EP2554721A1

EP2554721A1 - Hygroscopic fibre, and manufacturing method for same

Info

Publication number: EP2554721A1
Application number: EP11762512A
Authority: EP
Inventors: Kenji Itou; Kentaro Takagi; Takahiro Kuribayashi
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2010-03-31
Filing date: 2011-03-09
Publication date: 2013-02-06
Anticipated expiration: 2031-03-09
Also published as: EP2554721A4; US20130280513A1; WO2011122272A1; KR20130040793A; JP5741434B2; EP2554721B1; CN102834556A; KR101550960B1; JPWO2011122272A1; CN102834556B

Abstract

Disclosed is a hygroscopic fiber which is a fiber comprising polyamide 56 resin, and has a MR of at least 3.0%. Further disclosed is a method for manufacturing a polyamide 56 fiber by a direct spin draw method in which: a polyamide 56 fiber discharged through a spinneret is cooled and solidified by cooling air; a spinning oil is deposited thereon and the fiber is stretched; and the fiber is taken up. The disclosed manufacturing method satisfies the following conditions: (1) The spinneret discharge line rate is between 14m/min and 30m/mm; (2) The product of the take up velocity and the draw ratio is between 3900 and 4500. Thus provided are a high added value hygroscopic fiber which has high moisture absorptivity without losing the strength, chemical resistant, and heat resistant characteristics of polyamides.

Description

TECHNICAL FIELD

The present invention relates to a highly hygroscopic fiber comprising a polyamide 56 resin.

BACKGROUND ART

Synthetic fibers each made of a thermoplastic resin, such as a polyamide or a polyester, are widely used for clothing, and for industries since the fibers are excellent in strength, chemical resistant, heat resistant, and other characteristics.
In particular, polyamide fiber is widely used for innerwear, sportswear, and others while the fiber makes good use of a softness, a high tensile strength, a color developability when dyed, a high heat resistant and other characteristics peculiar to the fiber.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1 suggests a method in which after a polyamide fiber is formed, at the stage of post-treating the fiber a moisture absorbent is given to the surface of the fiber.
Attempts are also made for carrying out a method of making a polyamide resin itself hydrophilic, thereby giving hygroscopicity to a fiber therefrom. For example, Patent Document 2 suggests a method of using a polyamide resin into which a hydrophilic component, such as polyoxyalkylene glycol, is copolymerized to manufacture a fiber.
Patent Document 3 suggests a method of rendering the structure of a fiber a core-in-sheath structure having a core region made of a thermoplastic resin high in hygroscopicity, and a sheath region made of a thermoplastic resin excellent in mechanical properties, thereby forming the fiber with compatibility between hygroscopicity and mechanical properties.
Besides such chemical modifications of fiber-forming thermoplastic resins, a physical modification is suggested, the physical modification being a method of mixing a component that can be dissolved out, and extracting the dissolved-out component after the formation of a fiber to form fibrils and voids therein, so as to increase the fiber in moisture-absorbing surface area, thereby aiming to increase the fiber in moisture absorptivity and moisture absorption speed. For example, Patent Document 4 suggests a method of: melt-spinning a blend composite composed of an alcohol-soluble polyamide, and a fiber-forming thermoplastic resin compatible with the alcohol-soluble polyamide; and then partially dissolving out, from the resultant, the alcohol-soluble polyamide to yield a hygroscopic fiber similar to a natural fiber.
In general, about a method of adding a hydrophilic compound to a polyamide fiber, investigations have been most frequently made. For example, Patent Document 1 suggests a method of blending a polyamide with polyvinyl pyrrolidone as a hydrophilic polymer, and then spinning the resultant blend, thereby improving the resultant fiber in hygroscopicity.

Patent Document 1: JP 9-188917A
Patent Document 2: JP 5-209316A
Patent Document 3: JP 3-213519A
Patent Document 4: JP 60-246818A

