JPH01282329A - Infusibilization of pitch fiber - Google Patents

Abstract

PURPOSE:To obtain the subject infusibilized fiber capable of providing a carbon fiber with high strength and elongation and excellent in handling properties at a low cost by carbonization by oxidizing a pitch fiber with a specified diameter in a nitric acid solution in a range satisfying a specified relation about the reaction period, the reaction temperature and the concentration of nitric acid. CONSTITUTION:A mesophase pitch is melted and degassed at 320 deg.C under 60mm Hg using a bented extruder, etc., subsequently discharged through a spinning nozzle and drawn to prepare a pitch yarn with <=12mum diameter. The resultant pitch yarn is subjected to oxidation treatment in a nitric acid solution in a range satisfying formula I [t is reaction period (hr); T is reaction temperature ( deg.C); C is concentration of nitric acid (normality)], formula II and formula III to infusibilize the pitch fiber, thus obtaining the objective infusibilized fiber.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for making pitch fibers infusible.

[Prior art] Pitch-based carbon fiber is a synthetic pitch based on coal-based, petroleum-based, naphthalene, or polyvinyl chloride, and includes isotropic pitch, optically anisotropic pitch, mixtures thereof, and polymer compounds. Melt-spinning pitch, etc. with additives such as
Depending on the case, it may be obtained by dry or wet spinning to obtain a fiber form, followed by infusibility, pre-carbonization if necessary, carbonization, and further graphitization if necessary.

However, pitch yarn has relatively low strength and elongation, and is brittle, resulting in poor handling and easy surface defects during handling, resulting in decreased productivity and
This is a factor that reduces the strength and elongation properties of carbon fibers after firing.

Furthermore, pitch yarn needs to be infusible before firing;
Like the pitch yarn, the infusible yarn is extremely fragile and has poor handling properties. Furthermore, when heating with an oxidizing gas to make it infusible, the infusibility reaction rate is extremely low in a low temperature range, so a method is usually used in which the reaction is carried out while raising the temperature as the infusibility progresses. At this time, it is necessary to raise the temperature within a range that does not exceed the increase in the softening point accompanying the progress of the infusibility reaction.

The oxidation reaction, which is the infusibility reaction of pitch, is an exothermic reaction, so when the yarn is infusible in a bundled state, such as a seam shape or a bobbin shape, into a normal multifilament 1, local heat accumulation occurs. However, even if the temperature of the infusibility treatment is controlled, adhesion and fusion of adjacent fibers is extremely likely to occur. This adhesion and fusing of fibers causes surface defects and significantly reduces the physical properties of the yarn.

In addition, there are light valves, tar, dust, etc. that adhere to the surface of the pitch yarn during spinning, and especially when a sizing agent is used, the chemical and physical effects of these agents may cause the adhesion and fusion. This problem can easily occur.

Due to the above-mentioned properties, the infusibility reaction of pitch must go through an extremely slow temperature raising process to complete the infusibility, even though the reaction rate is faster at higher temperatures.

In other words, pitch yarn has the drawbacks of poor handling and easy adhesion/fusion during infusibility treatment, so there is an upper limit to the yarn speed, yarn handling method, and heating rate during infusibility treatment. It is necessary to adopt conditions as mild as possible for all of the above, and in other words, these problems have a major drawback in that they reduce productivity, economic efficiency, carbon fiber physical properties, etc.

In addition, when obtaining high-strength, high-modulus carbon fibers using optically anisotropic pitch, defects that occur during handling and infusibility are a major factor in deteriorating physical properties, and
There is a problem in that the handling of eliminated components during firing and the internal strain caused by shrinkage due to the formation of a structure due to the development of a carbon network surface tend to become a starting point for fracture, especially near the surface.

Methods using liquid oxides such as nitric acid, hydrogen peroxide, potassium permanganate, etc. without using oxidizing gases such as air are also known, but these methods also require uniform treatment,
This method was not sufficient in terms of efficiency and reaction design according to oxidizing power.

