JPH0397918A - Production of modified cross-sectional carbon fiber - Google Patents

Abstract

PURPOSE:To produce the subject fiber suitable as a reinforcing fiber by spinning a spinning raw solution comprising an acrylonitrile based polymer through a spinneret having a specific shape, coagulating in a specific coagulating solution bath and further subjecting to water washing, drawing and baking processes. CONSTITUTION:A spinning raw solution comprising an acrylonitrile based polymer containing >=95mol% of acrylonitrile and a solvent such as dimethyl sulfoxide is spun once in air or an inert atmosphere through a spinneret comprising non-circular, slit type or point contact type extrusion holes. The spun fibers are coagulated in a coagulating solution bath comprising the solvent and a coagulating agent and set in a skin layer formation-impossible concentration range, further washed with water, drawn and baked to provide the objective non-circular carbon fibers each having a cross section having a rotation symmetical angle theta of 3609 degree/n (n is 2-20).

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing carbon fibers with a modified cross section, and more specifically, a method for producing carbon fibers with a modified cross section suitable as a composite material as a reinforcing phase. Regarding.

(Prior Art) Conventionally, carbon fibers have been widely produced industrially as reinforcing fibers for composite materials, taking advantage of their excellent mechanical properties, especially their specific strength and specific modulus. There is an increasing demand for improved performance of carbon fiber, especially in sports and aerospace applications.

In response to this demand for higher performance, numerous improvements have been made to date, and the applications of composite materials using carbon fiber as a reinforcing material have been expanded. However, although significant progress has been made in the properties of carbon fiber itself, such as the strength and elastic modulus of resin-impregnated strands, the current situation is that satisfactory properties have not been obtained for composite materials that are actually used. .

In other words, the strength utilization factor in composite materials, rF! There was a problem that basic properties such as i-interval shear strength (ILSS), compressive strength, and strength did not improve.

Many methods have been proposed to address these problems, including methods to improve the surface properties of carbon fibers through electrolytic surface treatment, methods to improve the properties of the applied matrix resin, and methods to improve the arrangement of carbon fibers that make up composite materials. Although the means have been disclosed, carbon i! which constitutes the composite material family! This did not involve innovatively improving the characteristics of iI itself to improve its basic characteristics.

(Problem to be solved by the invention a) The problem of the present invention is to have extremely excellent basic properties such as strength utilization rate, inter-glabellar shear strength (ILSS), compressive strength, and bending strength in composite H class, and to achieve an outstanding reinforcing effect. The object of the present invention is to provide a method for manufacturing carbon fiber shown in the figure.

(Means for Solving Problem i!) The above-mentioned problem of the present invention is to spin a spinning dope consisting of an acrylonitrile polymer containing at least 95 mol% of acrylonitrile and a solvent for the polymer into a non-circular or slit spinning solution. After being spun into air or an inert atmosphere from a spinneret with a type-type or point-contact discharge hole, it is coagulated in a coagulation bath consisting of the solvent and a coagulant whose concentration is set at a concentration range that does not allow the formation of a skin layer. After washing with water and stretching,
An irregular cross-section carbon m characterized by firing a raw yarn in which the fiber cross section has a non-circular shape with a rotational symmetry angle θ (°) of θ = 360° /n (n is an integer from 2 to 20). The problem can be solved by changing the fiber manufacturing method.

The carbon fibers obtained by the production method of the present invention: ■ have a non-circular cross-sectional shape, ■ have no lamellar structure in the cross-section of the fiber, and have a substantially uniform crystal structure;
and ■ there is a minute uneven structure on the surface of ai Usui,
There are three main characteristics.

Many techniques have been disclosed so far for non-circular or irregular cross-section carbon fibers, particularly pitch-based carbon fibers. In these pitch-based carbon IIKs, great efforts have been made to the pitch as a raw material in order to maintain basic properties such as elastic modulus and strength, and mesophase pitch is commonly used. . When these mesophase pitches are used as raw materials, shear stress during spinning during the production of raw fibers (bricasa) generates a non-uniform crystal structure inside the raw fibers, and this creates lamellae inside the carbon fibers after firing. It remains as a non-uniform crystal structure observed as a structure, resulting in a decrease in strength and elastic modulus.

The creation of irregular cross-sections has been devised with the aim of improving these defects caused by the basic characteristics of the original family.

