JP5656185B2 - Method for producing flame-resistant acrylonitrile polymer - Google Patents

Description

  The present invention relates to a method for producing a flame-resistant acrylonitrile polymer that can also be used as a precursor of carbon fiber suitable as a reinforcing fiber material in various composite materials.

  For example, acrylic fiber made of acrylonitrile polymer is used as a precursor of carbon fiber. A so-called polyacrylonitrile carbon fiber (PAN-based carbon fiber) obtained using an acrylic fiber as a precursor is excellent in mechanical properties and good in productivity, and thus is widely industrially produced.

When producing carbon fibers from acrylic fibers, first, the acrylic fibers are heat-treated at 200 to 300 ° C. in an oxidizing atmosphere to make flame-resistant fibers (flame-proofing step), and then carbonized to obtain carbon fibers. . In the carbonization treatment, heat treatment is usually performed in an inert gas at 1000 to 2000 ° C. by a known technique (carbonization step). In addition, it is preferable to heat-treat in an inert atmosphere furnace having a rising temperature gradient of 400 to 700 ° C. (pre-carbonization step) before the carbonization step.
The carbon fiber thus obtained may be further processed in a high-temperature inert gas to obtain a graphite fiber.

In the flameproofing process, a cyclization reaction of a nitrile group bonded to a polymer chain constituting an acrylonitrile polymer such as acrylic fiber, and a structure in which a naphthyridine ring and an acridone ring are combined by oxidation or dehydrogenation of the cyclized structure The dehydrogenation reaction (which is referred to as “flame-resistant reaction” in combination) is performed.
However, in the flameproofing reaction in an oxidizing atmosphere at 200 to 300 ° C., the structure is likely to change due to the diffusion state of oxygen from the acrylonitrile polymer surface, and if the oxygen diffusion is insufficient, the reaction will continue until the dehydrogenation reaction. It was hard to progress. Therefore, the flame-resistant acrylonitrile polymer such as the flame-resistant fiber obtained depends on the diameter when the acrylonitrile polymer is fibrous, the particle size when it is powdery, and the thickness when it is a film, but the outside is A structure with a carbon double bond composed mainly of a naphthyridine ring and an acridone ring is the main structure, and the inside is mainly a structure without a carbon double bond, which is a cyclization reaction of a nitrile group. It was hard to become. The tendency to become such a structure became more prominent as the diameter, particle size, and thickness of the acrylonitrile polymer increased.

Further, when a homopolymer obtained by homopolymerizing acrylonitrile is used as the acrylonitrile polymer, the heat treatment in the flameproofing process tends to take time. For this reason, a copolymer obtained by copolymerizing a monomer (reaction promoting monomer) that accelerates the flameproofing reaction with acrylonitrile is usually used.
However, as the proportion of the reaction promoting monomer increases, the heat treatment time (flame resistance time) in the flame resistance process can be shortened, but on the other hand, the quality and performance of the obtained carbon fibers tend to decrease.

  As a method for accelerating the flameproofing reaction, for example, Patent Document 1 discloses a method of flameproofing an acrylic precursor under pressure.

Japanese Patent Laid-Open No. 3-76822

However, in the method described in Patent Document 1, although the flameproofing reaction can be promoted, for example, when an acrylic fiber having a large diameter (for example, an acrylic fiber having a diameter of 15 μm or more) is used, the flameproof fiber having a uniform structure up to the inside. It was not always easy to get.
Moreover, in the method of patent document 1, although a fiber bundle is heated and flame-resistant treatment is performed in the atmosphere of 200-300 degreeC pressurized to 0.05-100 kg / cm < ² > -G, Example The temperature and pressure ranges indicated by are not under supercritical atmosphere.

  The present invention has been made in view of the above circumstances, and the flame resistance time can be shortened, and a fiber having a large diameter, a powder having a large particle diameter, or a thick film acrylonitrile polymer can be used, An object is to provide a method capable of producing a flame-resistant acrylonitrile polymer having a uniform structure up to the inside.

The method for producing a flame-resistant acrylonitrile polymer of the present invention is characterized in that the acrylonitrile polymer is heat-treated at 200 to 300 ° C. in a supercritical fluid containing carbon dioxide as a main component to carry out cyclization and dehydrogenation reactions. to.
Et al is, it is preferable that the supercritical fluid containing an oxidizing agent.
The acrylonitrile polymer may be in the form of a fiber, particularly a fiber having a diameter of 15 μm or more, a powder, or a film.
Furthermore, it is preferable that the acrylonitrile polymer is a copolymer containing 90 to 98% by mass of acrylonitrile units, and the heat treatment time in the supercritical fluid is 60 minutes or less.

According to the method for producing a flame-resistant acrylonitrile polymer of the present invention, a flame-resistant time can be shortened, and a fiber having a large diameter, a powder having a large particle size, or a thick film-like acrylonitrile polymer is used. However, a flame-resistant acrylonitrile polymer having a uniform structure up to the inside can be produced.
The flame-resistant acrylonitrile polymer obtained by the present invention has a uniform structure up to the inside.

It is a schematic block diagram which shows the heat processing apparatus 1 used in the Example. It is a schematic block diagram which shows the heat processing apparatus 2 used in the Example. It is the figure which showed the solid ¹³ C-NMR spectrum of the flameproof fiber obtained in Example 1, 4, 12, and Comparative Example 1, 3. FIG. It is the figure which showed the infrared absorption spectrum of the flameproof fiber obtained in Example 7 and Comparative Example 2.

The present invention will be described in detail below.
The method for producing a flame-resistant acrylonitrile polymer of the present invention is characterized in that the acrylonitrile polymer is heated in a supercritical fluid to carry out cyclization and dehydrogenation reactions.
The shape of the acrylonitrile polymer used in the present invention may be a fiber, a powder, or a film.
Here, the case where the acrylonitrile polymer is particularly fibrous is referred to as “acrylic fiber”, and the fiber obtained by heat-treating the acrylic fiber is referred to as “flame-resistant fiber”.

