Film for tire inner liner, and method for manufacturing the same

Abstract

The present invention relates to a film for a tire inner liner including a base film layer including a copolymer or a mixture of a polyamide-based resin and a polyether-based resin, and an adhesive layer including a resorcinol-formalin-latex (RFL)-based adhesive, and having low shrinkage rate when elongated at a high temperature and then cooled to room temperature, and a method for manufacturing the same.

Claims

1. A film for a tire inner liner, comprising: a base film layer comprising a polyamide-based resin and an elastomer copolymer comprising polyamide-based segments and polyether-based segments; and an adhesive layer comprising a resorcinol-formalin-latex (RFL)-based adhesive, wherein the content of the polyether-based segments in the elastomer copolymer is 15 to 50 wt % based on total weight of the base film layer, and the base film layer comprises the polyamide-based resin and the elastomer copolymer in a weight ratio of 5:5 to 4:6, the thickness of the base film layer is 30 to 300 μm, and the film for a tire inner liner has a shrinkage rate of 5% or less when elongated 50 to 150% at 80 to 160° C. and then cooled to room temperature, wherein the elastomer copolymer has a weight average molecular weight of 50,000 to 300,000.

2. The film for a tire inner liner according to claim 1, wherein the film for a tire inner liner has a shrinkage rate of 3% or less when elongated 150% at 160° C. and then cooled to room temperature.

3. The film for a tire inner liner according to claim 1, wherein the film for a tire inner liner has a coefficient of thermal expansion of 100×10.sup.−6/° C. to 500×10.sup.−6/° C. at 80 to 160° C.

4. The film for a tire inner liner according to claim 1, wherein the film for a tire inner liner has tensile stress of 310 kg/cm.sup.2 or less when elongated 150% at 160° C.

5. The film for a tire inner liner according to claim 1, wherein the polyamide-based resin has relative viscosity (sulfuric acid 96% solution) of 3.0 to 3.5.

6. The film for a tire inner liner according to claim 1, wherein the elastomer copolymer comprises polyamide-based segments and polyether-based segments in a weight ratio of 6:4 to 3:7.

7. The film for a tire inner liner according to claim 1, wherein the base film layer is an unstretched film.

8. The film for a tire inner liner according to claim 1, wherein the adhesive layer is formed on at least one side of the base film layer to a thickness of 0.1 to 20 μm.

9. The film for a tire inner liner according to claim 1, wherein the resorcinol-formalin-latex (RFL)-based adhesive comprises 2 to 30 wt % of a condensate of resorcinol and formaldehyde, and 70 to 98 wt % of latex.

10. The film for a tire inner liner according to claim 1, wherein the base film layer has an equilibrium moisture content (25° C., 65% RH) of 5 to 9%.

11. A method for manufacturing a film for a tire inner liner, comprising: mixing at a weight ratio of 5:5 to 4:6 a polyamide-based resin and an elastomer copolymer comprising polyamide-based segments and polyether-based segments; melting and extruding the mixture of the polyamide-based resin and the elastomer copolymer comprising polyamide-based segments and polyether-based segments at 230 to 300° C. to form a base film layer having a thickness of 30 to 300 μm; and forming an adhesive layer comprising a resorcinol-formalin-latex (RFL)-based adhesive on at least one side of the base film layer, wherein the content of the polyether-based segments in the elastomer copolymer is 15 to 50 wt % based on total weight of the base film layer, and the film for a tire inner liner has a shrinkage rate of 5% or less when elongated 50 to 150% at 80 to 160° C. and then cooled to room temperature, wherein the elastomer copolymer has a weight average molecular weight of 50,000 to 300,000.

12. The method according to claim 11, wherein the manufactured tire inner liner has a coefficient of thermal expansion of 1×10.sup.−6/° C. to 5000×10.sup.−6/° C. at 80 to 160° C.

13. The method according to claim 11, wherein the elastomer copolymer comprises polyamide-based segments and polyether-based segments in a weight ratio of 6:4 to 3:7.

14. The method according to claim 11, further comprising a step of solidifying the base film layer formed by melting and extrusion in a cooling part maintained at 5 to 40° C.

15. The method according to claim 11, wherein the step of forming an adhesive layer comprises coating an adhesive comprising 2 to 30 wt % of a condensate of resorcinol and formaldehyde, and 68 to 98 wt % of latex, on at least one side of the base film layer to a thickness of 0.1 to 20 μm.

