but the preparation process needs a large amount of organic solvent, which not only harms the environment, but also greatly increases the production cost; patent CN106012045A discloses a preparation method of PVDF melt-spun fiber, but the thinnest monofilament is only 9.6 tex, the maximum tensile strength is only 31.2 cN / tex, and the crystallinity is 52.3%. If it is applied to filter fabric, the fineness, mechanical properties, surface wettability and other properties of the fiber need to be improved. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application innovatively provides a PVDF fiber for filter fabric and a preparation method thereof. The prepared PVDF fiber for filter fabric has a smooth surface, no holes, good and adjustable fiber fineness uniformity, high crystallinity, good macromolecular chain orientation, good mechanical properties, a tensile strength of 3.5 cN / dtex, an elongation at break of 10-25%, a heat shrinkage rate of <5% at 120 DEG C, a water contact angle of >110 DEG, an oil contact angle close to 0 DEG, excellent aging resistance, continuous use in a temperature range of -40-150 DEG C, and good chemical stability to common chemical reagents, acid and alkali solutions, etc. The method has simple process, environmental protection, high production efficiency, and is easy to be industrialized for large-scale production. The fiber performance fully meets the processing requirements of filter fabric, and the waste fiber or fabric is easy to be recycled and reused.

[0005] The technical scheme for solving the technical problem of the fiber is to provide a PVDF fiber for filter fabric. The fiber-forming system of the fiber comprises 0.2-3 wt.% of a perfluoropolymer compound, 0.5-4 wt.% of an oleophilic and hydrophobic nucleating agent, and 93-99 wt.% of a PVDF resin, and the sum of the components is 100 wt.%. The perfluoropolymer compound comprises a perfluoropolyether and a tetrafluoroethylene-perfluoroalkoxy vinyl ether blend. The oleophilic and hydrophobic nucleating agent is a blend of three forms of additives, i.e. hydrophobic silicon dioxide with an average particle size of 20-100 nm, carbon nanotubes with a length of 1-10 microns, and graphene with an average flake size of 1-10 microns, in a mass ratio of 1:1:1. The PVDF resin is a resin with a melt index of 3-13 g / 10 min under the condition of 230 DEG C / 2.16 kg. The perfluoropolyether has an average molecular weight of 500-6000, and the tetrafluoroethylene-perfluoroalkoxy vinyl ether is a perfluoropolymer compound with a melt index of 1-10 g / 10 min under the condition of 230 DEG C / 2.16 kg. The prepared PVDF fiber for filter fabric has a smooth surface, no holes, good and adjustable fiber fineness uniformity, high crystallinity, good macromolecular chain orientation, good mechanical properties, a tensile strength of 3.5 cN / dtex, an elongation at break of 10-25%, a heat shrinkage rate of <5% at 120 DEG C, a water contact angle of >110 DEG, an oil contact angle close to 0 DEG, excellent aging resistance, continuous use in a temperature range of -40-150 DEG C, and good chemical stability to common chemical reagents, acid and alkali solutions, etc.

[0006] The technical scheme for solving the technical problem of the preparation method is to provide a preparation method of a PVDF fiber for filter fabric. The preparation method uses the PVDF fiber-forming system for filter fabric according to the present application.

[0007] 1) first, the filter fabric is mixed with each component of the PVDF fiber-forming system using a high-speed mixer, and then the filter fabric is made into a PVDF composite master batch through a twin-screw extruder;

[0008] 2) the dried PVDF composite master batch is fed into a single-screw extruder hopper, and then the master batch is sequentially passed through a screw zone 1 with a temperature of 155-190°C, a screw zone 2 with a temperature of 185-220°C, a screw zone 3 with a temperature of 195-230°C, a screw zone 4 with a temperature of 215-250°C, a screw zone 5 with a temperature of 230-265°C, a screw flange with a temperature of 235-270°C, and a melt pipe with a temperature of 230-265°C under the shearing action of the screw, to obtain a fully mixed and molten melt;

[0009] 3) the fully mixed and molten melt is quantitatively passed through a spinning box flange with a temperature of 230-265°C and a spinning box body with a temperature of 235-270°C under the action of a metering pump, filtered, and finally extruded to obtain a molten extrudate;

[0010] 4) the molten extrudate is sequentially passed through multiple air baths, an oil bath, a first stretching roller, a second stretching roller, a third stretching roller, a heat setting roller, and a networker, and then wound to obtain the PVDF fiber for filter fabric.

[0011] Compared with the prior art, the PVDF fiber for filter fabric has the advantages of smooth surface, no pores, good fiber fineness uniformity and adjustability, high crystallinity, good macromolecular chain orientation, good mechanical properties, tensile strength of 3.5 cN / dtex, elongation at break of 10-25%, heat shrinkage rate of <5% at 120°C, water contact angle of >110°, oil contact angle close to 0°, excellent aging resistance, continuous use in a temperature range of -40-150°C, and good chemical stability to common chemical reagents, acid and base solutions, etc. The preparation method of the PVDF fiber for filter fabric has the characteristics of relatively simple process, environmentally friendly process, high production efficiency, easy industrialization scale production, fiber performance fully meeting the processing requirements of filter fabric, and easy recycling of waste fibers or fabrics. DETAILED DESCRIPTION

[0012] The application will be further described below in combination with specific embodiments of the application.