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

Conventional polyamide fibers are lower in hygroscopicity than natural fibers to cause, for example, a stuffy or sweaty state based on sweating-out from the skin. Thus, the polyamide fibers have a problem of being poorer in comfortableness than natural fibers.
Thus, suggested is a method in which after a fiber of a polyamide is formed, at the stage of post-treating the fiber a moisture absorber is given to the surface of the fiber.
However, the method has the following drawbacks: a fabric of the fiber is lowered in washing resistance; and further when the fabric receives the supply of a large amount of a moisture absorbent to gain a high hygroscopicity, the fabric gets slimy in the surface thereof because of moisture absorption to give an unpleasant feeling.
According to the method of Patent Document 2, in order to attain a sufficient hygroscopicity, the fiber is required to be made high in copolymerization proportion of comonomer. However, the requirement causes the fiber to be remarkably damaged in mechanical properties of the yarn, such as the strength and elongation thereof. Thus, a fiber satisfying hygroscopicity and mechanical properties simultaneously has not yet been attained.
The composite fiber of Patent Document 3 has a drawback that a manufacturing apparatus therefor becomes complex so that costs increase. The fiber also has, for example, the following drawback because of the difference in water absorbing power between the polymers used in the core region and in the sheath region: at the time of subjecting the fiber to treatments with hot water, such as refining and dyeing, the hygroscopic resin in the core region absorbs water to swell largely; thus, the surface of the fiber is cracked so that the polymer in the core region is unfavorably dissolved out.
In a method such as the method of Patent Document 4, a fiber cannot gain a sufficient hygroscopicity when the quantity of the dissolved-out component is small. Conversely, when the quantity of the dissolved-out component is large, the fiber turns insufficient in physical properties, such as strength. Thus, when clothing thereof is worn, for example, a drawback that the fabric (of the clothing) is whitened or made into fibrils is caused. In short, it is difficult that the fiber satisfies both of hygroscopicity and physical properties.
Although the fiber according to the method of Patent Document 1 is excellent as a hygroscopic fiber, the fiber is insufficient in heat resistance for being subjected to heat forming, because of the addition of polyvinyl pyrrolidone to the base of polyamide 6 as a polyamide, under such a situation that: in recent years, for example, there has been recognized a fashion trend that women who wear T-shirts fitted tightly to their bodies have been increasing; and with the trend, a demand for heat-formed brassieres, which are not easily reflected onto outerwear, has been increasing. When polyvinyl pyrrolidone is added to polyamide 66, which has a high melting point, as a base, the temperature for spinning polyamide 66 is high so that polyvinyl pyrrolidone is thermally deteriorated. Thus, there remains a problem that this blend material cannot be stably spun.
As described above, it is desired to invent a raw yarn having a hygroscopicity equivalent to that of natural fiber without damaging properties of polyamide fiber.
An object of the present invention is to overcome the problems in the prior art, and provide a highly value-added, hygroscopic synthetic fiber, which has a high moisture absorptivity, without damaging the strength, the chemical resistant, the heat resistant nor other characteristics s of polyamide.

SOLUTIONS TO THE PROBLEMS

The object of the invention is attained by the following:

A hygroscopic fiber, comprising a polyamide 56 resin, and having an ΔMR of 3.0% or more.

The object of the invention is also attained by a method for manufacturing a hygroscopic fiber by a direct spin draw method comprising cooling and solidifying a polyamide 56 fiber discharged from a spinneret by cooling wind, depositing a spinning oil onto the fiber, drawing the fiber, and then winding the fiber, wherein the following requirements (1) and (2) are satisfied:

(1) the spinning liner velocity ranges from 14 m/min or more to 30 m/min or less, and
(2) the product of the take up velocity and the draw ratio ranges from 3,900 or more to 4,500 or less.

The object of the invention is further attained by a fiber structure comprising the fabric.
The hygroscopic fiber of the invention preferably has a birefringence ranging from 30 x 10^-3 or more to 40 x 10^-3 or less. The fabric of the invention is preferably a fabric wherein the hygroscopic fiber is used, the fabric comprising a portion shaped by mold process.
The fiber structure of the invention is preferably an innerwear.

EFFECTS OF THE INVENTION

The invention makes it possible to yield a highly value-added, hygroscopic synthetic fiber, which has a high moisture absorptivity, without damaging the strength, the chemical resistant, the heat resistant nor other characteristics of polyamide.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 is a schematic view illustrating an example of a process for manufacturing a synthetic fiber according to the invention.

