JPH0233324A - Production of sulfur-containing acrylic flame-resistant fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber with high tensile strength excellent in alkali, heat and flame resistances and useful as an asbestos substitute fiber by heating and sulfurating an acrylic fiber in a mixture gas composed of gaseous sulfur and an inert gas. CONSTITUTION:(A) An acrylic fiber is heated and sulfurated in (B) a sulfur- containing mixture gas composed of (i) >=3mol% sulfur-containing gas and (ii) <=97mol% inert gas to produce the objective fiber. In addition the component (i) is preferably sulfur dioxide in an amount of 5-50wt.% and component (ii) is preferably steam and/or nitrogen in an amount of 95-50wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a sulfur-containing acrylic flame-resistant fiber that has high tensile strength and excellent alkali resistance, heat resistance, and flame resistance.

[Prior Art] Conventionally, protective equipment such as firefighting suits, furnace vests, and welding spark protection sheets, sealing materials such as gaskets and ground backings, insulation materials, and filter media represented by bag filters,
Asbestos has been widely used in products that require heat resistance and flame resistance, such as friction materials such as brakes and clutches, and electrical insulation materials.

Furthermore, asbestos has excellent alkali resistance at high temperatures, and asbestos cement boards and calcium silicate boards, etc.
It is also used in large quantities in high-performance hydraulic inorganic products made of calcareous or silica materials that are autoclaved in steam at 80°C.

However, in Japan, which relies on imports for most of its asbestos, in addition to the problem that product manufacturing costs fluctuate greatly depending on the import price of asbestos, in recent years, asbestos dust has become a serious health hazard for workers. As a result, its use has been legally regulated in the United States and some European countries, and the development of textile materials to replace asbestos is being researched and considered on a global scale, including in Japan. .

Various fibers have been proposed to replace asbestos, such as glass, rock wool, carbon fiber, phenol fiber, steel fiber, aramid fiber, and flame-resistant fiber. Acrylic flame-resistant fibers, which are obtained by using acrylic fibers as precursors, are attracting the most attention because they have small fibers, are flexible, have excellent flame retardancy, and are cheaper to manufacture than carbon fibers.

However, the above-mentioned flame-resistant fibers, which are manufactured by heating and oxidizing acrylic fibers in high-temperature air, have a non-uniform oxidation structure in which the surface area of the fibers is oxidized to a much greater degree than the inside of the fibers. In order to have mechanical strength,
In particular, the tensile strength and knot strength are low, and the toughness is low, making spinning or knitting difficult. Even if spinning or weaving is possible, the resulting product has poor abrasion resistance and heat resistance, such as When used for a long time at higher temperatures, the strength decreases and practical performance is lost.

Furthermore, the flame-resistant fiber obtained by heating and oxidizing the above-mentioned acrylic fiber in the air has significantly poor alkali resistance at high temperatures.
It cannot be used at all as a reinforcing material for hydraulic inorganic products that are autoclaved in steam at 80°C.

By the way, the present inventors first heated and sulfurized high-strength acrylic fibers in a sulfur-containing atmosphere such as sulfur dioxide, thereby achieving high tensile strength and toughness.
We proposed a sulfur-containing acrylic flame-resistant fiber that has excellent alkali resistance, heat resistance, and chemical resistance at high temperatures.

In addition, Japanese Patent Publication No. 47-36462 describes a special method for obtaining high-strength carbon fibers in which polyacrylonitrile fibers are mixed with sulfur dioxide, sulfur molecules, carbonyl sulfide, and the above-mentioned sulfur-containing gases in a flame-retardant process by nitrogen, argon, helium, -
A method is disclosed in which heat treatment is performed in a gas mixture with an inert gas such as carbon oxide and hydrogen.

[Problems to be Solved by the Invention] However, most of the sulfur-containing gases described in the above-mentioned known examples are toxic, and some of them are designated as specified chemical substances. The content of is regulated by law.

