HK1090395A1

HK1090395A1 - Polytrimethylene terephthalate hollow composite staple fibers and process for producing same

Info

Publication number: HK1090395A1
Application number: HK06110815A
Authority: HK
Inventors: 山田敏弘
Original assignee: 寿柔特克斯株式会社
Priority date: 2003-06-26
Filing date: 2004-06-22
Publication date: 2006-12-22
Also published as: US20090035568A1; WO2005001175A1; CA2519586A1; JP2005015957A; TW200504256A; EP1636405A4; CN100374633C; KR20060022643A; EP1636405A1; US20060210793A1; JP4205500B2; CN1768171A; MY140927A

Abstract

The polytrimethylene terephthalate hollow composite staple fibers exhibiting a latent crimping property and high bulkiness and elastic recovery and useful for nonwoven, woven and knitted fabrics and cushioning materials, have a hollow side-by-side or core-in-sheath type structure formed from two polytrimethylene terephthalate resin components one of which has an intrinsic viscosity of 0.50 to 1.40 dl/g and other one of which has an intrinsic viscosity of 0.40 to 1.30 dl/g and 0.1 to 0.5 dl/g below that of the former, and having a hollow part with a cross-sectional area of 2 to 15% of the total cross-sectional area, and exhibit, after the hollow composite staple fibers are formed into a web having a basis weight of 30 g/m2, and the web is heated at 120° C. for 10 minutes to cause the web to freely shrink, an area thermal shrinkage of 30 to 70% based on the original area of non-heated web.

Description

Polytrimethylene terephthalate hollow composite staple fibers and process for producing the same

Technical Field

The present invention relates to polytrimethylene terephthalate hollow composite staple fibers and a process for producing the same. In particular, the present invention relates to polytrimethylene terephthalate hollow composite staple fibers having latent crimp properties, and a process for producing the same with high efficiency. The polytrimethylene terephthalate hollow composite short fiber of the present invention is used for nonwoven fabrics, woven fabrics and knitted fabrics and padding having high bulkiness and excellent elastic recovery.

Background

Polytrimethylene terephthalate fibers have excellent dimensional stability, optical rotation resistance, and heat-set property and low water absorption and moisture absorption property which are normal for polyester fibers and, in addition, they show low elastic modulus and excellent elastic recovery and easy dyeability. Accordingly, it is desirable to develop polytrimethylene terephthalate fibers as fibers for clothing and for industrial use.

Known are composite fibers in which two polyester components different in intrinsic viscosity from each other are conjugated with each other, and which have latent crimping properties for providing a woven or knitted fabric or a nonwoven fabric woven with high stretchability. In order to realize a polyester composite fiber having a latent crimping property, various attempts have been made, for example, to increase the difference in intrinsic viscosity of two different types of polyesters as much as possible, to increase the difference in shrinkage between the two types of polyester components in the obtained composite fiber and to enhance the melt-spinning property of the polyester polymer. For example, japanese examined patent publication No.61-60163(1986) discloses a spinneret for melt-spinning two types of polyester resins having melt viscosities different from each other through a pair of melt extrusion orifices to form side-by-side type composite filaments. In this spinneret, the angle of inclination of each of a pair of melt extrusion orifices from a direction at right angles to the melt extrusion plane of the spinneret and the distance between the pair of melt extrusion orifices are specifically adjusted. Also, japanese unexamined patent publication No.2000-239927 discloses a polyester side-by-side type composite fiber in which two different types of polyester polymers are connected to each other in a specifically defined form in the cross-sectional profile of each composite fiber.

However, it has been found that when the intrinsic viscosity difference between the two types of polyester components in the composite fiber is increased to enhance the latent crimp properties of the resulting composite fiber, the extruded composite filament polymer melt stream bends during melt spinning, the degree of bending of the composite filament stream increases significantly with the increase in the intrinsic viscosity difference between the two polyester components and, as a result, the bent composite stream bonds to adjacent streams or to the spinneret and breaks. Therefore, the melt spinning process cannot be stably performed. In addition, since the polytrimethylene terephthalate composite filament exhibits lower rigidity than the conventional polyethylene terephthalate composite filament, when latent crimp of the composite fiber is achieved, a plurality of small crimps are generated on the composite filament and thus the obtained crimped composite filament hardly exhibits satisfactory bulkiness.

