JP2022551406A - Method for producing fiber containing meta-aramid - Google Patents

Abstract

A method for producing a fiber containing meta-aramid having a breaking strength of 300 mN/tex or more, comprising the steps of preparing a spinning dope containing meta-aramid and sulfuric acid having a concentration of 80 wt% or more, and sending the spinning dope through a spinneret to a coagulation bath. and wherein the spinning stock solution has a meta-aramid concentration of 10 wt% or more. The invention also relates to meta-aramid fibers, multifilament yarns, fabrics and protective clothing.

Description

The present invention relates to a method for producing meta-aramid fibers by preparing a spinning dope containing meta-aramid and sulfuric acid and passing the spinning dope through a spinneret, and meta-aramid fibers obtained by the method. Furthermore, the present invention also relates to meta-aramid fibers with a sulfonic acid group content of 1 meq/kg or more, multifilament yarns containing said fibers, and fabrics and protective clothing.

Methods of spinning aramid fibers are well known.

KR20100001782 describes aramid fibers and methods for their production. Various para-aramid polymers (such as paraphenylene terephthalamide, paraphenylene-4,4'-diphenylene dicarboxylic acid amide, paraphenylene-2,6-naphthalene dicarboxylic acid amide) can be used in the spinning method, where , para-aramid is dissolved in sulfuric acid, the spinning stock solution is put into a coagulation bath through a spinneret, and the filaments are washed, dried and wound up. The time in the coagulation bath may be adjusted to improve the circularity of the cross-section of the filaments. KR20100001782 does not describe dissolving meta-aramid in sulfuric acid.

A method for spinning meta-aramid fibers is disclosed in US3094511. This document discloses a dry spinning method in which meta-aramid is dissolved in an organic solvent and heated air columns are passed through a spinneret. Evaporation of the solvent occurs in the latter step.

Also known is a meta-aramid wet spinning method in which a spinning dope is passed directly from a spinneret to a coagulation bath, as described in EP 0226137 and the like. Organic solvents are also used in the wet spinning process.

The use of organic solvents has several drawbacks. Legal regulations may in the future prohibit the use of organic solvents or only allow them to be used under stricter conditions for environmental reasons. Also, fibers spun using organic solvents require extensive washing to remove the solvent, which is not economical. Meta-aramid fibers spun from organic solvents contain organic solvents despite extensive washing.

Therefore, there is a need for a meta-aramid spinning method that does not use an organic solvent.

KR20140075197 relates to meta-aramid compositions in which antioxidants are added to the spinning dope to prevent discoloration. KR20140075197 describes the production of meta-aramid fibers after dissolving a 20% strength meta-aramid composition in 99% strength sulfuric acid. After passing through the spinneret, the spinning dope is directly put into the coagulation bath without passing through the air gap, and the filaments are washed, dried and wound up. KR20140075197 does not disclose meta-aramid fibers having a breaking strength of 300 mN/tex or more.

It is an object of the present invention to provide meta-aramid fibers which are substantially free of organic solvents and have good mechanical properties, in particular high breaking strength. Another object of the present invention is to provide an improved meta-aramid fiber, particularly a meta-aramid fiber having improved flame retardancy and improved cross-sectional uniformity.

In order to achieve the above objects, the present invention provides a method for producing a fiber containing meta-aramid having a breaking strength of 300 mN/tex or more, which method comprises combining meta-aramid and sulfuric acid having a concentration of 80 wt% or more. and passing the spinning dope through a spinneret into a coagulation bath, wherein the spinning dope has a meta-aramid concentration of 10 wt% or more (based on the weight of the spinning dope).

Preferably, the fiber containing meta-aramid has a breaking strength of 350 mN/tex or more, more preferably 400 mN/tex or more, even more preferably 450 mN/tex or more. Also, the method can result in fibers comprising meta-aramid having a breaking strength of 500 mN/tex or more.

The breaking strength of fibers containing meta-aramid is measured according to ASTM D7269-17 for multifilament yarns and ASTM D3822 for single filaments.

Fibers containing meta-aramid are sometimes called meta-aramid fibers.

For the purposes of the present invention, the term meta-aramid is a class of wholly aromatic polyamide polymers and copolymers having 70% or more, preferably 80% or more, more preferably 90% or more meta-oriented linkages between the aromatic moieties. means In one embodiment, 95% or more or all (ie, 100%) of the bonds are meta-oriented bonds. Thus, the amide bond between the aromatic moieties is substantially positioned at or near the meta orientation of the aromatic ring (e.g., as in 1,3-phenylene or 1,3-naphthalene groups). ).

