JPS59106522A - Production of acrylic carbon fiber bundle having improved properties - Google Patents

Abstract

PURPOSE:To obtain an acrylic carbon fibre bundle having improved mechanical properties, especially tensile strength and elongation, by converting an acrylic fiber bundle to give an oxidized yarn bundle, heating it in an inert atmosphere until it reaches a particular specific gravity. CONSTITUTION:An acrylonitrile polymer fiber bundle is heated in an oxidizing atmosphere at 210-300 deg.C, and converted into an oxidized fibre bundle having >=2.8g/d tensile strength, >=10% tensile elongation, 1.25-1.38 specific gravity, 3.5-7% equilibrium water content, and low degree of oxidation. This oxidized fiber bundle is heated in an inert atmosphere of nitrogen, argon, etc. having the maximum temperature of >=1,200 deg.C at 50-300 deg.C set rate of heating until the specific gravity of the fiber reaches 1.45, it is then heated further in the inert atmosphere so that the specific gravity reaches >=1.75, to give the desired acrylic carbon fiber bundle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing carbon fiber bundles with excellent mechanical properties from acrylonitrile fiber bundles.

Conventionally, composite materials using carbon fiber as reinforcing fibers have been used in a wide range of applications as m-building materials due to their excellent mechanical properties, especially specific strength, specific modulus, electrical, and chemical properties. In fields where lightness and durability (reliability) are strongly required, such as for aerospace, automobiles, and shipboard applications, acrylic carbon fibers that use acrylonitrile polymer fibers as precursor fibers are used. Acrylic carbon fibers, which are widely used and have improved mechanical properties, are being studied to meet the above requirements.

However, in general, the method for producing acrylic carbon Ili fibers uses acrylic fibers as raw materials and
After converting the fibers into so-called flame-resistant fibers by heating in an oxidizing atmosphere such as air at 50°C,
The method employed is to carbonize the material by heating it in an inert atmosphere such as nitrogen at 600° C., and if necessary, further heat it in an inert atmosphere at a high temperature to form graphite fibers.

However, in the above carbon fiber manufacturing method, especially in the step of heating in the oxidizing atmosphere, acrylic mH undergoes complex reactions such as intramolecular cyclization and intermolecular crosslinking, resulting in thermal decomposition products. In addition to generating carbon fibers and tar-like substances, physical and chemical changes closely related to the physical properties of carbon fibers, such as partial heat storage in the carbon fibers and fusion between single fibers, occur. Are known.

Japanese Patent Publication No. 51-6244 discloses that acrylic fibers are oxidized in air to reduce damage to treated fibers in the oxidation process and to produce carbon fibers in a short time with high yield. Flame-resistant yarn with a content of 5 to 8%, and 320 to 8%
Method of heat treatment at 400°C for 30 seconds or more and then heat treatment in an inert atmosphere, and JP-A-57-2541
In Publication No. 8, the fiber density of acrylic fibers is mainly 459/c.
300~ in an inert atmosphere after flame resistant to i or more
Methods have been proposed to produce lightweight, high-performance carbon fibers by heating at a heating rate of 500°C/min or less at 800°C, and then carbonizing by heating to 800°C or higher. .

Although these proposals may be effective to some extent for their respective purposes, the inventors of the present invention have conducted extensive studies on improving the mechanical properties of carbon fibers, and have developed a method for producing the above-mentioned acrylic carbon fibers. discovered that the physical properties of carbon fibers obtained by combining the conditions of the oxidation or flame-retardant process with the initial carbonization treatment conditions before completely carbonizing the oxidizable fibers or flame-retardant fibers were significantly improved, and the present invention We have come to do this.

That is, an object of the present invention is to provide a method for producing carbon fibers having excellent mechanical properties, particularly tensile strength and elongation. The object of the present invention is to produce acrylic fibers each having a tensile strength and elongation of 2.8 s/d.
oxidized 11i fiber with a specific gravity of 1.25 to 1.38 and an equilibrium moisture content of 3.5 to 7%. This can be achieved by heating the fibers at a heating rate of 50 to 50 b until the specific gravity of the fibers reaches 1.45, and then continuing to heat the fibers until the specific gravity reaches at least 1.75.

