JP2020190040A - Surface treatment method for carbonized fiber, method for producing carbon fiber, and surface treatment device - Google Patents

Abstract

To provide a surface treatment method for carbonized fiber having an increased treatment capability.SOLUTION: A surface treatment method for carbonized fiber has an irradiation step for irradiating carbonized fiber 1d with atmospheric pressure plasma, and a contact step for bringing the carbonized fiber into contact with ozone gas, which is a by-product of the atmospheric pressure plasma.SELECTED DRAWING: Figure 2

Description

The present invention relates to a surface treatment for improving the wettability of the surface of carbonized fibers.

As the surface treatment, for example, there are gas phase oxidation treatment, liquid phase oxidation treatment, electrolytic oxidation treatment and the like, and as one method of the gas phase oxidation treatment, a method of converting various gases into plasma and surface treatment has been proposed (for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2016-07828 JP-A-2018-115395

Although the surface of carbonized fibers is improved by the techniques of the above patent documents, a surface treatment method having a higher treatment capacity is desired.

In view of the above problems, an object of the present invention is to provide a surface treatment method having a high processing capacity, a method for producing carbon fibers, and a surface treatment apparatus.

In order to achieve the above object, the surface treatment method for carbonized fibers according to one aspect of the present invention is to bring the carbonized fibers into contact with an irradiation step of irradiating the carbonized fibers with plasma and ozone gas produced as a by-product of the plasma. Includes contact steps.
In order to achieve the above object, the method for producing carbon fiber according to one aspect of the present invention includes a carbonization step for carbonizing the flame-resistant fiber and a carbonization step for carbonizing the flame-resistant fiber in the method for producing carbon fiber obtained by carbonizing the flame-resistant fiber. The surface treatment step includes a surface treatment step of modifying the surface of the carbonized fiber, and in the surface treatment step, the surface is modified by the above surface treatment method.
In order to achieve the above object, the carbonized fiber surface treatment device according to one aspect of the present invention is a surface treatment device for modifying the surface of a running carbonized fiber, wherein the carbonized fiber is used. It has a tubular tubular portion extending in the traveling direction of the above, and an irradiation portion provided in an intermediate portion in the longitudinal direction of the tubular portion and irradiating plasma. In the tubular portion, the plasma irradiated by the irradiation portion is used. By-product ozone gas comes into contact with the carbonized fibers in motion.

The surface treatment method, the manufacturing method, and the surface treatment apparatus according to one aspect of the present invention can relatively improve the surface treatment capacity.

It is the schematic which shows the manufacturing process of carbon fiber. It is the schematic of the surface treatment apparatus. It is a figure which shows the relationship between the ozone gas concentration and the surface oxygen concentration of a fiber.

<< Overview >>
The method for surface-treating carbonized fibers according to one aspect of the present invention includes an irradiation step of irradiating the carbonized fibers with plasma and a contact step of contacting the ozone gas produced as a by-product of the plasma.
In the case of atmospheric pressure plasma, the combination of plasma irradiation and ozone gas can be applied to non-radical oxygen in the raw material gas of plasma or oxygen in the atmosphere as in the reactions described in Documents 1 and 2 below. On the other hand, ozone may be generated by contact with oxygen radicals, but the oxygen radicals generated when the radicals that want to contribute to surface modification are consumed by ozone and converted to oxygen or converted to oxygen are generated. It is known to deprive the energy of electrons in the plasma, and it is common that the gas containing ozone produced as a by-product is rapidly discharged to the outside of the system.
Reference 1: Nobushi Kanbara, "Handbook of Atmospheric Pressure Plasma Reaction Engineering", NTS Co., Ltd., published on July 1, 2013 Reference 2: Hidetoshi Sugimitsu, "Basics and Applications of Ozone", Co., Ltd. Korin, published in February 1996