[0013] The application discloses a kind of PVDF fibers (abbreviation fiber) for filter fabric, it is characterized in that: the fiber formation system composition includes 0.2-3wt.% perfluoropolymer compound, 0.5-4wt.% lipophilic hydrophobic nucleating agent and 93-99wt.% PVDF resin, the sum of each component is 100wt.%;The perfluoropolymer compound includes the blend of perfluoropolyether and tetrafluoroethylene-perfluoroalkoxy vinyl ether;The lipophilic hydrophobic nucleating agent is the blend of three forms of additives, i.e. hydrophobic silicon dioxide with "spherical" average particle size of 20-100nm, carbon nanotube with "linear" length of 1-10 μm and graphene with "sheet" average sheet diameter of 1-10 μm, in a mass ratio of 1:1:1;The PVDF resin is a resin with a melt index of 3-13 g / 10 min under the condition of 230℃ / 2.16kg;The perfluoropolyether in the application has an average molecular weight of 500-6000, and the tetrafluoroethylene-perfluoroalkoxy vinyl ether has a melt index of 1-10 g / 10 min under the condition of 230℃ / 2.16kg;And the PVDF fiber for filter fabric made has smooth surface, no holes, good uniformity and adjustable fineness, high crystallinity, good macromolecular chain orientation, good mechanical properties, tensile strength up to 3.5 cN / dtex, elongation at break 10-25%, heat shrinkage rate <5% at 120℃, water contact angle >110°, oil contact angle close to 0°, excellent aging resistance, continuous use at-40-150℃, and good chemical stability to common chemical reagents, acid and base solutions, etc.

[0014] In the fiber formation system, the perfluoropolymer compound is a blend of perfluoropolyether and tetrafluoroethylene-perfluoroalkoxy vinyl ether. The addition of the perfluoropolymer compound plays a hydrophobic modification role, thereby improving the surface wettability of the fiber, increasing the filtration efficiency, and also playing a lubricating role, improving the difficulty of fully mixing the pure inorganic additive in the fiber matrix, increasing the spinnability of the fiber, and further improving the affinity between the perfluoropolymer compound and the fiber matrix PVDF resin, thereby improving the spinnability and mechanical properties of the fiber while adjusting the surface wettability of the fiber.

[0015] The oleophilic hydrophobic nucleating agent in the fiber-forming system is a blend of three forms of additives, hydrophobic silicon dioxide with a "spherical" average particle size of 20-100 nm, carbon nanotubes with a "linear" length of 1-10 μm, and graphene with an "sheet" average sheet size of 1-10 μm, in a mass ratio of 1:1:1. The oleophilic hydrophobic nucleating agent not only plays a role in oleophobic hydrophobic modification together with the perfluoropolymer compound to improve the filtration efficiency, but also acts as a nucleating agent for PVDF crystallization to promote the formation of crystals and improve the structure and performance of the fiber. In addition, the synergistic effect between the three different forms of oleophilic hydrophobic nucleating agents is more conducive to the improvement of the crystalline structure and mechanical properties of the fiber.

[0016] The application also designs a preparation method for the PVDF fiber for the filter fabric, and the preparation method is as follows:

[0017] 1) The components of the PVDF fiber-forming system for the filter fabric are first mixed sufficiently using a high-speed mixer, and then a PVDF composite master batch is prepared through a double-screw extruder.

[0018] The double-screw extruder has five-zone temperature control, the screw zone one temperature is 160-190℃, the screw zone two temperature is 190-220℃, the screw zone three temperature is 200-230℃, the screw zone four temperature is 210-240℃, the screw zone five temperature is 220-250℃, the pipe temperature and the die temperature are both 200-230℃, wherein the die temperature is 20℃ lower than the screw zone five temperature, and these parameter settings are mainly to reduce the influence of heat treatment history on the molecular structure of the fluorine-containing polymer on the basis of ensuring that the components are mixed sufficiently, so as to avoid degradation or carbonization. The temperature setting of the double-screw extruder provides technical support for the preparation of the composite master batch.

[0019] 2) The dried PVDF composite master batch is sent into the feeding hopper of a single-screw extruder, and then the master batch passes through the screw zone one with a temperature of 155-190℃, the screw zone two with a temperature of 185-220℃, the screw zone three with a temperature of 195-230℃, the screw zone four with a temperature of 215-250℃, the screw zone five with a temperature of 230-265℃, the screw flange with a temperature of 235-270℃, and the melt pipe with a temperature of 230-265℃ in sequence under the shearing action of the screw, to obtain a fully mixed melt.

[0020] The temperature of the second zone of the screw is 30 DEG C higher than that of the first zone, the temperature of the third zone is 10 DEG C higher than that of the second zone, the temperature of the fourth zone is 20 DEG C higher than that of the third zone, the temperature of the fifth zone is 15 DEG C higher than that of the fourth zone, the temperature of the screw flange is 5 DEG C higher than that of the fifth zone, and the temperature of the melt pipe and the fifth zone is consistent, since the viscosity of the fluoropolymer melt is large, a higher spinning temperature is used from the fifth zone to ensure smooth spinning.

[0021] 3) The melt is sufficiently mixed and quantitatively passed through the spinning box flange with a temperature of 230-265 DEG C and the spinning box body with a temperature of 235-270 DEG C under the action of the metering pump, filtered and finally extruded to obtain the melt extrudate.

[0022] The temperature of the single screw spinning box body is 5 DEG C higher than that of the fifth zone, which is different from the setting of the die temperature of the twin screw in step 1) which is 20 DEG C lower than that of the fifth zone, since the viscosity of the fluoropolymer melt is large, melt fracture is prone to occur during spinning, in order to avoid this phenomenon, the melt flowability must be ensured and the time required for internal stress relaxation must be reduced.

[0023] 4) The melt extrudate is sequentially passed through multiple air baths, an oil bath, a first drawing roller, a second drawing roller, a third drawing roller, a heat setting roller and a networker, and then wound to obtain the PVDF fiber for filter fabric.

