Regenerated carbon fiber bundle and manufacturing method therefor

Abstract

The present invention relates to a regenerated carbon fiber bundle and a manufacturing method therefor, the regenerated carbon fiber bundle comprising: a plurality of regenerated carbon fibers having pores between the plurality of regenerated carbon fibers and gathered in the form of threads; and a sizing agent positioned on the surfaces of the plurality of regenerated carbon fibers and in the pores between the plurality of regenerated carbon fibers, wherein the regenerated carbon fiber bundle has a bulk density of 0.25 g / ml or more.

Description

Recycled carbon fiber bundle and method for manufacturing the same

[0001] The present invention relates to a bundle of recycled carbon fibers and a method for manufacturing the same.

[0002] Carbon fiber is a material possessing high strength and elasticity compared to ordinary fibers, and by being composited with polymer materials, it is a key material capable of replacing existing steel or metal in many industrial fields. While the mechanical properties of carbon fiber composites are determined by the properties of the carbon fiber and the matrix resin, these properties are also significantly influenced by the interfacial bonding strength between the carbon fiber and the matrix resin.

[0003] Among carbon fibers, recycled carbon fiber is emerging as an important material to replace conventional materials in various industrial fields. However, de-sizing during the recycling process generates a large number of voids between the fibers, which can lead to weaknesses at the adhesive interface between the fibers and the matrix resin when applied to carbon fiber composites. Therefore, a sizing process is essential to minimize voids between the fibers and improve adhesion between them. Additionally, since recycled carbon fibers may have irregular lengths or widths during manufacturing, additional processes to ensure uniformity are also necessary.

[0004] Therefore, to address these issues, surface modification or sizing of recycled carbon fibers through additional processes is essential, and research is still needed to improve the compatibility between recycled carbon fibers and matrix resins.

[0005] We provide a recycled carbon fiber bundle with excellent mechanical properties manufactured through a method for manufacturing recycled carbon fiber bundles with a simple manufacturing process.

[0006] In one embodiment, a bundle of regenerated carbon fibers is provided, comprising a plurality of regenerated carbon fibers; and a sizing agent located on the surface of the plurality of regenerated carbon fibers, and having a bulk density of 0.25 g / ml or more.

[0007] In another embodiment, a method for manufacturing a bundle of recycled carbon fibers is provided, comprising: (i) a step of softening recycled carbon fibers manufactured from a carbon fiber composite material; (ii) a step of sizing the softened recycled carbon fibers by treating them with a sizing agent in an amount of 1% to 25% by weight relative to 100% by weight of the total softened recycled carbon fibers; (iii) a step of slitting the sized recycled carbon fibers; and (iv) a step of chopping the slit recycled carbon fibers.

[0008] According to a method for manufacturing a recycled carbon fiber bundle according to one embodiment, costs are reduced compared to using commercial carbon fibers, and at the same time, the recycled carbon fiber bundle manufactured by the method has excellent mechanical properties by increasing the interfacial bonding strength with the matrix resin.

[0009] Figure 1 is a graph showing the sizing agent pickup rate according to the sizing agent content of the recycled carbon fiber bundle according to the embodiment.

[0010] Figure 2 is a graph showing the sizing agent pickup rate according to the sizing agent treatment time of a recycled carbon fiber bundle according to an example.

[0011] Figure 3 is a graph showing the bulk density according to the pickup rate of a recycled carbon fiber bundle according to an embodiment.

[0012] Hereinafter, embodiments of the present disclosure are described in detail so that those skilled in the art to which the present disclosure pertains can easily implement them. However, the present disclosure may be embodied in various different forms and is not limited to the embodiments described herein.

[0013] In this specification, "combination thereof" means a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, a reaction product, etc.

[0014] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0015] In this specification, terms are used solely for the purpose of distinguishing one component from another. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0016] Recycled carbon fiber bundles

[0017] One embodiment provides a bundle of regenerated carbon fibers comprising: a plurality of regenerated carbon fibers; and a sizing agent located on the surface of the plurality of regenerated carbon fibers, and having a bulk density of 0.25 g / ml or more.

[0018] Recycled carbon fiber is emerging as an important material to replace conventional materials in various industrial fields; however, de-sizing during the recycling process generates a large number of voids between the fibers. Consequently, when applied to carbon fiber composites, this can lead to weaknesses at the adhesive interface between the fibers and the matrix resin. Therefore, a sizing process is essential to minimize voids between fibers and enhance adhesion between them. Furthermore, since recycled carbon fibers may exhibit irregular lengths or widths during manufacturing, additional processes to ensure uniformity are also necessary.

[0019] According to one embodiment, a bundle of recycled carbon fibers with improved bulk density can be produced by softening, sizing, slitting, and chopping recycled carbon fibers produced from a carbon fiber composite material. In particular, during the softening process, the penetration of the sizing agent is improved, and by controlling the content of the sizing agent, the bulk density of the recycled carbon fiber bundle can be controlled to optimize bonding with the matrix resin, thereby increasing interfacial bonding strength and providing a bundle of recycled carbon fibers with improved mechanical properties.

