JPS616316A - Graphite fiber - Google Patents

Abstract

PURPOSE:Graphite fibers, producible easily from pitch as a raw material, and having leaflike lamellar orientation in the cross section thereof and a specific tensile strength and modulus values and cross-sectional structure entirely different from the conventional cross-sectional structure. CONSTITUTION:Graphite fibers, obtained by spinning pitch, e.g. coal tar pitch, as a raw material, and having many lamellas in the lamellar orientation in the form of tree leaves extending to both sides at 15-90 deg. angle symmetrically from the central axis in >=30% cross section thereof, >=300kg/mm.<2>, preferably >=350kg/ mm.<2> tensile strength and >=30T/mm.<2>, preferably >=40T/mm.<2> modulus. The cross- sectional shape of the fibers is preferably circular.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-strength, high-modulus graphite rutted fiber VC made from pinch as a raw material and having an IL-T regularity and a unique internal structure.

Conventional technology Graphite edge ## was initially manufactured using rayon as raw material, but due to its characteristics and economic efficiency, it is now made of polyacrylate.
p-nitrile (PAN-based graphite made from PANJ fibers*
M and pinch type graphite laM made from coal or petroleum pitches. Among these, the technology to produce high-performance grade graphite FR fibers using pitch as a raw material is attracting attention because it is immediately economical. Infusibility and firing.

Graphitized graphite fibers have higher strength and higher modulus than the pinch type graphite fibers. (
(Refer to JP-A-49-19127) It has also been found that physical properties can be changed by controlling the internal cross-sectional structure of pitch-based graphite fibers.

That is, the pitch-based graphite fiber has a random, radial, onion structure, or a composite structure thereof as a cross-sectional structure, and while the radial structure has a high modulus, it is detrimental to the crank and causes a decrease in strength due to macro defects. In addition, the random structure in pitch-based graphite fibers is actually a radial structure with small lamella sizes, which is a preferable structure in terms of strength, but if the pitch preparation and spinning draft or rapid cooling are not sufficient, the crank will crack. Manufacturing conditions are limited. Also, in terms of modulus, it is inferior to the radial structure.

The onion structure can be obtained by spinning after raising the temperature to a temperature higher than the viscosity change temperature of the spinning pitch (see @Kokai No. 59-53717).
With normal optically anisotropic pitch, the viscosity change temperature is as high as 350°C or higher, resulting in poor spinning stability and the resulting fibers containing voids. Fibers with an onion structure are difficult to obtain stably.

Purpose of the Invention The purpose of the present invention is to have a cross-sectional structure completely different from that of conventional pitch-based graphite fibers, and to have a temperature lower than that of conventional pitch-based graphite fibers.
It has dramatically improved strength and modulus,
Furthermore, it is an object of the present invention to provide a new pitch-based graphite fiber that is less difficult to manufacture.

Structure of the Invention The inventors conducted intensive research to develop a pitch-based graphite fiber with unprecedented performance that maintains the advantages of pitch-based graphite fiber in terms of modulus and has excellent strength. In addition to melt-spinning pitch raw materials, the researchers discovered that by adding specific techniques, it is possible to control the arrangement of pitch molecules at will, creating a unique microstructure that is completely different from conventional radial, random, or onion structures. It has been discovered that a new pitch-based graphite fiber can be obtained that has both excellent strength and modulus that have not been achieved in the past, and based on this knowledge, the present invention was completed.

That is, the novel pitch-based graphite fiber of the present invention has a leaf-like lamellar arrangement in 30% or more of its cross section, and has a low tensile strength (3 sokg/J at least, and at least 30 T/- for Monyrus). Features of graphite 1R1tI
It is.

