WO2007139311A1

WO2007139311A1 - A filament for tire cord, a bundle for tire cord comprising the same, a twisted yarn for tire cord comprising the same, and a tire cord comprising the same

Info

Publication number: WO2007139311A1
Application number: PCT/KR2007/002534
Authority: WO
Inventors: Young-Se Oh; Gi-Woong Kim; Woo-Chul Kim; Tae-Won Son; Si-Min Kim
Original assignee: Kolon Industries, Inc.
Priority date: 2006-05-25
Filing date: 2007-05-25
Publication date: 2007-12-06
Also published as: KR101150899B1; KR100995932B1; EP2024541A4; EP2024541A1; KR20100087062A; KR20070114012A

Abstract

The present invention relates to a filament fiber for a tire cord, a bundle for a tire cord including the same, a twisted yarn for a tire cord including the same, and a tire cord including the same, and more particularly, to a non-circular cross-section filament fiber for a tire cord, wherein cross-section shape deviation thereof is more than 1 and 3 or less, a bundle for a tire cord including the same, a twisted yarn for a tire cord including the same, and a tire cord including the same.

Description

TITLE QF THE INVENTION

A FILAMENT FOR TIRE CORD, A BUNDLE FOR TIRE CORD COMPRISING THE SAME, A TWISTED YARN FOR TIRE CORD COMPRISING THE SAME, AND A TIRE CORD COMPRISING THE SAME BACKGROUND OF THE INVENTION (a) Field of the Invention

The present invention relates to a filament fiber for a tire cord, a bundle for a tire cord including the same, a twisted yarn for a tire cord including the same, and a tire cord including the same. More particularly, the present invention relates to a filament fiber for a tire cord having low stress by twisting and having superior mechanical properties, a bundle for a tire cord including the same, a twisted yarn for a tire cord including the same, and a tire cord including the same. (b) Description of the Related Art

Tire cords are used as a framework constituting a tire, and polyester, nylon, rayon, aramid, steel, etc., are used as materials for tire cords.

During driving, tires are exposed to high temperature due to friction, and at the same time, they must endure the weight of the car. The properties of the tires depend on the properties of the tire cord constituting a framework of the tire.

Therefore, the tire cord needs basic properties such as high tenacity and initial modulus, superior heat resistance, superior fatigue resistance and form stability, and good adhesiveness to rubber of the tire.

Recently, use of a tire cord has been determined by the inherent properties thereof, because most of the well-known tire cords satisfy some of the above properties but do not satisfy all of the properties at the same time. Generally, tire cords are prepared by the processes of preparing a cord yarn by twisting filament fibers together, dipping the same in an adhesive solution, and heat-treating the same to prepare a single cord.

Single cords are then formed into a cord fabric by a weaving process, but the properties of the filament fibers, that is the starting materials of the cords, tend to deteriorate as the process proceeds.

As an example, according to Korean Patent Publication No. 2004-0057550, when a tire cord is prepared by twisting and dipping lyocell fibers having 7.5 g/d of initial tenacity, the tenacity was deteriorated to 4.99 g/d, which is 33 % lower than the initial tenacity of the lyocell fibers. Although this result is different according to the kind of filament fiber, it is a general tendency in a tire cord. SUMMARY QF THE INVENTION

It is an aspect of the present invention to provide a non-circular cross-section filament fiber for a tire cord that may lessen the deterioration of the properties during the preparing process and so show superior properties.

It is another aspect of the present invention to provide a bundle including the non-circular cross-section filament fiber.

Still another aspect of the present invention is to provide a twisted yarn including the non-circular cross-section filament fiber. Still another aspect of the present invention is to provide a tire cord including the twisted yarn.

The present invention provides a non-circular cross-section filament fiber for a tire cord, wherein a cross-section shape deviation thereof represented by Equation 1 is more than 1 and 3 or less. [Equation 1]

MR = R²/R'

Wherein, MR is a cross-section shape deviation expressed by the Modification Ratio, R¹ is a radius of the maximum inscribed circle of the cross- section of the fiber, and R is a radius of the minimum circumscribed circle of the cross-section of the fiber.

