JP2780231B2 - Carbon fiber production method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing pitch-based carbon fibers having higher strength and higher elasticity.

(Prior art) Carbon fiber is a material having extremely high specific strength and specific elastic modulus, and has recently been particularly noted as a filler fiber of a high-performance composite material. The carbon fibers include polyacrylonitrile-based carbon fibers made of polyacrylonitrile as a raw material, and pitch-based carbon fibers made of carbonaceous material such as heavy oil, tar, and pitch.

By the way, when a carbonaceous raw material such as heavy oil, tar, and pitch is heated to a temperature of 350 to 500 ° C., a small particle having a particle diameter of several microns to several hundreds of microns exhibiting optical anisotropy under polarization in those substances. It is known that when spheres are formed and further heated, these small spheres grow and coalesce, and eventually show a state of optical anisotropy as a whole. This anisotropic structure is formed by layering and orienting high molecular aromatic hydrocarbons produced by a thermal polycondensation reaction of a carbonaceous raw material, and is considered to be a precursor of a graphite crystal structure.

A heat-treated product containing such an anisotropic structure is usually called a mesophase pitch, which is melt-spun through a nozzle, infusibilized, carbonized, and in some cases, graphitized to form a pitch-based material. High performance carbon fibers can be obtained.

(Problems to be Solved by the Invention) The pitch-based high-performance carbon fiber has a low raw material cost,
Although the yield in the carbonization step is large, the elastic modulus of the fiber is high, etc., it has various advantages as compared with the polyacrylonitrile-based carbon fiber, but the pitch-based carbon fiber manufactured from the mesophase pitch obtained by the conventionally known method is However, they generally have a drawback that elongation is slightly inferior to polyacrylonitrile-based carbon fibers.

Therefore, in the production of pitch-based carbon fibers, attempts have been made to produce higher-performance carbon fibers, and various proposals have been made so far. However, carbon fibers having high elongation performance comparable to polyacrylonitrile-based carbon fibers have not yet been obtained.

In general, in order to improve the characteristics of pitch-based carbon fibers, the presence of highly oriented molecules in the fibers is indispensable. However, if the molecules are excessively oriented, they become infusibilized and fired after spinning, causing crack-like defects in the fibers, leading to deterioration in strength.

That is, the mesophase pitch is highly oriented in the fiber axis direction by spinning, but at the same time, causes defects in the fiber to reduce the strength, and as a result, the elongation is reduced.

Therefore, the prior art obtains a spinning pitch that maintains spinnability by performing a heat treatment to a stage of forming a continuous phase of, for example, 35 to 95% without developing an anisotropic phase of the spinning pitch to 100% ( JP-A-53-119326, JP-A-59-119326
No. 26525, Japanese Patent Publication No. 55-37611). However, carbon fibers obtained from such a spinning pitch are unlikely to exhibit high elasticity.

(Means for Solving the Problems) Therefore, as a result of intensive studies to solve these problems, the present inventors focused on mesophase pitch, which is a spinning raw material, and vigorously improved these properties. The present inventors have found that the above problems can be solved by using specific raw materials, and have reached the present invention.

That is, an object of the present invention is to provide a method for producing a pitch-based carbon fiber having high elongation and high elasticity with good spinnability.

And the purpose is mesophase pitch 290 ~ 410 ℃
Melt spinning at the temperature of, then infusibilize, carbonize and, if necessary, in the method for producing carbon fiber, the reaction product obtained by reacting a crosslinking agent to the raw material pitch as mesophase pitch by heat treatment mesophase pitch It is easily attained by a method for producing carbon fiber, characterized in that a carbon fiber is used.

Hereinafter, the raw material pitch used in the method of the present invention for describing the present invention includes, for example, coal-based coal tar, coal tar pitch, coal liquefaction, petroleum heavy oil, tar, pitch, and the like. These raw material pitches usually contain impurities such as free carbon, undissolved coal, and ash, and these impurities are previously removed by a well-known method such as filtration, centrifugation, or stationary sedimentation using a solvent. It is desirable to keep.

