JP2005060871A - Method for producing flame-proofed fiber and method for producing carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing flame-proofed fiber and a method for producing carbon fiber therefrom, with quality and productivity compatible with each other through solving problems involved in the conventional technology despite being in the form a large tow. <P>SOLUTION: The method for producing the flame-proofed fiber comprises carrying out a flameproofing treatment of an acrylic filament yarn substantially as a straight tow with a single filament fineness of 0.7-1.3 dTex, a filament count of ≥30,000 and the number of crimps of ≤5/25 mm in an oxidative atmosphere for the flameproofing treatment time t(min) meeting the relationship:39A-7≤t≤67A( wherein, A is the single filament fineness of the acrylic filament yarn ). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing flame-resistant fibers and a method for producing carbon fibers.

  After making an acrylic fiber yarn into a flame-resistant fiber by a flameproofing process in which heat treatment is performed in an oxidizing atmosphere at 200 to 300 ° C., carbon is subsequently formed in a carbonization process in which heat treatment is performed in an inert atmosphere at 1,000 ° C. or higher. It is common to use fibers. The carbon fiber thus obtained is widely used as a reinforcing fiber material for high-performance composite materials for aerospace use, sports / leisure use, etc. due to its excellent mechanical properties.

  In recent years, there has been an increasing demand for applications in general industrial fields such as automobiles, ships, and building materials. Conventional so-called small tow (total fineness less than 21,000 dTex) carbon fiber is excellent in physical properties and quality. However, the manufacturing cost is high, and there is a tendency that it is not frequently used in the industrial field in which cost is important. Carbon fibers that satisfy both quality and productivity are required.

  By the way, the ratio of carbon fiber to the manufacturing cost is large in the flameproofing process having the longest processing time in the manufacturing process, and it is necessary to improve the productivity in order to reduce the cost. However, in the flameproofing process, the acrylic fiber yarn is accompanied by intense heat generation due to the oxidation reaction, so the internal temperature of the acrylic fiber yarn is extremely high, the temperature inside the acrylic fiber yarn becomes extremely higher than the processing temperature, and smoke is generated. It tends to occur. For this reason, production must be carried out at a reduced flameproofing temperature, and there is a problem that it takes a long time to obtain flameproofed fibers that have been sufficiently flameproofed. For this reason, in order to solve the above problem, a small amount of research has been conducted in the small tow. For example, Patent Document 1 discloses a method of defining the temperature of each temperature-controllable zone when flame resistance is achieved using at least four or more temperature-controllable zones in a hot air circulating furnace. The CF performance is low and it is difficult to say that the performance is high, and the productivity is insufficient.

On the other hand, large tow, which is expected to further reduce the cost, has more livestock heat than small tow because of its increased cross-sectional area, so it must be produced at a temperature lower than the flameproofing temperature for small tow. The productivity improvement was more difficult than the small tow. In order to solve such a problem in large tow, Patent Document 2 describes that the cross-sectional shape of the acrylic fiber yarn at the time of flameproofing is maintained at an average flatness defined by the yarn width / yarn thickness ratio in a substantially rectangular shape. Although a method is disclosed, the CF performance obtained is low and it is difficult to say that it is high performance.
Japanese Patent Laid-Open No. 2-139425 Japanese Patent Laid-Open No. 10-266024

  An object of the present invention is to provide a method for producing a flame-resistant fiber and a method for producing a carbon fiber that solves the problems in the prior art and is compatible with both quality and productivity while being a large tow.

  In the present invention, an acrylic fiber yarn consisting essentially of straight tow having a single yarn fineness of 0.7 to 1.3 dTex, a filament number of 30,000 or more and a crimp of 5 threads / 25 mm or less is expressed in the following formula in an oxidizing atmosphere. The gist of the present invention is a method for producing a flame-resistant fiber that is flame-resistant for a flame-resistant treatment time t (minutes) that satisfies the requirements.