The meta-aramids of the invention may be repeat units of formulas I and II:
-[-NH-Ar1-NH-CO-Ar2-CO-]- (Formula I)
-[-NH-Ar1-CO-]- (formula II),
Here, Ar1 and Ar2 are aromatic divalent meta-oriented radicals which may be the same or different, and at least one of Ar1 and Ar2 is an m-phenylene radical.

A meta-aramid can be produced by polymerizing a meta-type aromatic amine and a (meth)dicarboxylic acid halide.

Preferred aromatic (meth)diamines are metaphenylenediamine, 3,4'-diaminodiphenyl ether, and 3,4'-diaminodiphenyl sulfone; halogen atoms and/or 1 to Derivatives thereof having substituents such as alkyl groups having 3 carbon atoms, such as 2,4-toluylenediamine, 2,6-toluylenediamine, 2,4-diaminochlorobenzene, and 2,6-diaminochlorobenzene may be used. Preferably meta-phenylenediamine or mixed diamines containing 85 mol % or more, more preferably 90 mol % or more, even more preferably 95 mol % or more of meta-phenylenediamine are used.

Suitable aromatic (meta-)dicarboxylic acid dihalides are halides of isophthalic acid, such as isophthalic chloride and isophthalic bromide; substituents such as halogen atoms and/or alkoxy groups having 1 to 3 carbon atoms can be used such as 3-chloroisophthalic chloride and 3-methoxyisophthalic chloride. Preferably, isophthalic acid chloride and a mixed carboxylic acid halide containing isophthalic acid chloride in an amount of 85 mol % or more, more preferably 90 mol % or more, and still more preferably 95 mol % or more can be used.

The meta-aramid of the present invention may further contain monomers in addition to the meta-type aromatic diamine and the meta-type dicarboxylic acid halide. Suitable copolymerization components that can be used in combination with diamines and carboxylic acid halides include benzene derivatives such as para-phenylenediamine, 2,5-diaminochlorobenzene, 2,5-diaminobromobenzene, and aminoanisidine; 5-naphthylene diamine, 4,4'-diaminodiphenyl ether, 4,4,-diaminodiphenyl ketone, 4,4'-diaminodiphenylamine, and 4,4'-diaminodiphenylmethane and the like. Suitable comonomer aromatic dicarboxylic acid dihalides include terephthalic acid dichloride, 1,4-naphthalenedicarboxylic acid dichloride, 2,6-naphthalenedicarboxylic acid dichloride, 4,4'-diphenyldicarboxylic acid dichloride, and 4,4'-diphenyl ether. and dicarboxylic acid dichloride. In one embodiment, the meta-aramid polymer of the present invention may contain a content of such copolymerized components of 15 mol% or less, preferably 10 mol% or less, more preferably 5 mol% or less.

In one embodiment, the meta-aramid used in the present invention is a copoly(m-phenylene isophthalamide) containing no more than 5 mole percent aromatic moieties other than m-phenylene. In another embodiment, the meta-aramid is poly(m-phenylene isophthalamide).

In one embodiment, the spinning dope is free of para-aramid polymer, i.e. less than 5 wt%, preferably less than 1 wt%, more preferably less than 0.5 wt%, most preferably less than 0.1 wt% para-aramid polymer ( relative to the weight of the spinning dope).

In one embodiment, the spinning dope comprises sulfuric acid at a concentration of 80 wt% or greater and a polymer, the polymer consisting of a meta-aramid as defined above. The spinning dope may consist of a polymer, preferably a polymer consisting of a meta-aramid as defined above, and sulfuric acid. The spinning dope (and resulting fiber) may be free of additives, especially antioxidants.

The spinning dope preferably has a meta-aramid concentration in the range of preferably 10-30 wt%, more preferably 12-20 wt%, still more preferably 14-16 wt%, relative to the weight of the spinning dope.

The spinning dope may be prepared by mixing meta-aramid and sulfuric acid. Mixing of the sulfuric acid and the polymer may be carried out using a (twin-screw) extruder or (twin-screw) kneader, preferably including degassing.

Preferably, the spinning dope is prepared at a temperature in the range of 30-90°C.

Preferably, the spinning process of the present invention is a dry jet wet spinning process. This means that after the spinning dope leaves the spinneret it passes through a gaseous medium before entering the coagulation bath. A spinning stock solution containing meta-aramid and sulfuric acid is processed into fibers through a spinneret into a coagulation bath. The spinning mass is degassed and heated to spinning temperature. The spinning temperature, ie the temperature at which the dope is led through the spinneret, is preferably below 110°C, more preferably in the range of 25-80°C, or 45-60°C.

