Method for manufacturing polymer film and co-extruded film

Abstract

The present invention relates to: a method for manufacturing a polymer film, the method including a base film forming step for co-extruding a first resin containing a polyamide-based resin and a second resin containing a copolymer including polyamide-based segments and polyether-based segments; a co-extruded film including a base film including a first resin layer containing a polyamide-based resin, and a second resin layer containing a copolymer having polyamide-based segments and polyether-based segments; to a co-extruded film including a base film including a first resin layer and a second resin layer, which have different melting points; and to a method for manufacturing a polymer film, the method including a base film forming step including a step of co-extruding a first resin and a second resin, which have different melting points.

Claims

1. A co-extruded film for an inner liner: comprising a base film including a first resin layer containing a polyamide-based resin and a second resin layer containing a copolymer including polyamide-based segments and polyether-based segments wherein the first resin layer further includes a copolymer including polyamide-based segments and polyether-based segments, the second resin layer further includes a polyamide-based resin, and the first resin layer includes more polyamide-based resin than the second resin layer, and a difference between the content (wt %) of the polyamide-based resin in the first resin layer and the content (wt %) of the polyamide-based resin in the second resin layer is 5% to 85% by weight.

2. The co-extruded film according to claim 1, wherein the base film has a multilayer structure of two or more layers including one or more first resin layers and one or more second resin layers.

3. The co-extruded film according to claim 1, wherein the first resin layer includes 5% to 100% by weight of the polyamide-based resin, and the second resin layer includes 0% to 95% by weight of the polyamide-based resin layer.

4. The co-extruded film according to claim 1, wherein the total content of the polyether-based segments in the base film is 2% to 40% by weight.

5. The co-extruded film according to claim 1, wherein the base film has a multilayer structure of two or more layers including the first resin layer and one or more types of the second resin layer including less polyamide-based resin than the first resin layer.

6. A co-extruded film for an inner liner comprising a base film containing a first resin layer and a second resin layer, wherein the first resin layer includes 0% to 90% by weight of the polyamide-based resin and 10% to 100% by weight of the copolymer including polyamide-based segments and polyether-based segments and the second resin layer includes 5% to 95% by weight of the polyamide-based resin and 5% to 95% by weight of the copolymer including polyamide-based segments and polyether-based segments, and the first resin layer has a lower melt viscosity at a temperature of 240 C. to 270 C. compared to the second resin layer, and a difference in the melt viscosity between the first resin layer and the second resin layer is between 100 poise to 3,000 poise at a temperature of 240 C. to 270 C. and a shear rate of 500 s.sup.1.

7. The co-extruded film according to claim 6, wherein the base film includes one or more first resin layers and one or more second resin layers.

8. The co-extruded film according to claim 6, wherein the first resin layer has a melt viscosity of 600 poise to 6,000 poise at a temperature of 240 C. to 270 C. and a shear rate of 500 s.sup.1, and the second resin layer has a melt viscosity of 700 poise to 9,000 poise at a temperature of 240 C. to 270 C. and a shear rate of 500 s.sup.1.

9. The co-extruded film according to claim 6, wherein the total content of the polyether-based segments in the base film is 2% to 40% by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically illustrate the structure of a pneumatic tire.

(2) FIG. 2 schematically illustrates the process of manufacturing a film having a multilayer structure by using a feed block in examples.

(3) FIG. 3 schematically illustrates a layer separating device for interfacial surface generator) used in examples.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these examples are only to illustrate the invention and the scope of the invention is not limited thereto.

Example

Manufacture of a Polymer Film for an Inner Liner

Example 1

(1) Manufacturing of a Base Film

(5) A nylon 6 resin having a relative viscosity (96% sulfuric acid solution) of 3.6 manufactured from -caprolactam and a copolymer having a weight average molecular weight of 110,000 containing polyether-based segments whose main chain is an amine group-terminated polypropylene oxide and polyamide-based segments derived from -caprolactam (the weight ratio of polyether-based segments:polyamide-based segments is 1:3) were mixed in a weight ratio of 6:4 to produce a first resin.

(6) Then, the nylon 6 having a relative viscosity (96% sulfuric acid solution) of 3.6 and the copolymer having a weight average molecular weight of 110,000 were mixed in a weight ratio of 4:6 to produce a second resin.