[0024] The air bath is a multiple air bath, the first air bath is close to the spinneret outlet, the temperature is 120-140 DEG C, and the length is 100-150 cm, which is to prolong the crystallization time and adjust the fiber structure to obtain a fiber with high crystallinity and good mechanical properties; the second air bath has a temperature of 20-28 DEG C and a length of 50-100 cm, which is to fully solidify the fiber and obtain a fiber with uniform fineness.

[0025] The preparation method of the PVDF fiber for filter fabric according to the application is characterized in that the drying process of the PVDF composite master batch in step 2) is 10-12 h in a vacuum drying box at 40-50 DEG C.

[0026] The preparation method of the PVDF fiber for filter fabric according to the application is further characterized in that the rotation direction of the oiling roller in the oil bath in step 4) is opposite to the fiber conveying direction, which not only improves the oiling rate, but also helps the multifilament to better hold together, slightly increases the resistance of the fiber conveying at the backward stretching position, thereby helping to reduce the influence of the disturbance of the yarn at the backward stretching position on the yarn at the spinneret drafting position, and is more conducive to the stability of the spinning process.

[0027] The preparation method of the PVDF fiber for filter fabric according to the present application is further characterized in that the stretching temperature of the first stretching roller is 85-95 DEG C, the stretching temperature of the second stretching roller is 85-95 DEG C, the stretching temperature of the third stretching roller is 105-115 DEG C, and the temperature of the heat setting roller is 120-130 DEG C. This is because 90 DEG C is the most favorable temperature for the crystal type conversion of PVDF under the action of the post-stretching, and in addition, the temperature of the first stretching roller and the second stretching roller is set to 85-95 DEG C in consideration of the ambient temperature and the heating state of the machine. And 120 DEG C is the softening point of PVDF, so the temperature of the heat setting roller is set to 120-130 DEG C to properly release the internal stress of the fiber after stretching and reduce the creep property of the fiber. The fiber is in the third stretching roller and has completed the previous two-stage stretching, and starts to enter the heat setting stage, so the temperature of the third stretching roller is set to 105-115 DEG C, which is between the post-stretching temperature and the heat setting temperature.

[0028] The preparation method of the PVDF fiber for filter fabric according to the present application is further characterized in that the spinning head stretching ratio is 30-150, the first-stage stretching ratio is 1.5-3.5, the second-stage stretching ratio is 1.1-2, and the winding retraction rate is 90-97% during the process of extruding the melt from the spinning head to the final winding into the fiber. The setting of the spinning head stretching ratio, the post-stretching ratio and the winding retraction rate will directly affect the crystalline structure, the fineness, the mechanical property, the heat shrinkage property and the like of the fiber, and in addition, due to the special linear molecular structure of the PVDF polymer, the fiber has good spinnability and easy creep, so the preparation method according to the present application has a large spinning head stretching ratio and winding retraction rate.

[0029] The preparation method of the PVDF fiber for filter fabric according to the present application is further characterized in that the fineness of the prepared PVDF fiber is 40-2400D, and the number of fibers is 6f, 8f, 10f, 24f, 48f, 50f, 96f, 144f or 192f.

[0030] The following will give the specific embodiments of the present application. The specific embodiments are only used for further detailed description of the present application, and do not limit the protection scope of the claims of the present application.

[0031] Example 1

[0032] The present application prepares a PVDF fiber for filter fabric. The process method is as follows:

[0033] 1) PVDF resin with a melt index of 8 g / 10 min at 230 °C / 2.16 kg is used as a base phase, and the addition amount is 97 wt.%; perfluoropolyether with an average molecular weight of 1800 and tetrafluoroethylene-perfluoroalkoxy vinyl ether with a melt index of 5 g / 10 min (230 °C / 2.16 kg) are mixed in a mass ratio of 2:3 as a perfluoropolymer compound, and the addition amount is 1 wt.%; a blend of hydrophobic silica with a "spherical" average particle size of 40 nm, carbon nanotubes with a "linear" length of 5 μm, and graphene with a "sheet" average sheet size of 5 μm in a mass ratio of 1:1:1 is used as a lipophilic hydrophobic nucleating agent, and the addition amount is 2 wt.%. The PVDF resin, the perfluoropolymer compound, and the lipophilic hydrophobic nucleating agent are mixed well using a high-speed mixer, and then a PVDF composite master batch is prepared by a twin-screw extruder, wherein the twin-screw extruder has five temperature control zones, the screw zone one temperature is 180 °C, the screw zone two temperature is 210 °C, the screw zone three temperature is 220 °C, the screw zone four temperature is 230 °C, the screw zone five temperature is 240 °C, and the pipe temperature and the die temperature are both 220 °C.

[0034] 2) The PVDF composite master batch dried in a vacuum drying oven at 50 °C for 10 h is fed into the feed hopper of a single-screw extruder, and then the master batch passes through the screw zone one with a temperature of 180 °C, the screw zone two with a temperature of 210 °C, the screw zone three with a temperature of 220 °C, the screw zone four with a temperature of 240 °C, the screw zone five with a temperature of 255 °C, the screw flange with a temperature of 260 °C, and the melt pipe with a temperature of 255 °C in sequence under the action of the screw shearing, to obtain a fully mixed and melted melt.

[0035] 3) The fully mixed and melted melt is quantitatively passed through the spinning box flange with a temperature of 255 °C and the spinning box body with a temperature of 260 °C of a screw extrusion spinning machine under the action of a metering pump, filtered, and finally extruded to obtain a melt extrudate.

[0036] 4) The melt extrudate passes through an air bath (temperature of 130 °C, length of 125 cm), a second air bath (temperature of 25 °C, length of 75 cm), an oil bath (reversing), a first stretching roller (temperature of 90 °C), a second stretching roller (temperature of 90 °C), a third stretching roller (temperature of 110 °C), a heat setting roller (temperature of 125 °C), and a netting device in sequence, and then is wound to obtain the PVDF fiber for the filter fabric. The spinning head draw ratio is 100, the first-stage draw ratio is 2.5, the second-stage draw ratio is 1.5, and the winding retraction rate is 93%.

