Method for improving tensile modulus of large-tow carbon fiber, prepared large-tow carbon fiber and application

Abstract

The invention discloses a method for improving the tensile modulus of large-tow carbon fibers, the prepared large-tow carbon fibers and application of the large-tow carbon fibers. The method comprises the following steps: pre-oxidizing a large-tow precursor to obtain a pre-oxidized fiber, and carrying out low-temperature carbonization and high-temperature carbonization on the pre-oxidized fiber, wherein the low-temperature carbonization is carried out by adopting a multi-section gradient heating mode; the high-temperature carbonization is also carried out by adopting a multi-section gradient heating mode; the draft ratio in the high-temperature carbonization process is 0.9-1. According to the method for improving the tensile modulus of the large-tow carbon fibers, on the premise that an existing carbon fiber production device is not changed, the tensile modulus can be improved to 260 GPa or above through improvement of specific process conditions, and the application field of the large-tow carbon fibers can be effectively expanded. The problem that in the prior art, the tensile modulus is too low in the large-tow carbon fiber production process is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber preparation, and more particularly to a method for improving the tensile modulus of large-tow carbon fibers, the prepared large-tow carbon fibers, and applications thereof. Background Art

[0002] Due to the enormous market potential of large-tow carbon fiber in wind turbine blades, some domestic companies, driven by market trends, have initiated a series of large-tow carbon fiber technology development efforts and achieved breakthroughs. China's total carbon fiber demand has grown by an average annual rate of 20% over the past five years, marking the beginning of a period of rapid growth for the carbon fiber industry. Wind turbine blades have seen the most significant growth (nearly doubling annually), but this industry relies primarily on imported large-tow carbon fiber. Furthermore, with the increasing adoption of emerging industries such as new energy vehicles and marine development, as well as new energy applications such as wind power and solar power, industrial large-tow carbon fiber products are in short supply. Over the past two years, the domestic carbon fiber market has even seen a shortage of carbon. Major large-tow carbon fiber manufacturers in China and around the world have been expanding production, sparking a new wave of large-tow carbon fiber construction both domestically and internationally. According to incomplete statistics, the capacity of new carbon fiber projects already under construction or about to commence will exceed 150,000 tons. However, further analysis reveals hidden dangers beneath the apparent market boom: all new and under-construction capacity is concentrated in the 12K-48K product range. It is expected that the 48K-50K general-purpose large-tow carbon fiber will experience significant homogeneity and oversupply in the coming years. The technological advantages brought by the early layout of high-performance large-tow carbon fiber will put us in an advantageous position in the fierce market competition in the future.

[0003] In the field of high-performance large-tow carbon fiber research, domestic related research still has certain shortcomings and a large room for development compared with foreign research. It is still necessary to increase R&D efforts in basic theories and new technology development such as large-tow carbon fiber strength control, modulus control and quality control. Summary of the Invention

[0004] To address the problems encountered in the prior art, the present invention proposes a method for increasing the tensile modulus of large-tow carbon fibers, as well as the preparation and application of these fibers. This method, without changing existing carbon fiber production equipment, can increase the tensile modulus to over 260 GPa by improving specific process conditions, effectively expanding the application areas of large-tow carbon fibers. This effectively addresses the problem of low tensile modulus in the production of large-tow carbon fibers encountered in the prior art.

[0005] One of the objects of the present invention is to provide a method for improving the tensile modulus of large-tow carbon fibers, comprising the steps of pre-oxidizing large-tow precursor to obtain pre-oxidized fibers, and carbonizing the pre-oxidized fibers at low temperatures and high temperatures;

[0006] Among them, low-temperature carbonization is carried out in a multi-stage gradient heating manner; high-temperature carbonization is also carried out in a multi-stage gradient heating manner; and the draft ratio during the high-temperature carbonization process is 0.9 to 1 times.

