CN114423892A

CN114423892A - Method for making fibers comprising meta-aramid

Info

Publication number: CN114423892A
Application number: CN202080066120.5A
Authority: CN
Inventors: H·伯斯图尔; W·奈恩黑斯; R·居内斯; S·布德巴; 山口赖久; 佐藤友亮
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 2019-10-07
Filing date: 2020-10-06
Publication date: 2022-04-29
Also published as: WO2021070042A1; US20220380939A1; EP4041941A1; JP2022551406A

Abstract

A method of making a fiber comprising meta-aramid having a tenacity of at least 300mN/tex comprising the steps of: preparing a dope comprising meta-aramid and sulfuric acid at a concentration of at least 80 weight percent, and passing the dope through a spinneret into a coagulation bath, wherein the dope has a meta-aramid concentration of at least 10 weight percent. The invention also relates to meta-aramid fibers, multifilament yarns, textile sheets, and protective garments.

Description

Method for making fibers comprising meta-aramid

The present invention relates to a method for producing a meta-aramid fiber by preparing a spinning dope comprising meta-aramid and sulfuric acid and passing the spinning dope through a spinneret, and to a meta-aramid fiber obtained by the method. The invention further relates to a meta-aramid fiber having a sulfonic acid group content of at least 1meq/kg, to a multifilament yarn comprising said fiber, and to textile sheets and protective clothing.

Spinning processes for aramid fibers are known.

KR20100001782 describes aramid fibers and methods for their manufacture. Various para-aramid polymers (e.g., para-phenylene terephthalamide, para-phenylene-4, 4' -biphenylenedicarboxylic acid amide, or para-phenylene-2, 6-naphthalenedicarboxylic acid amide) can be used in the spinning process, wherein the para-aramid is dissolved in sulfuric acid, the dope is passed through a spinneret into a coagulation bath, and the filaments are washed, dried, and wound. The time in the coagulation bath can be adjusted to improve the roundness of the filament cross-section. KR20100001782 does not describe dissolving meta-aramid in sulfuric acid.

A method of spinning meta-aramid fiber is disclosed in US 3094511. This document discloses a dry spinning process wherein a meta-aramid is dissolved in an organic solvent and passed through a spinneret into a heated air column. The latter step evaporates the solvent.

Wet spinning processes for meta-aramids are also known, wherein the spinning dope is passed directly from the spinneret into a coagulation bath, for example as described in EP 0226137. For the wet spinning process, organic solvents are also used.

The use of organic solvents has several disadvantages. Due to legislation, the use of organic solvents may be prohibited or only allowed under more severe conditions in the future for environmental reasons.

Furthermore, fibers spun using organic solvents must be washed sufficiently to remove the solvent, which is uneconomical.

Despite the intensive washing, the meta-aramid fiber spun from the organic solvent still contains the organic solvent.

Thus, there is a need for a method of spinning meta-aramid without the use of organic solvents.

KR20140075197 relates to a meta-aramid composition that prevents discoloration by adding an antioxidant to the dope. KR20140075197 describes the production of meta-aramid fiber from a meta-aramid composition after dissolving the meta-aramid composition in sulfuric acid at a concentration of 99% to a meta-aramid concentration of 20%. After passing the dope through the spinneret, the dope enters the coagulation bath directly and without any air gap, and the filaments are washed, dried and wound. KR20140075197 does not disclose meta-aramid fibers having a breaking strength of at least 300 mN/tex.

It is an object of the present invention to provide a meta-aramid fiber that is substantially free of organic solvents and has good mechanical properties, particularly high breaking strength.

It is also an object of the present invention to provide an improved meta-aramid fiber, particularly having improved flame retardancy and an improved uniform cross-section.

In order to achieve the above object, the present invention provides a method for producing a fiber comprising a meta-aramid having a breaking strength of at least 300mN/tex, comprising the steps of: preparing a dope comprising meta-aramid and sulfuric acid at a concentration of at least 80 weight percent, and passing the dope through a spinneret into a coagulation bath, wherein the dope has a meta-aramid concentration (based on the weight of the dope) of at least 10 weight percent.

Preferably, the meta-aramid containing fiber has a breaking strength of at least 350mN/tex, more preferably at least 400mN/tex, still more preferably at least 450 mN/tex. The present process can also produce meta-aramid containing fibers having a tenacity (tenacity) of at least 500 mN/tex.

The breaking strength of the fibers comprising meta-aramid is determined according to ASTM D7269-17 for multifilament yarns and according to ASTM D3822 for monofilaments.

Fibers comprising meta-aramid may also be referred to as meta-aramid fibers.

For the purposes of the present invention, the term meta-aramid refers to a class of wholly aromatic polyamide polymers and copolymers having at least 70%, preferably at least 80%, more preferably at least 90% meta-oriented bonds between the aromatic moieties. In one embodiment, at least 95% or all (i.e., 100%) of the bonds are meta-oriented bonds. The amide linkage between the aromatic moieties is thus substantially in a meta orientation or a position near a meta orientation of the aromatic ring (e.g., in 1, 3-phenylene or 1, 3-naphthyl).