Still further, WO 02/31241-a1 discloses a spun yarn comprising a composite fiber comprising two types of polytrimethylene terephthalate resins having intrinsic viscosities different from each other. However, composite fibers have insufficient bulk and are therefore unsuitable for lofty nonwoven fabrics and dunnage.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a polytrimethylene terephthalate hollow composite staple fiber having excellent bulkiness and elastic recovery and one suitably used for forming a nonwoven fabric, a bulky yarn, a bulky woven fabric and knitted fabric and a padding therefrom, and a production method thereof.

The inventors of the present invention conducted extensive studies to achieve the above object and found that a hollow composite short fiber comprising two types of polytrimethylene terephthalate polymers having intrinsic viscosities different from each other and each having an intrinsic viscosity in a specific range, and having a hollow cross-sectional profile and a short fiber form, can achieve the above object. The present invention has been completed on the basis of this finding.

The polytrimethylene terephthalate hollow composite staple fibers of the present invention each comprise two parts, and a hollow part formed in each composite staple fiber and extending along the longitudinal axis of each composite staple fiber, the two parts being composed of polytrimethylene terephthalate resin components having intrinsic viscosities different from each other, arranged in a side-by-side or core-in-sheath arrangement, and extending along the longitudinal axis of each composite staple fiber,

wherein

(1) One of the two polytrimethylene terephthalate resin components having an intrinsic viscosity of 0.50 to 1.4dl/g and the other of the two polytrimethylene terephthalate resin components having an intrinsic viscosity of 0.40 to 1.30dl/g, and 0.1 to 0.5dl/g lower than the intrinsic viscosity of the polytrimethylene terephthalate resin having an intrinsic viscosity of 0.50 to 1.40dl/g, as measured in o-chlorophenol at a temperature of 35 ℃;

(2) the cross-sectional area of the cross-section of the hollow part corresponds to 2-15% of the total cross-sectional area of the composite fiber; and

(3) the composite staple fibers exhibit an average web (web) area heat shrinkage of 30 to 70 percent, as determined by the following measurement: composite short fibers having a fiber length of 51mm were formed into a base mass of 30g/m by a roller card²From the web, a plurality of samples having a size of 20cm × 20cm were prepared, and the samples were heat-treated in a hot air circulation dryer at a temperature of 120 ℃ for 10 minutes to allow the samples to freely shrink and the web area of the samples to be heat-shrunk according to the formula (1):

web area heat shrinkage (%) [ (a-B)/a ] × 100 (1)

Where a represents the area of each sample before heat treatment and B represents the area of the sample after heat treatment, and the average of the thermal shrinkage of the web area obtained for the samples was calculated.

In the polytrimethylene terephthalate hollow composite staple fibers of the present invention, the hollow portion is preferably located in one of the high and low intrinsic viscosity polytrimethylene terephthalate resin portions of each composite staple fiber.

The process of the present invention for producing the polytrimethylene terephthalate hollow composite staple fibers defined above comprises the steps of:

melt-spinning two polytrimethylene terephthalate resins having different intrinsic viscosities from each other through a spinneret for forming a composite filament of a hollow side-by-side or sheath-core type to provide an undrawn hollow composite filament;

the undrawn hollow composite filaments are drawn in two stages at a total draw ratio corresponding to 60-80% of the final elongation of the undrawn hollow composite filaments in the following manner: the stretching temperature is 45-60 ℃ in the first stage and then 85-120 ℃ in the second stage and the stretching ratio in the second stage is controlled to 0.90-1.0 to adjust the total stretching ratio to the above-mentioned value;

machine-crimping and drawing the hollow composite filaments at a temperature of 50-80 ℃;

heat treating the crimped hollow composite filaments at a temperature of 80 ℃ or less while allowing the crimped hollow composite filaments to relax, and

the heat-treated hollow composite filaments are cut to provide hollow composite staple fibers.

Brief Description of Drawings

Figure 1 shows a cross-sectional profile of an example of a polytrimethylene terephthalate hollow composite staple fiber of the present invention having a side-by-side structure,

figure 2 shows a cross-sectional profile of another example of a polytrimethylene terephthalate hollow composite staple fiber of the present invention having a side-by-side structure,

FIG. 3 shows a cross-sectional profile of an example of a polytrimethylene terephthalate hollow composite staple fiber of the present invention having an eccentric sheath-core structure, and

fig. 4 shows a cross-sectional profile of another example of polytrimethylene terephthalate hollow composite staple fiber of the invention having an eccentric sheath-core structure.

