JPS5922802B2 - Manufacturing method of flame-retardant nylon 6 fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing flame-retardant nylon 6 fibers.

Polyamides, especially nylon 6, are widely used as fibers and other molding materials because of their excellent mechanical properties, good dyeability, and beautiful appearance.

However, nylon 6 has the disadvantage of being easily combustible, which limits its use. Conventionally, as a method of imparting flame retardancy to nylon 6 fibers, a method of treating the fiber surface with a flame retardant such as thiourea is known. However, in order to obtain a sufficient flame retardant effect with this method, it is necessary to increase the amount of flame retardant applied, which not only significantly impairs the appearance and texture of the product, but also reduces the durability of the flame retardant effect. It has the disadvantage of being scarce. As a method of eliminating such drawbacks, various attempts have been made to add flame retardants internally to nylon 6 before forming the nylon 6.

However, the flame retardants proposed in the past do not have a sufficient flame retardant effect on nylon 6, and a large amount needs to be added to improve the effect. Moreover, since many flame retardants have reactivity with nylon 6, adding a large amount of flame retardants may cause undesirable phenomena such as significant decomposition, foaming, gelation, and coloring of nylon 6, which is inherent to nylon 6. The physical properties and commercial value of the product are significantly impaired. For example, Tokuko Sho 47-385
Publication No. 46 describes a nuclear brominated diphenyl compound as a flame retardant for polyamide, and states that this compound has excellent heat resistance and will hardly cause any deterioration of the polyamide even when mixed with polyamide and heated. According to additional experiments conducted by the present inventors, when nylon 6 is melt-spun with 10% by weight of hexaprom diphenyl ether among nuclear brominated diphenyl compounds, the deterioration of nylon 6 is caused by other halogens. Although the amount was certainly lower than that of the compound, the color tone was yellowish compared to that of the terminally modified nylon 6, and the flame retardancy of the resulting yarn was also insufficient. On the other hand, as a flame retardant, it is used in extremely large amounts (15 to 30% by weight).
) Nylon 6 blended with a nuclear halogenated aromatic compound as described above exhibits relatively good flame retardancy, but this method impairs the inherent physical properties and commercial value of nylon 6, and also increases costs. . Furthermore, this type of nylon 6 has a very serious defect in that it generates a large amount of toxic halogen gas when it is burned. In order to compensate for these drawbacks, various flame retardant aids such as metal oxides have been studied in order to reduce the amount of halogen flame retardant blended and to provide higher flame retardancy.

For example, antimony oxide is well known as a flame retardant aid for halogen flame retardants. However, with this method, nylon 6
By adding several percent or more of antimony oxide, which is insoluble in
This is a major technical obstacle in fiberization. That is, antimony oxide aggregates and causes clogging of the melt spinneret pack, or forms knots in the yarn, causing frequent spun yarn breakage and drawn yarn breakage, making fiberization substantially difficult.
As mentioned above, the conventionally known flame retardants for nylon 6 have various drawbacks, and the degree of difficulty increases dramatically when converting them into fibers, so no examples have been put into practical use yet. is the current situation.

The purpose of the present invention is to overcome the various deficiencies of the prior art and to provide a material that exhibits excellent flame retardant performance by incorporating a small amount of flame retardant without impairing the excellent physical properties inherent to nylon 6. Another object of the present invention is to provide a method for producing nylon 6 fibers industrially easily and at low cost.

That is, in the present invention, ε-caprolactam is 0.7 to 1.2.
Hexabrombenzene, pentapromtoluene, pentapromethylbenzene, and pentaprom were added to nylon 6 chips with a solution viscosity of 1.7 to 2.1, which was obtained by adding 5 mol % of a viscosity modifier, polymerizing, washing with water, and drying. Nylon 6 fiber from which at least one nuclear brominated aromatic compound selected from the group consisting of benzene, tribromoacetanilide, diphenyl ether compounds having 4 to 10 bromine atoms, and biphenyl compounds having 4 to 10 bromine atoms can be obtained. against 0.
The present invention provides a method for producing flame-retardant nylon 6 fibers by adding and mixing 5 to 15% by weight, melt spinning at a temperature of 225 to 245°C, and then hot drawing at a temperature of 50 to 140°C. As a viscosity modifier,
Examples include carboxylic acids such as acetic acid, caproic acid, benzoic acid, adipic acid, and sebacic acid, and amines such as stearylamine, ethylenediamine, and hexamethylenediamine. Among them, acetic acid is preferred from the viewpoint of cost and operability. The viscosity modifier is 0.0% per ε-caprolactam.
7-1.25 mol%, preferably 0.8-]. 0 mol%
After adding and polymerizing in the usual manner, washing with water and drying, the viscosity of the solution was 1/2. 7-2.1, preferably]. 9 to 2.0 nylon 6 chips are manufactured.

The viscosity of the solution depends on the polymerization conditions, i.e., polymerization temperature, time, pressure,
It can be easily adjusted by adjusting the presence or absence of a stirrer.

When the amount of viscosity modifier added is less than 0.7 mol%, the solution viscosity is 2.
．． If it is higher than 1, it is difficult to spin at a temperature of 245°C or lower, and if the spinning temperature is raised above 245°C, yarn is obtained, but it is colored and the flame retardant performance is insufficient. In addition, when the amount added is less than 0.7 mol% and the solution viscosity is 1.7 to 2.1, the flame retardant performance is slightly improved, but it is still insufficient, and it is difficult to extrude nylon 6 at the end of polymerization. It is. Further, if the amount added is less than 0.7 mol % and the solution viscosity is less than 1.7, extrusion of nylon 6 at the end of polymerization becomes almost impossible.

This is probably because the content of water-soluble components in the polymer is higher than usual (10% or less), so the melt viscosity of the polymer becomes even lower. Furthermore, the spinnability and stretchability of the obtained polymer are also poor. Addition amount of viscosity modifier is 1.25 mol%
If the amount is more, the viscosity will be difficult to increase and it will be difficult to obtain nylon 6 with a solution viscosity of 1.7 or more.

Furthermore, if the solution viscosity is less than 1.7, it will be difficult to extrude nylon 6 at the end of polymerization, and the spinnability and stretchability of the obtained polymer will also be poor. Addition amount of viscosity modifier is 0.7
Even if the solution viscosity is 1.25 mol%, if the solution viscosity is higher than 2.1, the flame retardant performance of the resulting nylon 6 fibers will not be sufficient, and if the solution viscosity is less than 1.7, polymerization will occur as described above. Extrusion at the end becomes difficult, and the spinnability and stretchability of the obtained polymer are also poor.

The thus obtained nylon 6 chips were treated with hexabromobenzene, pentapromotoluene, pentapromoethylbenzene, pentapromobenzene, tribromoacetanilide, a diphenyl ether compound having 4 to 10 bromine atoms, and 4 to 10 bromine atoms, as described above. At least one nuclear brominated aromatic compound selected from the group consisting of 10 biphenyl compounds is added and mixed and subjected to melt spinning. Enyl ether, hexaprombiphenyl and tribromoacetanilide are preferred;
Particularly preferred is pentapromoethylbenzene.

The amount of the nuclear brominated aromatic compound added can be appropriately selected depending on the intended use of the resulting nylon 6 fiber.

Generally, the flame retardant performance increases as the amount added increases, but it must be added within a range that does not adversely affect the workability and operability during spinning and drawing, as well as the quality of textile products. In contrast, the amount is 0.5 to 15% by weight, preferably 1 to 7% by weight, and more preferably 1 to 4% by weight.

If the amount added is less than 0.5% by weight, the flame retardant performance will not be sufficient, and if it is more than 15% by weight, the spinnability and stretchability will decrease, the color tone of the product yarn will deteriorate, and the product yarn will burn. This is not desirable as a large amount of halogen gas is generated.
In addition, in the present invention, the nuclear brominated aromatic compound is added to the nylon 6 chips and used by mixing.If added before, during, or at the end of the polymerization of the nylon 6, the nylon 6 Undesirable phenomena such as coloring of the polymer may occur.

The method of adding and mixing the nuclear brominated aromatic compound to the nylon 6 chips is not particularly limited.

For example, the specified nylon 6 chips and the compound may be placed in a rotating drum and mixed, or nylon 6 may be mixed using an automatic measuring and mixing device.
A mixture obtained by measuring and mixing the chips and the compound can be melt-kneaded using a known extruder or the like and then spun. It is also possible to prepare a master chip by previously mixing and melting the compound in nylon 6 at a high concentration, and then mixing and diluting ordinary nylon 6 chips to a predetermined concentration and spinning. In either method, it is desirable to mix until the mixture is sufficiently uniform. If the mixing is insufficient, problems such as yarn breakage will occur during the melt spinning process, and the quality of the resulting nylon 6 fibers will also be non-uniform. Therefore, the total time for mixing the nylon 6 and the compound according to the present invention in a molten state is 5 minutes including the melt spinning process.
Melt mixing times of minutes or more are desired. However, if the mixing time is too long, changes in the physical properties of nylon 6 will increase to an extent that cannot be ignored, so it is preferable to set the melt mixing time to a maximum of 45 minutes. As the melt spinning method, a conventionally known melt spinning method can be adopted.

