JPH1077524A - Polyester-based yarn for sheet belt and sheet belt using the same yarn - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject yarn without requiring dyeing and resin finishing and excellent in high strength, abrasion resistance, scratch resistance and light resistance by including a prescribed amount of inert inorganic fine particles having a prescribed average particle diameter and a specific Mohs'hardness into a polyesterbased resin. SOLUTION: This polyester-based yarn is obtained by including 100-20,000ppm inert inorganic fine particles of alumina, silica, calcium carbonate, etc., having 0.01-5.0μm average particle diameter and >=2.5 Mohs' hardness into a polyester- based resin and preferably, the yarn is a dope-dyed yarn colored with a carbon black-based coloring agent and has >=8.0g/denier strength. Furthermore, it is preferable that (A) 100 to 19,900ppm inorganic fine particles of alumina and/or silica having 0.01-0.1 average particle diameter and >=2.5 Mohs' hardness and (B) 19,900 to 100ppm inorganic fine particles of calcium carbonate having 0.1-5.0μm average particle diameter and 2.5-5 Mohs' hardness are included in the polyester-based resin as the inert inorganic fine particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester yarn for a seat belt, which is high in strength and excellent in abrasion resistance and abrasion resistance and does not require finishing resin processing in a seat belt manufacturing process. The present invention relates to a seat belt using the same.

[0002]

2. Description of the Related Art Conventionally, aromatic polyester fibers having excellent heat resistance, dimensional stability and light resistance have been widely used as raw yarns for seat belts. And when manufacturing a seat belt using the polyester-based yarn,
Weaving, dyeing, heat setting, finishing resin treatment and the like are performed to obtain a webbing for a seat belt. At this time,
In the conventional seat belt manufacturing process, it was assumed that white yarn was used and an arbitrary color tone was given by dyeing after weaving, but in recent years, in order to simplify the manufacturing process and reduce costs, In the subsequent steps, it is required to eliminate the need for dyeing and finishing resin treatment, and to eliminate the finishing resin treatment.

[0003] On the other hand, many proposals have been made for improving the performance of the original yarn for seat belts. For example, with respect to the improvement of the abrasion resistance, for example, JP-A-55-116361, JP-A-3-40829, etc. Discloses a technique for improving abrasion resistance by optimizing the single yarn fineness of the original yarn for seat belt.

[0004] However, these known techniques cannot sufficiently increase the wear resistance of the original yarn for seat belts, thereby simplifying the manufacturing process without finishing resin treatment.
As a result, cost reduction cannot be realized.

[0005] Japanese Patent Application Laid-Open No. 52-55724 and 6
Japanese Unexamined Patent Application Publication No. 3-123328 discloses an improvement technique relating to a so-called dyed yarn which is colored in a state of a polyester yarn, but all of these technologies relate to improvement of a color tone of a polyester yarn. In addition, the strength and wear resistance cannot be improved.

[0006] Further, JP-A-7-258918 discloses that
A technique for increasing the strength of the fiber for seat belts by defining the particle size distribution of the colorant has been disclosed, but the abrasion resistance is not drastically improved only by optimizing the particle size distribution. In addition, a combination use of a low-wear treatment agent is essential. The abrasion-reducing agent not only has a risk of falling off during the molding or weaving process, but also has a disadvantage that it loses its effect by being vaporized in a high-temperature processing atmosphere or a use atmosphere.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide high strength, excellent abrasion resistance and abrasion resistance, obstruction of dyeing and finishing resin treatment. To provide a seatbelt yarn that can be realized without any problem, and that can achieve simplification of the seatbelt manufacturing process and cost reduction, and furthermore, to provide a high-performance seatbelt using the yarn. It is assumed that.

[0008]

Means for Solving the Problems The yarn for a seat belt according to the present invention which can solve the above-mentioned problems is a polyester resin having an average particle diameter of 0.01 to 5.0 μm.
m, Mohs hardness: 1 inert inorganic fine particles of 2.5 or more
It has a characteristic feature in that it is contained in an amount of from 0.000 to 20,000 ppm and has improved slipperiness, abrasion resistance and abrasion resistance without adversely affecting the strength characteristics. Examples of the inorganic fine particles used here include alumina, silica, calcium carbonate, and the like.