For example, JP-A No. 61-0313, JP-A No. 32-1
No. 17821, JP-A-62-231024,
For example, Japanese Patent Application Laid-Open No. 131034/1983. However, in these disclosed techniques, the above-mentioned non-uniform crystal structure still exists and no improvement in compressive strength can be expected.

A leaf-like lamellar structure is observed in these irregular cross-section carbon fibers along the non-circular cross-section of the fibers.

The presence or absence of this leaf-like lamellar structure can be determined, for example, by
As described in Japanese Patent Application Laid-open No. 6313 and Japanese Patent Application Laid-open No. 117821/1982, when a cross section (fractured surface) of carbon fiber is observed using a scanning electron microscope (SEM), it is found that from the center of the fractured surface, It can be easily observed as a fractured tissue that extends outward in a feathered manner. Figure 1 shows a schematic diagram of the leaf-like lamellar structure that appears on the fracture surface.

The irregular cross-section carbon fibers obtained by the production method of the present invention do not have a nonuniform crystal structure corresponding to j=J in the leaf-like lamellar structure described above, and exhibit a substantially uniform internal structure. Regarding such irregular cross-section carbon fibers with a uniform internal structure, for example, 20th International
al SAMPE Technical Conference
ence (1988) Lecture Proceedings P414-422 describes that polyacrylonitrile (PAN) can be produced by firing a raw yarn obtained by a melt spinning method, and a cross-sectional photograph is published. However, although the proceedings describe the characteristics of the circular cross-section carbon fiber, it does not describe the specific characteristics of the irregular cross-section carbon fiber, and it is not at all clear what kind of characteristics or characteristics it will exhibit. It was something.

The irregular cross-section carbon fiber obtained by the production method of the present invention simultaneously satisfies the above-mentioned properties (1), (2), and (3), and the more important basic properties such as strength and elastic modulus are determined by the strand form described later. In the measurement, the strength was 300k
g/mm2 or more, preferably 320kg/mm2 or more
It is not less than mm2. Similarly, the elastic modulus is 20t/mm
2 or more, preferably 22t/mm2 or more.

Unless both the strength and elastic modulus reach these values, the composite material cannot demonstrate its advantages as a reinforcing material.

As described above, the irregular cross-section carbon fiber of the present invention is a completely new carbon fiber suitable for practical use in composite materials.

In particular, since the carbon fiber of the present invention has a non-circular cross section, it has extremely excellent basic properties such as interlaminar shear strength (ILSS), compressive strength, and tensile strength, which are important properties for composite materials.

In the manufacturing method of the present invention, elemental fibers having a cross-sectional shape different from the bean-shaped or cocoon-shaped carbon fibers produced by firing raw yarn spun from a conventional circular discharge hole can be obtained. The cross-sectional shape of the yarn of the present invention, which is a non-circular shape having a rotational symmetry angle θ (°) of θ = 360°/n (n is an integer from 2 to 20), may be, for example, a polygonal shape such as a triangle or a square. Examples include rectangular shapes, multi-lobed shapes such as trifoliate and quatrefoil shapes, and alphabetic shapes such as H. For reference, the relationships between these polygonal (multilobal) shapes and n and θ are shown below.

n θ (°) Triangle 3l2〇Square 490 FIG. 2 shows an example of the shape of the discharge hole of the spinneret and the shape of the cross section of the carbon fiber obtained.

Among these cross-sectional shapes, polygonal and multilobal shapes are preferred. In addition, it is important to appropriately set the proportion of leaves that are too large or too long, especially in the case of multi-lobed products, from the viewpoint of the properties obtained and the ease of passing through the manufacturing process.

From this point of view, it is preferable that the ratio (R/r) of the diameters of the circumscribed circle and the inscribed circle (r and R, respectively) of the cross section is within an appropriate range. FIG. 3 shows, as an example, the relationship between R and r in the Y cross section. R/r is preferably 1.1 to 7.0, more preferably 1.2 to 6. O, more preferably 1.3 to 5.0.

The cross section of the irregular cross-section carbon fiber obtained by the production method of the present invention is substantially uniform, and there is no leaf-like lamellar structure.
This is an extremely advantageous point in obtaining carbon fibers with high performance.

Such a homogeneous structure without a lamellar structure can be easily obtained by firing a raw yarn made of a polyacrylonitrile polymer.