[0037] The obtained filter fabric has a PVDF fiber fineness of 500D / 50f, a crystallinity of 60%±2%, a tensile strength of 4.2cN / dtex±0.2cN / dtex, an elongation at break of 18%±2%, a thermal shrinkage at 120℃ of 3%±1%, a water contact angle of 122°±2°, and an oil contact angle close to 0°.

[0038] Comparative Example 1

[0039] A PVDF fiber for filter fabric was prepared. The process method is as follows:

[0040] 1) PVDF resin with a melt index of 8g / 10min at 230℃ / 2.16kg was used as the matrix phase, with an addition amount of 97wt.%; polytetrafluoroethylene was used as the perfluoropolymer compound, with an addition amount of 1wt.%; a blend of hydrophobic silica with a "spherical" average particle size of 40nm, carbon nanotubes with a "linear" length of 5μm, and graphene with a "sheet" average sheet size of 5μm in a mass ratio of 1:1:1 was used as the oleophobic hydrophilic nucleating agent, with an addition amount of 2wt.%. The PVDF resin, perfluoropolymer compound, and oleophobic hydrophilic nucleating agent were mixed well using a high-speed mixer, and then a PVDF composite master batch was prepared by a twin-screw extruder. The twin-screw extruder had a total of five zone temperature controls, with a screw zone one temperature of 180℃, a screw zone two temperature of 210℃, a screw zone three temperature of 220℃, a screw zone four temperature of 230℃, a screw zone five temperature of 240℃, and a pipe temperature and die temperature of 220℃.

[0041] 2) The PVDF composite master batch dried in a vacuum drying oven at 50℃ for 10h was fed into the feed hopper of a single-screw extruder, and then the master batch was sequentially passed through a screw zone one with a temperature of 180℃, a screw zone two with a temperature of 210℃, a screw zone three with a temperature of 220℃, a screw zone four with a temperature of 240℃, a screw zone five with a temperature of 255℃, a screw flange with a temperature of 260℃, and a melt pipe with a temperature of 255℃ under the action of screw shearing, to obtain a fully mixed melt.

[0042] 3) The fully mixed melt was quantitatively passed through a spinning box flange with a temperature of 255℃ and a spinning box body with a temperature of 260℃ under the action of a metering pump, filtered, and finally extruded to obtain a melt extrudate.

[0043] 4) The melt extrudate successively passes through an air bath (temperature 130 °C, length 125 cm), two air baths (temperature 25 °C, length 75 cm), an oil bath (inverted), a first draw roller (temperature 90 °C), a second draw roller (temperature 90 °C), a third draw roller (temperature 110 °C), a heat setting roller (temperature 125 °C), a netter, and is wound to obtain the PVDF fiber for filter fabric. The spinneret draw ratio is 100, the first draw ratio is 2.5, the second draw ratio is 1.5, and the winding retraction rate is 93%.

[0044] It is detected that the PVDF fiber for filter fabric obtained has a fineness of 500 D / 50 f, a crystallinity of 53%±2%, a tensile strength of 3.5 cN / dtex±0.2 cN / dtex, an elongation at break of 12%±2%, a heat shrinkage at 120 °C of 3%±1%, a water contact angle of 120°±2°, and an oil contact angle close to 0°.

[0045] Comparative Example 2

[0046] A PVDF fiber for filter fabric is prepared. The process method is as follows:

[0047] 1) PVDF resin with a melt index of 8 g / 10 min at 230 °C / 2.16 kg is used as a matrix phase, and the content is 97 wt.%; polyperfluoroalkylvinylethers are used as perfluoropolymer compounds, and the content is 1 wt.%; a blend of three kinds of additives of hydrophobic silicon dioxide with a "spherical" average particle size of 40 nm, carbon nanotubes with a "linear" length of 5 μm, and graphene with an "sheet" average sheet size of 5 μm in a mass ratio of 1:1:1 is used as a lipophilic hydrophobic nucleating agent, and the content is 2 wt.%. The PVDF resin, the perfluoropolymer compounds, and the lipophilic hydrophobic nucleating agent are fully mixed using a high-speed mixer, and then a PVDF composite master batch is prepared by a twin-screw extruder. The twin-screw extruder has five zones of temperature control, the screw zone one temperature is 180 °C, the screw zone two temperature is 210 °C, the screw zone three temperature is 220 °C, the screw zone four temperature is 230 °C, the screw zone five temperature is 240 °C, and the pipe temperature and the die temperature are both 220 °C.

[0048] 2) The PVDF composite master batch dried in a vacuum drying oven at 50 °C for 10 h is fed into a single-screw extruder feed hopper, and then the master batch passes through a screw zone one with a temperature of 180 °C, a screw zone two with a temperature of 210 °C, a screw zone three with a temperature of 220 °C, a screw zone four with a temperature of 240 °C, a screw zone five with a temperature of 255 °C, a screw flange with a temperature of 260 °C, and a melt pipe with a temperature of 255 °C successively under the shearing action of the screw to obtain a fully mixed melt.

[0049] 3) The melt obtained by sufficiently mixing and melting is quantitatively passed through a temperature of 255°C of a spinning pack flange and a temperature of 260°C of a spinning pack body under the action of a metering pump, filtered, and finally extruded to obtain a melt extrudate.

[0050] 4) The melt extrudate is sequentially passed through an air bath (temperature of 130°C, length of 125 cm), two air baths (temperature of 25°C, length of 75 cm), an oil bath (inverted), a first draw roller (temperature of 90°C), a second draw roller (temperature of 90°C), a third draw roller (temperature of 110°C), a heat setting roller (temperature of 125°C), and a winder to obtain the PVDF fiber for filter fabric. The spinneret draw ratio is 100, the first-stage draw ratio is 2.5, the second-stage draw ratio is 1.5, and the winding retraction rate is 93%.

