JP3128363B2 - Heat-fusible composite fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-fusible conjugate fiber, and more particularly, to a heat-fusible conjugate fiber having excellent heat resistance and good fibrillation processability and excellent fiber properties.

[0002]

2. Description of the Related Art As heat-fusible fibers for producing a nonwoven fabric or the like by heat fusion between fibers, for example, polyethylene-polypropylene composite fibers having polyethylene as an adhesive component and polypropylene having copolymerized nylon as an adhesive component are known. And a composite fiber with polyethylene terephthalate using an ethylene-vinyl alcohol copolymer as an adhesive component. In recent years, the role of polyester fibers represented by polyethylene terephthalate in the field of textiles, especially nonwoven fabrics, has increased, and from the viewpoints of production effects, energy saving, etc.
In particular, there has been an increasing demand for manufacturing nonwoven fabrics, and various polyester-based heat-fusible fibers to be bonded to polyester fibers have been proposed.

[0003] Not only in the field of non-woven fabric products, it is not preferable that the cost is high, and it is very important how to produce a desired product at the lowest possible cost.
Therefore, copolymerized polyesters containing terephthalic acid, isophthalic acid, and ethylene glycol as main components have been proposed and commercialized as heat-adhesive and heat-fusible amorphous polyesters. However, the secondary transition temperature of this copolymerized polyester is as low as about 60 to 70 ° C., and if the drying after the production of the polymer is carried out at a temperature higher than such a temperature, the polymer is not cured.
Since agglomeration occurs in the middle and causes troubles, vacuum drying is performed for a long time at a temperature lower than the above temperature, which is not preferable in terms of cost and production efficiency. In addition, the physical properties of fibers obtained from such polymers are often insufficient. For example, when a core-sheath conjugate fiber using polyethylene terephthalate as the core component and the above-mentioned amorphous polyester as the sheath component is obtained, the drawing temperature cannot be too high. If the temperature is set higher than the secondary transition temperature of the amorphous polyester, agglomeration occurs between the fibers, and the post-process such as the carding process is extremely deteriorated. Therefore, the drawing temperature is higher than the secondary transition temperature of the polymer. I have to lower it. Therefore, the heat treatment for sufficiently orienting and crystallizing the polyethylene terephthalate as the core component during the subsequent stretching becomes insufficient, and the stretching strain is inherent in the fiber. As a result, the fiber shrinks when heated or wet. And the thermal dimensional stability of the textile is poor.

Another disadvantage in the case where the secondary transition temperature of the polymer is low is that, for example, when the tow after stretching when obtaining a nonwoven fabric for wet processing is cut into a length of 3 to 10 mm, the cutting time during the cutting is reduced. Adhesion between the fibers due to heat generation occurs, which causes poor dispersion of cut fibers during papermaking, and the resulting nonwoven fabric has a poor appearance. Further, when this nonwoven fabric is used as a bag such as a tea bag, troubles such as puncture are likely to occur due to poor heat resistance in hot water.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to maintain the performance of a polyester-based heat-fusible fiber that is heat-bonded and heat-fused to polyester fibers. An object of the present invention is to obtain a heat-fusible fiber for obtaining a fiber product such as a nonwoven fabric having good processability and easy handling for both dry and wet nonwoven fabrics. The present inventors have conducted intensive studies on how to increase the secondary transition temperature of a polymer as one of means for solving the above-mentioned problems, and as a result, have reached the present invention.

[0006]

That is, the present invention relates to a method for preparing 15 to 60 mol% of isophthalic acid and 2,2-bis (4
An amorphous copolymerized polyester obtained by copolymerizing an alkylene oxide adduct of (-hydroxyphenyl) sulfone in an amount of 5 to 40 mol% and having a secondary transition temperature of 70 ° C or higher;
It is a heat-fusible conjugate fiber composed of a fiber-forming polymer.

