WO2013048203A2

WO2013048203A2 - Polyester fiber and rope including the same

Info

Publication number: WO2013048203A2
Application number: PCT/KR2012/007950
Authority: WO
Inventors: Young-Jo Kim; Byoung-Wook An; Sang-Mok Lee; Young-Soo Lee; Gi-Woong Kim
Original assignee: Kolon Industries, Inc.
Priority date: 2011-09-30
Filing date: 2012-09-28
Publication date: 2013-04-04
Also published as: WO2013048203A3

Abstract

The present invention relates to a polyester fiber having high tenacity and high elongation, which is used for a rope for anchorage, mooring, towage, etc. of a ship. More specifically, the present invention relates to a polyester fiber having the elongation of 6.8% or more at 50% of the maximum load (MBL) measured at room temperature, and a polyester fiber rope comprising the same. The polyester fiber of the present invention can secure excellent shape stability, mechanical properties and abrasion resistance as well as high tenacity and elongation. Thereby, it can be used to prepare the fiber rope which may minimize the yarn breaking even under the changes of external environments such as wild marine, severe ship rolling, etc., remarkably improve the shock absorption performance, maintain the performance as a rope after exposure to the long-term deformation, and thus secure the sufficient safety along with the excellent life time of rope.

Description

[SPECIFICATION]

[TITLE OF THE INVENTION]

POLYESTER FIBER AND ROPE INCLUDING THE SAME

[TECHNICAL FIELD]

The present invention relates to a high tenacity polyester yarn for a rope used for anchorage, mooring, towage, etc. of a ship. More specifically, the present invention relates to a polyester fiber which has excellent mechanical properties together with excellent abrasion resistance, light resistance, shock absorption performance, workability, low moisture absorption, etc., and a rope including the same.

[BACKGROUND ART]

Marine ropes used for anchorage, mooring, towage, etc. of a ship or ropes for industrial materials used in a variety of construction sites have been developed toward securing the high tenacity and excellent mechanical properties.

In particular, wire ropes have been widely used in the ship area since they can secure high tenacity and excellent fatigue resistance, etc., and fiber ropes consisting of a high performance nylon fiber or polyolefin fiber have been mainly used as a synthetic fiber rope. However, since the wire rope may be eroded due to water and is too rigid to hold the movement of a ship caused by the wave and the tide, it is highly plausible to damage the ship. The wire rope is also difficult to handle due to the weight of the rope itself. The earlier nylon fiber rope, etc. show a serious tenacity reduction rate due to UV light so that they may lose the ability of holding a ship because of the significant reduction of the rope tenacity upon long term use and thus may cause the problem of requiring frequent replacement. Furthermore, the nylon fiber rope, etc. are not easy to handle during their use in the mooring or anchorage of a ship due to their high moisture absorption rate, and some problems such as causing personal injury may also occur since the rope is frozen in the state of moisture absorption in the winter.

On the other hand, polyesters represented by polyethyleneterephthalate ("PET," below) are excellent in the mechanical strength, chemical resistance, etc. and thus widely used in the applications of fiber, film, resin, etc. For example, in the case of a fiber, they are widely used in the applications as a variety of industrial materials such as tire cord, belt, hose, rope, etc. as well as in the application for clothes. However, the earlier polyester fibers show the characteristics of high modulus and low breaking elongation, whereby they could not sufficiently deal with the deformation caused by the movement of a ship according to the ocean change during the mooring, giving problems of fiber breaking, etc.

Accordingly, there has been a need for researches to develop high-performance synthetic fibers that may remarkably improve the shock absorption performance against the external environmental change and give the excellent mechanical property and workability when they are used as marine ropes for anchorage, mooring, towage, etc. of a ship or ropes for industrial materials.

[CONTENTS OF THE INVENTION]

[PROBLEMS TO BE SOLVED]

The present invention is to provide a polyester fiber capable of being used as a marine rope or a rope for industrial materials, which shows an excellent creep characteristic, high work/recovery ratio, etc. along with low modulus, high tenacity and high elongation and also has excellent shock absorption performance, shape stability, etc. along with excellent mechanical properties against repetitive deformation caused by the external environmental change.

The present invention is also to provide a fiber rope comprising said polyester fiber. [TECHNICAL MEANS]

The present invention provides a polyester fiber having the elongation of 6.8% or more at 50% of the maximum load (MBL) measured at room temperature.

The polyester fiber of the present invention may show the creep rate of 8.5% or less, which is defined by the following Equation 1, when it is allowed to stand for 7 days under the 50% load of the breaking tenacity of the fiber.

[Equation 1]

Creep rate of fiber = (LrL₂)/L₂ 100

in which Li is the length of yarn measured after applying the load for 7 days, and L₂ is the initial length of yarn.

The polyester fiber of the present invention may also show the work/recovery ratio of 90% or more which is measured at room temperature under the load condition of 10% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 10% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

The present invention also provides a polyester fiber rope comprising said polyester fiber.

The polyester fiber rope of the present invention may have the elongation of 9% or more at 50% of the maximum load (MBL) measured at room temperature.

The polyester fiber rope of the present invention may also show the creep rate of 15% or less, which is defined by the following Equation 2, when it is allowed to stand for 7 days under 50% load of the breaking tenacity of the rope.

[Equation 2]

Creep rate of rope = (L3-L₄)/L₄ x 100

in which L₃ is the length of rope measured after applying the load for 7 days, and L is the initial length of rope.

Hereinafter, the polyester fiber capable of being used as a marine rope or a rope for industrial materials, method for preparing the same and fiber rope comprising the same, each of which is according to the specific embodiment of the invention, will be explained in more detail. However, they are provided only for an illustration of the invention but it is not intended that the scope of the present invention is limited in any manner by them. It will be apparent for a skilled artisan that various modifications for the embodiments are possible within the scope of the invention.

Additionally, unless specifically noted in the present specification in its entirety, "comprising" or "containing" refers to comprising any element (or constituent) without special limitation, and cannot be interpreted as excluding the addition of other elements (or constituent).

The 'polyester fiber' as used herein conventionally refers to a fibrous polymer obtained by esterification reaction of a diol compound with dicarboxylic acids such as terephthalic acid, etc. It corresponds to the basic fiber composition for preparing the 'marine rope or a rope for industrial materials' of the present invention. In particular, since the polyester has an excellent tolerance against moisture, it is more preferable for preparing the fiber rope replacing the marine wire rope.

In the present invention, the polyester fiber may include any conventionally used polyester fibers, for example, polyalkylene terephthalates such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polycyclohexanedimethylene terephthalate (PCT), etc., or copolyesters, etc. comprising the same as the main component. In particular, polyethylene terephthalate is more preferable to be used as a marine rope in the aspect of physical properties such as strength, elongation, etc.

However, polyester is inferior to nylon in the polymerization efficiency and may be easily hydrolyzed by heat and moisture. Thus, when it is processed to a yarn, decomposition of chains may occur to make it difficult to obtain the chains having a high molecular weight. In order for the short chains to express high tenacity, it must be endowed with high stretch during the spinning, and accordingly it becomes to have such physical properties as high tenacity, low breaking elongation and high modulus. As such, the earlier polyesters have short chains and thus it is difficult for them to secure excellent shape stability and high work/recovery ratio. On the contrary, nylons have long chains and thus can express the physical properties such as low modulus, high tenacity, high elongation and excellent work/recovery ratio. If a ship is moored by a rope made of a yarn having low shape stability and work/recovery ratio, like the earlier polyester fibers, the rope may lose the initial mechanical properties due to the repetitive deformation by the external environment such as a rough ocean, etc., causing a low work/recovery ratio. Then, the rope cannot act as a buffer against the yarn breaking and the external shock, whereby the external environmental shock may be directly transferred to the ship to cause its damage.

Thus, it is a feature of the present invention that physical properties of the polyester fiber are changed so that the permanent deformation of the rope, which is caused by the mooring ship due to the repetitive movement of waves generally seen in the seaside, may be minimized. In particular, the present invention uses a highly viscous chip and performs spinning at a low temperature to secure a lot of long chains and cause a lot of tangles between the chains in the non-crystal region. Accordingly, the present invention can provide a yarn that does not easily get into the permanent deformation by external force and thus is excellent in the creep and the work/recovery ratio characteristics. Furthermore, the polyester fiber of the present invention can be effectively applied to the preparation of a fiber rope for marine or industrial materials wherein the rope has a sufficient tenacity and elongation for its tolerance against the extreme changes of external environment, continuously maintain its mechanical properties despite the long term deformation and can absorb the repetitive shocks.

