A method for producing a core-sheath type conductive fiber

Abstract

The present application relates to a kind of preparation methods of skin-core conductive fiber, the raw material of skin layer and the raw material of core layer are respectively melted and extruded to form melt stream after passing through skin-core composite spinning assembly, then conductive substance is combined with the melt stream skin layer by hot air flow, after which it is cooled to form and the skin-core composite conductive fiber is prepared;The melting point of the raw material of skin layer is 40-70 ℃ lower than the melting point of the raw material of core layer;The temperature of hot air flow is in the range of 20 ℃ above the melting point of the raw material of skin layer;Hot annealing temperature is 170-195 ℃;In the preparation method of the present application, the raw material of skin layer and core layer is two polymers with large difference in melting point, in the process of combining conductive substance with the melt stream skin layer, the core layer keeps stiff due to heat transfer, provides basic configuration and mechanical support for the skin-core composite conductive fiber, and is treated by hot annealing process at a temperature higher than the skin layer, which greatly improves the conductive performance and mechanical properties.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of conductive fibers, and relates to a preparation method of a skin-core type conductive fiber. BACKGROUND

[0002] In recent years, with the development of science and technology and the improvement of human living standards, people's requirements for clothing are also increasing. The conventional polymers such as polyacrylonitrile, polyamide and polyester have single function, and the market has been close to saturation. Therefore, it has become a trend to produce differentiated fibers with high added value. As a branch of differentiated fibers, the skin-core type composite fiber has greater improvement in performance compared with single-component fibers, and has a relatively wide application in the field of non-woven fabrics. The added value of the product determines its demand, and the market pays more attention to novel and multi-functional fibers. As one of the fibers, the conductive fiber has excellent anti-static and anti-magnetic field radiation functions, and can be applied to sensors, electromagnetic interference shielding fabrics, static protection fabrics and signal transmission textiles.

[0003] Conductive fibers are divided into inorganic conductive fibers, organic conductive fibers and composite conductive fibers. Among them, the composite conductive fiber is widely used in the fields of textiles and clothing due to its excellent and durable conductive performance.

[0004] The melt spinning method for preparing the composite conductive fiber has its own advantages. Compared with the wet spinning method, the melt spinning method avoids the use of a large amount of water and volatile chemicals, is more friendly to the environment, has lower production cost and higher production efficiency. At the same time, the fiber quality is stable in the process of fiber formation, and the situation of caking or breaking is less.

[0005] In the prior art, in order to achieve good conductive performance of the composite conductive fiber prepared by the melt spinning method, the amount of conductive material must be greatly increased, for example:

[0006] Document 1 (Melt blending of carbon nanotubes / polyaniline / polypropylene compounds and their melt spinning to conductive fibres [J]. Synthetic Metals, 2010.) prepared a blend of polypropylene, polyaniline and multi-walled carbon nanotubes by blending, and obtained conductive fibers by melt spinning. When the content of polyaniline polymer in the system is 20%, with the content of multi-walled carbon nanotubes increasing from 1.5% to 7.5%, the electrical conductivity is improved by two orders of magnitude, which is 0.13 S / m. When the conductive material in the system is only multi-walled carbon nanotubes, with the content of multi-walled carbon nanotubes increasing from 1.5% to 7.5%, the electrical conductivity is improved by one order of magnitude, which is 0.07 S / m. The electrical conductivity of the conductive fiber is enhanced with the increase of the content of multi-walled carbon nanotubes.

[0007] Document 2 (Structure and properties of melt-spun PET / MWCNT nanocomposite fibers [J]. Polymer Engineering and Science, 2010.) prepared conductive masterbatch by blending multi-walled carbon nanotubes (MWCNT) and polyethylene terephthalate (PET), and obtained conductive ultrafine fibers by melt spinning. With the increase of the content of multi-walled carbon nanotubes, the electrical conductivity of the fiber is improved. When the content of multi-walled carbon nanotubes increases from 1% to 3%, the growth rate of electrical conductivity is faster, which is improved by 8 orders of magnitude; when the content of multi-walled carbon nanotubes increases from 3% to 7%, the growth rate of electrical conductivity is relatively slow, which is improved by 3 orders of magnitude, and the final electrical conductivity is 1 S / m. It can be seen that with the increase of the content of conductive material, the electrical conductivity of the fiber is continuously improved.

[0008] Document 3 (Electrical conductivity and mechanical properties of melt-spun ternary composites comprising PMMA, carbon fibers and carbon black [J]. Composites Science and Technology, 2017.) studies the electrical conductivity of poly(methyl methacrylate) (PMMA) melt-spun composite materials, and prepares PMMA / CF (carbon fiber) and PMMA / CB (carbon black) composite materials. The electrical conductivity of the two materials is related to the filling amount of CB and CFR. The electrical conductivity of PMMA / CF increases significantly with the increase of CF content. When the CF content increases from 20% to 50%, the electrical conductivity increases by 7 orders of magnitude, reaching 10 S / m. The electrical conductivity of PMMA / CB also increases with the increase of CB content. When the CF content increases from 0 to 20%, the electrical conductivity increases by 7 orders of magnitude, reaching 10 S / m. The electrical conductivity of the two materials increases significantly with the increase of the content of the conductive material.