[0007] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0008] The K number of the large tow precursor is ≥48K, preferably 48K to 96K; more preferably 48K or 96K; and / or,

[0009] The material of the large tow precursor is polyacrylonitrile; and / or,

[0010] The step of drying the large tow precursor before pre-oxidation is also included; and / or,

[0011] The pre-oxidation is carried out in a multi-stage gradient temperature increase manner. Preferably, the pre-oxidation includes an early pre-oxidation period, a middle pre-oxidation period and a late pre-oxidation period, and the temperatures of the early pre-oxidation period, the middle pre-oxidation period and the late pre-oxidation period are increased in sequence; and / or,

[0012] The overall drafting ratio in the pre-oxidation process is 1 to 1.15 times.

[0013] In the technical solution of the present invention, the step of drying the large-tow precursor before pre-oxidation adopts existing commonly used drying conditions, such as hot air blowing drying. Preferably, the blowing direction of the hot air is along the wire feeding direction; and / or the temperature of the hot air is 100-120°C; and / or the effective heating time of the hot air is 10-60s.

[0014] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0015] The temperature at the initial stage of pre-oxidation is 210-230°C; and / or,

[0016] The temperature in the middle stage of pre-oxidation is 230-250°C; and / or,

[0017] The temperature in the late stage of pre-oxidation is 250-270°C; and / or,

[0018] The initial pre-oxidation time is 15 to 30 minutes; and / or,

[0019] The time of the middle stage of pre-oxidation is 15 to 30 minutes; and / or,

[0020] The time for the later stage of pre-oxidation is 15 to 30 minutes.

[0021] In the technical solution of the present invention, after the above-mentioned pre-oxidation, the parameters of the pre-oxidized fiber obtained are as follows:

[0022] The oxygen content of the preoxidized fiber prepared in the initial stage of preoxidation is 3 to 5 wt%; and / or,

[0023] The oxygen content of the pre-oxidized fiber prepared in the middle stage of pre-oxidation is 5 to 7 wt%; and / or,

[0024] The oxygen content of the preoxidized fiber prepared in the late stage of preoxidation is 7 to 10 wt%; and / or,

[0025] The density of the pre-oxidized fiber prepared in the initial stage of pre-oxidation is 1.18-1.22 g / cm 3 and / or,

[0026] The density of the pre-oxidized fiber prepared in the middle stage of pre-oxidation is 1.28-1.32 g / cm 3 and / or,

[0027] The density of the pre-oxidized fiber prepared in the late stage of pre-oxidation is 1.38-1.40 g / cm 3 .

[0028] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0029] The temperature of the low-temperature carbonization starting zone is 20-30° C. higher than the temperature of the last temperature zone of the pre-oxidation; and / or,

[0030] The low-temperature carbonization treatment adopts multi-stage gradient heating, and the temperature difference between adjacent temperature zones does not exceed 120°C; preferably 80-120°C; further preferably, the temperature difference between the last two temperature zones during the low-temperature carbonization treatment is not less than 100°C and not more than 120°C.

[0031] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0032] The initial temperature of the low-temperature carbonization treatment is 270-300°C; and / or, during the low-temperature carbonization treatment, the maximum temperature of the heating does not exceed 800°C; preferably, the maximum temperature of the low-temperature carbonization treatment is 700-800°C;

[0033] Preferably, the low-temperature carbonization treatment is performed using a 7-stage gradient heating method;

[0034] Further preferably, the temperature zones corresponding to the low-temperature carbonization treatment are 270-290°C, 290-370°C, 370-450°C, 450-530°C, 530-610°C, 610-700°C, and 700-780°C, respectively.

[0035] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0036] The drafting ratio during the low-temperature carbonization process is 1.02 to 1.15 times; preferably 1.08 to 1.12 times; and / or,

[0037] During the low-temperature carbonization treatment, the total carbonization treatment time is 60 to 120 seconds, and preferably the treatment time in each temperature zone is the same.

[0038] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0039] The starting temperature of the high-temperature carbonization is 90 to 200° C. higher than the temperature of the last temperature zone of the low-temperature carbonization; preferably 90 to 140° C.; and / or,

[0040] The high-temperature carbonization treatment adopts multi-stage gradient heating, and the temperature difference between adjacent temperature zones does not exceed 120°C; preferably 70-120°C; further preferably, the temperature difference between the last two temperature zones during the high-temperature carbonization treatment is not less than 100°C and not more than 120°C.