The meta-aramid of the present invention may have repeating units of formulas I and II:

- [ -NH-Ar1-NH-CO-Ar2-CO- ] - (formula I)

- [ -NH-Ar1-CO- ] - (formula II),

wherein Ar1 and Ar2 are aromatic, divalent, meta-oriented groups, which may be the same or different, and at least one of Ar1 and Ar2 is meta-phenylene.

Meta-aramid can be made by polymerization of meta-aromatic amines and meta-dicarboxylic acid halides.

Suitable aromatic meta-diamines are meta-phenylenediamine, 3,4 '-diaminodiphenyl ether and 3,4' -diaminodiphenyl sulfone; and derivatives thereof having a substituent such as a halogen atom and/or an alkyl group having 1 to 3 carbon atoms bonded to the aromatic ring structure thereof, for example, 2, 4-tolylenediamine, 2, 6-tolylenediamine, 2, 4-diaminochlorobenzene and 2, 6-diaminochlorobenzene, can be used. It is preferable to use m-phenylenediamine or a mixed diamine containing a content of m-phenylenediamine of 85 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% or more.

Suitable aromatic meta-dicarboxylic acid dihalides are isophthaloyl halides, such as isophthaloyl chloride and isophthaloyl bromide; and derivatives thereof having a substituent such as a halogen atom and/or an alkoxy group having 1 to 3 carbon atoms, such as 3-chloroisophthaloyl chloride and 3-methoxyisophthaloyl chloride, can be used. Preferably, isophthaloyl dichloride and mixed carboxylic acid halides containing isophthaloyl dichloride levels of 85 mole percent or greater, more preferably 90 mole percent or greater, and even more preferably 95 mole percent or greater are used.

The meta-aramid of the present invention may contain other monomers in addition to the meta-aromatic diamine and the meta-dicarboxylic acid halide. Suitable copolymeric components which may be used in combination with the diamines and carboxylic acid halides include benzene derivatives such as p-phenylenediamine, 2, 5-diaminochlorobenzene, 2, 5-diaminobromobenzene and aminoanisidine; and 1, 5-naphthalenediamine, 4 '-diaminodiphenyl ether, 4' -diaminobenzophenone, 4 '-diaminodiphenylamine and 4,4' -diaminodiphenylmethane. Suitable comonomer aromatic dicarboxylic acid dihalides include terephthaloyl dichloride, 1, 4-naphthalenedicarboxylic acid dichloride, 2, 6-naphthalenedicarboxylic acid dichloride, 4 '-biphenyldicarboxylic acid dichloride and 4,4' -diphenyl ether dicarboxylic acid dichloride. In one embodiment, the meta-aramid polymer of the invention may include such copolymerized components in an amount of up to 15 mole%, preferably up to 10 mole%, more preferably up to 5 mole%.

In one embodiment, the meta-aramid used in the present invention is a copolymer (metaphenylene isophthalamide) containing up to 5 mole percent of aromatic moieties other than meta-phenylene. In another embodiment, the meta-aramid is poly (m-phenylene isophthalamide).

In one embodiment, the spin dope is free of para-aramid polymer, i.e., contains less than 5 weight percent, preferably less than 1 weight percent, more preferably less than 0.5 weight percent, and most preferably less than 0.1 weight percent para-aramid polymer (based on the weight of the spin dope).

In one embodiment, the spin dope comprises sulfuric acid at a concentration of at least 80 weight percent and a polymer consisting of a meta-aramid as defined above. The dope may consist of a polymer, preferably a meta-aramid as defined above, and sulfuric acid. The spin-dope (and resulting fiber) may be free of additives, particularly antioxidants.

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

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

Preferably, the spinning dope is prepared at a temperature of 30 to 90 ℃.

Preferably, the spinning process of the present invention is a dry-jet wet spinning process. This means that the dope passes through the gaseous medium after leaving the spinneret and before entering the coagulation bath.

A dope comprising meta-aramid and sulfuric acid is processed into fibers by passing the dope through a spinneret into a coagulation bath.

The spinning mass is degassed and heated to the spinning temperature.

The spinning temperature, i.e. the temperature at which the dope passes to and through the spinneret, is preferably at most 110 ℃, more preferably in the range of 25 to 80 ℃ or 45 to 60 ℃.

In the dry-jet wet spinning process, the liquid spinning dope is first passed through a non-coagulating gas atmosphere, such as air, and immediately thereafter fed into a coagulation bath. In the gaseous zone (also referred to as the air gap) through which the spin mass passes, the meta-aramid is drawn.

After coagulation, the formed filaments are taken out of the coagulation bath, washed, dried and wound on bobbins.

