EP3822398A1

EP3822398A1 - Polyester-based fiber and pile fabric cloth using same, and methods respectively for producing these products

Info

Publication number: EP3822398A1
Application number: EP19833983.0A
Authority: EP
Inventors: Nobutaka Taoka; Yusuke Hirai
Original assignee: Kaneka Corp
Current assignee: Kaneka Corp
Priority date: 2018-07-11
Filing date: 2019-06-07
Publication date: 2021-05-19
Also published as: CN112352069A; JPWO2020012843A1; CN112352069B; EP3822398A4; CN114575007B; WO2020012843A1; JP7187559B2; CN114575007A

Abstract

The present invention relates to a polyester-based fiber having crimps, in which, when the polyester-based fiber is suspended vertically and subjected to dry heat treatment at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester based fiber under no load is less than 3%. This provides a polyester-based fiber capable of imparting good appearance, sag-recovery and voluminousness to a pile fabric, while imparting high crimp removability to a napped surface layer portion of the pile fabric in a polishing process at a low temperature of 90°C to 160°C, and a pile fabric in which the polyester-based fibers are used, a method for manufacturing the polyester-based fiber, and a method for manufacturing the pile fabric.

Description

Technical Field

The present invention relates to a polyester-based fiber capable of imparting good crimp removability to a napped surface layer portion of a pile fabric, a pile fabric in which the polyester-based fiber is used, and manufacturing methods therefor.

Background Art

Conventionally, acrylic fibers and/or acrylic-based fibers, which have similar texture and gloss to animal hair, have been widely used as pile fibers in a pile fabric (also referred to as a "napped fabric") as artificial fur that resembles natural fur. On the other hand, acrylic fibers and acrylic-based fibers have poor elasticity and lack fullness, and thus a pile fabric in which these fibers are used has inferior sag-recovery and voluminousness during use, and is different from natural fur.
In view of this, it has been proposed to use polyester-based fibers as pile fibers. However, a pile fabric in which polyester-based fibers are used has good sag-recovery and voluminousness, whereas, if the temperature of a polishing process during the production of a pile fabric is low, crimps in the pile fibers on the napped surface layer portion are not sufficiently removed, and the pile fibers are entangled with each other, resulting in a rough texture, and further, hair cracks, and the texture and appearance of the pile fabric are different from those of natural fur. Usually, a pile fabric in which polyester-based fibers are used need to be polished at a temperature close to 200°C, and from the viewpoint of heat resistance, it is difficult to use polyester-based fibers in combination with acrylic fibers and acrylic-based fibers that have been used heretofore.
In view of this, Patent Document 1 proposes that the crimp removability of a polyester-based fiber is improved by adjusting fiber cross-sections, fineness, fiber length, the number of crimps, the percentage of crimp, crimp fastness, and the like. Patent Document 2 proposes that the crimp removability of a polyester-based fiber in a polishing process is improved by imparting crimps after heat treatment at 160°C to 230°C is performed under 1% to 7% restricted shrinkage conditions in a yarn manufacturing process.

Prior Art Documents

Patent Document

[Patent Document 1] JP S60-162857A
[Patent Document 2] JP H5-140860A

Disclosure of Invention

Problem to be Solved by the Invention

However, when polyester-based fibers proposed in Patent Documents 1 and 2 are used for a pile fabric, the pile fabrics need to be polished at a temperature of about 170°C to 200°C in both cases, and thus the crimp removability needs to be further improved.
In order to resolve the above-described conventional issues, the present invention provides a polyester-based fiber capable of imparting, to a napped surface layer portion of a pile fabric, high crimp removability in a polishing process at a comparatively low temperature of 160°C or lower, and imparting a good appearance, and good sag-recovery and voluminousness to the pile fabric, and the invention provides a pile fabric in which the polyester-based fiber is used, a method for manufacturing the polyester-based fiber, and a method for manufacturing the pile fabric.

Means for Solving Problem

In one or more embodiments, the present invention relates to a polyester-based fiber having a crimp, in which, when the polyester-based fiber is suspended vertically and subjected to dry heat treatment at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester-based fiber under no load is less than 3%.
Preferably, in one or more embodiments of the present invention, when the polyester-based fiber is filled in a pressure resistant vessel together with pure water while applying a pressure of 3 kPa or more and 20 kPa or less and subjected to wet heat treatment at 98°C for 60 minutes, the wet-heat treated polyester-based fiber is suspended vertically and subjected to dry heat treatment at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester-based fiber under no load is less than 3%.
Preferably, in one or more embodiments of the present invention, the polyester-based fiber has a Young's modulus of 4 GPa or more. Preferably, in one or more embodiments of the present invention, the polyester-based fiber has a single fiber fineness of 10 dtex or less. Preferably, in one or more embodiments of the present invention, a fiber cross-section of the polyester-based fiber has a flat shape, and a flat ratio, which is represented by a ratio of a length of a long side of the fiber cross-section to a length of a short side of the fiber cross-section, is 2 or more and 8 or less.
In one or more embodiments, the present invention relates to a method for manufacturing a polyester-based fiber, the method including a crimp imparting step of imparting a crimp to a drawn yarn that has been drawn after a polyester-based resin or a polyester-based resin composition is melt spun, in which no heat treatment is performed on the drawn yarn before the crimp imparting step, after the crimp imparting step, or before and after the crimp imparting step; heat treatment is performed on the drawn yarn at a temperature of 25°C or more and 120°C or less before the crimp imparting step, after the crimp imparting step, or before and after the crimp imparting step; or heat treatment is performed on the drawn yarn at a temperature of 100°C or more and 200°C or less before the crimp imparting step, and heat treatment is performed on the drawn yarn at a temperature of 25°C or more and 140°C or less after the crimp imparting step.
Preferably, in one or more embodiments of the present invention, the drawn yarn provided with the crimp is subjected to heat treatment at a temperature of 25°C or more and 120°C or less after the crimp imparting step.
In one or more embodiments, the present invention relates to a pile fabric containing the polyester-based fiber in an amount of 30 wt% or more with respect to the entire pile portion.
The pile fabric of one or more embodiments of the present invention may include a long pile portion and a short pile portion, and a difference between an average pile length of the long pile portion and an average pile length of the short pile portion may be2 mm or more. With the pile fabric of one or more embodiments of the present invention, the long pile portion may include an acrylic-based fiber constituted by an acrylic-based copolymer containing acrylonitrile in an amount of 35 wt% or more and less than 95 wt%.
In one or more embodiments, the present invention relates to a method for manufacturing the pile fabric, in which polishing is performed at a temperature of 90°C or more and 160°C or less.