The method for surface-treating carbonized fibers according to one aspect of the present invention includes an irradiation step of irradiating the carbonized fibers with plasma and a contact step of contacting the ozone gas produced as a by-product of the plasma.
In the method for surface-treating carbonized fibers according to another aspect of the present invention, the surface treatment of the carbonized fibers is performed by running the carbonized fibers in the surface treatment apparatus, and the contact step. Is performed on the upstream side and the downstream side in the traveling direction of the carbonized fiber with respect to the position where the plasma is irradiated, and the ozone gas exposure time per carbon fiber mass is 15 to 1,000,000 sec / g. is there. As a result, the surface treatment capacity can be improved relatively efficiently.
In the method for surface-treating carbonized fibers according to another aspect of the present invention, the surface treatment apparatus includes a tubular tubular portion extending in the traveling direction of the carbonized fibers and a longitudinal direction of the tubular portion. The carbonized fiber has an irradiation portion provided in the intermediate portion and irradiates the plasma, and the carbonized fiber runs in the front cylinder portion, and the ozone gas concentration at the upstream entrance of the irradiation portion in the cylinder portion is increased. It is 20 to 200 ppm. As a result, the irradiated plasma can be effectively used, and it can be carried out without adding a new ozone gas generator.
In the method for surface-treating carbonized fibers according to another aspect of the present invention, the cross-sectional area of the tubular portion is 5 to 5 with respect to the total cross-sectional area of all carbonized fibers passing through the tubular portion at the same time. It has 4 × 10 ⁴ times the internal space. This makes it applicable to the surface treatment of many types of carbonized fibers.

The method for producing carbon fiber according to one aspect of the present invention is a method for producing carbon fiber obtained by carbonizing flame-resistant fiber, wherein the carbonization step of carbonizing the flame-resistant fiber and the surface of the carbonized fiber are used. The surface treatment step includes the surface treatment step of modifying the surface, and the surface is modified by the above surface treatment method. As a result, the surface treatment capacity is relatively improved, and carbon fibers can be efficiently produced.

The surface treatment device according to one aspect of the present invention is a surface treatment device that modifies the surface of a running carbonized fiber, wherein the surface treatment device extends in the running direction of the carbonized fiber and the tubular portion. The carbonized fiber provided in the middle portion in the longitudinal direction of the tubular portion and having an irradiation portion for irradiating plasma, and in the tubular portion, ozone gas produced as a by-product of the plasma irradiated by the irradiation portion is running. Contact with. As a result, a surface treatment apparatus having a relatively improved surface treatment capacity can be obtained.
In the surface treatment apparatus according to another aspect of the present invention, the cross-sectional shape of the tubular portion is circular or rectangular. As a result, the processing capacity can be improved with a simple structure.
In the surface treatment apparatus according to another aspect of the present invention, the cross-sectional area of the tubular portion is 5 to 4 × 10 ⁴ times the total cross-sectional area of all carbonized fibers passing through the tubular portion. Has space. This allows it to be used for surface treatment of many types of carbonized fibers.
In the surface treatment apparatus according to another aspect of the present invention, the irradiation port for irradiating plasma in the irradiation unit has a shape selected from slits, circles or ellipses, and polygons. As a result, the processing capacity can be increased with a simple structure.

<Embodiment>
A surface treatment method using the surface treatment apparatus of one embodiment and a method for producing carbon fibers will be described. Here, acrylonitrile-based fiber, which is an example of precursor fiber, is used.

1. 1. Carbon Fiber Manufacturing Process FIG. 1 is a schematic view showing a carbon fiber manufacturing process.

Carbon fibers are produced using precursor fibers, precursor fibers. One precursor is a bundle of a plurality of filaments, for example, 12,000 filaments. In some cases, it may be a precursor fiber bundle or a carbon fiber bundle.
The precursor 1a is obtained by spinning a spinning solution obtained by polymerizing a monomer containing 90% by mass or more of acrylonitrile by a wet spinning method or a dry wet spinning method, and then washing, drying and stretching. As the monomer to be copolymerized, alkyl acrylate, alkyl methacrylate, acrylic acid, acrylamide, itaconic acid, maleic acid and the like are used.
Usually, the speed at which the precursor 1a is produced and the speed at which the precursor 1a is carbonized to produce carbon fibers are different. Therefore, the manufactured precursor 1a is once housed in a carton or wound up on a bobbin.