16. The method according to claim 11, further comprising a step of aging the base film layer under constant temperature and humidity conditions.

17. The method according to claim 16, wherein the step of aging the base film layer under constant temperature and humidity conditions is conducted at a temperature selected from 20° C. to 30° C. and relative humidity selected from 60% to 70% for 12 hours to 48 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows the structure of a tire.

DETAILS FOR PRACTICING THE INVENTION

(2) Hereinafter, preferable examples are presented, but these examples are only to illustrate the invention and the scope of the invention is not limited thereto.

Examples and Comparative Examples: Manufacture of a Film for a Tire Inner Liner

Example 1

(3) (1) Manufacture of a Base Film

(4) 35 wt % of nylon 6 resin [relative viscosity (sulfuric acid 96% solution) 3.3], and 65 wt % of an elastomer copolymer resin (including 50 wt % of polyamide-based segments and 50 wt % of polyether-based segments, having an absolute weight average molecular weight 150,000) were mixed. The temperature of the mixture was controlled and it was dried so that coagulation may not occur between chips, and then the temperature of the feeder was controlled to 50 to 100° C. and the mixture was supplied to an extrusion die while preventing welding of the mixture in an extrusion screw and resulting faulty feeding.

(5) Further, the mixture was extruded at 260° C. through a T-type die (die gap: 1.0 mm) while maintaining a uniform flow of the molten resin, and the molten resin was cooled and solidified in a film shape with a uniform thickness on the surface of a cooling roll maintained at 25° C. using an air knife, to obtain an unstretched base film having a thickness of 100 μm at a speed of 15 m/min without passing stretching and heat treatment sections.

(6) (2) Coating of Adhesive

(7) Resorcinol and formaldehyde were mixed at a mole ratio of 1:2, and then condensation was conducted to obtain a condensate of resorcinol and formaldehyde. 12 wt % of the condensate of resorcinol and formaldehyde and 88 wt % of styrene/butadiene-1,3/vinylpyridine latex were mixed to obtain a resorcinol/formaldehyde-latex (RFL)-based adhesive at a concentration of 20%.

(8) The resorcinol/formaldehyde-latex (RFL)-based adhesive was coated on the base film to a thickness of 1 um using a gravure coater, and dried and reacted at 150° C. for 1 minute to form an adhesive layer.

Example 2

(9) (1) Manufacture of a Base Film

(10) A base film was manufactured by the same method as Example 1, except that 40 wt % of nylon 6 resin [relative viscosity (sulfuric acid 96% solution) 3.3] and 60 wt % of an elastomer copolymer resin (including 60 wt % of polyamide-based segments and 40 wt % of polyether-based segments, having an absolute weight average molecular weight of 150,000) were mixed.

(11) (2) Coating of Adhesive

(12) An adhesive layer was formed on the above manufactured base film by the same method as Example 1.

Example 3

(13) (1) Manufacture of a Base Film

(14) A base film was manufactured by the same method as Example 1, so except that 50 wt % of nylon 6 resin [relative viscosity (sulfuric acid 96% solution) 3.3] and 50 wt % of an elastomer copolymer resin (including 60 wt % of polyamide-based segments and 40 wt % of polyether-based segments, having an absolute weight average molecular weight of 150,000) were mixed.

(15) (2) Coating of Adhesive

(16) An adhesive layer was formed on the above manufactured base film by the same method as Example 1.

Example 4

(17) (1) Manufacture of a Base Film

(18) The unstretched base film manufactured in Example 1 was aged under a temperature of 25° C. and relative humidity of 65% for 24 hours, to obtain a base film.

(19) (2) Coating of Adhesive

(20) An adhesive layer was formed on the above manufactured base film by the same method as Example 1.

Example 5

(21) (1) Manufacture of a Base Film

(22) The unstretched base film manufactured in Example 2 was aged under a temperature of 25° C. and relative humidity of 65% for 24 hours, to obtain a base film.

(23) (2) Coating of Adhesive

(24) An adhesive layer was formed on the above manufactured base film by the same method as Example 1.

Example 6

(25) (1) Manufacture of a Base Film

(26) The unstretched base film manufactured in Example 3 was aged under a temperature of 25° C. and relative humidity of 65% for 24 hours, to obtain a so base film.

