KR100213311B1 - A process for manufacturing polyester filament and polyester tirecord - Google Patents

Abstract

A polyester filament yarn having a new internal structure, a tire cord made of such yarn, and a method of manufacturing the same are provided.

The polyester filament yarn of the present invention is 90 mol% or more of polyethylene terephthalate, has 3 to 5 denier fineness per filament, satisfies the properties of i) to iii) below, and is 3 minutes under a tension of 0.1 g / d at a temperature of 240 ° C. A polyester filament yarn is provided which satisfies the microstructure property change amount of the following iv) to vii) in the yarn after the treatment.

i) the density value is not less than 1.38 g / cm 3 and not more than 1.39 g / cm 3,

ii) non-governmental birefringence is 0.06 ~ 0.09,

iii) tan δ peak temperature is 140 ° C. or less,

iv) the degree of crystallinity increase (ΔXc) 10-20 (% by weight),

v) non-orientation coefficient reduction (ΔFa) not less than 0.05,

vi) the increase in the long period size (△ LP) 10Å or more,

vii) tan δ peak temperature decrease (Δtan δ _peak ) 5 ° C. or more.

These filament yarns are immersed in a rubber solution and made into a tire cord, which is incorporated into the tire's rubber matrix to exhibit excellent dimensional stability and fatigue resistance.

Description

Polyester filament yarn, polyester tire cords and their manufacturing method

The present invention relates to an industrial polyester filament yarn and a tire cord. More particularly, the present invention relates to polyester filament yarns, tyo cords and methods for their preparation having improved thermal dimensional stability and strength, and improved fatigue resistance by low shrinkage.

Typical examples of the fibers that are generally used as rubber reinforcements for tires include nylon, rayon, polyester, and the like. Among these, nylon tire cords have been used mainly for bias tires for trucks and large buses because of their superior strength and toughness depending on the inherent properties of nylon fibers. The rayon tyo cord has been mainly used in high-speed driving radial tires such as passenger cars because of its low shrinkage, excellent thermal dimensional stability and shape stability, depending on the inherent properties of rayon fibers.

However, nylon tyo cords have a low modulus, high shrinkage properties, poor dimensional stability, and low glass transition temperature (T _g ).

The rayon tire cord has a low modulus and a strong deterioration after the fiber is manufactured from the tire cord.

Polyester tire cords are widely used to eliminate the drawbacks of nylon and rayon as described above.

Conventionally, the polyester fiber used for a tire has a benzene ring in its molecular structure, and its molecular chain is rigid. Accordingly, the tire cord made of polyester yarn has good elastic modulus and fatigue resistance, little flat spot occurrence, and excellent creep resistance and durability. For this reason, polyester tire cords are widely used in radial tires for passenger cars.

However, despite these advantages, these conventional polyester tire cords have a problem in that physical property changes due to temperature are severe because of the large amount of heat generated by work loss. In particular, conventional industrial high strength polyethylene terephthalate typically exhibits significant shrinkage upon heating.

In addition, when such industrial polyester fibers are intervened in the rubber matrix of a tire, the fibers stretch and relax during every tire revolution as the tire rotates during use. In addition, tire rotation causes cyclic stress deformation, especially on uneven surfaces, as internal air pressure presses and axially compresses the fiber reinforcement of the tire.

Since more energy is consumed during the stretching of the fiber than it recovers during the relaxation of the fiber, this energy difference is dissipated as heat and is called hysteresis loss or work loss. Thus, significant temperature rises, at least in part due to this fiber hysteresis effect, have been observed in tires on the road.

Changes in physical properties due to exotherm occur due to moisture and amines contained in the known rubber liquids used for the processing of rubber solutions for the production of tire cords, especially when the concentration of carboxyl terminal groups in the polyester molecular chain increases. Decreases strength and reduces fatigue resistance.

Recently, as high performance radial tires are widely used, demand for polyester tire cords having excellent physical properties compared to nylon and rayon tire cords is increasing. Accordingly, research and development of polyesters that have improved fatigue resistance by minimizing heat generation due to the hysteresis effect have been actively made.

Prior art methods for improving the fatigue resistance of polyester fibers include a chemical method of increasing the stability by reducing the carboxyl group content of the polyester and a polyester fiber having a relatively low intrinsic viscosity or high speed to impart thermal dimensional stability. The method of extending | stretching the highly oriented undrawn yarn manufactured by spinning, etc. has been proposed.

As a method of imparting chemical stability, Japanese Patent Application Laid-Open No. 54-132696, 54-132697 discloses a technique for reducing the terminal carboxyl group of a polyester to prevent pyrolysis deterioration occurring when the exotherm is high. However, in the method of copolymerizing or melt blending the aliphatic polyester to reduce the terminal carboxyl group, the non-governmental fluidity is large, so that the calorific value is relatively reduced and the degree of pyrolysis is reduced, so that the fatigue resistance is improved, but a high crystalline polyester fiber cannot be obtained. A decrease in strength and initial elastic modulus is inevitable and the shrinkage rate is increased, so that the obtained product is unsuitable as a yarn for tire cords. In addition, the method of reducing the end group content by adding an end group blocking agent is undesirably low in the degree of polymerization and disadvantageous in terms of high production cost.