Particularly, as an experimental result of the present inventors, it has been found that if a fiber rope for marine or industrial materials is prepared using the polyester fiber having the given characteristics, the absorption performance of shock due to the frequent changes of external environment is remarkably improved and it is possible to secure more improved low moisture absorption, light resistance, etc. along with the excellent mechanical properties.

According to one embodiment of the invention, the present invention provides a polyester fiber having the given characteristics. Said polyester fiber may have the elongation of 6.8% or more, or 6.8% to 30%, preferably 7.0% or more, and more preferably 7.2% or more at 50% of the maximum load (MBL) measured at room temperature.

Herein, the maximum load of the polyester fiber refers to the maximum load at the breaking of the fiber measured from the tenacity-elongation curve of yarn, which is obtained according to the method of American Society for Testing and Materials ASTM D 2256 at room temperature.

Such a polyester fiber preferably comprises polyethylene terephthalate (PET) as a main component. Various additives may be added during the preparation of said PET. The polyester fiber may comprise PET in an amount of at least 70mol% or more and more preferably comprise 90mol% or more in order to secure the excellent mechanical properties when it is used for preparing a polyester fiber rope. In the following, the term polyethylene terephthalate (PET) means the case of comprising the polyethylene terephthalate (PET) polymer in an amount of 70mol% or more unless special explanation is provided. The polyester fiber according to one embodiment of the invention is prepared under the melt-spinning and stretch condition as mentioned below to show the excellent tenacity-elongation and modulus with the elongation of 6.8% or more at 50% of the maximum load (MBL) measured at room temperature.

The earlier polyesters generally have short chains and thus the fiber rope prepared therefrom may be deformed by the external force after a long-term use to lose the mechanical characteristics which the rope originally has. In this way, since the rope prepared from the polyester yarn having short chains shows significantly low elongation at 50% of the maximum load, a ship cannot sufficiently deal with the external environments such as changes caused by the typical tide or movement of the ship, leading to the damages of the ship and rope. However, the polyester fiber obtained via the controlled melt- spinning and stretch process according to the present invention has excellent shape stability and thus can maintain the original mechanical properties of the fiber. In particular, the polyester fiber of the present invention shows the elongation of 6.8% or more at 50% of the maximum load (MBL) measured at room temperature and can be used for providing a rope having excellent tenacity-elongation and shape stability. If the polyester fiber according to the present invention is used, the external environments such as changes caused by the typical tide or movement of a ship due to the wave can be sufficiently dealt with and the damages of ship and rope can be prevented.

When a rope is prepared using the polyester fiber of the present invention, the fiber rope must maintain excellent elongation value at 50% of the maximum load (MBL), and thus the twisted yarn needs to secure excellent physical properties which take account of the elongation and the twist contraction. For example, due to the twist of the rope, the maximum load (MBL) 50% is determined by the elongation and twist contraction of 50% or more of the yarn. Normally, 0.6~1.0% of the twist contraction may occur at 35-40 TPM of the twist. Considering this, the elongation at 50% of the maximum load (MBL) of the yarn may be represented by the sum of 50% of the yarn and the twist contraction generated by the twist.

Also, the polyester fiber can secure the optimum range of creep rate as defined by the following Equation 1. The creep rate of fiber as defined in the present invention is that the creep rate of fiber as defined by the following Equation 1 becomes 8.5% or less, when the yarn specimen is fixed to make the initial length of L₂ and it is allowed to stand for 24 h under 50% load of the breaking tenacity of the yarn.

[Equation 1 ]

Creep rate of fiber = (L L^/L^ ^χ 100

in the above Equation 1, Li is the length of yarn measured after applying the load for 7 days, and L₂ is the initial length of yarn when the yarn is fixed on the creep tester.

Here, the breaking tenacity of the yarn may be measured according to the method of ASTM 2256 to be 13 kgf or more, or 13 kgf to 25 kgf, preferably 13.5 kgf or more, and more preferably 14 kgf or more. Particularly, in the case the yarn of 2,000 denier, the 50% load of the breaking tenacity of the yarn may be 6 kg to 12 kg, preferably 8 kg to 10 kg, and more preferably 9 kg.

Since the polyester yarn of the present invention has the low creep rate of 8.5% or less, for example, 0 to 8.5%, preferably 1% to 8%, more preferably 2% to 6%, and still more preferably 3% to 5% when it is allowed to stand for 24 h, it shows little deformation according to the load change and excellent shape stability. Thus, such a polyester yarn gives little shape deformation of a product even when the product is deposited in the sea water for a long time during which the external environment is changed due to the movement of tide, etc. Therefore, such a polyester yarn is excellent in the shape stability, can minimize the tenacity deterioration when applied as the yarn for marine or ship anchorage, and can be effectively used for a long time of about 5~ 10 years.

The polyester fiber of the present invention may also show the work/recovery ratio of 90% or more, or 90% to 100%, preferably 92% or more, and more preferably 95% or more when measured at room temperature under the load condition of 10% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 10% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

The polyester fiber of the present invention may also show the work/recovery ratio of 45% or more, or 45% to 95%, preferably 48% or more, and more preferably 50% or more when measured at room temperature under the load condition of 50% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 50% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

The polyester fiber exhibits a superior work/recovery ratio after the repetitive deformation at room temperature in comparison to the earlier polyester yarns, and thus can exhibit very excellent tenacity-elongation and modulus in a certain repetitive deformation test.

As described above, the earlier polyester shows a low work/recovery ratio due to the typically short chains, and thus the fiber rope prepared therefrom is remarkably inferior in the long term shock absorption performance and abrasion resistance, etc. However, the polyester fiber obtained via the controlled melt-spinning and stretch process shows a high work/recovery ratio, whereby it raises the shock absorption performance of the fiber rope and can increase the life time of the rope. Furthermore, the polyester fiber of the present invention is characterized by the minimized stretch as well as the excellent work/recovery ratio. Due to this excellent work/recovery ratio, the polyester fiber solves the problems such as low abrasion resistance, deteriorated shock absorption performance, etc. of the fiber rope prepared from the earlier fibers having low work/recovery ratio, high modulus and low breaking elongation, and can provide the merits such as excellent mechanical properties, more improved shock absorption performance and increased life time of rope.

Herein, the work/recovery ratio of the polyester fiber can be defined as represented in the following Equation 3.

[Equation 3]

Work/recovery ratio of yarn (%) = W₂/Wi x 100

in which, is the value of total work done in extension in the tenacity-elongation curve of yarn measured at room temperature after the cycling test according to the method of American Society for Testing and Materials ASTM D 885; and W₂ is the value of work returned during recovery in the tenacity-elongation curve of yarn measured at room temperature after the cycling test according to the method of American Society for Testing and Materials ASTM D 885.

Herein, the total work done in extension (W_\) corresponds to the value of area of the tenacity-elongation curve of the yarn measured at room -temperature after performing the cycling test according to the method of American Society for Testing and Materials ASTM D 885, as depicted in Figure 1. Also, the work returned during recovery (W₂) corresponds to the value of area of the tenacity-elongation curve measured when the yarn is pulled with the force corresponding to 10%, 20%, 30%, 50%, etc. of the maximum load and then liberated, as depicted in Figure 1. In the case that the work/recovery ratio of a fiber is as low as that of the earlier polyester fibers in the field of marine rope used for the anchorage, mooring, etc. of a ship, the rope cannot sufficiently deal with the deformation due to the movement of a ship under the ocean change during the mooring of the ship, and furthermore it loses the work/recovery ratio after use for some period, resulting in lacking the ability of holding the ship during the mooring thereof.

In the polyester fiber of the present invention, the load condition of 10% or more of the maximum load in the cycling repetitive test related to the frequent external environmental changes means the range that a mooring ship is able to deform a rope through the usual movement of waves or the tide during the mooring of the ship. Also, the load condition of 50% or more of the maximum load means the range that a mooring ship is able to deform a rope through the typhoon or wild wind during the mooring of the ship. Here, the maximum load of the polyester fiber measured at room temperature corresponds to the value of load at breaking in the tenacity-elongation curve of yam measured at room temperature.