The amorphous copolyester of the present invention (hereinafter sometimes referred to as a copolyester) comprises isophthalic acid and 2,2-bis (4
The compound having a structure in which an alkylene oxide adduct of (-hydroxyphenyl) sulfone (hereinafter abbreviated as BSA) is randomly copolymerized is shown. As polyester,
Terephthalic acid is 40 mol% or more, preferably 5 mol%, in view of the physical properties, quality, fiberization processability and cost of the obtained fiber.
0 mol% or more, ethylene glycol is 45 mol% or more,
It is preferable that the copolymer is obtained by copolymerization of 50 mol% or more, and it is particularly preferable that 80 mol% or more of the repeating units are ethylene terephthalate units. The copolymerization amount of isophthalic acid is in the range of 15 to 60 mol%, preferably 20 to 50 mol%, based on all the acid components constituting the copolymerized polyester, and the copolymerization amount of BSA is the total amount constituting the copolymerized polyester. 5 to 40 mol% based on the diol component,
Preferably it is in the range of 10 to 30 mol%. More preferably, it is preferable to copolymerize isophthalic acid in excess of BSA in terms of heat resistance and cost. When the copolymerization amount of isophthalic acid or the copolymerization amount of BSA is out of the above range, the processability is good for both dry and wet nonwoven fabrics which are the object of the present invention, and handling is easy. Fiber products such as nonwoven fabrics cannot be obtained.

The above-mentioned BSA is represented by the following formula I.

[0009]

Embedded image (However, R ↓ 1 and R ↓ 2 are lower alkyl groups, and m and n are integers of 1 or more.)

R ↓ 1 and R ↓ 2 are lower alkyl groups, preferably an ethylene group or a propylene group. R ↓ 1 and R ↓ 2 may be the same alkyl group or different alkyl groups. m and n are integers of 1 or more, and there is no upper limit, but each is preferably 10 or less, particularly preferably 5 or less. m
And n may be the same integer or different integers. When the numbers of m and n are large, the molecular mobility of the polyester containing BSA as a copolymer component is too large, the secondary transition temperature of the polymer is lowered, and the heat resistance of the obtained amorphous copolyester is low. It is not preferable because it is insufficient.
In addition, the BSA may contain a compound having a phenolic OH group represented by a chemical formula wherein m and / or n is 0, such as bisphenol S, in the production process. In the case of polymerizing the copolymerized polyester in the above, if such a compound is contained in a large amount, the polycondensation reactivity during the polymerization is extremely reduced, and therefore the content is preferably 10% by weight or less of BSA.

As BSA, 2, represented by the following formula II,
2-Bis (4-hydroxyethoxyphenyl) sulfone is preferred because the secondary transition temperature of the copolymerized polyester can be easily increased.

[0012]

Embedded image

As described above, the copolymerization amount of BSA is 5 to all diol components constituting the copolymerized polyester.
-40 mol%, preferably 10-30 mol%. When the copolymerization amount is less than 5 mol%, the secondary transition temperature of the obtained copolymerized polyester cannot be sufficiently increased, and when the copolymerization amount exceeds 40 mol%, the secondary transition temperature of the copolymerized polyester cannot be increased. The point temperature can be made sufficiently high and the fiberization processability is very good, but there is a problem in terms of cost. Further, if the secondary transition temperature of the copolyester is too high, the processing temperature for heat bonding a nonwoven fabric made of a conjugate fiber containing such a copolyester as one component must be set at a considerably high temperature. , The consumption cost increases.

The amorphous copolyester having such a composition has a secondary transition temperature of 70 ° C. or higher, preferably 8 ° C.
Since it is higher than 0 ° C. and higher than the secondary transition temperature of the conventional amorphous copolymerized polyester, the conjugate fiber containing such a copolymerized polyester as a component has a good fiberization processability,
It is very useful as a heat-bonded / heat-bonded fiber.

Further, in the copolymerized polyester of the present invention, in addition to the above-mentioned copolymerization components, it is preferable to use copolymerization components A and / or B satisfying the following formulas (1) and (2) as a flow regulator.

[0016]

(Equation 1)

[0017]

(Equation 2) Here, the component A is an aromatic copolymer component excluding a main copolymer component constituting the copolymer polyester of the present invention, and B component
The components are aliphatic and / or alicyclic copolymer components excluding the main copolymer component constituting the copolymerized polyerythrate of the present invention. In the formula (1), Am and Bm represent the copolymer mol% based on the total acid components constituting the copolymerized polyester of the component A and the component B. In the formula (2), Bw
Is a [COOH] type and / or [OH]
% By weight based on the formed copolymerized polyester
Is shown.

The component A includes phthalic acid, methyl terephthalic acid, oxybenzoic acid, oxyethoxybenzoic acid, diphenoxyethane dicarboxylic acid, naphthalenedicarboxylic acid, bisphenol A, an alkylene oxide adduct of bisphenol A, p And compounds having one or two aromatic nuclei, such as -xylene glycol.

As the B component, the heat treatment temperature of the composite fiber or the bonding temperature of the nonwoven fabric made of the composite fiber is 150.
When the temperature is not more than ℃, in order to properly adjust the fluidity of the copolyester constituting the conjugate fiber, adipic acid having a large molecular structure with high mobility and a linear molecular structure without side chains , Sebacic acid, pentamethylene glycol, diethylene glycol, triethylene glycol and the like. On the other hand, the heat treatment temperature of the conjugate fiber or the bonding temperature of the nonwoven fabric made of the conjugate fiber is 150 to 20.
In the case of a relatively high temperature of 0 ° C., in order to properly adjust the fluidity of the copolyester constituting the conjugate fiber within the range of 150 to 200 ° C., it has a side chain and has a low molecular mobility at a low temperature. Cyclohexanedimethanol, 1,2-
Propylene glycol, neopentyl glycol and the like can be mentioned.

The total amount of the above components A and B is preferably 25 mol% or less, particularly preferably 15 mol% or less, from the viewpoint of production processability such as fiberization processability. It goes without saying that the types and copolymerization amounts of the component A and the component B are selected depending on the intended use of the final product such as the target composite fiber or nonwoven fabric.

The ester-forming group of the component B is represented by [COO
In the case of the [H] type and / or the [OH] type, the weight percentage based on the copolymerized polyester is preferably 25% by weight or less, particularly preferably 15% by weight or less. If the amount of the component B exceeds 25% by weight, the copolymerized polyester becomes flexible, and the subsequent fiberization processability may be undesirably reduced.

In the composite fiber of the present invention, the copolyester forming the core component is amorphous. Being amorphous means that the copolymerized polyester is melted, taken out as fine fibers or small pieces of thin film, cooled, and allowed to stand at room temperature for 3 days or more by a differential scanning calorimeter (DSC). The temperature can be raised at a rate of 10 ° C./min, and it can be confirmed by the presence or absence of an endothermic peak. If the endothermic peak is very broad and the endothermic peak cannot be clearly determined, it can be determined that there is substantially no endothermic peak. By using amorphous copolyester,
The problem of morphological change due to the occurrence of fiber shrinkage in the heat treatment step or the heat bonding treatment step of the composite fiber having the copolymerized polyester as the core or the nonwoven fabric made of the composite fiber does not occur. Moreover, pre-heat treatment is possible in the process up to the heat bonding treatment, so that not only product management such as dimensional stability is easy, but also heat treatment is performed with good thermal efficiency, which is advantageous in terms of operating cost. is there.

In the present invention, the “second order transition temperature” is defined as
The temperature distribution and tan δ were measured using Toyo Boldwin's “Vibron direct-reading dynamic viscoelasticity meter DDV-II”, and the dynamic loss elastic modulus was determined based on the tan δ measurement value. Indicates the temperature at which the modulus of elasticity is at a maximum.
The measurement conditions at this time were a driving frequency of 110 cps and a temperature rise from room temperature at a rate of 1 ° C./min. The measurement sample was prepared as a thin film with a thickness of 0.2 mm from molten polyester.
It was cut to a width of 5 mm and a length of 20 mm, cooled, and left at room temperature for 3 days or more. If the film had unevenness in thickness, the measured values would vary slightly. Therefore, the secondary transition temperatures of five separately prepared measurement samples were measured, and the average value was defined as the “secondary transition temperature”. This secondary transition temperature did not differ depending on the degree of polymerization, that is, the magnitude of the intrinsic viscosity, if the composition ratio of the copolymerized polyester was the same.

In the present invention, a matting agent such as titanium oxide, an antioxidant, a fluorescent whitening agent, a stabilizer, and an ultraviolet shielding absorption are added to the above-mentioned amorphous copolyester within a range not impairing the effects of the present invention. An additive such as an agent may be contained.

