WO1993010288A1

WO1993010288A1 - Improvements in continuous filaments, yarns and tows

Info

Publication number: WO1993010288A1
Application number: PCT/US1991/008380
Authority: WO
Inventors: Raymond Leslie Boles; Benjamin Hughes Knox; James Bennett Noe
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1991-11-18
Filing date: 1991-11-18
Publication date: 1993-05-27

Abstract

Drawing, especially cold-drawing, or hot-drawing, or other heat-treatments, of spin-oriented crystalline polyester filaments, and particularly polyester feed yarns, that have been prepared by spinning at speeds of, e.g., 4 km/min, and have low shrinkage and no natural draw ratio in the conventional sense, provides useful technique for obtaining uniform filaments of desired denier and thereby provides improved flexibility to obtain filaments and yarns mixed with nylon filaments.

Description

TITLE IMPROVEMENTS IN CONTINUOUS FILAMENTS. YARNS AND TOWS

This invention concerns improvements in and relating to continuous filaments, especially in the form of if 5 multifilament yarns, and more especially to a capability to provide from the same feed stock polyester continuous filaments of various differing deniers, as desired, such as can be co-drawn and/or co- mingled with nylon filaments to provide mixed yarns of

1₀ nylon filaments and polyester filaments, and of other useful properties, including improved processes; new yarns, resulting from such processes; and downstream products from such filaments and yarns.

According to the parent application PCT/US91/XXXXX

15 (DP-4040-B) , filed simultaneously herewith, and corresponding to USP 5,066,447, the disclosure of which is hereby incorporated herein by reference) , processes are provided for improving the properties of feed yarns of undrawn polyester filaments. Such processes involve

2₀ drawing with or without heat during the drawing and with or without post heat-treatment, and are most conveniently adapted for operation using a draw-warping machine, some such being sometimes referred to as draw- beaming or warp-drawing operations.

25

Preferred undrawn polyester feed yarns comprise spin-oriented polyester filaments of low shrinkage, such as have been disclosed in Knox U.S. Pat. No. 4,156,071. Alternatively, spin-oriented feed yarns of

₃₀ low shrinkage may be prepared at speeds higher than are used in the Knox patent, including speeds and conditions such as are disclosed by Frankfort &^'Knox in U.S. Patent Nos. 4,134,882 and 4,195,051.

The parent application is primarily concerned with the preparation of and improvement of undrawn polyester yarns and filaments, as indicated. The present invention is concerned primarily with the preparation and processing of mixed filament yarns, comprised of filaments of nylon as well as filaments of polyester.

Conventional nylon filament yarns, such as nylon 66 and nylon 6 partially-oriented yarns (PON) , have been capable of being uniformly fully or partially drawn. This drawing can be carried out hot or cold, with or without any post heat treatment. In contrast, conventional spin-oriented polyester POY, as described for example by Piazza and Reese (U.S. Patent 3,772,872), is not capable of being uniformly cold or partially drawn. Such conventional polyester POY is only capable of being drawn uniformly when hot drawn, and fully drawn to elongations less than about 30%. Otherwise, such polyester POY is not drawn uniformly, so gives along-end "thick-thin" denier variability that has been characteristic of drawing to elongations greater than about 30%, as reported, for instance, by Bosley, et al. U.S. Patent 4,026,098; Lipscomb, et al. U.S. Patent 4,147,749; Nakagawa, et al. U.S. Patent 4,084,622; Allen, et al. U.S. Patent 3,363,295. It has also been reported that such prior art drawing results in along-end spontaneous crimp on shrinkage (Schippers U.S. Patent 4,019,311; cόl. 10/lines 44-59 and col. 11/lines 24-31) . Both of these are undesirable defects for end-uses requiring uniform along-end dyeability.

According to the invention, in contrast to such prior suggestions, an improvement in the commercial drawing of undrawn polyester filaments is provided such as to permit the drawing of spin-oriented polyester filaments essentially "as if they were spin-oriented nylon filaments"; that is, the spin-oriented polyester filaments of low shrinkage according to the invention "may be treated as spin-oriented nylon filaments in their drawing behavior". So this invention permits the uniform co-drawing of spin-oriented polyester and nylon filaments over a wide range of draw ratios and temperatures.

According to the present invention, there are provided the following processes:-

A process for preparing a mixed filament textile yarn comprised of drawn polyester and nylon filaments, characterized in that spin-oriented polyester filaments and nylon feed filaments are completely or partially drawn to uniform filaments by hot-drawing or by cold- drawing, with or without heat setting, and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said drawing and/or heat setting treatments; wherein said spin-oriented polyester filaments are characterized by an intrinsic viscosity [17] 0.56 to 0.68, elongation-to-break (Eg) 60 to 90%, boil-off shrinkage (Si) less than 10%, thermal stability as measured by a (S2)-value less than +1%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon feed filaments are characterized by relative viscosity (RV) 40 to about 80, elongation-to-break (Eg) 60 to 90%, boil-off shrinkage (S-_j less than 10%, and dimensional stability as measured by a (ΔLi₃5_4o C)~ value less than 0.

Partial drawing and/or cold-drawing are expected to be particularly important embodiments of the present invention. Hot-drawing, with or without post-heat treatment may also be very useful embodiments, as will become clear.

If desired, a mixed filament textile yarn comprised of polyester and nylon filaments, may be prepared from such spin-oriented polyester filaments and nylon feed- filaments by heat treating them without drawing, and the polyester and nylon filaments may be combined to form a mixed filament yarn before or after said heat treatment.

If desired, a post-bulkable mixed filament yarn may be prepared, wherein such spin-oriented polyester filaments and nylon feed filaments are drawn to uniform drawn filaments by hot-drawing or by cold-drawing, and then said drawn filaments are post treated at temperatures (T_j*) _r selected to preferentially reduce the shrinkage of the drawn polyester filaments such that boil-off shrinkages (S^) of the resulting drawn polyester filaments and drawn nylon filaments differ from each other by at least about 5%; and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said drawing and/or heat treatment.