Best mode for carrying out the invention

The polytrimethylene terephthalate hollow composite staple fibers of the present invention each comprise two filament parts, and a hollow part formed in each composite staple fiber and extending along the longitudinal axis of each composite staple fiber, the two filament parts being constituted from polytrimethylene terephthalate resin components having intrinsic viscosities different from each other, arranged in a side-by-side or core-in-sheath arrangement, and extending along the longitudinal axis of each composite staple fiber.

Polymethylene terephthalate is a polyester containing trimethylene terephthalate as a main repeating unit. The trimethylene terephthalate resins useful in the present invention optionally comprise a comonomer component. The comonomer component includes comonomer dicarboxylic acids such as isophthalic acid, succinic acid, adipic acid, 2, 6-naphthalenedicarboxylic acid and metal-sulfoisophthalic acid and comonomer diols such as 1, 4-butanediol, 1, 6-hexanediol, cyclohexanediol and cyclohexanedimethanol. The comonomer compound is selected in consideration of the stability of the obtained copolymer during melt spinning.

The polytrimethylene terephthalate resin optionally further comprises an additive comprising at least one selected from the group consisting of: delusterants, heat stabilizers, antifoaming agents, color regulators, flame retardants, antioxidants, ultraviolet absorbers, infrared absorbers, fluorescent brighteners, and coloring pigments.

With respect to two polytrimethylene terephthalate resin components different in intrinsic viscosity from each other, the intrinsic viscosity of each resin component was measured at a temperature of 35 ℃ in a solution of the resin component in o-chlorophenol. The intrinsic viscosity of the high-viscosity resin component must be 0.5 to 1.4dl/g, preferably 0.8 to 1.30 dl/g.

If the intrinsic viscosity is more than 1.4dl/g, the high-viscosity resin component obtained when it is melted in the melt spinning process exhibits an extremely high viscosity and thus cannot be melt-spun in a usual melt spinning apparatus for polyester fibers, and in order to obtain a reduced melt viscosity at which the polymer melt obtained can be melt-spun smoothly, the melting temperature of the resin component must be increased to 280 ℃ or more, at which the resin component decomposes. If the intrinsic viscosity is less than 0.5dl/g, the difference in intrinsic viscosity between the obtained high-viscosity resin component and low-viscosity resin component is too small and thus the obtained composite short fiber cannot exhibit sufficient latent crimping properties.

The intrinsic viscosity of the low-viscosity resin component must be 0.4 to 1.30dl/g, preferably 0.5 to 1.0 dl/g. If the intrinsic viscosity is less than 0.4dl/g, the obtained resin component exhibits too low a viscosity during melt spinning, and the obtained low-viscosity melt causes frequent breakage of the extruded filament melt stream and fails to have sufficient process stability to produce the objective composite filaments. Also, if the intrinsic viscosity is more than 1.30dl/g, the difference in intrinsic viscosity between the obtained low-viscosity resin component and high-viscosity resin component is too small and thus the obtained composite short fiber cannot exhibit sufficient latent crimping properties.

Further, the intrinsic viscosity of the low-viscosity resin component must be lower by 0.10 to 0.50dl/g, preferably 0.2 to 0.40dl/g than that of the high-viscosity resin component. If the difference in intrinsic viscosity is less than 0.1dl/g, the obtained composite staple fiber shows insufficient latent crimping properties. Also, if the intrinsic viscosity difference is more than 0.5dl/g, the extruded composite filament melt stream is extremely bent and bonded to the adjacent melt stream and to the spinneret and thus, is broken during the melt spinning process. Therefore, the melt spinning process cannot be smoothly performed.

The mass ratio of the high-viscosity resin component to the low-viscosity resin component may be suitably established in consideration of the desired latent crimping property of the target composite short fibers and the melt-spinnability of the resin component and is preferably 30/70 to 70/30, more preferably 40/60 to 60/40, still more preferably about 50/50.

