Inflation film and manufacturing method thereof

Abstract

The present invention relates to an inflation film and a method for manufacturing the inflation film, wherein the inflation film includes a base film, including: a polyamide-based resin; a copolymer containing polyamide-based segments and poly-ether-based segments; and an olefin-based polymer compound, and has a small variation in physical properties between a machine direction (MD) and a transverse direction (TD) of the film.

Claims

1. A method for manufacturing the inflation film for a tire inner liner, comprising a step of inflation a molten resin composition including: a polyamide-based resin; a copolymer containing a polyamide-based segment and a poly-ether-based segment; and an olefin-based polymer compound at a blow-up ratio (BUR) of 1.5 to 3, wherein the molten resin composition is inflated at a draw-down ratio (DDR) of 1 to 20, wherein the olefin-based polymer includes an olefin-based polymer or copolymer grafted with a dicarboxylic acid or an acid anhydride thereof, wherein the polyamide-based resin and copolymer containing polyamide-based segments and poly-ether-based segments are included in a base film formed from the molten resin composition at a weight ratio of 9:1 to 1:9, and the content of the polyether-based segments in the base film is 2% by weight to 40% by weight, and a ratio of a machine direction modulus of the base film to transverse direction modulus of the base film at 25% elongation after heat-treating the base film at 170° C. for 30 minutes, is from 0.8 to 1.2.

2. The method for manufacturing the inflation film for a tire inner liner according to claim 1, wherein, in the step of inflating a molten resin composition at a blow-up ratio (BUR) of 1.5 to 3, a bubble diameter is 450 to 2000 mm, and a die diameter is 300 to 800 mm.

3. The method for manufacturing the inflation film for a tire inner liner according to claim 1, wherein, in the step of inflating a molten resin composition at a draw-down ratio (DDR) of 1 to 20, a die gap thickness is 0.5 to 3.5 mm, and the film thickness is 20 to 300 μm.

4. The method for manufacturing the inflation film for a tire inner liner according to claim 1, wherein the temperature inside a bubble of the molten resin composition formed in the step of inflating the molten resin composition is 10° C. to 60° C.

5. The method for manufacturing the inflation film for a tire inner liner according to claim 1, further comprising a step of melting and extruding the polyamide-based resin, the copolymer containing polyamide-based segments and poly-ether-based segments, and the olefin-based polymer compound at 200° C. to 300° C. to form the molten resin composition.

6. The method for manufacturing the inflation film for a tire inner liner according to claim 1, further comprising: a step of folding and cooling the molten resin composition by a nip roll; and a step of winding the cooled melt resin composition.

7. The method for manufacturing the inflation film for a tire inner liner according to claim 1, further comprising a step of forming an adhesive layer on at least one side of the base film and that includes a resorcinol-formalin-latex (RFL)-based adhesive.

Description

BRIEF DESCRIPTION OF THE DRAWING

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

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) 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: Preparation of Polymer Film

Example 1

(3) (1) Preparation of Base Film

(4) A polyamide-based resin (nylon 6) with a relative viscosity (96% sulfuric acid solution) of 3.2 prepared from ϵ-caprolactam, a copolymer resin with a weight average molecular weight of about 92,000 (synthesized using 35 wt % of polyether-based segments having a polytetramethylene oxide as a main chain and 65 wt % of polyamide-based segments derived from ϵ-caprolactam), and an ethylene-propylene copolymer grafted with maleic anhydride (0.9 wt %) (density: 0.890 g/cm.sup.3) were mixed at a weight ratio of 20:62:18, and 1 part by weight of an oxazoline-based compound and 0.3 parts by weight of a heat resistance agent [a mixture of copper iodide and potassium iodide—the content of copper (Cu) in the mixture: 7 wt %] were added relative to 100 parts by weight of the mixture to prepare a mixture for manufacturing a base film.

(5) Then, the mixture was extruded at a temperature of 240° C. through a circular die (die gap—2.0 mm, die diameter 500 mm) while maintaining uniform flow of molten resin, and the temperature inside the bubble was adjusted to 17° C. by using an air ring and inner bubble cooler (IBC). By adjusting the air volume and the discharge volume of the blower, the blow-up ratio (BUR) of the bubble was set to 2.1 and the draw-down ratio (DDR) was set to 11.9, thereby forming a bubble with a diameter of 1050 mm.

(6) Successively, the bubble was made in a flat form by using a nip-roll through a flat support, and both sides were cut with a knife-edge to make two flat films. Then, both sides of each film were cut and wound on a winder to obtain a flat base film having a thickness of 80 μm.

(7) (2) Coating of Adhesive

(8) Resorcinol and formaldehyde were mixed at a molar ratio of 1:2, and then subjected to a condensation reaction to obtain a condensate of resorcinol and formaldehyde. 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%.

(9) Then, the resorcinol-formalin-latex (RFL)-based adhesive was coated onto both sides of the base film using a gravure coater, dried at 150° C. for 1 minute, and reacted to form adhesive layers each having a thickness of 3 μm on both sides.

