JPS59199814A - Easily dyeable polyester fiber - Google Patents

Abstract

PURPOSE:Easily dyeable polyester fibers, having specific relationships between the crystallinity and birefringence and dynamic loss tangent and temperature, and dyeable in deep colors under boiling conditions and ordinary pressure. CONSTITUTION:Copolyester fibers, consisting of 80-98% ethylene terephthalate in repeating units, and having the relationship between the crystallinity (Xc) and birefringence (DELTAn) thereof satisfying formula I and a temperature (Tmax) at which the dynamic loss tangent (tandelta) shows the maximum at 110Hz measuring frequency within the range of formula II and the maximum of tandelta (tandelta)max within the range of formula III. For example, a copolyester is melt spun at >=5,000m/ min winding speed, passed through a heating zone kept at 150-300 deg.C for >=5cm length from the undersurface of a spinneret, and collected with a collecting guide provided in a zone at <=5cm below the point of completing the thinning of monofilaments under <=0.4g/denier tension at a position 5cm below the guide.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to easily dyeable polyester fibers. More specifically, it relates to polyester fibers that can be dyed in light colors under normal pressure boiling conditions, and it relates to modified polyethylene terephthalate fibers that have been imparted with easy dyeability while retaining the excellent properties of original polyethylene terephthalate fibers.

Polyester fibers, especially polyester fibers whose main component is polyethylene terephthalate (hereinafter abbreviated as PET fibers), are highly crystalline and have a high softening point, so they have poor mechanical properties such as strength and elongation. It exhibits excellent heat resistance, chemical resistance, etc., and is widely used in the fields of industrial materials and clothing items.

On the other hand, apart from the above-mentioned advantages, it is difficult to dye in dark colors,
It also has disadvantages such as being prone to pilling, being easily charged with static electricity, and having low hygroscopicity.

In particular, the range of uses for polyester fibers has been narrowed due to various drawbacks associated with dyeing, typified by the difficulty of dyeing them in deep colors.

Generally, when dyeing PET fibers, a disperse dye is used to dye the fibers due to the influence of hydrophobic groups in the fiber structure.

At that time, since PET fibers have high crystallinity and a dense structure, (1) high temperature and high pressure dyeing is performed at 120 to 130°C. Alternatively, (2) any method is used, such as dyeing using a carrier at a temperature of around 110° C. or under normal pressure boiling conditions.

However, the high-temperature, high-pressure dyeing method (1) above has problems such as complicated operation of the mechanical equipment used for dyeing and high energy costs. Furthermore, when blending with other types of fibers, if the same bath dyeing is carried out using high-temperature and high-pressure dyeing, the other types of fibers (especially acrylic, wool, etc.) may suffer from deterioration of physical properties such as sagging. The method is practically difficult to use because of the disadvantages it produces. Furthermore, in the dyeing method using a carrier (2), the carrier as a dyeing aid generally contains many harmful substances and is therefore difficult to handle, making it difficult to implement in terms of wastewater treatment, etc. Furthermore, because the carrier takes up the dyeing area of the dye in the fiber, it is difficult to dye it in a deep color, dye migration is likely to occur, and it causes the formation of beams during dyeing. be.

Therefore, many improvements and improvement methods have been proposed in order to improve the above-mentioned drawbacks of such PETm fibers. One of the representative methods is the method of introducing a copolymer component into PET polymer1, for example, Japanese Patent Publication No. 34-1097
As disclosed in Japanese Patent Publication No. 49-33766, etc., (a) a method of copolymerizing a metal sulfonate group-containing compound, and as disclosed in Japanese Patent Publication No. 54-38159, (b) ) A method of copolymerizing an amine group-containing compound has been proposed. The above methods (a) and (b) are characterized by being able to ride on disperse dyes and at the same time making it possible to dye with basic dyes and acidic dyes. (C) dicarboxylic acids such as isophthalic acid and adipic acid, and polyalkylene glycols such as polyethylene glycol are well known as copolymerization components aimed at improving the performance.