As the acrylonitrile polymer, a polymer obtained by homopolymerizing acrylonitrile (homopolymer) and / or a copolymer with a monomer copolymerizable with acrylonitrile can be used.
When the acrylonitrile polymer is a copolymer, the content of acrylonitrile units in the acrylonitrile polymer is preferably 90% by mass or more for the purpose of good carbonization. In particular, the content of the acrylonitrile unit is more preferably 95% by mass or more for the purpose of reducing defects caused by the acrylonitrile polymer when the carbon fiber is used and improving the quality and performance of the carbon fiber. On the other hand, the upper limit of the content of acrylonitrile units is preferably 98% by mass or less.

  A monomer copolymerizable with acrylonitrile is used to accelerate the flameproofing reaction. Although there is no restriction | limiting in particular as such a monomer, For example, in methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, etc. Representative acrylic acid esters: methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, uraryl methacrylate, 2-hydroxyethyl methacrylate, hydroxy methacrylate Methacrylic acid esters represented by propyl, diethylaminoethyl methacrylate, etc .; acrylic acid, methacrylic acid, itaconic acid acrylamide, N-methylol acrylamide, diacetone acrylic , Unsaturated monomers such as styrene, vinyl toluene, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl bromide, vinylidene bromide, vinyl fluoride, vinylidene fluoride; p-sulfophenylmethallyl ether, methallylsulfonic acid, Examples include allyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and alkali metal salts thereof. These may be one kind or a combination of two or more kinds.

As another monomer copolymerizable with acrylonitrile, a monomer having a carboxylic acid group or acrylamide is preferably used for the purpose of particularly promoting the cyclization reaction in the flameproofing step described later. In particular, from the viewpoint of improving solubility in a solvent, it is preferable that 1% by mass or more of acrylamide units are contained in the acrylonitrile polymer.
As the monomer having a carboxylic acid group, methacrylic acid and itaconic acid are preferable.

  The acrylonitrile polymer can be obtained by a known polymerization method such as solution polymerization or suspension polymerization. It is desirable to remove impurities such as unreacted monomers from the acrylonitrile polymer obtained by polymerization.

When the acrylonitrile polymer is fibrous, the acrylonitrile polymer thus obtained, preferably the acrylonitrile polymer from which impurities have been removed, is dissolved in a solvent to obtain a spinning stock solution, and the spinning stock solution is spun to obtain an acrylic fiber. .
As the solvent, organic solvents such as dimethylacetamide, dimethylsulfoxide, dimethylformamide, and aqueous solutions of inorganic compounds such as zinc chloride and sodium thiocyanate can be used. An organic solvent is preferable in that the metal is less likely to be mixed into the produced fiber and the process is simplified.
The concentration of the acrylonitrile polymer in the spinning dope is preferably 17% by mass or more, more preferably 19% by mass or more, depending on the degree of polymerization in the spinning process. Moreover, 25 mass% or less is preferable.

A known spinning method can be used as the spinning method. Specifically, a wet spinning method in which the spinning solution is directly spun into a coagulation bath through a nozzle hole, or a dry wet spinning method in which the spinning solution is once spun into air and then coagulated in the bath can be used.
For the coagulation bath, an aqueous solution containing a solvent used for the spinning dope is used. The concentration of the solvent in the aqueous solution depends on the type of solvent used, but for example, when dimethylacetamide or dimethylformamide is used, it is preferably 50 to 80% by mass.
The temperature of the coagulation bath is preferably 20 to 50 ° C. in terms of productivity.

The coagulated yarn obtained by spinning the spinning dope is washed with water, stretched and dried, and used as an acrylic fiber that is a carbon fiber precursor.
The stretching process and the drying process can be performed by a known method.
The stretching treatment is not limited and can be performed, for example, by a method in which a coagulated yarn is wound around two rolls and the rotation speed between the two rolls is changed. The atmosphere at the time of the stretching treatment is not limited, and for example, it can be appropriately selected from an aqueous solution containing the same kind of solvent as the coagulation bath, hot water, high-pressure steam, or the like, and can be combined.
Although it does not necessarily limit as a drying method, For example, the method of winding a coagulated yarn around a heated roll and making it pass can be illustrated.

In addition, when an acrylonitrile polymer is a powder form, it can obtain by shape | molding the acrylonitrile polymer after superposition | polymerization into a pellet form with a granulator etc., and making it dry.
In the case where the acrylonitrile polymer is in the form of a film, a cast solution is prepared by dissolving acrylonitrile polymer powder in a solvent, the cast solution is applied onto a substrate, and dried to remove the solvent. The cast solution can be obtained by extruding the cast solution with a T-die or the like and coagulating it in a coagulating liquid, and subsequently removing the solvent by washing with water and drying. As a solvent, the solvent illustrated by the manufacturing method of an acrylic fiber can be used.

Using the acrylonitrile polymer such as acrylic fiber thus obtained, the acrylonitrile polymer is heated in a supercritical fluid to obtain a flame resistant acrylonitrile polymer (flame resistant step).
The temperature during the heat treatment is preferably 200 to 300 ° C, more preferably 230 to 270 ° C. If temperature is 200 degreeC or more, a cyclization reaction will advance easily and processing time can be shortened. Since the reaction proceeds faster as the temperature becomes higher, 230 ° C. or higher is more preferable. On the other hand, if the temperature is 300 ° C. or lower, the decomposition reaction can be suppressed. In particular, when the temperature is 270 ° C. or lower, rapid progress of the reaction can be suppressed, so that the reaction can be easily controlled.
The time for the heat treatment varies depending on the composition of the acrylonitrile polymer, preferably 15 to 120 minutes in the case of a polymer composed of acrylonitrile alone, and 15 in the case of a copolymer of acrylonitrile and a copolymerizable monomer. ~ 60 minutes is preferred.