As a method for imparting thermal dimensional stability, for example, U.S. Patent Nos. 4,101,525 and 4,195,052 disclose methods for improving fatigue resistance by increasing molecular chain fluidity of non-government using high-speed spinning. However, this method using high-speed spinning is effective in improving fatigue resistance, but the molecular chain length in the non-uniform region becomes uneven and long, and loose molecular chains coexist, resulting in large loss of strength and physical property differences between inner and outer layers. It is disadvantageous in that physical property fluctuations due to deterioration in elongation and defects in microstructures are large.

In addition, as a conventional tire cord manufacturing method, for example, Japanese Patent Application Laid-Open No. 61-12952 uses a polyester polymer having an intrinsic viscosity of 1.0, a diethylene glycol content of 1.0 mol%, and a carboxyl group content of 10 equivalents / 10 ⁶ g. Unstretched yarn spun at a spinning speed of 2000 ~ 2500m / min at a temperature of 160 ℃ and heat-treated at 210 ~ 240 ℃ to immerse the yarn prepared in a conventional rubber solution in strength of 7.0g / d or more A method for producing a cord having an absorption peak temperature of 148 to 154 캜 and a dry heat shrinkage of 3.3 to 5% is described.

In addition, U.S. Patent Nos. 4,101,525 and 4,195,052 disclose high-oriented unstretched yarns by high-speed spinning using steam or the like, and single yarns composed of 85 mol% polyethylene terephthalate are also 1-20 deniers. It is exemplified to prepare a cord by immersing a multi-stranded yarn having a work loss of 0.004 to 0.02 lb.in at 150 ° C. in a rubber solution and using the same in a tire.

However, in the case of these methods, in the case of yarns produced by high-speed spinning and stretching, the tie-molecular chain, which has a decisive influence on the form stability of the yarn, especially dry heat shrinkage, is oriented, and remains as residual internal stress. This causes the fatigue resistance of the tire cord finally falls. Looking at the thermal stress in the case of most conventional yarns, the thermal stress continuously increases as the temperature increases due to the internal stress as described above. After all, even if the yarn is heat-treated in the rubber solution used, the residual internal stress remains, which causes the fatigue resistance of the tire cord to decrease. In addition, the yarn before the treatment in the rubber solution has a highly oriented stretched yarn, that is, a two-phase structure that crystals and amorphous are clear, the strong degradation occurs due to deterioration of the crystal part due to high heat during immersion heat treatment in the rubber solution.

In addition, a method of firstly treating an epoxy resin compound in a polyester stretched yarn and then immersing it in a rubber solution is described in Japanese Patent Application Laid-Open No. 54-77794, but it is difficult to solve a fundamental problem.

That is, most conventional methods form an ideal-structured yarn that minimizes the degree of non-precision while maintaining high crystallinity through a manufacturing process accompanied by high temperature heat treatment to improve mechanical properties and thermal contraction rate in the yarn state. After immersing in the rubber solution to achieve the required characteristics as the final tire cord as described above, in the case of such a manufacturing process to increase the residual thermal stress of the yarn by the high temperature process in the yarn to achieve the required cord characteristics In addition, it imposes a limit on yarn production at high speed by high temperature treatment, and increases energy use, and it is accompanied by higher heat energy than yarn to relax thermal stress accumulated during yarn manufacturing in the dipping process. As it should be, there is a limit in dipping speed. In addition, there is a limit on the amount of change in the microstructure during the dipping process, which is evaluated as a disadvantageous method for acquiring the mechanical properties and the dimensional stability of the cord.

The present invention is provided to solve all the problems of the prior art as described above. According to the present invention, the problem of fatigue resistance deterioration due to internal residual stress due to high-speed spinning and the strength deterioration due to deterioration of crystal parts when immersed in rubber solution are solved based on the following points.

Polyester yarns having high crystallinity have a large thermal history, so that the yarns have a large shrinkage stress due to heat. Therefore, in the subsequent high-temperature treatment such as a dipping process, folded crystals are mainly formed around free molecular chains in which the orientation is disturbed in the amorphous region, and thus the strength, modulus of elasticity, and retention of strength are large. It tends to be lowered.

In addition, the high crystalline yarn is excellent in thermal dimensional stability and fatigue resistance in terms of the microstructure of the yarn itself, but these properties alone are not sufficient because there is no functional group to bond with the rubber. Therefore, the yarn is twisted to improve fatigue resistance, and the adhesiveness with rubber is improved by passing a high temperature dipping process (latex treatment) for improving adhesion with rubber. In particular, in the dipping process, the mechanical properties and final dimensional stability of tire cords are determined by manufacturing conditions such as thermal energy, tension, and relaxation heat treatment. The inventors have found that from this change in physical properties, the amount of microstructure change during the series of processing from yarn to cord state can be an important technology point in improving code performance such as dimensional stability and fatigue resistance.

