JPS648086B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polyester fibers, and more particularly, to polyester fibers that have practically sufficient properties and good dyeability, particularly those that can be dyed by atmospheric pressure dyeing and have excellent color fastness. Generally, polyester fibers, particularly polyethylene terephthalate fibers, have many excellent properties such as strength and dimensional stability, and are used for various purposes. On the other hand, polyethylene terephthalate fibers have poor dyeability and require special equipment as they must be dyed at high temperatures and pressures around 130°C, and they are not compatible with fibers such as wool and acrylic whose physical properties deteriorate due to high pressure dyeing. It has drawbacks such as restrictions on mixed use. Several attempts have been made to improve the dyeability of polyethylene terephthalate fibers and to make them dyeable under normal pressure.For example, a method using a carrier during dyeing is known, but it requires a special carrier, and It has drawbacks such as difficulty in processing. In addition, polyethylene terephthalate with improved dyeability is known by copolymerizing metal sulfonate group-containing compounds and polyether, but although these modified polyesters improve dyeability, they are difficult to polymerize and spin. Alternatively, the excellent properties inherent to polyethylene terephthalate may be deteriorated, and furthermore, there have been disadvantages such as poor color fastness. In the end, it is inevitable that the above-mentioned chemical modification of the polymer to make it easier to dye will also change the original properties of polyethylene terephthalate because a third component that can serve as a dyeing seat is mixed into the polymer. I can say that. On the other hand, as methods that are not based on chemical modification, for example, denier per filament, intrinsic viscosity [η], relative disperse dye dyeing rate, modulus, modulus after boiling water treatment, amorphous asmoplastic Flat yarns and tows are disclosed that have specified tensile strength, boiling water shrinkage, shrinkage modulus, shrinkage values, and the like. According to this, the dyeability is certainly improved, but the invention described in the publication relates to polyester filament and tow that have properties suitable for use as a substitute for cellulose acetate, and the resulting fibers are It has a lower modulus and higher elongation than normal polyester, and there is no specific explanation regarding color fastness. In addition, JP-A-55-107511 discloses that the cross-sectional average birefringence △n has an orientation degree of 90×10 ^-3 or more, and that the birefringence in the cross section of the fiber has an appropriate difference between the outer layer and the inner layer. A method for obtaining a cross-sectional double-structure polyethylene terephthalate fiber is disclosed, and the fiber obtained by this method has mechanical properties similar to conventional polyethylene terephthalate fiber, sufficient natural crimp, and dye adsorption properties. It is said to have the following. However, the publication does not describe or suggest the unique fiber structure of the present invention at all, and the specification of the application does not give any concrete suggestions regarding the effects regarding dyeability, especially atmospheric dyeability, and color fastness. However, the polyethylene terephthalate fibers of the present invention, which can be dyed under normal pressure, cannot necessarily be obtained solely from the description in this publication. The present inventors have overcome the drawbacks of such conventional methods,
As a result of conducting research from a microstructural perspective on polyester fibers, which have good dyeability, in particular can be dyed under normal pressure, and have excellent color fastness, they also have desirable properties. By using fibers with a specific amorphous structure,
The inventors have discovered that the above object can be achieved and have arrived at the present invention. Initial modulus is 50g/d or more, elongation is 20% or more
The fiber consists essentially of 60% polyethylene terephthalate, and the peak temperature (Tmax) and peak value ((tanδ)max) of mechanical loss tangent (tanδ) at a measurement frequency of 110Hz are respectively 85℃≦
Satisfies the relationship Tmax≦110℃ and 0.115≦(tanδ) _nax ≦0.135, crystallinity (Xc) is 70% or more, average refractive index (n ₍₀₎ ), distance from the center of the fiber to 0.8 times the radius The difference ( _△
(0.8-0) ) has a local refractive index fraction of 10 × 10 ^-3 or more and 80 × 10 ^-3 or less, and the above distribution is symmetrical with respect to the fiber center, and can be dyed under normal pressure. It is related to. The polyester in the present invention essentially consists of polyethylene terephthalate and is obtained by a known polymerization method, but may also contain additives normally used for polyester, such as matting agents, stabilizers, antistatic agents, etc. . There is no particular restriction on the degree of polymerization as long as it is within the range for normal fiber formation, and copolymerization with small amounts of other components is of course possible within a range that does not impair the purpose of the present invention. The first characteristic of the polyester fiber of the present invention is the mechanical loss tangent (tan δ) at a measurement frequency of 110 Hz.
