JP2535448B2 - Deformed cross-section carbon fiber and carbon fiber reinforced composite material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to carbon fibers having excellent composite properties, particularly carbon fibers having excellent properties in the direction perpendicular to the fiber axis and compression properties in the fiber axis direction, and carbon thereof. The present invention relates to a composite material using fibers.

[Prior Art] Carbon fibers are prepared by spinning acrylic, rayon, pitch, or polyvinyl alcohol fibers, which are their precursors, and heating and firing in an oxidizing atmosphere such as air or nitric oxide at 200 to 400 ° C. After passing through the flameproofing process of converting to oxidized fiber, go through a carbonization and graphitization process of carbonizing and / or graphitizing by further heating to 300-2500 ° C in an inert atmosphere such as nitrogen, argon, helium or vacuum. The method of manufacturing is widely adopted industrially.

The carbon fiber thus obtained is widely used as a structural material by forming a composite with a so-called matrix material such as resin or metal. Carbon fiber as a structural material has high mechanical properties, heat resistance, electrical properties, microbial resistance, etc., so aerospace structural members such as airplanes and rockets, golf clubs, tennis rackets, fishing rods, etc. It is widely used and produced as a reinforcing fiber in composite materials for sports equipment. In recent years, its performance, in particular, tensile strength is further improved, and at the same time, by maintaining a high tensile modulus, a field requiring higher performance characteristics, for example, has been studied for use in primary structural members of aircraft, While the tensile strength in the fiber axis direction is remarkably improved, the compressive strength in the same direction and the so-called transverse strength in the direction perpendicular to the fiber axis are not significantly improved.

To solve these problems, for example, Japanese Patent Application Laid-Open No. 57-42927 describes that carbon fibers having an irregular cross section improve the characteristics. According to the above publication, the maximum size is
Carbon fibers having a cross-sectional shape of 100 nm or less and having a polygonal shape having three or more linear sides or close thereto have been proposed.

However, according to the studies conducted by the present inventors, when the sides of the polygonal cross-sectional shape of the monofilament are linear, the packing density of the fibers is high, but on the other hand, the straight sides of different monofilaments are different from each other. It has been found that it is difficult to obtain a material having high tensile strength because it obstructs scattering of decomposition gas generated in the baking step due to adhesion.

A method of obtaining a modified cross-section yarn by melt spinning of polyacrylonitrile (hereinafter abbreviated as PAN) system is also known. Although no detailed data is presented, it is stated that this method also improves the compressive strength and the transverse strength of the carbon fiber.

[Problems to be Solved by the Invention] An object of the present invention is to facilitate the production in the production process, particularly in the yarn production process of a precursor, and to improve the adhesive force, bending strength, and compression force with a resin as compared with conventionally known modified cross-section yarns. It is to provide a carbon fiber having a great effect of improving composite properties such as strength.

[Means for Solving the Problems] The above objects of the present invention are as follows: (1) A monofilament has a cross-sectional shape of 3 to 5 lobes, and
Each leaf has a bulge from its root toward the tip, and it consists of a shape in which a plurality of circles are joined.
And the ratio of the circumscribed circle radius R of the fiber cross-sectional shape to the inscribed circle radius r
A polyacrylonitrile-based carbon fiber having a modified cross section, characterized in that the deformation degree defined by R / r is 1.5 to 3.

(2) A carbon fiber reinforced composite material comprising the modified cross-section carbon fiber according to claim (1).

 Can be achieved by

Although it is not clear why the carbon fiber having such a shape has a great effect of improving the composite properties, it is considered as follows. Various factors are supposed to control the lateral characteristics of the carbon fiber reinforced composite material, but the physical shape and the specific surface area are important factors as physical factors. The carbon fiber of the present invention has a large specific surface area because the carbon fiber of the present invention has a multi-lobed shape and has a structure in which each leaf has a bulge from the root toward the tip, unlike the conventionally proposed cross-section yarn. It is considered that the adhesive force with the resin increases because the space exerts a so-called anchor effect that works like a kind of anchor.

In addition, because of the similar shape, the distance from the surface of the single fiber to the center is shorter than in the case of conventional irregularly shaped cross-section yarns, so oxygen diffusion to the center is easy and more uniform firing is possible, resulting in strength and elasticity of the carbon fiber. It is considered that as the modulus increases, the resistance to bending deformation increases, and the compressive strength and bending strength increase.

The modified cross-section carbon fiber of the present invention has a multi-lobed shape as shown in FIGS. 1A to 1C, has a bulge from the root of each leaf toward the tip, and has a shape in which a plurality of circles are substantially joined. And the degree of irregularity of the fiber cross section is in the range of 1.5 to 3.0.
When the degree of irregularity of the fiber cross section is less than 1.5, there is virtually no bulge from the root of each leaf toward the tip.
If it exceeds 3.0, the leaves will be damaged during the firing process, resulting in increased fuzz, which is not preferable.

Examples of the method for obtaining the carbon fiber of the present invention include a method of melt spinning PAN using a spinneret hole having a shape substantially similar to that of the single fiber shown in FIG. 2, or a method of wet spinning PAN at a low speed. Further, in particular, a method in which a plurality of circular holes shown in FIG. 2 are punched at regular intervals and used in combination and a polymer discharged from a die is joined to obtain a precursor having a desired shape is advantageous in terms of die accuracy and spinnability. preferable. Regarding the arrangement of the circular holes, it is preferable to have one hole at the center and three to five circular holes on the outer circumference thereof at rotationally symmetrical positions on the same circumference. One hole is arranged at the center. The leaves of the cross section of the fiber obtained by the above are given a shape that once bulges from the root toward the tip. The distance between the central hole and the peripheral hole is appropriately determined based on the shape of the obtained fiber.

The carbon fiber of the present invention uses an acrylic type as its precursor (precursor), and the cross-sectional shape of the monofilament is a multileaf shape of 3 to 5 leaves in the yarn making step, and each leaf has its root to its tip. The desired carbon fiber can be obtained by adjusting the die shape so as to have a bulge and firing the obtained fiber, but in the pitch system, the compression strength of the fiber itself is low, so that Even if it is used as a carbon fiber strength composite material, the compressive strength and bending strength of the composite material cannot be improved.

The acrylic fiber in this case is acrylonitrile (hereinafter
AN)) or containing AN as a main component, preferably 90% by weight or more, particularly preferably 93% by weight or more, and preferably 10% by weight or less, particularly preferably 0.2 to 7% by weight. And a copolymer with one or more vinyl group-containing compounds (hereinafter referred to as vinyl-based monomers).

Examples of vinyl monomers copolymerized with AN include allyl alcohol, methallyl alcohol, hydroxyalkyl acrylonitrile and its derivatives, acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts, alkyl esters, Examples thereof include acrylamide and its derivatives, methacrylonitrile, acrylic acid hydroxyl ester, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid and their alkali metal salts, vinyl acetate and vinyl chloride.

When the amount of these copolymers exceeds 10%, the heat resistance of the precursor is insufficient and sufficient physical properties cannot be obtained.
It is particularly preferable to use hydrophilic ones as the copolymerization component, since a precursor having good compactness can be easily obtained. The method for producing such an AN polymer is not particularly limited, and a general polymerization method such as emulsion suspension, lump and solution can be used. The degree of polymerization of the polymer has an intrinsic viscosity of 1.3 to 5.0, preferably 1.5 to 3.0.

As a method for producing an acrylic fiber from these polymers, dimethylformamide, dimethylacetamide,
Organic solvent such as dimethylsulfoxide, nitric acid, zinc chloride, a polymer solution of an inorganic solvent such as aqueous solution of rhodanesoda is used as a spinning dope, and is spun by an ordinary wet spinning method, a dry wet spinning method, and a dry spinning method to form a fiber. be able to.

Among these spinning methods, when spinning is performed by the dry-wet spinning method, carbon fiber having relatively high speed and high tensile property can be obtained, the take-up speed, the distance between the spinneret and the coagulating liquid surface, and the coagulating bath temperature concentration. It is particularly preferable because carbon fibers having various shapes can be obtained by adjusting the conditions.

The coagulated fiber spun in this manner has a total draw ratio of 5 times or more, preferably 7 times or more in the spinning process, and substantially 3 or more stages of drawing are finally conducted in a heating medium of 100 ° C. or more. It is preferable to carry out. The filament number of the precursor fiber obtained by such a spinning method is usually 50
You can select from 0 to 30,000. The single fiber fineness can be selected in the range of 0.1 to 5d, but the single yarn fineness of the obtained precursor is 3d or less, preferably 0.5 to
Those of 2.0d are particularly suitable for the purposes of the invention.

The oil used in this precursor is a silicone-based oil,
In particular, it is preferable that one component thereof contains a modifying group having an amino group, and it is desirable that 0.01% to 5.0% is attached to the fiber weight. If the adhered amount is less than 0.01%, the object of the present invention will not be achieved, and if the adhered amount is 5% or more, the tar content in the heating step will increase, and the oil agent will fall off in the yarn making step and the yarn Fluffing cannot be ignored.

This oil agent is usually applied alone or after being dissolved or dispersed in water or a solvent, to the swollen yarn. As an example of an emulsifier for dispersing in water, generally, for a silicon component,
Up to 30% by weight of surfactant is used. In particular, nonionic surfactants such as polyoxyethylene alkyl phenyl ether, polyethylene glycol (molecular weight
200-1000) Fatty acid esters are good. Especially nonyl,
Alternatively, derivatives of octyl and dodecyl phenyl ether are preferable.

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

In this example, carbon fiber performance (strength, elastic modulus) is JIS R
It is a physical property of a strand impregnated with an epoxy resin measured according to −7601, and is a value obtained from an average of the number of measurements n = 10.

ILSS and bending strength are Epicoat 828 resin / BF3 / MEA
(3 phr) is a composite value obtained by curing at 170 ° C. for 3 hours using a matrix base material.

Example Acrylonitrile 99.3% by weight, itaconic acid 0.7% by weight
A 20% dimethylsulfoxide solution of acrylic copolymer consisting of (polymer having a solution viscosity of 600 poise at 45 ° C) was once discharged into the air using the mouthpiece shown in Fig. 2 a, b, c. After passing through the space, dry-wet spinning is carried out in a stationary coagulation bath to coagulate using a coagulating liquid of dimethyl sulfoxide 30%, 5 ° C., and drawing in a liquid bath is performed while washing with water.
A swollen fiber was formed.

Amino-modified silicone (amino content of 0.
8%), and continuously stretched after drying, with a total magnification of 10
The film was stretched at twice and wound up. The yarn is oxidized in air with a temperature profile of 250/270 ° C and then the maximum temperature is 1350.
It was introduced into a carbonization furnace at ℃ and carbonized in a nitrogen atmosphere. The cross-sectional shape of the carbon fiber at this time is shown in FIG. 1 a, b, c.

 The composite properties of this fiber are shown in Table 1.

The modified cross-section carbon fiber of the present invention has good operability in the firing process for fiber production and excellent composite properties. On the other hand, e used for comparison was a fiber with a lot of fluff due to the adhesion between single yarns at the time of firing and the composite property was not improved.

[Advantages of the Invention] The carbon fiber of the present invention has a shape that once bulges from the root of each leaf toward the tip, so that when used in a composite, it has good adhesion to the matrix base material. In addition, a composite having excellent compressive strength and bending strength can be obtained by increasing the bending resistance derived from the single yarn shape.

In addition, the carbon fiber of the present cross-sectional shape is manufactured from a precursor of a substantially similar shape, but since the distance between the center of the fiber and the surface is smaller than conventional fibers, it is easy for oxygen to diffuse,
It has the effect of completing the oxidation reaction in a short time. In addition, since the contact area between single fibers is small because it does not have a substantially linear portion in its cross section, fusion during firing hardly occurs, and the generated decomposition gas easily diffuses out of the system. Becomes

[Brief description of drawings]

FIG. 1 shows the cross-sectional shape of carbon fiber, where a, b and c are the cross-sectional shape of the product of the present invention and d and e are the cross-sectional shape of the comparative product. FIG. 2 shows the hole shapes of the spinneret, where a, b and c are the hole shapes of the spinneret used in the product of the present invention, and d and e are the hole shapes of the spinneret used in the comparative product.

Claims (2)

(57) [Claims] 1. A monofilament has a cross-sectional shape of 3 to 5 leaves, and each leaf has a bulge from its root to its tip, and a shape in which a plurality of circles are substantially joined. A polyacrylonitrile-based carbon fiber having an irregular cross-section, characterized in that the irregularity degree defined by the ratio R / r of the circumscribed circle radius R and the inscribed circle radius r of the fiber cross-sectional shape is 1.5 to 3. 2. A carbon fiber reinforced composite material comprising the modified cross-section carbon fiber according to claim 1.