[0009] In summary, the addition amount of the conductive material has an important influence on the comprehensive performance of the fiber. For the electrical conductivity, too low an addition amount is not conducive to the formation of a continuous conductive path; and too much addition has little effect on the further improvement of the electrical conductivity of the fiber or even reduces the electrical conductivity of the fiber. When the conductive material forms a complete conductive path on the fiber, theoretically, too much addition has little effect on the complete conductive path, but in fact, the final electrical conductivity of the fiber is related to the forming process of the fiber, and too much addition may cause the agglomeration of particles on the micro-morphology of the fiber and the local appearance of gaps on the surface of the fiber after forming, thereby reducing the electrical conductivity of the fiber, and may also reduce the mechanical properties of the fiber, such as tensile properties, bending properties, etc.

[0010] Therefore, it is necessary to study a method for preparing a skin-core type conductive composite fiber by melt spinning, to ensure that the electrical conductivity is more excellent under the condition that the addition amount of the conductive material is equivalent to or even less than that of the prior art. SUMMARY

[0011] The purpose of the present application is to solve the problems existing in the prior art and provide a method for preparing a skin-core type conductive fiber.

[0012] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0013] A method for preparing a sheath-core composite conductive fiber, sheath layer raw materials and core layer raw materials are melted respectively and extruded into melt streams through a sheath-core composite spinning assembly, then a hot air stream is used to combine the conductive substance with the sheath layer of the melt stream, and then cooling, drawing and heat annealing are performed in sequence to obtain the sheath-core composite conductive fiber.

[0014] The melting point of the sheath layer raw materials is 40-70℃ lower than that of the core layer raw materials, so that heat transfer occurs between the core layer with higher temperature and the sheath layer with lower temperature, and the core layer appears to be stiff;

[0015] The temperature of the hot air stream is in the range of 20℃ above the melting point of the sheath layer raw materials; after the melt stream is extruded, heat exchange occurs between the core layer with higher temperature and the sheath layer, the sheath layer remains in a melt state at this temperature, and the combination of the conductive substance and the sheath layer of the melt stream is realized under the action of the hot air stream, while the core layer is relatively stiff due to heat loss;

[0016] The conductive substance can be single-walled and multi-walled carbon nanotubes, graphene, carbon black and other carbon-based materials, and also can be elemental metals such as gold, silver and zinc, and metal oxides such as magnesium oxide, zinc oxide and potassium oxide.

[0017] The heat annealing temperature is not lower than the melting point of the sheath layer raw materials, and the drawing ratio is 8-15 times during the heat annealing process. The heat annealing process can change the aggregation state of the conductive substance on the fiber, and better conductivity can be achieved on the fiber with a large difference in melting point between the sheath and the core. The reason for better conductivity is that the sheath and core raw materials with a large difference in melting point are used, and the heat annealing process is performed at a relatively high temperature. The high melting point of the core layer is similar to the stiff state at the heat annealing temperature, which ensures the basic configuration of the fiber and avoids problems such as breakage during the heat annealing process of the fiber. On this basis, the fiber is stretched at a high temperature, the aggregation state of the conductive substance is changed, and the conductive substance is rearranged along the fiber, thereby improving the conductivity of the fiber.

[0018] Specifically, the heat annealing can make the conductive substance and the polymer chain relax to a more isotropic state. The increase in polymer mobility allows the entropy-driven relaxation of the conductive substance, so that the conductive substance is rearranged along the fiber, thereby reducing the resistivity of the composite fiber and improving the conductivity. At the same time, the heat annealing process also improves the mechanical properties of the fiber.

[0019] As a preferred technical solution:

[0020] The method for preparing a sheath-core composite conductive fiber as described above, the content of the conductive substance in the sheath-core composite conductive fiber is 3.2-7wt%, and the electrical conductivity is 5.6-8.8×10 2 S / m.

[0021] The preparation method of the core-sheath composite conductive fiber as described above, the melt stream formed by the core-sheath composite spinning assembly extrusion is first treated by the heat preservation channel, and then enters the box loaded with the conductive substance, and the box has an annular hot air flow for realizing the compounding of the conductive substance and the sheath layer of the melt stream.

[0022] The preparation method of the core-sheath composite conductive fiber as described above, the temperature of the heat preservation channel is 165-195℃, and the heat preservation channel is a hollow column, and the temperature is set to ensure that the melt skin is in a melt state, and the wind speed of the hot air flow is 0.5-2m / s, and the temperature of the hot air flow is the same as that of the heat preservation channel.

[0023] The preparation method of the core-sheath composite conductive fiber as described above, the mass ratio of the sheath layer raw material to the core layer raw material is 20-50:50-80. In the control of the components, the core layer accounts for a large proportion, and the sheath layer accounts for a small proportion. The core layer is a high-melting-point polymer, which ensures the stiffness in the subsequent preparation of the conductive fiber, and the sheath layer is a low-melting-point polymer, which is conducive to compounding with the conductive substance. In order to ensure the stiffness of the fiber in the subsequent preparation of the conductive fiber, the proportion of the high-melting-point polymer of the core layer is relatively large.

[0024] The preparation method of the core-sheath composite conductive fiber as described above, the sheath layer raw material is PP, the melting point of the PP is 165-175℃, and the melt index under the test conditions of 2.16kg at 180-200℃ is 30-35g / 10min; the core layer raw material is PBT, the melting point of the PBT is 220-230℃, and the intrinsic viscosity is 0.75-0.86dl / g.

[0025] The preparation method of the core-sheath composite conductive fiber as described above, the hot annealing temperature is 170-195℃.

