YARN FOR TIRE CORD AND TIRE CORD

Abstract

This invention relates to high tenacity yarn for a tire cord comprising polyethyleneterephthalate multifilament obtained by melting and spinning a resin composition comprising first polyethyleneterephthalate and second polyethyleneterephthalate having different intrinsic viscosities, and a method for preparing the same.

Claims

1. Yarn for a tire cord comprising polyethyleneterephthalate multifilament obtained by melting and spinning a resin composition comprising first polyethyleneterephthalate and second polyethyleneterephthalate having different intrinsic viscosities, wherein the yarn has weight average molecular weight of 90,000 g/mol or more and polydispersity index of 1.9 to 2.3, and has tenacity of 8.0 gf/d or more.

2. The yarn for a tire cord according to claim 1, wherein the rate of melt viscosity at a temperature of 290° C. and a shear rate of 2000/s to melt viscosity at a temperature of 290° C. and a shear rate of 50/s of the resin composition is 50% or less, or the rate of melt viscosity at a temperature of 290° C. and a shear rate of 2000/s to melt viscosity at a temperature of 290° C. and a shear rate of 50/s of the yarn for a tire cord is 50% or less.

3. The yarn for a tire cord according to claim 1, wherein a difference between melt viscosity at a temperature of 290° C. and a shear rate of 50/s and melt viscosity at a temperature of 290° C. and a shear rate of 1000/s of the resin composition is 1,800 poise or less.

4. The yarn for a tire cord according to claim 1, wherein the resin composition has melt viscosity of 4,000 to 4,800 poise, at a temperature of 290° C. and a shear rate of 50/s, and has melt viscosity of 2,800 to 3,200 poise, at a temperature of 290° C. and a shear rate of 1000/s.

5. The yarn for a tire cord according to claim 1, wherein the resin composition has weight average molecular weight of 90,000 g/mol or more, Z average molecular weight of 125,000 to 132,000, and polydispersity index of 2.150 to 2.300.

6. The yarn for a tire cord according to claim 1, wherein the resin composition comprises first polyethyleneterephthalate having intrinsic viscosity of 0.80 dl/g to 1.40 dl/g, and second polyethyleneterephthalate having intrinsic viscosity of 1.50 dl/g to 1.90 dl/g.

7. The yarn for a tire cord according to claim 1, wherein a intrinsic viscosity difference between the first polyethyleneterephthalate and second polyethyleneterephthalate is 0.3 to 0.5 dl/g or more.

8. The yarn for a tire cord according to claim 1, wherein the resin composition comprises the second polyethyleneterephthalate in the content of 10 wt % to 40 wt %.

9. The yarn for a tire cord according to claim 1, wherein the first polyethyleneterephthalate has intrinsic viscosity of 1.00 dl/g to 1.25 dl/g, and the second polyethyleneterephthalate has intrinsic viscosity of 1.65 dl/g to 1.75 dl/g.

10. The yarn for a tire cord according to claim 1, wherein total filament number of the polyethyleneterephthalate multifilament is 100 to 1,500, and total fineness of the yarn for a tire cord is 500 to 5,000 denier.

11. The yarn for a tire cord according to claim 1, wherein the yarn for a tire cord has maximum draw ratio of 2.0 times or more.

12. A tire cord comprising the yarn for a tire cord of claim 1.

13. The tire cord according to claim 12, wherein the yarn for a tire cord has draw ratio of 2.0 to 2.5 times, and tensile strength of the tire cord according to ASTM D885 standard is 7.5 g/d or more.

14. The tire cord according to claim 12, wherein the yarn for a tire cord has draw ratio of 2.1 to 2.5 times, and tensile strength of the tire cord according to ASTM D885 standard is 8.5 g/d or more.

15. The tire cord according to claim 12, wherein the tire cord has tensile strength retention rate of the following General Formula 1, before and after fatigue resistance test, of 62% or more:
Tensile strength retention rate before and after fatigue resistance test=Tensile strength of tire cord after fatigue resistance test/tensile strength of tire cord before fatigue resistance test  [General Formula 1] in the General Formula 1, the tensile strength of tire cord is measured according to ASTM D885 standard, the Disk fatigue resistance test is evaluated according to JIS L 1017 standard, the tensile strength of a tire cord after fatigue resistance test is tensile strength of a tire cord, measured after removing rubber after the fatigue resistance test, and the fatigue resistance test is conducted by applying a temperature of 100° C., 2500 rpm and tensile-compression rate of ±8.0% for 24 hours for a specimen prepared by vulcanizing the tire cord with rubber at a temperature of 160° C. and a pressure of 20 kgf for 20 minutes, using a Disk fatigue tester.