The spinneret used in the process according to the invention may be of the type known per se in the dry-jet wet spinning of all-para-aramid. The gaseous non-solidifying medium preferably consists of air.

The gaseous medium (or air gap) preferably has a length of 2 to 20mm, more preferably 3 to 15mm, still more preferably 5 to 10 mm.

In the process according to the invention, the spinning material leaving the spinning orifices is drawn in a non-coagulating gaseous medium. The degree of drawing, i.e. the ratio between the length of the filaments leaving the coagulation bath and the average length of the spinning material leaving the spinning orifices of the spinneret, can be in the range from 1.5 to 15, preferably from 2 to 6.

The composition of the coagulation bath may vary. It may consist wholly or partly of water or other substances, such as bases, acids, salts and organic solvents. The coagulation bath preferably consists of a dilute aqueous sulfuric acid solution having a concentration of 0 to 40% by weight, preferably 2 to 20% by weight. In embodiments where the coagulation bath comprises a dilute aqueous sulfuric acid solution, the pH of the coagulation bath may have a pH below 7, preferably below 2.

According to another embodiment, the coagulation bath may consist of a dilute aqueous caustic solution, for example an aqueous NaOH solution having a concentration of 0-10% by weight, preferably 0.05 to 5% by weight, in particular 0.1 to 1% by weight. The coagulation bath may consist of water, in particular demineralized or desalted water.

The temperature of the coagulation bath may have any desired value. Depending on other spinning conditions, the temperature of the coagulation bath is generally in the range of-10 ℃ to 50 ℃, preferably between 0 ℃ to 25 ℃, more preferably between 2 and 10 ℃.

Since small amounts of residual acid may have a detrimental effect on the fiber properties, the sulfuric acid used should be completely removed from the spun fiber, in particular by washing or neutralization and washing. By using solutions of basic substances, e.g. NaOH, NaHCO, at room or elevated temperature₃Or Na₂CO₃The solidified fibers are treated with the caustic solution of (a) to effect neutralization. In one embodiment, the fibers are treated after coagulation with a solution having a NaOH concentration of 0.1 to 2 wt.%, preferably 0.3 to 1 wt.%. Preferably, the neutralizing solution has a pH of at least 9, more preferably at least 11.

In one embodiment, the fibers are treated with water only (e.g., desalted or demineralized) after coagulation, particularly once, twice, three times, or more than three times (only washed, not neutralized).

In a preferred embodiment, the fibers are washed, neutralized and washed again.

After they have been washed, the fibers are dried. This may be done online or offline in any convenient manner. Preferably, drying should be carried out immediately after (neutralisation) washing, for example by passing the fibres over heated rollers at a temperature in the range 50 to 220 ℃, preferably in the range 75 to 200 ℃, more preferably in the range 100 to 175 ℃ or 125 to 150 ℃.

In order to increase the tenacity of the fibres, the fibres obtained in the process according to the invention may optionally be subjected to a wet-drawing step. During the wet drawing step, tension is applied to the coagulated wet fibers so that the draw ratio is in the range of ≥ 1 to 2, preferably 1.1 to 1.5. At this stage of the process, the draw ratio may be defined as [ fiber length after wet drawing step ]/[ fiber length before wet drawing step ]. For a continuous on-line process, the draw ratio can also be determined based on the speed at which the godet guides the yarn before and after wet drawing, and is therefore [ godet speed after wet drawing step ]/[ godet speed before wet drawing step ].

Preferably, the wet stretching step is performed at a temperature above room temperature between coagulation and washing, during washing or after washing.

The fibers may be subjected to a heat treatment in which the fibers are heated under tension in an inert or non-inert gas. The heat treatment can be performed after the drying step (on-line) or after the fiber winding (off-line).

The heat treatment may comprise one or more steps of heating under tension.

In one embodiment, the process according to the invention comprises heating the fibers in at least one heating step to a temperature in the range of 250 to 400 ℃, preferably in the range of 280 to 350 ℃, preferably in the range of 300 to 320 ℃.

The heat treatment of the fibers may comprise at least two steps. In one method according to the invention, the fibers obtained in the first heating step as described above are heated in the second heating step to a temperature in the range of 250 to 400 ℃, preferably in the range of 280 to 350 ℃, preferably in the range of 300 to 320 ℃.

In a preferred embodiment, tension is applied during at least one heating step so that the draw ratio is in the range of 1.5 to 10, preferably 1.5 to 2.5, and no tension (slack) is applied during another heating step, or tension sufficient to transport the fibers over processing equipment (e.g., guide rolls) or tension such that the draw ratio is at most 1.5 is applied. Higher tension may be applied in the first or second heating step. Preferably, a higher draw ratio is applied in the first heating step.

In another embodiment, tension is applied during each heating step such that the total draw ratio is in the range of 1.5 to 10, preferably 1.5 to 2.5.