A mixed filament yarn, suitable for use as a textile yarn, may be provided of spin-oriented polyester filaments and of nylon filaments, wherein said spin- oriented polyester filaments are characterized by an intrinsic viscosity [ηy 0.56 to 0.68, elongation-to- break (Eg) 60 to 90%_f- boil-off shrinkage (S^ less than 10%, thermal stability as measured by a (S2)-value less than +1%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon filaments are characterized by rela¬ tive viscosity (RV) 40 to 80, elongation-to- break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, and dimensional stability as measured by a (ΔLi₃5_4o C)~ value less than 0.

A mixed filament textile yarn, may be provided of drawn polyester filaments and of drawn nylon filaments of elongation (E_B) between about 20 and about 90% and boil-off shrinkage (Si) less than about 10%, and wherein said drawn polyester filaments are of intrinsic viscosity [17] 0.56 to 0.68, tenacity at 7% elongation (T₇) at least 1 gram/denier, post yield modulus (PYM, g/d) such that its square root (VPYM) is 2.5 to 5, thermal stability as shown by an S₂-value less than +2%, net shrinkage (S 2) less than 8%, maximum shrinkage tension (ST) less than 0.5 g/d, density (p) 1.355 to 1.415 grams/cubic centimeter, and of crystal size (CS) 60 to 90 Angstroms and also at least the following value in the relation to density: CS > (250p- 282.5), Angstroms; and wherein said drawn nylon filaments are of relative viscosity (RV) 40 to 80, and a dimensional stability as given by a (ALi₃5_₄₀ c)~ value less than 0.

A process is provided for preparing a mixed filament yarn, of polyester filaments and nylon filaments, of elongation (E_B) 60% to 90% and boil-off shrinkage (Si) less than 10%, comprising co-spinning, attenuating, quenching, and winding said polyester and nylon filaments at a withdrawal speed of 3.5 km/min to 6.5 km/min, such that the relative viscosity (RV) of said nylon filaments is between 40 and 80 and less than the expression: [13.3(km/min) -(6.5-X)], wherein X is the weight percent of any copolyamide, with suitable dimensional stability, as measured by a (ΔL₁₃5-45 c)~ value less than 0; and wherein said polyester filments are of intrinsic viscosity [η] 0.56 to 0.68, thermal stability as measured by a (S2)-value^'less than +1%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to

1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms. Such a process lends itself to coupled spin/draw preparation of mixed filament yarns, e.g. as follows.

Such a process may be a coupled spin/draw process wherein, prior to winding, such co-spun polyester filaments and nylon filaments are partially drawn to provide uniform drawn polyester and drawn nylon filaments, by hot-drawing or by cold-drawing to drawn elongations (E_B) between 30% and 90% and wherein these drawn elongations (E_B) differ from each other by less than 5%, with or without heat setting to provide a boil-off shrinkage less than 10% and drawn nylon filaments of dimensional stability as given by a

(ΔLi₃5_ o c)~^{v ue} less than 0; and wherein said drawn polyester filaments are of tenacity at 7% elongation (T7) at least 1 gram/denier, post yield modulus (PYM, g/d) such that its square root (VPYM) is 2.5 to 5, thermal stability as shown by an S2~v lue less than +2%, net shrinkage (S12) ^' less than 8%, maximum shrinkage tension (ST) less than 0.5 g/d, density (p) 1.355 to 1.415 grams/cubic centimeter, and of crystal size (CS) 60 to 90 Angstroms and also at least (250p- 282.5) Angstroms.

Or such a process may be a coupled spin/draw process, wherein prior to winding, such co-spun polyester and nylon filaments are cold drawn to provide uniform drawn polyester and drawn nylon filaments, of drawn elongations (E_B) 20% to 90% and other provisions being similar to those set out above.

In such processes wherein yarns are post heat treated to reduce shrinkage, such post heat treatments are preferably carried out at temperatures (T-R in degrees C) less than (1000/[4.95 - 1.75(RDR)_D/N] - 273), where (RDR)D N i ^the calculated residual draw ratio of the drawn nylon filaments, and is at least 1.2 to provide for uniform dyeability of the nylon filaments with large molecule acid dyes.

These spin-oriented polyester and nylon filaments may be heated and/or drawn in the form of weftless warp sheets which may then be further processed, e.g., by knitting or weaving, or may be wound onto a beam. The filaments may be combined in the form of mixed filament yarns or the filaments need not be combined and may be drawn as separate yarn bundles, as to provide for drawing of a weftless pattern warp.

As indicated, the spin-oriented polyester feed yarn filaments are characterized by an intrinsic viscosity [η] 0.56 to 0.68 (preferably 0.62 to 0.68), elongation- to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, thermal stability as measured by a (S2)-value less than +1%, net shrinkage (S 2) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p- 282.5) Angstroms. The nylon feed yarn filaments are characterized by relative viscosity (RV) 40 to 80 (preferably 50 to 70) , elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, and dimen¬ sional stability as measured by a (ΔL1₃5--.4₀ c)~^{va ue} less than 0. The polyester and nylon polymers of said filaments may contain minor amounts of copolyesters and copolyamides, respectively, preferably about 2 to 10% by weight, and may contain minor amounts of chainbranching agents, preferably 0.02 to 0.2 mole %; wherein said copolymers are added to increase dyeability, shrinkage, and to a lesser extent, elongation; and wherein said chainbranching agents are added to increase elongation, dyeability, and for polyesters, to decrease shrinkage. Increasing polymer viscosity decreases elongation and shrinkage of the polyester filaments. For the nylon filaments, however, increasing polymer viscosity increases elongation, and has only minor effects on shrinkage. The filament denier and shape are generally selected primarily to meet the aesthetic and functional needs of the intended end-use; it is also known that decreasing filament denier, or increasing the surface-to-volume ratio via use of odd cross-sections, reduces the elongation and increases the shrinkage of the spin-oriented polyester filaments, and have only minor effects on the elongation and shrinkage of the spin-oriented nylon filaments.