[0026] The preparation method of the core-sheath composite conductive fiber as described above, the conductive substance is single-walled carbon nanotubes or multi-walled carbon nanotubes, and the single-walled carbon nanotubes or multi-walled carbon nanotubes are subjected to metal element doping treatment, and the contact resistance is reduced to 69%-82% of the original value after doping;

[0027] The multi-walled carbon nanotubes are improved by using the doping method, the metal element is introduced into the multi-walled carbon nanotubes, so as to reduce the contact resistance and improve the conductive performance. In this process, the multi-walled carbon nanotubes first undergo an acidification process, which is to open the multi-walled carbon nanotubes, which is conducive to the doping of the metal element. The acidification time is 3-8h. If the acidification time is too short, it is not conducive to the subsequent adsorption of gold nanoparticles. If the acidification time is too long, the carbon nanotubes will be broken. The low-temperature plasma technology is used to improve the multi-walled carbon nanotubes with -COOH or -OH activity. Then, a metal salt solution is added, and a reduction reaction is carried out by using hydrogen to introduce the metal element into the multi-walled carbon nanotube network.

[0028] The preparation method of the core-sheath composite conductive fiber as described above, wherein the cooling air temperature is 18-24 DEG C, and the air speed is 0.2-0.6 m / s.

[0029] The preparation method of the core-sheath composite conductive fiber as described above, wherein after cooling, the fiber is drawn through a first hot roller and a second hot roller in sequence, the temperature of the first hot roller is 80-95 DEG C, the temperature of the second hot roller is 105-120 DEG C, and the draw ratio is 2-5 times.

[0030] Invention mechanism:

[0031] Based on the process conditions of melt spinning, after the melt is extruded by the composite spinning assembly, heat exchange will occur between the core layer and the sheath layer due to the higher temperature of the core layer, and at this temperature, the sheath layer remains in a melt state, while the core layer is relatively hard due to heat loss. The conductive material is combined with the melt stream sheath by hot air flow, the flow rate of the air flow controls the amount of conductive material added to the final conductive fiber, and the composite conductive fiber is prepared by melt spinning in one step.

[0032] In the prior art, first, in the treatment of conductive material, low-temperature plasma technology and metal doping modification technology are combined to improve the activity of -COOH or -OH of the multi-walled carbon nanotube after oxidation treatment, which is beneficial to the subsequent doping of metal elements and the introduction of carbon nanotube network to improve the metal doping rate and reduce the resistance, thereby improving the conductivity of the conductive material itself.

[0033] In the prior art, the preparation of conductive fiber by melt spinning process mainly involves the modification of raw materials, which involves the blending of conductive material and the melt extrusion of double components. In addition to the verification of spinnability, the mixing of raw materials and conductive material and whether the conductive material can be distributed on the surface of the fiber need to be considered. The construction of the conductive network of the core-sheath fiber is located on the surface, which leads to the fact that the small amount of conductive material cannot be fully utilized by the method of raw material modification. In order to construct the conductive path of the sheath, how to fully utilize the small amount of conductive material to construct the conductive network on the sheath becomes the key. The present application combines the conductive particles in the sheath by hot air flow, and rapidly fixes the spatial position by cooling air flow to prevent further penetration along the direction perpendicular to the axial direction. The conductive material is distributed along the axial direction of the sheath and is relatively fixed on the sheath, which reduces the transverse distance between particles (the transverse distance is the distance between adjacent carbon nanotubes perpendicular to the axial direction of the fiber) when constructing the conductive network.

[0034] In order to further improve the conductive performance of the fiber, a post-processing method (i.e. heat annealing process) is used to process the fiber. The conductive substance is located on the low melting point skin layer, and the core layer is high melting point. At a relatively high heat annealing temperature of the skin layer, the fiber is stretched at a high ratio, and at this time the high melting point of the core layer is approximately hard at the heat annealing temperature, which ensures the basic configuration of the fiber, thereby avoiding problems such as breakage of the final fiber. On this basis, the fiber is stretched at a high temperature, so that the aggregation state of the conductive substance changes along the fiber, and the conductive substance will be rearranged, which is conducive to the formation of complete continuous path of the conductive substance. Through the overall preparation process of the conductive fiber, the effective use of the low content of the conductive substance is realized, and the conductive path is formed by the rearrangement of the conductive substance on the fiber, so that the conductive effect of the fiber is greatly improved.

[0035] Advantages:

[0036] (1) The preparation method of the skin-core composite conductive fiber of the present application is based on the method of melt spinning, and the composite conductive fiber is prepared by using a heat preservation channel and a preheating box loaded with conductive substance. On the basis of not affecting the spinnability of the skin-core fiber, the conductive substance is introduced. Compared with the traditional spinning method and the fiber surface coating of conductive coating, firstly, the complicated process of adding conductive substance in the master batch and then preparing conductive fiber (i.e. after adding conductive substance in the master batch, the spinnability needs to be verified) of the traditional melt spinning is avoided, secondly, the coating of the fiber after forming is avoided, the preparation process is simplified, the conductive fiber can be prepared by one-step method, and the use of a large amount of chemical reagents and the volatilization of the reagents in the drying process are avoided, thereby reducing the harm to the environment;

[0037] (2) The preparation method of the skin-core composite conductive fiber of the present application, the conductive substance is single-walled or multi-walled carbon nanotube doped with metal element, which can greatly reduce the contact resistance, and the heat annealing process is used for post-processing at a temperature higher than that of the skin layer, which further improves the aggregation state of the single-walled or multi-walled carbon nanotube, increases the conductive area, and greatly improves the conductive performance and mechanical properties;