In other words, the feature of the present invention is that it has a specific tensile strength and elongation, and a specific gravity of 1.25 to 1.38. Equilibrium moisture content is 3.5-7%,
Oxidized fibers, which can also be called incompletely flame-resistant yarns with a low degree of oxidation, preferably 4 to 5%, are heated in an inert atmosphere at at least 1.200°C to convert them into carbon fibers with a specific gravity of 1.75 or more. In this process, the temperature is heated at a heating rate of 50 to 50 b until the specific gravity of the fiber reaches 1.45. By this method, the high strength and elongation of carbon fibers, which is the objective of the present invention, was achieved for the first time.

The requirements of the present invention are that the tensile strength is 2.89/d or more, preferably 3.3 s/d or more, the elongation is 10% or more, the specific gravity is 1.25 to 1.38, and the equilibrium moisture content is 3. 5-7
%, preferably 4 to 5%, acrylonitrile (hereinafter referred to as AN) 94% is used for acrylic fibers.
~99.8 mol% of vinyl monomers that are copolymerizable with the AN and have the ability to promote flame resistance, such as acrylic acid, methacrylic acid, itaconic acid, etc., and other vinyl monomers that impart silk-spinning properties. Wet or Wet and dry spinning
It can be obtained by appropriately combining steps such as washing with water, stretching, drying, and heat setting.

In addition, the tensile strength and elongation are 2. El/d or more and 10
% or more, heating conditions in an oxidizing atmosphere are important in order to obtain a flame-resistant yarn with excellent physical properties. It is preferable to perform this under a tension of 0.05 to 0.5'il/d.

At this time, it is desirable to raise the temperature in stages to prevent fusion between single yarns or to shorten the flame resistance time.

The flame resistance time depends on the type and concentration of oxidizing atmosphere! Unfortunately, it is necessary to optimize the copolymerization composition, single yarn denier or total denier, etc., but in any case, by selecting such polymerization, spinning and flame resistance conditions, the above-mentioned specific gravity and equilibrium moisture content can be achieved. But each is 1.25～
1.38. It is essential to obtain incompletely oxidized fibers with 3.5 to 7% flame resistance.

The tensile strength and elongation thus obtained are 2.89/d and 10% or more, respectively, and the specific gravity and equilibrium moisture content are 1.
．． 25-1.38.3.5-7% oxidized fibers have insufficient degree of oxidation for conventional so-called flame resistant yarns, but are then oxidized in an inert atmosphere with a maximum temperature of at least 1.200 °C, e.g. Heated in an atmosphere of nitrogen, helium, argon, etc. When heating in this inert atmosphere, the heating rate should be set at 50 to 30 °C until the specific gravity of the fiber is 1.45.
Set within the range of 0℃. That is, the heating temperature is 300
When the temperature exceeds ℃/min, a large amount of microvoid is generated in the fiber due to the rapid generation of cracked gas due to the rapid thermal decomposition reaction, making it difficult to obtain carbon 1IiH with excellent mechanical properties. be. Conversely, even if the heating rate is lower than 50°C/min, carbon! The effect of improving the strength and elongation properties of 1iIIIt is saturated, and the length of the heating furnace becomes longer than necessary or the firing yarn speed becomes slower than necessary, which is not economically advisable. The fibers having a specific gravity of 1.45 or more obtained as described above are further heated in an inert atmosphere to have a specific gravity of 1.45 or more.
．． Preferably when converting to carbon fiber of 75 or more! It is preferable that the temperature increase rate while the specific gravity of the li group rises from 1.60 to 1.75 is 00°C/min or less, thereby producing carbon fibers with excellent mechanical properties with few microvoids. However, even if the temperature increase rate during this period is set to 100°C/min or higher, the effect of improving the mechanical properties of carbon fibers is small and economically disadvantageous. It is unsuitable for engineering In.

When manufacturing carbon fiber industrially, it is economically advantageous to pull together a large total denier oxidized fiber bundle or multiple oxidized fiber bundles, combine them, and perform carbonization treatment. The mechanical properties of the resulting carbon fiber bundle decrease as the total denier of the fiber bundle increases, so if the denier of the oxidized fiber bundle or the spliced oxidized fiber bundle exceeds 15,000 deniers, the tensile strength will increase to 400K.
It becomes difficult to obtain carbon i-fibers having excellent mechanical properties of g/mA or higher. However, as in the present invention, the heating rate while the specific gravity of the fiber increases from 1.45 to 50~b, and the heating rate while the specific gravity increases from 1.60 to 1.75 from 100~b. It becomes possible to convert oxidized fiber bundles with a total denier of more than 15,000 deniers into carbon fibers having excellent horn properties.