The elongation-to-break (Eb) of the spin-oriented polyester filaments and nylon feed ilaments are preferably very similar, any differences in the E_B values amounting desirably to less than about 5%. Especially desirable spin-oriented polyester and nylon feed filaments are in the form of mixed filament co- spun feed yarns.

Such spin-oriented- olyester filaments, used herein, may advantageously be treated with caustic applied to freshly-extruded filaments, as described by Grindstaff and Reese (allowed Application, Serial No. 07/420,459) to provide the polyester filaments with improved moisture-wicking properties, more akin to those of the nylon filaments.

Mixed filament textured yarns may be provided by air-jet texturing the resulting mixed filament drawn yarns.

Alternatively mixed filament false-twist textured yarns may be provided of elongation (E_B) between 20 and 60% and boil-off shrinkage (Si) less than 10%, comprised of uniform drawn polyester filaments and of uniform drawn nylon filaments, wherein said drawn polyester filaments are of intrinsic viscosity [η] 0.56 to 0.68, tenacity at 7% elongation (T₇) at least 1 gram/denier, post yield modulus (PYM, g/d) such that its square root (VPYM) is 2.5 to 5, thermal stability as shown by an S2~value less than +2%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.5 g/d, density (p) 1.355 to 1.415 grams/cubic centimeter, and of crystal size (CS) 60 to 90 Angstroms and also at least (250p- 282.5), Angstroms; and wherein said drawn nylon filaments are of relative viscosity (RV) 40 to 80, and a dimensional stability as given by a (ALi₃5_4Q c)~^val^ue less than 0.

These may be provided by a process characterized in that spin-oriented polyester filaments and nylon feed filaments are simultaneously partially drawn and false- twist textured to uniform filaments by hot-drawing with or without heat setting, and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said drawing and/or heat setting treatments; wherein said spin-oriented polyester filaments are characterized by an intrinsic viscosity [17] 0.56 to 0.68, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, thermal stability as measured by a (S₂)-value less than +1%, net shrinkage S12) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon feed filaments are characterized by relative viscosity (RV) 40 to 80, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (S ) less than 10%, and dimensional stability as measured by a (ΔLi₃5_4Q C)~ value less than 0.

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If desired, however, a process may be provided characterized in that spin-oriented polyester filaments and nylon feed filaments are sequentially partially drawn to uniform filaments by hot-drawing or by cold- I⁵ drawing, then false-twist texutred with heat setting, and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said drawing and/or texturing treatments; wherein said spin-oriented polyester filaments are characterized by an intrinsic ⁰ viscosity [77] 0.56 to 0.68, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, thermal stability as measured by a (S2)-value less than +1%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm-⁵, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon feed filaments are characterized by relative viscosity (RV) 40 to 80, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (S ) less than 10%, and 0 dimensional stability as measured by a (ΔL ₃5..40 c)~ value less than 0.

The polyester and/or nylon filaments may be modified, if desired, with 1 to 3 mole percent of ethylene-5-sodium-sulfo isophthalate to impart cationic dyeability with cationic dyestuffs. Representative copolyesters used to enhance dyeability with disperse dyes are mentioned in Most U. S. Patent 4,444,710, Pacofsky U. S. Patent 3,748,844, Hancock U. S. Patent 4,639,347, and Frankfort and Knox U. S. Patents 4,134,882 and 4,195,051, and representative chain¬ branching agents used to reduce shrinkage, especially of polyesters modified with ionic dye sites and/or copolyesters, are mentioned in Knox U. S. Patent 4,156,071 , MacLean U. S. Patent 4,092,229, and Reese U. S. Patent 4,883,032; 4,996,740; and 5,034,174. To obtain low shrinkage spin-oriented feed yarns with modified polyesters, it is advantageous to increase polymer viscosity by up to about 0.01 [η] units and/or add minor amounts of chain-branching agents (e.g., about 0.1 mole percent).

Resulting drawn polyester and nylon filaments of co- drawn polyester\nylon yarns according to the present invention are characterized, in addition to polymer type and viscosity as described above, by residual elongations between about 20 and 90%, preferably between about 20 and 60%, boil-off shrinkages (Si) less than about 10%, atmospheric dyeability, with advantages in that these drawn polyester filaments may be dyed to deep shades under the same dyebath conditions as used to dye the nylon filaments, as indicated, by having a Relative Disperse Dye Rate (RDDR) , described hereinbefore, greater than about 0.075, preferably greater than 0.09, as indicated by having a value of the square-root of the post-yield modulus (VPYM) about 2.5 to 5 Vgpd and preferably a RDDR-value at least about [0.165 -0.025 VPYM] .

Such drawn polyester filaments are preferably of intrinsic viscosity [77] 0.62 to 0.68 and such drawn nylon filaments are preferably of relative viscosity (RV) 50 to 70. Such drawn polyester and nylon filaments may preferably also be of denier less than about one.

As will be understood, feed filaments may be supplied and/or processed according to the inventiion in the form of a yarn or as a bundle of filaments that does not necessarily have the coherency of a true "yarn", but for convenience herein a plurality of filaments may often be referred to as a yarn or bundle, without intending specific limitation by such term.

Figures 1 and 2 are curves that show, respectively, elongations-to-break (E_B) and boil-off shrinkages (S ) , each plotted v. spinning speed.

Figure 3 shows a relationship between the heat relaxation temperature (TR) and the residual draw ratio of drawn yarns (RDR)-p. Other Figures relating to polyester filaments, are incorporated herein from the parent application, referred to above.