MODE FOR CARRYING OUT THE INVENTION

The polyamide 56 fiber of the invention is a fiber containing, as main constituting units, 1,5-diaminopentane units and adipic acid units.
The polyamide 56 fiber of the invention preferably contains 1, 5-diaminopentane units obtained by use of a biomass since the fiber is very good in environment adaptability. In order to make the environment adaptability better, it is preferred that the quantity of 1,5-diaminopentane units obtained by use of a biomass is 50% or more of the quantity of the 1,5-diaminopentane units constituting the polyamide 56. The quantity is more preferably 75% or more thereof, most preferably 100% thereof.
The polyamide 56 in the invention is preferably a polymer having a 98%-sulfuric acid relative viscosity ranging from 2.4 or more to 2.6 or less for an effective production of the advantageous effects of the invention. When the 98%-sulfuric acid relative viscosity is in this range, the polymer can gain a sufficient strength when made into a fiber. Additionally, when into a fiber, the polymer can gain an appropriate crystallinity degree and a sufficient hygroscopicity. Furthermore, when the polymer is spun, the pressure for feeding the polymer in a melted state, and the rate of a rise in the pressure with time are appropriate so that an excessive burden is not imposed to the manufacturing facilities and, for example, the period for changing the spinneret is not required to be shortened. Thus, a high manufacturability is kept.
The 98%-sulfuric acid relative viscosity referred to herein is a value obtained by dissolving 25 g of the fiber into 25 mL of 98% sulfuric acid and then using an Ostwald viscometer to make the viscosity thereof at 25°C.
In the polyamide 56 in the invention, a second component and a third component may be copolymerized or blended with the main component as far as the object of the invention can be attained. Examples of the copolymerizable component(s) that can be contained therein include structural units each derived from an aliphatic carboxylic acid, an alicyclic dicarboxylic acid, and an aromatic dicarboxylic acid.
The polyamide 56 may contain structural units each derived from an aliphatic diamine such as ethylenediamine or cyclohexanediamine, an alicyclic diamine such as bis-(4-aminocyclohexyl)methane, an aromatic diamine such as xylylenediamine, an amino acid such as 6-amino caproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, or p-aminomethylbenzoic acid, or a lactam such as ε-caprolactam or ω-laurolactam.
One or more out of various additives may be copolymerized into or blended with the polyamide 56 in the invention in a total content of 0.001 to 10% by weight, examples of the additives including a delustering agent, a flame retardant, an antioxidant, an ultraviolet absorbent, an infrared absorbent, a crystal nucleus agent, a fluorescent whitening agent, and an antistatic agent.
The shape or form of a cross section of a monofilament of the polyamide 56 fiber of the invention may be, besides a circular shape, various sectional shapes or forms, such as a flat shape, a Y-shape and a T-shape, or a hollow form, a cross-in-square form and a double-cross form. The cross section is preferably a Y-shape, T-shape or double-cross form cross section, or some other cross section in order that when the fiber is made into a fabric, gaps can be generated between adjacent ones of the filaments so that the fabric can express water absorptivity by a capillary phenomenon.
It is more preferred that in order to exhibit a high comfortableness when clothing of the fiber is worn, the fiber has a higher moisture absorption and desorption parameter ΔMR, which shows the moisture absorptivity. The ΔMR is an index for a purpose that the fiber can gain comfortableness by a matter that when the clothing is worn, the moisture inside the clothing is emitted to the outside air. The index is a difference between the moisture absorptivity at the temperature and the humidity of the inside of clothing of a person when the person works or exercises at a light or middle level, a typical example thereof being 30°C and 90% RH, and that at the temperature and the humidity of the outside air, a typical example thereof being 20°C and 65% RH. In the invention, this ΔMR as a parameter is used as an index for evaluating a fiber about moisture absorption performance. As a fiber has a larger ΔMR, the fiber is higher in moisture absorption and desorption power, which corresponds to a matter that when a person wears clothing thereof, the person feels more comfortable. In general, polyamide 6, polyamide 66 or some other polyamide fiber has a ΔMR of about 1.5 to 2.0. By contrast, the polyamide fiber of the invention has a ΔMR of 3.0% or more to show a high moisture absorption and desorption. If a fiber has a ΔMR less than 3.0%, the fiber is merely equivalent in moisture absorption and desorption to ordinary polyamide 6 or polyamide 66 species so as to result in a problem that when a person wears clothing thereof, the person does not feel a high comfortableness. The upper limit thereof is not limited. However, even when the ΔMR is made considerably large, a large difference is not generated for bodily sensation. Thus, the ΔMR is sufficient to be about 20%.
The moisture absorption and desorption power of the above-mentioned polyamide fiber largely depends on the crystal structure of the fiber. The moisture absorption of any polyamide fiber is classified into the following two cases: a case where water is coordinated to amide groups of the polyamide to be bonded thereto; and a case where water is taken into amorphous regions where polyamide molecular chains in the fiber are present in a random state. The ΔMR, or some other reversible moisture absorption and desorption power depends particularly on the proportion of the amorphous regions in the fiber. Accordingly, in order to improve a polyamide fiber in ΔMR, it is important to increase the proportion of amorphous regions therein as far as the fiber is not damaged in spinning operability nor quality.
In general, out of crystalline synthetic fibers, fibers wherein the orientation of molecular chains is enhanced are large in birefringence while fibers wherein the orientation is not enhanced are small therein. The orientation of the molecular chains is an important parameter since the orientation produces a large effect onto the water absorption coefficient of the fiber as will be described in the following: the moisture absorption of a polyamide fiber is classified into two cases, i.e., a case where water is coordinated to amide groups of the polyamide to be bonded thereto, and a case where water is taken into amorphous regions where polyamide molecular chains in the fiber are present in a random state; in particular, the proportion of the amorphous regions in the fiber produces a large effect onto the ΔMR value.
About any polyamide fiber, the proportion of its crystal regions is large while that of its amorphous regions, which can hold water, is small. When the crystal regions are large in proportion, water on the surface of the fiber cannot reach the vicinity of amide groups inside the polyamide fiber.