At this stage of the process, the draw ratio may be defined as [ fiber length after heating step ]/[ fiber length before heating step ]. The draw ratio relates to one heat treatment step and the total draw ratio relates to the draw (build up) achieved in all applied heat treatment steps. For a continuous in-line process, the draw ratio can also be determined based on the speed at which the godet guides the yarn before and after the heat treatment, and is therefore [ godet speed after at least one heating step ]/[ godet speed before at least one heating step ].

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

The process according to the invention is a solvent-based process.

As a solvent for the meta-aramid polymer, concentrated sulfuric acid is used. Preferably, the sulfuric acid has a concentration of at least 85 wt.%, more preferably at least 90 wt.%, still more preferably at least 95 wt.%. Sulfuric acid having a concentration of at least 98% by weight or at least 99% by weight is particularly preferred.

The process produces meta-aramid fibers, preferably multifilament yarns.

The present invention also relates to meta-aramid fibers obtainable by the process of the present invention as disclosed in any of the embodiments above.

Within the scope of the present invention, a fiber is understood to be a flexible material unit having a high aspect ratio (width is defined as the cross-sectional area perpendicular to the length of the fiber). The term fiber includes all the usual types of fibers, such as filaments of particularly unlimited length, filament yarns (both monofilament and multifilament yarns) comprising one or more twisted, co-twisted or untwisted filaments, tows consisting of a collection of a multitude of bundled filaments with hardly any twist applied to them, and the like. If desired, the nearly infinite length of filaments formed during the spinning process can be cut into staple fibers, which can then be processed into spun yarns (spun yarns). Filament yarns may also be cut to even smaller lengths, known as floe.

Furthermore, the filament yarn can also be processed into pulp.

These fiber variants are encompassed by the term "fiber".

Possibly, the multifilament yarn may comprise fibers according to the invention and fibers of other materials. The cross-section of the fibers or filaments of the present invention can be any shape, but is generally circular (circular).

The invention also relates to meta-aramid fibers having a breaking strength of at least 300mN/tex and a content of sulfonic acid groups of at least 0.001 wt.% (mass/mass fiber).

In general, the sulfonic acid group content is at most 1% by weight, preferably at most 0.5% by weight, more preferably at most 0.3% by weight. Alternatively, this can also be expressed in parts per million to give a sulfonic acid group content of >1ppm, preferably 5-300ppm, more preferably 10-100 ppm.

The sulfonic acid groups are formed as a result of using sulfuric acid as a solvent for the meta-aramid. To some extent, aromatic substitution reactions occur on the aryl group such that the hydrogen moiety on the aryl group is replaced by a sulfonic acid group. These groups are preferably neutralized.

By nuclear magnetic resonance analysis (NMR) of as-spun, non-heat treated samples, in particular¹H-NMR measurement of the sulfonic acid group content. Methods for determining the sulfonic acid group content are provided in the examples section.

Alternatively, the sulfur content can be measured to determine the degree of sulfonation of the fiber. In one embodiment, the fibres according to the invention have a sulphur content of at least 0.025 wt.%, preferably at least 0.05 wt.% (based on the weight of the fibres). The sulfur content can be determined for the resulting meta-aramid fiber, including for the heat treated fiber.

The sulfur content can be determined by inductively coupled plasma emission spectroscopy (ICP-OES) as detailed in the examples section.

Sulfonation of the meta-aramid fiber appears to contribute to the flame and fire resistance properties of the meta-aramid fiber. In particular, the fibers of the present invention have an LOI (limiting oxygen index) higher than meta-aramid fibers spun from organic solvents. Preferably, the LOI of the meta-aramid fiber according to the invention is increased by at least 10% compared to a fiber spun from an organic solvent.

LOI is determined according to ASTM D2863 as detailed in the examples section.

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

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

One of the advantages of the meta-aramid fiber of the present invention is the low content of organic solvents.

In one embodiment, the meta-aramid fiber has an organic solvent content of less than 250ppm, preferably less than 100ppm, more preferably less than 50ppm, corresponding to an organic solvent content of less than 0.025 wt.% (based on the weight of the yarn), preferably 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) and DMAc (dimethylacetamide), is less than 250ppm, preferably less than 100ppm, more preferably less than 50 ppm.

Meta-aramid fibers having an organic solvent content of less than 100ppm can be referred to as "substantially free of organic solvent. The very low residual organic solvent may be a result of the solvent used during the polymerization of the meta-aramid.

The organic solvent content can be determined by different methods, depending on the particular organic solvent. Typically, Gas Chromatography (GC), NMR (nuclear magnetic resonance) and MS (mass spectrometry) are suitable for determining the organic solvent content of the fibers, e.g., NMP or DMAc content. In the present invention, the organic solvent content is determined by gas chromatography as detailed in the examples section.

The present invention also relates to a meta-aramid multifilament yarn comprising meta-aramid fibers. The meta-aramid multifilament yarn may be composed of meta-aramid fibers.