In carrying out the invention, the inorganic fine particles (A) having an average particle diameter of 0.01 μm or more and less than 0.1 μm and a Mohs hardness of 2.5 or more are used as the inert inorganic fine particles. 100 to 19,900 ppm, average particle diameter: 0.1 to 5.0 μm, Mohs hardness: 2.5
It is preferable that the inorganic fine particles (B) having a content of less than 5 are contained in the polyester resin in an amount of 19,900 to 100 ppm, because the performance as a seat belt yarn can be further improved. The preferred inorganic fine particles (A) used at this time are alumina and / or silica, and the preferred inorganic fine particles (B) are calcium carbonate.

In the present invention, a polyester yarn colored in the original yarn state, preferably a polyester yarn colored with carbon black or the like, is not required to be subjected to a coloring treatment after yarn production or weaving. It will be more useful as a yarn. The strength of the polyester yarn is desirably 8.0 g / denier or more in order to satisfy the strength standard required for a seatbelt. A seatbelt using a polyester yarn having the above characteristics as a material is It has excellent performance in terms of strength, slipperiness, abrasion resistance, scratch resistance and the like.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The type of polyester used as a yarn material in the present invention is not particularly limited, but it is particularly preferable in consideration of strength characteristics, heat resistance and the like that an aromatic dicarboxylic acid and a glycol are used as main raw materials. Aromatic polyesters obtained by polycondensation are preferred, and particularly preferred are polyesters comprising 95% by mole or more of ethylene terephthalate. Other dicarboxylic acid components that can be used as the copolymerization component include isophthalic acid. Acid, p-β-oxyethoxybenzoic acid, 2,6-naphthalenedicarboxylic acid, 4,4-dicarboxyphenyl
4,4-dicarboxybenzophenone, bis (4-
Carboxyphenyl) ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, cyclohexane-1-dicarboxylic acid and the like; glycol components include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanedimethanol, bisphenol An ethylene glycol adduct of A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like; examples of the oxycarboxylic acid include p-oxybenzoic acid;
These can be used in combination of two or more if necessary.

Further, as a copolymerizable component other than the above, a small amount of a compound having an amide bond, a urethane bond, an ether bond, a carbonate bond or the like in the molecule can be used in combination.

Next, the inert inorganic fine particles used in the present invention impart abrasion resistance, abrasion resistance and the like to the polyester yarn for a seat belt without causing chemical deterioration due to the inertness with respect to the polyester. It is essential to select and use those having an average particle size of 0.01 to 5.0 μm and a Mohs hardness of 2.5 or more. However, in the case of coarse particles having an average particle diameter of more than 5 μm, yarn breakage is likely to occur when the polyester containing the particles is processed into a fibrous form, and also causes coarse projections on the fiber surface to cause dropout, and When extremely fine particles having a particle size of less than 0.01 μm are used, when the particles are mixed into the polyester, a part of the particles may cause agglomeration and coarsening, which also tends to cause thread breakage and dropout. The more preferable average particle diameter of the inorganic fine particles is 0.05 to
The range is 2.5 μm.

The inorganic fine particles preferably have a narrow particle size distribution in order to satisfy the above-mentioned average particle size and also to reduce the friction coefficient of the fiber surface and more reliably suppress the dropout, and more specifically, have a particle size of 10 μm or more. It is desirable to use a material having a sharp molecular weight distribution such that no coarse particles are present and the content of particles having a size of 2 μm or more is 5% by volume or less. The average particle diameter of the inorganic fine particles means a diameter at an integrated 50% of the equivalent sphere particle size distribution calculated by the Stokes' formula.

In addition, it is necessary to select the inorganic fine particles having a Mohs hardness of 2.5 or more in addition to the above particle size composition. Cannot be satisfactorily improved in the abrasion resistance and scratch resistance to be provided.

