JP2006283226A - Flame-proofed fiber, carbon fiber and method for producing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber usable when producing a composite by compounding a matrix material with the carbon fiber, and having excellent surface/interface characteristics; and to provide a method for producing the carbon fiber. <P>SOLUTION: The carbon fiber having a fiber cross section cut by an arbitrary cutting face passing the fiber axis, having both edge shapes in the width direction formed into a wave shape repeating bending, and further having independent hollow parts 8 in the fiber at the mountain 4 parts of the wave shape is produced by carbonizing the flame-proofed fiber having >0.6 ratio (f/e) of the thickness (f) of a not-flame-proofed part to the thickness (e) of an already flame-proofed part in a white-black image of a fiber cross section obtained by a scanning probe microscope observation, and 1.32-1.41 specific gravity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carbon fiber excellent in surface / interface characteristics used when a matrix material and a carbon fiber are composited to produce a composite, a flame resistant fiber useful for the production thereof, and a production method thereof. .

  As a method for producing carbon fiber, a method of obtaining carbon fiber by using a precursor fiber (precursor) such as polyacrylonitrile (PAN) as a raw material fiber and undergoing a flame resistance treatment and a carbonization treatment is widely known (for example, , See Patent Document 1). The carbon fibers thus obtained have good characteristics such as high specific strength and specific elastic modulus.

  In recent years, industrial applications of composite materials using carbon fibers [for example, carbon fiber reinforced plastic (CFRP) and the like] have been spreading to various purposes. Especially in the sports / leisure field, aerospace field, and automobile field, (1) higher performance (higher strength, higher elasticity), (2) lighter (fiber weight reduction and fiber content reduction), ( 3) There is an increasing demand for improving the appearance of higher composite properties when combined (improvement of carbon fiber surface / interface properties).

  In order to pursue high performance in the composite of carbon fiber and resin or other matrix material, the characteristics of the matrix material are also important, but it is essential to improve the surface characteristics of the carbon fiber itself. . In other words, by combining materials with high adhesion between the carbon fiber surface and the matrix material, and dispersing the matrix material and the carbon fiber more uniformly, the composite material with higher performance (high strength, high elasticity) can be obtained. Obtainable.

However, none of the above-mentioned requirements have been sufficiently satisfied.
JP 2001-131833 A (claims, page 5)

  While the present inventor has made various studies in order to solve the above problems, an image of a fiber cross section obtained by scanning probe microscope (SPM) observation according to the progress of the flame resistance of the precursor is the outer circumference of the fiber cross section. A double circle is observed which consists of an outer circle indicating the portion and an inner circle formed at the boundary between the flame-resistant portion formed from the outer surface of the fiber toward the fiber axis and the non-flame-resistant portion including the fiber axis. As described above, flameproofing fibers useful for the production of the following carbon fibers can be obtained by flameproofing the precursor while adjusting the gradient coefficient A indicating the flameproofing treatment time against the specific gravity increase at the time of temperature rise. I found it.

  That is, the carbon fiber obtained by carbonizing this flame resistant fiber is formed by alternately and continuously forming a large diameter portion and a small diameter portion along the fiber axis direction, and an independent hollow in the fiber of the large diameter portion. The large-diameter portion and the small-diameter portion have a predetermined interval and a predetermined diameter difference, so to speak, the shape of a shell of empty beans.

  Further, when this carbon fiber is combined with a matrix material to form a composite, it has been found that the carbon fiber exhibits good catching properties and adhesiveness with the matrix material, and the present invention has been completed.

  Accordingly, an object of the present invention is to provide a carbon fiber that has solved the above problems, a flame-resistant fiber that is useful for the production thereof, and a method for producing the same.

  The present invention for achieving the above object is described below.

  [1] In the black and white image of the fiber cross section obtained by scanning probe microscope observation of the flameproof fiber for carbon fiber production, the black and white density distribution of the fiber cross section image is an outer circle formed by the image of the fiber cross section outer periphery, It has a double circular structure with an inner circle formed at the boundary between the flame-resistant portion formed in the fiber axis direction from the outer surface of the fiber and the non-flame-resistant portion including the fiber axis, and the diameter of the flame-resistant portion. Flame resistance in which the ratio (f / e) of the directional thickness (e) and the thickness (f) of the non-flame resistant portion indicated by the inner circle radius is greater than 0.6 and the specific gravity is 1.32 to 1.41 Fiber.

[2] When a carbon fiber precursor is flameproofed, the following gradient coefficient A = flameproofing time (min) / specific gravity increase
(Here, specific gravity increase = flame-resistant fiber specific gravity−precursor specific gravity)
A method for producing a flame-resistant fiber, characterized in that the gradient coefficient A determined in step 1 is kept below 200.

