METHOD FOR THE PREPARATION OF A POLYAMIDE 6 COPOLYMER AND FILAMENTS, FLAME RETARDANT POLYAMIDE 6 COPOLYMER AND COPOLYMER FILAMENTS

Abstract

The invention relates to a method for the preparation of a polyamide 6 copolymer, characterised in that a copolymerization reaction is carried out between: o at least one caprolactam of formula (I): o at least one caprolactam, named substituted caprolactam, in which at least one of the carbon atoms is covalently linked to at least one A moiety, said A moiety being selected from the group formed of: # moieties comprising at least one group of formula: (A) # moieties comprising at least one group of formula: (B) # moieties comprising at least one group of formula: (C) The invention also relates to a polyamide 6, to polyamide 6 filaments and filaments yarns.

##STR00001##

Claims

1. Method for the preparation of a polyamide 6 copolymer, wherein a copolymerization reaction is carried out between: at least one caprolactam of formula (I): ##STR00029## at least one caprolactam, named substituted caprolactam, having a cycle formed of six carbon atoms and one nitrogen atom in which one of said carbon atoms, named C.sub.2, is linked by a double bond to an oxygen atom and at least one of said carbon atoms that is distinct from said C.sub.2 is covalently linked to at least one A moiety, said A moiety being selected from the group formed of: moieties comprising at least one group of formula (II): ##STR00030## moieties comprising at least one group of formula (III): ##STR00031## moieties comprising at least one group of formula (IV): ##STR00032##

2. Method according to claim 1, wherein said A moiety is selected from the group formed of phosphonates, phosphinates, phosphonamidates, phosphazenes and mixtures thereof.

3. Method according to claim 1, wherein said substituted caprolactam is of formula (V): ##STR00033## in which: C2, C3, C4, C5, C6, C7 designate carbon atoms, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10 are groups so that at least one of R1 to R10 comprises said A moiety and the others R1 to R10 are chosen from the group formed of H, hydroxy group (OH), nitrile, halogens, alkyl groups containing less than 5 carbon atoms, aryls containing less than 10 carbon atoms, halocarbons containing less than 5 carbon atoms, alkoxy containing less than 5 carbon atoms and hydrocarbons containing less than three oxygen atoms and less than 5 carbon atoms.

4. Method according to claim 1, wherein said substituted caprolactam is of formula (VII): ##STR00034##

5. Method according to claim 1, wherein prior to carrying out said copolymerization reaction, said substituted caprolactam is prepared from an α-amino-ε-caprolactam.

6. Method according to claim 1, wherein said copolymerization reaction is carried out in argon atmosphere.

7. Method according to claim 1, wherein copolymerization reaction is carried out at a temperature between 170° C. and 300° C.

8. Method according to claim 1, wherein said copolymerization reaction is carried out with 80% to 95% by weight of caprolactam of formula (I) and 5% to 20% of said substituted caprolactam compared to the total mass of said caprolactam of formula (I) and said substituted caprolactam.

9. Method according to claim 1, wherein said copolymerization reaction is carried out with water as an initiator of said copolymerization reaction.

10. Polyamide 6 copolymer containing at least 8% by weight of repeating units, named polyamide 6 substituted repeating units, of formula: ##STR00035## in which n′ designates the number of said substituted repeating units in said polyamide 6 copolymer, compared to the total weight of said polyamide 6 copolymer, as determined by inductively coupled plasma mass spectrometry said A moiety being selected from the group formed of: moieties comprising at least one group of formula (II): ##STR00036## moieties comprising at least one group of formula (III): ##STR00037## moieties comprising at least one group of formula (IV): ##STR00038##

11. Polyamide 6 copolymer according to claim 10, wherein it is formed of filaments.

12. Polyamide 6 copolymer according to claim 10, wherein it is formed of filaments yarns.

13. Method for the preparation of filaments of a polyamide 6 copolymer, wherein: a polyamide 6 copolymer containing at least 8% by weight of repeating units, named polyamide 6 substituted repeating units, of formula: ##STR00039## in which n′ designates the number of said substituted repeating units in said polyamide 6 copolymer, compared to the total weight of said polyamide 6 copolymer, a s determined by inductively coupled plasma mass spectrometry said A moiety being selected from the group formed of: moieties comprising at least one group of formula (II): ##STR00040## moieties comprising at least one group of formula (III): ##STR00041## moieties comprising at least one group of formula (IV): ##STR00042## is selected, a filament formation step chosen from the group formed of melt-spinning and extrusion of said polyamide 6 copolymer is carried out.