However, each case has drawbacks. for example,(
In method a), there are problems such as the metal sulfonate group-containing compound used as a raw material is expensive and lacks stability during polymerization and spinning. There is a problem with the thermal stability of Moreover, in both cases, as in case (C), multiple copolymerizations are required in order to dye sufficiently deep colors without a carrier and under normal pressure boiling conditions. PET
Furthermore, when polyethylene glycol is copolymerized, other disadvantages such as foaming during polymerization and discoloration of the polymer become apparent. 0 As another method for improving dyeability, JP-A-55-10
As seen in Japanese Patent No. 7511, there is a method using so-called high-speed spinning. Although dyeing properties are certainly improved by using this method, it is still insufficient to dye deep colors in a boiling state at normal pressure without a carrier. Furthermore, there is a drawback that the submerged shrinkage rate decreases extremely as the winding speed increases. Also known is a method intended to improve dyeability by spinning polyester copolymerized with a metal sulfonate compound at high speed (Japanese Unexamined Patent Publication No. 139820/1982). It is true that the dyeability is improved, and it is possible to dye a certain degree of deep color without a carrier under normal pressure boiling conditions, but as mentioned above, the disadvantages of the polymer itself still exist, and the problems caused by high-speed spinning The drawback of reduced diving shrinkage rate has also not been resolved.

In general, when polyester is spun at high speed, dyeability is improved to some extent, but as the winding speed increases, the submerged shrinkage rate decreases significantly, especially in the winding speed range of 6000'/min or more, it decreases to 4% or less. In the past, it was impossible to avoid doing this. In order to improve the dyeability by high-speed spinning and to achieve a good balance between strength and elongation, 5.
ooom/min or more p winding speed, preferably 600
It is necessary to spin at a winding speed of 0fi/min or higher, and in an attempt to further improve the dyeability, we have attempted to improve the decrease in submerged shrinkage that occurs with high-speed spinning even when using general copolymerized PET polymers. In order to solve the above-mentioned drawbacks, the inventor of the present invention, in the process of researching and considering high-speed spinning of copolymerized polyester, discovered a method to prevent the above-mentioned decrease in the submerged shrinkage rate and to improve the exhaustion rate. are the crystallinity (Xc) and birefringence (△n) of the copolymerized polyester fiber.
), and the temperature (Tmax) at which the mechanical loss tangent (-δ) at a measurement frequency of 110 Hz is at its maximum, and the maximum value of the theory δ ((the theory δ ax)) have found the need to have a specific relationship, This has led to the present invention.

That is, an object of the present invention is to maintain the excellent physicochemical properties of PET fibers, especially the value of submerged shrinkage ratio, at an appropriate level, and to dye the fibers with disperse dyes without using a carrier. To provide an easily dyeable polyester fiber which can be dyed in a sufficiently deep color under pressure boiling.

In addition, in the present invention, an appropriate state of the value of the diving shrinkage rate means that the value of the diving shrinkage rate is preferably in the range of 6 to 13 inches. teeth,
The exhaustion rate as described in this specification is preferably about 80 inches or more, more preferably about 85 inches or more, under dyeing conditions of 60 minutes under normal pressure boiling conditions.

The present invention consists of the following gist in order to achieve the above object.

That is, the present invention provides a copolyester fiber in which 80 to 98 units of repeating units are ethylene terephthalate, and the following formula (1) is expressed between the crystallinity Xc and the birefringence Δn of the fiber. The temperature Tmax at which the mechanical loss tangent -δ at a measurement frequency of 110 Hz is at its maximum and the maximum value (-δ)max of -δ is the range defined by the following equations (2) and (3). It is an easily dyeable polyester fiber characterized by the presence of .

(1) Xc (%il< -710X△n+ 110
(2) 90℃ (Tmax≦107℃ (3) 0.135 < (-δ)max≦0.30
0 Furthermore, to explain this in detail, the ratio of the copolymerized components of the copolymerized polyethylene terephthalate of the present invention is 2.
It is necessary to be in the range of ~20 molti, and furthermore, it is necessary to be in the range of 5 ~
Preferably it is 13 molti. If the copolymerization ratio is outside this range, the following (1), (2) and (3)
It is difficult to obtain a fiber that satisfies the formula at the same time, and therefore it is not possible to achieve a balance between improved dyeability and fiber physical properties.

The copolymerization components are (1) and (2) as described below.
Any substance may be used as long as it satisfies the formula (3), but 1,4-cyclohexane dimetatool and modified or 2,2-bis(:4-(2-hydroethoxy)phenyl)propane are relatively preferred. It is preferable because it has a large effect with a small amount.

In the copolymerized polyester fiber of the present invention, it is an important requirement that its crystallinity (Xc) and birefringence (Δn) satisfy the following formula.

(1) Xc (%) <-710X△ll+ 110X
If c (%)≧-710 . For example, high-speed spun fibers of copolyester disclosed in Japanese Patent Application Laid-open No. 139820/1982 fall under this category.

In the present invention, the temperature (Tmax) at which the mechanical loss tangent -δ) of the copolymerized polyester fiber at a measurement frequency of 110 Hz is maximum and the maximum value of -δ ((-δ)max)
must exist within the range shown by the formula below.

(2) 90℃< Tmax≦107℃ and (3)
0. 135<(tan δ) max≦0.300 If the above range is illustrated, it becomes the shaded area in FIG.

Tmax) 120℃ range and 107℃<Tma
x≦120℃ and 0.11.0>(ta++δ)ma
Fibers within the range of x cannot be expected to improve dyeability.

Fibers within this value range correspond to general drawn polyester yarns.

Tmax≦107℃ and (knδ)maz≦0.13
Copolymerized polyester fibers in the range of 5 have good dyeability, but are difficult to produce stably unless special operations such as lowering the viscosity are performed, so they are not preferred.

Tmax≦90℃ and (-δ)max>0.135
and 90℃<Tmax≦120℃ and 0.3
The copolymerized polyester fiber in the range of '00≦(-δ)max has a relatively large copolymerization ratio, which reduces other physical properties such as elongation, strength, and melting point (copolymerization ratio 2
0chi or more).

107℃<Tmaz≦120℃ and 0.110<(
Copolymerized polyester fibers in the range of mnδ)max≦0.300 have well-balanced physical properties and have improved dyeability to some extent, but are still insufficient to dye sufficiently deep colors under normal pressure boiling conditions. (corresponds to high-speed spun polyester fiber with a copolymerization ratio of 2% or less).

The polyester fiber of the present invention can be produced, for example, by the following method. That is, polyethylene terephthalate obtained by copolymerizing 2 to 20 moles of 1,4-cyclohexane dimetatool and/or 2,2-bis[4-(2-hydroethoxy)phenyl)7't=pan, is spun into a plurality of spinning holes. through a spinneret with 5000 m/min
At this time, the spun monofilaments are passed from the bottom surface of the spinneret to a length of 5 crn or more and passed through a heating zone maintained at a temperature of 150°C or higher and 300°C or lower. Then, the monofilament group is focused by a focusing guide placed at a position that satisfies both conditions a and b below to form a filament bundle. still,
It can be manufactured by appropriately selecting the discharge amount, cross-sectional shape of the filament, and winding speed.

a, Area below the point at which thinning of the monofilament group is completed by 500 or more.

b, 5c below the guide! The tension applied to the filament bundle at n is 0.4 f/denier or less.

The copolymerized polyester fiber of the present invention thus obtained is
In addition to maintaining the excellent mechanical and thermal properties originally possessed by PET fibers, we have achieved the dyeing performance of being able to dye sufficiently deep colors using disperse dyes without a carrier and under normal pressure boiling conditions. Furthermore, a feature of the present invention is that when improving the dyeability by high-speed spinning, etc., which was conventionally considered, the extreme The problem lies in the decrease in the value of diving contraction rate. This has led to the solution of post-processing problems such as sagging and standing. Furthermore, among the copolymerization components referred to in the present invention, when 1,4-cyclohexane dimetatool is used as the copolymerization component, it also has the advantage of exhibiting excellent light fastness.

As a result, the copolymerized polyester fiber is different from the conventional P
It can be used as is for various uses of ET fibers, and because of its excellent dyeability, it can be mixed with other types of fibers.

Hereinafter, the present invention will be specifically explained with reference to Examples.

The evaluation method of various characteristic values used in the present invention is as follows.

[Strength/Elongation]

Measurement is performed using an Autograph DC8100 tensile testing machine manufactured by Takasu Seisakusho, with an initial length of 20 tyn and a tensile speed of 20 cm/min.

[Diving shrinkage rate (B, W, 8)] Sample length under a load of 0.1 f/denier. After binding, removing the load, and treating in boiling water for 30 minutes, the length measured under the same load at 5° is defined as L, and the submergence shrinkage rate is defined and determined from the following formula.

[Exhaustion rate]

Dye: Re5olin Blue FBL (C,I
, DisperseBlue 56, Ba7e
r company) 3% o, w, f.

Dispersant: Disper TL iy/ Acidity: p
H = 6 (adjusted with acetic acid) Bath ratio: 1:100 Under the above conditions, the residual dye after dyeing at normal pressure and boiling for a predetermined time is diluted with a 1=1 mixed solution of water and acetone. Absorbance (=
It is defined and determined by the following formula from the absorbance (denoted as -U) of a similarly diluted dye stock solution.

[Light fastness] Dyeing density is 1%. , W, f9, A sample was stained in the same manner as in the measurement of the exhaustion rate, except that the staining time was 90 minutes.
According to JISLO842, 2 at 63℃ in a 7-dmeter
After being exposed for 75 hours, the light fastness was visually observed and evaluated in three grades: ◯, △, and ×.

[melting point]

Differential Sca manufactured by Perkin Elma
Using Nning Calorirneter-I B type, sample 7 was heated at a heating rate of 16°C/min.
Measurement is performed while performing two substitutions, and the apex of the endothermic peak in the obtained chart is taken as the melting point.

[Mechanical loss tangent (plow δ)]

Manufactured by Toyo Baldwin Co., Ltd., Reo Viplon (Reo V
-δ and E/ at each temperature in dry air at a sample temperature of approximately 0.1 iF, a measurement frequency of 110 Hz, and a heating rate of 5°C/min using a dynamic viscoelasticity measurement device. (dynamic modulus of elasticity). As a result, a −δ temperature curve as schematically shown in FIG. 2 is obtained. From this graph, the temperature Tmax at which −δ is maximum
(The maximum value (I71nδ) max of Q and −δ is obtained.

[Birefringence (△n)] Refractive index for light polarized at right angles to the fiber axis (
n±), the refractive index (nll) for light polarized parallel to the fiber axis, and 1. That is, birefringence (Δn) = n
It is expressed as ll-nL.

Measurement was performed using a polarizing microscope equipped with a Berek convensator using a conventional method. However, tricresyl phosphate was used as the immersion liquid.

[Crystallinity (Xc)] The crystallinity (Xc) can be determined by measuring the X-ray diffraction intensity in the equatorial direction by an equatorial reflection method.

The X-ray diffraction intensity was measured using an X-ray generator (R'U-
200PL) and a goniometer (SG-9R), a scintillation counter for the counter tube, and a pulse height analyzer for the counting section.Measurement is carried out at α-rays (wavelength λ-1,5418t) on Cu- monochromated with a nickel filter.Fiber Set the sample on an aluminum sample holder so that the fiber axis of the sample is perpendicular to the X-ray diffraction surface. At this time, set the sample so that the thickness is about 0.5 mm. 50 KV, 10
Operate the X-ray generator at 0 mA'''c, scanning speed 20/min, chart speed 20/min, time constant 0.5 seconds, tie vergeance 1/2°, receiving slip) 0.3+m, scan Record the diffraction intensity from 380 to 7 degrees in 2θ at a 1/2 degree slit.Set it so that it falls within the full scale of the recorder.

Polyethylene terephthalate fibers generally have three main reflections in the range of diffraction angle 2θ = 17° to 260 in the equatorial direction (from the low angle side (010), (110)
, (100) plane). Figure 3 shows an example of the X-ray diffraction intensity curve of polyethylene terephthalate fiber (in the figure, a indicates the crystalline part and b indicates the amorphous part).
The diffraction intensity curves between -35° are connected with a straight line to form a baseline. The valley near 2θ=20o is set as the apex, connected by a straight line along the skirts of the low angle side and the high angle side, separated into crystalline portions and amorphous portions, and determined by the area method according to the following formula.

Example 1 A PET polymer (melting point 23
3℃, intrinsic viscosity 0.6 s) rz pore diameter 0.23 mm
A spinning machine equipped with a spinneret with 24 holes and a heating tube with a length of 40 Crn, and a high-speed winder placed 3 m below the spinneret surface was used to perform melt spinning to produce a 50 denier/24 filament co-fiber. Polymerized polyester fibers were obtained. The winding speed at this time was 6000 m/min and p1
The temperature of the spinning head is 285℃, and the temperature inside the heating cylinder is 220℃.
A refueling nozzle guide was provided at 110 cTn below the spinneret.The values of O Tmax, (-δ) max, crystallization 1 (Xc), and birefringence (Δn) were measured, and are shown in Table 1. As shown in the figure, it was confirmed that each of them existed within the range defined by the present invention.

The results of physical property measurements are shown in Table 2. As is clear from Table 2, the water production shrinkage rate is high and in the same range as ordinary drawn polyester fibers, and both strength and elongation are sufficient. Furthermore, the value of the exhaustion rate in boiling for 60 minutes is far more than 80%9, indicating that dyeing is sufficiently deep under normal pressure boiling. Moreover, the light fastness was also good.

Example 2 The copolymer of Example 1 was wound at a winding speed of 8000 m.
Spinning was carried out in the same manner as in Example 1, except that the spinning speed was changed to /min. Tmax, (bnδ) max and crystallinity (
The values of Xc) and birefringence (Δn) were measured, and as shown in Table 1, it was confirmed that each of them was within the range defined by the present invention.

The results of physical property measurements are also shown in Table 2. Despite the increase in the winding speed, the water production shrinkage rate remains high, and both elongation and dyeability are more favorable values.

Example 3 A PET polymer (melting point 235°C, intrinsic viscosity 0.65) prepared by copolymerizing 10 mol of 2,2-bis(4-(2-hydroethoxy)phenyl)globan by a conventional polymerization method was used in Example 3. Among the methods described in 2, the temperature of the spindle head is set to 2.
Fibers were obtained by spinning in the same manner except at 90°C. The values of Tmax, (-δ)m&X, crystallinity (xc), and birefringence (Δn) were measured, and it was confirmed that each of them was within the range defined by the present invention (see Table 1).

The results of physical property measurements are shown in Table 2. It is clear from Table 2 that the values of throughput and water shrinkage are high, and the reeds are in the same range as ordinary drawn polyester fibers, and both strength and elongation are sufficient. Furthermore, the exhaustion rate in boiling for 60 minutes far exceeds 80%, indicating that dyeing is sufficiently deep under normal pressure boiling.
, (Example 4) A PET polymer (melting point: 230 °C , intrinsic viscosity 0.66), and the polyester was spun into fibers in the same manner as in Example 2. Tmax, (tan δ) max, crystallinity (Xc), and birefringence (Δn) The values were measured and it was confirmed that each of them was within the range defined by the present invention (see Table 1).

As in Examples 1 to 3, it can be seen that the water production shrinkage rate is an appropriate value, and that the dyeing is sufficiently deep in the normal pressure boiling state (see Table 2).

Example 5 A PET polymer (melting point 238
°C, intrinsic viscosity 0.68) was spun into fibers in the same manner as in Example 2. Trnax% (tIIIδ)
The values of max, crystallinity (Xc), and birefringence (Δn) were measured, and it was confirmed that each of the values shown in Table 1 was within the range defined by the present invention.

The results of physical property measurements are shown in Table 2. As is clear from Table 2, the water production shrinkage rate is high and in the same range as ordinary drawn polyester fibers, and both strength and elongation are sufficient. Furthermore, the exhaustion rate in boiling for 60 minutes far exceeds 80%, indicating that dyeing is sufficiently deep under normal pressure boiling. In addition, the light fastness was also good. Example 6 A PET polymer (melting point 22
(8°C, intrinsic viscosity 0.67) was spun into fibers in the same manner as in Example 2. The values of Tmax, (δ)max, crystallinity (Xc), and birefringence (Δn) were measured, and it was confirmed that each of them was within the range defined by the present invention (see Table 1).

The results of physical property measurements are also shown in Table 2. It is clear from Table 2 that the water production shrinkage rate shows a high value that could not be obtained with conventional high-speed spinning, and that the dyeing is sufficiently deep under normal pressure boiling conditions.0 Comparative Example 1 The copolymer of Example 1 was melt-extruded using the spinneret described in Example 1 at a melting temperature of 282°C, passed through a cooling section, and wound up at 800 m/min. Further, the fiber was made into an undrawn yarn, and immediately drawn to a ratio of 3.617 times at a temperature of 80°C.

When the values of Tmax and (-δ) max were measured, it was found that they were not within the range defined by the present invention (see Table 1).

The results of physical property measurements are shown in Table 2. As is clear from Table 2, the improvement in dyeability is small, and in practice, it is necessary to use high-pressure dyeing or carrier dyeing.

Comparative Example 2 Polyethylene terephthalate made from terephthalic acid and ethylene glycol (melting point 250°C, intrinsic viscosity 0.7
0) was spun in the same manner as in Example 1 except that the melting temperature was 292°C. Tmax.

The values of (t, Inδ) max, crystallinity (Xc), and birefringence (Δn) were measured and found to be within the range specified by the present invention.