  [3] A method for producing a carbon fiber, comprising heat-treating the flame-resistant fiber according to [1] in an inert gas atmosphere.

  In the carbon fiber of the present invention, the fiber surface has hollow bean shell-like irregularities in the axial direction, that is, both end shapes in the width direction of the fiber cross section cut at an arbitrary cut surface passing through the fiber axis are each wavy that repeats bending. Since it is formed into a shape, when it is combined with a matrix material to form a composite, it functions as a reinforcing material having good dispersibility, catching properties, and adhesiveness with the matrix material.

  In the flame-resistant fiber of the present invention, the image of the fiber cross section obtained by SPM observation shows the boundary between the outer circle showing the outer periphery of the fiber cross section, the flame-resistant part near the surface layer, and the non-flame-resistant part near the center of the circle. And a ratio (f / e) between the thickness (e) of the flameproofed portion and the thickness (f) of the nonflamed portion is larger than 0.6 and the specific gravity is 1 .32 to 1.41, it is useful for the production of the carbon fiber.

  According to the method for producing a flame-resistant fiber of the present invention, the precursor is flame-resistant while adjusting the gradient coefficient A indicating the flame resistance treatment time with respect to the increase in specific gravity at the time of temperature rise to a predetermined range. The resulting fiber cross-sectional image can stably produce the double-circle flame-resistant fiber.

  Hereinafter, the present invention will be described in detail.

  FIG. 1 is a schematic cross-sectional view showing an example of the carbon fiber of the present invention. As shown in FIG. 1, the carbon fiber 2 of this example is formed in a wavy shape in which both ends in the width direction of the fiber cross section cut at an arbitrary cut surface passing through the fiber axis repeat bending. In FIG. 1, 4 is a wave-shaped peak, and 6 is a wave-shaped valley. The carbon fiber 2 has an independent hollow portion 8 in the fiber of the corrugated crest 4 portion.

  The corrugated crest 4 forms a large diameter portion around the entire fiber surface. a shows the fiber diameter (fiber large diameter) in a large diameter part. The corrugated valley 6 forms a small diameter portion on the entire circumference of the fiber surface. b shows the fiber diameter (small fiber diameter) in a small diameter part.

  In the carbon fiber of the present invention, the average fiber diameter is preferably 8.5 to 12.0 μm, and more preferably 8.7 to 11.0 μm.

  The carbon fiber of the present invention can be obtained by heat-treating the following flame-resistant fiber of the present invention in an inert gas atmosphere.

  The flame-resistant fiber of the present invention is a flame-resistant fiber obtained by subjecting a carbon fiber precursor to flame resistance treatment, and has a specific gravity of 1.32 to 1.41. The fiber diameter of the flame resistant fiber is preferably 13 μm or more, and more preferably 14 to 19 μm.

  FIG. 2 is a schematic cross-sectional view showing an example of the flameproof fiber of the present invention. In FIG. 2, 12 is a flame resistant fiber, and 14 is an outer circle showing the outer periphery of the flame resistant fiber cross section. Inside the outer circle 14, an inner circle 22 is formed by a boundary between the flame-resistant portion 16 formed from the fiber surface to the fiber axis (center of the circle) 18 and the non-flame-resistant portion 20 near the center 18 of the circle. Is formed.

  The SPM is typified by an atomic force microscope (AFM). When the cross section of the flame-resistant fiber is observed using the SPM, the difference in physical properties between the flame-resistant portion 16 and the non-flame-resistant portion 20 in the fiber cross-section is imaged. That is, the SPM image of the cross section of the flameproof fiber 12 becomes a double circle.

  FIG. 3 is a SPM photograph in place of a drawing showing an example of the precursor 12 during the flameproofing treatment. In the precursor in the middle of the flameproofing treatment, as shown in FIG. 3, the black and white density distribution of the image of the fiber cross section is the outer circle formed by the image of the fiber cross section outer peripheral part, the flameproofed part and the non-flameproof part. A double circle with an inner circle formed at the boundary is shown.

  In FIG. 2, e indicates the thickness of the flameproof portion 16, and f indicates the thickness of the non-flameproof portion 20. In the flame-resistant fiber of the present invention, the ratio (f / e) of the thickness (e) of the flame-resistant portion to the thickness (f) of the non-flame-resistant portion is larger than 0.6, preferably 0.6 to 0.00. Nine.

  When the ratio (f / e), specific gravity, and fiber diameter of the flameproof fiber deviate from the above ranges, at least one of the orientation and strength of the obtained carbon fiber is not preferable.

