Method for producing polymer composite material with improved CNT dispersibility and polymer composite material produced thereby

Abstract

A method for manufacturing a polymer composite material with improved CNT dispersibility according to an embodiment of the present invention comprises the steps of:(S100) modifying a CNT surface by at least one of wet acid treatment or plasma treatment; (S200) introducing the surface-modified CNT and a solid-state monomer into a mixer, followed by mixing and dispersing to prepare a primary raw material mixture; (S300) reintroducing the primary raw material mixture into a ball mill disperser and performing secondary dispersion for a predetermined time to prepare a secondary raw material mixture in powder form having a finer particle size; (S400) introducing the secondary raw material mixture into a melting bath and removing moisture while melting the mixture for a predetermined time; (S500) adding an initiator and a catalyst to the molten secondary raw material mixture, followed by stirring; (S600) injecting the secondary raw material mixture to which the initiator and the catalyst have been added into a mold having a predetermined shape including a rod shape or a plate shape, and then heating the mold in an oven for a predetermined time to polymerize the secondary raw material mixture in the mold; and (S700) taking out the polymer completely polymerized in the above step from the mold and slowly cooling same at room temperature for a predetermined time.

Description

Method for manufacturing a polymer composite material with improved CNT dispersibility and a polymer composite material manufactured thereby

[0001] The present invention relates to a method for manufacturing a polymer composite material with improved CNT dispersibility, and more specifically, to a method for manufacturing a polymer composite material with improved CNT dispersibility applicable to various industrial fields by significantly reducing the process time for dispersion compared to conventional methods by improving the dispersibility of CNTs mixed into a solid-state monomer, thereby improving the productivity of the polymer composite material, and imparting semiconductor-level electrical conductivity to the finished composite material product along with significantly superior mechanical strength, and to a polymer composite material manufactured thereby.

[0002] Polymer materials exhibit unique mechanical, electrical, and thermal properties depending on their underlying monomers and chemical structures. While the properties of pure polymer materials are limited to a specific range, it is possible to improve various characteristics by adding reinforcements. A polymer composite is a material in which solid reinforcements, or fillers, are dispersed within a polymer matrix.

[0003] Nylon is an example of a polymer material, and in particular, Monomer Cast Nylon (MC nylon) (hereinafter abbreviated as 'MC nylon') is a type of engineering plastic and is a crystalline polymer manufactured by using a chemical component as a catalyst in caprolactam. MC nylon has a molecular weight about five times greater and a degree of crystallinity about twice greater than that of conventional nylon-6, and is gaining attention as a material that can be utilized in various industrial fields based on its excellent mechanical strength resulting from this.

[0004] However, since MC nylon, which is electrically insulating, lacks an electrostatic discharge function, it has limitations in that it cannot be used for equipment in the manufacturing or assembly processes of precision electronic products, such as PCBs and LCDs, which can suffer fatal damage even from minute spikes caused by static electricity, such as trolley wheels, work tools, and transport pallets. Therefore, efforts are being made to impart electrical conductivity (volume resistivity of about 106 Ω·cm) to MC nylon at least at the semiconductor level.

[0005] One method to impart specific electrical conductivity to MC nylon is to add carbon-based materials such as carbon black or graphite when melt-casting monomers such as caprolactam. However, MC nylon manufactured by adding a large amount of carbon black or graphite to molten liquid monomers generally has difficulty obtaining excellent physical properties and electrical conductivity.

[0006] In the case of carbon black, it has a large specific surface area, so it does not disperse well and adsorbs a large amount of raw monomer, existing in a paste-like form and hindering polymerization. As a result, the manufactured MC nylon has significantly degraded physical properties, and there is a problem that its electrical conductivity does not reach the desired level, that is, the semiconductor level.

[0007] Although graphite disperses relatively well compared to carbon black, it still tends to settle within molten monomers or molten polymers and does not disperse easily. Additionally, a large amount of graphite (more than 5% by weight of the total weight of MC nylon) must be used to impart the desired level of electrical conductivity to MC nylon, which can lead to a decrease in the mechanical strength of MC nylon, particularly a decrease in wear resistance.

[0008] Therefore, to address these issues, the use of carbon nanotubes (CNTs) is attracting attention. CNTs possess not only significantly superior electrical and thermal conductivity but also excellent mechanical strength compared to the two carbon-based materials described earlier.

[0009] These carbon nanotubes can impart specific electrical conductivity to MC nylon using small amounts, while significantly improving its mechanical strength, particularly wear resistance. Since the wear resistance of MC nylon is generally not superior to that of other engineering polymers, composites with carbon nanotubes are expected to greatly expand the industrial application range of MC nylon.

[0010] However, carbon nanotubes are fibrous materials that easily entangle and aggregate on their own, and consequently, no matter how much they are ground, mixed, or stirred within a molten monomer or molten polymer containing carbon nanotubes, the desired level of dispersion is not achieved.

[0011] If polymerization is performed under these conditions, it is highly likely that polymerization will not easily occur in the regions where carbon nanotubes are concentrated.