That is, for example, there is a method in which a mixture of the predetermined nylon 6 chips and the nuclear brominated aromatic compound is melted in an extruder, measured by a gear pump, and then extruded from a spinneret to form a thread and wind it up. At this time, it is also possible to melt the mixture, knead it in a kneading device such as a static mixer (for example, 1SG mixer manufactured by Tokushu Kika Kogyo Co., Ltd.), and then spin it. The spinning temperature of unmodified nylon 6 threads that is normally adopted is 255 to 280°C, but in the case of the present invention, it is necessary to spin at a temperature of 225 to 245°C, preferably 230 to 240°C. When the spinning temperature is higher than 245° C., the coloring of the spun nylon 6 yarn becomes noticeable, and yarn breakage occurs frequently during the spinning and drawing steps, reducing operability. On the other hand, if the temperature is lower than 225°C, spinning may not be possible, or even if spinning is possible, yarn breakage occurs frequently during the spinning and drawing steps. 225-245 when industrially manufacturing normal nylon 6 fibers
Spinning at a low temperature such as 225 to 245 degrees Celsius is not preferable because it causes frequent yarn breakage and reduces operability; however, in the method of the present invention, melt spinning at a temperature of 225 to 245 degrees Celsius ensures stable operation. It is an indispensable requirement.

After melt spinning by the above method, the obtained undrawn nylon 6 yarn is hot stretched at a draw ratio of 1.1 or more, preferably 3.0 or more.

Stretching temperature is 50-140°C, preferably 70-110°C
It is. If cold drawing is carried out, drawn yarn breakage occurs frequently and the quality becomes unstable, which is undesirable. Examples of hot stretching methods include hot pin stretching and hot roller stretching, but hot pin stretching is particularly preferred. According to the method of the present invention, excellent flame retardancy can be achieved very easily, and nylon 6
It is possible to obtain flame-retardant nylon 6 fiber without any deterioration of its original excellent properties.

In the present invention, since the specific nylon 6 mentioned above is used, the amount of halogen compound added may be much smaller than in the past, and therefore it is advantageous in terms of cost. Furthermore, by employing a specific spinning/drawing method, operability in the spinning/drawing process is good, and yarns with satisfactory light resistance, whiteness, etc. can be obtained.

Furthermore, it has become possible to greatly reduce the generation of toxic halogen gases during combustion of the nylon 6 fibers. In the method of the present invention, a third component such as a matting agent, an antioxidant, a heat stabilizer, a light stabilizer, an antistatic agent, a coloring agent, or a fluorescent whitening agent is added to the nylon 6 chips obtained during polymerization of nylon 6. There is no problem with adding it.

The present invention will be explained in detail below with reference to Examples.

In the examples, relative viscosity (ηRel) is shown as a value measured using an Ostwald viscometer at 25° C. after dissolving nylon 6 to a concentration of 1% concentrated sulfuric acid. Flame retardancy was evaluated using the limiting oxygen index (hereinafter L.O.I.) according to the following measurement method.
．． ) and the number of times of flame contact using the 45 element coil method. (a) L. O. l. The measurement method for cloth samples is JIS-K-7201-1972A method-2.
L. according to No. O. l. was measured.

The yarn sample is 0.5t in weight and 10 in length from the fiber to be tested.
0111 A twisted rod with a twist count of 10 was prepared, a wire was inserted into the center, and the rod was held vertically at the center bottom of the combustion cylinder, and measurements were made in the same manner. (b) Method for measuring the number of times of flame contact using the 45-meter coil method The number of times of flame contact of the cloth samples was measured according to the JIS-L-1091-1971D method.

The yarn sample is 1 ton in weight and 100 m in length from the fiber to be tested.
71L1 Create a twisted rod with a twist number of 10, and make this twisted rod 0.5
mW! Diameter 1071Lm1 made of φ stainless steel wire
Coil pitch 2m7! Insert it into the coil of L1 length 150m7IL and hold it at a 45 degree angle, the length of the flame will be 45m7!
Use the L micro burner to apply flame to the lower end for 10 seconds to burn it, and when the flame goes out, shift the position and apply flame to the lower end again in the same way. In this way, the number of times of flame contact until 10 cm of the twisted rod was completely burned out was measured, and the evaluation criteria for O coloration, which was expressed as the average value of the five times, were as follows.

That is, the colored state of the fibers was visually evaluated as follows. ◎
= Not colored at all, same as unmodified nylon 6 ○ = Slightly colored, but close to unmodified nylon 6.

△=Coloration is clearly observed when compared with undenatured nylon 6.

x = Significant coloring compared to unmodified nylon 6.

However, if the item is at an intermediate stage, an intermediate expression such as Δ× is used. Further, evaluation of spinnability and stretchability was carried out as follows.

○ = Fewer thread breakages like unmodified nylon 6, less than one thread breakage per 1 million m.

Δ = Yarn breaks approximately 5 to 20 times per million meters.

× = Yarn breakage occurred frequently, and satisfactory spun yarn and drawn yarn could not be obtained.

However, in the case of an intermediate stage, an intermediate expression such as OΔ was also used.

Example 1 100 parts of ε-caprolactam, 4 parts of water, 0.42 parts of acetic acid (0.8 mol%/lactam), and 0.3 parts of titanium oxide were placed in an autoclave and sealed under a nitrogen atmosphere at 260°C.
After maintaining the pressure for 3 hours, the pressure was gradually released over an hour to return to normal pressure, and then the pressure was gradually reduced over a period of 3 hours to a vacuum level of 30.
0m! It was made to reach Hf.

The resulting polymer was then discharged and treated with boiling water for 6 hours after cutting to remove the hot water extract, producing nylon 6 semital chips having a solution viscosity of 1.95 after drying.
This nylon 6 is designated as sample A. Next, in the same manner, a nylon 6 semidal tip having a solution viscosity of 2.70 after drying was produced using 0.13 parts of acetic acid (0.25 mol %/lactam).

This nylon 6 is designated as test phase B. These six nylon samples A and B were adjusted to have a moisture content of 0.08% by weight, and after adding 4% by weight of various compounds listed in Table 1 and thoroughly mixing, they were spun using an ordinary extruder type 1 spinning machine. Output temperature 240℃
, and melt-spun at a spinning speed of 600 m/min.

Next, hot stretching was performed at a magnification of 3.4 times and a pin temperature of 80°C.
A 70 denier fiber consisting of 8 filaments was obtained. The flammability test of the obtained fibers was conducted by L. O. l. measurement and 4
This was done by measuring the number of flame contacts using the 5-ill method. Also,
The spinnability and colorability were also evaluated as described above. The results are shown in Table 1.〇Test phase B nylon 6 was used/F6.
In the case of No. 7 to No. 11, when the spinning temperature was raised to 260° C., the spinnability improved, but the yarn became colored, and the flame retardant performance remained low without any improvement.

Example 2 ε-caprolactam 100 parts, water 4 parts, titanium oxide 1.
5 parts and a predetermined amount of acetic acid were placed in an autoclave, sealed under a nitrogen atmosphere, kept at 260°C for 3 hours, and then gradually depressurized over 1 hour to return to normal pressure, then heated under a nitrogen atmosphere for 26 hours.
Polymerization is carried out at 0°C for a predetermined period of time.

During this time, stirring was continued using a stirrer at a speed of 40 revolutions/minute. After completion of polymerization, the polymer was discharged, and after cutting, it was treated with boiling water for 6 hours to remove the hot water extract, thereby producing various types of nylon 6 full-dull chips having predetermined viscosity after drying.
The moisture content of these chips was adjusted to 0.09% by weight, 4% by weight of hexaprom diphenyl ether was added, and after thorough mixing, a spinning temperature of 235 °C (partially (2600C), spinning speed 60
Melt spinning was performed at 0 m/min. Next, hot stretching was carried out at a magnification of 3.4 times and a pin temperature of 90°C, and 40
Obtained denier fiber. The combustibility, colorability and spinnability of the obtained fibers were similarly evaluated. Second result
Shown in the table. In Table 2, the amount of acetic acid added is expressed in mol% relative to the lactam. Example of adding 2 mol% of acetic acid (
7f616), it was not possible to obtain a satisfactory polymer even at the end of polymerization.