Also, the polyester fiber of the present invention may show the tenacity retention of 90% or more, or 90% to 100%, preferably 92% or more, and more preferably 95% or more, and the breaking elongation retention of 90% or more, or 90% to 120%, preferably 92% or more, and more preferably 95% or more, when measured at room temperature under the load condition of 10% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 10% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

The polyester fiber may show the tenacity retention of 80% or more, or 80% to 100%, preferably 82% or more, and more preferably 85% or more, and the breaking elongation retention of 80% or more, or 80% to 120%, preferably 82% or more, and more preferably 85% or more, when measured at room temperature under the load condition of 50% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 50% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

Herein, the tenacity retention of the polyester fiber can be defined as represented in the following Equation 4.

[Equation 4]

Tenacity retention (%) after cycling test of yarn = (Tenacity of fiber after cycling test / Tenacity of fiber before cycling test) ^χ 100

Also, the breaking elongation retention of the polyester fiber can be defined as represented in the following Equation 5.

[Equation 5]

Breaking elongation retention (%) after cycling test of yarn = (Breaking elongation of fiber after cycling test / Breaking elongation of fiber before cycling test) ^χ 100

Due to the excellent work/recovery ratio and the excellent tenacity/breaking elongation retention characteristics in the repetitive deformation test, the polyester fiber of the present invention is capable of dealing with the deformation due to the movement of a ship under the ocean change during the mooring of the ship, and as well can exhibit excellent work/recovery ratio after a long-term use thereof to maintain the maximum performance of holding the ship during the mooring of the ship.

On the other hand, the earlier polyester generally has a molecular structure having a high stiffness, whereby it shows a high modulus and provides a fiber rope having significantly inferior shock absorption performance, abrasion resistance, etc. However, the polyester fiber obtained via the controlled melt-spinning and stretching steps exhibits the characteristics of high tenacity and low modulus, and also exhibits the initial modulus lower than the previously known polyester-based industrial yarn.

In particular, the polyester fiber of the present invention may exhibit the initial modulus as mentioned above of 40 to 100 g/d, preferably 50 to 100 g/d, and more preferably 55 to 100 g/d. The polyester fiber may also show the feature of minimized stretch along with such a low initial modulus. In other words, the polyester fiber may be elongated at room temperature by 0.5% or more, or 0.5% to 1.5%, preferably 0.7% or more, or 0.7%» to 1.2% at the stress of 1.0 g/d, it may be elongated by 4.3% or more, or 4.3% to 20%, preferably 4.5% or more, or 4.5% to 18% at the stress of 4.0 g/d, and it may be elongated by 7.5% or more, or 7.5% to 25%, preferably 7.8% or more, or 7.8% to 20% at the stress of 7.0 g/d. Due to such characteristics as low initial modulus and low stretch, the polyester fiber can solve the problem of the fiber rope comprising the earlier fiber of high modulus and low breaking elongation which shows low abrasion resistance and low shape stability, leading to the deterioration of the mechanical properties when used for a long time to result in the deteriorated performance, etc. as a rope, and can provide more improved shock absorption performance and increased life time of the rope as well as excellent mechanical properties.

On the other hand, the polyester fiber may have the Young's modulus measured according to the method of American Society for Testing and Materials ASTM D 885 of 60 to 100 g/de, preferably 75 to 95 g/de, at the degree of elongation of 1%, i.e., at the point that the fiber is elongated by 1%, and it may have the Young's modulus of 20 to 60 g/de, preferably 22 to 55 g/de, at the degree of elongation of 2%, i.e., at the point that the fiber is elongated by 2%. In comparison with the earlier polyester fiber as the typical industrial fiber which has the Young's modulus of 110 g/de or more at the point that the fiber is elongated by 1%, and that of 80 g/de or more at the point that the fiber is elongated by 2%, the polyester yarn of the present invention may be recognized as having remarkably low modulus.

Herein, the modulus of said polyester fiber is a physical property value of modulus of elasticity obtained from the slope of elastic region of the stress-strain curve created during a tensile test. It is a value corresponding to a modulus of elasticity which represents the degree of elongation and deformation when the object is elongated from both sides. Fibers with high modulus have high elasticity but cannot be easily deformed so that the force generated in the course of blocking the movement of a ship may be focused on the rope, leading to the rope break. On the contrary, when the fibers have extremely low modulus, the force focused on the rope may be reduced by deformation, but the severe movement of ship may cause the damage of the ship during the mooring. In this way, the fiber rope prepared from the polyester fiber having an initial modulus in the range lower than the earlier fibers solves the problems such as low abrasion resistance, deteriorated shock absorption performance, etc. of the fiber ropes prepared from the earlier polyester fibers, and solves the problems such as tenacity deterioration due to the UV, tenacity deterioration due to the moisture absorption, stiffness, etc. shown in the nylon ropes to give excellent mechanical properties and excellent physical properties such as abrasion resistance, shape stability, low moisture absorption, light resistance, shock absorption performance, etc.

Also, the polyester fiber may show the intrinsic viscosity more improved than the previously known polyester fibers, i.e., 0.8 dl/g or more, or 0.8 dl/g to 1.2 dl/g, preferably 0.85 dl/g or more, and more preferably 0.90 dl/g or more. It is desirable to secure the intrinsic viscosity in said ranges in order to express good mechanical properties and excellent abrasion resistance when a rope is prepared using the polyester fiber.

The intrinsic viscosity of yarn should preferably be 0.8 dl/g or more to exhibit high tenacity with low stretch and to satisfy the tenacity required in fiber ropes for marine or industrial materials. Otherwise, high stretch may be necessary for the expression of desirable physical properties. By applying such a low stretch to secure long chains, the tangles between chains and entropy are increased to prevent slipping between chains due to the external deformation. Otherwise, i.e., if short chains are secured, the slipping between chains is generated due to the external deformation, whereby shape deformation happen, mechanical and physical properties of rope are changed, and in particular elasticity is deteriorated, and accordingly the role as a buffer against the external deformation cannot be played. Thus, it is desirable to maintain the intrinsic viscosity of yarn at 0.8 dl/g or more so as to exhibit high tenacity property through the application of low stretch. Furthermore, if the intrinsic viscosity of the polyester fiber exceeds 1.2 dl/g, the stretch tension may be raised during the stretching step to cause some procedural problems, and thus 1.2 dl/g or less is more preferable. In particular, the polyester fiber of the present invention keeps such a high degree of intrinsic viscosity so that it may secure the high tenacity sufficient to be effectively used for anchorage, mooring, towage, etc. of a ship and at the same time it may be endowed with more improved shock absorption characteristic for the ship rolling, etc. according to the change of external environment.

Thus, it becomes possible to prepare the fiber rope for marine or industrial materials, which concurrently shows the excellent mechanical properties, abrasion resistance and shock absorption effect by using the polyester fiber exhibiting high elongation, preferably high intrinsic viscosity, under the condition of such repetitive deformations.

Therefore, if said polyester fiber is used, it is possible to sufficiently deal with the deformation due to the movement of a ship under the ocean change, and furthermore it is possible to exhibit excellent work/recovery ratio after a long-term use thereof to maintain the maximum performance of holding the ship during the mooring of the ship. Also, if said polyester fiber is applied for the fiber rope for marine or industrial materials, it significantly lowers the deterioration of tenacity caused by the movement of a ship according to the continuous ocean change and the deterioration of tenacity for moisture absorption, UV light, etc. to secure excellent mechanical properties and tenacity retention. Simultaneously, due to such characteristics of yarn as low initial modulus, high breaking elongation and excellent shape stability, deterioration of the characteristics of the fiber rope caused by the long term deformation thereof from the rolling, etc. of a ship or support according to the external changes of tide circulation, atmosphere circulation, etc. may be prevented to significantly reduce the occurrence of fiber break, etc.