As shown in FIG. 1, the precursor 1a is pulled out from, for example, the bobbin 30 and travels toward the downstream side. On the way, various treatments are performed and the carbon fibers are wound around the bobbin 39.
As shown in FIG. 1, the carbon fiber has a flame-resistant step of making the precursor 1a flame-resistant, and a carbonization step of carbonizing the flame-resistant fiber (hereinafter referred to as “flame-resistant fiber”) 1b while stretching it. A surface treatment step for improving the surface of the carbonized fiber 1d, a sizing step for attaching a resin to the surface-improved fiber (hereinafter, also referred to as “surface-treated fiber”) 1e, and a fiber to which the resin is attached. It is manufactured through a drying step of drying 1f. 1 g of the dried fiber is wound around the bobbin 39 as 1 g of carbon fiber. The carbon fiber is a fiber that has been subjected to at least a surface treatment on the carbonized fiber, and is distinguished from a carbonized fiber that has completed the carbonization step and has not undergone the surface treatment step.
Here, the treatment for making the precursor 1a flame-resistant is the flame-resistant treatment, the treatment for carbonizing the flame-resistant fiber 1b is the carbonization treatment, the treatment for improving the surface of the carbonized fiber 1d is the surface treatment, and the surface-treated fiber. The process of attaching the resin to 1e is called a sizing process, and the process of drying the fiber 1f to which the resin is attached is called a drying process. The processing and process will be described below.

(1) Flame resistance process (flame resistance treatment)
The flameproofing step is performed using the flameproofing furnace 3 in which the inside of the furnace is set to an oxidizing atmosphere of 200 [° C.] to 350 [° C.]. Specifically, flame resistance is achieved by passing the precursor 1a once or a plurality of times in the flame resistance furnace 3 in an air atmosphere. The oxidizing atmosphere may contain oxygen, nitrogen dioxide and the like.
The precursor 1a in the flame resistance step is stretched with a predetermined tension according to the carbon fiber to be produced. The draw ratio in the flame resistance step is, for example, in the range of 0.7 to 1.3. Stretching of the precursor 1a is performed by a plurality of rollers. For example, stretching is performed by two rollers 5 and 7 at the inlet of the flameproof furnace 3 and three rollers 9, 11 and 13 at the outlet.

(2) Carbonization process (carbonization treatment)
The carbonization step is a step of causing a thermal decomposition reaction by heating the flame-resistant fiber 1b to carry out carbonization, and is treated at a maximum temperature of 300 to 1,800 [° C.] in an inert atmosphere. ..
Carbonization is performed by the flame-resistant fiber 1b passing through the first carbonization furnace 15 and the fiber 1c passing through the first carbonization furnace 15 passing through the second carbonization furnace 17.
Here, the carbonization performed in the first carbonization furnace 15 is referred to as "first carbonization" or "first carbonization step", and similarly, the carbonization performed in the second carbonization furnace 17 is referred to as "first carbonization". It is referred to as "second carbonization" or "second carbonization step".

The first carbonization is treated, for example, at a maximum temperature of 300 to 800 [° C.], and the second carbonization is processed, for example, at a maximum temperature of 500 to 1,800 [° C.]. For heating in the carbonization step, for example, an electric heater, microwave, plasma, or the like is used.

The first carbonization furnace 15 and the second carbonization furnace 17 are provided in a form independent of each other, and an adjusting means for adjusting the tension of the fibers can be provided between the carbonization furnaces 15 and 17.
A roller 19 is located on the inlet side of the first carbonization furnace 15, a roller 21 is located between the first carbonization furnace 15 and the second carbonization furnace 17, and a roller 21 is located on the outlet side of the second carbonization furnace 17. Each of the rollers 23 is provided.
Specifically, it is preferable to apply a tension of 50 to 200 [g / dtex] in the first carbonization step and 200 to 1,000 [g / dtex] in the second carbonization step. By applying tension in this range, 1 g of carbon fiber having higher strength can be obtained. The density of the carbonized fiber 1d is preferably 1.77 to 1.82 [g / cm ³ ].

(3) Surface treatment process (surface treatment)
The surface treatment step is performed by passing the carbonized fiber 1d through the surface treatment device 25. A roller 26 is provided on the outlet side of the surface treatment device 25. By surface treatment, when 1 g of carbon fiber is used as a composite material, the affinity and adhesiveness between 1 g of carbon fiber and the matrix resin are improved.
The surface treatment is generally performed by oxidizing the surface of the carbonized fiber 1d. Atmospheric pressure plasma is used as a surface treatment. The surface treatment device 25 will be described later.

