US20100317248A1

US20100317248A1 - Fabric including low-melting fiber

Info

Publication number: US20100317248A1
Application number: US12/790,305
Authority: US
Inventors: Hoo-Sung Chang; Sung-Gun KIM
Original assignee: Woongjin Chemical Co Ltd
Current assignee: Toray Chemical Korea Inc
Priority date: 2009-06-12
Filing date: 2010-05-28
Publication date: 2010-12-16
Also published as: JP2010285738A; AU2009243456A1; EP2261405A2; KR20100133834A; CN101922077A; WO2010143777A1

Abstract

Fabrics including a low-melting fiber are provided. In an embodiment, the fabric includes a regular fiber and a low-melting fiber. The low-melting fiber is directly included in either warps or wefts or both. Alternatively, a blended or plied fiber of the regular fiber and the low-melting fiber is included in either warps or wefts or both. The low-melting fiber has a fusion rate of 30 to 100%. The fabric has a yarn slip length of 0.1 to 2.5 mm.

Description

TECHNICAL FIELD

The present invention relates to fabrics including a low-melting fiber, and more particularly to fabrics including a low-melting fiber whose fusion rate is controlled to achieve both shape stability and environmental stability simultaneously.

BACKGROUND ART

In recent years, the application of fabrics has been extended to industrial and living goods as well as clothes. The living goods are exemplified by screens. General applications of screens are window blinds and projectors. Screens for window blinds are fabric products that are installed in houses, hotels, restaurants and other buildings to protect people's private lives and block sunlight from entering the windows. A typical screen for a window blind is produced by cutting a fabric to a predetermined width and rolling the cut fabric on a roll. The screen is designed in such a way that the roll is fixed to the window and the fabric rolls down to cover the window or rolls up to secure a field of view when a user rotates the roll. Such screens may be called by different names, such as roll screens, panel screens or vertical blinds, according to the shape (e.g., roll or panel) of fabrics employed.
Screen fabrics should be imparted with stiffness because they have a large width when actually used. Various efforts have been made to impart stiffness to screen fabrics. As an example, a method is known in which a polyurethane resin is coated on the surface of a screen fabric to impart stiffness to the screen fabric while ensuring the inherent flexibility of the fabric.
However, the method essentially involves an additional coating process. Another problem of the method is indoor environmental pollution because the screen fabric is installed indoors and the coating material is classified as a volatile organic compound (VOC) in view of its characteristics.
The inventors of the present invention have focused on the fact that polyester fibers are used in various applications, including industrial materials as well as clothes such as men's business suits and shirts, for their advantages, for example, high strength, good chemical resistance, high melting point of 250 to 255° C., which implies good heat resistance, and sufficient elasticity against elongation and bending.
However, since polyester has a relatively high melting point, the curing of polyester fiber structures generally requires the use of an aqueous solution of formaldehyde (i.e. formalin), an organic solvent-based adhesive, or a hard resin (e.g., a phenolic, melamine or urea resin). The organic solvent-based adhesive does not penetrate into fabrics, resulting in poor adhesion to the fabrics and leaving a rough feeling after use. Further, the adhesive is very volatile, contains a number of substances harmful to humans and gives off toxic gases, which cause environmental problems.
In order to solve these problems, many proposals have been made, for example, a technique in which a woven fabric including a low-melting fiber is thermally processed to fuse the low-melting fiber to the fabric, thus eliminating the need for coating. This technique can solve the problems of prior art coating methods but fails to review the control of the physical properties of the fabric depending on the fusion rate of the low-melting fiber. Thus, the fabric cannot be applied to various products and does not possess physical properties suitable for use in desired applications.

DISCLOSURE

Technical Problem

The present invention has been made in an effort to solve the problems of the prior art, and it is an object of the present invention to provide a highly stable fabric that does not release any volatile substances.
It is another object of the present invention to provide a fabric whose physical properties are controllable depending on the fusion rate.
It is another object of the present invention to provide a fabric that can achieve stiffness suitable for use as a screen material while ensuring the inherent flexibility.
It is still another object of the present invention to provide optimum physical properties of a fabric that can simultaneously satisfy both flexibility and stiffness of the fabric.

Technical Solution

According to an aspect of the present invention, there is provided a fabric including a regular fiber and a low-melting fiber wherein the low-melting fiber is directly included in either warps or wefts or both, or a blended or plied fiber of the regular fiber and the low-melting fiber is included in either warps or wefts or both, and wherein the low-melting fiber has a fusion rate of 30 to 100%.
In an embodiment, the fabric has a yarn slip length of 0.1 to 2.5 mm.
In an embodiment, the fabric has an unweaving strength (for a single yarn) of 0.2 to 3.5 Kg.
In an embodiment, the fabric has an unweaving strength (for 5 mm) of 10 to 35 Kg.
In an embodiment, the fabric has a bending length of 3 to 10 cm.
In an embodiment, the weight ratio of the regular fiber to the low-melting fiber is from 50:50 to 75:25.
In an embodiment, the fabric further includes a flame retardant fiber.
In an embodiment, the low-melting fiber is a conjugate fiber in which a low-melting polyester resin is included in a sheath and a flame retardant polyester resin is included in a core.
According to another aspect of the present invention, there is provided a fabric including a flame retardant fiber and a low-melting fiber wherein the low-melting fiber is directly included in either warps or wefts or both, or a blended or plied fiber of the flame retardant fiber and the low-melting fiber is included in either warps or wefts or both, and wherein the low-melting fiber has a fusion rate of 30 to 100%.

ADVANTAGEOUS EFFECTS

The fabrics of the present invention do not undergo an additional coating finish that causes the release of volatile substances. Therefore, the fabrics of the present invention are effective as environmentally friendly industrial materials.
In addition, the fabrics of the present invention provide optimum physical properties that can simultaneously satisfy both flexibility of fabric and stiffness suitable for use as screen materials. As a result, the fabrics of the present invention possess physical properties suitable for use in desired applications.
Furthermore, the physical properties the fabrics according to the present invention can be appropriately controlled according to intended applications by varying the fusion rate of the low-melting fiber.

DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating the principle of how to measure the unweaving strength of a single yarn of a fabric according to a preferred embodiment of the present invention;

FIG. 2 is a conceptual diagram illustrating the principle of how to measure the unweaving strength of 5 mm of a fabric according to a preferred embodiment of the present invention;

FIGS. 3 and 4 are cross-sectional scanning electron microscope (SEM) images of fabrics produced in Example Section; and

FIG. 5 is a cross-sectional scanning electron microscope (SEM) image of a fabric produced in Comparative Example Section.

BEST MODE

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that whenever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. In describing the present invention, detailed descriptions of related known functions or configurations are omitted in order to avoid making the essential subject of the invention unclear.
As used herein, the terms “about”, “substantially”, etc. are intended to allow some leeway in mathematical exactness to account for tolerances that are acceptable in the trade and to prevent any unconscientious violator from unduly taking advantage of the disclosure in which exact or absolute numerical values are given so as to help understand the invention.
The term “fabrics” is used herein to refer to all woven fabrics, knitted fabrics, felt fabrics, plaited fabrics, non-woven fabrics, laminated fabrics, molded fabrics and webs.
In an embodiment, the present invention provides a fabric including a regular fiber and a low-melting fiber in a mixed state. Any kind of the regular fiber may be used without limitation in the fabric. As non-limiting examples of the low-melting fiber, there may be used sheath-core type conjugate fibers and split type conjugate fibers. The low-melting fiber may be used singly in warps and/or wefts. Alternatively, a blended and/or plied fiber of the low-melting fiber and a regular fiber may be used.
For example, the low-melting fiber may be a flame retardant polyester filament in which a low-melting polyester resin is included in a sheath and a flame retardant polyester resin is included in a core. The flame retardant polyester resin may be selected from the group consisting of a polyethylene terephthalate resin, a polybutylene terephthalate resin and a combination thereof. The low-melting polyester resin may contain isophthalic acid, terephthalic acid, ethylene glycol and diethylene glycol moieties.
The flame retardant polyester resin may have a melting point of 220 to 260° C. and the low-melting polyester resin may have a melting point of 110 to 220° C. The low-melting polyester resin having a melting point lower than 110° C. may be problematic in terms of shape stability. The low-melting polyester resin having a melting point higher than 220° C. may adversely affect the flame retardant polyester resin of the core. The weight ratio of the sheath to the core is preferably from 10:90 to 30:70. If the sheath is less than 10% by weight, deterioration in the thermal adhesion of the low-melting fiber is caused. Meanwhile, if the sheath exceeds 30% by weight (i.e. the content of the core is too low), the fiber characteristics of the polyester is considerably deteriorated and it is difficult to expect sufficient flame retardancy.
Preferably, the flame retardant polyester resin is one that is copolymerized with a phosphorus flame retardant. Preferably, the phosphorus flame retardant may be represented by Formula 1:
wherein R₁and R₂are independently a C₁-C₁₈alkyl group, an aryl group, a monohydroxyalkyl group or a hydrogen atom, R₃is a C₁-C₁₈alkyl group or an aryl group, and n is an integer from 1 to 4.
The phosphorus flame retardant is preferably present in an amount such that the concentration of phosphorus (P) atoms in the polyester resin is from 5,000 to 10,000 ppm. If the phosphorus (P) content is less than 5,000 ppm, sufficient flame retardancy is not exhibited. Meanwhile, if the phosphorus (P) content exceeds 10,000 ppm, the melt viscosity of the polyester resin is low, resulting in poor workability and physical properties upon spinning.
The fabric can be produced by weaving or knitting the regular fiber with the low-melting fiber according to a predetermined design. The fabric may include the regular fiber and the low-melting fiber in a weight ratio of 50:50 to 75:25. On the other hand, the regular fiber may be woven or knitted with a blended or plied fiber of the low-melting fiber and another regular fiber. In this case, the weight ratio of the regular fiber to the low-melting fiber blended or plied with the regular fiber may be from 70:30 to 0:100. The weight ratio 0:100 means that the low-melting fiber is used singly without being blended or plied.
The woven or knitted fabric undergoes a fusion process. The fusion process makes the fabric stiffer. The fusion rate of the low-melting fiber is a measure of the stiffness or shape stability of the fabric imparted when the low-melting fiber is fused to the other fiber. The fusion rate is measured by the following procedure. First, the cross section of the woven fabric is cut vertically (for example, in a weft direction when the low-melting fiber is provided as weft). The fabric piece is fixed and its cross section is observed using an electron microscope at a magnification of 200×. Two hundred cross sections of the fabric piece are chosen randomly. The number of the low-melting yarns fused to the other fiber in each cross section is counted and is expressed as a percent (%) of the number of the fused low-melting yarns.
The fusion rate of the low-melting fiber may be from 30 to 100%. Within this range, the fabric can be applied to various fabric products. The fabric may have a yarn slip length of 0.1 to 2.5 mm, an unweaving strength (for a single yarn) of 0.2 to 3.5 Kg, an unweaving strength (for 5 mm) of 10 to 35 Kg, and a bending length of 3 to 10 cm.
The slip length of a warp (or weft) of a fabric means the length when the warp (or weft) is partially shifted or pushed from its original intersection with the weft (or warp) by a physical force (e.g., friction) applied to the front or back surface of the fabric. The shape stability of a regular fabric is ensured by a physical binding force arising from a cover factor between the warps and the wefts of the fabric. In contrast, the shape stability of the fabric according to the present invention can be further improved because the fusion rate of the warps and/or wefts is ensured (see FIG. 4).
The yarn unweaving strength of the fabric means the force needed to separate the warps or wefts from the fabric. That is, a high yarn unweaving strength of the fabric means that the regular fiber is strongly fused to the low-melting fiber. Accordingly, the shape stability of the fabric is ensured when the fabric is used as a screen or blind material despite its large width or length.
The fabric may have a bending length of 3 to 10 cm. The bending length of the fabric can be evaluated by a suitable test method, which will be described below. The bending length of the fabric according to the present invention may be slightly different from that of common fabrics. The fabric of the present invention can ensure the inherent flexibility due to its sufficient bendability. If the bending length is excessively long, the fabric lacks flexibility, which makes it difficult to process in subsequent steps and makes the fabric unsuitable for use in a finished product (e.g., a blind).
When the fabric has physical properties within the ranges defined above, the fabric is imparted with shape stability suitable for use in screens and blinds. Further, the fabric encounters no significant problems during rolling (the fabric should be rolled when used as a blind material). In conclusion, the fabric of the present invention can simultaneously satisfy shape stability suitable for use as a screen material and the inherent flexibility, which are physical properties contradictory to each other.
The fabric may further include at least one additive selected from UV absorbers and processing aids. The UV absorbers serve to improve the light fastness of the fabric and may be benzotriazole and benzophenone compounds. Examples of processing aids usable in the fabric include antistatic agents, water/oil repellants, antifouling agents, antibacterial agents, water absorbers and antislip agents, which are commonly used in the art. It is to be understood that the addition of such well-known processing aids is encompassed within the scope of the present invention without departing from the substantial spirit of the invention.
In another embodiment, the present invention provides a fabric including a flame retardant fiber and a low-melting fiber. The low-melting fiber may be directly included in either warps or wefts or both. Alternatively, a blended or plied fiber of the flame retardant fiber and the low-melting fiber may be included in either warps or wefts or both. The physical properties and the fusion rate of the fabric may be the same as those of the fabric according to the previous embodiment, which is composed of a regular fiber and a low-melting fiber.

[Mode for Invention]

The following examples explain methods for producing fabrics according to the present invention and are not intended to limit the present invention.

EXAMPLES

Example 1

A regular polyester fiber as warp was woven with a sheath/core type conjugate fiber as weft by plain weaving to produce a fabric. The conjugate fiber was composed of a plied fiber of a low-melting polyester (30 wt %) as the sheath and a regular polyester (70 wt %) as the core. The fabric had a warp density of 100 yarns/inch and a weft density of 100 yarns/inch. The woven fabric was processed to adjust the fusion rate of the low-melting polyester to 30%.

Examples 2-5

Fabrics were produced in the same manner as in Example 1, except that the fusion rates were adjusted to 50%, 70%, 90% and 100%.

Examples 6-10

Fabrics were produced in the same manner as in Examples 1-5, except that the amount of the low-melting polyester was adjusted to 40 wt %.

Examples 11-15

Fabrics were produced in the same manner as in Examples 1-5, except that the amount of the low-melting polyester was adjusted to 50 wt %.

Examples 16-20

Fabrics were produced in the same manner as in Examples 1-5, except that the amount of the low-melting polyester was adjusted to 60 wt %.

Examples 21-25

Fabrics were produced in the same manner as in Examples 1-5, except that the amount of the low-melting polyester was adjusted to 70 wt %.

Examples 26-30

Fabrics were produced in the same manner as in Examples 1-5, except that the amount of the low-melting polyester was adjusted to 80 wt %.

Examples 31-35

Fabrics were produced in the same manner as in Examples 1-5, except that the amount of the low-melting polyester was adjusted to 90 wt %.

Examples 36-40

Fabrics were produced in the same manner as in Examples 1-5, except that the amount of the low-melting polyester was adjusted to 100 wt %.

Comparative Examples 1 and 2

Fabrics were produced in the same manner as in Example 1, except that the fusion rates were adjusted to 10% and 20%.

Comparative Example 3

A fabric was produced in the same manner as in Example 1, except that a regular polyester fiber was used instead of the low-melting polyester.

	TABLE 1

	Fabric structure

		Weft (Ply	Fusion
Properties	Warp	rate, wt %)	rate (%)

Example 1	Regular fiber	30	30
Example 2	Regular fiber	30	50
Example 3	Regular fiber	30	70
Example 4	Regular fiber	30	90
Example 5	Regular fiber	30	100
Example 6	Regular fiber	40	30
Example 7	Regular fiber	40	50
Example 8	Regular fiber	40	70
Example 9	Regular fiber	40	90
Example 10	Regular fiber	40	100
Example 11	Regular fiber	50	30
Example 12	Regular fiber	50	50
Example 13	Regular fiber	50	70
Example 14	Regular fiber	50	90
Example 15	Regular fiber	50	100
Example 16	Regular fiber	60	30
Example 17	Regular fiber	60	50
Example 18	Regular fiber	60	70
Example 19	Regular fiber	60	90
Example 20	Regular fiber	60	100
Example 21	Regular fiber	70	30
Example 22	Regular fiber	70	50
Example 23	Regular fiber	70	70
Example 24	Regular fiber	70	90
Example 25	Regular fiber	70	100
Example 26	Regular fiber	80	30
Example 27	Regular fiber	80	50
Example 28	Regular fiber	80	70
Example 29	Regular fiber	80	90
Example 30	Regular fiber	80	100
Example 31	Regular fiber	90	30
Example 32	Regular fiber	90	50
Example 33	Regular fiber	90	70
Example 34	Regular fiber	90	90
Example 35	Regular fiber	90	100
Example 36	Regular fiber	100	30
Example 37	Regular fiber	100	50
Example 38	Regular fiber	100	70
Example 39	Regular fiber	100	90
Example 40	Regular fiber	100	100
Comparative Example 1	Regular fiber	30	10
Comparative Example 2	Regular fiber	30	20
Comparative Example 3	Regular fiber	Regular fiber	—