39A-7 ≦ t ≦ 67A
A is the single yarn fineness of acrylic fiber yarn (dTex)

  According to the present invention, high-performance and high-quality carbon fibers can be stably supplied at a low cost.

"Acrylic fiber yarn"
The acrylic fiber yarn used in the present invention uses a polymer containing 90% by weight or more of acrylonitrile units as an acrylonitrile-based (co) polymer. The acrylonitrile unit is more preferably 95% by weight or more. A homopolymer or copolymer of acrylonitrile or a mixture of these polymers can be used.

  The acrylonitrile copolymer is a copolymerized product of a monomer that can be copolymerized with acrylonitrile and acrylonitrile. Examples of the monomer that can be copolymerized with acrylonitrile include methyl (meth) acrylate and ethyl (meth) acrylate. , (Meth) acrylic acid esters such as propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, vinyl halides such as vinyl chloride, vinyl bromide, vinylidene chloride, (meth) acrylic acid, Acids having a polymerizable double bond such as itaconic acid and crotonic acid and salts thereof, maleic imide, phenylmaleimide, (meth) acrylamide, styrene, α-methylstyrene, vinyl acetate, and further sodium styrene sulfonate, Allyl sulfonic acid soda, β-styrene sulfonic acid Polymerizable unsaturated monomers containing a sulfone group such as soda and methallyl sulfonic acid soda, polymerizable unsaturated monomers containing a pyridine group such as 2-vinylpyridine and 2-methyl-5-vinylpyridine, etc. However, it is not limited to these.

  Examples of the polymerization method of the acrylonitrile-based (co) polymer include, but are not limited to, redox polymerization in an aqueous solution, suspension polymerization in a heterogeneous system, and emulsion polymerization using a dispersant.

  The acrylonitrile-based (co) polymer solution is spun by a known acrylic fiber yarn spinning method such as wet spinning or dry wet spinning. For example, in normal wet spinning, after spinning, stretching, washing with water, oil agent treatment, and drying densification, post-stretching such as dry heat stretching and steam stretching is performed as necessary. The acrylic fiber yarn preferably does not contain surface defects such as impurities, internal voids, crazes and cracks.

  The acrylic fiber yarn used in the present invention is required to have a single yarn fineness of 0.7 to 1.3 dTex. When the single yarn fineness is less than 0.7 dTex, it becomes difficult to stably spin the acrylic fiber yarn. On the contrary, if the single yarn fineness exceeds 1.3 dTex, the cross-sectional double structure described later becomes remarkable and it is difficult to obtain a high-performance carbon fiber.

  The number of filaments of the acrylic fiber yarn is required to be 30,000 or more, which can improve the productivity, improve the performance by the method of the present invention, and make both compatible.

  The acrylic fiber yarn used in the present invention needs to be a substantially straight tow with a crimp of 5 threads / 25 mm or less. If it exceeds 5 ridges / 25 mm, a buckling deformation called a crimp is imparted. This buckling deformation inherently causes mechanical damage to the acrylic fiber yarn. This induces generation of fluff due to single yarn breakage in the carbon fiber production process, leading to troubles such as winding around the roll, and deterioration of the quality and performance of the obtained carbon fiber.

  In general, the speed of the process for producing acrylic fiber yarns for the production of flame-resistant fibers and carbon fibers is significantly different from the speed of the firing process for firing acrylic fiber yarns into flame-resistant fibers and carbon fibers. The acrylic fiber yarn is supplied to the firing step in a state once wound up on a bobbin, or in a state of being folded and laminated in a box (referred to as cans accommodation).

  When the acrylic fiber yarn used in the present invention is accommodated in a can, the shape of one tow is maintained when the can is accommodated, and when it is pulled out and used, it is divided into a plurality of small tows. It may be an acrylic fiber yarn having a splitting ability in the possible width direction.

