JPS6363647B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for easily producing carbon fibers with excellent properties from pitch-like materials, and more specifically, the present invention relates to a method for easily producing carbon fibers with excellent properties from pitch-like materials, and more specifically, the present invention relates to a method for easily producing carbon fibers with excellent properties from pitch-like materials. When producing carbon fiber from a pitch-like material such as depolymerized pitch or a reheated product of the pitch, the pitch-like material selected from the range of calorific value (ΔH) of 10 to 150 cal/g is melt-spun. The present invention relates to a method for producing carbon fibers by heat-treating the pitch fibers in the presence of oxygen to make them infusible, and then heat-treating them in an inert atmosphere.

In the conventional method for producing carbon fiber from a pitch-like material, the starting material, a pit-like material (hereinafter abbreviated as "pitch"), is used, for example, when the carbon content in the pitch is reduced to 91%.
~95%, methods to make the molecular weight large (molecular weight 400 or more), and softening point (℃)
Methods have been proposed to limit the mesophase content.

These methods are certainly effective as a means of avoiding fusion to some extent during the infusibility process, which is one process for producing carbon fiber from pitch.
However, since Pitch has a chemically very complex structure, it has been extremely difficult to find an effective method through all the steps of spinning, infusibility, and carbonization.

The reasons for this are: (1) The spinnability, that is, the spinnability, and the infusibility of Pitch have contradictory properties; in other words, the easier it is to spin, the more difficult it is to melt and make it infusible; The relationship is that those that easily become infusible cannot be spun at all.

(2) Even if Pituchi, which has good stringability, could be made infusible,
In the next carbonization process, the fibers fuse together, making it impossible to demonstrate the performance of the fiber.

(3) In addition, even if the above-mentioned pitch properties are specified, for example, even if the carbon content is 91 to 95%, the pitch will have a chemically very complex structure, and in an extreme case, the structure will become chain-like. Depending on whether it is circular or ring-shaped, it has a great influence on its stringability, infusibility, and even the performance of the carbonized product. The same thing can be said even if the softening point or molecular weight of pitch is specified.

(4) Furthermore, the fiber diameter is small (10 μm or less)
Otherwise, high-strength carbon fibers cannot be obtained, but for this purpose, it is necessary to spin the fibers by applying a draft from a nozzle with a hole diameter of 0.3 to 0.4 mm at a high spinning speed (approximately 300 m/min). It is extremely difficult to select a pitch suitable for this high-speed spinning.

The purpose of the present invention is to obtain easily from these pithus, which have a chemically complex structure and have many unknown points.
It is an object of the present invention to provide a method for manufacturing carbon fiber that is inexpensive and has excellent properties.

When a constant amount of heat per unit time is externally supplied to or removed from a substance, a change occurs in the rate of temperature rise or fall of the substance. Based on this principle, the so-called differential thermal analysis method is a well-known method that continuously measures the temperature of a sample while heating or cooling the sample at a constant rate to detect phase changes, the presence of transition temperatures, and the presence or absence of chemical reactions. ing. Recent trends include a shift from differential heat (internal electromotive force) to differential heat balance (calorific value), although the principle is the same.

The inventors of the present invention have worked hard to analyze pitches based on the above principle, and as a result, applied the above principles in an oxygen atmosphere, measured the calorific value (ΔH) of pitches, and determined pitches within a certain range of calorific values (ΔH). The above-mentioned problems were solved by selectively using carbon fibers, and a method for producing carbon fibers using high-speed spinning was established. The calorific value (ΔH) of the pitcher is 10 to 150 cal/g, preferably 15 to 150 cal/g.
If a fiber having a content in the range of 80 cal/g is used, the above-mentioned high-speed spinning can be carried out well. Pitch calorific value (ΔH)
If the pitch is less than 10 cal/g, the filaments will fuse to each other during infusibility, although there will be leakage properties, and if the pitch calorific value (ΔH) exceeds 150 cal/g, the leakage properties will be poor and the spinning nozzle will Since it becomes impossible to discharge the fiber, spinning becomes substantially difficult, which is not preferable. In addition, by adjusting carbonaceous raw materials other than pitch, such as polyvinyl chloride, to the above range by heat treatment, etc., we have developed a method for producing carbon fibers that have good spinnability, excellent infusibility, and excellent properties. I found it. Here, the calorific value (ΔH) is determined by placing a sample pitch of 7 to 13 mg in a differential calorimeter and heating it in the atmosphere at a temperature increase rate of 5 to 15° C./min.

The calorific value (ΔH) referred to in the present invention is determined as follows.

In other words, in the process of increasing the temperature of the pitch-like substance,
An oxidative exothermic peak as shown in Figure 1 is observed, and the calorific value (ΔH) is calculated from the area A using the formula ().

M・ΔH=K・A……() M: Mass of sample [mg] ΔH: Energy change per unit mass of sample [cal/g] K: Instrument constant [mcal/mcal] A: Peak area [mcal] ] That is, when a pitch-like substance is heated in an oxidizing atmosphere, the amount of heat generated by oxidation as shown in FIG. 1 can be detected as a change in temperature by a differential calorimeter. The total amount of heat generated by the oxidation of this pitch is defined as the peak area A, and ΔH is determined from this peak area A. A large peak area A can be considered to indicate that the pitch is susceptible to oxidation, but in the present invention, the peak area A is detected,
From this, ΔH is calculated and pitches are selected according to the range, making high-speed spinning possible.

The present invention will be further explained below with reference to Examples.

