JPH02251609A - Polyacrylonitrile yarn-based yarn for producing graphite yarn - Google Patents

Abstract

PURPOSE:To obtain the title yarn providing graphite yarn showing extremely high modulus of elasticity at a lower temperature, comprising a copolymer consisting essentially of a specific ratio of acrylonitrile and a specific ratio of flame resistance promoting component. CONSTITUTION:The objective yarn which comprises a copolymer consisting essentially of 85wt.% acrylonitrile and 0.1-4wt.% flame resistance promoting component (e.g. acrylic acid) and contains 0.05 to 3wt.% calculated as boron of boron-containing particles. The yarn, for example, is obtained by uniformly blending a solution of the copolymer in a solvent with a dispersion of boron- containing particles pulverized by a grinding-type mill into the same solvent while stirring to prepare a polymer solution containing dispersed boron- containing particles and making the solution into yarn by a well-known method. Ultrafine particles having <=0.1mu average particle diameter of boron simple substance obtained by gas phase method using laser are preferably as the particles.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to polyacrylonitrile-based a fibers for producing graphite fibers, particularly precursor fibers for producing high-performance graphite fibers used in composite materials having plastics as a matrix. Regarding.

[Prior art] Carbon fiber has higher specific strength and specific modulus than metal materials, so in recent years it has been used in large quantities as a lightweight structural material, mainly for golf shafts, fishing rods, sports, leisure fields, and aerospace applications. It has reached this point. With the expansion of M requirements, further improvements in quality are desired, and great progress has recently been made in improving strength. In addition, higher modulus of elasticity is being achieved along with improvements in handling characteristics. This is expected to result in thinner structural materials.

By the way, polyacrylonitrile-based graphite fibers are non-graphitic, and despite the above-mentioned technical improvements, it is difficult to easily obtain a high modulus of elasticity like pitch-based graphite fibers, so they are treated at a maximum treatment temperature of at least 2000°C. In many cases 2
The temperature exceeds 500°C. Graphite material is used for such high-temperature heat treatment equipment due to its heat resistance, but graphite material also has 2
At high temperatures exceeding 1,000°C, it gradually wears out due to sublimation, which is an obstacle to production. Since the degree of damage increases as the graphitization temperature increases, it is important from the viewpoint of productivity to increase the elastic modulus at as low a temperature as possible. Various improvement techniques have been proposed for this problem since ancient times. Many of them are related to the method or structure of graphitization furnaces,
The main topics were related to optimization of temperature increase rate or temperature decrease rate and tension during graphitization, and topics related to catalytic graphitization.

Catalytic graphitization related to the present invention has been studied for a long time in the field of graphite materials, and its effects have been recognized for many metals. Among these, boron is commonly used in carbon fibers and has been shown to improve physical properties. Unlike other metals, boron is characterized by its ability to form solid solutions, and this is thought to work to improve physical properties. For example, Japanese Patent Publication No. 47-50331, Japanese Patent Publication No. 48-9801, and US Pat. ing. Further, Japanese Patent Publication No. 48-43580 discloses a method in which a metal alkoxide compound such as boron propoxide is added before fiber formation.

Regarding boron particle-containing acrylic fibers and fired products thereof, Japanese Patent Publication No. 60-4738; No. 3 discloses a method for producing metal carbide-containing molded products, but this method is a subject of the present invention. It is not possible to obtain graphite fibers with high elastic modulus.

[Problems to be Solved by the Invention] However, the method of using a boron compound in the graphitization atmosphere has major problems such as the accumulation of decomposed products in the furnace and poor utilization efficiency of boron. In addition, the method of impregnating and adhering raw material fibers with boron has the problem that the boron compound is present inside the fibers as coarse particles, so that the catalytic effect is not fully utilized, and it has a negative effect on the denseness of the fibers.

Furthermore, in the method of incorporating a metal alkoxide compound before fiber formation, the water normally used for spinning polyacrylonitrile decomposes the compound, so benzene, ethanol, etc.
It is necessary to use an organic solvent such as xylene, which is a very disadvantageous industrial condition.

The prior art has such drawbacks.

The inventors of the present invention have conducted extensive studies on a more efficient and effective method of introducing boron into fibers for catalytic graphitization in light of such conventional techniques, and have arrived at the present invention. That is, an object of the present invention is to obtain graphite fibers having a higher elastic modulus through graphitization treatment at a lower temperature.

[Means for Solving the Problems] The object of the present invention is to make boron-containing particles consisting of a copolymer whose main components are 85 wt% or more of acrylonitrile and 0.1 to 4 wt% of a flame resistance promoting component. as 0
．． This problem can be solved by using polyacrylonitrile fibers for producing graphite fi&it containing 05 to 3 wt%.

First, the structure of the fiber of the present invention will be explained.

That is, the fiber of the present invention consists of a copolymerized component mainly consisting of acrylonitrile and a flame-resistant component. At this time, the amount of acrylonitrile is required to be 85 wt% or more, preferably 90 wt% or more, based on the total polymer. If the content is less than 85 wt%, the softening point of the fibers decreases and adhesion occurs during flame resistance, resulting in poor physical properties of the graphite fibers obtained.

Examples of the flame resistance promoting component which is a copolymerization component of acrylonitrile include vinyl monomers that have the ability to promote flame resistance, such as acrylic acid, methacrylic acid, itaconic acid, or their salts. be able to. These components are 0.1wt% of the total polymer
~4 wt%, preferably 0.3 wt% to 1 wt% is required.

If this component is less than 0.1 wt%, the effect will be small, and orientation relaxation will be large during firing, especially at the initial stage of flame resistance.
This results in a decrease in the elastic modulus of the graphite fibers obtained. Also 4wt%
In this case, undesirable side reactions other than the ring-closing reaction, which is the purpose of flame resistance, are likely to occur, resulting in a decrease in physical properties.

On the other hand, the 1m fiber of the present invention contains fibers made of the copolymer,
Furthermore, disperse the horso. Boron, a boron compound, or a mixture thereof can be used as the particles, but in order to effectively increase the elastic modulus, simple boron or boron carbide is preferable.

Further, the amount of the particles in the fiber is 0.05 wt% as boron.
~3 wt%, preferably 0.3 wt% to 1.5 wt% is required. At this time, if the amount of boron is less than 0.05 wt %, the catalytic effect of boron in the graphitization stage makes it impossible to lower the temperature of the graphitization treatment and to increase the elastic modulus of the resulting graphite fiber.

On the other hand, if it exceeds 3 wt%, boron carbide will be generated in the graphite fibers obtained, resulting in a decrease in physical properties. If the boron content is 3% or less, boron compounds are also converted during the process of converting raw material fibers into graphite fibers, and boron exists as a solid solution in the graphitized fibers obtained.

Furthermore, it is preferable that the average particle diameter of the particles is 0.1 μm or less. If the particle size is larger than this, the diameter is 0.1μ
The following particles are preferably as small as possible, and examples of such ultrafine particles include, for example, Journal of Ma
terials 5cience 22 p7
It is desirable to use ultrafine particles of simple boron produced by a gas phase method using a laser as described in No. 37.

The particle size of such ultrafine particles usually increases due to secondary particle formation, and when dispersing into a polymer solution, coarse particles are removed by wet grinding and filtration in the same solvent as the polymer solution. It is desirable to do so.

The average particle diameter of the boron-containing particles was determined by a counting method using a scanning electron microscope. The measuring device is B o
A USH&Lomb image analysis system was used.

As described above, the fiber of the present invention is a polyacrylonitrile fiber composed of acrylonitrile, a flame resistance promoting component, and boron-containing particles in a predetermined ratio, and this fiber is used as a raw material for graphite fiber laI! If fibers are used, it will be possible to lower the temperature of the graphitization process, which will further improve productivity. In addition, the obtained graphite fiber has a high modulus of elasticity, has mechanical properties corresponding to the high modulus, and has excellent handling characteristics.

Next, an example of manufacturing the fiber of the present invention will be explained.

First, acrylonitrile, a polyacrylonitrile polymer containing a flame resistance promoting component as a main component, can be produced by a known method. At this time, examples of solvents that can dissolve the polymer and allow spinning include dimethylformamide, dimethylacetamide, dimethylsulfoxide, and the like.

Next, the boron-containing particles are mixed with the polymer solution. At this time, a method for uniformly dispersing both particles is to use a homomixer, for example, to mill the particles in the same solvent as the polymer solution using a grinding mill. It is desirable to disperse the mixture using a mixer such as the following, and then further filter it using, for example, a glass fiber filter of about 0.1μ.

The particle dispersion liquid prepared in this manner and the polymer solution are uniformly mixed while being stirred using a stirrer to prepare a polymer solution in which the particles are uniformly dispersed.

The boron-containing particle-dispersed polyacrylonitrile polymer solution is made into fibers by a known wet spinning method or wet/dry method.

Furthermore, it is desirable that the yarn obtained here has particularly high density and orientation. That is, first of all, the density of the graphite fiber is important in order to maintain a high elastic modulus of the obtained graphite fiber. Due to its catalytic graphitization effect, boron increases the specific gravity, that is, the density, of graphite fibers, but it is difficult to maintain high density of graphite fibers by using boron alone without considering the fibers and firing conditions. For this reason, it is desirable to maintain the density of the yarn as high as possible, and the iodine adsorption amount, which is a measure of density, is preferably 3% or less.

The amount of iodine adsorbed by the yarn can be determined by the following method.

That is, 50 g of iodine, 10 g of 2,4-dichlorophenol, 90 g of acetic acid, and 100 g of potassium iodide.
Weigh it out and dilute it with water to make 1 liter of aqueous solution. Dip a dry sample amount of 0.5 g into 100 ml of the aqueous solution,
60f: Perform adsorption treatment at 0.5°C for 50 minutes. After the treatment, the sample is washed in running water for 30 minutes and then centrifuged to dehydrate. The dehydrated sample was heated and dissolved in 100 ml of dimethyl sulfoxide, and 1
The concentration of iodine is determined by potentiometric titration with a /10 normal silver nitrate aqueous solution, and the amount of iodine adsorbed to the dry sample is calculated. The amount of iodine adsorbed corresponds to the amount of microvoids or structurally coarse portions present within the yarn.

The density of the raw yarn mainly depends on the spinning conditions, spinning conditions, coagulation conditions, stretching conditions, and the oil agent applied. That is, during coagulation in wet spinning, it is preferable to set the spinneret dimensions and spinning speed so that the draft is as small as possible. In addition, compared to wet spinning, dry-wet spinning, in which the discharged yarn is once run in the air, causes thinning in the fluid state in the air before it comes into contact with the coagulating liquid, which reduces the effective draft and makes it easier to densify. This method is preferable because a raw yarn with a high quality can be obtained.

For the purpose of obtaining a dense raw yarn, stretching is carried out in a wet state before drying at a draw ratio as high as possible, for example 3 to 4 times, within a range that does not cause adhesion between single filaments. It is preferable to do this at a high temperature. Furthermore, since the oil applied before drying may diffuse into the interior of the wet yarn and impair its compactness, it is preferable to select one with as large a molecular weight as possible. In this respect, silicone-based oil agents with high water repellency are suitable for the present invention.

Next, the degree of orientation of the raw yarn is preferably 85% or more. The orientation of the raw yarn is the obtained graphite wcN! However, it is better to consider the orientation of the flame-resistant yarn rather than the original yarn, since orientation relaxation during firing, especially at the initial stage of flame resistance, has a large effect. In this sense, the degree of orientation of the flame-resistant yarn is preferably 78% or more. In addition, it is advantageous for the single fiber fineness of the raw yarn to be as thin as possible since structural differences within the single yarn occur during firing, in order to increase the elastic modulus. In this sense, the single fineness is preferably 1.5 denier or less, more preferably 0.75 denier or less.

The degree of orientation of the yarn can be determined by the following method.

That is, it is determined by the following formula from the intensity distribution of a diffraction image on the equatorial line obtained by making X-rays incident on the fiber axis from a direction perpendicular to the fiber axis.

π(%') = [(180-H)/180] X100
Here, H is the intensity distribution measured along the Debye ring of strong diffraction on the equatorial line, and in the case of raw yarn, it is derived from polyacryminitrile, and in the case of flame-resistant yarn, it is the surface index (002) derived from the graphite precursor structure. Equivalent to.

Of course, if we adopt converting polyacrylonitrile fiber containing boron-containing particles into graphite fiber, the effect will be obvious when compared with conventional technology, but in addition, in the firing process to convert raw material fiber into graphite fiber, However, by adopting conditions that increase density and orientation, it becomes easier to achieve an ultra-high modulus of elasticity that has not been achieved with conventional polyacrylonitrile fibers.

[Example code] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Acrylonitrile 99 wt%, methacrylic acid 1 wt%
%, an acrylonitrile-based polymer consisting of
A polymer solution [A] of Boies) was obtained. Add 10w of boron particles with a particle size of 001μ or less to this polymer solution, which was prepared separately.
Add 10 wt % of the polymer solution [B] containing t % and stir until it becomes homogeneous to make the polymer solution [C].

The polymer solution [8] is obtained by pulverizing boron fine particles made by a gas phase method using a laser etc. in DMSO using a grinding mill.
．． After filtering through a 1μ filter, the polymer solution [A] is added while stirring with a homomixer, and the viscosity and boron concentration are adjusted to make subsequent operations easier.

The polymer solution [C] was once discharged into the air using a nozzle with a diameter of 0.2 mm and 3000 holes, and then introduced into a 30% DMSO aqueous solution at 15° C. to solidify.

The coagulated thread was washed with water, stretched with hot water, applied with an oil agent mainly composed of aminosiloxane, and dried to a density of 5.5Kg/cm2G.
The fibers were drawn in pressurized steam, and a raw yarn with a total magnification of 12.4 times and a single fiber fineness of 0.7 d was collected.

This yarn had a strength of 7 g/d, an elongation of 11.2%, and an iodine adsorption amount of 2.1% as determined by the method described in the text. The degree of orientation determined by X-ray diffraction was 90.2%.

The obtained yarn was flame-resistant under tension in heated air having a temperature gradient of 240 to 270° C. so as not to become shorter than the original length.

The degree of orientation of the graphite precursor structure by X-ray diffraction of the flame-resistant fiber was 81.8%.

The flame-resistant fiber thus obtained was placed in a carbonization furnace sealed in a nitrogen atmosphere with a temperature gradient of 400 to 1000°C.
Carbonization was performed under tension so that the length did not become shorter than the original length, and graphitization treatment was performed while elongating by 15% by changing the maximum temperature. The physical properties of the graphite fiber obtained are as follows: J15-R-7
601 by the impregnated strand method. The results are shown in Table 1.

Comparative Example 1 A graphitized fiber was obtained from the polymer solution [A] of Example 1 in the same manner as in Example 1, and its physical properties are shown in Table 1.

Table 1 [Effects of the Invention] As mentioned above, the polyacrylonitrile wA fiber for producing graphite fiber of the present invention can make maximum use of the catalytic effect of boron when converted into graphite fiber, and has excellent mechanical properties, especially Graphite fibers with excellent elastic modulus can be obtained. In addition, the same elastic modulus as before can be obtained by graphitization treatment at a lower temperature than before. Furthermore, it is possible to achieve an ultra-high modulus of elasticity, which has been difficult to achieve with conventional polyacrylonitrile fibers.

Claims (1)

[Claims] 85wt% or more acrylonitrile, 0.1-4wt%
A polyacrylonitrile fiber for producing graphite fiber, which is made of a copolymer mainly composed of a flame resistance promoting component, and contains boron-containing particles in an amount of 0.05 to 3 wt% as boron.