Peak temperature (Tmax) and peak value ((tanδ)
_nax ) satisfies the following relationship. 85℃Tmax≦110℃ 0.115≦(tanδ) _nax ≦0.135 If Tmax is higher than 110℃, the dyeability will decrease and atmospheric pressure dyeing will not be possible, and if it is lower than 85℃, the mechanical properties (strength, elongation) degree, initial modulus)
On the other hand, if (tan δ) _nax is larger than 0.135, the thermal stability of the fiber will decrease, the dimensional stability (shrinkage rate) will be poor, the color fastness will decrease, and 0.115
The present inventor has revealed for the first time that even if the size is smaller, the dyeability decreases and normal pressure dyeing becomes impossible. Conventional polyester fibers have Tmax of 120℃ or higher, and as Tmax generally decreases,
(tanδ) _nax becomes higher. As a result, there is no known material that combines good dyeability, color fastness, and thermal stability. In addition, in the present invention, in order to exhibit the properties as a polyester, the initial modulus at 30°C is
It is necessary that it is 50g/d or more. For this purpose, the birefringence (Δn) is usually 30×10 ⁻³ or more. Here, the initial modulus at 30°C is expressed by the dynamic elastic modulus (E′ ₃₀ ) at 30°C. Regarding the fiber of the present invention having these characteristics,
Furthermore, as a result of examining the relationship between its structure, mechanical properties (strength, elongation, initial modulus, dynamic elastic modulus), and dyeability, the following was clarified. In the fiber of the present invention, crystallinity (Xc),
(010) crystallite size (ACS) and (010)
The degree of crystal orientation (Co) of the plane is related to the mechanical properties of the fiber, and the fiber of the present invention has sufficient strength (3 g/d or more) and elongation (20 to 60
%) In order to have an initial modulus (≧50 g/d), it is preferable that Xc be 70% or more, ACS be 50 Å or more, and Co be 90% or more. A more preferable range is
Xc is 75% or more and ACS is 55Å or more. here
Xc, ACS, and Co are values measured by X-ray diffraction using the methods described below. Next, in the fiber of the present invention, the central average refractive index (n ₍₀₎ ) of polarized light with an electric field vector in the fiber axis direction is
If it is smaller than 1.70 and 1.65 or more, it has appropriate elongation (20 to 60%) and dyeability, and is preferable as a textile fiber. The optimal range for (n ₍₀₎ ) is 1.65 to 1.68. In addition, the average birefringence (△n) of the present invention is 30×10 ^-3 or more in order for the fiber of the present invention to have an initial modulus of 50 g/d or more at 30°C; From the viewpoint of stability, dyeability, and color fastness, it is preferably 110×10 ⁻³ or less, and even more preferably 85×10 ⁻³ or less. △n is 110×
10 ^-3 or lower, the rate of decrease in dynamic elastic modulus (E′) in the temperature range of 150 to 220°C (at 150°C and 220°C
(where E' is E' ₁₅₀ and E' ₂₂₀ respectively, expressed as E' ₂₂₀ /E' ₁₅₀ ) becomes smaller and E' ₂₂₀ /E' ₁₅₀ becomes larger than 0.75. In other words, the structure becomes stable against heat. The color fastness is also improved. Furthermore, those with Δn smaller than 85×10 ⁻³ have extremely excellent normal pressure dyeability. Furthermore, the average refractive index at the center of the fiber (n ₍₀₎ ) and the average refractive index at a distance of 0.8 times the radius from the fiber center (n _(0.8) or n _(-0.8 ))
The difference (△ _(0.8-0) ) is preferably 10×10 ^-3 to 80×
