JPH062793B2 - Method for producing low softening point optically anisotropic pitch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Use) The present invention is an optical anisotropic material having excellent performance as a raw material for producing high-strength, high-modulus carbon fibers (high-performance carbon fibers) and other carbon materials. The present invention relates to a method for manufacturing a sex pitch.

More specifically, xylene is bound to four or more via a methylene group, a compound consisting of a xylene tetramer or higher fraction is used as a starting material, which has a low softening point, is homogeneous and has a molecular orientation. The present invention relates to a method for producing an excellent optically anisotropic pitch.

(Prior Art) First, in the present specification, "optical anisotropy" of pitch means that when a cross section of a pitch lump solidified near room temperature is polished and observed under a crossed Nicols with a reflection type polarization microscope. The part where light emission is recognized.

The ratio of optical anisotropy is shown by area%. "Toluene insoluble matter" and "quinoline insoluble matter" are JIS-K-2.
425.

The "softening point" refers to the temperature at which the pitch powder starts to deform when the pitch powder is heated at 10 ° C / min in a nitrogen atmosphere with a hot stage microscope.

By the way, in general, carbon fiber is industrially made of rayon,
Mainly made from PAN and pitch.

However, when PAN is used as a raw material, the raw material is expensive and the carbonization yield is low.

In this respect, the pitch is cheap and economically attractive.

However, among pitches, low-cost carbon fibers manufactured from isotropic pitches have poor molecular orientation and thus have low strength, and high performance products have not been obtained.

In contrast, carbon fibers produced from an optically anisotropic pitch called mesophase pitch have a high degree of molecular orientation, high strength and elastic modulus, and excellent mechanical properties.

Further, researches for producing mesophase pitch from catalytic cracking residual oil of oil, naphtha tar pitch or coal tar pitch have been widely promoted.

It has been confirmed in many experiments that high-performance carbon fibers can be obtained by spinning mesophase pitches using these as raw materials, with molecules centered on condensed polycyclic aromatics being aligned in the fiber axis direction. .

However, the above mesophase pitch has a high viscosity because of the large interaction between the condensed polycyclic aromatic compounds, and therefore,
There is a drawback that the softening point becomes high.

Generally, the spinning temperature of the pitch is 40-100 from the softening point.
It is said to be high in ° C, and if the softening point is high, it will be difficult to perform stable spinning for a long time.

Therefore, various studies have been conducted to lower the softening point and improve the spinnability.

However, conventional petroleum pitch and coal tar pitch are
A pitch in which a condensed polycyclic aromatic structure is developed by heating this catalytically cracked residual oil, naphthatal or coal tar, which is a complex mixture with various compositions, as a starting material, and its molecular weight is continuously wide. It is distributed.

For this reason, it has been difficult to control the chemical structure and to extremely lower the softening point with the conventional pitch of the starting material.

Conventionally, mesophase pitch with developed optical anisotropy is
It is difficult to spin at a temperature of 300 ° C or lower, and most of them were spun at a high temperature of 340 to 380 ° C.

For this reason, thermal decomposition and thermal condensation reactions are likely to occur during spinning, gas and high molecular weight substances tend to be produced, and stable spinning for a long time is difficult.

As an attempt to improve this drawback, for example, a method of partially hydrogenating mesophase pitch to appropriately weaken its laminated state and spinning it as an isotropic pitch (Japanese Patent Publication No. 59-30192), at the time of spinning, A method using a unique pre-mesophase pitch that is isotropic but converts to optical anisotropy during carbonization (Japanese Patent Laid-Open No. 58-18421)
and so on.

However, since all of them are spun at an isotropic stage where the molecular orientation is weak, the molecular orientation in the fiber is inferior to that of the optically anisotropic one.

Further, it is not industrially advantageous to hydrogenate a highly viscous pitch in which condensed polycyclic aromatics are laminated.