"Fireproofing"
The acrylic fiber yarn is subjected to a flameproofing treatment in an oxidizing atmosphere. In order to maximize the quality of the obtained flame-resistant fiber and the quality (strength and elastic modulus) of the carbon fiber obtained through the carbonization treatment, it is necessary to perform the flame-resistant treatment with an optimum flame-resistant treatment time. .

  The phenomenon in which the strength and elastic modulus are maximized by the optimum flameproofing treatment time is closely related to the diffusion state of oxygen into the flameproofed fiber single yarn being flameproofed. That is, the optimum flameproofing treatment time depends on the cross-sectional structure in the single yarn of the flameproofed fiber yarn.

  FIG. 1 shows the relationship between the flameproofing treatment time and the single yarn fineness of the acrylic fiber, which affects the cross-sectional structure in the single yarn of the fiber being flameproofed. When the density of fibers subjected to flame resistance is the same, the shorter the flame resistance treatment time, the more uneven the structure of the single yarn cross section of the fiber being flame resistant, that is, a double section structure. The blackened layer seen in FIG. 1 corresponds to an oxide layer, and oxygen is present in this region. In the same flameproofing treatment time, the thickness of the blackened layer increases as the single yarn fineness decreases, and conversely, the portion where the oxidation reaction has not progressed decreases.

  Therefore, the inventors of the present invention have conducted a flameproofing treatment time t (min) of 39A-7 to 67A (when the above-mentioned acrylic fiber is used and the single yarn fineness is A (dTex) through numerous experiments. It was found that a flame-resistant fiber in which the oxidation reaction appropriately proceeded can be obtained when it is in the range of (min).

  If the flameproofing treatment time is less than 39A-7 (minutes), it is necessary to flameproofing at a high temperature and the cyclization reaction rate is significantly increased, but oxygen diffusion into the single yarn of the fiber being flameproofed However, the strength and elastic modulus of the carbon fiber obtained in the portion where the cross-sectional double structure is developed in the flameproofing process and the oxidation reaction has not progressed are not converted into the highly oriented structure in the subsequent carbonization process are lowered.

  Conversely, if the flameproofing treatment time t exceeds 67A (minutes), it is necessary to flameproofing at a low temperature, and the above-described double structure of the cross section is not exhibited, but oxygen is excessive in the single yarn of the flameproofing fiber. As a result, oxygen is released as carbon monoxide from the fiber being carbonized in the subsequent carbonization step, generating voids, and the strength of the carbon fiber that can be a defect point is reduced.

  If the flameproofing treatment time t (min) is 39A + 3 to 67A-10, there is no expression of a double cross section, and there is no excessive introduction of oxygen into the flameproofing fiber yarn. It is more preferable because of its good properties.

  In the present invention, since the flameproofing treatment takes the longest treatment time in the production process of carbon fiber, the reduction in the cost of carbon fiber production is achieved by performing the flameproofing treatment in a short time and further adding the fiber width to the treatment. We considered increasing the fineness (referred to as input density in the present specification) and improving productivity.

  In the flameproofing treatment, the fiber yarn being flameproofed itself generates heat, and heat is rapidly accumulated in the inside of the fiber. Therefore, the temperature of the hot air applied to the fiber being flame-resistant must be controlled to be lower than the animal heat cutting temperature of the fiber yarn being flame-resistant so that the flame-resistant fiber is not cut by this. The livestock heat cutting temperature becomes higher as the degree of flame resistance of the fiber being flame-resistant increases (the density of the tip during the flame resistance also increases). Furthermore, the livestock heat cutting temperature of the fiber during flame resistance also depends on the input density, and the higher the input density, the lower the livestock heat cutting temperature. In general, the higher the temperature, the higher the reaction rate of flame resistance, and the higher the input density, the greater the rate of heat-cutting of the fiber during flame resistance in order to accelerate the flame resistance reaction and shorten the flame resistance time. Although lower, at a temperature as high as possible, the input density should be increased and the fiber being flameproofed should be flameproofed.