(4) Sizing process (sizing process)
The sizing step is performed, for example, by passing the surface-treated fiber 1e through the resin liquid 29. The resin liquid 29 is stored in the resin bath 27. The sizing step enhances the convergence of the surface-treated fibers 1e.
The surface-treated fibers 1e in the sizing step pass through the resin liquid 29 while changing the traveling direction by a plurality of rollers 31, 33 and the like arranged inside the resin bath 27 and around the resin bath 27. As the resin liquid 29, for example, a liquid or an emulsion liquid in which an epoxy resin, a urethane resin, a phenol resin, a vinyl ester resin, an unsaturated polyester resin or the like is dissolved in a solvent is used.

(5) Drying process (drying process)
The drying step is performed by passing the fiber 1f through the drying furnace 35. The dried fiber 1 g is wound around the bobbin 39 via a roller 37 on the downstream side of the drying furnace 35 (this is a winding step).

2. 2. Surface treatment device As shown in FIG. 2, the surface treatment device 25 is provided and large in the middle portion between the tubular portion 251 extending in the traveling direction of the carbonized fiber 1d and the tubular portion 251 in the longitudinal direction. It has an irradiation unit 255 for irradiating pressure plasma. The carbonized fiber 1d runs in the tubular portion 251.

(1) Cylinder portion The tubular portion 251 has, for example, a cross-sectional shape such as a circular shape, an elliptical shape, an oval shape polled shape, a rectangular shape, a square shape, a hexagonal shape, or the like. The tubular portion 251 has a function of storing ozone gas produced as a by-product by the plasma generated by the irradiation unit 255.
The total length of the tubular portion 251 (the total of the upstream side and the downstream side) is set so that the traveling carbonized fiber 1d stays inside within a range of 0.1 to 10 minutes. There is. The plasma irradiation may be performed once or a plurality of times while the carbonized fiber 1d stays in the tubular portion 251. When it is performed a plurality of times, it can be performed by arranging a plurality of irradiation units in the traveling direction.

The tubular portion 251 has a function of regulating the diffusion of ozone gas produced as a by-product by the plasma generated by the irradiation portion 255. In other words, the tubular portion 251 has a function of regulating the flow path of ozone gas. The ozone concentration at the inlet of the carbonized fiber 1d on the upstream side of the tubular portion 251 is preferably 20 to 200 [ppm]. As a result, the carbonized fiber 1d traveling inside the tubular portion 251 is exposed to plasma irradiation and ozone gas, and is efficiently surface-treated.
The cylinder portion 251 and the irradiation portion 255 are set so that the concentration of ozone gas is 20 to 200 [ppm]. Specifically, the tubular portion 251 has dimensions such as length and thickness, and the irradiation portion 255 has the concentration of supply gas, the voltage applied to the electrodes, and the like.

The total length of the tubular portion 251 in the traveling direction is preferably 100 to 10,000 times, more preferably 200 to 2,000 times, the dimension of the irradiation unit 255 in the traveling direction. The total length of the tubular portion 251 is preferably 20 to 2,000 times, more preferably 40 to 400 times, the dimension in the plasma irradiation direction of the tubular portion 251. The total length of the tubular portion 251 is preferably 100 to 10,000 [mm] in the traveling direction, and more preferably 200 to 2,000 [mm]. The dimensions of the irradiation unit 255 in the traveling direction will be described later.
Here, the tubular portion 251 has a through hole 253 in the center (intermediate portion) in the longitudinal direction thereof, and the atmospheric pressure plasma is irradiated into the tubular portion 251 from the irradiation unit 255 using the through hole 253.
The tubular portion 251 has an internal space of 5 to 4 × 10 ⁴ times the total cross-sectional area of all the carbonized fibers 1d running in the cross section.

The through hole 253 has a slit shape, a circular shape, an elliptical shape, or a polygonal shape such as a pentagon. The slit shape may be stretched in a direction intersecting the traveling direction of the carbonized fiber 1d or in a direction parallel to the traveling direction. The number of through holes 253 may be one or a plurality, and may be appropriately determined according to the number of carbonized fibers 1d to be run.
It is preferable that the through hole 253 is provided so that the carbonized fiber 1d can be seen through the through hole 253 when viewed from the plasma generating portion.