The hollow composite staple fibers of the present invention each have a hollow portion formed in the longitudinal center position of each fiber and processed in a filament-like manner along the longitudinal axis of each fiber. In the hollow composite fiber, the hollow portion is advantageous in that when two different resins for hollow side-by-side or core-in-sheath type composite filaments are melt-extruded through the melt-spinning spinneret, the hollow portion formed in the longitudinal central portion of the obtained composite filament melt stream causes a high amount of bending resistance to be generated in the hollow composite filament melt stream and enhances the stability of the melt-spinning process. Also, in the obtained hollow composite short fiber, the hollow portion causes an increase in the rigidity of the fiber, a spiral crimp having an appropriate form is generated in the composite fiber, and the obtained fiber shows an increased bulkiness. Also, the nonwoven fabric and the woven fabric and the knitted fabric formed of the hollow composite staple fiber of the present invention show excellent bulkiness and elastic recovery.

In the cross section of the hollow composite short fiber of the present invention, the cross sectional area of the hollow portion must correspond to 2 to 15%, preferably 5 to 10%, of the total cross sectional area of the hollow composite fiber. If the proportion (%) of the cross-sectional area of the hollow portion is less than 2%, it causes the melt flow of the extruded hollow composite filaments to be bent during the melt spinning process and the stability of the melt spinning process to be lowered. Also, a small crimp is generated on the obtained hollow composite fiber and thus the obtained fiber cannot have a sufficient bulkiness. Also, if the ratio of the cross-sectional area of the hollow portion is more than 15%, the bent area of the two resin components in each of the obtained hollow composite fibers is too small and thus the potential crimping property of the obtained hollow composite fiber is insufficient.

In the production of the hollow composite staple fiber of the present invention, the ratio of the cross-sectional area of the hollow portion to the total cross-sectional area of the hollow composite staple fiber can be easily controlled to 2 to 15% by appropriately controlling the form and size of the orifice of the melt-spinning plate, the temperature of the resin melt, and the flow rate of the cooling air during the melt spinning.

In the hollow composite short fiber of the present invention, the hollow portion is preferably located in one of the high-viscosity polyester resin component and the low-viscosity polyester resin component. In an embodiment, the hollow composite short fiber has a side-by-side structure, and one of the high-viscosity and low-viscosity resin components occupies half or more of a cross-sectional area of the hollow composite short fiber in a cross-sectional profile of the hollow composite short fiber. In general, the hollow portion is preferably formed in a portion including the high viscosity resin component.

FIG. 1 shows a cross-sectional profile of an example of a side-by-side type polytrimethylene terephthalate hollow composite fiber of the present invention. In fig. 1, a hollow composite fiber having a circular cross-sectional profile is composed of: (1) a large side portion 2 including a high-viscosity resin component, a hollow portion 4 having a circular cross-sectional profile being formed in the portion 2, and (2) a small side portion 3 including a low-viscosity resin component and conjugated with the large side portion 2 in a side-by-side arrangement.

FIG. 2 shows a cross-sectional profile of another example of a side-by-side type polytrimethylene terephthalate hollow composite fiber of the present invention. In fig. 2, a hollow composite fiber 1 having a quadrangular cross-sectional profile and a hollow portion 4 is constituted from a right-hand portion 2 and a left-hand portion 3. A hollow portion 4 is formed between the right and left side portions 2 and 3, and the right and left side portions 3 and 4 are connected to each other at positions above and below the hollow portion 4.

In another embodiment, the hollow composite fiber has an eccentric sheath-core structure, and the hollow portion is located in only one of the eccentric core portion and the sheath portion, and preferably in the core portion.

FIG. 3 shows a cross-sectional profile of still another example of a polytrimethylene terephthalate hollow composite fiber of the present invention having an eccentric sheath-core structure. In fig. 3, an eccentric sheath-core type hollow composite fiber 1 is constituted from: a sheath portion 2 formed from a low-viscosity resin component and having a circular cross section, and a core portion 3 formed from a high-viscosity resin component and arranged eccentrically in the sheath portion 3, the core portion 3 including a hollow portion 4 formed in the core portion 3 and having an elliptical cross sectional profile.

FIG. 4 shows a cross-sectional profile of a further example of a polytrimethylene terephthalate hollow composite fiber of the invention having an eccentric sheath-core structure. In fig. 4, a hollow composite fiber 1 is constituted from: comprising a low-viscosity resin component and a sheath portion 2 having a circular cross-sectional profile and comprising a high-viscosity resin component, arranged in the sheath portion 2, having an elliptical cross-sectional profile and an eccentric core portion 3 including a hollow portion 4, the hollow portion 4 being formed in the core portion 3 and having an approximately triangular cross-sectional profile.

In the above-described embodiment, the obtained hollow composite fiber is advantageous in that when the latent crimping property of the obtained hollow composite fiber is realized, the obtained crimp shows a large loop form.

In the hollow composite short fiber of the present invention, there is no limitation on the individual fiber and the cross-sectional profile and on the cross-sectional form of the individual hollow portion.

The cross-sectional profile of the individual fibers and hollow sections include round, triangular, flat, multilobal and multicannulated forms, and may be established from a variety of profiles in response to the use and purpose of the fiber.

The hollow composite staple fiber of the present invention preferably has an individual fiber thickness of 1 to 5 dtex, more preferably 1.5 to 3 dtex. Also, the hollow composite staple fibers of the present invention preferably have a fiber length of 3 to 150mm, more preferably about 30 to about 70 mm.

The average web shrinkage of the hollow composite staple fibers of the present invention must be 30 to 70%, preferably 40 to 60%. The average web shrinkage was determined by the following measurements: hollow composite short fibers having a fiber length of 51mm were formed into a base mass of 30g/m by a roller card²From the web, a plurality of samples having a size of 20cm × 20cm were prepared, and the samples were heat-treated in a hot air circulation dryer at a temperature of 120 ℃ for 10 minutes to allow the samples to freely shrink, the web area heat shrinkage of the samples being determined according to the formula (1):

web area heat shrinkage (%) [ (a-B)/a ] × 100 (1)

Where a represents the area of the sample before heat treatment and B represents the area of the sample after heat treatment, and the average of the thermal shrinkage of the web area obtained for the samples was calculated.

The average web shrinkage is an index of the potential crimp properties of the hollow composite staple fibers. When the average web shrinkage is 30 to 70%, the obtained hollow composite staple fiber can enable woven fabrics, knitted fabrics and non-woven fabrics obtained from the hollow composite staple fiber to show sufficient bulkiness and stretchability. If the average web shrinkage is more than 70%, the obtained crimped conjugated staple fiber contains a plurality of small spiral crimps and thus exhibits insufficient bulkiness and hard hand feeling, while the fiber is high in stretchability. Also in this case, when the machine-crimped hollow composite staple fiber is subjected to the spinning process, potential crimping is achieved, for example, in the carding step, and therefore, difficulty in processing occurs. Also, if the average web shrinkage is less than 30%, the latent crimp may not be sufficient to achieve and the resulting composite staple fiber may exhibit insufficient stretchability.

The average web shrinkage of the hollow conjugate staple fiber of the present invention can be controlled to 30 to 70% by appropriately controlling the draw ratio and temperature applied to the drawing process of the fiber and the ratio of the cross-sectional area of the hollow portion to the total cross-sectional area of the hollow conjugate fiber in consideration of the intrinsic viscosity of the polyester resin component for the conjugate fiber.

The hollow composite fibers of the present invention may be crimped using a mechanical crimping apparatus and, for example, a stuffing box type crimping box or gear crimping box machine. The percentage crimp of the machine crimp is preferably 10 to 25%, more preferably 15 to 20%. The crimp percentage of the hollow composite fiber crimped by the machine can be easily controlled as desired by appropriately controlling the number of crimps and the crimping temperature in the machine crimping process. The percent crimp of the fiber was measured according to JIS L1015, staple fiber test method, 8.12.2.

The hollow composite staple fibers of the present invention may be produced by the process of the present invention comprising the steps of:

melt-spinning two polytrimethylene terephthalate resins having different intrinsic viscosities from each other by forming a spinneret from a hollow side-by-side or core-in-sheath type composite filament to provide an undrawn hollow composite filament;

machine crimping the drawn hollow composite filaments at a temperature of 50-80 ℃;

In the process of the invention, the drawing temperature in the first stage is from 45 to 60 ℃ and preferably from 50 to 60 ℃. If the first stage drawing is carried out at a lower temperature of less than 45 ℃, a high drawing force must be applied to the filaments due to the low plasticity of the filaments at low temperatures and, therefore, the filaments often break during the drawing process. Also, if the drawing temperature of the first stage is more than 60 ℃, the degree of crystallinity of the filaments increases and thus the filaments become brittle and often break.