[0020] A recycled carbon fiber bundle according to one embodiment comprises a plurality of recycled carbon fibers. At this time, the recycled carbon fiber bundle may include 5,000 to 50,000 strands of recycled carbon fiber, and for example, 6,000 to 45,000 strands, 7,000 to 40,000 strands, 8,000 to 35,000 strands, 9,000 to 30,000 strands, or 10,000 to 25,000 strands. When the number of recycled carbon fibers included in the recycled carbon fiber bundle falls within the above range, the voids between the recycled carbon fibers are minimized, and the interfacial bonding strength between the recycled carbon fiber bundle and the matrix resin is increased, thereby providing excellent mechanical properties.

[0021] A recycled carbon fiber bundle according to one embodiment comprises a plurality of recycled carbon fibers, and the recycled carbon fibers may be in the form of threads. In this case, the length of the recycled carbon fiber may be 0.1 cm to 200 cm, for example, 0.5 cm to 150 cm, 1 cm to 100 cm, or 10 cm to 50 cm. Additionally, the thickness of the recycled carbon fiber may be 1 μm to 20 μm, for example, 2 μm to 18 μm, 3 μm to 15 μm, 4 μm to 12 μm, or 5 μm to 10 μm. When the length and thickness of the recycled carbon fiber fall within the above ranges, the voids between the recycled carbon fibers are minimized, and the interfacial bonding strength between the recycled carbon fiber bundle and the matrix resin is increased, thereby providing excellent mechanical properties.

[0022] According to one embodiment, a recycled carbon fiber bundle may be de-sized during the manufacturing process of the recycled carbon fibers to include voids between the plurality of recycled carbon fibers, and the porosity of the recycled carbon fiber bundle may be greater than 0% and less than or equal to 40%, for example, 5% to 35%, 10% to 30%, or 20% to 40%. When the porosity of the recycled carbon fiber bundle falls within the above range, the voids between the recycled carbon fibers are minimized, and the interfacial bonding strength between the recycled carbon fiber bundle and the matrix resin is increased, thereby providing excellent mechanical properties.

[0023] A recycled carbon fiber bundle according to one embodiment includes a sizing agent located on the surface of the plurality of recycled carbon fibers, and may further include a sizing agent in the voids that may be included between the plurality of recycled carbon fibers. By positioning the sizing agent on the surface of the plurality of recycled carbon fibers and / or in the voids between the plurality of recycled carbon fibers, the sizing agent is introduced into the recycled carbon fiber bundle in the form of small holes and squeezed, thereby minimizing the voids between the recycled carbon fibers, which can increase the cohesiveness of the recycled carbon fibers, increase bulk density, and increase bonding strength with the matrix resin.

[0024] As the above-mentioned sizing agent, polyurethane resin, epoxy resin, polyamide resin, or a combination thereof may be used.

[0025] Examples of the above polyurethane resins include polymeric polyols, organic diisocyanates, etc. Specific examples of the above polymeric polyols include polyester polyols (e.g., polyethylene adipate diol, polybutylene adipate diol, polyethylene butylene adipate diol, polyneopenyl adipate diol, polyneopenyl terephthalate diol, polycaprolactone diol, polyvalerolactone diol, and polyhexamethylene carbonate diol, etc.); polyether polyols [polyoxyethylene glycol, polyoxypropylene glycol, polyoxyethyleneoxypropylene glycol, polyoxytetramethylene glycol, and alkylene oxide adducts having 2 to 4 carbon atoms of bisphenols, etc.], etc. Specific examples of the above organic diisocyanates include aromatic diisocyanates such as 2,4'- or 4,4'-diphenylmethane diisocyanate (MDI), 2,4- or 2,6-tolylene diisocyanate (TDI), 4,4'-dibenzyl diisocyanate, 1,3- or 1,4-phenylene diisocyanate, 1,5-naphthylene diisocyanate, and xylene diisocyanate; aliphatic diisocyanates such as ethylene diisocyanate, hexamethylene diisocyanate (HDI), and lysine diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate (IPDI) and 4,4'-dicyclohexylmethane diisocyanate; and mixtures of two or more of these.

[0026] Examples of the above epoxy resins include bisphenol A type epoxy sizing agent, bisphenol F type epoxy sizing agent, bisphenol S type epoxy sizing agent, phenol novolak type epoxy sizing agent, cresol novolak type epoxy sizing agent, glycidyl ester type epoxy sizing agent, glycidylamine type epoxy sizing agent, polyalkylene glycol type epoxy sizing agent, and glycidyl compounds of aliphatic alcohols.

[0027] Examples of the above polyamide resins include polyamide 6, polyamide 12, polyamide 66, polyamide 6 / 66, polyamide 6 / 12, polyamide 6 / 6T, polyamide 6 / 6I, etc.