Therefore, when acrylic fibers are heated and sulfurized in an atmosphere containing a toxic sulfur-containing gas as described above, leakage from the running part of the fibers in the heating furnace and the backing part of peripheral equipment becomes a problem.

Therefore, it is desirable that the content of toxic sulfur-containing gas in the sulfur-containing atmosphere be as small as possible from the viewpoint of sealing performance. However, if the content of the sulfur-containing gas is too low, thermal deterioration precedes the sulfurization reaction, making it impossible to obtain a high-performance sulfur-containing acrylic flame-resistant fiber.

An object of the present invention is to produce flame-resistant sulfur-containing acrylic fibers obtained by heating and sulfurizing acrylic fibers in a sulfur-containing atmosphere. By using a sulfur-containing mixed gas that suppresses thermal deterioration in a sulfur-containing atmosphere and promotes the sulfurization reaction, the result is a sulfur-containing acrylic that has high tensile strength and excellent alkali resistance, heat resistance, and flame resistance at high temperatures. The purpose of the present invention is to provide a method for producing flame-resistant fibers (hereinafter simply referred to as flame-resistant fibers).

[Means for Solving the Problems] As described in the claims, an object of the present invention is to provide acrylic fibers with a sulfur-containing gas of 3 mol% or more and an inert gas of 97 mol% or less. This can be achieved by heating and sulfiding in a sulfur-containing mixed gas consisting of:

The sulfur-containing mixed gas used in the present invention is composed of a sulfur-containing gas and an inert gas. The content of sulfur-containing gas is 3
mol% or more, preferably 3 mol% or more and 80 mol% or less,
More preferably, it is 5 mol% or more and 50 mol% or less.

Here, if the content of sulfur-containing gas is less than 3 mol%,
Thermal deterioration precedes the reaction between acrylic fibers and sulfur-containing gas, that is, the sulfurization reaction, and the formation of sulfur-containing cyclized structures and sulfur cross-linked structures that exhibit excellent heat resistance is insufficient, resulting in However, it is not possible to obtain high-performance flame-resistant fibers with low sulfur content.

Furthermore, if the content of sulfur-containing gas is less than 3 mol%, thermal deterioration will precede it as described above, so when a large amount of acrylic fiber is used, runaway reactions may occur at low temperatures due to the reaction heat accumulated between the fibers. Therefore, the sulfurization reaction cannot be completed in a short time by raising the temperature, which increases manufacturing costs.

On the other hand, if the content of sulfur-containing gas is 3 mol% or more,
The higher the content, the higher the temperature at which the runaway reaction occurs, and the sulfurization reaction can be completed in a short time by raising the temperature. Also, the leakage of sulfur-containing gas from the backing part of peripheral devices is high (because of this, it is desirable that the content of sulfur-containing gas be as small as possible without impairing the performance of the flame-resistant fiber obtained).

In addition, sulfur-containing gas refers to sulfur dioxide, sulfur gas, carbon disulfide, hydrogen sulfide, carbonyl sulfide, etc. alone or in a mixture thereof. In particular, sulfur dioxide has excellent reactivity to acrylic fibers, and It is preferably used because it can be sulfurized uniformly.

Furthermore, when a mixed gas consisting of sulfur dioxide and hydrogen sulfide is used, the reaction of introducing sulfur into acrylic fibers becomes extremely fast, which shortens the reaction time and reduces manufacturing costs, or lowers the reaction temperature to prevent runaway reactions. danger can be avoided.

The flame-resistant fiber produced using the above mixed gas is
It has a high sulfur content, high tensile strength, and excellent alkali resistance and heat resistance at high temperatures.

Further, the inert gas is a gas that does not cause a chemical reaction with the acrylic fibers, and examples thereof include nitrogen, argon, helium, carbon dioxide, water vapor, and the like alone or in a mixture thereof.