(2) Irradiation unit The irradiation unit 255 uses, for example, a dielectric barrier discharge. The irradiation unit 255 includes a pair of electrodes in which a dielectric is arranged on at least one electrode, and a nozzle for supplying an oxidizing gas around the pair of electrodes, and the oxidizing gas supplied from the nozzle (for example, oxygen). Plasma is generated by discharging with a pair of electrodes under atmospheric pressure.
As a pair of electrodes, for example, a flat plate-shaped counter electrode (parallel flat plate electrode) is used. The counter electrode is arranged in a state of being stretched in a direction intersecting the traveling direction of the carbonized fiber 1d or in a direction parallel to the traveling direction, for example.
The generated plasma is irradiated from the through hole (irradiation port) 253 of the tubular portion 251 to the inside by the gas from the nozzle. As a result, the carbonized fiber 1d traveling inside the tubular portion 251 is irradiated with atmospheric pressure plasma.

(3) Length in the traveling direction of the irradiation unit The length in the traveling direction of the irradiation unit 255 is the length in the traveling direction in the region where the carbonized fibers are irradiated with plasma. The length of the irradiated portion varies depending on the configuration for generating plasma, the configuration for irradiating the carbonized fiber with plasma, and the like.
When plasma is irradiated through a through hole such as a slit, the maximum dimension of the through hole in the traveling direction is the length of the irradiated portion. When the counter electrode is arranged in the cylinder portion so that the carbonized fiber does not pass between the electrodes and the gas is sprayed toward the carbonized fiber from the opposite side to the carbonized fiber, the counter electrode is used. The dimension in the traveling direction is the length. When the carbonized fibers travel between the counter electrodes with the counter electrodes in the tubular portion and arranged parallel to the traveling direction, the dimension of the counter electrode in the traveling direction becomes the length.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.
Here, a surface treatment step for surface-treating the carbonized fiber 1d will be described.
First, the materials shown below were prepared prior to Examples and Comparative Examples.

<Carbonized fiber 1d>
The carbonized fiber 1d has a temperature of 300 in an inert atmosphere after undergoing a flame resistance step of treating 24,000 precursor fibers (plicasa) 1a in an oxidizing atmosphere at 200 to 350 [° C.]. The fiber is produced through a first carbonization step of about 800 [° C.] and a second carbonization step of a temperature of 500 to 1,800 [° C.].
The density of the carbonized fiber 1d is 1.5 to 1.9 [g / cm ³ ], the diameter of the fiber 1d is 10 [μm], and the oxygen concentration on the surface of the fiber 1d is 4 [%]. there were.

<Surface oxygen concentration (O / C)>
The surface oxygen concentration (O / C) of the surface-treated fiber (1e) after the surface treatment can be determined by XPS (ESCA) according to the following procedure. For the measurement, an X-ray photoelectron spectrometer ESCA JPS-9000MX manufactured by JEOL Ltd. was used. After cutting the fibers and arranging them on a stainless steel sample support, the photoelectron escape angle was set to 90 degrees, MgKα was used as the X-ray source, and the inside of the sample chamber was 1 × ^10-6 [Pa]. The degree of vacuum was maintained.
To correct the peak associated with charging during measurement, first, the binding energy value of the main peak of C1s B. E. To 284.6 [eV]. The O1s peak area was determined by drawing a straight baseline in the range of 528 to 540 [eV], and the C1s peak area was determined by drawing a straight baseline in the range of 282-292 [eV]. The surface oxygen concentration O / C on the surface of the carbon fiber was calculated and obtained by the ratio of the O1s peak area and the C1s peak area.

<Ozone gas concentration>
A detector tube "18M" for measuring ozone gas for a concentration of 4 to 400 [ppm] manufactured by Gastec Co., Ltd. is set in a dedicated gas suction device "GV-110S" and has a diameter of 3 [mm] opened in the cylinder 251. Insert the detector tube into the hole and pull the handle of the aspirator to introduce the gas into the detector tube. Since the color of the detector tube changes according to the ozone concentration, it is read as the ozone gas concentration. The temperature of ozone gas is measured by inserting a temperature detection end into a region irradiated with plasma through a hole provided in the irradiation portion or a peripheral portion thereof.