Effects of the Invention

According to the present invention, it is possible to provide a polyester-based fiber capable of imparting a good appearance, sag-recovery and voluminousness to a pile fabric while imparting, to a napped surface layer portion of the pile fabric, high crimp removability in a polishing process at a comparatively low temperature of 90°C or more and 160°C or less, and to provide a pile fabric in which the polyester-based fiber is used.
Also, according to the manufacturing method of the present invention, it is possible to produce a polyester-based fiber capable of imparting a good appearance, sag-recovery and voluminousness to a pile fabric while imparting, to a napped surface layer portion of the pile fabric, high crimp removability in a polishing process at a comparatively low temperature of 90°C or more and 160°C or less, and to produce a pile fabric in which the polyester-based fiber is used.

Brief Description of Drawings

[FIG. 1] FIG. 1 shows schematic views of cross-sections of fibers, FIG. 1(A) showing a schematic view of a circular fiber cross-section, FIG. 1(B) showing a schematic view of a rectangular fiber cross-section, FIG. 1(C) showing a schematic view of an elliptic fiber cross-section, FIG. 1(D) showing a schematic view of a flat multilobal fiber cross-section, and FIG. 1(E) showing a schematic view of a flat constriction fiber cross-section.
[FIG. 2] FIG. 2 is a flow chart showing one example of processes for manufacturing a pile fabric according to one or more embodiments of the present invention.
[FIG. 3] FIG. 3 is a diagram illustrating criteria for evaluating the crimp removability of a polyester-based fiber (pile fiber) in a pile fabric.
[FIG. 4] FIG. 4 is a diagram illustrating criteria for evaluating the sag-recovery and voluminousness of a pile fabric.
[FIG. 5] FIG. 5 is a diagram illustrating criteria for evaluating the appearance of a pile fabric.