The conjugate fiber of the present invention comprises the above-mentioned amorphous copolymerized polyester and a fiber-forming polymer. It has been found that in order to maintain the purpose of the heat-bonding nonwoven fabric and the good fiberization processability, it is suitable to use a fiber in a composite structure.

As the other fiber-forming polymer, a thermoplastic polymer having a melting point of 150 ° C. or more is preferable. Specifically, polyethylene terephthalate, polybutylene terephthalate, nylon 6, nylon 6 , 6, and polypropylene.

The composite ratio of the amorphous copolymerized polyester component and the fiber-forming polymer component is from 80:20 to 20:80.
(Weight ratio). If the former is less than 20% by weight, it is difficult to obtain a good heat-fusing property, and if it exceeds 80% by weight, the spinning property, the stretchability and other fiber-forming steps are undesirably reduced.

The cross-sectional form of the conjugate fiber of the present invention is a perfect core-sheath type, a core-sheath type having a modified core component, a multi-core sheath type, an eccentric core-sheath type, a modified cross-section core-sheath type, a side-by-side type, a multi-layer lamination. Various types, such as a combined type, are not particularly limited, but in order to exhibit a sufficient effect as a heat-fused fiber, the ratio of the amorphous copolymerized polyester component to the entire circumference of the composite fiber cross section, that is, The fiber cross-sectional circumference is preferably 50% or more, particularly preferably 60% or more. When the fiber cross-sectional circumference is less than 50%, it is difficult to obtain good heat-fusibility, which is not preferable.

The heat-fused conjugate fiber of the present invention has a length of 20 to 100 m.
m and used as a binder for a fiber aggregate such as a nonwoven fabric for a dry process, and 3 to 10 mm and used as a binder for a fiber aggregate such as a nonwoven fabric for a wet process. The content of the heat-fused conjugate fiber contained in the fiber assembly is preferably 10% by weight or more. When the content is less than 10% by weight, the heat-fusing property of the heat-fusible conjugate fiber is difficult to effectively exhibit.

When terephthalic acid-based polyesters such as polyethylene terephthalate and polybutylene terephthalate are used as the fibers forming the fiber aggregate in addition to the heat-fused conjugate fibers, the fibers may be interposed between the heat-fused conjugate fibers. In addition, the fusion between the heat-fused conjugate fiber and the polyester fiber is good, and a fiber aggregate having high strength can be obtained. Conventionally, the amount of fibers fused to the terephthalic acid-based polyester was small, and a good polyester-based fiber aggregate could not be obtained. The present invention facilitates the production of a polyester-based fiber assembly, and enables the production at low cost because conventional machines and devices can be used. In addition to the heat-fused conjugate fiber, a hydrophilic material such as wood pulp, rayon, or polyvinyl alcohol-based fiber may be used as the fiber forming the fiber aggregate in addition to the terephthalic acid-based polyester.

[0031]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples. The intrinsic viscosity [η] of the copolymerized polyester in the examples was determined by dissolving the copolymerized polyester in a mixed solvent of phenol / chloroethane (weight ratio 1/1).
It was measured at 0 ° C. The breaking length was measured in accordance with JIS P 8113, and the strength, elongation, and dry heat shrinkage were measured in accordance with JIS L 1013.

Example 1 A polycondensation reaction was carried out in a conventional manner at 280 ° C. using a polycondensation reaction apparatus, and terephthalic acid (hereinafter abbreviated as TA) 55 was used.
Mol%, isophthalic acid (hereinafter abbreviated as IPA) 45 mol%, ethylene glycol (hereinafter abbreviated as EG) 70
Mol%, 2,2-bis (4-hydroxyethoxyphenyl) sulfone (hereinafter abbreviated as BSAE) 20 mol%,
Then, a copolymerized polyester comprising 10 mol% of diethylene glycol was produced, and then extruded into water in a strand form from the bottom of the polymer vessel and cut into pellets. The intrinsic viscosity [η] of the obtained copolyester pellets was 0.69, the secondary transition temperature was 90 ° C., and no endothermic peak was observed by DSC measurement. When the pellets were dried at 80 ° C. in a vacuum dryer, no sticking was observed between the pellets.

Using the obtained copolyester as a sheath and a core of polyethylene terephthalate having an intrinsic viscosity [η] of 0.69, a composite fiber having a composite ratio of 50:50 and a cross-sectional shape shown in FIG. 1 is spun. Cap temperature 290 ° C, speed 1000m /
Wound in minutes. The wound conjugate fibers did not show any sticking between single fibers and between fiber bundles, and could be stably spun for a long time. The obtained spun yarn is put in a water bath for 80 minutes.
Stretched 4.2 times at 90 ° C, followed by 8% shrinkage at 90 ° C in a water bath to obtain a drawn yarn having a single fiber fineness of 2.0 denier, a strength of 3.5 g / denier and an elongation of 43%. Was. The dry heat shrinkage at 120 ° C. was 4%.

The drawn yarn cut into a length of 5 mm 70
After mixing 30 parts by weight with 30 parts by weight of polyethylene terephthalate fiber (single fiber fineness: 2 denier, fiber length: 5 mm), the mixture is mixed with a square tapi-paper machine (manufactured by Kumagaya Riki) to produce fiber paper. did. Subsequently, it is dried at 130 ° C. for 1 minute on a Yanke-Dryer type floe plate heating cylinder, and fused (bonded) to obtain a basis weight of 20 g / m ↑ 2, 40 g / m ↑ 2, 80 g / m ↑ 2.
Was made. In each case, there was no trouble such as adhesion between fibers or sticking, and paper having good fiber dispersibility and appearance could be easily made, and the strength was high enough to withstand practical use. A test was conducted using the obtained paper as a tea bag, but no trouble such as puncture occurred.

The above-mentioned drawn yarn cut into 5 mm 500 k
g was placed in a rectangular box 50 cm long, 1 m wide and 2 m high and sealed, and a load of 500 kg was placed on the lid to cover 40 g.
It was stored for one month in an atmosphere of ° C. When opened one month later, no sticking of the drawn yarn was observed. Then, for one year, they were actually packed in a warehouse and stored, but no adverse effects were observed.

Examples 2 to 8 Using the copolymerized polyester and polyethylene terephthalate obtained in Example 1, conjugate fibers and drawn yarns were produced under the conditions shown in Table 1, and papermaking was performed. Examples 2 and 3 were carried out by changing the core-sheath composite ratio. Examples 4 to 6 were carried out by changing the fiber cross-sectional shape. Example 7 is a polybutylene terephthalate having an intrinsic viscosity [η] of 0.67 as a core component.
In Example 8, a composite fiber was produced using nylon 6 (manufactured by Ube Industries, Ltd.) as a core component. In all cases, the fiberization processability was good, and no sticking or adhesion was observed between single fibers or fiber bundles. Also, the dispersibility of each fiber during papermaking was good, and the appearance of the obtained paper was also good.

Examples 9 to 16 Composite fibers and drawn yarns were produced in the same manner as in Example 1 except that the copolymerized polyester having the composition shown in Table 1 was used as a sheath component, and then papermaking was performed. In all cases, the fiberization processability was good, and no sticking or adhesion was observed between single fibers or fiber bundles. Also, the dispersibility of each fiber during papermaking was good, and the appearance of the obtained paper was also good.

COMPARATIVE EXAMPLE 1 A polycondensation reaction was carried out at 280 ° C. by a conventional method using a polycondensation reaction apparatus, and 55 mol% of TA, 45 mol% of IPA, EG
A copolymerized polyester consisting of 90 mol% and 10 mol% of diethylene glycol was produced, then extruded into water in a sheet form from the bottom of the polymer vessel, and cut into pellets. The intrinsic viscosity [η] of the obtained copolyester pellets was 0.75, the secondary transition temperature was 70 ° C, and D
No endothermic peak was observed by SC measurement. A drawn yarn was produced in the same manner as in Example 1 using the obtained copolymerized polyester as a sheath component and polyethylene terephthalate having an intrinsic viscosity [η] of 0.67 as a core component. The obtained drawn yarn has a single fiber fineness of 2.0 denier and a strength of 3.2 g.
/ Denier and elongation were 49%. The dry heat shrinkage at 120 ° C. was 12%, which was higher than that of Example 1.
Subsequently, papermaking was carried out in the same manner as in Example 1 by using the drawn yarn, and paper was obtained. The cut yarn before papermaking showed sticking between the single fibers, and the obtained paper also had a poor appearance due to poor dispersion of the fibers. When the above-mentioned cut yarn was subjected to a storage test in exactly the same manner as in Example 1, considerable sticking between the single fibers occurred within one month.