(27) (2) Coating of Adhesive

(28) An adhesive layer was formed on the above manufactured base film by the same method as Example 1.

Comparative Example 1

(29) A mold releasing agent and a finishing agent were introduced into butyl rubber and mixed, then refined to obtain a film for a tire inner liner with a thickness of 70 μm, and an adhesion rubber (tie gum) was formed on the inner liner film to a thickness of 1 μm.

Comparative Example 2

(30) (1) Manufacture of a Base Film

(31) A base film was manufactured by the same method as Example 1, except that 80 wt % of nylon 6 resin [relative viscosity (sulfuric acid 96% solution) 3.3] and 20 wt % of an elastomer copolymer resin (including 80 wt % of polyamide-based segments and 20 wt % of polyether-based segments having an absolute weight average molecular weight of 150,000) were mixed.

(32) (2) Coating of Adhesive

(33) A resorcinol-formalin-latex (RFL)-based adhesive was prepared by the same method as Example 1, and it was coated on the base film and dried to form an adhesive layer with a thickness of 1 μm.

Comparative Example 3

(34) (1) Manufacture of a Base Film

(35) A base film was manufactured by the same method as Example 1, except that 20 wt % of nylon 6 resin [relative viscosity (sulfuric acid 96% solution) 3.3], and 80 wt % of elastomer copolymer resin (including 20 wt % of polyamide-based segments and 80 wt % of polyether-based segments, having absolute weight average molecular weight of 150,000) were mixed.

(36) (2) Coating of Adhesive

(37) Resorcinol-formalin-latex (RFL)-based adhesive was prepared by the same method as Example 1, and it was coated on the base film and dried to form an adhesive layer with a thickness of 1 μm.

Comparative Example 4

(38) (1) Manufacture of a Base Film

(39) A chip was manufactured using only nylon 6 resin with relative viscosity of 3.4, and the manufactured chip was extruded with a circular die at 260° C. to obtain an unstretched base film having a thickness of 70 μm at a speed of 30 m/min without passing stretching and heat treatment sections.

(40) (2) Coating of Adhesive

(41) A resorcinol-formalin-latex (RFL)-based adhesive was prepared by the same method as Example 1, and it was coated on the base film and dried to form an adhesive layer with a thickness of 1 μm.

Comparative Example 5

(42) The chip manufactured in Example 1 was extruded with a circular die at 320° C. to attempt to manufacture a film for a tire inner liner. However, melt viscosity of the film became too low due to a high temperature, and thus a film shape could not be formed, and manufacture of a product failed due to generation of a carbide of the soft segment ingredients having a low melt viscosity.

Experimental Example

Experimental Example 1: Measurement of Coefficient of Thermal Expansion of Inner Liner Film

(43) The inner liner films obtained in the examples and comparative examples were cut to a size of 20*4*0.07 mm (length*width*thickness) and mounted on a sample holder. The sample holder was mounted on a TMA so chamber (Diamond TMA, PerkinElmer) and a primary load of 80 Mn was applied to the film. The length of the sample was then measured according to temperature while elevating the temperature in the range of −60 to 220° C. at a speed of 10° C. per minute, and the CTE (coefficient of thermal expansion) was calculated.
CTE=ΔL/L.sub.o*ΔT

(44) [ΔL: the amount of change in sample length (μm), L.sub.o: the length of sample (m), ΔT: the amount of change in temperature (° C.)]

Experimental Example 2: Measurement of Shrinkage Rate of Inner Liner Film

(45) When the tire inner liner films obtained in the examples and comparative examples were elongated 150% at 80° C., 100° C., 120° C., and 160° C., and then cooled to room temperature, the shrinkage rate was measured using a thermal shrinkage stressor (KANEBO Company).

Experimental Example 3: Measurement of Tensile Stress According to Elongation of Inner Liner Film

(46) Tensile stress of the inner liner film according to elongation was measured using a universal testing machine of Instron Corporation (Model 5566). Specifically, the tire inner liner films obtained in the examples and comparative examples were cut to a certain size of 10*100*0.07 mm (length*width*thickness) and mounted on a gripper, and then load per unit area of a load cell was measured when the film was elongated 150% in a longitudinal direction in a chamber at 160° C.