14. Composition comprising a polyamide 6 copolymer according to claim 10 and at least one additive chosen from the group formed of 6H-dibenz[c,e][1,2]oxaphosphorin,6′6-(1,2-phenethyl)bis-,6′6-dioxide of formula: ##STR00043## and 6H-dibenz[c,e][1,2]oxaphosphorin,6′6-(1,2-naphthalene)bis-,6′6-dioxide of formula: ##STR00044##

Description

[0077] Other aims, features and advantages of the invention will become apparent upon reading the following description given by way of non-limiting example and which makes reference to the attached figures in which:

[0078] FIG. 1 is a .sup.1H NMR spectrum of DOPO-CL phosphonamidate made in CDCl.sub.3 on 300 MHz NMR spectrometer,

[0079] FIG. 2 is a thermogravimetric curve of DOPO-CL phosphonamidate FR monomer in argon atmosphere,

[0080] FIG. 3 is a sheet specimen of a FR PA6 copolymer material in accordance with the invention before (A) and after (B and C) the UL94 standard test,

[0081] FIG. 4 shows photographs of FR PA6 copolymer in accordance with the invention in the form of multifilament yarn (E) and knit-fabric (F).

[0082] NMR spectrum of FIG. 1 was obtained with a Varian® NMR spectrometer sold under the name Unity Inova 300® by LABX® (Midland, Canada). FIG. 1 shows the intensity of the signal as a function of the chemical shift in ppm. Chemical shift identification of NMR spectrum of FIG. 1 is: 1H-NMR (CDCl.sub.3, 300 MHz): 7.85-7.95 ppm (m, 3H); 7.55-7.67 ppm (t, 1H); 7.37-7.5 ppm (m, 1H); 7.27-7.37 ppm (m, 1H); 7.10-7.25 ppm (m, 3H); 4.67 ppm (d, 1H); 4.60 ppm (d, 1H); 4.34 ppm (m, 2H); 4.31 ppm (m, 2H); 3.13 ppm (m, 2H); 2.12 ppm (s, 2H); 2.08 ppm (s, 2H); 1.93 ppm (m, 1H); 1.88 ppm (m, 1H); 1.73 ppm (m, 1H); 1.69 ppm (m, 1H); 1.65 ppm (m, 1H); 1.60 ppm (m, 1H); 1.56 ppm (m, 1H); 1.49 ppm (m, 1H); 1.26 ppm (m, 1H); 1.25 ppm (m, 1H), in which “s” is for singlet, “d” is for doublet, “t” is for triplet and “m” is for multiplet.

[0083] FIG. 2 is a curve obtained by thermal gravimetric analysis (TGA) of DOPO-CL phosphonamidate FR monomer in argon atmosphere. FIG. 2 shows the mass percentage (%) as a function of the temperature in ° C. (0° C. to 800° C.).

[0084] In accordance with this invention, flame retardant polyamide 6 thin films and sheets, fibres and textiles, can be prepared from flame retardant polyamide 6 copolymers obtained in ring-opening (hydrolytic or anionic) copolymerization reaction of ε-caprolactam (CL) and flame-retardant modified ε-caprolactam (FR-CL). Bonding type of flame retardant functionality on the caprolactam ring is responsible for obtaining various FR-CL co-monomers: caprolactam based phosphates, phosphonates, phosphinates, phosphonamidates and other phosphorous based molecules. Including 10 wt % of FR-CL phosphonamidate in the copolymerisation process, where phosphorous content in the copolymerisation mixture is between 0.01 and 3%, enables obtaining flame retardant polyamide 6 copolymer with relative viscosity of 2.0 Pa.Math.s (according to DIN 51562 of year 1999). Obtained copolymer is suitable for extrusion and melt-spinning process for production of filament yarns, which can be knitted in fabrics. In addition, it was found that high weight percentage FR PA6 contains small fraction of low molecular weight copolymers and therefore can be used as reactive flame retardant additive for in-situ polymerization process of ε-caprolactam or in the melt-compounding process with PA6 of different viscosities.

