JPS62117814A - Acrylic fiber precursor for high-strength and high-modulus carbon fiber and production thereof - Google Patents

Abstract

PURPOSE:An acrylic fiber precursor, having a specific value or more or tensile strength and tensile modulus and useful for obtaining high-strength and high- modulus carbon fibers. CONSTITUTION:A solution of an acrylonitrile based polymer containing >=90% acrylonitrile is extruded through a spinneret, passed through an inert atmosphere and introduced into a coagulation bath to form a filament yarn consisting of water-swelled fibers having voids with <=100Angstrom diameter. An oiling agent is then applied to the yarn, which is dried, densified and drawn at >=100 deg.C at >=7 times draw ratio. As a result, the aimed precursor having >=0.3g/denier tensile strength and >=2.0g/denier tensile modulus at 240 deg.C is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an acrylic fiber precursor for producing high-strength, high-modulus carbon fibers, that is, an acrylic fiber useful as a raw material for producing carbon fibers, and a method for producing the same.

(Prior Art) Conventionally, acrylic fibers and carbon fibers have been widely used as precursor fibers for producing carbon fibers.

That is, in the production of carbon fibers, acrylic fibers are used as raw materials, and the fibers are converted into stabilized fibers by heat treatment in an oxidizing atmosphere maintained at 200 to 300°C. A method of heating and carbonizing in an inert atmosphere at a temperature of at least 1000° C. is widely used industrially.

The carbon pIi fibers obtained in this way are mixed with so-called matrix materials such as resins and metals or composite materials (
It is used as a structural material by forming composites. This carbon fiber has advanced mechanical strength properties, heat resistance, electrical properties, and microbial resistance properties, so it is used in aerospace structural components such as airplanes and rockets, and sports materials such as golf clubs, tennis rackets, and fishing rods. It is widely used and produced as a reinforcing fiber in composites for supplies.

In recent years, studies have been conducted to further improve its performance, particularly tensile strength, and at the same time maintain a high tensile modulus for use in fields that require higher performance characteristics, such as primary structural components of aircraft. Demand for improved performance of carbon fibers is becoming stronger and stronger.

In response to these demands, many proposals have been made in the past, but even if attempts were made to improve or improve the tensile strength of carbon fibers in accordance with these proposals, no improvement or improvement in the tensile modulus was observed. On the other hand, when trying to improve or improve the tensile modulus, the problem often arises that the tensile strength actually decreases. For example, JP-A-60-88126 states that the tensile modulus of carbon fiber depends on the carbonization temperature;
It has been technically described and explained that by increasing the final heating temperature in the carbonization step, the tensile modulus of the resulting carbon fiber increases, but as the modulus increases, the tensile strength decreases.

Therefore, in the above-mentioned Japanese Patent Application Laid-Open No. 60-8812'6, instead of increasing the temperature in the carbonization step, oxidation treatment is performed under a specific elongation until a specific density is reached, and then in an inert atmosphere. A method has been proposed in which carbonization is carried out in two or more stages under elongation and tension.

However, according to the inventors' investigation,
If the elongation is increased in an attempt to further bring out the effect of the elongation of the precursor fiber in the oxidation process, it may be necessary to There is a limit to its effectiveness, and unless a specific precursor is used, if a certain elongation ratio is exceeded, part of the precursor yarn will break, causing fluff and a significant drop in quality. It was found that the effect did not appear on the quality of the carbonized yarn even if the carbonized yarn was applied.

In addition, the tensile strength and tensile modulus of the above acrylic fiber precursor are the values measured at temperature and humidity around room temperature, which is used to conventionally measure the tensile strength and tensile modulus of clothing fibers. The first step in the process, oxidation treatment, is performed under extremely harsh conditions, typically at a high temperature of 200 to 300 degrees Celsius, compared to the conventional heat treatment at room temperature for clothing fibers that has been widely used. In this case, the tensile strength and tensile modulus of the acrylic fiber precursor rapidly decrease as the temperature rises during this process, and in addition, carbon fibers having higher tensile strength and tensile modulus are removed from the precursor. In order to produce this, it is necessary to elongate or tension the precursor in the above-mentioned severe oxidation process, and to oxidize the fibers without adhering or fusing them to each other through this heating.
It can be said that the fiber properties of the precursor at around room temperature have no meaning.