Example 3 ε-100 parts of caprolactam, 4 parts of water, 1.
5 parts of acetic acid and 0.48 parts of acetic acid (0.9 mol%/lactam) were placed in an autoclave and sealed under a nitrogen atmosphere.
After keeping the temperature at 3 hours, the pressure was gradually released over 1 hour to return to normal pressure, and then normal pressure polymerization was carried out at 260° C. for 3 hours under a nitrogen stream.

During this time, stirring was continued at a speed of 40 revolutions/minute using a stirrer. After the polymerization was completed, the polymer was discharged, and after cutting, it was treated with boiling water for 6 hours to remove the hot water extract, producing nano-40-6 full dal chips having a solution viscosity of 1.95 after drying.
The moisture content of the chips was adjusted to 0.08% by weight, a predetermined amount of hexaprom diphenyl ether was added as shown in Table 3, and after thorough mixing, the chips were spun at a spinning temperature of 235°C using a conventional extruder type 1 spinning machine. Melt spinning was carried out at a speed of 650 m/min. Next, hot roller stretching was performed at a magnification of 3.3 times and a roller temperature of 80° C. to obtain a 40 denier fiber consisting of 10 filaments. The combustibility, colorability and spinnability of the obtained fibers were similarly evaluated. The results are shown in Table 3.

Further, when 4% by weight of hexaprom diphenyl ether was added during polymerization, coloring was extremely undesirable.

Example 4 The solution viscosity after washing with water and drying was 1.9 in the same manner as in Example 3.
A nylon 6 full-dull chip of No. 5 was manufactured.

The moisture content of the chips was adjusted to 0.08% by weight, 3% by weight of pentapromethylbenzene was added, and after thorough mixing, the chips were melt-spun using a conventional extruder type spinning machine at a spinning speed of 600 m/min and at a predetermined spinning temperature. . Next, the magnification is 3.4x,
Hot roller stretching was carried out at a roller temperature of 80° C. to obtain a 40 denier fiber consisting of 10 filaments. The spinnability, colorability, and flame retardant performance of the obtained fibers were evaluated in the same manner. The results are shown in Table 4.

In an example where the spinning temperature was 270°C (/F6.7), the spinnability was very poor and a satisfactory yarn could not be obtained.

Example 5 100 parts of ε-caprolactam, 4 parts of water, 0.3 parts of titanium oxide, and 0.48 parts of acetic acid (0.9 mol%/lactam) were placed in an autoclave, sealed under a nitrogen atmosphere, and heated to 260°C for 3 After maintaining the pressure for an hour, the pressure was gradually released to return to normal pressure over a period of one hour, and then the pressure was gradually reduced over a period of three hours to reach a trueness of 400 mmH7.

The resulting polymer was then discharged and treated with boiling water for 6 hours after cutting to remove the hot water extract, and the solution viscosity after drying was . 90 nylon 6 semi-dual chips were manufactured.
The moisture content of the chips was adjusted to 0.08% by weight, 4% by weight of hexaprombiphenyl was added, and after thorough mixing, the chips were spun at a speed of 600 m/min using a conventional extruder type 1 spinning machine.
Melt spinning was carried out at a spinning temperature of 235°C. The obtained undrawn yarn is designated as A.

Separately, nylon 6 semidal chips having a solution viscosity of 2.72 after drying were produced by polymerization and water washing in the same manner except that the amount of acetic acid added was 0.13 parts (0.25 mol %/lactam).

The moisture content of this chip was adjusted to 0.08% by weight, and it was melt-spun using the same extruder type spinning machine at a spinning speed of 600 m/min and a spinning temperature of 260°C. The obtained undrawn yarn is designated as B. Using the obtained undrawn yarns A and B, the drawing ratio was 3.4.
Stretching was carried out by various methods as shown in Table 5. Table 5 shows the measurement results of stretchability and unevenness (R%) of the drawn yarn. The yarn unevenness (R%) was measured using an evenness tester (manufactured by Keizoku Kogyo Co., Ltd.).

When cold drawing was performed using the undrawn yarn A according to the present invention (/F69, A61O), the drawability was poor regardless of the presence or absence of pins, and the R% value was also high.

