JP2018145540A - Method for production of carbon fiber bundle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing high-quality carbon fiber excellent in resin impregnability without decomposing at a carbonization step, capable of obtaining a flame-resistant fiber bundle made fire-resistant uniformly to the inside thereof even if having large single fiber fineness.SOLUTION: This invention relates to a method that satisfies the following (1) to (3): (1) density of a fire-resistant fiber is 1.37 g/cmor more; (2) an area of an inner layer in a cross-sectional dual structure of the fire-resistant fiber is 18 μmor less per 1 dtex of a single fiber fineness; (3) in a pre-carbonization treatment, the time taken to pass through an inert atmosphere at 500°C-900°C is 20 seconds or more per 1 dtex of the single fiber fineness in a fire-resistant fiber bundle.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a carbon fiber bundle.

  Conventionally, a carbon fiber precursor acrylic fiber bundle (hereinafter sometimes referred to as “PAN precursor fiber bundle”) is converted into a carbon fiber bundle through the following steps. First, the PAN-based precursor fiber bundle is subjected to a flame-resistant heat treatment in an oxidizing atmosphere at 200 to 300 ° C. in the flame-proofing process, and the resulting flame-resistant fiber bundle is subjected to an inert atmosphere at 300 ° C. or higher in the carbonization process. Carbonization is performed to obtain a carbon fiber bundle.

  The flameproofing process and the carbonization process are important processes that affect the performance and productivity of the carbon fiber. In the flameproofing process, the polymer chain constituting the PAN-based precursor fiber is oxidized and the nitrile group bonded to the polymer chain is cyclized to be thermally stable to the extent that it can pass through the subsequent carbonization process. It can be converted to a fiber having a structure. And in a carbonization process, the carbon fiber which has high intensity | strength and elastic modulus can be obtained by accelerating | stimulating the structure formation of a graphite crystal | crystallization in a still higher temperature inert atmosphere.

  Recently, carbon fiber reinforced resin CFRP (carbon fiber reinforced plastics) in which a carbon fiber bundle having a strength higher than that of a metal and a lighter carbon fiber bundle is combined with a thermosetting resin has attracted particular attention. The composite material is used in aviation and automobile applications because it has a strength equal to or higher than that of metal and has a low density. However, since it takes time for thermosetting and the shape does not change after molding, in recent years, the demand for carbon fiber reinforced thermoplastic resin CFRTP (carbon fiber reinforced thermoplastics) using a thermoplastic resin as a matrix is increasing. .

  In the case of using a thermosetting resin as a matrix, the carbon fiber bundle is impregnated with the resin composition before curing, so that the impregnation property has not been regarded as a problem. However, since the viscosity of the thermoplastic resin is very high, it is difficult to impregnate. With respect to the impregnation between the carbon fiber and the resin, the carbon fiber having a large single fiber fineness is more advantageous from the viewpoint that the gap between the single fibers becomes large. Oxygen diffusion cannot catch up, and only the fiber surface layer forms a flame-resistant double-section structure. Flame resistant fibers having such a structure are likely to cause troubles such as yarn breakage in the carbonization process, and it is difficult to produce carbon fibers having stable and sufficient performance.

In order to solve these problems, for example, Patent Document 1 discloses a technical technique capable of efficiently producing a high-quality carbon fiber bundle by suppressing the cross-sectional double structure of the flame-resistant fiber in high-speed firing. ing.
Patent Document 2 discloses a technique that can efficiently provide a flame-resistant fiber bundle by contact with a high-temperature heating body.
Patent Document 3 discloses a method for producing flame-resistant fibers that can make flame-resistant fibers and acrylic fibers, which are carbon fiber precursors, flame-resistant in a short time, and are optimal for obtaining high-quality carbon fibers.

WO2012 / 50171 JP 2014-125700 A JP-A-10-251923

However, the invention described in each of the above patent documents has the following problems.
In the technique of Patent Document 1, in the case of a carbon fiber precursor fiber bundle having a large single fiber fineness, even if heat treatment is performed for a long time, diffusion of oxygen does not catch up with the inside of the fiber, and only the surface layer is made flame resistant. Therefore, there is a problem that the flameproofing reaction does not proceed to the inside and the cross-sectional double structure becomes remarkable.
In the technique described in Patent Document 2, when the carbon fiber precursor fiber bundle and the heating body are contacted, only the surface layer is made flame resistant without the diffusion of oxygen inside the fiber, and the obtained flame resistant fiber When carbonization treatment was performed on a bundle, a lot of fluff was generated, and it was difficult to say that it was a method for producing a flame-resistant fiber bundle suitable for producing a carbon fiber bundle.
In the technique described in Patent Document 3, flame-resistant fibers with uniform progress of flame resistance can be obtained, while carbon fiber precursor fibers having a large single fiber fineness are not flame-resistant to the inside, and the flame-proofing process step. There is a problem that a rapid decomposition reaction of the polymer occurs in the pre-carbonization step and the carbonization step, which are subsequent steps.
In order to solve the above-mentioned problems, the present inventors have intensively studied and have completed the present invention. That is, an object of the present invention is to provide a carbon fiber bundle manufacturing method capable of obtaining a high-quality carbon fiber bundle by treatment under economical flameproof heat treatment conditions even if the single fiber fineness is large. .