The drawing temperature and the drawing ratio in the second stage affect the latent crimping properties of the drawn filaments obtained and must be adjusted in the range of 85 to 120 c, preferably 90 to 110 c and in the range of 0.9 to 1.0, preferably 0.92 to 0.98, respectively. If the drawing temperature in the second stage is less than 85 ℃, the latent crimp properties of the drawn staple fibers obtained are easily achieved by machine processes. For example, when the obtained hollow composite staple fiber is passed through a carding process in a spinning process or a nonwoven fabric production process, latent crimping is achieved to the extent that defects such as neps or voids are not formed in the obtained web. Also, if the second stage drawing temperature is greater than 120 ℃, the resulting staple fibers exhibit reduced latent crimp properties. If the second stage drawing process is carried out at a draw ratio of more than 1.0, when they are subjected to the machine crimping process, a plurality of spiral crimps are imparted to the obtained short fibers, and the obtained crimped short fibers of the spiral crimps are difficult to pass through the carding process. During the second stage of drawing, a heat treatment of the fibers must be applied to the first drawn filaments at a fixed fiber length or under a restriction to shrinkage. If the draw ratio is less than 0.90, the filaments are excessively heat-set and thus the obtained short fibers show deteriorated latent crimping properties.

The total draw ratio in% in the first and second drawing stages in the process of the present invention must be controlled to a level corresponding to an undrawn hollow composite filament final elongation of 60 to 80%, preferably 65 to 75%. If the total draw ratio is less than 60%, the obtained short fibers exhibit insufficient latent crimping properties. Also, the total draw ratio is more than 80%, the filaments are often broken in the drawing step and thus the drawn filaments are difficult to be smoothly produced.

In the process of the present invention, the stretched hollow composite filaments may be crimped using a mechanical crimping apparatus and, for example, a stuffing box type crimp box or gear crimp box machine. The machine crimping process is carried out at a crimping temperature of 50-80 c, preferably 60-70 c.

If the machine crimping temperature is less than 50 ℃, the obtained crimped filaments show an insufficient percentage of crimp. Also, if the machine crimp temperature is greater than 80 ℃, latent crimp that should remain unrealized is undesirably realized during machine crimping, and the realized spiral crimp causes the obtained hollow composite staple fiber to show deteriorated card passing performance. The machine crimping process is preferably controlled to the extent that the number of crimps of the machine crimped filaments obtained is 10-15 crimps/25 mm, in order to impart satisfactory carding performance to the short fibers obtained.

After the machine carding step, the machine-crimped hollow composite filaments are heat-treated at a temperature of 80 ℃ or/and less preferably 40-50 ℃ while allowing the crimped hollow composite filaments to relax. If the relaxation temperature of the heat treatment is higher than 80 ℃, the latent spiral crimp is undesirably achieved. There is no lower limit to the temperature at which the heat treatment is performed while allowing the crimped hollow filaments to relax.

Typically, the filaments will be oiled with an aqueous finish-oiler emulsion prior to the machine crimping process and, therefore, the heat treatment should be conducted at a temperature sufficient to dry the filaments by evaporating water from the filaments. Therefore, the heat treatment is preferably performed at a temperature of 40 ℃ or more. The simultaneous heat treatment and relaxation process is preferably carried out for a period of 30 to 60 minutes.

After completion of the simultaneous heat treatment and relaxation processes, the hollow composite filaments obtained by using a tow cutter, for example, a gruugru cutter (grugrugrurru cutter) and a rotary cutter, are cut to provide hollow composite staple fibers having a desired fiber length of preferably 3 to 15 mm.

Examples

The invention is further illustrated by the following examples.

In examples and comparative examples, the following measurements were made.

(1) Intrinsic viscosity [ eta ]

The intrinsic viscosity of the polyester resin was measured by using an Ubbelohde viscometer at a temperature of 35 ℃ in a solution of the polyester resin in a solvent composed of o-chlorophenol.

(2) Speed of cooling air blast

The speed of the cooling air blast having a temperature of 25 ℃ and a humidity of 65% was measured by an anemometer, and applied to the filament stream of the extruded polyester resin melt melted in the melt spinning apparatus at an appropriate angle to the moving direction of the filament stream to cool and solidify the filament stream.

