JPH04272236A - Carbon fiber containing fine particle - Google Patents

Abstract

PURPOSE:To improve the tensile strength of a carbon fiber containing fine particles for improving the performance of the fiber or imparting additional function to the fiber. CONSTITUTION:The objective carbon fiber contains fine particles exclusively in the inner layer of single fiber. The fine particle-containing carbon fiber has high tensile strength and is hardly producible by conventional process. The fiber has high tensile strength as well as improved performance or imparted additional function by the mixing of fine particles. Since the carbon fiber has high tensile strength and excellent elastic modulus, compressive strength, electrical conductivity, electric wave shielding property or heat-resistance, it is useful as a reinforcing fiber for a composite material containing thermosetting resin, thermoplastic resin, ceramic, metal, etc., as a matrix, concretely, aircraft such as supersonic flying object, space articles such as rocket and truss, sports goods such as fishing rod and golf shaft, electric wave shielding material and heat- resistant member.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carbon fibers containing fine particles, particularly carbon fibers containing fine particles only in the inner layer of the single fiber.

0002

[Prior Art] As the use of carbon fibers has expanded in recent years, there has been an increasing demand for improved mechanical properties and functionality such as specific strength, specific modulus of elasticity, heat resistance, electrical conductivity, radio wave shielding properties, and thermal conductivity. . A technique of mixing fine particles as a functional material into conventional carbon fibers for the purpose of imparting functionality (Japanese Patent Publication No. 61-58404, Japanese Patent Application Laid-Open No. 1986-2-
251615, etc.) have been proposed.

0003

[Problems to be Solved by the Invention] However, in the above-mentioned fine particle-containing carbon fiber, the diameter of the fine particles is usually 0.1 μm.
There are many of the above-mentioned substances, and they become large foreign substances for carbon fibers having a single fiber diameter of about 5 to 10 μm, causing a decrease in mechanical properties such as tensile strength. Studies have been conducted to apply so-called ultrafine particles with a diameter of 0.01 to 0.1 μm with the aim of preventing a decrease in tensile strength. There was a problem in that it was not possible to sufficiently suppress the decrease in .

[0004] The inventors of the present invention have conducted intensive studies on fine-particle-mixed carbon fibers that contain fine particles and have high tensile strength, and have arrived at the present invention. That is, an object of the present invention is to provide a fine particle-containing carbon fiber having a high tensile strength that could not be achieved with the above-mentioned conventional techniques.

[0005]

[Means for Solving the Problems] The above-mentioned problems of the present invention can be solved by a carbon fiber characterized by containing fine particles only in the inner layer of the single fiber.

That is, the carbon fiber of the present invention is a carbon fiber containing fine particles only in the inner layer. Preferably, carbon fibers have a concentric two-layer structure, containing fine particles only in the inner layer thereof, and not containing fine particles in the outer layer including the fiber surface. However, the presence of a small amount of fine particles in this outer layer is allowed as long as it does not impair the purpose of the present invention.

[0007] In general, carbon fibers have a higher elastic modulus in the outer layer than in the inner layer, and stress concentrates on the fiber surface under tensile stress, so if there is a surface defect, this becomes the starting point for fracture. Since the carbon fiber of the present invention substantially does not contain fine particles in the outer layer, there are no surface defects caused by the mixing of fine particles, and therefore the tensile strength before mixing with fine particles can be maintained. It is an excellent carbon fiber that has the effect of improving performance or imparting functionality through fine particles.

The inner layer of the fiber of the present invention refers to a portion that does not include the surface of the single fiber, and the thickness of the so-called outer layer between the inner layer and the surface is preferably 0.01 μm or more, more preferably 0.01 μm or more. It is 1 μm or more, more preferably 1 μm or more. That is, if the thickness of the outer layer is less than 0.01 μm, it is difficult to prevent stress concentration on surface defects caused by fine particles, and therefore it may be difficult to prevent a decrease in tensile strength due to mixing of fine particles, which is not preferable. The upper limit of the outer layer thickness is preferably 95% of the single fiber radius.
or less, more preferably 70% or less, even more preferably 40%
% or less. That is, when the thickness of the outer layer exceeds 95%, the thickness of the inner layer becomes less than 5% of the single fiber radius, and it may become difficult to substantially improve performance or impart functionality by mixing fine particles.

Regarding the state of the fine particles mixed in the inner layer, they may be mixed uniformly throughout the inner layer, but it is also possible to mix them with a concentration distribution. Further, the inner layer portion may have a multilayer structure including a layer containing fine particles and a layer not containing fine particles. It is preferable to optimize the configuration depending on the purpose.

[0010] As fine particles, boron carbide, silicon carbide,
Carbides such as titanium carbide, oxides such as titanium oxide, silica, boron oxide, zirconia, nitrides such as silicon nitride, boron nitride, titanium nitride, borides such as titanium boride, nitrogen boride, nickel, tungsten, etc. Examples include metal fine particles, inorganic fine particles such as carbon black, organic fine particles such as polystyrene, and mixtures thereof.

[0011] The diameter of the fine particles is preferably 1 μm or less, more preferably 0.5 μm or less, and even more preferably 0.1 μm or less.
Preferably less than μm. That is, if the diameter exceeds 1 μm, stress will be concentrated around the foreign material as an internal foreign material, which may become a starting point of fracture and reduce the tensile strength, which is not preferable.

The amount of fine particles mixed is optimized depending on the purpose, but is preferably 0.5 to 50 wt%, more preferably 1
The content is generally about 20 wt%. That is, 0.5w
If it is less than t%, the effect of improving performance or imparting functionality is small, and if it exceeds 50wt%, the tensile strength may decrease, which is not preferable.

[0013] The tensile strength of the fiber of the present invention is preferably 550 kgf/mm2 or more, more preferably 6
00kgf/mm2 or more, more preferably 650k
gf/mm2 or more. On the other hand, the elastic modulus is 35×10
For graphitized yarns of 3 kgf/mm2 or more, preferably 4
50kgf/mm2 or more, more preferably 500kg
f/mm2 or more, more preferably 550 kgf/m
m2 or more. That is, the carbonized yarn and graphitized yarn have tensile strengths of less than 550 kgf/mm2 and 450 kgf/mm2, respectively.
If it is less than kgf/mm2, it is at the level of conventional general-purpose carbon fibers, and is not preferable for applications requiring high strength and high elastic modulus.

[0014] An example of the manufacturing method for the above carbon fiber will be explained. The most suitable method for manufacturing carbon fibers that do not contain fine particles on the surface is to contain fine particles only in the inner layer of the precursor by core-sheath type composite spinning of acrylic polymer or pitch. An example of manufacturing carbon fiber from an acrylic polymer by composite spinning will be explained.

That is, the acrylic polymer constituting the acrylic fiber (precursor), which is the raw material fiber of the acrylic carbon fiber, is a homopolymer of acrylonitrile or a vinyl monomer copolymerizable with acrylonitrile, such as acrylic acid. , methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and their salts or copolymers with alkyl esters, etc. be able to. The copolymerization amount of the copolymer is preferably 10 mol% or less, more preferably 5.0 mol% or less, even more preferably 2.0 mol% or less.

Regarding the polymerization method, conventionally known solution polymerization, suspension polymerization, emulsion polymerization, etc. can be applied, but the degree of polymerization is 1.0 or more in terms of intrinsic viscosity ([η]), preferably 1. It is common to set it to .5 or more. The polymer composition and degree of polymerization of the inner layer and the outer layer may be the same, or may be changed depending on the purpose. The outer layer polymer does not substantially contain fine particles, and the inner layer polymer contains fine particles, but the fine particles can be mixed with the polymer before, during, or after polymerization. Good too. In either case, uniform dispersion is important for improving tensile strength, and it is preferable to mix materials that have been sufficiently uniformly dispersed with a solvent in advance.

[0017] For the core-sheath type composite spinning of the acrylic polymer, a wet spinning method, a wet-dry spinning method, or a dry spinning method can be employed, but the wet-dry spinning method is preferred because it can easily obtain a fineness. In the composite spinning, a core-sheath spinneret is used to introduce a polymer mixed with fine particles into the core. The base may be a known core/sheath base such as a concentric type or an eccentric type, but a concentric type base is preferable. The number of cap holes is generally about 300 to 10,000. By adjusting the discharge amount of the core and sheath, the thickness of the inner layer mixed with fine particles can be adjusted.

[0018] The drawing ratio for the yarn is generally about 2 to 20 times, but if the ratio is too high, the sheath may be crushed, so it is preferably about 4 to 15 times.

The acrylic fiber having a core-sheath structure thus obtained is made flame resistant in an oxidizing atmosphere at 200 to 300°C, and then carbonized in an inert atmosphere at 1000°C or higher. In order to obtain higher tensile strength, it is preferable to set the firing temperature in an inert atmosphere to a range of 1200 to 1600°C, but if necessary, graphitization can be performed at 2000°C or higher.

[0020] In order to increase the density of carbon fibers and improve their strength and elastic modulus, it is effective to make them flame resistant in an oxidizing atmosphere and carbonize them in an inert atmosphere under tension or stretching conditions. It is. Especially flame resistance, 300-5
It is more effective to stretch in the carbonization range of 00°C and graphitization range of 2400-3000°C. Specifically, it is desirable that the stretching ratio be approximately 1.0 to 1.4 times.

The obtained carbon fibers can be subjected to surface treatment and sizing by known methods.

[0022]

[Examples] The present invention will be explained in more detail with reference to Examples below. Note that the tensile strength and single fiber compressive strength in the present invention were determined by the resin-impregnated strand evaluation method and the loop method, respectively.

Tensile strength "Bakelite" ERL-4221/Boron trifluoride monoethylamine (BF3/MEA)/Acetone=10
Carbon fiber is impregnated with 0/3/4 part, and the resulting resin-impregnated strand is cured by heating at 130°C for 30 minutes.
It was measured according to the resin-impregnated strand test method specified in SR-7601.

A single fiber having a compressive strength of about 10 cm is placed on a slide glass, 1 to 2 drops of glycerin is added to the center, the single fiber is twisted to form a loop, and a preparation is placed on top of the loop. While holding both ends of the loop with your fingers, apply a tensile strain at a constant speed.
Measure the short axis (D) and long axis (φ) of the loop until it breaks. Strain (ε) is calculated from the single fiber diameter (d) and D using the following equation, and plotted on a graph with ε on the horizontal axis and the ratio of major axis to minor axis (φ/D) on the vertical axis. ε=1.07×d/D The strain at which φ/D suddenly begins to increase from a constant value (approximately 1.3) was measured as the compressive yield strain for approximately 10 single fibers, and the average value thereof was determined. The obtained average value was multiplied by the tensile modulus determined in the above strand tensile test to obtain the single fiber compressive strength.

Example 1 Using a copolymer consisting of 99.5 mol% acrylonitrile (AN) and 0.5 mol% methacrylic acid, the concentration was 19.
% by weight dimethyl sulfoxide (DMSO) solution (polymer A) was prepared, and polymer A had a particle size of 0.
Polymer B was prepared by mixing 5 wt % of 9 μm boron carbide fine particles.

Polymer A and Polymer B were used as sheath and core polymers, respectively, and the temperature was adjusted to 35° C., and they were once discharged into the air through a concentric type core-sheath nozzle with a hole diameter of 0.12 mmφ and 500 holes. After running through a space of approximately 4 mm, it was coagulated in an aqueous DMSO solution at a temperature of 5° C. and a concentration of 30%. The withdrawal speed was 20 m/min. The ratio of discharge amount for the core portion was 2 to 1 for the sheath portion. After washing the coagulated yarn with water, it was stretched 2.5 times in a three-stage hot water stretching bath, and a silicone oil was applied thereto, and then it was brought into contact with a roller surface heated to 110°C to make it dry and dense. Another 3.7 kgf
The fiber bundle was drawn three times in a pressurized steam of /cm2 to obtain a fiber bundle with a single fiber fineness of 0.8 d and a total denier of 400 D. The obtained acrylic fiber contained boron carbide fine particles in the core.

[0027] This core-sheath acrylic fiber has a molecular weight of 240 to 270
The fibers were made flame resistant in air at a temperature of 1,700 degrees Celsius and converted into flame resistant fibers at a stretching ratio of 1.05, and then carbonized in a nitrogen atmosphere at a maximum temperature of 1,700 degrees Celsius to obtain carbon fibers. The obtained core-sheath carbon fiber was further fired in a nitrogen atmosphere at 2600° C. at a draw ratio of 1.05 to obtain a graphitized fiber.

The obtained graphitized fiber contained fine particles in the inner layer and did not contain fine particles in the outer layer having a thickness of about 1 μm. As for the tensile properties of the strand, the tensile modulus was as high as 62 x 103 Kgf/mm2, and the tensile strength was as high as 480 kgf/mm2.

Comparative Example 1 The yarn was spun and fired in the same manner as in Example 1, except that Polymer A was also added to the core in Example 2.
Although the tensile strength was high at 490 kgf/mm2, it did not contain catalyst fine particles and the tensile modulus was 55 x 103 K.
gf/mm2.

Comparative Example 2 The yarn was spun and fired in the same manner as in Example 1 except that Polymer B was also added to the sheath.
Although the tensile modulus was high at 64 x 103 Kgf/mm2, the tensile strength was low at 330 kgf/mm2.

Example 2 A yarn was spun under the same conditions as in Example 1 except that 6 wt % of silica fine particles with a particle size of 0.05 μm were mixed in Polymer A in Example 1 to obtain a single fiber fineness of 0.8 d and total denier. 4
A fiber bundle of 00D was obtained. The obtained acrylic fiber contained silica fine particles in the core.

[0032] This core/sheath acrylic fiber has a molecular weight of 240 to 270
By making the fiber resistant to flame at a stretching ratio of 1.05 in air at a temperature of 1.05°C, and then firing it in a nitrogen atmosphere at a maximum temperature of 1500°C, the core part contains fine particles uniformly, and the sheath part contains fine particles. Concentric carbon fibers containing no fine particles were obtained.

[0033] As for the tensile properties of the strand, the tensile modulus is 30×
103 Kgf/mm2 and tensile strength of 570 kg
f/mm2, and has a single fiber compressive strength of 720.
It had a high strength of kgf/mm2.

Comparative Example 3 The yarn was spun and fired in the same manner as in Example 1, except that Polymer A was also added to the core.
Tensile modulus and tensile strength are respectively 30×103 K
gf/mm2 and 580 kgf/mm2, but the single fiber compressive strength was 630 kgf/mm2.
The strength was lower than that of a mixture of 2 and silica.

Comparative Example 4 The yarn was spun and fired in the same manner as in Example 1 except that Polymer B was also added to the sheath.
The tensile strength was low at 430 kgf/mm2.

[0036]

[Effects of the Invention] The fine particle-mixed carbon fiber of the present invention is a fine particle-containing carbon fiber with high tensile strength, which is extremely difficult to achieve with conventional techniques, and satisfies both the performance improvement or function imparting effect and high tensile strength by mixing fine particles. It is carbon fiber. The fibers of the present invention are high tensile strength carbon fibers with excellent elastic modulus, compressive strength, conductivity, radio wave shielding properties, and heat resistance.
Using this carbon fiber as a reinforcing fiber and a matrix of thermosetting and thermoplastic resins, ceramics, metals, etc., a highly functional and high-strength composite material can be obtained. Specifically, it can be used for aircraft applications such as supersonic flying vehicles, space applications such as rockets and trusses, sports applications such as fishing rods and golf shafts, radio wave shielding materials, heat-resistant members, etc.

Claims (1)

[Claims] 1. A carbon fiber containing fine particles, characterized in that the fine particles are contained only in the inner layer of the single fiber.