The present inventors have excellent overall physical properties such as strength compared to the prior art methods, high strength conversion efficiency and high dimensional stability even after high temperature dipping treatment, while maintaining the strength of the yarn and having excellent dimensional stability. Studying the manufacturing method has been completed the present invention.

That is, in order to improve the mechanical properties and thermal shrinkage of the yarn, most conventional methods form yarns of an ideal structure that maintains high crystallinity and minimizes the degree of orientation of amorphous portions through processes involving high temperature heat treatment. Is immersed in a rubber solution to achieve the properties required for the final tire cord. However, the high temperature processes involved in this method increase the residual thermal stress, limit the high speed production of the yarn, and increase the cost due to the increase of required energy. In addition, since the thermal energy required in the dipping process should be higher than the energy required in the yarn production to mitigate the thermal stress accumulated in the yarn production, the dipping speed is limited. This method also limits the microstructural changes in the dipping process and is therefore undesirable to achieve the mechanical properties and dimensional stability of the cord.

The present invention uses the heat energy generated during dipping in a rubber solution to limit the density indicating crystallization to within a limited range in the production of yarns, to maximize the birefringence of non-refining to form fibrous microstructures, and to rearrange the fibrous microstructures. And a method for producing a polyester tire cord having a stable two-phase structure of a crystal part and an irrespective state by recrystallization by recrystallization.

High-orientation non-uniformity present in the yarn is easily crystallized when subjected to heat treatment during dipping. The size of such crystals in the yarn of the present invention is at least 10% smaller than that of conventional yarns. Therefore, this yarn has a network crystal structure in which the crystal parts and the non-finger parts are uniformly distributed in the cord, thereby showing excellent dimensional stability. In particular, the content of the bound tie molecular chains connecting the crystals can be increased by minimizing the formation of folded crystals during recrystallization so that high modulus of elasticity can be maintained.

In addition, the inventors have found special spinning and stretching methods to achieve the above properties. In other words, the process conditions required to produce a good polyester yarn was found. More specifically, by drawing an undrawn yarn having a molecular chain highly oriented at a non-negative level to the extent that crystal diffraction is not clearly observed by X-ray, drawing by drawing at low draw ratio at low temperature (below crystallization temperature). Minimize the tension of the non-negative molecular chains that are induced, then heat treatment and relax at low temperatures so that no further crystallization occurs. These yarns are immersed in a rubber solution and heat treated at specific temperature and tension conditions that can be recrystallized into final tire cords.

It is a first object of the present invention to provide a polyester filament yarn having excellent fatigue resistance and dimensional stability even under conditions subject to repeated fatigue movements at a high temperature of 210 ° C. or higher before and after arrangement in a rubber matrix.

A second object of the present invention is to provide a tire cord including a polyester yarn having excellent dimensional stability and fatigue resistance as a rubber reinforcing material.

It is a third object of the present invention to provide a tire with remarkably improved fatigue resistance and dimensional stability even under repeated fatigue movements under high temperature.

Therefore, in order to achieve the above objects, the present invention is a polyester filament yarn made of polyethylene terephthalate of 90 mol% or more and having a fineness of 3 to 5 denier per filament, satisfying the following physical properties of i) -iii) A polyester filament yarn is provided, characterized in that:

i) the density value is not less than 1.38 g / cm 3 and not more than 1.39 g / cm 3,

ii) non-governmental birefringence is 0.06 ~ 0.09,

iii) tan δ peak temperature is 140 ° C. or less.

The polyester filament yarn of the present invention simultaneously satisfies the microstructural property change of the following i) to iv) after treatment for 3 minutes under a 0.1 g / d tension at a temperature of 240 ° C .:

i) Crystallinity increase amount (ΔXc) 10 to 20 (% by weight)

ii) decrease in non-orientation coefficient (ΔFa) not less than 0.05,

iii) the increase in the long period size (△ LP) 10 Å or more,

iv) tan δ peak temperature decrease (Δtan δ _peak) 5 ° C. or more.

Here, the long period is obtained by using an X-ray scattering apparatus (manufactured by Rigaku Co., Ltd., Japan) using Cu-K α-radiative light having a wavelength of 1.54 Å to obtain an incinerated X-ray scattering pattern under the conditions of a voltage of 50 kV and a current of 200 mA. Can be calculated with Bragg's equation.

d = λ / 2θ (Bragg equation)

Where λ = 1.54 Hz and θ = scattering angle.

Polyester filament yarns of 90% by mole or more of polyethylene terephthalate are treated under dipping conditions where relaxation and tension are imparted at high temperatures, that is, heating zone temperatures of 230 to 250 ° C during tension, relaxation and dipping of 0.2 to 0.6 g / d. When dipping at, a microstructure change occurs in the yarn while the filament yarn becomes the processing code. This microstructure change is the same as before and after the microstructure change when treated for 3 minutes under a 0.1g / d tension at a temperature of 240 ℃.