(3) Cross-sectional ratio of hollow portion in hollow composite fiber

In the cross-sectional profile of the hollow composite fiber, the ratio of the area of the hollow portion of the hollow composite fiber to the total area of the fiber was measured.

(4) Ultimate elongation of undrawn filaments

The final elongation of the undrawn hollow composite filament bundle was measured by a constant elongation rate tensile tester at a distance between the grippers of 10cm at a drawing rate of 100cm/mm in accordance with JIS L1013-.

(5) Percent crimp

The percent crimp of the fiber was measured according to JIS L1015-.

(6) Stability of melt spinning process

The number of breaks of undrawn filaments generated during melt spinning every 8 hours per melt-spinneret except for the breaks of filaments generated due to human and mechanical reasons was counted to classify the stability of the melt spinning process according to the number of breaks as follows.

Stability of	Number of filament bundle breaks
Stability of	Number of filament bundle breaks	Is excellent in	0
Good effect	1-2/8 hours spinneret plate	Is excellent in	0
Good effect	1-2/8 hours spinneret plate	Difference (D)	3 or more/8 hours spinneret

(7) Web area heat shrinkage (%)

Hollow composite short fibers having a fiber length of 51mm were formed into a base mass of 30g/m by a roller card²From a web, a plurality of samples having a size of 20cm x 20cm were prepared, the samples were heat-treated in a hot air circulation dryer at a temperature of 120 ℃ for 10 minutes to allow the samples to freely shrink, and the web area heat shrinkage of the samples was determined according to the formula (1):

web area heat shrinkage (%) [ (a-B)/a ] × 100 (1)

(8) Elastic recovery and bulk of nonwoven fabrics prepared from hollow composite staple fibers.

Forming hollow composite short fibers having a fiber length of 51mm into a nonwoven web by using a roller card; laminating the plurality of obtained webs to each other; the laminated web was needle punched to provide a basis mass of about 50g/m²The nonwoven fabric of (1); heat treating the nonwoven fabric in an oven at a temperature of 120 ℃ for 10 minutes; the bulkiness of the nonwoven fabric was measured according to JIS L-1908; then a plurality of test pieces in the form of 25 mm-width tapes were prepared from the nonwoven fabric, and each of them was subjected to measurement of the final elongation at a distance between a pair of mechanical jaws of 100mm and at a drawing speed of 100mm/min in accordance with JIS L-1908-1999; and from the data obtained, the elastic recovery of the specimen was calculated according to the formula (2):

elastic recovery (%) ═ E_B-E_C)/E_B×100

Where EB denotes an elongation (%) corresponding to 80% of the final elongation of the sample, and EC denotes an elongation (%) of the sample after the sample is elongated until the elongation of the sample reaches the elongation EB, and then the sample is released from the tension applied thereto and left for one minute, based on the initial length of the sample.

(9) General evaluation

General evaluation of the hollow composite staple fibers was performed according to the stability of the melt spinning process, the bulkiness of the nonwoven fabric and the elastic recovery of the nonwoven fabric. The evaluation results are shown in the following two categories.

General evaluation	Performance of
General evaluation	Performance of	Good effect	No filament breakage occurred in each melt-spinneret during the 8 hour melt spinning process, and the bulkiness of the nonwoven fabric was 15cmG or more, and the elastic recovery of the nonwoven fabric is 80% or more
Difference (D)	At least one of the above items does not reach the above-mentioned level	Good effect

Examples 1 and 2 and comparative examples 1 to 6

In each of examples 1 and 2 and comparative examples 1 to 6, the high-viscosity polytrimethylene terephthalate resin component (a) and the low-viscosity polytrimethylene terephthalate resin component (B) having intrinsic viscosities shown in table 1 or 2 were subjected to a melt spinning process using a melt-spinneret containing 1000 extrusion spinnerets for a hollow eccentric sheath-core type composite filament. In each spinneret for the hollow composite fiber, the diameter of the annular slit for forming the hollow portion in the hollow composite fiber (PCD) is shown in table 1 or 2.

