US20230087214A1

US20230087214A1 - Method for splitting carbon fiber tow

Info

Publication number: US20230087214A1
Application number: US17/482,416
Authority: US
Inventors: Hao-Chia WU; Yu-Jie WU
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-09-22
Filing date: 2021-09-22
Publication date: 2023-03-23

Abstract

Provided is a method for splitting a carbon fiber tow, which comprises heating a carbon fiber tow sized with a first sizing material to soften the first sizing material and form a spread carbon fiber tow; passing the spread carbon fiber tow through at least one splitter and corresponding cutter to obtain multiple carbon fiber strands spaced apart; and sizing the carbon fiber strands with a second sizing material. With the method, multiple small carbon fiber tows having better tensile strength and/or modulus than the commercially available small carbon fiber tow products can be obtained. Products made of the small carbon fiber tows obtained by the present invention are lighter but stronger, and the production cost is relatively reduced. The present invention also achieves the purpose of energy saving and carbon reduction.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing a carbon fiber tow; more particularly, to a method for producing a small carbon fiber tow having high tensile strength and/or high modulus which is not commercially offered for sale yet.

2. Description of the Prior Arts

High-performance fibers refer to fibers that have exceptional characteristics compared to ordinary fibers. High-performance fibers have high tensile strength, high modulus, good heat resistance, good corrosion resistance, good wear resistance, good incombustibility, and high chemical stability. So the high-performance fibers are important in general industries (e.g. wind power generation, new energy vehicles, 3C products, sporting goods, and the like) and defense industries (e.g. drones, and aerospace, aviation and military applications, and the like).
Carbon fibers can be made of polyacrylonitrile (PAN), pitch, basalt and the like. Among all carbon fibers, PAN-based carbon fibers are the most popular products. The PAN-based carbon fibers have a variety of tensile strength and/or high modulus, and all the products available on the market are provided in specific specifications. This results in various limitations of the applications of these high-performance fibers.
Carbon fibers are often offered as carbon fiber tows, and their specifications are decided by the number of carbon filaments contained therein. For example, a 3K carbon fiber tow refers to the carbon fiber tow that contains 3000 carbon filaments, while a 12K carbon fiber tow refers to the carbon fiber tow that contains 12000 carbon filaments.
Carbon fiber tows are essential for composite materials used in pioneer technologies. The raw material of carbon fiber tows needs to be processed by oxidation, high-temperature (e.g. 1280° C.) carbonization, etc. in a route more than 900 meters so as to produce black carbon filaments having high tensile strength and/or high modulus. Since the process includes passing the raw material through a series of guide rollers and more than twelve tension devices, the process is only suitable for large carbon fiber tows which have a large number of carbon filaments (e.g. 36000 carbon filaments or more, such as 36K, 48K, 50K, 60K or higher). In contrast, for small carbon fiber tows which have a small number of carbon filaments (e.g. 24000 carbon filaments or less, such as 24K, 12K, 6K, 3K or 1K), the above-mentioned process cannot be used because the small carbon fiber tows are prone to be broken during the process, so an alternative method with a shorter route for oxidation and/or carbonization is needed. Therefore, the tensile strength and/or modulus of a small carbon fiber tow are usually less than those of a large carbon fiber tow. In addition, the small carbon fiber tows available on the market have a much shorter length than the large carbon fiber tows (e.g. 2400 meters for 1K, 3K carbon fiber tows) because of the processing difficulties, and this is disadvantageous for cost reduction.
In the products of Toray, a famous carbon fiber manufacturer, the specifications of carbon fiber tows with different tensile strength are obviously different. For 1K carbon fiber tows, the only product provided is made of T300 which has the lowest tensile strength; and for 3K carbon fiber tows, the only products are made of T300 or T400 series which have lower tensile strength. As for products of T700 or T1100 series which have higher tensile strength, only 12K or 24K carbon fiber tows can be found, and no 1K or 3K carbon fiber tows are offered for sale. Similarly, for Toray products of M35 to M55 series which have higher modulus and higher tensile strength, only 6K or 12K products can be found, and no 1K or 3K products are offered for sale. Because the diameters of 1K and 3K carbon fiber tows are smaller than those of 12K and 24K carbon fiber tows, 1K and 3K carbon fiber tows can be used to produce carbon fiber fabric with finer texture and various patterns. However, the tensile strength of 1K and 3K carbon fiber tows is lower in the commercially available products. In the case of using small carbon fiber tows (e.g. having 1000 to 6000 carbon filaments), multiple layers of carbon fiber fabrics are required to increase the structural strength of the product, resulting in not only increased weight and/or thickness, but also increased cost of the production. Therefore, in order to simultaneously improve the tensile strength and/or modulus of carbon fiber fabrics and reduce the thickness and weight of the product, it is necessary to develop a method for manufacturing small carbon fiber tows (e.g. having 1000 to 3000 carbon filaments) with high tensile strength and/or modulus so as to produce lighter, smaller products with higher structural strength and flexural rigidity, thus achieving the purpose of energy saving and carbon reduction.
In addition, the price of carbon fiber tows is inversely proportional to the size of carbon fiber tows. That is, 1K, 3K, and 6K carbon fiber tows are more expensive than 12K, 24K carbon fiber tows or carbon fiber tows containing more carbon filaments. Therefore, it is necessary to develop a low cost method to obtain 1K, 3K, and 6K carbon fiber tows.
Moreover, 2K, 4K, and 5K carbon fiber tows are not commercially available. In order to diversify the pattern of woven fabric made of carbon fiber tows, it is necessary to develop a method to produce the carbon fiber tows in these sizes.