Description of the Invention

The inventors of the present invention conducted intensive studies to resolve the above-described issues. As a result, the inventors found that when a polyester-based fiber having crimps, which is obtained by performing no heat treatment on a drawn yarn before a crimp imparting step, after a crimp imparting step, or before and after a crimp imparting step; performing heat treatment on a drawn yarn at a temperature of 25°C or more and 120°C or less before a crimp imparting step, after a crimp imparting step, or before and after a crimp imparting step; or performing heat treatment on a drawn yarn at a temperature of 100°C or more and 200°C or less before a crimp imparting step, and performing heat treatment on a drawn yarn at a temperature of 25°C or more and 140°C or less after a crimp imparting step, is suspended vertically, and is subjected to dry heat treatment at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester-based fiber under no load is less than 3%, and it is possible to realize a pile fabric with good appearance, sag-recovery, and voluminousness due to crimps on a surface layer portion of the pile fabric being removed moderately by polishing the pile fabric in which the fiber (may be referred to as "crimped tow") is used, at a temperature of 90°C or more and 160°C or less. In one or more embodiments of the present invention, "when a polyester-based fiber is suspended vertically and is subjected to dry heat treatment at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester-based fiber under no load is less than 3%" means that, when, in a temperature range of 90°C or more and 120°C or less, a polyester-based fiber is suspended vertically and is subjected to dry heat treatment for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the polyester-based fiber under a load of 4 mg/dtex after the heat treatment and a fiber length of the polyester-based fiber under no load after the heat treatment is less than 3%. That is, the above means that a case where the difference between the fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and the fiber length of the heat-treated polyester-based fiber under no load is less than 3% when dry heat treatment is performed at a temperature of less than 90°C for 60 seconds, and a case where the difference between the fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and the fiber length of the heat-treated polyester-based fiber under no load is less than 3% when dry heat treatment is performed at a temperature of more than 120°C for 60 seconds are excluded.
In one or more embodiments of the present invention, a polyester-based resin constituting a polyester-based fiber is not particularly limited, and it is possible to use polyalkylene terephthalate and/or a copolyester containing polyalkylene terephthalate as the main component. There is no particular limitation to the polyalkylene terephthalate, and examples thereof include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate. In particular, polyethylene terephthalate is preferable from the viewpoint of heat characteristics. There is no particular limitation to the copolyester containing polyalkylene terephthalate as the main component, and examples thereof include copolyesters containing, as the main component, polyalkylene terephthalate such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, or polytrimethylene terephthalate and containing the other copolymer components. In particular, copolyester containing polyethylene terephthalate as the main component is preferable from the viewpoint of heat characteristics. In the present invention, the term "main component" means a component that is contained in an amount of 50 mol% or more, and "a copolyester containing polyalkylene terephthalate as the main component" refers to a copolyester containing polyalkylene terephthalate in an amount of 50 mol% or more. A "copolyester containing polyalkylene terephthalate as the main component" contains polyalkylene terephthalate preferably in an amount of 60 mol% or more, more preferably in an amount of 70 mol% or more, and even more preferably in an amount of 80 mol% or more.
Examples of the other copolymer components include the following: polycarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, paraphenylenedicarboxylic acid, trimellitic acid, pyromellitic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid, and their derivatives; dicarboxylic acids and their derivatives including a sulfonic acid salt such as 5-sodiumsulfoisophthalic acid and dihydroxyethyl 5-sodiumsulfoisophthalate; and 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, polyethylene glycol, trimethylolpropane, pentaerythritol, 4-hydroxybenzoic acid, ε-caprolactone, and ethylene glycol ethers of bisphenol A. These other copolymer components may be used alone or in combination of two or more.
Specific examples of the copolyester containing the polyalkylene terephthalate as the main component include polyesters obtained through copolymerization of polyethylene terephthalate as the main component with one or more compounds selected from the group consisting of ethylene glycol ether of bisphenol A, 1,4-cyclohexanedimethanol, isophthalic acid, and dihydroxyethyl 5-sodiumsulfoisophthalate.
The polyalkylene terephthalates and/or the copolyesters containing polyalkylene terephthalate as the main component may be used alone or in a combination of two or more. In particular, it is preferable that polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, a polyester obtained through copolymerization of polyethylene terephthalate as the main component with ethylene glycol ether of bisphenol A, a polyester obtained through copolymerization of polyethylene terephthalate as the main component with 1,4-cyclohexanedimethanol, a polyester obtained through copolymerization of polyethylene terephthalate as the main component with isophthalic acid, and a polyester obtained through copolymerization of polyethylene terephthalate as the main component with dihydroxyethyl 5-sodiumsulfoisophthalate are used alone or in a combination of two or more.
The intrinsic viscosity (IV value) of the polyester-based resin is not particularly limited, and is preferably 0.3 or more and 1.2 or less, and more preferably 0.4 or more and 1.0 or less. When the intrinsic viscosity thereof is 0.3 or more, the mechanical strength of a fiber that can be obtained does not decrease. Also, when the intrinsic viscosity is 1.2 or less, the molecular weight thereof does not increase excessively, the melt viscosity thereof does not increase excessively, melt spinning method can be easily used, and the fineness of the fiber obtained by using the melt spinning method is likely to be uniform.
An additive agent such as a delustering agent, a lubricant, an antioxidant, a color pigment, a stabilizing agent, a flame retardant, and a toughening agent may be added to a polyester-based resin constituting the polyester-based fiber as needed, for example. An example of the delustering agent includes titanium dioxide. Examples of the lubricant include silica microparticles and alumina microparticles.
The polyester-based fiber has crimps. In one or more embodiments of the present invention, the crimps refer to crimps imparted by a known crimp imparting method such as a gear crimping method or a stuffing box method, and there is no particular limitation thereto. There is no particular limitation to the number of crimps in the polyester-based fiber, and from the viewpoint of bulkiness and processability in a carding machine, for example, the number of crimps is preferably 5 crimps/25 mm or more and 18 crimps/25 mm or less, and more preferably 8 crimps/25 mm or more and 14 crimps/25 mm or less. In one or more embodiments of the present invention, the number of crimps is measured according to JIS L-1015.
In one or more embodiments of the present invention, examples of the form of the polyester-based fiber having crimps includes, although not particularly limited, a filament form, a staple form, and a tow form in which filaments are bundled together.
The polyester-based fiber has good crimp removability, and when the polyester-based fiber is suspended vertically and subjected to dry heat treatment at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester-based fiber under no load is less than 3%. A "difference between a fiber length under a load of 4 mg/dtex and a fiber length under no load is less than 3%" means that crimps have been removed. That is, the polyester-based fiber has a crimp removal temperature of 90°C or more and 120°C or less. In one or more embodiments of the present invention, the crimp removal temperature of the polyester-based fiber is calculated as follows: the polyester-based fibers are bundled to prepare a fiber bundle with 9000 dtex, two ends of the fiber bundle are trimmed such that the resulting sample has a length of about 200 mm, the sample is suspended vertically in a convection hot-air dryer, a load of 4 mg/dtex is applied to this fiber bundle (specifically, a 36 g-weight is suspended from a lower end of the fiber bundle), and heat treatment is performed for 60 seconds under a predetermined temperature starting from 50°C and increasing in increments of 10°C. After each instance of heat treatment, a length A of the fiber bundle to which a load of 4 mg/dtex is applied, and a length B of the fiber bundle to which no load is applied after the load has been removed are measured, and the minimum value of temperatures at which the difference therebetween (that is, the rate of change in the length calculated by Mathematical Formula (1) below) is less than 3% is obtained five times, and the average thereof is calculated to obtain the crimp removal temperature of the polyester-based fiber. $Rate of change in length (%) = (A - B) / A \times 100$