Further, the present invention provides a filament bundle for a tire cord including the non-circular cross-section filament fibers, wherein the total number of filament fibers is in the range of 200 to 2000. Further, the present invention provides a twisted yarn for a tire cord including the non-circular cross-section filament fibers, wherein the total number of the filament fibers is in the range of 400 to 6000.

In addition, the present invention provides a tire cord including the twisted yarn for a tire cord.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an example of the cross-section of the non-circular cross-section filament fiber.

Fig. 2 is a drawing showing the definition of Z twisting and S twisting. Fig. 3 is a drawing showing the definition of the twisting angle.

Fig. 4 is a graph showing the changes of tensile strength according to an increase of the twisting level (TPM) of the tire cords prepared by Examples 1 to 5 and Comparative Examples 1 to 5.

Fig. 5 is a graph showing the changes of elongation according to an increase of the twisting level (TPM: twisting per meter) of the tire cords prepared by Examples 1 to 5 and Comparative Examples 1 to 5.

Fig. 6 is a cross-sectional photograph of the triangular cross-section filament fiber prepared by Example 6. Fig. 7 is a photograph showing an example for measuring the cross-section shape deviation of the non-circular cross-section filament fiber prepared by Example 6.

Fig. 8 is a graph showing the strength maintaining rate according to an increase of the twisting level (TPM) of the tire cords prepared by Examples 6 to 9 and Comparative Examples 6 to 9.

Fig. 9 is a graph showing the strain maintaining rate according to an increase of the twisting level (TPM) of the tire cords prepared by Examples 6 to 9 and Comparative Examples 6 to 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention is explained in more detail.

Generally, filament fibers having circular cross-section are used as a yarn for a tire cord. However, the properties of the filament fibers having circular cross- section are deteriorated by the twisting process. Also, generally, a fiber, such as yarn, cord, cable, etc., has a twisting structure formed by a twisting process, and clockwise twisting is called S-twisting and counter-clockwise twisting is called Z-twisting, as shown in Fig. 2 ^Perspective in Textile Engineering" , Hyongseol press, 1991. 02. 25., page 216").

Specifically, the tire cord shows changes in strength, elongation, fatigue resistance, intermediate elongation, etc., according to the twisting level (TPM: twisting per meter), and in particular, the strength deteriorates rapidly as the twisting level (TPM) increases.

Through studies for preventing the property deterioration during the twisting process, the present inventors discovered that the filament fibers suffer many stresses in a spiral direction from the axis of the fibers due to the twisting of the fibers, and that the stresses cause the property deterioration. Especially, the tendency worsens as the twisting level increases, and it is more dominantly shown in fibers having a stiff structure. According to the study of the present inventors, the stresses caused by the twisting may be looser on the surface of the filament fibers, and the stresses caused by the twisting lessen as the surface area is large when comparing with filament fibers having the same cross-sectional area.

The present invention is derived from these studies, and it is a technical feature of the present invention that the tire cord includes a non-circular cross- section filament fiber.

The present invention may prevent the properties of the tire cord deteriorating during the manufacturing process or when driving a car, because the surface area of the non-circular cross-section filament fibers of the present invention is larger than that of the circular cross-section filament fibers, and the stress caused by the twisting is therefore decreased.

Therefore, the cross-section shape deviation represented by Equation 1 of the non-circular cross-section filament fibers for the tire cord of the present invention may be more than 1 and 3 or less, further may be 1.1 to 3.0, and further may be 1.3 to 2.5.

When the MR is 1 , it means a substantially circular cross-section fiber and so property deterioration may occur. When the MR is 3 or less, the properties sufficient for a tire cord may be obtained without deterioration of the properties of the filament fibers themselves.

[Equation 1]

MR = R²/R*

Wherein, the maximum inscribed circle is determined as a circle having a maximum area that has an arbitrary center point on the cross-section of the filament fiber and the periphery of the circle does not go out of the cross-section area, and the minimum circumscribed circle is determined as a circle having a minimum area that has an arbitrary center point on the cross-section of the filament fiber and the periphery of the circle does not intrude into the cross-section area.