On the other hand, the polyester fiber according to one embodiment of the invention may show the tensile strength of 8.8 g/d or more, or 8.0 g/d to 32.0 g/d, and preferably 9.0 g/d or more, and the breaking elongation of 15% or more, or 15% to 30%, and preferably 16% or more. Also, when said polyester fiber is subjected to the cycling test as specifically mentioned above, it may show the strength at break of 7.0 g/d or more, or 7. g/d to 11.0 g/d, preferably 7.3 g/d or more, and more preferably 7.5 g/d or more, and the elongation at break of 15% or more, or 15% to 30%, and preferably 16% or more.

Said polyester fiber may also show the dry heat shrinkage of 1.0% or more, or 1.0% to 15%), and preferably 1.2% or more, and the toughness value of25x10^"1 g/d or more, or 25x10^" g/d to 46x10^"1 g/d, and preferably 31 10^"1 g/d or more. As above, the polyester fiber of the present invention keeps the optimum high level of dry heat shrinkage and toughness, whereby it secures the mechanical properties enabling the toleration against the external environment.

As already explained in detail above, by securing the intrinsic viscosity, initial modulus, elongation, etc. in optimum ranges, the polyester fiber of the present invention can have the excellent strength and physical properties as well as exhibit excellent performances in abrasion resistance and UV tenacity retention, etc. when it is converted to a fiber rope.

The polyester fiber may have the monofilament fineness of 21 DPF or less, or 3 to 21 DPF, preferably 20 DPF or less, or 4 to 20 DPF. In order for said polyester fiber to be effectively used as a rope for marine, industrial materials, etc., it must be produced to have thick-fineness in the aspect of productivity. For the expression of physical properties, the lower fineness the fiber has, the better it is. Thus, the total fineness of the applicable polyester fiber may be 900 denier or higher, or 900 to 4,500 denier, and preferably 1,000 denier or higher, or 1 ,000 to 4,000 denier. As the number of filament of yarn increases, it can give softer touch. However, if the number is too high, the spinning ability and the abrasion resistance are not good. Thus, the number of filament may be 110 to 550, preferably 120 to 550.

Also, said polyester fiber may further comprise additives, if needed, in order to prevent the filament damage during the spinning, improve the friction resistance of the yarn, and minimize the tenacity deterioration. In particular, said polyester fiber, i.e., polyester yarn may comprise one or more inorganic additives selected from the group consisting of Ti0₂, Si0₂, BaS0₄, etc. In this case, the inorganic additives may be contained in the amount of 100 to 1,500 ppm, preferably 200 to 1,200 ppm, with respect to said polyester fiber, i.e., polyester yarn. The inorganic additives may be contained in the amount of 100 ppm or more, preferably 200 ppm, in the aspect of spinning ability, and may be contained in the amount of 1,500 ppm or less, preferably 1,200 ppm or less, in the aspect of expression of excellent tenacity.

On the other hand, the polyester fiber according to one embodiment of the invention as mentioned above may be prepared by performing melt-spinning of the polyester polymer to give undrawn yarn and by stretching the undrawn yarn. As mentioned above, the specific condition or procedure of each step may be directly/indirectly reflected to the physical properties of the polyester fiber to give the polyester fiber having the above stated physical properties.

In particular, it has been found that the process optimization as above may secure the polyester fiber which has the creep characteristic so that the permanent deformation may not easily occur by the external force and which is remarkably excellent in the work/recovery ratio according to the repetitive deformation, in comparison to the earlier polyester yarns. Particularly, through such optimization of the process, there may be prepared the polyester fiber characterized by the high tenacity, high breaking elongation, i.e., the elongation of 6.8% or more at 50% of the maximum load (MBL) measured at room temperature, which enable to sufficiently deal with the deformation due to the movement of a ship under the ocean change during the mooring of the ship. Thus, such polyester fiber shows some ranges of high elastic recovery, high tenacity and high elongation at the same time and may be desirably applied to the rope for marine or industrial materials having excellent mechanical properties, abrasion resistance and shock absorption performance.

The process for preparing such polyester fiber will be explained step by step more in detail as follows.

The process for preparing the polyester fiber comprises the steps of performing melt-spinning of the polyester polymer having the intrinsic viscosity of 0.9 dl/g or more at 260 ^°C to 310 ^°C to give undrawn polyester yarn, and stretching the undrawn polyester yarn.

First, by referring to the appended drawings, the embodiments of melt-spinning and stretching of the present invention can be briefly explained so that a skilled artisan in this field may easily practice.

Figure 2 is a diagram schematically showing process for preparing the polyester fiber, which comprises the steps of said melt-spinning and stretching. As shown in Figure 2, the inventive polyester fiber for a rope is prepared by melting the polyester chip obtained as explained above, cooling the melted polymer which is spun through a spinneret using quenching-air, adding spinning oil to the undrawn yarn using a spinning oil roll (220, or oil-jet), and uniformly dispersing the spinning oil added to the undrawn yarn on the surface of yarn at a constant air pressure using a pre-interlacer (230). Then, the stretching step is performed in a multi-stage stretching machine (241~246), and finally the yarn is intermingled at a constant pressure in the second interlacer (250) and is wound in a winding machine to give a yarn.

In the process of the present invention, the polyethylene terephthalate-containing polymer having high viscosity is first subjected to melt-spinning to give the polyester undrawn yarn.

In this case, in order to obtain the polyester undrawn yarn satisfying the ranges of low initial modulus and high elongation, it is desirable to carry out said melt-spinning step at a range of low temperature so that the thermal decomposition of the polyester polymer may be minimized. In particular, in order to minimize the property deterioration during the process in regard to the intrinsic viscosity, CEG content, etc. of the highly viscous polyester polymer, i.e., in order to maintain high intrinsic viscosity and low CEG content, spinning may be carried out at a low temperature of, for example, 260 to 310 ^°C , preferably 270 to 305 ^°C, more preferably 272 to 300 ^°C, and still more preferably 280 to 298 ^°C . Herein, the spinning temperature refers to the temperature of an extruder. When the melt-spinning step is carried out at a temperature exceeding 310 ^°C, the thermal decomposition of polyester polymer occurs in a large amount, leading to the lowering of intrinsic viscosity, decrease of molecular weight and increase of CEG content, which is not desirable since the overall deterioration of physical properties may be caused due to the surface damage of the yarn. On the contrary, if the melt-spinning step is carried out at less 260 ^°C , the melting of polyester polymer can hardly be carried out and the spinning ability may be deteriorated due to the N/Z surface cooling. Thus, it is desirable to carry out the melt-spinning step at the temperature within the above mentioned range.

It is desirable that the polyester polymer comprises polyethylene terephthajate (PET) as the main component. Polyethylene terephthalate (PET) may contain a variety of additives which have been added during the step of preparation. In order to secure excellent physical properties of the fiber rope, it may be comprised in an amount of at least 70 mol% or more, more preferably 90 mol% or more. Also, the polyester polymer may further comprise one or more inorganic additives selected from the group consisting of Ti0₂, Si0₂, BaS0₄, etc., if necessary. These inorganic additives may be contained in the amount of 100 to 1,500 ppm, preferably 200 to 1,200 ppm, with respect to the polyester polymer. The inorganic additives may be contained in the amount of 100 ppm or more, preferably 200 ppm or more, in the aspect of spinning ability, and may be contained in the amount of 1,500 ppm or less, preferably 1 ,200 ppm or less, in the aspect of expression of excellent tenacity.

As a result of experiment, it has been found that as the melt-spinning step of PET is carried out at such a low temperature range, the decomposition reaction of the polyester polymer is minimized to give the polymer having high intrinsic viscosity and high molecular weight. Accordingly, in the subsequent stretching step, a yarn having high tenacity can be obtained without applying a high stretch rate. Since a low stretching step can be applied in this way, it becomes possible to effectively lower the modulus to obtain the polyester fiber satisfying the above stated physical properties.

Furthermore, melt-spinning of the polyester polymer may be controlled to a low speed of 300 to 1,000 m/min, preferably 350 to 700 m/min, so that the melt-spinning step may be carried out under low spinning tension, i.e., the spinning tension may be minimized, in the aspect of minimizing the decomposition reaction of the polyester polymer. If the melt-spinning step of the polyester polymer is carried out under the selectively low spinning tension and spinning speed as above, the decomposition reaction of the polyester polymer can be further minimized.