In particular, when water vapor is used as the inert gas, when recovering sulfur-containing gas from the waste gas after the sulfidation reaction is completed, the water vapor is separated as water, and then the sulfur-containing gas dissolved in water can be easily recovered by fractional distillation. Moreover, the collection equipment can be downsized,
This is extremely advantageous in reducing recovery costs.

Next, the acrylic fiber used in the present invention is not particularly limited, but has high tensile strength and toughness.
In order to obtain flame-resistant fibers with excellent properties, it is desirable that the acrylic fibers have high strength and high elastic modulus. For example, a high polymerization degree polyacrylonitrile (hereinafter abbreviated as AN) based polymer having an intrinsic viscosity of at least 1.5, preferably 2.0 to 5.0, and a tensile strength of at least 7 g/d, preferably It is desirable to form acrylic fibers of 9 g/d or more, more preferably Log/d or more.

Here, the AN-based polymer used in the production of acrylic fibers includes AN alone or at least 90 mol% of AN.
and 10 mol% or less of monomers copolymerizable with the AN, such as carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid, and their lower alkyl esters, hydroxymethyl acrylate, hydroxyethyl acrylate, and hydroxymethyl methacrylate. Hydroxy alkyl acrylate containing a hydroxyl group in a carboxylic acid such as acrylate, acrylamide, methacrylamide, α-chloroacrylonitrile, hydroxyethyl acrylic acid,
Examples of copolymerizable monomers include allylsulfonic acid and methacrylsulfonic acid. Among these copolymerizable monomers, acrylamide has a fast sulfurization reaction, little oxidative deterioration due to oxygen, and produces flame-resistant fibers with high tensile strength. Particularly desirable.

These AN-based polymers are dimethyl sulfoxide (DMS
O), organic solvents such as dimethylformamide (DMF) and dimethylacetamide (DMAc), concentrated aqueous solutions of inorganic salts such as calcium chloride, zinc chloride, and rhodan soda;
When dissolved in an inorganic solvent such as nitric acid, the solution viscosity is 2000.
Poise or more, preferably 3000 to 10000 poise,
A spinning dope having a polymer concentration of 5 to 20% is prepared.

In order to produce dense fibers with as high strength and high modulus as possible and with little difference in internal and external structures from the solvent solution (spinning stock solution) of the high polymerization degree AN polymer thus obtained, it is necessary to use this high polymerization degree AN. A so-called wet-dry spinning method is adopted, in which the spinning stock solution of the polymer is once discharged into an inert atmosphere such as air through a spinneret, and then the discharged spinning stock solution is introduced into a coagulation bath to complete coagulation. It is desirable to stretch it to

The specific conditions for this dry-wet spinning are as follows: The distance between the spinneret surface and the coagulation bath liquid level is set within the range of 1 to 20 mm, preferably 3 to 10 mm, and the distance between the spinneret surface and the coagulation bath liquid is After discharging into the microspace formed by the surface, the fiber thread is introduced into a coagulation bath and coagulated, and then the obtained fiber thread is washed with water, desolventized, first stretched, dried and densified, second stretched,
It is made into a drawn fiber thread by passing through a post-processing process such as heat treatment. The fiber yarn obtained by this dry-wet spinning has extremely excellent drawability. Preferably, as a secondary drawing method, at least 1.1
Stretched to a total effective stretching ratio of at least 10 times, preferably 12 times or more, with a fineness of 0.5 to 7 deniers (d), preferably 1 to 1.5 times, preferably 1.5 times or more. It is preferable to set it within the range of 5d.

If the fineness is smaller than 0.5d, the spinnability of the resulting flame-resistant fiber will be reduced, making it difficult to obtain textile products with good abrasion resistance.If the fineness is larger than 7d, the fiber during sulfurization will This is not preferable because sulfurization becomes uneven in the cross section.