The leaf-like lamellar arrangement referred to here can be identified by observing a cross section cut almost perpendicular to the longitudinal direction of graphite fibers using a scanning electron microscope, and is basically symmetrical about the central axis. 15~90'' Q angle refers to a leaf-like lamella arrangement in which many lamellae extend on both sides, and is a completely new, previously unknown structure.In this leaf-like lamella arrangement, the central axis is What becomes clear or disappears is also self. In such a case, the central axis is also virtual (thereby, it can be determined that it is a leaf-like lamella arrangement according to the above definition).

FIGS. 1 to 4 are diagrammatic cross-sectional views schematically showing the cross-sectional structure of the graphite fiber of the present invention. A plurality of leaf-like lamella arrays can exist in one cross section. For example, when four leaf-like lamellas are combined as shown in Fig. 1, three leaf-like lamellas as shown in Figs. 2 to 4 are combined. When the lamellae are combined, two leaf-like lamellae are combined as shown in Fig. 75, and there are cases where it looks like one leaf-like lamella.

The central axis of each leaf-like lamella may be six loops or a curved line, and the same is true when there are eight loops imagining the central axis.

Further, the size of each leaf-like lamella and the number of leaf-like lamellae are not particularly limited. Generally, when the number of leaf-like lamellae existing in a fiber cross section is large, the leaf-like lamellae of that i=zoit become relatively small, and when the number is small, each leaf-like lamella becomes large.

Generally, the number of leaf-like lamellae inherent in the fiber cross section is 2 to 8.
Preferably. In addition, the proportion (area ratio) of leaf-like lamellae in the cross-sectional area of the fiber is preferably at least 30 cm.
% or more is particularly preferred.

That is, in many cases, the graphite fiber of the present invention has a leaf-like structured part (4) having a leaf-like lamella arrangement and a part (B) with an unclear structure around it, but the area of A/ It is preferable that the area ratio of (A 1 B) is at least 30% or more, and 50% or more.

The cross-sectional shape (external shape) of the graphite fibers according to the present invention can be multi-lobal shapes such as circular (Fig. 1), elliptical (Fig. 5), tri-P-pal (Fig. 4), triangular (Fig. figure)
In addition to multi-angle shapes such as , it can take any shape such as a flat shape or a single curved lens shape.

The diameter of the fiber is preferably in the range of 5 to 50p in terms of circular cross section, and the fiber length can be selected arbitrarily.

The graphite fibers of the present invention having the special leaf-like lamellar arrangement described above have a strength of at least 300 Y/- and a modulus of at least 3 oT/-, and in most cases have a strength of 350 kli+/- or more. and 40T/-
It exhibits excellent physical properties that have not been seen in the past, with a modulus of In particular, as shown in the examples below, depending on the manufacturing conditions, there are cases where the strength exceeds 9/- for 400 and the modulus exceeds 45 T/-. It has physical properties.

Such excellent physical properties of the graphite fiber of the present invention are as follows:
Since the cross-sectional structure of the fiber has a leaf-like lamellar arrangement as described above, the generation of cranks during the infusibility, sintering, and graphitization stages is prevented, and the structure can be made denser. This is considered to be due to a high modulus.

The graphite fiber of the present invention, which has such excellent performance, is obtained by melting a spinning pitch having an optical anisotropy region of 50% or more, then melt-spinning it through a spinning hole that forms a specific shape, and making it infusible. .

It can be easily and stably produced by firing and graphitizing.

Next, this manufacturing method will be explained in detail.

As a raw material for producing the graphite fiber of the present invention, pitch having an optical anisotropy area of 50% or more, preferably 80 inches or more is used. Optically anisotropic pitch with an optically anisotropic region ratio of less than 50% has poor spinnability, making it difficult to obtain homogeneous and stable physical properties, and also resulting in graphite fibers with poor physical properties. becomes.

