PREPARATION METHOD OF SELF-CRIMPING ELASTIC COMBINED FILAMENT YARN FOR KNITTING

Abstract

A preparation method of self-crimping elastic combined filament yarns for knitting is disclosed, wherein the combined filament yarns are extruded from the same spinneret; a first fiber-forming polymer melt is divided into two ways, one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a second fiber-forming polymer melt; the first fiber-forming polymer and the second fiber-forming polymer are compatible or partially compatible; on the same spinneret, a ratio of the number of spinneret holes m for direct extrusion to the number of spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:(5-10); the self-crimping elastic combined filament yarns for knitting are prepared according to specific spinning processes, wherein the combined filament yarn mainly comprises a first fiber-forming polymer monofilament and a first/second fiber-forming polymer side-by-side composite monofilament; wherein the monofilament crimping directions are randomly distributed.

Claims

1. A method for preparing a self-crimping elastic combined filament yarn for knitting, comprising: extruding the self-crimping elastic combined filament yarn for knitting from a same spinneret; wherein a first fiber-forming polymer melt is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a second fiber-forming polymer melt; wherein the first fiber-forming polymer melt and the second fiber-forming polymer melt are compatible or partially compatible; on the same spinneret, wherein a ratio of a number of spinneret holes for direct extrusion to a number of spinneret holes for extrusion after the distribution by side-by-side composite spinning is 1:(5-10); wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on a same circle are all the spinneret holes for the direct extrusion or all the spinneret holes for the extrusion after the distribution by side-by-side composite spinning, while the spinneret holes on an outermost circle are all the spinneret holes for the extrusion after the distribution by side-by-side composite spinning; wherein each of the spinneret holes for the direct extrusion comprises a first guide hole, a first transition hole and a first capillary micropore connected sequentially, each of the spinneret holes for the extrusion after the distribution by side-by-side composite spinning comprises a second guide hole, a second transition hole and a second capillary micropore connected sequentially, the first guide hole is connected with a first distribution hole, and the second guide hole is connected with a second distribution hole and a third distribution hole at the same time; wherein the first distribution hole, the second distribution hole and the third distribution hole are located on a distribution plate in a third spinning box; wherein a division is to transport the first fiber-forming polymer melt through a first spinning box to the first distribution hole and the second distribution hole, while transport the second fiber-forming polymer melt through a second spinning box to the third distribution hole; after the extrusion, wherein the self-crimping elastic combined filament yarn for knitting is prepared according to specific spinning processes: a POY process, an FDY process, a POY-DTY process or a POY-DT process, wherein the POY process, the FDY process and the POY-DT process are followed by a relaxation heat treatment of a fiber, and monofilament crimping directions are randomly distributed after the relaxation heat treatment; wherein the relaxation heat treatment has a temperature of 90-120° C. and a time of 20-30 min.

2. The method of claim 1, wherein a ratio of a mass of the first fiber-forming polymer melt extruded from the spinneret holes for the extrusion after the distribution by side-by-side composite spinning to a mass of the second fiber-forming polymer melt extruded from the spinneret holes for the extrusion after the distribution by side-by-side composite spinning is 50:50, and a ratio of an equivalent diameter of the spinneret holes for the direct extrusion to an equivalent diameter of the spinneret holes for the extrusion after the distribution by side-by-side composite spinning is 1:1; wherein the first fiber-forming polymer melt and the second fiber-forming polymer melt are of same materials with different viscosities, or of different materials; wherein the materials of the first fiber-forming polymer melt and the second fiber-forming polymer melt are selected from polyester or polyamide, wherein the polyester is PET, PBT, or PTT, and the polyamide is PA6.

3. The method of claim 1, wherein each of the spinneret holes for the direct extrusion is a circular, oval, triangular, Y-shaped, cross-shaped, “8”-shaped, rectangular or in-line spinneret hole, and each of the spinneret holes for the extrusion after the distribution by side-by-side composite spinning is a circular, oval or “8”-shaped spinneret hole.

4. (canceled)

5. (canceled)

6. The method of claim 1, wherein an apparent viscosity of the first fiber-forming polymer melt differs from an apparent viscosity of the second fiber-forming polymer melt by no more than 5% in the spinning components.

7. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWING

[0030] FIGURE is a schematic diagram of the structure of the spinneret in the present invention;

[0031] wherein A, B and C are mutually independent distribution holes, and D and E are mutually independent guide holes.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Based on above mentioned method, the following embodiments are carried out for further demonstration in the present invention. It is to be understood that these embodiments are only intended to illustrate the invention and are not intended to limit the scope of the invention. In addition, it should be understood that after reading the contents described in the present invention, those technical personnel in this field can make various changes or modifications to the invention, and these equivalent forms also fall within the scope of the claims attached to the application.

[0033] The crimp shrinkage and crimp stability in the present invention are obtained by testing the tow by using GB6506-2001 “Synthetic fiber—Test method for crimp contraction properties of textured filament yarns”;

[0034] The text methods of the shrinkage elongation (reflecting the degree of elasticity and crimp of textured filament yarns, wherein the fibers are subjected to a light load and then to a heavy load, and the ratio of the difference in length to the curl length is calculated for both loads) and the crimp elastic recovery rate are as follows:

[0035] Firstly, cut two fiber samples of about 50 cm in length, put them into 100° C. hot water for 30 minutes, take them out and dry them naturally, next intercept a sample of about 30 cm in length, wherein fix one end and load another end with a load of 0.0018 cN/dtex for 30 seconds, and mark it at 20 cm, that is, the initial length l1 of the sample; then load another end with a load of 0.09 cN/dtex for 30 seconds, and measure the position of the marked point, which is the length l2 of the sample under heavier load; finally remove the load and let the sample retract for 2 minutes, next add a load of 0.0018 cN/dtex for 30 seconds and measure the position of the marked point, which is the recovery length l3; the shrinkage elongation (CE) and the crimp elastic recovery rate (SR) are calculated as follows:

CE=(l.sub.2−l.sub.1)/l.sub.1;

SR=(l.sub.2−l.sub.3)/(l.sub.2−l.sub.1).

EXAMPLE 1

[0036] A self-crimping elastic combined filament yarns for knitting, prepared as follows:

[0037] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0038] wherein a PET melt with an intrinsic viscosity of 0.57 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PTT melt with an intrinsic viscosity of 1.17 dL/g;

[0039] on the same spinneret, wherein a ratio of the number of circular spinneret holes m for direct extrusion to the number of circular spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:6, the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1, and the ratio of the mass of the PET melt extruded from the spinneret hole n to the mass of the PTT melt extruded from the spinneret hole n is 50:50; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0040] as shown in the figure, wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PET melt through a spinning box Ito the distribution hole A and the distribution hole B, while transport the PTT melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 276° C., the temperature of the spinning box II is 260° C., and the temperature of the spinning box III is 275° C.;

[0041] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by a POY process (obtaining a pre-oriented yarn), a DT stretching process (obtaining a drawn yarn), and then a relaxation heat treatment;

[0042] wherein the POY process has a cooling temperature of 24° C. and a winding speed of 2580 m/min; wherein the DT stretching process has a hot godet temperature of 85° C., a hot plate temperature of 120° C., and a multiplier of 1.6; wherein the relaxation heat treatment has a temperature of 109° C., and a time of 26 minutes;

[0043] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PET monofilament and the PTT/PET side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 69%, a crimp stability of 94%, a shrinkage elongation of 111%, a crimp elastic recovery rate of 83%, a breaking strength of 3.2 cN/dtex, an elongation at break of 46.5%, and a total fineness of 130 dtex.

EXAMPLE 2

[0044] A self-crimping elastic combined filament yarns for knitting, prepared as follows:

[0045] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0046] wherein a PET melt with an intrinsic viscosity of 0.58 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PTT melt with an intrinsic viscosity of 1.15 dL/g;

[0047] on the same spinneret, wherein a ratio of the number of oval spinneret holes m for direct extrusion to the number of oval spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:10, the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1, and the ratio of the mass of the PET melt extruded from the spinneret hole n to the mass of the PTT melt extruded from the spinneret hole n is 50:50; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0048] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PET melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the PTT melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 280° C., the temperature of the spinning box II is 265° C., and the temperature of the spinning box III is 273° C.;

[0049] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by a POY process (obtaining a pre-oriented yarn), a DT stretching process (obtaining a drawn yarn), and then a relaxation heat treatment;

[0050] wherein the POY process has a cooling temperature of 25° C. and a winding speed of 2550 m/min; wherein the DT stretching process has a hot godet temperature of 85° C., a hot plate temperature of 124° C., and a multiplier of 1.8; wherein the relaxation heat treatment has a temperature of 115° C., and a time of 22 minutes;

[0051] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PET monofilament and the PTT/PET side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 66%, a crimp stability of 93%, a shrinkage elongation of 112%, a crimp elastic recovery rate of 84%, a breaking strength of 3.1 cN/dtex, an elongation at break of 48.3%, and a total fineness of 115 dtex.