[0041] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0042] The initial temperature of the high-temperature carbonization treatment is 800-900°C; and / or, during the high-temperature carbonization treatment, the maximum temperature does not exceed 1800°C;

[0043] Preferably, the high-temperature carbonization treatment is carried out in an 8-stage gradient heating manner;

[0044] Further preferably, the temperature zones corresponding to the high-temperature carbonization treatment are 840-860°C, 860-940°C, 940-1030°C, 1030-1110°C, 1110-1200°C, 1200-1290°C, 1290-1360°C, and 1360-1440°C, respectively.

[0045] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0046] The drafting ratio during the high-temperature carbonization process is 0.95 to 0.98 times; and / or,

[0047] During the high-temperature carbonization treatment, the total carbonization treatment time is 60 to 120 seconds, and preferably the treatment time in each temperature zone is the same.

[0048] In the method for improving the tensile modulus of large-tow carbon fibers according to the present invention, preferably,

[0049] The method further comprises a post-treatment step after the high-temperature carbonization treatment; preferably, the post-treatment step comprises the steps of electrochemical surface treatment, water washing, drying, sizing, and drying.

[0050] The second object of the present invention is to provide a large-tow carbon fiber prepared by the method for improving the tensile modulus of large-tow carbon fiber as described in one of the objects of the present invention;

[0051] Preferably, the K number of the fibers in the large-tow carbon fiber is ≥48K, preferably 48K or 96K; and / or,

[0052] The large-tow carbon fiber has a tensile strength of ≥4000 MPa, preferably 4000-4500 MPa, and / or a tensile modulus of ≥260 GPa, preferably 260-280 GPa.

[0053] The third object of the present invention is to provide a large-tow carbon fiber prepared by the method for improving the tensile modulus of large-tow carbon fiber as described in one of the objects of the present invention, or the application of the large-tow carbon fiber as described in the second object of the present invention in the preparation of new energy vehicles, marine development, wind power, and solar energy related products.

[0054] As can be seen, the present invention provides a method for increasing the tensile modulus of large-tow carbon fibers. The method of the present invention for increasing the tensile modulus of large-tow carbon fibers comprises pre-oxidizing large-tow precursors to obtain pre-oxidized fibers, and subjecting the pre-oxidized fibers to low-temperature carbonization, high-temperature carbonization, and surface treatment to obtain large-tow carbon fibers. The method of the present invention is simple, does not require the addition of other additional materials or equipment modifications, and significantly improves the tensile modulus of large-tow carbon fibers, effectively expanding the application scenarios of large-tow carbon fibers.

[0055] The endpoints and any values of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and a separate point value, and the separate point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be considered as specifically disclosed in this article.

[0056] Compared with the prior art, the advantages of the present invention are:

[0057] The method of improving the tensile modulus of large-tow carbon fibers of the present invention does not require changes to existing production equipment or increase utility consumption. By simply adjusting the process, the tensile modulus of large-tow carbon fibers can be significantly improved, effectively expanding the application scenarios of large-tow carbon fibers. DETAILED DESCRIPTION

[0058] The present invention will be described in detail below with reference to specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0059] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0060] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the scope of protection of the present invention.

[0061] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0062] Source of raw materials:

[0063] The raw materials used in the present invention are all conventional commercially available products.

[0064] Test method:

[0065] The tensile strength and tensile modulus of carbon fiber are determined according to GB / T3362-2005 Test method for tensile properties of carbon fiber multifilament.

[0066] Example 1

[0067] After unwinding, 48k large-tow polyacrylonitrile (PAN) precursor yarn with a fineness of 1.3 dtex passes through a drying unit between the payoff and pre-oxidation furnace. This unit uses hot air, blowing along the direction of the wire feed at a temperature of 108°C for 50 seconds. Tension between the payoff and drying furnace is 1500 cN, and between the drying furnace and oxidation furnace is also 1500 cN. Upon entering the continuous pre-oxidation furnace, the temperature is ramped up: 220°C in the initial pre-oxidation stage, 240°C in the middle, and 260°C in the final stage. The oxidation time for each of these three stages is 20 minutes. The overall draft ratio during the pre-oxidation process is 1.1.