JP-A-60-231825 also proposes applying a nitric acid solution to concentrate the particles and leaving them in the air to make them infusible.
There were problems such as insufficient infusibility due to the low oxygen content, and damage to the threads due to exposure to sudden high temperatures with nitric acid still attached.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for uniformly and efficiently rendering pitch yarn infusible.

[Means for Solving the Problems] The present invention provides pitch yarns with a diameter of 12μ or less according to the following relational expression (
1) (II) A method for making pitch fibers infusible, which is characterized by oxidizing in a nitric acid solution within a range that satisfies (II[).

15-3C-T/7≦t≦24-3C-T/7…(1)
0<T<100...(II>0.01<
C<8...(III) t: Reaction time (hr
) D: Reaction temperature ('C) C: Nitric acid concentration (specified) In the present invention, the pitch component is a synthetic pitch based on coal, petroleum, naphthalene, or polyvinyl chloride, and has isotropy and optical anisotropy. This refers to pitch, mixtures thereof, and pitch to which additives such as polymer compounds are added.

The optically anisotropic pitch can be within a range that provides orientation of the liquid crystal component during spinning. The amount of the optically anisotropic component is preferably 60% or more, more preferably 80% or more, from the viewpoint of the physical properties and spinning properties of the carbon fiber obtained.

In the present invention, the oxidizing power and oxidation reaction amount of the nitric acid solution used need to be within a specific range.

As a result of various changes in nitric acid concentration, reaction time, and reaction temperature, as shown in FIGS. 1 and 2, the optimum range at 20.60° C. was the shaded area in the figure.

In other words, it is necessary to perform this within a range that satisfies the following relational expression.

15-3C-T/7≦t≦24-3 C-T/7...(1
)0<T<100...(1)0.01<
C<8...(III) t: Reaction time (h
r) T: Reaction temperature (°C) C: Nitric acid concentration (specified) If the upper limit is exceeded, oxidation progresses too much and the obtained carbon fiber deteriorates, resulting in low strength.

In extreme cases, the infusible thread becomes powder. Moreover, below the lower limit, oxidation is insufficient and therefore infusibility is insufficient, resulting in fusion during firing.

In addition, when oxidizing with nitric acid, the diameter of the pitch yarn is 12
If it exceeds μ, sufficient oxidation will not occur and the infusibility effect will be insufficient. The reason is not clear, but it is thought that when nitric acid is used, although the oxidizing power is strong, the diffusion of oxygen into the pitch yarn is slower than in the case of gas, and the oxidation does not progress sufficiently to the center of the yarn.

However, in the present invention, if the surface is efficiently oxidized to prevent surface fusion and then oxidized in an oxidizing gas such as air, the pitch can be heated to a high temperature from the beginning during air oxidation, and the processing time can be reduced. It has the advantage of being able to shorten the time.

After the nitric acid treatment, the infusible yarn can be directly fed into the carbonization process, but in that case, the gold nitric acid will be scattered into the environment.
From the viewpoint of rapid oxidation, it is preferable to wash and remove nitric acid before firing. It is preferable to wash with water, and in order to avoid the negative effects of metal ions in the water,
It is preferable to wash with ion-exchanged water or pure water.

If the nitric acid treatment temperature is too low, the reactivity will be poor, and if it is too high, there will be problems with stabilizing the liquid concentration and handling.
'C is preferable, and 10 to 90'C is more preferable.

If the nitric acid concentration is too high, the surface will suffer deterioration such as etching, so it needs to be 8N or less, and 6N or less is preferable from the viewpoint of handling. Further, if it is too low, the reaction time becomes too long, so it is necessary to set it to 0°01N or more, and more preferably 0.1N or more.

Nitric acid treatment methods include running the thread through the liquid with a roll, storing it in a container such as a net or can and immersing it in the nitric acid solution, or winding it around a bobbin to a low bulk density and immersing it in the nitric acid solution. There is a way.

The method of running the yarn is advantageous in terms of uniformity of processing, and the method of processing with a container or bobbin is advantageous in terms of processing efficiency and economy. Further, the processing method can be either continuous processing or batch processing.

Carbonization treatment includes, for example, heating to 800 to 1700°C in an inert gas atmosphere or vacuum, and graphitization treatment includes heating at 170°C in an inert gas atmosphere, for example.
There is a method of heating to 0'C or higher.

[Examples] Example 1 Hydrogen gas was blown into coal tar and left unreacted at 450'C for 120 minutes. The obtained hydrogenated tar was passed through a 1μ filter to remove solid matter, and then heated at 350°C to obtain hydrogenated pitch. Then, it was heat-treated at 505° C. and 117 mmHg for 7 minutes to obtain mesophase pitch. The obtained mesophase pitch has a softening point of 265℃, 0122%, 8192%
, the anisotropy was 90%.

The obtained pitch is 32 mm using a bent extruder.
After melting 0'C160C16O and treating the lid scum, it was discharged from a 100μ nozzle with a diameter of 0.2 mm and a hole length Q of 3 mm, and was taken off at 450 m/min to obtain a pitch yarn with a diameter of 10 μ.

Then, after making it infusible in nitric acid under various conditions, washing with water, drying, and firing at 500.2500'C, carbon fibers were obtained.

The results are shown in Table 1.

Experiment No. 2, 3, 5, 6, 8, 10 to 13 of the present invention example.
No. 15 had sufficient infusibility and good carbon fiber physical properties.

In Experiment No. 1 as a comparative example, infusibility was insufficient and fusion occurred during firing, resulting in poor physical properties.

In experiments Nos. 4, 7, 9, 14, and 16 as comparative examples, the oxidation treatment was excessive, and the infusible yarn turned into powder when handled.

Example 2 In the same manner as in Example 1, pitch yarns with different diameters were obtained by varying the discharge amount. Then, in the same manner as in Example 1, the infusible yarn obtained by treating with 1N nitric acid for 60'Cl8 hours was fired in the same manner as in Example 1 to obtain carbon fibers. The oxygen content was determined from elemental analysis of the infusible yarn and compared with the physical properties of carbon fiber. The results are shown in Table 2 Experiment Nos. 17-19. For comparison, 0.5°C/min from 50°C to 3C0°C in air.
The example in which the temperature was raised to 3C and held at 0℃ for 15 minutes was shown in Experiment No.
2O.~22.

Table 2 Experiment No. 17.18 of the invention example compared to Experiment No. 18 of the comparative example
No. 19 was insufficiently oxidized and had low strength.

Further, in Experiment No. 17.18 of the present invention example, the oxygen content after infusibility was lower and the physical properties of the carbon fiber were good compared to Experiment NO. 21, which was a comparative example and carried out ordinary air oxidation.

Example 3 A pitch yarn with a diameter of 5 μm was obtained in the same manner as in Example 1. Then, after making it infusible at 60'C18 [1r] in 1N nitric acid, it was washed with running water and ion-exchanged water, and after drying, it was heated at 50'C to 13
The carbonization heating rate of C0'C was changed and graphitization was performed at 2500'C. The results are shown in Table 3.

Table 3 In Experiment No. 25.26, good physical properties were obtained without any fusion of the graphitized yarn, but in Experiment No. 23.24, the physical properties were poor due to fusion to the graphitized yarn.

[Effects of the Invention] According to the present invention, by controlling the humidity, time, and nitric acid concentration when pitch yarn is infusible with nitric acid, carbon fibers with high physical properties can be produced at a low cost of 1 to 1 q.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the optimum range of nitric acid concentration and time at 20'C, and Figure 2 shows the relationship between the optimum range of nitric acid concentration and time at 60'C. Formula Company Business 1 Figure 2

Claims (1)

[Claims] (1) Pitch yarn with a diameter of 12μ or less is expressed using the following relational formula (I
) (II) A method for infusible pitch fiber, characterized by oxidizing it in a nitric acid solution within a range that satisfies (III). 15-3C-T/7≦t≦24-3C-T/7…(I
) 0<T<100...(II) 0.01<C<8...(III) t: Reaction time (hr) T: Reaction temperature (°C) C: Nitric acid concentration (normal)