EXAMPLE 3

[0052] A self-crimping elastic combined filament yarns for knitting, prepared as follows:

[0053] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0054] wherein a PET melt with an intrinsic viscosity of 0.55 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PTT melt with an intrinsic viscosity of 1.2 dL/g;

[0055] on the same spinneret, wherein a ratio of the number of triangular spinneret holes m for direct extrusion to the number of “8”-shaped spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:5, the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1, and the ratio of the mass of the PET melt extruded from the spinneret hole n to the mass of the PTT melt extruded from the spinneret hole n is 50:50; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0056] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PET melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the PTT melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 278° C., the temperature of the spinning box II is 264° C., and the temperature of the spinning box III is 275° C.;

[0057] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by a POY process (obtaining a pre-oriented yarn), a DT stretching process (obtaining a drawn yarn), and then a relaxation heat treatment;

[0058] wherein the POY process has a cooling temperature of 24° C. and a winding speed of 2640 m/min; wherein the DT stretching process has a hot godet temperature of 88° C., a hot plate temperature of 126° C., and a multiplier of 1.8; wherein the relaxation heat treatment has a temperature of 120° C., and a time of 20 minutes;

[0059] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PET monofilament and the PTT/PET side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 69%, a crimp stability of 93.8%, a shrinkage elongation of 113%, a crimp elastic recovery rate of 84%, a breaking strength of 3.3 cN/dtex, an elongation at break of 49.2%, and a total fineness of 125 dtex.

EXAMPLE 4

[0060] A self-crimping elastic combined filament yarns for knitting, prepared as follows:

[0061] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0062] wherein a high-viscosity PET melt with an intrinsic viscosity of 0.75 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a low-viscosity PET melt with an intrinsic viscosity of 0.5 dL/g;

[0063] wherein a ratio of the number of circular spinneret holes m for direct extrusion to the number of circular spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:8; wherein the ratio of the mass of the high-viscosity PET melt extruded from the spinneret hole n to the mass of the low-viscosity PET melt extruded from the spinneret hole n is 50:50; wherein the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1;

[0064] wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0065] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the high-viscosity PET melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the low-viscosity PET melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 286° C., the temperature of the spinning box II is 275° C., and the temperature of the spinning box III is 283° C.;

[0066] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by an FDY process (obtaining a fully drawn yarn), and then a relaxation heat treatment;

[0067] wherein the FDY process involves technological parameters: a cooling temperature of 25° C., an interlacing pressure of 0.2 MPa, a godet roller 1 speed of 2300 m/min, a godet roller 1 temperature of 85° C., a godet roller 2 speed of 3560 m/min, a godet roller 2 temperature of 150° C., and a winding speed of 3460 m/min; wherein the relaxation heat treatment has a temperature of 104° C., and a time of 30 minutes;

[0068] wherein the self-crimping elastic combined filament yarn for knitting is composed of the high-viscosity PET monofilament and the high-viscosity PET/low-viscosity PET side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 53%, a crimp stability of 87%, a shrinkage elongation of 98%, a crimp elastic recovery rate of 96%, a breaking strength of 3.1 cN/dtex, an elongation at break of 45%, and a total fineness of 130 dtex. The self-crimping elastic combined filament yarn for knitting prepared above is made into the knitted fabric, which is tested for strip unevenness, and the fabric has a D value of 0.51.

EXAMPLE 5

[0069] A self-crimping elastic combined filament yarns for knitting, prepared as follows:

[0070] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0071] wherein a high-viscosity PET melt with an intrinsic viscosity of 0.73 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a low-viscosity PET melt with an intrinsic viscosity of 0.54 dL/g;

[0072] wherein a ratio of the number of oval spinneret holes m for direct extrusion to the number of circular spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:6; wherein the ratio of the mass of the high-viscosity PET melt extruded from the spinneret hole n to the mass of the low-viscosity PET melt extruded from the spinneret hole n is 50:50; wherein the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1;

[0073] wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0074] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the high-viscosity PET melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the low-viscosity PET melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 282° C., the temperature of the spinning box II is 271° C., and the temperature of the spinning box III is 278° C.;

[0075] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by an FDY process (obtaining a fully drawn yarn), and then a relaxation heat treatment;

[0076] wherein the FDY process involves technological parameters: a cooling temperature of 20° C., an interlacing pressure of 0.25 MPa, a godet roller 1 speed of 2350 m/min, a godet roller 1 temperature of 95° C., a godet roller 2 speed of 3660 m/min, a godet roller 2 temperature of 160° C., and a winding speed of 3530 m/min; wherein the relaxation heat treatment has a temperature of 103° C., and a time of 28 minutes;

[0077] wherein the self-crimping elastic combined filament yarn for knitting is composed of the high-viscosity PET monofilament and the high-viscosity PET/low-viscosity PET side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 52.8%, a crimp stability of 85%, a shrinkage elongation of 95%, a crimp elastic recovery rate of 95.4%, a breaking strength of 3.1 cN/dtex, an elongation at break of 44.2%, and a total fineness of 115 dtex. The self-crimping elastic combined filament yarn for knitting prepared above is made into the knitted fabric, which is tested for strip unevenness, and the fabric has a D value of 0.39.

EXAMPLE 6

[0078] A self-crimping elastic combined filament yarns for knitting, prepared as follows:

[0079] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0080] wherein a high-viscosity PET melt with an intrinsic viscosity of 0.73 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a low-viscosity PET melt with an intrinsic viscosity of 0.55 dL/g;

[0081] wherein a ratio of the number of triangular spinneret holes m for direct extrusion to the number of circular spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:8; wherein the ratio of the mass of the high-viscosity PET melt extruded from the spinneret hole n to the mass of the low-viscosity PET melt extruded from the spinneret hole n is 50:50; wherein the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1;

[0082] wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0083] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the high-viscosity PET melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the low-viscosity PET melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 283° C., the temperature of the spinning box II is 275° C., and the temperature of the spinning box III is 279° C.;

[0084] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by an FDY process (obtaining a fully drawn yarn), and then a relaxation heat treatment;

[0085] wherein the FDY process involves technological parameters: a cooling temperature of 21° C., an interlacing pressure of 0.23 MPa, a godet roller 1 speed of 2300 m/min, a godet roller 1 temperature of 86° C., a godet roller 2 speed of 3500 m/min, a godet roller 2 temperature of 151° C., and a winding speed of 3430 m/min; wherein the relaxation heat treatment has a temperature of 120° C., and a time of 29 minutes;

[0086] wherein the self-crimping elastic combined filament yarn for knitting is composed of the high-viscosity PET monofilament and the high-viscosity PET/low-viscosity PET side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 52%, a crimp stability of 85.5%, a shrinkage elongation of 96%, a crimp elastic recovery rate of 95.1%, a breaking strength of 3 cN/dtex, an elongation at break of 46%, and a total fineness of 125 dtex. The self-crimping elastic combined filament yarn for knitting prepared above is made into the knitted fabric, which is tested for strip unevenness, and the fabric has a D value of 0.68.

EXAMPLE 7

[0087] A method for preparing a self-crimping elastic combined filament yarns for knitting, comprising:

[0088] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0089] wherein a PBT melt with an intrinsic viscosity of 0.97 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PTT melt with an intrinsic viscosity of 1.03 dL/g; wherein the ratio of the mass of the PBT melt extruded from the spinneret hole n to the mass of the PTT melt extruded from the spinneret hole n is 50:50, and the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1; wherein a ratio of the number of circular spinneret holes m for direct extrusion to the number of circular spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:6;

[0090] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PBT melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the PTT melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 269° C., the temperature of the spinning box II is 272° C., and the temperature of the spinning box III is 279° C.; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0091] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by a POY-DTY process; wherein the POY process has a cooling temperature of 24° C., an interlacing pressure of 0.2 MPa and a winding speed of 2800 m/min; wherein the DTY process has a spinning speed of 750 m/min, a setting over-feed ratio of 3.5%, a winding over-feed ratio of 3%, a first heating chamber temperature of 200° C., a second heating chamber temperature of 173° C., a stretching multiplier of 1.5, a D/Y value of 1.9, and an interlacing pressure 0.05 MPa;

[0092] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PBT monofilament and the PBT/PTT side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed;

[0093] wherein the prepared PBT/PET bicomponent elastic yarn with random distribution of monofilament crimping directions comprises mechanical performance indices: a crimp shrinkage of 65%, a crimp stability of 85%, a shrinkage elongation of 108%, a crimp elastic recovery rate of 98%, a breaking strength of 27 cN/dtex, an elongation at break of 49%, and a total fineness of 200 dtex.

[0094] Comparison 1

[0095] A method for preparing a self-crimping elastic combined filament yarn for knitting comprises steps basically the same as those in example 7, except for the spinning process, wherein the PBT melt is not divided into two ways, but all together with the PTT melt and extruded after distribution by side-by-side composite spinning together; therefore, the prepared self-crimping elastic combined filament yarns for knitting does not have the PTT monofilament.

[0096] The self-crimping elastic combined filament yarns for knitting prepared by the comparison 1 and example 7, are separately used in plain knitted fabrics knitted on a seamlessly formed circular knitting machine to test the stripe unevenness of the two plain knitted fabrics, the testing process of each plain knitted fabric is as follows: first, the plain knitted fabric image is captured and converted into a grayscale image, and then the parameter D will be calculated after the first processing and the second processing of the grayscale image, using the parameter D characterizes the degree of strip unevenness, where the grayscale image includes the strip shade area, the high gray value area of the non-strip shade area and the low gray value area of the non-strip shade area; the first processing is to change the pixel points in the high gray value area of the non-strip shade area in the grayscale image into pure white points; the second processing is to change the pixel points in the low gray value area of the non-strip shade area in the grayscale image into pure white points; the parameter D is calculated by the formula: D=ΣB/A, wherein ΣB represents the number of pixel points in the grayscale image when the gray value is 0, and A represents the total number of pixel points in the grayscale image.

[0097] The test results are as follows: the D value of the plain knitted fabric made of the self-crimping elastic combined filament yarns for knitting in example 7 is 0.7%; the D value of the plain knitted fabric made of the self-crimping elastic combined filament yarns for knitting in comparison 1 is 16.8%; it is shown that the strip unevenness of the plain knitted fabric made of the self-crimping elastic combined filament yarns for knitting in example 7 has been reduced. This is because some PBT/PTT side-by-side composite monofilaments are replaced by a part of PBT monofilaments in example 7, thus breaking the neat left and right spiral shapes of the pure PBT/PTT bicomponent composite fibers; so that the crimp shape of each PBT/PTT side-by-side composite monofilament is different from other fibers, and the stripe unevenness will not appear on the fabric surface after making the plain knitted fabric; however, the plain knitted fabric made of the self-crimping elastic combined filament yarns for knitting in comparison 1, will show uneven stripes on the fabric surface due to the neat left and right spiral shapes of the fibers.

EXAMPLE 8

[0098] A method for preparing a self-crimping elastic combined filament yarns for knitting, comprising:

[0099] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0100] wherein a PBT melt with an intrinsic viscosity of 0.95 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PTT melt with an intrinsic viscosity of 1.05 dL/g; wherein the ratio of the mass of the PBT melt extruded from the spinneret hole n to the mass of the PTT melt extruded from the spinneret hole n is 50:50, and the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1; wherein a ratio of the number of circular spinneret holes m for direct extrusion to the number of oval spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:7;

[0101] among them, wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PBT melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the PTT melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 272° C., the temperature of the spinning box II is 275° C., and the temperature of the spinning box III is 276° C.; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0102] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by a POY-DTY process; wherein the POY process has a cooling temperature of 25° C., an interlacing pressure of 0.21 MPa and a winding speed of 3000 m/min; wherein the DTY process has a spinning speed of 800 m/min, a setting over-feed ratio of 3.8%, a winding over-feed ratio of 3.3%, a first heating chamber temperature of 220° C., a second heating chamber temperature of 180° C., a stretching multiplier of 1.9, a D/Y value of 2.2, and an interlacing pressure 1.5 MPa;

[0103] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PBT monofilament and the PBT/PTT side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed;

[0104] wherein the prepared PBT/PET bicomponent elastic yarn with random distribution of monofilament crimping directions comprises mechanical performance indices: a crimp shrinkage of 61%, a crimp stability of 86%, a shrinkage elongation of 108%, a crimp elastic recovery rate of 97%, a breaking strength of 25 cN/dtex, an elongation at break of 55%, and a total fineness of 105 dtex.

EXAMPLE 9

[0105] A method for preparing a self-crimping elastic combined filament yarns for knitting, comprising:

[0106] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0107] wherein a PBT melt with an intrinsic viscosity of 0.98 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PTT melt with an intrinsic viscosity of 1.1 dL/g; wherein the ratio of the mass of the PBT melt extruded from the spinneret hole n to the mass of the PTT melt extruded from the spinneret hole n is 50:50, and the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1; wherein a ratio of the number of circular spinneret holes m for direct extrusion to the number of “8”-shaped spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:5;

[0108] among them, wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PBT melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the PTT melt through a spinning box II to the distribution hole C; wherein the temperature of the spinning box I is 269° C., the temperature of the spinning box II is 276° C., and the temperature of the spinning box III is 276° C.; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0109] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by a POY-DTY process; wherein the POY process has a cooling temperature of 24° C., an interlacing pressure of 0.22 MPa and a winding speed of 3100 m/min; wherein the DTY process has a spinning speed of 770 m/min, a setting over-feed ratio of 4.5%, a winding over-feed ratio of 3.9%, a first heating chamber temperature of 178° C., a second heating chamber temperature of 130° C., a stretching multiplier of 1.5, a D/Y value of 1.8, and an interlacing pressure 1.4 MPa;

[0110] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PBT monofilament and the PBT/PTT side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed;

[0111] wherein the prepared PBT/PET bicomponent elastic yarn with random distribution of monofilament crimping directions comprises mechanical performance indices: a crimp shrinkage of 65%, a crimp stability of 87%, a shrinkage elongation of 110%, a crimp elastic recovery rate of 98%, a breaking strength of 26 cN/dtex, an elongation at break of 50%, and a total fineness of 120 dtex.

EXAMPLE 10

[0112] A method for preparing a self-crimping elastic combined filament yarns for knitting, comprising:

[0113] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0114] wherein a PET melt with an intrinsic viscosity of 0.5 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PET-PA6 copolymer melt with an intrinsic viscosity of 0.65 dL/g; wherein the ratio of the mass of the PET melt extruded from the spinneret hole n to the mass of the PET-PA6 copolymer melt extruded from the spinneret hole n is 50:50;

[0115] wherein a ratio of the number of circular spinneret holes m for direct extrusion to the number of circular spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:7; wherein the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0116] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PET melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the PET-PA6 copolymer melt through a spinning box II to the distribution hole C;

[0117] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by an FDY process (obtaining a fully drawn yarn), and then a relaxation heat treatment;

[0118] wherein the FDY process involves technological parameters: a temperature of the spinning box I of 282° C., a temperature of the spinning box II of 274° C., a temperature of the spinning box III of 280° C., a cooling temperature of 25° C., an interlacing pressure of 0.2 MPa, a godet roller 1 speed of 2300 m/min, a godet roller 1 temperature of 70° C., a godet roller 2 speed of 3560 m/min, a godet roller 2 temperature of 125° C., and a winding speed of 3480 m/min; wherein the relaxation heat treatment has a temperature of 104° C., and a time of 30 minutes;

[0119] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PET monofilament and the PET/PET-PA6 copolymer side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 53%, a crimp stability of 87%, a shrinkage elongation of 90%, a crimp elastic recovery rate of 93%, a breaking strength of 3.4 cN/dtex, an elongation at break of 45%, and a total fineness of 130 dtex.

[0120] The self-crimping elastic combined filament yarn for knitting prepared above is made into the knitted fabric, which is tested for strip unevenness, and the fabric has a D value of 0.54%.

EXAMPLE 11

[0121] A method for preparing a self-crimping elastic combined filament yarns for knitting, comprising:

[0122] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0123] wherein a PET melt with an intrinsic viscosity of 0.56 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PET-PA6 copolymer melt with an intrinsic viscosity of 0.63 dL/g; wherein the ratio of the mass of the PET melt extruded from the spinneret hole n to the mass of the PET-PA6 copolymer melt extruded from the spinneret hole n is 50:50;

[0124] wherein a ratio of the number of oval spinneret holes m for direct extrusion to the number of circular spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:6; wherein the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0125] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PET melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the PET-PA6 copolymer melt through a spinning box II to the distribution hole C;

[0126] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by an FDY process (obtaining a fully drawn yarn), and then a relaxation heat treatment;

[0127] wherein the FDY process involves technological parameters: a temperature of the spinning box I of 280° C., a temperature of the spinning box II of 271° C., a temperature of the spinning box III of 270° C., a cooling temperature of 20° C., an interlacing pressure of 0.25 MPa, a godet roller 1 speed of 2350 m/min, a godet roller 1 temperature of 80° C., a godet roller 2 speed of 3660 m/min, a godet roller 2 temperature of 130° C., and a winding speed of 3570 m/min; wherein the relaxation heat treatment has a temperature of 103° C., and a time of 28 minutes;

[0128] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PET monofilament and the PET/PET-PA6 copolymer side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 52.8%, a crimp stability of 85%, a shrinkage elongation of 89%, a crimp elastic recovery rate of 91.4%, a breaking strength of 3.15 cN/dtex, an elongation at break of 46%, and a total fineness of 115 dtex.

[0129] The self-crimping elastic combined filament yarn for knitting prepared above is made into the knitted fabric, which is tested for strip unevenness, and the fabric has a D value of 0.82%.

EXAMPLE 12

[0130] A method for preparing a self-crimping elastic combined filament yarns for knitting, comprising:

[0131] (1) extruding the self-crimping elastic combined filament yarn for knitting from the same spinneret;

[0132] wherein a PET melt with an intrinsic viscosity of 0.58 dL/g is divided into two ways: one is directly extruded after distribution; and the other is extruded after distribution by side-by-side composite spinning together with a PET-PA6 copolymer melt with an intrinsic viscosity of 0.63 dL/g; wherein the ratio of the mass of the PET melt extruded from the spinneret hole n to the mass of the PET-PA6 copolymer melt extruded from the spinneret hole n is 50:50;

[0133] wherein a ratio of the number of triangular spinneret holes m for direct extrusion to the number of circular spinneret holes n for extrusion after distribution by side-by-side composite spinning is 1:7; wherein the ratio of the equivalent diameter of the spinneret hole m to the equivalent diameter of the spinneret hole n is 1:1; wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, while the spinneret holes on the outermost circle are all n;

[0134] wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole D, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A, and the guide hole D is connected with a distribution hole B and a distribution hole C at the same time; wherein the distribution hole A, the distribution hole B and the distribution hole C are located on the distribution plate in the spinning box III; wherein the division is to transport the PET melt through a spinning box I to the distribution hole A and the distribution hole B, while transport the PET-PA6 copolymer melt through a spinning box II to the distribution hole C;

[0135] (2) after extrusion, the self-crimping elastic combined filament yarn for knitting is prepared by an FDY process (obtaining a fully drawn yarn), and then a relaxation heat treatment;

[0136] wherein the FDY process involves technological parameters: a temperature of the spinning box I of 280° C., a temperature of the spinning box II of 274° C., a temperature of the spinning box III of 276° C., a cooling temperature of 21° C., an interlacing pressure of 0.23 MPa, a godet roller 1 speed of 2300 m/min, a godet roller 1 temperature of 76° C., a godet roller 2 speed of 3500 m/min, a godet roller 2 temperature of 127° C., and a winding speed of 3430 m/min; wherein the relaxation heat treatment has a temperature of 120° C., and a time of 29 minutes;

[0137] wherein the self-crimping elastic combined filament yarn for knitting is composed of the PET monofilament and the PET/PET-PA6 copolymer side-by-side composite monofilament, and its monofilament crimping directions are randomly distributed; wherein the self-crimping elastic combined filament yarn for knitting comprises mechanical performance indices: a crimp shrinkage of 52%, a crimp stability of 85.5%, a shrinkage elongation of 88%, a crimp elastic recovery rate of 91.1%, a breaking strength of 3 cN/dtex, an elongation at break of 51.2%, and a total fineness of 125 dtex.

[0138] The self-crimping elastic combined filament yarn for knitting prepared above is made into the knitted fabric, which is tested for strip unevenness, and the fabric has a D value of 0.38%.