JPH0226923A - Production of fire-resistant yarn of sulfur-containing acrylic base - Google Patents

Abstract

PURPOSE:To produce the title yarn having high tensile strength, excellent heat resistance, etc., in heating and sulfurizing a yarn bundle comprising acrylic fiber in a sulfur-containing atmosphere by bringing the yarn bundle into contact with a heating material having a hole or groove to promote sulfurization reaction. CONSTITUTION:A bundle 1 of acrylic fiber which more preferably consists an acrylonitrile-based polymer having >=2.5 intrinsic viscosity and high degree of polymerization and has mechanical properties of >=10g/d tensile strength, >=180g/d modulus in tension and >=2.2g/d knot strength is heated and sulfurized in a sulfur-containing atmosphere having >=5mol% sulfur-containing gas at 230-400 deg.C while bringing the yarn into contact with a heating material 3 having holes 2 to give the aimed yarn having 1-20wt.% sulfur content and >=40g/d tensile strength.

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 is made of calcareous or silicic materials that are autoclaved in steam at 180°C, such as asbestos cement boards, calcium silicate boards, and lightweight aerated concrete boards (ALC). It is also used in large quantities in high-performance hydraulic inorganic products.

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. Among these alternative fibers, flame-resistant fibers that have a low specific gravity, flexibility, excellent flame retardancy, and are cheaper than carbon fibers, ie, acrylic flame-resistant fibers, are attracting the most attention.

However, flame-resistant fibers produced by heating and oxidizing acrylic fibers in high-temperature air have a highly uneven oxidation structure, with the surface area of the fibers being oxidized to a much greater degree than the inside of the fibers. As a result, mechanical strength, especially tensile strength and knot strength, is low, and toughness is low, making spinning, knitting and weaving difficult.Even if spinning, knitting and weaving were possible, 1q The resulting products have poor abrasion resistance and heat resistance, and when used for a long time at high temperatures of 150° C. or higher, for example, the strength decreases and practical performance is lost.

Furthermore, flame-resistant fibers obtained by heating and oxidizing the above-mentioned acrylic fibers in the air have 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 180'C.

Therefore, 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, flame resistance, and chemical resistance at high temperatures.

In addition, Japanese Patent Publication No. 53-21396 describes a method for manufacturing carbon products in which 200 to
A method is disclosed in which flame resistance is achieved by intermittently and repeatedly contacting the surface of a heating element maintained at 400'C.

In general, JP-A-61-174423 discloses that when obtaining flame-resistant fibers, acrylic fiber bundles are heat-treated by contacting them with a heating element at 200 to 350°C in an oxidizing atmosphere such as air. A method of heat treatment in the oxidizing atmosphere at ~350°C is disclosed.

[Problems to be Solved by the Invention] By the way, when a fiber bundle made of acrylic fibers is heated and sulfurized in a sulfur-containing atmosphere, the reaction heat is much less than when heated and oxidized in air. When the thickness of the fiber bundle increases, reaction heat accumulates within the fiber bundle, which causes a runaway reaction and breaks the fiber bundle.

Therefore, to prevent this runaway reaction, increase the width of the fiber bundle,
Although the thickness must be reduced, it is desirable to increase the thickness of the fiber bundle as much as possible in order to increase productivity.

Therefore, as described in the above-mentioned known example, it is an effective method to bring the fiber bundle into contact with a heating element having good thermal conductivity in order to remove the reaction heat accumulated within the fiber bundle and suppress the runaway reaction. It is.

However, the reaction of heating and sulfurizing acrylic fibers in a sulfur-containing atmosphere is slower than the reaction of heating and oxidizing them in air. Therefore, it is necessary to bring the acrylic fiber into sufficient contact with the sulfur-containing gas in order to uniformly and extensively sulfurize the cross section of the acrylic fiber.

The purpose of the present invention is to remove the reaction heat accumulated in the fiber bundle in the production of sulfur-containing acrylic flame-resistant fiber obtained by heating and sulfurizing a fiber bundle made of acrylic fiber in a sulfur-containing atmosphere, A sulfur-containing acrylic flame-resistant fiber that suppresses runaway reactions and promotes the sulfurization reaction between acrylic fibers and sulfur-containing gases, resulting in 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 stated in the claims, an object of the present invention is to provide a method for heating and sulfurizing fiber bundles made of acrylic fibers in a sulfur-containing atmosphere. Hole and/or
Alternatively, this can be achieved by contacting a heating element with grooves.

The present invention will be explained in detail below.

The acrylic fiber used in the present invention is not particularly limited, but in order to obtain a flame-resistant fiber with high tensile strength and excellent toughness, the acrylic fiber also has high strength and high modulus. For example, the degree of polymerization is at least 1.5 in intrinsic viscosity, preferably 2.0 to 5.
It is desirable to use a highly polymerized acrylonitrile (hereinafter abbreviated as AN) polymer with a tensile strength of at least 7 Cl/d, preferably 9 q/d or more, and more preferably 10 Q/d or more to form acrylic fibers. .