Preferably, the meta-aramid multifilament yarn has a breaking tenacity of at least 350mN/tex, more preferably at least 400mN/tex, even more preferably at least 450 mN/tex.

Preferably, the meta-aramid multifilament yarn has an elongation at break of at least 15%, preferably at least 20%, more preferably at least 25%.

In one embodiment, the meta-aramid multifilament yarn has a tenacity at break of at least 350mN/tex and an elongation at break of at least 25%.

The mechanical properties of the meta-aramid yarn were determined according to ASTM D7269-17.

In one embodiment the invention relates to a multifilament yarn, wherein at least 50% of the filaments have a circular cross-section such that the average ratio of [ minimum circumcircle diameter ] to [ maximum inscribed circle diameter ] is at most 1.3, preferably at most 1.1.

The term "minimum circumscribed circle" refers to the smallest circle circumscribing the contour of the cross-section of one filament of the multifilament yarn at least two points and encompassing the entire area of the cross-section of this filament. The term "maximum inscribed circle" refers to the largest circle that inscribes the profile of the cross-section at least two points and is contained within the cross-sectional profile.

The average ratio of [ minimum circumcircle diameter ] to [ maximum inscribed circle diameter ] was determined by preparing a cross section of the multifilament yarn and determining the minimum circumcircle diameter, the maximum inscribed circle diameter and the respective ratios of 50 individual filaments and calculating the average of the ratios.

For a perfectly circular circle, the minimum circumscribed circle and the maximum inscribed circle would overlap, and therefore have the same diameter, to achieve a ratio of 1.0.

A circular cross-section is another advantage of the meta-aramid fiber of the present invention over meta-aramid fibers of the prior art.

The meta-aramid fibers of the present invention have lower porosity than prior art meta-aramid fibers. The fibers of the present invention may have better mechanical properties due to lower porosity.

Particularly advantageous is the combination of properties of the meta-aramid fiber of the present invention. The fibers have a uniform circular cross section, improved flame retardancy, and lower porosity.

The present application also relates to a textile sheet comprising the meta-aramid fiber and/or meta-aramid multifilament yarn of the present invention. The textile sheet may have the form of a woven, knitted or braided (woven) textile sheet or a woven or non-woven textile sheet.

The meta-aramid fibers of the invention are useful in textile applications, such as in textile sheets, including knitted and woven fabrics, or as cords for hose reinforcement, in protective apparel, and particularly in fire resistant applications.

The meta-aramid fibers of the present invention are particularly useful in textile applications where the meta-aramid fibers or fabrics comprising the fibers are in direct contact with the skin.

The invention also relates to protective garments comprising the textile sheet of the invention. The protective garment may be, for example, a glove, a jacket, pants, or a shirt.

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

Examples

Method

1. Mechanical Properties

The meta-aramid multifilament yarn was measured for breaking strength, elongation at break and fracture toughness according to ASTM D7269-17.

2. Content of sulfonic acid group

By passing¹H-NMR measurement of the sulfonic acid group content. 20 mg as-spun, non-heat treated sampleThe product was dissolved in 1 ml DMSO-d6 and 550. mu.l of it was transferred to a 5mm NMR sample tube. Recording at 300K on a Bruker Avance III 400MHz NMR spectrometer equipped with a BBFO-plus 5mm broadband probe¹H NMR spectrum. Spectra were recorded by adding 64 scans together at 30 ° excitation pulse using a pre-scan delay of 6s and an acquisition time of 4 s. The resulting 1H NMR spectrum is quoted by setting the DMSO-d6 residual solvent signal to 2.5 ppm.

The sulfonic acid group content was calculated by the following formula and expressed in meq/kg (mmol/kg):

A_sMPDintegrated (singlet @8.97ppm) [ mol]

A_{meta aramid}(integral 8.86-7.08 ppm- (6 × asppd))/8 [ mol [, mol [% ]]

sMPD＝(A_sMPD*186.1844)[mg]

Meta-aramid ═ a_{meta aramid}*238.2414)[mg]

S ═ 100% (mpd/(mpdd + meta-aramid)) (32.065/186.1844)%

Sulfonic acid group content 106 ═ (S/100)/32.065[ meq/kg ]

3. Sulfur content

The sulfur content can be determined by inductively coupled plasma emission spectroscopy (ICP-OES). To 100 mg of fiber was added 9 ml of concentrated nitric acid (70 wt%). This mixture was exposed to microwave digestion in ultrawave (milestone) until a clear liquid was obtained. The volume was adjusted to 25 ml by adding MilliQ water. The precipitate was removed from the solution by filtration. The clear filtrate was analyzed by ICP-OES in a Perkin Elmer Optima 8300DV instrument. For the determination of the sulfur content, the emission lines at the wavelengths of 181,972nm and 180,669nm were used.