[0012] Even after polymerization is completed, if carbon nanotubes are not sufficiently dispersed, the effect of improving mechanical strength may be minimal or non-existent, and in some cases, mechanical strength may decrease in areas where carbon nanotubes are unevenly distributed. Additionally, electrical conductivity may appear only in parts of the MC nylon, or it may be impossible to achieve the desired electrical conductivity across the entire product.

[0013] In another aspect, uneven carbon nanotubes can cause secondary problems by blooming during operation in environments such as cleanrooms, thereby contaminating the cleanroom workplace.

[0014] If the aforementioned problem is solved, the composite material composed of MC nylon and carbon nanotubes will possess not only superior mechanical strength but also semiconductor-level electrical conductivity, making it suitable for use as an all-weather engineering material applicable to various industrial fields requiring these characteristics.

[0015] For example, Korean Patent Registration No. 2273847 (hereinafter referred to as the "prior art"), previously filed by the applicant of the present invention, discloses a polymer composite material technology including carbon nanotubes that improves upon the aforementioned problems.

[0016] According to prior art, a method for manufacturing a polymer composite material containing carbon nanotubes (CNT) is disclosed, which significantly improves the problem of carbon nanotubes not easily dispersing within conventional molten monomers or molten polymers by first preparing a solid-state raw material mixture by mixing and dispersing solid-state monomers and solid-state carbon nanotubes in a stirrer having a specific structure at a predetermined time and speed.

[0017] However, the polymer composite material containing carbon nanotubes disclosed in the aforementioned prior art had a problem in that the electrical properties and mechanical strength of the manufactured polymer composite material did not meet expectations because the carbon nanotubes were not evenly dispersed among the monomers during the process of introducing, mixing, and dispersing the solid-state monomers and carbon in a disperser.

[0018] Accordingly, the present invention has been devised to resolve the aforementioned problems. It aims to provide a method for manufacturing a polymer composite material with improved CNT dispersibility applicable to various industrial fields, and a polymer composite material manufactured thereby, by improving the dispersibility of CNTs mixed into a solid-state monomer, thereby significantly reducing the process time for dispersion compared to existing methods, and consequently improving the productivity of the polymer composite material, as well as imparting semiconductor-level electrical conductivity to the finished composite product along with significantly superior mechanical strength.

[0019] According to one embodiment, the present invention for achieving the above objectives comprises: (S100) a step of modifying the surface of a CNT by at least one of wet acid treatment or plasma treatment; (S200) a step of introducing the surface-modified CNT and a solid monomer into a stirrer, mixing and dispersing them to produce a primary raw material mixture; (S300) a step of introducing the primary raw material mixture into a ball mill disperser and dispersing it for a certain period of time to produce a secondary raw material mixture in the form of a powder with a denser particle size; (S400) a step of introducing the secondary raw material mixture into a melting tank and removing moisture while melting it for a certain period of time; (S500) a step of adding an initiator and a catalyst to the molten secondary raw material mixture and stirring; (S600) a step of injecting the secondary raw material mixture with the added initiator and catalyst into a mold of a certain shape including a rod or a plate, and then polymerizing the secondary raw material mixture within the mold by heating the mold in an oven for a certain period of time. and (S700) a step of removing the polymer, which has been polymerized in the above step, from the mold and cooling it slowly at room temperature for a certain period of time; is included.

[0020] In addition, according to one embodiment, the wet acid treatment of step (S100) comprises: (S110) introducing CNTs into a container containing an acid solution; (S120) dispersing CNTs in a nitric acid solution by applying ultrasound inside the container for a certain period of time; (S130) introducing the nitric acid solution in which the CNTs are dispersed into a reflux device and then acid treating it at room temperature for a certain period of time to impart functional groups (surface modification) to the surface of the CNTs; (S140) neutralizing the CNTs by mixing the surface-modified CNTs with distilled water; and (S150) drying the neutralized CNTs for a certain period of time.

[0021] In addition, according to one embodiment, the acid solution in step (S110) comprises at least one selected from the group including nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, or chlorosulfonic acid.

[0022] In addition, according to one embodiment, the plasma treatment of step (S100) comprises: (S111) a step of introducing CNTs into a plasma reactor; and (S121) a step of generating argon plasma inside the plasma reactor and then simultaneously injecting oxygen and hydrogen to impart functional groups to the surface of the CNTs.

[0023] In addition, according to one embodiment, in step (S500), at least one of toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) is added in an amount of 0.1 to 0.5 wt% as an initiator, and sodium (Na) is added in an amount of 0.1 to 0.5 wt% as a catalyst.

[0024] In addition, according to one embodiment, the stirrer of step (S200) comprises: a stirring chamber for receiving a raw material mixture; a shaft disposed inside the stirring chamber; a first impeller having a plurality of bottom scrapers having a wedge shape and rotating in a manner close to the bottom surface of the stirring chamber while coupled to the shaft; and a second impeller having an edge scraper having a curved blade shape and rotating in a manner close to the bottom surface of the stirring chamber while coupled to the shaft together with the first impeller.