The orientation of the molecular chains can be represented through the birefringence. When the fiber becomes larger in birefringence, the fiber tends to become larger in water absorption coefficient. If the fiber is too large in water absorption coefficient, the fiber excessively absorbs the spinning oil, and water in the air so that the yarn swells. Thus, stable spinning cannot be attained, and further structures of the fiber are varied so that the fiber is deteriorated in quality. Moreover, if the fiber is small in birefringence, the orientation and crystallization of the molecular chains in the fiber are enhanced, so that the fiber tends to be declined in moisture absorptivity.
In the polyamide fiber of the invention, the birefringence is preferably set into the range of 30 x 10^-3 or more to 40 x 10-³ or less. When the birefringence is set into this range, a polyamide 56 fiber having high moisture absorption and desorption is obtained without damaging the spinning operability of the polyamide 56 fiber nor the quality of the yarn.
By setting the ΔMR into the above-mentioned range about the polyamide fiber of the invention, clothing which gives a high comfortableness when worn can be obtained.
The polyamide fiber of the invention may be manufactured by the following method:
With reference to Fig. 1, a specific description is made about an example of a manufacturing method for the polyamide fiber of the invention. Fig. 1 is a schematic view illustrating an example of a process for manufacturing a synthetic fiber according to the invention.
A melted polyamide is weighted and fed through a metering pump, and then discharged from a spinneret 2. A cooling device 3, such as a chimney, is used to blow cooling wind onto the resultant to cool the fiber to room temperature. Through an oiling device 4, a spinning oil is supplied thereto while the filaments of the fiber are collected into a bundle. Through a first interlacer 5, the collected filaments are interlaced with each other, and the resultant fiber is passed through a take up roller 6 and a draw roller 7. At this time, the fiber is drawn in accordance with the ratio between the peripheral velocity of the take up roller 6 and that of the draw roller 7. Furthermore, by means of the draw roller 7, the yarn is thermally set, and then wound up onto a winder 8.
In the method of the invention for manufacturing a polyamide fiber, the discharged fiber gives a spinning liner velocity ranging from 14 m/min or more to 30 m/min or less. The spinning liner velocity is a value obtained by dividing the discharged volume per unit time of the polymer from holes in the spinneret, from which the yarn is discharged, by the area of the holes in the spinneret, and is a parameter which controls the degree of the orientation of the yarn-form polymer discharged from the spinneret. If this spinning liner velocity is small, the ratio between the spinning liner velocity and the velocity of the take up roller 6 is large when the yarn is taken up through the take up roller 6. Thus, an excessive draw tension is applied to the filaments which are being taken up, so that the single yarn is broken. As a result, the polyamide cannot be stably spun. If the spinning liner velocity is too large, the orientation of the fiber is excessively promoted after the yarn is taken up through the take up roller 6 and then drawn through the draw roller 7. As a result, the fiber unfavorably becomes a fiber small in moisture absorptivity.
A condition for the spinning is set to adjust, to 3,900 or more and 4,500 or less, the product of the take up velocity (m/min) of the yarn taken up through the take up roller 6, and the draw ratio, which is a value of the ratio between the peripheral velocity of the take up roller 6 and that of the draw roller 7. This numerical value represents the total draw quantity of the polymer discharged from the spinneret while the polymer is drawn until the spinning liner velocity is turned to the peripheral velocity of the take up roller 6 and further drawn until the peripheral velocity of the take up roller 6 is turned to the peripheral velocity of the draw roller 7. If this value is too small, the fiber is low in orientation degree to become a fiber having an excessively large moisture absorptivity. Thus, the fiber excessively absorbs the spinning oil, or water in the air, so that the yarn swells. Thus, the polyamide cannot be stably spun. If this value is too large, the fiber is excessively enhanced in orientation degree to become a fiber small in moisture absorptivity.
The spinning oil, which is given by means of the oiling device 4, is preferably a water-free oil. When the water-free oil is given thereto, it is not feared that water is absorbed into the polyamide 56 while the oil is given. Thus, the so-called polyamide swelling is not caused, so that the fiber length is not varied in the spinning. As a result, the yarn can be stably wound up.
About the polyamide fiber of the invention, the tensile strength is preferably 3.5 cN/dtex or more. When the tensile strength of the fiber is set to 3.5 cN/dtex or more, the fiber can realize an actual strength for a fabric for clothing, such as innerwear, for which the polyamide fabric is mainly used. The tensile strength is more preferably 4.0 cN/dtex or more.
About the polyamide fiber of the invention, the elongation is preferably 35% or more. When the elongation is set to 35% or more, the fiber becomes good in processability in higher-order steps such as weaving, knitting, and false-twisting.
In connection with the fineness of the polyamide fiber of the invention, the total fineness is preferably 100 dtex or less, more preferably 60 dtex or less from the viewpoint of the thickness obtained when the fiber is worked into a fabric. The single filament fineness is preferably 4.0 dtex or less, more preferably 2.0 dtex or less from the viewpoint of the softness attained when the fiber is worked into a fabric.
The structure of the hygroscopic fiber yielded in the above-mentioned way is not limited to the above-mentioned structure, and may be a filament or staple. The structure is selected in accordance with an article to which the fiber is applied. The form of the fabric may be selected from textile, knitting, nonwoven fabric, and others in accordance with a purpose thereof, and may be a clothing form. In an ordinary manner, the fiber of the invention is woven or knitted, subsequently worked, and then sewn to be made into various products for clothing, such as innerwear, panty stockings, and tights. Since the fabric of the invention has both of heat resistance and water absorptivity, which are not easily compatible with each other in conventional polyamide fibers, the fabric is in particular preferably a fabric containing a region shaped by mold process. Specifically, the fiber structure of the invention is preferably used as an innerwear molded to create a curved surface of a concave, a convex, a narrow region for, for example, cups of a brassier, panties, or a waist or hip portion of a girdle, or as an innerwear having such a molded portion.
The molding is a working of inserting a fabric, such as woven fabric, knitted fabric or nonwoven fabric, into a gap between parts of a mold, and then subjecting the fabric to heat treatment to make the fabric roundish. About conditions for the heat treatment, the surface temperature of the mold is usually from 160 to 230°C, preferably from 170 to 220°C, more preferably from 190 to 200°C. The treatment period is preferably from 0.5 to 3 minutes.