4. Organic solvent content

The organic solvent content was determined by gas chromatography. Approximately 1.0 mg of fiber was collected and heated in an electric furnace to over 500 ℃. The amount of the amide solvent vaporized from the fiber was measured using gas chromatography (Shimadzu Corporation, Ltd., model: GC-2010). Subsequently, the residual solvent concentration in the fiber was calculated using a calibration curve prepared using an amide-based solvent as a standard sample.

5. Relative viscosity

The polymer sample was dried in a vacuum oven at 50 ℃ for 2 hours to remove water. The dried sample was then dissolved in sulfuric acid at room temperature overnight. The flow time of a 0.25% (w/V) sample solution in 96% (w/w) sulfuric acid is then measured in an Ubbelohde viscometer (e.g., Schott AVS370) at 25 ℃. Under the same conditions, the flow time of the solvent was also measured. The relative viscosity was then calculated as the ratio between these two observed flow times.

6. Microscopy

The yarn was embedded in molten paraffin, allowed to stand for about 5 minutes and cured. Thereafter, the embedded sample was cut perpendicularly to the fiber axis with a microtome to obtain a section 5 to 7 μm thick. The sections were then placed on a glass slide, which was heated to melt the paraffin. Thereafter, the molten paraffin was removed with xylene and ethanol. Next, a cross section of the fiber was observed using an optical microscope (manufactured by NIKON CORPORATION; trade name "ECLIPSE" LV100N) and photographed to obtain a cross-sectional photograph. The magnification is selected as desired in the range of 100 to 1000.

7.LOI

Limiting Oxygen Index (LOI) was determined according to ASTM D2863.

168000dtex yarn samples were prepared from each sample by combining the required number of yarns. The yarn was wound on a precision reel with a yarn tension of 5 + -3 mN/tex during winding, based on the nominal linear density of the yarn. The sample was surrounded by a thin copper wire. Each specimen had a length of about 150mm, a width of about 10. + -. 0.5mm and a thickness of about 3. + -. 0.25 mm. The specimen is marked at a distance of about 50mm from the tip to be ignited. Immediately prior to testing, the samples were conditioned at 23. + -. 2 ℃ and 50. + -. 5% relative humidity for at least 88 hours. The test specimens were tested according to ASTM D2863, option a (top-firing).

Example 1

Fibers were spun from a dope containing a meta-aramid polymer (poly (m-phenylene isophthalamide)) having a relative viscosity of 1.55.

The meta-aramid polymer was mixed with 99.8 wt% sulfuric acid to a polymer concentration of 18 w/w% in a Theysohn 20mm twin screw extruder at a temperature of 85 ℃ and a speed of 300rpm to obtain a dope.

The dope was processed into filaments by passing it through a filter at 55 ℃ and through a spinneret at 85 ℃, through an air gap and into a static coagulation bath (under the conditions indicated in table 1). The coagulation bath had a temperature of 3 ℃.

TABLE 1 setup in the spinning Process

The multifilament yarns obtained after coagulation were washed and neutralized by subsequently passing them through a water bath, a 0.4% NaOH bath and again through a water bath. The yarn was dried at 150 ℃ and wound on a bobbin.

The properties of the yarn obtained after drying (also indicated as "as-spun") were determined.

TABLE 2 mechanical Properties of as-spun yarns

Sample (I)	Linear Density (dtex)	Breaking Strength (mN/tex)	Elongation at Break (%)	Fracture toughness (J/g)
					1-1	232	195	56.3	81
1-2	237	197	56.9	83

For sample 1-1, the sulfonic acid group content was determined to be 116 meq/kg.

Sample 1-1 was heat treated in a two-step process. The yarn was unwound from a bobbin and passed through a first oven, in which a draw ratio of 1.6 was applied, and a second oven, which was maintained at a temperature of 333 ℃ and in which the draw ratio was maintained at 1, the draw ratio being defined as the speed after the oven divided by the speed before the oven. The residence time in the two furnaces (based on the velocity between the furnaces) was 18.8 s.

TABLE 3 mechanical Properties of Heat-treated yarns

Example 2

Fibers were spun from a dope comprising a meta-aramid polymer having a relative viscosity of 1.55. The meta-aramid polymer was mixed with 99.8 wt% sulfuric acid to a polymer concentration of 16 wt/wt% or 17.5 wt/wt% in a Theysohn 20mm twin screw extruder at a temperature of 55 deg.C (2-1 and 2-3) or 60 deg.C (2-2 and 2-4) and a speed of 450rpm to obtain a dope.

The dope was processed into filaments by passing it through a filter and through a spinneret, through a 5mm air gap (where a draw ratio of 3.41 was applied) and into a static coagulation bath (under the conditions indicated in table 4). The coagulation bath had a temperature of 5 ℃.

TABLE 4 spin set-up for example 2

The multifilament yarns obtained after coagulation were washed and neutralized by subsequently passing them through a water bath, a 0.25% NaOH bath and again through a water bath. The yarn was dried at 150 ℃ and wound on a bobbin.