[0038] (3) The preparation method of the skin-core composite conductive fiber of the present application, the raw materials of the skin layer and the core layer are two polymers with large difference in melting point, the skin layer is a low melting point polymer, and the core layer is a high melting point polymer; during the process of combining the conductive substance with the melt stream skin layer, the core layer remains hard due to heat transfer, providing basic configuration and mechanical support for the skin-core composite conductive fiber; the orientation structure of the core layer remains unchanged after heat annealing treatment, and the defects of the fiber are eliminated, and the crystal structure gradually returns to normal;

[0039] (4) The preparation method of the skin-core composite conductive fiber of the present application has low cost and simple process, and has great application prospect in the field of textiles;

[0040] (5) The present invention provides a method for preparing a core-sheath composite conductive fiber, which achieves the composite of conductive material and melt stream by controlling the spinning speed and the hot air flow speed. The hot air flow uses the kinetic energy of its circulation process to drive the movement of conductive material. By controlling the hot air flow at a certain speed, the gas-solid (air flow and conductive material) two-phase material is uniformly dispersed, thereby realizing the transfer of conductive material to the sheath of the core-sheath composite conductive fiber. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating the preparation process of core-sheath composite conductive fibers.

[0042] Figure 2 This is a schematic diagram of the structure of a core-sheath composite conductive fiber;

[0043] Figure 3 This is a schematic diagram of the insulation equipment;

[0044] Figure 4 This is a top view of the insulation equipment;

[0045] Figure 5 A schematic diagram of a device for combining conductive materials with a molten fine flow skin;

[0046] Figure 6 A schematic diagram of the internal hot air flow of a device that combines a conductive material with a molten fine flow skin.

[0047] Among them, 1-skin layer, 2-core layer, 3-multi-walled carbon nanotubes, 4-insulation channel, 5-insulation box, 6-preheating box, 7-hot airflow guide plate, 8-conductive material supply end, 9-annular gas distributor, 10-air guide hole, 11-airflow inlet, 12-hot airflow. Detailed Implementation

[0048] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0049] In the description of this invention, the terms "upper," "lower," "left," "right," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0050] The following is some information about the substances used in the examples:

[0051] Multi-walled carbon nanotubes: Manufacturer: Sigma-Aldrich, Product No.: 659258;

[0052] Single-walled carbon nanotubes: Manufacturer: Sigma-Aldrich, Product No.: 698695.

[0053] In embodiments of the present invention, the melt stream formed by extrusion via the core-sheath composite spinning assembly is first heat-insulated through a heat-insulating channel. The melt stream exiting the heat-insulating channel then enters a box containing a conductive material. The box contains an annular hot airflow to achieve the composite of the conductive material and the melt stream skin. Figures 3-4 As shown, the insulation channels 4 are symmetrically distributed 0.5m apart on both sides of the vertical bisector of the width of the insulation box 5. The insulation channels on both sides are perforated vertically and run through the insulation box 5. There are 12 openings on each side, and the lines connecting the openings on both sides are parallel to the length of the insulation box 5 and spaced 25cm apart (for ease of demonstration). Figure 3 (Only one pair of insulated channels is shown in the image); Figure 5 As shown, the box containing the conductive material (i.e., the preheating box 6) has a length × width × height of 3.2 × 2.8 × 3.4 m. Along the vertical direction, the conductive material supply end 8 is located on the vertical axis of symmetry on the left side of the box and is 0.4 m from the bottom. The annular gas distributor 9 is located at the center of the bottom of the box. The height of the annular gas distributor 9 is 0.7 m. The annular gas distributor 9 has vertically upward-opening air guide holes 10 distributed in a ring. The air inlet 11 is located at the center of the annular gas distributor 9. The hot air flow guide plate 7 has a length of 3.14 m, a thickness of 2 cm, and a height of 1.6 m. The lower edge of the hot air flow guide plate 7 is 0.5 m from the annular gas distributor. The two hot air flow guide plates 7 are located 0.9 m from the front and rear sides of the annular gas distributor 9, respectively.

[0054] Table 1. Melting process parameters in each embodiment.

[0055]

[0056]

[0057] Example 1

[0058] A method for preparing gold-doped multi-walled carbon nanotubes, the specific steps of which are as follows:

[0059] (1) First, prepare a 40wt% concentrated sulfuric acid solution, then add 300mg of multi-walled carbon nanotubes (contact resistance of 80kΩ, diameter of 170nm, and length of 9μm) to 500ml of concentrated sulfuric acid solution, then sonicate for 2h, and finally heat in an oil bath at 80℃ for 3h and filter.

[0060] (2) The filtered material of step (1) is washed with ultrapure water to pH 7, then dissolved in ethanol, and then centrifuged to discard the supernatant to obtain a precipitate, which is finally dried in an oven at 50°C;

[0061] (3) The product of step (2) is treated with low-temperature plasma technology at 150W for 25min;

[0062] (4) First, prepare a 2mg / mL potassium gold chloride aqueous solution, then add the product of step (3) to the potassium gold chloride aqueous solution, ultrasonic dispersion for 2h, then stand at room temperature for 8h, then filter and dry, and then add the filtered and dried material to a tubular furnace at 120°C, and pass hydrogen gas for reduction reaction, finally obtain gold-doped multi-walled carbon nanotubes.

[0063] The gold doping rate of the gold-doped multi-walled carbon nanotubes is 0.25%, the average diameter of the gold particles is 30μm, and the contact resistance is reduced to 69% of the original.