The present invention is characterized in that a reaction product obtained by reacting a crosslinking agent with these raw material pitches is used as a raw material for mesophase pitch.

The crosslinking agent to be used is not particularly limited as long as it can be crosslinked by reacting with the raw material pitch.For example, formaldehyde or a derivative of formaldehyde such as formalin, diethylformal, paraformaldehyde, and trioxane; Dihydroxynaphthalene,
Examples thereof include aromatic dihydric alcohol compounds such as p-xylylene diglycol and aromatic dihalogen compounds such as p-xylylene dichloride. The cross-linking reaction can be carried out at normal pressure or under pressure. When pressurized, the reaction is carried out by an induction-stirring autoclave or the like.
~ 30wt%, reaction temperature 50 ~ 400 ℃, reaction time 10min ~ 50
It can be carried out for a time, preferably 100 to 300 ° C., for 1 to 20 hours.

The reaction may use a solvent, for example, benzene, xylene, aromatic oil, or the like. The reaction is more effective when a catalyst is used. For example, a Lewis acid such as aluminum chloride or boron fluoride, or a protic acid such as hydrochloric acid, sulfuric acid, or organic sulfonic acid is used. At that time, the catalyst is added by adding 1 to 200 mol%, preferably 5 to 50 mol% to the crosslinking agent. The reaction product thus obtained is converted into a mesophase pitch by a heat treatment, but it is desirable to perform a preliminary treatment by the following method before the heat treatment.

That is, (1) the reaction product is heat-treated at a temperature of 350 to 500 ° C. and a pressure of normal pressure to 10 kg / cm ² G for about 0.5 to 20 hours so that the optically anisotropic portion is usually 30% or more, preferably 50%. As described above, particularly preferably, a heat-treated product containing at least 70% is obtained, and then this heat-treated product and an aromatic oil such as anthracene oil having a boiling point or an initial boiling point of 150 ° C. or more are added to the heat-treated product / parts by weight. A method of obtaining the aromatic oil-soluble component by contacting the aromatic oil at a ratio of 0.1 to 3 parts by weight, (2) the reactant or the aromatic oil-soluble component in the above (1), for example, tetralin,
Quinoline, naphthalene oil, which can be treated with a hydrogen-donating solvent such as decalin, tetrahydroquinoline, or hydrogenated aromatic oil, or can be easily converted to a hydrogen-donating solvent with the reaction product or the aromatic oil-soluble matter. , A solvent such as anthracene oil, iron-based, molybdenum-based, nickel-based, chromium-based, zinc-based or sulfur-based catalyst and the like, 10-500k
g / cm ² G, preferably 20 to 300 kg / cm ² G, under hydrogen gas pressure, after hydrogenation at a temperature of 360 to 500 ° C. for 1 to 24 hours,
Pretreatment is performed by a method of removing solids by filtration or the like as necessary, and removing a solvent by distillation or the like as necessary to obtain a residue.

In the method of the present invention, the reactant or the pretreated reactant, usually in the presence of an inert gas, 350 ~ 500 ℃,
Preferably at a temperature in the range of 380-450 ° C for 2 minutes to 50
Heating is performed for a time, preferably 5 minutes to 5 hours, to obtain a spinning pitch containing an optically anisotropic phase. At that time, blowing or stirring of an inert gas may be performed.

In the present invention, the softening point of the mesophase pitch is 28
Selection of the above pretreatment conditions and heat treatment conditions so as to obtain a mesophase pitch of 0 to 350 ° C, preferably 300 to 320 ° C and an optical anisotropy ratio of 90% or more, preferably 100%, or a softening point. Needs to be adjusted. At this time, it is desirable that the mesophase pitch has a toluene-insoluble content of 90% or more, preferably 94 to 98%, and a quinoline-insoluble content of 40% or less, preferably 15 to 35%.