In the dry-jet wet spinning method, a liquid spinning dope first passes through a non-coagulating gas atmosphere such as air, and is immediately led to a coagulating bath. The meta-aramid is stretched in a gas zone (also called an air gap) through which the spinning mass passes. After coagulation, the formed filaments are removed from the coagulation bath, washed, dried and taken up on bobbins. The spinnerets used in the process of the invention may be of the type known per se in dry-jet wet spinning of wholly para-aromatic polyamides. The gaseous non-coagulating medium preferably consists of air.

The gas medium (or air gap) preferably has a length in the range 2-20 mm, more preferably 3-15 mm, even more preferably 5-10 mm.

In the method of the present invention, the spinning mass exiting the spinneret mouth is drawn in a non-coagulating gaseous medium. The degree of drawing, which is the ratio of the filament length as it leaves the coagulation bath to the average length of the spinning mass as it leaves the spinneret, may range from 1.5 to 15, preferably from 2 to 6. .

The composition of the coagulation bath varies. Consists in whole or in part of water and other substances such as bases, acids, salts and organic solvents. The coagulation bath preferably consists of dilute aqueous sulfuric acid having a concentration of 0-40 wt%, preferably 2-20 wt%. In embodiments in which the coagulation bath comprises dilute aqueous sulfuric acid, the pH of the coagulation bath may have a pH of less than 7, preferably less than 2. In another embodiment, the coagulation bath consists of a dilute aqueous caustic solution, such as an aqueous NaOH solution, having a concentration in the range 0-10 wt%, preferably 0.05-5 wt%, especially 0.1-1 wt%. may The coagulation bath may consist of water, especially softened or demineralized water.

The temperature of the coagulation bath can be any desired value. Depending on other spinning conditions, the temperature of the coagulation bath generally ranges from -10°C to 50°C, preferably from 0°C to 25°C, more preferably from 2°C to 10°C.

The sulfuric acid used must be completely removed from the spun fibers, especially by washing or neutralization and washing, since small amounts of residual acid can adversely affect the properties of the fibers. Neutralization may be carried out by treating the fibers obtained by coagulation with a solution of an alkaline substance, such as a caustic solution of NaOH, NaHCO ₃ or Na ₂ CO ₃ at room temperature or elevated temperature. In one embodiment, the fibers are treated after coagulation with a solution having a NaOH concentration in the range of 0.1-2 wt%, preferably 0.3-1 wt%. Preferably, the neutralization solution has a pH of 9 or higher, more preferably 11 or higher.

In one embodiment, the fibers are only treated with water (e.g., demineralized or softened water) after coagulation, and in particular washed once, twice, three times, or more than three times (without neutralization). only). In a preferred embodiment, the fibers are washed, neutralized and washed again. After washing, the fibers are dried. This may be done in any convenient way, online or offline. Immediately after (neutralization and) washing, the fibers are passed over heated rollers having a temperature in the range of, for example, 50-220°C, preferably 75-200°C, more preferably 100-175°C or 125-150°C. Therefore, drying is preferably performed.

Optionally, the fibers obtained by the process according to the invention can be subjected to a wet drawing step in order to improve the breaking strength of the fibers. In the wet drawing step, tension is applied to the coagulated wet fibers to a draw ratio of 1 to 2 times, preferably 1.1 to 1.5 times. At this stage of the process, the draw ratio can be [length of fiber after wet drawing step] divided by [length of fiber before wet drawing step]. In a continuous on-line process, the draw rate may be determined based on the speed of the yarn guiding godets (guide rollers) before and after wet drawing. That is, [speed of godet (guide roller) after wet stretching process]÷[speed of godet (guide roller) before wet stretching process]. Preferably, the step of wet stretching is performed above room temperature between coagulation and washing, during washing, or after washing.

The fibers may be subjected to a heat treatment in which they are heated under tension in an inert or non-inert gas. The heat treatment may be done after the drying step (online) or else after winding the fiber (offline). Heat treatment may include one or more heating steps under tension. In one embodiment, the method according to the invention comprises heating the fibers in at least one heating step to a temperature in the range 250-400°C, preferably 280-350°C, preferably 300-320°C.

The heat treatment of the fibers may consist of at least two stages. In one method according to the invention, the fibers obtained in the first heating step as described above are heated in a second heating step to a Heat to temperature.