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 a monomer copolymerizable with the AN, such as carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid, and lower alkyl esters thereof;
Hydroxyalkyl acrylates containing carboxylic acid hydroxyl groups such as hydroxymethyl acrylate, hydroxyethyl acrylate, and hydroxymethyl methacrylate; Examples include polymerized monomers. Among these copolymerization materials, the sulfurization reaction is fast, there is little oxidative deterioration due to oxygen,
Acrylamides are particularly desirable because they produce flame-resistant fibers with high strength.

These AN-based polymers are dimethyl sulfoxide (DM
SO), dimethylformamide (DMF), dimethylacetamide (DMAC>, etc.), concentrated aqueous solutions of inorganic salts such as calcium chloride, zinc chloride, rhodan soda, etc., and inorganic solvents such as nitric acid to achieve a solution viscosity of 200%.
A spinning dope having a polymer concentration of 5 to 20% is prepared, with a polymer concentration of 0 poise or more, preferably 3000 to 10000 poise.

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 polymer. The polymer spinning stock solution 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 wet-dry spinning are such that the spinning dope is separated from the spinneret surface and the coagulating bath liquid level by setting the distance between the spinneret surface and the coagulating bath liquid level to be within a range of 1 to 20 mm, preferably 3 to 10 mm. After discharging it into the microspace formed by the surface, it is guided to a coagulation bath and coagulated, and then the obtained fiber thread is washed with water, desolventized, primary stretching, drying/densification, and secondary stretching by conventional methods. The fibers are then subjected to post-processing steps such as heat treatment to form drawn fiber threads.

The fiber yarn obtained by this dry-wet spinning has extremely excellent drawability, but preferably as a secondary drawing method,
Stretched at least 1.1 times, preferably 1.5 times or more under dry heat at 150 to 270'C, and stretched so that the total effective stretching ratio is at least 10 times, preferably 12 times or more, and its fineness is adjusted. 0°5-7 denier (d), preferably 1
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 cross section will This is not preferable because the sulfurization becomes uneven.

The fibers thus obtained usually have mechanical properties such as a tensile strength of 7 q/d or more and a tensile modulus of 130 C1/d or more. More preferably, it is made of a high degree of polymerization AN-based polymer having an intrinsic viscosity of 2.5 or more, a tensile strength of 10 CJ/d or more, a tensile modulus of 1800/d or more, and a knot strength of 2.2 Cl/d.
It is better to use fibers with the above mechanical properties.

Furthermore, the sulfur-containing atmosphere refers to a sulfur-containing gas consisting of sulfur dioxide, sulfur gas, carbon disulfide, hydrogen sulfide, carbonyl sulfide, etc. alone or a mixture thereof, or a mixture of the above sulfur-containing gas and an inert gas. Among these, sulfur dioxide is particularly preferably used because it has excellent reactivity with acrylic fibers and can uniformly sulfurize the cross section of the fibers. In addition, the inert gas is a gas that does not cause a chemical reaction with the acrylic fibers, such as nitrogen,
Examples include argon, helium, and carbon dioxide.

Here, the content of the sulfur-containing gas in the sulfur-containing mixed gas is 3 mol% or more, preferably 5 mol% or more. If the content of the sulfur-containing gas is less than 3 mol%, thermal deterioration precedes the sulfurization reaction between the acrylic fiber and the sulfur-containing gas, making it impossible to obtain high-performance flame-resistant fibers.

Roughly speaking, the oxygen content contained in a sulfur-containing atmosphere is 1
It is preferably 0.5 mol% or less, more preferably 0.1 mol% or less. If the oxygen content exceeds 1 mol%, the reaction with oxygen will precede the sulfurization reaction between the acrylic fiber and the sulfur-containing gas, causing molecular chain scission and creating a non-uniform oxidation structure in the cross section of the fiber. or inhibit the formation of cyclized structures and crosslinked structures containing sulfur bonds, making it impossible to obtain high-performance flame-resistant fibers.

Next, the fiber bundle made of the acrylic fiber of the present invention is heated,
The sulfiding method will be explained using drawings.

In FIG. 1, a fiber bundle 1 made of acrylic fibers is heated and sulfurized while contacting a heating body 3 having holes 2 in a sulfur-containing atmosphere.

Further, in FIG. 2, the fiber bundle 1 is heated and sulfurized while being in contact with a heating element 5 having grooves 4.

Here, the shape of the heating body is not particularly limited, and for example, plates, rollers, and those having various curved surfaces can be used. The holes and grooves provided in the heating body may be provided individually or in combination.

Further, the shape, size, number, etc. of the holes and grooves can be appropriately selected depending on the polymer composition, fineness, bulk density, etc. of the acrylic fiber bundle to be heated and sulfurized.