Further, the catalytic cracking residual oil of coal tar, naphtha tar, or petroleum fraction, which is a starting material in the prior art, contains inorganic substances such as free carbon and catalyst powder that become ash.

These substances not only hinder the spinning of the pitch, but when these fine particles are contained in the fiber, they cause defects in the carbon fiber and cause the strength to be weakened.

Therefore, various removal methods have been devised,
It is difficult to remove even submicron particles, which causes the strength and elastic modulus not to increase.

(Problems to be Solved by the Invention) In order to obtain a high-performance carbon fiber, it is important that the molecules are oriented along the fiber axis direction in the towed state. Therefore, it is desirable that the pitch has high optical anisotropy.

Further, in order to increase the strength of the fiber, it is advantageous that the structure of the oriented molecules is long in the fiber axis direction.

Furthermore, it is desirable that the softening point of the pitch is low. When the softening point is low, spinning becomes easy and stable spinning can be performed for a long time.

However, if the softening point becomes too low, the fibers ejected from the spinning nozzle will be fused and cannot be used.

The present invention is completely different from the conventional pitch raw material, and uses a compound having a limited chemical structure prepared by means of chemical synthesis as a starting raw material, and is easily and stable at a temperature much lower than that of the conventional mesophase pitch. It is an object of the present invention to provide a method for producing an optically anisotropic pitch that has a low softening point, is homogeneous, and has excellent molecular orientation that can be spun.

(Means for Solving Problems) (1) Starting Material The method for producing a low softening point optically anisotropic pitch of the present invention starts with a compound having a limited chemical structure, which has hardly been used until now. Use as raw material.

This compound is a compound composed of a xylene tetramer or higher fraction in a form in which four or more xylenes are bonded via a methylene group.

The optically anisotropic pitch obtained from a compound in which two and / or three xylenes are bonded has a low yield, requires a large manufacturing apparatus, and is uneconomical in terms of energy.

This compound can be used as the starting material of the present invention, as long as it has the above-mentioned chemical structure, regardless of the preparation method.

This compound can be obtained, for example, from a polymer obtained by polymerizing xylene and formaldehyde as raw materials using a protonic acid as a catalyst.

Alternatively, it can be obtained by dehydration condensation using xylene and xylene formalin resin as raw materials and a protonic acid as a catalyst.

Alternatively, it can be obtained by reacting xylene and xylene formalin resin as raw materials with paratoluenesulfonic acid as a catalyst and then distilling under reduced pressure.

It can also be obtained by adding dimethylstyrene to xylene under an acid catalyst.

The above raw materials are all petrochemical raw materials or petrochemical products.

And, unlike coal tar, naphtha tar, or catalytic cracking residual oil containing ash fine particles described above, it essentially contains no inorganic matter such as free carbon and catalyst powder, and is therefore an extremely excellent raw material.

Furthermore, the above raw materials are highly refined and contain almost no foreign elements such as sulfur.

When the starting material is adjusted by polymerization or condensation reaction, the oxygen content in the starting material (fraction of xylene tetramer or higher) needs to be 5% by weight or less, preferably 2% by weight or less.

Those having a high oxygen content are easily decomposed during heat treatment, resulting in a low pitch yield. Further, the softening point of the pitch becomes high, and it cannot be used for the purpose of the present invention.

(2) Production method The starting materials are reacted in an inert atmosphere under reflux or under pressure at a temperature of 380 to 460 ° C. for a time of 0.5 to 10 hours, and then an inert gas is blown in. Or by vacuum distillation to form a mesophase pitch while removing light components, it is possible to produce an optically anisotropic pitch having a low softening point, which is uniform and excellent in molecular orientation, which is the object of the present invention. it can.

Alternatively, the optically anisotropic pitch that is the object of the present invention can be obtained by heat treatment while removing light components from the beginning to form a mesophase pitch.

(3) Pitch property To obtain high performance carbon fiber and other carbon materials,
The optical anisotropy of the material pitch is 85% or more, preferably 9
It should be 5% or more.