The moisture content of the flame-resistant yarn was measured by the following method. That is, about 2
The flame-resistant yarn No. 9 was collected and placed in a weighing bottle, and with the weighing bottle opened, the flame-resistant yarn was left in a desiccator containing an in-phase coexistence ammonium sulfate aqueous solution at the bottom for about 16 hours at room temperature to allow the flame-resistant yarn to absorb moisture.

The weight of the flame-resistant thread taken out from the desiccator is quickly piled up, and the weight is set as Wl. Put the above flame-resistant thread into a weighing bottle,
Dry in an open drying mold at 120° C. for 2 hours, then quickly stopper the weighing bottle, quickly transfer it to a desiccator containing phosphorus pentoxide at the bottom, and leave it to cool in the desiccator for about 5 minutes. After cooling, it is taken out from the weighing bottle, and the weight of the dry flame-resistant yarn is quickly piled up to give a weight of Wo.

Ru.

The specific gravity of the flame-resistant yarn was measured by the following method (Archimedes method). That is, take 1 m of flame-resistant thread and put it in a weighing bottle.
Dry the weighing pin in a drying mold at 160°C for 30 minutes with the cap open, then quickly cap the weighing bottle, transfer it to a desiccator containing phosphorus pentoxide at the bottom, and leave it to cool in the desiccator for about 30 minutes. do. After cooling, take it out from the weighing bottle and quickly weigh the dry flame-resistant yarn. After degassing the weight,
After standing in ethyl alcohol for 30 seconds, submerged type I
Measure W3. The liquid ratio type of ethyl alcohol is measured with a Baume hydrometer, and its specific gravity is defined as ρL. The specific gravity of the flame-resistant yarn is as follows: Examples 1 to 4, Comparative Examples 1 to 3 A dimethyl sulfoxide (DMSO) solution of an acrylic copolymer containing 99.0 mol% of acrylonitrile and 1.0 mol% of ammonium methacrylate was used as a spinning stock solution. The fibers were wet-spun in a DMSO-water bath using a conventional method to produce an acrylic fiber bundle having a single yarn fineness of O denier and a total number of filaments of 12,000.

This III bundle was used as a precursor in air at 240°C.
．． The flameproofing treatment was performed under a tension of 29/d for about 55 minutes to obtain an oxidized fiber bundle having an equilibrium moisture content of 4.5%, a specific gravity of 1.31, a strength of 3.59/d, and an elongation of 11.1%.

The above oxidized fiber bundle was heated linearly from 350℃ to 750℃■
In a nitrogen atmosphere with an increasing temperature profile, the fibers are cut at the furnace exit while being processed continuously at a yarn speed of 500°C/min. 1i
As a result of extracting the navy blue from the furnace inlet side and tracing the specific gravity of the obtained fiber in the longitudinal direction of the fiber, ! The specific gravity of a fiber is oxidized lIa
There was a rapid increase from 1.31 to 1.45 for dark blue, and a relatively slow increase from 1.45 to 1.60. Roughly, the specific gravity is 1.31 to 1.45.
The sudden change in ambient temperature from 350°C to 4.
It corresponded to a temperature range of 50°C.

Based on the above description, oxidized m-fibers were prepared at 35% in nitrogen atmosphere.
After heat treatment by changing the heating rate in the temperature range of 0 to 450°C as shown in Table 1, the heating rate was 1.050 to 1.0°C in a nitrogen atmosphere with a temperature profile of a maximum temperature of 1,300'C.
．． The temperature increase rate in the 150°C region was 500°C/min.
It was heat treated and converted into carbon fiber bundles.

After electrolytic surface treatment of each carbon fiber bundle obtained, 4J
l5R-7601-1980 (resin with Chissonox 2
21/Boron trifluoride monoethylamine/Acetone = 1
The strand strength was measured using 00/3/4) and the results are shown in Table 1.