On the other hand, the undrawn yarn obtained from such melt-spinning step may exhibit the intrinsic viscosity of 0.8 dl/g or more, or 0.8 dl/g to 1.2 dl/g, preferably 0.85 dl/g or more, or 0.85 dl/g to 1.2 dl/g, and more preferably 0.9 dl/g or more, or 0.9 dl/g to 1.2 dl/g.

In particular, as specifically mentioned above, in order to prepare the polyester fiber having high tenacity and low modulus, it is desirable that the highly viscous polyester polymer, e.g., the polyester polymer having the intrinsic viscosity of 0.9 dl/g or more, is used in the preparing process of undrawn yarn, whereby the viscosity range is maintained as high as possible through the melt-spinning and stretching to effectively lower the modulus by exhibiting the high tenacity with low stretch. However, it is more preferable that the polymer has the intrinsic viscosity of 2.0 dl/g or less to prevent both the chain break due to the melting temperature increase of the polyester polymer and the pressure increase due to the amount of extrusion in the spinning pack.

And, it is desirable that the PET chip is spun through a spinneret designed so that the polyester may have the monofilament fineness of 21 DPF or less, or 3 to 21 DPF, and preferably 20 DPF or less, or 4 to 20 DPF. In other words, it is desirable that the monofilament fineness of said fiber is 4.0 DPF or more in order to reduce the possibility of yarn breaking caused by the interference with each other upon cooling and the occurrence of yarn breaking during the spinning. It is more desirable that the monofilament fineness of said fiber is 20 DPF or less to increase the cooling efficiency.

Also, said PET undrawn yarn may be prepared by adding a cooling step after the melt-spinning of said PET. Such a cooling step is preferably carried out by giving cooling air of 15 to 60 ^°C , and it is desirable to control the cooling air speed to 0.4 to 1.5 m/s at each temperature condition of the cooling air. The PET undrawn yarn showing all the physical properties according to one embodiment of the invention may thus be more easily prepared.

On the other hand, after the polyester undrawn yarn is prepared through such a spinning step, the undrawn yarn is stretched to give a drawn yarn. Here, the stretching step may be carried out under the total stretch ratio condition of 5.0 to 6.5, preferably 5.0 to 6.2. The above polyester undrawn yarn is under the situation that the high intrinsic viscosity and low initial modulus are kept by optimizing the melt-spinning step. Thus, if the stretching step is carried out under the condition of high stretch ratio exceeding 6.5, the overstretch level may generate yarn breaking, broken yarn, etc. in said drawn yarn, and a yarn having low elongation and high modulus may be prepared due to the high degree of orientation of fiber. Particularly, in the case that the elongation of yarn is deteriorated and the modulus thereof is increased under such a high stretch ratio condition, the fiber rope thus prepared may not be good in abrasion resistance, shape stability, tenacity retention, etc. On the contrary, if the stretching step is carried out under comparatively low stretch ratio, the degree of orientation of fiber is low and thus the polyester fiber prepared therefrom may have somewhat low strength. However, if the stretching step is carried out under the stretch ratio of 5.0 or more in the aspect of physical properties, it is possible to prepare a polyester fiber having high tenacity and low modulus to be suitably applied to, for example, a fiber rope for marine and industrial materials. Thus, it is desirable to carry out the stretching step under the stretch ratio condition of 5.0 to 6.5.

According to another suitable embodiment of the invention, the preparation of polyester fiber having low modulus and at the same time satisfying high strength and low shrinkage by a direct spinning stretching step may comprise the steps of melt-spinning the highly viscous polyethylene terephthalate polymerization chip, followed by passing through the multi-stage godet roller, subjecting to stretching, thermal fixing, releasing and winding until being wound in a winder.

The stretching step may be carried out after the undrawn yarn is passed through the godet roller under the condition of oil pick up amount of 0.2% to 2.0%.

The release rate during the releasing step is preferably 1% to 14%. In the case of less than 1%, the shrinkage rate can hardly be expressed, and it may be difficult to prepare the fiber having high elongation and low modulus due to the formation of high degree of orientation of fiber, as in the condition of high stretch ratio. In the case of exceeding 14%, workability cannot be secured due to the severe tremor of filament on the godet roller.

In addition, the stretching step may further comprise the thermal fixing step wherein said undrawn yarn is subjected to thermal treatment under the temperature of about 170 to 250 ^°C . The thermal treatment may be performed preferably at the temperature of 175 to 240 ^°C , more preferably at the temperature of 180 to 245 ^°C , for the appropriate progress of the stretching step. If the temperature is less than 170 ^°C , the thermal effect is not sufficient so that the release efficiency may be deteriorated, making the achievement of shrinkage rate difficult. If the temperature exceeds 250 ^°C , the strength of yarn may be lowered due to the thermal decomposition and the tar formation on the roller may be increased to deteriorate workability.

The winding speed may be controlled to 2,000 to 4,000 m/min, preferably 2,500 to 3,700 m/min.

On the other hand, the polyester fiber of the present invention shows remarkably excellent characteristics such as high tenacity, high elongation, creep characteristic which prevents the permanent deformation by the external force and high work/recovery ratio against the repetitive deformation, in comparison to the earlier polyester yarns. Thus, it may be suitably applied to industrial materials of various utilities such as marine ropes used for anchorage, mooring, towage, etc. of a ship, ropes for industrial materials used in a variety of construction sites, etc.

Particularly, the polyester fiber of the present invention may be converted to the polyester fiber ropes for marine or industrial materials via the steps of twisting or twining threads. The fiber rope may be prepared by the steps of twisting and twining threads in one same apparatus.

The present invention provides the polyester fiber rope comprising said polyester fiber. When a rope is prepared from said polyester fiber, the elongation at 50% of the maximum load (MBL) measured at room temperature may be 9% or more.

As specifically mentioned above, if a rope is prepared using the inventive polyester fiber having the elongation of 6.8% or more at 50% of the maximum load (MBL) measured at room temperature, excellent tenacity-elongation characteristics as well as excellent shape stability may be concurrently secured. In particular, the rope prepared from the polyester fiber according to the present invention shows the excellent elongation of 9% or more at 50% of the maximum load, whereby the external environments such as changes caused by the typical tide or movement of a ship caused by the waves can be sufficiently dealt with to prevent damages of the ship and rope.

The polyester fiber rope of the present invention may have the elongation at 50% of the maximum load (MBL) measured at room temperature of 9% or more, or 9% to 30%, preferably 9.5% or more, and more preferably 10% or more. Due to the excellent shape stability and the excellent elongation at 50% of the maximum load (MBL), the inventive rope is capable of sufficiently dealing with the deformation caused by the movement of a ship according to the ocean change during the mooring, and can maintain the maximum performance of holding the ship during the mooring thereof without losing its mechanical properties when used for a long time.

The polyester fiber rope may have the creep rate of 15.0% or less, which is defined by the following Equation 2, when it is allowed to stand for 7 days under 50% load of the breaking tenacity of the rope.

[Equation 2]

Creep rate of rope = (L₃-L₄)/L₄ x 100

in which L₃ is the length of rope measured after applying the load for 7 days, and

L₄ is the initial length of rope.

When the rope is allowed to stand for 7 days under 50% load of the breaking tenacity of the fiber, the creep rate calculated by the above mentioned method may be 15.0% or less, preferably 14% or less, and more preferably 13% or less.

The fiber rope prepared from the polyester fiber of the present invention may have the breaking tenacity per unit diameter (mm) of rope of 0.57 ton/mm or more, or 0.57 to 1.2 ton/mm or more, preferably 0.59 ton/mm or more, or 0.67 ton/mm or more, 0.69 ton/mm or more, or 0.72 ton/mm or more. The breaking elongation may be 15% or more, or 15% to 45%, preferably 17% or more, or 18% or more, 20% or more, or 24% or more. Also, the fiber rope may have the moisture absorption rate of 2% or less, preferably 1% or less, or preferably 0.5% or less wherein the moisture absorption rate of the rope is the result measured under the conditions of 25 ^°C and 65% relative humidity.

The polyester fiber rope of the present invention may show the work/recovery ratio of 90% or more, or 90% to 100%, preferably 92% or more, and more preferably 95% or more when measured at room temperature under the load condition of 10% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 10% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

The polyester fiber rope of the present invention may show the work/recovery ratio · of 50% or more, or 50% to 95%, preferably 52% or more, and more preferably 55% or more when measured at room temperature under the load condition of 50% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 50% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

Herein, the work/recovery ratio of the polyester fiber rope can be defined as represented in the following Equation 6.