TABLE 5 mechanical Properties of as-spun yarns

TABLE 6 relative viscosity and sulfonic acid group content of the fibers

Sample (I)	Relative viscosity	Sulfonic acid group content (meq/kg)
			2-1	1.52	17.6
2-2	1.52	23.5
			2-3	1.48	55.6

Samples 2-3 were heat treated in a two-step process. The yarn was unwound from a bobbin and passed through a first oven in which various draw ratios were applied at a temperature of 305 ℃ and a second oven which was maintained at a temperature of 333 ℃ and in which the draw ratio was maintained at 1, the draw ratio being defined as the speed after the oven divided by the speed before the oven. The residence time in the two furnaces was calculated based on the velocity between the furnaces. The sulfur content of samples 2-3 was determined to be 0.18 wt%.

TABLE 7 Heat treatment and mechanical Properties of meta-aramid yarn treated in a two-step heating Process

Example 3

Fibers were spun from a dope comprising meta-aramid polymer having a relative viscosity of 1.58.

The meta-aramid polymer was mixed with 99.8 wt% sulfuric acid to a polymer concentration of 12 w/w% in a Clextral 53mm twin screw extruder at a temperature of 45 ℃ and a speed of 250rpm to obtain a dope.

The dope was processed into filaments by passing it through a filter at 50 ℃ and a spinneret containing 1000 capillaries of 65 μm diameter at 50 ℃, through an air gap in which the filaments were drawn 2.9 times and into a falling jet coagulation bath (under the conditions indicated in table 1). The coagulation bath had a temperature of 5 ℃.

The multifilament yarns obtained after coagulation were washed and neutralized by subsequently passing them through a water bath, a 0.35% NaOH bath and again through a water bath. The yarn was dried at 160 ℃. The yarn is optionally hot drawn on a heated godet and wound onto a bobbin.

TABLE 8 setup in the spinning Process

The properties of the resulting yarn were determined and are shown in table 9.

TABLE 9 mechanical Properties of the yarns

Example 4

Fibers were spun from a dope comprising a meta-aramid polymer having a relative viscosity of 1.55. The meta-aramid polymer was mixed with 99.8 wt% sulfuric acid to a polymer concentration of 16 wt/wt% in a Theysohn 20mm twin screw extruder at a temperature of 60 ℃ and a speed of 450rpm to obtain a dope. The dope was processed into filaments by passing it through a filter and through a spinneret, through a 5mm air gap (where a draw ratio of 2.08 was applied) and into a dynamic coagulation bath (under the conditions indicated in table 10). The coagulation bath had a temperature of 5 ℃. After the coagulation bath, the yarn was wet drawn between 2 sets of rollers.

TABLE 10 setup in the spinning Process

The multifilament yarns obtained after coagulation and wet drawing were washed and neutralized by subsequently passing them through a water bath, a 0.25% NaOH bath and again through a water bath. The yarn was dried at 150 ℃ and wound on a bobbin.

TABLE 11 mechanical Properties of as-spun yarns

Sample (I)	Linear Density (dtex)	Breaking Strength (mN/tex)	Elongation at Break (%)	Fracture toughness (J/g)
					4-1	480	157	105	122
4-2	430	176	98	124
					4-3	390	196	84	120
4-4	363	202	67	100

Sample 4-2 was heat treated in a two-step process. The yarn was unwound from a bobbin and passed through a first oven in which a draw ratio of 1 was applied at a temperature of 315 c, and a second oven which was maintained at a temperature of 315 c and in which the draw ratio was varied, the draw ratio being defined as the speed after the oven divided by the speed before the oven.

TABLE 12 Heat treatment and mechanical Properties of meta-aramid yarn treated in a two-step heating Process

Example 5

Fibers were spun from a dope comprising a meta-aramid polymer having a relative viscosity of 1.55. The meta-aramid polymer was mixed with 99.8 wt% sulfuric acid to a polymer concentration of 16 wt/wt% in a Theysohn 20mm twin screw extruder at a temperature of 50 ℃ and a speed of 300rpm to obtain a dope. The dope was processed into filaments by passing it through a filter and through a spinneret containing 106 capillaries of 65 μm diameter, maintained at a temperature of about 75 ℃, through a 10mm air gap (where a draw ratio of 1.95 was applied) and into a dynamic coagulation bath. The speed after the coagulation bath was 40 m/min. After the coagulation bath, the yarn was wet drawn 1.4 times between 2 roller sets. The yarns obtained after coagulation and wet drawing were washed and neutralized by subsequently passing them through a water bath, a 0.25% NaOH bath and again through a water bath. The yarn was dried on the roll stack at 220 ℃. The yarn moves to 2 successive sets of rolls, the settings of which are shown in table 13.