[0064] Example 2

[0065] A method for preparing gold-doped multi-walled carbon nanotubes, the specific steps are as follows:

[0066] (1) First, prepare a 45wt% concentrated nitric acid solution, then add 300mg of multi-walled carbon nanotubes (contact resistance 80kΩ, diameter 170nm, length 9μm) to 500ml of the concentrated nitric acid solution, then ultrasonic oscillation for 2h, and finally place in an 80°C oil bath for heating for 5h and filter;

[0067] (2) The filtered material of step (1) is washed with ultrapure water to pH 7, then dissolved in ethanol, and then centrifuged to discard the supernatant to obtain a precipitate, which is dried in an oven at 50°C;

[0068] (3) The product of step (2) is treated with low-temperature plasma technology at 250W for 20min;

[0069] (4) First, prepare a 2mg / mL chloroauric acid trihydrate aqueous solution, then add the product of step (3) to the chloroauric acid trihydrate aqueous solution, ultrasonic dispersion for 2h, then stand at room temperature for 8h, then filter and dry, and then add the filtered and dried material to a tubular furnace at 120°C, and pass hydrogen gas for reduction reaction, finally obtain gold-doped multi-walled carbon nanotubes.

[0070] The gold doping rate of the gold-doped multi-walled carbon nanotubes is 0.38%, the average diameter of the gold particles is 25μm, and the contact resistance is reduced to 82% of the original.

[0071] Example 3

[0072] A preparation method of gold-doped multi-walled carbon nanotubes, the specific steps are as follows:

[0073] (1) First, prepare a mixed solution of sulfuric acid and nitric acid with a volume ratio of 5:5 and a total concentration of 60wt%, then add 300mg of multi-walled carbon nanotubes (contact resistance 80kΩ, diameter 170nm, length 9μm) to 500ml of the mixed solution of sulfuric acid and nitric acid, then ultrasonic oscillation for 2h, finally placed in an 80℃ oil bath for heating for 6h and filtration;

[0074] (2) The filtered material in step (1) is washed with ultrapure water until the pH is 7, then dissolved in ethanol, centrifuged to discard the supernatant to obtain the precipitate, and the precipitate is dried in a 50℃ oven;

[0075] (3) The product of step (2) is treated with low-temperature plasma technology at 300W for 15min;

[0076] (4) First, prepare a 2mg / mL aqueous solution of ammonium tetrachloroaurate, then add the product of step (3) to the aqueous solution of ammonium tetrachloroaurate, ultrasonic dispersion for 2h, then stand at room temperature for 8h, then filter and dry, and then add the filtered and dried material to a tube furnace at 120℃, pass hydrogen gas for reduction reaction, and finally obtain gold-doped multi-walled carbon nanotubes.

[0077] The gold doping rate of the gold-doped multi-walled carbon nanotubes is 0.29%, and the average diameter of the gold particles is 15μm, and the contact resistance is reduced to 74% of the original.

[0078] Example 4

[0079] A preparation method of gold-doped multi-walled carbon nanotubes, the specific steps are as follows:

[0080] (1) First, prepare a mixed solution of sulfuric acid and nitric acid with a volume ratio of 3:7 and a total concentration of 55wt%, then add 300mg of multi-walled carbon nanotubes (contact resistance 80kΩ, diameter 170nm, length 9μm) to 500ml of the mixed solution of sulfuric acid and nitric acid, then ultrasonic oscillation for 2h, finally placed in an 80℃ oil bath for heating for 8h and filtration;

[0081] (2) The filtered material in step (1) is washed with ultrapure water until the pH is 7, then dissolved in ethanol, centrifuged to discard the supernatant to obtain the precipitate, and the precipitate is dried in a 50℃ oven;

[0082] (3) The product of step (2) is treated with low-temperature plasma technology at 200W for 15min;

[0083] (4) First, prepare a 2 mg / mL solution of chloroauric acid trihydrate in water, then add the product of step (3) to the solution of chloroauric acid trihydrate in water, ultrasonically disperse for 2 h, then stand at room temperature for 8 h, then filter and dry, and add the filtered and dried material to a tube furnace at 120°C, pass in hydrogen to perform a reduction reaction, and finally obtain gold-doped multi-walled carbon nanotubes.

[0084] The gold doping rate of the gold-doped multi-walled carbon nanotubes is 0.32%, the average diameter of the gold particles is 22 μm, and the contact resistance is reduced to 78% of the original.

[0085] Example 5

[0086] A method for preparing gold-doped single-walled carbon nanotubes, the specific steps being as follows:

[0087] (1) First, prepare a 45 wt% concentrated sulfuric acid solution, then add 300 mg of single-walled carbon nanotubes (contact resistance 30 kΩ, diameter 10 nm, length 5 μm) to 500 ml of the concentrated sulfuric acid solution, then ultrasonically oscillate for 2 h, and finally place in an 80°C oil bath to heat for 3 h and filter;

[0088] (2) Wash the filtered material of step (1) with ultrapure water until the pH is 7, then dissolve in ethanol, then centrifuge and discard the supernatant to obtain a precipitate, and finally dry in a 50°C oven;

[0089] (3) Treat the product of step (2) using low-temperature plasma technology at 300 W for 15 min;

[0090] (4) First, prepare a 2 mg / mL solution of potassium chloroaurate in water, then add the product of step (3) to the solution of potassium chloroaurate in water, ultrasonically disperse for 2 h, then stand at room temperature for 8 h, then filter and dry, and add the filtered and dried material to a tube furnace at 120°C, pass in hydrogen to perform a reduction reaction, and finally obtain gold-doped single-walled carbon nanotubes.