[1] A carbon fiber precursor acrylic fiber bundle having a single fiber fineness of 4 dtex or more is 200 ° C to
Flame-proofing treatment for obtaining a flame-resistant fiber bundle by passing through an acidified atmosphere at 300 ° C., and pre-heat-treating the obtained flame-resistant fiber bundle through an inert atmosphere having a maximum temperature of 500 ° C. to 900 ° C. And a carbonization treatment in which the pre-carbonized fiber bundle thus obtained is passed through an inert atmosphere having a maximum temperature of 1200 ° C. to 2500 ° C. for heat treatment, and the density is 1.7 to 2.0 g / cm. ³ , a method for producing a carbon fiber bundle to obtain a carbon fiber bundle having a single fiber fineness of 2.4 to 5 dtex, which satisfies the following 1) to 3):
A method for producing a carbon fiber bundle.
1) The density of the fibers of the flameproof fiber bundle is 1.37 g / cm ³ or more.
2) The average inner layer area of the flame-resistant fiber bundle measured by the following method is 18 μm ² or less with respect to 1 dtex single fiber fineness of the flame-resistant fiber bundle.
<Measurement method of inner layer area of flameproof fiber bundle>
The flame-resistant fiber bundle is embedded in a transparent resin, cut perpendicularly to the fiber axis direction, polished, observed using an epifluorescence microscope, photographed at a magnification of 500 times, and image analysis software. After the valuation treatment, the fluorescent color development partial area is measured to obtain the inner layer area per flame-resistant fiber.
3) In the pre-carbonization treatment, the time for passing through an inert atmosphere at 500 ° C. to 900 ° C. is 20 seconds or more with respect to 1 dtex of the single fiber fineness of the flame-resistant fiber bundle.

[2] The method for producing a carbon fiber bundle according to [1], wherein the carbon fiber bundle is a carbon fiber bundle having an impregnation depth measured by the following measurement method of 0.12 mm or more.
<Measurement method of impregnation depth>
1) A 50 mm × 50 mm square having a melt viscosity of 300 Pa · s at 200 ° C., a 120 μm thick polypropylene film heated on a hot stage so that the surface temperature is 200 ° C., a square of 100 mm × 100 mm, a thickness of 5 mm Place on an iron plate and melt.
2) A carbon fiber bundle adjusted so that the total fineness becomes 24,000 dtex or more is uniformly spread over the melted PP film so as to have a width of 50 mm, and heated to 200 ° C. in advance of 50 mm × 50 mm. A square and 5 mm thick iron plate is placed and immediately compressed at 0.2 MPa for 60 seconds, and the sample is taken out and cooled.
3) The prepared sample is embedded in resin, cut and polished, and the thickness at which the carbon fiber bundle is impregnated with polypropylene is measured as the impregnation depth with an optical microscope.

  According to the present invention, even if the single fiber fineness is large, the flame-resistant fiber that is uniformly flame-resistant up to the inside of the single fiber is carbonized without being decomposed in the carbonization process. A carbon fiber bundle made of carbon fibers can be obtained.

The following is a detailed description of the present invention.
(Carbon fiber precursor acrylic fiber bundle)
The polyacrylonitrile polymer used for the spinning solution of the PAN precursor fiber bundle used for the production of the carbon fiber bundle of the present invention preferably contains 90% by weight or more, preferably 96% by weight or more of acrylonitrile units.
The polyacrylonitrile polymer used in the spinning dope has no restrictions on the copolymer component, molecular weight distribution, stereoregularity, etc., and the flame resistance is promoted as a copolymer component in order to promote the flame resistance treatment for carbon fiber. It is good to copolymerize the monomer which has an effect | action 0.1 to 5 mol%. As the flame resistance promoting component, those having at least one hydroxylalkyl group, carboxyl group, or amide group are preferably used. Moreover, it is desirable to increase the amount of copolymerization of the flame resistance promoting component because the higher the flame resistance promoting action, the faster the flame resistance treatment can be achieved and the higher the productivity. However, on the other hand, as the amount of copolymerization increases, the exothermic rate increases and the risk of runaway reaction may occur. Therefore, the range is preferably not more than 5 mol%, more preferably 0.5 to 3 mol%. Preferably, it is more preferable to set it as 1-3 mol%.

