Thermally Adhesive Sheath-core Conjugate Fiber And Tricot Fabric

Abstract

A thermally adhesive sheath-core conjugate fiber has, as a core part, a polyester having a melting point of at least 250.degree. C., and has, as a sheath part, a polyester having a melting point which is at least 215.degree. C. and is 20-35.degree. C. lower than the melting point of the polyester constituting the core part. The thermally adhesive sheath-core conjugate fiber is characterized by having a strength of 3.8 cN/dtex or higher and an elongation of 35% or higher.

Description

TECHNICAL FIELD

[0001] This disclosure relates to a thermally adhesive sheath-core conjugate fiber having low fuzz generation in a high-order process, exhibits excellent high-order passability even in uses such as tricot use and the like, requiring a high quality level, enables a woven or knitted fabric having excellent strength, dimensional stability, and durability after thermal adhesion, and having an excellent quality level as a flow path material of a liquid filtration membrane.

BACKGROUND

[0002] A polyester fiber is suitable as a raw material fiber for clothing and industrial materials and the like due to its excellent dimensional stability, weather resistance, mechanical properties, durability, and productivity that can be mass-produced relatively inexpensively and the like, and used in various fields and uses.

[0003] In recent years, in material uses such as a flow path material for a water treatment membrane and a filter, interior uses such as a chair and a partition, and other various clothing uses, utilization of a thermally adhesive polyester fiber capable of improving the form retention and rigidity of a fabric proceeds. The thermally adhesive polyester fiber is obtained by forming a polyester fiber into a woven or knitted fabric, and then subjecting the fabric to a heat treatment such as calendering to partially melting fibers, thereby thermally adhering the fibers. Above all, the demand for a water treatment membrane increases year by year to mainly solve serious water shortage caused by a population increase in the Middle East and Africa regions. In a member serving as a flow path of permeation water filtered in a water treatment device, the demand for a polyester tricot flow path material obtained by thermally adhering a polyester tricot fabric rapidly increases.

[0004] As the thermally adhesive polyester fiber, a yarn composed of 2 or more types of polyesters having different melting points or softening points is suitable. Examples include a mixed fiber including a filament yarn, and a sheath-core type or side-by-side type conjugate fiber. A conjugate fiber in which a filament single yarn includes polymers having different melting points has an excellent quality level after thermal adhesion compared to a mixed yarn in which filaments having different melting points are mixed at a single yarn level. In particular, a thermally adhesive sheath-core conjugate fiber is actively used. The thermally adhesive sheath-core conjugate fiber is a sheath-core conjugate yarn having an excellent quality level such as productivity of an original yarn or surface smoothness of a fabric after a heat treatment, wherein a sheath component has a melting point or a softening point lower than that of a core component.

[0005] A sheath-core conjugate fiber including a core part including a polyester whose main repeating unit includes ethylene terephthalate and a sheath part including a polymer having a softening temperature of 130 to 200.degree. C. has been proposed as the thermally adhesive sheath-core conjugate fiber in Japanese Patent Laid-Open Publication No. 62-184119.

[0006] The above-mentioned sheath-core conjugate fiber makes it possible to provide a high-quality thermally adhesive woven or knitted fabric having predetermined strength and elongation characteristics without causing occurrence of yarn slippage and embossing due to slippage at a thermal adhesion intersection. However, as exemplified by a polyester obtained by copolymerizing isophthalic acid as a preferred composition of a polymer used for a sheath component, the polymer of the sheath part has low crystallinity which does not have a clear melting point. For this reason, when the woven or knitted fabric made of the sheath-core conjugate fiber is subjected to a thermal adhesion treatment, unevenness occurs in adhesion between the conjugate fibers. This causes dimensional stability and variation in the strength and elongation of the fabric, which disadvantageously causes a poor quality level when used as a flow path material of a liquid filtration membrane.

[0007] Meanwhile, a sheath-core conjugate fiber has been proposed in Japanese Patent Laid-Open Publication No. 2000-119918. The sheath-core conjugate fiber includes a core part including a polymer whose 90% by mole or more of repeating units include ethylene terephthalate and a sheath part including copolymerized polybutylene terephthalate whose 60 to 90% by mole of repeating units include butylene terephthalate.

[0008] In the above-mentioned sheath-core conjugate fiber, appropriate crystallinity is imparted to the sheath component, and the sheath-core conjugate fiber has good fiber physical properties such as a boiling water contraction ratio and a peak temperature of heat contraction stress, whereby a thermally adhered woven or knitted fabric product having a good quality level can be obtained.

[0009] A tricot fabric using a thermally adhesive sheath-core conjugate fiber described in Japanese Patent Laid-Open Publication Nos. 2011-245454 or 2014-070279 has also been reported. In those techniques, a polyester is used, which includes a sheath component having a melting point significantly lower than that of a high melting point polyester of a core component. When a spinning temperature is set based only on the melting point of the core component polyester, the heat deterioration of the sheath component is apt to proceed. Meanwhile, when the spinning temperature is lowered in consideration of the melting point of the sheath component polyester, the strength and elongation characteristics of the core component cannot be maximized so that the conjugate fiber has a poor strength and elongation.