By the way, since the sulfur-containing gas normally flows at a certain flow rate in a heating furnace, the sulfur-containing gas penetrates into the fiber bundle through the holes and grooves provided in the heating element and reacts with the acrylic fibers, but it does not cause roughness. By actively suctioning or pressurizing the sulfur-containing gas through the holes and grooves, it is possible to increase the penetration of the sulfur-containing gas into the fiber bundle and further promote the reaction between the sulfur-containing gas and the acrylic fibers.

Furthermore, the temperature of the sulfur-containing gas in the sulfur-containing atmosphere is 2
The heating temperature in the sulfurization process may be from 30 to 400°C, and may be at a constant temperature or at an elevated temperature, and the acrylic fiber bundle may be under tension, constant length, or relaxed. −
As an example, the first stage heating is performed in a heating furnace maintained at a temperature range of 230 to 280 °C, and the second stage heating is performed at a temperature of 280 to 40 °C.
A method of completing sulfidation within a temperature range of 0° C. in a heating furnace in which temperature raising conditions are set in stages can be mentioned.

The thus obtained flame-resistant fiber of the present invention has a sulfur-containing layer of at least 0.5% by weight, preferably 1 to 20% 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. It is Oq/d or more.

The flame-resistant fibers of the present invention can be widely used as asbestos substitute fibers, such as autoclave-cured cement reinforcing materials, friction materials, ground backing, sealing materials such as gaskets, firefighting uniforms, and welding spark protection sheets, and this industrial significance is Extremely large.

EXAMPLES Hereinafter, the effects of the present invention will be explained in detail using Examples.

[Example] In the present invention, tensile strength and intrinsic viscosity are values measured by the following measuring method.

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

(2) A dry AN polymer with an intrinsic viscosity of near 5 mCl was placed in a flask, and the intrinsic viscosity was 0. D containing IN sodium thiocyanate
Add 25 mg of MF and dissolve completely. The specific viscosity of the obtained polymer solution was measured at 20° C. using an Ostauld viscometer, and the intrinsic viscosity was calculated according to the following formula.

1 [[= [+, x >-1110,19
8 Example 1 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, 15°C 155% DMSO
An 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, 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 8.
1q of acrylic fiber bundles are secondly drawn at 5%, have a single fiber fineness of about 2 denier, a tensile strength of 14 g/d, and a filament count of 6000.

This fiber bundle was introduced into a sulfur-containing mixed gas consisting of 10% sulfur dioxide and 90% nitrogen, and heated under tension at 300"C for 10 minutes while contacting a heating plate with holes 1 mm in diameter at 1 mm intervals. Sulfurized.

At this time, the sulfur-containing mixed gas was forced to flow through the holes.

The obtained flame-resistant fiber had a sulfur content of 3.5% by weight and a tensile strength of 8.2 g/d. As a result, in the present invention, there is no accumulation of reaction heat within the fiber bundle, and sulfur dioxide penetrates smoothly into the fiber bundle, so that flame-resistant fibers with high tensile strength were obtained.

Comparative Example 1 An acrylic fiber bundle obtained in the same manner as in Example 1 was heated and sulfurized in the same manner as in Example 1 while being in contact with a heating plate without holes.

The sulfur content of the obtained flame-resistant fibers was 1.5 to 2.8% by weight, and the tensile strength was 4.8 to 7.5 C1/d, and both the sulfur content and tensile strength were low with many variations.

[Effects of the Invention] In the present invention, a fiber bundle made of acrylic fibers is heated and sulfurized in a sulfur-containing gas while being brought into contact with a heating element having holes and/or grooves, so that the reaction heat accumulated within the fiber bundle is reduced. At the same time, the sulfur-containing gas can be sufficiently penetrated into the fiber bundle through the holes and/or grooves. Therefore, the sulfurization reaction caused by the sulfur-containing gas proceeds smoothly and uniformly over the fiber cross section.

Therefore, the obtained flame-resistant fibers have high tensile strength and are excellent in alkali resistance, heat resistance, flame resistance, etc. at high temperatures.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a state in which an acrylic fiber bundle is heated and sulfurized while being brought into contact with a heating body having holes according to the present invention. FIG. 2 is a schematic perspective view showing a state in which an acrylic fiber bundle is heated and sulfurized while being brought into contact with a heating body having grooves according to the present invention. 1; Fiber bundle made of acrylic fibers 2: Holes 3; Heating body 4 having holes; Grooves 5; Heating body having grooves

Claims (2)

[Claims] (1) Sulfur-containing acrylic flame-resistant fiber characterized in that when heating and sulfurizing a fiber bundle made of acrylic fiber in a sulfur-containing atmosphere, the fiber bundle is brought into contact with a heating element having holes and/or grooves. manufacturing method. (2) The method for producing a sulfur-containing acrylic flame-resistant fiber according to claim 1, wherein the sulfur-containing atmosphere is a sulfur-containing gas containing sulfur dioxide.