Specific examples of the monomer having flame resistance promoting action include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide, methacrylamide, 2-hydroxyethyl methacrylate , 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, monoglyceryl methacrylate and the like are preferably used. From the viewpoint of promoting flame resistance in the firing step and improving solubility in solvents, 2-hydroxyethyl methacrylate, acrylamide, methacrylamide, and the like are more preferably used.
Any of known polymerization methods such as solution polymerization and suspension polymerization can be used to produce the polyacrylonitrile-based polymer used in the spinning dope. When employing solution polymerization, a solvent in which a polyacrylonitrile-based polymer such as dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc) or the like is soluble is used. Among these, DMAc is more preferably used from the viewpoint of solubility of the polyacrylonitrile-based polymer.

(spinning)
In the production of the carbon fiber precursor acrylic fiber bundle used in the present invention, the above-mentioned spinning solution is spun from a die by a wet spinning method or a dry-wet spinning method and introduced into a coagulation bath to coagulate the fibers. From an industrial viewpoint, a wet spinning method excellent in productivity is preferable.
For the coagulation bath, an aqueous solution containing materials used for the spinning dope is preferably used, and the concentration of the solvent contained is adjusted so as to reduce the porosity of the coagulated yarn. Depending on the solvent used, for example, when DMAc is used, the concentration of DMAc is 50 to 80% by weight, preferably 60 to 75% by weight. The temperature of the coagulation bath is preferably low, and is usually 50 ° C. or lower, more preferably 40 ° C. or lower. If the temperature of the coagulation bath is lowered, a denser coagulated yarn can be obtained. However, if the temperature is lowered too much, the take-up speed of the coagulated yarn is lowered and the productivity is lowered.
The coagulated yarn obtained above is washed and drawn in a washing and drawing process. In addition, about the order of washing | cleaning and extending | stretching, you may perform washing | cleaning first and may carry out simultaneously. Although there is no restriction | limiting in particular as a washing | cleaning method, The method of immersing in water generally used, especially warm water is good.
The stretching method may be a method of stretching by immersing in water or warm water, a dry heat stretching method using a hot plate or a heating roller, or stretching in a box furnace where hot air is circulated. It is not limited to. From an economical viewpoint, it is preferable to carry out in warm water. The draw ratio is preferably 1 to 8 times. However, when performing secondary stretching later, it is preferable to set in consideration of the stretching ratio.
In the method for producing a carbon fiber precursor acrylic fiber bundle used in the present invention, the thread obtained after washing and stretching obtained in the oil agent application step is guided to an oil bath containing a silicone-based oil agent, and silicone is applied to the yarn. Apply a base oil. As the oil agent, a silicone-based oil agent containing a silicone compound is used. As the silicone oil, dimethyl silicone oil or organically modified silicone oil is preferably used, and amino-modified silicone oil having high heat resistance is more preferable. Usually, a silicone compound and a nonionic emulsifier are mixed and emulsified as an oil bath liquid. In some cases, an antioxidant, various additives, and an organic substance not containing a silicone atom can be mixed.

Furthermore, in the method for producing a carbon fiber precursor acrylic fiber bundle used in the present invention, it is preferable to dry and densify the yarn provided with the silicone-based oil obtained as described above in dry densification. As a method for drying and densifying, it is generally performed by contacting with a hot plate or a heating roller, and drying with a heating roller is preferably used. The higher the drying temperature is, the more the crosslinking reaction of the silicone oil agent is promoted, and it is also preferable from the viewpoint of productivity. Therefore, it can be set as high as possible without causing fusion between single fibers of acrylic fibers. Specifically, 150 ° C. or higher is preferable, and 180 ° C. or higher is more preferable. Moreover, it is preferable that the drying time is a time for the yarn to dry sufficiently.
If necessary, the dried and densified yarn obtained above can be subjected to secondary stretching. Examples of the secondary stretching method include dry heat stretching and steam stretching.

  The single fiber fineness of the carbon fiber precursor acrylic fiber bundle used in the present invention is preferably 2.4 dtex or more, and more preferably 4 dtex or more. The single fiber fineness is preferably 10 dtex or less, and more preferably 8 tex or less. The number of filaments in the PAN-based precursor fiber bundle is preferably 1,000 to 100,000, more preferably 3,000 to 30,000. If the single fiber fineness of the PAN-based precursor fiber bundle is 4 dtex or more, it is difficult for the single fibers to be entangled with each other inside the PAN-based precursor fiber bundle, the spreadability of the obtained carbon fiber bundle can be maintained, and good resin impregnation Sex can be obtained. On the other hand, if the single fiber fineness of the PAN-based precursor fiber bundle is 10 dtex or less, the cross-sectional double structure does not become prominent in the flameproofing step, and a uniform quality carbon fiber bundle can be produced stably.