However, in general, the higher the optical anisotropy, the higher the softening point.

The surprising feature of the optically anisotropic pitch obtained by the present invention is that even if the optical anisotropy is 100%, the softening point is 200.
It is ~ 250 ° C.

Further, if further necessary, the pitch having a softening point of 250 ° C. or higher can be adjusted.

Further, in the state where the optical anisotropy is developed and the softening point is lowered, the H / C (atomic ratio of hydrogen and carbon) value, which is an index of the progress of carbonization, is 0.60 to 0. 75, especially 0.
65 to 0.70 is preferable. This point is significantly different from the conventional H / C value of the mesophase pitch of 0.5 to 0.6.

Further, what is more surprising is that the pitch obtained by the present invention is an optically anisotropic pitch in which the content of insolubles in toluene is small, that is, it is soluble in toluene.

The amount of toluene-insoluble matter can be adjusted by the molecular weight of the starting material or heat treatment conditions.

To increase the optical anisotropy at a low softening point, the toluene insoluble content is 50% by weight or less, preferably 20 to 40% by weight. The quinoline insoluble content is 10% by weight or less, preferably 3% by weight or less.

(Function) Starting material used in the present invention (a fraction of xylene tetramer or more in a form in which four or more xylene are bonded via a methylene group)
Is heat-treated, benzene rings adjacent to each other via an alkyl side chain are cyclized, so that a so-called “cata” type condensed ring structure is relatively likely to be formed.

Moreover, the non-cyclized alkyl substituents are retained to some extent during the heat treatment stage.

For this reason, despite the high optical anisotropy, the interaction of the condensed polycyclic aromatic compounds becomes slower than that of the starting material used in the prior art, and the softening point is lowered and the solvent is soluble. Bring .

Therefore, when the pitch produced by the present invention is used as a raw material, high-performance carbon fibers having high strength and high elastic modulus and other carbon materials can be obtained.

(Examples) Next, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to this.

Example 1 A flask equipped with a stirring blade and a reflux condenser was charged with 550 g of xylene, 100 g of paraformaldehyde and 200 g of 83% sulfuric acid, and reacted at a reaction temperature of 110 ° C. for 5 hours.

After completion of the reaction, the mixture was diluted with 500 g of toluene, and the mixture of toluene and the reaction solution was washed with pure water until the aqueous layer became neutral.

Then, unreacted substances were removed by vacuum distillation (120 ° C / 10 mmHg) to obtain 300 g of a polymer.

Then, further vacuum distillation (240 ° C / 1 mmHg) was performed to obtain 190 g of distillate oil and 110 g of a heavy product as a bottom residue.

As a result of measuring the molecular weight distribution of this heavy material by elemental analysis, GPC and mass spectrometry, it was confirmed that the main component was a fraction in which four or more xylenes were bonded via a methylene group.

60 g of this heavies in an inert atmosphere with nitrogen, 4
After reacting for 7 hours while refluxing at 20 ° C., mesophase pitching was performed while removing light components by vacuum distillation (400 ° C./10 mmHg) to obtain a pitch of 25.8 g.

The properties of this pitch are 100% optical anisotropy and 2 softening points.
At 25 ° C., H / C value was 0.670, toluene insoluble content was 38.2% by weight, and quinoline insoluble content was 2.8% by weight.

This pitch, spinning temperature 270 ℃, nozzle hole 0.5mm
When melt spinning was carried out using a φ spinning nozzle, a pitch fiber diameter of 15 μm could be smoothly spun without yarn breakage.

This pitch fiber (original yarn) was finally made infusible at 300 ° C. while gradually raising the temperature in an air atmosphere, and then carbonized to 1000 ° C. in an inert gas atmosphere.

The tensile strength of the obtained carbon fiber was 18.3 Ton / cm ² and the elastic modulus was 1660 Ton / cm ² .

Example 2 and Example 3 The same method as in Example 1 was carried out by changing the starting material adjustment conditions and the pitching conditions.