SUMMARY OF THE INVENTION

To overcome the shortcomings, one of the objectives of the present invention is to develop a method for producing a small carbon fiber tow (e.g. having 1000 to 3000 carbon filaments) with high tensile strength and/or high modulus. Products produced from the small carbon fiber tows of the present invention are lighter but stronger than the products made of commercially available small carbon fiber tows, so as to reduce the amount of raw materials (carbon fiber tows) and achieve the purpose of energy saving and carbon reduction.
Another objective of the present invention is to develop a method to reduce the cost of manufacturing a small carbon fiber tow (e.g. having 1000 to 3000 carbon filaments) with high tensile strength (e.g. having a tensile strength of 4500 MPa or higher), or with high modulus and high tensile strength (e.g. having a modulus of 300 or higher and a tensile strength of 4000 MPa or higher).
Another objective of the present invention is to manufacture carbon fiber tows in a specification not commercially offered for sale, such as 2K, 4K and 5K.
To achieve the aforementioned objectives, the present invention provides a method for splitting a carbon fiber tow, which comprises the following steps: (A) providing a carbon fiber tow comprising multiple carbon filaments sized with a solution containing a first sizing material; (B) passing the carbon fiber tow through a first heating device to heat the carbon fiber tow at a temperature of between 45° C. and 140° C., so as to soften the first sizing material and form a spread carbon fiber tow; (C) adjusting the tension of the spread carbon fiber tow; (D) passing the spread carbon fiber tow through at least one splitter to obtain a plurality of multiple carbon fiber strands spaced apart; (E) passing the spread carbon fiber tow through at least one cutter to cut the carbon filaments connected between the carbon fiber strands; (F) adjusting the tension of the carbon fiber strands; (G) sizing the carbon fiber strands with a solution containing a second sizing material to obtain multiple sized carbon fiber strands; and (H) passing the multiple sized carbon fiber strands through a second heating device to heat the sized carbon fiber strands.
With the method for splitting a carbon fiber tow of the present invention, a larger carbon fiber tow (e.g. having more than 12000 carbon filaments) can be used to produce multiple smaller carbon fiber tows (e.g. having 1000 to 6000 carbon filaments), wherein the plurality of the small carbon fiber tows produced by the method of the present invention has better tensile strength and/or modulus than the commercially available equivalents having the same number of carbon filaments. Since the commercially available small carbon fiber tows are expensive, the method of the present invention provides small carbon fiber tows of better quality and at lower cost.
In addition, the method for splitting a carbon fiber tow of the present invention can produce carbon fiber tows containing a number of carbon filaments which are not yet commercially offered. For example, a 12K carbon fiber tow can be used to produce six 2K carbon fiber tows with five splitters; a 50K carbon fiber tow can be used to produce ten 5K carbon fiber tows with nine splitters; and a 60K carbon fiber tow can be used to produce fifteen 4K carbon fiber tows with fourteen splitters.
In some embodiments of the present invention, the spread carbon fiber tow has a maximum width for the carbon fiber tow. In some embodiments of the present invention, the maximum width for the carbon fiber tow is the maximum width that a carbon fiber tow can reach while the spread carbon fiber tow has an even top surface or a consistent thickness. The maximum width may vary because of the source of the carbon fiber tows. For example, the maximum width of 12K carbon fiber tows can be 16 mm to 20 mm, such as 18 mm to 20 mm. The maximum width of 24K carbon fiber tows can be 32 mm to 40 mm, such as 36 mm to 40 mm. The maximum width of 48K carbon fiber tows can be 60 mm to 68 mm. The maximum width of 50K carbon fiber tows can be 70 mm to 80 mm. The maximum width of 60K carbon fiber tows can be 80 mm to 100 mm, such as 90 mm to 100 mm.
In some embodiments of the present invention, the step (B) can be repeated multiple times to obtain the spread carbon fiber tow. In some embodiments of the present invention, the step (B) can be repeated multiple times for the carbon fiber tow having 24000 to 60000 carbon filaments (e.g., 24K, 36K, 48K, 60K) to make the spread carbon fiber tow has a maximum width for the carbon fiber tow. In some embodiments of the present invention, the step (B) can be repeated twice or more. In some embodiments of the present invention, the step (B) can be repeated three times or more.
In some embodiments of the present invention, when the step (B) is repeated multiple times, the carbon fiber tow stands still for a period of time between each step (B). In some embodiments of the present invention, the carbon fiber tow stands still until the carbon fiber tow cools down.
In some embodiments of the present invention, the method for splitting a carbon fiber tow of the present invention further comprises adjusting the tension of the carbon fiber tow after the step (A) and before the step (B).
In some embodiments of the present invention, the method for splitting a carbon fiber tow of the present invention further comprises, in the step (H), passing the multiple sized carbon fiber strands through a cooling device after passing the multiple sized carbon fiber strands through a second heating device.
In some embodiments of the present invention, the method for splitting a carbon fiber tow of the present invention further comprises adjusting the width of the multiple sized carbon fiber tows. In some embodiments of the present invention, the method for splitting a carbon fiber tow of the present invention further comprises adjusting the width of the multiple sized carbon fiber tows.
In some embodiments of the present invention, the method for splitting a carbon fiber tow of the present invention further comprises adjusting the tension of the carbon fiber strands after passing the multiple sized carbon fiber strands through a second heating device and before adjusting the width of the multiple sized carbon fiber tows.
In some embodiments of the present invention, the method for splitting a carbon fiber tow of the present invention further comprises adjusting the tension of the carbon fiber strands after passing the multiple sized carbon fiber strands through a cooling device and before adjusting the width of the multiple sized carbon fiber tows.