[0010] Since the sheath-core conjugate fiber described in JP '918 has a poor strength and elongation, the sheath-core conjugate fiber is processed at a high tension and a high speed, which disadvantageously makes it difficult to develop the sheath-core conjugate fiber into a tricot use in which quality defects of an original yarn such as fuzz notably appear as defects of a fabric. Since the melting point of the sheath component is low, a thermal adhesion temperature after weaving cannot be increased so that the contraction of the conjugate fiber constituting the fabric becomes insufficient. In uses such as a water treatment membrane flow path material in which high dimensional accuracy is required in designing the fabric, there is a problem in dimensional stability when used for a long time under a high pressure. The thermally adhesive sheath-core conjugate fibers described in JP '454 and JP '279 have a poor strength and elongation so that the thermally adhesive sheath-core conjugate fibers disadvantageously have not only low high-order passability, but also an insufficient strength and elongation of the fabric to be formed, which disadvantageously causes poor durability when used as the flow path material for a long time. For the same reason as that in JP '918, the thermal adhesion temperature after weaving cannot be increased so that the contraction of the fibers constituting the fabric becomes insufficient. In uses such as a water treatment membrane flow path material in which high dimensional accuracy is required in designing the fabric, there remains a problem in dimensional stability when used for a long time under a high pressure.

[0011] It could therefore be helpful to provide a thermally adhesive sheath-core conjugate fiber having low fuzz generation in a high-order process, exhibits excellent high-order passability even in uses such as tricot use and the like, requiring a high quality level, enables a woven or knitted fabric having excellent strength, dimensional stability, and durability after thermal adhesion, and having an excellent quality level as a flow path material of a liquid filtration membrane.

SUMMARY

[0012] We thus provide: [0013] (1) A thermally adhesive sheath-core conjugate fiber including: a core part which includes a polyester having a melting point of 250.degree. C. or higher; and a sheath part which includes a polyester having a melting point of 215.degree. C. or higher and lower by 20 to 35.degree. C. than that of the polyester constituting the core part, wherein the thermally adhesive sheath-core conjugate fiber has a strength of 3.8 cN/dtex or more and an elongation of 35% or more. [0014] (2) The thermally adhesive sheath-core conjugate fiber according to (1), wherein the sheath-core conjugate fiber has a total fineness of 30 dtex or more and a single yarn fineness of 3.0 dtex or less. [0015] (3) A tricot fabric including the thermally adhesive sheath-core conjugate fiber according to (1) or (2).

[0016] We provide a thermally adhesive sheath-core conjugate fiber having low fuzz generation in a high-order process, exhibits excellent high-order passability even in uses such as tricot use and the like, requiring a high quality level, enables a woven or knitted fabric having excellent strength, dimensional stability, and durability after thermal adhesion, and having an excellent quality level as a flow path material of a liquid filtration membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows an example of the cross-sectional shape of a single yarn of a thermally adhesive sheath-core conjugate fiber.

[0018] FIG. 2 shows an example of the cross-sectional shape of a single yarn of a thermally adhesive sheath-core conjugate fiber, and is a diagram for describing a cross-sectional eccentricity ratio.

DESCRIPTION OF REFERENCE SIGNS

[0019] 1: Core component [0020] 2: Sheath component [0021] 3: Position of center of gravity of core component [0022] 4: Position of center of gravity of conjugate fiber [0023] 5: Radius of conjugate fiber [0024] 10: Thermally adhesive sheath-core conjugate fiber

DETAILED DESCRIPTION

[0025] Hereinafter, a thermally adhesive sheath-core conjugate fiber will be described in detail.

[0026] A sheath-core conjugate fiber includes a core component including a polyester having a melting point of 250.degree. C. or higher, and a sheath component including a polyester having a melting point of 215.degree. C. or higher and lower by 20 to 35.degree. C. than the melting point of the polyester constituting a core part.

[0027] By setting the melting point of the core component polyester to 250.degree. C. or higher, a spinning temperature can be increased to such an extent that the strength and elongation characteristics of the polyester can be maximized, which provides an excellent strength and durability of a fabric to be formed. The melting point of the core component polyester is preferably 270.degree. C. or lower from the practical upper limit. When the melting point of the core component polyester is 270.degree. C. or lower, the need for extremely high temperature spinning is avoided to enable spinning to be performed using a general-purpose melt spinning device, which is preferable. More preferably, the melting point is 253.degree. C. or higher and 260.degree. C. or lower.

[0028] The melting point of the sheath component polyester is 215.degree. C. or higher, and preferably 250.degree. C. or lower. When the sheath component polyester has a melting point of 250.degree. C. or lower, a versatile device can be used to thermally adhere the fabric, and smoking caused by an oil agent component in a thermal adhesion treatment can be suppressed, which is preferable. More preferably, the melting point is 220.degree. C. or higher and 235.degree. C. or lower. By setting a melting point difference between the sheath component polyester and the core component polyester to 20.degree. C. or higher, the thermal adhesion temperature of the fabric can be made sufficiently lower than the melting point of the core component polyester, whereby a highly durable fabric utilizing the strength of an original yarn can be provided. By setting the melting point difference to 35.degree. C. or lower, the spinning temperature can be set to a temperature that maximizes the strength and elongation of the core component polyester and suppresses the thermal deterioration of the sheath component polyester as much as possible, whereby a conjugate fiber having an excellent strength and elongation, less original yarn fuzz, and an excellent quality level is provided. The melting point difference between the sheath component polyester and the core component polyester is preferably 23.degree. C. or higher and 30.degree. C. or lower.