Preferably, the yarn of the present invention exhibits a significant reduction in thermal shrinkage between the yarn and the treated cord as the microstructure changes in the dipping process. If the polyester yarn satisfies the above properties, the yarn after the dipping process can be changed into an ideal microstructure.

In addition, the present invention is a method of producing a polyester filament yarn by melt-spun and direct stretching a polyester of 90 mol% or more polyethylene terephthalate and intrinsic viscosity of 0.85 or more,

i) The cooling wind temperature of 25 ° C. to the glass transition temperature (T _g ) of the polymer such that the polyester resin is spun at a spinning speed of 2,500 to 4,000 m / min and then a solidification point is formed within two thirds of the total length of the cooling zone. Cooling and solidifying to produce undrawn yarn having a density value of 1.355 g / cm 3 to 1.360 g / cm 3 of undrawn yarn;

ii) drawing the undrawn yarn so that its breaking elongation is 15% or less at a drawing temperature of more than a glass transition temperature (T _g ) or less than a crystallinity temperature; And

iii) The drawn yarn obtained was 210 deg. Provided is a method for producing a polyester filament yarn, comprising the step of heat setting at the following temperature.

According to the present invention, a density value of 1.355 to 1.360 g / cm 3 polyester undrawn yarn is drawn at a drawing temperature of glass transition temperature (ie, secondary transition temperature) or more and below crystallinity temperature, preferably 80 to 120 ° C, and 210 ° C. Heat treatment is performed below to make the elongation at break of 15% or less.

In addition, the present invention is a tire formed from the above-described polyester filament yarn made of polyethylene terephthalate of 90 mol% or more and having a fineness of 3 to 5 denier per filament, and satisfies the following characteristics in accordance with the microstructural change during dipping. The code is provided:

i) Dimensional stability index (DS)

ii) cord strength [T (g / e)] ≥0.1DS + 4.8,

iii) Dry heat shrinkage is less than 3.5%.

The polyester filament yarns of the present invention contain at least 90 mol%, preferably at least 95 mol% polyethylene terephthalate. In addition, the polyester of the present invention may contain 10 mol% or less, preferably 5 mol% or less of copolymerized ester units other than polyethylene terephthalate. Examples of ester-forming components useful as ester units other than polyethylene terephthalate include dicarboxylic acids such as diethyl glycol, trimethylene glycol, detramethylene glycol, hexamethylene glycol and the like.

The polyester filament yarns of the present invention usually have a fineness of about 3 to 5 denier per filament, but this value can vary widely as will be apparent to those skilled in the art.

According to the present invention, in order to facilitate the microstructure change of polyester filament yarn and increase the amount of change, the density value representative of the crystallization level from yarn production is limited within a certain range, and the birefringence of the non-government is maximized. This microstructure limitation minimizes the X-ray scattering peak intensity of the yarn. The fiber microstructure of the yarn is rearranged through a recrystallization process using heat energy in the dipping process into the rubber solution, so that the polyester tire cord has a stable two-phase structure of crystal and amorphous.

The microstructure of the characteristic yarn defined in the present invention can be obtained by quantitatively counting the intensity of diffraction lines by scanning the X-ray diffraction intensity in the ultraviolet direction within the incineration range. The density value ρ can be obtained by measuring at 25 ° C. by using a density gradient tube method using n-heptane and carbon tetrachloride.

The yarn of the present invention is characterized in that the density value obtained by the above method is 1.38 g / cm 3 or more and 1.39 g / cm 3 or less. If the density is smaller than the above range, there is a disadvantage in that the filament is soft and the cutting often occurs during yarn production. On the contrary, when the density exceeds the above-mentioned range, there is an advantage in that good mechanical properties and low heat shrinkage in the yarn state can be obtained, but the residual thermal stress of the yarn is increased by entailing a high temperature heat treatment process such as a yarn manufacturing process, This results in a lower code strength and also limits the amount of microstructure change during the dipping process.

In addition, the polyester filament yarn of the present invention is characterized in that the non-refining birefringence (Δn _a ) value is 0.06 ~ 0.09, preferably 0.07 ~ 0.09. The yarn of the present invention exhibits non-finite suitable orientation characteristics in Δn _a in the above range. If Δn _a is out of the above range, the orientation of the non-government is insufficient, and the amount of incorporation of the amorphous region into the crystal region is small in the dipping process, and thus a large amount of thermal energy is required to increase it. As a result, the code has low strength and poor dimensional stability. It will have poor physical properties.

Non- governmental birefringence (Δn _a ) can be obtained by the following equation.

Where Δn = average birefringence

X _c = crystallinity

f _c = crystal orientation coefficient

The average birefringence (Δn) is obtained by measuring the retardation obtained from the interference chromaticity of the sample using a Berek compensator attached to the polarizing microscope and calculating it by the following equation.

Δn = R / d

Where d is the thickness of the sample (nm) and R is the retardation (nm).

The crystallinity X _c can be obtained by calculating the following formula using a density value (ρ: g / cm 3).

Where ρ _c (g / cm 3) = 1.455, ρ _a (g / cm 3) = 1.335

The crystal orientation coefficient f _c can be obtained by averaging the orientation coefficients obtained from the width at half the height of the wide-angle X-ray diffraction patterns of the (010) and (100) crystal planes of the material according to the following equation.

If the density of the yarn and the birefringence of the non-government are out of the above-mentioned range, the distinction between the crystal region and the amorphous region is distinct, which leads to undesired crystal growth and strong degradation due to the formation of folded chains on the crystal surface. Etc., results in poor physical properties in the final deep code.

In addition to these facts, the following facts are very important factors in rubber reinforcing fibers such as tire reinforcing materials. That is, the rubber reinforcing fibers used in tires and the like are under fatigue movement such as repeated tension, compression, and bending under high temperature during use, so it is important to improve toughness due to extreme strength and decrease in elastic modulus and high dimensional stability is required. This requires structurally uniform distribution of crystal regions. Shrinkage, an important indicator of dimensional stability, is observed when the length of the molecular chain decreases as the non-negative molecular orientation is disturbed when heat is applied to the molecular chain. Part of the reduction in this form change is the decision to continuously adjoin the NGO. If these crystals form a dense net structure, the change of modulus at high temperature, which can be represented by the peak temperature value of tangent delta, prevents morphological changes such as heat shrinkage. In other words, it plays the same role as crosslinking with sulfur in the rubber.

In other words, there is a limit in improving the physical properties of the rubber reinforcing fiber without improving the tangential delta peak temperature in improving shape stability. Yarns of the present invention have a lower tan delta peak temperature than conventional yarns. The tan delta peak temperature of the yarn of the present invention is 140 ° C or lower, preferably 135 ° C or lower.

In addition, in order to reduce the stress used in the relaxation process in a limited way, as shown in US Patent 4,101,525 and US Patent 4,195,052, when the orientation of the amorphous region is reduced, the folded molecular chain of the crystal surface during the high crystallization and the recrystallization process by the post-process Due to the many defects in the crystal interface, it is not possible to completely free the restraint of the non-molecular chains, and it is not easy to obtain high elastic properties due to the decrease of the Thai molecular chain fraction.

As described above, according to the yarn of the present invention, the accumulation of stress due to inferiority is minimized, and the following microstructure property changes are simultaneously generated between yarns and treated codes by using thermal energy and tension during dipping:

i) 10 to 20% by weight increase in crystallization rate (ΔXc),

ii) the decrease in non-orientation coefficient (ΔFa) not less than 0.05,

iii) the increase in the long period size (△ LP) 10 Å or more,

iv) tan δ peak temperature decrease (Δtan δ _peak ) 5 ° C. or more.

Therefore, the present invention exhibits a remarkable drop in thermal contraction rate by minimizing the accumulation of stress due to heat in the yarn and at the same time as using the mechanical force such as thermal energy and tension at the time of dipping, and the properties as described above between the yarn and the treatment cord. Provided is a polyester filament yarn causing an amount of change.

The highly oriented scaffolds present in the filament yarns are more crystallized when subjected to heat treatment during dipping. The size of such crystals in the yarns of the present invention is at least 10% smaller than conventional ones. Therefore, the filament yarn of the present invention has an excellent dimensional stability because it has a network crystal structure in which the crystal part and the non-uniformity are uniformly distributed. In particular, the content of the constrained tie-molecular chains connecting between the crystals can be increased by minimizing the formation of folded crystals to maintain high elastic modulus.

Therefore, the yarn itself of the present invention exhibits a high shrinkage rate without tension in a hot air oven at 150 ° C. for 30 minutes, but the cord prepared by dipping the yarn in a rubber matrix has excellent properties as described below through the above-described microstructure change. Indicates:

i) Dimensional stability index (DS) ≥0.80,

ii) cord strength [T (g / d)] ≥0.1DS + 4.8,

iii) Code dry heat shrinkage of 3.5% or less

In general, a tire cord having a network structure has a large amount of heat generated due to a large amount of activation energy required to move molecular chains in an amorphous region while undergoing elongation and compression deformation. It is known that the fatigue resistance of tire cords deteriorates and their life is shortened, but the opposite is actually the case. In addition, the present inventors have found that such a network structure is excellent in fatigue resistance, because the fatigue mechanism of the tire cord is much larger due to chemical degradation than physical degradation.