10 ^-3 , more preferably 10 x 10 ^-3 to 40 x 10 ^-3 , and when the local average refractive index distribution of the fiber is symmetrical with respect to the center of the fiber, it has sufficient strength, There are few staining spots, strong elongation spots, etc. Here, the fact that the local average refractive index distribution is symmetrical with respect to the center of the fiber means that the minimum value of the average refractive index n is (n ₍₀₎ −10×
10 ^-3 ) or more, and the difference between n _(-0.8) and n _(0.8) is
It refers to a case where it is 50×10 ^-3 or less, more preferably 10×10 ^-3 or less. In addition, the above n ₍₀₎ , n _(0.8) , n _(-0.8) ,
Values such as Δ _(0.8-0) and Δn were measured using an interference microscope using the method described later. In addition, in the fiber of the present invention, the smaller the mechanical loss tangent (tan δ ₂₂₀ ) at 220°C, the better;
The decrease in initial modulus due to temperature rise becomes smaller. When tan δ ₂₂₀ is 0.25 or less, the amount of initial modulus reduction becomes significantly small. In other words, the fiber has a structure that is extremely stable against heat. The fibers of the present invention can be used, for example, as shown in the examples below.
It can be obtained by a take-up method using a combination of a take-up speed of 7,000 m/min or more, preferably 8,000 m/min or more, and specific cooling conditions. The process of spinning and winding does not include a stretching process. If the drawing speed is 7000 m/min or more, a crystallinity (Xc) of 70% or more is achieved.
During spinning, the cooling solidification and thinning deformation of the polymer flow spun from the spinneret are controlled by appropriately adjusting the polymer viscosity, spinning temperature, atmospheric conditions under the spinneret, cooling method, take-up speed, etc. Thus, fibers with good spinnability and desired properties can be obtained. In particular, control of cooling and solidification of the spun yarn is important. As exemplified in Example 1 below, it is possible to control the solidification and thinning deformation of the yarn by cooling the yarn with a flow of air supplied from the entire periphery of the spun yarn in parallel to the running direction of the yarn. can. Most preferably, Examples 2-
As illustrated in 4, a fluid suction device is used to localize the cooling, solidification, and thinning deformation of the yarn. By using the above-described cooling and solidifying effect at a high take-up speed of 7000 m/class, a polyester fiber unique to the present invention having a unique fine structure, refractive index distribution, and symmetry of the distribution can be obtained. In order to obtain spinnability and desired properties, rapid cooling and solidification, particularly cooling and solidification by low-temperature cooling air perpendicular to the yarn from one direction, is not very preferable. When such a rapid cooling method or the conventionally known cross-blowing cooling method is adopted, the local refractive index distribution of the fiber becomes large and the distribution becomes asymmetrical with respect to the center of the fiber. . As a result, the strength is insufficient and natural crimp occurs, making it impossible to obtain the fiber of the present invention. Note that the take-up speed here refers to the speed of the first driving roll at which the cooled and solidified yarn is taken off after being spun, after being further bundled, treated with oil, etc., if necessary. FIG. 1 shows an example of the apparatus used in the examples.