In a preferred embodiment, at least one heating step is tensioned to a draw ratio in the range of 1.5 to 10, preferably 1.5 to 2.5, and the other heating step is untensioned. (relaxation), tension is applied to the extent that the fiber can be transported on a processing device (guide rolls, etc.), or tension is applied to a draw ratio of 1.5 or less. Higher tension may be applied to either the first heating step or the second heating step. It is preferred to apply a higher draw ratio in the first heating step. In another embodiment, tension is applied during each heating step, resulting in a total draw ratio in the range of 1.5-10, preferably 1.5-2.5. At this stage of the method, the draw ratio may be [length of fiber after heating] divided by [length of fiber before heating]. The draw ratio refers to that of one heat treatment step and the total draw ratio refers to the draw (cumulative) achieved in all heat treatment steps processed. In a continuous on-line process, the draw rate may be determined based on the speed of the yarn guiding godets (guide rollers) before and after heat treatment. That is, [speed of godet (guide roller) after at least one heating step]÷[speed of godet (guide roller) before at least one heating step].

The method may include a wet drawing step and a heat treatment.

The method according to the invention is a solvent-based method. Concentrated sulfuric acid is used as a solvent for the meta-aramid polymer. Preferably, the sulfuric acid is at a concentration of 85 wt% or higher, more preferably 90 wt% or higher, even more preferably 95 wt% or higher. Sulfuric acid with a concentration of 98 wt % or higher or 99 wt % or higher is particularly preferred.

Meta-aramid fibers, preferably multifilament yarns, are obtained from this process. The invention also relates to meta-aramid fibers obtainable by the method of the invention, as disclosed in any of the embodiments above.

Within the scope of the present invention, a fiber is understood as a unit of flexible material with a high length to width ratio (width defined across the cross-sectional area perpendicular to the length of the fiber). Fibers specifically include filaments of unlimited length, filament yarns containing one or more twisted commingled or untwisted filaments (monofilament and multifilament yarns), and collections of multiple filaments bundled together with substantially no twist. All types of ordinary fibers are included, such as tow consisting of The substantially unlimited length filaments formed during spinning may optionally be cut into staple fibers, which in turn can be processed into spun yarn. Filament yarns may be cut into smaller lengths called flocks. Additionally, the filament yarn may be processed into a pulp. These fiber variations are encompassed by the term "fiber". Multifilament yarns may contain fibers according to the invention and fibers of other materials. The cross-section of the fibers or filaments of the invention can be of any shape, but are typically circular (rounded).

The present invention also relates to a meta-aramid fiber having a breaking strength of 300 mN/tex or more and a sulfonic acid group content of 0.001 wt % (mass/fiber mass) or more. Generally, the content of sulfonic acid groups is 1 wt% or less, preferably 0.5 wt% or less, more preferably 0.3 wt% or less. It may also be expressed in ppm, so that the content of sulfonic acid groups is >1 ppm, preferably 5-300 ppm, more preferably 10-100 ppm. Sulfonic acid groups are formed as a result of using sulfuric acid as a solvent for the meta-aramid. Aromatics undergo some degree of aromatic substitution reaction in which the hydrogen portion of the aromatic group is replaced by a sulfonic acid group. It is preferred that these groups are neutralized.

The content of sulfonic acid groups is determined by nuclear magnetic resonance spectroscopy (NMR), in particular ¹ H-NMR, on samples of untreated yarn that have not been heat treated. A method for measuring the sulfonic acid group content is described in the Examples section.

Sulfur content can also be measured to obtain the degree of sulfonation of the fiber. In one embodiment, the sulfur content of the fibers according to the invention is 0.025 wt% or more, preferably 0.05 wt% or more (relative to the weight of the fibres). Sulfur content may be measured on the resulting meta-aramid fibers (including heat treated fibers). Sulfur content may be measured by inductively coupled plasma-optical emission spectroscopy (ICP-OES), as detailed in the Examples section.

Sulfonation of meta-aramid fibers appears to be advantageous in improving the flame retardancy and flame resistance of meta-aramid fibers. In particular, the LOI (limiting oxygen index) of the fibers of the present invention is higher than meta-aramid fibers spun from organic solvents. Preferably, the LOI of meta-aramid fibers according to the present invention is increased by 10% or more compared to fibers spun from organic solvents. LOI is measured according to ASTM D2863, as detailed in the Examples section.

Preferably, the meta-aramid fiber has a breaking strength of 350 mN/tex or more, more preferably 400 mN/tex or more, still more preferably 450 mN/tex or more. The meta-aramid fiber may have a breaking strength of 500 mN/tex or more.

The breaking strength of meta-aramid fibers is measured according to ASTM D7269-17 for multifilament yarns and ASTM D3822 for single filaments.