(Flame resistance)
In the flameproofing step, the carbon fiber precursor acrylic fiber bundle is heat-treated in an oxidizing atmosphere. At this time, the carbon fiber precursor acrylic fiber bundle is oxidized and generates heat. The reaction heat needs to be stored in the fiber bundle so that the fiber bundle does not melt or ignite.

(Flame resistance treatment by atmospheric heating method)
As a device for performing flameproofing treatment by an atmospheric heating method, a hot air circulating furnace of a method of circulating heated oxidizing gas can be suitably employed. Usually, in a hot air circulating furnace, a fiber bundle that has entered the furnace is once taken out of the furnace, and then folded by a folding roll disposed outside the furnace and repeatedly passed through the furnace.
As the oxidizing atmosphere, known oxidizing atmospheres such as air, oxygen and nitrogen dioxide can be adopted, but air is preferable from the viewpoint of economy.
In the atmosphere heating method, heat transfer efficiency is low, and reaction heat is likely to be stored inside the fiber bundle. Therefore, it is necessary to perform oxidation treatment at a relatively low temperature for a long time. Since the oxidation treatment is performed for a long time, there is an advantage that the treatment can be performed uniformly.
One index indicating the progress of the flameproofing reaction is the density of the flameproofed fiber. As the density of the flameproof fiber increases, the exothermic reaction decreases and the heat resistance also improves.
As atmosphere heating, it is 90 until the density of the fiber (flame-resistant fiber) after atmosphere heating becomes 1.35 to 1.43 g / cm ³ , more preferably 1.37 to 1.43 g / cm ^3. Heat for more than a minute. When the density of the flameproof fiber obtained by heating in the atmosphere is lower than 1.37 g / cm ³ , a decomposition reaction is likely to occur when passing through the carbonization step.
When the precursor fiber bundles are placed side by side into the flameproofing process, the higher the input density, the more preferable in terms of productivity.However, if the density is increased, the temperature of the fiber bundle becomes higher due to an exothermic reaction during the atmosphere heat treatment described later, causing a decomposition reaction. Occurs rapidly, and the fiber bundle is cut. Therefore, it is preferably 1500 to 5000 dtex / mm, more preferably 2000 to 4000 dtex / mm in terms of the fineness per width in which the precursor fiber bundles are arranged.

(Inner layer area of double cross section)
It is preferable that the area of the non-blackened inner layer of the double cross-sectional structure of the single fiber of the flame resistant fiber bundle is 18 μm ² or less per 1 dtex of single fiber fineness. However, the area of the inner layer of the double cross-sectional structure of the flameproof fiber bundle is obtained by the following method.
1) The flame-resistant fiber bundle is embedded in an epoxy resin Epomount 27-771 manufactured by Refine Tech Co., left at room temperature for 24 hours, cured, and then cut so that the fiber cross section can be observed perpendicular to the fiber axis direction. .
2) After pre-polishing the cut surface with sandpaper of # 120-1200, the polishing cloth is polished for about 10 minutes by containing an alumina suspension (0.3 μm diameter) manufactured by Kasai Shoko Co., Ltd.
3) The obtained sample is observed using an epifluorescence microscope manufactured by Nikon Corporation. The part where the oxidation reaction has progressed is black, and the part where the oxidation reaction has not progressed appears fluorescent and bright. This is magnified 500 times and a photograph is taken.
4) After this image was binarized by Nikon Corporation's image analysis software NIS-Elements, the ratio of the fluorescent coloring portion to the fiber cross-sectional area was calculated, and the area of the inner layer of the double cross-section structure Ask for. The analysis of the area of the inner layer is performed using 20 images in which 100 cross-sections of flame-resistant fibers are photographed per sheet.

The area of the inner layer of the double-cross-section structure of the flameproof fiber bundle shown above becomes smaller as the flameproofing reaction in the atmosphere heating proceeds. Even if heat treatment is performed under the same atmospheric conditions and flameproofing time, the area of the inner layer increases as the single fiber fineness increases.
That the area of the inner layer of the double cross-sectional structure is 18 μm ² or less per 1 dtex of the single fiber fineness indicates that the flameproofing reaction proceeds from the surface of each single fiber to a place close to the core, and the flameproofing treatment step In the pre-carbonization step and the carbonization step, which are subsequent steps, rapid gas generation accompanying the polymer decomposition reaction is suppressed. If a single fiber having an insufficient flame resistance reaction is present in the flame resistant fiber bundle, it is cut in the pre-carbonization step or the carbonization step to become fluff of the carbon fiber bundle. If the area of the inner layer of the double cross-sectional structure is 18 μm ² or less per 1 dtex of the single fiber fineness of the flameproof fiber, the carbon fiber bundle obtained has excellent process passability in the pre-carbonization step and the carbonization step, and the resulting carbon fiber bundle has less fluff. .

(Pre-carbonization treatment)
In the pre-carbonization treatment, the flame-resistant fiber bundle subjected to the flame resistance treatment is put into a first carbonization furnace and subjected to the pre-carbonization treatment. The first carbonization furnace has an inert atmosphere at a temperature of 300 to 800 ° C., and the flameproof fiber bundle is pre-carbonized while traveling in the inert atmosphere. In addition, the flow of the inert atmosphere in a 1st carbonization furnace may be a parallel direction with respect to the to-be-processed fiber to travel, or a perpendicular direction, and is not specifically limited. As the inert atmosphere, a known inert atmosphere such as nitrogen, argon, or helium can be adopted, but nitrogen is desirable from the viewpoint of economy. The pre-carbonization treatment time is 20 seconds or more with respect to the single fiber fineness of 1 dtex of the flameproof fiber bundle, so that even if the flameproof fiber has a large single fiber fineness, Rapid gas generation accompanying the decomposition reaction is suppressed, and high-quality carbon fibers can be obtained.

(Carbonization treatment)
In the carbonization treatment, the pre-carbonized flame-resistant fiber bundle (pre-carbonized fiber bundle) is charged into a second carbonization furnace for carbonization treatment. In the second carbonization furnace, the maximum temperature is an inert atmosphere of 1000 to 2500 ° C., and the pre-carbonized fiber bundle is carbonized while traveling in the inert atmosphere. . The carbonization treatment time is preferably 0.6 to 3 minutes from the viewpoint of carbon fiber productivity and carbon fiber strength development. In addition, the flow of the inert atmosphere in a 2nd carbonization furnace may be a parallel direction with respect to the to-be-processed fiber to travel, or a perpendicular direction, and is not specifically limited. The inert atmosphere can be selected from the known inert atmospheres exemplified above, but nitrogen is desirable from the viewpoint of economy.

(surface treatment)
The carbon fiber obtained by the carbon fiber production method of the present invention is preferably subjected to electrolytic oxidation surface treatment using an electrolytic solution. Examples of the electrolyte include inorganic acids such as sulfuric acid, nitric acid, phosphoric acid, boric acid and carbonic acid, organic acids such as acetic acid butyric acid, oxalic acid and maleic acid, and alkali metal salts and ammonium salts thereof, or a mixture of two or more thereof. Can be used. The carbon fiber surface after carbonization has tar components sintered and adhered in the firing process or deposited in the microvoids between the graphite crystals, and is dropped from the carbon fiber surface by dipping in an electrolytic bath and performing surface treatment. To do. Here, the amount of electricity required for the electrolytic oxidation treatment can be appropriately selected from the carbon fiber bundle to be applied. By such electrolytic oxidation treatment, the adhesiveness between the carbon fiber and the matrix resin in the composite material can be optimized, and excellent strength characteristics can be expressed. After the surface treatment, a sizing treatment can also be performed in order to give the carbon fiber obtained with a focusing property. As the sizing agent, a sizing agent having good compatibility with the matrix resin of the composite material can be appropriately selected according to the type of the matrix resin to be used.

(Carbon fiber bundle)
By the production method of the present invention, a carbon fiber bundle composed of carbon fibers having a single fiber fineness of 2.4 dtex or more and 5 dtex or less and an average density of the single fibers of 1.7 g / cm ³ or more and 2 g / cm ³ or less is obtained. In the present invention, the cross-sectional shape of the single fiber constituting the PAN-based precursor fiber bundle is similar to the cross-sectional shape of the single fiber constituting the carbon fiber bundle to a certain extent.
According to the production method of the present invention, even if the fineness of the single fiber is increased, the carbonization process causes little decomposition and a high-quality carbon fiber can be obtained. Also, carbon fiber bundles having good resin impregnation properties (large impregnation depth) can be obtained because there is little deformation of single fibers of carbon fibers when the carbon fiber bundles are compressed and gaps between the single fibers are maintained. I can do it.

(Molding)
The carbon fiber bundle thus obtained can be impregnated with a thermosetting resin or a thermoplastic resin, prepregized, and then molded into a composite material. Further, after forming a preform such as a woven fabric, it can be formed into a composite material by a hand lay-up method, a pultrusion method, a resin transfer molding method, or the like. Further, it can be formed into a composite material by injection molding after filament winding, chopped fiber or milled fiber.
The carbon fiber bundle of the present invention is easily impregnated with a thermoplastic resin and exhibits a large impregnation depth. Since the cross section of the single fiber is large and the fiber bundle has the characteristic that it is difficult to cause deformation due to lateral compression, the impregnation of the thermoplastic resin having a high viscosity and difficult to impregnate also proceeds in a very short time. Impregnation depth, which is an index of ease of impregnation of thermoplastic resin, is determined by the following method.
1) A 50 mm × 50 mm square having a melt viscosity of 300 Pa · s at 200 ° C., a 120 μm thick polypropylene film heated on a hot stage so that the surface temperature is 200 ° C., a square of 100 mm × 100 mm, a thickness of 5 mm Place on an iron plate and melt.
2) A carbon fiber bundle adjusted to have a total fineness of 24,000 dtex or more is placed on the melted PP film so as to have a width of 50 mm, and is spread to a width of 50 mm. A square and 5 mm thick iron plate is placed and immediately compressed at 0.2 MPa for 60 seconds, and the sample is taken out and cooled.
3) The prepared sample is embedded in resin, cut and polished, and the impregnation depth is measured as the thickness of the polypropylene impregnated into the carbon fiber bundle with an optical microscope.