16. A method for preparing the yarn for a tire cord of claim 1, comprising a step of melting and spinning a resin composition comprising first polyethyleneterephthalate and second polyethyleneterephthalate having different intrinsic viscosities at 200 to 300° C., to form polyethyleneterephthalate multifilament.

Description

DETAILED DESCRIPTION

[0066] Hereinafter, the invention will be explained in more detail in the following Examples. However, these examples are presented only as the illustrations of the invention, and the invention is not limited thereby.

[0067] [Measurement Method]

[0068] Hereinafter, the properties of polyethyleneterephthalate chip, polymer resin composition and yarn were respectively measured as follows.

[0069] 1. Measurement Method Using Capillary Rheometer

[0070] Using Rheo-tester 2000 device of Gottfert company, 100 g of chips were inserted in a barrel, and retained at 290° C. for 5 minutes, and then, passed through outlet L/D 20 mm/1 mm according to shear rate (/s), thus measuring Poise (Pa.Math.s) viscosity value.

[0071] 2. Method for Measuring Crystallinity

[0072] The crystallinity of fiber was measured by density gradient column method. A density gradient fluid was prepared using light liquid with low density and heavy liquid with high density, and using standard float with known density, the density of a fiber sample was measured and the crystallinity was measured by the following Formula.

Crystallinity (Xc)(%)=[(density of fiber sample−specific density of fiber)/(crystal density of fiber−amorphous density of fiber)]×100 [0073] crystal density of PET: 1.457 (g/cm), amorphous density of PET: 1.336 (g/cm.sup.2)

[0074] 3. Method for Measuring Birefringence

[0075] Birefringence of fiber was measured with polarization microscope. Using a compensator, phase difference of fiber was measured to measure birefringence.

[0076] The polarization microscope can directly measure refractive index in a parallel direction and refractive index in a vertical direction, thus measuring the difference value as birefringence.

[0077] 4. Method for Measuring Molecular Weight

[0078] Number average molecular weight, weight average molecular weight, and Z-average molecular weight were measured by gel permeation chromatography (GPC). Specifically, a sample was dissolved in hexafluoroisopropanol (HFIP), and then, additionally diluted with o-chlorophenol (OCP):chloroform=1:4 (volume/volume) and the solution was filtered with 0.45 μm membrane filter, and then, injected in Stryragel HT column (10.sup.3 to 10.sup.5 Å) equipped in GPC device, and measured.

[0079] 5. Measurement of Tenacity and Elongation

[0080] According to the method of ASTM D885, using universal testing machine (Instron Engineering Corp, Canton, Mass.), tensile strength (g/d) and elongation at break (%) of PET yarn were respectively measured (initial load: 0.05 gf/d, sample length: 250 mm, testing speed: 300 mm/min)

[0081] 6. Intrinsic Viscosity (I.V.)

[0082] Intrinsic viscosity (I.V.)(dl/g) of each PET yarn was measured using capillary viscometer according to the method of ASTM D4603-96. The solvent used was a mixed solution of phenol/1,1,2,2-tetrachloroethane (60/40 wt %).

Examples 1 to 2 and Comparative Examples 1 to 2: Preparation of Polymer Resin Composition

Comparative Example 1

[0083] Polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g were molten and extruded under conditions of a temperature of 290° C. and a shear rate of 112.40 S.sup.−1 to prepare strand type pellets. Wherein, load by the internal pressure of the extruder was 66%.

Comparative Example 2

[0084] Polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g and polyethyleneterephthalate chips having intrinsic viscosity of 1.70 dl/g were mixed at a weight ratio of 50:50, molten and extruded under conditions of a temperature of 290° C. and a shear rate of 112.40 S.sup.−1 to prepare strand type pellets. Wherein, load by the internal pressure of the extruder was 71%.

Example 1

[0085] Polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g and polyethyleneterephthalate chips having intrinsic viscosity of 1.70 dl/g were mixed at a weight ratio of 80:20, molten and extruded under conditions of a temperature of 290° C. and a shear rate of 112.40 S.sup.−1 to prepare strand type pellets. Wherein, load by the internal pressure of the extruder was 69%.