[Equation 6]

Work/recovery ratio of rope (%) = W₄/W₃ 100

in which, W₃ is the value of total work done in extension in the tenacity-elongation curve of rope measured at room temperature after the cycling test according to the method of American Society for Testing and Materials ASTM D 885; and W is the value of work returned during recovery in the tenacity-elongation curve of rope measured at room temperature after the cycling test according to the method of American Society for Testing and Materials ASTM D 885.

Herein, the total work done in extension (W₃) and the work returned during recovery (W₄) of the fiber rope may be defined as specifically mentioned above in regard to the polyester fiber. Also, the maximum load of the polyester fiber rope measured at room temperature corresponds to the load value at breaking from the tenacity-elongation curve of the fiber rope measured at room temperature.

On the other hand, the polyester fiber rope of the present invention may show the tenacity retention of 90% or more, or 90% to 100%, preferably 92% or more, and more preferably 95% or more, and the breaking elongation retention of 90% or more, or 90% to 120%, preferably 92% or more, and more preferably 95% or more, when measured at room temperature under the load condition of 10% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 10% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

The polyester fiber rope may also show the tenacity retention of 80% or more, or 80% to 100%, preferably 82% or more, and more preferably 85% or more, and the breaking elongation retention of 80% or more, or 80% to 120%, preferably 82% or more, and more preferably 85% or more, when measured at room temperature under the load condition of 50% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 50% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

Herein, the tenacity retention of the polyester fiber rope can be defined as represented in the following Equation 7. [Equation 7]

Tenacity retention after cycling test of rope (%) = (Tenacity of rope after cycling test / Tenacity of rope before cycling test) x 100

Also, the breaking elongation retention of the polyester fiber rope can be defined as represented in the following Equation 8.

[Equation 8]

Breaking elongation retention after cycling test of rope (%) = (Breaking elongation of rope after cycling test / Breaking elongation of rope before cycling test) ^χ 100

The polyester fiber rope of the present invention shows high tenacity, high elongation, excellent shape stability, high work/recovery ratio, etc. and at the same time minimizes moisture absorption rate. Thereby, it can have excellent mechanical properties in the fields of anchorage, mooring, towage, etc. of a ship, or a variety of construction sites, etc. and can effectively deal with the external environmental changes, securing the extended life t^'ime of rope and sufficient safety.

The matters other than those described above regarding the present invention can be added or deleted, if necessary. Thus, they are not specifically limited in the present invention

[EFFECT OF THE INVENTION]

According to the present invention, there is provided a polyester fiber having excellent mechanical properties as well as excellent abrasion resistance, tenacity retention, etc. by optimizing the elongation range at 50% of the maximum load (MBL) measured at room temperature to a high level, on the basis of the maximum load which is the deformation of a fiber rope from the rolling, etc. of a ship according to the marine environment during the actual mooring of a ship.

Such a polyester fiber can secure sufficient degree of tenacity-elongation, excellent mechanical properties and shock absorption performance by optimizing the high tenacity, high elongation, excellent shape stability, work/recovery ratio after repetitive deformations, etc. to given ranges. Thereby, it can be used to prepare the polyester fiber rope which may minimize the yarn breaking even under the changes of external environments such as wild marine, severe ship rolling, etc., remarkably improve the shock absorption performance through the high elongation, and secure the sufficient safety along with the excellent life time of rope.

[BRIEF DESCRIPTION OF THE DRAWINGS]

Figure 1 represents tenacity-elongation curve of a typical fiber, and work/recovery ratio (%) can be measured from the area of such tenacity-elongation curve.

Figure 2 represents a diagram schematically showing the process for preparing the polyester fiber according to one embodiment of the present invention.

Figure 3 represents a schematic diagram of a creep tester used for the measurement of creep rate according to one embodiment of the present invention.

[BESTMODE FOR CARRYING OUT THE INVENTION]

Hereinafter, the Examples are provided to assist the understanding of the present invention but the following Examples are only for the illustration of the present invention and it is not intended that the scope of the present invention is limited in any manner by them.

Examples 1~5

A polyester undrawn yarn was prepared by subjecting the polyester polymer having a given intrinsic viscosity to melt-spinning and cooling. This undrawn yam was stretched by a given stretch ratio and subjected to thermal treatment to give a polyester fiber. The intrinsic viscosity of the polyester polymer, spinning speed, spinning tension, spinning temperature, stretch ratio and temperature of the thermal treatment at the time of melt-spinning step are represented in the following Table 1. The other conditions were the same as typical conditions for preparing the polyester fiber.

[Table 1]

Spinning temperature ( ^°C ) 282 285 288 290 292

Stretch ratio 5.8 5.78 5.75 5.65 5.60

Temperature of thermal 233 235 236 238 240

treatment (^°C)

Physical properties of the polyester fibers obtained from Examples 1~5 were measured according to the following methods, and the physical properties thus measured are summarized in the following Table 2.

1) Tensile strength and elongation

Tensile strength and elongation of a fiber are measured using a universal testing . machine (Instron) according to the method of American Society for Testing and Materials ASTM D 2256 wherein the length of sample is 250 mm, the tensile speed is 300 mm/min and the initial load is 0.05 g/d.

In addition, the tensile strength and elongation of the fiber are further measured after 5 to 10 times of cycling tests under the load of 3.5 g/d according to the method of American Society for Testing and Materials ASTM D 885.

2) Initial modulus

Young's modulus and tenacity-elongation are measured according to the method of American Society for Testing and Materials ASTM D 885, and are represented in the following Table 2.

3) Elongation at 50% of the maximum load

Tenacity-elongation of the yarn is measured at room temperature according to the method of American Society for Testing and Materials ASTM D 2256 to confirm the maximum load at break. Then, elongation (%) of yarn at 50% of this maximum load is measured.

4) Creep rate Creep rate is measured using a creep tester as depicted in Figure 3. Using such a creep tester, 50% of the breaking tenacity is exerted as the initial load to the polyester yarns obtained from Examples 1 to 5 (initial length of sample L₂ = 1,400 mm) to measure the length change. In particular, as represented in the following Equation 1 , the fiber is fixed by hanging it to the creep tester so that the initial length L₂ becomes 1 ,400 mm, and then the fiber is allowed to stand for 7 days under the 50% load of the breaking tenacity of the fiber before the total length (mm) of thus deformed fiber is measured.

[Equation 1]

Creep rate of fiber = (Li-L₂)/L₂ 100

in which

is the length of yarn measured after applying the load for 7 days, and

L₂ is the initial length of yarn when the sample is fixed to the creep tester, which is 1 ,400 mm here.

5) Work/recovery ratio

After confirming the maximum load through the measurements of breaking tenacity and breaking elongation of yarn according to the method of American Society for Testing and Materials ASTM D 885, deformations as much as corresponding to 10% and 50% of the final load are exerted. After 10 times of repetition, the work/recovery ratio (%) of the yarn is measured according to the following Equation 3.

[Equation 3]

Work/recovery ratio of yarn (%) = W₂/Wi ^χ 100

in which,

the value of total work done in extension in the tenacity-elongation curve of yarn measured at room temperature after the cycling test according to the method of American Society for Testing and Materials ASTM D 885; and W₂ is the value of work returned during recovery in the tenacity-elongation curve of yarn measured at room temperature after the cycling test according to the method of American Society for Testing and Materials ASTM D 885.

6) Tenacity retention and breaking elongation retention

Tenacity retention of yarn is measured as represented in the following Equation 4 under the load condition of 10%, 50% of the maximum load measured at room temperature, after 10 times repetition of cycling tests under the load condition of 10%, 50% of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

[Equation 4]

[Equation 5]

Breaking elongation retention (%) after cycling test of yarn = (Breaking elongation of fiber after cycling test / Breaking elongation of fiber before cycling test) x 100

7) Dry heat shrinkage

Dry heat shrinkage is measured using Testrite MK-V instrument from the British company Testrite under the conditions of 180 ^°C , 2 min and initial load of 0.05 g/d.