[0028] The aforementioned sizing agent is a special emulsion type in which modified polyurethane resin or modified polyester resin is dispersed, and has the characteristic of having anionic or nonionic properties on the surface of the emulsion resin for water-based formulation.

[0029] The above recycled carbon fiber bundle may contain 1% to 25% by weight of the sizing agent based on 100% by weight of the total recycled carbon fiber bundle, for example, 1% to 10% by weight, 3% to 10% by weight, 5% to 10% by weight, or 8% to 10% by weight. When the content of the sizing agent falls within the above range, the pickup rate of the recycled carbon fiber can be optimized, and the bonding with the matrix resin can be optimized by controlling the bulk density of the recycled carbon fiber.

[0030] A recycled carbon fiber bundle according to one embodiment may contain char in an amount greater than 0 weight% to 5 weight% or less, for example, greater than 0 weight% to 4 weight% or less, greater than 0 weight% to 3 weight% or less, greater than 0 weight% to 2 weight% or less, or greater than 0 weight% to 1 weight% or less, based on 100 weight% of the total recycled carbon fiber bundle. The recycled carbon fiber bundle may exhibit a char content within the above range by removing char in two stages, air injection and a physical method, as described below, thereby improving the flexibility and processability of the recycled carbon fiber and reducing physical contact between the recycled carbon fibers, which facilitates the penetration of the sizing agent described below.

[0031] The bulk density of the recycled carbon fiber treated with the above-mentioned sizing agent is 0.25 g / ml or higher, and may be, for example, 0.25 g / ml to 0.5 g / ml, 0.25 g / ml to 0.45 g / ml, 0.25 g / ml to 0.4 g / ml, or 0.25 g / ml to 0.35 g / ml. Bulk density minimizes voids between fibers of the recycled carbon fiber and reflects its cohesiveness and structural density. When the bulk density falls within the above range, the cohesiveness and feeding properties of the recycled carbon fiber are improved, making it possible to apply it as an application product with plastic materials. Although the method for measuring bulk density is not limited to a specific method, the bulk density may be measured using the tap density measurement method. In this case, tap density refers to the apparent density obtained by mechanically tapping a measuring container containing a powder sample. The above tap density can be measured by confirming the weight of the object to be measured and then pressing it against a graduated cylinder or the like to minimize the empty space. At this time, the empty space can be minimized by applying about 50 impacts to ensure it is pressed against the underside of the graduated cylinder. Subsequently, the bulk density can be measured using the volume of the object to be measured and the above tap density.

[0032] In one embodiment, the pickup rate of the sizing agent may be 3% or more, for example, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, or 9% or more. The pickup rate of the sizing agent may be 10% or less, for example, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, or 3% or less. When the pickup rate of the sizing agent falls within the above range, an appropriate amount of the sizing agent is applied to the softened recycled carbon fibers to minimize the voids between the recycled carbon fibers, thereby increasing the cohesiveness of the recycled carbon fibers and increasing the bulk density.

[0033] The above pickup rate refers to the ratio of the difference between the weight of the recycled carbon fiber after sizing agent treatment and the weight of the recycled carbon fiber before sizing agent treatment to the weight of the recycled carbon fiber before sizing agent treatment, and can be calculated by the following Equation 1.

[0034] [Equation 1]

[0035] Pickup rate (%) = [(Weight of recycled carbon fiber after sizing agent treatment - Weight of recycled carbon fiber before sizing agent treatment) / Weight of recycled carbon fiber before sizing agent treatment] × 100

[0036] Method for manufacturing recycled carbon fiber bundles

[0037] One embodiment provides a method for manufacturing a bundle of recycled carbon fibers comprising: (i) a step of softening recycled carbon fibers manufactured from a carbon fiber composite material; (ii) a step of sizing the softened recycled carbon fibers by treating them with a sizing agent in an amount of 1% to 25% by weight relative to 100% by weight of the total softened recycled carbon fibers; (iii) a step of slitting the sized recycled carbon fibers; and (iv) a step of chopping the slit recycled carbon fibers.

[0038] Recycled carbon fiber is emerging as an important material to replace conventional materials in various industrial fields; however, de-sizing during the recycling process generates a large number of voids between the fibers. Consequently, when applied to carbon fiber composites, this can lead to weaknesses at the adhesive interface between the fibers and the matrix resin. Therefore, a sizing process is essential to minimize voids between fibers and enhance adhesion between them. Furthermore, since recycled carbon fibers may exhibit irregular lengths or widths during manufacturing, additional processes to ensure uniformity are also necessary.

[0039] According to one embodiment, recycled carbon fibers with improved bulk density can be produced by softening, sizing, slitting, and chopping recycled carbon fibers produced from carbon fiber composite materials. In particular, during the softening process, the penetration of the sizing agent can be improved, and the bulk density of the recycled carbon fibers can be controlled by adjusting the content of the sizing agent to optimize bonding with the matrix resin. Through this, the bulk density of the recycled carbon fibers can be improved, thereby increasing interfacial bonding strength and providing recycled carbon fibers with improved mechanical properties.