An example of the cross-section of the non-circular cross-section filament fiber is shown in Fig. 1 to explain R¹ and R² defined in Equation 1. The shape of the cross-section of the non-circular cross-section filament fiber is not limited in the present invention. Therefore, it may be a random shape; a polygon such as a triangle, a square, or a pentagon; a cruciform; a Y form; or star- shaped. More preferably, it may be substantially a triangle.

Furthermore, the non-circular cross-section filament fiber has specific technical features due to the shape of the cross-section, and thus the material of the fiber is not limited in the present invention since the effect of the present invention may be obtained from all filament fibers being used for a tire cord.

Therefore, the non-circular cross-section filament fiber of the present invention may include a cellulose-based polymer, an aramid-based polymer, a polyester-based polymer, a nylon-based polymer, a polyvinylalcohol-based polymer, or a mixture of at least two of them. In the polymers, the cellulose-based fiber may be a rayon or a lyocell, and the cellulose-based polymer may preferably contain alpha-cellulose in an amount of 94 wt% or more, and more preferably in an amount of 96 wt% or more, to secure sufficient mechanical properties such as tenacity and elongation. Furthermore, the polyester-based polymer may be poly(ethylene terephthalate) or poly(ethylene naphthalate), and the nylon-based polymer may be

Nylon 6 or Nylon 66.

The denier of the non-circular cross-section filament fiber is not particularly limited, however it may be in the range of 0.8 to 6 d to be used for a tire cord, and further may be in a range of 1 to 5 d.

The non-circular cross-section filament fibers are prepared in a form of a bundle, in which a plurality of filament fibers are clustered, before preparing a tire cord, and the present filament bundle for a tire cord may include 200 to 2,000 total filaments for showing enhanced tenacity.

Also, the total denier of the bundle may be in the range of 200 to 3,000 d, and it may be in the range of 500 to 2,500 d if necessary.

The filament bundle may constitute one ply in a tire cord.

The filament bundle includes a plurality of non-circular cross-section filament fibers, and thus it may include at least two kinds of non-circular cross- section filament fibers respectively containing different polymers to make up for insufficient properties, if necessary. Also, the filament bundle may include at least two kinds of non-circular cross-section filament fibers respectively having different cross-section shape deviations to control the effect of the strength maintaining rate and the elongation maintaining rate, if necessary. Also, the filament bundle may include at least two kinds of non-circular cross-section filament fibers respectively having a different cross-sectional shape to control a packing state of the filament fibers in a tire cord, if necessary. The filament bundle may be formed into a twisted yarn for preparing a tire cord, and the twisted yarn includes the non-circular cross-section filament fibers, and the total number of filament fibers may be in the range of 400 to 6,000.

Also, the total denier of the twisted yarn may be in the range of 400 to 9000 d, and may be in the range of 1,000 to 7,500 d, if necessary. At this time, the twisted yarn is prepared from the filament bundle, and thus it may include at least two kinds of non-circular cross-section filament fibers respectively containing different polymers to make up for insufficient properties, if necessary, like the preceding. Also, the twisted yarn may include at least two kinds of non-circular cross-section filament fibers respectively having different cross- section shape deviations to control the effect of the strength maintaining rate and the elongation maintaining rate, if necessary. Also, the twisted yarn may include at least two kinds of non-circular cross-section filament fibers respectively having a different cross-sectional shape to control a packing state of the filament fibers in a tire cord, if necessary. Furthermore, the twisted yarn for a tire cord is prepared by a first twisting process of Z twisting (or S twisting) the bundle and a second twisting process of S twisting (or Z twisting) 2 or 3 ply of the first twisted yarns together. Therefore, the first twisted yarn may include at least two filament fibers having different materials, cross-section shape deviations, or cross-sectional shapes, and the second twisted yarn may include two or three kinds of the first twisted yarns having different materials, cross-section shape deviations of filaments, or cross-sectional shape of the filaments, therein.

In the twisted yarn for a tire cord, the twisting level of the first twisting (i.e. Z twisting or S twisting) and the second twisting (i.e. S twisting or Z twisting) may be in a range of 200 to 600 TPM, respectively.

Furthermore, the twisted yarn of the present invention has 30 to 55° of twisting angle (θ) from the perpendicular direction (D) to the vertical direction (L), in the above twisting level, as illustrated in Fig. 3, and thus the twisted yarn of the present invention has a higher twisting level than a twisted yarn including a circular cross-section fiber in the same twisting angle, and the elongation maintaining effect of the present invention is specifically good.