  Accordingly, it is desired to control the temperature to be as high as possible, although it is lower than the temperature as the livestock cutting temperature of the fiber being flame-resistant increases. As a method for enabling such control, a method using a flameproof furnace divided into zones that can be individually controlled in temperature has been conventionally known.

  The more the number of zones that can be controlled with temperature, the shorter the flameproofing time, and when there are many zones, there is room for the heat-cutting temperature of the fiber being flameproofed compared to when there are few. Flame resistance can be achieved at a low temperature, and operation with less trouble is possible with the same flame resistance time.

  However, as the number of zones increases, the price of the flameproofing furnace increases accordingly, and the effect of improving productivity decreases. From the viewpoint of enabling fine temperature control without impairing the effect of improving productivity, the number of zones is preferably 3 to 8, and more preferably 3 to 5.

  It is preferable that the input density of the fibers input to the flameproofing treatment is 2,500 to 6,500 dTex / mm. If it is less than 2,500 dTex / mm, the yarn width increases, the number of yarns of the fiber with respect to the flameproof furnace width decreases, and the equipment productivity decreases. On the other hand, if it exceeds 6,500 dTex / mm, the cross-sectional double structure becomes conspicuous and it becomes difficult to obtain high-performance carbon fibers. Due to heat and runaway reaction, yarn breakage, smoke, etc. are likely to occur, and when the obtained carbon fiber is processed into a prepreg, the openability is likely to occur.

  As a method for controlling the density of the fibers fed into the flameproofing furnace, there are a method of installing a grooved roll outside the flameproofing furnace and a method of installing a comb and a flat roll. Grooved rolls cause fiber fluff during flame resistance. Also, there are rare cases where two fibers enter into one groove due to interference between adjacent fibers that are flameproofed, and a combined yarn is generated. However, since the fiber is twisted by the side wall of the groove, it is easy to cause yarn breakage, smoke, etc. due to heat removal failure.

  On the other hand, the use of a flat roll is preferable in terms of process stability because there is no occurrence of twisting and twisting due to groove jumping. In the case of a flat roll, it is preferable to control the acrylic fiber by performing an entanglement process by a known technique. The entanglement treatment condition is appropriately determined depending on the total fineness of the acrylic fiber yarn.

  The wind direction in the flameproofing furnace is parallel to the plane formed by the flame resistant fiber yarns in the middle of the multiple spindles, and is parallel to the flameproofing fiber yarns in the middle, perpendicular to the perpendicular flow, Examples include, but are not limited to, a vertical flow that is perpendicular to the surface formed by the flame resistant fiber yarn in the middle of the spindle and perpendicular to the flame resistant fiber yarn in the middle. The wind speed is preferably 0.3 to 5 m / scc. If it is less than 0.3 m / sec, it becomes difficult to obtain a heat removal action by the wind in the flameproofing furnace, and smoke due to poor heat removal tends to occur. If it exceeds 5 m / sec, the fluttering of the flame-resistant fiber yarn due to the wind in the flame-proofing furnace becomes large, and single yarn breakage due to the contact of the flame-resistant fiber yarn tends to occur.

The density of the flameproof fiber yarn after completion of the flameproofing treatment is preferably 1.33 to 1.40 g / cm ³ , and preferably 1.34 to 1.37 g / cm ³ . If it is less than 1.33 g / cm ³ , the flame-resistant yarns are fused in the subsequent carbonization step and fluffing occurs, so that it is difficult to obtain high-performance and high-quality carbon fibers. If it exceeds 1.40 g / cm ³ , the strength tends to decrease due to excessive introduction of oxygen into the flame-resistant fiber yarn.

  The flame resistant fiber yarn obtained by the above method is preferably carbonized in an inert atmosphere at 1,000 ° C. or higher. When the temperature is lower than 1,000 ° C., it is difficult to obtain high-performance carbon fibers.