The softening point of the mesophase pitch is a value measured by the Mettler method, and the ratio of the optical anisotropy was determined as the area ratio of the portion showing the optical anisotropy in the mesophase pitch sample by a polarizing microscope at room temperature. Value. Specifically, a spinning pitch sample crushed into a few mm square was buried in a substantially front surface of a resin having a diameter of about 2 cm according to a conventional method,
After polishing the surface, the entire surface is observed under a polarizing microscope (100 magnification), and the area ratio of the optically anisotropic portion to the total surface area of the sample is measured.

The mesophase pitch obtained by the method of the present invention in this way can be obtained by spinning infusibilizing and carbonizing according to a conventional method and graphitizing as necessary, whereby a high-performance carbon fiber or graphite fiber can be obtained. In the case where the temperature is 300-350 ° C, a device is provided with a shearing material layer or a mesh layer upstream of the spinning nozzle proposed in Japanese Patent Application Nos. 59-131641 and 60-96975 to adjust the molecular orientation. By taking the method of opening and spinning, carbon fibers or graphite fibers having further properties can be obtained.

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

Example 1 While stirring a mixture of 100 parts of coal tar pitch, 5 parts of paraxylene glycol as a crosslinking agent and 1 part of paratoluenesulfonic acid in a 2 liter glass flask equipped with a stirrer under a normal atmosphere of nitrogen atmosphere at 140 ° C., Process for 10 hours,
A cross-linking reaction was performed.

Next, 100 parts of this reaction mixture was charged into an autoclave having a 5 l internal volume equipped with a stirrer, 100 parts of creosote oil, 5 parts of iron oxide and 2.4 parts of sulfur were charged, and a hydrogen pressure of 150 kg / cm ² , a temperature of 450 ° C.
It was hydrogenated for 0 minutes. After passing the reaction solution to remove the iron catalyst, the solvent was distilled off under reduced pressure to obtain a hydrogenated pitch. While bubbling nitrogen gas into this 100g pitch, 43
Heat treatment was performed at 0 ° C for 3 hours. The anisotropy ratio of the obtained pitch was 100%. This was melt-spun using a spinning nozzle having a diameter of 0.3 mm. The spinning at this time could be stably performed for a long time.

The fiber obtained here is infusibilized at 310 ° C in air, and then fired at 1600 ° C in an argon atmosphere to reduce the diameter to about
8 mm carbon fiber was obtained. The tensile strength of this carbon fiber is 405kg
/ mm ² , the tensile modulus was 33 ton / mm ² , and the elongation was 1.2%.

Example 2 A carbon fiber was obtained in the same manner as in Example 1, except that 13 parts of trioxane was used as a crosslinking agent. The tensile strength was 365 kg / mm ² , the tensile modulus was 33 ton / mm ² , and the elongation was 1.1%.

Comparative Example 1 A carbon fiber was obtained in the same manner as in Example 1, except that the coal tar pitch was not treated with a crosslinking agent. In that case, the tensile strength was 304 kg / mm ² , the tensile modulus was 33 ton / mm ² , and the elongation was 0.9%.

(Effect of the Invention) As described in detail above, according to the present invention, carbon fibers having high elongation and high elastic modulus can be manufactured with good spinnability by using specific raw materials.

Claims (2)

(57) [Claims] In a method for producing carbon fibers, a mesophase pitch is melt-spun at a temperature of 290 to 410 ° C., and then infusibilized, carbonized and, if necessary, graphitized. A method for producing a carbon fiber, comprising using a reaction product obtained by reacting the product with a mesophase pitch by heat treatment. 2. The method for producing carbon fiber according to claim 1, wherein the crosslinking agent is a formalin or formaldehyde derivative, an aromatic dihydric alcohol compound or an aromatic dihalogen compound.