JPS58156027A - Preparation of carbon fiber - Google Patents

Abstract

PURPOSE:To obtain sufficiently uniform carbon fibers having improved crystallinity and high strength, by heat-treating an aromatic composition with a solvent, heat-treating components insoluble in the solvent, melt spinning the heat-treated components, making the resultant fibers infusible, and calcining the resultant infusibilized fibers. CONSTITUTION:An aromatic composition, e.g. coal tar (pitch), is treated with an aromatic solvent, preferably benzene, and an aliphatic solvent, e.g. hexane, and components insoluble in the solvents are heat-treated, molten at 250-400 deg.C temperature range and extruded through a nozzle into fibers, which are then made infusible, carbonized at 1,000-1,500 deg.C temperature range in an inert gas phase, and if necessary graphitized at 2,000 deg.C or above to give the aimed carbon fibers.

Description

[Detailed description of the invention] The present invention relates to a method for producing carbon fiber from coal-based raw materials.

In particular, the present invention relates to a method for producing excellent carbon fibers by treating coal tar and/or coal tar pitch, which are coal-based raw materials, with a solvent to recover a fraction useful as carbon fibers.

In recent years, carbon fiber has been highly evaluated for its performance as a composite material with metal or plastic, but there is a demand for lower cost.

Therefore, recently, research has been actively conducted on pitch-based carbon fibers using pitch, which is an inexpensive raw material, from the viewpoint of raw material preparation methods and birch fiber manufacturing methods.

Pitch-based grade carbon fiber, that is, pitch-based high-strength cylindrical elastic modulus carbon fiber, is a mesophase (optically anisotropic region) which is a liquid crystalline graphitizable carbon crystal produced during the heat treatment process of pitch. In this case, the homogeneity and thermoplasticity of the mesophase produced are important.

However, ordinary pitches have a fairly wide molecular weight distribution ranging from low molecular weight to high molecular weight.

In general, molecules that have undergone thermal polycondensation to a certain size participate in the formation of mesophase sequentially, so there is a time difference in the development of mesophase within the pitch, and at the same time, the carbon fiber raw material is crystallized by light. It takes a long time in the mind. therefore.

Until a predetermined amount of pitch of the raw material is converted into mesophase, the initially generated mesophase undergoes excessive heat treatment, and as a result, the mesophase passes through the liquid crystal state and changes to carbon crystals with poor thermoplasticity. One thing. The presence of such carbon crystals not only deteriorates the uniform thermal plasticity of the entire Pi4-Tsuchi tree, but also causes yarn breakage or knots during spinning and forming.

By the way, in order for the pitch to be spun into carbon fiber to be homogeneous and exhibit thermoplastic properties, the growth rate of the graphitizable component in the pitch must be uniform, and the pitch must have the same root as the pitch phase.
It must have a good thermoplasticity to the corpse. In order for the degree of growth of mesophase, which is an easily graphitizable component in pitch, to be more uniform, the sizes of the molecules that participate in mesophase formation are uniform. That is, it is required that the molecular weight distribution of the raw material pitch, which is an aromatic composition, be [1] or narrower. In addition, in order to exhibit high thermoplasticity of this Ak mesophase pitch, it is important to homogeneously generate a predetermined amount of mesophase fluorescence by heat treatment at a lower temperature and for a shorter time. The aromatic composition of the aromatic composition before phase formation, RZ homogeneous molecular t of the star family hit, is set as high as possible so that the pitch containing all of the mesophase to be generated is not subjected to excessive heat treatment. There is a need to.

51 The inventors have determined that the raw material pitch, which is a monoaromatic group, is 25
Before the heat treatment in the temperature range of 0°C to 500"C, organic solvent treatment with a mixed solvent of an aromatic solvent and an aliphatic solvent (treatment described in JP-A-53-66901 by the present applicant) is performed. The present invention was completed based on the fact that the insoluble phase in the pitch zone or crystal zone that is precipitated at that time has a relatively uniform molecular weight.

This makes it possible to produce pitch that has better crystallinity, is sufficiently homogeneous, and has thermoplasticity as high as 1 or more.