The fibers obtained in this way usually have mechanical properties such as a tensile strength of 7 g/d or more and a tensile modulus of 130 g/d or more. 10g/d or more, tensile modulus is 180
It is preferable to use fibers having mechanical properties of 2.2 g/d or more and a knot strength of 2.2 g/d or more.

The obtained acrylic fiber is heated and sulfurized in the temperature range of 230 to 400 ° C in the sulfur-containing mixed gas,
The heating in the sulfurization step may be performed under constant temperature conditions or under elevated temperature conditions, and the acrylic fibers may be under tension, constant length, or relaxed conditions. - As an example, the first stage heating is 230 ~
A method in which sulfurization is carried out in a heating furnace maintained at a temperature range of 280°C, and the second stage heating is performed within a temperature range of 280 to 400°C, and sulfurization is completed in a heating furnace set to temperature increasing conditions in stages. can be mentioned.

The thus obtained flame-resistant fiber of the present invention has a sulfur content of at least 0.5% by weight, preferably 1 to 50% by weight, and a tensile strength of 3.5 g/d or more, preferably 4.0 g/d.
g/d or more, more preferably 5.0 g/d or more.

The sulfur-containing acrylic flame-resistant fiber obtained by the present invention can be widely used as an asbestos substitute fiber, such as autoclave curing cement reinforcing materials, friction materials, ground backing, sealing materials such as gaskets, firefighting suits, and welding spark protection sheets. , this industrial significance is extremely large.

Hereinafter, the effects of the present invention will be explained in more detail with reference to Examples.

[Example] In the present invention, tensile strength, intrinsic viscosity, runaway reaction occurrence temperature, and alkali resistance are values measured by the following measuring method.

(1) Tensile strength: Measured according to the measuring method specified in J15-L-1069.

(2) Put 5 mg of dry AN polymer with an intrinsic viscosity of near 0.0 in a flask. DM containing IN sodium thiocyanate
Add 25 mg of F and dissolve completely. The specific viscosity of the obtained polymer solution was measured at 20° C. using an Ostwald viscometer, and the intrinsic viscosity was calculated according to the following formula.

Intrinsic viscosity = [+, x -1] 10.198 (3) Runaway reaction occurrence temperature: 12,000 denier acrylic fiber was cut into a length of 20 mm, and the bulk density was 2400 denier/
Create a bundle of yarn by winding the wire into a coil so that it has a length of ``mm''.

Next, a thermocouple was installed near the yarn bundle, and the thermocouple was introduced into a reactor in which a sulfur-containing mixed gas consisting of sulfur dioxide and nitrogen heated to a predetermined temperature was flowing at a flow rate of 10 cm/min. The lowest temperature at which a runaway reaction occurs due to heat accumulation was measured.

(4) Alkali resistance: Sample fibers were immersed in a relaxed state in the supernatant liquid of an aqueous solution containing 10% by weight of cement and treated under pressure at 180°C for 6 hours.

The tensile strength of the fibers before and after treatment with the cement supernatant liquid was measured, and from both values, the tensile strength retention rate (%) was calculated using the following formula, and this was taken as the alkali resistance.

(Tensile strength retention rate) = (Strength after treatment) / (Strength before treatment) x 100 Example 1
~4. Comparative Example 1.2 2 mol% of acrylamide and 98 mol% of AN were solution polymerized in DMSO to create an AN-based polymer with an intrinsic viscosity of 3.0. The obtained polymer solution was used as a spinning stock solution, and wet-dry spinning was performed. As a coagulation bath, a 15°C 155% DMSO aqueous solution was used. Further, the distance between the spinneret and the coagulation bath liquid level was set to 5 mm, and the distance from the coagulation bath liquid level to the focusing guide was 400 mm.

The obtained undrawn fiber yarn was drawn 5 times in a hot water bath, then applied with an oil agent and dried and densified at 110°C.

Then, in a dry heat tube at 180°C, the highest stretching ratio was 85.
% to obtain an acrylic fiber having a single fiber fineness of about 2 denier and a tensile strength of 14 g/d.