Test Methods
1. Yarn slip length: Measured according to KSK0408
2. Yarn unweaving strength
(1) Unweaving Strength for Single Yarn
Each of the fabrics was cut to a size of 7×7 cm². 1 cm of a single yarn of the fabric sample was unwoven from the sample and was fixed to a tensile tester (KSK 0520). The load needed to unweave the remaining length (6 cm) of the yarn completely from the sample was measured. All fabric samples had the same texture density (100×100 yarns/inch²).
(2) Unweaving Strength for 5 mm of Fabric
Each of the fabrics was cut to a size of 7×7 cm². A hook was fixedly fitted into a position at a distance of 5 mm below the center of the upper side of the sample. The hook was made of a material having not undergone any deformation by a force of at least 60 Kg. The hook and the sample were clamped to upper and lower portions of a tensile tester, respectively. The load needed to separate the yarns positioned above the hook from the sample was measured. The load when the yarns were not separated from the sample and the breakage of the sample occurred was regarded as data. The maximum load value during the measurement was determined as an unweaving strength for the 5 mm yarns. All fabric samples had the same texture density (100×100 yarns/inch²).
3. Bending Lengths of the Fabrics
Each of the fabrics was cut to a size of 7×7 cm². The sample was positioned on a platform in such a manner that one end of the sample was parallel to the lengthwise direction of the platform. The sample was moved forward in the lengthwise direction of the platform. The sample protruded from the platform and was bent down by its own weight. The end of the protruding portion of the sample was free and the other portion of the sample was allowed to slip on the platform by an appropriate pressure. When the front end of the sample was bent down at an angle of 41.5° with respect to a horizontal plane passing through the line extending from the front end of the platform, the length of the sample protruding from the platform was two times that of the bending length of the sample.
The test results of Examples 1-40 and Comparative Examples 1-3 are summarized in Table 2. As can be seen from Table 2, the fabrics of Examples 1-40 showed better fused states than the fabrics of Comparative Examples 1-3, and as a result, the yarns were not readily separated from the fabrics of Examples 1-40. That is, the fabrics of Examples 1-40 were stiffer than the fabrics of Comparative Examples 1-3. These results lead to the conclusion that the stiffness of the fabrics of Examples 1-40 can be controlled by selectively varying the fusion rates and the blending rate of the low-melting fiber according to desired applications. FIGS. 3 and 4 are cross-sectional scanning electron microscope (SEM) images of two of the fabrics produced in Examples 1-40. FIG. 5 is a cross-sectional scanning electron microscope (SEM) image of one of the fabrics produced in Comparative Examples 1-3.

TABLE 2

Slip	Unweaving strength	Bending
length	(Kg)	length

Properties	(mm)	1 yarn	5 mm	(cm)