[0029] The softening temperature of the core component polyester is preferably 245.degree. C. or higher, and the softening temperature of the sheath component polyester is preferably 205.degree. C. or higher. The softening temperature of the core component polyester is 245.degree. C. or higher, whereby the dimensional change of the fabric is less, and the form of the fabric is stable when the fabric is subjected to a thermal adhesion treatment at a temperature equal to or higher than the melting point of the sheath component polyester, which is preferable. The softening temperature of the core component polyester is more preferably 250.degree. C. or higher. The upper limit of the softening temperature of the core component polyester is practically 270.degree. C.

[0030] When the softening temperature of the sheath component polyester is 205.degree. C. or higher, high-speed passability is stabilized without causing fusion of the conjugate fiber to a heater during thermal setting in a processing step, which is preferable. The softening temperature of the sheath component polyester is more preferably 215.degree. C. or higher. By setting the melting point of the sheath component polyester to 215.degree. C. or higher, and setting the softening point to 205.degree. C. or higher, the thermal adhesion temperature of the fabric to be formed can be sufficiently increased, whereby the thermal adhesion treatment causes the thermal contraction of the sheath-core conjugate fiber to proceed to improve the dimensional stability of a final product, which is preferable. The upper limit temperature of the softening temperature of the sheath component polyester is practically 250.degree. C.

[0031] As the core component polyester, optional polyesters can be selected as long as the melting point is within the above range, but the core component polyester is preferably polyethylene terephthalate (hereinafter, referred to as PET) from the viewpoint of dimensional stability and strength and elongation characteristics. The PET is a polyester obtained by using terephthalic acid as a main acid component and ethylene glycol as a main glycol component. The core component polyester may appropriately include a copolymerization component as long as the melting point is within the range described above. Examples of compounds copolymerizable with, for example, PET include dicarboxylic acids such as isophthalic acid, succinic acid, cyclohexanedicarboxylic acid, adipic acid, dimeric acid, sebacic acid, and 5-sodium sulfoisophthalic acid, and diols such as ethylene glycol, diethylene glycol, 2,2-dimethyl-1,3-propanediol, butanediol, neopentyl glycol, cyclohexane dimethanol, polyethylene glycol, polypropylene glycol, and bisphenol A ethylene oxide adduct. It is more preferable that 100% of the compound is homo PET including repeating units of ethylene terephthalate from the viewpoint of dimension stability and strength and elongation characteristics. If necessary, inorganic fine particles made of titanium dioxide and the like as a matting agent, and silica fine particles and the like as a lubricant may be added.

[0032] As the sheath component polyester, optional polyesters can be selected as long as the melting point is within the above-mentioned range. In addition to PET, polytrimethylene terephthalate and polybutylene terephthalate are preferable. When the PET is used as the core component polyester, the PET is particularly preferably used as the sheath component polyester, in consideration of the peeling suppression of a composite interface. As the sheath component polyester, an optional copolymerization component can be added at an optional ratio as long as the melting point is within the above-mentioned range. When 70% by mole or more of copolymerized PET includes repeating units of ethylene terephthalate, moderate crystallinity can be imparted to a polymer, to provide stabilized spinning operability, which is preferable. When the fabric is subjected to thermal adhesion, thermal adhesion unevenness is less likely to occur, which is preferable. It is more preferable that 80% by mole or more of copolymerized PET includes repeating units of ethylene terephthalate. When a polymer other than PET is used as the sheath component polyester, a copolymerization component can be appropriately added as long as original yarn productivity and the quality level of the fabric after a thermal adhesion treatment are not impaired. As the copolymerization component, optional components such as the above-mentioned copolymerization component can be copolymerized. Regardless of the type of a polymer selected, if necessary, inorganic fine particles made of titanium dioxide and the like as a matting agent, and silica fine particles and the like as a lubricant may be added.

[0033] Next, the intrinsic viscosity (hereinafter, referred to as IV) of the conjugate fiber is preferably 0.55 to 0.75. When IV is 0.55 or more, the toughness of the conjugate fiber sufficient for withstanding practical use can be achieved without a degree of polymerization being too low, which is preferable. Meanwhile, when IV is 0.75 or less, IV is not too high during spinning. This makes it possible to suppress an increase in the amount of COOH during melt spinning without making it necessary to perform extreme high temperature spinning, and provide a uniform conjugate fiber without causing melt fracture, and causes no decrease in the toughness, which is preferable. More preferably, IV is 0.60 to 0.70.

[0034] FIG. 1 is a schematic cross-sectional view of a sheath-core conjugate fiber. In a sheath-core conjugate fiber 10, a core component 1 is surrounded by a sheath component 2.

[0035] The cross-sectional shape of the conjugate fiber is not particularly limited as long as a high melting point component is disposed in a core part and a low melting point component is disposed in a sheath form to cover the core part, but it is preferable that the sheath component completely covers the core component without exposing the core component. The eccentricity ratio of the center of gravity of the core component with respect to the center of gravity of the entire conjugate fiber is preferably 5% or less in the cross section of the conjugate fiber because of the productivity of the original yarn and the stability of physical properties such as Uster unevenness U %. When the eccentricity ratio is 5% or less, coiled crimp is not expressed even if the combination of the polymers of the core component and the sheath component is a combination which causes a difference in contraction, which preferably provides an excellent quality level of the fabric. More preferably, the eccentricity ratio is 1% or less.

[0036] The cross-sectional outer peripheral shape of the conjugate fiber is preferably a substantially circular shape with a flat ratio represented by AB and being 1.1 or less, where A is a major axis of an outer peripheral shape and B is a minor axis thereof. Such a shape can uniformly disperse and receive a force when an external tension is applied, and provides also less variation in strength and elongation in the S-S curve of the conjugate fiber, which is preferable. More preferably, the flat ratio is 1.0.

[0037] The composite ratio of the core component and the sheath component in the sheath-core conjugate fiber is set such that the cross-sectional area ratio (core:sheath) is preferably 40:60 to 90:10, and more preferably 55:45 to 75:25. By setting the composite ratio to be within the above range, the conjugate fiber can be stably produced, has an excellent strength and elongation, has low fuzz generation, and can maintain a strength and an elongation even during thermal adhesion of the fabric, which is preferable.

[0038] The content of inorganic particles included in the core component is 3.0% by weight or less, to improve the toughness, which is preferable. The content is more preferably 0.5% by weight or less. The content of inorganic fine particles included in the sheath component is 0.05% by weight or more, to improve the process passability, which is preferable. More preferably, the content of the inorganic fine particles included in the sheath component is 0.05% by weight or more and 0.5% by weight or less because a guide is not excessively abraded during process passing, and unnecessary falling of the inorganic particles when the conjugate fiber is used as a flow path material is not caused. The inorganic fine particles are preferably made of titanium oxide from the viewpoint of the process passability as the conjugate fiber.

[0039] The conjugate fiber preferably has a total fineness of 30 dtex or more. By setting the total fineness to 30 dtex or more, a sufficient strength and rigidity can be ensured by a thermal adhesion treatment. When the conjugate fiber is used as the flow path material, a sufficient passing amount of a permeation liquid can be secured even if a water pressure acts. The total fineness is preferably 90 dtex or less, and more preferably 40 dtex or more. By setting the total fineness to 90 dtex or less, the thinning of the fabric can be achieved. When the conjugate fiber is used as the flow path material, the number of laminated layers per unit formed by bonding the filtration membrane and the flow path material can be increased, which is preferable.

[0040] The single yarn fineness of the conjugate fiber is preferably 3.0 dtex or less. By setting the single yarn fineness to 3.0 dtex or less, the specific surface area is increased. This can cause even a short time thermal adhesion treatment to provide uniform thermal adhesion, and provide a suppressed decrease in the strength of the fabric due to the thermal adhesion treatment, whereby the fabric having high durability can be obtained. The single yarn fineness is preferably 0.7 dtex or more, and more preferably 1.5 dtex or more and 2.5 dtex or less. By setting the single yarn fineness to 0.7 dtex or more, less yarn unevenness and original yarn fuzz are provided, which enables stable production, and knitting yarn breakage is less, which provides excellent high-order passability, and appropriate rigidity of the fabric to be formed, which is preferable.

[0041] The conjugate fiber has a strength of 3.8 cN/dtex or more and an elongation of 35% or more. By setting the strength to 3.8 cN/dtex or more, a fabric to be formed has a high strength. The fabric has excellent durability when the fabric is used as a flow path material. The practical upper limit of the strength is 7.0 cN/dtex. By setting the elongation to 35% or more, the fuzz of the original yarn can be prevented, and the fabric has less warping fuzz during weaving, and less yarn breakage during knitting, excellent high-order passability, and an excellent quality level with few defects. The elongation is more preferably 35 to 50%. A woven or knitted fabric obtained by setting the elongation to 50% or less has excellent dimensional stability, which is preferable.

[0042] To obtain a highly uniform fabric, Uster unevenness U % which is an index of thickness unevenness in the fiber longitudinal direction of the conjugate fiber is preferably set to 1.4% or less. When the Uster unevenness U % is 1.4% or less, the surface of the fabric after thermal adhesion becomes smooth, and a uniform flow path can be formed when the fabric is used as the flow path material, which is preferable. More preferably, the Uster unevenness U % is 1.0% or less.

[0043] The dry-heat contraction ratio of the conjugate fiber is preferably 20% or less. By setting the dry-heat contraction ratio to 20% or less, a dimensional change due to a thermal adhesion treatment can be suppressed, which is preferable. The practical lower limit of the dry-heat contraction ratio is 2.0%.

[0044] A preferred yarn production method will be described. As a spinneret used for a melt spinning method of a thermally adhesive sheath-core conjugate fiber, an existing composite spinning spinneret can be used.

[0045] Examples of the melting method include a pressure melter method and an extruder method, but melting provided by an extruder is preferable from the viewpoint of efficiency and suppression of decomposition. A melting temperature is preferably set to be higher by 10 to 40.degree. C. than the melting point of a polymer to be used.

[0046] The spinning temperature is preferably 280 to 295.degree. C. More preferably, the spinning temperature is 285.degree. C. to 293.degree. C. By employing such a spinning temperature, a conjugate fiber having a high toughness and good yarn producing properties can be obtained. A heater may be provided below a spinneret to alleviate rapid cooling immediately below the spinneret.

[0047] By shortening a melting passage time and a heating time from melting to discharging as much as possible, a decrease in the molecular weight of each of the core component and the sheath component can be suppressed, which is preferable. The core component and the sheath component are separately melt-kneaded, precisely discharged and measured through a heating zone, passed through a filter layer for trapping extraneous matters, and discharged, stringed, and cooled using a composite spinneret to provide a sheath-core form. When a polymer residence time which is a passage time from melting to discharging is within 30 minutes, the thermal deterioration of the polymer can be reduced, and a decrease in IV is suppressed, whereby a decrease in the toughness of the yarn can be prevented. An increase in the amount of COOH in the conjugate fiber can be suppressed, whereby suppressed fuzz, excellent heat resistance, excellent high-order passability, and improved durability of the fabric to be formed can be provided, which is preferable. More preferably, the polymer residence time is 20 minutes or less.