The twisted yarn is prepared in a form of a dipped cord by introducing an adhesive on the surface of the twisted yarn, and the characteristics of the yarn are applied to the present tire cord, as they are.

In a general tire cord, as the twisting level decreases, the strength thereof increases but the fatigue resistance thereof decreases, while, as the twisting level increases, the fatigue resistance thereof increases but the strength thereof decreases. However, the tire cord of the present invention includes the non-circular cross-section filament fibers having a large surface area, and thus the stresses of the tire cord caused by the twisting may be reduced, and the strength of the tire cord may be less deteriorated or may rather be larger than that of the tire cord including circular cross-section filament fibers, in the range of 200 to 600 TPM of Z and S twisting level, or S and Z twisting level (Cable & Cord 3type twister by Allma Co.), respectively, according to the material of the filament fiber. Therefore, the twisting level of the tire core of the present invention may be in a range of 200 to 600 TPM of Z and S twisting level, or S and Z twisting level, respectively.

In particular, at 350 TPM level of S and Z twisting, the tire cord including the cellulose-based non-circular cross-section filament fibers shows a 90 % or more strength maintaining rate, and a 120 % or more elongation maintaining rate, more preferably a 130 % or more of elongation maintaining rate. At 420 TPM of S and Z twisting, the tire cord shows a 80 % or more strength maintaining rate, and a 120 % or more elongation maintaining rate, preferably a 160 % or more elongation maintaining rate, while at 470 TPM of S and Z twisting, the tire cord shows a 70 % or more strength maintaining rate, and a 120 % or more elongation maintaining rate, preferably a 170 % or more elongation maintaining rate.

In the present invention, the strength maintaining rate means the percentage of the relative ratio of the strength at any specific TPM to the strength at 0 TPM, and the elongation maintaining rate means the percentage of the relative ratio of the elongation at any specific TPM to the elongation at 0 TPM.

The tire cord including the non-circular cross-section filament fibers of the present invention may have 12 kgf to 70 kgf of tensile strength. In a case of synthetic fibers such as polyester, the tensile strength of the cord may be 14 kgf to 70 kgf, and may be 15 kgf to 60 kgf in a range of 200 to 600 TPM. Furthermore, in a case of cellulose-based fibers, the tensile strength of the cord may be 12 kgf to 60 kgf, and may preferably be 14 kgf to 30 kgf in a range of 200 to 600 TPM.

The tire cord of the present invention may be prepared by a method including the steps of double twisting the non-circular cross-section filament bundles to make a twisted yarn, introducing an adhesive solution for a cord to the plied yarn, and drying and heat-treating the same.

The Modification Ratio of the non-circular cross-section filament fibers can be controlled to be in the range of the present invention by controlling the shape of spinning nozzles, and the detailed spinning conditions are controlled by the conventional method according to the sort of the polymer. Therefore, the detailed explanation related to the method of preparing the non-circular cross-section fibers is not disclosed in the present invention.

However, in the case of cellulose-based non-circular cross-section filament fibers, they may be prepared by a method including the steps of preparing a spinning dope by dissolving cellulose in a solvent mixture of N-methylmorpholine-N-oxide

(hereinafter 'NMMO') and water; spinning cellulose-based filament fibers from the spinning dope by using a spinning system possessing non-circular cross-section nozzles; and cleaning and drying the spun cellulose-based filament fibers so that the prepared filament fibers have a Modification Ratio of more than 1 and 3 or less.

Herein, the spinning dope may contain 7 to 18 wt% of cellulose in a solvent mixture containing NMMO and water in a weight ratio of 93:7 to 85:15. The spinning dope may be prepared by swelling cellulose in a solvent mixture containing NMMO and water in a weight ratio of 90:10 to 50:50 and then eliminating water so that the spinning dope contains 5 to 35 wt%, preferably 7 to 18 wt% of cellulose in a solvent mixture containing NMMO and water in a weight ratio of 93:7 to 85:15. However, the ratio of the solvent mixture and the content of the cellulose are only selected for the most suitable condition to prepare the cellulose-based non-circular cross-section filament fibers and the present invention is not limited to or by them.

Furthermore, the cross-sectional shape of the non-circular cross-section filament fibers depends on the shape of the spinning nozzles, and it may be preferable to use Y shaped nozzles for obtaining triangular cross-section fibers.

A conventional adhesive solution may be used in the present invention, and more preferably, RFL solution may be used. The drying temperature of the adhesive solution and the heat treating conditions follow conventional processing conditions.

Furthermore, the process conditions except for using the non-circular cross- section filament fibers follow conventional processing conditions. Therefore, addition and subtraction of the conditions are possible, and the present invention is not limited.

Hereinafter, the present invention is described in further detail through examples. However, the following examples are only for the understanding of the present invention and the present invention is not limited to or by them.

Example 1

Polyester (PET) filament fibers having a substantially triangular cross- section were prepared from PET having an intrinsic viscose value of 0.65 by using Y shaped nozzles, wherein the spinning speed was 4,500 m/min, the spinning temperature was 289 ^°C , the quenching air speed was 0.5 m/sec, the discharge amount was 500g/min, the temperature of the first godet roller was 85 ^°C , and the temperature of the second godet roller was 125^°C .

The total number of prepared filaments was 250, and the total denier of the filaments was 1 ,000 d.

The average denier of the prepared filament fibers was 4 d, the Modification Ratio thereof was 1.4, the dry tenacity thereof was 7.0g/d, the and breaking elongation thereof was 15 %.

The cross-section shape deviation (MR) of the filament fibers was calculated by obtaining a cross-section image of the filament fibers by using scanning electronic microscopy (SEM), and drawing the maximum inscribed circle and the minimum circumscribed circle of the cross-section of the fiber and measuring radii

(R¹ and R²) of the circles by using a CAD program (Auto CAD). At this time, the average was calculated from at least 10 cross-sections of the filament fibers for reliability of the measurement.

The non-circular cross-section filaments were S twisted with 200 TPM and then 2 ply of the Z twisted yarns were S twisted with 200 TPM to prepare a raw cord in the Cable & Cord 3type twister, that is, CC Twister, by Allma Co.. However, it is possible to Z twist 2 ply of S twisted yarns, too. The raw cords were dipped into a resorcinol/formaldehyde/latex (RFL) adhesive solution containing resorcinol, formaldehyde, sodium hydroxide, styrene/butadiene/vinylpyridine (15/70/15) rubber, and water so that the pickup rate of the adhesive was 5 wt%, and then the cords were dried for 2 minutes at 150⁰C and heat treated for 2 minutes at 240 ^°C . Example 2

The tire cord was prepared substantially according to the same method as in Example 1, except that the Z and S twisting level was changed to 370 TPM, respectively.

Example 3

The tire cord was prepared substantially according to the same method as in Example 1, except that the Z and S twisting level was changed to 460 TPM, respectively.

Example 4

The tire cord was prepared substantially according to the same method as in Example 1, except that the Z and S twisting level was changed to 600 TPM, respectively.

Example 5

The tire cord was prepared substantially according to the same method as in Example 1, except that the Z and S twisting level was changed to 750 TPM, respectively.

Comparative Example 1

The tire cord was prepared substantially according to the same method as in Example 1, except that the circular cross-section fibers had 4 d average denier, 8.0 g/d dry tenacity, 14 % breaking elongation, and 250 total filaments.

Comparative Example 2

The tire cord was prepared substantially according to the same method as in Comparative Example 1, except that the Z and S twisting level was changed to 370 TPM, respectively.

Comparative Example 3

The tire cord was prepared substantially according to the same method as in Comparative Example 1, except that the Z and S twisting level was changed to 460 TPM, respectively.

Comparative Example 4

The tire cord was prepared substantially according to the same method as in Comparative Example 1, except that the Z and S twisting level was changed to 600 TPM, respectively.

Comparative Example 5

The tire cord was prepared substantially according to the same method as in Comparative Example 1, except that the Z and S twisting level was changed to 750 TPM, respectively.