As described above, Table 1 shows the adjustment conditions and properties of the starting materials for Examples 1 to 3.

Table 3 shows the pitch manufacturing conditions and properties.

Table 4 shows the carbon fiber properties.

Example 4 A flask equipped with a stirring blade and a reflux condenser was charged with 100 g of xylene, 100 g of a commercially available xylene formalin resin (trade name Nikanol L, oxygen content 8.8% by weight), and 20 g of paratoluenesulfonic acid, and a reaction temperature. 120 ° C
And reacted for 5 hours.

After completion of the reaction, the mixture was diluted with 300 g of toluene, and the mixture of toluene and the reaction solution was washed with pure water until the aqueous layer became neutral.

Then, vacuum distillation (240 ° C / 1 mmHg) was performed to obtain 140 g of a heavy product as a residue of the kettle.

As a result of measuring the molecular weight distribution of this heavy product by elemental analysis, GPC and mass spectrometry, it was confirmed that xylene was a fraction in which four or more xylenes were bonded via a methylene group.

The oxygen content of this fraction was 0.4% by weight.

60 g of this heavies in an inert atmosphere with nitrogen, 4
After reacting for 8 hours under reflux at 00 ° C., put a nitrogen introduction tube in the liquid, and while flowing nitrogen of 400 cc / min,
Light components were removed at 00 ° C. to obtain a pitch of 24.0 g.

The properties of this pitch are 90% optical anisotropy and 23 softening points.
At 5 ° C, H / C value was 0.668, toluene insoluble content was 39.2% by weight, and quinoline insoluble content was 9.0% by weight.

When this pitch was melt-spun at 290 ° C. using a spinning nozzle having a nozzle hole of 0.5 mmφ, the pitch fiber diameter was 13
The yarn could be spun without breakage in μm.

This pitch fiber was finally infusibilized at 300 ° C. while gradually raising the temperature in an air atmosphere, and then carbonized to 1000 ° C. in an inert gas atmosphere.

The tensile strength of the obtained carbon fiber was 17.8 Ton / cm ² and the elastic modulus was 1650 Ton / cm ² .

Table 2 shows the adjustment conditions and properties of the starting materials.

Table 3 shows the pitch manufacturing conditions and properties.

Table 4 shows the carbon fiber properties.

Example 5 The same method as in Example 4 was carried out by changing the starting material adjustment conditions and the pitching conditions.

Table 2 shows the adjustment conditions and properties of the starting materials.

Table 3 shows the pitch manufacturing conditions and properties.

Comparative Example 1 Commercially available xylene formalin resin (trade name Nikanol L)
Was used as the starting material.

The oxygen content of this resin was analyzed and found to be 8.8.
% By weight.

100 g of this resin was reacted in an inert atmosphere using nitrogen under reflux at 400 ° C. for 7 hours as in Example 1, and then light distillation was performed by vacuum distillation (400 ° C./10 mmHg). When mesophase pitching was performed, the yield of pitch was only 2.0 g.

The properties of this pitch are 90% optical anisotropy and 30 softening points.
At 0 ° C., the toluene insoluble content was 66.0% by weight and the quinoline insoluble content was 35.0% by weight.

The spinnability was poor.

Table 3 shows the pitch manufacturing conditions and properties.

Comparative Example 2 500 g of dimer and trimer fraction of xylene obtained in Example 1
Then, in the same manner as in Example 1, after reacting for 12 hours under reflux at 400 ° C. in an inert atmosphere using nitrogen, vacuum distillation (400 ° C./10 mmHg) was performed to remove light components and mesophase pitch. As a result, the pitch yield was only 10.0 g.

Table 3 shows the properties of the pitch.

Comparative Example 3 A pitch was produced under the same conditions as in Example 1 using a heavy oil of fluid catalytic cracking residual oil at 400 ° C. or higher as a raw material.

The properties of this pitch are 90% optical anisotropy and 28 softening points.
The H / C value was 0.58 at 0 ° C.