In addition, the mesophase in the pitch can be freely sized from large to small particle size depending on the purpose.

Using the pitch obtained in this way, it is spun into carbon fiber,
The carbon fiber obtained by firing after infusibility treatment has an excellent pouring pot.

That is, the present invention is based on the following: ``An aromatic composition is treated with a solvent, heat-treated to make it insoluble in the solvent, and then subjected to bath-melt spinning to desensitize it.

6. Method 2 for producing carbon fiber characterized by further firing. Method 3 for producing carbon fiber according to claim 1, characterized in that the solvent is an aliphatic solvent and an aromatic solvent. The component insoluble in quinoline is 0.1
For more than 0.1% by weight of an aromatic composition, mix an aromatic solvent and an aliphatic solvent and collect the precipitated insoluble phase in the pitch zone, or add 0.1% by weight or more of a substance insoluble in quinoline. An insoluble phase material obtained by mixing an aromatic solvent and an aliphatic solvent with an aromatic composition containing the aromatic composition, collecting the precipitated insoluble phase in the pitch zone, and removing the substances insoluble in the quinoline contained therein. Alternatively, substances insoluble in quinoline are removed from an aromatic composition containing 0.1% by weight or more of substances insoluble in quinoline, and then an aromatic solvent and an aliphatic solvent are mixed and precipitated. The carbon fiber according to claim 1, characterized in that the insoluble phase in the pitch zone is recovered, and then the recovered material is distilled under normal pressure or reduced pressure to remove the low point fraction, and then the pitch is heat-treated. Manufacturing method 7-4 A crystal zone in which an aromatic solvent and an aliphatic solvent are mixed for an aromatic thread composition in which the solvent-insoluble component contains 01% by weight or less of a quinoline-insoluble substance, and the crystal zone is precipitated. The insoluble phase of 0.0% is recovered, or the material insoluble in quinoline is added to 0.0% of the insoluble phase.
Mixing an aromatic solvent and an aliphatic solvent to an aromatic composition containing 1@quantity or more. Collect the insoluble phase material of the precipitated crystal zone and remove the quinoline-insoluble substances contained therein to recover the insoluble phase, or from an aromatic composition containing 0.1% by weight or more of quinoline-insoluble substances. After removing substances insoluble in quinoline, mixing an aromatic solvent and an aliphatic solvent, recovering the insoluble phase of the precipitated crystal zone, and then distilling the recovered material under normal pressure or Biao pressure, 2. The method for producing carbon fibers according to claim 1, further comprising heat-treating the pitch from which all low-boiling fractions have been removed.

It is.

The substances insoluble in quinoline referred to here are solid mimic particles contained in the aromatic composition that is the raw material, mainly consisting of coke, carbon black, etc., and are generally non-graphitizable. This is said to be 100% QI.

If such a QI of 1 is present in the raw material, the growth of mesophase, which is a secondarily generated graphitizable component, is inhibited. In the present invention, if the content of such 1st QI is 0.1% by weight or less, the growth of mesophase will not be so great. When using QI, the growth of the mesophase is inhibited, so it is necessary to remove the QI. Furthermore, the presence of non-graphitizable components such as the primary QI significantly deteriorates the physical properties of carbon fibers when made into carbon fibers.

The method for producing carbon fibers of the present invention utilizes the raw material pitch t as an aromatic composition, an aromatic solvent and an aliphatic solvent completely mixed in advance, and an insoluble phase precipitated through the pores. By carrying out the treatment of the present invention, pitch having a narrow molecular weight distribution and a good average molecular weight can be obtained. This can be easily confirmed using gel permeation chromatography.

9-Here, the concept of the precipitation state of this insoluble phase will be explained. You may refer to Japanese Patent Application Laid-Open No. 53-56901 by Mizushunin, but the main parts will be explained here.

The present inventors discovered the following important fact while conducting a detailed study on the conventionally known solvent analysis of pitches. That is, when performing solvent analysis on an aromatic composition such as coal tar, an aliphatic solvent, which is a poor solvent for the composition and the aromatic solvent, is added to the composition under heating. An insoluble phase material is produced by simultaneous mixing with a family solvent and then cooling or cooling.