The changes in tensile strength according to the increase of the twisting level (TPM) of the tire cords prepared by Examples 1 to 5 and Comparative Examples 1 to 5 are presented in Fig. 4. As shown in Fig. 4, the tire cords including the non- circular cross-section filament fibers of Examples 1 to 5 show an increasing tendency of strength maintaining rate as the twisting level increases. On the other hand, the tire cords including the circular cross-section fibers of Comparative Examples 1 to 5 show a decreasing tendency of strength maintaining rate as the twisting level increases.

Furthermore, the changes of elongation according to the increase of the twisting level (TPM) of the tire cords prepared by Examples 1 to 5 and Comparative Examples 1 to 5 are presented in Fig. 5. As shown in Fig. 5, the tire cords including the non-circular cross-section fibers of Examples 1 to 5 show higher elongation maintaining rates according to the twisting level than the tire cords including the circular cross-section fibers of Comparative Examples 1 to 5.

It is known from the above results that the tire cords of the present invention show superior strength maintaining rates against twisting, and the elongation thereof is higher than the tire cords including the circular cross-section fibers.

Example 6

Cellulose sheet (V-81, buckeye Ltd.) was introduced into a pulverizer equipped with a 100 mesh filter to prepare cellulose powders having a diameter of 1700 m or less.

The cellulose powders were swelled in a 50 wt% NMMO aqueous solution, wherein the content of the cellulose in the NMMO aqueous solution was 6.5 wt% and an anti-oxidant was further introduced in the solution in an amount of 0.01 wt% of the cellulose. The swelled cellulose slurry was introduced into a kneader where the inner temperature was maintained at 90 ^°C, and the absolute pressure was maintained at 50 mmHg by a rotary valve-type pump with a speed of 16 kg/hour. After dissolving the cellulose completely by eliminating water from the slurry to prepare a spinning dope including 89 wt% of the NMMO aqueous solution, the spinning dope was discharged through a discharging screw, wherein the cellulose content of the discharged spinning dope was 11 wt% and there was no undissolved cellulose particles in the spinning dope.

The cellulose dope was spun by using a die having 1000 nozzles so that the total denier of the prepared filament fibers was 1,650 d, wherein the nozzles had a Y form and an area of 0.047mπf. There was a 30 mm air gap between the nozzles and a solidifying bath.

The NMMO was eliminated from the discharged and solidified multifilament fibers by a Nelson type roller with sprayed washing water, and the un-dried multi-filament fibers having 170 % water content were dried by 3 step drying rolls to prepare lyocell filament fibers, wherein the tension between the first and second drying rolls was controlled to be 0.5 g/d, the tension between the second and third drying rolls was controlled to be 0.8 g/d, and the temperature of the rolls was adjusted to 100 "C, 130^°C , and 150⁰C , successively. The total number of the lyocell filament fibers prepared by the above method was 1,000, the average denier thereof was 1.5 d, the Modification Ratio thereof was 1.44, the dry tenacity thereof was 6.0g/d, and the breaking elongation thereof was 9 %. Fig. 6 is a cross-sectional photograph of the prepared triangular cross-section fiber. The cross-section shape deviation (MR) of the filament fibers was calculated by the same method of Example 1, and the photograph of the cross-section showing an example for measuring the MR is illustrated in Fig. 7.

Comparative Example 6

The tire cord was prepared substantially according to the same method as in Example 6, except that the die comprised 1000 circular nozzles having a diameter of 0.2 mm, and the prepared circular cross-section fibers had 1.5 d average denier, 6.2 g/d dry tenacity, 8 % breaking elongation, and 1000 total filaments.

Example 7

The triangular cross-section lyocell filament fibers prepared by Example 6 were Z twisted with 350 TPM and then 2 ply of the Z twisted yarns were S twisted with 350 TPM to prepare a raw cord. The raw cords were dipped into an RFL adhesive solution containing resorcinol, formaldehyde, sodium hydroxide, styrene/butadiene/vinylpyridine (15/70/15) rubber, and water so that the pickup rate of the adhesive was 5 wt%, and then the cords were dried for 2 minutes at 150^°C and heat treated for 2 minutes at 240 ^°C .