In other words, in one or more embodiments of the present invention, the polyester-based fiber has a minimum temperature (crimp removal temperature) that satisfies Mathematical Formula (2) below is 90°C or more and 120°C or less. $(A - B) / A \times 100 < 3$
where, in Formula (2), A indicates the length of the fiber bundle of the polyester-based fiber in a state in which a load of 4 mg/dtex is applied thereto after dry heat treatment is performed for 60 seconds under a predetermined temperature in a state in which a load of 4 mg/dtex is applied thereto, and B indicates the length of the fiber bundle obtained when the load is removed after the same operation is performed.
In one or more embodiments of the present invention, it is preferable that, when a pressure resistant vessel is filled with the polyester-based fiber together with pure water while applying a pressure of 3 kPa or more and 20 kPa or less, hot-water treatment is performed at 98°C for 60 minutes, the hot-water treated polyester-based fiber is suspended vertically, and dry heat treatment is performed at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester-based fiber under no load is less than 3%. That is, in one or more embodiments of the present invention, it is preferable that, after the pressure resistant vessel is filled with the polyester-based fiber together with pure water while applying a pressure of 3 kPa or more and 20 kPa or less, and hot-water treatment is performed at 98°C for 60 minutes, the hot-water treated polyester-based fiber also has a temperature (crimp removal temperature), which satisfies Formula (2) above, of 90°C or more and 120°C or less.
In the present invention, when a polyester-based fiber has a crimp removal temperature of 90°C or more and 120°C or less, crimps are removed moderately from the polyester-based fiber in a comparatively low temperature range of 90°C or more and 160°C or less in a polishing step, which is one of the pile fabric processing steps, and specifically, only crimps on the napped surface layer portion of the pile fabric are likely to be removed, and thus, it is possible to obtain a pile fabric having good appearance, sag-recovery, and voluminousness. If the crimp removal temperature exceeds 120°C, crimps are not sufficiently removed in a polishing step under a low temperature of 90°C or more and 160°C or less, and crimps in the pile fibers are hardly removed, resulting in a pile fabric having poor appearance and texture. On the other hand, if the crimp removal temperature is lower than 90°C, crimps in the pile fibers are almost completely removed in a polishing process under a temperature of 90°C or more and 160°C or less, resulting in a pile fabric with inferior sag-recovery and voluminousness. When the hot-water treated polyester-based fiber also has a crimp removal temperature of 90°C or more and 120°C or less, crimps are removed moderately in the polishing step under a low temperature of 90°C or more and 160°C or less even through a process such as dyeing under hot-water conditions, and specifically, only the crimps on the napped surface layer portion of the pile fabric are likely to be removed, and thus, it is possible to obtain a pile fabric having good appearance and good sag-recovery and voluminousness.
The single fiber fineness of the polyester-based fiber is, although not particularly limited, preferably 10 dtex or less, for example, and more preferably 5 dtex or less. If the single fiber fineness exceeds 10 dtex, heat is not sufficiently transferred in a polishing process, and there are cases where the number of instances of polishing needs to be increased to moderately remove crimps. Also, there is a risk that soft texture will deteriorate due to an increase in the number of instances of polishing. From the viewpoint of fiber handleability, the single fiber fineness of the polyester-based fiber is, although not particularly limited, preferably 1 dtex or more, for example.
The polyester-based fiber may have, although not particularly limited, a circular cross-sectional shape, or a flat cross-sectional shape, for example. From the viewpoint of increasing the sag-recovery of a pile fabric, the polyester-based fiber preferably has a flat shape in which a length (b) of a long side of a fiber cross-section is larger than a length (a) of a short side of the fiber cross-section, and the length (b) of a long side of a fiber cross-section is more preferably two times or more the length (a) of a short side of the fiber cross-section. From the viewpoint of increasing the voluminousness of a pile fabric, the length (b) of a long side of a fiber cross-section of the polyester-based fiber is, although not particularly limited, preferably eight times or less, and more preferably six times or less the length (a) of a short side of the fiber cross-section. A "long side of a fiber cross-section" refers to a straight line having the maximum length of a fiber cross-section, that is, a straight line having the maximum length, out of straight lines connecting any two points on an outer circumference of the fiber cross-section. A "short side of a fiber cross-section" refers to a straight line having the maximum width of a fiber cross-section, that is, a straight line connecting two points having the maximum length when connecting any two points on an outer circumference of a fiber cross-section to be perpendicular to the long side of the fiber cross-section. Note that, in the case of a circular shape, the length (b) of the long side of a fiber cross-section is the same as the length (a) of the short side of the fiber cross-section.
Although the cross-sectional shape of the polyester-based fiber is not particularly limited, specifically, examples thereof include a circular shape (FIG. 1A) and a flat shape such as a rectangular shape (FIG. 1B), an elliptic shape (FIG. 1C), a flat multilobal shape (FIG. ID), and a flat constriction shape (FIG. IE).
In one or more embodiments of the present invention, the polyester-based fiber can be produced using a manufacturing method that is similar to that for a usual polyester-based fiber, except that no heat treatment is performed on a drawn yarn before a crimp imparting step, after a crimp imparting step, or before and after a crimp imparting step; heat treatment is performed on a drawn yarn at a temperature of 25°C or more and 120°C or less before a crimp imparting step, after a crimp imparting step, or before and after a crimp imparting step; or heat treatment is performed on a drawn yarn at a temperature of 100°C or more and 200°C or less before a crimp imparting step, and heat treatment is performed on a drawn yarn at a temperature of 25°C or more and 140°C or less after a crimp imparting step.
In one or more embodiments of the present invention, "before a crimp imparting step" indicates a time period starting from the completion of the step of drawing a polyester-based fiber to the start of the step of imparting crimps, and "after a crimp imparting step" indicates a time period starting from the completion of the step of imparting crimps until a final polyester-based fiber having crimps is obtained. If "heat treatment is performed on a drawn yarn at 100°C after a crimp imparting step", heat treatment at 100°C is performed in a time period starting from the completion of the step of imparting crimps until a final polyester-based fiber having crimps is obtained, for example. Before and after a crimp imparting step, it is possible to include steps other than the heat treatment step, such as an oil applying step, a constant length cutting step, and a rewinding step, for example.
By performing no heat treatment on a drawn yarn before the crimp imparting step, after the crimp imparting step, or before and after the crimp imparting step, or by performing heat treatment on a drawn yarn at a temperature of 25°C or more and 120°C or less before the crimp imparting step, after the crimp imparting step, or before and after the crimp imparting step, crystallization of the polyester-based fiber is not facilitated before and/or after the crimp imparting step. Therefore, it is possible to obtain a polyester-based fiber having a crimp removal temperature of 90°C or more and 120°C or less, and as described above, due to this polyester-based fiber being used in a pile fabric, crimps are moderately removed from the polyester-based fiber in a polishing step at a low temperature of 90°C or more and 160°C or less in the pile fabric processing steps. Specifically, only the crimps on a napped surface layer portion of the pile fabric are likely to be removed, and thus it is possible to obtain a pile fabric having good appearance, sag-recovery, and voluminousness.