Comparative Example 2 A conjugate fiber and a drawn yarn were produced in the same manner as in Example 1 except that a copolymerized polyester having the composition shown in Table 1 was used as a sheath component, and then papermaking was performed. In the drawn yarn, considerable sticking was observed between the single fibers. When the drawing temperature was 70 ° C. or lower, no sticking between the single fibers was observed, but the dry heat shrinkage of the drawn yarn was increased. In addition, the paper obtained by papermaking also had poor fiber dispersion and poor appearance.

Comparative Example 3 A conjugate fiber and a drawn yarn were produced in the same manner as in Example 1 except that a copolymerized polyester having the composition shown in Table 1 was used as a sheath component, and then papermaking was performed. Although the fiberization processability was good and there was no problem, the obtained paper had insufficient heat-fusibility and was not practically usable.

Comparative Example 4 A conjugate fiber and a drawn yarn were produced in the same manner as in Example 1 except that the copolymerized polyester having the composition shown in Table 1 was used as a sheath component, and then papermaking was performed. The endothermic peak was observed by DSC measurement and the copolymerized polyester was crystalline. The fiberization processability was good and there was no problem,
The obtained paper had a low breaking length of 0.1 km and low strength.

Comparative Example 5 A copolymerized polyester having the composition shown in Table 1 was polymerized in the same manner as in Example 1, and extruded in a strand form from the bottom of the polymerization vessel. Since the secondary transition temperature of this polyester is as low as 18 ° C., the strand is soft and difficult to cut into pellets, and the operation of the cutter is often stopped due to the fusion of the polyester to the cutter. became.
For this reason, the pelleting yield was increased by extruding the strands into ice water at 0 ° C. When the obtained pellets were dried in a vacuum dryer at 45 ° C., the pellets were agglomerated and clumped, so that the drying was performed at room temperature. Next, a composite fiber was obtained in the same manner as in Example 1. However, adhesion between single fibers and between fiber bundles was severe, and satisfactory fibers could not be obtained.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

According to the present invention, a heat-fusible conjugate fiber comprising an amorphous copolymerized polyester having a specific composition and a fiber-forming polymer has a good fibrillation processability, and is particularly suitable for polyester fiber. It has good fusion and adhesion properties and excellent long-term storage stability.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a fiber cross section of a conjugate fiber of the present invention.

FIG. 2 is a diagram showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 3 is a diagram showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 4 is a view showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 5 is a diagram showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 6 is a diagram showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 7 is a view showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 8 is a view showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 9 is a view showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 10 is a view showing another example of the fiber cross section of the conjugate fiber of the present invention.

FIG. 11 is a view showing another example of the fiber cross section of the conjugate fiber of the present invention.

[Explanation of symbols]

 (A) Amorphous copolymerized polyester (b) Fiber-forming polymer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-18108 (JP, A) JP-A-3-294554 (JP, A) JP-A-3-180531 (JP, A) JP-A-3-18053 180530 (JP, A) JP-A-63-315610 (JP, A) JP-A-57-167418 (JP, A) JP-A-2-289120 (JP, A) JP-A 64-52818 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) D01F 8/14

Claims (2)

(57) [Claims] 1. A copolymer comprising 15 to 60 mol% of isophthalic acid and 5 to 40 mol% of an alkylene oxide adduct of 2,2-bis (4-hydroxyphenyl) sulfone, and having a second transition point temperature. A heat-fusible conjugate fiber comprising an amorphous copolyester having a temperature of 70 ° C. or higher and a fiber-forming polymer. 2. A fiber assembly comprising the fiber according to claim 1 in an amount of 10% by weight or more and subjected to a fusion treatment at a temperature equal to or higher than the secondary transition temperature of the amorphous copolymerized polyester constituting the fiber.