(7) After drying the first resin and the second resin, respectively, a base film was manufactured by using two extruders and a feed block of a three-layer structure. In the first extruder, the first resin which is a raw material constituting the first resin layer (B layer) was injected and then extruded at 255 C. In the second extruder, the second resin which is a raw material constituting the second resin layer (A layer) was injected and then extruded at 260 C.

(8) As schematically shown in FIG. 2, a feed block having a three-layer structure was provided on the top of the extrusion die to form a multilayer structure, and a flow of the molten resin of the multilayer film having a three-layer structure in which a first resin layer (B layer) forms a core layer and a second resin layer (A layer) forms a skin layer [second resin layer (A layer)/first resin layer (B layer)/second resin layer (A layer)] was produced.

(9) The flow of the molten resin of the multilayer film formed with the above-described structure and composition was extruded through a T-type die (die gap-1.5 mm), and then the molten resin was cooled and solidified into a film with a uniform thickness using an air knife on the surface of a cooling roll that was controlled to 20 C. to obtain an unstretched base film of a three-layer structure having a thickness of 100 m at a speed of 15 m/min.

(10) At this time, one second resin layer (A layer) accounted for 10% of the entire base film and the first resin layer (B layer) accounted for 80% of the thickness of the entire base film.

(2) Coating of Adhesive

(11) Resorcinol and formaldehyde were mixed in a mole ratio of 1:2 and then subjected to a condensation reaction to obtain a condensate of resorcinol and formaldehyde.

(12) 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-formalin-latex (RFL)-based adhesive with a concentration of 20%.

(13) Then, the resorcinol-formalin-latex (RFL)-based adhesive was coated on the unstretched base film of a three-layer structure using a gravure coater, then dried and reacted at 150 C. for 1 min to form an adhesive layer having a thickness of 3 m.

Example 2

(1) Manufacturing of a Base Film

(14) A polyamide-based resin having a relative viscosity (96% sulfuric acid solution) of 3.8 synthesized by using 95 wt % of -caprolactam and 5 wt % of 2-azacyclononanone, and a copolymer having a weight average molecular weight of 100,000 containing polyether-based segments whose main chain is an amine group-terminated polypropylene oxide and polyamide-based segments derived from -caprolactam (the weight ratio of polyether-based segments:polyamide-based segments is 1:4), were mixed in a weight ratio of 7:3 to produce a first resin.

(15) The polyamide-based resin having a relative viscosity (96% sulfuric acid solution) of 3.8 and the copolymer having a weight average molecular weight of 100,000 were mixed in a weight ratio of 4:6 to produce a second resin.

(16) Then, the copolymer having a weight average molecular weight of 100,000 was used alone as another second resin.

(17) The first resin and two types of the second resins were used, and three extruders, a feed block of a three-layer structure, and a continuously connected two-layer separating device (2 channel interfacial surface generator) were used to manufacture a base film.

(18) Specifically, in the first extruder, the first resin in which the polyamide-based resin and the copolymer having a weight average molecular weight of 100,000 were mixed in a weight ratio of 7:3 was dried, and then injected and extruded at 255 C. In the second extruder, the other second resin (a copolymer having a weight average molecular weight of 100,000) was dried and then injected and extruded at 260 C. In the third extruder, the second resin in which the polyamide-based resin and the copolymer having a weight average molecular weight of 100,000 were mixed in a weight ratio of 4:6 was dried, and then injected and extruded at 260 C.

(19) After the extrusion, in order to form a multilayer structure, in the feed block of a three-layer structure installed on the top of the two layer separating device, a core layer (B-layer) was formed from the product extruded from the first extruder, and a skin layer (A layer and C layer) was formed from the product extruded from the second extruder and the third extruder, to form a flow of the molten resin having a three-layer structure [A layer/B layer/C layer].

(20) In the three-layer structure of A layer/B layer/C layer formed from the feed block, the layer structure was constituted so that the thickness of the A layer accounted for 5% of the entire thickness of a three-layer structure, the thickness of the B layer accounted for 85% of the entire thickness of a three-layer structure, and the thickness of the C layer accounted for 10% of the entire thickness of a three-layer structure.

(21) Continuously, in order to multilayer the flow of the molten resin having a three-layer structure with a thinner thickness, the layers were separated by using a two-layer separating device (2-channel interfacial surface generator) connected in series to the feed block, and then laminated to form a multilayer.

(22) That is, the three-layer structure of A layer/B layer/C layer formed in the feed block was passed through the first two-layer separating device (2-channel interfacial surface generator), and then the three-layer structure was separated and laminated to form a multilayer of a six-layer structure (A/B/C/A/B/C). Subsequently, the six-layer structure was passed through the second two-layer separating device (2-channel interfacial surface generator), and then the six-layer structure was separated and laminated in the same manner to form a 12-layer structure (A/B/C/A/B/C/A/B/C/A/B/C).

(23) The flow of the molten resin of the multilayer film formed with the above-described structure and composition was extruded through a T-type die (die gap-1.5 mm), and then the molten resin was cooled and solidified into a film with a uniform thickness using an air knife on the surface of a cooling roll that was controlled to 18 C. to obtain an unstretched base film of a multilayer structure having a thickness of 100 m at a speed of 10 m/min.

(2) Coating of Adhesive

(24) Resorcinol and formaldehyde were mixed in a mole ratio of 1:2 and then subjected to a condensation reaction to obtain a condensate of resorcinol and formaldehyde.

(25) 15 wt % of the condensate of resorcinol and formaldehyde and 85 wt % of styrene/butadiene-1,3/vinylpyridine latex were mixed to obtain a resorcinol-formalin-latex (RFL)-based adhesive with a concentration of 25%.

(26) The resorcinol-formalin-latex (RFL)-based adhesive was then coated on the unstretched base film of a 12-layer structure using a gravure coater, and dried and reacted at 150 C. for 1 min to form an adhesive layer having a thickness of 5 m.

Example 3

(1) Manufacturing of a Base Film

(27) A nylon 6 resin having a relative viscosity (96% sulfuric acid solution) of 3.8 manufactured from -caprolactam, and a copolymer having a weight average molecular weight of 120,000 containing polyether-based segments whose main chain is an amine group-terminated polyethylene oxide and polyamide-based segments derived from -caprolactam (the weight ratio of polyether-based segments:polyamide-based segments is 1:4), were mixed in a weight ratio of 4:6 to produce a first resin.

(28) The first resin was injected into liquid nitrogen using Freezer Mill 6750 (SPEX CertiPrep) equipment and pulverized, and then the melt viscosity was measured using Rheo-Tester 2000 (GttFert) equipment. As a result, the product had a melt viscosity of 4,100 poise at a temperature of 255 C. and a shear rate of 500 s.sup.1.

(29) Then, the nylon 6 having a relative viscosity (96% sulfuric acid solution) of 3.8 and the copolymer having a weight average molecular weight of 120,000 were mixed in a weight ratio of 6:4 to produce a second resin.

(30) The melt viscosity was measured by using the same equipment and measuring method as the first resin. As a result, the second resin had a melt viscosity of 4,610 poise at a temperature of 255 C.

(31) After drying the first resin and the second resin, respectively, a base film was manufactured by using two extruders and a feed block of a three-layer structure. In the first extruder, the first resin which is a raw material constituting the first resin layer (B layer) was injected and then extruded at 255 C. In the second extruder, the second resin which is a raw material constituting the second resin layer (A layer) was injected and then extruded at 255 C.

(32) As schematically shown in FIG. 2, a feed block having a three-layer structure was provided on the top of the extrusion die to form a multilayer structure. In the feed block, a flow of the molten resin of the multilayer film having a three-layer structure in which the first resin layer (B layer) forms a core layer and the second resin layer (A layer) forms a skin layer [second resin layer (A layer)/first resin layer (B layer)/second resin layer (A layer)] was produced.

(33) The flow of the molten resin of the multilayer film formed with the above-described structure and composition was extruded through a T-type die (die gap-1.0 mm), and then the molten resin was cooled and solidified into a film with a uniform thickness using an air knife on the surface of a cooling roll that was controlled to 17 C. to obtain an unstretched base film of a three-layer structure having a thickness of 100 m at a speed of 10 m/min.

(34) At this time, the flow rate of the first resin was set to 176.4 kg/h and the total flow rate of the second resin was set to 75.6 kg/h, so that one second resin layer (A layer) accounted for 15% of the entire base film and the first resin layer (B layer) accounted for 70% of the thickness of the entire base film.