The molten polyester is spun from a spinneret (not shown) in a heated spinning head 2 and becomes a yarn 1 which is cooled in the atmosphere. At this time, a tubular heating area 3 surrounding the spun yarn is provided below the spinneret, and a fluid suction device 4 for cooling and suctioning the yarn is provided below it. The yarn that has passed through the tubular heating zone and the fluid suction device passes through an oil application device 5 and a convergence device 6, and then is taken off by a take-off roll 7. This process combining a heating zone and a fluid suction device is optimal for stably producing fibers with a stable and highly crystalline structure. The fibers of the present invention can be used as filaments as they are, or after undergoing false twisting, fluid processing, etc., alone or in combination with other fibers to make products such as knitted fabrics and woven fabrics. can be used as spun yarn or blended yarn,
When dyeing, it has good dyeability even under normal pressure (100°C), and its unique microstructure shows little structural change even when heat is applied during the product manufacturing process, making it particularly useful as a textile for clothing. The method for measuring the structural properties of the fibers of the present invention will be described below. <Mechanical loss tangent (tanδ) and dynamic elastic modulus (E′)
> Using a RcoVibron DDV-c dynamic viscoelasticity measuring device manufactured by Toyo Baldwin, approximately 0.1 mg of sample was measured at each temperature in dry air with a measurement frequency of 110 Hz and a temperature increase rate of 10°C/min. tanδ,
and E' are measured. From the tanδ-temperature curve, the tanδ peak temperature (Tmax) [℃] and the same peak height ((tanδ) _n
ax ) is obtained. Figure 2a shows the tan δ of the fiber A of the present invention, the conventional drawn yarn B, the undrawn yarn C, and the partially oriented yarn D.
-Temperature curve, Fig. 2b schematically shows an example of the curve shape of the E'-temperature curve. <Average refractive index (n, n⊥) and average birefringence> From the surface measurement of the fiber by the interference fringe method using a transmission quantitative interference microscope (for example, interference microscope Interfaco manufactured by Karl Zeiss Jena, East Germany) The observed average refractive index distribution can be measured. ) This method applies to fibers with a circular cross section. The refractive index of a fiber is characterized by the refractive index n for polarized light with an electric field vector parallel to the fiber axis and the refractive index n⊥ for polarized light with an electric field vector perpendicular to the fiber axis. All measurements described here are performed using green light (wavelength λ =
549mμ). The fibers are made using optically flat glass slides and cover glasses, which have a refractive index (N) that provides a shift of the interference fringes within the range of 0.2 to 2 wavelengths, and are placed in a mounting medium that is inert to the fibers. immersed. Several fibers are immersed in this encapsulant so that the single threads do not touch each other. Furthermore, the fibers should have their fiber axes perpendicular to the optical axis of the interference microscope and the interference fringes. This interference fringe pattern is photographed, magnified approximately 1,500 times, and analyzed. In Figure 3, the refractive index of the fiber encapsulant is N, and the refractive index between points S ¹ and S ¹¹ on the outer periphery of the fiber is n (or n⊥).
The thickness between S ¹ and S ¹¹ is t, the wavelength of the light beam used is λ, and the distance between parallel interference fringes in the background (corresponds to 1λ)
Let D be the deviation of the interference fringes caused by the fibers, and the optical path difference R is expressed as R=d/Dλ=(n (or n⊥)−N) t. When the radius of the fiber is R, the distribution of the refractive index n (or n⊥) of the fiber at each position can be determined from the optical path difference at each position from the fiber center R ⁰ to the outer periphery R. When r is the distance from the fiber center to each position, x=r/R=0, that is, the refractive index at the fiber center is the average refractive index (n ₍₀₎ or n⊥ ₍₀₎ )
That's what it means. x is 1 on the outer circumference and takes a value between 0 and 1 on the other parts, for example x = 0.8
The refractive index at the point is expressed as n _(0.8) (or n⊥ _(0.8) ). Further, from the average refractive index n ₍₀₎ and n⊥ ₍₀₎ , the average birefringence (Δn) is expressed as Δn=n ₍₀₎ −n⊥ ₍₀₎ . FIG. 4 shows the conventional drawn yarn B and the fiber A of the present invention.
The distribution of n is shown. In the figure, the distance from the center x=r/R is plotted on the horizontal axis, and n is plotted on the vertical axis, but x=
0 is the center of the fiber, x=1 and x=-1 are points on the outer periphery of the fiber. <Size of Microcrystals (ACS)> The size of microcrystals (ACS) can be determined by measuring the X-ray diffraction intensity in the equator direction using an equatorial reflection method. X-ray diffraction intensity was measured using an X-ray generator (RU-200PL) manufactured by Rigaku Corporation and a goniometer (SG-9R).