In one or more embodiments of the present invention, from the viewpoint of reducing the shrinkage percentage of the polyester-based fiber, it is preferable to perform heat treatment on a drawn yarn at a temperature of 25°C or more and 120°C or less, it is more preferable to perform heat treatment at a temperature of 60°C or more and 110°C or less, and it is further preferable to perform heat treatment at a temperature of 80°C or more and 110°C or less, after the crimp imparting step without performing heat treatment before the crimp imparting step. Although there is no particular limitation to the heat treatment time, the heat treatment time may be 10 minutes or more and 50 minutes or less, for example. Specifically, heat treatment after the crimp imparting step is performed preferably at a temperature of 60°C or more and 110°C or less for 10 minutes or more and 50 minutes or less, and more preferably at a temperature of 80°C or more and 110°C or less for 20 minutes or more and 40 minutes or less. If a drawn yarn is subjected to heat treatment only after the crimp imparting step and the temperature of the heat treatment exceeds 120°C, crimps imparted to the polyester-based fiber may be tightly fixed thereto, and the crimp removal temperature of the polyester-based fiber may exceed 120°C. If the heat treatment time is 50 minutes or less, the productivity and production processability will be improved.
In one or more embodiments of the present invention, if a drawn yarn is subjected to heat treatment before and after the crimp imparting step, heat treatment may be performed on the drawn yarn at a temperature of 100°C or more and 200°C or less before the crimp imparting step, and heat treatment may also be performed on the drawn yarn at a temperature of 25°C or more and 140°C or less after the crimp imparting step. In this case, heat treatment is performed on the drawn yarn preferably at a temperature of 100°C or more and 170°C or less, and more preferably at a temperature of 100°C or more and 150°C or less, before the crimp imparting step. Also, after the crimp imparting step, it is preferable to perform heat treatment at a temperature of 25°C or more and 130°C or less, and it is more preferable to perform heat treatment at a temperature of 25°C or more and 120°C or less. Although there is no particular limitation to the heat treatment time, the heat treatment time may be 10 seconds or more and 5 minutes or less, and 20 seconds or more and 4 minutes or less before the crimp imparting step, for example, and may be 5 minutes or more and 40 minutes or less, and 10 minutes or more and 30 minutes or less after the crimp imparting step, for example. The crimp removal temperature of the obtained polyester-based fiber is reduced by subjecting the drawn yarn to heat treatment under the above-described conditions before and after the crimp imparting step. In particular, if the drawn yarn is subjected to heat treatment under the above-described conditions before and after the crimp imparting step, the obtained polyester-based fiber is likely to have a crimp removal temperature of 90°C or more and 120°C or less even after hot-water treatment, and crimps are moderately removed in the polishing step at a low temperature of 90°C or more and 160°C or less even through a process such as dyeing under hot-water conditions, and specifically, only the crimps on the napped surface layer portion of the pile fabric are likely to be removed, and thus, it is possible to obtain a pile fabric having good appearance, sag-recovery, and voluminousness.
Heat treatment performed before the crimp imparting step and/or after the crimp imparting step may be dry heat treatment or wet heat treatment. Dry heat treatment is preferable because the process is simple. It is possible to perform dry heat treatment, using a uniform hot-air dryer, a suction dryer, or the like. The heat treatment may be performed in a relaxed state. The relaxation rate is not particularly limited, and may be set to 20% or less, for example.
It is possible to produce a polyester-based fiber, using a manufacturing method that is similar to that for a normal polyester-based fiber, except for the above-described steps. A polyester-based fiber can be produced by pelletizing a polyester-based resin composition obtained by dry blending a polyester-based resin or a polyester-based resin and additive agents, through melt kneading using various general kneading machines, and melt spinning the resulting pellets. Melt spinning method is performed while the temperatures (spinning temperatures) of an extruder, a gear pump, a spinneret, and the like are set to 250°C or more and 300°C or less, and the obtained spun yarns are allowed to pass through a heated tube, cooled to a temperature of not more than the glass transition point of the polyester-based resin, and wound up at a speed of 50 m/min or more and 4500 m/min or less, and thus spun yarns (undrawn yarns) are obtained. The spun yarns (undrawn yarns) can be drawn through hot drawing. The heating means for the hot drawing may be a heating roller, a heat plate, a steam jet apparatus, or a hot water bath, and they can be used in combination as appropriate.
Crimps may be imparted using a known crimp imparting apparatus such as a gear crimper or a stuffing box crimper. Similarly to ordinary crimping, it is possible to impart crimps in a state in which a polyester-based fiber is preheated to a temperature that is higher than or equal to a softening temperature. Similarly to ordinary crimping, preheating may be performed by wet heat, for example, by steam at 85°C or more and 110°C or less, for example.
In one or more embodiments of the present invention, the polyester-based fibers preferably have a Young's modulus of 4.0 GPa or more, and more preferably has a Young's modulus of 5.0 GPa or more. This is because the higher the Young's modulus is, the higher the rigidity of the fiber and the better the voluminousness of the pile fabric are.
In one or more embodiments of the present invention, the pile fabric includes the polyester-based fiber in the pile portion. In the present invention, the pile portion refers to a napped portion of the pile fabric other than the base fabric (also referred to as "ground weave") portion. From the viewpoint of sag-recovery and voluminousness, the pile fabric preferably contains the polyester-based fiber in an amount of 30 wt% or more, more preferably contains the polyester-based fiber in an amount of 40 wt% or more, and further more preferably contains the polyester-based fiber in an amount of 50 wt% or more with respect to the entire pile portion. Fibers constituting the pile portion also refer to as pile fibers below.
From the viewpoint of realizing a two layer structure similar to that of natural fur, the pile fabric preferably includes a long pile portion and a short pile portion that have different pile lengths, and the difference between the average pile length of the long pile portion and the average pile length of the short pile portion is preferably 2 mm or more, and more preferably 5 mm or more and 50 mm or less. In the present invention, the "average pile length" indicates the average of lengths obtained by measuring the length from the root (the root on a surface of the pile fabric) of fibers to a leading end portion of the pile at ten positions, the fibers constituting the pile portion of the pile fabric and being made to stand vertically so that the fibers are lined up.
The pile portion may also include other fibers such as acrylic-based fibers, and polyvinyl chloride-based fibers, for example, in addition to the polyester-based fibers. From the viewpoint of obtaining soft texture, the long pile portion preferably includes acrylic-based fibers constituted by an acrylic-based copolymer that contains acrylonitrile in an amount of 35 wt% or more and less than 95 wt%. It is possible to provide a pile fabric having extremely good texture, and good sag-recovery and voluminousness, due to the polyester-based fiber being used in combination with acrylic-based fibers. The acrylic-based copolymer preferably contains another monomer that is copolymerizable with acrylonitrile in an amount of more than 5 wt% and 65 wt% or less, in addition to acrylonitrile. Although there is no particular limitation, it is preferable to use, as the other monomers, one or more monomers selected from the group consisting of vinyl halides, vinylidene halides, and metal salts of sulfonic acid-containing monomers, and it is more preferable to use one or more monomers selected from the group consisting of vinyl chloride, vinylidene chloride, and sodium styrenesulfonate.
The pile fabric can be produced using a manufacturing method that is similar to that for a normal pile fabric, except that polishing is performed at a temperature of 90°C or more and 160°C or less. A sliver constituted by pile fibers is knitted with a sliver knitting machine into a pile fabric (may be referred to as a "knitted fabric"), pre-polishing and pre-shirring are performed at a temperature of 90°C or more and 160°C or less, crimps are then removed through polishing at a temperature of 90°C or more and 160°C or less, and shirring is then performed. Polishing may also be performed multiple times at different temperatures. Also, a lining (opposite side of the napped portion) of the pile fabric may be coated with a backing material in order to inhibit pile fibers from coming off and increase width. It is possible to use acrylic acid ester-based adhesives, polyurethane-based adhesives, and the like for the backing material. FIG. 2 is a flow chart showing one example of processes for manufacturing a pile fabric according to one or more embodiments of the present invention.