By taking advantage of similarities in the drawing behavior of existing undrawn nylon filaments and in the (surprising) characteristics of the undrawn polyester feed filaments according to the invention, it is now possible for the first time to provide a practical pro¬ cess for the making of uniformly drawn mixed polyes¬ ter/nylon filament yarns by the drawing of a feed yarn of undrawn mixed polyester/nylon filaments. This (mixed filament) feed yarn may be formed by: (i) the co-mingling of undrawn nylon filaments and of undrawn polyester filaments, (selected according to the criteria described herein) such as by co-feeding separate or pre-comingled undrawn polyester and nylon filament yarns into the draw zone, for example, of a single-end draw machine, of a draw air-jet texturing process, or of a draw-warping process; and preferably by: (ii) co-extruding, such polyester and nylon filaments from the same or from separate spin packs, wherein the freshly extruded nylon filaments (especially) are protected from oxidative degradation, preferably by use of steam blanketing of the face of the spinneret, attenuating and quenching such freshly extruded polyester and nylon filaments, and co-mingling said polyester and nylon filaments, especially after converging and applying finish to these filaments by use of a ceramic tip metered finish applicator guide

(such as described by Agers U.S. Patent 4,926,661) , wherein the length of convergence, L_c, is adjusted preferably over a distance within the range 50 to 150 cm, to achieve optimum along end uniformity, to form a single filament bundle using an inert gaseous interlace jet (such as described by Bunting and Nelson U.S. Patent 2,985,995 and by Gray U.S. Patent 3,563,029) and winding the resulting co-mingled polyester/nylon filament yarn from packages for co-drawing generally in separate downstream textile processes (such as, draw air-jet texturing, draw false-twist texturing, single- end drawing for fill yarns, draw-warping of weftless warp sheets wound onto beams) ; or (iii) , if desired, by • . coupling the co-spinning and co-drawing process steps into a coupled spin/draw process, wherein, after drawing, the retractive forces of the spun/drawn filaments are decreased, if required, to suitable levels for winding into packages by overfeeding between rolls, and/or application of mild heat conditions, such as passing over heated rolls or through a steam jet, the coupled spin/drawn polyester/nylon filament yarn being wound up into packages suitable for direct-use without further drawing and/or heat treatments; or such coupled spin/drawn direct-use yarns may be used as feed yarns for downstream textile processing, wherein the primary draw-ratio (DR^ , taken in the coupled spin/draw step, and the secondary draw ratio (DR2) taken in a separate split process, are selected such that their product (DR12) [iⁿ other words D 1XDR2] is less than about the maximum draw ratio (DRj^χ) . This draw ratio (D _jι^ ) is obtained by dividing (RDR)χ- by 1.2, (RDR)L being the residual draw-ratio of the component having the lowest elongation-to-break (E_B)L, and being defined by the relationship (RDR)_L = [1+(E_B)_I 100]. For example, if the (RDR)- values for the undrawn polyester and nylon filaments are, respectively, 1.9 and 1.75, and the selected primary draw ratio (DR ) is 1.3, then partially co- drawn polyester and nylon filaments are provided with drawn (RDR)-ø-values of 1.46 (i.e. 1.9/1.3) and 1.346

(i.e. 1.75/1.3), respectively. The partial co-drawn yarn may then be used "as-is" or may be drawn again in a separate step with a maximum secondary draw-ratio (DR2)MAX ^of 1.122 [i.e. 1.346/1.2], where (DR2)MAX s calculated by taking the (RDRjp-value of the component having the lowest spin/drawn RDR-value (in this example, the spun/drawn nylon filaments with a (RDR)-_Q- value of 1.346) and dividing this (RDR)-_Q-value by 1.2, being a minimum (RDRJ^-value, selected to avoid filament breakage that would result from overdrawing to

RDR-values less than about 1.2. The mixed yarns of this invention may, if desired, be co-drawn to (RDR)-_Q- values less than 1.20, while recognizing that this will increase the tendency for the filaments to break, and at some level this will become unacceptable for commercial use. In the above processes (designated by (i) , (ii) and (iii) , the level and type of spin finish and interlace are selected based on the particular end- use processing needs (e.g., inter-filament friction, mixing, and configuration) . Polyester polymer LRV is determined as described in Broaddus U. S. Patent 4,712,998 where 20.8 LRV corresponds approximately with [17] of 0.65.

Examples of the polyester filaments are incorporated herein from the parent application, referred to above, referring especially to Tables 1-XV, and the accompanying disclosure. For this reason, Examples of the nylon filaments are provided primarily in the form of Tables that are numbered consecutively XVI and XVII. Four types of high speed spun undrawn nylon filaments suitable for cospinning (or co-mingling after having been wound up) with polyester undrawn filaments are summarized in Table XVI as items A, B, C and D, and the drawing of said four types of undrawn nylon filaments (A, B, C and D) are summarized in Tables XVIIA, XVIIB, XVIIC, and XVIID, respectively. The warp knit fabric ratings in Table XVII (denoted by LMDR=Large Molecule Dye Rating) were measured by the method described in Boles et al Application PCT/US91/04244 filed June 21, 1991.

Acceptable dyed fabric uniformity is defined as that suitable for critically dyed fabrics for use in automotive upholstery and fashion swimwear herein are denoted by a + sign in Table XVII.

Nylon polymer RV in Tables XVI and XVII are determined as described at Col. 2, lines 42-51, in Jennings U. S. Patent 4,702,875.

The undrawn nylon filaments used according to this invention are selected to provide dimensional stabil¬ ity; that is, are selected to avoid or minimize any tendency to spontaneously elongate (grow) at moderate temperatures (referred to in degrees C) e.g., over the temperature range of 40 to 135, as measured by the dynamic length change (ΔL135-40)-value less than 0 under a 5 mg/d load at a heating rate of 50/minute as described in Knox et al EP Al 0411774 (page 18, lines 43 thru 56) and is similar to a stability criterion (TS1 ₀ c~^τs90 c) described by Adams in U.S. Patent 3,994,121 (Col. 17 and 18). In conventional spinning of undrawn nylon filaments, dimensional stability, as described hereinabove, is provided by treating the freshly extruded filaments, prior to winding, with steam (Adams U.S. Patent 3,994,121) or dry heat (Koschinek U.S. Patent 4,181,697). Dimensional stability can also be provided without thermal treatments of any kind by spinning nylon polymer of conventional RV (35-45) at spinning speeds greater than about 5 Km/min (Koschinek U.S. Patent 4,181,697) ; by spinning nylon polymer of RV greater than 46, preferably greater than about 53 RV, at spinning speeds greater than 3.5 Km/min (Chamberlin, et al. U.S. Patent 4,583,357); by spinning conventional RV nylon containing minor amounts of chainbranching agents at spin speeds greater than about 3.5 Km/min (Nunning, et al. U.S. Patent 4,721,650); or by spinning nylon polymer of RV greater than about 50 containing minor amounts of copolyamides, e.g., 5% by weight of nylon 6, or 5% by weight of 2-methyl-pentamethylene adipamide comonomer at spin speeds greater than about 4.5 Km/min (Knox, et al EP Al 0411774) . Preferably, the undrawn polyester/nylon mixed filament yarns are prepared by a process in which the dimensional stability of the undrawn nylon filaments is provided without use of steam or dry heat, since it may not always be desirable to heat treat the undrawn polyester filaments. In such cases, if needed, separate yarn paths can be used to permit heat treatment of just the nylon filaments prior to combining them with un(heat)treated polyester filaments. However, a simplified cospinning process is preferred wherein dimensionally stable nylon filaments are formed without use of steam or thermal treatments by selecting nylon polymer (base polymer type, RV, amount of copolymers and/or chainbranchers) such that spinning at speeds greater than about 3.5 Km/min, preferably greater than about 4 Km/min, is sufficient to develop dimensional stability without having to use steam or dry heat treatments.

For instance, Table XVI shows how undrawn nylon filaments for our mixed feed yarns may be spun without need for thermal stabilization by spinning nylon 66 polymer of 50 RV at about 3.9 Km/min (Table XVI-1 and 2) and by spinning nylon 66 polymer of 65 RV (Table XVI-3) and nylon 6/66 of 65 RV containing 5% by weight of nylon 6 (Table XVI-4) at 5.3 Km/min. We have found that selecting nylon polymer and spinning speed to provide undrawn nylon filaments with an elongation (E_B) less than about 90% is usually sufficient to achieve dimensional stability (ΔLι₃5_ ₀) • The relationship of elongation (E_B) v spinning speed is discussed hereinafter with reference to Figure 21 of the accompanying drawings. Polymer RV, amount of copolyamide, and spinning speed (Km/min) are preferably selected for nylon using the following relationship to provide dimensionally stable undrawn nylon filaments with elongations less than about 90%: RV < [0.0133V- (6.5-X)], wherein V is the spinning speed (in Km/min) and is between about 3.5 and about 6.5 (preferably between about 4 and about 6) , polymer RV is between about 40 and about 80 (preferably between about 50 and about 70) , and polymer is nylon 66 which may be modified with up to about 10% by weight of copolyamides, any such percentage amount being denoted by X. If minor amounts of chainbranching agents (typically about 0,02 to about 0.12 mole percent) are incorporated into the nylon polymer, then lower RV polymer and/or higher spin speeds may be used to obtain the same desirable undrawn yarn elongation. This may be preferred rather than raising the nylon polymer RV by solid phase polymerization.

In Examples XVI-3 and -4, nylon polymer of 65 RV was spun at a nominal spin speed of 5.3 Km/min to form dimensionally stable undrawn nylon filaments having elongations-to-break (E_B) on the same order as that in Example XVI-2 (spun at slower spin speed and lower RV) . Examples XVI-3 and -4 illustrate the use of high polymer RV and of incorporating a minor amount of copolyamide (e.g., 5% nylon 6 in nylon 66 - denoted as N6/66 in Example XVI-4) to increase or maintain spun yarn elongation with increasing spinning speeds and thus to better match the typically higher spun elongations of the polyester filaments. Examples of other suitable undrawn filament yarns suitable for combining with undrawn polyester yarns of the invention are described in Knox, et al (EP Al 0411774) .

The undrawn polyester/nylon mixed filament yarns, according to this invention, may be uniquely drawn, fully or partially, cold, or hot, with or without post heat treatment, to provide uniform drawn yarns, to residual elongations of at least about 1.2 (that is, drawn such that the residual elongation-to-break of the component having the lowest elongation is at least about 20%) so to avoid the likelihood of forming broken filaments which may be unsuitable for certain textile end-uses. The maximum draw ratio (DRj^χ) without broken filaments is herein defined by the elongation of the undrawn component having the lowest elongation prior to drawing:

= (RDR)_FfL 1.2. Since both components of the mixed feed yarn of this invention may be partially drawn, there is no lower limit for the draw ratio, except as required to maintain a stable threadline during drawing and subsequent winding of package or beam. To maximize drawing productivity, it is preferred to select components such that any dif¬ ference in elongations between the undrawn polyester (E_B)p and nylon (E_B)JJ filaments be less than about 10%, preferably less than about 5%.

Referring to Figure 1, for example, to obtain a better match between the elongations of undrawn polyester and nylon filaments, one may compare how typical elongation values for polyester (I) and for nylon (II) vary with different spin speeds. Between about 3.5 Km/min and 6.5 Km/min (denoted by region ABCD in Figure 1) and especially between about 4 and 6 Km/min, the elongations of undrawn polyester and nylon filaments are of the same order. The elongation of the undrawn nylon filaments may be increased by increasing polymer RV (Chamberlin U.S. Patent 4,583,357 and 4,646,514), by use of chainbranching agents (Nunning U.S. Patent 4,721,650), or by use of selected copolyamides and higher RV (Knox EP Al 0411774) . The elongation of the undrawn polyester may be increased by lower intrinsic viscosity and use of copolyesters (Knox U.S. Patent 4,156,071 and Frankfort and Knox U.S. Patents 4,134,882 and 4,195,051), and by incorporating minor amounts of chainbranching agents (MacLean U.S. Patent 4,092,229, Knox U.S. Patent 4,156,051 and Reese U. S. Patents 4,883,032, 4,996,740, and 5,034,174). The elongation of polyester filaments is especially responsive to changes in filament denier and shape, with elongation decreasing with increasing filament surface-to-volume (i.e., with either or both decreasing filament denier and non-round shapes) .

Referring to Figure 2, the variations of shrinkage (S_j vs spinning speed are compared for conventional undrawn polyester POY (I') and of undrawn polyester feed filaments used herein (I") with that of undrawn nylon filaments (II) . Undrawn polyester yarns with shrinkages less than about 10% (for instance, those below the line AB in Figure 2) are found to have drawing characteristics comparable to those of undrawn nylon filaments. The Si shrinkage of polyester filaments spun at any particular speed may, for example, be decreased to be comparable to that of (I"), by raising the polymer viscosity, increasing filament surface-to-volume ratio, using a chainbrancher, lowering polymer melt viscosity via reduced bulk polymer temperature and/or capillary shear, and shorter delay quench lengths. Selection of polyester polymer (RV, amount and type of comonomers, and chainbranching agents) and spinning parameters are made to obtain the desired shrinkage and elongation to match those of the nylon filaments for making the preferred polyester/nylon mixed filament yarns of the invention. The overall shrinkage of the drawn polyester/nylon mixed filament yarns is typically determined by the shrinkage of the drawn nylon filaments, herein, since the latter usually have a higher shrinkage potential than the drawn polyester filaments of the invention. The shrinkages of the drawn nylon filaments vary in range between about 6 and 10% for nylon 66, and between about 8 to 12% for nylon 6, with shrinkages in the lower end of the range being obtainable by heat relax¬ ing the drawn filaments. The shrinkages of the cold drawn polyester filaments are typically 6 to 10% without heat setting, and may be as low as about 2-3% with heat setting. A mixed shrinkage drawn filament yarn may be obtained by cold or hot co-drawing the said polyester/nylon mixed filament yarns followed by mild heat-relaxing (e.g., up to about 10% overfeed at less than about 150 C) , whereby the shrinkage of the polyester filaments may be typically reduced to a greater extent than that of the nylon filaments.

The uniformity of co-drawn polyester/nylon mixed filament yarns wherein the nylon filaments are dyed with large acid-dye molecules (such as are used in critically dyed warp knits for automotive upholstery and swimwear) may not be satisfactory if the co-drawn yarns are heat-set above about 150 C. It has been found that the along-end dye uniformity of nylon with large molecule acid dyes (such as Anthraquinone Milling Blue BL - Color Index Acid Blue 122) is reduced to unsatisfactory levels if drawn to low elongations (low RDR values) with heat setting at high temperatures. Acceptable along-end dye uniformity is achieved if the extent of drawing and heat setting are balanced as described by the relationship:

[1000/(T_R + 273)] >/= [4.95 - 1.75(RDR)_D] _f wherein, T_R is the heat relaxation temperature (in degrees C) , and (RDR)D is the residual draw ratio of the drawn nylon filaments defined by (1+E_B,%/100)_D.

Figure 3 shows the relationship between T_R and (RDR)D for nylon graphically by a plot of [1000/(TR+273) ] vs. (RDR)^*Q. Drawn filaments, suitable for critically dyed end-uses are obtained by selecting conditions met by the regions I (ABCD) and II (ADEF) . Mixed-shrinkage yarns suitable for critically dyed end- uses are preferably obtained by cold or hot drawing the polyester/nylon mixed yarns followed by heat relaxing to reduce the shrinkage of the polyester filaments by selecting relaxation temperatures T_R characteristic of Region II (ADEF) . Co-drawn filament yarns wherein shrinkages of the polyester and nylon filaments are similar with maximum dyeability (that is dye rate) are preferably drawn cold (e.g., less than about 70 C, the nominal _Q of polyester filaments) and heat set at temperatures less than about 90 C, as represented by Region I (ABCD) .

The drawn polyester/nylon textile yarns prepared by the invention are suitable for critically dyed end-uses and have the unique advantage (especially if prepared by cold drawing without heat setting) of being capable of being dyed using conditions typical of nylon; (that is, under atmospheric conditions and without the use of organic carriers used in dyeing of conventional drawn polyester yarns) ; wherein, disperse dyestuffs are used to dye the polyester filaments and disperse or acid dyestuffs are used to dye the nylon filaments. If cationically modified polyester and/or nylon filaments are prepared by incorporation of typically 1 to 3 mole% of ethylene 5-M-sulfo-isophthalate, wherein M is an aklali metal cation (such as sodium) , then cationic dyestuffs may be used.

Uniform drawing of the undrawn polyester/nylon feed yarns of the invention may be carried out in a coupled spin draw process, a split single-end process (including draw air-jet and false-twist texturing) , and in a draw-warping process, wherein said drawing may be done cold (i.e., without external heating) or hot with or without heat setting to provide drawn filaments hav¬ ing a residual elongation of at least about 20%, and even may be uniformly partially drawn with residual elongations of at least about 30%. In contrast, uniform drawing of a polyester/nylon feed yarn to elongations greater than about 30% would not be possible if one were to try to use the same processing conditions on a feed yarn in which the polyester filaments were of conventional POY (such as described by Piazza and Reese, U.S. Patent 3,772,872) with shrinkages greater than about 10%, such filaments would give the results taught in Schippers U.S. Patent

4,019,311. The combination according to the invention is of polyester undrawn filaments, characterized herein by low shrinkage and large crystals, with dimensionally stable nylon undrawn filaments, characterized by polymer RV greater than about 40, especially greater than about 50, with both filament types formed by spinning at speeds greater than about 3.5 Km/min, preferably greater than about 4 Km/min, such to provide polyester and nylon filaments both having elongations less than about 90% and shrinkages (Si) less than about 10%, preferably by co-spinning the polyester and nylon filaments and winding up a mixed feed yarn for co- drawing.

Claims

CLAIMS:

1. A process for preparing a mixed filament textile yarn comprised of drawn polyester and nylon filaments, characterized in that spin-oriented polyester filaments and nylon feed filaments are completely or partially drawn to uniform filaments by hot-drawing or by cold- drawing, with or without heat setting, and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said drawing and/or heat setting treatments; wherein said spin-oriented polyester filaments are characterized by an intrinsic viscosity [η] 0.56 to 0.68, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, thermal stability as measured by a (S2)-value less than +1%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon feed filaments are characterized by relative viscosity (RV) 40 to 80, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, and dimensional stability as measured by a (ΔL1₃₅--.4₀ c)~ value less than 0.

2. A process according to Claim 1, wherein the feed filaments are drawn to uniform filaments by partial drawing.

3. A process according to Claim 1 or 2, wherein the feed filaments are drawn to uniform filaments by cold- drawing.

4. A process for preparing a mixed filament textile yarn comprised of polyester and nylon filaments, characterized in that spin-oriented polyester filaments and nylon feed filaments are heat treated without drawing, and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said heat treatment; wherein said spin-oriented polyester filaments are characterized by an intrinsic viscosity [17] 0.56 to 0.68, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (S ) less than 10%, thermal stability as measured by a (S2)-value less than +1%, net shrinkage (S-^) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon feed filaments are characterized by relative viscosity (RV) 40 to 80, elongation-to- break (E_B) 60 to 90%, boil-off shrinkage (S ) less than 10%, and dimensional stability as measured by a (ΔLi₃5_4o c)~ value less than 0.

5. A process for preparing a post-bulkable mixed filament yarn, wherein spin-oriented polyester filaments and nylon feed filaments are drawn to uniform drawn filaments by hot-drawing or by cold-drawing, and then said drawn filaments are post treated at temperatures (TR) , selected to preferentially reduce the shrinkage of the drawn polyester filaments such that boil-off shrinkages (Si) of the resulting drawn polyester filaments and drawn nylon filaments differ from each other by at least 5%; and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said drawing and/or heat treatment; wherein said spin-oriented polyester filaments are characterized by an intrinsic viscosity [77] 0.56 to 0.68, elongation-to-break (Eg) 60 to 90%, boil-off shrinkage (S^) less than 10%, thermal stability as measured by a (S₂)-value less than +1%, net shrinkage (S 2) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon feed filaments are characterized by relative viscosity (RV) 40 to 80, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, and dimensional stability as measured by a (ΔLi35_4Q C)~ value less than 0.

6. A process according to any one of Claims 1 to 5, wherein said spin-oriented polyester filaments and said nylon feed filaments are provided in the form of a mixed filament spin-oriented co-spun feed yarn, and wherein the elongation-to-break (Eb) of said spin- oriented polyester and of said nylon feed filaments differ from each other by less than 5%, and wherein any post heat treatment is carried out at a temperature (TR in degrees C) less than (1000/[4.95 - 1.75(RDR)D_/N] ~ 273), where (RDR)D,N is the calculated residual draw ratio of the drawn nylon filaments, and is at least 1.2.

7. A process according to any one of Claims 1 to 6, wherein said spin-oriented polyester and nylon feed filaments are provided in the form of a plurality of mixed filament spin-oriented co-spun feed yarns, and said spin-oriented feed yarns are processed in the form of a weftless warp sheet suitable for knitting, weaving, or winding onto a beam.

8. A process according to any one of Claims 1 to 6, wherein the resulting drawn mixed filament yarn is air-jet textured to provide a mixed filament textured yarn.

9. A process for preparing a mixed filament textured yarn comprised of polyester filaments and nylon filaments, characterized in that spin-oriented polyester filaments and nylon feed filaments are simultaneously partially drawn and false-twist textured to uniform filaments by hot-drawing with or without heat setting, and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said drawing and/or heat setting treatments; wherein said spin-oriented polyester filaments are characterized by an intrinsic viscosity [77] 0.56 to 0.68, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, thermal stability as measured by a (S₂)-value less than +1%, net shrinkage

C^S1₂) l s than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon feed filaments are characterized by relative viscosity (RV) 40 to 80, elongation-to-break (E_B) 60 to 90%, ^>oil-off shrinkage (S-i) less than 10%, and dimensional stability as measured by a (ΔLi₃5_ o c)~^val^ue less than 0.

10. A process for preparing a mixed filament textured yarn comprised of polyester filaments and nylon filaments, characterized in that spin-oriented polyester filaments and nylon feed filaments are sequentially partially drawn to uniform filaments by hot-drawing or by cold-drawing, then false-twist textured with heat setting, and the polyester and nylon filaments are combined to form a mixed filament yarn before or after said drawing and/or texturing treatments; wherein said spin-oriented polyester filaments are characterized by an intrinsic viscosity [77] 0.56 to 0.68, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (S ) less than 10%, thermal stability as measured by a (S2)-value less than +1%, net shrinkage (S^) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon feed filaments are characterized by relative viscosity (RV) 40 to 80, elongation-to-break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, and dimensional stability as measured by a (ΔLi₃₅_₄o c)~ value less than 0.