[0068] The low-temperature carbonization treatment adopts a multi-stage gradient heating method with the temperatures of 285°C, 342°C, 430°C, 510°C, 580°C, 660°C, and 760°C. The drafting ratio during the low-temperature carbonization process is 1.12 times. After the low-temperature carbonization treatment, high-temperature carbonization is carried out. The high-temperature carbonization temperatures are 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C, and 1420°C. The drafting ratio during the high-temperature carbonization process is 0.92 times.

[0069] The carbon fibers are obtained through electrochemical surface treatment, water washing, drying, sizing and drying.

[0070] The large-tow carbon fiber prepared by the above method has a tensile strength of 4500 MPa and a tensile modulus of 273 GPa.

[0071] Example 2

[0072] After unwinding, 48k large-tow polyacrylonitrile (PAN) precursor yarn with a fineness of 1.3 dtex passes through a drying unit between the payoff and pre-oxidation furnace. This unit uses hot air, blowing along the direction of the wire feed at a temperature of 108°C for 50 seconds. Tension between the payoff and drying furnace is 1500 cN, and between the drying furnace and oxidation furnace is also 1500 cN. Upon entering the continuous pre-oxidation furnace, the temperature is ramped up: 220°C in the initial pre-oxidation stage, 240°C in the middle, and 260°C in the final stage. The oxidation time for each of these three stages is 20 minutes. The overall draft ratio during the pre-oxidation process is 1.1.

[0073] The low-temperature carbonization treatment adopts a multi-stage gradient heating method with the temperatures of 285°C, 342°C, 430°C, 510°C, 580°C, 660°C, and 760°C. The drafting ratio during the low-temperature carbonization process is 1.12 times. After the low-temperature carbonization treatment, high-temperature carbonization is carried out. The high-temperature carbonization temperatures are 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C, and 1430°C. The drafting ratio during the high-temperature carbonization process is 0.92 times.

[0074] The carbon fibers are obtained through electrochemical surface treatment, water washing, drying, sizing and drying.

[0075] The large-tow carbon fiber prepared by the above method has a tensile strength of 4486 MPa and a tensile modulus of 278 GPa.

[0076] Example 3

[0077] After unwinding, 48k large-tow polyacrylonitrile (PAN) precursor yarn with a fineness of 1.3 dtex passes through a drying unit between the payoff and pre-oxidation furnace. This unit uses hot air, blowing along the direction of the wire feed at a temperature of 108°C for 50 seconds. Tension between the payoff and drying furnace is 1500 cN, and between the drying furnace and oxidation furnace is also 1500 cN. Upon entering the continuous pre-oxidation furnace, the temperature is ramped up: 220°C in the initial pre-oxidation stage, 240°C in the middle, and 260°C in the final stage. The oxidation time for each of these three stages is 20 minutes. The overall draft ratio during the pre-oxidation process is 1.1.

[0078] The low-temperature carbonization treatment adopts a multi-stage gradient heating method with the temperatures of 285°C, 342°C, 430°C, 510°C, 580°C, 660°C, and 750°C. The drafting ratio during the low-temperature carbonization process is 1.12 times. After the low-temperature carbonization treatment, high-temperature carbonization is carried out. The high-temperature carbonization temperatures are 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C, and 1430°C. The drafting ratio during the high-temperature carbonization process is 0.92 times.

[0079] The carbon fibers are obtained through electrochemical surface treatment, water washing, drying, sizing and drying.

[0080] The large-tow carbon fiber prepared by the above method has a tensile strength of 4519 MPa and a tensile modulus of 284 GPa.