(2) Coating of Adhesive

(35) Resorcinol and formaldehyde were mixed in a mole ratio of 1:2 and then subjected to a condensation reaction to obtain a condensate of resorcinol and formaldehyde.

(36) 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-formalin-latex (RFL)-based adhesive with a concentration of 20%.

(37) The resorcinol-formalin-latex (RFL)-based adhesive was then coated on two sides of the unstretched base film of a three-layer structure using a gravure coater, and dried and reacted at 150 C. for 1 min to form an adhesive layer having a thickness of 3 m on the two sides.

Example 4

(1) Manufacturing of a Base Film

(38) A polyamide-based copolymer resin having a relative viscosity (96% sulfuric acid solution) of 3.6 [synthesized by using -caprolactam and adipic acid in a weight ratio of 94:6], a copolymer having a weight average molecular weight of 80,000 [synthesized by using polyether-based segments whose main chain is polytetramethylene oxide:polyamide-based segments derived from -caprolactam in a weight ratio of 1:4], and a copolymer having a weight average molecular weight of 110,000 [synthesized by using polyether-based segments whose main chain is an amine group-terminated polypropylene oxide:polyamide-based segments derived from -caprolactam in a weight ratio of 1:3] were mixed in a weight ratio of 1:2:1 to produce a first resin.

(39) Similarly to Example 3, the first resin was injected into liquid nitrogen using Freezer Mill 6750 (SPEX CertiPrep) equipment and pulverized, and then the melt viscosity was measured using Rheo-Tester 2000 (GttFert) equipment. As a result, the product had a melt viscosity of 3,150 poise at a temperature of 255 C. and a shear rate of 500 s.sup.1.

(40) Then, the polyamide-based copolymer resin having a relative viscosity (96% sulfuric acid solution) of 3.6, the copolymer having a weight average molecular weight of 80,000, and the copolymer having a weight average molecular weight of 110,000 were mixed in a weight ratio of 2:1:1 to produce a second resin.

(41) The melt viscosity was measured by using the same equipment and measuring method as the first resin. As a result, the second resin had a melt viscosity of 4,230 poise at a temperature of 255 C.

(42) After drying the first resin and the second resin, respectively, a base film was manufactured by using two extruders and a feed block of a three-layer structure. In the first extruder, the first resin which is a raw material constituting the first resin layer (B layer) was injected and then extruded at 255 C. In the second extruder, the second resin which is a raw material constituting the second resin layer (A layer) was injected and then extruded at 255 C.

(43) As schematically shown in FIG. 2, a feed block having a three-layer structure was provided on the top of the extrusion die to form a multilayer structure. In the feed block, a flow of the molten resin of the multilayer film having a three-layer structure in which the first resin layer (B layer) forms a core layer and the second resin layer (A layer) forms a skin layer [second resin layer (A layer)/first resin layer (B layer)/second resin layer (A layer)] was produced.

(44) The flow of the molten resin of the multilayer film formed with the above-described structure and composition was extruded through a T-type die (die gap-1.2 mm), and then the molten resin was cooled and solidified into a film with a uniform thickness using an air knife on the surface of a cooling roll that was controlled to 15 C. to obtain an unstretched base film of a three-layer structure having a thickness of 100 m at a speed of 15 m/min.

(45) At this time, the flow rate of the first resin was set to 113.4 kg/h and the total flow rate of the second resin was set to 264.6 kg/h, so that one second resin layer (A layer) accounted for 35% of the entire base film and the first resin layer (B layer) accounted for 30% of the thickness of the entire base film.

(2) Coating of Adhesive

(46) Resorcinol and formaldehyde were mixed in a mole ratio of 1:2, and then subjected to a condensation reaction to obtain a condensate of resorcinol and formaldehyde.

(47) 15 wt % of the condensate of resorcinol and formaldehyde and 85 wt % of styrene/butadiene-1,3/vinylpyridine latex were mixed to obtain a resorcinol-formalin-latex (RFL)-based adhesive with a concentration of 25%.

(48) The resorcinol-formalin-latex (RFL)-based adhesive was then coated on two sides of the unstretched base film of a three-layer structure using a gravure coater, and dried and reacted at 150 C. for 1 min to form an adhesive layer having a thickness of 2 m on the two sides.