11. A process for preparing a mixed filament yarn, of polyester filaments and nylon filaments, of elongation (E_B) 60% to 90% and boil-off shrinkage (Si) less than 10%, comprising co-spinning, attenuating, quenching, and winding said polyester and nylon filaments at a withdrawal speed (V) of 3.5 km/min to 6.5 km/min, such that the relative viscosity (RV) of said nylon filaments is between 40 and 80 and less than the expression: [13.3V -(6.5-X)], wherein X is the weight percent of any copolyamide, with suitable dimensional stability, as measured by a (ΔLi₃₅__{45 c})- value less than 0; and wherein said polyester filments are of intrinsic viscosity [η 0.56 to 0.68, thermal stability as measured by a (S2)-value less than +1%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms.

12. A process according to Claim 11 that is a coupled spin/draw process wherein, prior to winding, said polyester filaments and nylon filaments are partially drawn to provide uniform drawn polyester and drawn nylon filaments, by hot-drawing or by cold- drawing to drawn elongations (E_B) between 30% and 90% and wherein these drawn elongations (E_B) differ from each other by less than 5%, with or without heat setting to provide a boil-off shrinkage less than 10% and drawn nylon filaments of dimensional stability as given by a (ΔLi35_4Q c)~^value less than 0; and wherein said drawn polyester filaments are of tenacity, at 7% elongation (T₇) at least 1 gram/denier, post yield modulus (PYM, g/d) such that its square root (VPYM) is 2.5 to 5, thermal stability as shown by an S₂-value less than +2%, net shrinkage (S ) less than 8%, maximum shrinkage tension (ST) less than 0.5 g/d, density (p) 1.355 to 1.415 grams/cubic centimeter, and of crystal size (CS) 60 to 90 Angstroms and also at least (250ρ-282.5) Angstroms.

13. A process according to Claim 11 that is a coupled spin/draw process, wherein prior to winding, said polyester and nylon filaments are cold drawn to provide uniform drawn polyester and drawn nylon filaments, of drawn elongations (E_B) 20% to 90% and said drawn elongations (E_B) differ from each other by less than 5%, with or without heat setting to provide boil-off shrinkage (S ) less than 10% and drawn nylon filaments of dimensional stability as given by a

(ΔLI35_4Q c)"*^{va ue} less than 0; and wherein said drawn polyester filaments are of tenacity at 7% elongation (T₇) at least 1 gram/denier, post yield modulus (PYM, g/d) such that its square root (VPYM) is 2.5 to 5, thermal stability as shown by an S2~value less than +2%, net shrinkage (S 2) less than 8%, maximum shrinkage tension (ST) less than 0.5 g/d, density (p) 1.355 to 1.415 grams/cubic centimeter, and of crystal size (CS) 60 to 90 Angstroms and also at least (250p- 282.5) Angstroms.

14. A process according to any of Claims 11^'to 13, wherein any said heat setting treatment is carried out at a temperature (TR, in degrees C) less than (1000/[4.95 - 1.75(RDR)_D/N] - 273), where (RDR)_D/N is the calculated residual draw ratio of the drawn nylon filaments, and is at least 1.2.

15. A mixed filament yarn, suitable for use as a textile yarn, comprised of spin-oriented polyester filaments and of nylon filaments, wherein said spin- oriented polyester filaments are characterized by an intrinsic viscosity [77] 0.56 to 0.68, elongation-to- break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, thermal stability as measured by a (S₂)-value less than +1%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.3 gpd, density (p) 1.35 to 1.39 g/cm³, and crystal size (CS) 55 to 90 Angstroms and also at least (250p-282.5) Angstroms; and wherein said nylon filaments are characterized by rela- tive viscosity (RV) 40 to 80, elongation-to- break (E_B) 60 to 90%, boil-off shrinkage (Si) less than 10%, and dimensional stability as measured by a (ΔL135.-.4₀ c)~ value less than 0.

16. A mixed filament textile yarn, comprised of drawn polyester filaments and of drawn nylon filaments of elongation (E_B) between 20 and 90% and boil-off shrinkage (Si) less than 10%, and wherein said drawn polyester filaments are of intrinsic viscosity [77] 0.56 to 0.68, tenacity at 7% elongation (T7) at least 1 gram/denier, post yield modulus (PYM, g/d) such that its square root (VPYM) is 2.5 to 5, thermal stability as shown by an S2~value less than +2%, net shrinkage (S12) less than 8%, maximum shrinkage tension (ST) less than 0.5 g/d, density (p) 1.355 to 1.415 grams/cubic centimeter, and of crystal size (CS) 60 to 90 Angstroms and also at least the following value in the relation to density: CS > (250p- 282.5) Angstroms; and wherein said drawn nylon filaments are of relative viscosity (RV) 40 to 80, and a dimensional stability as given by a (ΔLi35_4o c) "^value less than 0.

17. A mixed filament false-twist textured yarn of elongation (E_B) between 20 and 60% and boil-off shrinkage (S ) less than 10%, comprised of uniform drawn polyester filaments and of uniform drawn nylon filaments, wherein said drawn polyester filaments are of intrinsic viscosity [77] 0.56 to 0.68, tenacity at 7% elongation (T7) at least 1 gram/denier, post yield modulus (PYM, g/d) such that its square root (VPYM) is 2.5 to 5, thermal stability as shown by an S₂-value less than +2%, net shrinkage (S 2) less than 8%, maximum shrinkage tension (ST) less than 0.5 g/d, density (p) 1.355 to 1.415 grams/cubic centimeter, and of crystal size (CS) 60 to 90 Angstroms and also at least (250p- 282.5) Angstroms; and wherein said drawn nylon filaments are of relative viscosity (RV) 40 to 80, and a dimensional stability as given by a (ΔLi₃5_4 c)-value less than 0.