Example 2

[0086] Polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g and polyethyleneterephthalate chips having intrinsic viscosity of 1.70 dl/g were mixed at a weight ratio of 70:30, molten and extruded under conditions of a temperature of 290° C. and a shear rate of 112.40 S.sup.−1 to prepare strand type pellets. Wherein, load by the internal pressure of the extruder was 70%.

[0087] The details of the preparation of polymer resin compositions in Examples 1 to 2 and Comparative Examples 1 to 2 are as described in the following Table 1.

TABLE-US-00001 TABLE 1 Comparative Comparative Example Example No Example 1 Example 2 1 2 Chip I.V. 1.2 dl/g 100 50 80 70 content 1.7 dl/g 0 50 20 30 (wt %) Ext temp. (° C.) 200/250/280/290/280/280/280/280/290 Ext L/D (mm) 1200/32 Die Nozzle 12/4 (3 Holes) L/D (mm) Load (%) 66 71 69 70 Discharge 300 speed (g/min) Shear rate (s.sup.−1) 112.40

Experimental Example 1: Evaluation of the Properties of Polymer Resin Compositions of Examples 1 to 2 and Comparative Examples 1 to 2

[0088] For the polymer resin compositions used in Examples and Comparative Examples, molecular weight and melt viscosity measurement results were shown in the following Table 2.

TABLE-US-00002 TABLE 2 I.V. 1.7 dl/g Melt Viscosity @ 290° C. Poise (Pa .Math. s) content GPC (g/mol) Shear rate (1/s) (wt %) Mn Mw Mz PD 50 500 1000 2000 Comparative 0 41440 86643 121940 2.091 4,081 3,154 2,748 2,284 Example1 Example1 20 39740 90507 129970 2.278 4,350 3,401 2,977 2,351 Example2 30 39784 91105 131055 2.290 4,415 3,456 3,012 2,394 Comparative 50 40044 92810 134520 2.318 5,603 4,105 3,450 2,679 Example2

[0089] As confirmed in the Table 2, the polymer resin compositions of Examples 1 and 2 wherein polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g and polyethyleneterephthalate chips having intrinsic viscosity of 1.70 dl/g were mixed at a weight ratio 70:30 or 80:20, have polydispersity index of 2.278 to 2.290, melt viscosity at a temperature of 290° C. and a shear rate of 50/s, of 4,000 to 4,800 poise, and melt viscosity at a temperature of 290° C. and a shear rate of 1000/s, of 2,800 to 3,200 poise, wherein a difference between the melt viscosity at a temperature of 290° C. and a shear rate of 50/s and melt viscosity at a temperature of 290° C. and a shear rate of 1000/s was 1,800 poise or less.

[0090] Namely, the polymer resin compositions of Examples 1 and 2 have high polydispersity index compared to the composition of Comparative Example 1 having the equivalent level of number average molecular weight, and thus, high mechanical properties may be secured in the final product, and melt viscosity in the low shear rate region at a temperature of 300° C. or less may not be so high, and even if shear rate increase, melt viscosity may not significantly decrease, thereby securing mechanical properties as well as sufficient formability.

[0091] To the contrary, the polymer resin composition of Comparative Example wherein polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g were used in the content of 100 wt %, exhibits relatively low polydispersity index, and has low molecular weight, and thus, it may be difficult to secure sufficient mechanical properties in the final product.

[0092] And, in the case of the polymer resin compositions of Comparative Example 2 wherein polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g and polyethyleneterephthalate chips having intrinsic viscosity of 1.70 dl/g were mixed at a weight ratio 50:50, melt viscosities at a temperature of 290° C. and shear rates of 50/s and 1000/s are all greater than 3,200 poise, and thus, it does not have sufficient formability, or may cause load or failure in the manufacturing device such as an extruder.

Example 3 to 5 and Comparative Example 3: Preparation of Yarn for a Tire Cord

Comparative Example 3

[0093] Polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g were molten and extruded under conditions of a temperature of 290° C. and a shear rate of 500 to 2000 S.sup.−1, and initial spinning speed (1st Godet Roller, G/R) of 2800 m/min was applied to wind undrawn yarn, and finally, draw 2.15 times and wind, thus preparing polyester drawn yarn. Pack pressure by discharge was 92 kgf/cm.sup.2.

Example 3

[0094] Polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g and polyethyleneterephthalate chips having intrinsic viscosity of 1.70 dl/g were mixed at a weight ratio of 90:10, and molten and extruded under conditions of a temperature of 290° C. and a shear rate of 500 to 2000 S.sup.−1, and initial spinning speed (1st Godet Roller, G/R) of 2800 m/min was applied to wind undrawn yarn, and finally, draw 2.15 times and wind, thus preparing polyester drawn yarn. Pack pressure by discharge was 94 kgf/cm.sup.2.