[0085] This product is preferably made of ε-caprolactam and flame retardant functionalized ε-caprolactam that, once completely polymerized, enables production of fibre materials and textiles of a sufficient strength, and instantaneous self-extinguishing properties.

[0086] The process according to this invention therefore consist of several independent steps of flame retardant polyamide 6 fibres preparation; synthesis of monomers, copolymerization of ε-caprolactam and flame retardant functionalized ε-caprolactam, which enables preparation of flame retardant polyamide 6 copolymers of proper viscosity used for and fibres production execution of the following interrelated steps: [0087] step (i) flame retardant modification of ε-caprolactam is achieved by using different also ε-caprolactam based precursors (sugars, L-lysine, α-amino-ε-caprolactam, α-bromo-ε-caprolactam, etc., see Table 1). Precursors for flame retardant caprolactam (FR-CL) synthesis, preferably ε-caprolactam based precursors, are obtained from bio-sources or synthesised from precursors obtained from bio-sources. ε-caprolactam based precursors for FR-CL synthesis could be —OH, —X (X═Cl, Br, I) or —NH.sub.2 functionalized ε-caprolactam analogues where functional groups are located also on other than α-position (see Table 1). Preference is on amino group reaction for comonomer obtaining. In different embodiments different phosphorus compounds i.e. different dialkylphosphites can be used for phosphonamidates comonomer obtaining. FR functionalization is made in such a way that does not influence the polymerization reaction. Polymerizable part of FR molecule is ε-caprolactam and phosphorous containing part of the molecule stays covalently attached to PA6 polymer chain. Preferably, Atherton-Todd reaction of α-amino-ε-caprolactam with dimethylphosphite, dibenzylphosphite, diphenylphosphite or DOPO is used for obtaining caprolactam based phosphonamidates. [0088] step (ii) copolymerization of ε-caprolactam and ε-caprolactam flame retardant analogue (FR-CL) without or with the addition of DOPO2-phenethyl and DOPO2-naphthalene alone and in the mixture in different molecular ratios, FR-CL in different molecular ratios with addition of water and/or amino caproic acid and/or sodium ε-caprolactamate in order to achieve proper molecular weight and assure relative viscosity equals to 2.0 proper for melt spinning process. This initiator is only limitedly integrated into polymer structure and can thus be present in limited quantities; [0089] step (iii) masterbatch production in order to tune final copolymer FR properties; [0090] step (iv) melt spinning process of flame retardant polyamide 6 copolymer for flame retardant PA6 fibres production used in different technical textile products.

[0091] In the preferred embodiment of the invention, in step (i) precursor for FR-CL synthesis can be selected between ε-caprolactam molecules from table 1 bearing functional group where covalent bonding of FR molecule is feasible. In Atherton-Todd reaction of α-amino-ε-caprolactam and DOPO, DOPO-CL phosphonamidate comonomer is obtained. In different embodiments different phosphorus compounds can be used i.e. DOPO, dimethylphosphite, dibenzylphosphite, diphenylphosphite . . .

TABLE-US-00001 TABLE 1 Substituted 3-R 4-R 5-R 6-R 7-R CL 3-R’ 4-R’ 5-R’ 6-R’ 7-R’ a H H H H H H H H H b H H H H H H H H c H H CH.sub.3 H H H H H H d H H CH.sub.3 H H H H H H e Br H H H H H H H H H f Br H H H H Br H H H H g H H Br Br H H H H H H h Br H H Ph H H H H H H i Br H H H Ph H H H H H j H H H H CH.sub.2—CH.sub.2—Br H H H H H k I H H H H H H H H H 1 H H CH.sub.2—I H H H H H H H m H H H H H H H CH.sub.2—I H H n NH.sub.2 H H H H H H H H H o NH.sub.2 H H OH H H H H H H P OH H H H H Ph H H H H q OH H H H H CN H H H H r H H CH.sub.2OH H H H H H H H s H H H H H H H CH.sub.2OH H H t CH.sub.2CH.sub.2OH H H H H H H H H H u H H OH H H H H H H H v H H H H H H H OH H H w Ph.sub.2C—OH H H H H H H H H H x H H OH CH.sub.3 H H H H H H Y H H H H H H H OH CH.sub.3 H z H H H CH.sub.3 H H H OH H H B H H H H CH.sub.2CH.sub.2OH H H H H H C H OH H CH.sub.3 H H H H CH.sub.3 H D NH.sub.2 H H CH.sub.3 H H H H CH.sub.3 H E H H CH.sub.3 H H H H CH.sub.3 H F H Ph H H H H CH.sub.3 H H G Br OH H H H H CH.sub.3 H H H H OH Br H H H CH.sub.3O H H H H I OH Br H H H OH H H H H J H OH OH OH H H H H H H K OH H OH COOCH.sub.3 H H H H H H L H Ph H H H CH.sub.3 H H M H H OCH.sub.3 CH.sub.3 H H H OCH.sub.3 CH.sub.2OH H N OH OH OH OH H H H H H H