  The flame-resistant fiber yarn obtained by the above method is preferably heat-treated in an inert atmosphere at 300 ° C. to 1,000 ° C. for 0.5 minutes or more between the flame resistance treatment and the carbonization treatment. If the time is less than 0.5 minutes, fluffing tends to occur, which may lead to yarn breakage, and the product quality is poor, making it difficult to obtain high-performance carbon fibers.

  The carbon fiber thus obtained can be further subjected to surface treatment, sizing application, and the like by a conventionally known technique as necessary.

  Hereinafter, the specific structure of the manufacturing method of the flameproof fiber of this invention is demonstrated based on an Example. Strand strength and strand elastic modulus were measured by the method of JIS R7601. In Table 1, the strand strength and the strand elastic modulus were expressed as CF strength and CF elastic modulus, respectively.

Also, the CF performance in Table 1 shows that the strand strength (CF strength) is
In case of 5.0 (GPa) or more → ◎
In the case of 4.7 to 4.9 (GPa) → ○
For 4.5 to 4.6 (GPa) → △
4.4 (GPa) or less → ×
Respectively.

Productivity is a numerical value expressed by dividing the input density (dTex / mm) by the flameproofing treatment time (minutes).
If 100 or more → ◎
For 60-99 → ○
In case of 45-59 → △
44 or less → ×
Respectively.

More comprehensively than CF performance and productivity,
If either one is × → ×
If both are ◎ → ◎
Otherwise → ○
Respectively.

An acrylic fiber yarn having a single yarn fineness of 1.2 dTex, a filament number of 50,000, a total fineness of 60,000 dTex, and a crimped crest / 25 mm was obtained by a wet spinning method. The acrylic fiber yarn was subjected to flameproofing treatment continuously for 60 minutes in total at an input density of 6,000 dTex / mm and flameproofing treatment temperatures of 226 ° C, 229 ° C, 234 ° C, 239 ° C, and 244 ° C for 12 minutes each. A flame-resistant fiber yarn having a density of 1.36 g / cm ³ was obtained. The process tension during the flameproofing treatment was 136 × 10 ⁻³ cN / dTex, and the shrinkage of the yarn during the treatment was restricted.

Subsequently, while applying a tension of 68 × 10 ⁻³ cN / dTex in a carbonization furnace composed of a nitrogen atmosphere having a temperature distribution of 300 to 700 ° C., the shrinkage of the flameproof fiber yarn is limited. A pre-carbonization treatment is applied for 5 minutes, followed by a tension of 68 × 10 ⁻³ cN / dTex in a nitrogen atmosphere carbonization furnace having a temperature distribution of 1,000 to 1,300 ° C. Carbon fibers were produced by subjecting the pre-carbonized fiber yarns to a carbonization treatment for 1.5 minutes while limiting the shrinkage of the pre-carbonized fiber yarns. The performance is shown in Table 1.

In Example 1, the input density of the acrylic fiber yarn was 3,000 dTex / mm, and the flameproofing treatment temperatures were 240 ° C., 246 ° C., 251 ° C., 255 ° C., and 262 ° C. for 9 minutes each for 45 minutes in total. The treatment was performed to obtain a flame-resistant fiber yarn having a density of 1.35 g / cm ³ . All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

In Example 1, with an input density of acrylic fiber yarns of 6,000 dTex / mm, flame resistance was continuously made for 75 minutes for a total of 75 minutes at a flame resistance treatment temperature of 222 ° C., 227 ° C., 232 ° C., 237 ° C., and 242 ° C., respectively. The treatment was performed to obtain a flame-resistant fiber yarn having a density of 1.36 g / cm ³ . All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

<Comparative Example 1>
In Example 1, flame resistance treatment was continuously performed for 35 minutes in total for 7 minutes each at 232 ° C., 238 ° C., 243 ° C., 248 ° C., and 253 ° C. at a flame resistance treatment temperature of 6,000 dTex / mm of acrylic fiber yarns. As a result, thread breakage occurred and carbon fiber could not be produced.