The present invention is capable of achieving excellent fiber properties that exceed conventional standards only by measuring the fiber properties required for such acrylic fiber precursors for carbon fiber production based on measurement standards that are completely different from ordinary fiber properties. Based on the prediction that we would be able to obtain carbon fiber with physical properties, we carried out intensive studies,
It was discovered that the tensile strength and tensile modulus values of an acrylic fiber precursor measured under a temperature condition of 240°C as a measurement standard are extremely important for the performance as an acrylic fiber precursor for carbon fiber production, and the present invention I've reached that point.

(Problems to be Solved by the Invention) An object of the present invention is to use an acrylic fiber precursor, that is, as an acrylic fiber raw material for manufacturing carbon fiber, to have highly dense physical properties that can withstand high temperature and high tension, and to An object of the present invention is to provide an acrylic fiber precursor and a method for producing the same, which enable the production of carbon fibers with high strength and physical properties that exceed the standards of the above, and which are free from yarn breakage and fluff, and have excellent quality and performance.

(Means for Solving the Problems) The object of the present invention is to achieve the invention described in the claims, that is, the tensile strength at 240° C. is at least 0.3 Cl/d.
Acrylic fiber precursor for high-strength, high-modulus carbon fiber with a tensile modulus of 2.0 g/d or more and 90%
The acrylonitrile-based polymer solution containing the above acrylonitrile is once discharged into an inert atmosphere through a spinneret placed above the surface of the coagulation bath, and then spun into 100 angstroms using a dry/wet spinning method in which the solution is introduced into the coagulation bath. (
(Hereinafter abbreviated as A) A water-swollen side fiber yarn having a void diameter of the following is formed, and this fiber yarn is quickly dried and densified by adding an oil agent, and the total draw ratio is at least 7 times at a temperature of 100°C or higher. By making the drawn fiber yarn with
The degree of X-ray orientation defined by 400) is 91% or more, and 24
This can be achieved by a method for producing an acrylic fiber precursor having a tensile strength at 0° C. of at least 0.3 q/d and a tensile modulus of 2°0 Cl/d or more.

The present invention will be explained in detail below.

First, the acrylic fiber precursor of the present invention is 24
The tensile strength at 0°C is at least 0.3 q/d and the modulus of elasticity is 2. Oc+/d or higher, and only by using a precursor that satisfies these fiber physical properties can industrially advantageous carbon fibers with not only tensile strength but also high tensile modulus be produced. can be manufactured.

That is, if the tensile strength of the acrylic fiber precursor at 240°C is less than 0.3 g/d, the acrylic fiber precursor may not be used in the high temperature oxidation and carbonization process to convert the acrylic fiber precursor into carbon fiber. It becomes difficult to maintain and heat carbon fibers under high elongation, making it impossible to obtain carbon fibers with high strength and high elastic modulus.
In addition, thread breakage and fuzz occur, greatly reducing its quality and performance. When the tensile modulus of the acrylic fiber precursor at 240°C is less than 2°0 g/d, the effect of heating the precursor under elongation in the oxidation step and carbonization step is This is not reflected in the physical properties and similarly makes it difficult to achieve the object of the present invention.

In the present invention, the tensile strength and tensile modulus of the acrylic fiber precursor are not values measured at temperature and humidity near normal temperature, which are used for conventional measurement of the tensile strength and tensile modulus of clothing fibers. It is important that the value is measured at a high temperature of 240°C. That is, as mentioned above, unlike the heat treatment of clothing fibers, acrylic fiber precursors are subjected to extremely harsh conditions, usually 200°C.
In the oxidation process heated in an oxidizing atmosphere at a high temperature of ~300°C, the acrylic fiber precursor not only loses its initial tensile strength and tensile modulus with increasing temperature, but also loses its initial tensile strength and modulus from the precursor to a higher degree. In order to produce carbon fibers that have the right tensile strength and tensile modulus, the precursor is stretched or strained in the harsh oxidation process described above, and this heating oxidizes the fibers without adhering or fusing them to each other. Therefore, it cannot be said that the physical properties of the fiber at around room temperature immediately indicate the performance of the precursor as a raw material for producing carbon fiber.

Only when the tensile strength and tensile modulus of the acrylic fiber precursor measured under the temperature condition of 240°C of the present invention satisfy the requirements of 0.3Cl/d or more and 2°OC1/d or more, respectively. It can be used as an excellent raw material for producing carbon fibers, and it becomes possible to greatly improve and increase the tensile strength and tensile modulus of the corresponding carbon fibers. .