The inert inorganic fine particles have the above-mentioned particle size and mode.
Satisfies hardness and inert to polyester
Type is not particularly limited as long as it is
Titanium oxide (TiO_Two ), Ferric oxide (Fe_Two O_Three ),
Silicon dioxide (silica: SiO _Two ), Silicon carbide (Si
C), alumina (Al_Two O_Three ), Calcium carbonate (Ca
CO_Three ), Barium sulfate (BaSO)_Four ), Calcium fluoride
(CaF_Two ), Etc. are exemplified.
However, among these, particularly preferred are polyester and
Rich in affinity and high effect of improving sliding characteristics and abrasion resistance
Alumina, silica and calcium carbonate.
Can be used alone or in combination of two or more.
Thus, the features of the present invention can be achieved more effectively.

In order to effectively exhibit the above characteristics of the inert inorganic fine particles, the amount of the inert inorganic fine particles to be added to the polyester should be 100 to 100%.
In the range of 20,000 ppm, more preferably 500 to
It is necessary to be in the range of 7,000 ppm, and 10
If the amount is less than 0 ppm, sufficient slip properties and abrasion resistance cannot be imparted to the polyester yarn.
If it is excessively contained in excess of 000 ppm, spinning,
In addition to the fact that the machine base is easily damaged at the time of drawing and weaving, there is a problem that yarn breakage occurs at the time of spinning and drawing and satisfactory yarn strength cannot be obtained.

The effect of the addition of the above-mentioned inert inorganic fine particles can be effectively exerted even when only one kind is contained in the polyester in an appropriate amount. In addition, it is preferable to use fine particles having a high Mohs hardness and fine particles having a relatively large particle diameter and a low Mohs hardness in combination, since the effect of addition can be more effectively exhibited.

That is, even if the particle size falls within the above-mentioned preferred particle size range, if a relatively large particle size is independently blended, the frictional force applied to the surface of the polyester fiber is borne by only one type of fine particle. However, when a large force acts on the interface between the particles and the polyester-based resin, the fine particles tend to drop out easily. The force applied to the interface is mainly carried by fine particles of a relatively small particle size, and the force applied to the fiber surface is mainly carried by the fine particles of a large particle size. And abrasion resistance can be effectively increased. Use of a material having a relatively large particle size and a high Mohs' hardness is not preferred because fine particles which are present in large amounts on the fiber surface are liable to cause scratches on a machine base or the like.

For particles having a relatively small particle size, a material having a relatively low Mohs hardness may be used. This is preferable because the effect of dispersing the force applied to the interface is exhibited and the abrasion resistance can be increased.

Specifically, the primary average particle size is 0.01 μm
The inorganic particles (A) having a Mohs hardness of not less than 0.1 μm and a Mohs hardness of not less than 5 are contained in the polyester resin in an amount of 100 to 1 μm.
9,900 ppm and an average particle size of 0.1
Inorganic fine particles (B) having a Mohs hardness of 2.5 to less than 5 and a Mohs hardness of 2.5 to less than 5 in the polyester resin. 19,900-100 ppm [However,
Inorganic fine particles to be contained in polyester resin (A)
And the sum of (B) is within the range of 100 to 20,000 ppm], the above-mentioned effect of adding the inorganic fine particles can be exhibited more efficiently.

These two or more kinds of inorganic fine particles (A),
When (B) is used in combination, preferred inorganic fine particles selected are at least one selected from alumina, silica and calcium carbonate. Preferred alumina fine particles include gibbsite, bayerite, northstrandite, boehmite, and diaspore. Hydrate, amorphous alumina hydrate such as amorphous gel, boehmite gel, bayerite gel, etc., and ρ, η, γ, χ, κ, δ, θ type etc. Intermediate activated alumina, α-type alumina and the like are included, and particularly preferred are δ-type and γ-type intermediate activated alumina fine particles.

The silica fine particles can be effectively used in any form, but spherical silica fine particles are particularly preferred from the viewpoint of the effect of improving the slipperiness and abrasion resistance. Calcium carbonate fine particles are classified into three types: calcite classified into trigonal or hexagonal according to their crystal structures, aragonite classified into orthorhombic, and vaterite classified into hexagonal or pseudo-hexagonal. Although it is divided into crystal forms, any type can be effectively used in the present invention, and the shape thereof is also a chain-like particle or cubic crystal, a spindle shape, a columnar shape, a needle shape, a spherical shape, an egg shape. Any shape can be used.