In some embodiments of the present invention, the method for splitting a carbon fiber tow of the present invention further comprises adjusting the tension of the multiple sized carbon fiber strands after passing the multiple sized carbon fiber strands through a second heating device and before passing the multiple sized carbon fiber strands through a cooling device.
In some embodiments of the present invention, the method for splitting a carbon fiber tow of the present invention further comprises, after the step (E) and before the step (F), guiding each of the carbon fiber strands to one of guiding rollers respectively, wherein any two adjacent carbon fiber strands were guided to guiding rollers at different height level.
In some embodiments of the present invention, the first sizing material and the second sizing material are the same or different. In some embodiments of the present invention, the concentrations of first sizing material and the second sizing material can be 0.8%, 1.0% or 1.2%.
In some embodiments of the present invention, the first sizing material is a thermosetting material.
In some embodiments of the present invention, the second sizing material comprises a thermoplastic material or a thermosetting material.
In some embodiments of the present invention, when the first sizing material and/or the second sizing material are a thermosetting material, the solution containing first sizing material or the second sizing material substantively does not comprise any curing agent. In some embodiments of the present invention, the solution containing first sizing material or the second sizing material comprises one or more surfactants.
In some embodiments of the present invention, the second sizing material comprises a thermoplastic material. In some embodiments of the present invention, when the second sizing material comprises a thermoplastic material, a cooling step is needed after the step (H), that is, passing the multiple sized carbon fiber strands through a cooling device. In some embodiments of the present invention, the thermoplastic material is selected from a group consisting of an acrylonitrile butadiene styrene (ABS), a polypropylene (PP), a polyethylene (PE), a polycarbonate (PC), a polyurethane (PU), a polystyrene (PS), a polyethylene terephthalate (PET), and a polyetheretherketone (PEEK).
In some embodiments of the present invention, the second sizing material comprises a thermosetting material. In some embodiments of the present invention, the thermosetting material is an epoxy resin.
In some embodiments of the present invention, the carbon fiber tow is heated at a temperature of between 80° C. and 120° C. in Step (B).
In some embodiments of the present invention, the multiple sized carbon fiber strands are heated at a temperature of between 80° C. and 120° C. in Step (H).
In some embodiments of the present invention, after the step (H), the multiple sized carbon fiber strands are cooled at a temperature of between 2° C. and 10° C.
In some embodiments of the present invention, the at least one splitter may be made of metal.
In some embodiments of the present invention, each splitter contains a pointed end, in which each pointed end contacts the spread carbon fiber tow first to split the spread carbon fiber tow into multiple carbon fiber strands spaced apart.
In some embodiments of the present invention, the at least one splitter is configured to equally split the spread carbon fiber tow into multiple carbon fiber strands spaced apart. In some embodiments of the present invention, the at least one splitter is configured to split the spread carbon fiber tow into multiple carbon fiber strands spaced apart in an inequal manner.
In some embodiments of the present invention, the carbon filaments connected between the carbon fiber strands were cut by at least one cutter. In some embodiments of the present invention, the at least one cutter may be made of metal, such as tungsten steel, titanium, or silicon carbide (carborundum). In some embodiments of the present invention, the at least one cutter is a circular blade, such as, a circular saw blade.
In some embodiments of the present invention, the splitters and the cutters are correspondingly arranged. In some embodiments of the present invention, the number of the splitters and the number of the cutters are the same.
In some embodiments of the present invention, the carbon fiber tow is passed through the first heating device at a speed of 8 meters per minute (m/min) to 15 m/min.
In some embodiments of the present invention, the spread carbon fiber tow is passed through the at least one splitter at a speed of 8 m/min to 15 m/min.
In some embodiments of the present invention, the split carbon fiber tows have a breaking strength of 16.0 kgf or higher and a breaking elongation of 4.8% or higher.
In some embodiments of the present invention, the split carbon fiber tows have a tensile strength of 4500 million pascals (MPa) or higher, 5000 MPa or higher, 5500 MPa or higher, 6000 MPa or higher, or 7000 MPa or higher; while each of the split carbon fiber tows contains 3000 carbon filaments or less, 2000 carbon filaments or less, or 1000 carbon filaments or less.
In some embodiments of the present invention, the split carbon fiber tows have a modulus of 300 gigapascals (GPa) or higher, or 350 GPa or higher, or 400 GPa or higher, or 450 GPa or higher, or 500 GPa or higher, or 540 GPa or higher; and a tensile strength of 4000 MPa or higher, 4100 MPa or higher, 4200 MPa or higher, 4300 MPa or higher, 4400 MPa or higher, 4500 MPa or higher, 4600 MPa or higher, or 4700 MPa or higher; while each of the split carbon fiber tows contains 3000 carbon filaments or less, 2000 carbon filaments or less, or 1000 carbon filaments or less. In some embodiments of the present invention, the split carbon fiber tows also have a modulus of 550 GPa or lower, or 600 GPa or lower.
In some embodiments of the present invention, the split carbon fiber tows have a length of about 5000 meters. In the context, the term “about” means represents ±3% of the measured value. The length of the split carbon fiber tows is equal to the original carbon fiber tow. Therefore, the split carbon fiber tows have a much longer length (about twice longer) than those small carbon fiber tows available on the market.
Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a carbon fiber tow wound on a bobbin;