The acrylonitrile polymer forming the groove of the acrylic fiber precursor of the present invention is at least 90%
% (weight %) of acrylonitrile (hereinafter abbreviated as AN)
It is an AN-based polymer containing, in addition to a homopolymer of AN, monomers that are copolymerizable with the AN, such as acrylic acid, methacrylic acid, itaconic acid, their alkali metal salts or ammonium salts, and Examples include AN copolymers in which alkyl esters, acrylamide, methacrylamide, allylsulfonic acid, methallylsulfonic acid, metal salts thereof, and the like are copolymerized in an amount of 10% or less. The amount of these copolymerized components is 10
%, it is not preferable because it becomes technically extremely difficult to produce acrylic fibers having the above-mentioned strength and elastic modulus at 240°C. is more advantageous for the purpose of the present invention because it contributes to improving the denseness of the fibers obtained.

The degree of polymerization of these AN-based polymers is 1.3 to 1.3 in terms of intrinsic viscosity.
3.01, preferably in the range of 1.5 to 2.5.

Such an acrylic fiber precursor of the present invention cannot be obtained by applying conventionally known acrylic fiber manufacturing methods as is, but can be manufactured for the first time by adopting the manufacturing method detailed below. I can do it.

First, as a spinning means for the acrylic fiber precursor of the present invention, there are various spinning methods known for producing acrylic fibers, such as wet spinning, dry spinning, dry/wet spinning, and melt spinning.・It is necessary to adopt a wet spinning method, and only by adopting this spinning method can the strength at 240°C specified in the present invention be 0.3 C1/d or more and the elastic modulus be 2.0 g/d. This makes it possible to obtain fibers with excellent density.

In other words, if you apply the dry spinning method or wet spinning method, which has been commonly used up to now, instead of the dry/wet spinning method, the draft during spinning will be high and a developed skin layer will be formed on the fiber surface. It is difficult to form and tends to become fibers with a marked fibrillar structure.

Although such fibers exhibit relatively high strength and elastic modulus under low temperature conditions, they have poor heat resistance, and their tensile strength and tensile elastic modulus are low under severe high temperatures such as in the carbon fiber manufacturing process described above. In other words, fibers satisfying the fiber physical properties specified in the present invention cannot be obtained. The dry/wet spinning conditions for the acrylic fiber precursor are as follows:
N-based polymers are treated with solvents such as organic solvents such as dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc>, and dimethyl formamide (DMF>), concentrated inorganic salt solutions such as zinc chloride and alkali thiocyanate, nitric acid, etc. A spinning stock solution is prepared by dissolving in an inorganic solvent, and the distance between the spinneret surface and the coagulation bath liquid level is 1 to 30 mm.
The spinning stock solution is removed from the spinneret by air, nitrogen,
Discharge into an inert atmosphere such as helium or argon or into a vacuum, that is, dry or wet spinning. The discharged polymer is introduced into a coagulation bath using an aqueous solution of the AN polymer solvent as a coagulant to complete coagulation, and then washed with water, stretched, and
It is passed through various post-treatment steps such as drying and treatment with an oil, preferably a silicone oil.

After the dry-spun and wet-spun fiber threads undergo the water washing process, the temperature is gradually raised within a temperature range of 0 to 100°C in a liquid bath to prevent adhesion between the fiber threads. It is preferable to perform stretching, preferably at least two stages.

Furthermore, it is preferable to use a silicone oil for oil treatment. After the oil treatment, the fiber threads are dried and densified, and then 1
The film is stretched in a heat medium at a temperature of 00° C. or higher, such as steam, silicone oil, a hot air atmosphere, a hot plate, a hot drum, etc., and is re-lubricated as necessary and then wound up.

The single fiber fineness of the precursor fiber obtained by such dry/wet spinning can be selected within the range of about 0.1 to 3 d, but if the single fiber fineness of the precursor fiber in the range of 1 is 1 d or less, especially 0. .1 to O, ad are particularly useful for the purposes of the present invention. In addition, the total number of single fibers is 50
It can be selected from 0 to 30,000.

The dry/wet spinning conditions are such that the void diameter contained in the water-swollen fiber obtained by this dry/wet spinning is 100A.
After spinning, it is necessary to densify as follows. If the void diameter of the fiber yarn before drying exceeds 100A, even if the voids above appear to disappear due to the densification of the water-swelled fibers, the fiber properties at high temperatures will be insufficient, and the carbon Defects are likely to occur inside the fibers, making it impossible to obtain carbon fibers with high strength and high modulus of elasticity.

In order to make the void diameter of the water-swollen fibers subjected to this densification to be 100A or less, the coagulation conditions after the above-mentioned dry/wet spinning and the subsequent drawing conditions are important. Low temperature, preferably 30
It is preferable to complete the coagulation at a temperature of 10°C or lower, more preferably 10°C or lower.