<Comparative example 2>
In Example 1, flame resistance treatment was continuously performed for 90 minutes in total at an injection density of 6,000 dTex / mm of acrylic fiber yarns at a flame resistance treatment temperature of 222 ° C., 226 ° C., 230 ° C., 234 ° C., and 238 ° C. for 18 minutes each. A flame resistant fiber yarn having a density of 1.36 g / cm ³ was obtained. All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

<Comparative Example 3>
An acrylic fiber yarn having a single yarn fineness of 1.2 dTex, a filament number of 12,000, a total fineness of 14,400 dTex, and a crimped crest / 25 mm was obtained by a wet spinning method. With this acrylic fiber yarn input density of 1,800 dTex / mm, flameproofing treatment is performed continuously for 50 minutes in total for 10 minutes each at a flameproofing treatment temperature of 225 ° C, 234 ° C, 244 ° C, 249 ° C, 260 ° C, A flame-resistant fiber yarn having a density of 1.35 g / cm ³ was obtained. All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

<Comparative example 4>
In Comparative Example 3, the flame resistance treatment was continuously performed for 35 minutes in total for 7 minutes each at 235 ° C., 245 ° C., 250 ° C., 255 ° C., and 265 ° C. at an injection density of 1,800 dTex / mm of acrylic fiber yarn. And a flame resistant fiber yarn having a density of 1.35 g / cm ³ was obtained. All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

<Comparative Example 5>
In Comparative Example 3, the flame resistance treatment was continuously applied for 90 minutes in total, with an acrylic fiber yarn input density of 1,800 dTex / mm and flame resistance treatment temperatures of 224 ° C., 229 ° C., 234 ° C., 237 ° C., and 242 ° C. for 18 minutes each. A flame resistant fiber yarn having a density of 1.36 g / cm ³ was obtained. All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

An acrylic fiber yarn having a single yarn fineness of 0.8 dTex, a filament number of 50,000, a total fineness of 40,000 dTex, and a crimped crest / 25 mm was obtained by a wet spinning method. With this acrylic fiber yarn input density of 4,000 dTex / mm, the flameproofing treatment temperature is continuously 237 ° C, 241 ° C, 246 ° C, 251 ° C, 256 ° C for 8 minutes each, for a total of 40 minutes, A flame-resistant fiber yarn having a density of 1.35 g / cm ³ was obtained. All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

<Comparative Example 6>
In Example 4, flame resistance treatment was continuously performed for 20 minutes in total at a density of 4,000 dTex / mm of acrylic fiber yarns and at flame treatment temperatures of 235 ° C., 245 ° C., 255 ° C., 265 ° C., and 275 ° C. for 4 minutes each. As a result, thread breakage occurred and carbon fiber could not be produced.

<Comparative Example 7>
In Example 4, the flame resistance treatment was continuously applied for 90 minutes in total at an injection density of 4,000 dTex / mm at an acrylic fiber yarn temperature of 225 ° C, 229 ° C, 233 ° C, 237 ° C, and 241 ° C for 18 minutes each. A flame resistant fiber yarn having a density of 1.35 g / cm ³ was obtained. All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

<Comparative Example 8>
An acrylic fiber yarn having a single yarn fineness of 0.8 dTex, a filament count of 12,000, a total fineness of 9,600 dTex, and a crimped crest / 25 mm was obtained by a wet spinning method. With this acrylic fiber yarn input density of 1,600 dTex / mm, flameproofing treatment was continuously performed for 40 minutes in total for 8 minutes each at a flameproofing treatment temperature of 226 ° C, 236 ° C, 246 ° C, 256 ° C, 266 ° C, A flame-resistant fiber yarn having a density of 1.35 g / cm ³ was obtained. All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

<Comparative Example 9>
In Example 1, the acrylic fiber yarn having 10 crimps / 25 mm crimp was subjected to the same flameproofing treatment as in Example 1 to obtain a flameproof fiber yarn having a density of 1.35 g / cm ³ . All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