FIG. 2 is a schematic diagram showing the spreading of the carbon fiber tow;

FIG. 3 is a schematic diagram of guide roller assemblies;

FIG. 4 is a schematic diagram of a spread carbon fiber tow wound on a bobbin;

FIG. 5 is a schematic diagram showing the splitting and subsequent treatment of the carbon fiber tow;

FIG. 6 is a schematic diagram of a guide roller with eight grooves;

FIG. 7 is a schematic diagram of the carbon fiber tow produced by the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example is exemplified below to illustrate the implementation of the method for splitting a carbon fiber tow of the present invention. A person skilled in the art can easily realize the advantages and effects of the present invention in accordance with the example and the accompanied drawings. It should be understood that the descriptions proposed herein are just preferable embodiments for the purpose of illustration only, not intended to limit the scope of the present invention. Various modifications and variations can be made to the present invention, without departing from the spirit and scope of the invention.

Example

As shown in FIG. 1 , a commercial PAN carbon fiber tow 1 (manufacturer: Toray Industries, Inc., Japan; product no.: T700SC) having a width of W1, which was wound on a bobbin, was provided. The carbon fiber tow 1 had a length of 5000 meters (m) and a width (W1) of 7 millimeters (mm). The carbon fiber tow 1 contained 12000 carbon filaments (e.g. 12K), and was sized with an epoxy resin. In the following example, the 12K carbon fiber tow 1 was equally split and further sized into four split carbon fiber tows 21 by the method of the present invention, wherein each of the split carbon fiber tows 21 had a length of 5000 m and contained 3000 carbon filaments (e.g. 3K).
In the method of the present invention, the carbon fiber tow 1 was spread, split, and sized. The carbon fiber tow 1 was unwound and heated to be spread; the spread carbon fiber tow 7 was wound for further use first, and then unwound to be split and sized. The tension of the carbon fiber tow 1, the spread carbon fiber tow 7 and the split carbon fiber tows 21 was adjusted between steps for many times. The whole production line in the example is about 15 meters (m), and two spread carbon fiber tows 7 can be split at the same time to obtain eight split carbon fiber tows 21 because all rollers are wide enough to accommodate the tows and strands. The process was described in detail below.
First of all, an additional segment of sub-quality carbon fiber tow was stuck to the end of the carbon fiber tow 1 as a first guiding tow (not shown) by super glue. As shown in FIG. 2 , the commercial carbon fiber tow 1 glued with the first guiding tow was provided on a feed creel 2. The free end of the first guiding tow was guided by hand from the feed creel 2 through a direction adjuster 3 to a tension device 4A first, and guided to a series of guide rollers 5 including a first guide roller 5A, multiple guide roller assemblies 5B and a second guide roller 5C. The feed creel 2 could regulate the tension of the carbon fiber tow 1 so that the carbon fiber tow 1 left the feed creel 2 with a constant tension. The direction adjuster 3 enabled the carbon fiber tow 1 to go straight to the tension device 4A and the series of guide rollers 5. The tension device 4A regulated the tension of the carbon fiber tow 1 before spreading, so that the carbon fiber tow 1 was not too tight, or too slack and sagged.
While the carbon fiber tow 1 arrived at the section between the first guide roller 5A and the second guide roller 5C, the carbon fiber tow 1 was guided to pass through an infrared heater 6 and heated at a temperature between 80° C. and 120° C., so as to soften the epoxy resin that sized the carbon fiber tow 1. As a result, the width of the carbon fiber tow 1 was gradually increased, as the tow schematically illustrated below between the two dashed lines in FIG. 2 . Each of the plurality of guide roller assemblies 5B comprised a guide roller 51 and a track 52, as shown in FIG. 3 . The position of the guide roller 51 was adjustable along the track 52 so as to adjust the route length of the carbon fiber tow 1 between the first guide roller 5A and the second guide roller 5C. As the vertical distance between two guide rollers 51 in adjacent guide roller assemblies 5B increased, the route length of the carbon fiber tow 1 increased, so that the heating time could be adjusted to sufficiently soften the epoxy resin that sized the carbon fiber tow 1. In order to further increase the heating time, the number of the plurality of guide roller assemblies 5B could be increased, which resulted in a longer route length of the carbon fiber tow 1. In this example, the number of the plurality of guide roller assemblies 5B is five; in other embodiments, the number of the plurality of guide roller assemblies 5B may be from four to twelve. In this example, the adjacent guide roller assemblies 5B are positioned at different height levels; in other embodiments, all guide roller assemblies 5B may be positioned at the same height level.