One advantage of the meta-aramid fibers of the present invention is their low organic solvent content. In one embodiment, the meta-aramid fibers have an organic solvent content of less than 250 ppm, preferably less than 100 ppm, more preferably less than 50 ppm, which is less than 0.025 wt% (based on the weight of the yarn), preferably 0 This corresponds to an organic solvent content of less than 0.01 wt%, more preferably less than 0.005 wt%. This means that the total content of organic solvents, in particular NMP (N-methylpyrrolidone), THF (tetrahydrofuran), DMAc (dimethylacetamide) is less than 250 ppm, preferably less than 100 ppm, more preferably less than 50 ppm. A meta-aramid fiber having an organic solvent content of less than 100 ppm is sometimes referred to as "substantially free of organic solvent". The very low residual organic solvent content may be due to the solvent used during the polymerization of the meta-aramid.

The organic solvent content may be measured in various ways depending on the specific organic solvent. Gas chromatography (GC), NMR (nuclear magnetic resonance) and MS (mass spectrometry) are generally suitable for measuring the content of organic solvents in fibers, such as the content of NMP and DMAc. In the context of the present invention, the organic solvent content is determined by gas chromatography, as detailed in the Examples section.

The invention also relates to a meta-aramid multifilament yarn containing this meta-aramid fiber. The meta-aramid multifilament yarn may consist of meta-aramid fibers.

Preferably, the meta-aramid multifilament yarn has a breaking strength of 350 mN/tex or more, more preferably 400 mN/tex or more, even more preferably 450 mN/tex or more. Preferably, the meta-aramid multifilament yarn has an elongation at break of 15% or more, preferably 20% or more, more preferably 25% or more. In one embodiment, the meta-aramid multifilament yarn has a breaking strength of 350 mN/tex or more and a breaking elongation of 25% or more. Mechanical properties of meta-aramid yarn are measured according to ASTM D7269-17.

In one embodiment, the present invention provides that 50% or more of the individual filaments have an average ratio of [minimum circumscribed circle diameter] to [maximum inscribed circle diameter] of 1.3 or less, preferably 1.1. It relates to a multifilament yarn with a round cross section such that:

By "minimum circumscribed circle" is meant the smallest or smallest circle that circumscribes the profile of a cross-section of a single filament of a multifilament yarn at at least two points and encompasses the entire area of the cross-section of a single filament. "Largest inscribed circle" means the largest or largest circle that inscribes the cross-sectional profile at least two points and that fits within the cross-sectional profile. The average value of the ratio of [minimum circumscribed circle diameter] to [maximum inscribed circle diameter] was obtained by preparing a cross-section of the multifilament yarn and measuring the minimum circumscribed circle diameter and the maximum inscribed circle diameter for 50 separate filaments. It is obtained by obtaining the diameter and the corresponding ratio and calculating the average value. For a perfect circle, the smallest circumscribed circle and the largest inscribed circle overlap and have the same diameter, so the ratio is 1.0.

This round cross-section is another advantage of the meta-aramid fibers of the present invention over prior art meta-aramid fibers.

The meta-aramid fibers of the present invention have a lower porosity than prior art meta-aramid fibers. Due to the low porosity, the fibers of the invention may have better mechanical properties. Particularly advantageous is the combination of properties of the present meta-aramid fibers. The fibers have a uniform, round cross-section, improved flame retardancy and low porosity.

The application also relates to fabrics comprising the meta-aramid fibers and/or meta-aramid multifilament yarns of the invention. The fabric may have the form of woven, knitted or braided fabric, or woven or non-woven fabric.

The meta-aramid fibers of the present invention may be used, for example, in textile applications, including textiles, including knitted and woven fabrics, or cords used to reinforce hoses, or protective apparel, particularly in fire resistant applications. The meta-aramid fiber of the present invention is particularly suitable for textile applications in which the meta-aramid fiber or fabric containing the fiber is in direct contact with the skin.

The invention also relates to protective garments comprising the fabric of the invention. Protective clothing may be, for example, gloves, jackets, pants, shirts, and the like.

Photomicrograph of the cross section of the filament.

The invention is described in more detail with reference to the following examples, which should not be construed as limiting the scope of the invention.

Measurement method 1. Mechanical Properties The breaking strength, breaking elongation and breaking toughness of the meta-aramid multifilament yarn are measured according to ASTM D 7269-17.