[0040] In one embodiment, the recycled carbon fiber is recovered from a carbon fiber composite material, and the method for recovering the recycled carbon fiber from the carbon fiber composite material may include the steps of: introducing a pretreated carbon fiber composite material into a cartridge; moving the cartridge into which the pretreated carbon fiber composite material is introduced; exposing the cartridge to superheated steam and an oxidizing agent; removing a matrix resin and char from the pretreated carbon fiber composite material to produce a recycled carbon fiber; and moving the cartridge containing the recycled carbon fiber and collecting the recycled carbon fiber.

[0041] That is, the pretreated carbon fiber composite material is decomposed by superheated steam into recycled carbon fibers and a matrix resin, the recycled carbon fibers are sequentially moved through the cartridge and recovered, and the matrix resin is converted from a gaseous state into a liquid state condensate by cooling water as described below and moved to a condensate tank, after which it can be recycled through separation and purification processes. The recovered recycled carbon fibers can be reused through chopping and milling.

[0042] In other words, according to the method for manufacturing recycled carbon fibers according to one embodiment, recycled carbon fibers with minimized degradation of physical properties and a recyclable matrix resin can be easily obtained simultaneously from a carbon fiber composite material through a series of continuous processes.

[0043] In one embodiment, the step of exposing the cartridge to superheated steam and an oxidizing agent may be a step of first exposing the cartridge into which the pretreated carbon fiber composite material is introduced to superheated steam, and then moving the cartridge and exposing it to an oxidizing agent. Exposing the cartridge to superheated steam first may be more advantageous for removing matrix resin and char than exposing it to an oxidizing agent first.

[0044] For example, a method for recovering recycled carbon fibers from a carbon fiber composite material according to one embodiment may further include the step of first exposing a cartridge into which the pretreated carbon fiber composite material is introduced to superheated steam, and then, before exposing it to an oxidizing agent, using cooling water to condense the gaseous matrix resin decomposed from the pretreated carbon fiber composite material into a liquid state and remove it. By condensing the matrix resin decomposed from the pretreated carbon fiber composite material using cooling water instead of ambient air, the matrix resin can be removed much more easily and more completely. Specifically, the gaseous matrix resin decomposed from the pretreated carbon fiber composite material by exposure to superheated steam exits the cartridge and reacts with cooling water that is separated from the cartridge and exists separately to become liquid condensate, and the condensate can be moved to a separate condensate tank and finally removed.

[0045] Carbon fiber reinforced polymer (CFRP) materials that can be used for superheated steam decomposition generally consist of a mixture of a reinforcing material and a matrix resin. The fibrous material used as the reinforcing material may be carbon fiber, and the matrix resin may include thermosetting resins such as epoxy, phenol, unsaturated polyester, polyurethane, melamine, and urea, as well as thermoplastic resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide, polycarbonate, and polyimide. The carbon fiber reinforced polymer materials generally used are in a form in which the reinforcing material and the matrix resin are mixed in a certain ratio, and the ratio of the reinforcing material to the resin may vary depending on the application.

[0046] For example, the matrix resin may include an aromatic hydrocarbon compound, and the aromatic hydrocarbon compound may include a phenolic compound, and the phenolic compound may include phenol, o-cresol, p-cresol, p-ethylphenol, p-isopropylphenol, p-isopropenylphenol, p-hydroxy-2,2-diphenylpropane, p-hydroxy-3-methyl-2,2-diphenylpropane, 2-(4-hydroxyphenyl)-2-(4'-methoxyphenyl)propane, bisphenol A, 2-(4-hydroxy-3-methylphenyl)-2-(4'-hydroxyphenyl)propane, 2-(benzofu-5-yl)-2-(p-hydroxyphenyl)propane, or a combination thereof, but is not necessarily limited thereto.

[0047] However, the above aromatic hydrocarbon compound, specifically the phenolic compound, may include the above bisphenol A.

[0048] For example, the above bisphenol A may be included in the largest amount among the above aromatic hydrocarbon compounds (specifically phenol compounds), for example, 30% by weight or more based on the total amount of the above phenol compounds, for example, 50% by weight or more. When the composition of a matrix resin containing aromatic hydrocarbon compounds (specifically phenol compounds) containing bisphenol A in the above content range is as described above, it may be very easy to recover it separately and recycle it through separation, filtration, and purification.

[0049] For example, the pretreated carbon fiber composite material may be a crushed or cut carbon fiber composite material. For carbon fiber composite materials used in decomposition with superheated steam, crushing or cutting them into a specific size and shape for use in the process may be advantageous in terms of preventing the degradation of the physical properties of the finally obtained recycled carbon fiber. For example, the crushing methods include shredders, choppers, cracker mills, and hammer mills, which can crush the carbon fiber composite material into a specific range of sizes. However, the crushed carbon fiber composite material has non-uniform sizes and generates a large amount of dust and powder, which may reduce the effectiveness of preventing the degradation of the quality and yield of the recovered recycled carbon fiber and may also worsen the working environment. However, in the case of carbon fiber composite materials manufactured using a cutter, the amount of dust and powder generated is small, increasing the yield, and since they can be cut into a consistent size, the fiber length of the recovered recycled carbon fiber is relatively uniform, and recycled carbon fiber with minimized quality degradation can be obtained. In other words, the above pretreatment may be more advantageous than crushing in terms of preventing the degradation of the physical properties of recycled carbon fibers.

