Manufacturing method of monofilament

Abstract

A method for preparing a monofilament is disclosed, comprising: a) melt spinning a thermoplastic polyurethane to form a monofilament, b) cooling the monofilament at a temperature between 0° C. and 40° C., c) drawing the monofilament by at least two roller groups, d) heat setting the monofilament, and e) winding the monofilament, wherein the thermoplastic polyurethane has a Shore hardness of 65D or greater measured according to DIN ISO 7619-1. Also disclosed is a monofilament prepared from the method.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims the benefit of International Application CN2022 / 077711, filed February 24, 2022.

[0002] background Thermoplastic polyurethane (TPU) materials are used in large quantities in the manufacture of fibers, fabrics, and clothing. One method of processing TPU materials is melt spinning, in which the TPU material is melted and then spun to form rigid monofilaments. The rigid monofilaments are then knitted or woven to make, for example, articles of clothing.

[0003] One problem with this method is that the as-spun rigid TPU monofilaments exhibit high boiling water shrinkage (BWS), often greater than 10%, a property that can cause significant shrinkage when articles made from the monofilaments are treated with boiling water or steam.

[0004] Furthermore, as-spun stiff TPU monofilaments exhibit high elongation at break, ranging from 60% to 120%. This property can make it difficult to control the tension of the monofilament in subsequent processing steps, such as winding, unwinding, twisting, knitting, etc., where uniformity in hank tension is required for the monofilament. In turn, hank tension variations are the source of several defects in the final product, e.g., garments.

[0005] US Patent Publication No. 20090311529 disclosed a method for producing high tenacity monofilaments, in which a thermoplastic elastomer is melted and extruded, followed by orientation and dynamic annealing. A TPU composition with a Shore hardness of 57D was used. The heat shrinkage of the prepared monofilaments was greater than 10%.

[0006] US Patent Publication No. 20210238338 disclosed a method for producing TPU fibers. The TPU fibers were prepared with TPU having a Shore hardness ranging from 35D to 75D. The TPU fibers still had a high elongation at break, exceeding 70%.

[0007] US Patent No. 11136431 disclosed a method for producing filaments. A crystalline thermoplastic polyurethane composition was extrusion spun at a speed of at least 1500 m / min to form filaments. The filaments had a shrinkage of less than 15% after exposure to 80° C. for 90 seconds.

[0008] overview In one aspect of the present disclosure, a method for producing a monofilament includes the steps of: a. melt spinning a thermoplastic polyurethane to form a monofilament; b. Cooling the monofilament at a temperature of 0℃ to 40℃; c. drawing the monofilament through at least two roller groups; d. heat setting the monofilament; and e. Winding the monofilament; Including,

[0009] A method is provided, wherein the thermoplastic polyurethane has a Shore hardness of ≧65D, measured according to DIN ISO 7619-1.

[0010] Through these steps, monofilaments with low elongation at break and low boiling water shrinkage can be prepared.

[0011] In another aspect of the disclosure, a monofilament prepared according to the method is provided. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 illustrates a method for preparing a monofilament according to some embodiments of the present disclosure. [Diagram 2] FIG. 1 illustrates a schematic system for preparing monofilaments according to some embodiments of the present disclosure.

[0013] Detailed Description Unless otherwise defined, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which this disclosure belongs. As used herein, the following terms have the meanings set forth below unless otherwise specified.

[0014] The articles "a," "an," and "the" refer to one or more of the species designated by the term following the article.

[0015] In the context of this disclosure, any specific values ​​recited for a characteristic (including specific values ​​recited in a range as endpoints) can be recombined to form a new range. Further embodiments of the present disclosure can be seen from the claims, the specification, and the examples.

[0016] It will be understood that the above-mentioned features of the subject matter of the present disclosure, and also those further described below, can be used not only in the specific combinations shown, but also in other combinations without departing from the scope of the present disclosure.

[0017] For purposes of this disclosure, the following terms have the respective definitions set forth below.

[0018] "Boiling water shrinkage" refers to the rate at which a test specimen loses length as a result of heat treatment in boiling water, expressed as a percentage of the original length of the test specimen. In this disclosure, boiling water shrinkage is measured under tension before and after treatment according to standard ASTM D2259-02.

[0019] "Elongation at break" refers to the ratio of the changed length after break of a test specimen to its initial length, measured according to method A of standard ISO 2062:2009.

[0020] "Spinning speed" refers to the length of filament produced by melt spinning per unit time.

[0021] The "linear velocity" of a rotating object refers to the distance that a point on the rotating object travels in a unit of time.

[0022] The "linear density" of a filament refers to the mass per unit of length of the filament. In practice, the linear density of a filament is measured according to standard ISO 2060:1994 and is often calculated or expressed in units of "denier" (abbreviated as "De").

[0023] "Stress at 20% strain" refers to the stress at which the strain of a material reaches 20% of its original dimension, measured according to standard DIN 53504-S2.

[0024] "Toughness" of a filament refers to the breaking load of the filament (in grams-force) divided by its linear density, expressed in centinewtons per decitex (cN / dtex), measured according to method A of standard ISO 2062:2009.

[0025] 1, a flow chart shows a method for preparing a monofilament. The method includes steps 102 to 112.

[0026] In step 102, the thermoplastic polyurethane is melt spun to form a monofilament.

[0027] In step 104, the monofilament is cooled at a temperature of 0°C to 40°C.

[0028] In step 106, the monofilament is drawn through at least two rollers.

[0029] Optionally, in step 106, the monofilament is relaxed by a set of relaxation rollers.

[0030] In step 110, the monofilament is heat set.

[0031] In step 112, the monofilament is wound.

[0032] 2 illustrates a chart of an operating system for preparing monofilaments according to some embodiments of the present disclosure. A melt spinning apparatus 210 melt spins thermoplastic polyurethane to form a plurality of monofilaments.

[0033] The monofilaments then enter a quench tank 220 filled with cooling water or other coolant. Two directing rollers 224 and 230 are configured to redirect the monofilaments. Directing roller 224 is installed inside the quench tank and is submerged in the cooling water or coolant. Directing roller 230 is installed outside the quench tank. Directing rollers 224 and 230 pull the monofilaments out of the quench tank and redirect them to the next roller for drawing.

[0034] The three roller groups 242, 244, and 246 are set at different linear speeds R1, R2, and R3, respectively. The two heating devices 252 and 254 are disposed between the roller groups 242 and 244 and between the roller groups 244 and 246, respectively. The following requirements are met: R2 is greater than R1, and R3 is greater than R2. The monofilament is drawn by the roller groups 242 and 244 and the roller groups 244 and 246. The heating devices 252 and 254 heat the monofilament. Any of the roller groups 242, 244, and 246 may comprise multiple rollers, preferably three rollers. The heating device 252 or 254 may be a hot water tank, a hot air oven, or other heating device. The heating device 252 may be different from the heating device 254. In one embodiment, the heating device 252 is a hot water tank, while the heating device 254 is a hot air oven.

[0035] After the monofilament passes through roller group 246, it is drawn into relaxation roller group 260. Relaxation roller group 260 rotates at a linear speed Rr less than R3. Relaxation roller group 260 may include multiple rollers, preferably three rollers.

[0036] The monofilament then enters a hot air oven 270 where it is heat set, passes through orientation rollers 280 and is then wound by a winder 290 to form one or more bobbins.

[0037] Thermoplastic Polyurethane The thermoplastic polyurethane used in the present disclosure has a Shore hardness of 65D or more, measured according to DIN ISO 7619-1. Preferably, the thermoplastic polyurethane has a Shore hardness of 68D to 90D, more preferably a Shore hardness of 70D to 80D, measured according to DIN ISO 7619-1.

[0038] The thermoplastic polyurethane has a stress at 20% strain of 18 MPa or more, preferably a stress at 20% strain of 22 MPa to 45 MPa, and more preferably a stress at 20% strain of 25 MPa to 38 MPa.

[0039] The thermoplastic polyurethane used in the method of the present disclosure comprises the reaction product of (A) a polyol, (B) a diisocyanate, and (C) a chain extender.

[0040] The thermoplastic polyurethanes used in the method of the present disclosure are generally obtained by reacting the essential components of polyol, diisocyanate and chain extender together, optionally in the presence of a catalyst and / or auxiliary, but not limited thereto. The reaction can be, in one embodiment, a one-step reaction in which all of the essential components are reacted together in one step in the presence of optional components such as auxiliary, or a multi-step reaction in which some of the polyol and diisocyanate are reacted together to form a prepolymer, and then the prepolymer and the remaining essential components are reacted together, preferably in the presence of auxiliary.