According to the Japan Rubber Association, Vol. 64, No. 4, 1991, p260-266, 80% of fatigue deterioration is due to hydrolysis and amine decomposition of ester bonds bound in the molecular chain, and the rest is caused by physical deformation. It is known. In other words, the structure of the tire cord inside the tire is very difficult to move the molecular chain due to external elongation, compression, and bending deformation when the network structure is well developed. Although it is large, it is very insignificant. On the contrary, since the degree of orientation in the amorphous region is high and the penetration of moisture and amine is difficult, chemical deterioration is reduced and it is considered to be excellent in fatigue resistance.

Hereinafter, a method of manufacturing the polyester filament yarn of the present invention will be described in more detail.

Polyesters used as starting materials are polyesters of high polymerization having an intrinsic viscosity of at least 0.85. Intrinsic viscosity (η) is calculated by the following equation by measuring the relative viscosity (η _r ) of a solution in which 8 g of the sample is dissolved in 100 ml of ortho-chlorophenol using an Ostwald viscometer.

here,

t: Falling time of solution (seconds), t ₀ : Falling time of ortho-chlorophenol (seconds)

d: density of solution (g / cm 3), d ₀ : density of ortho-chlorophenol (g / cm 3)

Polymerization degree of polymer is very important in terms of morphological stability and fatigue resistance. In particular, low molecular weight polymers are advantageous in form stability, but high molecular weight polymers are preferable in fatigue resistance. In the present invention, a polymer having an intrinsic viscosity of 0.85 or more, preferably 1.0 or more, may be used to optimize overall physical properties and minimize fatigue reduction.

Unstretched yarn having a density value of 1.355 g / cm 3 or more is obtained by high stress spinning. It is important to prepare an undrawn yarn showing the degree of packing of the unique molecular chain as a preliminary step for producing the yarn forming the microstructure according to the present invention.

If the density value is less than 1.355 g / cm 3 and excessive stretching is required during the stretching process to give sufficient strength and elastic modulus as a rubber reinforcing fiber. Due to the excessive stretching tension, the residual stress increases, and the crystallization caused by the stretching of the yarn increases, and thus the amount of structural change of the final deep cord cannot be adjusted.

The density value of the undrawn yarn is proportional to the amount of tension received at the point where the emitter is cooled by the cooling wind and reaches the glass transition temperature. The tension size depends on the spinning speed, the single hole discharge amount and the temperature of the cooling wind. In general, the density of undrawn yarn is achieved at the point where the emitter leaving the spinneret is cooled by the cooling wind and reaches below the glass transition temperature. In the present invention, by using a method of increasing the spinning speed in order to increase the tensile strain rate of the emitting yarn, or by fixing the spinning speed and reducing the single hole discharge amount, the density of the undrawn yarn is increased to 1.355 g / cm 3 or more by increasing the tension of the freezing point. It was made. In this case, in order to increase the tension at the freezing point, it is preferable to gradually cool the melt discharged yarn to move the freezing point down from the spinneret. More specifically, when the yarn is cooled after melt spinning from the mold, it is preferable that the freezing point is formed within two thirds or less of the entire length of the cooling region. Since the density of the undrawn yarn varies depending on the location of the solidification point, the location of the solidification point can be predicted by measuring the density of the undrawn yarn.

In addition, in order to reduce the temperature difference between the filament and the outer layer at the freezing point in the high-speed spinning process, if the cooling wind temperature is increased to 25 ° C. or more and below the glass transition temperature of the polymer, preferably 40 to 60 ° C., the strong decrease due to the structural difference between the filament and the outer layer Can be reduced. If the temperature is less than 25 ° C., the filament is quenched to lower the freezing point tension, making it difficult to obtain highly oriented undrawn yarn.

The change in the single hole discharge amount greatly affects the mechanical properties of the yarn. It is preferable to maintain the single yarn fineness of 3 to 5 denier after the final stretching through the stretching process by controlling the spinning conditions and preventing uneven cooling.

This production method is characterized by stretching at a low magnification below the crystallization temperature of the undrawn yarn. Stretching is a two-stage or more multistage stretching. The crystallization temperature of highly oriented undrawn yarn produced by high speed spinning is usually 10 ° C. or lower than that of undrawn yarn by low speed spinning. Therefore, the stretching temperature is adjusted to the glass transition temperature of the polymer to 120 ° C or lower, preferably 80 to 120 ° C, more preferably 80 to 90 ° C. If the stretching temperature is too high, microcrystals already exist before the molecular chains are oriented, leading to lowered stretchability. At too low a temperature, the fluidity of the molecular chain is lost and the drawing efficiency is lowered.

The total draw ratio should be about 1.4: 2.2: 1, preferably about 1.4: 1 times to about 1.8: 1. When the total draw ratio is less than 1.4: 1, the strength of the fiber is insufficient, and when the 2.2: 1 is exceeded, high modulus value and low shrinkage cannot be achieved, and the strength decrease rate is also high.

In the present invention, it is preferable to use two-stage or more multistage stretching in the first stretching zone when stretching to 70% or more in the first stretching zone. This is because the time is short and remains entangled, which acts as a defect in the structure, and the shrinkage rate due to heat increases.