There are minute irregularities on the side surfaces of the irregular cross-section carbon fiber of the present invention, but this feature is closely related to the fiber formation mechanism in the manufacturing method of the present invention, and a leaf-like lamellar structure is present in the cross section. In addition to having a uniform crystal structure without
This point is clearly different from pitch-based irregular cross-section carbon fibers. These fine irregularities on the surface function extremely effectively in improving the adhesion with the matrix resin when forming a composite material.

Acrylic fiber II (7) used in the present invention contains acrylonitrile (hereinafter referred to as AN) as a main component, and contains A of 95 mol% or more, preferably 98 mol% or more.
N and preferably 5 mol% or less, particularly preferably 2 mol% or less of the A.N. A copolymer with a vinyl group-containing compound (hereinafter referred to as a vinyl monomer) that is copolymerizable with N and promotes a flame-retardant reaction is used.

Examples of vinyl monomers that promote severe inflammation include acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts, ammonium salts, α(1
-hydroxylethyl)acrylic nitrile, acrylic acid hydroxyl ester, and the like. In addition to these vinyl monomers that have the ability to promote flame resistance, AN
Spinnability of polymers or,! ! In order to improve thread properties and the like, lower alkyl esters of acrylic acid and methacrylic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid and their alkali metal salts, 3rd By. The total amount of copolymerized components may be 5 mol% or less, preferably 2 mol% or less.

Such AN-based copolymers (PAN) can be polymerized using emulsion suspension, bulk polymerization, VA liquid polymerization methods, and the like.

Acrylic fibers are produced from a spinning stock solution in which PAN is dissolved in a solvent, and examples of solvents for PAN include dimethylformamide, dimethyl sulfoxide, nitric acid, rhodan soda aqueous solution, and zinc chloride aqueous solution.

The spinning method used in the method for producing the irregular cross-section carbon fiber navy blue of the present invention is to use a spinning nozzle with a non-circular, slit-shaped, or point-contact type discharge hole that mimics the cross-sectional shape of the raw yarn, and then place the fiber in air or an inert atmosphere. After spinning, it is coagulated in a coagulation chamber consisting of a PAN solvent and a coagulant whose concentration is set in a range that makes it impossible to form a skin layer. The coagulated thread obtained in this way does not have a surface skin layer, or even if it does exist, it is extremely thin, so the subsequent water washing and drawing processes may cause the development of a fine uneven structure on the surface of the thread. It is possible.

In the present invention, the above-mentioned dry-wet spinning method is particularly used as the spinning method, which can relieve the tension generated during the coagulation process in the space between the spinneret and the coagulation bath, resulting in less defects and uniformity. This is because it is possible to obtain excellent yarn.

The composition of the coagulation bath consists of the above-mentioned PAN solvent and coagulant. Examples of the coagulant include water, methanol, ethanol,
Examples include acetone, but water is suitable from the standpoint of safety and recovery.

The concentration range at which skin layer formation is not possible varies depending on the PAN composition, that is, the molecular weight, copolymer components and additives, the combination of solvent and coagulant, and the temperature of the spinning dope and coagulation bath. It can be set by the method described in JP-A-61-119707 (PIO-11). When the coagulant is water, it is 60-90% by weight for organic solvents such as dimethylacetamide, dimethylsulfoxide, and dimethylformamide, and 40-5% for nitric acid.
0% by weight, 20-40% by weight for subchloride and rhodanate.
It is.

The obtained coagulated fibers were washed with water and then stretched in warm water, and then a process oil was applied in an amount of 0.2 to 1.5% by weight based on the weight of the dry fibers.
Give. As a component of the oil agent, it is preferable to add a silicone-based compound or a modified silicone-based compound, which is particularly effective in preventing the fusion of single fibers during firing.

After applying the process oil, drying and densification treatment is performed to obtain densified fibers. Next, if necessary, secondary stretching is performed, for example, in steam.

Incidentally, the single filament weave of the raw yarn is an extremely important factor in determining the characteristics of the obtained irregular cross-section carbon m-fiber. In the present invention, the denier is preferably 0.1 to 2.5 denier, more preferably 0.2 to 2.0 denier, and even more preferably 0.3 to 2.0 denier.
It is 1.5 denier. If the denier is less than 0.1 denier, single yarn breakage will easily occur, while if the denier exceeds 2.5 denier, it will be difficult to uniformly fire the inner and outer layers of the single yarn, making it difficult to obtain carbon wc with excellent properties. becomes. In order to achieve a uniform fA as described above, it is preferable that the fineness is 2.6 denier or less, but such a fine-grained irregular cross-section yarn for manufacturing carbon fibers has not been disclosed so far. be.