When the carbon fiber tow 1 was guided out of the second guide roller 5C, the 12K carbon fiber tow 1 had been spread into the spread carbon fiber tow 7 having a width (W2) of 16 mm. The tension of the spread carbon fiber tow 7 was further regulated by the tension device 4B, so that the spread carbon fiber tow 7 was not too tight, or too slack and sagged. After that, the spread carbon fiber tow 7 was further guided to a first winder 8. When the free end of the first guiding tow arrived at the first winder 8, the joint of the first guiding tow and the spread carbon fiber tow 7 left the feed creel 2. At this point, the first winder 8 started to operate at a winding speed of 25 meters per minute (m/min) so that the carbon fiber tow 1 was left the feed creel 2 at the same speed. Therefore, the feeding speed could be controlled by the first winder 8. When the spread carbon fiber tow 7 started to be wound on first the winder 8, the first guiding tow was removed. As shown in FIG. 4 , the spread carbon fiber tow 7 having a width of W2 was wound on a bobbin. It is noted that W2 is larger than W1.
Similarly, an additional segment of sub-quality spread carbon fiber tow was stuck to the end of the spread carbon fiber tow 7 as a second guiding tow (not shown in figures) by super glue.
As shown in FIG. 5 , a spread carbon fiber tow 7 was provided on a feed creel 9. In this example, two spread carbon fiber tows 7 spaced apart were provided in parallel to enhance product yield.
The free end of each second guiding tow was guided by hand to a tension device 10. The tension device 10 regulated the tension of each spread carbon fiber tow 7 so that the spread carbon fiber tows 7 were not too tight, or too slack and sagged.
Subsequently, the free end of each second guiding tow was guided by hand to a splitting device 11. In this example, the splitting device 11 comprised two sets of splitters 11A, wherein each of the sets contained three evenly spaced splitters 11A. The six splitters 11A were arranged on a hypothetical straight line perpendicular to the moving direction of the carbon fiber tows. When each spread carbon fiber tow 7 passed through one set of the splitters 11A, the spread carbon fiber tows 7 having 12000 carbon filaments were equally divided into four carbon fiber strands 20, each of which contained 3000 carbon filaments and had a width of 4 mm. The eight carbon fiber strands 20 were guided to eight grooves G on a first grooved guiding roller 11B and then to eight corresponding grooves G on a second grooved guiding roller 11D. Each groove G had a width of 4 mm, and the distance between two adjacent grooves G was 2 mm. The rollers arranged after the first grooved guiding roller 11B contained the same number of grooves G to accommodate the eight carbon fiber strands 20.
Since the carbon filaments comprised in the spread carbon fiber tows 7 might be skewed, not kept completely straight in the whole spread carbon fiber tows 7, there were carbon filaments connected between the carbon fiber strands 20 after splitting by the splitters 11A. Six cutters 11C were arranged on a hypothetical straight line perpendicular to the moving direction of the carbon fiber strands 20 between the first grooved guiding roller 11B and second grooved guiding roller 11D, to cut the carbon filaments connected between the carbon fiber strands 20.
After the second grooved guiding roller 11D, the eight carbon fiber strands 20 were then guided by hand to a third grooved guiding roller 11E, which also had eight grooves G as the first grooved guiding roller 11B, and arranged at a lower height level than the first grooved guiding roller 11B and second grooved guiding roller 11D. The difference of height level was advantageous to evenly transport the carbon fiber strands 20. FIG. 6 schematically shows the guide roller 11B which has eight grooves G. The first grooved guiding roller 11B, second grooved guiding roller 11D and third grooved guiding roller 11E contained the same number of grooves G to accommodate the carbon fiber strands 20.