Example 1	2.5	0.2	10	3
Example 2	2.1	0.9	10.9	3.4
Example 3	1.8	2.1	11.7	3.9
Example 4	1.2	2.5	18.3	4.3
Example 5	0.5	2.7	21.1	4.7
Example 6	2.5	0.3	10.2	5
Example 7	1.9	2.1	11.4	4.4
Example 8	1.2	2.4	15.1	5.1
Example 9	0.5	2.9	19.1	6
Example 10	0.4	3.1	22.5	6.9
Example 11	2.4	0.3	10.2	4.1
Example 12	1.7	2.2	13.4	4.6
Example 13	0.9	2.6	17.1	5.4
Example 14	0.4	3.2	23.5	6.2
Example 15	0.4	3.3	26.8	7.2
Example 16	2.2	0.5	10.6	4.2
Example 17	1.3	2.2	18.3	4.8
Example 18	0.6	2.7	21.4	5.7
Example 19	0.4	3.3	26.9	6.6
Example 20	0.3	3.4	29.4	7.3
Example 21	2.1	0.7	10.9	4.6
Example 22	1.2	1.9	19.3	5.3
Example 23	0.6	2.2	25.3	6.1
Example 24	0.3	3.1	31	7
Example 25	0.2	3.4	32.1	7.6
Example 26	2	0.7	11.2	5
Example 27	1.1	1.6	22.1	5.8
Example 28	0.5	2.6	30.1	6.5
Example 29	0.2	3.3	34.1	7.3
Example 30	0.1	3.4	34.8	8
Example 31	2.1	0.7	13.2	5.5
Example 32	0.9	1.9	25.4	6.2
Example 33	0.4	2.8	33.2	7.2
Example 34	0.2	3.4	34.5	8.2
Example 35	0.1	3.5	35	8.8
Example 36	1.9	0.8	14.3	6.1
Example 37	0.8	1.9	30.4	7
Example 38	0.2	3.1	34.2	8.3
Example 39	0.1	3.5	34.9	9.2
Example 40	0.1	3.5	35	10
Comparative Example 1	4.5	0.12	3.85	2.7
Comparative Example 2	4.3	0.15	5.76	2.9
Comparative Example 3	6.7	0.1	2.14	2.6

Although the present invention has been described herein with reference to the foregoing embodiments and accompanying drawings, the scope of the present invention is not limited to the embodiments. Therefore, it will be evident to those skilled in the art that various substitutions, modifications and changes are possible, without departing from the spirit of the invention as disclosed in the accompanying claims.

Claims

1. A fabric including a regular fiber and a low-melting fiber wherein the low-melting fiber is directly included in either warps or wefts or both, or a blended or plied fiber of the regular fiber and the low-melting fiber is included in either warps or wefts or both, and wherein the low-melting fiber has a fusion rate of 30 to 100%.

2. The fabric of claim 1, wherein the fabric has a yarn slip length of 0.1 to 2.5 mm.

3. The fabric of claim 1, wherein the fabric has an unweaving strength (for a single yarn) of 0.2 to 3.5 Kg.

4. The fabric of claim 1, wherein the fabric has an unweaving strength (for 5 mm) of 10 to 35 Kg.

5. The fabric of claim 3, wherein the fabric has an unweaving strength (for 5 mm) of 10 to 35 Kg.

6. The fabric of claim 1, wherein the fabric has a bending length of 3 to 10 cm.

7. The fabric of claim 3, wherein the fabric has a bending length of 3 to 10 cm.

8. The fabric of claim 5, wherein the fabric has a bending length of 3 to 10 cm.

9. The fabric of claim 1, wherein the weight ratio of the regular fiber to the low-melting fiber is from 50:50 to 75:25.

10. The fabric of claim 1, further including a flame retardant fiber.

11. The fabric of claim 1, wherein the low-melting fiber is a conjugate fiber in which a low-melting polyester resin is included in a sheath and a flame retardant polyester resin is included in a core.

12. A fabric including a flame retardant fiber and a low-melting fiber wherein the low-melting fiber is directly included in either warps or wefts or both, or a blended or plied fiber of the flame retardant fiber and the low-melting fiber is included in either warps or wefts or both, and wherein the low-melting fiber has a fusion rate of 30 to 100%.

13. The fabric of claim 2, wherein the fabric has an unweaving strength (for a single yarn) of 0.2 to 3.5 Kg.

14. The fabric of claim 2, wherein the fabric has an unweaving strength (for 5 mm) of 10 to 35 Kg.

15. The fabric of claim 13, wherein the fabric has an unweaving strength (for 5 mm) of 10 to 35 Kg.

16. The fabric of claim 2, wherein the fabric has a bending length of 3 to 10 cm.

17. The fabric of claim 13, wherein the fabric has a bending length of 3 to 10 cm.

18. The fabric of claim 15, wherein the fabric has a bending length of 3 to 10 cm.

19. The fabric of claim 2, wherein the weight ratio of the regular fiber to the low-melting fiber is from 50:50 to 75:25.

20. The fabric of claim 2, wherein the low-melting fiber is a conjugate fiber in which a low-melting polyester resin is included in a sheath and a flame retardant polyester resin is included in a core.