8) Intrinsic viscosity

After extracting the spinning oil from the sample using carbon tetrachloride and dissolving in OCP (Ortho Chloro Phenol) at 160±2 ^°C , the viscosity of sample in a viscosity tube is measured using an automatic viscometer (Skyvis-4000) at the temperature of 25 ^°C , and the intrinsic viscosity (IV) of the polyester fiber is calculated according to the following Equation 9.

[Equation 9]

Intrinsic viscosity (IV) = {(0.0242 ^χ Rel) + 0.2634} ^χ F

in which

Rel = (seconds of solution x specific gravity of solution ^χ viscosity coefficient) / (OCP viscosity), and

F = (IV of the standard chip) / (average of three IV measured from the standard chip with standard action) 9) Monofilament fineness

Monofilament fineness is measured according to the method of picking the yarn of 9000 m by using a reel, weighing the fiber to obtain the total fineness (Denier) of the yarn, and dividing the total fineness by the number of filaments.

10) Breaking tenacity of fiber

Breaking tenacity (kgf) of fiber is measured using a universal testing machine (Instron) according to the method of American Society for Testing and Materials ASTM D 2256 wherein the length of sample is 250 mm, the tensile speed is 300 mm/min and the initial load is 0.05 g/d.

[Table 2]

Creep rate (%) 7.8 6.9 6.2 5.6 4.8

Elongation at stress of 1.Og/d

0.71 0.82 0.85 0.93 1.10 (%)

Elongation at stress of 4. Og/d

6.02 6.51 7.12 7.61 8.51 (%)

Elongation at stress of 7. Og/d

7.60 7.81 8.12 9.22 10.41 (%)

Work/recovery ratio at 10% of 95.9 96.1 96.2 96.5 96.9 the maximum load (%)

Work/recovery ratio at 50% of 51.2 52.6 53.8 54.9 55.9 the maximum load (%)

Tenacity retention after cycling

test at 10% of the maximum 95.1 94.8 96.5 95.8 96.0 load (%)

Comparative Examples 1-5

Polyester fibers of Comparative Examples 1~5 were prepared according to the same procedure as Examples 1~5 except for the conditions as represented in the following Table 3:

[Table 3]

Physical properties of the polyester fibers obtained from Comparative Examples 1~5 were measured in the same manner as specified above and summarized in the following Table 4.

[Table 4]

Work/recovery ratio at 50% of 38.2 38.5 38.7 39.2 39.3 the maximum load (%)

Tenacity retention after cycling

test at 10% of the maximum load 86.2 87.7 87.6 88.5 88.2

(%)

Preparations 1~5

The polyester fibers obtained from Examples 1-5 were primary-twisted and then secondary-twisted to prepare fiber ropes. Seven (7) fibers were used for the primary twisting and four (4) fibers were used for the secondary twisting, and the sixteen (16) ply yarns thus prepared were combined to make one (1) strand, and eight (8) strands were combined to prepare the final rope. This fiber rope was controlled to have the same final fineness and the diameter of 36 mm.

Physical properties of thus obtained polyester fiber rope were measured according to the following methods. a) Breaking tenacity and breaking elongation

Tenacity and elongation at the time of final breaking of the fiber rope are measured in the manner that both ends of a rope are fixed on rings wherein the length of fiber rope sample is 5,000 mm and the ring at one side is moved at the speed of 1 m per 1 min, i.e., at the speed of 1 m/min, until the rope is broken. b) Elongation at 50% of the maximum load

Breaking tenacity and breaking elongation of a rope are measured to confirm the maximum load. Then, elongation (%) of rope at 50% of this maximum load is measured. c) Creep rate of rope

Creep rate of a fiber rope is measured using a creep tester as depicted in Figure 3. Using such a creep tester, 50% of the breaking tenacity is exerted as the initial load to the polyester fiber ropes obtained from Preparations 1 to 5 (initial length of sample L₄ = 3,000 mm) to measure the length change. In particular, as represented in the following Equation 2, the fiber rope is fixed by hanging it to the creep tester so that the initial length L₄ becomes 3,000 mm, and then the fiber rope is allowed to stand for 7 days under the 50% load of the breaking tenacity of the rope before the total length (mm) of thus deformed rope is measured.

[Equation 2]

Creep rate of rope = (L₃-L₄)/L₄ ^χ 100

in the above Equation 2, L₃ is the length (mm) of rope measured after applying the load for 7 days, and L₄ is the initial length (mm) of rope when the sample is fixed to the creep tester, which is 3,000 mm here. d) Work/recovery ratio

After confirming the maximum load through the measurements of breaking tenacity and breaking elongation of a fiber rope according to the method of American Society for Testing and Materials ASTM D 885, deformations as much as corresponding to 10% and 50% of the final load are exerted. After 10 times of repetition, the work/recovery ratio (%) of the rope is measured according to the folio whig Equation 6.

[Equation 6]

Work/recovery ratio of rope (%) = W₄/W₃ * 100

in which, W₃ is the value of total work done in extension in the tenacity-elongation curve of rope measured at room temperature after the cycling test according to the method of American Society for Testing and Materials ASTM D 885; and W₄ is the value of work returned during recovery in the tenacity-elongation curve of rope measured at room temperature after the cycling test according to the method of American Society for Testing and Materials ASTM D 885. e) Tenacity retention and breaking elongation retention

Tenacity retention of rope is measured as represented in the following Equation 7 under the load condition of 10%, 50% of the maximum load measured at room temperature, after 10 times repetition of cycling tests under the load condition of 10%, 50% of the maximum load according to the method of American Society for Testing and Materials ASTM D 885.

[Equation 7]

Tenacity retention (%) after cycling test of rope = (Tenacity of rope after cycling test / Tenacity of rope before cycling test) ^χ 100

[Equation 8]

Breaking elongation retention (%) after cycling test of rope = (Breaking elongation of rope after cycling test / Breaking elongation of rope before cycling test) * 100 f) Moisture absorption rate

A rope is weighed under the conditions of 25 ^°C and 65% relative humidity, dried for 6 h at 100 ^°C using a drier, and then weighed again. The moisture absorption rate at 25 ^°C and 65% relative humidity is calculated according to the following Equation 10.

[Equation 10]

Moisture absorption rate (%) = (Weight of fiber rope before drying - Weight of fiber rope after drying) / (Weight of fiber rope after drying) ^χ 100 Physical properties of the fiber ropes prepared using the polyester fibers obtained from Examples 1~5 are represented in the following Table 5.

[Table 5]

Work/recovery ratio at 10% 99.2 99.5 98.8 99.3 98.9 of the maximum load (%)

Work/recovery ratio at 50% 65.3 64.8 66.4 66.8 67.4 of the maximum load (%)

Tenacity retention after

cycling test at 10% of the 98.1 97.8 99.5 98.8 99.0 maximum load (%)

Breaking elongation

retention after cycling test at

100.2 99.9 99.6 100.5 101.5 10% of the maximum load

(%)

Tenacity retention after

cycling test at 50% of the 82.6 82.8 83.2 83.8 84.1 maximum load (%)

Breaking elongation

retention after cycling test at

80.4 80.7 81.3 81.7 82.7 50% of the maximum load

(%)

Moisture absorption rate (%) 0.4 0.4 0.4 0.4 0.4

Comparative Preparations 1~5

Fiber ropes were prepared according to the same procedure as Preparations 1~5 except that the polyester fibers obtained from Comparative Examples 1~5 were used. Physical properties of the ropes were measured and represented in the following Table 6. [Table 6]

Breaking elongation (%) 14.1 14.5 15.6 16.3 16.8

Elongation at 50% of the 7.1 7.4 8.1 8.3 8.5 maximum load (%)

Creep rate (%) 18.2 17.5 16.8 16.2 15.8

Work/recovery ratio at 10% 85.2 85.7 86.2 86.5

84.2

of the maximum load (%)

Work/recovery ratio at 50% 47.8 47.1 48.3 48.8 49.1 of the maximum load (%)

Tenacity retention after

cycling test at 10% of the 84.2 85.7 85.6 85.5 85.2 maximum load (%)

Breaking elongation

retention after cycling test at

86.1 86.7 85.5 84.2 85.5 10% of the maximum load

(%)

Tenacity retention after

cycling test at 50% of the 51.1 51.7 53.1 53.1 53.6 maximum load (%)

Breaking elongation

retention after cycling test at

50.6 51.2 51.5 51.9 52.1 50% of the maximum load

(%)

Moisture absorption rate (%) 0.4 0.4 0.4 0.4 0.4

Comparative Preparation 6

A fiber rope was prepared according to the same procedure as Preparation 1 except that a nylon yarn (l,840d, strength 9.0g/d, elongation 26%) was used. Physical properties of the rope were measured and represented in the following Table 7.