The carbon fiber strands 20 were then sequentially guided to two sets of guide rollers 11F, wherein each set contained four guide rollers 11F at different height levels. Each of the carbon fiber strands 20 was guided to one of the guide rollers 11F to expand the distance between any of two adjacent carbon fiber strands 20. Any two adjacent guide rollers 11F were space apart by a vertical distance of 10 cm. Guide rollers 11F were not grooved. The horizontal distance between two carbon fiber strands 20 on two adjacent guide rollers 11F was about 5 mm. Therefore, the carbon fiber strands 20 are vertically and horizontally spaced apart.
The eight carbon fiber strands 20 were guided to a tension device 12. The route lengths of the carbon fiber strands 19 were different, so the tension device 12 was arranged to regulate the tension of the eight carbon fiber strands 20 so that the carbon fiber strands 20 were not too tight, or too slack and sagged. Since the carbon fiber strands 20 were split, cut and spaced apart with appropriate vertical and horizontal distances.
Subsequently, the eight carbon fiber strands 20 were then sized, heated and cooled.
After the tension device 12, the eight carbon fiber strands 20 were guided to a sizing device 13, which comprised a sizing bath 13A, a grooved guide roller 13B, a grooved guide roller 13C, and a roller 13D. The grooved guide roller 13B and the grooved guide roller 13C were made of stainless steel while the roller 13D was made of synthetic rubber. In this example, the sizing bath 13A was filled with a thermoplastic slurry comprising acrylonitrile butadiene styrene (ABS) polymer. The ABS polymer was dissolved in water to obtain the sizing solution with sizing content of 1%. After the eight carbon fiber strands 20 were guided through the sizing bath 13A, each of the eight carbon fiber strands 20 was sized with the sizing solution so as to eliminate carbon fiber fuzz and thus smooth the surfaces of the eight carbon fiber strands 20. When the eight carbon fiber strands 20 were guided through the grooved guide roller 13C, these carbon fiber strands 20 were pressed by the roller 13D in order to squeeze extra sizing solution. Eight carbon fiber strands 20 were sized.
Subsequently, the eight carbon fiber strands 20 were guided to a heating device 14, which comprised multiple grooved guide rollers 14A and multiple infrared heaters 14B. The temperature of the plurality of infrared heaters 14B was set between 120° C. and 140° C. so as to evaporate the water in the eight carbon fiber strands 20. The eight carbon fiber strands 20 were then guided to a tension device 15 to adjust the tension of the eight carbon fiber strands 20.
The eight carbon fiber strands 20 were then guided to a cooling chamber 16, which contained multiple grooved guide rollers 16A. The temperature of the cooling chamber 16 was set between 3° C. and 7° C. to cool the eight carbon fiber strands 20 and facilitate the cure of the thermoplastic sizing material (e.g. ABS polymer). The eight carbon fiber strands 20 were then guided to a tension device 17 to adjust the tension of the eight carbon fiber strands 20. After that, eight split carbon fiber tows 21 were obtained. The eight carbon fiber tows 21 could be optionally guided by hand to grooved roller 18 to adjust the width of the sized carbon fiber tows 21. The width of the grooves on the grooved roller 18 was 2.9 mm. After the width adjustment, the width of the eight split carbon fiber tows 21 was adjusted to 2.9 mm (W3). When the width of the split carbon fiber tows 21 was not adjusted, the grooves on the grooved roller 18 could be removed or replaced by another roller without grooves for width adjustment.
When the eight free ends of the split second guiding tows arrived at the eight winders 19A in a winding device 19, the winding device 19 started to operate at a winding speed of 12.5 m/min to pull the two spread carbon fiber tows 7. Therefore, the feeding speed of the spread carbon fiber tows 7 could be controlled by the winding device 19. After the strands split from the second guiding tows were totally wound, the second guiding tows were removed and the split carbon fiber tows 21 after the second guiding tows were wound. As shown in FIG. 7 , the split carbon fiber tows 21 having a width of W3 were wound on a bobbin. As above, the width adjustment step is optional, and the split carbon fiber tows 21 without width adjustment had a width of W3′ (not shown). It is noted that W3 and W3′ are both smaller than W1, and W3 is smaller than W3′. In this example, there were eight split carbon fiber tows 21 produced from the two spread carbon fiber tows 7, wherein each of the carbon fiber tows 21 had a length of 5000 m and contained 3000 carbon filaments (e.g. 3K). In addition, the length of the eight split carbon fiber tows 21 was the same as that of the carbon fiber tow 1.

Test Example: Breaking Strength and Breaking Elongation of Produced 3K Carbon Fiber Tow

In this test example, a section of the carbon fiber strands 21 without width adjustment, which had a width of 4 mm, was used as a test sample.
Breaking strength and breaking elongation of the test sample were measured in accordance with ASTM D2256-2002, Option A1, wherein the test sample was loaded into grips, the gage length (length of thread between grips) was 25 cm, and the speed of testing was 30±1 centimeters per minute (cm/min).
For the test sample, the breaking strength was 16.0 kilogram-force (kgf) and the breaking elongation was 4.8%. From comparison of breaking strength and breaking elongation with the control test samples, it is found the test sample is the equivalent of T500 and T550 of the carbon fiber tow produced by Toray Industries, Inc.
With the method for splitting a carbon fiber tow of the present invention, a commercial 12K PAN carbon fiber tow, which has better tensile strength than other commercially available 3K carbon fiber tow, can be used to produce four 3K carbon fiber tows. The 3K carbon fiber tows obtained by splitting the 12K PAN carbon fiber tow have better tensile strength than other commercially available 3K carbon fiber tows. From the above description, a small carbon fiber tow (e.g. 1K to 6K) with higher tensile strength or modulus can be produced by the method for splitting a carbon fiber tow of the present invention. Thus, the products manufactured from the small carbon fiber tow obtained by the present invention have enhanced strength, and can be applied to many other technical fields.
In summary, the method for splitting a carbon fiber tow of the present invention can provide small carbon fiber tows (e.g. having 1000 to 6000 carbon filaments) with increased tensile strength and/or modulus than corresponding commercial products, and reduce the production cost thereof. The split carbon fiber tows produced by the present invention can be applied to many a variety of products, such as 3C products, sporting goods, wind power generation, new energy vehicles, drones, aerospace, aviation and military applications, and the like, and they can also be used as the raw material for 3D printing. The products produced from the small carbon fiber tows obtained by the present invention are lighter but stronger.
Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the features of the invention, the disclosure is illustrative only. Changes may be made in the details, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