[0048] A spinneret surface temperature is preferably set to 270.degree. C. or higher and 290.degree. C. or lower from the balance between the strength and elongation and the productivity. By setting the spinneret surface temperature to 270.degree. C. or higher, the characteristics of the core component can be maximized, whereby a yarn having an excellent strength and elongation can be obtained. By setting the spinneret surface temperature to 290.degree. C. or lower, an increase in yarn breakage due to the deposition of a polymer hydrolyzate immediately below the spinneret is suppressed, which provides excellent original yarn productivity, which is preferable.

[0049] The sheath-core conjugate fiber can be manufactured by any of a two-step method in which a discharged polymer is once wound up as an undrawn yarn and then drawn, and a one-step method such as a direct spinning drawing method in which spinning and drawing steps are continuously performed, or a high speed yarn producing method.

[0050] A stretching temperature is preferably 60.degree. C. or higher and 100.degree. C. or lower, which is near the glass transition temperature of the undrawn yarn. By setting the stretching temperature to 60.degree. C. or higher, uniform stretching can be provided, and by setting the stretching temperature to 100.degree. C. or lower, deterioration in productivity due to fusion of fibers to a stretching roll or spontaneous extension of the fibers can be prevented. More preferably, the stretching temperature is 75.degree. C. or higher and 95.degree. C. or lower.

[0051] It is preferable that the fiber is thermally set at a temperature which the crystallization rate of the undrawn yarn becomes the largest after stretching. The temperature is preferably set to 110.degree. C. or higher and 180.degree. C. or lower. The thermal setting at 110.degree. C. or higher makes it possible not only to promote the crystallization of the fiber to increase the strength but also to stabilize various kinds of yarn physical properties including contraction stress and a dry-heat contraction ratio, which is preferable. The thermal setting at 180.degree. C. or lower makes it possible to prevent deterioration in productivity due to the fusion of the conjugate fiber to a thermal setting device, which is preferable.

EXAMPLES

[0052] Hereinafter, our fibers and fabrics will be specifically described by way of Examples. Main measured values of Examples were measured by the following methods.

(1) Intrinsic Viscosity (IV)

[0053] In the definition formula .eta.r, a relative viscosity .eta.r is obtained according to the following formula by dissolving 0.8 g of a sample in 10 mL of O-chlorophenol (OCP) having a purity of 98% or more, and using an Ostwald viscometer at 25.degree. C., to calculate an intrinsic viscosity (IV).

.eta.r=.eta./.eta.0=(t.times.d)/(t0.times.d0)

Intrinsic viscosity (IV)=0.0242.eta.r+0.2634

[.eta.: viscosity of polymer solution, .eta.0: viscosity of OCP, t: drop time of solution (sec), d: density of solution (g/cm.sup.3), t0: drop time of OCP (sec), d0: density of OCP (g/cm.sup.3)].

(2) Melting Point

[0054] 10 mg of a dried sample was weighed by using a differential scanning calorimetry (DSC) Q100 manufactured by TA Instruments, sealed in an aluminum pan, and then measured at a heating rate of 16.degree. C./min from room temperature to 300.degree. C. under a nitrogen atmosphere. After first measurement (1st run), the sample was held for 5 minutes and then rapidly cooled to room temperature. Second measurement (2nd run) was continuously performed, and the peak top temperature of a melting peak in the 2nd run was taken as a melting point.

(3) Softening Temperature

[0055] A dried sample was placed on a sample stage by using a thermal mechanical device (TMA/SS-6000) manufactured by Seiko Instruments Inc., and measured at a heating rate of 16.degree. C./min from room temperature to 300.degree. C. under a nitrogen atmosphere using a needle probe having a tip diameter of 1.0 mm in a state where a measurement load was set to 10 g. A temperature at the start of displacement was taken as a softening temperature.

(4) Cross-Sectional Eccentricity Ratio

[0056] The cross section of a fiber was observed by using a microscope VHX-2000 manufactured by Keyence Corporation, and each value was measured with an attached image analysis software. When the position of center of gravity of a core component was taken as C1 (numeral number 3 in FIG. 2); the position of center of gravity of a conjugate fiber was taken as Cf (numeral number 4 in FIG. 2); and the radius of the conjugate fiber was taken as rf (numeral number 5 in FIG. 2), the cross-sectional eccentricity ratio was calculated from the following formula:

Cross-sectional eccentricity ratio (%)={|Cf-C1|/rf}.times.100.

(5) Cross-Sectional Flat Ratio

[0057] In the same manner as in (4), the cross section of the conjugate fiber was observed. Among diameters passing through the center of the cross section, the longest diameter was taken as a major axis A, and the shortest diameter was taken as a minor axis B. The cross-sectional flat ratio was calculated according to the following formula:

Cross-sectional flat ratio=major axis A/minor axis B.

(6) Fineness, Strength, Elongation, and Toughness

[0058] The fineness, the strength, the elongation, and the toughness were measured according to JIS L1013 (2010, chemical fiber filament yarn test method). The toughness was calculated according to the following formula:

(Toughness)=(Strength).times.(Elongation).sup.0.5.

(7) Uster Unevenness U %

[0059] The Uster unevenness U % was measured in a normal mode using USTER TESTER 4-CX manufactured by Zellweger while feeding a yarn at a speed of 200 m/min for 5 minutes.

(8) Boiling Water Contraction Ratio and Dry-Heat Contraction Ratio

[0060] Ten skeins were produced using a frame measuring device having a frame circumference of 1.0 m, and the boiling water contraction ratio and the dry-heat contraction ratio were calculated according to the following formula. Both an original length and a length after treatment were measured in a state where a load was applied {(notified fineness (dtex).times.2)g}. Regarding a contraction treatment, the boiling water contraction ratio was obtained by immersing in boiling water for 15 minutes, and the dry-heat contraction ratio was obtained by treating at 200.degree. C. for 5 minutes.

Contraction ratio (%)={(original length (L1)-length after treatment (L2))/original length (L1)}.times.100.

(9) Number of Fuzz Defects

[0061] Using Fly Counter (MFC-120S) manufactured by Toray Engineering Co., Ltd., 48 conjugate fibers were measured under measurement conditions of an unraveling speed of 500 m/min and a measuring length of 50000 m, and the number of detected fuzzes was counted. Based on the counted number of fuzzes, the following scores were made:

[0062] Score 3: The number of fuzzes in all of the 48 fibers: 0

[0063] Score 2: The average number of fuzzes of the 48 fibers: less than 0.1, and the maximum number of fuzzes in the 48 fibers: 1

[0064] Score 1: The average number of fuzzes of the 48 fibers: 0.1 or more and less than 0.3, and the maximum number of fuzzes in the 48 fibers: 1

[0065] Score 0: The average number of fuzzes in the 48 fibers: 0.3 or more, or the maximum number of fuzzes in the 48 fibers: 2 or more.

(10) High-Order Passability

[0066] After the conjugate fiber was warped, the following evaluation scores were made according to the number of warping fuzzes detected and the number of knitting yarn breakages when knitting was performed at a double denby structure seam using a tricot knitting machine (36 gauges) including two guide bars using the original yarn obtained for both a front yarn and a back yarn:

[0067] Score 3: The number of warping fuzzes: less than 0.3/10 million m, and the number of knitting yarn breakages: less than 0.5/200 m

[0068] Score 2: The number of warping fuzzes: 0.3/10 million m or more and less than 0.6/10 million m, and the number of knitting yarn breakages: less than 0.5/200 m, or the number of warping fuzzes: less than 0.3/10 million m, and the number of knitting yarn breakages: 0.5/200 m or more and less than 1.0/200 m

[0069] Score 1: The number of warping fuzzes: 0.3/10 million m or more and less than 0.6/10 million m, and the number of knitting yarn breakages: 0.5/200 m or more and less than 1.0/200 m

[0070] Score 0: The number of warping fuzzes: 0.6/10 million m or more, or the number of knitting yarn breakages: 1.0/200 m or more.

(11) Strength of Fabric After Thermal Adhesion

[0071] A tricot fabric was produced by the method of (10), and a heat treatment was performed at a melting point of a sheath component+10.degree. C. with a pin tenter dryer in a non-loaded state to produce a thermally adhered fabric. The density of the fabric after thermal adhesion was adjusted so that 66 yarns/2.54 cm (=inch) in a wale direction and 53 yarns/2.54 cm (=inch) in a course direction were set. The strength of the fabric after thermal adhesion was measured in accordance with JIS 1096: 2010 (testing methods for woven and knitted fabrics) in a wale (vertical) direction and a course (horizontal) direction, and the following scores were made based on the strength values:

[0072] Score 3: 600 N/5 cm or more in vertical direction and 100 N/5 cm or more in horizontal direction

[0073] Score 2: 500 N/5 cm or more and less than 600 N/5 cm in vertical direction and 100 N/5 cm or more in horizontal direction, or 600 N/5 cm or more in vertical direction, and 80 N/5 cm or more and 100 N/5 cm or less in horizontal direction0

[0074] Score 1: 500 N/5 cm or more and less than 600 N/5 cm in vertical direction, and 80 N/5 cm or more and less than 100 N/5 cm in horizontal direction

[0075] Score 0: less than 500 N/5 cm in vertical direction or less than 80 N/5 cm in horizontal direction.

(12) Flow Path Material Water Resistance Test (Salt Removal Rate (%), Water Production Amount (m.sup.3/day))

[0076] A tricot fabric after thermal adhesion produced in the same manner as in (11) was sandwiched between two RO separation membranes each having a thickness of 150 .mu.m, to form a spiral type unit. The spiral type unit was incorporated into a module having a diameter of 0.2 m and a length of 1 m. Sea water having a TDS (soluble evaporation residue) of 3.5% by weight was filtered at a liquid temperature of 25.degree. C. under a differential pressure of 4.5 MPa for 5 days. The electrical conductivity of the permeation liquid was measured after 5 days, and the removal rate of magnesium sulfate was calculated. The amount of a permeation liquid after 5 days was measured, and a water production amount per day was calculated. Based on the results of the test, the following evaluation scores were made:

[0077] Score 3: The removal rate of magnesium sulfate: 99.8% or more, and the water production amount: 45 m.sup.3/day or more

[0078] Score 2: The removal rate of magnesium sulfate: 99.8% or more, and the water production amount: 40 m.sup.3/day or more and less than 45 m.sup.3/day, or the removal ratio of magnesium sulfate: 99.0% or more and less than 99.8%, and the water production amount: 45 m.sup.3/day or more

[0079] Score 1: The removal rate of magnesium sulfate: 99.0% or more and less than 99.8%, and the water production amount: 40 m.sup.3/day or more and less than 45 m.sup.3/day

[0080] Score 0: The removal rate of magnesium sulfate: less than 99.0%, or the water production amount: less than 40 m.sup.3/day.