2. Sulfonic Acid Group Content The content of sulfonic acid groups is measured by ¹ H-NMR. Dissolve 20 mg of the untreated sample of untreated thread in 1 mL of DMSO-d6 and transfer 550 μL of it to a 5 mm NMR sample tube. ¹ H NMR spectra are recorded at 300 K using a Bruker Avance III 400 MHz NMR spectrometer equipped with a BBFO-plus 5 mm broadband probe. Spectra are recorded in 64 integrated scans with a 30° excitation pulse using a prescan delay of 6 seconds and an acquisition time of 4 seconds. The ¹ H NMR spectra obtained were referenced to the DMSO-d6 residual solvent signal set at 2.5 ppm. The sulfonic acid group content is calculated by the following formula and expressed in meq/kg (mmol/kg).
A _sMPD =integral(singlet@8.97 ppm) [mol]
A _{meta aramid} = (integral 8.86 - 7.08 ppm - (6 * AsMPD)) / 8 [mol]
sMPD = (A _sMPD * 186.1844) [mg]
meta aramid = (A _{meta aramid} * 238.2414) [mg]
S=(sMPD/(sMPD+meta aramid))*(32.065/186.1844)*100%
Sulfonic acid group content = 106 * (S/100) / 32.065 [meq/kg]

3. Sulfur Content Sulfur content may be measured by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Add 9 ml of concentrated nitric acid (70 wt %) to 100 mg of fiber. The mixture is decomposed by microwave exposure in an Ultrawave (Milestone) until a clear liquid is obtained. Add MilliQ water to adjust the volume to 25 ml. The precipitate is removed from this solution by filtration. The clarified filtrate is analyzed by ICP-OES in a Perkin Elmer Optima 8300 DV instrument. Emission lines at wavelengths of 181,972 nm and 180,669 nm are used to measure sulfur content.

4. Organic Solvent Content The organic solvent content is determined by gas chromatography. about l.p.m. 0 mg of fiber was taken and heated to 500° C. or higher in an electric furnace. Gas chromatography (Shimadzu Corporation, model: GC-2010) was used to measure the amount of amide solvent evaporated from the fiber. After that, the residual solvent concentration in the fiber was calculated using a calibration curve prepared using an amide solvent as a standard sample.

5. Relative Viscosity Polymer samples are dried in a vacuum oven at 50° C. for 2 hours to remove moisture. The dried sample is then dissolved in sulfuric acid overnight at room temperature. Subsequently, a 0.25% (w/V) sample solution dissolved in 96% (w/w) sulfuric acid was measured at 25° C. in an Ubbelohde viscometer (such as Schott AVS370) for the run-off time. Under the same conditions, the outflow time of the solvent was also measured. Relative viscosity was calculated as the ratio of the two observed efflux times.

6. Microscopic Observation Embed the thread in melted paraffin and leave to harden for about 5 minutes. The embedded samples are then cut perpendicular to the fiber axis with a microtome to obtain sections with a thickness of 5-7 μm. The cut pieces are then placed on glass slides and heated to melt the paraffin. After that, the dissolved paraffin was removed with xylene and ethanol. Next, an optical microscope (manufactured by Nikon Corporation, trade name "ECLIPSE" LV100N) is used to observe and photograph the cross section of the fiber to obtain a photograph of the cross section. The magnification is selected within the range of 100 to 1000 as required.

7. LOIs
Limiting oxygen index (LOI) is measured according to ASTM D2863. From each sample, combine the required number of yarns to create a yarn sample of 168000 dtex. The yarn is wound onto a precision reel with a winding yarn tension of 5±3 mN/tex, based on the nominal linear density of the yarn. This sample is surrounded by a thin copper wire. Each specimen is about 150 mm long, about 10±0.5 mm wide, and about 3±0.25 mm thick. The specimen is marked approximately 50 mm from the igniting edge. Immediately prior to testing, the specimens are conditioned at 23±2° C. and 50±5% relative humidity for at least 88 hours. The specimens were tested according to ASTM D2863, Option A (top firing).

Example 1
Fibers were spun from a spinning dope containing an m-aramid polymer (poly(m-phenylisophthalamide)) with a relative viscosity of 1.55. In a 20 mm twin-screw extruder manufactured by Theysohn, 99.8 wt% of sulfuric acid was added to the m-aramid polymer so that the polymer concentration was 18 w/w%, and mixed at a temperature of 85°C and a rotation speed of 300 rpm to obtain a spinning dope. rice field. The spinning dope was processed into filaments by passing through a filter at 55° C., a spinneret at 85° C. and an air gap into a static coagulation bath (under the conditions shown in Table 1). The temperature of the coagulation bath was 3°C.

The multifilament yarn obtained after coagulation was washed and neutralized by subsequently passing through a bath of water, 0.4% NaOH, and water again. The yarn was dried at 150° C. and wound onto a bobbin.

The properties of the yarn obtained after drying (also referred to as "untreated yarn") were measured.

The sulfonic acid group content of sample 1-1 was measured and found to be 116 meq/kg. Sample 1-1 was heat treated in a two step process. The yarn was pulled from the bobbin and passed through a first oven applying a draw ratio of 1.6 and a second oven maintaining a draw ratio of 1 and a temperature of 333°C. Stretch ratio is defined as the post-oven speed divided by the pre-oven speed. Residence time in both ovens (based on speed between ovens) was 18.8 seconds.