  The “supercritical fluid” in the present invention refers to a high-density fluid that does not condense even when a temperature and pressure above the critical point are applied. This state has the same diffusivity as a gas while having the same density as a liquid. Therefore, the supercritical fluid is a fluid that penetrates into the details of the polymer material and has a large plasticizing effect.

  As the fluid of the supercritical fluid, carbon dioxide (critical temperature 31.0 ° C., critical pressure 7.38 MPa), nitrous oxide (critical temperature 36.5 ° C., critical pressure 7) at a temperature and pressure above the critical point. .27 MPa), ethane (critical temperature 32.2 ° C., critical pressure 4.88 MPa), and ethylene (critical temperature 9.34 ° C., critical pressure 5.04 MPa).

The supercritical fluid used in the present invention contains carbon dioxide as a main component. Since carbon dioxide has a critical temperature of 31.0 ° C. and a critical pressure of 7.38 MPa, it is relatively easy to handle, nonflammable, inert, non-toxic, inexpensive, and suitable for supercritical conditions. .
The “main component” in the present invention means that the ratio of carbon dioxide in the supercritical fluid (100% by volume) is 80 to 100% by volume.

The supercritical fluid may be composed only of carbon dioxide, or may be composed of a plurality of components. In particular, it is preferable to contain an oxidizing substance.
Examples of the oxidizing substance include nitrogen dioxide, sulfur dioxide, and oxygen. From the viewpoint of economy, it is preferable to use air containing oxygen which is an oxidizing substance.
In the present invention, “the supercritical fluid contains an oxidizing substance” means a state where the supercritical fluid dissolves the oxidizing substance or a mixed fluid in a supercritical state.

As described above, conventionally, the heat treatment in the flameproofing process has been easy to take time. For this reason, a copolymer obtained by copolymerizing acrylonitrile and a accelerating monomer (that is, a monomer copolymerizable with acrylonitrile) was used as an acrylic fiber, for example, to shorten the flame resistance time. In addition, the performance tended to decrease.
In addition, flame-resistant acrylonitrile polymers such as flame-resistant fibers obtained in the flame-resistant process mainly have a structure with a carbon double bond composed of a naphthyridine ring and an acridone ring on the outside, and a nitrile group on the inside undergoes a cyclization reaction. However, it was difficult to obtain a uniform structure up to the inside. The tendency to have such a structure becomes more prominent as the diameter increases when the acrylonitrile polymer is fibrous, the particle diameter when it is powder, and the thickness when it is a film.

  However, according to the method for producing a flame-resistant acrylonitrile polymer of the present invention, since the acrylonitrile polymer is heated in the supercritical fluid, heat transfer from the supercritical fluid to the acrylonitrile polymer is good. Accordingly, the thermochemical reaction (flame-proofing reaction) in the flame-proofing step can be performed faster than in the atmosphere, and the flame-proofing time can be shortened.

The progress of the flameproofing reaction of the acrylonitrile polymer was measured by solid ¹³ C-NMR measurement, and the peak of the nitrile group (about 120 ppm) and the peak of the carbon double bond (about 137 ppm) generated by cyclization dehydrogenation. ) And the degree of progress can be confirmed with these peak intensities.

Further, the progress of the flame resistance reaction of the acrylonitrile polymer can also be confirmed by the KBr tablet method using a micro-infrared spectrometer. Specifically, performs transmission measurements, C-H absorption peak of nitrile group to the absorption peak (2940 cm ^-1) of the vibration (2240 cm ^-1), the absorption peak of the carbon-carbon double bonds of the naphthyridine ring caused by cyclization ( 1610 cm ⁻¹ ), and the peak intensity of an absorption peak (1580 cm ⁻¹ ) of a carbon double bond generated by dehydrogenation, and the degree of progress is confirmed by these peak intensities. As the peak intensity of the nitrile group decreases and the peak intensity of the carbon double bond increases, it means that the flameproofing reaction proceeds.

  Further, according to the present invention, the supercritical fluid plasticizes the molecules of the acrylonitrile polymer, and the components (particularly oxidizing substances) in the supercritical fluid reach the inside of the polymer, so that the dehydrogenation reaction proceeds uniformly. Therefore, a flame-resistant acrylonitrile polymer having a uniform structure up to the inside can be produced even by using acrylic fibers having a larger diameter than conventional ones, powders having a large particle diameter, and films having a large thickness. That is, the present invention is also suitable when acrylic fibers having a large diameter, particularly acrylic fibers having a diameter (average value) of 15 μm or more, powder having a large particle diameter, and a film having a thickness are used.

The structure of the flame-resistant acrylonitrile polymer can be confirmed by transmission measurement using a micro-infrared spectrometer. For example, when an acrylic fiber is used as the acrylonitrile polymer, measurement is performed by changing the position from the surface of the obtained flame-resistant fiber in a direction perpendicular to the fiber axis, and the strength of the absorption peak (1580 cm ⁻¹ ) of the carbon double bond is measured by the fiber. This can be confirmed by plotting against the position of the diameter (fiber diameter). When the dehydrogenation reaction occurs uniformly to the inside of the fiber, the peak intensity tends to be proportional to the fiber diameter.