(13) Decision to Pass or Fail

[0081] In the evaluation items in (9) to (12), all items having score 2 or more was taken as pass, and when having at least one item was score 1 or less was taken as fail.

Example 1

[0082] There were prepared a homo PET polymer of IV 0.67 not including titanium oxide (high melting point component, melting point: 255.degree. C.), and a copolymerized PET polymer (low melting point component, melting point: 230.degree. C.) obtained by copolymerizing 7.1% by mole of isophthalic acid and 4.4% by mole of bisphenol A ethylene oxide adduct as copolymerization components with respect to total acid components and having a titanium oxide content of 0.05% by weight and IV of 0.65. The high melting point component was melted at 285.degree. C. in an extruder, and the low melting point component was melted at 260.degree. C. in the extruder. A spinning temperature was set to 290.degree. C., and weighing was performed by a measuring pump. After filtration in a pack, by a spinneret nozzle, the components were discharged in a sheath-core conjugate form having a composite area ratio of 65:35 to form a concentric sheath-core cross-sectional shape as shown in FIG. 1 (cross-sectional eccentricity ratio: 0%, and cross-sectional plat ratio: 1.0). At this time, the high melting point component was disposed in a core and the low melting point component was disposed in a sheath.

[0083] As a take-up device, a direct spinning method (DSD) which drawing and winding were consistently performed was adopted, and the discharged polymer was taken up by a take-up roll (1st HR) set to a surface temperature of 85.degree. C. at a speed of 1728 m/min through a cooling part and a fueling part. The polymer was continuously wound around a heat treatment roll (2nd HR) set at 128.degree. C. at 4489 m/min without being wound once, and a 2.6-fold stretching was performed. The tensions of the stretched and heat-treated yarns were adjusted with a godet roller (3rd GR, 4th GR) set to 4549 m/min and 4584 m/min. A cheese-shaped package was wound at a speed of 4500 m/min and a tension of 0.20 cN/dtex, to obtain a sheath-core conjugate fiber having 56 dtex-24 filaments. The evaluation results for the obtained fibers were shown in Table 1. Uster unevenness U % was 0.4%; a boiling water contraction ratio was 10.3%; and a dry-heat contraction ratio was 17.2%.

[0084] As shown in Table 1, the fiber had an excellent strength and elongation, an excellent toughness, and low original yarn fuzz generation. The obtained original yarn was used for both a front yarn and a back yarn, and knitting was performed at a double denby structure seam using a tricot knitting machine (36 gauges) including two guide bars. The fiber had less warping fuzz generation, less yarn breakage during knitting, and excellent high-order passability. Furthermore, a fabric strength after a thermal adhesion treatment with a pintenter at 240.degree. C. (the melting point of the sheath component+10.degree. C.) was high. When the fabric was used as a flow path material of a water treatment membrane, the high temperature heat treatment caused a tricot flow path material to have excellent dimensional stability, and could secure a stable water production amount while maintaining membrane performance without causing the breakage or clogging of the flow path material in continuous use.

Examples 2 to 4 and Comparative Examples 1 to 3

[0085] Examples 2 to 4 and Comparative Examples 1 to 3 were the same as Example 1 except that the melting points of a core component polyester and a sheath component polyester were adjusted as shown in Table 1 such that a copolymerization ratio was changed by using the copolymerization component used in the sheath component of Example 1, and an appropriate spinning temperature was adopted according to the adjustment. The evaluation results are as shown in Table 1.

Example 5

[0086] Example 5 was the same as Example 1 except that a DSD for a spinning machine was changed to a two-step method, and a spinning condition and the like was incidentally adjusted. The evaluation results are as shown in Table 1.

Examples 6 and 7

[0087] Examples 6 to 7 were the same as Example 1 except that the discharge hole shape of a spinneret was changed, and a cross-sectional shape and the eccentricity ratio of a core-sheath were changed as shown in Table 2. The evaluation results are as shown in Table 2.

Examples 8 to 11

[0088] Examples 8 to 11 were the same as Example 1 except that the fineness of a conjugate fiber and the number of filaments were changed as shown in Table 2. The evaluation results are as shown in Table 2.

Examples 12 to 14

[0089] Examples 12 to 14 were the same as Example 1 except that the amounts of titanium oxide added to a core component polyester and a sheath component polyester were changed as shown in Table 3. The evaluation results are as shown in Table 3.

Examples 15 to 17

[0090] Examples 15 to 17 were the same as Example 1 except that the discharge amounts of a core component polyester and a sheath component polyester were changed, and the ratio of a core-sheath was as shown in Table 3. The evaluation results are as shown in Table 3.