Example 4

[0095] Polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g and polyethyleneterephthalate chips having intrinsic viscosity of 1.70 dl/g were mixed at a weight ratio of 80:20, and molten and extruded under conditions of a temperature of 290° C. and a shear rate of 500 to 2000 S.sup.−1, and initial spinning speed (1st Godet Roller, G/R) of 2800 m/min was applied to wind undrawn yarn, and finally, draw 2.15 times and wind, thus preparing polyester drawn yarn. Pack pressure by discharge was 92 kgf/cm.sup.2.

Example 5

[0096] Polyethyleneterephthalate chips having intrinsic viscosity of 1.20 dl/g and polyethyleneterephthalate chips having intrinsic viscosity of 1.70 dl/g were mixed at a weight ratio of 70:30, and molten and extruded under conditions of a temperature of 290° C. and a shear rate of 500 to 2000 S.sup.−1, and initial spinning speed (1st Godet Roller, G/R) of 2800 m/min was applied to wind undrawn yarn, and finally, draw 2.15 times and wind, thus preparing polyester drawn yarn. Pack pressure by discharge was 103 kgf/cm.sup.2.

Experimental Example 2: Measurement of Properties of Undrawn Yarn for a Tire Cord

[0097] The details of Examples 3 to 5 and Comparative Example 3 were respectively described in the following Table 3, and the properties of each obtained undrawn yarn were described in the following Table 4.

TABLE-US-00003 TABLE 3 I.V. I.V. 1.7 dl/g 1.20 dl/g Spinning Spinning Pack Maximum chip chip temperature speed pressure draw ratio Conditions wt % wt % ° C. m/min kgf/cm.sup.2 D/R Example 3 10 90 295 2800 94 x2.15 Example 4 20 80 92 x2.2 Example 5 30 70 103 x2.13 Comparative 0 100 92 x2.15 Example 3 [0098] total fineness is 1000 De., and the fineness of mono-filament is 4 De. (applying spinneret L/D 2.1/0.7, 250H)

TABLE-US-00004 TABLE 4 Intrinsic viscosity Tenacity Elongation Crystallinity of yarn of yarn of yarn of yarn Conditions dl/g gf/d % % Example 3 1.025 2.81 158.27 13.1 Example 4 1.124 2.92 151.62 13.4 Example 5 1.081 2.92 152.96 13.1 Comparative 0.951 2.79 163.92 12.6 Example 3 [0099] Tensile strength and elongation at break of yarn were measured under conditions of initial load 0.05 fg/de, sample length 250 mm and tensile speed 300 mm/min, according to ASTM D885, using universal testing machine of Instron.

[0100] As shown in the Tables 3 and 4, it was confirmed that in Examples 3 to 4, compared to Comparative Example 3, similar pack pressure was exhibited, and in Examples 3 to 5, intrinsic viscosity of prepared yarn significantly increased compared to Comparative Example, and thus, tenacity and crystallinity of yarn significantly increased.

Experimental Example 3: Measurement of Properties of Drawn Yarn for a Tire Cord

[0101] The details of Examples 3 to 5 and Comparative Example 3 were described in the following Table 5, and the properties of each obtained drawn yarn were described in the following Table 6.

TABLE-US-00005 TABLE 5 draw Winder Tenacity Elongation Polydispersity ratio speed of yarn of yarn Mw index birefringence Crystallinity Conditions D/R m/min gf/d % g/mol — Δn % Example 3 x2.0 5600 8.51 13.32 92371 2.0250 0.2095 50.1 X2.15 6020 10.12 10.51 93012 1.9755 0.2128 49.9 Example 4 x2.0 5600 8.83 13.01 94145 2.0008 0.2120 50.3 x2.2 6160 11.27 10.11 94971 1.9638 0.2155 49.8 Example 5 x2.0 5600 8.96 12.97 93618 2.0160 0.2160 50.1 x2.13 5960 10.31 10.25 93914 1.9824 0.2183 49.8 Comparative x2.0 5600 7.91 13.22 88754 2.0320 0.2093 50.3 Example 3 x2.15 6020 9.73 10.13 89152 1.9995 0.2115 50.1

[0102] As shown in the Table 5, the drawn yarn obtained in Example 4 exhibited maximum draw ratio up to 2.2 times, winder speed up to 6160 m/min, and tenacity up to about 11.3 fg/d, and thus, it can be seen that compared to tenacity of 9.73 gf/d at maximum draw ratio of 2.15 times in Comparative Example 3, tenacity improved 1.5 gf/d or more

[0103] And, as results of analyzing yarn of Comparative Example 3 and Examples 3 to 5 at draw ratio of 2.0 times, it was confirmed that in Examples 3 to 5, compared to Comparative Example 3, crystallinity is similar, but degree of orientation of birefringence and molecular weight increase, and molecular weight distribution is narrow.