EXAMPLES

The invention will be described in detail by way of examples. Measuring methods used in the examples are the following methods:

[Measuring Methods]

A. Sulfuric acid relative viscosity

0.25 g of a sample is dissolved into 25 mL of sulfuric acid having a concentration of 98 wt% to give a solution for measurement. An Ostwald viscometer is used to measure the flow-down period (T1) thereof at 25°C. Subsequently, the flow-down period (T2) of only sulfuric acid having a concentration of 98 wt% is measured. The ratio of T1 to T2, i.e., the ratio T1/T2, is defined as the sulfuric acid relative viscosity.

B. Terminated amino group concentration

Into 50 mL of a mixed solution of phenol and ethanol (phenol/ethanol = 80/20) is dissolved 1 g of a sample at 30°C while the mixed solution is vibrated. In this way, a solution is prepared. This solution is subjected to neutralization titration with 0.02 N hydrochloric acid. In this way, the amount of 0.02 N hydrochloric acid required therein is determined. Only the above-mentioned mixed solution of phenol and ethanol (the amount of which is the same as described above) is subjected to neutralization titration with 0.02 N hydrochloric acid. In this way, the amount of 0.02 N hydrochloric acid required therein is determined. From the difference therebetween, the terminated amino group quantity per gram of the sample is determined.

C. Melting point (Tm)

A differentialscanning calorimetry (PerkinElmer, DSC-7), is used to measure 10 mg of a sample at a temperature-raising rate of 15°C/minute. In the thus-obtained differential calorie curve, a peak showing an extreme value at the endothermic side thereof is determined to be the melt peak thereof. The temperature at which the extreme value is given is defined as the melting point Tm (°C). When plural extreme values are present, the temperature at which an extreme value is given at a higher temperature out of the values is used as the melting point.

D. Hygroscopicity (ΔMR)

An amount of about 1 to 2 g of a sample is weighed into a weighing bottle. The bottle is kept at 110°C for 2 hours to dry the sample. The weight of the sample is then measured (W₀). Next, the subject substance is kept at 20°C and a relative humidity of 65% for 24 hours, and then the weight thereof is measured (W₆₅). This is then kept at 30°C and a relative humidity of 90% for 24 hours, and then the weight thereof is measured (W₉₀). Calculations are then made in accordance with the following equations:
${MR}_{1} = [(W_{65} - W_{0}) / W_{0}] x 100 %$
$MR$ $_{2} = [(W_{90} - W_{0}) / W_{0}] x 100 %$
$ΔMR = {MR}_{2} - {MR}_{1}$

E. Birefringence

A polarization microscope (Nikon, POH) is used to measure each of two monofilaments taken out from a fiber about the retardation and the diameter thereof, using a white light ray as a light source. Thus, the respective birefringences are measured. The average thereof is then calculated.

F. Total fineness, and single filament fineness

A reel having a length of 1 m per circumference is caused to make ten turns to form five 10-turn reeled threads that are each in a loop form. These are used as samples for weight-measurement. In the same way, 10-turn reeled threads in a loop form are formed, and then ends of each of the reeled threads are tied with each other. Thus, the reeled threads in each of which the knot is not untied are prepared, the number of which is five. The reeled threads are used as samples for sample-length-measurement. First, the samples, the total number of which is 10, are allowed to stand still in an environment of 25°C and 55% relative humidity for 48 hours in the state that no load is applied thereto. In this way, the reeled threads are conditioned. Thereafter, in the same environment, the respective weights of the loop-form reeled threads for weight-measurement are measured, and the average A (g) thereof is calculated. Next, in the same way, the respective reeled thread lengths of the loop-form samples for sample-length-measurement are measured in the same environment. The loop-form reeled threads for sample-length-measurement are each hung onto a hook. A load corresponding to 0.05 cN/dtex is applied to the loop-form reeled thread, and the reeled thread length thereof is measured. When the load is determined, the apparent fineness (= A (g) x 10,000/10) of the sample is used. The length 20 times the reeled thread length is equal to the sample length. The average B (m) of the five sample lengths is calculated. The value A is divided by the value B, and then the resultant value is multiplied by 10, 000. In this way, the total fineness is determined. The monofilament fineness is determined by dividing the total fineness by the number of the filaments.

G. Mold processability

A stretchable fabric is fixed between two fixing tools in the state of being relaxed without being loosened, the tools each having a thickness of 2 cm, and being each hollowed to have a diameter of 15 mm. A semispherical, hot iron ball having a diameter of 10 cm and a surface heated to 200°C is pushed against the fabric to dent the fabric into a depth of 10 cm. Immediately after 60 seconds, the hot iron ball is pulled out. About the surface form of the bump-shaped region, before and after the working, the external appearance is evaluated in accordance with the following criterion:
Good: The appearance is hardly changed.
Bad: The surface is rough so that the shaped fabric is unsuitable for a commercial product.