However, at this time, the composition ratio of each solvent combination and the aromatic thread composition must be appropriately selected.

In order to understand the state of precipitation of an insoluble phase due to mixing of a solvent with an aromatic composition, explanation will be made using a composition diagram. Below, the distributions in the text correspond to the composition points in Figure 1 at that time.

Aromatic composition and aromatic '#jn. are mixed while being heated to a temperature below the boiling point of the solvent, and formed into a cooling trench or layer 1 (point A). This mixture is usually in a 10-liquid state at room temperature. When an aliphatic solvent is gradually added to this, a plate-like insoluble phase begins to precipitate at point B. As the aliphatic solvent is further added, at point C the precipitated insoluble phase begins to take on a sticky tone, and at point D a black pitch-like substance begins to deposit in one part of the container. After point D, the state of the insoluble phase does not change even if the aliphatic solvent gold is continued to be added. When an aromatic solvent is mixed and heated to the composition at point D and left to cool or cooled, a sticky plate-like insoluble phase precipitates again at point E, and then an aromatic solvent is added. This results in a non-sticky, plate-like insoluble phase (point F). When the solvent to be added is then returned to the aliphatic system, the insoluble phase reaches the 0 point and begins to become granular, and after the H point, everything becomes granular.

In such a change in the precipitation state of the insoluble phase due to mixing of solvents, the region from point A to point B is called an oily zone because oily substances may precipitate depending on the case. B
In the region from point C to point C, a plate-like crystal-like precipitate appears, so it is called the crystal zone.■) In the region where the point exists, a black pitch-like substance appears, so it is called the pitch zone. . As explained above, the period from point E to point F and then to point 0 is again a crystal zone, but since the insoluble phase in the region where point H exists takes on a slurry state, it is called a slurry zone.

The insoluble phase, which is a precipitate in the pitch zone or crystal zone used in the present invention, has a black pitch or crystal shape, and is precipitated at the bottom of the container.
Although the softening point is higher than that of R&B method, separation of the insoluble phase itself is extremely easy. This is the effect of adding an aliphatic solvent.

The range of each of these regions also varies depending on the combination of solvents used. An example thereof is shown in Table 1, Example 11, Example 2. In combinations of solvents such as those shown in Table 2, in which 110,000 components are precipitated at compositions that do not completely dissolve each other, the aromatic composition and the aromatic solvent When the mixture is completely mixed and then the aliphatic electric medium is mixed, an insoluble phase can be similarly precipitated toward the 0th stage.

Table 1 Examples of changes in the precipitation state of the insoluble phase due to differences in solvent combinations and ratios (Example 1) Unit Car m
%=13-14- Table 2 Examples of solvent combinations that do not completely dissolve each other By such solvent treatment, the insoluble phase used in the present invention can be recovered very easily.

Next, non-invention will be explained in detail.

The aromatic composition can be prepared by using coal tar and coal tar pitch as a starting material, and mixing it with an aromatic solvent and a fatty acid solvent at a temperature ranging from 250°C under full pressure to the above-mentioned composition. In the vituna zone or crystal zone of the composition diagram, an insoluble phase occurs. In the present invention, this insoluble substance is used, but when an insoluble phase from a raw material containing 0.1 weight percent or more of a substance which is a quinoline soluble substance is used.

Substances insoluble in quinoline contained in the raw material or in the insoluble phase precipitated in the sipitz zone or crystal zone by solvent treatment are removed by means such as filtration or centrifugation.

Coal tar used in the present invention is produced during high-temperature carbonization of coal, and coal tar pitch is obtained by distilling this to remove light oil components. The aromatic solvent used in the present invention is not limited to any particular one, and may be any aromatic hydrocarbon as a constituent, such as benzene, toluene, quinoline, naphthalene, anthracene, phenanthrene, or a mixture thereof. Relatively heavy oils such as creosote oil, anthracene oil, or pre-by-product oil obtained by coal tar distillation are generally preferred.