Table 1 Examples 5 to 8, Comparative Examples 4 to 6 The oxidized fiber bundle obtained in Example 1 was heated to a maximum temperature of 75
350 ~ in a nitrogen atmosphere with a temperature profile of 0 °C
A pre-carbonized fiber bundle was obtained by heat treatment at a heating rate of 200°C/min in a temperature range of 450°C.

The above pre-carbonization treatment! 1i paper bundle from 1,000℃ to 1,30℃
In a nitrogen atmosphere with a linearly increasing temperature profile at 0'C1:, the fibers are processed continuously at a yarn speed of 700°C/min during which the temperature rises, and the fibers are processed at the furnace outlet side. After cutting, the fibers were instantly pulled out from the furnace inlet side, and the specific gravity of the obtained fibers was tracked in the longitudinal direction of the fibers. As a result, the specific gravity of U & miscellaneous rose sharply from 1.60 to 1.75, and then From 1.75 to 1.80, it rose relatively slowly. Furthermore, the reason why the specific gravity suddenly changed from 1.60 to 1.75 was because the ambient temperature was 1.050℃ to 1.75℃.
It corresponded to a temperature range of 150°C. Based on the above facts, the pre-carbonized fiber bundle was heated at 1.050°C to 1.1°C in a nitrogen atmosphere.
The heating rate in the temperature range of 50°C was changed as shown in Table 2, and the carbon fiber bundle was converted into a carbon fiber bundle by heat treatment at a maximum temperature of 1.300°C.

After each of the obtained carbon fiber bundles was subjected to electrolytic surface treatment, the strand strength was measured in the same manner as in Example 1, and the results are shown in Table 2.

Table 2 Examples 9 to 14, Comparative Examples 7 to 8 A dimethyl sulfoxide (DMSO) solution of an acrylic copolymer containing 98.8 mol% acrylonitrile and 1.2 mol% ammonium acrylate was used as a spinning stock solution and D
Wet-spun in MSO-water bath, single yarn yarn 1 denier,
An acrylic i-fiber bundle having aooo number of 1-tal filaments was prepared.

Using this fiber bundle as a precursor, we
．． Flame resistance time from 15 minutes to 100 minutes under tension of 2'a/d
8 shown in Table 3.
Different types of oxidized fiber bundles were created. Table 3 also lists the tensile strength and elongation, specific gravity, and equilibrium moisture content of these eight types of oxidized fiber bundles. After heating these oxidized m-fibers in a nitrogen atmosphere at a heating rate of 150°C/min in the temperature range of 350 to 450°C and a heating rate of 850°C/min in the temperature range of 450°C to 700°C, the maximum temperature was 1. Heat treatment in a nitrogen atmosphere with a temperature profile of 300°C at a heating rate of 500°C/min in the 1,050°C to 1,150°C range,
Converted to carbon fiber bundles.

Each obtained carbon fiber bundle was subjected to electrolytic surface treatment 1 [after J l5
R-7601-1980 (Chissonox 221 resin)
/3 boron monoethylamine fluoride/acetone = 10
Strand strength was measured using 0/3/4). The results are also shown in Table 3.

Table 3

Claims (1)

[Scope of Claims] (1) Acrylonitrile polymer fiber bundle of 210~
At least 2.
89/d and tensile strength elongation of 10% or more, 1.25 ~
The oxidized fiber bundle is converted into an oxidized fiber bundle having a specific gravity in the range of 1.38 and an equilibrium moisture content in the range of 3.5 to 7%, and the oxidized fiber bundle is heated in an inert atmosphere at a maximum temperature of at least 1.200°C. An advantage characterized in that the heating rate is set within the range of 50 to 100 b yen to heat the fibers until the specific gravity reaches 1.45, and then heating is continued to reach the specific gravity of at least 1.75. A method for producing an acrylic carbon fiber bundle having excellent performance. (2. In claim 1, the specific gravity is 1.60
A method for producing an acrylic carbon fiber bundle having excellent performance, comprising the step of converting fibers that have reached a temperature of 100 to 1.75 m to a specific gravity of 1.75 m at a heating rate of 100 to 1. (3) In the step of converting an oxidized fiber bundle into a carbon fiber bundle in claim 1,
A method for producing an acrylic carbon fiber bundle having excellent performance in which the total denier of the aggregate of combined oxidized fiber bundles is 15,000 denier or more.