Hereinafter, the present invention will be described more specifically with reference to examples. In this example, various characteristics were measured as follows.
<Measurement of total fineness of PAN-based precursor fiber bundle and carbon fiber bundle>
The total fineness of the PAN-based precursor fiber bundle and the carbon fiber bundle was measured according to JIS R 7605.

<Measurement of single fiber fineness of PAN-based precursor fiber bundle and carbon fiber bundle>
Single fiber fineness is the mass (g) per 10000 m of one fiber. Two fiber bundles having a length of 1 m are cut out from a continuous fiber bundle, each mass (g) is measured, and each mass is divided by the number of filaments in the fiber bundle (that is, the number of holes in the die), and then multiplied by 10,000. The average value of the two values obtained in this way was defined as “single fiber fineness”.
<Measurement of density of flame-resistant fiber and carbon fiber>
The density of the flameproof fiber and carbon fiber was measured in accordance with JIS R 7603.

<Measurement of input density to flameproofing process>
The input density to the flameproofing process was obtained from the following formula.
Density to the flameproofing process (dtex / mm) = total fineness of the precursor fiber bundle introduced / total width of the precursor fiber bundle

<Area of inner layer of cross-sectional double structure of flameproof fiber bundle>
The area of the inner layer of the cross-sectional double structure of the flameproof fiber bundle was determined by the following method.
1) Embed the flame-resistant fiber bundle in epoxy resin Epomount 27-771 manufactured by Refine Tech, leave it at room temperature for 24 hours, cure, and cut it so that the fiber cross section can be observed perpendicular to the fiber axis direction. .
2) After preliminarily polishing the cut surface with sandpaper of # 120 to 1200, an alumina suspension (0.3 μm diameter) manufactured by Kasai Shoko Co., Ltd. is included in the polishing cloth and polished for about 10 minutes.
3) The obtained sample is observed using an epifluorescence microscope manufactured by Nikon Corporation. The part where the oxidation reaction has progressed is black, and the part where the oxidation reaction has not progressed appears fluorescent and bright. Magnify this 500 times and take a picture.
4) After binarizing this photograph with Nikon Corporation's image analysis software NIS-Elements, the ratio of the fluorescent coloring portion was calculated in the fiber cross-sectional area, and the area of the inner layer of the cross-sectional double structure Ask for. The analysis of the area of the inner layer is performed using 20 images in which 100 cross-sections of flame-resistant fibers are photographed per sheet.

<Resin impregnation depth>
The resin impregnation depth of the carbon fiber bundle was determined by the following measurement method.
1) A 50 mm × 50 mm square having a melt viscosity of 300 Pa · s at 200 ° C., a 120 μm thick polypropylene film heated on a hot stage so that the surface temperature is 200 ° C., a square of 100 mm × 100 mm, a thickness of 5 mm It was placed on an iron plate and melted.
2) A carbon fiber bundle matched to the total fineness with a total fineness of 24,000 dtex or more is uniformly spread over the melted PP film so as to have a width of 50 mm, and heated to 200 ° C. in advance of 50 mm × 50 mm. A square iron plate having a thickness of 5 mm was placed and immediately compressed at 0.2 MPa for 60 seconds, and the sample was taken out and cooled.
3) The prepared sample was embedded in a resin, cut and polished, and the impregnation depth was measured with an optical microscope as the thickness of the polypropylene impregnated into the carbon fiber bundle.

