JPS59137512A - Production of high-strength carbon fiber - Google Patents

Abstract

PURPOSE:Acrylonitrile synthetic fiber is treated to give preoxidized fiber of a specific density and the fiber is heat treated stepwise under tension in an inert atmosphere, then heat treated at high temperature to produce the titled carbon fiber with high orientation, uniformity and performance without yarn defects. CONSTITUTION:Acrylonitrile synthetic fiber is treated so that its density becomes 1.25-1.37g/cm<3> to give preoxidized fiber and the resultant fiber is heat treated under tension in an inert atmosphere to adjust its density to 1.40- 1.57g/cm<3>. Further, the tension is increased and the heat treatment is continued until the density reaches 1.57-1.70g/cm<3>, subsequently the heat treatment is conducted in an inert atmosphere over 800 deg.C to give the objective high-strength carbon fiber. The preoxidation temperature at the first step preferably ranges 250-600 deg.C and at the second step, 400-800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-strength carbon fibers by heat treating acrylonitrile-based synthetic fibers.

Carbon fiber has high specific strength and specific modulus, and is used in aviation, space, and other industries.
It is widely used as a reinforcing material in various composite materials for leisure goods and industrial materials.

However, it is still difficult to say that its strength is sufficient, and the development of high-strength carbon fiber is desired.

Conventionally developed methods for producing high-performance carbon fiber include:
For example, Japanese Patent Application Laid-open No. Sho F14-147222 is known.

In this method, flame-resistant fibers with a fiber density of 1.30 to 1.42.97c are carbonized in an inert atmosphere at a temperature of 300 to 800C while being stretched up to 25%, and then It is made into carbon fiber by heat treatment at a temperature of 8,000 or higher. Flame resistant thread '1i80
It is well known that when heat treated under a constant load at a temperature of 0C or higher, the fiber length changes as shown in the first factor in response to the change in density. The fiber itself undergoes significant physical changes in this heat treatment area, and the structural changes in the yarn are complex. In order to prevent problems from occurring, methods have been used in which the yarn is heat-treated under tension that causes the yarn to shrink in length. However, in such a method, as described in the invention of the above-mentioned published patent, high-strength specification 1, title of the invention: Method for producing high-strength carbon fiber 2, claims: acrylonitrile-based synthetic fiber with a density of L2fi~1. , 8
711/an? The flame-retardant fibers were heat-treated under tension in an inert atmosphere to reduce the density to L4.
01/c- or above 1. After reaching R71/caF or less, heat treatment is performed by applying tension in an inert atmosphere to reach a density tl-Lfi7~1.7011/Qni', and then heat treatment is performed in an inert atmosphere at 800C or higher. A method for producing high-strength carbon fiber, which is characterized by:

a Detailed Description of the Invention The present invention relates to a method for producing high-strength carbon fibers by heat treating acrylonitrile-based synthetic fibers.

Carbon fiber has high specific strength and specific modulus, and is used in aviation, space, and other industries.
It is widely used as a reinforcing material in various composite materials for leisure goods and industrial materials.

However, it is still difficult to say that its strength is sufficient, and the development of high-strength carbon fiber is desired.

Conventionally developed methods for producing high-performance carbon fiber include:
For example, Japanese Patent Application Laid-open No. Sho F14-147222 is known.

In this method, flame-resistant fibers with a fiber density of 1.30 to 1.42.97c are carbonized in an inert atmosphere at a temperature of 300 to 800C while being stretched up to 25%, and then It is made into carbon fiber by heat treatment at a temperature of 8,000 or higher. Flame resistant thread '1i80
It is well known that when heat treated under a constant load at a temperature of 0C or higher, the fiber length changes as shown in the first factor in response to the change in density. The fiber itself undergoes significant physical changes in this heat treatment area, and the structural changes in the yarn are complex. In order to prevent problems from occurring, methods have been used in which the yarn is heat-treated under tension that causes the yarn to shrink in length. However, with this method, it was not possible to produce high-strength carbon fibers as described in the invention of the above-mentioned published patent; It has achieved its purpose.

However, in this method, the yarn length changes drastically when elongating to a total elongation rate of 25%, and uniform elongation cannot be performed, so it is extremely difficult to produce carbon fibers that are always uniform and exhibit high performance.

Therefore, the present inventors conducted research to find a manufacturing method that would consistently obtain high-performance carbon fibers, and as a result, they completed the present invention.

The gist of the present invention is to use acrylonitrile synthetic fibers with a density of 1. "25 ~ 1.8711/c-" 1-4011/crTI
After fc (hereinafter referred to as the first pre-carbonization step), the density is set to 1,57~1.70 &
/ c- (hereinafter referred to as pre-carbonization second step),
Furthermore, there is a method for completely producing high-strength carbon fibers, which is characterized in that carbonization is then completed in an inert atmosphere at 800C or higher.

The precursor for producing flame-resistant yarn used in the present invention is preferably an acrylonitrile fiber, particularly polyacrylonitrile, or a monomer copolymerizable with 85% by weight or more of acrylonitrile, such as methyl acrylate, ethyl acrylate, etc. Ethyl acrylate, or an unsaturated carboxylic acid such as methacrylic acid, acrylic acid, itaconic acid, etc., and a polymer obtained by appropriately copolymerizing vinyl chloride, styrene, acrylamide, diacetone acrylamide, allylsulfonic acid, etc., was dissolved in a solvent. It is preferable that the fibers are then made into fibers by a wet method or a dry method.