Example 1 Petroleum pitch having a softening point of 200°C and a ΔH of 10.6 cal/g was melted at 290°C and melt-spun into fibers from a nozzle with a diameter of 0.3 mm and 72 holes at a winding speed of about 300 m/min. The resulting pitch fiber was heated to 260°C in air at a heating rate of 30°C/hr, held at this temperature for 1 hour to make it infusible, and then heated to 260°C in a nitrogen stream at a heating rate of 100°C/hr. It was heat-treated to ℃ to obtain carbon fiber.

The obtained fiber bundle maintains its fiber shape, although it is slightly fused, and its tensile strength is 42Kg/mm ²
The carbonization yield was 66.1%.

Example 2 Coal-based pitch with a softening point of 198°C and ΔH of 10.2 cal/g was melted at 300°C and made into carbon fiber under the same conditions as in Example 1.

The obtained fiber bundle was similar to the fiber bundle of Example 1,
Although it is slightly fused, it maintains its fiber shape,
Its tensile strength is 66Kg/ ^mm2 and carbonization yield is 66.3%
It was hot.

Example 3 PVC pitch (obtained by thermally decomposing PVC at 400°C for 1 hour in an inert atmosphere) with a softening point of 182°CΔH21.1cal/g was melted at 280°C, and then carbonated under the same conditions as in Example 1. It was made into fiber.

The obtained fiber bundle was flexible and had no fusion.
Its tensile strength is 79.5Kg/ ^mm2 and carbonization yield is 66.5
It was %.

Example 4 PVC pitch (obtained by thermally decomposing PVC at 400°C for 1 hour in an inert atmosphere) with a softening point of 210°C and ΔH of 14.5 cal/g was melted at 290°C, and then carbon was melted under the same conditions as in Example 1. It was made into fiber.

The obtained fiber bundle was flexible and had no fusion.
Its tensile strength is 82.5Kg/ ^mm2 and carbonization yield is 66.9
It was %.

Example 5 Coal-based pitch with a softening point of 246°C and a ΔH of 53.2 cal/g was melted at 300°C and made into carbon fiber under the same conditions as in Example 1.

The obtained fiber bundle was flexible and had no fusion.
Its tensile strength is 81.8Kg/ ^mm2 and carbonization yield is 69.7
It was %.

Example 6 Petroleum-based pitch with a softening point of 280°C and a ΔH of 150 cal/g was melted at 370-385°C and melt-spun into fibers from a nozzle with a diameter of 0.4 mm and 19 holes at a winding speed of about 250 m/min. The resulting pitch fiber was heated in air at 30℃/
Raise the temperature to 330℃ at a rate of hr.
Hold for an hour to make it infusible, then 100 hours in a nitrogen stream.
The carbon fiber was heat-treated to 1000°C at a heating rate of °C/hr.

The tensile strength of the obtained fiber was 45 Kg/mm ² and the carbonization yield was 68.4%.

Comparative example 1 Petroleum-based pitcher with a softening point of 185℃ and ΔH3.7cal/g
The fibers were melted at 280° C. and heat treated under the same conditions as in Example 1, but some fusion occurred during the infusibility process and the fibers stuck together during the carbonization process.
The carbonization yield was 62.2%.

Comparative example 2 Coal-based pitcher with a softening point of 158°C and a ΔH of 1.8 cal/g
It was melted at 260°C and heat treated under the same conditions as in Example 1, but it fused during the infusibility process.
Furthermore, the fiber shape could not be maintained during the carbonization process. The carbonization yield was 61.5%.

Comparative Example 3 Regarding coal-based coal with a softening point of 310℃ and ΔH of 174.0cal and PVC pitch with a softening point of 325℃ and ΔH of 270.0cal/g.
Melt spinning was performed at 400-430°C. However, the dissolution of the pitch was uneven and it was not possible to obtain pitch fiber continuously.

Comparative Example 4 Coal-based pitch with a softening point of 295°C and ΔH of 153 cal/g was melted at 390°C and melt-spun at a winding speed of 100 m/min from a nozzle with a diameter of 0.4 mm and 19 holes.

However, continuous fibers could not be obtained because the fluidity in the molten state was uneven and yarn breakage occurred frequently.

As is clear from the comparison of the above examples and comparative examples, in the present invention, by adjusting the pitch of the calorific value of 10 to 150 cal/g, the pore diameter required to obtain fibers with a fiber diameter of 10 μm or less is 0.3 to 0.4 mm. It can be spun from a nozzle at a spinning speed of around 300 m/min without yarn breakage, and the harsh conditions for infusibility are 30°C/hr in air and held at 260 to 330°C for 1 hour, increasing productivity. It can be raised.

Furthermore, the present invention does not provide pitches with good spinnability, pitches with excellent infusibility, or carbon fibers with excellent properties, but includes all of the above three items, and furthermore, It also provides high carbonization yield.

[Brief explanation of drawings]

FIG. 1 is a graph showing the oxidation exothermic peak during the temperature rising process of a pitch-like substance.

Claims (1)

[Claims] 1. A pitch-like substance is blown into the atmosphere using a differential calorimeter.
Area of oxidation exothermic peak obtained by heating at a temperature increase rate of ~15°C/min: Amount of energy change per unit mass calculated from the following formula from A [m cal]: ΔH
[cal/g] is a process of sorting out pitch-like substances with a value of 10 to 150 cal/g, and ΔH=K・A/M where K: device constant [m cal/m cal] M: mass of sample [mg] A method for producing carbon fibers, which comprises the steps of melt-spinning the selected pitch-like material through a nozzle with a hole diameter of 0.3 to 0.4 mm at a spinning speed of 250 to 300 m/min, making it infusible, and further carbonizing it.