[0050] After the pre-treated carbon fiber composite material is introduced into the cartridge, it moves automatically and is exposed to superheated steam and an oxidizing agent (specifically, the superheated steam and oxidizing agent are sequentially sprayed into the automatically moved cartridge), causing the decomposition of the pre-treated carbon fiber composite material to occur.

[0051] For example, according to the method for manufacturing recycled carbon fibers according to the present invention, the decomposition rate of the carbon fiber composite material is excellent. Here, the decomposition rate refers to the value according to the following mathematical formula 1.

[0052] [Mathematical Formula 1]

[0053] Decomposition rate (wt%) = {(A - B) / (A x C)} x 100

[0054] In the above mathematical formula 1,

[0055] A is the weight (g) of the carbon fiber composite material before decomposition, and

[0056] B is the weight (g) of the carbon fiber composite material after decomposition, and

[0057] C is the matrix resin content (wt%) in the carbon fiber composite material based on the total amount of the carbon fiber composite material before decomposition.

[0058] The superheated steam injected into the cartridge into which the above-mentioned pretreated carbon fiber composite material is introduced is injected using a superheated steam generator, and superheated steam heated to a temperature of, for example, 400°C to 900°C, for example, 400°C to 800°C, for example, 500°C to 900°C, for example, 500°C to 800°C may be used. If the temperature of the superheated steam is less than 400°C, a problem may occur in which the decomposition rate decreases rapidly, and if the temperature of the superheated steam exceeds 900°C, the tensile strength of the recovered (manufactured) recycled carbon fiber may decrease, which may not be desirable.

[0059] For example, superheated steam having the above temperature range may be sprayed into the cartridge for 30 to 120 minutes, for example, 30 to 110 minutes, for example, 30 to 100 minutes, for example, 30 to 90 minutes. If superheated steam within the above temperature range is sprayed into the cartridge for less than 30 minutes, a problem may occur in which the decomposition rate decreases rapidly, and if superheated steam within the above temperature range is sprayed into the cartridge for more than 120 minutes, the increase in decomposition rate and the decrease in tensile strength are not significant, so it may be uneconomical to expose the pretreated carbon fiber composite material to superheated steam within the above temperature range for more than 120 minutes.

[0060] For example, superheated steam within the above temperature range may be injected into the cartridge at a flow rate of 10 kg / h to 30 kg / h, for example 10 kg / h to 25 kg / h, for example 10 kg / h to 20 kg / h within the above time range. If the flow rate of the superheated steam is less than 10 kg / h or greater than 30 kg / h, the tensile strength of the recycled carbon fiber produced may be lowered, which may be undesirable.

[0061] Char, composed of trace amounts of carbon originating from the matrix resin decomposed from the carbon fiber composite material upon exposure to the aforementioned superheated steam, may remain on the surface of the reinforcing material (carbon fiber and / or glass fiber). Char occurs at a rate of approximately 5% to 10% by weight of the resin contained in the carbon fiber composite material, and due to the char, the reinforcing material is manufactured in a clumped form rather than being separated individually. Reinforcing materials containing char have low flexibility and need to be removed because they act as impurities in subsequent processes. Char is a carbonaceous substance that is difficult to remove using only superheated steam in an inert atmosphere and can be removed by the introduction of an oxidizing agent. Here, the oxidizing agent may be an active gas such as air or oxygen.

[0062] Specifically, the reinforcing material containing the char is transported while contained in a cartridge, and subsequently, air is automatically injected into the cartridge containing the reinforcing material containing the char. Through this continuous process, that is, through the additional injection of air, the char can be removed. At this time, high temperature heat and an appropriate flow rate of air are required to remove the char; if the temperature is low or the air flow rate is low, the char is not removed, and if the temperature is too high or the air flow rate is too high, the char can be completely removed, but the reinforcing material may be damaged and its physical properties may deteriorate. Therefore, appropriate temperature, time, and air flow rate are important, and to remove the char, processing can be performed within a range of a temperature of 400°C to 900°C, a time of 10 minutes to 90 minutes, and an air flow rate of 5 L / min or more, and preferably within a range of a temperature of 500°C to 800°C, a time of 30 minutes to 60 minutes, and an air flow rate of 5 L / min. In particular, even if the temperature and time range of the air sprayed above are controlled to the above range, if the air flow rate is less than 5 L / min, the effect of improving the decomposition rate may be negligible.

[0063] If the above-mentioned char is not removed, it acts as an impurity and lowers the decomposition rate; therefore, it is preferable to remove it. However, as mentioned above, if the char is removed by introducing air, while the decomposition rate increases, there is a problem in that the tensile strength retention rate and elasticity retention rate of the finally recovered recycled carbon fiber may decrease slightly. To solve this problem, the flow rate of the injected air is controlled in the method for manufacturing recycled carbon fiber according to the present invention.

[0064] Furthermore, the method for manufacturing recycled carbon fiber according to the present invention may further include a step of exposing the cartridge to nitrogen before exposing it to superheated steam after the step of introducing the pretreated carbon fiber composite material into the cartridge, or a step of exposing the cartridge containing the recycled carbon fiber to nitrogen before moving it after the step of manufacturing the recycled carbon fiber. In this case, it may be more advantageous to prevent a decrease in the tensile strength retention rate and elasticity retention rate of the recovered recycled carbon fiber.

[0065] In this manner, the reinforcing material from which char has been removed is automatically transported while contained in a cartridge, and recycled carbon fiber can be manufactured by collecting the reinforcing material (recycled carbon fiber) from the cartridge. The weight of the recovered recycled carbon fiber is checked, and finally, the decomposition rate and yield are calculated to verify the physical properties of the recycled carbon fiber.

[0066] The tensile strength of the above recycled carbon fiber (reinforcement) can be measured by the Single Fiber method (ASTM C1557-03). In the Single Fiber method, a single strand of reinforcement of 25 mm or more is separated, and the average value is measured by using a Universal Testing Machine (UTM) at a test speed of 1 mm / min, a grip spacing of 25 mm, and an initial load of 1 cN / tex, with at least 30 measurements.

[0067] A method for manufacturing a bundle of recycled carbon fibers according to one embodiment includes a step of softening the recycled carbon fibers by removing char remaining in the recycled carbon fibers manufactured from the carbon fiber composite material. Even after removing char according to the method described above, char may remain; however, the remaining char can be removed through physical methods such as a roll or a press, and this step can be described as a softening step. By physically removing char through the softening step, the flexibility and processability of the recycled carbon fibers are improved, and physical contact between the recycled carbon fibers is reduced, thereby facilitating the penetration of the sizing agent described later.

[0068] Since de-sizing occurs during the manufacturing process of recycled carbon fibers, resulting in a large number of voids between the fibers and potentially causing weaknesses at the adhesive interface with plastic materials, a sizing process is essential to minimize these voids and improve surface adhesion. In this process, a sizing agent is applied to the softened recycled carbon fibers to inject the agent into the fiber bundles in the form of small holes and squeeze them. By minimizing the voids between the fibers through this squeezing, the fibers can be increased in terms of cohesion, bulk density, and bonding strength with the matrix resin.

[0069] The step of sizing the softened recycled carbon fiber may include, for example, a step of immersing the softened recycled carbon fiber in a sizing agent and heat-treating it; and a step of drying the sizing agent-treated recycled carbon fiber. Although not particularly limited, the immersion time to ensure that an appropriate amount of sizing agent is applied to the softened recycled carbon fiber may be performed for 5 to 60 minutes, for example, 5 to 50 minutes, or about 10 to 40 minutes. In addition, the heat treatment of the softened recycled carbon fiber immersed in the sizing agent may be performed for 3 to 30 seconds at a temperature of, for example, 200 to 500°C, or 250 to 300°C, taking into consideration sufficient drying of the sizing agent and inhibition of heat-induced damage. If the immersion time of the sizing agent is within 5 minutes, the time is too short and the amount of sizing agent applied may not be sufficient. If the heat treatment temperature is 200℃ or lower, sufficient drying after sizing agent treatment is not achieved, and the residence time in the dryer for complete drying may be prolonged, which may cause an increase in manufacturing costs and a decrease in physical properties due to moisture. If the heat treatment temperature is 500℃ or higher, there is a problem that the recycled carbon fiber may be damaged due to the high temperature.

[0070] The above sizing agent is included in an amount of 1% to 25% by weight based on 100% by weight of the total softened recycled carbon fiber, and may be included, for example, in an amount of 1% to 10% by weight, 3% to 10% by weight, 5% to 10% by weight, or 8% to 10% by weight. Additionally, the step of treating the sizing agent may be performed for 5 minutes to 60 minutes, for example, in an amount of 10 minutes to 60 minutes, or in an amount of 20 minutes to 60 minutes. When the content of the sizing agent and the time of treating the sizing agent fall within the above ranges, the pickup rate of the recycled carbon fiber can be optimized, and the bonding with the matrix resin can be optimized by controlling the bulk density of the recycled carbon fiber.

[0071] The step of drying the recycled carbon fiber treated with the sizing agent above can be performed for 30 minutes to 120 minutes, for example, 30 minutes to 100 minutes, 40 minutes to 80 minutes, or 40 minutes to 60 minutes, at a temperature range of 90°C to 130°C, for example, 100°C to 130°C, 110°C to 130°C, or 120°C to 130°C.

[0072] After sizing the softened recycled carbon fibers, the pickup rate of the sizing agent may be 3% or more, for example, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, or 9% or more. In addition, the pickup rate of the sizing agent may be 10% or less, for example, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, or 3% or less. When the pickup rate of the sizing agent falls within the above range, an appropriate amount of the sizing agent is applied to the softened recycled carbon fibers to minimize the voids between the recycled carbon fibers, thereby increasing the cohesiveness of the recycled carbon fibers and increasing the bulk density.

[0073] The above pickup rate refers to the ratio of the difference between the weight of the recycled carbon fiber after sizing agent treatment and the weight of the recycled carbon fiber before sizing agent treatment to the weight of the recycled carbon fiber before sizing agent treatment, and can be calculated by the following Equation 1.

[0074] [Equation 1]

[0075] Pickup rate (%) = [(Weight of recycled carbon fiber after sizing agent treatment - Weight of recycled carbon fiber before sizing agent treatment) / Weight of recycled carbon fiber before sizing agent treatment] × 100

[0076] The bulk density of the recycled carbon fiber treated with the above sizing agent may be 0.25 g / ml or higher, for example, 0.25 g / ml to 0.5 g / ml, 0.25 g / ml to 0.45 g / ml, 0.25 g / ml to 0.4 g / ml, or 0.25 g / ml to 0.35 g / ml. The bulk density minimizes the voids between the fibers of the recycled carbon fiber and reflects the cohesiveness and structural density. When the bulk density falls within the above range, the cohesiveness and feeding properties of the recycled carbon fiber are improved, making it possible to apply it as an application product with plastic materials.

[0077] A method for manufacturing a bundle of recycled carbon fibers according to one embodiment includes the step of slitting the sized recycled carbon fibers. Through the slitting process, the sized recycled carbon fibers can be cut to a required width. The slitting process can maintain a constant and uniform width of the recycled carbon fibers, thereby enabling the production of recycled carbon fibers having a uniform width during the chopping process.

[0078] A method for manufacturing a bundle of recycled carbon fibers according to one embodiment includes the step of chopping the slit recycled carbon fibers. The slit recycled carbon fibers can be processed into a finer shape by chopping. At this time, the chopping length can be adjusted to 1 mm to 100 mm, for example, 3 mm to 80 mm, or 5 mm to 70 mm. Through the chopping step, recycled carbon fibers having uniform length and improved bulk density can be manufactured.

[0079] Hereinafter, embodiments are described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0080] Examples

[0081] 130g of a cut piece of hydrogen tank (50 mm x 100 mm) was inserted into a cartridge within the input port of an automatic regenerated fiber manufacturing device of the cartridge push type, and the cartridge was moved to expose it to superheated steam at 700°C. After the superheated steam was injected, the cartridge was moved again and air was injected to expose the cartridge to air, with the air flow rate controlled at 5 L / min. After the superheated steam injection and before the air injection, cooling water was used to condense and remove the matrix resin decomposed from the cut piece of hydrogen tank inside the cartridge where the superheated steam was injected. After the air injection, the cartridge was moved, and carbon fibers were recovered from the cartridge.

[0082] The recovered carbon fibers must be separated and sorted into Unidirectional (UD) and diagonal forms. The UD is easily separated into a total of 5 layers, while the diagonal form consists of layers separated from each other. The separated UD forms a hard structure due to the char generated during the decomposition process, and each UD layer is passed through a compression roll for softening. The number of passes is continued until the carbon fibers are separated into Tow units to manufacture recycled carbon fibers.

[0083] To treat the sizing of the softened recycled carbon fiber, the stock solution of Sanyo Chemical’s CHEMITYLEN UA-4035% sizing agent is diluted, the softened recycled carbon fiber is dipped into a container containing the sizing agent, and after removing the remaining solution, it is dried.

[0084] The UD layer of the sized recycled carbon fiber is slit into approximately 8 mm units to separate it into a Tow form. Subsequently, the slit recycled carbon fiber is chopped into 6 mm units for compounding evaluation. Cutting is performed using a guillotine-type cutting machine, and the length of the recycled carbon fiber is cut according to the application.

[0085]

[0086] Evaluation Example 1: Change in pickup rate according to sizing agent content

[0087] To verify the change in pickup rate according to the sizing agent content, the sizing agent concentrate was diluted to contain 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, 7 wt%, and 10 wt% of the sizing agent relative to 100 wt% of the total recycled carbon fiber. Then, 20 g of recycled carbon fiber was prepared and dipped into the diluted solutions according to the content to perform sizing treatment. After treatment for approximately 60 minutes, the remaining solution was removed, and the fiber was placed in a dryer and dried at 130°C for 60 minutes. By checking the weight after drying under each condition, the sizing agent pickup rate could be verified through the change in weight before and after the sizing treatment, and the results are shown in Figure 1.