  FIG. 4 is a SPM photograph in place of a drawing showing an example of a conventional flameproof fiber having a ratio (f / e) of 0. Since this flame-resistant fiber has only a flame-resistant portion and no non-flame-resistant portion, the SPM image has a black and white density distribution with a uniform fiber cross section, and does not show a specific shape due to any bias in the black and white density. That is, as shown in FIG. 4, the image forming the circle in the fiber cross-sectional image is only the outer periphery of the fiber cross-section, and the image of the fiber cross-section obtained by SPM observation is not a double circle as shown in FIG.

  The measurement principle of SPM is to trace the sample surface with an electron beam probe, discretely measure the sample shape (the height of the sample surface), and perform image analysis processing on a computer. The feature is that the accuracy of the height information is high.

  This image analysis processing can be performed using a known method as disclosed in, for example, Japanese Patent Laid-Open No. 2003-293264.

  The flame resistant fiber of the present invention can be produced, for example, by the following method.

  Since a flame-resistant fiber suitable as an intermediate raw material for obtaining the highest quality carbon fiber can be obtained, the precursor that is a raw material of the flame-resistant fiber of the present invention is preferably a PAN-based precursor. In addition to the PAN-based precursor, a pitch-based, phenol-based, cellulose-based, rayon-based precursor or the like can also be used.

  PAN-based precursors, for example, a spinning solution containing a homopolymer or copolymer obtained by polymerizing a monomer containing 95% by mass or more of acrylonitrile in a wet or dry-wet spinning method such as spinning, washing, drying, stretching, etc. Can be obtained by doing As the monomer to be copolymerized, methyl acrylate, itaconic acid, methyl methacrylate, acrylic acid and the like are preferable.

  The fiber diameter of the precursor is adjusted to 14 to 19 μm.

  The precursor thus obtained is flame-resistant according to the method for producing flame-resistant fibers of the present invention to obtain flame-resistant fibers.

In the flameproofing process in the method for producing a flameproofed fiber of the present invention, when the precursor is flameproofed, the following gradient coefficient A = flameproofing time (minutes) / specific gravity increase
(Here, specific gravity increase = flame-resistant fiber specific gravity−precursor specific gravity)
Is less than 200, preferably 150 to 199.

  In the method for producing flame-resistant fibers of the present invention, fibers obtained by SPM observation are obtained by flame-treating the precursor while adjusting the gradient coefficient A indicating the flame resistance treatment time with respect to the increase in specific gravity at the time of temperature rise to the above range. It is possible to obtain a flame-resistant fiber whose cross-sectional image is a double circle in which the ratio (f / e) of the thickness (e) of the flame-resistant part to the thickness (f) of the non-flame-resistant part is larger than 0.6. it can.

  Next, the flame-resistant fiber is baked and carbonized in an inert gas atmosphere such as a nitrogen atmosphere to obtain a carbon fiber. The firing conditions are not particularly limited, and follow known conditions. Furthermore, it is preferable that the carbon fiber is sized for the purpose of facilitating the post-processing of the carbon fiber and improving the handleability. The sizing method can be carried out by a conventionally known method, and the sizing agent is preferably used after changing its composition as appropriate according to the application, and after uniformly adhering to the carbon fiber.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Moreover, the evaluation method about the various physical properties of the precursor in each Example and a comparative example, a flame-resistant fiber, and carbon fiber was implemented by the above-mentioned method or the following methods.

<Fiber specific gravity>
Measured by Archimedes method. Precursor or flameproof fiber sample fibers were degassed in acetone and measured.

<SPM observation>
Sample preparation method: Flame-resistant fibers were embedded in an epoxy resin (Epomount: manufactured by Refinetech), and a cross-sectional sample was prepared using a diamond knife with a microtome.

  SPM device: SPM Dimension3100 manufactured by Digital Instrument was used to observe the cross section of the flameproof fiber.

<Tensile strength>
It was measured by the method defined in JIS R7601.

Examples 1-5 and Comparative Examples 1-5
Copolymer spinning stock solution consisting of 95% by weight of acrylonitrile / 4% by weight of methyl acrylate / 1% by weight of itaconic acid is wet or dry-wet spun, washed with water, dried and stretched, and fiber diameter: Examples 1-4 and Comparative Examples Precursors of 15.5 μm for 1-4, 18.5 μm for Example 5, and 8.5 μm for Comparative Example 5 were obtained.

  This precursor was made into a flame resistant fiber under the conditions shown in Table 1 in an oxidizing atmosphere using a hot air circulation type flame resistant furnace set at 240 to 250 ° C. Table 1 shows the physical properties of the obtained flame-resistant fiber. These flame-resistant fibers are heat-treated in an inert gas atmosphere in a first carbonization furnace set at 350 to 600 ° C, and subsequently heat-treated in an inert gas atmosphere in a second carbonization furnace set at 700 to 1500 ° C. The carbon fiber was obtained. Table 1 shows the physical properties of the obtained carbon fibers.