[0081] Example 4

[0082] After unwinding, 48k large-tow polyacrylonitrile (PAN) precursor yarn with a fineness of 1.3 dtex passes through a drying unit between the payoff and pre-oxidation furnace. This unit uses hot air, blowing along the direction of the wire feed at a temperature of 108°C for 50 seconds. Tension between the payoff and drying furnace is 1500 cN, and between the drying furnace and oxidation furnace is also 1500 cN. Upon entering the continuous pre-oxidation furnace, the temperature is ramped up: 220°C in the initial pre-oxidation stage, 240°C in the middle, and 260°C in the final stage. The oxidation time for each of these three stages is 20 minutes. The overall draft ratio during the pre-oxidation process is 1.1.

[0083] The low-temperature carbonization treatment adopts a multi-stage gradient heating method with the temperatures of 285°C, 342°C, 430°C, 510°C, 580°C, 660°C and 750°C. The drafting ratio during the low-temperature carbonization process is 1.12 times. After the low-temperature carbonization treatment, high-temperature carbonization is carried out. The high-temperature carbonization temperatures are 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C and 1430°C. The drafting ratio during the high-temperature carbonization process is 0.95 times.

[0084] The carbon fibers are obtained through electrochemical surface treatment, water washing, drying, sizing and drying.

[0085] The large-tow carbon fiber prepared by the above method has a tensile strength of 4229 MPa and a tensile modulus of 285 GPa.

[0086] Example 5

[0087] After unwinding, 48k large-tow polyacrylonitrile (PAN) precursor yarn with a fineness of 1.3 dtex passes through a drying unit between the payoff and pre-oxidation furnace. This unit uses hot air, blowing along the wire feed direction at a temperature of 108°C for 50 seconds. Tension between the payoff and drying furnace is 1500 cN, and between the drying furnace and oxidation furnace is 1500 cN. Upon entering the continuous pre-oxidation furnace, the temperature is ramped up: 220°C in the initial pre-oxidation phase, 240°C in the middle phase, and 260°C in the final phase. The oxidation time for each of these three stages is 25 minutes. The overall draft ratio during the pre-oxidation process is 1.1.

[0088] The low-temperature carbonization treatment adopts a multi-stage gradient heating method with the temperatures of 285°C, 342°C, 430°C, 510°C, 580°C, 660°C and 750°C. The drafting ratio during the low-temperature carbonization process is 1.12 times. After the low-temperature carbonization treatment, high-temperature carbonization is carried out. The high-temperature carbonization temperatures are 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C and 1430°C. The drafting ratio during the high-temperature carbonization process is 0.95 times.

[0089] The carbon fibers are obtained through electrochemical surface treatment, water washing, drying, sizing and drying.

[0090] The large-tow carbon fiber prepared by the above method has a tensile strength of 4561 MPa and a tensile modulus of 279 GPa.

[0091] Example 6

[0092] After unwinding, 48k large-tow polyacrylonitrile (PAN) precursor yarn with a fineness of 1.3 dtex passes through a drying unit between the payoff and pre-oxidation furnace. This unit uses hot air, blowing along the wire feed direction at a temperature of 108°C for 50 seconds. Tension between the payoff and drying furnace is 1500 cN, and between the drying furnace and oxidation furnace is 1500 cN. Upon entering the continuous pre-oxidation furnace, the temperature is ramped up: 220°C in the initial pre-oxidation phase, 240°C in the middle phase, and 260°C in the final phase. The oxidation time for each of these three stages is 25 minutes. The overall draft ratio during the pre-oxidation process is 1.1.

[0093] The low-temperature carbonization treatment adopts a multi-stage gradient heating method with the temperatures of 285°C, 342°C, 430°C, 510°C, 580°C, 660°C and 750°C. The drafting ratio during the low-temperature carbonization process is 1.09 times. After the low-temperature carbonization treatment, high-temperature carbonization is carried out. The temperatures of the high-temperature carbonization are 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C and 1430°C. The drafting ratio during the high-temperature carbonization process is 0.95 times.

[0094] The carbon fibers are obtained through electrochemical surface treatment, water washing, drying, sizing and drying.

[0095] The large-tow carbon fiber prepared by the above method has a tensile strength of 4266 MPa and a tensile modulus of 268 GPa.