Example 2
Fibers were spun from a spinning dope containing an m-aramid polymer with a relative viscosity of 1.55. In a Theysohn 20 mm twin screw extruder, 99.8 wt% sulfuric acid was added to the m-aramid polymer to give a polymer concentration of 16 wt/wt% or 17.5 wt/wt%, and the temperature was 55°C (2-1 , 2-3) or 60° C. (2-2, 2-4) at a rotation speed of 450 rpm to obtain a spinning dope. The spinning dope was processed into filaments through a filter, spinneret, and a static coagulation bath through a 5 mm air gap with an applied draw ratio of 3.41 (under conditions shown in Table 4). The temperature of the coagulation bath was 5°C.

The multifilament yarn obtained after coagulation was subsequently washed and neutralized by passing through a bath of water, 0.25% NaOH, and water again. The yarn was dried at 150° C. and wound onto a bobbin. The properties of the yarn obtained after drying (also referred to as "untreated yarn") were measured.

Samples 2-3 were heat treated in a two step process. The yarn was pulled from the bobbin and passed through a first oven that applied various draw ratios at a temperature of 305°C and a second oven that was maintained at a draw ratio of 1 and a temperature of 333°C. Stretch ratio is defined as the post-oven speed divided by the pre-oven speed. The residence time in both ovens was calculated from the speed between both ovens. The sulfur content of sample 2-3 was measured to be 0.18 wt%.

Example 3
Fibers were spun from a spinning dope containing m-aramid polymer with a relative viscosity of 1.58. In a 53 mm twin-screw extruder manufactured by Clextral, 99.8 wt% sulfuric acid was added to the m-aramid polymer so that the polymer concentration was 12 wt/wt%, and the mixture was mixed at a temperature of 45°C and a rotation speed of 250 rpm to obtain a spinning dope. Obtained.

The spinning dope is passed through a filter at 50°C, a spinneret with 1000 65 μm diameter capillaries at 50°C, an air gap, where the filaments are drawn 2.9 times and placed in a falling jet coagulation bath, processed into filaments (under the conditions shown in Table 1). The temperature of the coagulation bath was 5°C. The multifilament yarn obtained after coagulation was washed and neutralized by subsequently passing through a bath of water, 0.35% NaOH, and water again. The yarn was dried on a godet (guide roller) at 160°C. Alternatively, the yarn may be hot drawn on a heated godet (guide roller) and wound onto a bobbin.

The properties of the yarn obtained were measured and are shown in Table 9.

Example 4
Fibers were spun from a spinning dope containing a meta-aramid polymer with a relative viscosity of 1.55. In a 20 mm twin-screw extruder manufactured by Theysohn, 99.8 wt% of sulfuric acid was added to the m-aramid polymer so that the polymer concentration was 16 wt/wt%, and the mixture was mixed at a temperature of 60°C and a rotation speed of 450 rpm to obtain a spinning dope. Obtained. The spinning dope was processed into filaments through a filter, a spinneret, a 5 mm air gap applied with a draw ratio of 2.08, and into a dynamic coagulation bath (under the conditions shown in Table 10). The temperature of the coagulation bath was 5°C. After the coagulation bath, the yarn was wet drawn between two roller sets.

The multifilament yarn obtained after coagulation and wet drawing was subsequently washed and neutralized by passing through a bath of water, 0.25% NaOH, and water again. The yarn was dried at 150° C. and wound onto a bobbin.

The properties of the yarn obtained after drying (also referred to as "untreated yarn") were measured.

Sample 4-2 was heat treated in a two step process. The yarn was pulled from the bobbin and passed through a first oven applied with a draw ratio of 1 at a temperature of 315°C and a second oven with a temperature of 315°C with varying draw ratios. Stretch ratio is defined as the post-oven speed divided by the pre-oven speed.

Example 5
Fibers were spun from a spinning dope containing a meta-aramid polymer with a relative viscosity of 1.55. In a 20 mm twin-screw extruder manufactured by Theysohn, 99.8 wt% sulfuric acid was added to the m-aramid polymer so that the polymer concentration was 16 wt/wt%, and the mixture was mixed at a temperature of 50°C and a rotation speed of 300 rpm to obtain a spinning dope. Obtained. This spinning dope is passed through a filter, a spinneret with 106 65 μm diameter capillaries maintained at a temperature of about 75° C., a 10 mm air gap with a draw ratio of 1.95 applied, and placed in a dynamic coagulation bath to form filaments. processed to The speed after the coagulation bath was 40 m/min. After the coagulation bath, the yarn was wet drawn 1.4 times between two roller sets. The yarn obtained after coagulation and wet drawing was subsequently washed and neutralized by passing through a bath of water, 0.25% NaOH, and water again. The yarn was dried on rollers set at 220°C. The yarn traveled through two successive sets of rollers, the settings of which are shown in Table 13.