[0041] Examples of the auxiliary agent are not particularly limited, and may be selected from antioxidants, hydrolysis stabilizers, ultraviolet absorbers, flame retardants, plasticizers, flow improvers, and crosslinking agents, and one or more selected from these may be used. The amount of the auxiliary agent may be determined by one skilled in the art according to the actual application.

[0042] The thermoplastic polyurethanes used in the methods of the present disclosure may have a weight average molecular weight in the range of 50,000 to 400,000 g / mol, preferably 60,000 to 300,000 g / mol, for example 80,000 to 200,000 g / mol.

[0043] Polyol The thermoplastic polyurethane used in the method of the present disclosure has (A) a polyol as one of its raw materials.

[0044] The polyol used in the present disclosure may be a compound generally known as an isocyanate-reactive compound. In particular, the polyol used in the present disclosure may be selected from the group consisting of polyester polyols, polyether polyols, and any mixture thereof.

[0045] Preferably, the functionality of the polyols used in the present disclosure is in the range of 1.5-2.5, preferably 1.8-2.3, more preferably 1.9-2.1, for example 2.

[0046] Polyether polyols can be obtained by known methods, for example by polymerization of alkylene oxides in the presence of a catalyst to which at least one starter molecule containing 2 to 8, preferably 2 to 6, reactive hydrogen atoms has been added. As catalysts, alkali metal hydroxides such as sodium hydroxide or potassium hydroxide, or alkali metal alkoxides such as sodium methoxide, sodium ethoxide, potassium ethoxide, or potassium isopropoxide, or, in the case of cationic polymerization, Lewis acids such as antimony pentachloride, boron trifluoride etherate, or bleaching earth, can be used. In addition, complex metal cyanide compounds known as DMC catalysts can also be used as catalysts.

[0047] As alkylene oxide, preference is given to using one or more compounds having 2 to 4 carbon atoms in the alkylene group, for example ethylene oxide, 1,2-propylene oxide, tetrahydrofuran, 1,2- or 2,3-butylene oxide, preferably ethylene oxide, 1,2-propylene oxide and / or tetrahydrofuran, most preferably tetrahydrofuran, in each case either alone or in the form of a mixture.

[0048] Possible starter molecules are, for example, ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, sugar derivatives such as sucrose, sugar alcohols such as sorbitol, and other di- or polyhydric alcohols.

[0049] Examples of polyether polyols include ring-opened polymers of tetrahydrofuran (polytetramethylene glycol, PTMEG), natural oil-based polyether polyols such as alkoxylated castor oil, or other polyether polyols based on natural oils or fats, such as those obtained by ring-opening reactions of epoxidized unsaturated vegetable oils, and also saccharide-based polyether polyols.

[0050] Polyester polyols may be prepared by condensation of polyfunctional alcohols having 2-12 carbon atoms with polyfunctional carboxylic acids having 2-12 carbon atoms. The polyfunctional alcohols or polyfunctional carboxylic acids may have a functionality of about 2. Examples of polyfunctional alcohols may include ethylene glycol, diethylene glycol, butanediol, or combinations thereof. Examples of polyfunctional carboxylic acids may include succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, isomers of naphthalenedicarboxylic acid, or esters or anhydrides of the listed acids.

[0051] Preferably, the polyol used in the present disclosure is selected from the group consisting of polyester diols, polyether diols, and any mixtures thereof.

[0052] Diisocyanates The thermoplastic polyurethane used in the method of the present disclosure has as one of its raw materials a (B) diisocyanate.

[0053] The diisocyanates of the present disclosure may be selected from any organic compound having two isocyanate groups per molecule.

[0054] The diisocyanates of the present disclosure may be aliphatic diisocyanates, or araliphatic diisocyanates, or cycloaliphatic diisocyanates, or aromatic diisocyanates.

[0055] For example, the diisocyanate may contain 3 to 40 carbon atoms, and in various embodiments the diisocyanate may contain 4 to 20, 5 to 24, or 6 to 18 carbon atoms. In certain embodiments, the diisocyanate is a symmetric aliphatic or cycloaliphatic diisocyanate.