As a specific example, it is preferable to use a coagulant containing 10 to 70% solvent in the coagulation bath composition and carry out coagulation at 10°C.

As a specific example, a coagulant containing 10 to 70% solvent is used in the coagulation bath, and after coagulation is completed at about 5°C, washing with water is performed.
An example of this method is multi-stage stretching at a low temperature of 100° C. or lower, whereby the acrylic fiber precursor having a small void diameter can be advantageously produced.

In order to obtain the acrylic fiber precursor of the present invention, the total stretching ratio in the spinning process should be at least 7 times,
Preferably, the stretching ratio is 9 times or more, and the stretching is preferably performed in substantially two or more stages in a heat medium of 100° C. or higher.

However, no matter how large the draw ratio is to obtain highly oriented fibers, if the fiber structure does not have a degree of X-ray orientation of 91% or more, the fiber yarns will become fluffy or This is not preferable because only low tensile strength and low tensile modulus can be obtained.

That is, the degree of X-ray orientation defined in the present invention is a measure indicating the degree of orientation in the fiber axis direction of the pseudocrystals constituting the fiber, and when this degree of X-ray orientation is lower than 91%,
No matter how good a raw material polymer is used, it is difficult to obtain fibers with good physical properties at high temperatures.

The reason why the acrylic fiber precursor obtained by dry/wet spinning of the present invention has excellent heat resistance is not clear, but it is believed that a fibril structure exists in the cross section of the carbon fiber obtained from the acrylic fiber. (Refer to "Carbon Fiber Industry" by Morita, p. 11, published by Kindai Editorial Company, 1984), and it is thought that the structure of the fiber before drying and densification is directly reflected in the structure of carbon fiber. Reducing the above-mentioned void diameter inside the fiber reduces structural disorder that causes defects at high temperatures, and allows for highly oriented and dense fibers to be drawn at high magnification. This is presumed to be due to the formation of fibers.

(Effects of the Invention) The acrylic fiber precursor of the present invention is a highly oriented fiber with excellent density, and its strength and elastic modulus when heated at high temperature are within the above range. In other words, during the oxidation and carbonization processes, it is possible to heat-treat the product by holding it under a high degree of elongation, which results in extremely high levels of both tensile strength and elastic modulus, and fewer defects such as fuzz and scratches. This made it possible to manufacture carbon fiber.

Hereinafter, the present invention will be roughly and concretely explained based on examples.

In the present invention, the degree of X-ray orientation, void diameter, strand strength and elastic modulus, and tensile strength and tensile modulus of the precursor at high temperature are values measured by the method described below.

(1) X-ray crystal orientation degree: A sample of 20 mcs/4 cm is solidified in a 1 mm wide Nicolodione mold and used for measurement. As an X-ray source, alpha rays (wavelength 1° 5418 A) were used for Cu monochromatized with a Ni filter, and the measurement was performed at an output of 35 KV and 1.5 mA, and 2θ = 17
．． Half width H (°) of the peak obtained by scanning the peak of plane index (400) observed near 0' in the circumferential direction
It was determined from the formula: Yoroku = (180-H>/180 (%)).

In addition, the slit system of the goniometer is 2 mmφ.
A cinderella counter was used as the counter. The scanning speed was 4°/min.

Time constant 1 second, dart speed 10m/
It is min.

(2) Wash the fiber yarn void diameter sample thoroughly with water, wipe off the water adhering to the surface with filter paper,
After removal, approximately 5 mq was placed in a sealed sample container, and the melting point of the water present in the voids in the sample was measured using a differential thermal analyzer (DSC) in the range of 0°C to room temperature. The void diameter was calculated from the value of the existing peak according to the following formula.The temperature increase rate was 2.5° C./min, pure water was used for temperature calibration, and indium was used for calorific value calibration.

Void diameter (A>=164/[melting point] (℃) (3) Strand strength and strand elastic modulus: J l5-R-7
The physical properties of the epoxy resin-impregnated strand were measured in accordance with the method specified in 601, and the average value of 10 measurements is shown.

(4) Tensile strength and tensile modulus of precursor at high temperature The precursor was introduced into an air heating furnace (effective furnace length 2°6 m) set at 240°C at a yarn speed of 1 m/min, and the speed of the take-up roller was varied. The tensile strength and tensile modulus were calculated based on the fineness of the introduced precursor.

Note that the tensile modulus is a value determined from the slope of the maximum slope line of the stress-extension curve in this case.