When this pitch was melt-spun at 350 ° C. using a spinning nozzle having a nozzle hole of 0.5 mmφ, the pitch fiber diameter was 13
The yarn could be spun without breakage in μm.

This pitch fiber was finally infusibilized at 300 ° C. while gradually raising the temperature in an air atmosphere, and then carbonized to 1000 ° C. in an inert gas atmosphere.

The tensile strength of the obtained carbon fiber was 16.3 Ton / cm ² and the elastic modulus was 1370 Ton / cm ² .

Table 4 shows the carbon fiber properties.

(Effects of the Invention) The method for producing an optically anisotropic pitch of the present invention is characterized in that a starting material is a compound having a limited chemical structure, which has been hardly used in the past.

And, it is a completely new type of optically anisotropic pitch manufacturing method capable of spinning at a temperature much lower than that of the conventional mesophase pitch.

The pitch produced according to the present invention has a highly developed optical anisotropy.

For this reason, carbon fibers and other carbon materials produced using this pitch, the graphite structure of the fibers and the like easily develop,
A high elastic modulus is obtained.

Further, as in the case of conventional mesophase pitch, impurities such as ash that cause defects in fibers are small, and thus high fiber strength can be obtained.

And even if the optical anisotropy is 100%, the softening point is 200 to
Since it is 250 ° C., spinning is possible at a low temperature of 250 to 300 ° C., which is difficult in the conventional technique.

Moreover, there is no change in pitch, phase separation does not occur, and there are few obstacles such as yarn breakage during spinning. Therefore, stable spinning can be performed for a long time.

Furthermore, by mixing the pitch produced according to the present invention with a conventional mesophase pitch, it is possible to lower the softening point and improve the spinnability without reducing the optically anisotropic content.

Claims (7)

[Claims] 1. A compound comprising a xylene tetramer or more distillate represented by the following general formula as a starting material, and the starting material is refluxed or under pressure in an inert atmosphere at a temperature of 380 to 4.
After reacting at 60 ° C for 0.5 to 10 hours, blow an inert gas or distill under reduced pressure to remove light components and form mesophase pitch. Low softening point Optically anisotropic Method for manufacturing sex pitch. (However, m ≧ 3 R is hydrogen or a methyl group.) 2. A compound consisting of a xylene tetramer or more distillate represented by the following general formula as a starting material, which is not refluxed or pressurized and has a temperature of 380 to 460 ° C. and a time of 0. A method for producing a low softening point optically anisotropic pitch, which comprises heat-treating for 5 to 10 hours to form a mesophase pitch while removing light components. (However, m ≧ 3 R is hydrogen or a methyl group.) 3. The compound according to claim 1 or 2, wherein the starting material is a compound consisting of a xylene tetramer or higher distillate obtained by polymerizing xylene and formaldehyde as a raw material using a protonic acid as a catalyst. Method for producing low softening point optically anisotropic pitch of. 4. A compound comprising a xylene tetramer or more fraction obtained by dehydration condensation of xylene and xylene formalin resin as a raw material using a protonic acid as a catalyst, as a starting material. The method for producing a low softening point optically anisotropic pitch according to item 2. 5. A compound comprising a xylene tetramer or more fraction obtained by reacting xylene and xylene formalin resin as raw materials with paratoluenesulfonic acid as a catalyst and then distilling under reduced pressure is used as a starting raw material. A method for producing a low softening point optically anisotropic pitch according to claim 1 or 2. 6. The low softening point optical anisotropy according to claim 3, 4 or 5, wherein the oxygen content of the compound consisting of a xylene tetramer or higher fraction is 5% by weight or less. Method for manufacturing anisotropic pitch. 7. The low softening point optical anisotropy according to claim 3, 4, or 5, wherein the oxygen content of the compound consisting of a xylene tetramer or higher fraction is 2% by weight or less. Method for manufacturing anisotropic pitch.