[0025] Meanwhile, the polymer composite material with improved dispersibility of CNTs according to the present invention is manufactured according to any one of the manufacturing methods described above.

[0026] The present invention, as described above, improves the dispersibility of CNTs mixed into solid-state monomers, thereby making the structure denser (particle size 10 μm or less) compared to existing ones and significantly reducing the processing time for dispersion. Consequently, the productivity of polymer composite materials is improved, and the finished composite material product is endowed with superior mechanical strength and semiconductor-level electrical conductivity, which can be usefully utilized in various industrial fields.

[0027] In addition, the present invention has the effect of effectively analyzing solid-state monomers and CNTs by improving the problem in which carbon nanotubes are not easily dispersed within conventional molten monomers or molten polymers.

[0028] FIG. 1 is a flowchart showing a method for manufacturing a polymer composite material with improved dispersibility of CNTs according to the present invention.

[0029] FIG. 2 is a flowchart showing the wet CNT surface modification process according to one embodiment of the present invention in steps.

[0030] FIG. 3 is a flowchart showing the steps of a dry CNT surface modification process according to another embodiment of the present invention.

[0031] FIG. 4 is a schematic diagram showing the configuration of a stirrer according to one embodiment of the present invention.

[0032] Figures 5 and 6 are graphs of the X-ray photoelectron spectroscopy (XPS) analysis results of CNTs after wet (acid treatment) and dry (plasma treatment) surface modification according to the present invention, respectively.

[0033] The terms used herein are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “having,” or “having” are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described herein, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0034] Unless otherwise defined in this specification, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains.

[0035] Terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this specification.

[0036] Hereinafter, with reference to the attached drawings, the configuration of a method for manufacturing a polymer composite material with improved CNT dispersibility according to one embodiment of the present invention will be described in detail as follows.

[0037] FIG. 1 is a flowchart showing a method for manufacturing a polymer composite material with improved dispersibility of CNTs according to the present invention.

[0038] First, referring to FIG. 1, the step configuration according to one embodiment of the method for manufacturing a polymer composite material with improved dispersibility of CNTs according to the present invention is as follows.

[0039] Step (S100): The surface of the CNT is modified by at least one of wet acid treatment or dry plasma treatment.

[0040] By undergoing one of the above-mentioned wet acid treatment or dry plasma treatment surface modification treatments, functional groups (-OH, -COOH, etc.) are introduced onto the surface of the CNT, thereby improving electrical conductivity, wear resistance, and uniformity within the system.

[0041]

[0042] FIG. 2 is a flowchart showing the wet CNT surface modification process according to one embodiment of the present invention in steps.

[0043] Referring to FIG. 2, according to one embodiment, the wet acid treatment of step (S100) is performed according to the following steps.

[0044] Step (S110): CNTs are added to a container holding an acid solution.

[0045] According to one embodiment, the acid solution in step (S110) may comprise at least one selected from the group comprising nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, or chlorosulfonic acid.

[0046] Step (S120): Ultrasound is applied inside the container for a certain period of time to disperse CNTs in a nitric acid solution.

[0047] Step (S130): The nitric acid solution in which the CNTs are dispersed is introduced into a reflux device and then acid-treated at room temperature for a certain period of time to impart functional groups to the surface of the CNTs (surface modification).

[0048] Step (S140): The surface-modified CNT is neutralized by mixing it with distilled water.

[0049] Step (S150): The CNTs from which the neutralization is completed are dried for a certain period of time.

[0050]

[0051] FIG. 3 is a flowchart showing the steps of a dry CNT surface modification process according to another embodiment of the present invention.

[0052] Referring to FIG. 3, according to another embodiment, the plasma treatment of step (S100) may be performed according to the following steps.

[0053] Step (S111): CNTs are introduced into the plasma reactor.

[0054] Step (S121): After generating an argon plasma inside the plasma reactor, oxygen and hydrogen are simultaneously injected to impart functional groups to the surface of the CNTs.

[0055]

[0056] Step (S200): Surface-modified CNTs and solid monomers are fed into a stirrer and then mixed and dispersed to produce a primary raw material mixture.

[0057]

[0058] FIG. 4 is a schematic diagram showing the configuration of a stirrer according to one embodiment of the present invention.

[0059] Referring to FIG. 4, according to one embodiment, the stirrer (1000) of step (S200) may comprise: a stirring chamber (1100) for receiving a raw material mixture; a shaft (1200) disposed inside the stirring chamber; a first impeller (1300) having a plurality of bottom scrapers (1320) having a wedge shape on a rod-shaped frame (1310) and rotating in a state close to the bottom surface of the stirring chamber (1100) with the rod-shaped frame (1310) coupled to the shaft (1200); and a second impeller (1400) having an edge scraper (1410) having a curved blade shape and rotating in a state close to the bottom surface of the stirring chamber (1100) with the first impeller (1300) coupled to the shaft (1200).