[0091] The gold doping rate of the gold-doped single-walled carbon nanotubes is 0.45%, the average diameter of the gold particles is 10 μm, and the contact resistance is reduced to 65% of the original.

[0092] Example 6

[0093] A method for preparing a core-sheath composite conductive fiber, as shown in Figure 1 , the specific steps being as follows:

[0094] (1) Preparation of raw materials:

[0095] The sheath raw material is PP, the melting point is 165°C, the melt index under test conditions of 185°C and 2.16 kg is 30 g / 10 min, the water content after drying at 35°C for 6 h is 100 ppm, and the water content after drying at 35°C for 6 h is 100 ppm.

[0096] The core layer raw material is PBT, the melting point is 230℃, and the intrinsic viscosity is 0.86dl / g; dried at 110℃ for 6h, the water content is 25ppm;

[0097] The conductive substance is the gold-doped multi-walled carbon nanotube 3 of Example 1;

[0098] (2) As shown in Figure 2 , the skin layer 1 raw material and the core layer 2 raw material are melted respectively and extruded into melt streams through the skin-core composite spinning assembly, then pass through the hollow cylindrical heat preservation channel in the heat preservation box with a temperature of 170℃ for heat preservation treatment, and the melt streams out of the heat preservation channel enter the box containing the conductive substance (i.e. the gas upflowing area between the annular gas distributor and the two side hot gas flow guide plates), and there is an annular hot air flow with a wind speed of 0.5m / s in the box;

[0099] As shown in Figure 6 , compressed air is introduced into the bottom of the annular gas distributor 9, and the compressed air is injected into the box containing the conductive substance through the annular gas distributor 9, and the gas is guided by the hot gas flow guide plate 7 to rise upward, and when it reaches the top of the box, the gas is divided and continues to move downward, thereby forming a complete circulating gas flow (i.e. annular hot air flow 12); the conductive substance is driven by the first circulating gas flow and combined with the skin layer 1 melt stream, at this time the content of the dispersed conductive substance in the gas flow is reduced, and the bottom conductive substance is driven by the second circulating gas flow to supplement the conductive substance in the gas flow and then move upward to continue to provide the skin layer 1 with conductive substance, and so on. The circulating gas flow will continue to supplement the conductive substance, and the conductive substance will be combined with the skin layer 1 under the driving of multiple circulating gas flows, thereby increasing the load of the conductive substance in the skin layer;

[0100] Wherein, the mass ratio of the skin layer 1 raw material to the core layer 2 raw material is 50:50, the temperature of the spinning box is 260℃, the length of the heat preservation channel is 3.4m, and the diameter is 4mm; the temperature of the hot air flow 12 is the same as that of the heat preservation channel;

[0101] (3) The product of step (2) is cooled at a wind temperature of 24℃ and a wind speed of 0.6m / s, and then drawn through a first hot roller and a second hot roller in sequence, the temperature of the first hot roller is 80℃, the temperature of the second hot roller is 105℃, the draw ratio is 2 times, and the spinning speed is 800m / s;

[0102] The specification of the drawn fiber is 74.8dtex / 24f, the breaking strength is 3.78cN / dtex, the breaking elongation is 58%, the content of the conductive substance is 3.2wt%, and the electrical conductivity is 2.4×10 2 S / m;

[0103] (4) The fiber after drawing in step (3) is subjected to heat annealing treatment, the heat annealing temperature is 195℃; drawing is carried out at the heat annealing temperature, the drawing ratio is 15 times, and finally the skin-core composite conductive fiber is prepared.

[0104] The prepared skin-core composite conductive fiber has a breaking strength of 8.53 cN / dtex, an elongation at break of 102%, a content of conductive substance of 3.2 wt%, and an electrical conductivity of 6.9 x 10 2 S / m.

[0105] Example 7

[0106] A method for preparing a skin-core composite conductive fiber, the specific steps are as follows:

[0107] (1) Preparation of raw materials:

[0108] The skin layer raw material is PP, the melting point is 175℃, the melt index under the test condition of 200℃ and 2.16kg is 35g / 10min; dried at 35℃ for 6h, the water content is 100ppm;

[0109] The core layer raw material is PBT, the melting point is 220℃, the intrinsic viscosity is 0.8dl / g; dried at 102℃ for 2h, the water content is 40ppm;

[0110] The conductive substance is the gold-doped multi-walled carbon nanotube of Example 2;

[0111] (2) After the skin layer raw material and the core layer raw material are respectively melted and extruded into melt streams through a skin-core composite spinning assembly, the melt streams first pass through a hollow columnar heat preservation channel with a temperature of 195℃ for heat preservation treatment, and then enter a box loaded with the conductive substance, and the box has a circular hot air flow with a wind speed of 2m / s, which is used to realize the compounding of the conductive substance and the skin layer of the melt stream;

[0112] Among them, the mass ratio of the skin layer raw material to the core layer raw material is 40:60, and the temperature of the spinning box is 262℃; the length of the heat preservation channel is 3.4m, and the diameter is 4mm; the temperature of the hot air flow is the same as that of the heat preservation channel;

[0113] (3) The product of step (2) is cooled at a wind temperature of 18℃ and a wind speed of 0.2m / s, and then drawn through a first hot roller and a second hot roller in sequence, the temperature of the first hot roller is 85℃, the temperature of the second hot roller is 115℃, the drawing ratio is 3 times, and the spinning speed is 1000m / s;

[0114] The specification of the drawn fiber is 79.4dtex / 24f, the breaking strength is 3.85 cN / dtex, the elongation at break is 65%, the content of conductive substance is 7wt%, and the electrical conductivity is 3.9 x 10 2S / m;

[0115] (4) The fiber after the drawing of step (3) is subjected to heat annealing treatment, the heat annealing temperature is 195℃; the drawing is carried out at the heat annealing temperature, the drawing ratio is 15 times, and finally the skin-core composite conductive fiber is prepared.

