TITLE OF THE INVENTION

PREPARATION METHOD FOR LYOCELL FILAMENT FIBERS, LYOCELL FILAMENT FIBERS, TIRE CORD, AND PREPARATION METHOD FOR TIRE CORD

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method of preparing lyocell filament fibers for rubber reinforcement, lyocell filament fibers prepared therefrom, a tire cord, and a method of preparing the same.

(b) Description of the Related Art

A tire is a complex body of fibers/steel/rubber, and generally has a structure as illustrated in Fig. 1. Namely, the steel and the fiber cords have the role of reinforcing the rubber and form a basic skeletal structure in the tire. It is, so to speak, like the role of bones in a human body.

As a reinforcement of the tire, the cord requires characteristics such as fatigue resistance, shear strength, durability, repelling elasticity, adhesive power to rubber, and the like. Therefore, various cords made of suitable materials are used according to the performance required of the tire.

Recently, rayon, nylon, polyester, steel, aramid, and the like have generally been used as materials for a cord, with rayon and polyester used for a body ply (or a carcass) (6 in Fig. 1), nylon mainly used for a cap ply (4 in Fig. 1), and steel and aramid mainly used for a tire-belt part (5 in Fig. 1). The structure and characteristics of the tire represented in Fig. 1 are briefly disclosed hereinafter.

Tread 1: A part contacting to the road surface; this part must provide a friction force necessary for braking and driving, be good in abrasion resistance, and also be able to withstand an external shock, and its heat generation must be small. Body ply (or Carcass) 6: A cord layer inside the tire; this part must support a

load and withstand a shock, and its fatigue resistance against bending and stretching movement during driving must be good.

Belt 5: This part is located between the body plies and mostly composed of steel wire, and it lessens external shock and also makes the ground contacting surface of the tread wide and the driving stability good.

Side wall 3: A rubber layer between the lower part of the shoulder 2 and the bead 9; it takes a role of protecting the internal body ply 6.

Bead 9: A square or hexagonal wire bundle, wherein rubber is coated on the steel wires; it has a role of fitting and fixing the tire to a rim. Inner liner 7: A part located inside the tire instead of a tube; it makes a pneumatic tire possible by preventing air leakage.

Cap ply 4: A special cord fabric located on the belt of a radial tire for some passenger cars; it minimizes the movement of the belt during driving.

Apex 8: A triangular rubber packing material used for minimizing the dispersion of the bead, protecting the bead by relieving external shock, and preventing an air inflow during shaping.

Generally, nylon, polyester, rayon, and the like are used as materials for a tire cord, and the standard and use of the tire are limited according to the merits and demerits of the materials. Nylon fiber is mainly used in tires of heavy-duty trucks subjected to heavy weight loads, or in tires mainly used for an irregular load like an unpaved road, because it has high tensile elongation and strength. However, the nylon fiber is unsuitable for a passenger car requiring high speed driving and riding comfort, because it generates intensive heat accumulation inside of the tire, and has a low modulus.

Polyester fiber has good shape stability and good competitive price in comparison with nylon, and its strength and adhesive strength are being improved by continuous studies, and so the amount used in the field of tire cords is tending to increase. However, it is unsuitable for a tire for high speed driving because, as yet, there are limitations in heat resistance, adhesive strength, and so on.

Rayon fiber, a regenerated cellulose fiber, shows superior tenacity maintaining rate and shape stability in high temperatures. Therefore, the rayon fiber is known as the most suitable material for a tire cord. However, it requires thorough moisture control when preparing the tire because the tenacity is severely deteriorated by moisture and the rate of inferior goods is high due to the heterogeneity during preparation of the fiber. First of all, its performance per price (tenacity per price) is very low in comparison with the other materials, and thus it is only applied to an ultra high speed driving tire or a high-priced tire.

Furthermore, though a general wet spinning method used for preparing cellulose-based fibers, such as rayon and the like, is advantageous for revealing tenacity, it is disadvantageous for preparing good elongation property, because the surface of the final fibers prepared thereby is too dense. Therefore, a method able to prepare suitable mechanical properties and structure is required.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide lyocell filament fibers having good shape stability and fatigue resistance and being suitable for a tire cord for high speed driving, and a method of preparing the same.