A scintillation counter is used as the counter, a pulse height analyzer is used as the counting section, and the measurement is performed using Cu-Kα rays (wavelength λ = 1.5418 Å) made monochromatic with a nickel filter. The fiber sample was placed in an aluminum sample holder so that the fiber axis was perpendicular to the X-ray diffraction plane. At this time, the thickness of the sample is 0.5m/m
Set it so that it is in the correct position. X at 30KV, 80mA
Operate the line generator at a scanning speed of 1°/min.
Chart speed 10m/min, time constant 1
Record the diffraction intensity from 35° to 7° in 2θ at a divergence slit of 1/2°, a receiving slit of 0.3 m/m, and a scattering slit of 1/2°. The full scale of the recorder is set so that the resulting diffraction intensity curve falls within the scale. Polyethylene terephthalate fibers generally have three main reflections in the range of equatorial diffraction angle 2θ = 17° to 26° ((100), (101), (11) from the low angle side).
0) side). To find the ACS, for example, "Polymer X-ray Diffraction" by L. E. Alexander, Kagaku Doujin Publishing,
Use Scherrer's formula in Chapter 7. A straight line connects the diffraction intensity curves between 2θ = 7° and 2θ = 35° to form the baseline. Draw a perpendicular line from the top of the diffraction peak to the baseline, and mark the midpoint between the peak and the baseline. A horizontal line through the midpoint is drawn between the diffraction intensity curves and the diffraction peaks. 2 of the peaks of the curve if the main reflections are well separated.
It intersects two shoulders, but in case of poor separation it intersects only one shoulder. Measure the width of this peak.
If it only intersects one shoulder, measure the distance between the intersecting point and the midpoint and double it. If it crosses two shoulders, measure the distance between both shoulders.
These measured values are converted into radians and used as the line width. Furthermore, this line width is corrected using the following equation. β=√ ² − ² B is the measured line width, and b is the broadening constant, which is the line width (half width) expressed in radians of the peak of (111) plane reflection of the Si single crystal. The size of the crystallite (ACS) is given by the following formula: ACS(Å) = K.λ/βcosθ. Here, K is 1, λ is the wavelength of X-rays (1.5418 Å), β is the corrected line width, and θ is the Bragg angle, which is 1/2 of 2θ. <Crystallinity (Xc)> X obtained in the same manner as the measurement of the size of microcrystals
From the line diffraction intensity curve, connect the diffraction intensity curves between 2θ = 7° and 2θ = 35° with a straight line to form the baseline. As shown in Figure 2, the valley around 2θ = 20° is the peak,
Connect with a straight line along the base of the low angle side and the high angle side, separate into crystalline part and amorphous part, and calculate by area method according to the following formula. Xc (%) = Scattering intensity of crystal part / Total scattering intensity x 100 <Crystal orientation (Co)> Rigaku X-ray generator (RU-200PL), fiber sample measuring device (FS-3), goniometer (SG-9), a scintillation counter is used for the counter, a pulse height analyzer is used for the counting part, and Cu-Kα rays (wavelength λ =
Measures at 1.5418 Å. Polyethylene terephthalate fibers generally have three main reflections on the equator line, and the (010) plane reflection is used to measure the degree of crystal orientation (Co). The 2θ of the (010) surface reflection used is determined from the diffraction intensity curve in the equatorial direction. The X-ray generator operates at 30KV and 80mA. Attach the sample to the fiber sample measuring device so that the single yarns are parallel to each other. The thickness of the sample
It is appropriate to set the distance to about 0.5m/m. Set the goniometer at the 2θ value determined from the equatorial diffraction intensity curve. The azimuthal direction is scanned from −30° to +30° using the symmetrical transmission method, and the diffraction intensity in the azimuthal direction is recorded. Furthermore, the diffraction velocities in the azimuth directions of −180° and +180° are recorded. At this time, scanning speed 4°/min, cart speed 10mm/min, time constant 1 second, collimator 2m/mφ, receiving slit vertical width 19m/m, width 3.5m/min.
It is m. To determine Co from the obtained diffraction intensity curve in the direction of the azimuth angle, take the average value of the diffraction intensities obtained at ±180°, draw a horizontal line, and use it as the baseline. Draw a perpendicular line from the top of the peak to the baseline and find the midpoint of its height. Draw a horizontal line through the midpoint,
The distance between the two intersection points of this and the diffraction intensity curve is measured, and this value is converted into an angle (°), and the value is defined as the orientation angle H (°). The degree of crystal orientation is given by the following formula: Co (%) = 180° - H/180° x 100. <Dyeability> Dyeability was evaluated based on the equilibrium dyeing rate. Disperse dye Resolin Blue
Dyeing was carried out at 100° C. using FBL (trade name of Bayer) at a 3% owf. bath ratio of 1:50. as a dispersant
Add 1g of Disper TL and further add acetic acid.
Adjust to PH=6. The dyeing rate is determined by the specified time (2 hours)
After the dyeing liquid was collected, the amount of dye in the residual liquid was calculated from the absorbance, and this was subtracted from the amount of dye used for dyeing to calculate the dyeing rate (%).
In addition, as a sample, the raw yarn was knitted in one piece, and it was scoured at 60℃ for 20 minutes using a score roll FC2g/, dried,
A humidity-controlled (20°C x 65% RH) was used. <Dyeing fastness> A sample was dyed in the same manner as in the dyeability evaluation except that the dye concentration was 1% owf and the dyeing time was 90 minutes. Hydrosulfite 1g/, sodium hydroxide 1g/, surfactant ( Sunmaur RC-700)
The product was evaluated after reduction cleaning using 1g/1g/1:50 bath ratio at 80°C for 20 minutes. Color fastness is light fastness (based on JIS L-1044), rubbing fastness (based on JIS L-0849), and hot pressing fastness (based on JIS L-0850).
was evaluated. <Initial Modulus> The value of E ¹ at 30°C in the dynamic viscoelasticity test described above was taken as the initial modulus. <Strong elongation> TENSILON UTM manufactured by Toyo Baldwin Co., Ltd.
- Initial length 5 cm, tensile speed 20 using a 20 type tensile tester
Measured in mm/min. <Boiling water shrinkage rate> When the length of the sample under a load of 0.1 g/d is Lo, and the length L is the length measured again under the same load after removing the load and treating it in boiling water for 30 minutes, the boiling water shrinkage rate is It is expressed as boiling water shrinkage rate (%)=Lo-L/L×100. The present invention will be described above using examples. Example 1 Intrinsic viscosity [η] (hereinafter [η]) measured at 35°C in a 2/1 mixed solvent of phenol/tetrachloroethane
) 0.63 polyethylene terephthalate was spun at a spinning temperature of 300°C from a spinneret with a hole diameter of 0.35φ and 7 holes, and a 22°C polyethylene terephthalate was fed from the entire periphery of the yarn in parallel to the running direction of the yarn. After being cooled and solidified by air flow, a finishing agent is applied and the
The fibers were wound at a speed of 9000 m/min to 35 d/7 f. Table 1 shows the relationship between the microstructural features and physical properties. Nos. 1 to 3 in the table are fibers of the present invention,
Nos. 4 to 7 are comparative fibers outside the scope of the present invention. Comparative Example 1 Polyethylene terephthalate with [η] 0.63 was spun at a spinning temperature of 290°C from a spinneret with a hole diameter of 0.35φ and a hole diameter of 36, and after cooling with an air flow from one direction perpendicular to the yarn at 22°C, it was spun for 1500 m/ It was wound up at a speed of 1 minute.
255d/36f undrawn yarn, drawing ratio 3.3 times, drawing temperature
A drawn yarn of 75d/36f was obtained by hot drawing at 160°C. Table 1 shows the relationship between the microstructural characteristics and physical properties of the drawn yarn. From Table 1, it can be seen that the fibers of Nos. 1 to 3 of the present invention have sufficient mechanical properties, thermal stability, normal pressure dyeability, and color fastness. Nos. 4 to 7 and the comparative fiber (No. 8) of Comparative Example 1 are unsatisfactory in any of the above properties. Examples 2 to 4 Using the apparatus shown in Fig. 1, polyethylene terephthalate with [η] 0.65 was spun from a spinneret with a hole diameter of 0.25φ and a number of holes of 24 at a spinning temperature of 290°C. After passing through a heating cylinder with a diameter of 20 cm, it is sucked and cooled by a fluid suction device installed at a position 20 cm from the heating cylinder exit, and then passed through ambient air at room temperature to cool and solidify, after which a finishing agent is applied. It was wound up at a predetermined speed to form a 50d/24f filament. Furthermore, the temperature of the atmospheric air inside the heating cylinder is
200℃, the pressure of the air supplied to the fluid suction device is 0.5
Kg/cm ² G, flow rate was 8 Nm/hr, and temperature was 30°C. Table 2 shows the relationship between the microstructural characteristics and practical properties of the obtained fibers. As is clear from Table 2, the fiber of the present invention satisfies all of the normal pressure dyeability, mechanical properties, and thermal stability.

【table】

【table】

【table】

[Table] Comparative Example 3 In Example 1, air at 20°C was cooled from one direction perpendicular to the filaments at a wind speed of 0.2 m/sec and solidified, and wound at a speed of 7000 m/min to form 35d/7f fibers. I got it. Table 3 shows the relationship between the microstructural characteristics and physical properties of the fiber, as well as its practical properties. Note that when the wind speed under the conditions of this comparative example was set to 0.3 m/sec, the yarn swayed so much that normal winding was not possible.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a schematic diagram of the apparatus used in the embodiment of the present invention. In the figure, 1 is a yarn, 2 is a spinning head, 3 is a tubular heating area, 4 is a fluid suction device, 5 is an oil application device, and 6 is a The focusing device 7 is a take-up roll. Figures 2a and 2b are mechanical loss tangent (tan δ) - temperature (T) curves, dynamic elastic modulus (E ¹ ) -
It is a graph schematically showing a temperature (T) curve. FIG. 3 is an example of an interference fringe pattern used to measure the radial refractive index (n or n⊥) distribution within the fiber cross section. In the figure, a is a cross-sectional view of the fiber, b is an interference fringe pattern diagram, 1 is the fiber, 2 is the interference fringe due to the mounting medium, and 3 is the interference fringe due to the fiber. FIG. 4 is a graph showing an example of the radial refractive index (n) distribution of the fiber of the present invention and a conventional drawn yarn. FIG. 5 is a graph showing an example of an X-ray diffraction intensity curve of polyethylene terephthalate fiber.

Claims (1)

[Claims] 1. Initial modulus is 50 g/d or more, elongation is 20%.
Peak temperature (Tmax) of mechanical loss tangent (tan δ) at a measurement frequency of 110 Hz for fibers consisting essentially of ~60% polyethylene terephthalate
and peak value ((tanδ)max) at 85℃, respectively.
≦Tmax≦110℃ and 0.115≦(tanδ)max≦
0.135, the crystallinity (Xc) is 70% or more, the average refractive index (n ₍₀₎ ) and the refractive index of the part at a distance of 0.8 times the radius from the center of the fiber (n _(0.8) ) and has a local refractive index distribution in which the difference (△ _(0.8-0) ) is 10 × 10 ^-3 or more and 80 × 10 ^-3 or less, and the above distribution is symmetrical with respect to the fiber center. Possible polyester fiber. 2. The polyester fiber according to claim 1, which has an average refractive index of 1.65 to 1.7. 3. The polyester fiber according to claim 1, which has an average birefringence index (Δn) of 110×10 ^-3 or less. 4. The polyester fiber according to claim 1 or 2, which has an average birefringence (Δn) of 85×10 ^-3 or less.