The melting point of the pitch for spinning is preferably 260 to 320°C, and 2
More preferably, the temperature is 70 to 310°C. Further, the proportion of the quinoline-soluble portion of the spinning pitch is preferably 30% by weight or more, and particularly preferably 40 to 80% by weight f1. These parameters vary depending on the raw material pitch, but are usually correlated.
The amount of optical anisotropy is high, the melting point is high, and the proportion of quinoline soluble portion is low. The higher the ratio of the spinning pitch region (hereinafter referred to as the amount of optical anisotropy) preferably used in the present invention, the better. With such a pitch, the yarn is homogeneous and has excellent spinnability.

Examples of raw materials for such spinning pitch include coal tar and coal tar pitch.

Coal-based heavy oil such as coal liquefied oil, residual oil at normal pressure,
Refined petroleum heavy oils such as tar, pitch, oil sand, and bitumen, which are by-products of vacuum distillation residual oil and heat treatment of these residual oils, are used and subjected to heat treatment 3.
! l.

It is obtained by a combination of solvent extraction, hydrogenation treatment, etc.

In order to produce the graphite fiber of the present invention, the shape of the spinning hole (nozzle) of the spinneret when melt-spinning the above-mentioned spinning pitch is particularly important.

That is, the melt of the spinning pitch as described above is expressed by the following formula (1
) <[1.

As for such a spinning hole, when the center line distance in the spinning hole is Ln and the corresponding wetting edge width is Wn, (however, at least one of the integer numbers Ln of n=1 to 10 is such that Ln < 5.0 (m)...-(■r1.
5riLn/~Vn<20 -- (Use one that satisfies Ill as a simultaneous trap.

Such spinning holes include a spinning hole consisting of a single straight or curved slit, a spinning hole consisting of a plurality of linear or curved slits crossing each other, and a spinning hole consisting of a plurality of mutually independent slits. Examples include units. Here, 15 center line distance Ln is the length of the center line of the slit in the case of a single slit, and is the center line distance, and in the case of a spinning hole where multiple slits intersect, the inscribed circle at the intersection is excluded. Length LL of the center line of each slit in the section
l LX IL,...Ln is the center line distance, and in a spinning hole where multiple independent slits are combined into one spinning hole unit, the length of the center line of each slit is L□ILI... ...Ln is the center distance.

Further, the wet edge eWn refers to the maximum width of the slit in the direction perpendicular to the center line.

Graphite FI1 of the present invention. To form a fiber, at least one #1 of the Ln and Wn satisfies the formula +1) Tl! ] must be satisfied at the same time, but when there are multiple sets of Ln and Wn, all or most of them satisfy the above formula (11
It is preferable to simultaneously satisfy (It).

According to research conducted by the inventors, among such special spinning holes, a spinning hole consisting of a single slit is preferable, and among these, a spinning hole that satisfies K 3 <I, n/Wn (15) is preferable.

In contrast, when using a spinneret with circular spinning holes, which is used for conventional melt spinning of pitch fibers, and when using Ln
When using a spinneret with irregularly shaped spinning holes where /Wn is outside the above range, the cross section of the graphite diagram will have a radial structure;
The leaf-like lamella arrangement content becomes extremely small.

In such a case, it is possible to partially include fibers that do not generate cracks, but it is impossible to completely prevent cracks, and as a result, the physical properties of the graphite fibers obtained deteriorate.

The spinning temperature in melt spinning is 40 to 100 degrees Celsius above the melting point.
Although a high temperature is used, temperatures exceeding 380°C should be avoided in order to obtain the excellent physical properties described in the present invention.
Furthermore, temperatures exceeding 370°C should be avoided. This is because at temperatures above such a temperature, the carbonization reaction does not start, and the generation of gas accompanied by Tl, K has a non-negligible adverse effect on the physical properties.

The reason why a leaf-like lamellar arrangement is produced when optically anisotropic pitch is spun from the spinning hole as described above is still not fully understood and will have to wait for detailed investigation in the future, but the idea is as follows. Ranel.