What is claimed is:

1. A method for splitting a carbon fiber tow, comprising:

(A) providing a carbon fiber tow comprising multiple carbon filaments sized with a solution containing a first sizing material;

(B) passing the carbon fiber tow through a first heating device to heat the carbon fiber tow at a temperature of between 45° C. and 140° C., so as to soften the first sizing material and form a spread carbon fiber tow;

(C) adjusting the tension of the spread carbon fiber tow;

(D) passing the spread carbon fiber tow through at least one splitter to obtain a plurality of multiple carbon fiber strands spaced apart;

(E) passing the spread carbon fiber tow through at least one cutter to cut the carbon filaments connected between the carbon fiber strands;

(F) adjusting the tension of the carbon fiber strands;

(G) sizing the carbon fiber strands with a solution containing a second sizing material to obtain multiple sized carbon fiber strands; and

(H) passing the multiple sized carbon fiber strands through a second heating device to heat the sized carbon fiber strands to obtain multiple split carbon fiber tows.

2. The method as claimed in claim 1, wherein the spread carbon fiber tow has a maximum width for the carbon fiber tow.

3. The method as claimed in claim 1, the step (B) is repeated multiple times to obtain the spread carbon fiber tow.

4. The method as claimed in claim 1, further comprising, in the step (H), passing the multiple sized carbon fiber strands through a cooling device after passing the multiple sized carbon fiber strands through a second heating device.

5. The method as claimed in claim 1, further comprising adjusting the width of the multiple sized carbon fiber tows.

6. The method as claimed in claim 4, further comprising adjusting the width of the multiple sized carbon fiber tows.

7. The method as claimed in claim 1, further comprising, after the step (E) and before the step (F), guiding each of the carbon fiber strands to one of guiding rollers respectively, wherein any two adjacent carbon fiber strands were guided to guiding rollers at different height level.

8. The method as claimed in claim 1, wherein the first sizing material is a thermosetting material.

9. The method as claimed in claim 1, wherein the second sizing material comprises a thermoplastic material or a thermosetting material.

10. The method as claimed in claim 9, wherein the thermoplastic material is selected from a group consisting of an acrylonitrile butadiene styrene (ABS), a polypropylene (PP), a polyethylene (PE), a polycarbonate (PC), a polyurethane (PU), a polystyrene (PS), a polyethylene terephthalate (PET), and a polyetheretherketone (PEEK).

11. The method as claimed in claim 9, wherein the thermosetting material is an epoxy resin.

12. The method as claimed in claim 1, wherein the carbon fiber tow is heated at a temperature of between 80° C. and 120° C. in Step (B).

13. The method as claimed in claim 1, wherein the multiple sized carbon fiber strands are heated at a temperature of between 80° C. and 120° C. in Step (H).

14. The method as claimed in claim 4, wherein the multiple sized carbon fiber strands are cooled at a temperature of between 2° C. and 10° C.

15. The method as claimed in claim 6, wherein the multiple sized carbon fiber strands are cooled at a temperature of between 2° C. and 10° C.

16. The method as claimed in claim 1, wherein the at least one splitter is made of metal.

17. The method as claimed in claim 1, wherein the at least one splitter is configured to equally split the spread carbon fiber tow.

18. The method as claimed in claim 1, wherein the at least one cutter is a circular saw blade.

19. The method as claimed in claim 1, wherein the split carbon fiber tow has a breaking strength of 16.0 kgf or higher and a breaking elongation of 4.8% or higher.

20. The method as claimed in claim 19, wherein the split carbon fiber tow has a length of about 5000 meters.