[0092] In all of these compounds of Table 1 the two substituents for R and R′ for each carbon atom can be positioned either forward or backward (in accordance with Cram representation).

[0093] In Table 1 each R and R′ group refer to formula (VIII) and “Ph” symbolizes a phenyl group.

[0094] In Table 1, the groups that can be substituted by FR moieties are: Br, Cl, CHCl.sub.2, CCl.sub.3, OH, CH.sub.2OH, CH.sub.2CH.sub.2OH, Ph.sub.2C—OH, CH.sub.2—I, CH.sub.2—CH.sub.2—Br and NH.sub.2.

EXAMPLE 1: SYNTHESIS OF α-AMINO-ε-CAPROLACTAM

[0095] First part of step (i) is related to synthesis reaction of α-amino-ε-caprolactam where 0.8 mol (146.08 g) of L-lysine hydrochloride is neutralized with 0.8 mmol of NaOH and then 7.2 mols (689.09 g) of Al.sub.2O.sub.3 is added, followed by 4 L of 1-hexanol. This mixture is heated preferably in temperature range 156-158° C. and is refluxed preferably for 5 hours. The yield of α-amino-ε-caprolactam, produced by this reaction is above 70%. Cooled reaction mixture can be filtered and hexanol can be reduced under reduced pressure. Light yellow crude material can be obtained.

##STR00023##

[0096] ε-caprolactam based precursors for FR comonomer synthesis can be also i.e. halogen or hydroxy functionalized caprolactam, (see Table 1). These kinds of precursors are suitable for i.e. phosphate or phosphonate based FR comonomer obtaining. Also it could be used as starting material in synthesis of its amino derivatives-precursors for synthesis of new phosphonamidate based comonomers.

EXAMPLE 2: SYNTHESIS OF ε-CAPROLACTAM BASED DOPO PHOSPHONAMIDATE, DOPO-CL

[0097] Below is the synthesis procedure example for production of α-amino-ε-caprolactam:

##STR00024##

[0098] Crude material prepared in Example 1 is then used for flame retardant functionalization of said α-amino-ε-caprolactam and preparation of flame retardant monomers, where 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) (86.48 g, 0.4 mol) is dissolved in 400 ml of dichloromethane (DCM), stirred and cooled down to temperature 0° C. Sulphuryl chloride (54.24 g, 0.4 mol) dissolved in 200 ml of dichloromethane and added dropwise into the reaction mixture at a rate that the reaction temperature does not exceed temperature 10° C. HCl and SO.sub.2 gasses obtained from reaction mixtures are captured by KOH solution. After entire sulphuryl chloride is added to the reaction mixture, solution should be warmed up to room temperature and mixed till bubbling of KOH solution stopped. Reaction is prosecuted after cooling. Separately, into the cooled reaction mixture (on ice bath) 44.52 g of triethylamine (0.44 mol) and 53.8 g of α-amino-ε-caprolactam (0.4 mol) dissolved in 200 ml of dichloromethane were added drop-wised respectively. After those solutions have been added completely the solution is allowed to warm up to room temperature and stiffing is continued until all the starting material has been consumed-overnight. After ended reaction, dichloromethane was reduced by evaporation. Crude residue was treated with different organic solvents such as acetone, tetrahydrofurane and dichloromethane for product isolation. Procedure should be repeated till all of the product is isolated. Reaction yield of DOPO functionalized caprolactam (DOPO-CL) obtained as a final product of step (i) was 86.5 g (60%). The formula for DOPO functionalized caprolactam (DOPO-CL) is formula (VII):

##STR00025##

[0099] Molecular structure of said DOPO-CL is confirmed by .sup.1H NMR presented in FIG. 1.