[0116] The prepared skin-core composite conductive fiber has a breaking strength of 10.31 cN / dtex, an elongation at break of 110%, a content of conductive substance of 7wt%, and an electrical conductivity of 8.8*10 2 S / m.

[0117] Example 8

[0118] A preparation method of a skin-core composite conductive fiber, the specific steps are as follows:

[0119] (1) Preparation of raw materials:

[0120] The skin layer raw material is PP, the melting point is 170℃, the melt index under the test condition of 190℃, 2.16kg is 32g / 10min; dried at 35℃ for 6h, the water content is 100ppm;

[0121] The core layer raw material is PBT, the melting point is 225℃, the intrinsic viscosity is 0.75dl / g; dried at 108℃ for 4h, the water content is 32ppm;

[0122] The conductive substance is the gold-doped multi-walled carbon nanotube of example 3;

[0123] (2) After the skin layer raw material and the core layer raw material are respectively melted and extruded into melt streams through a skin-core composite spinning assembly, the melt streams first pass through a hollow cylindrical heat preservation channel with a temperature of 185℃ for heat preservation treatment, and then enter a box loaded with conductive substances, and the box has a circular hot air flow with a wind speed of 1m / s, which is used to realize the compounding of the conductive substances and the skin layer of the melt streams;

[0124] Among them, the mass ratio of the skin layer raw material to the core layer raw material is 30:70, and the temperature of the spinning box is 265℃; the length of the heat preservation channel is 3.4m, and the diameter is 4mm; the temperature of the hot air flow is the same as that of the heat preservation channel;

[0125] (3) The product of step (2) is cooled at a wind temperature of 20℃ and a wind speed of 0.5m / s, and then drawn through a first hot roller and a second hot roller in sequence, the temperature of the first hot roller is 95℃, the temperature of the second hot roller is 120℃, the drawing ratio is 5 times, and the spinning speed is 1100m / s;

[0126] The fiber specification after drawing is 83 dtex / 24 f, the breaking strength is 3.62 cN / dtex, the breaking elongation is 42%, the content of the conductive substance is 6.5 wt%, and the conductivity is 3.5 x 10 2 S / m.

[0127] (4) The fiber after drawing in step (3) is subjected to heat annealing treatment, the heat annealing temperature is 180℃; drawing is carried out at the heat annealing temperature, the drawing ratio is 10 times, and finally the skin-core composite conductive fiber is prepared.

[0128] The breaking strength of the prepared skin-core composite conductive fiber is 7.54 cN / dtex, the breaking elongation is 92%, the content of the conductive substance is 6.5 wt%, and the conductivity is 7.6 x 10 2 S / m.

[0129] Example 9

[0130] A method for preparing a skin-core composite conductive fiber, the specific steps are as follows:

[0131] (1) Preparation of raw materials:

[0132] The skin layer raw material is PP, the melting point is 175℃, the melt index under the test condition of 190℃, 2.16kg is 30g / 10min; dried at 35℃ for 6h, the water content is 100ppm;

[0133] The core layer raw material is PBT, the melting point is 225℃, the intrinsic viscosity is 0.82dl / g; dried at 108℃ for 4h, the water content is 34ppm;

[0134] The conductive substance is the doped gold multi-walled carbon nanotube of example 4;

[0135] (2) The skin layer raw material and the core layer raw material are respectively melted and extruded into melt streams through a skin-core composite spinning assembly, then the melt streams are subjected to heat preservation treatment in a hollow cylindrical heat preservation channel with a temperature of 175℃, and then the melt streams out of the heat preservation channel enter a box loaded with the conductive substance, and the box has a circular hot air flow with a wind speed of 1.5m / s, which is used to realize the compounding of the conductive substance and the skin layer of the melt stream;

[0136] Among them, the mass ratio of the skin layer raw material to the core layer raw material is 20:80, the temperature of the spinning box is 268℃, the length of the heat preservation channel is 3.4m, and the diameter is 4mm; the temperature of the hot air flow is the same as that of the heat preservation channel;

[0137] (3) cooling the product of step (2) at a wind temperature of 22°C and a wind speed of 0.3 m / s, and then drawing the cooled product through a first hot roller and a second hot roller, the first hot roller having a temperature of 90°C and the second hot roller having a temperature of 115°C, the draw ratio being 4 times, and the spinning speed being 1400 m / s;

[0138] The drawn fiber has a size of 90.2 dtex / 24 f, a breaking strength of 3.43 cN / dtex, a breaking elongation of 39%, a content of the conductive substance of 3.8 wt%, and an electrical conductivity of 2.1 x 10 2 S / m;

[0139] (4) heat annealing the drawn fiber of step (3) at a temperature of 180°C, and then stretching the heat annealed fiber at the temperature of 180°C, the draw ratio being 8 times, to obtain a sheath-core composite conductive fiber.

[0140] The obtained sheath-core composite conductive fiber has a breaking strength of 7.12 cN / dtex, a breaking elongation of 85%, a content of the conductive substance of 3.8 wt%, and an electrical conductivity of 5.6 x 10 2 S / m.