TABLE-US-00001 TABLE 1 Unit Example 1 Example 2 Example 3 Example 4 Spinning Production method -- DSD DSD DSD DSD condition Spinning temperature .degree. C. 290 285 280 295 Spinneret surface temperature .degree. C. 281 278 273 287 Raw material Core component melting point .degree. C. 255 250 250 255 polymer Core component softening .degree. C. 253 247 247 253 temperature Core component polymer -- PET CoPET CoPET PET Sheath component melting point .degree. C. 230 220 215 235 Sheath component softening .degree. C. 227 215 208 232 temperature Sheath component polymer -- CoPET CoPET CoPET CoPET Melting point difference of .degree. C. 25 30 35 20 core and sheath Conjugate fiber IV -- 0.65 0.64 0.63 0.65 Fiber physical Strength cN/dtex 4.0 3.9 3.8 4.0 properties Elongation % 40 41 38 36 Toughness -- 25 25 23 24 Evaluation Number of fuzz defects Score 3 3 2 2 Higher-order passability Score 3 3 2 2 Strength of fabric after Score 3 3 3 2 thermal adhesion Flow path material water Score 3 3 3 2 resistance test Comparative Comparative Comparative Unit Example 1 Example 2 Example 3 Example 5 Spinning Production method -- DSD DSD DSD Two-step condition method Spinning temperature .degree. C. 275 290 280 286 Spinneret surface temperature .degree. C. 267 281 273 285 Raw material Core component melting point .degree. C. 245 255 255 255 polymer Core component softening .degree. C. 239 253 253 253 temperature Core component polymer -- CoPET PET PET PET Sheath component melting point .degree. C. 215 245 210 230 Sheath component softening .degree. C. 208 239 200 227 temperature Sheath component polymer -- CoPET CoPET CoPET CoPET Melting point difference of .degree. C. 30 10 45 25 core and sheath Conjugate fiber IV -- 0.53 0.75 0.60 0.66 Fiber physical Strength cN/dtex 3.5 4.1 3.6 4.1 properties Elongation % 39 40 36 44 Toughness -- 22 26 22 27 Evaluation Number of fuzz defects Score 1 3 2 3 Higher-order passability Score 1 3 1 3 Strength of fabric after Score 1 0 1 3 thermal adhesion Flow path material water Score 1 -- 2 3 resistance test

TABLE-US-00002 TABLE 2 Unit Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Raw material Core component melting point .degree. C. 255 255 255 255 255 255 polymer Core component softening .degree. C. 253 253 253 253 253 253 temperature Sheath component melting point .degree. C. 230 230 230 230 230 230 Sheath component softening .degree. C. 227 227 227 227 227 227 temperature Melting point difference of .degree. C. 25 25 25 25 25 25 core and sheath Conjugate fiber Core-sheath eccentricity ratio % 1.0 5.0 0 0 0 0 Cross-sectional flat ratio -- 1.0 1.1 1.0 1.0 1.0 1.0 Total fineness dtex 56 56 33 44 84 96 Number of filaments -- 24 24 24 24 36 24 Single yarn fineness dtex 2.3 2.3 1.4 1.8 2.3 4.0 Fiber physical Strength cN/dtex 4.0 3.9 3.8 4.0 4.1 4.1 properties Elongation % 39 38 39 38 40 40 Toughness -- 25 24 24 25 26 26 Effect Number of fuzz defects Score 3 2 2 2 3 3 Higher-order passability Score 3 2 2 2 3 3 Strength of fabric after Score 3 3 2 3 3 3 thermal adhesion Flow path material water Score 3 2 2 2 3 2 resistance test

TABLE-US-00003 TABLE 3 Unit Example 12 Example 13 Example 14 Example 15 Example 16 Example 17 Raw material Core component melting point .degree. C. 255 255 255 255 255 255 polymer Core component softening .degree. C. 253 253 253 253 253 253 temperature Sheath component melting point .degree. C. 230 230 230 230 230 230 Sheath component softening .degree. C. 227 227 227 227 227 227 temperature Melting point difference of .degree. C. 25 25 25 25 25 25 core and sheath Amount of titanium oxide of wt % 0 0.3 2.0 0 0 0 core component Amount of titanium oxide of wt % 0 0.3 2.0 0.05 0.05 0.05 sheath component Conjugate fiber Core-sheath ratio -- 65:35 65:35 65:35 75:25 55:45 80:20 Fiber physical Strength cN/dtex 4.0 4.0 3.8 4.1 4.0 4.1 properties Elongation % 38 39 40 40 40 42 Toughness -- 25 25 24 26 25 27 Evaluation Number of fuzz defects Score 2 3 2 3 3 3 Higher-order passability Score 2 3 2 3 2 3 Strength of fabric after Score 3 3 2 2 2 2 thermal adhesion Flow path material water Score 3 3 2 2 2 2 resistance test

Claims

1-3. (canceled)

4. A thermally adhesive sheath-core conjugate fiber comprising: a core part including a polyester having a melting point of 250.degree. C. or higher; and a sheath part including a polyester having a melting point of 215.degree. C. or higher and lower by 20 to 35.degree. C. than that of the polyester constituting the core part, wherein the thermally adhesive sheath-core conjugate fiber has a strength of 3.8 cN/dtex or more and an elongation of 35% or more.

5. The thermally adhesive sheath-core conjugate fiber according to claim 4, wherein the sheath-core conjugate fiber has a total fineness of 30 dtex or more and a single yarn fineness of 3.0 dtex or less.

6. A tricot fabric comprising the thermally adhesive sheath-core conjugate fiber according to claim 4.

7. A tricot fabric comprising the thermally adhesive sheath-core conjugate fiber according to claim 5.

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