EXAMPLE 3: SYNTHESIS OF ε-CAPROLACTAM BASED DIMETHYLPHOSPHONAMIDATE, DMP-CL

[0100] α-amino-ε-caprolactam (ACLM): 67.3 g (0.525 mol) [0101] dimethylphosphite (DMP): 55.3 g (0.502 mol) [0102] dichloromethane (DCM): 400 mL [0103] sulphuryl chloride: 67.8 g (0.502 mol) [0104] triethylamine (TEA): 56.5 g (0.55 mol)

[0105] Crude material prepared in Example 1 is used in similar way as in Example 2 where dimethylphosphite is used instead of DOPO.

[0106] Obtained DMP-CL (DMP substituted caprolactam) is of formula:

##STR00026##

EXAMPLE 4: SYNTHESIS OF ε-CAPROLACTAM BASED DIBENZYLPHOSPHONAMIDATE, DBP-CL

[0107] α-amino-ε-caprolactam (ACLM): 33.6 g (0.26 mol) [0108] dibenzylphosphite (DBP): 65.6 g (0.25 mol) [0109] dichloromethane (DCM): 300 mL [0110] sulphuryl chloride: 33.9 g (0.251 mol) [0111] triethylamine (TEA) 56.5 g (0.55 mol)

[0112] Crude material prepared in Example 1 is used in similar way as in Example 2 where dibenzylphosphite is used instead of DOPO.

[0113] Obtained DBP-CL (DBP substituted caprolactam) is of formula:

##STR00027##

EXAMPLE 5: SYNTHESIS OF ε-CAPROLACTAM BASED DIPHENYLPHOSPHONAMIDATE, DPP-CL

[0114] α-amino-ε-caprolactam (ACLM): 33.6 g (0.26 mol) [0115] diphenylphosphite (DPP): 62.5 g (0.25 mol) [0116] dichloromethane (DCM): 300 mL [0117] sulphuryl chloride 33.9 g (0.251 mol) [0118] triethylamine (TEA) 56.5 g (0.55 mol)

[0119] Crude material prepared in Example 1 is used in similar way as in Example 2 where diphenylphosphite is used instead of DOPO.

[0120] Obtained DPP-CL (DPP substituted caprolactam) is of formula:

##STR00028##

[0121] Step (ii) is related to preparation of FR polyamide 6 copolymer in bulk by hydrolytic or anionic ringopening polymerization. ε-Caprolactam and substituted caprolactam (FR-CL) can be added in polytetrafluoroethylene (PTFE sold under the name Teflon®) autoclave reactor or other polymerization tool in different ratio, melted under inert atmosphere and stirred, followed by addition of polymerization initiator (catalytic amount of water and/or aminocaproic acid and/or Sodium caprolactamate) and heated under enhanced pressure preferably over three hours (see FIG. 2). Other examples are presented below.

[0122] The polymer obtained can be crushed and refluxed in dichloromethane (DCM), filtrated and then dried in an oven overnight at 90° C. under vacuum, wherein the remaining monomers and short polymers are removed from the bulk polymer, in particular the same step can be done only through reduced pressure.

[0123] In polymerization process, the comonomers can be a combination of two or more different FR monomers mentioned above in combination with ε-caprolactam. Given partial polymerization, the copolymers can be heated and incorporated in flame retardant structure again later in a separate follow-up process.

EXAMPLE 6: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 BY HYDROLYTIC POLYMERIZATION

[0124] ε-caprolactam, DOPO-CL and H.sub.2O were used in the 94:5:1 weight percent ratio. After uniform melt mixing of ε-caprolactam and DOPO-CL with stirring and under argon atmosphere, water as initiator was added and co-polymerization reaction was carried out at 230° C. for 6 h.

EXAMPLE 7: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 BY HYDROLYTIC POLYMERIZATION

[0125] ε-caprolactam, DOPO-CL and H.sub.2O were used in the 89:10:1 weight percent ratio. After uniform melt mixing of ε-caprolactam and α-DOPO-ε-caprolactam with stirring and under argon atmosphere, water as initiator was added and co-polymerization reaction was carried out at 230° C. for 6 h.