According to the present invention, when heat is applied after the highly-oriented non-drawn yarn prepared by high-speed spinning is drawn under a specific condition, shrinkage does not occur, but rather it deforms like a liquid, thereby significantly reducing dry heat shrinkage in the deep cord. .

In experiments in which the initial oriented amorphous polymer was left under a temperature between the glass transition temperature and the melting temperature to observe the stressed behavior, shrinkage occurred due to the disturbance of the molecular chain in the oriented amorphous region. Elongational strain, such as has been reported to occur as the orientation of the molecules increases when a stress greater than the above shrinkage force is applied. Elongation or contraction behavior caused by heating can be regarded as a phenomenon that occurs due to the difference in elongation force by crystallization of the oriented amorphous molecular chain. Therefore, the present invention minimizes the contraction rate by applying the mechanism of extension and contraction behavior.

The inventors have found that in order to maximize the elongation behavior such as liquid, crystallization by heat should not occur at the time of stretching, so that the stretching should be made at a stretching temperature and a low magnification below the crystallization temperature of the unstretched yarn. In other words, when the crystallization by heat at the time of stretching occurs beforehand, since the oriented amorphous region is changed into a crystalline region, elongation deformation occurring while the oriented amorphous region is oriented in crystallization can no longer occur. Dry heat shrinkage becomes large because only shrinkage behavior occurs by disorientation of the non-molecular chain present in the amorphous region.

The production method of the present invention is characterized in that the heat treatment is carried out at a temperature of 150 ~ 210 ℃, preferably 190 ~ 200 ℃. If the heat treatment temperature exceeds 210 ° C, the crystal region and the amorphous region are already clearly distinguished, so the orientation of the crystal region is extremely increased and the orientation of the amorphous region is lowered, thereby minimizing physical property degradation due to abnormal crystal growth during subsequent dipping. There will be no. This temperature is one of the important factors that determine the structure of the yarn, especially because the yarn is heat-treated in a state of almost complete orientation. In order to produce the polyester yarn for tire cords of the present invention, this temperature is required to be maintained at 150 to 210 ° C, preferably 190 to 200 ° C.

In general, the unstretched yarn before stretching expresses its properties due to the crystallization and orientation of the molecular chains due to the stretching heat treatment during the stretching process. The orientation during stretching is simultaneously performed in the crystalline and amorphous regions, and the stretching tension is rather amorphous. Takes even greater. Therefore, the yarn for tires having such a fine structure rapidly loses mechanical properties during twisting or immersion in a known rubber solution during cord manufacturing.

In the present invention, this problem is solved by controlling the temperature at which the non-negative molecular chain starts to flow after stretching, i.e., the temperature at which the loss tangent value tan δ is maximum. For example, this problem can be solved by adjusting the tan delta peak temperature to 140 ° C. or lower and reducing the temperature by 5 ° C. or higher during the dipping process.

Yarn of the present invention is produced in a tire cord by processing in a known rubber solution in the order of immersion, drying, heat treatment and normalizing process. In the hot stretch heat treatment step of the dipping process, the tension is 0.2 ~ 0.6g / d, the treatment temperature is most suitable 220 ~ 250 ℃. If the tension exceeds 0.6 g / d or the temperature exceeds 250 ° C., a much greater stress acts on the yarn than the stretching force due to crystallization of the oriented non-molecular chain, which in turn will remain as a residual stress in the final deep coat. Dry heat shrinkage will increase. In addition, when the tension is less than 0.2 g / d, dry heat shrinkage decreases but is strongly reduced due to undesirable growth of amorphous molecular chains by molecular chain disorientation and folding in the amorphous region. In addition, if the temperature is less than 220 ℃, the adhesive strength of the rubber solution is insufficient and the dry heat shrinkage rate is increased to obtain a deep code with good dimensional stability.

When the filament yarn of the present invention is based on 1000 denier, at least two yarns are twisted and woven, and then immersed in a known rubber solution, dried, and subsequently heat treated at the temperature and tension to obtain cord paper. Get deep code. The dry cord shrinkage ratio S obtained in this way is 3.5% or less. In addition, the dimensional stability value DS indicates 0.80 or more. Here, the DS value is a value obtained by dividing the dry heat shrinkage rate S by the intensity (g / d) under 10% elongation.

Hereinafter, the present invention will be described in more detail by Examples and Comparative Examples, which are intended to be illustrative only and not to limit the scope of the present invention.

[Examples 1.1-1.7, Comparative Examples 1.1-1.6]

A polyethylene terephthalate polymer having an intrinsic viscosity of 1.0 and a terminal carboxyl content of 15 eq / 106 g was melt spun at 305 ° C. using a starting material. In the melt spinning, it was extruded into a spinneret having a diameter of 0.60 mm and a number of 250 detention holes, and a thermostat was installed directly under the cap, and cooled and solidified at a cooling wind temperature of 80 ° C. or lower under the thermostat.