<Comparative Example 10>
In Example 1, the flame-proofing treatment was carried out continuously for 90 minutes in total at an injection density of 7,500 dTex / mm and a flame-proofing temperature of 222 ° C., 225 ° C., 229 ° C., 233 ° C. and 236 ° C. for 18 minutes each. A flame resistant fiber yarn having a density of 1.36 g / cm ³ was obtained. All other conditions were the same as in Example 1 to produce a carbon fiber. The performance is shown in Table 1.

In Example 1, the same flameproofing treatment was performed at an input density of 6,000 dTex / mm of the acrylic fiber yarn to obtain a flameproofed fiber yarn having a density of 1.36 g / cm ³ . The process tension during the flameproofing treatment was 136 × 10 ⁻³ cN / dTex, and the shrinkage of the yarn during the treatment was restricted.

Subsequently, in a carbonization furnace composed of a nitrogen atmosphere having a temperature distribution of 300 to 700 ° C., a tension of 68 × 10 ⁻³ cN / dTex is applied, and the shrinkage of the flameproof fiber yarn is limited. A pre-carbonization treatment is applied for 8 minutes, followed by a tension of 68 × 10 ⁻³ cN / dTex in a carbonization furnace composed of a nitrogen atmosphere having a temperature distribution of 1,000 to 1,300 ° C. The carbon fiber was produced by subjecting it to a carbonization treatment for 0.8 minutes while restricting the shrinkage of the pre-carbonized fiber yarn. The performance is shown in Table 1.

  ADVANTAGE OF THE INVENTION According to this invention, although it is large tow, the problem in a prior art can be solved and the manufacturing method of the flame resistant fiber and the manufacturing method of carbon fiber which can make quality and productivity compatible can be provided.

It is a correlation diagram of the flameproofing process time which affects the cross-sectional structure in the single yarn of a flameproof fiber yarn, and the single yarn fineness of an acrylic fiber yarn.

Explanation of symbols

A ... Blackening layer B ... Unpromoted part of oxidation reaction

Claims (6)

Flame resistance of acrylic fiber yarns consisting essentially of straight tows with a single yarn fineness of 0.7-1.3dTex, 30,000 filaments, and 5 crimps / 25mm or less satisfying the following formula in an oxidizing atmosphere A method for producing a flame-resistant fiber, which is flame-resistant for a treatment time t (minutes).
39A-7 ≦ t ≦ 67A
A is the single yarn fineness of acrylic fiber yarn (dTex) Flame resistance of acrylic fiber yarns consisting essentially of straight tows with a single yarn fineness of 0.7-1.3dTex, 30,000 filaments, and 5 crimps / 25mm or less satisfying the following formula in an oxidizing atmosphere A method for producing a flame-resistant fiber, which is flame-resistant for a treatment time t (minutes).
39A + 3 ≦ t ≦ 67A-10
A is the single yarn fineness of acrylic fiber yarn (dTex)   The method for producing flame-resistant fibers according to claim 1 or 2, wherein when the acrylic fiber yarns are flame-resistant in an oxidizing atmosphere, the input density of the acrylic fiber yarns is 2,500 to 6,500 dTex / mm.   The method for producing flame-resistant fibers according to any one of claims 1 to 3, wherein a flame-resistant furnace in which the rolls installed on both sides thereof are flat rolls is used as the flame-resistant furnace used for the flame resistance treatment.   The manufacturing method of the carbon fiber which carbonizes the flameproof fiber obtained by the method of any one of Claims 1-4 in an inert atmosphere of 1,000 degreeC or more.   6. The method for producing carbon fiber according to claim 5, wherein the heat treatment is performed in an inert atmosphere at 300 ° C. to 1,000 ° C. for 0.5 minutes or more between the flameproofing treatment and the carbonizing treatment.

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