EXAMPLE 8: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 BY HYDROLYTIC POLYMERIZATION

[0126] ε-caprolactam, DOPO-CL and H.sub.2O were used in the 79:20:1 weight percent ratio. After uniform melt mixing of ε-caprolactam and DOPO-CL with stirring and under argon atmosphere, water as initiator was added and co-polymerization reaction was carried out at 230° C. for 6 h.

EXAMPLE 9: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 BY ADDITION OF AMINOCAPROIC ACID AS POLYMERIZATION INITIATOR

[0127] ε-caprolactam, DOPO-CL and amino caproic acid were used in the 89:10:1 weight percent ratio. After uniform melt mixing of α-caprolactam and DOPO-CL with stirring and under argon atmosphere, amino caproic acid as initiator was added and co-polymerization reaction was carried out at 230° C. for 6 h.

EXAMPLE 10: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 By Addition Of Sodium ε-Caprolactamate As Polymerization Initiator

[0128] ε-caprolactam, DOPO-CL and sodium ε-caprolactamate were used in the 89:10:1 weight percent ratio. After uniform melt mixing of ε-caprolactam and DOPO-CL with stirring and under argon atmosphere, sodium ε-caprolactamate as initiator was added and co-polymerization reaction was carried out at 230° C. for 6 h.

EXAMPLE 11: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 BY HYDROLYTIC POLYMERIZATION

[0129] ε-caprolactam, DOPO-CL, DOPO2-phenethyl (FED) and H.sub.2O were used in the 89:5:5:1 weight percent ratio. After uniform melt mixing of ε-caprolactam and DOPO-CL and DOPO2-phenethyl (FED) with stirring and under argon atmosphere, water as initiator was added and co-polymerization reaction was carried out at 250° C. for 10 h.

EXAMPLE 12: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 BY HYDROLYTIC POLYMERIZATION

[0130] ε-caprolactam, DOPO-CL, DOPO2-naphthalene (NED) and H.sub.2O were used in the 89:5:5:1 weight percent ratio. After uniform melt mixing of ε-caprolactam and DOPO-CL and DOPO2-naphthalene with stiffing and under argon atmosphere, water as initiator was added and co-polymerization reaction was carried out at 250° C. for 10 h.

EXAMPLE 13: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 BY HYDROLYTIC POLYMERIZATION

[0131] ε-caprolactam, DOPO2-phenethyl (FED) and H.sub.2O were used in the 89:10:1 weight percent ratio. After uniform melt mixing of ε-caprolactam and DOPO2-phenethyl (FED) with stiffing and under argon atmosphere, water as initiator was added and co-polymerization reaction was carried out at 250° C. for 10 h.

EXAMPLE 14: POLYMERIZATION OF FLAME RETARDANT POLYAMIDE 6 BY HYDROLYTIC POLYMERIZATION

[0132] ε-caprolactam, DOPO2-naphthalene and H.sub.2O were used in the 89:5:5:1 weight percent ratio. After uniform melt mixing of ε-caprolactam and DOPO2-naphthalene (NED) with stiffing and under argon atmosphere, water as initiator was added and co-polymerization reaction was carried out at 250° C. for 10 h.

EXAMPLE 15: MELT-SPINNING

[0133] The DOPO/PA6 was grounded into pellets and dried at 100° C. for 3 hours before the processing. The DOPO/PA6 composite multifilament yarns were produced in a melt-spinning process using a laboratory melt-spinning device (sold by the company EXTRUSION SYSTEM®, Ltd. (Bradford, Great Britain)). Pellets were filled in a screw extruder, which was turning and acting with friction on them. The spinning temperature for DOPO/PA6 was set to 210° C. in all zones, i.e., the extruder, spinning pump and spin pack. The melt passed through a 35 μm filter. The spinneret for multifilament spinning had 10 holes with diameters of 0.35 mm. The melt was extruded through the holes of the spin nozzles, cooled in the cooling zone in air at 20° C. and the created multifilament yarn was wounded onto a first galette at the velocity of 50 m/min or onto tubes before knitting.

[0134] Good mechanical properties of the spun fibres enabled successful knitting, which enabled production of a flame retardant PA6 textile with instantaneous flame extinguishment and UL-94 test V-0 ratings.