On the other hand, the aliphatic heating medium is not limited in any way as long as its constituent components are aliphatic hydrocarbons such as n-hexano, naphtha, kerosene, fuel oil, etc. To recover the insoluble phase in the separation zone, static separation, hydrocyclone, Δ3
- Methods such as filtration, centrifugation, etc. or a combination thereof can be adopted.

The insoluble phase used in the present invention has a higher average molecular weight and a relatively rough molecular weight distribution 'f:! compared to the raw material before solvent treatment. , 1. ing. In order to further enhance these properties, the present invention employs atmospheric or reduced pressure distillation operations.
It can be adjusted as needed to have a higher average molecular weight and sharper molecular weight distribution depending on the required application.

The insoluble phase prepared in this way is
The heat treatment is preferably carried out at a temperature in the range of 300 to 450 degrees Celsius, but since the molecular weights are uniform as described above, a homogeneous mesophase is formed in a relatively short period of time by this heating. If the heating temperature is 500° C. or higher, the rate of crystallization will be too fast to control the progress of crystallization fk, so it cannot be said that the degree of convergence is appropriate. A heating temperature of 250° C. or lower may be sufficient, but it takes too much time to form a membrane which is an easily graphitizable component. The temperature 17
- The pitch produced according to the invention is heated at

This is the time taken to show fluidity even at a temperature of 200°C to 400°C as measured using a fluidity tester. The heating time is about 10 minutes to 5 hours depending on the heating temperature.

To adjust the particle size of the mesophase, two heating source degrees and time are controlled. For example, if the treatment is carried out at a low temperature of about 250° C. to 380° C. for a long time, a large number of small diameter mesophases will be produced. In fact, the higher the processing temperature, the faster the mesofaces are formed, resulting in larger diameter mesofaces. In either case, the heating time can be shortened by condensing the raw pitch that has been distilled and treated with a bath agent in advance.

It can be seen that the particles observed with the Pitchke polarizing microscope produced in this manner contain mesophase particles having uniformly sized optical anisotropy. By adjusting the heating temperature and heating time in this manner, the particle size and thermoplasticity of the mesophase can be freely controlled to suit the purpose.

Qgo, 1 as a pitch for carbon fiber used in the present invention
8- A'-! , V) Mesophase' or non-giant is preferred.

The mesoface of pitch 11 used in the present invention is:
It is preferable to use a pitch such that no mesophase can be confirmed at 200 times magnification using a polarizing microscope, or the presence of a mesophase can be confirmed for the first time.

In other words, if the diameter of the mesophase present in the pitch is larger than the diameter of the spinning ridge or fiber, knots or voids will form in that part during spinning of the fiber, making it impossible to perform continuous spinning. However, the tensile strength of the carbon fiber becomes weaker, and the original performance of carbon fiber cannot be exhibited.

The pitch produced by the method of the present invention is melted in a temperature range of 2z5o to 400°C, extruded through a nozzle, and spun. As usual, the spun fibers are made infusible at 200 to 300°C, then carbonized at 1000 to 1500°C in an inviscid gas phase, and if necessary, further graphitized at 2000°C or higher to form carbon fibers. Manufacture.

The carbon fiber produced according to the present invention can be produced by appropriately selecting the temperature in the carbonization and graphitization steps.

It is possible to produce general-purpose or high-quality carbon fiber.

The method for producing carbon fibers of the present invention is characterized by the preparation of raw materials for carbon fibers, and the homogenization of the raw materials is reduced by treating the material with a hot medium and making its molecular distribution as uniform as possible. The carbon fiber produced using this method has high strength and uniform quality.

Next, the present invention will be explained using examples.

Example operation 1 A substance insoluble in quinoline with a softening point of 25°C was added to 2.1
Aromatic light oil (initial boiling point 191°C according to JI'S K-2254,
175 parts of the solution (soft point: 328°C) were added, and 14 filtration was performed at 120°C to obtain a j:I solution with a recovery rate of 966% by weight.

Step 2 Apply industrial gasoline (JI) to this t44 part.
Add 1/2 part of S K-2201), heat mix at 70°C, collect the pitch-like insoluble phase that settles in the pitch zone, and distill under reduced pressure to obtain a mixture with a softening point of 90'C and 0 substances insoluble in quinoline. A pitch of .03% was obtained.