H. Evaluation of a water-absorbable stretchable knitted fabric in the state of being worn

The yarn of each of Example 1, and Comparative Examples 1, 5 and 7 is to be used to make evaluations as follows: the yarn is knitted into knitted fabrics, and the fabrics are each sewn to be fitted to a body. In this way, T-shirt samples are produced. Inside a room of 25°C and 65% relative humidity, five examinees each wear one of the T-shirts. In this state, the examinee goes for a jog at 12 km/hour for 5 minutes. Thereafter, the examinee makes a comparative evaluation of the T-shirts about the feeling of stickiness when the examinee sweats, on the basis of his/her own sense, in accordance with the following evaluating criterion:
Excellent: The examinee has no stickiness feeling, and also has a good touch feeling.
Good: The examinee has no stickiness feeling.
Fair: The examinee has a bearable stickiness feeling.
Bad: The examinee has a stickiness feeling to be displeased therefor.
The five examinees each make a comparative evaluation of the fabrics about the comfortableness thereof, which is related to the fabric-softness felt when the examinee wears T-shirts, on the basis of his/her own sense, in accordance with the following evaluating criterion:
Good: The T-shirt is soft to be comfortable.
Bad: The T-shirt is hard in touch, and is stiff.

I. Spinning stability

A polymer is evaluated about spinning stability on the basis of the following: the number of times of yarn breakage caused when the yarn from the polymer is wound, over 1 hour, by a quantity corresponding to two packages per winder under spinning conditions that will be described later.
Good: The breakage is not caused, or is caused only once.
Bad: The breakage is caused two or more times.

Production Example 1 (Production of a polyamide 56 resin)

While an aqueous solution wherein 12.3 kg of 1,5-diaminopentane was dissolved in 30.0 kg of ion exchange water was stirred in the state of being immersed in an ice bath, 17.7 kg of adipic acid (manufactured by CaHC Co., Ltd.) was added bit by bit to the solution. At a point near the point of neutralization, the solution was heated in a water bath of 40°C temperature to adjust the inside temperature to 33°C. In this way, prepared was 60.0 kg of a 50%-by-weight solution of an equimolar salt made from 1,5-diaminopenane and adipic acid in water, the pH of this aqueous solution being 8.32. The following were charged into a batch-type polymerizing can having an internal volume of 80 L, and equipped with a stirrer having a double-helical ribbon vane and further with a heat medium jacket: the aqueous solution; 86.4 g of 1,5-diaminopentane; and 28.2 g of a slurry wherein titanium dioxide was dispersed in ion exchange water to give a concentration of 20%. The inside of the polymerizing can was sufficiently purged with nitrogen, and then the can was started to be heated to 260°C while the inside was stirred. From a time when the pressure in the can reached to 0.2 MPa (gauge pressure), the concentration of the slurry was started. The open degree of the pressure discharge valve was adjusted to keep the internal pressure of the polymerizing can constant. When the distillated water volume reached to 24.7 kg, the pressure discharge valve was closed and then the heating temperature was changed to 285°C. After the pressure in the can reached to 1.7 MPa (gauge pressure), the pressure in the can was kept. Over 50 minutes from a time when the inside temperature reached to 255°C, the pressure was gradually decreased to the atmospheric pressure. Thereafter, nitrogen gas was caused to flow at 5 L/minute to be blown into the can for 15 minutes. Thereafter, a nitrogen pressure of 0.4 MPa (gauge pressure) was applied to the inside of the can to jet out the polymer into a water bath. The polymer was pelletized with a strand cutter. The resultant polyamide 56 resin had a sulfuric acid relative viscosity of 2.54, and a terminated amino group quantity of 2.77 x 10^-5 mol/g. The Tm thereof, measured with the differential scanning calorimetry, was 254°C.

Production Example 2 (Production of a polyamide 66 resin)

The following were charged into a batch-type polymerizing can having an internal volume of 80 L, and equipped with a stirrer having a double-helical ribbon vane and further with a heat medium jacket: an aqueous solution wherein 30.0 kg of hexamethylenediammonium adipate (manufactured by Rhodia) was dissolved in 30.0 kg of ion exchange water; 140.4 g of adipic acid (manufactured by CaHC Co., Ltd.); and 28.5 g of a slurry wherein titanium dioxide was dispersed in ion exchange water to give a concentration of 20%. The inside of the polymerizing can was sufficiently purged with nitrogen, and then the can was started to be heated to 260°C while the inside was stirred. From a time when the pressure in the can reached to 0.2 MPa (gauge pressure), the concentration of the slurry was started. The open degree of the pressure discharge valve was adjusted to keep the internal pressure of the polymerizing can constant. When the distillated water volume reached to 24.7 kg, the pressure discharge valve was closed and then the heating temperature was changed to 295°C. After the pressure in the can reached to 1.7 MPa (gauge pressure), the pressure in the can was kept. Over 50 minutes from a time when the inside temperature reached to 255°C, the pressure was gradually decreased to the atmospheric pressure. Thereafter, nitrogen gas was caused to flow at 5 L/minute to be blown into the can for 10 minutes. Thereafter, a nitrogen pressure of 0.4 MPa (gauge pressure) was applied to the inside of the can to jet out the polymer into a water bath. The polymer was pelletized with a strand cutter. The resultant polyamide 66 resin had a sulfuric acid relative viscosity of 2.52, and a terminated amino group quantity of 2.88 x 10^-5 mol/g. The Tm thereof, measured with the differential scanning calorimetry, was 262°C.

Production Example 3 (Production of a polyamide 6 resin)

ε-Caprolactam containing 1 wt% of water was continuously supplied at a rate of 30 kg/hour into a first polymerizing reactor having a volume of 0.2m³ and equipped with a thermostat. The heating temperature was set to 270°C to polymerize the monomer. From a lower region of the first polymerizing reactor, a polymerization intermediate, the amount of which corresponded to the supplied amount, was discharged, and then supplied to a second polymerizing reactor having a volume of 0.08 m³ and equipped with a condenser and a thermostat. The temperature for heating the second polymerizing reactor was set to 250°C, and the intermediate was continuously polymerized under a normal pressure, and then the discharge of a polycapramide, which was a polymerization reaction product, was started. From a time when ε-caprolactam having a volume 1.5 times the volume of the first polymerizing reactor was supplied, the polymer was pelletized to yield a polycapramide spinning material.
The resultant polycapramide spinning material was treated with hot water of 95°C for 16 hours to remove low molecular weight components therefrom. The resultant polyamide 6 resin had a sulfuric acid relative viscosity of 2.60, and a terminated amino group quantity of 5.10 x 10^-5 mol/g. The Tm thereof, measured with the differential scanning calorimetry, was 230°C.

[Example 1]

The direct spin draw machine illustrated in Fig. 1 was used to perform melt spinning, drawing and thermal treatment continuously to yield a polyamide 56 fiber.
First, the polyamide 56 resin yielded in Production Example 1 was conditioned to have water content of 0.11%, and then charged into a spinning machine. When the resin was melted at 290°C and passed through a polymer pipe to be introduced into the spinneret 2, the polymer was weighed in the metering pump 1, discharged therefrom, introduced into the spinneret 2, the temperature of which was set to 290°C, and then spun out from the spinneret 2, which had 24 round holes each having a discharge hole diameter of 0.25 mm and a hole length of 0.5 mm.
At this time, the rotation number of the metering pump 1 was selected to adjust the total fineness of the polyamide 56 fiber to be obtained to 78 dtex, and the discharged amount thereof was set to 31.2 g/min. The yarn was cooled and solidified in the cooling device 3, and a water-free oil was supplied thereto through the oiling device 4. Thereafter, the filaments of the yarn were interlaced with each other through the first interlacer 5, and then wound under conditions that the peripheral velocity of the take up roller 6, which was a first roll, was 2,066 m/min, that of the draw roller 7, which was a second roller, was 4,123 m/min, and the winding rate was 4,000 m/min. In this way, a cheese package was yielded. Through these steps, a polyamide 56 fiber composed of 24 filaments each having a fineness of 78 dtex was yielded, which had been subjected to the spinning, the drawing and the thermal treatment at one stage. Physical properties of the resultant fiber are shown in Table 1. The resultant fiber was knitted into a tricot knitted fabric. This was molded and then the resultant was evaluated. The result of the evaluation is shown in Table 1.

[Example 2]

A polyamide 56 fiber composed of 24 filaments each having a fineness of 78 dtex was yielded in the same way as in Example 1 except that the discharged amount of the metering pump 1 was changed to 34.1 g/min, the peripheral velocity of the first roll to 4,250 m/min, the peripheral velocity of the second roll to 4,463 m/min, and the winding rate to 4,400 m/min. Physical properties of the resultant fiber are shown in Table 1. The resultant fiber was knitted into a tricot knitted fabric. This was molded and then the resultant was evaluated. The result of the evaluation is shown in Table 1.

[Example 3]

A polyamide 56 fiber composed of 68 filaments each having a fineness of 78 dtex was yielded in the same way as in Example 1 except that the spinneret was changed to a spinneret having 68 round holes each having a discharge hole diameter of 0.20 mm and a hole length of 0.4 mm, and the discharged amount of the metering pump 1 was changed to 30.42 g/min, the peripheral velocity of the first roll to 3,600 m/min, the peripheral velocity of the second roll to 3, 960 m/min, and the winding rate to 3, 900 m/min. Physical properties of the resultant fiber are shown in Table 1. The resultant fiber was knitted into a tricot knitted fabric. This was molded and then the resultant was evaluated. The result of the evaluation is shown in Table 1.

[Comparative Example 1]

A polyamide 56 fiber composed of 13 filaments each having a fineness of 78 dtex was yielded in the same way as in Example 1 except that the discharged amount of the metering pump 1 was changed to 30.9 g/min, and the spinneret was changed to a spinneret having 13 round holes each having a diameter of 0.30 mm and a hole length of 0.6 mm, , the peripheral velocity of the first roll to 1,500 m/min, the peripheral velocity of the second roll to 4, 440 m/min, and the winding rate to 4, 050 m/min. Physical properties of the resultant fiber are shown in Table 1. The resultant fiber was knitted into a tricot knitted fabric. This was molded and then the resultant was evaluated. The result of the evaluation is shown in Table 1.

[Comparative Example 2]

A polyamide 56 fiber composed of 24 filaments each having a fineness of 78 dtex was yielded in the same way as in Example 1 except that the discharged amount of the metering pump 1 was changed to 35.1 g/min, the peripheral velocity of the first roll to 4,400 m/min, the peripheral velocity of the second roll to 4,600 m/min, and the winding rate to 4,550 m/min. Physical properties of the resultant fiber are shown in Table 1.

[Comparative Example 3]

Melt spinning was performed in the same way as in Example 1 except that the discharged amount of the metering pump 1 was changed to 28.9 g/min, the peripheral velocity of the first roll to 2,000 m/min, the peripheral velocity of the second roll to 3,730 m/min, and the winding rate to 3,700 m/min. However, thread breakage was frequently caused in the spinning. Thus, stable spinning was not succeeded.

[Comparative Example 4]

Melt spinning was performed in the same way as in Example 1 except that the spinneret was changed to a spinneret having 24 round holes each having a diameter of 0.40 mm and a hole length of 0.8 mm. However, thread breakage was frequently caused in the spinning. Thus, stable spinning was not succeeded.

[Comparative Example 5]

A polyamide 66 fiber was yielded in the same way as in Example 1 except that instead of the polyamide 56 resin, the polyamide 66 resin produced in Production Example 2 was used. Physical properties of the resultant fiber are shown in Table 1. The resultant fiber was knitted into a tricot knitted fabric. This was molded and then the resultant was evaluated. The result of the evaluation is shown in Table 1.

[Comparative Example 6]

Melt spinning was performed in the same way as in Example 1 except that instead of the polyamide 56 resin, a mixed resin was used which was obtained by blending polyvinyl pyrrolidone with the polyamide 66 resin produced in Production Example 2 to give a content of 5% by weight. However, thread breakage was frequently caused in the spinning. Thus, stable spinning was not succeeded.

[Comparative Example 7]

A polyamide 6 fiber was yielded in the same way as in Example 1 except that instead of the polyamide 56 resin, a mixed resin was used which was obtained by blending polyvinyl pyrrolidone with the polyamide 6 resin produced in Production Example 3 to give a content of 5% by weight, and further the melting temperature and the spinneret temperature were each set to 260°C. Physical properties of the resultant fiber are shown in Table 1. The resultant fiber was knitted into a tricot knitted fabric. This was molded and then the resultant was evaluated. The result of the evaluation is shown in Table 1.

[Table 1]

	Example 1	Example 2	Example 3	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4	Comparative Example 5	Comparative Example 6	Comparative Example 7
Resin	Polyamide 56	Polyamide 56	Polyamide 56	Polyamide 56	Polyamide 56	Polyamide 56	Polyamide 56	Polyamide 66	Polyamide 66	Polyamide 6
Spinning linear velocity (m/min)	27.0	27.0	14.9	34.3	30.4	25.0	10.6	27.0	27.0	27.0
Multiplication of take-over speed and draw ratio	4.123	4.463	3.960	4.440	4.600	3.730	4.123	4.123	4.123	4.123
Spinning stability	good	good	good	good	good	bad	bad	good	bad	good
Birefringence (×10^-3)	32.6	37.4	30.3	41.5	43.7	-	-	49.8	-	420
ΔMR (%)	3.80	3.30	4.20	2.78	2.52	-	-	2.06	-	3.50
Evaluation in the state of being worm (clunny) [numbers of examines]	excellent:5	excellent:4	excellent:5	good3	good:3	-	-	fair:4	-	excellent:2
	excellent:5	good:1	excellent:5	fair2	fair:2	-	-	bad:1	-	good:3
Evaluation in the state of being worn (wear comfort) [numbers of examinees]	good:5	good:5	good:5	good:5	good:5	-	-	good:5	-	good:3
	good:5	good:5	good:5	good:5	good:5	-	-	good:5	-	bad:2
Mold processability	good	good	good	good	good	-	-	good	-	bad

DESCRIPTION OF REFERENCE SIGNS

1: metering pump
2: spinneret
3: cooling device
4: oiling device
5: first interlacer
6: take up roller
7: draw roller
8: winder

INDUSTRIAL APPLICABILITY

The invention makes it possible to yield a highly value-added, hygroscopic synthetic fiber, which has a high moisture absorptivity, without damaging the strength, the chemical resistant, the heat resistant nor other characteristics of polyamide.
Accordingly, the hygroscopic synthetic fiber of the invention is suitable for being used for clothing, in particular, innerwear, sportswear, and others.

Claims

A hygroscopic fiber, comprising a polyamide 56 resin, and having an ΔMR of 3.0% or more.
The hygroscopic fiber according to claim 1, wherein the fiber has a birefringence ranging from 30 x 10^-3 or more to 40 x 10^-3 or less.
A method for manufacturing a hygroscopic fiber by a direct spin draw method, comprising cooling and solidifying a polyamide 56 fiber discharged from a spinneret by cooling wind, depositing a spinning oil onto the fiber, drawing the fiber, and then winding the fiber, wherein the following requirements (1) and (2) are satisfied:
(1) the spinning liner velocity ranges from 14 m/min or more to 30 m/min or less, and

(2) the product of the take up velocity and the draw ratio ranges from 3,900 or more to 4,500 or less.
A fabric, wherein the hygroscopic fiber according to claim 1 or 2 is used.
A fabric, wherein the hygroscopic fiber according to claim 1 or 2 is used, the fabric comprising a portion shaped by mold process.
A fiber structure, comprising the fabric according to claim 4 or 5.
The fiber structure according to claim 6, which is an innerwear.