The thus produced acrylic line navy blue (hereinafter referred to as breaker) is fired to convert it into carbon fiber. The firing, oxidation (flame-proofing), and carbonization conditions of the breaker are not particularly limited, but! I! It is preferable to set conditions in which structural defects such as voids are unlikely to occur inside the fibers. For example, for a single cow carbonized in an inert atmosphere such as nitrogen, the temperature increase rate in the temperature range of 300 to 700°C and 1000 to 1200°C should be IO00°C/min or less, preferably 500°C/min or less. It is preferable to do so. Furthermore, for example, 1400℃
It is also possible to obtain graphitized threads by firing in an inert atmosphere at ~3000°C.

(Example) The present invention will be explained in more detail with reference to Examples below.

Note that the physical property values used in the text and examples were measured by the following method.

(A) Resin-impregnated strand strength measurement method JIS R-7
90. “Bakelite” ERL-422
1 100 parts 3-boron fluoride monoethylamine (BF3MEA) 3 parts acetone 4 parts Curing conditions: 1
30°C x 30 minutes (B) Characteristic values for composite material (composite) a6 Tensile strength, bending strength, N shear strength (ILSS) ) is 60%, and after pouring the resin, it is heated and degassed under vacuum.

After defoaming, heat the resin while applying pressure with a press to harden it and create a test piece. Measured using an Instron testing machine and converted to Vf = 60%.

Main resin: ELM434 [Sumitomo Chemical Co., Ltd.] 35 parts Ep
828 [Petrochemicals Co., Ltd.] 35 parts Epicron 1
52 [Dainippon Ink Co., Ltd.] 30 parts 4,4'-diaminodiphenylsulfone [Sumitomo Chemical (
Co., Ltd.] 32 parts 3 Boron fluoride monoethylamine 0.5 parts (solvent: methyl ethyl chloride, jtA fat concentration = 55%) *Molding conditions Defoaming: under vacuum (10n+mlg or less), 70°C x 2
Time molding: Press pressure = 50kg/cm2,170
℃ × 1 hour post cure: After taking out the test piece from the mold, 170℃
℃×2 hours Molding: Tensile test: Width 6rnm, thickness 1. 6mm bending strength, ILSS; Width (3mm, thickness 2.5mm) Actual measurement Tensile strength: The length of the test piece is 150mm, and aluminum tabs with a length of 45mm are glued to both ends.

A radius of 75 mm is machined from both sides in the thickness direction of the center of the test piece, and the test piece is used for measurement.

The cross-sectional area is determined by measuring the thickness and width of the thinnest part of the rounded part.

Bending strength: The length of the test piece is 150 mm, and it is measured using a 3-point bending test jig.

ILSS: The length of the test piece is 18 mm, and a three-point bending test jig is used to measure the support span as four times the thickness of the test piece.

b. Compressive strength Toray Industries, Inc.! ! 1$3620 Carbon fibers are arranged in one direction on a resin film coated with silicone resin-coated barber, and the resin film is layered on top of that again, and the resin is impregnated into the carbon fibers using a pressure roll. Create a Bripreg sheet. These sheets were stacked with their fiber axes aligned and heated to 180°C using an autoclave.
, a pressure of 6 kg/cm'' for 2 hours to harden the resin and create a flat plate with a thickness of about 1 mm. This flat plate is cut using a diamond cutter and cut into a length of 80 mm along the fiber axis.
A test piece with a width of 12 mm in the direction perpendicular to the fiber axis is prepared. Leave 5 mm in the center of the test piece, and glue composite tabs made of carbon i, navy blue, and epoxy resin with a thickness of about 1 mm to both ends to form a test piece for compressive strength measurement.

(C) Observation of the fracture surface using a scanning electron microscope (SEM) The carbon fiber single yarn to be measured was measured using a tensile tester under the following conditions to prevent the fracture surface from being complicatedly disturbed by the impact of the fracture. break in water.

Chuck interval: 5 cm Tensile speed: 0.5 mm/min [1% strain/min] Sample length: 15 cm Gold was deposited on the obtained sample, and the acceleration voltage was 15 ~
25kv (25kv), magnification 5000 ~ 15000
Observe or photograph with SEM at magnification (10,000x).