As described above, according to the present invention, since the acrylonitrile polymer is heat-treated in the supercritical fluid, the flame resistance time can be shortened. Accordingly, the flame resistance time can be sufficiently shortened without using a copolymer obtained by copolymerizing acrylonitrile and an accelerating monomer as the acrylonitrile polymer, so that the ratio of copolymerization of the accelerating monomer can be reduced and obtained. Good quality and performance of carbon fiber can be maintained.
Even if acrylic fibers having a large diameter, particularly acrylic fibers having a diameter (average value) of 15 μm or more, powder having a large particle diameter, and a film having a large thickness are used, the dehydrogenation reaction proceeds evenly inside the polymer. A flame-resistant acrylonitrile polymer having a uniform structure is obtained. Therefore, for example, if an acrylic fiber is used as the acrylonitrile polymer, it is possible to produce a carbon fiber having a larger diameter than usual.

  The flame-resistant acrylonitrile polymer obtained by the present invention has a uniform structure up to the inside. Further, since the flame resistance time can be shortened without using a copolymer obtained by copolymerizing acrylonitrile and a accelerating monomer as a raw material, the rate of copolymerization of the accelerating monomer can be reduced. Accordingly, the quality and performance of the carbon fiber obtained from the flame-resistant acrylonitrile polymer can be maintained well.

The flame-resistant acrylonitrile polymer obtained by the present invention is used as, for example, carbon fiber through a known pre-carbonization step and carbonization step.
In the pre-carbonization step, heat treatment is performed with a rising temperature gradient of 400 to 700 ° C. The rising temperature gradient can be realized by setting a plurality of furnaces and increasing the temperature of the furnaces arranged in each. The pre-carbonization step can be performed in an inert atmosphere furnace. The inert atmosphere is not limited, but it is preferable to use nitrogen economically.
In the carbonization step, heat treatment is performed at 1000 to 2000 ° C., preferably 1000 to 1500 ° C. Moreover, the carbonization process can be performed in an inert gas. The inert gas is not limited, but it is preferable to use nitrogen economically.
The obtained carbon fiber may be further graphitized by a known technique in an inert atmosphere furnace at 2000 to 3000 ° C.

In addition, the flame-resistant acrylonitrile polymer obtained by heat-treating a powdery acrylonitrile polymer is, for example, a fiber, a film, a hollow body, or a molded body containing the flame-resistant acrylonitrile polymer by mixing with another polymer. Can be formed from a solution or a melt. Further, the powdery flame-resistant acrylonitrile polymer is further carbonized to form powdery carbon, and is used, for example, as an electrode active material of a lithium ion battery.
Moreover, the flame-resistant acrylonitrile polymer obtained by heat-treating a film-like acrylonitrile polymer is used as a film-like carbon material, for example.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.
The acrylic fiber, heat treatment apparatus, and measurement method used in this example are as follows.

[Measurement of diameter of single fiber]
The diameter of the cross section of 10 single fibers arbitrarily sampled was measured using an optical microscope (manufactured by Olympus Co., Ltd., system polarization microscope, product name: BX50-33P), and the average value was obtained. It was.

[Measurement of average particle size of powder]
Using a SK laser micronizer (product name: LMS-350, manufactured by Seishin Enterprise Co., Ltd.) based on the principle of laser diffraction / scattering method, the particle size distribution of the powder has a refractive index of 1.330-0.01i, a shape factor of 1. The value of 50% normal distribution calculated from the volume average was used as the average particle size.

[Production of acrylic fiber A]
Acrylonitrile polymer A (acrylonitrile unit content: 100% by mass, number average molecular weight 200,000) was dissolved in dimethylformamide to a concentration of 24% by mass to obtain a spinning dope, and the temperature was adjusted to 60 ° C. Acrylic fibers were obtained by dry and wet spinning using the spinning solution. Specifically, after spinning the spinning dope into air using a nozzle having 100 round cross-section discharge holes with a diameter of 150 μm, the first coagulation bath (concentration 79.5 mass%, dimethylformamide at a temperature of 15 ° C. Solidified in an aqueous solution) to obtain a coagulated yarn. Next, the coagulated yarn was stretched 2.7 times in the second coagulation bath (95 ° C. warm water), further stretched 1 time in water at 90 to 100 ° C., and then in steam at a temperature of 180 ° C. and a pressure of 220 kPa. Was stretched 3 times, the total stretch ratio was 8 times, and a bundle of acrylic fibers A (fiber A) was obtained.
The diameter of the single fiber constituting the bundle of acrylic fibers A was 16.3 μm as a result of measurement with an optical microscope.

[Preparation of acrylic fiber B]
Under the same conditions as for obtaining a bundle of acrylic fibers A, stretching was performed in water at 90 to 100 ° C., and this was used as a bundle of acrylic fibers B (fibers B).
The diameter of the single fiber constituting the bundle of acrylic fibers B was 25.4 μm as a result of measurement with an optical microscope.

[Preparation of powder]
Acrylonitrile, acrylamide and methacrylic acid were copolymerized by aqueous suspension polymerization in the presence of ammonium persulfate-ammonium hydrogen sulfite and iron sulfate, and from acrylonitrile unit / acrylamide unit / methacrylic acid unit = 96/3/1 (mass ratio). An acrylonitrile polymer B was obtained. The water content of the acrylonitrile polymer B was 45% by mass.
The obtained acrylonitrile polymer B was formed into pellets with a pelletizer and dried with a drier to obtain a powder having a water content of 1% by mass. The average particle size of the powder was 38.0 μm.