[0096] Example 7

[0097] After unwinding, 48k large-tow polyacrylonitrile (PAN) precursor with a fineness of 1.3 dtex passes through a drying unit between the payoff and pre-oxidation furnace. This unit uses hot air, blowing along the direction of the wire feed at a temperature of 108°C for 50 seconds. Tension between the payoff and drying furnace is 1500 cN, and between the drying furnace and oxidation furnace is 1500 cN. Upon entering the continuous pre-oxidation furnace, the temperature is ramped up: 220°C in the initial pre-oxidation stage, 240°C in the middle, and 260°C in the final stage. The oxidation time for each of these three stages is 25 minutes. The overall draft ratio during the pre-oxidation process is 1.12.

[0098] The low-temperature carbonization treatment adopts a multi-stage gradient heating method with the temperatures of 285°C, 342°C, 430°C, 510°C, 580°C, 660°C and 750°C. The drafting ratio during the low-temperature carbonization process is 1.09 times. After the low-temperature carbonization treatment, high-temperature carbonization is carried out. The temperatures of the high-temperature carbonization are 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C and 1430°C. The drafting ratio during the high-temperature carbonization process is 0.95 times.

[0099] The carbon fibers are obtained through electrochemical surface treatment, water washing, drying, sizing and drying.

[0100] The large-tow carbon fiber prepared by the above method has a tensile strength of 4438 MPa and a tensile modulus of 275 GPa.

[0101] Example 8

[0102] After unwinding, 48k large-tow polyacrylonitrile (PAN) precursor with a fineness of 1.3 dtex passes through a drying unit between the payoff and pre-oxidation furnace. This unit uses hot air, blowing along the direction of the wire feed at a temperature of 108°C for 50 seconds. Tension between the payoff and drying furnace is 1500 cN, and between the drying furnace and oxidation furnace is 1500 cN. Upon entering the continuous pre-oxidation furnace, the temperature is ramped up: 225°C in the initial pre-oxidation stage, 245°C in the middle, and 265°C in the final stage. The oxidation time for each of these three stages is 25 minutes. The overall draft ratio during the pre-oxidation process is 1.12.

[0103] The low-temperature carbonization treatment adopts a multi-stage gradient heating method with the temperatures of 285°C, 342°C, 430°C, 510°C, 580°C, 660°C and 750°C. The drafting ratio during the low-temperature carbonization process is 1.09 times. After the low-temperature carbonization treatment, high-temperature carbonization is carried out. The temperatures of the high-temperature carbonization are 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C and 1430°C. The drafting ratio during the high-temperature carbonization process is 0.95 times.

[0104] The carbon fibers are obtained through electrochemical surface treatment, water washing, drying, sizing and drying.

[0105] The large-tow carbon fiber prepared by the above method has a tensile strength of 4232 MPa and a tensile modulus of 271 GPa.

[0106] Example 9

[0107] The preparation method is basically the same as that of Example 1, except that the low-temperature carbonization temperature is 285°C, 342°C, 430°C, 510°C, 580°C, 660°C, and 770°C;

[0108] The large-tow carbon fiber prepared by the above method has a tensile strength of 4562 MPa and a tensile modulus of 277 GPa.

[0109] Example 10

[0110] The preparation method is basically the same as that of Example 8, except that the drafting ratio during the low-temperature carbonization process is 1.01 times.

[0111] The large-tow carbon fiber prepared by the above method has a tensile strength of 4068 MPa and a tensile modulus of 252 GPa.

[0112] Example 11

[0113] The preparation method is basically the same as that of Example 8, except that the low-temperature carbonization treatment adopts a multi-stage gradient temperature increase, with the temperatures being 400°C, 450°C, 500°C, 550°C, 660°C, 700°C, and 810°C;

[0114] The large-tow carbon fiber prepared by the above method has a tensile strength of 3689 MPa and a tensile modulus of 236 GPa.

[0115] Example 12

[0116] The preparation method is basically the same as that of Example 8, except that the high-temperature carbonization temperature is 1050°C, 1100°C, 1300°C, 1400°C, 1500°C, 1600°C, 1650°C, and 1700°C;

[0117] The large-tow carbon fiber prepared by the above method has a tensile strength of 3562 MPa and a tensile modulus of 238 GPa.

[0118] Example 13

[0119] The preparation method is basically the same as that of Example 8, except that the low-temperature carbonization temperature is 285°C, 342°C, 430°C, 510°C, 580°C, 660°C, and 730°C;

[0120] The large-tow carbon fiber prepared by the above method has a tensile strength of 3358 MPa and a tensile modulus of 227 GPa.

[0121] Example 14

[0122] The preparation method is basically the same as that of Example 8, except that the high-temperature carbonization temperature is 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C, and 1400°C;

[0123] The large-tow carbon fiber prepared by the above method has a tensile strength of 3294 MPa and a tensile modulus of 223 GPa.

[0124] Example 15

[0125] The preparation method is basically the same as that of Example 8, except that the high-temperature carbonization temperature is 850°C, 920°C, 1000°C, 1080°C, 1160°C, 1250°C, 1320°C, and 1460°C;

[0126] The large-tow carbon fiber prepared by the above method has a tensile strength of 3362 MPa and a tensile modulus of 220 GPa.

[0127] Comparative Example 1

[0128] The preparation method is basically the same as that of Example 8, except that the drafting ratio during the high-temperature carbonization process is 1.01 times.

[0129] The large-tow carbon fiber prepared by the above method has a tensile strength of 3287 MPa and a tensile modulus of 225 GPa.

[0130] From the above results, it can be seen that the temperature settings of low-temperature carbonization, high-temperature carbonization, and the draft ratio setting will affect the tensile strength and tensile modulus of large-tow carbon fibers. Under the joint regulation of specific temperature gradient settings and draft ratio settings, the orderly growth of the graphite-like structure can be better controlled, the orientation degree can be improved, and thus the tensile modulus can be improved.

[0131] In summary, the method of the present invention can achieve the purpose of improving the tensile modulus of large-tow carbon fiber without changing the production process or increasing utility consumption. It can be achieved by only making some adjustments to the relevant process conditions. It has great technical advantages and can be used in the industrial production of large-tow carbon fiber.

[0132] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

[0133] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of conflict, the definitions in this specification shall prevail.

[0134] When this specification uses the prefix "well known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, the objects introduced by the prefix include those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become generally recognized in the art to be suitable for similar purposes.

[0135] In the context of this specification, any matters or items not mentioned are directly applicable to those known in the art without any changes except those explicitly stated.

Claims

1. A method for increasing the tensile modulus of large-tow carbon fibers, comprising the steps of pre-oxidizing large-tow precursor to obtain pre-oxidized fibers, and carbonizing the pre-oxidized fibers at low temperatures and high temperatures; in, Low-temperature carbonization is carried out in a multi-stage gradient heating manner; high-temperature carbonization is also carried out in a multi-stage gradient heating manner; and the draft ratio during the high-temperature carbonization process is 0.9 to 1 times.

2. The method for improving the tensile modulus of large-tow carbon fibers according to claim 1, wherein: The K number of the large tow precursor is ≥48K, preferably 48K to 96K; more preferably 48K or 96K; and / or, The material of the large tow precursor is polyacrylonitrile; and / or, The step of drying the large tow precursor before pre-oxidation is also included; and / or, The pre-oxidation is carried out in a multi-stage gradient temperature increase manner. Preferably, the pre-oxidation includes an early pre-oxidation period, a middle pre-oxidation period and a late pre-oxidation period, and the temperatures of the early pre-oxidation period, the middle pre-oxidation period and the late pre-oxidation period are increased in sequence; and / or, The overall drafting ratio in the pre-oxidation process is 1 to 1.15 times.

3. The method for improving the tensile modulus of large-tow carbon fibers according to claim 2, wherein: The temperature at the initial stage of pre-oxidation is 210-230°C; and / or, The temperature in the middle stage of pre-oxidation is 230-250°C; and / or, The temperature in the late stage of pre-oxidation is 250-270°C; and / or, The initial pre-oxidation time is 15 to 30 minutes; and / or, The time of the middle stage of pre-oxidation is 15 to 30 minutes; and / or, The time for the later stage of pre-oxidation is 15 to 30 minutes.