Operation 3: This pitch is under atmospheric pressure in a total nitrogen atmosphere.

When heat-treated at 380℃ for 8 hours, a pitch with a quinolinated content of 45% was obtained.+ When observed under a polarizing microscope with a magnification of 500 times, optically anisotropic spheres with a diameter of about 5 to 10μ were seen over the entire field of view. . The softening point of the pitch at this time is 23
The f1 liquid obtained in Step 1 was distilled under reduced pressure to form a gel using quinoline as a mobile phase using pinch having a softening point of 92°C and pitch having a softening point of 90°C obtained in Step 2. When the elution patterns were compared using a permeation chromatography tray, the pitch obtained from Step 2 had a higher proportion of large molecules than the pitch obtained from Step 1.
The molecular type distribution was also narrow, and the average molecular weight was high overall.

Operation 4 When the Pitchke obtained from Operation 2 (2) was bath-melt spun at 330°C, continuous spinning was possible for 1 hour. After the fiber was infusible at 210°C, it was carbonized at 1500°C. This carbon fiber had an average fiber diameter of 15μ, a tensile strength of 210 Kg/, j, and an elastic modulus of 15 t,/mA.

Example 2 To 1 part of coal tar containing 1.5% by weight of a substance insoluble in quinoline and having a softening point of 31°C, 4 parts of toluene and 5 parts of n-hexane were added and allowed to mix at 75°C.

The insoluble phase precipitated in the crystal zone had a black pitch plate-like crystal shape, and settled at the bottom of the container. This insoluble phase was collected, and 1 part of quinoline was added to the insoluble phase, and the mixture was subjected to pressurization for 1 time. The obtained p liquid was distilled under reduced pressure to a softening point of 8.
Pitch containing 0.02% of material insoluble in quinoline at 8°C was recovered. This pitch was placed in a nitrogen atmosphere, under a reduced pressure of 35
When heat-treated at 0° C. for 40 minutes, a pitch weighing 3 parts by weight of the quinoline bath was obtained. The softening point of this pitch was 220°C. This pitch was determined by a flow tester to 30
When measured in the temperature range of 0 to 350℃, it was extremely uniform.
- It showed a certain flow. Also, when this pitch was observed with a 200x polarizing microscope, it was found that the diameter was approximately 〕-μ over the entire field of view.
The following optically anisotropic spheres were observed to be produced.

The pitch was melt-spun, subjected to an infusibility treatment, a carbonization step, and then graphitized at 2800° C. The tensile strength of the carbon fiber obtained was 260 Ky/mA and an elastic modulus of 20 t/mA.

Example 3 Aromatic light oil (initial boiling point 19 according to JIS K 2254) was added to one part of coal tar soft pitch having a softening point of 23°C, 79% of toluene insoluble matter, and 22% of quinoline insoluble substances.
1°C, soft point 328°C) 1/6 part care Mixed and stirred at 0°C and left to cool, industrial gasoline No. 4 (JIS K 220)
722 parts of ) were mixed. The precipitated insoluble phase basin was collected and filtered to obtain pitch containing 0.0.5% of quinoline-insoluble material.

This pitch was softened to 220'C by distillation under reduced pressure, and then heat-treated for 390'Cl2O minutes under a reduced pressure of 3n+1+E fj in a total nitrogen atmosphere. When the obtained pitch was observed under a polarizing microscope with a magnification of 200 times,
Almost no mesophase was observed. The softening point of this pitch was 210"C.

The pitch was manufactured in the same process as in Example 2. The tensile strength of the carbon fiber was 230 Kg/mA, and the elastic modulus was 17 t.
/aa.

Example 4 The pitch having a softening point of 88°C obtained in Example 2 and containing 0.02% by weight of a substance insoluble in quinoline was placed in a nitrogen atmosphere.

Heat treatment was performed at 400° C. for 2 hours under atmospheric pressure. This pitch (
When observed using a polarizing microscope with a magnification of 5,200 times, optically anisotropic spheres having a particle size of 1 to 5 μm were found to occupy 5% of the entire field of view. Also, when we measured the quinoline solubility of this pitch, we found that]
It was 8% of the vehicle volume. Tensile strength i1”f of carbon fiber manufactured in the same process as the pitch full flow example 2: 200 Kg/
mA, and the elastic modulus was 17 t/rnA.