The acrylic fibers thus obtained were heated and sulfurized for 30 minutes in a sulfur-containing mixed gas of sulfur dioxide (802) and nitrogen (N2) at 280°C as shown in Table 1.

Table 1 shows the sulfur content and tensile strength of the flame-resistant fibers obtained. In addition, the temperatures at which runaway reactions occurred in each sulfur-containing mixed gas were measured and are shown in Table 1.

In the method for producing flame-resistant fibers of the present invention, the sulfurization reaction with sulfur dioxide proceeds smoothly, so the same tensile strength as in the case of 100% S0□ can be obtained, and the temperature at which the runaway reaction occurs is high, so it is possible to increase the temperature. The sulfurization reaction can be completed in a short time.

Examples 5 to 7 The acrylic fibers obtained in Example 1 were heated and sulfurized at 260°C in a sulfur-containing mixed gas consisting of sulfur dioxide, hydrogen sulfide (N2S), and nitrogen.

Table 2 shows the sulfur content, tensile strength, and alkali resistance of the flame-resistant fibers obtained.

When a mixed gas consisting of sulfur dioxide and hydrogen sulfide is used as the sulfur-containing gas, the sulfurization reaction proceeds in a significantly short time, producing flame-resistant fibers with high sulfur content, high tensile strength, and excellent alkali resistance. In terms of reaction time, flame-resistant fibers with a high sulfur content, which greatly contributes to heat resistance, were obtained.

Examples 8 and 9 The acrylic fibers obtained in Example 1 were reacted at 260° C. for 1 hour in a sulfur-containing mixed gas consisting of sulfur dioxide, water vapor, and nitrogen. Table 3 shows the tensile strength and sulfur content of the flame-resistant fibers obtained.

Even when a large amount of water vapor was used as the inert gas, flame-resistant fibers with the same performance as nitrogen were obtained. Further, after the reaction was completed, the wash gas was cooled to 100° C. or lower, and the sulfur dioxide dissolved in the coagulated water could be easily recovered by fractional distillation.

On the other hand, when a large amount of nitrogen was used as the inert gas, it was necessary to cool the waste gas to -15°C or lower in order to recover sulfur dioxide from the waste gas.

[Effect of the invention] The method for producing the sulfur-containing acrylic flame-resistant fiber of the present invention includes:
Acrylic fibers are heated and sulfurized in a sulfur-containing mixed gas consisting of 3 mol% or more of sulfur-containing gas and 97 mol% or less of inert gas, so the content of toxic sulfur-containing gas is low, making it easy to use in the manufacturing process. leakage can be reduced.

Furthermore, since the sulfurization reaction with acrylic fibers is fast and there is little thermal deterioration, the resulting flame-resistant fibers have high tensile strength and are excellent in alkali resistance, heat resistance, flame resistance, etc. at high temperatures.

Claims (1)

[Scope of Claims] (1) A sulfur-containing acrylic fiber characterized by heating and sulfurizing acrylic fibers in a sulfur-containing mixed gas consisting of a sulfur-containing gas of 3 mol% or more and an inert gas of 97 mol% or less. Method for producing flame-resistant fiber (2) The sulfur-containing mixed gas is
The method for producing a sulfur-containing acrylic flame-resistant fiber according to claim (1), wherein the sulfur-containing gas is ~50 mol% sulfur-containing gas and 95-50 mol% inert gas (3) the sulfur-containing gas is sulfur dioxide. Claim (1)
Or the method for producing a sulfur-containing acrylic flame-resistant fiber according to (2). (4) The method for producing a sulfur-containing acrylic flame-resistant fiber according to claim 1 or 2, wherein the sulfur-containing gas is a mixed gas consisting of sulfur dioxide and hydrogen sulfide. (5) The method for producing a sulfur-containing flame-resistant acrylic fiber according to claim (1) or (2), wherein the inert gas is water vapor and/or nitrogen.