Another aspect of the present invention is to provide a tire cord suitable to be applied to a tire, and a method of preparing the same.

The present invention provides a method of preparing lyocell filament fibers including the steps of preparing filaments by spinning a lyocell spinning dope, solidifying the filaments in a solidifying bath of 30 to 60 "C , washing the solidified filaments with washing fluid, drying the washed filaments, and winding the dried filaments.

The average diameter of voids remained on the cross-section of the lyocell filament fibers of the present invention is 100 nm or less.

The present invention also provides a tire cord including a twisted yarn of lyocell filament fibers and an adhesive, wherein the pick up rate of the adhesive is 6 to 10 wt%, and the degree of fatigue resistance (%) defined by the following Calculation

Formula 1 is 70% or more at the fatigue condition of extension and contraction of ±2% according to the American Society of Testing Materials (ASTM) D 6588 method by using a disk fatigue tester: Calculation Formula 1 Degree of fatigue resistance (%) = (Remained strength after fatigue testing /

Strength before fatigue testing) x 100

In addition, the present invention provides a method of preparing a tire cord including the steps of dipping a twisted yarn of the lyocell filament fibers into an adhesive solution with a tension of 20 to 2000 g/cord, drying the dipped twisted yarn at the temperature of 105 to 160°C while giving a tension of 20 to 2000 g/cord, and heat-treating the dried twisted yarn at the temperature of 105 to 220 ^° C while giving a tension of 20 to 2000 g/cord.

BRIEF DESCRIPTION QF THE DRAWINGS Fig. 1 is a partial cut-away perspective view illustrating a structure of a general tire.

Fig. 2 is a constructive drawing representing the device for preparing the lyocell filament fiber according to one embodiment of the present invention.

Fig. 3 is a transmission electron microscope (TEM) photograph representing the lyocell filament fiber of Example 1.

Fig. 4 is a TEM photograph representing the lyocell filament fiber of Example 2.

Fig. 5 is a TEM photograph representing the lyocell filament fiber of Comparative Example 1.

Explanations for reference numerals of the principal parts of the drawings> 10: gear pump

20: spinning die 30: non-solidified fiber

40: first solidifying bath 42: second solidifying bath 50: pulling part 60: washing device

70: drying device

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the present invention is explained in more detail. In the present invention, the filament bundle including a plurality of filament fibers is called 'multi-filaments', the raw cord prepared by Z twisting (counterclockwise twisting) and S twisting (clockwise twisting) the multi filaments is called 'twisted yarn', and the dipped cord prepared by treating the twisted yarn with an adhesive for a tire cord is called a 'tire cord'. The present invention is for resolving the problem of a surface void structure of usual cellulose-based fibers, such as rayon and the like, by the wet spinning method during the preparing process thereof, and the present inventors accomplished the present invention by knowing that lyocell filament fibers have a dense structure while showing proper strength and elongation by increasing the activity of the solvent by raising the temperature of the solidifying bath in the spinning process.

Therefore, the lyocell multi-filaments prepared according to the present method make the penetration of the dipping solution easy during preparing a tire cord and have superior fatigue resistance.

The method of preparing lyocell filament fibers according to the present invention includes the steps of preparing filaments by spinning a lyocell spinning dope, solidifying the filaments in a solidifying bath of 30 to 60 ^° C , washing the solidified filaments with washing fluid, drying the washed filaments, and winding the dried filaments.

When a tire cord is prepared by using the lyocell filament fibers of the present invention, the shape stability and the fatigue resistance of the tire cord may be improved more excellently since a pick up rate of the adhesive included in the tire cord is limited within a specific range.

Especially, the tire cord of the present invention includes a twisted yarn of lyocell filament fibers and an adhesive, wherein the pick up rate of the adhesive is 6 to 10 wt%, and the degree of fatigue resistance (%) defined by the following Calculation

Formula 1 is 70% or more, which is measured after fatigue testing with a fatigue condition of extension and contraction of ±2% according to the American Society of Testing Materials (ASTM) D 6588 method by using a disk fatigue tester. At this time, the twisted yarn of lyocell filament fibers may include the lyocell filament fibers of the present invention:

Calculation Formula 1

Degree of fatigue resistance (%) = (Remained strength after fatigue testing / Strength before fatigue testing) x 100

Hereinafter, the method of preparing the lyocell multi-filaments according to one embodiment of the present invention is explained by referring to the attached drawings, so as to enable a person with ordinary skill in the art to which the present invention pertains to carry out the invention easily.

At this time, the method of preparing the lyocell multi-filaments of the present invention is not limited to or by the following preferable embodiments, and it is understandable to a person skilled in the related art that various modifications and parities are possible from the present embodiment.

Therefore, the scope of the right of the present invention is not limited to or by the embodiments, and it is also included in the scope of the right of the present invention that a person in the related art carries out various modifications and reforms by using the basic concept defined in the present claims.

Fig. 2 is a constructive drawing representing the device for preparing the lyocell multi-filaments according to one embodiment of the present invention, however, the spinning method of the present invention is not limited particularly to or by the same. Referring Fig. 3, the device for preparing the lyocell filament fibers is equipped with a gear pump 10 for providing a spinning dope with a regular pressure, a spinning die 20 for spinning the dope provided by the pump into a form of fiber, and a first solidifying bath 40 and a second solidifying bath 42 for solidifying the non- solidified fibers 30 discharged from the spinning die 20. The filaments passed through the first solidifying bath 40 are passed through the second solidifying bath 42

by the driving force of a pulling part 50, and the solvent included in the spinning dope is eliminated in a washing device 60 with water. Subsequently, the filaments passed through the washing device 60 are dried in a drying device 70 and then final lyocell filaments can be obtained by winding them on a winding roll. Furthermore, the present invention makes cellulose sheets into powders by introducing the same into a pulverizer equipped with a screen filter, and the powders are stored in a storage tank, and consequently a mixture of the cellulose powders and a liquid spinning solution may be introduced into a feeding part of a twin extruder equipped with the spinning die 20, even though it is not illustrated in the figures. The lyocell multi-filaments of the present invention may be prepared by using the preparing device according to the preparing method including the steps of preparing a dope for spinning lyocell by dissolving the cellulose into a solvent mixture of N-methylmorpholine-N-oxide (NMMO) and water, preparing filaments by spinning the spinning dope with the spinning device equipped with spinning nozzles, solidifying the filaments, washing the solidified filaments with washing fluid, drying the washed filaments, and winding the dried filaments.

For one embodiment of the method of preparing the lyocell multi-filaments of the present invention, the cellulose sheets are made into powders by introducing the same into a pulverizer equipped with a screen filter, and the powders are stored in a storage tank, and consequently a mixture of the cellulose powders and a liquid spinning solution are introduced into a feeding part of a twin extruder.

After this, the mixture becomes an homogeneous solution by passing through a mixing part and a dissolving part, and the solution is spun into the vertical solidifying bathes 40, 42 through a spinning pack equipped with spinning nozzles. N-methylmorpholine-N-oxide (NMMO) is eliminated from the filaments solidified in the vertical solidifying bathes by NMMO free water in the washing device 60.

Consequently, the filaments passed through the washing device 60 are dried through the drying device 70 and the final multi-filaments can be obtained by winding the same. At this time, the lyocell multi-filaments have a void structure on their surface

because of a characteristic of being prepared by the wet spinning method of dissolving a pulp into the NMMO solvent and solidifying the same in the solidifying bath, and the voids greatly affect the mechanical properties and structure of the fibers. Furthermore, if the surface structure is too dense, although it is advantageous for revealing the strength because the interaction between the fibrils is large, it may affect the elongation property. Therefore, a proper void structure may act as an advantageous factor for revealing the elongation property. Furthermore, when they are applied to a tire cord, a lyocell dipped cord having good fatigue resistance may be prepared, because a dipping solution may easily penetrate to the fibers and the fatigue property becomes good.

Therefore, the present invention can obtain the dense structure of the lyocell fibers by increasing the activity of the solvent and inducing smooth solvent elimination by raising the temperature of the solidifying bath, in order to satisfy this condition. For this, the temperature of the solidifying bath may be 30 to 60 ^° C in the spinning process of the present invention. The solidifying bath of the present invention includes the first solidifying bath 40 and the second solidifying bath 42. The temperature condition of the solidifying bath may be independently applied to each of the first solidifying bath 40 and the second solidifying bath42, or to both of them, and it is preferable that the second solidifying bath 42 satisfies the temperature condition.

Furthermore, since the first solidifying bath 40 and the second solidifying bath 42 are to solidify the lyocell filament fibers discharged from the spinning die 20, it is preferable that they possess a control means of controlling the temperature. The present invention can provide lyocell filament fibers of which the average diameter of the voids remained on the cross-section of the fibers is 100 nm or less, and preferably 10 to 80 nm, according to the above method. At this time, it is preferable that the specific surface area of the filament fibers is 2 mVg or less, because the gas adsorption amount increases as the specific surface area increases. The specific surface area can be measured by using Flow sorb II 2300 of Micromeritics Co. More

concretely, the gas amount adsorbed to a specimen is measured by introducing nitrogen into the specimen, and then the specific surface area (raVg) is calculated by dividing the same by the weight of the specimen.

Furthermore, in the preparing method of the present invention, it is preferable to use the spinning dope in which 7 to 18 wt% of the cellulose is dissolved in the solvent mixture containing NMMO and water in a weight ratio of 93:7 to 85:15, and the spinning dope may be prepared by swelling the cellulose in the solvent mixture containing NMMO and water in a weight ratio of 90:10 to 50:50 and then eliminating the water so that the weight ratio of NMMO and water is 93:7 to 85:15 and the final content of the cellulose is 5 to 35 wt%, and preferably 7 to 18 wt%. 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 filaments and the present invention is not limited to or by them.

The drying temperature may be controlled to be 90 to 200 ^° C or 100 to 150 ^° C in the drying step of the filaments. The drying step can be carried out with a one step drying process, and also can be carried out with a multi-step drying process that is divided into a plurality of sections and in which different drying conditions are applied to each section. In the multi-step drying process, actual drying conditions can be selected arbitrarily within the range of the temperature as necessary. Furthermore, the range of the tension and the temperature in the drying step of the multi-filaments can be selected arbitrarily as necessary, and the conditions are not particularly limited.

The washing, drying, and post-treating techniques after spinning of the lyocell multi-filaments can follow those of the general wet spinning method. Furthermore, the spinning method used for preparing a rayon filament fiber, which is a cellulose- based fiber, can be modified and used for the lyocell process.

The present invention also provides a tire cord including the lyocell multifilament (the lyocell filament fibers).

Especially, the present invention provides a tire cord including a twisted yarn of the lyocell filament fibers and an adhesive, wherein the pick up rate of the adhesive

is 6 to 10 wt%, and the degree of fatigue resistance (%) defined by the Calculation Formula 1 is 70% or more, which is measured after fatigue testing with a fatigue condition of extension and contraction of ±2% according to the ASTM D 6588 method by using a disk fatigue tester. The twisted yarn of the lyocell filament fibers may include the lyocell multifilament (the lyocell filament fibers). The twisted yarn may be 2 to 3 ply twisted yarn of which the total number of filaments, the total fineness, the twisting level, and so on are optimized.

In the cord, the pick up rate of the adhesive means the amount of the adhesive adhered to the cord. The cord may be damaged during a heat-treating situation with a high tension, in view of the rigid structure of cellulose, but the adhesive penetrates into the twisted yarn of the rigid lyocell filament fibers, and buffs and gives the cord sufficient adhesive strength to rubber, in the tire cord of the present invention. Therefore, the pick up rate of the adhesive may be 6 wt% or more so that the role of the adhesive is sufficiently provided, and the pick up rate may be 10 wt% or less for the light weight of the cord.

The fatigue test is carried out according to the ASTM D 6588 method, and particularly, the test can be carried out by the method of preparing a specimen by vulcanizing the tire cord with rubber, and repeating extension and contraction of the specimen for 8 hours by using the disk fatigue tester while rotating at 2500 rpm at 100 ^° C, and the remained tenacity after fatigue testing calculated by Calculation Formula 1 means the remained strength measured for the cord separated from the rubber after the fatigue testing, and the remained strength means the breaking strength (kgf) measured after drying at 105 ^° C for 2 hours by using a tensile strength tester. The conditions of the fatigue test are merely a standard for measuring the properties of the tire cord of the present invention, and the tire cord of the present invention is not limited to or by the details of the test standard.

The degree of fatigue resistance of the tire cord of the present invention may be 70% or more, or may be 75 to 95%, in the case of testing fatigue at the fatigue condition of extension and contraction of +2% according to the above method.

Furthermore, the degree of fatigue resistance of the tire cord of the present invention may be 70% or more, or may be 73 to 90%, in the case of testing fatigue at the fatigue condition of extension and contraction of ±4% according to the above method. Generally, the temperature of the tire rises by friction during driving of a car, and the tire cord is also exposed to repeating fatigue conditions of high temperature and high pressure because the conditions of high temperature and high pressure are continued for a long time during high speed driving particularly.

At this time, the properties rapidly deteriorate by repeated extension and contraction, the driving performance may be decreased according to this when the fatigue resistance of the tire cord is low, and there is a danger that the tire cord can burst during driving in a severe case.

Therefore, it is preferable that the degree of fatigue resistance of the tire cord is high, particularly that the degree of fatigue resistance of the tire cord is 70 % or more at the fatigue conditions of extension and contraction of ±2% and ±4%, respectively, considering the characteristic tenacity of the cellulose-based material.

Furthermore, the factor as important as the fatigue resistance is the characteristic strength of the tire cord, and the breaking tenacity of the tire cord of the present invention may be 4 to 8 g/d, in order to provide suitable properties as a tire cord. Even though the fatigue resistance of the cord is superior, the suitable properties as a tire cord cannot be provided when the tenacity of the tire cord itself is low, and durability against fatigue is not good when elongation is low.

The twisted yarn may be a twisted yarn of 2 to 3 ply, of which the total number of filaments is 400 to 6000, the total fineness is 400 to 9000 denier, and the twisting level is 200 to 600 TPM, in order to provide suitable properties as the tire cord of the present invention.

Furthermore, the adhesive for a tire cord is included in the tire cord for improving the adhesive strength to rubber.

The tire cord of the present invention has good shape stability and durability, and can be applied to a body ply or a cap ply for a pneumatic tire. Furthermore, the

tire in which the tire cord of the present invention is included shows less shape deformation and can show stable high speed driving performance.

The tire cord of the present invention can be prepared by treating the twisted yarn of 2 to 3 ply including the lyocell filament fibers with an adhesive solution for a tire cord according to the conventional dipping method, and drying and heat-treating the same.

At this time, a conventional adhesive solution for a tire cord may be used as the adhesive solution, and a resorcinol-formaldehyde-latex (RFL) solution may be used preferably. The twisted yarn passed through the adhesive solution is prepared into the tire cord after passing through the drying process and the heat-treating process. At this time, a tension of 20 to 2000 g/cord is applied to the twisted yarn passing through the adhesive solution, and the drying process is carried out with a tension of 20 to 2000 g/cord at 105 to 160 ^° C for 1 to 10 minutes, and the heat-treating process may be carried out with a tension of 20 to 2000 g/cord at 105 to 220 ^° C for 1 to 10 minutes. The reason for applying the tension in the processes of passing through the adhesive solution, drying, and heat-treating is for controlling the pick-up rate of the adhesive included in the cord.

That is, the tension of 2000 g/cord or less may be applied independently in each process in order to give superior fatigue resistance by raising the permeability of the adhesive. Furthermore, the tension of 20 g/cord or more may be applied independently in each process in order to prevent the adhesive penetrating excessively into the tie cord.

Particularly, the penetrating speed of the adhesive can be delayed by the rapid drying of the adhesive and properties advantageous for providing tenacity can be obtained by minimizing damage of the dried cord, when the cord is dried in the temperature range while giving the tension with the above conditions. Furthermore, the effect of improving the adhesive strength can be obtained, while causing less damage to the cord by promoting the reaction between the lyocell filament fibers and the adhesive, when the cord is heat-treated in the temperature range while giving the

tension with the above conditions.