The thread was wound onto the bobbin. Table 14 shows the mechanical properties of this yarn.

Example 6 - Organic Solvent Content The NMP and DMAc contents of commercial ^{TeijinConex®} B, ^Nomex® and Yantai Tayho Advanced Materials meta-aramid yarns were determined by gas chromatography. The results are shown in Table 13. The yarn according to the invention does not contain organic solvents.

Example 7 - Filament Cross-Sections Comparative Samples 1-3 (used in Example 6) and bundles embedded with meta-aramid yarns according to the present invention were photomicrographed. FIG. 1 shows a photomicrograph of the cross section of the filament. Panel a) shows the filament of Comparative Example 1, panel b) the filament of Comparative Example 2, panel c) the filament of Comparative Example 3 and panel d) the filament cross section of a meta-aramid yarn according to the invention.

As can be seen from this comparison, the filaments of the invention have a uniform circular cross-section, while the filaments of the comparative example have oval cross-sections and cross-sections of varying diameters.

Example 8 - Limiting Oxygen Index The LOI of a meta-aramid yarn according to the invention and a commercial meta-aramid yarn were determined. The results are shown in Table 14.

This data shows that the samples according to the invention have higher LOI values than the comparative samples according to the prior art.

Claims (18)

A method for producing a fiber containing meta-aramid having a breaking strength of 300 mN/tex or more, comprising the steps of preparing a spinning dope containing meta-aramid and sulfuric acid having a concentration of 80 wt% or more, and sending the spinning dope through a spinneret to a coagulation bath. and wherein the spinning dope has a meta-aramid concentration of 10 wt% or more. 2. The method according to claim 1, wherein the fiber containing meta-aramid has a breaking strength of 350 mN/tex or more, preferably 400 mN/tex or more, more preferably 450 mN/tex or more. Process according to claim 1 or 2, wherein said spinning dope has a meta-aramid concentration in the range of 10-30 wt%, preferably 12-20 wt%, more preferably 14-16 wt%. The method according to any one of claims 1 to 3, wherein the meta-aramid is copoly(m-phenylene isophthalamide) containing 5 mol% or less of aromatic moieties other than m-phenylene. The method according to any one of claims 1 to 4, wherein the spinning dope is prepared by mixing meta-aramid and sulfuric acid. A process according to any preceding claim, wherein the spinning dope is prepared at a temperature in the range of 30-90°C. A process according to any preceding claim, wherein the spinning dope passes through a gaseous medium after exiting the spinneret and before entering the coagulation bath. Process according to claim 7, wherein the spinning dope is passed through a gaseous medium with a length in the range of 2-20 mm, preferably 3-15 mm, more preferably 5-10 mm. A method according to any preceding claim, wherein the sulfuric acid has a concentration of 85 wt% or more, preferably 90 wt% or more, more preferably 95 wt% or more. Said fibers are heated in at least one heating step to a temperature in the range 250-400°C, preferably in the range 280-350°C, more preferably in the range 300-320°C, optionally followed by a further heating step between 250-400°C. A process according to any preceding claim, wherein the heating is at a temperature in the range 400°C, preferably in the range 280-350°C, more preferably in the range 300-320°C. A meta-aramid fiber having a breaking strength of 300 mN/tex or more, obtained by the method according to any one of claims 1 to 10. A meta-aramid fiber having a breaking strength of 300 mN/tex or more and a sulfonic acid group content of 0.001 wt % or more. 13. The meta-aramid fiber according to claim 11 or 12, having a breaking strength of 350 mN/tex or more, preferably 400 mN/tex or more, more preferably 450 mN/tex or more. A meta-aramid fiber according to any one of claims 11 to 13, having an organic solvent content of less than 250 ppm, preferably less than 100 ppm, more preferably less than 50 ppm. A meta-aramid multifilament yarn comprising the meta-aramid fiber according to any one of claims 11-14. 50% or more of the individual filaments have a circular cross section such that the average ratio of the [minimum circumscribed circle diameter] to the [maximum inscribed circle diameter] is 1.3 or less, preferably 1.1 or less. 16. The meta-aramid multifilament yarn of claim 15, comprising: A fabric comprising a meta-aramid fiber according to any one of claims 11 to 14 and/or a meta-aramid multifilament yarn according to claim 15 or 16, preferably a knitted, woven or non-woven fabric. A protective garment comprising the fabric of claim 17.

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