Experimental Example 4: Oxygen Permeability Test

(47) Oxygen permeability of the tire inner liner films obtained in the examples and comparative examples was measured. The specific measurement method is as follows.

(48) (1) Oxygen permeability: measured according to ASTM D 3895, using an oxygen permeation analyzer (Model 8000, Illinois Instruments Company) under a 25° C. and 60% RH atmosphere.

Experimental Example 5: Measurement of Equilibrium Moisture Content

(49) Equilibrium moisture content of each base film layer obtained in the examples and comparative examples was measured by evaluating a weight reduction rate after aging at 150° C. for 3 minutes using PRECISA XM60 equipment at 25° C. and 65% RH.

(50) The results of Experimental Examples 1 to 4 are summarized in the following Table 1.

(51) TABLE-US-00001 TABLE 1 Results of Experimental Examples 1 to 4 for Examples 1 to 4 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Shrinkage  80° C./150% 3.3 3.6 3.6 2.0 2.1 2.1 rate (%) elongation 100° C./150% 3.5 3.7 3.7 2.3 2.1 2.1 elongation 120° C./150% 3.6 3.8 3.9 2.4 2.2 2.2 elongation 160° C./150% 3.7 3.8 3.8 2.4 2.2 2.2 elongation Coefficient of (*10.sup.−6/° C.) 380 300 360 145 155 158 thermal expansion MD (ppm/° C.) Tensile stress at 150% 211 225 227 150 155 170 elongation at 160° C. (kg/cm.sup.2) Oxygen permeability 150 120 120 150 120 120 cc/(m.sup.2 .Math. 24 hr .Math. atm) Equilibrium moisture content 3.5 3.2 3.3 6.2 6.0 6.0 (25° C., RH 65%)

(52) As shown in Table 1, it was confirmed that shrinkage rates measured when the tire inner liner films of the examples were elongated 150% at 80 to 160° C. and cooled to room temperature were all 4% or less. Specifically, since the tire inner liner film has a low shrinkage rate even if elongated or deformed at a high temperature and then cooled, excellent formability and high shape stability may be secured even in a tire manufacturing process during which high elongation and deformation occur at a high temperature.

(53) It was also confirmed that the tire inner liner films of the examples have coefficients of thermal expansion of 145×10.sup.−6/° C. to 380×10.sup.−6/° C. at 80° C. to 160° C. Specifically, the tire inner liner films of the examples may exhibit low coefficients of thermal expansion thus exhibiting excellent shape stability, and minimized deformation or shrinkage due to heat thus preventing cracks or peel-off from a carcass layer due to repeated deformations or elongation-shrinkage in a high temperature tire manufacturing process or in an automobile running process.

(54) It was also confirmed that the tire inner liner films of the examples generate tensile stress of 230 kg/cm.sup.2 or less even when elongated 150% at 160° C. Specifically, since a small load is generated even if the tire inner liner films of the examples are elongated under specific conditions in a tire manufacturing process, shape stability of a green tire or a final tire may be improved.

(55) It was also confirmed that the tire inner liner films of the examples may exhibit low oxygen permeability of 200 cc/(m.sup.2.Math.24 hr.Math.atm) or less while having a thick thickness, thus achieving a high gas barrier property.

(56) Further, the tire inner liner films of Examples 4 to 6 passing aging under constant temperature and humidity conditions exhibited an equilibrium moisture content of 6.0% to 6.2% under a temperature of 25° C. and relative humidity of 65%.

(57) TABLE-US-00002 TABLE 2 Results of Experimental Examples 1 to 4 for Comparative Examples 1 to 4 Compar- Compar- Compar- Compar- ative ative ative ative Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 Shrinkage  80° C./ 10.2 5.7 7.7 5.7 rate (%) 150% elon- gation 100° C./ 16.3 5.9 7.2 5.4 150% elon- gation 120° C./ 16.2 5.4 7.4 5.9 150% elon- gation 160° C./ 16.1 4.4 7.5 5.4 150% elon- gation Coeffi- (*10.sup.−6/ 580 167 450 150 cient of ° C.) MD thermal expansion (ppm/° C.) Tensile stress at 150% 181 450 200 526 elongation at 160° C. (kg/cm.sup.2) Oxygen permeability 300 226 387 180 cc/(m.sup.2 .Math. 24 hr .Math. atm) Equilibrium moisture 6.0 5.8 6.0 5.8 content (25° C., RH 65%)

(58) As shown in Table 2, it was confirmed that the inner liner film of Comparative Example 1 obtained using butyl rubber exhibits a shrinkage rate of about 10% to 16.3% as measured when elongated 150% at 80 to 160° C. and cooled to room temperature, and thus the length and the shape of the film are significantly changed when elongated at a high temperature.