The values in ( ) are the measurement conditions in this example.

Example-1 Intrinsic viscosity [η] consisting of 99.5 mol% acrylonitrile (hereinafter referred to as AN) and 0.5 mol% itaconic acid
Dimethyl sulfoxide (
DMSO) solution was blown with ammonia and the carboxyl end groups of the copolymer were replaced with ammonium groups to modify the polymer. A DMSO solution with a concentration of 20% by weight of the modified polymer σ was prepared and mixed with the spinning stock solution. did.

This spinning stock solution was once spun into the air at 50°C through a spinneret with Y, 10, and H holes with a slit width of 0.03 mm and 500 holes, and then spun into the air at 10°C using 75% D
It was introduced into an MSO aqueous solution to form a coagulated thread.

For comparison, a coagulated thread was similarly obtained using a conventional die having a circular discharge hole with a diameter of 0.12 mm.

After washing the coagulated yarn with water, it was drawn in four stages in warm water.
A bath-drawn yarn was obtained. The overall stretching ia ratio was 3.5 times. Next, an oil agent containing a modified silicone compound as a main component was applied to the swamp-drawn yarn, followed by drying and densification using a heated roll at 130°C. Furthermore, 2. 51p, to obtain an acrylic fiber yarn having a single yarn weave of 1.0 denier and a total fineness of 1500 denier.

This acrylic fiber thread was flame-retardant treated while being stretched 1605 times in air at 240-260°C, and then stretched 300 times in a nitrogen atmosphere with a maximum temperature of 1400°C.
The heating rate in the temperature range of ~700℃ is 250℃/min.
The temperature increase rate in the temperature range of 1000 to 1200℃ is 4.
It was processed in a carbonization furnace set at 00°C/min to convert it into carbon fiber. Furthermore, the carbon fiber obtained here is 1600 ~
Graphite threads having various elastic moduli were obtained by graphitization in a Tammann furnace at 3000°C.

In order to improve compatibility with the resin, appropriate anodization treatment was performed in a sulfuric acid or nitric acid aqueous solution.

When the single filament of the irregular cross-section carbon fiber string obtained here was broken in water and the broken surface was observed with an SEM, no lamellar structure on the leaf was observed in any of them. Furthermore, when the side surfaces of the fibers were similarly observed using SEM, fine uneven structures were observed in all cases.

Table 1 shows the strand properties and combo properties. Furthermore, FIG. 4 shows the relationship between the elastic modulus and compressive strength of circular cross-section carbon fibers and Y-section carbon fibers. It can be seen from FIG. 4 that the irregular cross-section carbon fiber of the present invention exhibits superior compressive strength than the circular cross-section carbon tIIA fiber.

(Effects of the Invention) By the manufacturing method of the present invention, ■ the cross-sectional shape of the fiber is non-circular, ■ the cross-section of the fiber has a substantially uniform crystal structure, and ■ the surface of the fiber has a fine uneven structure. (1) A carbon fiber string having a strength of 300 kg/mm2 or more and an elastic modulus of 20 t/mm2 or more is obtained.

By applying irregular cross-section carbon fibers with these characteristics, the interlaminar qq shear strength (ILSS), which is an important property, can be improved.
), compressive strength, and bending strength.

[Brief explanation of drawings]

FIG. 1 shows an example of a schematic diagram of a leaf-like lamellar structure that appears on the fracture surface of a pitch-based carbon fiber. FIG. 2 shows examples of the shape of the spinneret spout and the cross-sectional shape of the carbon fibers obtained. Figure 3 shows Y-section carbon fiber. The relationship between R and r is shown. FIG. 4 shows the relationship between the elastic modulus and compressive strength of the circular cross-section carbon fiber string and the Y-section carbon fiber string in Examples.

Claims (1)

[Claims] A spinning dope consisting of an acrylonitrile polymer containing at least 95 mol% of acrylonitrile and a solvent for the polymer is passed through a spinneret having non-circular, slit-shaped, or point-contact discharge holes. Once spun in air or an inert atmosphere, the fibers are coagulated in a coagulation bath consisting of the solvent and a coagulant whose concentration is set at a concentration range that does not allow the formation of a skin layer, followed by washing with water and stretching. A method for producing irregular cross-section carbon fibers, characterized by firing a raw yarn having a non-circular shape with a rotational symmetry angle θ (°) of θ = 360°/n (n is an integer from 2 to 20). .