[Table 7] Item Com. Preparation 6

Breaking tenacity (Ton) 28.5

Breaking elongation (%) 32.8

Work/recovery ratio at 10% of the maximum load (%) 55.8

Work/recovery ratio at 50% of the maximum load (%) 49.5

Tenacity retention after cycling test at 10% of the 89.2

maximum load (%)

Breaking elongation retention after cycling test at 10% 100.1

of the maximum load (%)

Tenacity retention after cycling test at 50% of the 78.2

maximum load (%)

Breaking elongation retention after cycling test at 50% 88.1

of the maximum load (%)

Moisture absorption rate (%) 4.2

As can be seen from the above Table 5, fiber ropes of Preparations 1~5 prepared from the polyester fibers which are prepared in Examples 1~5 and have high tenacity, high breaking elongation and excellent shape stability have such excellent characteristics as the breaking tenacity of 26.5 to 28.6 ton and breaking elongation of 24.6% to 29.6%. At the same time, the fiber ropes of Preparations 1~5 show the elongation of 10.2% to 13.2% at 50% of the maximum load and thus have the feature of sufficient shock absorption that may be caused by the rolling, etc. of a ship according to the marine environment during the actual mooring of a ship. Also, since the creep rate of rope for 7 days at 50% of the maximum load is between 8.5% and 10.5%, the polyester fiber rope having excellent shape stability may be prepared.

Furthermore, the fiber ropes of Preparations 1-5 show the superior work/recovery ratio of 98.8% to 99.5% after 10 times of repetitive tests at 10% of the maximum load and the superior tenacity retention of 97.8% to 99.5% after the repetitive tests. Also, it is confirmed that the breaking elongation retention is superior as much as 99.5% to 101.5%. Moreover, they show very good results of the work/recovery ratio of 64.8% to 67.4%, tenacity retention of 82.6% to 84.1% and breaking elongation retention of 80.4% to 82.7% even after 10 times of repetitive tests at 50% of the maximum load under the simulated emergent marine environment caused by typhoon and storm.

Accordingly, it can be confirmed that the fiber ropes of Preparations 1~5 have the excellent shape stability, low modulus, high tenacity, high elongation, shock absorption performance, etc. as well as excellent mechanical properties.

On the contrary, as is confirmed by the above Table 6, the fiber ropes of Comparative Preparations 1~5 obtained using the polyester fibers of Comparative Examples 1-5 do not meet such characteristics. In particular, since the fiber ropes of Comparative Preparations 1-5 have the breaking tenacity of 22.4 to 23.3 ton and the breaking elongation of 14.1% to 16.8%, it can be seen that they do not satisfy the physical properties required for the ropes for mooring of a ship and general industrial ropes. Particularly, the fiber ropes of Comparative Preparations 1-5 have insignificant elongation value of 7.1% to 8.5% at 50% of the maximum load which is the deformation of a rope from the rolling, etc. of a ship according to the marine environment during the actual mooring of a ship. Thus, they may not have sufficient absorption performances against shocks from external deformations when they are applied to the mooring or towage of a ship or construction sites.

Also, it can be seen that the ropes show too high creep rate of 15.8% to 18.2% at 50% of the maximum load for 7 days to maintain the excellent shape stability. In particular, if the polyester fiber rope showing such a high creep rate is used for a long time, the initial physical properties of the rope may be easily lost, not satisfying the mechanical properties required under the wild environmental conditions in the waterfront for mooring a ship and causing such problems of not exhibiting suitable performances as a rope.

Moreover, after the repetitive tests in the simulation of actual environment of use, the fiber ropes of Comparative Preparations 1-5 are confirmed to show less than 90% of tenacity retention and breaking elongation retention at 10% of the maximum load and less than 80% thereof at 10% of the maximum load. If the toughness of fiber rope is remarkably deteriorated in this way, the rope may not secure the sufficient mechanical properties when applied to the mooring or towage of a ship or to construction sites. Additionally, as is confirmed by the above Table 7, the fiber rope of Comparative Preparation 6 using a nylon fiber as a typical synthetic fiber shows the moisture absorption of 4.0% at 25 ^°C and 65% relative humidity, and such a remarkably low work/recovery ratio of 55.8% after 10 times of repetitive tests at 10% of the maximum load. In such case of low work/recovery ratio, the initial physical properties of the rope may be easily lost, not satisfying the mechanical properties required under the wild environmental conditions in the waterfront for mooring a ship and causing such problems of not exhibiting suitable performances as a rope.

Claims

[CLAIMS]

[Claim 1 ]

Polyester fiber having the elongation of 6.8% or more at 50% of the maximum load (MBL) measured at room temperature.

[Claim 2]

The polyester fiber according to Claim 1 , wherein the creep rate of fiber as defined by the following Equation 1 is 8.5% or less when it is allowed to stand for 7 days under the 50% load of the breaking tenacity of the fiber:

[Equation 1]

Creep rate of fiber = (L_!-L₂)/L₂ ^χ 100

[Claim 3]

The polyester fiber according to Claim 1, wherein the breaking tenacity of fiber is 13 kgfor more.

[Claim 4]

The polyester fiber according to Claim 1, wherein the tensile strength is 8.8 g/d or more and the breaking elongation is 15% or more.

[Claim 5]

The polyester fiber according to Claim 1, wherein the work/recovery ratio measured at room temperature under the load condition of 10% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 10% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885 is 90% or more.

[Claim 6] The polyester fiber according to Claim 1, wherein the work/recovery ratio measured at room temperature under the load condition of 50% of the maximum load after 10 times or more repetition of cycling tests under the load condition of 50% or more of the maximum load according to the method of American Society for Testing and Materials ASTM D 885 is 45% or more.

[Claim 7]

The polyester fiber according to Claim 5, wherein the tenacity retention is 90% or more and the breaking elongation retention is 90% or more under the load condition of 10% of the maximum load when measured at room temperature after repetition of said cycling tests.

[Claim 8]

The polyester fiber according to Claim 6, wherein the tenacity retention is 80% or more and the breaking elongation retention is 80% or more under the load condition of 50% of the maximum load when measured at room temperature after repetition of said cycling tests.

[Claim 9]

The polyester fiber according to Claim 1, wherein the initial modulus is 40 to 100 g/d, and the fiber is elongated at room temperature by 0.5%» or more at the stress of 1.0 g/d, by 4.3%o or more at the stress of 4.0 g/d, and by 7.5% or more at the stress of 7.0 g/d.

[Claim 10]

The polyester fiber according to Claim 1 , wherein the total fineness is 900 denier or higher.

[Claim 11]

The polyester fiber according to Claim 1 , which shows the monofilament fineness of 21 DPF or less and comprises the number of filament of 110 to 550.

[Claim 12]

A polyester fiber rope comprising the fiber according to any one of Claims 1 to 1 1.

[Claim 13 ]

The polyester fiber rope according to Claim 12, wherein the elongation at 50% of the maximum load (MBL) measured at room temperature is 9% or more.

[Claim 14]

The polyester fiber rope according to Claim 12, wherein the creep rate of rope as defined by the following Equation 2 is 15.0% or less when it is allowed to stand for 7 days under the 50% load of the breaking tenacity of the rope:

[Equation 2]

Creep rate of rope = (L₃-L₄)/L4 ^χ 100

L₄ is the initial length of rope.

[Claim 15]

The polyester fiber rope according to Claim 12, wherein the breaking tenacity per unit diameter (mm) of fiber rope is 0.67 ton/mm or more.

[Claim 16]

The polyester fiber rope according to Claim 12, wherein the breaking elongation is 18% or more.

[Claim 17]

The polyester fiber rope according to Claim 12, wherein the moisture absorption rate is 2% or less.