It was found that there was no such thing (see Table 1).

The results of physical property measurements are shown in Table 2. As is clear from Table 2, in terms of dyeability, it has not yet been dyed in a sufficiently deep color under normal pressure boiling conditions. Furthermore, the value of spring water contraction rate is extremely low.

Comparative Example 3 The polymer of Comparative Example 2 was wound at a winding speed of sooom/mi.
□ Spun in the same manner as in Comparative Example 2 except for n.
When the values of Tmax, (-δ)max, crystallinity (Xc), and birefringence (Δn) were measured, it was found that they were not within the range specified by the present invention (see No. 1 @).

The results of physical property measurements are shown in Table 2. As shown in Table 2, the dyeability and dyeability are slightly improved compared to Comparative Example 2, but the dyeing is still not light enough under normal pressure boiling conditions.

Furthermore, drawbacks such as a decrease in the spring water shrinkage rate become apparent.

Comparative Example 4 Polyethylene terephthalate copolymerized with 10 mol of adipic acid was spun by the method shown in Example 2 (melting point 24
0°C, intrinsic viscosity 0.67) □ Tmax, (-δ)
The value of max is within the range specified by the present invention (see Table 1), and therefore the dyeing is sufficiently deep in the normal pressure boiling state (see Table 2), but the birefringence (△n) and crystal degree (Xc
) is not within the range defined by the present invention (see Table 1), and it can be seen that the spring water shrinkage rate is low (see Table 2).

Table 1

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between Tmax and (mδ)max,
FIG. 2 is a graph showing a -δ temperature curve, and FIG. 3 is a graph showing an X-ray diffraction intensity curve of polyethylene terephthalate fiber. Patent Applicant: Asahi Kasei Kogyo Co., Ltd. Patent Attorney: Akira Aoki, Patent Attorney: Kazuyuki Nishidate, Patent Attorney: Yoshi 1) Io, Patent Attorney: Akira Yamaguchi, Figure 1: 90 100 110 120 1
30I. Tmax (C) Procedural Amendment (Spontaneous) April 1998) Memorial Day, Kazuo Wakasugi, Commissioner of the Japan Patent Office1, Indication of the case, Patent Application No. 068333, filed in 1982,2, Name of the invention, Easy dyeability & lyester fiber3 , Relationship with the person making the amendment Patent applicant name (003) Asahi Kasei Corporation 4, Agent address 5-8-10 Toranomon-chome, Minato-ku, Tokyo 105
Subject of amendment (1) Column 6 of "Claims" of the specification, contents of amendment (1) The scope of claims will be amended in Annex 9. (2) Page 4, line 7 of the specification, “Special Publication No. 34-1097
No. 10497” and “Special Publication No. 34-10497”. 7. Amended list of attached documents Claims 1 '1 2. Claim 1. A copolyester fiber in which the 80th to 98th repeating units are ethylene terephthalate, and the crystallinity Xc and birefringence are The temperature Tmax at which the mechanical loss tangent -δ at a measurement frequency of 110 Hz is maximum and the maximum value (-δ)max of -δ are as follows: An easily dyeable polyester fiber characterized by being present in the ranges shown by formulas (2) and (3). (1) Xc (%) <-710xΔn+110 (2)
90℃<Tmax≦107℃(3) 0.135<(
-δ)max≦0.3002, copolymerization component is 1,4-
Cyclohexane dimetatool and/or 2,2-bisC
The polyester fiber according to claim 1, which is 4-C2-hydroethoxy)phenyl]zolonone.

Claims (1)

[Claims] 1. A copolymerized polyester fiber in which 80 to 98% of the repeating units are ethylene terephthalate, and the following formula (1) is present between the crystallization temperature Xc and the birefringence △n. The temperature Tmax that satisfies the relationship and also exhibits the maximum mechanical loss tangent -δ at a measurement frequency of 110 Hz and the range in which the maximum value of -δ (study δ) max is determined by the following equations (2) and (3). Easily dyeable polyester fiber with the presence of 'r% characteristic. (1) Xc(%)<-710XΔn+ 110(2
)90℃<Tm&x≦107℃ (3) 0.135<(ta++δ) max≦o, ao
. 2. The polyester fiber according to claim 1, wherein the copolymerization component is 1,4-cyclohexane dimetatool and/or 2,2-bisC4-<2-hydroethoxy)phenyl]propane.