[0051] It is detected that the PVDF fiber for filter fabric obtained has a fineness of 500D / 50f, a crystallinity of 50%±2%, a tensile strength of 3.4cN / dtex±0.2cN / dtex, an elongation at break of 15%±2%, a heat shrinkage rate at 120°C of 5%±1%, a water contact angle of 115°±2°, and an oil contact angle close to 0°.

[0052] Comparative Example 3

[0053] A PVDF fiber for filter fabric is prepared. The process method is as follows:

[0054] 1) The PVDF resin with a melt index of 8g / 10min at 230°C / 2.16kg is used as a matrix phase at a content of 97wt.%; the perfluoropolyether with an average molecular weight of 1800 and the tetrafluoroethylene-perfluoroalkoxy vinyl ether with a melt index of 5g / 10min (230°C / 2.16kg) are mixed at a mass ratio of 2:3 as a perfluoropolymer compound at a content of 1wt.%; the carbon nanotube with a "linear" length of 5μm is used as a lipophilic hydrophobic nucleating agent at a content of 2wt.%. The PVDF resin, the perfluoropolymer compound, and the lipophilic hydrophobic nucleating agent are sufficiently mixed using a high-speed mixer, and then a PVDF composite master batch is prepared by a twin-screw extruder. The twin-screw extruder has a total of five zone temperature controls, the screw zone one temperature is 180°C, the screw zone two temperature is 210°C, the screw zone three temperature is 220°C, the screw zone four temperature is 230°C, and the screw zone five temperature is 240°C, and the pipe temperature and the die temperature are both 220°C.

[0055] 2) The PVDF composite master batch dried in a vacuum oven at 50°C for 10h was fed into the hopper of the single screw extruder, and then the master batch was sequentially passed through the screw zone 1 with a temperature of 180°C, the screw zone 2 with a temperature of 210°C, the screw zone 3 with a temperature of 220°C, the screw zone 4 with a temperature of 240°C, the screw zone 5 with a temperature of 255°C, the screw flange with a temperature of 260°C and the melt channel with a temperature of 255°C under the shearing action of the screw, to obtain a fully mixed and molten melt.

[0056] 3) The fully mixed and molten melt was quantitatively passed through the spinning box flange with a temperature of 255°C and the spinning box body with a temperature of 260°C under the action of the metering pump, filtered and finally extruded to obtain a molten extrudate.

[0057] 4) The molten extrudate was sequentially passed through an air bath (with a temperature of 130°C and a length of 125cm), an air bath (with a temperature of 25°C and a length of 75cm), an oil bath (reversed), a first stretching roller (with a temperature of 90°C), a second stretching roller (with a temperature of 90°C), a third stretching roller (with a temperature of 110°C), a heat setting roller (with a temperature of 125°C) and a netter, and then wound to obtain the PVDF fiber for filter fabric. The spinning head draw ratio was 100, the first-stage draw ratio was 2.5, the second-stage draw ratio was 1.5, and the winding retraction rate was 93%.

[0058] It was detected that the PVDF fiber for filter fabric had a fineness of 500D / 50f, a crystallinity of 54%±2%, a tensile strength of 3.6cN / dtex±0.2cN / dtex, an elongation at break of 18%±2%, a heat shrinkage rate at 120°C of 3%±1%, a water contact angle of 117°±2° and an oil contact angle close to 0°.

[0059] Comparative Example 4

[0060] A PVDF fiber for filter fabric was prepared. The process method was as follows:

[0061] 1) PVDF resin with a melt index of 8 g / 10 min at 230 °C / 2.16 kg is used as a matrix phase in an amount of 97 wt.%; perfluoropolyether with an average molecular weight of 1800, tetrafluoroethylene-perfluoroalkoxy vinyl ether with a melt index of 5 g / 10 min (230 °C / 2.16 kg) are mixed in a mass ratio of 2:3 as a perfluoropolymer compound in an amount of 1 wt.%; graphene with an average flake size of 5 μm as a lipophilic-hydrophobic nucleating agent in an amount of 2 wt.%. The PVDF resin, the perfluoropolymer compound and the lipophilic-hydrophobic nucleating agent are mixed well using a high-speed mixer, and then a PVDF composite master batch is prepared by a twin-screw extruder. The twin-screw extruder has five zones of temperature control, the temperature of the first screw zone is 180 °C, the temperature of the second screw zone is 210 °C, the temperature of the third screw zone is 220 °C, the temperature of the fourth screw zone is 230 °C, the temperature of the fifth screw zone is 240 °C, and the temperature of the pipe and the die is 220 °C.

[0062] 2) The PVDF composite master batch dried in a vacuum drying oven at 50 °C for 10 h is fed into the hopper of a single-screw extruder, and then the master batch passes through the first screw zone at a temperature of 180 °C, the second screw zone at a temperature of 210 °C, the third screw zone at a temperature of 220 °C, the fourth screw zone at a temperature of 240 °C, the fifth screw zone at a temperature of 255 °C, the screw flange at a temperature of 260 °C and the melt pipe at a temperature of 255 °C in turn under the shearing action of the screw, to obtain a melt which is mixed well.

[0063] 3) The melt which is mixed well is quantitatively extruded through the spinning box flange at a temperature of 255 °C and the spinning box body at a temperature of 260 °C under the action of a metering pump, filtered and finally extruded to obtain a melt extrudate.