4. The method for improving the tensile modulus of large-tow carbon fibers according to claim 1, wherein: The temperature of the low-temperature carbonization starting zone is 20-30° C. higher than the temperature of the last temperature zone of the pre-oxidation; and / or, The low-temperature carbonization treatment adopts multi-stage gradient heating, and the temperature difference between adjacent temperature zones does not exceed 120°C; preferably 80-120°C; further preferably, the temperature difference between the last two temperature zones during the low-temperature carbonization treatment is not less than 100°C and not more than 120°C.

5. The method for improving the tensile modulus of large-tow carbon fibers according to claim 4, wherein: The initial temperature of the low-temperature carbonization treatment is 270-300°C; and / or, during the low-temperature carbonization treatment, the maximum temperature of the heating does not exceed 800°C; preferably, the maximum temperature of the low-temperature carbonization treatment is 700-800°C; Preferably, the low-temperature carbonization treatment is performed in a 7-stage gradient heating manner; Further preferably, the temperature zones corresponding to the low-temperature carbonization treatment are 270-290°C, 290-370°C, 370-450°C, 450-530°C, 530-610°C, 610-700°C, and 700-780°C, respectively.

6. The method for improving the tensile modulus of large-tow carbon fibers according to claim 1, wherein: The drafting ratio during the low-temperature carbonization process is 1.02 to 1.15 times; preferably 1.08 to 1.12 times; and / or, During the low-temperature carbonization treatment, the total carbonization treatment time is 60 to 120 seconds, and preferably the treatment time in each temperature zone is the same.

7. The method for improving the tensile modulus of large-tow carbon fibers according to claim 1, wherein: The starting temperature of the high-temperature carbonization is 90 to 200° C. higher than the temperature of the last temperature zone of the low-temperature carbonization; preferably 90 to 140° C.; and / or, The high-temperature carbonization treatment adopts multi-stage gradient heating, and the temperature difference between adjacent temperature zones does not exceed 120°C; preferably 70-120°C; further preferably, the temperature difference between the last two temperature zones during the high-temperature carbonization treatment is not less than 100°C and not more than 120°C.

8. The method for improving the tensile modulus of large-tow carbon fibers according to claim 7, wherein: The initial temperature of the high-temperature carbonization treatment is 800-900°C; and / or, during the high-temperature carbonization treatment, the maximum temperature does not exceed 1800°C; Preferably, the high-temperature carbonization treatment is carried out in an 8-stage gradient heating manner; Further preferably, the temperature zones corresponding to the high-temperature carbonization treatment are 840-860°C, 860-940°C, 940-1030°C, 1030-1110°C, 1110-1200°C, 1200-1290°C, 1290-1360°C, and 1360-1440°C, respectively.

9. The method for improving the tensile modulus of large-tow carbon fibers according to claim 7, wherein: The drafting ratio during the high-temperature carbonization process is 0.95 to 0.98 times; and / or, During the high-temperature carbonization treatment, the total carbonization treatment time is 60 to 120 seconds, and preferably the treatment time in each temperature zone is the same.

10. The method for improving the tensile modulus of large-tow carbon fibers according to claim 1, wherein: The method further comprises a post-treatment step after the high-temperature carbonization treatment; preferably, the post-treatment comprises the steps of electrochemical surface treatment, water washing, drying, sizing, and drying.

11. A large-tow carbon fiber prepared by the method for improving the tensile modulus of large-tow carbon fiber according to any one of claims 1 to 10; Preferably, the K number of the fibers in the large-tow carbon fiber is ≥48K, preferably 48K or 96K; and / or, The large-tow carbon fiber has a tensile strength of ≥4000 MPa, preferably 4000-4500 MPa, and / or a tensile modulus of ≥260 GPa, preferably 260-280 GPa.

12. Use of a large-tow carbon fiber prepared by the method for increasing the tensile modulus of large-tow carbon fiber according to any one of claims 1 to 10, or a large-tow carbon fiber according to claim 11, in the preparation of products related to new energy vehicles, marine development, wind power, and solar energy.