[0135] During polymerization process in which unmodified ε-caprolactam is polymerized, copolymers presented above can be used as flame retardant additives, although copolymers can be used without pre-treatment with water or reduced pressure, so that polymerization reaction can be optimally adjusted.

[0136] During polymerization process in which unmodified ε-caprolactam is polymerized, copolymers presented above or co-oligomers can be used as flame retardant additives without and with the presence of the DOPO2-phenethyl and DOPO2-naphthalene, although copolymers can be used without pre-treatment with water or reduced pressure, so that polymerization reaction can be optimally adjusted.

TABLE-US-00002 TABLE 2 Relative viscosity, melting temperature and crystallization temperature for selected examples Crystallisation Melting Relative temperature temperature ΔHm2 Example viscosity (−) (° C.) (° C.) (J/g) 6 1.6 163 209 58 7 1.5 155 202 49 8 1.4 139 187 33 9 1.6 146 199 45 10 1.1 152 187 37 11 2.0 166 203 52

[0137] ΔHm2 is the latent heat of melting of said polyamide 6 copolymer.

[0138] However, the proportion of repeating units of polyamide 6 having an A moiety (flame retardant moiety) in the obtained copolymer is a significant parameter for successful flame retardant action. Flame retardant polyamide 6 possesses flame retardant properties preferably if the concentration of flame retardant comonomer (i.e. FR-CL) in flame retardant structure contains at least 0.01 and/or not more 10 wt %, it being preferred for the flame retardant polyamide to contain 0.01 to 1.3 wt % of phosphorous. The high 8 wt % of FR monomer is essential for uniformly distribution of flame retardant comonomer in polymeric structure in order that flame retardant polyamide of invention have non-flammable characteristic evaluated by UL94 protocol resulted.

[0139] However, it is also possible to apply comonomer in smaller concentrations that contain 0.01 to 0.8 wt % of flame retardant monomer in FR PA6 polymer structure, wherein low quality of non-easy flammability is achieved evaluated by UL94 protocol.

[0140] During masterbatch production in step (iii) PA6 polymers can be mixed with crushed FR copolymer powders, wherein the concentration of phosphorous may be identified between 0.01 and 1.3 wt %.

[0141] However, invention opens up further possibilities for modification of FR PA6 including modified platelets graphene and/or multi walled carbon nanotubes for improvement of flame retardant polyamide 6 conductivity and/or antibacterial properties where carbon based and/or silver based additives are added in melt.

[0142] In accordance with the invention flame retardant polyamide 6 can be prepared by extruding and/or melt-spinning/winding process and to be taken off under spinneret speed from 500 m/min to 1500 m/min in multifilament yarn. Moreover, it is advantageous that produced filaments or multifilaments can be used for producing textile structures, more especially knitted textile, woven and nonwoven fabrics.

[0143] Moreover, it is advantageous that flame retardant polyamide 6 can be used as additive for other polyamides, wherein the concentration of phosphorous may be adjusted between 0.01 wt % and 1.3 wt %.

EXAMPLE 16: PRODUCTION OF FIBRES

[0144] FIG. 7 shows a photograph of FR PA6 multifilament yarn (E) and a photograph of FR PA6 composite of knit-fabric (F).

[0145] Commercial polyamide 6 sold under the name ECONYL® by the company AquafilSLO® (Ljubljana, Slovenia) and FR copolyamide 6 can be used in a weight ratio 7:1. This is done using melt spinning unit, comprises a single-screw extruder, a melt spinning pump and 10 nozzles and also high speed winder, with which the produced fibres are elongated and produced in final thickness. The final yarn consists of 10 individual filaments with the thickness between 20 μm and 120 μm.

[0146] However, testing of burning behaviour of formed-loop knit produced from filaments mentioned above resulted in unignited knit even a Bunsen burner flame was applied several times for 8 seconds.

[0147] FIG. 3 shows a sheet specimen prepared by the FR PA6 copolymer material included 10 wt % DOPO-functionalized ε-caprolactam before (A) and after (B and C) the UL94 standard test. The sheet does not burn (B) and the melted drop from the specimen does not ignite the cotton indicator (C). The FR PA6 copolymer material is classified V-0.

[0148] The invention can be varied in many ways with respect to the embodiments and variations described above and in the examples and illustrated in the figures. Further, a polyamide 6 copolymer according to the invention can be added to other polymers and act as a flame retardant for these polymers.