TABLE 13 setup during spinning and Hot stretching

The yarn is wound on a spool. The mechanical properties of the yarn are shown in table 14.

TABLE 14 mechanical Properties of the yarns

Sample (I)	Linear Density (dtex)	Breaking Strength (mN/tex)	Elongation at Break (%)
				5-1	199	488	18.6
5-2	197	501	15.6

Example 6 organic solvent content

Determination of commercial Teijin by gas chromatography

B、

And the NMP and DMAc content of meta-aramid yarns from Yantai Tayho Advanced Materials. The results are shown in Table 13. The yarn according to the invention is free of organic solvents.

TABLE 15 organic solvent content

n.d. ═ not determined

Example 7 filament Cross section

Micrographs of embedded bundles of comparative samples 1 to 3 (as used in example 6) and meta-aramid yarns according to the invention were prepared. A micrograph depicting a cross section of the filament is shown in fig. 1. Panel a) shows a cross section of the filaments of comparative sample 1, panel b) is comparative sample 2, panel c) is comparative sample 3 and panel d) is a meta-aramid yarn according to the invention.

From this comparison, it can be seen that the filaments of the present invention have a uniform circular cross-section, while the comparative filaments have an elliptical cross-section or a cross-section that varies in diameter.

Example 8 limiting oxygen index

The LOI of the meta-aramid yarn according to the invention and the commercial meta-aramid yarn were determined. The results are shown in table 14.

TABLE 16 LOI of meta-aramid yarn according to the invention and of commercially available meta-aramid yarn

The data show that the samples according to the invention have a higher LOI value than the comparative samples according to the prior art.

Claims

1. A method of making a fiber comprising meta-aramid having a tenacity of at least 300mN/tex comprising the steps of: preparing a dope comprising meta-aramid and sulfuric acid at a concentration of at least 80 weight percent, and passing the dope through a spinneret into a coagulation bath, wherein the dope has a meta-aramid concentration of at least 10 weight percent.

2. The method according to claim 1, wherein the meta-aramid comprising fiber has a breaking strength of at least 350mN/tex, preferably at least 400mN/tex, even more preferably at least 450 mN/tex.

3. The process according to claim 1 or 2, wherein the dope has a meta-aramid concentration of 10 to 30 wt.%, preferably 12 to 20 wt.%, more preferably 14 to 16 wt.%.

4. The process according to any one of the preceding claims, wherein the meta-aramid is a co-polymer comprising up to 5 mole% of aromatic moieties other than meta-phenylene (m-phenylene isophthalamide).

5. The process according to any one of the preceding claims, wherein the dope is prepared by mixing meta-aramid and sulfuric acid.

6. The process according to any one of the preceding claims, wherein the spinning dope is prepared at a temperature of 30 to 90 ℃.

7. The process according to any one of the preceding claims, wherein the spinning dope is passed through a gaseous medium after exiting the spinneret and before entering the coagulation bath.

8. The process according to claim 7, wherein the dope is passed through a gaseous medium having a length of 2 to 20mm, preferably 3 to 15mm, more preferably 5 to 10 mm.

9. The process according to any one of the preceding claims, wherein the sulfuric acid has a concentration of at least 85 wt.%, preferably at least 90 wt.%, more preferably at least 95 wt.%.

10. The method according to any one of the preceding claims, wherein the fibres are heated in at least one heating step to a temperature in the range of 250 to 400 ℃, preferably in the range of 280 to 350 ℃, more preferably in the range of 300 to 320 ℃, optionally followed by a further heating step at a temperature in the range of 250 to 400 ℃, preferably in the range of 280 to 350 ℃, more preferably in the range of 300 to 320 ℃.

11. Meta-aramid fiber having a breaking strength of at least 300mN/tex obtainable by the process according to any one of claims 1 to 10.

12. Meta-aramid fiber having a breaking strength of at least 300mN/tex and a sulfonic acid group content of at least 0.001 wt.%.

13. Meta-aramid fiber according to claim 11 or 12 having a breaking strength of at least 350mN/tex, preferably at least 400mN/tex, even more preferably at least 450 mN/tex.

14. Meta-aramid fiber according to any of claims 11 to 13 having an organic solvent content of less than 250ppm, preferably less than 100ppm, more preferably less than 50 ppm.

15. A meta-aramid multifilament yarn comprising the meta-aramid fiber of any one of claims 11 to 14.

16. Meta-aramid multifilament yarn according to claim 15 wherein at least 50% of the filaments have a circular cross-section such that the average ratio of [ smallest circumscribed circle diameter ] to [ largest inscribed circle diameter ] is at most 1.3, preferably at most 1.1.

17. A textile sheet comprising the meta-aramid fiber of any one of claims 11 to 14 and/or the meta-aramid multifilament yarn of claim 15 or 16, preferably a knitted, woven or non-woven textile sheet.

18. A protective garment comprising the textile sheet of claim 17.