[0060] According to one embodiment, the stirring chamber (1100) is composed of an inner chamber (1110) and an outer chamber (1130), and the open upper surface of the stirring chamber (1100) can be sealed by a chamber cover (1600). Accordingly, by sealing the stirring chamber (1100) with the chamber cover (1600), it is possible to prevent the powdered stirring material (first raw material mixture) from scattering and leaking to the outside during the process of crushing and dispersing.

[0061] Additionally, the impeller (1500) may include a first impeller (1300) and a second impeller (1400). The first impeller (1300) may be coupled to the shaft (1200) to rotate together, positioned adjacent to the bottom surface of the inner chamber (1110), and formed to be inclined toward the direction of rotation.

[0062] Meanwhile, the bottom scraper (1320) of the first impeller (1300) rotates together with the shaft (1200) and performs the function of stirring while evenly turning over and dispersing the solid agitated material on the bottom surface of the inner chamber (1110).

[0063] In addition, the first impeller (1300) continuously rotates together with the shaft (1200), thereby dispersing the mixture on the bottom surface of the inner chamber (1110) by flipping it upward and lifting it, and in this process, it serves to crush the mixture (first raw material mixture) into small pieces. That is, after different types of solid monomers and CNTs are introduced together into the inner chamber, the first impeller (1300) continuously rotates to lift the mixture upward and simultaneously crush and disperse the two types of mixtures so that they are well mixed.

[0064] Additionally, the second impeller (1400) may be coupled to the shaft (1200) to rotate together and positioned between the first impeller (1300). At this time, the second impeller (1400) is equipped with an edge scraper (1410) in the form of a curved blade, thereby guiding the agitated material introduced into the inner chamber (1110) to the edge of the inner chamber (1110). That is, as shown in FIG. 4, the edge scraper (1410) of the second impeller (1400) has a structure that is curved toward the rotational direction of the shaft (1200), so in the part adjacent to the inner surface of the inner chamber (1110), the agitated material (first raw material mixture) can be effectively mixed by the edge scraper (1410) of the second impeller (1400) while simultaneously crushing and gathering it inward.

[0065]

[0066] Step (S300): The above primary raw material mixture is reintroduced into a ball mill disperser and dispersed for a certain period of time to produce a secondary raw material mixture in the form of a powder with a denser particle size.

[0067] According to one embodiment, the first dispersion of step (S200) and the second dispersion of step (S300) were performed by dispersing a solid-state monomer (caprolactam) and CNTs in two steps as follows.

[0068] 1) Distributor

[0069] - Primary dispersion: Using an impeller stirrer, two solid substances of completely different sizes, namely flake-shaped caprolactam and nano-sized CNTs, are primarily mixed.

[0070] - Secondary dispersion: The primary mixture is densely dispersed to a particle size of 10㎛ or less.

[0071] High-shear dispersers that can be used in the above secondary dispersion process include ball mills, streamlined ball mills, jet mills, fin mills, etc. In this embodiment, dispersion was carried out using the most suitable streamlined ball mill, taking into account the dispersion efficiency and productivity of the material to be dispersed.

[0072] 2) Operating conditions of the primary disperser (impeller stirrer)

[0073] - Rotation speed: 50~150rpm

[0074] - Processing time: 20~30 minutes

[0075] 3) Operating conditions of the secondary disperser (streamlined ball mill disperser)

[0076] - Rotation speed: 300~500rpm

[0077] - Processing time: Average 30 minutes

[0078] - Ball size: Use a 1:1 mixture of 3mm and 5mm diameters.

[0079] - Ball : Sample ratio = 10 : 1

[0080]

[0081] Step (S400): The above secondary raw material mixture is introduced into a melting tank and then melted for a certain period of time to remove moisture.

[0082]

[0083] Step (S500): An initiator and a catalyst are added to the molten secondary raw material mixture and then stirred.

[0084] According to one embodiment, in step (S500), at least one of isocyanates including toluene diisocyanate (TDI) or methylene diphenyl diisocyanate (MDI) is added in an amount of 0.1 to 0.5 wt% as an initiator, and sodium (Na) is added in an amount of 0.1 to 0.5 wt% as a catalyst. (For specific content and composition of each component, refer to the examples and Table 1 described below.)

[0085]

[0086] Step (S600): The secondary raw material mixture to which the initiator and catalyst have been added is injected into a mold of a certain shape, such as a rod or a plate, and then the secondary raw material mixture in the mold is polymerized by heating the mold in an oven for a certain period of time.

[0087]

[0088] Step (S700): The polymer that has been polymerized in the above step is removed from the mold and slowly cooled at room temperature for a certain period of time, thereby completing the manufacture of the polymer composite material of the present invention.