[0056] Examples of suitable diisocyanates of the present disclosure include the isomers of diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, the isomers of tolylene diisocyanate, 3,3'-dimethyldiphenyl diisocyanate, 1,2-diphenylethane diisocyanate, phenylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, octamethylene diisocyanate, 2-methylpentamethylene-1,5-diisocyanate, 2-ethylbutylene-1,4-diisocyanate, isophorone diisocyanate, the isomers of bis(isocyanatomethyl)cyclohexane, 1-methyl-2,4-cyclohexane diisocyanate, and the like. diisocyanate, 1-methyl-2,6-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, 2,2'-dicyclohexylmethane diisocyanate, and any mixtures thereof, more preferably the diisocyanate is selected from the group consisting of isomers of diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, isomers of tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and any mixtures thereof, in particular the diisocyanate is diphenylmethane diisocyanate, hexamethylene diisocyanate, and any mixtures thereof, in particular 4,4'-diphenylmethane diisocyanate.

[0057] In one embodiment of the present disclosure, one diisocyanate is used.

[0058] Chain extender The thermoplastic polyurethane used in the method of the present disclosure has as one of its ingredients (C) a chain extender.

[0059] The chain extenders of the present disclosure may include aliphatic, araliphatic, aromatic and / or cycloaliphatic compounds having two functional groups. For example, chain extenders suitable for the present disclosure may be selected from difunctional alcohols, particularly diols, such as alkanediols having 2 to 10 carbon atoms in the alkylene group.

[0060] Examples of chain extenders suitable for the present disclosure include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,10-decanediol, 1,2-dihydroxycyclohexane, 1,3-dihydroxycyclohexane, 1,4-dihydroxycyclohexane, diethylene and triethylene glycols, dipropylene and tripropylene glycols, 1,6-hexanediol and bis(2-hydroxyethyl)hydroquinone, triols such as 1,2,4-trihydroxycyclohexane, 1,3,5-trihydroxycyclohexane, glycerol and trimethylolpropane. Particularly preferred chain extenders include 1,3-propanediol, 1,4-butanediol, or 1,6-hexanediol. In certain cases, it is possible to use a mixture of two chain extenders.

[0061] Preferably, to form the thermoplastic polyurethane of the present disclosure, the polyol, diisocyanate, and chain extender are used in a molar ratio of isocyanate groups from the diisocyanate to isocyanate-reactive groups from both the polyol and the chain extender in the range of 0.9:1.0 to 1.1:1.0, preferably 0.95:1.0 to 1.05:1.0, and more preferably 0.97:1.0 to 1.03:1.0.

[0062] The method for preparing the monofilaments is detailed below.

[0063] In step (a), the thermoplastic polyurethane is passed through a spinneret operating at a spinning temperature. The spinning temperature may be greater than 150° C., preferably in the range of 180° C. to 250° C., more preferably in the range of 200° C. to 240° C. The spinning temperature may keep the thermoplastic polyurethane in a molten state.

[0064] The thermoplastic polyurethane has a Shore hardness of 65D or more, preferably a Shore hardness of 68D to 90D, more preferably a Shore hardness of 70D to 80D, measured according to DIN ISO 7619-1.

[0065] Step (a) of the method of the present disclosure is not particularly limited and can be performed by a person skilled in the art. Melt spinning is a technique in which a molten raw material composition obtained by heating the raw material composition to a temperature above the melting point using an extruder or the like is discharged from a spinneret into a quenching tank. The position of the spinneret is not limited. However, it is preferable to face the spinneret downward so that the molten composition (molten filament) is discharged (drawn down) downward. The discharged monofilament is cooled and solidified in the atmosphere while being finely divided, and then taken at a constant speed.

[0066] Preferably, in step (a), the thermoplastic polyurethane is melt spun at a spinning speed of less than 500 m / min.

[0067] In step (b), the monofilament is cooled under a temperature between 0° C. and 40° C. Cooling can be accomplished by using a quench tank filled with water, ice water, or other coolant.

[0068] Preferably, the monofilament is cooled at a temperature of 4°C to 30°C.

[0069] In step (c), the monofilament is stretched by at least two roller groups. The roller groups may rotate at different linear speeds. The rollers may be heated or unheated. The rollers are preferably driven rollers, i.e., the rollers are not driven by the monofilament.

[0070] In some embodiments, the at least two roller groups have a first roller group rotating at a first linear speed R1 and a second roller group rotating at a second linear speed R2, in that order. R2 is equal to or greater than R1, and each roller group includes at least three rollers. The first roller group is closer to the spinneret, while the second roller group is farther from the spinneret. The difference in linear speed at which the first and second roller groups rotate causes the monofilament to be drawn.

[0071] In some embodiments, the rollers are godet rollers. The first and / or second groups of rollers comprise three, five, or more rollers.

[0072] Preferably, R1 is in the range of 10 to 100 m / min.

[0073] Preferably, the ratio of R2 to R1 is in the range of 1.5 to 5. The larger the ratio of R2 to R1, the stronger the drawing that the monofilament undergoes between the first roller group and the second roller group.

[0074] Preferably, the monofilament is heated at a temperature between 70° C. and 100° C. after the monofilament passes through the first set of rollers and before the monofilament passes through the second set of rollers. Heating can be achieved by passing the monofilament through a tank filled with hot water or an oven filled with hot air.

[0075] In some embodiments, the at least two roller groups further include a third roller group operating at a third linear speed R3, where R3 is greater than or equal to R2, and the third roller group comprises at least three rollers.

[0076] Preferably, the ratio of R3 to R1 is in the range of 1.5 to 10. The higher the ratio of R3 to R1, the stronger the overall stretching that the monofilament undergoes between the first roller group and the third roller group.

[0077] Preferably, the monofilament is heated at a temperature between 100° C. and 130° C. after the monofilament passes through the second set of rollers and before the monofilament passes through the third set of rollers. Heating is accomplished by passing the monofilament through an oven filled with hot air or steam. Alternatively, heating is accomplished by contacting the monofilament with a heated surface.

[0078] Optionally, after the monofilament is drawn by the at least two roller groups in step (c) and before it is heat set in step (d), it is relaxed by a relaxation roller group in step (f). The relaxation roller group rotates at a relaxation linear speed that is slower than the linear speed at which the last group of the at least two roller groups rotates. For example, if the monofilament is drawn by three roller groups rotating at linear speeds in the order R1, R2, and R3, the linear speed Rr of the relaxation roller group is slower than the linear speed R3 of the third roller group. The reduction in linear speed can relax the monofilament and relieve stress along and / or within the monofilament.

[0079] The relaxation roller group may comprise three or more rollers.

[0080] In step (d), the monofilament is heat set, preferably at a temperature between 130° C. and 170° C. Heat setting allows the monofilament to retain its dimensions and properties. Heat setting can be achieved by using a hot air oven.

[0081] The monofilament may be wound in step (e) to form one or more bobbins and collected and packaged for transport or storage.

[0082] In some embodiments, the monofilaments have a linear density, measured according to ISO 2060:1994, of between 70 denier and 700 denier.

[0083] In some embodiments, the monofilaments have a boiling water shrinkage of 10% or less, preferably 9% or less, measured according to ASTM D2259-02.

[0084] In some embodiments, the monofilament has a bicomponent or hollow structure. EXAMPLES

[0085] The table below lists the relevant test methods. [Table 1]

[0086] The TPU materials used in the examples were as follows:

[0087] TPU1 (obtained from BASF and having a Shore hardness of 64D) had a weight average molecular weight of 80,000-160,000 and was based on poly(1,4-butylene adipate) with a number average molecular weight of 1,000 g / mol, methylenediphenyl diisocyanate (MDI), and 1,4-butanediol and was used to prepare the monofilaments.

[0088] TPU2 (obtained from BASF and having a Shore hardness of 74 D) had a weight average molecular weight of 80,000 to 160,000 and was based on poly(1,4-butylene adipate) with a number average molecular weight of 1,000 g / mol, MDI, and 1,4-butanediol and was used to prepare the monofilaments.

[0089] TPU3 (obtained from BASF and having a Shore hardness of 78 D) had a weight average molecular weight of 80,000 to 160,000 and was based on poly(1,4-butylene adipate) with a number average molecular weight of 1,000 g / mol, MDI, and 1,4-butanediol and was used to prepare the monofilaments.

[0090] TPU4 (obtained from BASF and having a Shore hardness of 74D) based on poly(tetramethylene ether) glycol with a weight average molecular weight of 80,000-160,000 and a number average molecular weight of 1,000 g / mol, MDI, and 1,4-butanediol, was used to prepare the monofilaments.

[0091] TPU5 (obtained from BASF and having a Shore hardness of 78D) based on poly(tetramethylene ether) glycol with a weight average molecular weight of 80,000-160,000 and a number average molecular weight of 1,000 g / mol, MDI, and 1,4-butanediol was used to prepare the monofilaments.

[0092] The TPU material was melt spun by a spinning machine operating at a temperature of 220-240°C to form a monofilament. The monofilament was then cooled in a quenching tank filled with water at 25°C. Then, after cooling, the monofilament was passed through a first, second, and third set of rollers rotating at linear speeds R1, R2, and R3, respectively. Between the first and second set of rollers, the monofilament was heated by a first hot water tank at a temperature of 80°C. Between the second and third set of rollers, the monofilament was heated by a second hot air oven at a temperature of 110°C. The monofilament was then heat set at a temperature of 145°C.

[0093] The following table lists the parameters and test data of the TPU materials and monofilaments prepared therefrom. [Table 2]

[0094] The above data suggests that the hard TPU with Shore hardness of more than 65D can produce monofilaments with low boiling water shrinkage and low elongation at break after melt spinning and processing.Furthermore, compared with the complicated and energy-consuming methods, this method is simple and the production cost of monofilaments is low.

Claims

1. A method for producing a monofilament, comprising the steps of: (a) melt spinning a thermoplastic polyurethane to form a monofilament; (b) cooling the monofilament at a temperature between 0°C and 40°C; (c) drawing the monofilament through at least two roller groups; (d) heat setting the monofilament; and (e) winding the monofilament; The method of claim 1, wherein the thermoplastic polyurethane has a Shore hardness of 65D or greater, measured according to DIN ISO 7619-1.

2. 2. The method according to claim 1, wherein the thermoplastic polyurethane has a Shore hardness of 68D to 90D, preferably 70D to 80D, measured according to DIN ISO 7619-1.

3. 10. The method of claim 1, wherein in step (a), the thermoplastic polyurethane is melt spun at a spinning speed of less than 500 m / min.

4. 2. The method of claim 1, wherein the thermoplastic polyurethane has a stress at 20% strain of 18 MPa or more, preferably a stress at 20% strain of 22 MPa to 45 MPa, more preferably a stress at 20% strain of 25 MPa to 38 MPa, measured according to DIN 53504-S2.

5. 2. The method of claim 1, wherein the monofilament is cooled in step (b) at a temperature between 4°C and 30°C.

6. 2. The method of claim 1, wherein the at least two roller groups include, in that order, a first roller group rotating at a first linear velocity R1 and a second roller group rotating at a second linear velocity R2, where R2 is greater than or equal to R1, and each roller group comprises at least three rollers.

7. The method according to claim 6, wherein R1 is in the range of 10 to 100 m / min.

8. 7. The method of claim 6, wherein the ratio of R2 to R1 is in the range of 1.5 to 5.

9. 7. The method of claim 6, wherein the monofilament is heated at a temperature of 70° C. to 100° C. after the monofilament passes through the first set of rollers and before the monofilament passes through the second set of rollers.

10. 7. The method of claim 6, wherein the at least two roller groups further comprise a third roller group operating at a third linear speed R3, R3 being greater than or equal to R2, and the third roller group comprising at least three rollers.

11. The method of claim 10, wherein the ratio of R3 to R1 ranges from 1.5 to 10.

12. 7. The method of claim 6, wherein the monofilament is heated at a temperature of 100° C. to 130° C. after the monofilament passes through the second set of rollers and before the monofilament passes through a third set of rollers.

13. 10. The method of claim 1, further comprising the step (f) of relaxing the monofilament by a set of relaxation rollers after step (c) and before step (d).

14. 7. The method of claim 6, wherein the monofilament is heat set in step (d) at a temperature of 130°C to 170°C.

15. A monofilament prepared according to the method of any one of claims 1 to 12.

16. 16. The monofilament of claim 15 having a linear density, measured according to ISO 2060:1994, of from 70 denier to 700 denier.

17. 16. The monofilament according to claim 15, having a boiling water shrinkage of less than or equal to 10%, preferably less than or equal to 9%, measured according to ASTM D2259-02.

18. 16. The monofilament according to claim 15, having a bicomponent or hollow structure.

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