Example 8

The tire cord was prepared substantially according to the same method as in Example 7, except that the Z and S twisting level was changed to 420 TPM, respectively. Example 9

The tire cord was prepared substantially according to the same method as in Example 7, except that the Z and S twisting level was changed to 470 TPM, respectively.

Comparative Example 7

The tire cord having a 350 TPM twisting level was prepared substantially according to the same method as in Example 7, except that the circular cross-section fibers prepared by Comparative Example 1.

Comparative Example 8

The tire cord was prepared substantially according to the same method as in Comparative Example 7, except that the Z and S twisting level was changed to 420 TPM, respectively.

Comparative Example 9

The tire cord was prepared substantially according to the same method as in Comparative Example 7, except that the Z and S twisting level was changed to 470 TPM, respectively.

Samples of the tire cords prepared by Examples 6-9 and Comparative Examples 6-9 were pre-dried for 2 hours at 110^°C so that the moisture thereof was below the regain of allowance, and then placed under standard conditions of KSK 0901 (textile testing room standard state) for 24 hours to be in an equilibrium state.

The strength and strain of the prepared samples were tested by a slow straining type of UTM of INSTRON Ltd. under the KSK 0412 standard, with conditions of a sample length of 250 mm and a straining speed of 300 mm/min. Furthermore, the filament fibers prepared by Example 6 and Comparative Example 6 were dipped into the adhesive solution according to the same method as above, except that they were not twisted (0 TPM) and the strength and elongation of the prepared samples were measured for reference by the same method as above.

The strengths and the strength-maintaining rates of the tire cords prepared by Examples 6-9 and Comparative Examples 6-9 are listed in Table 1, and the change of the strength maintaining rate according to the increase of the twisting level (TPM) are presented in Fig. 8. [Table 1]

As shown in Table 1 and Fig. 8, the tire cords including the non-circular cross-section filament fibers of Examples 7 to 9 show a gentle decrease of the strength maintaining rates as the twisting level increases. On the other hand, the tire cords including the circular cross-section fibers of Comparative Examples 7 to 9 show a rapid decrease of the strength maintaining rates as the twisting level increases. Furthermore, the changes in the elongation and the elongation maintaining rates according to the increase of the twisting level of the tire cords prepared by Examples 6 to 9 and Comparative Examples 6 to 9 are listed in Table 2, and the change in the elongation maintaining rate according to the increase of the twisting level are presented in Fig. 9. [Table 2]

As shown in Table 2 and Fig. 9, the tire cords including the non-circular cross-section filament fibers of Examples 7 to 9 show higher elongation maintaining rates according to the twisting level than the tire cords including the circular cross- section fibers of Comparative Examples 7 to 9.

It is known from the above results that the tire cords of the present invention show superior strength maintaining rates against twisting, and the elongation thereof is higher than the tire cords including the circular cross-section filament fibers.

As mentioned above, the reason for the superior strength maintaining rate of the tire cord of the present invention is due to the non-circular cross-section filament fiber having a large surface area is more appropriate for twisting compared to the circular cross-section filament fiber. Particularly, it is due to the density (appearance density) of the non-circular cross-section filament bundle being increased as the twisting level increases.

The non-circular cross-section filament fiber of the present invention has large surface area and good resistance to twisting. Therefore, the tire cord of the present invention may lessen the stresses due to twisting, and has superior strength maintaining rate and elongation maintaining rate.

Claims

WHAT IS CLAIMED IS:

1. A non-circular cross-section filament fiber for a tire cord, wherein a cross-section shape deviation thereof represented by Equation 1 is more than 1 and 3 or less:

[Equation 1] MR = R²/R* wherein, MR is cross-section shape deviation expressed by the Modification Ratio, R¹ is a radius of the maximum inscribed circle of the cross-section of the fiber, and R² is a radius of the minimum circumscribed circle of the cross-section of the fiber.

2. The non-circular cross-section filament fiber according to Claim 1, wherein the MR is in the range of 1.1 to 3.

3. The non-circular cross-section filament fiber according to Claim 2, wherein the MR is in the range of 1.3 to 2.5.

4. The non-circular cross-section filament fiber according to Claim 1, wherein the filament fiber has a substantially triangular cross-sectional shape.