[0089]

[0090] Meanwhile, the effects of the manufacturing method of the present invention and the polymer composite material produced thereby are explained below through various examples and comparative examples. The components used in the following examples are as follows:

[0091] - Monomer: Caprolactam

[0092] - Carbon nanotubes: Multicarbon nanotubes (abbreviated as CNT), diameter: approximately 7 to approximately 20 nm (average diameter: approximately 12 nm); bulk density: 0.08 g / cm³ 3 ; Length: approx. 10 to approx. 200 μm; Carbon purity: 94 wt% or higher; Moisture content: less than 3% having physical properties

[0093] - Polymerization-inducing additives: Toluene diisocyanate (referred to as TDI), methylene diphenyl diisocyanate (referred to as MDI), and sodium (referred to as Na)

[0094] <Example 1>

[0095] Wet acid treatment process:

[0096] 2.5 L of 3M nitric acid (HNO3) is prepared in a container, and 10 g of carbon nanotubes are added to the container containing the nitric acid solution. Then, primary dispersion is carried out by ultrasonication for 10 minutes. Afterward, the mixed solution is acid-treated at room temperature for 12 hours using a reflux device to impart functional groups to the surface.

[0097] Vacuum filtration is performed using a 0.2 µm PTFE membrane filter, and a primary wash is carried out using distilled water during this process. The filtered carbon nanotube aggregate is mixed with distilled water and centrifuged at high speed to separate the supernatant, and the process of mixing with distilled water and centrifuging is repeated to neutralize the acid-treated carbon nanotubes until the pH reaches 7. The neutralized carbon nanotubes are vacuum-dried for more than 12 hours to remove moisture.

[0098] 1st and 2nd order dispersion processes:

[0099] 1,000 g of solid caprolactam and 10 g of solid CNTs treated by the surface modification method using the wet acid treatment described above were introduced into a stirrer (first dispersion device) as shown in Fig. 4. Subsequently, a primary raw material mixture in a solid state was prepared by stirring at a speed of 100 rpm for 20 minutes at room temperature. To further finely disperse the primary mixture, the primary mixture was transferred to a streamlined ball mill disperser (second dispersion device) and secondary dispersion was completed at 350 rpm for 30 minutes. The secondary dispersed mixture was transferred to a melting tank and water was removed by melting under vacuum at 100 degrees for about 30 minutes.

[0100] Next, the molten secondary raw material mixture was divided equally into different containers, and 2g of initiator TDI and 2g of catalyst Na were added to each container of the molten secondary raw material mixture, and stirred at approximately 60 rpm under vacuum at approximately 100 degrees.

[0101] The molten secondary raw material mixtures contained in each container were combined into one and heated in an oven at 100–120 degrees for 10 minutes. Afterward, the molten secondary raw material mixture was transferred to a mold heated to approximately 160 degrees and polymerized for 30 minutes. The polymer was then removed from the mold and slowly cooled at room temperature to complete the manufacture of the polymer composite material.

[0102] <Example 2>

[0103] Wet acid treatment process:

[0104] 2.5 L of 3M nitric acid (HNO3) is prepared in a container, and 10 g of carbon nanotubes are added to the container containing the nitric acid solution. Then, primary dispersion is carried out by ultrasonication for 10 minutes. Afterward, the mixed solution is acid-treated at room temperature for 12 hours using a reflux device to impart functional groups to the surface.

[0105] Vacuum filtration is performed using a 0.2 µm PTFE membrane filter, and a primary wash is carried out using distilled water during this process. The filtered carbon nanotube aggregate is mixed with distilled water and centrifuged at high speed to separate the supernatant, and the process of mixing with distilled water and centrifuging is repeated to neutralize the acid-treated carbon nanotubes until the pH reaches 7. The neutralized carbon nanotubes are vacuum-dried for more than 12 hours to remove moisture.

[0106] 1st and 2nd order dispersion processes:

[0107] 1,000 g of solid caprolactam and 10 g of solid CNTs treated by the surface modification method using the wet acid treatment described above were introduced into a stirrer as shown in Fig. 4. Subsequently, a primary raw material mixture in solid state was prepared by stirring at a speed of 100 rpm for 20 minutes at room temperature. To finely disperse the primary mixture, the mixture was transferred to a streamlined ball mill disperser and secondary dispersion was completed at 350 rpm for 30 minutes. The secondary raw material mixture was transferred to a melting tank and water was removed by melting under vacuum at 100 degrees for about 30 minutes.

[0108] Next, the molten secondary raw material mixture was divided equally into different containers, and 3g of initiator MDI and 5g of catalyst Na were added to each container of the molten secondary raw material mixture, and stirred at approximately 60 rpm under vacuum at approximately 100 degrees.

[0109] The molten secondary raw material mixtures contained in each container were combined into one and heated in an oven at 100–120 degrees for 10 minutes. Afterward, the molten secondary raw material mixture was transferred to a mold heated to approximately 160 degrees and polymerized for 30 minutes. The polymer was then removed from the mold and slowly cooled at room temperature to complete the manufacture of the polymer composite material.