Comparative Example 1 Substance insoluble in quinoline 1j (1, Owt%, coal tar soft pitch with a softening point of 40°C) was heat-treated at 4.10°C under atmospheric pressure in a room atmosphere for 5 hours without solvent treatment. However, the mesophase was small, and the quinoline solubility at this time was 30 wt%.

When this pitch was spun as usual, yarn breakage occurred and continuous spinning was not possible. 51 spun carbon fiber Example 1
When carbon fiber was manufactured using a process similar to that described above, its tensile strength was only 60 S/-.

Comparative Example 2 Using the coal tar soft pitch used in Example 1, substances insoluble in quinoline were removed by filtration, and then the mixture was heated at 380° C. under reduced pressure for 30 days in a nitrogen atmosphere without solvent treatment. After heat treatment for several hours, a pitch with a softening point of 250°C was obtained. When this pitch was observed with a polarizing microscope at 200 ft!i, a mesophase of about 1 to 200 μ was present. The quinolinated content was 30 wt. %.This pitch had poor spinnability as well as soft-coated yarn.

As described above, in the present invention, by treating raw materials with an aliphatic solvent and an aromatic solvent, it is possible to produce a pitch having excellent crystallinity, homogeneity, and high thermoplasticity. When carbon fibers were produced using this pitch, they had good spinnability and had excellent performance as carbon fibers.

[Brief explanation of the drawing]

FIG. 1 shows the mixing ratio of the solvent to the aromatic composition and the state of precipitation of the insoluble phase. 26-

Claims (1)

[Claims]] Carbon fiber manufacturing method 2, characterized in that an aromatic composition is treated with a solvent, components insoluble in the solvent are heat-treated, and then melt-spun to make it infusible and further fired.Solvent is an aliphatic solvent and an aromatic solvent. 3. A method for producing carbon fiber according to claim 1, wherein the component insoluble in the solvent is a substance insoluble in quinoline or 0.1
For an aromatic composition of less than 0.1% by weight, an aromatic solvent and an aliphatic solvent are mixed and the insoluble phase in the precipitated pitch zone is collected, or 0.1% of the insoluble substance is added to the quinoline.
The aromatic solvent and fat, □ aliphatic solvent are mixed with the aromatic composition containing more than % by weight, and the insoluble phase of the precipitated pitch zone is collected, and the insoluble phase in the keynoline contained in this is collected. The insoluble phase from which substances have been removed 7 times 1- Or, the substances insoluble in quinoline are removed from the aromatic composition containing 0.1% by weight or more of substances insoluble in quinoline, and then the aromatic solvent and fat are removed. The pitch is mixed with a group-based solvent, the insoluble phase of the precipitated pitch zone is collected, and then the same is distilled under normal pressure or reduced pressure to remove the low-boiling fraction, and the pitch is then heat-treated. Claim 1:
Method for producing carbon fibers described in Section 4 The component insoluble in the solvent is the substance insoluble in quinoline is 0.1
For an aromatic composition of less than % by weight, an aromatic solvent and an aliphatic solvent are mixed and the insoluble phase of the precipitated crystal zone is collected, or the substance insoluble in quinoline is removed.
．． An aromatic solvent and an aliphatic solvent are mixed with an aromatic composition containing 1% by weight or more, the insoluble phase of the precipitated crystal zone is collected, and all the substances insoluble in quinoline contained in the mixture are collected. Collect the removed insoluble phase, or remove the quinoline-insoluble substances from the aromatic composition containing 0.1% by weight or more of substances insoluble in quinoline, and then combine the aromatic solvent and the aliphatic solvent. The pitch is mixed with a solvent, the insoluble phase of the precipitated crystal zone is collected, and then the collected product is distilled under normal pressure or reduced pressure, and the pitch from which the low-boiling fraction has been removed is heat-treated. A method for producing carbon fiber according to claim 1.