"Example 1"
An acrylonitrile-based polymer comprising 98.7% acrylonitrile units and 2-hydroxyethyl methacrylate (the amount of carboxylic acid groups is 7.0 × 10 ⁻⁵ equivalent, the intrinsic viscosity [η] is 1.7), polyacrylonitrile-based polymer The polymer was dissolved in DMAc so that the total solid content concentration was 21.2% by weight to obtain a spinning solution of carbon fiber precursor acrylic fiber. Subsequently, it was discharged from a spinneret having a hole number of 3000 into a DMAc aqueous solution (coagulation bath) having a temperature of 38 ° C. and a concentration of 68% to obtain coagulated yarn by a wet spinning method. Next, the coagulated yarn was stretched 7 times while removing the solvent in warm water of 60 ° C to 98 ° C. The drawn yarn was immersed in a 1% aqueous solution of an aminosilicon-based oil, and then dried and densified with a heating roller at 180 ° C. to obtain a carbon fiber precursor acrylic fiber. The single fiber fineness of this PAN-based precursor fiber bundle was 4.0 dtex, the number of filaments was 3000, the total fineness was 12000 dtex, and the fiber density was 1.18 g / cm ³ .
The obtained PAN-based precursor fiber bundle was heated in air at 250 to 290 ° C. under a tension of 1.0 cN / dtex for 90 minutes to convert to a flameproof fiber bundle having a density of 1.41 g / cm ³ .
The area of the inner layer of the double-section cross section of this flameproof fiber bundle was 14.4 μm ² per 1 dtex of single fiber fineness.
This carbonized fiber bundle is heated for 90 seconds in total for 22.5 seconds per 1 dtex of the single fiber fineness of the flameproofed fiber in a nitrogen atmosphere under a tension of 700 ° C. and a tension of 0.1 cN / dtex in a nitrogen atmosphere. It was a bunch. The heating rate at 400 to 500 ° C. in the pre-carbonization treatment was 200 ° C./min.
The obtained pre-carbonized fiber bundle was heated in a nitrogen atmosphere at a maximum temperature of 1350 ° C. under a tension of 0.1 cN / dtex for 1 minute to obtain a carbon fiber bundle. The rate of temperature increase at 1000 to 1200 ° C. in this carbonization treatment was 400 ° C./min.
The obtained carbon fiber bundle was subjected to surface treatment and then a sizing agent was applied. The elongation rate from the flameproofing process to the carbonization process was -3.8%. This carbon fiber bundle had a single fiber fineness of 2.43 dtex, a filament count of 3000, a total fineness of 7290 dtex, and a fiber density of 1.79 g / cm ³ . The impregnation depth of this carbon fiber bundle was 0.12 mm.

"Examples 2 to 4"
For Examples 2 to 4 and Comparative Examples 1 to 6 of the carbon fiber precursor acrylic fiber, flameproofing heat treatment was performed under the processing conditions shown in Table 1. The obtained flame-resistant fiber bundle was subjected to pre-carbonization treatment, carbonization treatment, surface treatment, and sizing treatment under the same conditions as in Example 1 to obtain a carbon fiber bundle.
The carbon fiber density obtained in Examples 2 to 4 is 1.7 g / cm ³ or more and the density is 2.0 g / cm ³ or less, the single fineness is 2.4 dtex or more, the strand tensile modulus is 240 GPa or more, and the strand tensile strength is 3 .5 GPa or more. Further, the impregnation depth of the thermoplastic resin was 0.12 mm or more, indicating a good resin impregnation property.

"Comparative Example 1"
As in Example 1, a carbon fiber precursor fiber bundle having a single fiber fineness of 4.0 dtex and a total fineness of 12000 dtex was used for flame resistance treatment for 50 minutes to convert to a flameproof fiber bundle having a density of 1.41 g / cm ³ . The area of the inner layer of the double-section cross section of this flameproof fiber bundle was 20.2 μm ² per 1 dtex of single fiber fineness.
Thereafter, carbonization was carried out under the same conditions as in Example 1. However, rapid gas generation accompanying the decomposition reaction of the polymer occurred in the carbonization step, and the carbonization step was not passed.

"Comparative Example 2"
As in Example 1, a carbon fiber precursor acrylic fiber bundle having a single fiber fineness of 4.0 dtex and a total fineness of 12000 dtex was used to perform a flameproofing treatment for 90 minutes to convert to a flameproofing fiber bundle having a density of 1.35 g / cm ³ . . The area of the inner layer of the double-section cross-section of this flameproof fiber bundle was 19.7 μm ² per dtex single fiber fineness. Thereafter, carbonization was carried out under the same conditions as in Example 1. However, rapid gas generation accompanying the decomposition reaction of the polymer occurred in the carbonization step, and the carbonization step was not passed.

“Comparative Example 3”
A carbon fiber bundle having a single fiber fineness of 2.34 dtex was used in the same manner as in Example 1 except that the precarbonization heating time was 15 seconds per single fiber fineness of 1 dtex for a total of 60 seconds to obtain a precarbonized fiber bundle. Obtained. The impregnation depth of this carbon fiber bundle was 0.08 mm. Compared to Example 1, the decomposition reaction in the carbonization step was large, and the tow strength was low.

“Comparative Example 4”
As in Example 5, a carbon fiber precursor acrylic fiber bundle having a single fineness of 8.0 dtex and a total fineness of 800 dtex was used to perform a flameproofing treatment for 50 minutes to convert to a flameproofing fiber bundle having a density of 1.41 g / cm ³ . The area of the inner layer of the double-section cross section of this flameproof fiber bundle was 20.2 μm ² per 1 dtex of single fiber fineness.
Thereafter, carbonization was carried out under the same conditions as in Example 1. However, rapid gas generation accompanying the decomposition reaction of the polymer occurred in the carbonization step, and the carbonization step was not passed.