Pitch having optical anisotropy is presumed to be plate-like molecules, and such plate-like molecules tend to be arranged at right angles to the uniform velocity JiK in the nozzle (spinning hole) of the spinneret. Since the constant velocity line in the circular nozzle is circular and the pitch iK molecules are arranged at right angles, the pitch molecules are arranged radially within the cross section of the resulting pitch fiber. For this reason, it is made infusible and fired.

During the graphitization stage, stress distortion tends to occur when the molecular spacing contracts, resulting in cracks.

The constant velocity line I in the nozzle having the above-mentioned center line for this hK
When the molecules are arranged at right angles to this, the pitch molecules are arranged in a leaf-like manner within the fiber cross section. This arrangement is caused by the contraction of the molecular spacing during the infusibility, firing, and complexing stages. It is thought that because the arrangement is such that it can easily absorb stress strain, cracks do not occur due to the fact that the molecules are packed tightly, etc., and extremely excellent physical properties are developed.

Furthermore, if necessary, a method of installing a K rectifier plate above the mouth hole (upstream '111) can also be used for effective pressure.

Such a rectifying plate may have any shape, such as parallel slits, a lattice shape, or an aggregated shape of minute circles, etc., with a cross section perpendicular to the streamlines. It is necessary that the streamlines of the two do not intertwine with each other in the streamline direction. When streamlines intertwine, it causes turbulence in the flow;
This is not preferable because the axial orientation is inhibited.

Fibers spun from such slit-shaped spinning holes are
It is suitable to take over at a tow raft ratio of 30 or more, preferably 50 or more. Here, the draft rate is a value defined by the following formula, and the larger this value is, the higher the deformation speed during spinning is.If other conditions are the same, the larger the draft rate is, the sharper the quenching effect will be. .

It is preferable to take the material at a draft rate of 30 or more, especially 50 or more, because it is easier to develop suitable physical properties than the subsequent infusibility, calcination, and graphitization treatments.

The spinning take-off speed is 1000 m/m under the above-mentioned spinning conditions.
Although spinning can be carried out very smoothly even at high speeds of 300 to 2000111 minutes per minute or more, the preferred range is usually 300 to 2000111 minutes.

The pitch fiber obtained by employing the above-mentioned special spinneret at °C is then treated to be infusible in the presence of oxygen.

This infusibility treatment step is an important step that affects productivity and fiber properties, and is preferably carried out in as short a time as possible. For this reason, it is necessary to appropriately select the infusibility temperature, heating rate, air gas, etc. for the spun pitch fiber.
The pitch fiber of the present invention uses optically anisotropic pitch with a high melting point, and the fiber cross section and shape are non-circular (irregularly shaped pitch fibers have a large surface area per unit cross-sectional area, etc.). Processing time can be reduced compared to conventional pitch fibers spun from circular cross-sections.

Further, in this process, an anti-fusing agent such as an inorganic fine powder may be used to prevent fusing. Furthermore, in order to shorten the time of infusibility treatment, iodine,
Chlorine and the like are also suitably used. The fibers thus infusible are directly placed in an inert gas at a temperature of 2,000 to 30
Although it may be heated to 00CK, it is usually heated once to 1000 to 1500°C in an inert gas, and then further heated to 2000 to 3000°C in an inert gas to form graphite fibers.

Effects of the Invention The pitch-based graphite fiber of the present invention as described above has a leaf-like lamellar arrangement in its cross-sectional structure, which prevents cracking and further makes it infusible.

Because the contraction occurs smoothly during the firing and graphitization stages, the strength increases dramatically, and in addition to the modulus advantages of the liquid crystal pitch system, graphite fibers have unprecedented strength and modulus. Become. Therefore, it is suitably used as reinforcing fibers in composite materials.

Methods for Measuring Each Index Next, methods for measuring each index representing spinning pinch and fiber properties in the present invention will be explained.

(a) Melting point of pitch for spinning Using a PerkinElmer ffDsc-ID type, put lO ~ of pitch finely ground into a cell made of aluminium (inner diameter 5 m/m) to a size of K100 or less, press it down from above, and then add nitrogen to the cell. Measured in an atmosphere while heating at a heating rate of 10° C./min to about 400° C. (The endothermic peak indicating the melting point in the DSC chart is taken as the melting point of the spinning pinch.