実施例１〜５において得られた耐炎化繊維は、観察より得られる繊維断面の画像が二重円を示し、既耐炎化部分の厚み(ｅ)と未耐炎化部分の厚み(ｆ)との比(ｆ／ｅ)が０．６より大きく、この耐炎化繊維から得られた炭素繊維は、繊維軸を通る任意の切断面で切断した繊維断面の幅方向両端形状がそれぞれ曲折を繰返す波状形状(繊維表面がその軸方向に脈状の凹凸を有すること)を示すものであった。

In the flame-resistant fibers obtained in Examples 1 to 5, the image of the fiber cross section obtained by observation shows a double circle, and the thickness (e) of the flame-resistant part and the thickness (f) of the non-flame-resistant part The ratio (f / e) is greater than 0.6, and the carbon fiber obtained from the flame-resistant fiber has a wavy shape in which both ends in the width direction of the fiber cross section cut at an arbitrary cut surface passing through the fiber axis are repeatedly bent. (The fiber surface has vein-like irregularities in its axial direction).

  The flame resistant fiber obtained in Comparative Example 1 deviates from the configuration of the present invention in that the specific gravity is 1.30 and 1.32 to 1.41, and this flame resistant fiber passes through the carbonization step. I could n’t.

  The flame-resistant fibers obtained in Comparative Examples 2 to 4 show that the image of the fiber cross section obtained by observation shows a double circle, the thickness (e) of the flame-resistant part and the thickness (f) of the non-flame-resistant part. The ratio (f / e) of at least one of 0.6 and the specific gravity of 1.32 to 1.41 deviate from the structure of the present invention, and are obtained from the flameproof fiber. The obtained carbon fiber is formed in a wavy shape in which both ends in the width direction of the cross section of the fiber cut at an arbitrary cut surface passing through the fiber axis are repeatedly bent (the fiber surface has pulse-like irregularities in the axial direction). It was a deviation from the structure of the present invention.

  In the flame-resistant fiber obtained from Comparative Example 5, the image of the fiber cross section obtained by observation does not show a double circle, and the ratio between the thickness (e) of the flame-resistant part and the thickness (f) of the non-flame-resistant part (f / e) is 0, which deviates from the configuration of the present invention, and the carbon fiber obtained from the flameproof fiber has a shape in both ends in the width direction of the fiber cross section cut at an arbitrary cut surface passing through the fiber axis. However, each did not show a wave-like shape that repeatedly bends (the fiber surface has vein-like irregularities in its axial direction), and deviated from the configuration of the present invention.

It is a schematic sectional drawing which shows an example of the carbon fiber of this invention. It is a schematic sectional drawing which shows an example of the flameproof fiber of this invention. It is a drawing SPM photograph which shows an example of the precursor in the middle of a flameproofing process. It is a SPM photograph instead of drawing which shows an example of the conventional flameproof fiber.

Explanation of symbols

2 Carbon fiber 4 Wave-shaped peak 6 Wave-shaped valley 8 Hollow part 12 Flame-resistant fiber 14 Outer circle showing the outer peripheral part of the flame-resistant fiber 16 Flame-resistant part formed from the outer surface of the fiber to the fiber axis direction 18 Fiber Axis (center of circle)
20 Non-flame-resistant part including fiber axis 22 Inner circle showing boundary between flame-proof part and non-flame-resistant part a Fiber diameter at large diameter part (fiber large diameter)
b Fiber diameter in small diameter part (fiber small diameter)
e Thickness of flameproofed part f Thickness of nonflamed part

Claims (3)

In the black and white image of the fiber cross section obtained by scanning probe microscope observation of the flame resistant fiber for carbon fiber production, the black and white density distribution of the fiber cross section image is the outer circle formed by the image of the outer periphery of the fiber cross section, and the outside of the fiber. It has a double circular structure with an inner circle formed at the boundary between the flame-resistant part formed in the fiber axis direction from the surface and the non-flame-resistant part including the fiber axis, and the radial thickness of the flame-resistant part ( A flame-resistant fiber having a ratio (f / e) of e) and a thickness (f) of the non-flame-resistant portion indicated by the inner circle radius of greater than 0.6 and a specific gravity of 1.32 to 1.41. When a carbon fiber precursor is flameproofed, the following gradient coefficient A = flameproofing time (min) / specific gravity increase
(Here, specific gravity increase = flame-resistant fiber specific gravity−precursor specific gravity)
A method for producing flame-resistant fibers, characterized in that the slope coefficient A determined in step 1 is less than 200. A method for producing carbon fiber, comprising heat-treating the flame-resistant fiber according to claim 1 in an inert gas atmosphere.

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