[0088] Referring to Figure 1, it can be seen that the pickup rate of recycled carbon fibers increases as the sizing agent content increases.

[0089] Evaluation Example 2: Change in Pickup Rate According to Sizing Agent Treatment Time

[0090] To verify the change in pickup rate according to the sizing agent treatment time, the undiluted sizing agent was diluted so that the sizing agent constituted 7% by weight relative to 100% by weight of the total recycled carbon fiber. Then, 20g of recycled carbon fiber was prepared and sizing treatment was performed by dipping it in the sizing solution for 5, 10, 20, 30, and 60 minutes. After treatment, the remaining solution was removed, and the fiber was placed in a dryer and dried at 130°C for 60 minutes. By checking the weight after drying under each condition, the sizing agent pickup rate could be determined through the change in weight before and after the sizing treatment, and the results are shown in Figure 2.

[0091] Referring to Figure 2, it can be seen that the pickup rate of recycled carbon fibers is relatively similar depending on the sizing agent treatment time.

[0092] Evaluation Example 3: Change in bulk density according to pickup rate

[0093] According to Evaluation Example 1, 20g of recycled carbon fiber samples sized with different sizing agent contents were cut to a size of 6 mm through a chopping process to prepare samples for tap density measurement. Then, the volume of the input samples was checked to calculate the bulk density, and the results are shown in Fig. 3.

[0094] Referring to Figure 3, the sample without sizing treatment showed a level of 0.17 g / ml, while the bulk density increased to 0.3 g / ml as the pickup rate increased, and a similar trend was observed at a level of 0.32 g / ml even at a pickup rate of 8% or higher.

[0095] Although preferred embodiments have been described in detail above, the scope of the rights is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts defined in the following claims are also included within the scope of the rights.

Claims

1. Multiple recycled carbon fibers; and A sizing agent located on the surface of the plurality of regenerated carbon fibers; comprising Regenerated carbon fiber bundles with a bulk density of 0.25 g / ml or higher.

2. In Paragraph 1, The above recycled carbon fiber bundle is a recycled carbon fiber bundle comprising 5,000 to 50,000 strands of the above recycled carbon fiber.

3. In Paragraph 1, The length of the above recycled carbon fiber is 0.1 cm to 200 cm, and A bundle of recycled carbon fibers having a thickness of 1 μm to 10 μm.

4. In Paragraph 1, A bundle of recycled carbon fibers containing voids between the plurality of recycled carbon fibers.

5. In Paragraph 4, A recycled carbon fiber bundle having a porosity greater than 0% and less than or equal to 40%.

6. In Paragraph 4, A regenerated carbon fiber bundle further containing a sizing agent in the above voids.

7. In Paragraph 1, The above recycled carbon fiber bundle comprises 1% to 25% by weight of the sizing agent based on 100% by weight of the total recycled carbon fiber bundle.

8. In Paragraph 1, The above recycled carbon fiber bundle is a recycled carbon fiber bundle containing more than 0 weight% and less than or equal to 5 weight% based on 100 weight% of the total recycled carbon fiber bundle.

9. In Paragraph 1, A recycled carbon fiber bundle having a pickup rate of 3% or more according to Formula 1 below for the above-mentioned sizing agent. [Equation 1] Pickup rate (%) = [(Weight of recycled carbon fiber after sizing agent treatment - Weight of recycled carbon fiber before sizing agent treatment) / Weight of recycled carbon fiber before sizing agent treatment] × 100 10. (i) A step of softening recycled carbon fibers manufactured from carbon fiber composite materials; (ii) a step of sizing the softened regenerated carbon fibers by treating 1% to 25% by weight of a sizing agent with respect to 100% by weight of the total softened regenerated carbon fibers; (iii) a step of slitting the above-sized recycled carbon fiber; and (iv) a step of chopping the slit recycled carbon fibers to produce recycled carbon fibers; a method for manufacturing a bundle of recycled carbon fibers.

11. In Paragraph 10, A method for manufacturing a recycled carbon fiber bundle comprising 3% to 10% by weight of the sizing agent based on 100% by weight of the total softened recycled carbon fiber.

12. In Paragraph 10, A method for manufacturing a bundle of recycled carbon fibers comprising: a step of sizing the softened recycled carbon fibers; a step of immersing the softened recycled carbon fibers in a sizing agent and heat-treating them; and a step of drying the recycled carbon fibers treated with the sizing agent.

13. In Paragraph 12, The above immersion is performed for 5 to 60 minutes, and A method for manufacturing a recycled carbon fiber bundle, wherein the above heat treatment is performed at 200°C to 500°C for 3 seconds to 30 seconds.

14. In Paragraph 12, A method for manufacturing a recycled carbon fiber bundle, wherein the above drying is performed at a temperature of 90°C to 130°C for 30 minutes to 120 minutes.

15. In Paragraph 10, The above-mentioned recycled carbon fiber bundle is a method for manufacturing a recycled carbon fiber bundle having a bulk density of 0.25 g / ml or higher.

Images