[Production of acrylic fiber C]
Acrylonitrile polymer B was obtained in the same manner as the preparation of the powder.
The obtained acrylonitrile polymer B was dissolved in dimethylacetamide to prepare a 21% by mass spinning dope. This spinning dope was discharged through a spinneret having a pore number of 3000 and a pore diameter of 75 μm into a first coagulation bath composed of a dimethylacetamide aqueous solution having a concentration of 55% by mass and a temperature of 30 ° C. to obtain a coagulated yarn. The obtained coagulated yarn was taken out from the first coagulation bath at a take-up speed of 0.8 times the spinning solution discharge linear speed. Subsequently, the coagulated yarn was led to a second coagulation bath composed of a dimethylacetamide aqueous solution having a concentration of 60% by mass and a temperature of 30 ° C., and drawn 2.8 times in the bath to obtain a fiber bundle.
Next, the obtained fiber bundle was stretched 3 times at the same time as washing with water, and the aminosilicone oil prepared to 1.5% by mass was added thereto. The fiber bundle after the oil addition was dried with a hot roll, and stretched 1.9 times with a steam stretching machine. Thereafter, the moisture content of the fiber bundle was adjusted with a touch roll, and the fiber bundle contained 5% by mass of water per fiber. Subsequently, the fiber bundle was entangled with air having an air pressure of 405 kPa, and wound with a winder to obtain a bundle of acrylic fibers C having a single fiber fineness of 1.2 dtex.
The diameter of the single fiber constituting the bundle of acrylic fibers C was 11.0 μm as a result of measurement with an optical microscope.

[Production of film]
The powder obtained previously was dissolved in dimethylacetamide as a solvent to prepare a cast solution having a concentration of 21.2% by mass.
Next, the cast solution was cast on a smooth glass plate, and the cast solution was developed with a glass rod provided with an appropriate clearance to obtain a uniform cast. The cast was held in a dryer at 110 ° C. for 24 hours while being spread on a glass plate to remove the solvent. Subsequently, the cast body from which the solvent was removed from the glass plate was collected, and further dried under reduced pressure in a vacuum dryer at 80 ° C. By this operation, a film having a thickness of about 150 μm was obtained.

[Heat treatment apparatus 1]
The schematic block diagram of the heat processing apparatus 1 used for heat processing is shown in FIG.
A heat treatment apparatus 1 shown in FIG. 1 has a gas pump (Japan) connected to one flow valve (carbon dioxide supply valve) 12 connected to a high-pressure reactor (made by pressure-resistant glass industry) having an internal volume of 240 mL and a maximum working pressure of 20 MPa. Precision Science Co., Ltd., product name: NP-KX-500J) 13 is connected, and the gas pump 13 and the liquefied carbon dioxide cylinder 14 are connected via a cylinder (manufactured by Soshokai Co., Ltd.). In addition, a pressure regulating valve (manufactured by JASCO Corporation, product name: SCF-Bpg) 16 is connected to the other flow valve (carbon dioxide release valve) 15 connected to the high-pressure reactor 11 so that the pressure can always be kept constant. I did it. A pressure gauge 17 and a safety valve 18 are provided between the high pressure reactor 11 and the flow valve 15.

[Heat treatment apparatus 2]
The schematic block diagram of the heat processing apparatus 2 used for heat processing is shown in FIG.
A heat treatment apparatus 2 shown in FIG. 2 includes a gas pump (Nippon Seimitsu) connected to a flow valve (carbon dioxide supply valve) 22 connected to a high-pressure reactor (product name: MMJ-100, manufactured by OM Labotech Co., Ltd.) 21 having an internal volume of 100 mL. Scientific Co., Ltd., product name: NP-KX-500J) 23 is connected, and the gas pump 23 and the liquefied carbon dioxide cylinder 24 are connected via a cylinder (manufactured by Soshokai Co., Ltd.). Further, a manual leak valve 25, a pressure gauge 26, and a safety valve 27 are provided. The high-pressure reactor 21 has an insertion port for a thermocouple 28, and the thermocouple 28 was installed therein to measure the temperature in the high-pressure reactor 21. The high-pressure reactor 21 is provided with a stirring shaft 29 and a stirring blade. Since stirring was not performed this time, the stirring blade was removed from the stirring shaft 29 and used for the experiment.

[Solid ¹³ C-NMR measurement]
Solid ¹³ C-NMR measurement was performed on the flameproof fiber obtained by heat treatment using a bundle of acrylic fibers A.
For the measurement, a solid-state NMR measuring apparatus (Bruker Biospin, product name: AVANCE II) and a MAS probe having a sample tube of 2.5 mm were used. In addition, the CP / MAS method was used as the measurement method, the H90 ° pulse width was 3.0 μs, the contact time was 3 ms, the repetition time was 10 s, and the number of integrations was 4096. The reference was adjusted with glycine so that the TMS peak was 0 ppm.

[IR measurement 1]
Using a bundle of acrylic fibers A to C, a powder, or a film, flame-resistant fiber bundles, flame-resistant powder, or chloride-resistant film obtained by heat treatment are subjected to IR measurement by the KBr tablet method according to a conventional method. It was. IR tablets were prepared by adding 1 mg of sample to 200 mg of KBr.
For the IR measurement, an FT-IR apparatus (manufactured by Nicolet, product name: AVATAR330) was used, and measurement was performed as follows under the conditions of transmission mode measurement and 64 integrations.
First, an IR background spectrum was measured with a tablet of KBr alone. The IR spectrum of the sample was then measured. The peak height of each absorption spectrum (1580, 1610, 2940 cm ⁻¹ ) is read, the ratio of the remaining peak height to the peak height of 2940 cm ⁻¹ (peak intensity ratio) is obtained, and “peak height of 1610 cm ⁻¹ is determined. is / indicators cyclization peak intensity ratio of 1 indicated by the peak height "of 2940 cm ^-1, the peak intensity ratio of 2 represented by the peak height" of the "peak of 1580 cm ^-1 height / 2940 cm ^-1 dehydrogenation It was used as an indicator of conversion.
The peak height was defined as the peak height by drawing a reference line before and after the peak in accordance with the general rules for infrared spectroscopy (JIS K-0117) to obtain the distance from the peak to the reference line.