[0104] Namely, it was confirmed that the yarn of Examples 3 to 5 can be subjected to a melting process at the same shear rate as in Comparative Example 3, and the rate of thermal decomposition significantly decreases, and thus, intrinsic viscosity of the final yarn is relatively high, and tenacity is also high.

Example 6 to 8 and Comparative Example 4: Manufacture of Tire Cord

[0105] Each drawn yarn of Examples 3 to 5 and Comparative Example 3 was Z twisted at predetermined total fineness and twist per unit length (TPM), and 2 strands of the yarn were plied to S twist yarn with the same twist multiplier, and dipped in a RFL adhesive solution, and then, dried and heat treated to prepare a PET tire cord.

[0106] Wherein, drawn yarn used, fineness of drawn yarn, twist multiplier (TM) and cord heat treatment conditions are shown in the following Table 6, and the composition of the RFL adhesive solution and drying conditions were in accordance with common PET tire cord manufacturing conditions.

TABLE-US-00006 TABLE 6 Fineness of drawn Twist per Cord heat Preparation Drawn yarn meter treatment of cord yarn used (denier) (TPM) Ply conditions Example 6 Example 3 1000 430 2 240~245° C., 90 sec or more Example 7 Example 4 1000 430 2 240~245° C., 90 sec or more Example 8 Example 5 1000 430 2 240~245° C., 90 sec or more Comparative Comparative 1000 430 2 240~245° C., Example 4 Example 3 90 sec or more

Experimental Example 4: Measurement of Properties of Tire Cord

[0107] For each tire cord of Examples 6 to 8 and Comparative Example 4, properties were measured as follows, and the measured properties were shown in the following Table 7.

[0108] 1) Tensile Strength (g/d)

[0109] Tenacity of cord was measured using universal testing machine according to ASTM D885 standard.

[0110] 2) Fatigue Resistance (%)

[0111] Each tire cord of Examples 6 to 8 and Comparative Example 4 were vulcanized with rubber under conditions of a temperature of 160° C. and a pressure of 20 kgf for 20 minutes to prepare a specimen. And, for the specimen, a temperature of 100° C., 2500 rpm and ±8.0% tensile-compression rate were applied using Disk fatigue tester (manufacturing company: UESHIMA, model name: Belt tester FT-610) to alternatively apply repeated compressive strain and tensile strain for 24 hours. And then, the rubber was removed from the specimen, and tensile strength after fatigue resistance test was measured by the same method as the above method, and based thereon, tensile strength retention rate (%) before and after fatigue resistance test was calculated

TABLE-US-00007 TABLE 7 Tensile strength retention rate Tensile strength before and Properties Draw Tensile after fatigue after fatigue of cord ratio strength resistance test resistance test Unit (D/R) (g/d) (g/d) (%) Example 6 X2.0 7.66 5.37 70.1 X2.15 8.80 5.55 63.1 Example 7 X2.0 7.95 5.55 69.8 X2.2 9.61 6.04 62.8 Example 8 X2.0 8.06 5.59 69.3 X2.13 8.82 5.50 62.4 Comparative X2.0 7.12 4.95 69.5 Example 4 X2.15 8.27 5.15 62.3

[0112] As shown in the Table 7, it was confirmed that the tire cords of Examples 6 to 8 have tensile strength of 7.5 g/d or more in case the yarn of Examples 3 to 5 having draw ratio of 2.0 or more is used, and particularly, have tensile strength of 8.5 g/d or more in case yarn having draw ratio of 2.1 or more is used.

[0113] It was also confirmed that, in the case of tire cords having relatively high tenacity, tensile strength significantly decreases if repeated compressive strain and tensile strain are applied, but the tire cords of Examples 6 to 8 have high tensile strength as explained above, and yet, compared to Comparative Example 4 having relatively low tensile strength, have equivalent or more excellent tensile strength retention rate before and after fatigue resistance test.