(59) Further, it was confirmed that although the inner liner films of Comparative Examples 2 and 4 exhibit a low shrinkage rate of about 4 to 5% compared to Comparative Example 1, as measured when elongated 150% at 80 to 160° C. and cooled to room temperature, the shrinkage rate is high compared to the inner liner films of the examples, and thus the deformation rate of the length or the shape is relatively high when elongated at a high temperature and then cooled. It was also confirmed that the inner liner films of Comparative Examples 2 and 4 respectively exhibit stress of 450 kg/cm.sup.2 and 526 kg/cm.sup.2 when elongated 150% at 160° C., and thus they may not be easily formed in a tire manufacturing process.

(60) In addition, it was confirmed that the inner liner film of Comparative Example 3 exhibits a shrinkage rate of about 7.2% to 7.7%, as measured when elongated 150% at 80 to 160° C. and cooled to room temperature, and thus the length and the shape of the film are significantly changed when elongated at a high temperature, and that it exhibits oxygen permeability of 387 cc/(m.sup.2.Math.24 hr.Math.atm) and thus the gas barrier property is low.

(61) It was also confirmed that the inner liner films of Comparative Examples 1 and 3 exhibit coefficients of thermal expansion of greater than 400*10.sup.−6/° C., and thus the shape or the length is significantly changed at a high temperature.

Experimental Example 6: Measurement of Formability

(62) Tires were manufactured using the tire inner liner films of the examples and comparative examples, applying the 205R/65R16 standard. During the tire manufacturing process, manufacturability and appearance were evaluated after manufacturing a green tire, and then the final appearance of the tire was examined after vulcanization.

(63) Herein, it was judged as “good” when there is no crushing of a green tire or a tire after vulcanization, and a standard deviation of diameter is within 5%. Also, it was judged as “shape faulty” when crushing of a green tire or a tire after vulcanization is generated and thus a tire is not properly manufactured, the inner liner in the tire is dissolved or torn and damaged, or a standard deviation of diameter is greater than 5%.

Experimental Example 7: Measurement of Internal Pressure Retention

(64) Using tires manufactured in Experimental Example 3, 90 day IPR (internal pressure retention) was measured and compared/evaluated under a 21° C. temperature and a 101.3 kPa pressure according to ASTM F 1112-06.

(65) The measurement results of Experimental Examples 6 to 7 are summarized in the following Table 3.

(66) TABLE-US-00003 TABLE 3 Results of Experimental Examples 6 and 7 Manufactured state State of Internal pressure of green tire final tire retention (%) Example1 Good Good 96.2 Example2 Good Good 97.1 Example3 Good Good 96.3 Example4 Good Good 96.4 Example5 Good Good 96.7 Example6 Good Good 97.1 Comparative Good Good 91.4 Example1 Comparative Good Good Not Applicable Example2 Comparative Good Good Not Applicable Example3 Comparative Good Good Not Applicable Example4

(67) As shown in Table 3, if the tire inner liner films of the examples are applied, sufficient stretching may be achieved even if the expansion pressure is applied in a tire manufacturing process, and thus the manufactured state of the final tire is good.

(68) Meanwhile, as shown in the results of Experimental Example 7, the tires manufactured using the tire inner liner films of the examples exhibit internal pressure retention of 95% or more, when 90 day IPR (internal pressure retention) of the tires using the tire inner liner films is measured at 21° C. and 101.3 kPa according to ASTM F1112-06, thus preventing overturning accidents and mileage lowering due to low internal pressure.

(69) To the contrary, the tires manufactured using the tire inner liner films of the comparative examples exhibit relatively low internal pressure retention, or internal pressure retention could not be measured due to inferior performance of retaining internal pressure for a long time.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

(70) 1. Tread 2. Shoulder 3. Side Wall 4. Cap ply 5. Belt 6. Body Ply 7. Inner Liner 8. Apex 9. Bead