“Comparative Example 5”
Using a carbon fiber precursor acrylic fiber bundle having a single fineness of 2.5 dtex and a total fineness of 60000 dtex, a flameproofing treatment was performed for 70 minutes to convert to a flameproof fiber bundle having a density of 1.41 g / cm ³ . The area of the inner layer of the double-section cross section of this flameproof fiber bundle was 8.7 μm ² per 1 dtex of single fiber fineness. Thereafter, a carbon fiber bundle having a single fiber fineness of 1.38 dtex was used in the same manner as in Example 1 except that the heating time for precarbonization was 24 seconds per 1 fiber fineness of the single fiber fineness, and a total of 60 seconds was used to obtain a precarbonized fiber bundle. Got. The impregnation depth of this carbon fiber bundle was 0.04 mm. Compared with Example 1, the single fiber fineness of the carbon fiber is small, and the impregnation rate of polypropylene is low.

“Comparative Example 6”
As in Comparative Example 5, a carbon fiber precursor acrylic fiber bundle having a single fineness of 2.5 dtex and a total fineness of 60000 dtex was used to perform a flameproofing treatment for 70 minutes to convert to a flameproofing fiber bundle having a density of 1.33 g / cm ³ . . The area of the inner layer of the double-section cross-section of this flameproofed fiber bundle was 18.4 μm ² per dtex single fiber fineness. Thereafter, carbonization was carried out under the same conditions as in Example 1. However, rapid gas generation accompanying the decomposition reaction of the polymer occurred in the carbonization step, and the carbonization step was not passed.

  According to the present invention, it is possible to obtain a high-quality carbon fiber excellent in resin impregnation property, and a carbon fiber-reinforced thermoplastic resin using a thermoplastic resin as a matrix can be stably supplied at high speed.

Claims (2)

Flame-resistant treatment for obtaining a flame-resistant fiber bundle by passing a carbon fiber precursor acrylic fiber bundle having a single fiber fineness of 4 dtex or more through an acidified atmosphere at 200 ° C. to 300 ° C., and the resulting flame-resistant fiber bundle at the highest temperature Is passed through an inert atmosphere at 500 ° C to 900 ° C for heat treatment, and the obtained precarbonized fiber bundle is passed through an inert atmosphere at a maximum temperature of 1200 ° C to 2500 ° C. A carbon fiber bundle manufacturing method for obtaining a carbon fiber bundle having a density of 1.7 to 2 g / cm ³ and a single fiber fineness of 2.4 to 5 dtex by sequentially performing a carbonization treatment by heat treatment. The manufacturing method of the carbon fiber bundle which satisfy | fills.
1) The density of the fibers of the flameproof fiber bundle is 1.37 g / cm ³ or more.
2) The average inner layer area of the flame resistant fiber bundle measured by the following method is 18 μm ² or less with respect to the single fiber fineness 1 dtex of the flame resistant fiber bundle.
<Measurement method of inner layer area of flameproof fiber bundle>
The flame-resistant fiber bundle is embedded in a transparent resin, cut perpendicularly to the fiber axis direction, polished, observed using an epifluorescence microscope, photographed at a magnification of 500 times, and image analysis software. After the valuation treatment, the fluorescent color development partial area is measured to obtain the inner layer area per flame-resistant fiber.
3) In the pre-carbonization treatment, the time for passing through an inert atmosphere at 500 ° C. to 900 ° C. is 20 seconds or more with respect to 1 dtex of the single fiber fineness of the flame-resistant fiber bundle. The method for producing a carbon fiber bundle according to claim 1, wherein the carbon fiber bundle is a carbon fiber bundle having an impregnation depth of 0.12 mm or more measured by the following measurement method.
<Measurement method of impregnation depth>
1) A 50 mm × 50 mm square having a melt viscosity of 300 Pa · s at 200 ° C., a 120 μm thick polypropylene film heated on a hot stage so that the surface temperature is 200 ° C., a square of 100 mm × 100 mm, a thickness of 5 mm Place on an iron plate and melt.
2) A carbon fiber bundle adjusted so that the total fineness becomes 24,000 dtex or more is uniformly spread over the melted PP film so as to have a width of 50 mm, and heated to 200 ° C. in advance of 50 mm × 50 mm. A square and 5 mm thick iron plate is placed and immediately compressed at 0.2 MPa for 60 seconds, and the sample is taken out and cooled.
3) The prepared sample is embedded in resin, cut and polished, and the thickness at which the carbon fiber bundle is impregnated with polypropylene is measured as the impregnation depth with an optical microscope.