When carrying out the present invention, first, acrylonitrile synthetic fibers are heat treated in an oxidizing atmosphere, especially at 20%
Flame resistant treated at 0~aooc, 1.25~L 871!
'/c- density. If the fiber density of the flame resistant treatment system is less than L2511/c-, the flame resistant treatment system will soften in subsequent steps, causing problems such as thread breakage in subsequent treatment steps. On the other hand, the density is 1.871. /c
- In the above cases, it is not possible to apply a large elongation in the subsequent heat treatment step, and the carbon fiber tensile strength cannot be improved.

Therefore, the fiber density of the flame-retardant treatment system used in carrying out the present invention is 1.25 to 1.877 i', / c &
Seven things are necessary.

As shown in Figure 1, in the subsequent first pre-carbonization step and second pre-carbonization step of the flame-retardant yarn in an inert atmosphere, the fiber structure changes most drastically, and the yarn in this heat treatment step If the treatment is not carried out properly, not only will high-performance carbon fiber not be obtained, but it will also lead to the occurrence of yarn defects such as yarn breakage. Therefore, in the present invention, under an inert atmosphere, while applying tension to the fibers, the fiber density is L40g/C-1 or more.
．． Pre-carbonization first so that Fl is less than 7 g/C-
After heat treatment in the process, the fiber density is further increased to 1.571.
/ C♂ or above 1.・By applying tension to the fiber so that it is 701/c- or less and heat-treating it in the second pre-carbonization step, it was possible to prevent the above-mentioned disadvantages and to produce high-performance carbon fiber. That's what I did.

The tension applied during the first pre-carbonization step refers to a tension treatment such that the elongation of the fibers during this heat treatment step is 15% or less, particularly 5 to 10%. If the elongation rate in this elongation step is too small, it will be difficult to produce high-performance, especially high-strength, carbon fibers.On the other hand, if the elongation rate is too high, troubles such as thread breakage will occur, which is undesirable. Furthermore, by using several nip rolls in this heat treatment step, the elongation rate can be controlled in detail, thereby making it possible to obtain carbon fibers with even better uniformity.

Furthermore, the tension applied when carrying out the second pre-carbonization step refers to a process in which the yarn length is stretched by 1 to 20 inches in this heat treatment step. It is difficult to produce carbon fibers with high performance if the carbon fibers are heat-treated under tension that causes the yarn to shrink during this heat treatment process.On the other hand, if the elongation rate of the remaining fibers becomes high, problems such as yarn breakage will occur.

In addition, the heat treatment temperature in this heat treatment step is 250 to 8
00C range, especially the temperature of the first step of pre-carbonization is 2
．． The temperature of the pre-carbonization second step treatment is preferably in the range of 400 to 800C.

As mentioned above, the fibers obtained by treating flame-retardant yarn to a specific fiber density under a specific tension are free from yarn defects and have better orientation than conventionally developed heat treatment systems. Because of this, its structure is well maintained even during the subsequent carbonization process in an inert atmosphere at 800C or higher, especially 1000 to 3000C, making it possible to produce carbon fibers that are always uniform and have high performance. It can be done.

The present invention will be explained in more detail with reference to Examples below, and the strength was determined by the method shown below.

Epoxy resin (manufactured by Shell Chemical Co., Ltd.: Epicoat 528) e
The carbon fiber bundle that had been impregnated and hardened was subjected to a tensile rupture test method under the conditions of 220 μL trial and 5 ML/min tensile rate.

Example 1 A copolymer of acrylonitrile/methyl acrylate/methacrylic acid = 95/4/1 was made into fibers by wet spinning to obtain a multifilament with 6000 filaments and a single tenier L5d.

This fiber bundle was subjected to flame-retardant treatment by being stretched in air with a temperature gradient of 220 to 260 C. Table 1 shows the treatment conditions of each step and the performance evaluation results of the obtained carbon fibers. Here, the ambient temperature in the first pre-carbonization step is 250-600C and the treatment time is 3 minutes.The ambient temperature in the second pre-carbonization step is 4F10-800C and the treatment time is 3 minutes. In addition, carbonization is carried out under a nitrogen atmosphere at a temperature of 800 to 180
The test was carried out under the conditions of 0t;'.

Aa Aa in Table 1 was obtained by the method of the present invention, 41. A5- and Aa are cases where only one stage of pre-carbonization step has been conventionally performed.

This shows that the method of the present invention is effective. Further, A 2.4.7 and A 9.10 indicate cases where the conditions are different from the conditions of the present invention, and when implementing the present invention, it is necessary that the conditions are within the range specified by the present invention.

[Brief explanation of the drawing]

Figure 1 shows the change in fiber length when the flame-retardant system was heat-treated, with the vertical axis representing the change in yarn length and the horizontal axis representing the density. It is something that Patent Applicant Mitsubishi Rayon Co., Ltd. Agent Patent Attorney 1) Takeshi Mura 1 Figure Review (9/Crn'1 Procedure Amendment (Method) % Formula % 1, Indication of Case 1988 Patent Application No. 9259 No. 2, Name of the invention Process for producing high-strength carbon fibers 3, Relationship with the amended person's case Patent applicant Osamu Kanazawa, President and CEO of Mitsubishi Rayon Co., Ltd., 2-3-19 Kyobashi, Chuo-ku, Tokyo (603) 4. Agent: 2-8-1 Toranomon, Minato-ku, Tokyo Sent on April 26, 1982 6. Subject to amendment

Claims (1)

[Claims] Acrylonitrile synthetic fiber with density L2fi~1,8
711/an? The flame-retardant fibers were heat-treated under tension in an inert atmosphere to reduce the density to L4.
01/c- or above 1. After reaching R71/caF or less, heat treatment is performed by applying tension in an inert atmosphere to reach a density tl-Lfi7~1.7011/Qni', and then heat treatment is performed in an inert atmosphere at 800C or higher. A method for producing high-strength carbon fiber, which is characterized by: