TITLE QF THE INVENTION

LYOCELL FILAMENT FIBERS AND TIRE CORD USING THE SAME BACKGROUND OF THE INVENTION

(a) Field of the Invention The present invention relates to lyocell filament fibers that can be used for rubber reinforcements, and tire cords included in tires.

(b) Description of the Related Art

A tire is a complex body of fiber/steel/rubber, and generally has a structure as illustrated in Fig. 1. Namely, the steel and the fiber cord take a 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 performance such as fatigue resistance, shear tenacity, durability, repelling elasticity, adhesive power to a rubber, and the like. Therefore, various cords made of suitable materials are used according to the performances required to the tire.

Recently, rayon, nylon, polyester, steel, aramid, and the like have been generally used as materials for a cord, rayon and polyester have been used for a body ply (or a carcass) (6 in Fig. 1), nylon has been mainly used for a cap ply (4 in Fig. 1), and steel and aramid have been mainly used for a tire-belt part (5 in Fig. 1). The structure and the 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 stand against 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 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 is mostly composed of steel wire, and it lessens the 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 a rubber is coated on the steel wires; it takes 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 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 air inflow during shaping.

Generally, nylon, polyester, rayon, and the like are use as materials for a tire cord. The rating and the use of the tire are limited according to the merits and demerits of the materials.

Nylon fiber is mainly used in tires for heavy-duty trucks that are subjected to heavy weight loads, or in tires mainly used on irregular surfaces such as unpaved roads, 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 low modulus.

Polyester fiber has good dimensional stability and a competitive price in comparison with the nylon, its tenacity and adhesive strength are being improved by continuous studies, and 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 there are still limitations in heat resistance, adhesive strength, and so on.

Rayon fiber, a regenerated cellulose fiber, shows a superior strength maintaining rate and dimensional stability at high temperatures. Therefore, the rayon fiber is known as the most suitable material for a tire cord. However, it requires substantial moisture control when preparing the tire, because the strength 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 by price (strength by 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, a general cellulose-based tire cord, such as rayon and the like, has characteristics of stiff molecular structure and low elongation, and thus it is difficult to withstand repeated expansion and contraction at high temperatures inside the tire, and technical developments to improve the difficulty are required.

Furthermore, there is a problem of that the dimensional stability deteriorates at high temperatures during preparation of the tire because the dimensional stability is superior as the elongation at yield point is low, but a general cellulose-based tire cord, such as rayon and the like, has a stiff molecular structure, and the elongation at yield point is high and the yield stress is also low.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide lyocell filament fibers for preparing a tire cord that is superior in durability and driving performance.

Another aspect of the present invention is to provide a tire cord that is superior in driving stability and riding comfort during high speed driving, and that is prepared by using the lyocell filament fibers.

Still another aspect of the present invention is to provide a tire cord that is superior in dimensional stability at high temperatures and high pressures.

Still another aspect of the present invention is to provide a tire cord that is superior in not only durability and driving performance but also dimensional stability at high temperatures.

According to the first embodiment of the present invention, the present invention provides lyocell filament fibers of which the shrinkage behavior factor (SBF) defined by the following Calculation Formula 1 is 0.1 (cN/tex)/% or more at a temperature of 180 °C :

[Calculation Formula 1]

Shrinkage behavior factor (SBF) = Shrinkage stress (cN/tex) / Shrinkage rate (%).

The present invention also provides a tire cord prepared by treating the lyocell filament fibers with an adhesive for a tire cord.

According to the second embodiment of the present invention, the present invention provides a lyocell tire cord of which the length deformation rate (LDR) defined by the following Calculation Formula 2 is -1.5% to 1.5%: [Calculation Formula 2]

Length deformation rate (LDR) = (L _t - Lj)ZLj x 100 wherein

Lj is the initial length of the cord, and

L _t is the terminal length measured at 180 ^° C after loading the initial load of 0.0565gZd.

According to the third embodiment of the present invention, the present invention provides a lyocell tire cord including a twisted yarn of lyocell filament fibers and an adhesive, of which the flat spot factor defined by the following Calculation Formula 3 is 2.0 or less: [Calculation Formula 3]

Flat spot factor (%) = (Li - L ₂ )ZL ₀ x 100 wherein

L ₀ is the initial length of the cord,

Li is the length of the cord measured after loading the load corresponding to 13% of the breaking tenacity of the cord to the cord at a temperature of 120 ^° C for 5 minutes and cooling the same to 20 ^° C while maintaining the load, and

L ₂ is the length of the cord measured after loading the load corresponding to 13% of the breaking tenacity of the cord to the cord at the temperature of 120 ^° C for 5 minutes and cooling the same to 20 ^° C while maintaining a load of 0.01 gZd. According to the fourth embodiment of the present invention, the present invention provides lyocell filament fibers of which the elongation at yield point, which is defined by the Meredith equation in the stress-strain curve measured at 120 ^° C , is 1.7% or less.

The present invention also provides a tire cord including the lyocell filament

fibers.

According to the fifth embodiment of the present invention, the present invention provides a tire cord of which the elongation at yield point, which is defined by the Meredith equation in the stress-strain curve measured at 120 ^" C , is 2.7% or less. According to the sixth embodiment of the present invention, the present invention provides lyocell filament fibers of which the ratio Mt/Mi of the terminal modulus Mt to the initial modulus Mi is 0.05 to 0.5.

The present invention also provides a tire cord including the lyocell filament fibers. According to the seventh embodiment of the present invention, the present invention provides a tire cord including the lyocell filament fibers of which the ratio Mt/Mi of the terminal modulus Mt to the initial modulus Mi is 0.1 to 1.0.

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

Fig. 2 is a drawing representing the Meredith drawing figure for defining the yield point of the fiber.

Fig. 3 is a constructive drawing representing the device for preparing the lyocell filament fiber according to one embodiment of the present invention.

Fig. 4 is an enlarged constructive drawing of a pulling part and a washing device of the spinning device of Fig. 3.

Fig. 5 is a schematic drawing of a shrinkage behavior tester used for measuring shrinkage behavior factor (SBF).

Fig. 6 is a length deformation graph of the tire cord prepared according to Example 6.

Fig. 7 is a length deformation graph of the tire cord prepared according to Example 8. Fig. 8 is a length deformation graph of the tire cord prepared according to

Example 9.

Fig. 9 is a length deformation graph of the tire cord prepared according to Example 10.

Fig. 10 is a graph representing the stress-strain curve of Comparative Example 1 and Examples 11 and 12.

Fig. 11 is a graph representing the stress-strain curve of Examples 13 and 14.

Fig. 12 is a graph representing the tenacity and elongation of the filament fibers of the dried condition of Examples 15-17 and Comparative Example 2.

Fig. 13 is a graph representing the tenacity and elongation of the filament fibers of the standard condition of Examples 15-17 and Comparative Example 2.

Fig. 14 is a graph representing the tenacity and elongation of the tire cord of the dried condition of Examples 18-20 and Comparative Example 3.

Explanations for signs of the principal parts of the drawings>

10: gear pump 20: spinning die 30: non-coagulated fiber

40: first coagulating bath 42: second coagulating 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 (counter-clockwise twisting) and S twisting (clockwise twisting) (or S twisting and Z 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 "tire cord" or "cord".

The lyocell filament fibers according to the first embodiment of the present invention that the present invention intends to develop have the most suitable properties to be used for a tire cord, and specifically they are characterized by the shrinkage behavior factor being defined by the following Calculation Formula 1 at 0.1 (cN/tex)/% or more.

Because the lyocell filament fibers of the present invention have the shrinkage behavior factor of 0.1 (cN/tex)/% or more at 180 ^° C which corresponds to the tire forming temperature, the superior properties of the filament fibers themselves can be revealed in the tire as they are. It is preferable for the shrinkage behavior factor to be higher, and thus the maximum value of the shrinkage behavior factor is not limited particularly to or by them. It may preferably be 0.1 (cN/tex)/%, or less.

The shrinkage stress and the shrinkage rate are based on the values measured at a temperature condition of 180 ^° C for 2 minutes after fixing the specimen with the initial load of 0.0565 g/d by using a shrinkage behavior tester (made by Testrite Co.), in the present invention.

In order to be applied to a tire via the preparation process of the tire cord, the shrinkage rate of the lyocell filament fibers of the present invention may be 2.0% or less

at 180 TC, and preferably 0.1 to 2.0%.

The lyocell filament fibers may be multi-filament fibers, of which the total number of filaments is 200 to 2000 and the total fineness is 200 to 3000 denier.

Furthermore, the present tire cord may have the shrinkage stress of 0.01 cN/tex or more, or 0.01 to 1 cN/tex at 180 ^° C . Furthermore, the shrinkage rate of the present tire cord may be a negative value at 180 ^° C, and preferably a value of -0.1 to -2%.

When the shrinkage rate of the tire cord has a negative value, the buffer effect against severe conditions, such as high temperatures and high tensions, which can occur during high speed driving, can be expected, and the superior dimensional stability can be maintained because the shrinkage rate has a negative value in the narrow range of -0.1 to -2%.

The present lyocell filament fibers according to the first embodiment have the most suitable properties to be applied to a tire cord, because they have both superior shrinkage stress and low shrinkage rate. The tire cord according to the second embodiment of the present invention that the present invention intends to develop has high dimensional stability at high temperature and good durability, and particularly has characteristics in the length deformation rate defined by the following Calculation Formula 2. That is, the lyocell tire cord of the present invention is excellent in maintaining its shape inside the tire, because the elongation or the contraction of the length occurs in a small quantity at a high temperature.

[Calculation Formula 2]

Length deformation rate = (L _t - L ₁ )ZL ₁ x 100 wherein

Lj is the initial length of the cord, and

L _t is the terminal length measured at 180 ^° C after loading the initial load of 0.0565g/d.

In Calculation Formula 2, L _t is based on the value measured by using the shrinkage behavior tester (made by Testrite Co.) after loading the initial load of 0.0565 g/d and passing 2 minutes at the temperature of 180 ^° C . The initial load of 0.0565 g/d is a supposed load that the cord suffers in a tire fitted to a car.

Generally, the internal temperature of the tire rises by friction during driving of a car, and the tire cord is exposed to severe conditions of high temperature and high pressure because the conditions of high temperature and high pressure are continued for a long time particularly during high speed driving.

At this time, the tire cord of the present invention hardly deforms, and the driving performance of the tire is maintained. Furthermore, there is an effect that the buffer property against external stress appears and a rupture of the tire can be prevented so far as the permanent deformation of the cord does not occur, when the length deformation rate is a positive value of 1.5% or less. There is also an effect of supporting the tire more firmly by inhibiting the deformation of the tire during high speed driving so far as the permanent deformation of the cord does not occur, when the length deformation rate is a negative value of -1.5% or more. However, it is more preferable that the length deformation rate is 0 to 1.5%, because safety is given a great deal of weight rather than the property of supporting the tire during high speed driving.

Furthermore, the stress of the present lyocell tire cord measured by using the shrinkage behavior tester (made by Testrite Co.) after loading the initial load of 0.0565 g/d and passing 2 minutes at the temperature condition of 180 ^° C may be 0 cN/tex or

more, and also may be 0.01 to 0.1 cN/tex. As the stress is large, the cord performs a role of standing against the expansion of the tire due to the centrifugal force generated during high speed driving and inhibits the deformation of the tire, and thus it can raise stability. The lyocell tire cord of the present invention according to the second embodiment has good durability when it is applied to the tire, because the cord has good dimensional stability at high temperature.

Hereinafter, the lyocell tire cord according to the third embodiment of the present invention is explained. A tire is exposed to conditions of high temperature, expansion, and high pressure and the cord deforms toward its length direction during driving, and the difference between the tension of the cord positioned at the contacting part of the tire to the ground and the tension of the cord positioned at an upper part of the tire occurs when the cord cools down from the deformed state when a vehicle therewith is parked. At this time, the cord positioned at the contacting part of the tire to the ground cannot recover from the shape deformation that occurs during driving by the load, and the cord positioned at the other part of the tire recovers from the shape deformation by disappearing of the load, and thus the shape deformation between the tire cord positioned at the contacting part of the tire to the ground and the tire cord positioned at the other part of the tire becomes different. Such phenomenon is called a "flat spot", and the present invention is characterized by maintaining the flat spot factor to be within a specific range or less.

That is, the present inventors understood that the flat spot phenomenon may cause clattering and may affect riding comfort while driving the car, and that when the

flat spot phenomenon is not out of the specific range, the stability and the riding comfort particularly during high speed driving may be secured, and accomplished the present invention.

Therefore, the lyocell tire cord according to the third embodiment provided in the present invention is a dipped lyocell cord including the lyocell filament fibers having a flat spot factor securing the stability and making the riding comfort good during high speed driving, and the adhesive. The flat spot factor of the dipped cord defined by the following Calculation Formula 3 may be 2.0% or less, and may be 0.5 to

2.0%, and also may be 0.5 to 1.5%, in order to secure the stability and the riding comfort during high speed driving of a car:

[Calculation Formula 3]

Flat spot factor (%) - (Li - L ₂ )IL ₀ x 100 wherein

L ₀ is the initial length of the cord, Li is the length of the cord measured after loading the load corresponding to

13% of the breaking tenacity of the cord to the cord at the temperature of 120 °C for 5 minutes and cooling the same to 20 ^° C while maintaining the load, and

L ₂ is the length of the cord measured after loading the load corresponding to 13% of the breaking tenacity of the cord to the cord at the temperature of 120 ^° C for 5 minutes and cooling the same to 20 ^° C while maintaining a load of 0.01 g/d.

L ₂ corresponds to the length of the cord in the condition that the load is substantially eliminated, and the reason for maintaining the load of 0.01 g/d is for maintaining the straight line of the cord so far as no tension is substantially applied to the cord, when L ₂ is measured, and accordingly the contribution of the load of 0.01 g/d

to the L ₂ is substantially ignorable.

Furthermore, the length deformation rate defined by the following Calculation Formula 4 of the tire cord of the present invention may be 5% or less, and may be 0 to 5%: [Calculation Formula 4]

Length deformation rate (%) = (Li - L _o )/L _o x 100 wherein

L ₀ is the initial length of the cord, and

Li is the length of the cord measured after loading the load corresponding to 13% of the breaking tenacity of the cord to the cord at the temperature of 120 ^° C for 5 minutes and cooling the same to 20 ^° C while maintaining the load.

The tire cord of the present invention hardly deforms even in the condition of high temperature and high load, and maintains superior driving performance of the tire. Furthermore, when the length deformation rate is 5% or less, the driving stability increases because the shape deformation of the tire is restrained by the centrifugal force during high speed driving, and the local pressure and the like caused by the shape deformation of the tire is prevented and the durability is improved by the scattering effect of the external force.

At this time, the length deformation rate of the present invention is based on the value measured under the above conditions by using the shrinkage behavior tester

(made by Testrite Co.) according to the shrinkage rate testing method of ASTM D 5591.

The lyocell tire cord of the present invention according to the third embodiment has an effect of improving the riding comfort by restraining the flat spot phenomenon generated by the length deformation caused by the local difference of the tension during

parking after driving.

The fourth embodiment of the present invention is for resolving the problem of the dimensional stability deterioration of the rayon fiber, which is usually used for the tire cord, at high temperature. That is, the fourth embodiment is to provide lyocell filament fibers having low elongation and high yield stress at 120 ^° C , which is the temperature corresponding to the high speed driving state and making the dimensional stability good when they are made into a tire cord.

Such lyocell filament fibers according to the present invention are characterized in that the elongation at yield point, which is defined by the Meredith equation in the stress-strain curve measured at the high temperature of 120 ^° C , is 1.7% or less.

Furthermore, the lyocell filament fibers have elongation of 0.4% or less in the initial elastic section of the stress-strain curve measured at 120 ^° C .

Furthermore, the lyocell filament fibers have an elongation maintaining rate (S) of 95% or more, or 95 to 100%, which is defined by the following Calculation Formula 5:

[Calculation Formula 5]

S = Si _2O /Sios x 100 wherein

S is the elongation maintaining rate, S i ₂ o is the elongation at yield point measured at 120 ^° C , and

Sio ₅ is the elongation at yield point measured at 105 ^° C .

In Calculation Formula 5, Si ₂₀ is for representing the properties at high temperatures, and Si ₀₅ is for representing the properties in a dried condition, in order to exclude the influence of moisture.

The stress at yield point of the lyocell filament fibers, which is defined by the Meredith equation in the stress-strain curve measured at 120 ^° C, is 4 g/d or more, and preferably 4 to 4.5 g/d.

Each value of the properties of the lyocell filament fibers in the initial elastic section is based on the value measured according to Korean Industrial Standard KSK 0412 by using a low speed extension type of tensile tester (universal testing machine made by Instron Co.).

In addition, the definitions of the yield point and the Meredith equation are explained as follows. Firstly, the strain increases in proportion to the increase of the stress, and the stress and the strain form linear relations in the stress-strain curve when the external force is given to the specimen in the beginning, and the yield point means the point of that the linear part is finished and the specimen start to deform easily. The industrial material like a metal shows a clear yield point, but it is difficult to determine the yield stress and the yield strain in polymeric material like a fiber.

Therefore, Meredith defined the yield point of the fiber as the contacting point of the stress-strain curve and its tangent line parallel to the straight line linking the origin and the breaking point of the stress-strain curve of the fiber ("Textile physics",

Bando press, 1995. 08. 25., pages 119-120; R. Meredith, J.T.I (Journal of Textile Institute), 36, T107, 1945). Fig. 2 represents the drawing method by Meredith.

Furthermore, a small deformation of the molecular chain occurs and the elastic recovery of the fiber is possible in the section until the yield point. Therefore, the present invention satisfies the conditions and can provide the tire cord capable of high speed driving, because the modulus in the section changes less at a high temperature

condition and the dimensional stability against the external stress is good.

The lyocell filament fibers of the present invention according to the fourth embodiment have low elongation and high yield stress at 120 ^° C corresponding to the condition of high speed driving, and there is an effect of making the dimensional stability good while preparing the tire cord.

The tire cord according to the fifth embodiment of the present invention has low elongation and high yield stress at 120 ^° C corresponding to the condition of high speed driving, and its dimensional stability is superior.

The lyocell tire cord according to the present invention may have elongation at yield point, which is defined by the Meredith equation in the stress-strain curve measured at a high temperature of 120 ^° C, of 3.3% or less, and preferably 2.7% or less.

Furthermore, the lyocell tire cord of the present invention may have elongation of 1.3% or less, and preferably 1.1% or less, in the initial elastic section of the stress-strain curve measured at 120 ^° C . At this time, the initial elastic section means the section of the tangent line to the stress-strain curve at the origin of the stress-strain curve.

Furthermore, the elongation maintaining rate of the lyocell tire cord of the present invention, which is defined by the following Calculation Formula 6, may be 95% or more, or may be 95 to 110%, or may be 95 to 98%: [Calculation Formula 6] s = s _12O /s _1O5 ^χ ioo wherein

S is the elongation maintaining rate, Sj ₂₀ is the elongation at yield point measured at 120 °C, and

Sio ₅ is the elongation at yield point measured at 105 ^° C .

In Calculation Formula 6, S ₁₂₀ represents the properties at high temperatures, and Sio ₅ represents the properties in a dried condition in order to exclude the influence of moisture. Furthermore, the lyocell tire cord has the stress at yield point, which is defined by the Meredith equation in the stress-strain curve measured at 120 ^° C, of 3.4 g/d or more, and preferably of 3.5 to 4 g/d.

Each value of the properties of the lyocell tire cord in the initial elastic section is based on the value measured according to KSK 0412 standard by using a low speed extension type of tensile tester (universal testing machine made by Instron Co.).

Furthermore, the terminology of each property is the same as what is defined in the fourth embodiment.

The lyocell tire cord of the present invention according to the fifth embodiment has low elongation and high yield stress at 120 "C , corresponding to the condition of high speed driving, and it has an effect of improving the dimensional stability.

The sixth embodiment of the present invention provides lyocell filament fibers of which the initial modulus and the terminal modulus are included in a specific range.

In the present invention, firstly, the initial modulus (Mi), the terminal modulus (Mt), and the elongation at maximum point of the lyocell filament fibers are based on the values measured by using the universal testing machine (UTM) of Instron Co. according to the method of the American Society of Testing Materials (ASTM) D 885. The elongation at maximum point means the elongation at the point representing maximum tenacity. The initial modulus means the modulus value at the initial state of the stress. In the measuring method, the initial modulus is defined as the ratio

(δSt_i/δSr_i) of the increase in the stress (δSt_i) to the increase in the elongation (δSr_i), when the elongation increases from 0% to 0.5%. The terminal modulus means the modulus value at the stress state at break, and it is defined as the ratio (δSt_t/δSr_t) of the increase in the stress (δSt_t) to the increase in the elongation (δSr_t), when the elongation increases from breaking elongation - 0.5% to the breaking elongation.

In a common method of preparing a tire cord and a method of preparing a tire by using the same, the initial modulus value of the lyocell filament fibers has a very important meaning. As the initial modulus value of the lyocell filament fibers is high, resistance against the external stress is large, and the effect that the shape deformation, which can occur during the preparing process of the tire cord, is low can be obtained.

Furthermore, the terminal modulus of the lyocell filament fibers has a very important meaning to the tire including the tire cord prepared by using the lyocell filament fibers, according to the driving condition. Furthermore, the temperature of the tire increases generally by friction when the car is driving, and the tire cord is also exposed to severe conditions of high temperature and high pressure, as the conditions of high temperature and high pressure are maintained for a long time during high speed driving. At this time, when the terminal modulus of the filament fibers included in the tire cord is low, the shape of the cord deforms and the driving performance may be deteriorated, and when the terminal modulus of the filament fibers is too high, the buffer property against the external stress in an extreme situation is not particularly good and there is a danger that the tire cord may burst.

Therefore, it is preferable that the initial modulus of the lyocell filament fibers

for the tire cord is higher, and it is also preferable that the terminal modulus is within a specific range.

Accordingly, the present inventors carried out studies for improving the dimensional stability and the fatigue resistance of the tire cord, which is used as a reinforcement of the tire, and the durability and the driving performance of the tire. As the result, the present inventors found that such characteristics can be obtained by maintaining the initial modulus of the lyocell filament fibers to be high and controlling the ratio of the initial modulus and the terminal modulus to be included in a specific range. Namely, the parameter Mt/Mi defined in the present invention is used to determine the most suitable property range of the initial modulus Mi and the terminal modulus Mt of the lyocell filament fibers.

Considering the characteristics of the material called lyocell, the process conditions of preparing the tire, the durability against severe conditions presented during driving, and so on, the value of Mt/Mi of the lyocell filament fibers of the present invention may be 0.05 to 0.5.

The Mt value and the Mi value may be based on the values measured after conditioning the twisted yarn of the filaments, of which the total number of filaments is 1000, the total fineness is 1650 denier, and the twisting number is 80 TPM, at the standard condition (25 ^° C , 65%RH) for 24 hours, and drying the same at 105 ^° C for 4 hours (hereinafter "dried condition" means the specimen treated by the above conditions). However, the above numerical values are merely a standard for the measurement, and the lyocell filament fibers of the present invention are not limited to have the above number of filaments, the fineness, and the twisting number.

The initial modulus Mi of the lyocell filament fibers of the present invention

measured according to the standard may be 0.5 (g/d)/% or more, and may also be 0.5 to 2.0 (g/d)/%.

Furthermore, the lyocell filament fibers of the present invention may have an elongation at maximum point of 5 to 10%, in order to show the basic characteristics as a reinforcement for a tire cord.

Furthermore, general cellulose-based fibers, especially rayon-based fibers, have a problem in that the properties are severely changed by moisture, but the lyocell filament fibers of the present invention have an advantage in that the change of the properties by moisture is low. For example, the filament fibers of the present invention may have

(Mt/Mi) _c /(Mt/Mi) _D of 0.5 to 1.0, wherein (Mt/Mi) _D is defined by Mt/Mi of the filament fibers of the dried condition and (Mt/Mi)c is defined by Mt/Mi of the filament fibers conditioned in the standard condition (25 ^° C, 65%RH). As the value of (Mt/Mi)c/(Mt/Mi)o becomes near 1 , the effect by moisture is low, and when the value is included at least in the above range, the deterioration of the properties due to the moisture during the process can be prevented.

At this time, the value of (Mt/Mi)c and the value of (Mt/Mi)D may be based on the values measured by using the twisted yarn of which the total number of filaments is 1000, the total fineness is 1650 denier, and the twisting number is 80 TPM, however, the above numerical values are also merely a standard for the measurement, and the lyocell filament fibers of the present invention are not limited to have the above number of filaments, the fineness, and the twisting number.

The lyocell filament fibers of the present invention according to the sixth embodiment have superior dimensional stability and fatigue resistance effect, when the

ratio of the terminal modulus to the initial modulus is included in the specific range.

The seventh embodiment of the present invention is to provide a lyocell tire cord, of which the initial modulus and the terminal modulus are included in the specific range. It is preferable that the initial modulus of the tire cord is higher, and it is also preferable that the terminal modulus is included in a specific range.

Considering the characteristics, it is the parameter Mt/Mi of the present invention that determines the most suitable property range of the initial modulus and the terminal modulus of the tire cord. Therefore, considering the characteristics of the lyocell filament fibers, the process conditions of preparing the tire, the durability against the severe conditions presented during driving, and so on, the lyocell tire cord of the present invention is characterized by the cord including the lyocell filament fibers as the main component and the ratio (Mt/Mi) of the terminal modulus Mt and the initial modulus Mi being 0.1 to 1.0.

In the present invention, the initial modulus (Mi), the terminal modulus (Mt), and the elongation at maximum point of the lyocell filament fibers are based on the values measured by using the universal testing machine (UTM) of Instron Co. according to the method of the American Society of Testing Materials (ASTM) D 885. Further, the elongation at maximum point, the initial modulus, the measuring method, and the like are the same as defined in the sixth embodiment.

The lyocell tire cord of the present invention according to the seventh embodiment has superior dimensional stability and fatigue resistance effect, as the ratio of the terminal modulus to the initial modulus is included in the specific range.

Hereinafter, the method of preparing the lyocell filament fibers according to one preferable 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 easily carry it out. At this time, the method of preparing the lyocell filament fibers 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 can carry out various modifications and reforms by using the basic concept defined in the present claims.

Fig. 3 is a constructive drawing representing the device for preparing the lyocell filament fibers according to one embodiment of the present invention. 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 coagulating bath 40 and a second coagulating bath 42 for coagulating the non-coagulated fibers 30 discharged from the spinning die. The filaments having passed through the first coagulating bath 40 are passed through the second coagulating 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 are dried in a drying device 70 and then final lyocell filaments can be obtained by winding them on a winding roll.

At this time, the spinning method of the lyocell filament fibers of the present invention is not limited to or by the method illustrated in Fig. 3, and both of a noncontinuous type and a continuous type can be used.

The noncontinuous type is classified into a centrifugal spinning method and a bobbin spinning method, and a Nelson type, an Oscar-Corn type and the like can be used in the case of the continuous type. Furthermore, the spinning method used for preparing a rayon filament fiber, a cellulose-based fiber, can be modified and used in the lyocell process. Furthermore, the coagulating baths 40, 42 are for coagulating the filament fibers discharged from the spinning die, and common baths can also be used. For one embodiment of the present method of preparing the lyocell filament fibers of the present invention, the present invention makes cellulose sheets into powders by introducing the same into a pulverizer equipped with a screen filter, the powders are stored in a pulp powder 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, which is not illustrated in the Figs.

After this, the mixture becomes a homogeneous solution by passing a mixing part and a dissolving part, and the solution is spun into the vertical coagulating baths 40,

42 through a spinning pack equipped with spinning nozzles.

N-methylmorpholine-N-oxide (NMMO) is eliminated from the filaments coagulated in the vertical coagulating baths by NMMO-free water in the washing device 60.

At this time, the present invention can secure superior spinning stability and provide good elongation and modulus by effectively controlling the coagulating draft ratio of the filaments passing through the pulling part before the washing step, during the spinning process of the present filaments.

Furthermore, the filaments of the present invention passed through the coagulating baths 40, 42 can be transferred by the driving force of the pulling part 50 illustrated in Fig. 3.

Fig. 4 is an enlarged constructive drawing of the pulling part 50 and the washing device 60 according to one embodiment of the present invention. The coagulating draft ratio can be controlled by controlling the progressing speed Vi of the filaments at the pulling part 50 and the progressing speed V ₂ of the filaments at the washing device 60.

The present invention controls the coagulating draft ratio of the filament represented by the following Calculation Formula 7 to be 1 or less between the pulling part 50 and the washing device 60, in order to raise the elongation and the modulus of the lyocell filament fibers finally produced:

[Calculation Formula 7]

Coagulating draft ratio = V ₂ /Vj wherein

Vi is the progressing speed of the filaments coming out of the pulling part 50, and

V ₂ is the progressing speed of the filaments entering the washing device 60.

Explaining in more detail, the progressing speed Vi of the filaments coming out of the pulling part is the progressing speed of the filaments at the final pulling roll of the pulling part before applying the coagulated filaments to the washing process, and the progressing speed V ₂ of the filaments entering the washing device is the progressing speed of the filaments at the first washing roll where the filaments passed through the pulling part are firstly applied to the washing process.

The coagulating draft ratio may be controlled to be 1 or less, and preferably to be 0.8 to 0.99, and more preferably to be 0.95 to 0.99. When the coagulating draft ratio is over 1, it is impossible to give sufficient elongation to the lyocell filament fibers.

Consequently, the solvent is eliminated at the washing device 60, and 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.

Here, the lyocell filament fibers of the present invention may be prepared according to the preparing method including the steps of preparing a spinning dope by dissolving the cellulose in a solvent mixture of N-methylmorpholine-N-oxide (NMMO) and water, spinning filament fibers from the spinning dope by using the spinning device equipped with spinning nozzles, washing the spun filament fibers, and drying the washed filament fibers.

As the spinning dope, 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 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 conditions to prepare the cellulose-based filaments and the present invention is not limited to or by them.

Furthermore, the tension of 0.1 to 2 g/d or 0.3 to 1 g/d can be given to the filaments and 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, concrete drying conditions can be selected arbitrarily in the range of the tension and the temperature under necessity. The range of the tension and the temperature in the drying step of the multi-filaments can also be selected arbitrarily under necessity, and the conditions are not particularly limited. Furthermore, the washing, the drying, and the post-treating techniques after spinning of the filament fibers can follow those of a general wet spinning method. Furthermore, the spinning method used for preparing a rayon filament fiber, a cellulose-based fiber, can be modified and used to the lyocell process.

Furthermore, the preparing method can further include the process of applying spinning oil to the filaments before or during the drying step of the filament fibers. The present invention makes it possible to show the most suitable modulus value by controlling uniform adhesion property and permeability of the oil by controlling the moisture regain of the filaments to be 50 to 100 wt% before applying the spinning oil. That is, the moisture regain of the filaments may be 50 wt% or more in order to prevent the oil from penetrating too deeply into the filaments and decreasing the modulus, and the moisture regain of the filaments may be 100 wt% or less in order to cause the adhesion property of the oil to the filaments. On the other hand, the tire cord of the present invention may be prepared by twisting the cellulose-based filament fibers (that is, the lyocell filament fibers) satisfying the properties, treating the twisted yarn with an adhesive solution for a tire cord according to a conventional dipping method, and drying and heat-treating the same.

In the first embodiment to the seventh embodiment of the present invention, the shape of the tire cord is not particularly limited, and the cellulose-based twisted yarn including the lyocell filament fibers can be used. However, it may include the 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.

The lyocell tire cord of the present invention has good dimensional stability and can be applied to a body ply or a cap ply for a pneumatic tire.

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. At this time, the other processing conditions except that the lyocell filament fibers are used can be added and subtracted under necessity, and they are not limited particularly in the present invention.

An adhesive solution having the same components of a conventional adhesive solution for a tire cord may be used as the adhesive solution used for preparing the tire cord, and a resorcinol/formaldehyde/latex (RFL) solution may be preferably used.

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, the tension of 20 to 2000 g/cord can be granted to the twisted yarn passing through the adhesive solution, when preparing the tire cord according to the third embodiment. The drying process is carried out with the tension of 20 to 2000 g/cord at 105 to

160 ^° C for 1 to 10 minutes. When drying the cord while giving the tension with the above condition in the temperature range, it is possible to delay the penetrating speed of the adhesive because of the rapid drying of the adhesive solution, and the advantageous properties for showing the strength can be obtained by minimizing the damage of the

dried cord.

The heat-treating process may be carried out with the tension of 20 to 2000 g/cord at 105 to 220 ^° C , or 150 to 220 ^° C , for 1 to 10 minutes. When heat-treating the cord while giving the tension with the above condition in the temperature range, it is possible to raise the adhesive power while decreasing the damage of the cord by promoting the reaction between the lyocell twisted yarn and the adhesive.

The reason for giving 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 granted 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 granted independently in each process in order to prevent the adhesive from penetrating excessively into the tire cord.

The moisture included in the lyocell cord and the adhesive solution is dried in the drying process, and the heat-treating process gives adhesive power to the tire cord by making the adhesive react.

Details except those disclosed above can be added under necessity, 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.

Example 1

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.

The cellulose powders were swelled in a 50 wt% NMMO aqueous solution. At this time, the content of the cellulose in the NMMO aqueous solution was 6.5 wt%. After dissolving the cellulose completely while eliminating the remaining water from the swelled cellulose slurry so as to make the 50 wt% NMMO aqueous solution be an 89 wt% NMMO aqueous solution, the spinning dope was discharged through a discharging screw. At this time, the cellulose content of the discharged spinning dope was 11 wt% and it was recognized that the dope was homogeneous in which undissolved cellulose particles were not included.

The cellulose dope was spun by using a die, of which the total number of nozzles was 1000 and the cross-sectional area of the nozzle was 0.047mirf, so that the total fineness of the final filament fibers was 1650 denier.

The NMMO was completely eliminated from the discharged and coagulated multi-filament fibers by being sprayed with washing water, and the un-dried multi-filament fibers were dried at the 3-step drying rolls and the cellulose-based multi-filaments (the lyocell filament fibers) were obtained. The tension between the first and second drying rolls was controlled to be 0.2 g/d, the tension between the second and third drying rolls was controlled to be 0.3 g/d, and the temperatures of the rolls were adjusted to 120 "C , 120 "C , and 105 °C , successively.

Example 2

The multi-filament fibers were prepared substantially according to the same method as in Example 1, except that the tension between the first and second drying

rolls was controlled to be 0.3 g/d, the tension between the second and third drying rolls was controlled to be 0.4 g/d, and the temperatures of the rolls were adjusted to 120 ^" C , 140 ^° C , and 120 ^° C , successively.

Example 3

The multi-filament fibers were prepared substantially according to the same method as in Example 1, except that 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 temperatures of the rolls were adjusted to 130 ^° C, 140 ^° C, and 105 ^° C, successively.

Examples 4 to 6

The 2 ply twisted yarns were prepared by Z twisting the multi-filament fibers according to Examples 1 to 3 with 400 TPM and then S twisting the Z twisted yarns with 400 TPM by using the Cable & Cord 3type twister, that is, a CC. Twister, by Allma Co.

The tire cords were prepared by dipping and passing the twisted yarns through a resorcinol/formaldehyde/latex (RFL) adhesive solution, drying the same at 150 ^" C for 2 minutes, and heat-treating the same at 180 ^° C for 2 minutes. The filament fibers prepared according to Examples 1 to 3 and the tire cords prepared according to Examples 4 to 6 were stored in the standard condition (25 ^° C, 65%RH) for 24 hours, and the shrinkage stress and the shrinkage rate were measured by the following method according to ASTM D 5591 by using the shrinkage behavior tester (made by Testrite Co.) of Fig. 5, and the shrinkage behavior factor of the filament

fibers was calculated from the measured shrinkage rate and shrinkage stress of the filament fibers.

The measured results of the filament fibers are listed in the following Table 1 , and the measured results of the cords are listed in the following Table 2.

- The shrinkage stress (cN/tex): the stress was measured at the temperature of 180 ^° C after fixing the filament fibers and the cords with the load of 0.0565 g/d by using the shrinkage behavior tester.

- The shrinkage rate (%): the shrinkage rate was measured at the temperature of 180 ^° C after fixing the filament fibers and the cords with the load of 0.0565 g/d by using the shrinkage behavior tester.

[Table 1]

As shown in Table 1 , it can be recognized that the lyocell filament fibers of the present invention show high shrinkage behavior factor of 0.1 (cN/tex)/% or more, because they have low shrinkage rate and high shrinkage stress.

[Table 2]

As shown in Table 2, the lyocell tire cords of the present invention show the shrinkage rates of negative value.

Example 7

The multi-filament fibers were prepared substantially according to the same method as in Example 1, except that the tension between the first and second drying rolls was controlled to be 0.2 g/d, the tension between the second and third drying rolls was controlled to be 0.3 g/d, and the temperatures of the rolls were adjusted to 130 °C , 150 ^° C , and 105 ⁰ C, successively.

Experimental Example 1

The shrinkage stresses of the tire cords prepared according to Examples 4 to 7 were measured according to the above method by using the testing method of ASTM D 5591 and the shrinkage behavior tester of Fig. 5. Furthermore, their length deformation rates were also measured and the results are listed in the following Table 3.

[Table 3]

As shown in Table 3, the length deformation of the lyocell tire cord of the present invention is less in the condition of high temperature, and not only the stability during high speed driving is good but it is also possible to secure durability when it is applied to the tire.

Example 8

The lyocell tire cord was prepared substantially according to the same method as in Example 4, except that the twisted yarn of the lyocell multi-filaments prepared in

Example 1 was dipped in and passed through a common adhesive RFL solution under the tension of 500 g/cord, dried at 150 ^° C for 1 minute, and heat-treated at 180 ^° C for 2 minutes under the tension of 500 g/cord.

Example 9

The lyocell tire cord was prepared substantially according to the same method as in Example 4, except that the tension between the first and second drying rolls was controlled to be 0.3 g/d, the tension between the second and third drying rolls was controlled to be 0.4 g/d, and the temperatures of the rolls were adjusted to 120 ^° C , 120 ^° C , and 105 "C , successively, in the drying process of the lyocell multi-filament fibers of Example 1.

Example 10

The lyocell tire cord was prepared substantially according to the same method as in Example 4, except that the tension between the first and second drying rolls was controlled to be 0.3 g/d, the tension between the second and third drying rolls was controlled to be 0.4 g/d, and the temperatures of the rolls were adjusted to 120 ^° C , 140 ^° C, and 120 °C, successively, in the drying process of the lyocell multi-filament fibers of Example 1.

Experimental Example 2

[Measurement of the flat spot factor and the length deformation rate of the cord]

As to the lyocell tire cords prepared according to Examples 6 and 8-10, the length deformation was measured by using the shrinkage behavior tester (made by Testrite Co.) on the basis of the shrinkage rate testing method of ASTM D 5591, and specifically the deformation of the length Li when the situation was changed from the high temperature and high load state to the low temperature and high load state and the deformation of the length L ₂ when the situation was changed from the high temperature and high load state to the low temperature and low load state were measured, respectively.

The initial length L ₀ of the cord specimen used in the measurement was 270mm.

The high temperature and high load state is a supposed condition of the temperature and the load given to the tire cord during driving, and the load corresponding to 13% of the breaking tenacity of the cord was given at the temperature of 120 "C for 5 minutes.

The low temperature and high load state of Li is a supposed condition of the temperature and the load given to the tire cord located in the ground contacting part of the tire when parking after driving, the temperature was cooled to 20 ^° C while maintaining the load, and the state was continued for 3 minutes.

The low temperature and low load state of L ₂ is a supposed condition of the temperature and the load given to the tire cord except in the ground contacting part of the tire when parking after driving, the temperature and the load were lowered from the high temperature and high load state to 20 ^° C and 0.01 g/d, respectively, and the state

was continued for 3 minutes.

The measured length deformation graph is illustrated in Figs. 6 to 9 and the flat spot factor and the length deformation rate obtained therefrom are listed in the following Table 4.

[Table 4]

As shown in Table 4, the tire cords according to Examples 6 and 8-10 of the present invention are superior in the dimensional stability, because their flat spot factor and length deformation rate are low.

Comparative Example 1

Rayon fibers (Supper III, product of CORDENKA Co.), of which the total fineness was 1650 denier, were used.

Example 11 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.

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%.

After dissolving the cellulose completely while eliminating water from the swelled cellulose slurry so as to make the 50 wt% NMMO aqueous solution be an 89 wt% NMMO aqueous solution, the spinning dope was prepared by discharging the same. At this time, the cellulose content of the discharged spinning dope was 11 wt% and it was recognized that the dope was homogeneous in which undissolved cellulose particles were not included. Furthermore, the filament fibers were prepared by spinning the dope, and coagulating, washing, and drying the same with the spinning device having the basic components same as to Fig. 3. Furthermore, the cellulose dope was spun by using a die, of which the total number of nozzles was 1000 and the cross-sectional area of the nozzle was 0.047mnf, so that the total denier of the final filament fibers was 1650 denier.

The discharged and coagulated multi-filament fibers were passed through the pulling part of Fig. 4 and transferred to the washing device. At this time, the coagulating draft ratio V ₂ /Vi of the progressing speed Vi of the filaments at the final pulling roll of the pulling part and the progressing speed V ₂ of the filaments at the first washing roll of the washing device was controlled to be 0.99.

Then, the NMMO was completely eliminated from the filaments transferred to the washing device, and the lyocell filament fibers were obtained by drying the filament at the drying device and winding the same.

Example 12

The lyocell multi-filament fibers were prepared substantially according to the same method as in Example 11 , except that the temperature condition of each drying

roll was increased 5 ^° C , respectively.

Experimental Example 3

The rayon fibers and the lyocell filaments obtained by Comparative Example 1 and Examples 11 and 12 were selected and stored in the standard condition (25 ^° C , 65%RH) according to KSK 0901 for 24 hours or more so as to be in the state of moisture equilibrium, and then dried at 105 ^° C or 120 ^° C for 2 hours.

The strength, the elongation, and the elongation in the initial elastic section of the dried specimens having the length of 250 mm were measured by using a low speed extension type of tensile tester of Instron Co. with the extension speed of 300 mm/min according to KSK 0412 standard, and the results are listed in the following Table 5. Furthermore, the stress-strain curve of Comparative Example 1 and Examples 11 and 12 is illustrated in Fig. 10. In Fig. 10, the signs A- 105 ^° C and A- 120 ^° C correspond to Comparative Example 1, the signs B- 105 "Cand B- 120 °C correspond to Example 11, and the signs C-105 ⁰ C and C-120 ^° C correspond to Example 12.

[Table 5]

Referring to the above results, it can be recognized that the lyocell filament fibers of the present invention have low elongation at yield point of 1.7% or less and high yield stress (the tenacity at yield point) at high temperature, in comparison with the usual rayon fibers.

Example 13

The 2 ply lyocell twisted yarn was prepared by Z twisting the lyocell filament fibers of Example 11 with 400 TPM and then S twisting the Z twisted yarn with 400 TPM by using the Cable & Cord 3type twister, that is, a CC. Twister, by Allma Co. The lyocell tire cord was prepared by dipping and passing the prepared lyocell twisted yarn through a common RFL solution under the tension of 300 g/cord, drying the same at 150 ^° C for 2 minutes, and heat-treating the same under the tension of 500 g/cord at 180 ^° C for 3 minutes.

Example 14

The lyocell tire cord was prepared substantially according to the same method as in Example 13, except that the temperature condition of each drying roll was increased 5 ^° C , respectively, when preparing the multi-filaments.

Experimental Example 3

The specimens of the tire cords prepared by Examples 13 and 14 were stored in the standard condition (25 ^° C , 65%RH) according to KSK 0901 for 24 hours or more so as to be in the state of moisture equilibrium, and then dried at 105 ^° C or 120 ^° C for 2

hours.

The strength, the elongation, and the elongation in the initial elastic section of the dried specimens having the length of 250mm were measured by using the low speed extension type of tensile tester of Instron Co. with the extension speed of 300 mm/min according to KSK 0412 standard, and the results are listed in the following Table 6. Furthermore, the stress-strain curve of Examples 13 and 14 is illustrated in Fig. 11. In Fig. 11, the signs A- 105 ^° C and A- 120 ^° C correspond to Example 13, and the signs B-105 ^° Cand B-120 ^° C correspond to Example 14.

[Table 6]

Referring to the above results, it can be recognized that the lyocell tire cords of the present invention have the elongation at yield point of 3.2% or less and the elongation is very low and the yield stress (the tenacity at yield point) is high at high temperature.

Example 15

The lyocell filament fibers were prepared substantially according to the same method as in Example 1 , except that the process of giving a diester compound based spinning oil to the filament fibers was further included between the first and second

drying rolls, and the process was controlled so that the oil was given to the filaments fibers having the moisture regain of 50 wt%.

Example 16 The lyocell filament fibers were prepared substantially according to the same method as in Example 1, except that the cellulose concentration of the discharged spinning dope, the tension between the first and second drying rolls, the tension between the second and third drying rolls, and the temperature of the rolls were changed as disclosed in the following Table 7. That is, the cellulose concentration of the discharged spinning dope was controlled to be 10.5 wt%, the tension between the first and second drying rolls was controlled to be 0.18 g/d, the tension between the second and third drying rolls was controlled to be 0.25 g/d, and the temperatures of the rolls were adjusted to 120 ^° C , 120 ^° C , and 100 ^° C , successively.

Example 17

The lyocell filament fibers were prepared substantially according to the same method as in Example 1, except that the cellulose concentration of the discharged spinning dope, the tension between the first and second drying rolls, the tension between the second and third drying rolls, and the temperature of the rolls were changed as disclosed in the following Table 7. That is, the cellulose concentration of the discharged spinning dope was controlled to be 11.5 wt%, the tension between the first and second drying rolls was controlled to be 0.22 g/d, the tension between the second and third drying rolls was controlled to be 0.34 g/d, and the temperatures of the rolls were adjusted to 125 ^° C , 125 ^° C , and 105 ^° C , successively.

Comparative Example 2

CORDENKA 700 Super 3 filament bundle (the number of filaments was 1000, the total fineness was 1840) was used.

Experimental Example 5

[Measurement of the modulus of the filaments of the dried condition]

The test specimens were prepared by twisting each filament fibers of Examples 15 to 17 and Comparative Example 2 with 80 TPM, respectively, and the specimens were dried in an oven at 105 ^° C for 4 hours. The tenacity and the elongation of the filaments of the dried condition were measured in regard to the specimens by using the universal testing machine (UTM) of Instron Co. according to ASTM D 885 method in the condition of 25 ^° C and 65%RH, and the results are shown in Fig. 12 and Table 7.

Furthermore, the initial modulus Mi, the terminal modulus Mt, the elongation at maximum point, and the intermediate elongation at 4.5 kgf were measured in regard to the specimens from the measured value of the tenacity and the elongation, and the results are listed in the following Table 7.

[Measurement of the modulus of the filaments of the standard state (25 ^° C , 65%RH)]

The test specimens were prepared by twisting each of the filament fibers of Examples 15 to 17 and Comparative Example 2 with 80 TPM, respectively, and the specimens were treated in the conditioning room of the standard state (25 ^° C , 65%RH) for 24 hours. After this, the tenacity and the elongation of the filaments of the

standard state were measured in regard to the specimens by using the universal testing machine (UTM) of Instron Co. according to JIS-L 1017 method in the condition of 25 ^° C and 65%RH, and the results are shown in Fig. 13 and Table 7.

Furthermore, the initial modulus MiC, the terminal modulus MtC, the breaking elongation, and the intermediate elongation at 4.5 kgf were measured in regard to the specimens of the standard condition from the measured value of the tenacity and the elongation, and the results are listed in the following Table 7.

[Table 7]

Notes) In Table 7,

(Mt/Mi)D'- means the Mt/Mi value of the filament fibers of the dried condition,

(Mt/Mi)c: means the MtC/MiC value of the filament fibers conditioned in the standard condition.

As shown in Table 7, the filament fibers according to Examples 15 to 17 of the present invention have high initial modulus and low terminal modulus, and the Mt/Mi maintains an optimum level, and thus it is expected that the dimensional stability and the durability may be superior when they are produced into a cord. Furthermore, it is possible to know that the filament fibers according to Examples 15 to 17 of the present invention are less affected by moisture even in the standard condition in comparison with Comparative Example 2. On the contrary, the filament fibers according to Comparative Example 2 may cause deterioration of the dimensional stability and the long-term durability due to the shape deformation, because the shape deforms largely because of the low initial modulus when preparing the tire cord and driving.

Example 18 to 20 and Comparative Example 3

The raw yarn for tire cord was prepared by Z twisting the filament bundle according to Example 18 to 20 and Comparative Example 3 with 350 TPM by using the Cable & Cord 3type twister, that is, a CC. Twister, by Allma Co., respectively.

The raw cord was prepared by co-twisting 2 ply of the raw yarns for cord, and the co-twisting was carried out with 350 TPM of S twisting.

The tire cord was prepared by dipping the prepared raw cord into the RFL adhesive solution containing 2.0 wt% of resorcinol, 3.2 wt% of formaldehyde (37%), 1.1 wt% of sodium hydroxide (10%), 43.9 wt% of styrene/butadiene/vinylpyridine (15/70/15) rubber (41%), that is, a styrene/butadiene/vinylpyridine latex including 41%

of rubber, and the remainder of water, and passing through the same, drying the same under the tension of 300 g/cord at 150 ^° C for 2 minutes, and heat-treating the same under the tension of 500 g/cord at 180 "C for 2 minutes.

Experimental Example 6

[Measurement of the modulus of the cord]

The tenacity and the elongation were measured in regard to the tire cord prepared according to Examples 18 to 20 and Comparative Example 3 by using the universal testing machine (UTM) of Instron Co. according to JIS-L1017 method in the standard state, and the results are shown in Fig. 14 and Table 8.

Furthermore, the initial modulus Mi_cord, the terminal modulus Mt_cord, the breaking elongation, and the intermediate elongation at the load of 4.5 kgf were measured in regard to each cord from the measured value of the tenacity and the elongation, and the results are listed in the following Table 8.

[Measurement of the fatigue resistance]

The properties of the tire cord were tested according to the following Calculation Formula 8 after repeating the extension of 4% and the contraction of 4% with 2500 rpm at the circumstance of 80 ^° C for 10 hours. [Calculation Formula 8]

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

[Table 8]

As shown in Table 8, the tire cords according to Examples 18 to 20 represent superior dimensional stability and durability.

On the contrary, the tire cord according to Comparative Example 3 may cause deterioration of the dimensional stability and the long-term durability due to the shape deformation, because the shape largely deforms because of the low initial modulus and the high intermediate elongation when preparing the tire and driving.

Example 21 The 2 ply twisted yarn of the lyocell filament fibers was prepared by Z twisting the multi-filament fibers prepared according to Example 15 with 400 TPM and then S twisting the Z twisted yarn with 400 TPM by using the Cable & Cord 3type twister, that is, a CC. Twister, by Allma Co.

The lyocell tire cord was prepared by dipping and passing the prepared twisted yarn of the lyocell filament fibers through the RFL adhesive solution, drying the same under the tension of 300 g/cord at 150 ^° C for 2 minutes, and heat-treating the same under the tension of 500 g/cord at 180 ^° C for 3 minutes.

Experimental Example 7

[Measurement of the modulus of the cord]

The modulus of the tire cord of Example 21 was measured substantially according to the same method as in Experimental Example 6, and the results are listed in the following Table 9.

[Table 9]

Elongation at

Mi_cord|Mt cord Intermediate elongation (% Degree of fatigue maximum point (g/d)/% (g/d)/% @ 4.5kgf resistance (%)

Example

0.37 0.098 7.7 1.8 93.5 21

As disclosed above, the lyocell filament fibers having the properties according to the present invention deform less and can exhibit stable high driving performance when they are applied to the tire cord, because they have good dimensional stability, fatigue resistance, and durability, and deform less at a high temperature. Furthermore, the lyocell tire cord of the present invention can raise the stable high speed driving performance of the tire and improve the riding comfort, because the length deformation of the lyocell tire cord of the present invention is small and the stress is low at a high temperature condition. The lyocell tire cord of the present invention can be applied to a body ply, a cap ply, and the like for a pneumatic tire.