<Surface treatment>
The surface treatment device 25 has a tubular portion 251 and an irradiation portion 255. One remote atmospheric pressure plasma surface treatment device is used as the irradiation unit 255, and the upstream side cylinder of 600 [mm] is on the upstream side of the one irradiation unit 255, and the downstream side of 300 [mm] is on the downstream side. It has a tubular part. The cross-sectional shape of these cylinders is rectangular, and the ratio of the cross-sectional area of the internal space of the cylinder to the total cross-sectional area of the inserted fibers is 40.
The surface treatment device 25 adjusts the concentration of ozone gas produced as a by-product when plasma is generated by changing the oxygen concentration in the oxidizing gas supplied from the nozzle of the irradiation unit 255. The oxygen concentration is adjusted by adjusting the oxygen concentration in an oxidizing gas containing nitrogen and oxygen.
By adjusting the speed of the carbonized fiber 1d traveling in the surface treatment device 25 (cylinder portion 251), the plasma irradiation time (plasma exposure time) and the ozone gas exposure time can be adjusted.

[Example 1]
The carbonized fiber 1d was surface-treated by plasma irradiation and ozone gas. The voltage applied to the electrodes of the irradiation unit 255 is 30,000 [V]. The traveling speed of the carbonized fiber 1d was 1.2 [m / min], and the irradiation time was 0.1 [second] (which is also the time for the carbonized fiber 1d to pass through the irradiation unit 255. ).
The oxygen concentration in the oxidizing gas (also referred to as carrier gas) supplied to the periphery of the electrode was 0.15 [Vol%]. The ozone concentration of the ozone gas produced by plasma was 40 [ppm], and the gas temperature was 70 [° C.]. The total ozone gas exposure time was 45 [seconds], the exposure time on the upstream side of the irradiation unit 255 was 30 [seconds], and the exposure time on the downstream side was 15 [seconds].
The surface oxygen concentration (O / C) of the surface-treated fiber 1e subjected to the above surface treatment was 16 [%].
Table 1 summarizes the surface treatment conditions and the surface oxygen concentration of the surface-treated fiber 1e. The temperature of ozone gas was measured in a region irradiated with plasma by inserting a temperature detection end through a hole having a diameter of 3 mm provided in or near the irradiation unit 255.

[Example 2]
The carbonized fiber 1d was surface-treated under the same conditions as in Example 1 except that the oxygen concentration in the carrier gas was changed to 0.5 [Vol%]. By changing the oxygen concentration, the ozone concentration became 100 [ppm]. The surface treatment conditions of Example 2 and the surface oxygen concentration of the surface-treated fiber 1e are summarized in Table 1.

[Example 3]
The carbonized fiber 1d was surface-treated under the same conditions as in Example 1 except that the oxygen concentration in the carrier gas was changed to 1.0 [Vol%]. By changing the oxygen concentration, the ozone concentration became 160 [ppm]. The surface treatment conditions of Example 3 and the surface oxygen concentration of the surface-treated fiber 1e are summarized in Table 1.

[Comparative Example 1]
The carbonized fiber 1d was surface-treated by plasma irradiation. Specifically, a surface treatment device from which the tubular portion 251 was removed was used.
The voltage applied to the electrode of the irradiation unit 255, the traveling speed of the carbonized fiber 1d, and the plasma irradiation time were the same as in Example 1.
The oxygen concentration in the carrier gas was 0.15 [Vol%], the ozone concentration of the ozone gas produced by plasma was 40 [ppm], and the gas temperature was 70 [° C.].
When the carbonized fiber 1d was irradiated with plasma, the ozone gas exposure time was set to 0.1 [sec], which is the irradiation time, in order to travel in the ozone gas produced by the plasma.
The surface oxygen concentration (O / C) of the surface-treated fiber 1e subjected to the above surface treatment was 13 [%]. Table 1 summarizes the surface treatment conditions of Comparative Example 1 and the surface oxygen concentration of the surface-treated fiber 1e.
[Comparative Example 2]
The carbonized fiber 1d was surface-treated under the same conditions as in Comparative Example 1 except that the oxygen concentration in the carrier gas was changed to 0.5 [Vol%]. By changing the oxygen concentration, the ozone concentration became 100 [ppm]. Table 1 summarizes the surface treatment conditions of Comparative Example 2 and the surface oxygen concentration of the surface-treated fiber 1e.

[Comparative Example 3]
The carbonized fiber 1d was surface-treated under the same conditions as in Comparative Example 1 except that the oxygen concentration in the carrier gas was changed to 1.0 [Vol%]. By changing the oxygen concentration, the ozone concentration became 160 [ppm]. The surface treatment conditions of Example 3 and the surface oxygen concentration of the surface-treated fiber 1e are summarized in Table 1.
[Reference example]
Table 1 also shows the surface oxygen concentration of the carbonized fiber 1d when no surface treatment was performed.

表１の実施例及び比較例の結果から、オゾンガス濃度と表面酸素濃度との関係を図３に示す。

From the results of Examples and Comparative Examples in Table 1, the relationship between the ozone gas concentration and the surface oxygen concentration is shown in FIG.

<Exposure of ozone gas>
Example 1 having an ozone gas concentration of 40 [ppm] and an exposure time of 45 [sec] has a surface oxygen concentration of 23 as compared with Comparative Example 1 having the same ozone gas concentration and an exposure time of 0.1 [sec]. [%] Improved.
Similarly, Example 2 having an ozone gas concentration of 100 [ppm] and an exposure time of 45 [sec] has surface oxygen as opposed to Comparative Example 2 having the same ozone gas concentration and an exposure time of 0.1 [sec]. Example 3 in which the concentration was improved by 14 [%], the ozone gas concentration was 160 [ppm], and the exposure time was 45 [sec] was compared with Comparative Example 3 in which the ozone gas concentration was the same and the exposure time was 0.1 [sec]. On the other hand, the surface oxygen concentration was improved by 27 [%].
In this way, by running the carbonized fiber 1d in the ozone gas, the surface oxygen concentration of the fiber could be improved.
The ozone gas exposure time per carbon fiber mass takes into consideration the treated amount of the fiber to be treated (the number of exposed fibers), the traveling speed of the fiber to be treated, the brand (fineness) of the fiber to be treated, and the like. ..
More specifically, if there is exposure to ozone gas, the surface oxygen concentration is improved, and there is no particular upper limit to the exposure time. However, considering the actual productivity, the upper limit of the exposure time is 10 min. Further, the traveling speed of the fiber is 0.01 to 0.2 [m / sec] in consideration of the actual productivity, and the processing amount with respect to the machine base width (dimension in the traveling direction) is 2 to 200 [lines]. / M]. Considering these parameters, the ozone gas exposure time per carbon fiber mass is preferably in the range of 15 to 1,000,000 [sec / g].
In addition, considering productivity such as ease of yarn conduction, the cross-sectional area of the tubular portion is 5 to 4 × 10 with respect to the total cross-sectional area of all carbonized fibers that pass through the tubular portion at the same time. It is preferable to have ^four times as much internal space.

Since ozone gas is produced as a by-product by plasma generation, it does not require energy for generating ozone gas. That is, by effectively utilizing the ozone gas produced as a by-product when plasma is generated, the surface oxygen concentration can be increased with the same energy as compared with the surface treatment by mere plasma irradiation.
Further, the surface treatment apparatus can improve the surface oxygen concentration by a simple structure in which the cylinder portion 251 is provided in the irradiation portion 255. By adjusting the length of the tubular portion 251 in the longitudinal direction, the exposure time of ozone gas can be adjusted, and the exposure time can be adjusted without changing the traveling speed of the carbonized fiber 1d.

<Ozone gas concentration>
In Examples 1-3, as shown in FIG. 3, the surface oxygen concentration was the maximum when the ozone gas concentration was 100 [ppm]. Even in Comparative Example 1-3 in which the exposure time of ozone gas was 0.1 [sec], the surface oxygen concentration was the maximum when the ozone gas concentration was 100 [ppm].
The reason for this is that if the concentration of ozone gas becomes too high (for example, 160 [ppm]), the collision between oxygen radicals in the ozone gas increases, the average free process of oxygen radicals decreases, and the concentration of ozone gas becomes too low. (For example, 40 [ppm]), the density of oxygen radicals is considered to be low.

<< Modification example >>
Although the above description is based on the embodiment, the present invention is not limited to the embodiment. For example, any of the modified examples and the embodiments described below may be appropriately combined, or a plurality of modified examples may be appropriately combined.

In the embodiment, a method for producing carbon fibers having 12,000 filaments has been described, but other precursor fibers having 3,000 filaments, 6,000, 24,000 filaments, etc. are used. It can also be applied to a method for surface treatment of carbonized fibers and a method for producing carbon fibers.
In the embodiment, the method for producing the carbon fiber including the carbonization step has been described, but for example, the graphitization treatment may be further performed before the surface treatment step. That is, in the embodiment, the method for producing carbon fiber of a general-purpose product (elastic modulus 240 [GPa]) has been mainly described, but the surface treatment step is performed on carbon of a high-performance product such as a high-elasticity product and a medium-elasticity high-strength product. It can also be used for carbonized fibers for fibers. Naturally, it can also be used as a method for producing high-performance carbon fiber.

The irradiation unit 255 of the embodiment uses a parallel flat plate electrode, but for example, a coaxial cylindrical electrode or the like may be used. Further, although the irradiation unit 255 uses a dielectric barrier discharge to generate plasma, other means such as corona discharge and atmospheric pressure glow discharge may be used.
The irradiation unit 255 of the embodiment blows plasma generated outside the cylinder portion 251 into the inside through the through hole 253. For example, a pair of electrodes are arranged inside the cylinder portion, and the space between the pair of electrodes is carbonized. The fibers may be allowed to run.

In the embodiment, one irradiation unit 255 is provided, but a plurality of carbonized fibers may be arranged in the traveling direction.

1 Fiber 1a Precursor 1b Flame resistant fiber 1d Carbonized fiber 25 Surface treatment device 251 Cylinder part 255 Irradiation part

Claims (9)

An irradiation process that irradiates carbonized fibers with plasma,
A method for surface treatment of carbonized fibers, which comprises a contact step of contacting ozone gas produced as a by-product of the plasma. The surface treatment of the carbonized fiber is performed by running the carbonized fiber in the surface treatment device.
The contact step is performed on the upstream side and the downstream side in the traveling direction of the carbonized fiber with respect to the position where the plasma is irradiated, and the ozone gas exposure time per carbon fiber mass is 15 to 1,000,000 sec. The surface treatment method according to claim 1, wherein / g. The surface treatment apparatus has a tubular tubular portion extending in the traveling direction of the carbonized fiber, and an irradiation portion provided in an intermediate portion in the longitudinal direction of the tubular portion and irradiating the plasma.
The carbonized fiber runs in the front cylinder portion and runs inside the front cylinder portion.
The surface treatment method according to claim 2, wherein the ozone gas concentration at the upstream entrance of the irradiation portion in the cylinder portion is 20 to 200 ppm. The surface treatment according to claim 3, wherein the cross-sectional area of the tubular portion has an internal space of 5 to 4 × 10 ⁴ times the total cross-sectional area of all carbonized fibers passing through the tubular portion at the same time. Method. In the method for producing carbon fiber obtained by carbonizing flame-resistant fiber,
The carbonization step of carbonizing the flame-resistant fiber and
Including a surface treatment step to modify the surface of carbonized fiber,
A method for producing carbon fibers, wherein in the surface treatment step, the surface is modified by the surface treatment method according to any one of claims 1 to 4. In a surface treatment device that modifies the surface of running carbonized fibers
A tubular tubular portion extending in the traveling direction of the carbonized fiber and a tubular portion
It has an irradiation portion provided in the middle portion in the longitudinal direction of the cylinder portion and irradiates plasma.
A surface treatment device in which the ozone gas produced as a by-product of the plasma irradiated by the irradiation unit comes into contact with the running carbonized fibers in the cylinder portion. The surface treatment apparatus according to claim 6, wherein the cross-sectional shape of the tubular portion is circular or rectangular. The surface according to claim 6 or 7, wherein the cross-sectional area of the tubular portion has an internal space 5 to 4 × 10 ⁴ times the total cross-sectional area of all carbonized fibers passing through the tubular portion. Processing equipment. The surface treatment apparatus according to any one of claims 6 to 8, wherein the irradiation port for irradiating plasma in the irradiation unit has a shape selected from a slit, a circle, an ellipse, and a polygon.

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