Other process conditions used to prepare the polyester filament yarns are shown in Tables 1-2 and 1-2 below. Physical properties of the obtained yarn are shown in Tables 2-1 and 2-2. In addition, the physical properties after the filament yarn treated at 240 ° C. under 0.1 g / d tension for 3 minutes are shown in Tables 3-1 and 3-2.

Tests of the physical properties shown in Tables 2-1 to 3-2 were performed by the following methods.

◎ Strength and elongation rate: According to JIS-L1017 method

Instrument: Instron's low speed elongated tensile strength tester

Tensile speed: 300mm / min, sample length: 250mm

Atmosphere condition: 25 ℃, 65% RH

◎ Dry heat shrink rate of yarn (Δδ,%): Calculated by the following formula. In the formula, L ₀ represents the length of the sample after treatment at 25 ° C. and 65% RH for 24 hours, and the length of the sample measured at 20 g load, and L ₁ is treated at 150 ° C. in an oven under no load for 30 minutes.

◎ Dry heat shrink rate of the cord (S,%): Calculated by the following formula. In the formula, L ₀ represents the length of the cord paper measured at 20 g static load after standing at 25 ° C. and 65% RH for 24 hours, and L ₁ represents the length after treatment at 20 g static load for 30 minutes at 150 ° C. in an oven.

◎ Strong maintenance rate of cord: According to ASTM D 885 method, tube strength is 3.5kg / ㎠, rotational speed 850rpm, tube strength is obtained from the following formula by measuring the strength of cord sample taken from tire before and after 48 hours of rotation at 80 °.

◎ Incineration x-ray peak intensity (cps)

Instrument: X-ray diffractometer from Rigaku Co., Ltd., Japan

Light source: Cu-K α-radiation light, voltage: 50 kV, current: 180 mA

◎ tanδ peak temperature: 100Hz, measured at 3 ℃ / min.

[Examples 2.1 to 2.7]

The filament yarn prepared in the above example was twisted and produced in a lower row of 49 times / 10cm in the Z direction, and an upper two pairs of 49 times / 10cm in the S direction. The resulting fabric was immersed in a resorcinol formalin latex solution and then dried for 160 ° C. × 60 seconds. Thereafter, heat treatment, 1.5% relaxation, and normalizing at 245 ° C. for 60 seconds to prepare a polyester denier cord of 2500 denier. The physical properties of the tire cord thus treated are shown in Table 4 below.

From the results of Table 4, it can be seen that the polyester tire cord according to the present invention exhibits excellent dimensional stability with a dry heat shrinkage of 3.5% or less at a dimensional stability coefficient of 0.80 or more.

While the invention has been described as preferred embodiments, it will be apparent that modifications and variations will be apparent to those skilled in the art. Such changes and modifications are considered to be within the spirit and scope of the following claims.

Claims (5)

Polyester yarns of more than 90 mol% polyethylene terephthalate and having a fineness of 3 to 5 denier per filament satisfy the physical properties of i) to iii) below, and after treatment for 3 minutes under 0.1g / d tension at a temperature of 240 ° C A polyester filament yarn characterized by satisfying the microstructure property change amount of the following iv) ~ vii): i) the density value is not less than 1.38 g / cm 3 and not more than 1.39 g / cm 3, ii) non-governmental birefringence is 0.06 ~ 0.09, iii) tan δ peak temperature is 140 ° C. or less. iv) the degree of crystallinity increase (ΔXc) 10-20 (% by weight), v) non-orientation coefficient reduction (ΔFa) not less than 0.05, vi) the increase in the long period size (△ LP) 10Å or more, vii) tan δ peak temperature decrease (Δtan δ _peak ) 5 ° C. or more. A method of producing polyester filament yarn by melt spinning and directly stretching a polyester having 90 mol% or more of polyethylene lephthalate and having an intrinsic viscosity of 0.85 or more, i) spinning a polyester resin with a spinning speed of 2,500 to 4,000 m / min. After the spinning, the solidification point was cooled and solidified at a cooling wind temperature of 25 ° C. to the glass transition temperature (T _g ) of the polymer so that the solidification point was formed within two thirds of the total length of the cooling zone. Manufacturing a non-drawn yarn having ˜1.360 g / cm 3; ii) drawing the undrawn yarn so that its breaking elongation is 15% or less at a drawing temperature not lower than a glass transition temperature (T _g ) or less than a crystallinity temperature; And iii) heat-setting the obtained stretched yarn at a temperature of 210 ° C. or lower. Tire cord made of polyethylene terephthalate of 90 mol% or more and having a fineness of 3 to 5 denier per filament, and having the following characteristics according to the microstructural property change during dipping: i) Dimension Stability index (DS) ≥ 0.80, ii) code strength [T (g / d)] ≥ 0.1DS + 4.8, iii) code dry heat shrinkage 3.5% or less. The tire cord according to claim 3, wherein the polyester filament yarn is the filament yarn of claim 1. A tire comprising a rubber matrix and the polyester tire cord according to claim 3.