The method for adding the above-mentioned inert inorganic fine particles is not particularly limited, either. The method for addition in the esterification step, the transesterification step and the polycondensation step in the production of polyester, and the method for drying the polyester chips obtained by the polycondensation. , A method of directly adding at the time of spinning, a method of melting a master chip containing a high concentration of inorganic fine particles and blending it with a separately melted base polyester before spinning (melt blending method), a method of melting the inorganic fine particles at a high concentration It is possible to employ any known method such as a method of blending a contained master chip and a base chip (chip blending method). However, in consideration of quality stability, operation stability, productivity, etc. It is preferable to prepare a master chip in advance, blend it with the base polyester and spin it. It is the law.

The polyester resin used in the present invention can be colored by adding a coloring agent, if necessary, and the dyeing step can be omitted, which is preferable. Particularly preferred as the colorant is carbon black having excellent light resistance, and the preferred amount thereof is in the range of 0.3 to 0.7% by weight in terms of the concentration in the fiber. The method of adding the colorant is also obtained by the method described as the method of adding the inorganic fine particles, that is, the method of adding in the esterification step, the transesterification step, the polycondensation step when producing the polyester, and the polycondensation. Method of blending dried polyester chips when drying, method of directly adding during spinning, method of melting master chips containing a high concentration of a coloring agent and blending them with a separately melted base polyester before spinning (melt blending method) ,
Any known method such as a method of blending a master chip containing a coloring agent at a high concentration and a base chip (chip blending method) can be employed, but the stability of quality, operation stability, and productivity can be improved. The most preferable method is to prepare a master chip in advance, blend it with a base polyester, and spin it.

Further, the polyester yarn for a seat belt according to the present invention needs to have a strength enough to withstand an impact at the time of a vehicle collision, and in order to satisfy such strength characteristics, it is required to be 8.0 g / d or more. More preferably 8.5 g / d
It is desirable to have the above strength.

The method of producing the polyester yarn for a seat belt according to the present invention is not particularly limited, but typical methods are as follows. That is, a base chip made of a polyester resin as described above, and a polyester master chip containing inert inorganic fine particles are weighed and mixed in a predetermined amount, and the mixture is supplied to a melt extruder and fed from a spinneret. By discharging, spinning is performed to an arbitrary cross-sectional dimension. The spun yarn was passed through a heating cylinder and a heat retaining cylinder, cooled and solidified by cold air, and subsequently applied with an oil agent, and then controlled at a peripheral speed of about 300 to 1,000 m / min. Taken by the roll.

The drawn undrawn polyester yarn is then drawn continuously, or once wound up and then drawn. Stretching is usually performed between two pairs of rollers and a heating zone controlled at about 70 to 180 ° C.
The drawing is performed at a magnification of about 5 to 6.0 times, and the drawn yarn is wound up into a package.

It is desirable that the intrinsic viscosity of the obtained polyester-based yarn for a seat belt is 0.7 or more, more preferably 0.8 or more. Not only does it tend to be insufficient in strength, but also the toughness tends to be insufficient, and the wear resistance and light resistance also tend to be insufficient.

The polyester yarn for a seat belt thus obtained has high tenacity and is very excellent in abrasion resistance, scratch resistance and light resistance, and is preferably used for both warp and weft yarns. Alternatively, if at least using as a warp and performing seat belt webbing with a needle loom by a conventional method, a seat belt with extremely excellent strength, abrasion resistance, abrasion resistance, light resistance without performing a finishing resin treatment, etc. Obtainable.
In addition, in the process of preparing the raw material used for the production of the polyester yarn, if carbon black or any other coloring agent is blended in the raw material, the raw yarn itself can be colored, and after spinning or weaving. Since it is not necessary to perform a coloring process, the production as a seat belt can be further simplified and the cost can be reduced.

[0031]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention is not limited thereto. Of course, the present invention can be embodied with modifications, all of which are included in the technical scope of the present invention. The test methods for various performances employed in the following examples are as follows. In addition, the test methods of various performances adopted in the following examples are as follows.

(1) Average particle diameter: The point of 50% integration in the equivalent spherical distribution obtained using a centrifugal sedimentation type particle size distribution analyzer “SA-CP-2 or CP-3” manufactured by Shimadzu Corporation is the average particle diameter. And (2) Intrinsic viscosity: Orthochlorophenol was used as a solvent and measured at 25 ° C. using an Ostwald viscometer. (3) Raw yarn elongation: Using a Tensilon tensile tester manufactured by Orientic, sample length 100 mm, tensile speed 10
It was measured at 0 mm / min.

(4) Abrasion resistance retention rate: JIS L109
5 Use the tester specified in 7.10.2B,
After 3,000 reciprocating rubbing motions, the strength was measured by the method described in (3) above, and the abrasion resistance retention was determined by the strength of the yarn after rubbing with respect to the strength of the yarn without rubbing. I asked. (5) Degree of surface protrusion of the added fine particles: After washing a single yarn of polyester fiber with carbon tetrachloride, the surface of the single yarn is observed at a magnification of 10,000 times by a scanning electron microscope, and is present within a certain visual field. The number of protrusions was counted.

(6) Evaluation of abrasion resistance: A drawn polyester fiber is applied to a plastic pin with a tension of 0.5 g / d and a winding angle of 9%.
The vehicle is run at 0 degree at a running speed of 150 m / min while being worn by 27,000 m. Then, after aluminum deposition was performed on the abraded surface, the amount of scratches was visually determined with a stereoscopic microscope, and ranked according to the following criteria. 1: No scratches are found at all 2: Slight scratches are found but very small 3: Small scratches are found 4: Large scratches are found (Ranks 1 and 2 are evaluated as good) .

Example 1 A polyethylene terephthalate-based chip having an intrinsic viscosity of 1.0 or more was mixed with a master chip resin containing 2% by weight of calcium carbonate (Mohs hardness: 4) having an average particle size of 0.56 μm. Is 2,000 ppm
The mixture is supplied to a melt-mixing extruder and discharged from a die to perform melt spinning. Cooling air is blown onto the yarn discharged from the spinneret to cool and solidify, and the yarn is taken off at a spinning take-up speed of 376 m / min while applying an oil agent.
It was drawn twice to obtain a drawn yarn of about 5 d / f.

The intrinsic viscosity, high elongation, wear resistance, surface protrusion of added fine particles, and scratch resistance of the obtained drawn yarn are as shown in Table 1 below, showing excellent performance as a seat belt yarn. It turns out that it has.

Example 2 A master chip resin containing 2% by weight of calcium carbonate (Mohs hardness: 4) having an average particle size of 0.56 μm in a polyethylene terephthalate-based chip having an intrinsic viscosity of 1.0 or more, A master chip resin containing 2% by weight of 08 μm silica (Mohs hardness: 8) was mixed with calcium carbonate and silica having a content of 2,0, respectively.
Except for using a mixture blended to be 00 ppm,
Melt spinning and drawing were performed in the same manner as in Example 1 to obtain a drawn yarn.

The intrinsic viscosity, high elongation, abrasion resistance retention, surface protrusion of the added fine particles and scratch resistance of the obtained drawn yarn are as shown in Table 1 below, showing excellent performance as a seat belt yarn. It can be seen that this has Further, in this embodiment, large fine particles and small fine particles are used in combination as the inorganic fine particles, so that a higher abrasion resistance retention rate than that of the first embodiment is obtained.

Example 3 In Example 2, when mixing calcium carbonate and silica into a polyethylene terephthalate-based chip,
Carbon black having an average particle size of 0.04 μm
Except that the master chip resin containing 4% by weight was blended so that the carbon black content was 0.4% by weight.
Melt spinning and drawing were performed in the same manner as in Example 2 to obtain a drawn yarn.

The intrinsic viscosity, high elongation, abrasion resistance retention, surface protrusion of added fine particles and scratch resistance of the obtained drawn yarn are as shown in Table 1 below, and are excellent performance as a seat belt yarn. have. Moreover, in this embodiment, since the coloring is performed by blending the carbon black, the dyeing step can be omitted.

Comparative Example 1 A drawn yarn for seat belt was produced in exactly the same manner as in Example 1 except that the polyethylene terephthalate base chip was used alone. The properties of the obtained drawn yarn are as shown in Table 1. Although the intrinsic viscosity and the strength of the polyester yarn are good, the surface smoothness is poor and the abrasion resistance retention is low, and the polyester yarn is suitable for seat belts. Lacks.

Comparative Example 2 A polyethylene terephthalate-based chip having an intrinsic viscosity of 1.0 or more, a master chip resin containing 2% by weight of calcium carbonate (Mohs hardness: 4) having an average particle size of 0.56 μm, A master chip resin containing 2% by weight of 08 μm silica (Mohs hardness: 4)
Each content of calcium carbonate and silica is 10,000
A drawn yarn was produced in the same manner as in Example 2 except that a mixture blended to give ppm and 20,000 ppm was used. The performance of the drawn yarn is as shown in Table 1,
Although the abrasion resistance retention rate is good, it has low strength and lacks practicality as a seat belt.

Comparative Example 3 A master chip resin containing 2% by weight of talc (talc, Mohs hardness: 1) having an average particle size of 0.5 μm was added to a polyethylene terephthalate-based chip having an intrinsic viscosity of 1.0 or more. Of 2,000 ppm, and a drawn yarn was produced in the same manner as in Example 1 above. The performance of the drawn yarn is as shown in Table 1 below. Since the surface smoothness is not improved, the retention of abrasion resistance is low and the yarn is not practical as a seat belt yarn.

Comparative Example 4 A polyethylene terephthalate-based chip having an intrinsic viscosity of 1.0 or more was mixed with a master chip resin containing 2% by weight of calcium carbonate (Mohs hardness: 4) having an average particle diameter of 6.0 μm. Of 2,000 ppm, and a drawn yarn was produced in the same manner as in Example 1 above. The performance of the drawn yarn is as shown in Table 1 below, and the intrinsic viscosity and strength required for the polyester yarn cannot be obtained, and the yarn is not practical as a seat belt yarn. Also, filter clogging was induced during spinning, and operability was very poor.

[0045]

[Table 1]

[0046]

The present invention is constituted as described above, and performs a finishing resin treatment or the like by including a specific amount of inert inorganic fine particles having a specified average particle size and Mohs hardness in a polyester resin. It is possible to obtain a polyester yarn which gives a seat belt having excellent strength, abrasion resistance, abrasion resistance, and light resistance. In particular, when relatively large particles and small particles are used in combination as inert inorganic particles, excellent slipperiness can be imparted while suppressing dropout of the inorganic particles more reliably, and abrasion resistance and light resistance can be obtained. Further, the polyester yarn spun after blending a coloring agent such as carbon black into the raw material does not need to be subjected to a coloring treatment after spinning or weaving. This is preferable because simplification of the process and cost reduction can be promoted. And the seat belt manufactured by the usual method using the polyester yarn for the seat belt, the above-mentioned properties of the original yarn are effectively exhibited, and excellent strength, abrasion resistance, abrasion resistance, without finishing resin treatment, It has light resistance.

Claims (8)

[Claims] 1. An average particle diameter in a polyester resin:
A polyester yarn for a seat belt, characterized by containing 100 to 20,000 ppm of inert inorganic fine particles having a Mohs hardness of at least 0.01 to 5.0 [mu] m. 2. As the inert inorganic fine particles, inorganic fine particles (A) having an average particle diameter of 0.01 μm or more and less than 0.1 μm and a Mohs hardness of 2.5 or more are contained in the polyester resin in an amount of 100 to 19,900 ppm. Average particle diameter: 0.1 to 5.0 μm, Mohs hardness is 2.5
The inorganic fine particles (B) having a content of not less than 5 are contained in the polyester resin in an amount of 19,900 to 100 ppm,
The polyester-based yarn for a seat belt according to claim 1. 3. The polyester yarn for a seat belt according to claim 2, wherein the inorganic fine particles are at least one selected from the group consisting of alumina, silica, and calcium carbonate. 4. The polyester yarn for a seat belt according to claim 2, wherein the inorganic fine particles (A) are alumina and / or silica, and the inorganic fine particles (B) are calcium carbonate. 5. The polyester yarn for a seat belt according to claim 1, wherein the polyester yarn is a native yarn. 6. The polyester yarn for a seat belt according to claim 5, wherein the original yarn is colored with a carbon black colorant. 7. The polyester yarn for a seat belt according to claim 1, which has a strength of 8.0 g / denier or more. 8. A seat belt using the polyester yarn according to claim 1.