JP2870932B2 - Method for producing hollow acrylic carbon fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a hollow acrylic carbon fiber.

[Prior Art] In recent years, as the application development of carbon fiber has been expanded, demands for improvement in specific strength and specific elastic modulus have been more and more increased. Especially in aerospace applications where weight reduction effect is great,
There is a need for lighter carbon fibers to reduce the weight even slightly.

Conventional carbon fibers have a specific gravity of about 1.75 to 2.10, which is higher than the specific gravity of resins of 1.2 to 1.4, which causes the specific gravity of carbon fiber reinforced composite materials to increase.

As a technique for lowering the specific gravity, there is a technique for hollowing carbon fibers. However, a conventionally known hollow carbon fiber is a technique for hollowing out by dissolving or dissolving the core in a firing or post-treatment step (Japanese Patent Laid-Open No. 55-55). No. 45866, Japanese Patent Publication No. 1-53362
Therefore, there is a problem that defects such as voids are easily generated and the tensile strength level is lowered to less than 300 kg / mm ^2, and the strength is insufficient as a reinforcing carbon fiber. In addition, as a technique for producing hollow carbon fibers by firing hollow acrylic fibers, a hollow carbon fiber is manufactured by firing thick 10 denier hollow acrylic fibers spun using a slightly bonded type die ( There is JP-B-53-14650, Example 2), but the firing stability is poor due to the use of thick hollow acrylic fiber, and the strength is 270k.
g / mm ² , a low level.

[Problems to be Solved by the Invention] Accordingly, the present inventors have earnestly studied a high-strength hollow carbon fiber that maintains the tensile strength of a conventional high-strength type carbon fiber, and reached the present invention. That is, an object of the present invention is to provide a method for producing a hollow acrylic carbon fiber having a high tensile strength, which cannot be achieved by the above-described conventional technology.

[Means for Solving the Problems] The object of the present invention is to form fibers by using a core-sheath die and putting an acrylic polymer in a sheath and a polymer soluble in a coagulation, washing or stretching solution in a core. After that, the hollow acrylic fiber having a single fiber denier of 1.5 denier or less obtained by dissolving the core is made flame-resistant in an oxidizing atmosphere of 200 to 300 ° C., and then carbonized at 1000 ° C. or more in an inert atmosphere. A hollow carbon fiber having a hollow ratio of 4 to 40% and a tensile strength of 350 kg / mm ² or more.

 Can be solved by

First, the hollow acrylic carbon fiber (hereinafter, simply referred to as hollow carbon fiber) obtained in the present invention will be described.

That is, the hollow carbon fiber obtained in the present invention has a hollow ratio of 4 to 40% obtained by firing a hollow acrylic fiber having a single fiber denier of 1.5 denier or less and a tensile strength of 350 k.
g / mm ² or more, which is a hollow carbon fiber satisfying high strength, which is very difficult with conventional techniques. The tensile strength while maintaining conventional high strength type carbon fibers equivalent 350 kg / mm ² or more, by having a hollow portion of the hollow rate 4-40% in the core portion, an apparent specific gravity of 1.7 to 1.0
As a result, a high strength carbon fiber having a considerably low degree can be obtained, and the specific strength of the composite material can be greatly improved. Further, since the cross section of the single fiber becomes hollow, a remarkable effect such that the bending rigidity is improved and the bending characteristics of the composite material are significantly improved is obtained.

If the hollow ratio is less than 4%, the hollowing effect is insufficient, and if it exceeds 40%, the thickness of the sheath is reduced, and the sheath is easily broken or crushed, and the strength is undesirably reduced.

In order to obtain a hollow carbon fiber having a high tensile strength, it is important to fire the hollow acrylic fiber instead of dissolving or dissolving the core in the firing or post-treatment step. That is, if the core is decomposed and scattered or melted in the firing or post-treatment step, it becomes a defect such as a void and the strength is reduced, which is not preferable. Furthermore, in order to stably sinter high-strength hollow carbon fibers, it is important that the hollow acrylic fibers have a single fiber denier of 1.5 denier or less.

In addition, the tensile strength in this invention was calculated | required by the resin impregnated strand evaluation method. That is, "Bakelite" ERL-4
221/1 Boron trifluoride monoethylamine (BF3.MEA) / acetone = 100/3/4 parts is impregnated into carbon fiber, and the obtained resin-impregnated strand is cured by heating at 130 ° C for 30 minutes, JIS
-Measured according to the resin impregnated strand test method specified in R-7601. The cross-sectional area including the hollow was used as the fiber cross-sectional area.

The hollow ratio was determined from the area ratio by observing the cross section of the resin-impregnated strand with an SEM.

The apparent specific gravity is a value obtained by the Archimedes method. That is, the weight in the air (W1) and the weight in the liquid (W2) of the carbon fiber having a unit length were measured, and were obtained by the following equation. Note that dichlorobenzene was used as the liquid.

Apparent specific gravity = (W1 / (W1-W2)) × liquid specific gravity Next, the method for producing hollow acrylic carbon fibers in the present invention will be described more specifically.

That is, in order to stably obtain a hollow carbon fiber having a tensile strength of 350 kg / mm ² or more, it is necessary to bake a hollow acrylic fiber having a single fiber denier of 1.5 denier or less.

As a spinning method for producing a hollow acrylic fiber having a single fiber denier of 1.5 denier or less, a wet spinning method, a dry-wet spinning method or a dry spinning method can be adopted, but a wet spinning method or a dry-wet spinning method is preferable. More preferably, a dry-wet spinning method, in which fineness is easily obtained, is preferred. In order to obtain a stable hollow acrylic fiber with a fine fineness and without the hollow part being crushed or the sheath part being torn, an acrylic polymer is put into the sheath part using a core-sheath die and solidified into the core part. It is effective to dissolve the core by adding a soluble polymer to the washing or stretching bath solution.

The polymer soluble in coagulation, washing or stretching bath
Organic solvents such as acetone, methanol, acetonitrile, dimethylsulfoxide, and dimethylformamide used for the coagulation bath solution, or inorganic solvents such as zinc chloride, nitric acid, rodane soda, and rodane nitrate salt, and water washing. It is soluble in any of the solvents such as steam and glycerin. Specifically, synthetic polymers such as polyvinyl ether, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyacrylamide, polyacrylic acid, polyvinylpyrrolidone, polyethyleneimine, sodium polyphosphate, and viscose, methylcellulose, ethylcellulose,
Semi-synthetic polymers such as hydroxyethylcellulose, carboxymethylcellulose, dextrin, dialdehyde starch, carboxystarch, and starch,
A mixture of one or more selected from natural polymers such as dextrin and tragacanth rubber can be shown.

As the acrylic polymer to be put in the sheath, at least
85 mol% or more of acrylonitrile and 15 mol% or less of copolymerizable vinyl monomers such as acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters, acrylamide and its derivatives, allyl Copolymers with sulfonic acid, methallyl sulfonic acid and salts or alkyl esters thereof can be given.

As the polymerization method, conventionally known solution polymerization, suspension polymerization, emulsion polymerization and the like can be applied, and the polymerization degree is preferably 1.0 or more, preferably 1.5 or more in intrinsic viscosity ([η]). General.

The hollow ratio can be adjusted by adjusting the discharge amount of the core and the sheath. 4-50 for hollow ratio
%, Preferably about 10 to 30%, and is preferably adjusted according to the purpose.

As the base, a known core-sheath base can be used, but a concentric type base is preferable. The number of base holes is generally about 300 to 10,000. The stretching ratio is generally about 2 to 15 times, but if the ratio is too high, the hollow may be crushed. Also in the drying and densification step, if the drying is performed rapidly, the hollows may be crushed. Therefore, it is preferable to perform the drying at a low temperature of 60 to 150 ° C, preferably 100 to 130 ° C.

It is necessary to carbonize the hollow acrylic fiber having a denier of 1.5 denier or less in the oxidizing atmosphere of 200 to 300 ° C. in an oxidizing atmosphere at 1000 ° C. or more in an inert atmosphere after the flame resistance is obtained. .

To obtain high strength, set the firing temperature in an inert atmosphere
The temperature should be in the range of 1200 to 1600 ° C, but if necessary, 2000
It can be graphitized at a temperature of at least ℃.

In order to further increase the denseness and improve the strength and elastic modulus, it is effective to carry out flame resistance in an oxidizing atmosphere and carbonization in an inert atmosphere under tension or stretching conditions, particularly 300 Stretching in the range of -500 ° C and 2400-3000 ° C is more effective. Specifically, it is desirable that the stretching ratio is about 1.0 to 1.4 times.

The obtained carbon fiber can be subjected to surface treatment and sizing by a known method. A composite material having a low specific gravity and a high specific strength can be obtained by using the carbon fiber as a reinforcing fiber and a thermosetting and thermoplastic resin, ceramics, metal or the like as a matrix.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 Acrylonitrile (AN) 99.5 mol% and methacrylic acid 0.
A dimethylsulfoxide (DMSO) solution (polymer A) having a concentration of 19% by weight was prepared using a copolymer consisting of 5 mol%, and a 8% by weight DMSO solution (polymer B) of polyvinyl alcohol having a degree of polymerization of 3000 was prepared. ) Was prepared. Polymer A and polymer B were used as sheath and core polymers, respectively, and both were adjusted to a temperature of 35 ° C. and had a pore diameter of 0.12 mm.
Once the air is discharged into the air through a concentric-type core-and-sheath base with φ, 500 holes and runs through a space of about 5 mm, the temperature is 5
Coagulation was carried out in a 30% aqueous solution of DMSO at a temperature of 30 ° C. The take-up speed is
It was 40 m / min. The ratio of the discharge amount is 7 for the sheath portion with respect to the core portion 1.
Met. After washing the coagulated yarn with water, 2.5
After applying a silicone oil, the film is contacted with the surface of a roller heated to 110 ° C to be dried and densified, and further stretched 3 times in a 3.7 kg / cm ² pressure steam to obtain a single yarn fineness of 1d. Thus, a fiber bundle of total denier 500D was obtained. The obtained acrylic fiber had a hollow part continuous in the fiber axis direction in the core part.

The hollow acrylic fiber is oxidized at 240 to 270 ° C. in air at a draw ratio of 1.05 to convert it into oxidized fiber, and then fired in a nitrogen atmosphere at a maximum temperature of 1500 ° C. to provide a stable fiber core. A true concentric hollow carbon fiber having a hollow portion continuous in the direction was obtained.

The hollow carbon fiber obtained has a hollow ratio of 13% and an apparent specific gravity of
The tensile strength was as low as 1.58 and the tensile strength was as high as 510 kg / mm ² .

Comparative Example 1 In Example 1, when the yarn was formed and fired in the same manner as in Example 1 except that the polymer A was also added to the core, the hollow carbon fiber was not obtained because it was solid.

Examples 2 to 3 and Comparative Example 2 In Example 1, the discharge amount ratio between the core and the sheath polymer is shown in Table 1.
The hollow acrylic fibers having different hollow ratios were produced in the same manner as described above, and were fired under the same conditions as in Example 1 to obtain carbon fibers. The properties of the obtained carbon fiber are shown in Table 1.

Example 4 The hollow carbon fiber obtained in Example 1 was further baked to 2800 ° C. in a nitrogen atmosphere to obtain a graphitized fiber.

The obtained graphitized fiber is a hollow graphitized fiber having a hollow portion continuous in the fiber axis direction at the core, having a hollow ratio of 14%, an apparent specific gravity as low as 1.62, and a tensile strength of 390 kg / mm ² . High strength.

Comparative Example 3 A yarn was produced in the same manner as in Example 1 except that the discharge amounts of the core and the sheath polymer were both 2.5 times.
A hollow acrylic fiber having a single fiber denier of 2.5 denier was obtained. When the obtained hollow acrylic fiber was fired in the same manner as in Example 1, the yarn was broken due to heat storage at the same flame resistance temperature, and the maximum temperature was lowered by 20 ° C. to perform the flame resistance. Further, as in Example 1, firing in a nitrogen atmosphere at a maximum temperature of 1500 ° C. resulted in thread breakage at the same speed, which prevented stable firing. As a result of firing by reducing the firing rate to 1/2, the obtained carbon fiber there was a hollow carbon fiber having a hollow portion continuous in the fiber axis direction in the core portion, fluff Many strength and 310 kg / mm ² Only a low one was obtained.

[Effects of the Invention] According to the present invention, it is possible to obtain a high-strength hollow acrylic carbon fiber which is very difficult with the conventional technology, and the obtained hollow carbon fiber is different from the conventional acrylic carbon fiber. It is possible to greatly reduce the apparent specific gravity,
Significant improvement in specific strength has made it possible to expand the use of primary structural materials in aircraft.

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Claims (1)

(57) [Claims] 1. Using a core-sheath die, an acrylic polymer is put in a sheath portion, and a polymer soluble in a coagulation, washing or drawing solution is put in a core portion to form fibers, and then the core portion is dissolved. After the hollow acrylic fiber having a denier of 1.5 denier or less is flame-resistant in an oxidizing atmosphere of 200 to 300 ° C, the hollow fiber is carbonized at 1000 ° C or more in an inert atmosphere to have a hollow ratio of 4 to
A method for producing a hollow acrylic carbon fiber, comprising obtaining a hollow carbon fiber having a tensile strength of 350 kg / mm ² or more at 40%.