[0110] <Example 3>

[0111] Wet acid treatment process:

[0112] 2.5 L of 3M nitric acid (HNO3) is prepared in a container, and 10 g of carbon nanotubes are added to the container containing the nitric acid solution. Then, primary dispersion is carried out by ultrasonication for 10 minutes. Afterward, the mixed solution is acid-treated at room temperature for 12 hours using a reflux device to impart functional groups to the surface.

[0113] Vacuum filtration is performed using a 0.2 µm PTFE membrane filter, and a primary wash is carried out using distilled water during this process. The filtered carbon nanotube aggregate is mixed with distilled water and centrifuged at high speed to separate the supernatant, and the process of mixing with distilled water and centrifuging is repeated to neutralize the acid-treated carbon nanotubes until the pH reaches 7. The neutralized carbon nanotubes are vacuum-dried for more than 12 hours to remove moisture.

[0114] 1st and 2nd order dispersion processes:

[0115] 1,000 g of solid caprolactam and 10 g of solid CNTs treated with a surface modification method via wet acid treatment were introduced into a stirrer as shown in Fig. 4. Subsequently, a primary raw material mixture in solid state was prepared by stirring at a speed of 100 rpm for 20 minutes at room temperature. To finely disperse the primary mixture, the mixture was transferred to a streamlined ball mill disperser and secondary dispersion was completed at 350 rpm for 30 minutes. The secondary raw material mixture was transferred to a melting tank and water was removed by melting under vacuum at 100 degrees for about 30 minutes.

[0116] Next, the molten secondary raw material mixture was divided equally into different containers, and 5g of initiator MDI and 3g of catalyst Na were added to each container of the molten secondary raw material mixture, and stirred at about 60 rpm under vacuum at about 100 degrees.

[0117] The molten secondary raw material mixtures contained in each container were combined into one and heated in an oven at 100–120 degrees for 10 minutes. Afterward, the molten secondary raw material mixture was transferred to a mold heated to approximately 160 degrees and polymerized for 30 minutes. The polymer was then removed from the mold and slowly cooled at room temperature to complete the manufacture of the polymer composite material.

[0118] <Example 4>

[0119] Dry Plasma Treatment Process:

[0120] Carbon nanotubes were continuously fed into a plasma reactor under an argon gas atmosphere at 40 kW output and 300 torr pressure for plasma treatment. During the plasma treatment of carbon nanotubes, oxygen and hydrogen gases were simultaneously flowed to modify functional groups such as -COOH, -OH, and =O on the surface of the carbon nanotubes.

[0121] 1st and 2nd order dispersion processes:

[0122] 1,000 g of solid caprolactam and 7 g of solid CNTs surface-modified by the dry plasma treatment method were introduced into a stirrer as shown in Fig. 4. Subsequently, a primary raw material mixture in a solid state was prepared by stirring at a speed of 100 rpm for 20 minutes at room temperature. To perform secondary dispersion for fine dispersion of the primary mixture, the primary mixture was transferred to a streamlined ball mill disperser and secondary dispersion was completed at 350 rpm for 30 minutes. The secondary dispersed mixture was transferred to a melting tank and water was removed by melting under vacuum at 100 degrees for about 30 minutes.

[0123] Next, the molten raw material mixture was divided equally into different containers, and 2g of initiator TDI and 2g of catalyst Na were added to the molten raw material mixture in each container, and stirred at about 60 rpm under vacuum at about 100 degrees.

[0124] The molten secondary raw material mixtures contained in each container were combined into one and heated in an oven at 100–120 degrees for 10 minutes. Afterward, the molten secondary raw material mixture was transferred to a mold heated to approximately 160 degrees and polymerized for 30 minutes. The polymer was then removed from the mold and slowly cooled at room temperature to complete the manufacture of the polymer composite material.

[0125] <Examples 5 to 9>

[0126] A polymer composite material was manufactured using the same method as in Example 4, except that the content of the solid-state raw material mixture was changed as shown in Table 1.

[0127] <Comparative Example 1>

[0128] 1,000 g of solid caprolactam and 10 g of solid CNT were added to a stirrer as shown in Fig. 4. Then, a primary raw material mixture in a solid state was prepared by stirring at a speed of 100 rpm for 20 minutes at room temperature. To finely disperse the primary mixture, the mixture was transferred to a streamlined ball mill disperser and secondary dispersion was completed at 350 rpm for 30 minutes. The secondary dispersed mixture was transferred to a melting tank and water was removed by melting under vacuum at 100 degrees for about 30 minutes.

[0129] Next, the molten raw material mixture was divided equally into separate containers, and 2g of initiator TDI and 2g of catalyst Na were added to the molten raw material mixture in each container, and the mixture was stirred at approximately 60 rpm under vacuum at approximately 100 degrees. Subsequently, the molten mixtures in each container were combined into one, and then heated again at 100–120 degrees for 10 minutes. Afterward, the molten mixture was transferred to a mold overheated to approximately 160 degrees and polymerized for 30 minutes. The polymer was then removed from the mold and slowly cooled at room temperature to complete the preparation of the polymer composite material.

[0130] <Comparative Example 2>

[0131] 1,000 g of solid caprolactam and 3 g of solid CNT were added to a stirrer as shown in Fig. 4. Then, a primary raw material mixture in solid state was prepared by stirring at a speed of 100 rpm for 20 minutes at room temperature. To finely disperse the primary mixture, the mixture was transferred to a streamlined ball mill disperser and secondary dispersion was completed at 350 rpm for 30 minutes. The secondary dispersed mixture was transferred to a melting tank and water was removed by melting under vacuum at 100 degrees for about 30 minutes.

[0132] Next, the molten raw material mixture was divided equally into separate containers, and 3g of initiator MDI and 5g of catalyst Na were added to the molten raw material mixture in each container, respectively, and stirred at approximately 60 rpm under vacuum at approximately 100 degrees. Then, the molten mixtures in each container were combined into one, and heated again at 100–120 degrees for 10 minutes. Afterward, the molten mixture was transferred to a mold overheated to approximately 160 degrees and polymerized for 30 minutes. The polymer composite material was then manufactured by removing the completed polymer from the mold and slowly cooling it at room temperature.

[0133] Classification Monomer (Caprolactam) CNT Initiator (Content, wt%) Catalyst (Content, wt%) Untreated (Content, wt%) Treatment Method Content (wt%) TDIMDISodium(Na) Example 1 100-Wet 1.0 0.2-0.2 Example 2 100-Wet 1.0-0.3 0.5 Example 3 100-Wet 1.0-0.5 0.3 Example 4 100-Dry 0.7 0.2-0.2 Example 5 100-Dry 0.7-0.3 0.5 Example 6 100-Dry 0.7-0.5 0.3 Example 7 100-Dry 0.3 0.2-0.2 Example 8 100-Dry 0.3-0.3 0.5 Example 9100-Dry 0.3-0.5 0.3 Comparative Example 1100 1.0--0.2-0.2 Comparative Example 2100 0.3---0.3 0.5

[0134] <Experimental Example 1: Evaluation of Physical Properties>

[0135] The physical properties of the polymer composite materials prepared in Examples 1 to 9 and Comparative Examples 1 and 2 were measured using the following test methods, and the results are shown in Table 2 below.

[0136] - Tensile strength: Measured according to ASTM D638

[0137] - Elongation: Measured according to ASTM D638

[0138] - Flexural strength: Measured according to ASTM D790

[0139] - Flexural modulus: Measured according to ASTM D790

[0140] - Impact strength: Measured by ASTM D256

[0141] - Heat distortion temperature: Measured according to ASTM D648

[0142] - Volume resistivity: Measured by ASTM D257

[0143] - Wear Rate: The wear rate is measured by comparing the weight of the polymer composite material before and after grinding, using a CALIBRADE H-18 grinding stone from TABER INDUSTRIES, USA, to grind a wear specimen (80x80x50mm) 2,000 times at a load of 1 kg and 70 rpm.

[0144] Item Tensile Strength (Kgf / cm²) Elongation (%) Flexural Strength (Kgf / cm²) Flexural Modulus (Kgf / cm²) Impact Strength (Kgf·cm / cm) Heat Distortion Temperature (°C, 18.6 Kg / cm²) Abrasion Rate (W / %) Volume Resistivity (Ω·cm) Average Value Range Example 1 1,050 101,500 43,000 217 50.028 7×10E4 10E4~5 Example 2 9 50 301,350 38,500 518 50.025 2×10E4 Max.10E4 Example 3 9 80 401,420 41,000 6.5 19 50.025×10E3 Max.10E3 Example 4960151,43037,5002.51700.0328×10E510E5~6 Examples 587020125036,00041750.0285×10E5Max.10E5 Example 690030135037,0005.51850.0253×10E5Max.10E5 Example 7860171,32035,50031680.043×10E710E7~8 Examples 8800231,15033,0004.21720.0367×10E6Max.10E6 Example 9840281,23034,0005,71750.0325×10E6Max.10E6 Comparative Example 1850101,28037,5001.51600.0464X10E610E5~7 Comparative Example 27001592028,5002.81650.0636X10E810E7~9

[0145] Referring to Table 2 above, it can be seen that Examples 1 to 9 show superior effects compared to Comparative Examples 1 and 2.

[0146] All embodiments exhibited superior physical properties compared to the comparative examples, such as tensile strength, elongation, flexural strength, flexural modulus, impact strength, heat distortion temperature, wear rate, and volume resistivity. This is attributed to the fact that the CNTs were well dispersed by performing the manufacturing method according to the present invention. Furthermore, embodiments in which the raw material mixture was dispersed and mixed by dividing the process into multiple stages with different stirring speeds obtained relatively better wear rate results.

[0147] In particular, it is worth noting that the wear rate of the example is improved by at least about 3 times and up to about 10 times or more compared to the comparative example. This means that when parts, tools, devices, equipment, etc. are manufactured using the MC nylon of the present invention as a material, their lifespan can be dramatically improved, and furthermore, the operating rate of the process using them can be improved.