A high R% value means that the thickness of the yarn is non-uniform, and a partially unstretched state is expected, which is undesirable as it causes problems such as dyeing spots. A6l~., which was hot-stretched using undrawn yarn A. In S8, the stretchability and R% value are relatively good for both hot pin stretching and hot roller single stretching. However, when the stretching temperature is 40°C (F67), the R(Fb value tends to increase, and the stretchability decreases somewhat, which is not preferable. On the other hand, when the stretching temperature is 150°C (/F67), the R(Fb value is good) However, this is not preferable because the drawability becomes poor, and the threads tend to fuse together, resulting in frequent thread breakage at the start of drawing.When undrawn thread B, which is a normal nylon 6 thread, is used (rotation 1
1) is cold-stretched, which is generally practiced, and has sufficiently good stretchability and R% value. Example 6 Polymerization was carried out in the same manner as in Example 3 except that 0.42 parts of acetic acid (0.8 mol%/lactam) was used to produce nylon 6-fila chips having a solution viscosity of 2.00 after drying. .

The moisture content of the chips was adjusted to 0.08% by weight, and 12% by weight of pentapromethylbenzene was thoroughly mixed in advance, followed by melt-kneading at 235° C. using a 3-screw extruder to obtain master chips. Next, the master chips and the above-mentioned full-dull chips were thoroughly mixed so that the content of pentapromethylbenzene was 3% by weight, and melt spinning was carried out using an extruder type spinning machine at a spinning temperature of 235°C and a spinning speed of 600 m/min. I did it.

Subsequently, hot drawing was carried out using a hot pin at a drawing ratio of 3.3 times to obtain a 40 denier fiber consisting of 10 filaments. The strength of this fiber was 4.7, and the elongation at r/d1 was 35%, which was not much different from ordinary unmodified nylon 6 yarn. Using this fiber, normal diameter adjustment and knitting were performed to obtain a tricot sample.

Unmodified nylon 6 with no problems in diameter adjustment or workability during knitting
It was the same as in the case of . The tricot sample was also subjected to conventional scouring and dyeing. Dyeing was carried out by both dispersion dyeing and acid dyeing, and the dyeability was good, with no major difference from unmodified nylon 6. 10 of the obtained dyed tricot cloth
After washing the sample cloth several times, the number of times it was exposed to flame was measured using the JIS method.

As a result, the tricot cloth according to the present invention was exposed to flame four times, and its flame retardant performance was good. On the other hand, ordinary unmodified nylon 6 tricot cloth was used only once. As described above, the flame-retardant nylon 6 fiber according to the present invention has no particular problems in post-processing steps such as diameter adjustment, knitting, and dyeing, and the flame-retardant performance of the obtained product fabric is also good. It was found that the washing resistance was also excellent.

Example 7 ε-caprolactam 100 parts, water 4 parts, titanium oxide 0.
Various types of nylon 6 semi-dual chips were obtained in the same manner as in Example 2, using predetermined amounts of various viscosity modifiers as shown in Table 6 in 3 parts.

Claims (1)

[Claims] 1 0.7 to 1.25 mol% based on ε-caprolactam
Hexabromobenzene, pentabromotoluene, pentabromoethylbenzene, pentabromobenzene, tri- 0.5 per nylon 6 fiber from which at least one nuclear brominated aromatic compound selected from the group consisting of bromoacetanilide, diphenyl ether compounds with 4 to 10 bromine atoms, and biphenyl compounds with 4 to 10 bromine atoms can be obtained. ~15
A method for producing flame-retardant nylon 6 fibers by adding and mixing % by weight, melt spinning at a temperature of 225 to 245°C, and then hot stretching at a temperature of 50 to 140°C. 2. The manufacturing method according to claim 1, wherein the viscosity modifier is acetic acid. 3 The amount of the viscosity modifier added to ε-caprolactam is 0.8 to 1.0 mol%, and the solution viscosity of the nylon 6 chips obtained by washing and drying with water is 1.90 to 2.0. The manufacturing method according to scope 1 or 2. 4. The production method according to claim 1, wherein the nuclear brominated aromatic compound is at least one compound selected from pentabromoethylbenzene, hexabromo diphenyl ether, hexabromo biphenyl, and tribromoacetanilide. 5. The production method according to claim 4, wherein the nuclear brominated aromatic compound is pentabromoethylbenzene. 6. Claim 1, wherein the amount of the nuclear brominated aromatic compound added to the obtained nylon 6 fiber is 1 to 7% by weight.
5. The manufacturing method according to item 4, item 5, or item 5. 7. The manufacturing method according to claim 1, wherein the melt spinning temperature is 230 to 240°C. 8. The manufacturing method according to claim 1, wherein the hot stretching temperature is 70 to 110°C. 9. The manufacturing method according to claim 1 or 8, wherein the hot stretching is hot pin stretching or hot roller stretching. 10. The manufacturing method according to claim 1, wherein the stretching ratio by hot stretching is 1.1 or more.