5. The non-circular cross-section filament fiber according to Claim 1, wherein the filament fiber includes a cellulose-based polymer, an aramid-based polymer, a polyester-based polymer, a nylon-based polymer, or a polyvinylalcohol-based polymer.

6. The non-circular cross-section filament fiber according to Claim 5, wherein the cellulose-based polymer is a lyocell.

7. The non-circular cross-section filament fiber according to Claim 1, wherein the denier of the filament fiber is in the range of 0.8 to 6 d.

8. A filament bundle for a tire cord including the non-circular cross-section filament fibers according to any one of Claims 1 to 7, wherein the total number of filament fibers is in the range of 200 to 2,000.

9. The filament bundle according to Claim 8, wherein the total denier of the bundle is in the range of 200 to 3,000 d.

10. The filament bundle according to Claim 9, wherein the total denier of the bundle is in the range of 500 to 2,500 d.

11. The filament bundle according to Claim 8, including at least two kinds of the non-circular cross-section filament fibers respectively containing different polymers.

12. The filament bundle according to Claim 8, including at least two kinds of the non-circular cross-section filament fibers respectively having different cross-section shape deviations.

13. The filament bundle according to Claim 8, including at least two kinds of the non-circular cross-section filament fibers respectively having different cross- sectional shapes.

14. A twisted yarn for a tire cord including the non-circular cross-section filament fibers according to any one of Claims 1 to 7, wherein the total number of filament fibers is in the range of 400 to 6,000.

15. The twisted yarn according to Claim 14, wherein the total denier of the twisted yarn is in the range of 400 to 9,000 d.

16. The twisted yarn according to Claim 14, wherein the total denier of the twisted yarn is in the range of 1,000 to 7,500 d.

17. The twisted yarn according to Claim 14, including at least two kinds of the non- circular cross-section filament fibers respectively containing different polymers.

18. The twisted yarn according to Claim 14, including at least two kinds of the non- circular cross-section filament fibers respectively having different cross-section shape deviations.

19. The twisted yarn according to Claim 14, including at least two kinds of the non- circular cross-section filament fibers respectively having different cross-sectional shapes.

20. The twisted yarn according to Claim 14, wherein the twisted yarn is prepared by first Z twisting or S twisting a filament bundle including 200 to 2,000 of the non- circular cross-section filament fibers to prepare a first twisted yarn, and then second S twisting or Z twisting 2 to 3 ply of the first twisted yarn together.

21. The twisted yarn according to Claim 14, wherein the twisting level of the first Z twisting or S twisting and the second S twisting or Z twisting is in the range of 200 to 600 TPM, respectively.

22. The twisted yarn according to Claim 21, wherein a twisting angle (θ) from the perpendicular direction (D) to the vertical direction (L) is in the range of 30 to 55°.

23. A tire cord including the twisted yarn according to Claim 14.

24. The tire cord according to Claim 23, wherein the total denier of the twisted yarn is in the range of 400 to 9,000 d.

25. The tire cord according to Claim 24, wherein the total denier of the twisted yarn is in the range of 1,000 to 7,500 d.

26. The tire cord according to Claim 23, including at least two kinds of the non- circular cross-section filament fibers respectively containing different polymers.

27. The tire cord according to Claim 23, including at least two kinds of the non- circular cross-section filament fibers respectively having different cross-section shape deviations.

28. The tire cord according to Claim 23, including at least two kinds of the non- circular cross-section filament fibers respectively having different cross-sectional shapes.

29. The tire cord according to Claim 23, wherein the twisted yarn is prepared by first Z twisting or S twisting a filament bundle including 200 to 2,000 of the non-circular cross-section filament fibers to prepare a first twisted yarn, and then second S twisting or Z twisting 2 to 3 ply of the first twisted yarn together.

30. The tire cord according to Claim 23, wherein the twisting level of the first Z twisting or S twisting and the second S twisting or Z twisting is in the range of 200 to 600 TPM, respectively.

31. The tire cord according to Claim 30, wherein a twisting angle (θ) from the perpendicular direction (D) to the vertical direction (L) is in the range of 30 to 55°.

32. The tire cord according to Claim 23, wherein the tensile strength of the tire cord is in the range of 12 to 70 kgf.