JPH01282345A - Production of pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To stably obtain in high-speed spinning the title fiber to be used in thermal insulating materials, electrical material parts, etc., by melt spinning of pitch incorporated with an additive capable of enhancing the critical spinning speed. CONSTITUTION:For example, pref. pitch to give a yarn 200kg/mm<2> in tensile strength with optical anisotropy developed is incorporated with an additive capable of enhancing the critical spinning speed, i.e. at least one kind of substance selected from polystyrene and polyphenylene sulfide in finely granular or powdery form followed by heating the blend in a spinning machine to be made fully compatible and then making into a yarn, which is then insolubilized and carbonized at 900-1,700 deg.C in an inert atmosphere followed by graphitization at 1,700-3,000 deg.C, thus obtaining the objective carbon fiber.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing pitch-based carbon fiber.

(Conventional technology) Pitch-based carbon fiber has low raw materials, high carbonization yield,
Due to the physical and chemical structure of the raw material, it has characteristics such as the ability to easily obtain a high elastic modulus, and is attracting attention.

Generally, the manufacturing process for high strength, high modulus pitch-based carbon fibers involves the steps of melt spinning, infusibility, carbonization, and graphitization. have.

In other words, pitch itself is a mixture of compounds with various molecular weights and chemical structures, so it not only has poor spinnability, but also has a wider molecular weight distribution and more foreign substances than synthetic polymers. The uneven viscosity caused thread jams, which limited high-speed winding and led to thread breakage.

Furthermore, since the viscosity of pitch has extremely high temperature dependence, it has the disadvantage that stable spinning is difficult.

Therefore, methods have also been proposed for producing short fibers by centrifugal spinning, such as low-grade, ie, GP-level, carbon fibers. However, in the case of carbon fibers for reinforcing structural fibers, it is desirable to make them as continuous fibers, and improving the spinnability is an important technique. In particular, when spinning high-strength, high-modulus carbon fibers, the spinning temperature is as high as 280'C or higher, which makes the above-mentioned problems more pronounced.

On the other hand, attempts have been made in the past to add additives to bitge to improve its processability. Tokukai Showa 4
No. 7-6465 and JP-A No. 6466 propose adding stearic acid or the like to pitch in an attempt to improve stringiness.

However, the low molecular weight compounds such as stearic acid used in the invention do not show sufficient improvement in stringiness.

Furthermore, such additives are undesirable because they decompose due to heating during melting.

(Problems to be Solved by the Invention) An object of the present invention is to solve these problems and provide a method for stably spinning pitch-based carbon fibers at high speed.

(Means for Solving the Problems) In order to achieve the above object, the present invention has the following configuration.

The present invention relates to a method for producing pitch-based carbon fiber, which is characterized by adding an additive to pitch to increase the limit spinning speed and performing melt spinning.

The present invention will be explained in detail below.

The pitch used in the present invention is not particularly limited, and may be either petroleum-based pitch or coal-based pitch.Also, pitch with developed optical anisotropy or isotropic pitch may be used, but The characteristics of the present invention can be utilized to the fullest when the spinning temperature is 280'C or higher.In other words, the pitch is high enough to produce a so-called high-strength yarn with a tensile strength of 200 kg/mm2 and developed optical anisotropy. This is the case.

Spinning in the present invention can be performed by ordinary melt spinning. Winding is not particularly regulated as long as no load is applied to the fragile yarn, and bobbin style, net lamination style, etc. are possible, and depending on the case, infusibility may be performed following spinning.

In the present invention, the type, speed, addition method, etc. of the additive added to the pitch can be appropriately selected within the range that improves the spinnability.

The degree of improvement in stringiness is, for example, when the limit stringing speed is 1.
It is preferably 2 times or more, and more preferably 1.5 times or more. Normally, the finer the pitch fiber, the more difficult it is to spin, so the present invention is preferably applied to spinning of less than 10μ, more preferably 8μ or less.

The additive used in the present invention is, for example, a polymer that is meltable and has high heat resistance. When adding the polymer to the pitch and performing melt spinning, there are no particular limitations as long as the polymer is compatible or dispersed uniformly in the pitch. That is, at the spinning temperature, for example, 280'C
It is preferable that it melts and exists stably without causing thermal decomposition or the like at a temperature of ~400'C. Even polymers that cannot exist stably for a long period of time at the above temperature can be used as long as they are stably melted during the residence time in the spinning machine.

Specific examples of polymers to be added include polyethylene, ultra-high polymer polyethylene, polystyrene, polyphenylene sulfide, polyarylate, polyetheretherketone, polyetherimide, ABS resin, etc. Polystyrene and polyphenylene sulfide are more preferred in terms of stability and little change in pitch viscosity before and after addition.

In the present invention, the amount of polymer to be added is not particularly limited and can be determined depending on the type of polymer.

However, if the addition interval is too short, the effect of the present invention will be small, and if the addition interval is too small, it will not only reduce the spinnability but also the physical properties of the final carbon fiber. It is 0°3χ to 50%, more preferably 0.5χ to 30%. In addition, by adding the above additives to the pitch, the mechanical properties of the pitch fiber can be improved.
It is more preferable to use a material that can improve handling properties.

As materials satisfying such effects, ultrahigh molecular weight omega polyethylene, polystyrene, polyphenylene sulfide, etc. are preferably used.

In the present invention, the method of adding the polymer to pitch is not particularly limited. That is, it is sufficient that the material is uniformly phased or dispersed when discharged from the spinneret of the spinning machine. Specifically, it is sufficient to simply mix them in solid form at room temperature. In this case, both are uniformly dissolved or dispersed by heating during spinning. Further, in order to improve compatibility, pitch and polymer may be mixed in advance using a mortar or the like. Alternatively, the mixture may be mechanically mixed using a kneader or the like. The polymer is preferably added in granular or powdered form to improve compatibility;
The smaller the particle size, the better.

Next, the obtained thread undergoes infusibility, carbonization, and graphitization.
The final product is carbon fiber. If necessary, a pre-carbonization step may be included between infusibility and carbonization.

Air oxidation is typical for infusibility treatment, but gas phase oxidation using sulfur dioxide gas, ozone, etc., and liquid phase oxidation using nitric acid, hydrogen peroxide, etc. are also possible. It is only necessary to make it infusible, and depending on the case, physical means such as electron beam crosslinking may be used.

Pre-carbonization is carried out at several hundred degrees, e.g. 400'C, in an inert atmosphere.
Can be performed at ~800'C. The higher the temperature, the higher the strength, but since the elongation has a single maximum at 500°C to 650°C, the balance between the two can be determined depending on the processing conditions after carbonization. That is, when it is desired to apply tension during carbonization, emphasis should be placed on obtaining high elongation.

The form of the yarn in the pre-carbonization treatment may be the same as in the infusible treatment, such as a bobbin form or a state deposited on a net, as long as it does not impose an excessive load on the yarn.

Carbonization and graphitization can be performed by known methods,
For example, carbonization is carried out at temperatures between 900'C and 1700' in an inert atmosphere.
C1 graphitization was performed at 1700°C to 30°C in an inert atmosphere.
This can be achieved by heating to 00'C.

Hereinafter, the present invention will be explained in more detail using Examples.

(Example) Method for Measuring Critical Threading Speed Pitch to which additives have been added is placed in a stainless steel container with an inner diameter of 20111111 mm and a length of 150 mm. The stainless steel container is inserted into a through hole provided in the center of an aluminum block heated to a predetermined temperature, and heated to a predetermined temperature to melt the pitch. The inner diameter of the through hole matches the outer diameter of the stainless steel container. Next, from a cap with a diameter of 0.2 mm and a hole length of 0.2 mm attached to the bottom of the stainless steel container,
Extrude the pitch using nitrogen pressure.

At that time, the nitrogen pressure was 600 m with a take-up roll of 100 mm diameter installed so that the center was at 11 Il below the mouthpiece.
The pressure is set so that the pitch fiber diameter becomes 10μ when spun at /min. The roll is provided at a position where the vertical line of the nozzle discharge hole is tangent to the roll. Next, the circumferential speed of the roll is set to 200 m/min, and after winding the pitch fibers, the circumferential speed of the roll is increased at a rate of 50 m/Sec. The peripheral speed of the roll at which yarn breakage occurs is measured 10 times, and the average value is defined as the critical stringing speed.

Example 1 Hydrogen gas was blown into coal tar and heated to 120°C at 450'C.
It was allowed to react for a minute. The obtained hydrogenated tar was filtered using a 1μ filter to remove solid matter, and then heated at 350'C to obtain hydrogenated pitch. Then 505°C, 17
Heat treatment was performed at mmHg for 7 minutes to obtain mesophase pitch. The obtained mesophase pitch has a softening point of 265°C,
The QI was 22%, the BI was 92%, and the anisotropy was 90%.

Various additives were added to this mesophase pitch in a variety of ways, and mixed at 300'C to 350'C for 5 minutes using a niegu to make them compatible. The critical string speed of the resulting pitch containing the additive was measured by the method described above.

The results are shown in Table 1.

Table 1 As is clear from the above examples, when polystyrene and polyphenylene sulfide were added, the limit spinning speed was higher and the stringiness was improved compared to the blank with no additives. . - On the other hand, when polyphenylene oxide was added, only a lower limit stringing speed was obtained compared to the blank, and no improvement in stringiness was observed.

Furthermore, when polyamide-imide was added, spinning itself became difficult, and rather had a negative effect.

(Effects of the Invention) According to the present invention, pitch-based carbon fiber can be stably spun at high speed.

The pitch-based carbon fiber obtained by the present invention is used for heat insulating materials, sealing materials, electrical material parts, structural members, cooling materials, carbon electrodes, and the like.

Claims (2)

[Claims] (1) A method for producing pitch-based carbon fiber, which is characterized by adding an additive to pitch to improve the limit spinning speed and performing melt spinning. (2) The method for producing pitch-based carbon fiber according to claim 1, wherein the additive is at least one of polystyrene and polyphenylene sulfide.