In the melt spinning process, the high and low viscosity polyester resin components (A) and (B) were used in a mass ratio A/B of 50/50, melted at a temperature of 245-290 ℃ shown in Table 1 or 2, and melt-extruded at an overall extrusion rate of 690 g/mm. The extruded melt filament stream was cooled and solidified by applying cooling air blowing to the stream at the blowing speed shown in table 2, and the obtained undrawn hollow composite filament bundle was wound up and wound up around a winding roll at a winding speed of 1,300 m/min. The melt spinning process was continuously carried out over a period of 8 hours by counting the number of breaks of the filaments to check the stability of the melt spinning process.

The obtained undrawn hollow composite filament bundle was drawn in two stages under drawing conditions, i.e., drawing temperature and drawing ratio of the first and second stages and total drawing ratio, as shown in table 1 or 2. The drawn hollow composite filament bundle was then subjected to a machine crimp process at a temperature of 75 ℃ to impart mechanical crimp to the individual filaments at the crimp percentages shown in tables 1 or 2. The machine-crimped hollow composite filament bundle was heat-treated at a temperature of 55 ℃ for 30 minutes while the filaments were relaxed. The relaxed and heat-treated filaments were cut at a fiber length of 51mm to prepare hollow composite staple fibers.

The obtained short fibers were formed into a web by using a carding machine, and the area heat shrinkage of the web was measured. The results are shown in Table 1 or 2.

The webs were subjected to elastic recovery and bulk measurements as mentioned above for the corresponding nonwoven fabrics. The results are shown in Table 1 or 2.

In comparative example 3, the melt spinning process did not proceed smoothly due to frequent breakage of the extruded filaments and thus the desired undrawn filaments could not be obtained.

Comparative example 7

In comparative example 7, the same procedure and measurement as in example 1 were carried out except that in the melt extrusion spinneret hole, PCD was changed to 2.0mm as shown in Table 2.

The results of the measurements are shown in Table 2.

Comparative example 8

In comparative example 8, the same procedure as in example 1 was conducted except that the melt extrusion orifice did not contain a hollow forming slit, the speed of cooling air blowing was changed from 0.6m/sec to 0.7m/sec, and the obtained composite fiber did not contain voids.

The results of the measurements are shown in Table 2.

TABLE 1

TABLE 2

Industrial applicability of the invention

The polytrimethylene terephthalate hollow composite staple fibers of the present invention have high latent crimp properties and, therefore, exhibit excellent bulk and elastic recovery. Thus, they are used for non-woven, woven or knitted fabrics and padding.

Claims

1. A polytrimethylene terephthalate hollow composite staple fibers each comprising two parts composed of a polytrimethylene terephthalate resin component having different intrinsic viscosities from each other, arranged in a side-by-side or sheath-core arrangement and extending along a longitudinal axis of each composite staple fiber, and containing a hollow part formed in each composite staple fiber and extending along the longitudinal axis of each composite staple fiber,

wherein

(1) One of the two polytrimethylene terephthalate resin components having an intrinsic viscosity of 0.50 to 1.4dl/g and the other of the two polytrimethylene terephthalate resin components having an intrinsic viscosity of 0.40 to 1.30dl/g, the other of the two polytrimethylene terephthalate resin components having an intrinsic viscosity of 0.40 to 1.30dl/g having an intrinsic viscosity of 0.1 to 0.5dl/g lower than the intrinsic viscosity of the polytrimethylene terephthalate resin having an intrinsic viscosity of 0.50 to 1.40dl/g, the intrinsic viscosity being measured in o-chlorophenol at a temperature of 35 ℃;

(3) the composite staple fibers exhibit an average web area heat shrinkage of 30 to 70 percent, as determined by the following measurement: composite short fibers having a fiber length of 51mm were formed into a base mass of 30g/m by a roller card²From the web, a plurality of samples having a size of 20cm × 20cm were prepared, and the samples were heat-treated in a hot air circulation dryer at a temperature of 120 ℃ for 10 minutes to allow the samples to freely shrink, the web area heat shrinkage of the samples being determined according to the formula (1):

web area heat shrinkage (%) [ (a-B)/a ] × 100 (1)

2. The polytrimethylene terephthalate hollow composite staple fiber of claim 1, wherein the hollow portion is located in one of the high and low intrinsic viscosity polytrimethylene terephthalate resin portions of each composite staple fiber.

3. A method of producing the polytrimethylene terephthalate hollow composite staple fiber of claim 1 or 2, comprising the steps of: