JPH03241014A - Carbon fiber having low specific gravity - Google Patents

Abstract

PURPOSE:To provide the subject fiber having high carbon content, containing single hollow part in the core part, having low apparent specific gravity and high tensile strength and useful for aerospace material, fishing rod, etc. CONSTITUTION:The objective fiber contains a single hollow part at the core and has a carbon content of >=90%, an apparent specific gravity of <=1.65 and a tensile strength of >=350kg/mm<2>. The hollowness of the fiber is preferably 10-30%.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to low specific gravity carbon fibers, particularly low specific gravity carbon fibers that have a single hollow part in the core, have low apparent specific gravity, and have high tensile strength. Regarding.

[Prior Art] In recent years, as the use of carbon fibers has expanded, there has been an increasing demand for improvements in specific strength and specific modulus.

Particularly in aerospace applications where the weight reduction effect is significant, lighter carbon fibers are required to reduce weight as much as possible.

Conventional carbon fibers mainly have a specific gravity of about 1.75 to 2.10, and the specific gravity of resin is about 1.2 to 1. Higher than 4,
This caused an increase in the specific gravity of carbon fiber reinforced composite materials.

By the way, as a technique for lowering the apparent specific gravity of carbon fibers, it is known to make carbon fibers hollow. However, conventionally known hollow carbon fibers are made hollow by disassembling or dissolving the core in the firing or post-treatment process (Japanese Patent Laid-Open No. 55-45866,
(Special Publication No. 1-53362). Therefore, defects such as voids occur and the tensile strength level is 300 kg/mm2.
There was a problem that the strength was insufficient as a reinforcing carbon fiber because of the low strength.

On the other hand, it is known that a pyrolyzable polymer that decomposes at a temperature of 600°C or less is mixed and spun, and the pyrolyzable polymer component is dispersed in the firing process to make it porous and have a low specific gravity (especially Publication No. 2-140242). However, carbon fiber produced by this method has a low strength level because it has a large number of internal voids, and the amount of decomposed gas generated during the firing process is large, so the burden of exhaust gas treatment is heavy. Furthermore, there is a problem in that the tar-like decomposition products produced during firing tend to cause adhesion between single yarns.

In addition, among pitch-based general-purpose carbon fibers, there is low specific gravity carbon fiber with a specific gravity of around 1°65, but the tensile strength is 100 kg.
/nm+2, which was low and insufficient as a reinforcing carbon fiber.

[Problems to be Solved by the Invention] Therefore, the present inventors have intensively studied carbon fibers that maintain strength comparable to conventional high-strength type carbon fibers and have significantly lower apparent specific gravity, and have arrived at the present invention. That is, an object of the present invention is to provide carbon fibers with low apparent specific gravity and high strength, which could not be achieved with the above-mentioned conventional techniques.

[Means for Solving the Problems] The above object of the present invention is to have a carbon content of 90% by weight or more, a single hollow part in the core, and an apparent specific gravity of ↓.

This problem can be solved by using low specific gravity carbon fiber, which is characterized by having a tensile strength of 65 kg/mm2 or less and a tensile strength of 350 kg/mm2 or more.

First, the low specific gravity carbon fiber of the present invention will be explained.

That is, the carbon fiber of the present invention has a very low apparent specific gravity of 1°65 or less, and a tensile strength of 350 kg/Trm2 or more, which is comparable to conventional high-strength carbon fibers, so the specific strength can be significantly improved. . Therefore, the low specific gravity carbon fiber of the present invention makes it possible to lower the specific gravity of the composite material, thereby making it possible to significantly improve specific strength and specific modulus. Particularly in space applications, 1 gram is said to be equivalent to more than 10,000 yen, and specific gravity is a very important point. Moreover, since the carbon fiber of the present invention has a single hollow part in the core, the moment of inertia of the area is significantly improved compared to a circular cross section with the same cross-sectional area, and the bending properties when made into a composite material are greatly improved. can be improved.

Note that it is possible to reduce the specific gravity of carbon fiber to 1.65 or less by lowering the firing temperature to 1000°C or less, but the tensile strength decreases, so in order to obtain high strength, the carbon content must be reduced to 90°C. It is necessary to bake until the amount reaches % by weight or more.

The carbon content in the present invention is a value measured by elemental analysis, and the apparent specific gravity is a value determined by the Archimedes method. That is, the weight in air (Wl) and the weight in liquid (W2) of a unit length of carbon fiber were measured and calculated from the following equation.

Note that dichlorobenzene was used as the liquid.

Apparent specific gravity = (Wl/(Wl-W2)') x liquefaction amount In addition, the tensile strength was determined by the resin-impregnated strand evaluation method. That is, carbon fiber was impregnated with "Bakelite" ERL-4221/boron trifluoride monoethylamine (BF3/MEA)/acetone = 100/3/4 parts, and the resulting resin-impregnated strand was heated at 130°C for 30 minutes. The resin-impregnated strand was measured according to the resin-impregnated strand test method specified in JIS-R-7601. As the fiber cross-sectional area, the cross-sectional area including hollow space was used.

Next, an example of a manufacturing method for the low specific gravity carbon fiber of the present invention will be explained using acrylic carbon fiber as an example.

That is, in order to lower the apparent specific gravity to 1.65, it is necessary to have a single hollow in the core. In addition, in order to maintain a high tensile strength of 350 kg/m112 or more, hollow acrylic carbon fibers with a single fiber denier of preferably 1.5 or less and with few defects obtained by firing hollow acrylic fibers are used. It is preferable that there be.

The hollowness ratio is preferably 4 to 40%, more preferably 10 to 30%. That is, if it is less than 4%, the hollowing effect will be insufficient, and if it exceeds 40%, the sheath will become thinner and more likely to crack or collapse, resulting in a decrease in strength, which is not preferable.

A wet spinning method, a wet-dry spinning method, or a dry spinning method can be adopted as the spinning method for producing hollow acrylic fibers, but preferably a wet spinning method or a wet-dry spinning method is used, and more preferably a method that can obtain fine fineness. The easy dry-wet spinning method is preferable. The fineness allows for stable firing, and the hollow part does not collapse.
In order to produce stable hollow acrylic fibers that do not tear the sheath, the core is coagulated using a core-sheath die.

It is effective to dissolve the core portion during the spinning process by adding a soluble polymer to the water washing or drawing bath solution.

Polymers that are soluble in coagulation, water washing, or stretching bath solutions include organic solvents used for coagulation such as acetone, methanol, acetonitrile, dimethyl sulfoxide, and dimethyl formamide, or zinc chloride, nitric acid, rhodan soda,
Inorganic solvents such as rhodan nitrate and water used in washing and stretching bath solutions.

It is soluble in any solvent such as hot water, steam, or glycerin. Specifically, synthetic polymers such as polyvinyl ether, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyacrylamide, polyacrylic acid, polyvinylpyrrolidone, polyethyleneimine, and sodium polyphosphate, as well as viscose, methylcellulose, ethylcellulose, hydroxyethylcellulose, and carboxyl It can include one or a mixture of two or more selected from semi-synthetic polymers such as methylcellulose, dextrin, dialdehyde starch, and carboxyl starch, as well as natural polymers such as starch, dextrin, and gum tragacanth.

The acrylic polymer to be put into the sheath is at least 8
5 mol% or more of acrylonitrile and 15 mol% or less of a copolymerizable vinyl monomer, such as acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts;
Examples include copolymers with ammonium salts and lower alkyl esters, acrylamide and its derivatives, allylsulfonic acid, methallylsulfonic acid and their salts or alkyl esters.

The polymerization method is conventionally known solution polymerization.

Suspension polymerization, emulsion polymerization, etc. can be applied, and the degree of polymerization is generally set to an intrinsic viscosity ([η]) of 1.0 or more, preferably 1.5 or more.

By adjusting the discharge amount of these cores and sheaths, the hollowness ratio can be adjusted, and it is preferable to adjust it depending on the purpose.

As the base, a known core/sheath base can be used, but a concentric type base is preferable. Regarding the number of cap holes: 3
Generally, it is about 00 to 10,000. The stretching ratio is generally about 2 to 15 times, but is preferably about 4 to 10 times because if the ratio is too high, the hollow space may be crushed. Also in the drying and densification step, the temperature is 60 to 150°C, as rapid drying may cause the hollow to collapse.

Preferably, it is carried out at a low temperature of 100 to 130°C.

The hollow acrylic fibers obtained in this way are
It is preferable to make the film resistant to flame under tension or stretching in an oxidizing atmosphere at 300°C, and then carbonize it under tension or stretching at 1000°C or higher in an inert atmosphere.

To obtain high strength, the firing temperature in an inert atmosphere must be set to 1.
It is more preferable to set the temperature in the range of 200 to 1600°C, but graphitization can be carried out at 2000°C or higher if necessary.

In order to increase density and improve strength and elastic modulus, it is more effective to stretch in the range of 300 to 500 °C and 2400 to 3000 °C, and specifically, the stretching ratio is LO~↑, 4 It is best to double the amount.

The obtained carbon fibers can be subjected to surface treatment and sizing by known methods. Using this carbon fiber as a reinforcing fiber and a matrix of thermosetting and thermoplastic resins, ceramics, metals, etc., a composite material with low specific gravity and high specific strength can be obtained.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A dimethyl sulfoxide (DMSO) solution (polymer A) with a concentration of 20% by weight was prepared using a copolymer consisting of 99.6 mol% acrylonitrile (AN) and 0.4 mol% itaconic acid, and A DMSO solution (polymer B) containing polyvinyl alcohol having a degree of polymerization of 3500 and having a concentration of 7% by weight was prepared.

Polymer A and Polymer B were used as sheath and core polymers, respectively, and the temperature was adjusted to 35°C, and the pore size was 0.
It was once discharged into the air through a concentric core-sheath type cap with 12 dishes φ and 1000 holes, and was allowed to run through a space of about 4 mm, and then coagulated in a DMSO aqueous solution with a concentration of 30% at a temperature of 5°C. The withdrawal speed was 30 m/min. The discharge amount ratio was 1 for the core and 6 for the sheath. After washing the coagulated yarn with water,
After stretching to 2.5 times in a hot water stretching bath and applying a silicone oil agent, it was brought into contact with a roller surface heated to 110°C to dry and densify it, and then 3. The fiber bundle was drawn three times in pressurized steam at 5 kg/d to obtain a fiber bundle with a single yarn fineness of 0°8 d and a total denier of 800 D.

The obtained acrylic fiber had a hollow portion in the core portion that was continuous in the fiber axis direction.

This hollow acrylic fiber is converted into a flame-resistant fiber by making it flame-resistant in air at 240-270°C at a stretching ratio of 1.05, and then fired in a nitrogen atmosphere at a maximum temperature of 1500°C, thereby stably forming the core. A hollow carbon fiber having a hollow portion continuous in the axial direction of the fiber was obtained.

The obtained hollow carbon fiber had a carbon content of 96% by weight, a hollowness ratio of about 15%, an apparent specific gravity as low as 1.55, and a high tensile strength of 560 kg/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.
The carbon content was 96% by weight, which is the same as in Example 1, but
There are no hollow parts and it becomes a solid carbon fiber with an apparent specific gravity of 1.8.
I could only get something as high as 2.

Examples 2 to 4 Hollow carbon fibers were obtained by spinning and firing in the same manner as in Example 1 except that the discharge rate ratio of the core and sheath was changed as shown in Table 1. Table 1 shows the properties of the obtained carbon fiber.

Note that the carbon content was 96% by weight in all cases.

(Hereinafter, blank spaces) Table 1 Example 5 The hollow carbon fiber obtained in Example 1 was further fired to 2800°C to obtain a graphitized fiber.

The obtained graphitized fiber is a hollow graphitized fiber having a hollow part continuous in the fiber axis direction in the core, and the carbon content is 99%.
, 8% by weight, the apparent specific gravity was as low as 1.58, and the tensile strength was as high as 460 kg/mm2.

Comparative Example 2 The hollow acrylic fiber obtained in Example 1 was fired at 8.degree. C. to obtain hollow carbon fiber. Although the apparent specific gravity was low at 1.63, the carbon content was low at 83% and the strength was 290 kg.
Only a low value of /mm2 was obtained.

[Effect of the invention] The carbon fiber of the present invention has a weight of 350 kg/a2 or more.

It is a carbon fiber that has the same strength as conventional high-strength type carbon fibers, and has an apparent specific gravity of 1.65 or less, which is extremely low compared to conventional carbon fibers, and is suitable for aerospace materials and sports materials such as fishing rods. lighter materials.

This makes it possible to make carbon fiber even thinner, further expanding the scope of use of carbon fiber.

Claims (1)

[Claims] The carbon content is 90% by weight or more, the core has a single hollow part, the apparent specific gravity is 1.65 or less, and the tensile strength is 350kg.
/mm^2 or more low specific gravity carbon fiber.