[0064] 4) The melt extrudate passes through an air bath (temperature 130 °C, length 125 cm), an air bath (temperature 25 °C, length 75 cm), an oil bath (reversing), a first stretching roller (temperature 90 °C), a second stretching roller (temperature 90 °C), a third stretching roller (temperature 110 °C), a heat setting roller (temperature 125 °C) and a netter in turn, and is wound to obtain the PVDF fiber for filter fabric. The spinning head draw ratio is 100, the first-stage draw ratio is 2.5, the second-stage draw ratio is 1.5, and the winding retraction rate is 93%.

[0065] It is detected that the PVDF fiber for filter fabric obtained has a fineness of 500 D / 50 f, a crystallinity of 56% ± 2%, a tensile strength of 3.7 cN / dtex ± 0.2 cN / dtex, an elongation at break of 14% ± 2%, a heat shrinkage at 120 °C of 3% ± 1%, a water contact angle of 118° ± 2° and an oil contact angle close to 0°.

[0066] Comparative Example 5

[0067] A PVDF fiber for filter fabric was prepared. The process method is as follows:

[0068] 1) PVDF resin with a melt index of 8 g / 10 min at 230 °C / 2.16 kg was used as a base phase in an amount of 97 wt.%; perfluoropolyether with an average molecular weight of 1800, tetrafluoroethylene-perfluoroalkoxy vinyl ether with a melt index of 5 g / 10 min (230 °C / 2.16 kg) were mixed in a mass ratio of 2:3 as a perfluoropolymer compound in an amount of 1 wt.%; a blend of three types of additives, hydrophobic silica with a "spherical" average particle size of 40 nm, carbon nanotubes with a "linear" length of 5 μm, and graphene with an "sheet" average sheet size of 5 μm, were blended in a mass ratio of 1:1:1 as a lipophilic hydrophobic nucleating agent in an amount of 2 wt.%. The PVDF resin, perfluoropolymer compound, and lipophilic hydrophobic nucleating agent were mixed well using a high-speed mixer, and then a PVDF composite master batch was prepared by a twin-screw extruder. The twin-screw extruder had a total of five zone temperature controls, with a screw zone one temperature of 180 °C, a screw zone two temperature of 210 °C, a screw zone three temperature of 220 °C, a screw zone four temperature of 230 °C, a screw zone five temperature of 240 °C, and a pipe temperature and die temperature of 220 °C.

[0069] 2) The PVDF composite master batch, which was dried in a vacuum drying oven at 50 °C for 10 h, was fed into the feed hopper of a single-screw extruder, and then the master batch was sequentially passed through a screw zone one with a temperature of 180 °C, a screw zone two with a temperature of 210 °C, a screw zone three with a temperature of 220 °C, a screw zone four with a temperature of 240 °C, a screw zone five with a temperature of 255 °C, a screw flange with a temperature of 260 °C, and a melt pipe with a temperature of 255 °C under the action of screw shearing to obtain a fully mixed and melted melt.

[0070] 3) The fully mixed and melted melt was quantitatively passed through a spinning box flange with a temperature of 255 °C and a spinning box body with a temperature of 260 °C under the action of a metering pump, filtered, and finally extruded to obtain a melt extrudate.

[0071] 4) The melt extrudate was passed through an air bath (temperature of 25 °C, length of 75 cm), an oil bath (inverted), a first stretching roller (temperature of 90 °C), a second stretching roller (temperature of 90 °C), a third stretching roller (temperature of 110 °C), a heat setting roller (temperature of 125 °C), and a netting device, and then wound to obtain the PVDF fiber for filter fabric. The spinneret draw ratio was 100, the first-stage draw ratio was 2.5, the second-stage draw ratio was 1.5, and the winding retraction rate was 93%.

[0072] The obtained filter fabric has a PVDF fiber fineness of 500D / 50f, a crystallinity of 45%±2%, a tensile strength of 3.0cN / dtex±0.2cN / dtex, an elongation at break of 20%±2%, a thermal shrinkage at 120℃ of 5%±1%, a water contact angle of 122°±2°, and an oil contact angle close to 0°.

[0073] Example 2

[0074] A PVDF fiber for filter fabric was prepared. The process method is as follows:

[0075] 1) PVDF resin with a melt index of 8g / 10min at 230℃ / 2.16kg was used as a matrix phase at a content of 97wt.%; perfluoropolyether with an average molecular weight of 1800 and tetrafluoroethylene-perfluoroalkoxy vinyl ether with a melt index of 5g / 10min (230℃ / 2.16kg) were used as perfluoropolymer compounds at a mass ratio of 2:3 at a content of 3wt.%. The PVDF resin and perfluoropolymer compounds were mixed well using a high-speed mixer, and then a PVDF composite master batch was prepared by a twin-screw extruder. The twin-screw extruder had a total of five zone temperature controls, with screw zone one at 180℃, screw zone two at 210℃, screw zone three at 220℃, screw zone four at 230℃, and screw zone five at 240℃, and the pipe temperature and die temperature were both 220℃.

[0076] 2) The PVDF composite master batch dried in a vacuum drying oven at 50℃ for 10h was sent to the feeding hopper of a single-screw extruder, and then the master batch was sequentially passed through screw zone one at 180℃, screw zone two at 210℃, screw zone three at 220℃, screw zone four at 240℃, screw zone five at 255℃, screw flange at 260℃, and melt pipe at 255℃ under the shearing action of the screw, to obtain a fully mixed melt.

[0077] 3) The fully mixed melt was quantitatively passed through the spinning box flange at 255℃ and the spinning box body at 260℃ under the action of a metering pump, filtered, and finally extruded to obtain a melt extrudate.

[0078] 4) The melt extrudate successively passes through an air bath (temperature 130 °C, length 125 cm), two air baths (temperature 25 °C, length 75 cm), an oil bath (inverted), a first draw roller (temperature 90 °C), a second draw roller (temperature 90 °C), a third draw roller (temperature 110 °C), a heat setting roller (temperature 125 °C), a winder, to obtain the PVDF fiber for filter fabric. Wherein, the spinneret draw ratio is 75, the first stage draw ratio is 1.5, the second stage draw ratio is 1.2, and the winding retraction rate is 95%.

[0079] It is detected that the PVDF fiber for filter fabric obtained has a fineness of 700 D / 50 f, a crystallinity of 51%±2%, a tensile strength of 3.2 cN / dtex±0.2 cN / dtex, an elongation at break of 20%±2%, a heat shrinkage rate at 120 °C of 5%±1%, a water contact angle of 119°±2°, and an oil contact angle of 10°±2°.

[0080] Example 3

[0081] A PVDF fiber for filter fabric is prepared. The process method is as follows:

[0082] 1) PVDF resin with a melt index of 8 g / 10 min at 230 °C / 2.16 kg is used as a matrix phase, with a content of 95 wt.%; perfluoropolyether with an average molecular weight of 1800, tetrafluoroethylene-perfluoroalkoxy vinyl ether with a melt index of 5 g / 10 min (230 °C / 2.16 kg) are used as a perfluoropolymer compound, with a mass ratio of 2:3, and a content of 1 wt.%; a blend of hydrophobic silica with a "spherical" average particle size of 40 nm, carbon nanotubes with a "linear" length of 5 μm, and graphene with a "sheet" average sheet size of 5 μm in a mass ratio of 1:1:1 is used as a lipophilic hydrophobic nucleating agent, with a content of 4 wt.%. The PVDF resin, the perfluoropolymer compound, and the lipophilic hydrophobic nucleating agent are mixed well using a high-speed mixer, and then a PVDF composite master batch is prepared by a twin-screw extruder. The twin-screw extruder has five zones of temperature control, with a screw zone one temperature of 180 °C, a screw zone two temperature of 210 °C, a screw zone three temperature of 220 °C, a screw zone four temperature of 230 °C, and a screw zone five temperature of 240 °C, and a pipe temperature and a die temperature of 220 °C.

[0083] 2) The PVDF composite masterbatch dried in a vacuum oven at 50°C for 10h is fed into the hopper of the single screw extruder, and then the masterbatch is sequentially passed through the screw zone 1 with a temperature of 180°C, the screw zone 2 with a temperature of 210°C, the screw zone 3 with a temperature of 220°C, the screw zone 4 with a temperature of 240°C, the screw zone 5 with a temperature of 255°C, the screw flange with a temperature of 260°C and the melt channel with a temperature of 255°C under the shearing action of the screw, to obtain a fully mixed and molten melt.

[0084] 3) The fully mixed and molten melt is quantitatively passed through the spinning box flange with a temperature of 255°C and the spinning box body with a temperature of 260°C under the action of the metering pump, filtered and finally extruded to obtain a molten extrudate.

[0085] 4) The molten extrudate is sequentially passed through an air bath (with a temperature of 130°C and a length of 125cm), an air bath (with a temperature of 25°C and a length of 75cm), an oil bath (reversed), a first stretching roller (with a temperature of 90°C), a second stretching roller (with a temperature of 90°C), a third stretching roller (with a temperature of 110°C), a heat setting roller (with a temperature of 125°C) and a netter, and then wound to obtain the PVDF fiber for filter fabric. The spinning head draw ratio is 50, the first-stage draw ratio is 1.3, the second-stage draw ratio is 1.2, and the winding retraction rate is 96%.

[0086] It is detected that the PVDF fiber for filter fabric obtained has a fineness of 800D / 50f, a crystallinity of 56%±2%, a tensile strength of 3.8cN / dtex±0.2cN / dtex, an elongation at break of 10%±2%, a heat shrinkage rate at 120°C of 3%±1%, a water contact angle of 123°±2° and an oil contact angle close to 0°.

[0087] Example 4

[0088] A PVDF fiber for filter fabric is prepared. The process method is as follows:

[0089] 1) PVDF resin with a melt index of 8 g / 10 min at 230 °C / 2.16 kg is used as a matrix phase in an amount of 93 wt.%; perfluoropolyether with an average molecular weight of 1800, tetrafluoroethylene-perfluoroalkoxy vinyl ether with a melt index of 5 g / 10 min (230 °C / 2.16 kg) are used as a perfluoropolymer compound in a mass ratio of 2:3 in an amount of 3 wt.%; a blend of three kinds of morphological additives, hydrophobic silica with a "spherical" average particle size of 40 nm, carbon nanotubes with a "linear" length of 5 μιη, and graphene with a "sheet" average sheet size of 5 μιη, are blended in a mass ratio of 1:1:1 and used as a lipophilic hydrophobic nucleating agent in an amount of 4 wt.%. The PVDF resin, the perfluoropolymer compound, and the lipophilic hydrophobic nucleating agent are mixed well using a high-speed mixer, and then a PVDF composite master batch is prepared by a twin-screw extruder. The twin-screw extruder has five zones for temperature control, the temperature of the first screw zone is 180 °C, the temperature of the second screw zone is 210 °C, the temperature of the third screw zone is 220 °C, the temperature of the fourth screw zone is 230 °C, the temperature of the fifth screw zone is 240 °C, and the temperature of the pipe and the die is 220 °C.

[0090] 2) The PVDF composite master batch dried in a vacuum drying oven at 50 °C for 10 h is fed into the hopper of a single-screw extruder, and then the master batch is sequentially passed through the first screw zone at a temperature of 180 °C, the second screw zone at a temperature of 210 °C, the third screw zone at a temperature of 220 °C, the fourth screw zone at a temperature of 240 °C, the fifth screw zone at a temperature of 255 °C, the screw flange at a temperature of 260 °C, and the melt pipe at a temperature of 255 °C under the shearing action of the screw, to obtain a melt that is mixed well and melted.

[0091] 3) The melt that is mixed well and melted is quantitatively passed through the spinning box flange at a temperature of 255 °C and the spinning box body at a temperature of 260 °C under the action of a metering pump, filtered, and finally extruded to obtain a melt extrudate.

[0092] 4) The melt extrudate is sequentially passed through an air bath (temperature of 130 °C, length of 125 cm), a second air bath (temperature of 25 °C, length of 75 cm), an oil bath (reversing), a first drawing roller (temperature of 90 °C), a second drawing roller (temperature of 90 °C), a third drawing roller (temperature of 110 °C), a heat setting roller (temperature of 125 °C), and a netting device, and then wound to obtain the PVDF fiber for the filter fabric. The spinning nozzle draw ratio is 30, the first-stage draw ratio is 1.3, the second-stage draw ratio is 1.2, and the winding retraction rate is 97%.

[0093] The obtained filter fabric has a fineness of 900D / 50f, a crystallinity of 54%±2%, a tensile strength of 3.4cN / dtex±0.2cN / dtex, an elongation at break of 8%±2%, a heat shrinkage at 120℃ of 3%±1%, a water contact angle of 125°±2°, and an oil contact angle close to 0°.

Claims

1. A method for preparing polyvinylidene fluoride fiber for filter fabrics, characterized in that: Includes the following steps, (1) Mix 0.2-3 wt.% of perfluorinated polymer, 0.5-4 wt.% of oleophilic-hydrophobic nucleating agent and 93-99 wt.% of polyvinylidene fluoride resin, and add the mixture to a twin-screw extruder to prepare polyvinylidene fluoride composite masterbatch; wherein the perfluorinated polymer is composed of perfluorinated polyether and tetrafluoroethylene-perfluoroalkoxy vinyl ether; the oleophilic-hydrophobic nucleating agent includes one or more of hydrophobic silica, carbon nanotubes and graphene; (2) The polyvinylidene fluoride composite masterbatch is fed into a single-screw extruder to melt and form a melt; (3) The melt is extruded through a screw extrusion spinning machine to obtain a melt extrudate; the melt extrudate is passed through an air bath, a second air bath, an oil bath, a first stretching roller, a second stretching roller, a third stretching roller, a heat setting roller, and a networker, and then wound to obtain the polyvinylidene fluoride fiber; In step (3), the temperature of the first air bath is 120-140℃ and the length is 100-150cm; the temperature of the second air bath is 20-28℃ and the length is 50-100cm. The winding process involves a spinneret draw ratio of 30–150, a primary draw ratio of 1.5–3.5, a secondary draw ratio of 1.1–2, and a winding shrinkage rate of 90–97%.

2. The method for preparing polyvinylidene fluoride fiber for filter fabrics according to claim 1, characterized in that: In step (1), the melt index of the polyvinylidene fluoride resin is 3 to 13 g / 10 min.

3. The method for preparing polyvinylidene fluoride fiber for filter fabrics according to claim 1 or 2, characterized in that: In step (1), the mass ratio of perfluoropolyether to tetrafluoroethylene-perfluoroalkoxy vinyl ether is 2:3, the average molecular weight of perfluoropolyether is 500-6000, and the melt index of tetrafluoroethylene-perfluoroalkoxy vinyl ether is 1-10 g / 10 min.

4. The method for preparing polyvinylidene fluoride fiber for filter fabrics according to claim 1 or 2, characterized in that: In step (1), the oleophilic and hydrophobic nucleating agent is composed of spherical hydrophobic silica with an average particle size of 20-100 nm, linear carbon nanotubes with a length of 1-10 μm, and sheet graphene with an average sheet diameter of 1-10 μm in a mass ratio of 1:1:

1.

5. The method for preparing polyvinylidene fluoride fiber for filter fabrics according to claim 1 or 2, characterized in that: In step (1), the twin-screw extruder includes five temperature control zones: the temperature of screw zone 1 is 160-190℃, the temperature of screw zone 2 is 190-220℃, the temperature of screw zone 3 is 200-230℃, the temperature of screw zone 4 is 210-240℃, the temperature of screw zone 5 is 220-250℃, the pipe temperature and the die temperature are both 200-230℃, and the die temperature is 20℃ lower than the temperature of screw zone 5.

6. The method for preparing polyvinylidene fluoride fiber for filter fabrics according to claim 1 or 2, characterized in that: In step (2), the polyvinylidene fluoride composite masterbatch is fed into a single-screw extruder and passes sequentially through screw zone 1 (temperature 155-190℃), screw zone 2 (temperature 185-220℃), screw zone 3 (temperature 195-230℃), screw zone 4 (temperature 215-250℃), screw zone 5 (temperature 230-265℃), screw flange (temperature 235-270℃), and melt pipe (temperature 230-265℃) to obtain a fully mixed and molten melt.

7. The method for preparing polyvinylidene fluoride fiber for filter fabrics according to claim 1 or 2, characterized in that: In step (3), the melt is passed through the spinning box flange of a screw extrusion spinning machine at a temperature of 230-265°C and the spinning box body at a temperature of 235-270°C, and then filtered and extruded to obtain the molten extrudate.

8. The method for preparing polyvinylidene fluoride fiber for filter fabrics according to claim 1 or 2, characterized in that: The stretching temperature of the first stretching roller is 85-95℃, the stretching temperature of the second stretching roller is 85-95℃, the stretching temperature of the third stretching roller is 105-115℃, and the temperature of the heat setting roller is 120-130℃.

9. The polyvinylidene fluoride fiber for filter fabric prepared by the method for preparing filter fabric according to claim 1.