The moisture included in the lyocell cord is dried in the drying process, and the heat-treating process gives an adhesive power to the tire cord by making the dipping solution reacted. The details other than those disclosed above can be added as necessary, and the present invention is not specifically 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.

Examples

Example 1: Preparation of the lyocell filament fibers The lyocell filament fibers were prepared by using the spinning device of Fig. 2. A 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 μm or less, and the powders were stored in a pulp powder storage tank.

Subsequently, the cellulose powders (feeding speed = 561 g/h) and a liquefied

NMMO (89 °C, water content = 13%, feeding speed = 6,000 g/h) for swelling the cellulose were introduced into a feeding part of a twin extruder (diameter of screw (D)

= 48 mm, L/D = 52), of which the rotating speed of the screw was 120 rpm and the temperature was 80 ^° C .

The mixture was made into a spinning dope by passing through a mixing part and a dissolving part, and the cellulose content of the spinning dope was 11 wt%. Furthermore, the spinning dope was spun into a solidifying bath by using a die, of which the total number of nozzles was 1000 and the cross-sectional area of each nozzle was 0.047mnf, so that the total fineness of the final filaments was 1650 denier.

The NMMO was completely eliminated from the discharged and solidified multi-filament fibers by sprayed washing water. At this time, the temperature of the solidifying bath was maintained at 42 "C and rapid solvent elimination was induced.

Consequently, the lyocell multi-filament raw fibers were obtained by heating and drying the filaments by the drying device in order to eliminate the moisture from the raw fibers, and winding the same.

Furthermore, undried multi-filament fibers were dried in drying rolls and made into the lyocell multi-filament raw fibers.

Example 2: Preparation of the lyocell filament fibers

The lyocell multi-filament raw fibers were prepared substantially according to the same method as in Example 1, except that the cellulose spinning dope was prepared by the following method.

After preparing the cellulose powders according to the same method as in Example 1, the cellulose powders were swelled in a 50 wt% NMMO aqueous solution so that the content of the cellulose in the NMMO aqueous solution was 6.5 wt%, and then the cellulose was dissolved while eliminating the remaining water so as to make the NMMO aqueous solution to be 89 wt% of the NMMO aqueous solution, so that the cellulose content of the spinning dope was 11 wt%. At this time, it was recognized that the dope was homogeneous in which undissolved cellulose particles were not included.

Comparative Example 1: Preparation of the lvocell filament fibers in a solidifying bath of low temperature

The lyocell filament fibers were prepared substantially according to the same method as in Example 1 , except that the temperature of the vertical solidifying bath was controlled to be 25 "C .

Example 3: Preparation of the tire cord

2 ply twisted yarn was prepared by Z twisting the lyocell multi-filaments prepared by Example 1 with 400 TPM, and then S twisting the Z twisted yarn with 400 TPM by using the Cable & Cord 3 type twister, that is, a CC. Twister, by Allma Co.

The tire cords, of which the pick up rate of the adhesive was 8.1 wt%, were prepared by dipping and passing the prepared lyocell twisted yarn through a conventional RFL solution under a tension of 300 g/cord, drying the same at 150 °C for 1 minute, and heat-treating the same at 180 °C under a tension of 500 g/cord for 2 minutes.

Example 4: Preparation of the tire cord

The lyocell tire cord, of which the pick up rate of the adhesive was 9.1 wt%, was prepared substantially according to the same method as in Example 3, except that the lyocell multi-filaments prepared by Example 2 were used.

Example 5: Preparation of the tire cord

The lyocell tire cord, of which the pick up rate of the adhesive was 7.5 wt%, was prepared substantially according to the same method as in Example 3, except that the tension of 600 g/cord was given in the RFL adhesive granting process.

Example 6: Preparation of the tire cord

The lyocell tire cord, of which the pick up rate of the adhesive was 6.0 wt%, was prepared substantially according to the same method as in Example 3, except that the tension of 1000 g/cord was given in the RFL adhesive granting process.

Comparative Example 2: Preparation of the tire cord by using the Iyocell filament fibers prepared in a solidifying bath of low temperature

The lyocell tire cord, of which the pick up rate of the adhesive was 8.3 wt%, was prepared substantially according to the same method as in Example 3, except that the lyocell multi-filaments prepared by Comparative Example 1 were used.