[Examples]

The following specifically describes one or more embodiments of the present invention based on examples and comparative examples. Note that the present invention is not limited to these examples.
First, a measuring method and an evaluation method used in examples and comparative examples will be described below.

Number of crimps

The number of crimps was measured according to JIS L-1015.

Young's modulus

Young's modulus was measured according to JIS L-1013.

Crimp removal temperature

Polyester-based fibers were bundled to prepare a fiber bundle with 9000 dtex, two ends of the fiber bundle were trimmed such that the resulting sample had a length of about 200 mm, the sample was suspended vertically in a convection hot-air dryer, a load of 4 mg/dtex was applied to this fiber bundle, specifically, a 36 g-weight was suspended from a lower end of the fiber bundle, and heat treatment was performed for 60 seconds under a predetermined temperature starting from 50°C and increasing in increments of 10°C. After each instance of heat treatment, the length A of the fiber bundle to which a load of 4 mg/dtex was applied, and the length B of the fiber bundle to which no load was applied after the load has been removed were measured, and the minimum value of temperatures at which the difference therebetween (that is, the rate of change in the length calculated by Mathematical Formula (1) below) was less than 3% was conducted five times, and the average thereof was calculated to obtain the crimp removal temperature of the polyester-based fibers. $Rate of change in length (%) = (A - B) / A \times 100$

Crimp removal temperature after hot-water treatment

20 g of the fiber bundle of polyester-based fibers was weighed, wrapped with gauze, and introduced into a 300 mL-pressure resistant vessel made of stainless steel together with 200 mL of pure water. In order to prevent crimps from being removed in hot-water treatment, the pressure resistant vessel was packed with polyester-based fibers as waste fibers such that the vessel was completely filled with the polyester-based fibers. The filling pressure at this time was 10 kPa. Then, the pressure resistant vessel was put with a lid and was completely sealed, and was heated in a polyethylene glycol bath at 98°C for 60 minutes. After heating completed, the vessel was cooled and the polyester-based fibers were removed from the vessel, moisture was removed through centrifugal dehydration, and the polyester-based fibers were dried in a dryer heated to 60°C for 2 hours. The crimp removal temperature of the hot-water treated polyester-based fibers was measured using the polyester-based fiber bundle that was subjected to wet heat treatment in this manner, using the same method as the above-described method.

Crimp removability

The crimp removability of pile portions of pile fabrics were sensory evaluated based on the following five criteria. Also, reference photographs for the following criteria are shown in FIG. 3. Specifically, FIG. 3(a) shows the reference photograph for criterion 5, FIG. 3(b) shows the reference photograph for criterion 4, FIG. 3(c) shows the reference photograph for criterion 3, FIG. 3(d) shows the reference photograph for criterion 2, and FIG. 3(e) shows the reference photograph for criterion 1. If the criterion of the crimp removability is 3, crimps only on a napped surface layer portion of the pile fabric were removed.

5: The directions of pile fibers were aligned, and crimps were removed neatly from the roots to leading ends of the pile fibers.
4: The directions of pile fibers were aligned, and crimps were removed neatly up to middle portions of the pile fibers.
3: The directions of pile fibers were aligned, and crimps were removed neatly only from the leading ends of the pile fibers.
2: The directions of pile fibers were aligned, but crimps were not removed at all.
1: The directions of pile fibers were not aligned, and crimps were not removed at all.

Sag-recovery and voluminousness

The sag-recovery and voluminousness of pile fabrics were evaluated based on the following criteria. Reference photographs for the respective criteria are shown in FIG. 4. Specifically, FIG. 4(a) shows reference photographs when a pile fabric had good sag-recovery and voluminousness, and FIG. 4(b) shows reference photographs when a pile fabric had poor sag-recovery and voluminousness.
Good: The thickness of a pile fabric obtained when napped portions of two pile fabrics were placed on each other and a pressure of 300 Pa was applied thereto was about 60% or more of the thickness of the pile fabric obtained before the pressure was applied, and the pile fabric had sufficient sag-recovery and voluminousness.
Poor: The thickness of a pile fabric obtained when napped portions of two pile fabrics were placed on each other and a pressure of 300 Pa was applied thereto was less than about 60% of the thickness of the pile fabric obtained before the pressure was applied, and the pile fabric had insufficient sag-recovery and voluminousness.

Appearance

A surface of a napped portion (pile portion) of a pile fabric was observed, and was sensory evaluated based on the following criteria. Reference photographs for the respective criteria are shown in FIG. 5. Specifically, FIG. 5(a) shows a reference photograph when a pile fabric had good appearance, and FIG. 5(b) shows a reference photograph when a pile fabric had poor appearance.
Good: There was no convergence of pile fibers, and the surface of a pile fabric looked flat.
Poor: Pile fibers converged, and a pile fabric looked cracked.

Example 1

Production of polyester-based fiber

Spinning was performed by a normal spinning machine at a spinning temperature of 290°C and a speed of 320 m/min using polyethylene terephthalate (PET) having an intrinsic viscosity (IV value) of 0.65 and a spinneret with 48 holes having a diameter of 0.4 mm and a circular cross-section, and then the obtained spun yarns were drawn and stretched by 375% using a hot roller at 80°C to obtain drawn yarns. Note that titanium oxide was added to PET as a delustering agent in an amount of 0.3 parts by weight with respect to 100 parts by weight of PET. Then, after the drawn yarns were blended to an appropriate fineness, crimps were imparted through preheating at 98°C using a stuffing box crimper, heat treatment was performed for 30 minutes in a uniform hot-air dryer set at 110°C in a relaxed state in which the relaxation rate was 15% or less, and thus crimped yarns having a single fiber fineness of 3 dtex was obtained.

Production of pile fabric

Staple fibers for a pile fabric was obtained by cutting the PET crimped yarns obtained above to 51 mm. A sliver was made of 100% of the staple fibers, and a pile fabric was produced using a sliver knitting machine. Then, a pre-polishing process and pre-shirring were performed at 120°C, and the napped portions of the pile fabric were trimmed to a length of 18 mm, and a tentering process was performed after back-coating the lining of the fabric with an acrylic acid ester-based adhesive. Then, a polishing process was performed at 160°C three times, at 130°C three times, and at 100°C three times. Thereafter, the napped portions were trimmed through shirring to a length of 20 mm, and thus a pile fabric having a basis weight of about 800 g/m² was obtained.

Example 2

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 3 dtex were obtained in a manner similar to that of Example 1, except that heat treatment was performed in a uniform hot-air dryer set at 60°C for 30 minutes after crimps were imparted.

Production of pile fabric

A pile fabric was produced in a manner similar to that of Example 1, except that the PET crimped yarns obtained above were used.

Example 3

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 3 dtex were obtained in a manner similar to that of Example 1, except that heat treatment was performed in a uniform hot-air dryer set at 120°C for 30 minutes after crimps were imparted.

Production of pile fabric

Example 4

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 3 dtex were obtained in a manner similar to that of Example 1, except that no heat treatment was performed after crimps were imparted.

Production of pile fabric

Example 5

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 3 dtex were obtained in a manner similar to that of Example 1, except that a spinneret having 72 holes and an oval cross-section ((b + a) / 2 = 0.46 mm, b/a = 5.5) was used.

Production of pile fabric

Example 6

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 4.4 dtex were obtained in a manner similar to that of Example 1, except that using a spinneret having 200 holes and a flat multilobal cross-section (FIG. ID, a = 0.44 mm, b = 2.07 mm), and heat treatment was performed in a uniform hot-air dryer set at 150°C for 1 minute before crimps were imparted, and in a uniform hot-air dryer set at 100°C for 15 minutes after crimps were imparted.

Example 7

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 4.4 dtex were obtained in a manner similar to that of Example 6, except that heat treatment was performed in a uniform hot-air dryer set at 170°C for 1 minute before crimps were imparted, and in a uniform hot-air dryer set at 100°C for 15 minutes after crimps were imparted.

Comparative Example 1

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 3 dtex were obtained in a manner similar to that of Example 1, except that heat treatment was performed in a uniform hot-air dryer set at 130°C for 30 minutes after crimps were imparted.

Production of pile fabric

Comparative Example 2

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 3 dtex were obtained in a manner similar to that of Example 1, except that heat treatment was performed in a uniform hot-air dryer set at 140°C for 30 minutes after crimps were imparted.

Production of pile fabric

Comparative Example 3

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 3 dtex were obtained in a manner similar to that of Example 1, except that heat treatment was performed in a uniform hot-air dryer set at 150°C for 30 minutes after crimps were imparted.

Production of pile fabric

Comparative Example 4

Production of polyester-based fiber

Crimped yarns having a single fiber fineness of 3 dtex were obtained in a manner similar to that of Example 1, except that drawn yarns were subjected to heat treatment in a uniform hot-air dryer set at 180°C for 30 minutes, the resulting yarns were blended to an appropriate fineness, crimps were imparted through preheating at 98°C using a stuffing box crimper, and no heat treatment was performed after crimps were imparted.

Production of pile fabric

The percentages of crimp, dry-heat shrinkage percentages, and crimp removal temperatures of the PET crimped yarns obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were measured as described above. The crimp removability, appearance, and sag-recovery and voluminousness of the pile fabrics obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were evaluated as described above. These results are shown in Table 1 below. In Table 1 below, "-" indicates unmeasured.

[Table 1]

	Polyester-based fiber						Pile fabric
	Fiber cross-section	Heat treatment conditions		Number of crimps	Young's modulus	Crimp removal temperature	Crimp removability	Appearance	Sag-recovery and voluminousness
	Fiber cross-section	Before crimp was imparted	After crimp was imparted	(crimps/25mm)	(GPa)	(°C)	Crimp removability	Appearance	Sag-recovery and voluminousness
Ex. 1	circular	no heat treatment was performed	110°C×30 min	12.8	5.42	120	3	good	good
Ex. 2	circular	no heat treatment was performed	60°C×30 min	11.4	5.47	90	3	good	good
Ex. 3	circular	no heat treatment was performed	120°C×30 min	-	5.19	120	3	good	good
Ex. 4	circular	no heat treatment was performed	no heat treatment was performed	10.8	3.70	90	3	good	good
Ex. 5	oval	no heat treatment was performed	110°C×30 min	11.8	-	120	3	good	good
Ex. 6	flat multilobal	150°C×1 min	100°C×15 min	10.9	5.49	100	3	good	good
Ex. 7	flat multilobal	170°C×1 min	100°C×15 min	11.4	6.20	110	3	good	good
Comp. Ex. 1	circular	no heat treatment was performed	130°C×30 min	-	5.44	130	2	poor	good
Comp. Ex. 2	circular	no heat treatment was performed	140°C×30 mm	-	5.17	140	2	poor	good
Comp. Ex. 3	circular	no heat treatment was performed	150°C×30 min	12.7	5.15	150	1	poor	good
Comp. Ex. 4	circular	180°C×5 min	no heat treatment was performed	10.7	-	80	5	good	poor

As can be seen from data in Table 1 above, the PET crimped yarns of Examples 1 to 5 had a crimp removal temperature of 90°C or more and 120°C or less in which no heat treatment was performed on the drawn yarns before and/or after the crimp imparting step, or in which heat treatment was performed on the drawn yarns at a temperature of 25°C or more and 120°C or less after the crimp imparting step, and pile fabrics in which these PET crimped yarns were used had good appearance and good sag-recovery and voluminousness because crimps were removed only from the napped surface layer portions of the pile fabrics through treatment at 90°C or more and 160°C or less.
Also, the PET crimped yarns of Examples 6 and 7 had a crimp removal temperature of 90°C or more and 120°C or less in which heat treatment was performed at a temperature of 100°C or more and 200°C or less before the crimp imparting step, and heat treatment was performed at a temperature of 25°C or more and 140°C or less after crimps were imparted, and the pile fabrics in which these PET crimped yarns were used had good appearance and good sag-recovery and voluminousness because crimps were removed only from the napped surface layer portions of the pile fabrics in the treatment at 90°C or more and 160°C or less.
On the other hand, the PET crimped yarns of Comparative Examples 1 to 3 had a crimp removal temperature of more than 120°C in which no heat treatment was performed before the crimp imparting step and heat treatment was performed on the drawn yarns at a temperature of more than 120°C after the crimp imparting step, and the pile fabrics in which these PET crimped yarns were used had bad appearance because crimps were not removed at all from the pile fibers of the pile fabrics in the polishing process at 90°C or more and 160°C or less. Also, the PET crimped yarn of Comparative Example 4 had a crimp removal temperature of less than 90°C, and the pile fabric in which these PET crimped yarns were used had poor sag-recovery and voluminousness because crimps were neatly removed from the roots to the leading ends of the pile fibers in the polishing process at 90°C or more and 160°C or less.
Based on these results, it was found that all of the PET crimped yarns described in the examples can be suitably used for pile fabrics.
In particular, the PET crimped yarns of Examples 1 to 3 and 5 in which heat treatment was performed at a temperature of 25°C or more and 120°C or less after crimps were imparted, and the PET crimped yarns of Examples 6 and 7 in which heat treatment was performed at a predetermined temperature before and after crimps were imparted had a Young's modulus of 5 GPa or more, and had good fiber physical properties.