Example 1 20% DMSO solution of AN copolymer made from 99% AN and 1% methacrylic acid (melt viscosity at 45°C is 60%)
0 poise) into the air through a spinneret with a diameter of 0.1 mm and 1500 holes under the conditions shown in Table 1,
The fibers were introduced into a 130% N DMSO aqueous solution and coagulated, and the resulting coagulated fiber threads were taken out of the bath.

The precursor was washed with water, stretched, applied with an oil agent, dried and densified according to a conventional method, and then stretched in steam to produce a precursor having a total stretching ratio of 12 times and a single fiber fineness of 0.7 d.

The obtained precursor is heated and oxidized in air with a warm IN gradient of 245 to 275°C under a tension of 0.24 g/d, and the obtained oxidized fiber yarn is finally oxidized under high tension.
It was carbonized by heating in a nitrogen atmosphere at 50°C. The physical properties of the obtained carbon fibers are shown in Table 1.

From the upper table of Table 1, precursors No., 2.3 and 5 of the present invention can make the void diameter of the fiber yarn before drying 100A or less by adjusting the spinning conditions, and the tensile strength at high temperature It can be seen that precursors with excellent strength and elastic modulus and carbon fibers with excellent strand strength and elastic modulus can be obtained.

However, under dry and wet spinning conditions, the void diameter is 1.
It can be seen that when spinning conditions exceeding 00A are adopted (Nos. 1 and 4), drawing at a high magnification cannot be performed, the degree of orientation decreases, and the physical properties of the resulting carbon fibers are also significantly poor.

Example 2 A 20% DMSO solution of an AN-based copolymer consisting of 99.3 mol% AN and 110.7 mol% Itacone (solution viscosity at 45°C was 700 poise) was prepared in a diameter of 0.15 m.
The fibers were once discharged into the air at a temperature of 35° C. through a spinneret with 3,000 holes, and then introduced into a 130% DMSO aqueous solution at 5° C. for coagulation, and the resulting coagulated fiber thread was taken out of the bath.

Washing with water, stretching, applying oil, drying and densifying according to the usual method, then roughly stretching in steam by changing the stretching ratio,
A precursor having a single yarn fineness of 0.7 d was created.

Example 1 except that the oxidation tension was changed as shown in Table 2.
Carbon fibers having fiber properties shown in Table 2 were obtained by oxidation and carbonization in the same manner as above.

From the above table, precursors No. 2 and 3 of the present invention are excellent in degree of orientation, tensile strength and elastic modulus when heated at high temperature,
It can be seen that the physical properties of the carbon fiber with a weight of 1q are also excellent.

In addition, the precursor (No.

It can be seen that in case 1), the tension applied in the oxidation step must be lowered, and carbon fibers with excellent physical properties cannot be obtained.

Comparative Example 1 In Example 2, a cap with a diameter of 0.05 mm was used,
In addition, the spinning solution is directly discharged without being discharged into the air.
It was discharged into a 0% DMSO aqueous solution and coagulated. In this case, when the temperature of the coagulation bath was set at 5°C, yarn breakage occurred, so the temperature was set at 45°C. Except for these conditions, a precursor with a single yarn fineness of 0.7 d was prepared in the same manner as in Example 2, and the precursor was oxidized and oxidized in the same manner as in Example 2, except that the oxidation tension of this precursor was changed to the one shown in Table 2. After carbonization, carbon fibers having physical properties shown in Table 2 were obtained.

As shown in Table 2, precursors obtained by wet spinning have a low degree of orientation, as well as low tensile strength and elastic modulus at high temperatures, making them prone to fluff and thread breakage.
The tension in the oxidation process had to be set low, and as a result only carbon fibers with poor physical properties were obtained.

Table 2

Claims (2)

[Claims] (1) Tensile strength at 240°C is at least 0.3g
/d, and has a tensile modulus of 2.0g/d or more.
Acrylic fiber precursor for high modulus carbon fiber. (2) A dry/wet spinning method in which an acrylonitrile polymer solution containing 90% or more of acrylonitrile is discharged into an inert atmosphere through a spinneret placed above the surface of the coagulation bath, and then introduced into the coagulation bath. Spun to form a water-swollen fiber thread having a void diameter of 100 angstroms (A) or less, and after applying an oil agent to this fiber thread, it is dried and densified, and stretched at a temperature of 100°C or higher to obtain a total stretching ratio. by at least 7 times the A method for producing an acrylic fiber precursor for high-strength, high-modulus carbon fiber.