[0148] Furthermore, the embodiments exhibited significantly superior intrinsic volume resistivity compared to the comparative examples, and these results suggest that the present invention clearly resolves what conventional MC nylon has failed to achieve.

[0149]

[0150] Figures 5 and 6 are graphs of the X-ray photoelectron spectroscopy (XPS) analysis results of CNTs after wet (acid treatment) and dry (plasma treatment) surface modification according to the present invention, respectively.

[0151] Referring to Figure 5, peaks corresponding to the CC, CO, C=O, and OC=O functional groups, respectively, can be observed as part of the C1s spectrum. It can be seen that the peaks for CO, which develop around 285.3 eV and 286 eV after wet acid treatment and plasma treatment, increase compared to the raw material, and it was confirmed that the peak at 288.4 eV, corresponding to OC=O in wet acid treatment, also increases.

[0152] In addition, referring to Figure 6, which is a graph showing the ratio of carbon to oxygen content by XPS analysis, it was confirmed that the oxygen content of the raw material increased from 1.53% to 7.43% when wet acid treatment was performed, and to 3.5% when plasma treatment was performed, although there were slight differences depending on the treatment conditions.

[0153] Based on the above results, it was possible to confirm the introduction of oxygen functional groups by wet acid treatment with a nitrogen solution and plasma surface treatment.

[0154]

[0155] Furthermore, the present invention is not limited solely to the embodiment described above. Since the same effect can be achieved even when changing the detailed configuration, number, or arrangement structure of the device, it is hereby specified that those skilled in the art can add, delete, or modify various configurations within the scope of the technical concept of the present invention.

Claims

1. (S100) A step of modifying the CNT surface by at least one of wet acid treatment or plasma treatment; (S200) A step of introducing surface-modified CNTs and solid-state monomers into a stirrer, and then mixing and dispersing them to produce a primary raw material mixture; (S300) A step of reintroducing the above primary raw material mixture into a ball mill disperser and dispersing it for a certain period of time to produce a secondary raw material mixture in the form of a powder with a denser particle size; (S400) A step of removing moisture while melting the above secondary raw material mixture for a certain period of time after introducing it into a melting tank; (S500) A step of adding an initiator and a catalyst to the molten secondary raw material mixture and then stirring; (S600) A step of polymerizing the secondary raw material mixture in the mold by injecting the secondary raw material mixture to which the initiator and catalyst have been added into a mold of a certain shape including a rod or a plate, and then heating the mold in an oven for a certain period of time; and (S700) A step of removing the polymer, which has been polymerized in the above step, from the mold and cooling it slowly at room temperature for a certain period of time; comprising, Method for manufacturing a polymer composite material with improved CNT dispersibility.

2. In Paragraph 1, The wet acid treatment of the above step (S100) is, (S110) Step of introducing CNTs into a container containing an acid solution; (S120) A step of dispersing CNTs in a nitric acid solution by applying ultrasound inside the container for a certain period of time; (S130) A step of introducing the nitric acid solution in which the above CNTs are dispersed into a reflux device and then acid-treating it at room temperature for a certain period of time to impart functional groups (surface modification) to the surface of the CNTs; (S140) A step of neutralizing the CNT by mixing the surface-modified CNT with distilled water; and (S150) A step of drying the CNTs after the neutralization is completed for a certain period of time; comprising, Method for manufacturing a polymer composite material with improved CNT dispersibility.

3. In Paragraph 2, In the above step (S110), the acid solution is, Comprising at least one selected from the group comprising nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, or chlorosulfonic acid, Method for manufacturing a polymer composite material with improved CNT dispersibility.

4. In Paragraph 1, The plasma treatment of the above step (S100) is, (S111) Step of introducing CNTs into a plasma reactor; and (S121) A step of imparting functional groups to the surface of CNTs by simultaneously injecting oxygen and hydrogen after generating an argon plasma inside the plasma reactor; Method for manufacturing a polymer composite material with improved CNT dispersibility.

5. In Paragraph 1, In the above step (S500), Adding 0.1 to 0.5 wt% of at least one of isocyanates including toluene diisocyanate (TDI) or methylene diphenyl diisocyanate (MDI) as an initiator, and 0.1 to 0.5 wt% of sodium (Na) as a catalyst, Method for manufacturing a polymer composite material with improved CNT dispersibility.

6. In Paragraph 1, The stirrer of the above step (S200) is, A stirring chamber for receiving a raw material mixture; A shaft disposed inside the above stirring chamber; A first impeller having a plurality of bottom scrapers having a wedge shape and rotating in a state close to the bottom surface of the stirring chamber while coupled to the shaft; and A second impeller having a curved blade-shaped edge scraper and rotating in a state close to the bottom surface of the stirring chamber while coupled to a shaft together with the first impeller; comprising Method for manufacturing a polymer composite material with improved CNT dispersibility.

7. A polymer composite material manufactured according to any one of claims 1 to 6.

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