Comparative Example 3

The lyocell tire cord, of which the pick up rate of the adhesive was 4.4 wt%, was prepared substantially according to the same method as in Example 3, except that

the tension of 2200 g/cord was given in the RPL adhesive granting process.

Comparative Example 4

The lyocell tire cord, of which the pick up rate of the adhesive was 12.2 wt%, was prepared substantially according to the same method as in Example 3, except that the tension of 10 g/cord was given in the RPL adhesive granting process.

Experimental Example 1; Measurement of void diameter, strength, and elongation of the lyocell fibers The fibers obtained by Examples 1-2 and Comparative Example 1 were selected and stored in the standard condition (25 ^° C, 65 %RH) according to Korean Industrial Standard KSK 0901 for 24 hours or more so as to be in a state of moisture equilibrium, and then dried at 105 °C for 2 hours.

The average diameter of the voids remained on the cross-section of the fiber was measured in regard to the dried specimens, and the results are listed in Table 1. Among them, the transmission electron microscope (TEM) photographs of the specimens of Examples 1-2 and Comparative Example 1 are illustrated in Figs. 3-5.

Furthermore, the tenacity and elongation of the specimens of Examples 1-2 and Comparative Example 1 were measured according to a conventional method and the results are listed in Table 1.

[Table 1]

Experimental Example 2; Measurement of tenacity of the cord

The breaking strength (kgf) and the breaking elongation (%) of the tire cords prepared according to Examples 3-7 and Comparative Examples 3-6 were measured according to the KSK 0412 standard by using a low speed extension type of tensile tester of Instron Co., wherein the length of the specimen was 250 mm and the extension speed was 300 mm/min, and the results are listed in Table 2.

Experimental Example 3; Measurement of pick up rate of the adhesive

The pick up rate of the adhesive was measured in regard to the tire cords prepared according to Examples 3-6, and Comparative Examples 2-4, according to the adhesive pick up rate testing method for rayon cord of ASTM D 885.

Experimental Example 4: Measurement of degree of fatigue resistance

Fatigue testing specimens were prepared by vulcanizing the tire cords prepared according to Examples 3-6 and Comparative Examples 2-4 with rubber, and the fatigue testing was carried out by using a disc fatigue tester.

After the fatigue testing, the remained tenacity was measured and the degree of the fatigue resistance (%), which is a rate to the original tenacity, was evaluated according to the following Calculation Formula 1. Calculation Formula 1

Degree of fatigue resistance (%) = (Remained strength after fatigue testing / Strength before fatigue testing) x 100

The fatigue testing was individually carried out according to ASTM D 6588 at 100 ^° C with 2500 rpm and the extension & contraction rates of 2% and 4% for 8 hours, and the remained strength was measured after swelling the rubber by dipping the fatigue testing specimens in trichloroethane for 24 hours and separating the cord from the rubber, after the fatigue testing.

The breaking strength (kgf) was measured according to the above method as the remained strength, after drying the specimen at 105 ^° C for 2 hours by using the

tensile strength tester.

[Table 2]

From the results of Table 1 and Figs. 3-5, the filament fibers of Comparative Example 1 show low strength because the diameter of the voids remained on the cross- section of the fiber is very large, and thus there is a problem in that the fatigue resistance decreases because the dipping solution is difficult to penetrate properly when they are applied to a tire cord, while the lyocell filament fibers according to Examples 1 and 2 of the present invention have dense structure and superior strength and elongation.

Particularly, as shown in Table 2, it can be recognized that the tire cords according to Examples 3 to 6 are superior in the tensile property and especially superior in the durability against fatigue. Furthermore, it can be also recognized that the remained strength is low because the strength maintaining rate after the fatigue testing is low in Comparative Examples 2 to 4.

As shown above, the lyocell filament fibers according to the present invention are effective to be applied for the preparation of a lyocell tire cord having good fatigue resistance. Furthermore, the tire cord of the present invention shows good high speed driving performance and can be used for preparing a tire having good durability, because it has superior fatigue resistance property.