[0141] Example 10

[0142] A method for preparing a sheath-core composite conductive fiber, the specific steps of which are as follows:

[0143] (1) Preparation of raw materials:

[0144] The sheath layer raw material is PP, having a melting point of 165°C and a melt index of 30 g / 10 min under a test condition of 185°C and 2.16 kg, and being dried at 35°C for 6 h, the water content being 100 ppm;

[0145] The core layer raw material is PBT, having a melting point of 230°C and a specific viscosity of 0.86 dl / g, and being dried at 110°C for 6 h, the water content being 25 ppm;

[0146] The conductive substance is the single-walled carbon nanotube doped with gold of Example 5;

[0147] (2) The sheath layer raw material and the core layer raw material are respectively melted and extruded into melt streams through a sheath-core composite spinning assembly, and then the melt streams are first subjected to heat preservation treatment in a hollow columnar heat preservation passage having a temperature of 175°C, and then enter a box loaded with the conductive substance, the box having a circular hot air flow with a wind speed of 1.5 m / s for realizing the composite of the conductive substance and the sheath layer of the melt stream;

[0148] The mass ratio of the sheath raw material to the core raw material is 30:70, the temperature of the spinning box is 270°C, the length of the heat preservation channel is 3.4 m, and the diameter of the heat preservation channel is 4 mm; the temperature of the hot air flow is the same as that of the heat preservation channel;

[0149] (3) The product of step (2) is cooled at a wind temperature of 20°C and a wind speed of 0.4 m / s, and then is drawn through a first hot roller and a second hot roller after cooling, the temperature of the first hot roller is 90°C, the temperature of the second hot roller is 110°C, the draw ratio is 3 times, and the spinning speed is 1000 m / s;

[0150] The specification of the drawn fiber is 85.4 dtex / 24 f, the breaking strength is 4.83 cN / dtex, the breaking elongation is 82%, the content of the conductive substance is 4.6 wt%, and the electrical conductivity is 3.5 x 10 2 S / m;

[0151] (4) The drawn fiber of step (3) is subjected to heat annealing treatment, the heat annealing temperature is 180°C; and the fiber is stretched at the heat annealing temperature, the stretching ratio is 10 times, and finally a sheath-core composite conductive fiber is obtained.

[0152] The breaking strength of the obtained sheath-core composite conductive fiber is 9.26 cN / dtex, the breaking elongation is 108%, the content of the conductive substance is 4.6 wt%, and the electrical conductivity is 8.5 x 10 2 S / m.

Claims

1. A method for producing a core-sheath type conductive fiber, characterized by: The sheath layer material and the core layer material are melted respectively and extruded into melt streams through a sheath-core composite spinning assembly, then the conductive substance is combined with the sheath layer of the melt streams through a hot air flow, and then cooling, drawing and heat annealing are sequentially performed to obtain the sheath-core composite conductive fiber; The melting point of the sheath layer material is 40-70℃ lower than that of the core layer material; The temperature of the hot air flow is in the range of 20℃ higher than the melting point of the sheath layer material; The heat annealing temperature is not lower than the melting point of the sheath layer material, and the drawing ratio is 8-15 times during the heat annealing process; The conductive substance is single-walled carbon nanotube or multi-walled carbon nanotube, and the single-walled carbon nanotube or multi-walled carbon nanotube is subjected to metal element doping treatment; The melt streams extruded through the sheath-core composite spinning assembly are first subjected to heat preservation treatment in a heat preservation channel, and then enter a box loaded with the conductive substance, and the box has a ring-shaped hot air flow for combining the conductive substance with the sheath layer of the melt streams; The content of the conductive substance in the core-sheath composite conductive fiber is 3.2-7 wt%, and the conductivity is 5.6-8.8×10 2 S / m.

2. The method of claim 1, wherein the core-sheath type conductive fiber is prepared by extruding a core material and a sheath material through a T-die, and then cooling the extruded material. The temperature of the heat preservation channel is 165-195℃, the wind speed of the hot air flow is 0.5-2m / s, and the temperature of the hot air flow is the same as that of the heat preservation channel.

3. The method of claim 1, wherein the core-sheath type conductive fiber is prepared by extruding a core material and a sheath material through a T-die, and then cooling the extruded material. The mass ratio of the sheath layer material to the core layer material is 20-50:50-80.

4. The method of claim 3, wherein the core-sheath type conductive fiber is prepared by extruding a core material and a sheath material through a T-die, and then cooling the extruded material. The sheath layer material is PP, the melting point of the PP is 165-175℃, and the melt index of the PP under the test condition of 180-200℃ and 2.16kg is 30-35g / 10min; The core layer material is PBT, the melting point of the PBT is 220-230℃, and the intrinsic viscosity of the PBT is 0.75-0.86dl / g.

5. The method of claim 4, wherein the core-sheath type conductive fiber is prepared by extruding a core material and a sheath material through a T-die, and then cooling the extruded material. The heat annealing temperature is 170-195℃.

6. The method of claim 1, wherein the core-sheath type conductive fiber is prepared by extruding a core material and a sheath material through a T-die, and then cooling the extruded material. The wind temperature for cooling is 18-24℃, and the wind speed is 0.2-0.6m / s.

7. The method of claim 6, wherein the core-sheath type conductive fiber is prepared by extruding a core material and a sheath material through a T-die, and then cooling the extruded material. After cooling, the melt streams are sequentially drawn through a first hot roller and a second hot roller, the temperature of the first hot roller is 80-95℃, the temperature of the second hot roller is 105-120℃, and the drawing ratio is 2-5 times.

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