Example 5

(1) Manufacturing of a Base Film

(49) A copolymer having a weight average molecular weight of 65,000 containing polyether-based segments whose main chain is a polytetramethylene oxide and polyamide-based segments derived from -caprolactam (the weight ratio of polyether-based segments:polyamide-based segments is 1:3) was prepared as a first resin.

(50) Similarly to Example 3, the first resin was injected into liquid nitrogen using Freezer Mill 6750 (SPEX CertiPrep) equipment and pulverized, and then the melt viscosity was measured using Rheo-Tester 2000 (GttFert) equipment. As a result, the product had a melt viscosity of 2,658 poise at a temperature of 255 C. and a shear rate of 500 s.sup.1.

(51) The polyamide-based resin [relative viscosity (96% sulfuric acid solution) of 3.8] synthesized by using 95 wt % of -caprolactam and 5 wt % of -valerolactam, and a copolymer resin having a weight average molecular weight of 65,000, were mixed in a weight ratio of 3:7 to produce a second resin.

(52) The melt viscosity was measured by using the same equipment and measuring method as the first resin. As a result, the second resin had a melt viscosity of 3,494 poise at a temperature of 255 C.

(53) The polyamide-based resin [relative viscosity (96% sulfuric acid solution) of 3.8] and the copolymer having a weight average molecular weight of 65,000 were then mixed in a weight ratio of 6:4 to produce another second resin.

(54) The melt viscosity was measured by using the same equipment and measuring method as the first resin. As a result, the other second resin had a melt viscosity of 4,331 poise at a temperature of 255 C.

(55) A base film was manufactured by using the first resin, the second resin, and another second resin, by means of two continuously connected two-layer separating devices (2 channel interfacial surface generators).

(56) Specifically, in the first extruder, the first resin in which the polyamide-based resin and the copolymer having a weight average molecular weight of 65,000 were mixed in a weight ratio of 3:7 was dried, and then injected and extruded at 255 C. In the second extruder, the first resin in which the copolymer having a weight average molecular weight of 65,000 was used alone was dried, then injected and extruded at 255 C. In the third extruder, the other second resin in which the polyamide-based resin and the copolymer having a weight average molecular weight of 65,000 were mixed in a weight ratio of 6:4 was dried, and then injected and extruded at 255 C.

(57) After the extrusion, in order to form a multilayer structure, in the feed block of a three-layer structure installed on the top of the two-layer separating device, a core layer (B-layer) was formed from the product extruded from the second extruder, and a skin layer (A layer and C layer) was formed from the product extruded from the first extruder and the third extruder, to form a flow of the molten resin having a three-layer structure [A layer/B layer/C layer].

(58) In the three-layer structure of A layer/B layer/C layer formed from the feed block, the flow rate of the first resin was set to 201.6 kg/h, the flow rate of the second resin was set to 151.2 kg/h and the flow rate of the other second resin was set to 151.2 kg/h, so that the thickness of the A layer accounted for 30% of the entire thickness of a three-layer structure, the thickness of the B layer accounted for 40% of the entire thickness of a three-layer structure, and the thickness of the C layer accounted for 30% of the entire thickness of the three-layer structure.

(59) Continuously, in order to multilayer the flow of the molten resin having a three-layer structure with a thinner thickness, the layers were separated by using a two-layer separating device (2-channel interfacial surface generator) connected in series to the feed block, and then laminated to form a multilayer.

(60) That is, the three-layer structure of A layer/B layer/C layer formed in the feed block was passed through the first two-layer separating device (2-channel interfacial surface generator), and then the three-layer structure was separated and laminated to form a multilayer of a six-layer structure (A/B/C/A/B/C). Continuously, the six-layer structure was passed through the second two-layer separating device (2-channel interfacial surface generator), and then the six-layer structure was separated and laminated in the same manner to form a 12-layer structure (A/B/C/A/B/C/A/B/C/A/B/C).

(61) The flow of the molten resin of the multilayer film formed with the above-described structure and composition was extruded through a T-type die (die gap-1.5 mm), and then the molten resin was cooled and solidified into a film with a uniform thickness using an air knife on the surface of a cooling roll that was controlled to 20 C. to obtain an unstretched base film of a multilayer structure having a thickness of 100 m at a speed of 20 m/min.

(2) Coating of Adhesive

(62) Resorcinol and formaldehyde were mixed in a mole ratio of 1:2 and then subjected to a condensation reaction to obtain a condensate of resorcinol and formaldehyde.

(63) 15 wt % of the condensate of resorcinol and formaldehyde and 85 wt % of styrene/butadiene-1,3/vinylpyridine latex were mixed to obtain a resorcinol-formalin-latex (RFL)-based adhesive with a concentration of 25%.

(64) Then, the resorcinol-formalin-latex (RFL)-based adhesive was coated on two sides of the unstretched base film of a three-layer structure using a gravure coater, and dried and reacted at 150 C. for 1 min to form an adhesive layer having a thickness of 5 m on the two sides.

Experimental Example

Experimental Example 1

Measurement of Heat-Resistant Toughness and Heat-Resistant Toughness Retention

(65) (1) Measurement of Heat-Resistant Toughness

(66) The heat-resistant toughness of the base film obtained in Examples 1 and 2 was measured as follows.

(67) The base film sample was left for 24 h at 23 C. and 50 RH % conditions and then left in a hot air oven at 170 C. for 1 h. Immediately thereafter, the sample was continuously left in a hot air oven at 100 C. for 1 h, and the sample was set to a length of 30 mm, a width of 30 mm, and a tensile speed of 300 mm/min under a 23 C. and 50 RH % atmosphere. The strength at break and the elongation at break in a machine direction (MD) and transverse direction (TD) of the heat-treated base film were measured ten times using a universal tensile testing machine (Instron) to obtain the average of eight values excluding the maximum value and the minimum value.

(68) In order to minimize deviation caused by the external environment during the heat treatment, the sample for the tensile test was cut to a size required for the measurement before the heat treatment, and subjected to heat treatment to minimize the change in the physical properties. The measurement was completed within 15 min of heat treatment.

(69) Using the values of the strength at break and the elongation at break of the base film after the heat treatment, the toughness in a machine direction (MD) and transverse direction (TD) of the base film was measured in accordance with the following Equation 1.
Heat-resistant toughness of base film (MPa)=strength at break (MPa)SORT [elongation at break (%)]<Equation 1>

(70) (wherein SQART means a square root)

(71) (2) Measurement of Heat-Resistant Toughness Retention

(72) The heat-resistant toughness retention of the base film obtained in Examples 3 to 5 was measured as follows.

(73) The base film sample was left for 24 h at 23 C. and 50 RH % conditions and then left in a hot air oven at 170 C. for 1 h. Immediately thereafter, the sample was continuously left in a hot air oven at 100 C. for 1 h, and the sample was set to a length of 30 mm, a width of 30 mm, and a tensile speed of 300 mm/min at 23 C. under a 50 RH % atmosphere. The strength at break and the elongation at break in a machine direction (MD) and a transverse direction (TD) of the heat-treated base film were respectively measured ten times using a universal tensile testing machine (Instron) to obtain the average of eight values excluding the maximum value and the minimum value.

(74) In addition, the base film sample was left for 24 h at 23 C. and 50 RH % conditions, and then the strength at break and the elongation at break in a machine direction (MD) and transverse direction (TD) of the heat-treated base film were calculated in the same manner as described above without the heat treatment.

(75) In order to minimize the deviation caused by the external environment during the heat treatment, the sample for the tensile test was cut to a size required for the measurement before the heat treatment, and subjected to heat treatment to minimize the change in the physical properties. The measurement was completed within 15 min of the heat treatment.

(76) Using the values of the strength at break and the elongation at break of the base film after the heat treatment, the heat-resistant toughness retention in a machine direction (MD) and a transverse direction (TD) of the base film was measured in accordance with the following Equation 2.
Heat-resistant toughness retention (%)=Toughness of base film after heat treatment (MPa)/Toughness of base film before heat treatment (MPa)100<Equation 2>

Experimental Example 2

Oxygen Permeability Test

(77) The oxygen permeability of the polymer film for a tire inner liner obtained in the examples was measured at 25 C. under a 60 RH % atmosphere using a Gas Transmission Rate Tester (Model BR-1/BT-2, Toyoseiki Seisaku-Sho) in accordance with the test method of ASTM D 1434.

Experimental Example 3

Measurement of Molding Easiness

(78) Tires were manufactured with a size of 205R/65R16 in groups of 100 using the polymer film for a tire inner liner of the examples. During the tire manufacturing process, the manufacturing easiness and appearance were evaluated after manufacturing a green tire, and then the final appearance of the tire was observed after vulcanization.

(79) In this case, when there was no distortion in a green tire or a tire after vulcanization and a standard deviation of diameter was within 5%, it was evaluated as good. Also, when distortion was generated in a green tire or a tire after vulcanization and thus the tire was not properly manufactured or the inner liner inside the tire was melted or torn and broken or when a standard deviation of the diameter was greater than 5%, it was evaluated as bad. In the 100 tires manufactured by applying the polymer film for an inner liner according the embodiment of the invention, the number of tires having a good appearance was evaluated to determine the molding easiness. The molding easiness was calculated in accordance with the following Equation 3.
Molding easiness (%)=Number of tires evaluated as good/100 (number of manufactured tires)100(%)<Equation 3>

Experimental Example 4

Measurement of Durability

(80) The durability of the tires manufactured in Experimental Example 3 was evaluated while increasing a load using a measurement method of FMVSS139 tire durability.

(81) The durability measurement was conducted by two methods of an endurance test of increasing a load by steps, and a high speed test of increasing a speed, to verify the presence or absence of cracks inside of the tire. When there were no cracks, it was indicated as good, and when cracks occurred, it was indicated as bad.

(82) The final appearance of the tire was evaluated by the method of Experimental Example 3. The tires having a good appearance were selected in groups of 20, and the endurance test and the high speed test were conducted for groups of 10, respectively, to confirm the presence or absence of cracks. After measuring the durability for the 10 tires, the durability of the tires was determined based on the number of good tires without the occurrence of cracks, according to the endurance test and the high speed test as shown in the following Equation 4.
Durability of tires (%)=Number of good tires/10 (number of evaluated tires)100(%)<Equation 4>

Experimental Example 5

Measurement of Internal Pressure Retention

(83) The internal pressure retention for 90 d as shown in the following Equation 5 was measured for the tire manufactured in Experimental Example 3 at a temperature of 21 C. under a pressure of 101.3 kPa in accordance with the test method ASTM F1112-06.
Internal Pressure Retention (%)={1(Tire inflation pressure upon initial testingTire inflation pressure after having left for 90 d)/(Tire inflation pressure upon initial testing)}100<Equation 5>

(84) The results of the Experimental Examples 1 to 5 are shown in Table 1 below.

(85) TABLE-US-00001 TABLE 1 Example 1 Example 2 Oxygen permeability [cc/(m.sup.2 .Math. 24 h .Math. atm)] 58 45 Base film heat- Machine direction 1,652 1,587 resistant toughness (MD) (MPa) Transverse direction 1,399 1,250 (TD) Molding easiness (%) 100 99 Durability of tire (%) Endurance test 100 100 High speed test 100 100 Internal pressure retention (%) 97.1 97.8

(86) As shown in Table 1, it was confirmed that the polymer film for an inner liner obtained in Examples 1 and 2 could exhibit oxygen permeability of 60 cc/(m.sup.2.Math.24 h.Math.atm) or less even at a thickness of about 103 m to 105 m and thus achieve an excellent gas barrier property even with tires having a thin thickness, secure high durability together with excellent moldability when applied to tires, and have heat-resistant toughness of 1250 MPa or more in both the machine direction and the transverse direction.

(87) TABLE-US-00002 TABLE 2 Example 3 Example 4 Example 5 Oxygen permeability 62 68 73 [cc/(m.sup.2 .Math. 24 h .Math. atm)] Base film heat- Machine 91 89 83 resistant toughness direction (MD) retention (%) Transverse 86 83 75 direction (TD) Molding easiness (%) 100 99 100 Durability Endurance test 100 100 100 of tire (%) High speed test 100 100 100 Internal pressure retention (%) 98.3 95.4 93.7

(88) As shown in Table 2, it was confirmed that the polymer film for an inner liner obtained in Examples 3 to 5 could exhibit oxygen permeability of 80 cc/(m.sup.2.Math.24 hr.Math.atm) or less even at a thickness of about 104 m to 110 m and thus achieve an excellent gas barrier property even with tires having a thin thickness, secure high durability together with excellent moldability when applied to tires, and have heat-resistant toughness retention of 70% or more in both the machine direction and the transverse direction.