Also, the crimp removability of the hot-water treated PET crimped yarns obtained in Examples 3, 4, 6, and 7 and Comparative Example 1 was measured. These results are shown in Table 2 below. In Table 2 below, "-" indicates unmeasured.

[Table 2]

	Heat treatment conditions		Crimp removability temperature (°C)
	Before crimp was imparted	After crimp was imparted	Unprocessed	After hot-water treatment
Ex. 3	no heat treatment was performed	120°C×30 min	120	130
Ex. 4	no heat treatment was performed	no heat treatment was performed	90	120
Ex. 6	150°C×1 min	100°C×15 min	100	120
Ex. 7	170°C×1 min	100°C× 15 min	110	120
Comp. Ex. 1	no heat treatment was performed	130°C×30 min	130	140

As shown in Table 2, the crimp removal temperatures of the PET crimped yarns of Examples 3, 4, 6, and 7 were in a range of 90°C or more and 120°C or less without hot-water treatment, and these PET crimped yarns had crimp characteristics suitable for a pile fabric in a normal state. In particular, the crimp removal temperatures of the PET crimped yarns of Example 4 in which no heat treatment was performed before and after crimps were imparted, and the crimp removal temperatures of the PET crimped yarns of Examples 6 and 7 in which heat treatment was performed at predetermined temperatures before and after crimps were imparted were in a range of 90°C or more and 120°C or less even after hot-water treatment was performed. The PET fibers of Examples 4, 6, and 7 not only had crimp characteristics suitable for a pile fabric in a normal state but also had crimp characteristics suitable for a pile fabric after wet heat treatment. Therefore, even if these PET fibers are dyed under hot-water conditions, for example, crimps are removed only from the napped surface layer portions of the pile fabric in the treatment at 90°C or more and 160°C or less, and thus a pile fabric having good appearance and good sag-recovery and voluminousness can be easily obtained.
Note that the crimp removal temperature of the unprocessed PET crimped yarn of Comparative Example 1 and the crimp removal temperature of the hot-water treated PET crimped yarn of Comparative Example 1 exceeded 120°C, and thus it is inferred that, when used in a pile fabric, the PET crimped fibers of Comparative Example 1 will be inferior to the PET fibers of Examples 3, 4, 6, and 7 in this respect.

Description of Reference Numerals

a: Short side of fiber cross-section
b: Long side of fiber cross-section

Claims

A polyester-based fiber having a crimp,
wherein, when the polyester-based fiber is suspended vertically and subjected to dry heat treatment at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester-based fiber under no load is less than 3%.
The polyester-based fiber according to claim 1,
wherein, when the polyester-based fiber is filled in a pressure resistant vessel together with pure water while applying a pressure of 3 kPa or more and 20 kPa or less and subjected to hot-water treatment at 98°C for 60 minutes, the hot-water treated polyester-based fiber is suspended vertically and subjected to dry heat treatment at a temperature of 90°C or more and 120°C or less for 60 seconds under a load of 4 mg/dtex, a difference between a fiber length of the heat-treated polyester-based fiber under a load of 4 mg/dtex and a fiber length of the heat-treated polyester-based fiber under no load is less than 3%.
The polyester-based fiber according to claim 1 or 2,
wherein the polyester-based fiber has a Young's modulus of 4 GPa or more.
The polyester-based fiber according to any one of claims 1 to 3,
wherein the polyester-based fiber has a single fiber fineness of 10 dtex or less.
The polyester-based fiber according to any one of claims 1 to 4,
wherein a fiber cross section of the polyester-based fiber has a flat shape, and a length of a long side of the fiber cross section is two times or more and eight times or less a length of a short side of the fiber cross section.
A method for manufacturing a polyester-based fiber, comprising:
a crimp imparting step of imparting a crimp to a drawn yarn that has been drawn after a polyester-based resin or a polyester-based resin composition is melt spun,

wherein no heat treatment is performed on the drawn yarn before the crimp imparting step, after the crimp imparting step, or before and after the crimp imparting step;

heat treatment is performed on the drawn yarn at a temperature of 25°C or more and 120°C or less before the crimp imparting step, after the crimp imparting step, or before and after the crimp imparting step; or

heat treatment is performed on the drawn yarn at a temperature of 100°C or more and 200°C or less before the crimp imparting step, and heat treatment is performed on the drawn yarn at a temperature of 25°C or more and 140°C or less after the crimp imparting step.
The method for manufacturing a polyester-based fiber according to claim 6,
wherein the drawn yarn provided with the crimp is subjected to heat treatment at a temperature of 25°C or more and 120°C or less after the crimp imparting step.
The method for manufacturing a polyester-based fiber according to claim 6,
wherein heat treatment is performed on the drawn yarn at a temperature of 100°C or more and 200°C or less before the crimp imparting step, and heat treatment is performed on the drawn yarn at a temperature of 25°C or more and 140°C or less after the crimp imparting step.
A pile fabric comprising
the polyester-based fiber according to any one of claims 1 to 5 in an amount of 30 wt% or more with respect to the entire pile portion.
The pile fabric according to claim 9,
wherein the pile fabric comprises a long pile portion and a short pile portion, and a difference between an average pile length of the long pile portion and an average pile length of the short pile portion is 2 mm or more.
The pile fabric according to claim 9 or 10,
wherein the long pile portion comprises an acrylic-based fiber comprised by an acrylic-based copolymer containing acrylonitrile in an amount of 35 wt% or more and less than 95 wt%.
A method for manufacturing the pile fabric according to any one of claims 9 to 11,
wherein polishing is performed at a temperature of 90°C or more and 160°C or less.