<Qualitative evaluation of cyclization / dehydrogenation>
(Peak intensity ratio of 1: Peak of 1610 cm ^-1 height / 2940 cm peak height ^-1)
A peak intensity ratio of 1 was determined, and qualitative evaluation of cyclization was performed according to the following evaluation criteria. In addition, it means that cyclization is progressing, so that the value of peak intensity ratio 1 becomes large.
A: The peak intensity ratio 1 is larger than 1.5.
A: The peak intensity ratio 1 is greater than 1.0 and 1.5 or less.
Δ: Peak intensity ratio 1 is greater than 0.5 and 1.0 or less.
X: The peak intensity ratio 1 is 0.5 or less.

(Peak intensity ratio of 2: Peak of 1580 cm ^-1 height / 2940 cm peak height ^-1)
A peak intensity ratio of 2 was obtained and qualitative evaluation of dehydrogenation was performed according to the following evaluation criteria. In addition, it means that dehydrogenation has progressed, so that the value of peak intensity ratio 2 becomes large.
A: Peak intensity ratio 2 is larger than 1.5.
A: The peak intensity ratio 2 is greater than 1.0 and 1.5 or less.
(Triangle | delta): The peak intensity ratio 2 is larger than 0.5 and is 1.0 or less.
X: The peak intensity ratio 2 is 0.5 or less.

[IR measurement 2]
Using a bundle of acrylic fibers B, IR measurement was performed on the flame-resistant fibers obtained by heat treatment.
As a measuring apparatus, FT-IR (manufactured by JASCO Corporation, product name: FT / IR-4100) and a two-dimensional infrared microscope (manufactured by JASCO Corporation, product name: IRT-5000) are connected, and FT- An IR laser incorporated into a two-dimensional infrared microscope was used.
When measuring, take out one flame-resistant fiber in advance, paste it on the stage of a two-dimensional infrared microscope with cellophane tape, adjust the focus of the microscope, and then change the position by 4 μm in the direction perpendicular to the fiber axis. 6 points were measured. As a measurement method, a transmission method was used, the number of integrations was 10 times, and the resolution was 4 cm ⁻¹ .

[Example 1]
A bundle of acrylic fibers A was cut out by 80 cm, and placed in a high-pressure reactor 11 in a non-tension state using the heat treatment apparatus 1 shown in FIG. When entering, the bundle of fibers A was folded back at about 10 cm, supported by aluminum foil, and extended in the longitudinal direction of the pressure vessel. The pressure regulating valve 16 is set to 10 MPa, and the pressure is increased from the liquefied carbon dioxide cylinder 14 using the gas pump 13 from the state in which the air remains in the high pressure reactor 11 without being replaced with carbon dioxide, and the inside of the high pressure reactor 11 When liquefied carbon dioxide was introduced and the pressure reached 10 MPa, the flow valve 12 was closed to raise the temperature. In FIG. 1, reference numeral 19 denotes a sample (a bundle of acrylic fibers).
The temperature was raised to 240 ° C. over 45 minutes, then held for 120 minutes, and the bundle of acrylic fibers A was heat-treated in a supercritical fluid. Immediately after the holding time had elapsed, the pressure adjustment valve 16 was set to atmospheric pressure, the pressure was released, and a bundle of flame-resistant fibers was taken out.

About the obtained flame-resistant fiber, after cutting to a length of 0.5 mm or less, the peak height of each absorption spectrum (1580, 1610, 2940 cm ⁻¹ ) is read by the method of IR measurement 1 described above. Strength ratios 1 and 2 were obtained, and qualitative evaluation of cyclization / dehydrogenation was performed. The results are shown in Table 1.

Moreover, solid ¹³ C-NMR measurement was performed about the obtained flameproof fiber. The solid ¹³ C-NMR spectrum is shown in FIG.
From FIG. 3, it can be seen that the peak at 137 ppm indicating carbon having a double bond bonded to hydrogen is larger than the peak at 122 ppm indicating nitrile group, and the flameproofing reaction is most advanced. The intensity ratio between the peak at 137 ppm and the peak at 122 ppm (peak intensity at 137 ppm / peak intensity at 122 ppm) was 0.36.

[Examples 2 and 3]
Except for changing the time for heat treatment (heat treatment time) to the value shown in Table 1, pressure was applied in the same manner as in Example 1 and heat treatment was performed in a supercritical fluid to obtain a bundle of flame-resistant fibers. It was.
The obtained flame-resistant fiber bundle was cut to a length of 0.5 mm or less and IR measurement 1 was performed to evaluate the qualitative evaluation of cyclization / dehydrogenation. The results are shown in Table 1.

[Example 4]
After putting the bundle of acrylic fibers A in the high-pressure reactor 11 and sealing it, pressure was applied in the same manner as in Example 1 except that the inside of the high-pressure reactor 11 was replaced with carbon dioxide, heat treatment was performed in a supercritical fluid, and flame resistance A bundle of modified fibers was obtained.
The obtained flame-resistant fiber bundle was cut to a length of 0.5 mm or less and IR measurement 1 was performed to evaluate the qualitative evaluation of cyclization / dehydrogenation. The results are shown in Table 1.

Moreover, solid ¹³ C-NMR measurement was performed about the obtained flameproof fiber. The solid ¹³ C-NMR spectrum is shown in FIG.
As can be seen from FIG. 3, the peak at 137 ppm is the second largest after Example 1 with respect to the peak at 122 ppm, and the flameproofing reaction proceeds. The intensity ratio between the peak at 137 ppm and the peak at 122 ppm (peak intensity at 137 ppm / peak intensity at 122 ppm) was 0.33.

[Examples 5 and 6]
After the bundle of acrylic fibers A was put in the high pressure reactor 11 and sealed, the inside of the high pressure reactor 11 was replaced with carbon dioxide, and the pressure was changed in the same manner as in Example 1 except that the heat treatment time was changed to the values shown in Table 1. Then, heat treatment was performed in a supercritical fluid to obtain a bundle of flame-resistant fibers.
The obtained flame-resistant fiber bundle was cut to a length of 0.5 mm or less and IR measurement 1 was performed to evaluate the qualitative evaluation of cyclization / dehydrogenation. The results are shown in Table 1.

[Example 7]
A bundle of flame-resistant fibers was obtained by applying pressure in the same manner as in Example 1 except that a bundle of acrylic fibers B was used instead of the bundle of acrylic fibers A, and performing heat treatment in a supercritical fluid.
IR measurement 2 was performed about the obtained flame-resistant fiber. The infrared absorption spectrum is shown in FIG. In FIG. 4, the horizontal axis represents the measurement position of the fiber, and the vertical axis represents the peak intensity of 1580 cm ⁻¹ indicating a double bond between carbons.
From FIG. 4, it was found that there was a peak at the center of the fiber. When the dehydrogenation reaction occurs uniformly to the inside of the fiber, the peak intensity tends to be proportional to the fiber diameter. Therefore, it can be seen that the flameproof fiber obtained in Example 7 has a double bond to the inside and has a uniform structure.

[Examples 8 and 9]
After the bundle of acrylic fibers A is put into the high pressure reactor 11 and sealed, the inside of the high pressure reactor 11 is replaced with carbon dioxide, and the temperature (heat treatment temperature) and the heat treatment time in the high pressure reactor 11 are set to the values shown in Table 1. Except for the change, pressure was applied in the same manner as in Example 1, and heat treatment was performed in a supercritical fluid to obtain a bundle of flame-resistant fibers.
The obtained flame-resistant fiber bundle was cut to a length of 0.5 mm or less and IR measurement 1 was performed to evaluate the qualitative evaluation of cyclization / dehydrogenation. The results are shown in Table 1.

[Example 10]
Using the heat treatment apparatus 2 shown in FIG. 2, 2.8 g of acrylonitrile polymer B powder was placed in a high-pressure reactor 21 and sealed. Subsequently, after replacing the air in the high-pressure reactor 21 with carbon dioxide introduced from the liquefied carbon dioxide cylinder 24, liquefied carbon dioxide was further introduced. The internal temperature of the high-pressure reactor 21 was 14 ° C. and the pressure was 5.0 MPa.
When the high pressure reactor 21 was heated by a heater (not shown), the thermometer in the high pressure reactor 21 showed 202 ° C. and the pressure showed 9.0 MPa in 15 minutes from the start of heating. The heater was controlled so that the temperature in the high-pressure reactor 21 did not exceed 210 ° C., and the leak valve 25 was controlled manually so that the pressure was maintained at 9.0 MPa.
Heat treatment was performed for 15 minutes in a supercritical fluid having a heat treatment temperature of about 202 ° C. and a heat treatment pressure of 9.0 MPa, and then the heater was turned off.
After standing for about 2 hours until the temperature in the high-pressure reactor 21 fell below 50 ° C. by natural cooling, the pressure in the high-pressure reactor 21 was released, and the flame-resistant powder was taken out.
About the obtained flame-resistant powder, IR measurement 1 was performed and qualitative evaluation of cyclization / dehydrogenation was performed. The results are shown in Table 1.

[Examples 11 and 12]
Using a heat treatment apparatus 2 shown in FIG. 2, a bundle of acrylic fibers C (length 2.5 m, weight 3.6 g) was wound around a stirring shaft 29 in the high-pressure reactor 21 and sealed. Except that the heat treatment temperature, the heat treatment pressure, and the heat treatment time were changed to the values shown in Table 1, pressure was applied in the same manner as in Example 10 and heat treatment was performed in a supercritical fluid to obtain a bundle of flame resistant fibers. It was. In FIG. 2, reference numeral 30 denotes a sample (a bundle of acrylic fibers).
The obtained flame-resistant fiber bundle was cut to a length of 0.5 mm or less and IR measurement 1 was performed to evaluate the qualitative evaluation of cyclization / dehydrogenation. The results are shown in Table 1.

Further, the flame-resistant fiber obtained in Example 12 was subjected to solid ¹³ C-NMR measurement. The solid ¹³ C-NMR spectrum is shown in FIG.
From FIG. 3, the intensity ratio of the peak at 137 ppm to the peak at 122 ppm (peak intensity at 137 ppm / peak intensity at 122 ppm) was 0.34. In the case of Example 12, it turns out that it is reacting as much as Example 4.
From this, it is understood that when an acrylonitrile copolymer obtained by copolymerizing acrylamide and methacrylic acid is used as a raw material, the flameproofing reaction proceeds at a lower temperature and in a shorter time than when a polymer of acrylonitrile alone is used.

[Example 13]
A film of acrylonitrile polymer B was cut out to a width of 2 cm, a length of 5 cm, and a weight of 0.35 g, and the heat cut apparatus 2 shown in FIG. Except that the heat treatment temperature, the heat treatment pressure, and the heat treatment time were changed to the values shown in Table 1, pressure was applied in the same manner as in Example 10 and heat treatment was performed in a supercritical fluid to obtain a flame resistant film.
The obtained flame resistant film was pulverized in a mortar and then IR measurement 1 was performed to evaluate the qualification of cyclization / dehydrogenation. The results are shown in Table 1.

[Comparative Example 1]
Flame proofing was carried out in the same manner as in Example 1 except that a bundle of acrylic fibers A was put in the high pressure reactor 11 and sealed, and then heat treatment was performed under atmospheric pressure without carbon dioxide in the high pressure reactor 11. A bundle of fibers was obtained.
The obtained flame-resistant fiber was subjected to solid ¹³ C-NMR measurement. The solid ¹³ C-NMR spectrum is shown in FIG. The intensity ratio between the peak at 137 ppm and the peak at 122 ppm (peak intensity at 137 ppm / peak intensity at 122 ppm) was 0.12.
In the case of Comparative Example 1, the intensity ratio of the 137 ppm peak and the 122 ppm peak is smaller than in Examples 1, 4, and 12, indicating that the flameproofing reaction has not progressed sufficiently.

[Comparative Example 2]
Instead of the bundle of acrylic fibers A, a bundle of acrylic fibers B is used. After the bundle of acrylic fibers B is put in the high pressure reactor 11 and sealed, the carbon dioxide is not put in the high pressure reactor 11 at atmospheric pressure. A bundle of flameproof fibers was obtained in the same manner as in Example 1 except that the heat treatment was performed.
IR measurement 2 was performed about the obtained flame-resistant fiber. The infrared absorption spectrum is shown in FIG.
FIG. 4 shows that the center part of the fiber is flat and the dehydrogenation reaction has not sufficiently progressed to the inside of the fiber. That is, the flameproof fiber obtained in Comparative Example 2 did not have a uniform structure up to the inside.

[Comparative Examples 3 and 4]
After the bundle of acrylic fibers A was put in the high pressure reactor 11 and sealed, the inside of the high pressure reactor 11 was replaced with carbon dioxide, and the heat treatment pressure and the heat treatment time were changed to the values shown in Table 1 and Example 1. Similarly, a heat treatment was performed by applying pressure to obtain a bundle of flame-resistant fibers. The carbon dioxide during the heat treatment was not in a supercritical fluid state but in a gaseous state.
The flame-resistant fiber bundle obtained in Comparative Example 4 was cut to a length of 0.5 mm or less, then IR measurement 1 was performed, and qualitative evaluation of cyclization / dehydrogenation was performed. The results are shown in Table 1.

Further, the flame-resistant fiber obtained in Comparative Example 3 was subjected to solid ¹³ C-NMR measurement. The solid ¹³ C-NMR spectrum is shown in FIG.
From FIG. 3, the intensity ratio of the peak at 137 ppm to the peak at 122 ppm (peak intensity at 137 ppm / peak intensity at 122 ppm) was 0.12. In the case of Comparative Example 3, the intensity ratio of the 137 ppm peak and the 122 ppm peak is smaller than in Examples 1, 4, and 12, indicating that the flameproofing reaction has not progressed sufficiently.

[Comparative Example 5]
After putting the bundle of acrylic fibers A in the high-pressure reactor 11 and sealing it, and applying pressure in the same manner as in Example 1 except that the inside of the high-pressure reactor 11 is replaced with nitrogen, heat treatment is performed in a supercritical fluid, and flame resistance A bundle of modified fibers was obtained.
The obtained flame-resistant fiber bundle was cut to a length of 0.5 mm or less and IR measurement 1 was performed to evaluate the qualitative evaluation of cyclization / dehydrogenation. The results are shown in Table 1.

[Comparative Example 6]
Using a heat treatment apparatus 2 shown in FIG. 2, a bundle of acrylic fibers C (length 2.5 m, weight 3.6 g) was wound around a stirring shaft 29 in the high-pressure reactor 21 and sealed. Except that the heat treatment temperature, the heat treatment pressure, and the heat treatment time were changed to the values shown in Table 1, the heat treatment was performed in the same manner as in Example 10 to obtain a bundle of flame resistant fibers. The carbon dioxide during the heat treatment was not in a supercritical fluid state but in a gaseous state.
The obtained flame-resistant fiber bundle was cut to a length of 0.5 mm or less and IR measurement 1 was performed to evaluate the qualitative evaluation of cyclization / dehydrogenation. The results are shown in Table 1.

As is clear from Table 1, the value of the peak intensity ratio 1 was large in the flameproofed fiber, flameproofed powder, and flameproofed film obtained in each example. From this result, it can be seen that the cyclization of the nitrile group proceeds. Moreover, the value of the peak intensity ratio 2 is also large, indicating that dehydrogenation is in progress.
On the other hand, the flame resistant fiber obtained in each comparative example had a small peak intensity ratio of 1. From this result, it can be seen that cyclization of the nitrile group does not proceed sufficiently. Moreover, the value of peak intensity ratio 2 is also small, and it turns out that dehydrogenation has not fully advanced.

1, 2: heat treatment apparatus,
11, 21: high pressure reactor,
12, 22: Flow valve,
13, 23: Gas pump,
14, 24: liquefied carbon dioxide cylinder,
15: Flow valve,
16: Pressure regulating valve,
17, 26: pressure gauge,
18, 27: Safety valve,
19, 30: sample,
25: Leak valve
28: thermocouple,
29: Stirring shaft.

Claims (7)

A method for producing a flame-resistant acrylonitrile polymer, comprising subjecting an acrylonitrile polymer to a heat treatment at 200 to 300 ° C. in a supercritical fluid containing carbon dioxide as a main component, followed by cyclization and dehydrogenation reactions. The method for producing a flame-resistant acrylonitrile polymer according to claim 1, wherein the supercritical fluid contains an oxidizing substance. The method for producing a flame-resistant acrylonitrile polymer according to claim 1 or 2 , wherein the acrylonitrile polymer is fibrous. The method for producing a flame-resistant acrylonitrile polymer according to claim 3 , wherein the fiber has a diameter of 15 μm or more. The method for producing a flame-resistant acrylonitrile polymer according to claim 1 or 2 , wherein the acrylonitrile polymer is in a powder form. The manufacturing method of the flame-resistant acrylonitrile polymer of Claim 1 or 2 whose said acrylonitrile polymer is a film form. The flame resistance according to any one of claims 1 to 6 , wherein the acrylonitrile polymer is a copolymer containing 90 to 98% by mass of acrylonitrile units, and the heat treatment time in the supercritical fluid is 60 minutes or less. A method for producing a acrylonitrile polymer.

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