JPH0735614B2 - Method for producing highly graphitized carbon fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to carbon fiber and a method for producing the same, and in particular,
The present invention relates to a carbon fiber having a high degree of graphitization and a method for producing the same, which is suitable for applications requiring high chemical resistance and high electrical conductivity.

[Conventional technology]

Carbon fibers are manufactured by a method of carbonizing organic fibers such as polyacrylonitrile fibers and pitch fibers by heat treatment. The heat treatment is usually carried out in two stages. In the first stage, it is fired in an atmosphere containing oxygen gas at a relatively low temperature (stabilization process), and in the second stage, it is fired in an inert gas atmosphere at a relatively high temperature ( Carbonization process). Important applications of carbon fibers are those where a high degree of electrical conductivity and / or a high degree of chemical resistance (e.g. use in saturated chlorine solution) is required. In such applications, it is necessary to maximize the degree of graphitization of carbon fiber.

As a method for producing such highly graphitized carbon fibers, there is known a method of applying tension to the fibers in the heat treatment step (stabilization step and / or carbonization step) of the organic fibers to suppress stretching or shrinkage thereof. (For example, Japanese Patent Publication No. 44-2117)
5, ibid. 46-10469, ibid. 54-156822, ibid. 51-16542). However, it is difficult to carry out such a method industrially and inexpensively, especially when the organic fibers which are the starting materials are short fibers and fiber aggregates.

[Problems to be Solved by the Invention]

The present invention relates to a form of organic fibers for producing carbon fibers used as a starting material (short fibers for wet papermaking or the like, aggregates thereof,
Alternatively, it is an object of the present invention to provide an inexpensive carbon fiber having a high degree of graphitization regardless of continuous fibers and the like, and a method for easily producing the carbon fiber industrially.

[Means for Solving the Problems]

According to the present invention, the above-mentioned object is: by adhering a solution of a thermosetting resin to an organic fiber for producing carbon fiber and then drying the same, the surface of the organic fiber is dried by a dry weight. A step of coating the thermosetting resin in an amount of 5% by weight or more; a step of thermally curing the thermosetting resin;
Comprising a step of preparing a precursor fiber by stabilizing treatment at a temperature of 0 to 350 ° C. for 5 hours or more, and a step of firing the precursor fiber at a temperature of 1800 ° C. or more in an inert gas atmosphere, Franklin's p-value is 0.60
It is achieved by the following method for producing highly graphitized carbon fiber, which comprises producing graphitized carbon fiber.

The present inventor has found that a high degree of graphitization can be obtained by subjecting organic fibers for producing carbon fibers to a stabilizing treatment for a sufficiently long time in a state of being coated with a thermosetting resin, and then performing carbonization firing.

The coated resin cures during the initial stage of the stabilization process or during heating, and restrains the shrinkage of the organic fibers during the stabilization process and during the carbonization and firing, which is the same effect as the conventional tensioning operation by external force. It is presumed that this causes the increase in the graphitization degree of the carbon fiber.

That is, the first important point of the present invention is to coat the surface of the organic fiber with a thermosetting resin. If this coating is not sufficient, the graphitization degree of the fiber is very low even under the same heat treatment conditions. The coating amount is 5% by weight based on the dry weight of the organic fiber.
The above is necessary, and 10% by weight or more is desirable.

The second important point of the present invention is the stabilization processing time.
If the time for the stabilization treatment carried out at 150 to 350 ° C. in an oxygen gas-containing atmosphere is not sufficient, graphitization will not proceed sufficiently in the subsequent carbonization and firing step. The stabilization treatment time is required to be 5 hours or longer, preferably 20 hours or longer. The configuration of the present invention will be described below.

Organic fiber As the organic fiber used in the present invention, regenerated cellulose, pitch fiber, polyacrylonitrile fiber, etc., usually,
Any fiber can be used as long as it is a fiber used for producing carbon fiber. From the viewpoint that it is easy to obtain a high degree of graphitization,
Poloacrylonitrile fiber is most suitable. The thinner the fiber, the easier the graphitization, but it may be selected according to the purpose of use and is not particularly limited. It is not necessary to limit the form of the organic fiber either, and short fibers, aggregates thereof, continuous fibers and the like can be used depending on the application. For example, it is possible to sprinkle short fibers on a shelf and heat-treat them, or to subject the short fiber aggregate once formed into a sheet to the treatment of the present invention and then pulverize to obtain carbon fibers. Is.

Thermosetting resin Any resin having a property of being dissolved in some medium and thermosetting and carbonized by heat treatment may be used, and a phenol resin, a furan resin, an epoxy resin or the like can be used. From the viewpoint of easy handling, the phenol resin is most preferable.

Coating (i) Attachment method A general method such as a method of immersing the organic fiber in a thermosetting resin solution may be used. The adhesion amount is adjusted so that a predetermined coating amount can be obtained after drying.

(Ii) Drying method Normal hot air drying or the like may be used.

Thermosetting The thermosetting resin is cured under the conditions usually used.

Stabilization Treatment Prior to firing, stabilization treatment is performed at a temperature of 150 to 350 ° C. in an atmosphere containing oxygen gas (for example, in air). The stabilization treatment time required to obtain a sufficient degree of graphitization depends on the type and thickness of the organic fiber and the desired degree of graphitization, but at least 5 is required to obtain Franklin's p-value of 0.60 or less.
I need time. Since the degree of graphitization monotonically increases with the stabilization treatment time, the treatment time may be determined in consideration of the required performance such as chemical resistance and economical efficiency.

The stabilizing treatment can also serve as the thermosetting treatment.

Firing treatment Stabilized fibers are fired at a high temperature of 1800 ° C or higher in an atmosphere of an inert gas such as nitrogen or argon. At this time, first, in a nitrogen gas atmosphere, firing and carbonization at a relatively low temperature of around 1,000 ° C to volatilize most of the volatile components, and then heat-treat at 1,800 ° C or higher in an argon gas atmosphere is a manufacturing process. It is advantageous. In any case, the final temperature is 1,800 ° C or higher.

The degree of graphitization of the obtained carbon fiber is represented by Franklin's p-value. This value is the average layer spacing d obtained from the X-ray diffraction pattern.
It is calculated by the following formula using (Å).

d = 3.440-0.086 (1-p ² ) In order to obtain sufficient chemical resistance, the p value needs to be 0.60 or less.

When the p value is 0.40 or less, particularly excellent chemical resistance is obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Parts and% in the examples are parts by weight and% by weight, respectively.

Example 1 A polyacrylonitrile fiber having a thickness of 10 denier and a length of 100 mm was immersed in a methanol solution of a phenol resin (manufactured by Gunei Chemical Co., PL2215) and dried at 105 ° C. using hot air. The resin coverage was 60% dry weight to fiber. Put this in a crucible and perform stabilization treatment in air at 220 ° C for 6 hours, then heat carbonize at 1,000 ° C for 1 hour in a nitrogen gas atmosphere, then in an argon gas atmosphere at 2,800 ° C for 30 minutes,
Heat treatment was performed to obtain carbon fibers.

Example 2 A carbon fiber was produced in the same manner as in Example 1. However, the stabilization treatment time was 12 hours.

Example 3 A carbon fiber was produced in the same manner as in Example 1. However, the stabilization treatment time was 24 hours.

Example 4 A carbon fiber was produced in the same manner as in Example 1. However, the stabilization treatment time was 48 hours.

Example 5 A carbon fiber was manufactured in the same manner as in Example 1. However, the resin coating amount was 7.5% and the stabilization treatment time was 12 hours.

Example 6 A carbon fiber was produced in the same manner as in Example 5. However, the resin coating amount was 39.6%.

Example 7 A carbon fiber was produced in the same manner as in Example 5. However, the resin coating amount was 69.6%.

Example 8 A carbon fiber was produced in the same manner as in Example 5. However, the resin coating amount was 110.6%.

Comparative Example 1 A carbon fiber was produced in the same manner as in Example 1. However, the stabilization treatment time was 3 hours.

Comparative Example 2 A polyacrylonitrile fiber having a thickness of 10 denier and a length of 100 mm was put in a crucible, stabilized at 220 ° C. for 12 hours in air, and then heated at 1,000 ° C. for 1 hour in a nitrogen gas atmosphere. Carbonized, and further in argon gas atmosphere at 2,800 ℃
And heat treated for 30 minutes.

The carbon fibers obtained in Examples 1 to 8 and Comparative Examples 1 to 2 were subjected to Franklin p-value measurement and chemical resistance test.

Chemical resistance is as follows: Carbon fiber sheet (2 mm thick × 10 cm square) is immersed in 500 ml of deionized water, chlorine is blown into it to saturate it, and the temperature is kept at 40 ° C for 10 days. The change was graded and evaluated as follows. Rating Judgment Liquid color 1 Excellent Transparent 2 Good Light yellow 3 Yes Yellow to brown 4 No Black color The results are shown in Table 1.

[Effect of the Invention] According to the present invention, when producing a highly graphitized carbon fiber from an organic fiber for carbon production, without the industrially difficult method of heat treatment at a high temperature while imparting tension to the fiber,
The highly graphitized fiber can be easily manufactured at low cost. The highly graphitized fiber according to the present invention is useful as a raw material for producing a material having high electric conductivity or chemical resistance by itself or when mixed with other materials.

Claims (1)

[Claims] 1. A solution of a thermosetting resin is applied to an organic fiber for producing a carbon fiber and then dried, whereby the surface of the organic fiber is dried at a weight ratio of 5% by weight with respect to the organic fiber.
The step of coating with the thermosetting resin in the above amount, the step of thermally curing the thermosetting resin, the coated organic fiber, in an oxygen gas-containing atmosphere, 15
Comprising a step of preparing a precursor fiber by stabilizing treatment at a temperature of 0 to 350 ° C. for 5 hours or more, and a step of firing the precursor fiber at a temperature of 1800 ° C. or more in an inert gas atmosphere, Franklin's p-value is 0.60
A method for producing a highly graphitized carbon fiber, which comprises producing the following graphitized carbon fiber.