(bl Amount of optical anisotropy of spinning pitch Using a reflective polarizing microscope (・Polarized Sq microscopic photograph of spinning pitch
Take a sheet, use an image analysis processing device to calculate the area fraction (@) of the isotropic region, and take the average value of this as the amount of optical anisotropy.

(c) Physical properties of carbon fiber Fiber diameter (single yarn diameter) and tensile strength of carbon fiber.

Elongation and modulus are measured according to JIS R-7601r Carbon Fiber Test Method. The fiber diameter was measured using a single laser for fibers with a circular cross section, and for fibers with a non-circular cross section, n = 15 was measured using a scanning electron microscope photograph.
Calculate the average value of the cross-sectional area. In addition, in Examples etc., the fiber diameter is expressed as a diameter when converted into a circle having a corresponding cross-sectional area.

(d) IJ - Fraction of leaf-like lamellar arrangement Based on a scanning electron microscopy image y of a cross section of a carbon fiber, it is expressed as the area ratio of the leaf-like lamella arrangement per cross-sectional area.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way.

Example 173 Using commercially available Fool's Rubich as raw material, JP-A-59-5
According to the method described in Japanese Patent No. 3717, a spinning pitch having an optical anisotropy of 88%, a quinoline welding area of 39, and a melting point of 274° C. was prepared by full-flow GT production.

The spinning pitch is charged into a quantitative feeder equipped with a heating heater, and after melting and degassing, it is passed through a separately provided heating zone and then passed through a separately provided heating zone using a spinneret having a linear single slit spinning hole with a slit width of 60 μm and a center line distance of 540 μm. , spinning was performed.

In this case, the feeder discharge amount is 0.061//min/hole,
Feeder part temperature (TI) = 320tl:.

Heating zone temperature (T, ) = 320℃, mouthpiece temperature (T
s) = Spinning at 340°C, take-up speed 800 m/
I rolled it up in minutes.

After coating this pitch fiber with fine silica powder as an anti-fusing agent, it was heated to 200°C at a heating rate of 10°C/min in dry air.
The temperature was increased from 1:1 to 300°C and held at 300°C for 30 minutes.

Then, in a nitrogen atmosphere at a heating rate of 500°C/min,
The mixture was heated to 00°C and held for 5 minutes to be fired, and then heated to 2300 to 2700°C in an argon atmosphere to obtain graphite fibers. The leaf-like lamella fraction of the obtained fiber was 97%. The physical properties corresponding to each graphitization temperature are shown in the following vg1 table.

Table 1

[Brief explanation of the drawing]

Fig. 11-5 has a cross-sectional height of -C which schematically shows the cross-sectional structure of the graphite fiber according to the present invention, and A in the figure is a portion with a leaf-like structure, and B is a portion where the structure around it is not. Show clear parts. 1 Kasumi Kaya 2 Kokushō 3 reasons Kaya 4゜to y diagram

Claims (6)

[Claims] (1) A graphite fiber made from pitch, which has a leaf-like lamella arrangement in 30% or more of its fiber cross section, and has a tensile strength of at least 300 kg/mm^2 and a modulus of at least 30 T/mm^2. A graphite fiber characterized by: (2) The graphite fiber according to claim (1), wherein the cross-sectional shape of the fiber is substantially circular. (3) The graphite fiber according to claim (1), wherein the fiber has an elliptical cross-sectional shape. (4) The graphite fiber according to claim (1), wherein the fiber has a multi-angle cross-sectional shape. (5) The graphite fiber according to claim (1), wherein the cross-sectional shape of the fiber is multilobal. (6) The graphite fiber according to claim (1), which has an array of 2 to 8 leaf-like lamellas in the fiber cross section.