Example 2

(10) (1) Preparation of Base Film

(11) A polyamide-based copolymer resin with a relative viscosity (96% sulfuric acid solution) of 3.8 [synthesized using ϵ-caprolactam and adipic acid at a weight ratio of 94:6], a copolymer resin with a weight average molecular weight of about 123,000 (synthesized using 20 wt % of polyether-based segments having an amine terminal group-containing polytetramethylene oxide as a main chain and 80 wt % of polyamide-based segments derived from ϵ-caprolactam), and an ethylene-propylene copolymer grafted with maleic anhydride (0.7 wt %) (density: 0.920 g/cm.sup.3) were mixed at a weight ratio of 30:65:5, and 0.4 parts by weight of an oxazoline-based compound and 0.2 parts by weight of a heat resistance agent [a mixture of copper iodide and potassium iodide—the content of copper (Cu) in the mixture: 7 wt %] were added relative to 100 parts by weight of the mixture to prepare a mixture for manufacturing a base film.

(12) Then, the mixture was extruded at a temperature of 230° C. through a circular die (die gap—3.0 mm, die diameter 400 mm) while maintaining uniform flow of molten resin, and the temperature inside the bubble was adjusted to 25° C. by using an air ring and inner bubble cooler (IBC). By adjusting the air volume and the discharge volume of the blower, the blow-up ratio (BUR) of the bubble was set to 2.88 and the draw-down ratio (DDR) was set to 8.0, thereby forming a bubble with a diameter of 1150 mm.

(13) Successively, the bubble was made in a flat form by using a nip-roll through a flat support, and both sides were cut with a knife-edge to make two flat films. Then, both sides of each film were cut and wound on a winder to obtain a flat base film having a thickness of 130 μm.

(14) (2) Coating of Adhesive

(15) An adhesive layer was formed in the same manner as in Example 1, except that the adhesive layer with a thickness of 2 μm was formed on both sides of the base film.

Example 3

(16) (1) Preparation of Base Film

(17) A polyamide-based copolymer resin with a relative viscosity (96% sulfuric acid solution) of 3.8 [synthesized using ϵ-caprolactam and hexamethylene diamine at a weight ratio of 94:6], a copolymer resin with a weight average molecular weight of about 137,000 (synthesized using 16 wt % of polyether-based segments having an amine terminal group-containing polytetramethylene oxide as a main chain and 84 wt % of polyamide-based segments derived from ϵ-caprolactam), and an ethylene-propylene copolymer grafted with maleic anhydride (0.9 wt %) (density: 0.850 g/cm.sup.3) were mixed at a weight ratio of 10:80:10, and 0.4 parts by weight of an oxazoline-based compound and 0.4 parts by weight of a heat resistance agent [a mixture of copper iodide and potassium iodide—the content of copper (Cu) in the mixture: 7 wt %] were added relative to 100 parts by weight of the mixture to prepare a mixture for manufacturing a base film.

(18) Then, the mixture was extruded at a temperature of 230° C. through a circular die (die gap—2.5 mm, die diameter 700 mm) while maintaining uniform flow of molten resin, and the temperature inside the bubble was adjusted to 35° C. by using an air ring and inner bubble cooler (IBC). By adjusting the air volume and the discharge volume of the blower, the blow-up ratio (BUR) of the bubble was set to 1.64 and the draw-down ratio (DDR) was set to 15.2, thereby forming a bubble with a diameter of 1150 mm. Successively, the bubble was made in a flat form by using a nip-roll through a flat support, and both sides were cut with a knife-edge to make two flat films. Then, both sides of each film were cut and wound on a winder to obtain a flat base film having a thickness of 100 μm.

(19) (2) Coating of Adhesive

(20) An adhesive layer was formed in the same manner as in Example 1, except that the adhesive layer with a thickness of 5 μm was formed on both sides of the base film.

Example 4

(21) (1) Preparation of Base Film

(22) A polyamide-based copolymer resin with a relative viscosity (96 sulfuric acid solution) of 3.6 [synthesized using ϵ-caprolactam and hexamethylene diamine at a weight ratio of 94:6], a copolymer resin with a weight average molecular weight of about 74,000 (synthesized using 42 wt % of polyether-based segments having an amine terminal group-containing polytetramethylene oxide as a main chain and 58 wt % of polyamide-based segments derived from ϵ-caprolactam), and an ethylene-propylene copolymer grafted with maleic anhydride (0.8 wt %) (density: 0.910 g/cm.sup.3) were mixed at a weight ratio of 70:20:10, and 0.5 parts by weight of an oxazoline-based compound and 0.7 parts by weight of a heat resistance agent [a mixture of copper iodide and potassium iodide—the content of copper (Cu) in the mixture: 7 wt %] were added relative to 100 parts by weight of the mixture to prepare a mixture for manufacturing a base film.

(23) Then, the mixture was extruded at a temperature of 255° C. through a circular die (die gap—0.8 mm, die diameter 800 mm) while maintaining uniform flow of molten resin, and the temperature inside the bubble was adjusted to 20° C. by using an air ring and inner bubble cooler (IBC). By adjusting the air volume and the discharge volume of the blower, the blow-up ratio (BUR) of the bubble was set to 1.53 and the draw-down ratio (DDR) was set to 17.5, thereby forming a bubble with a diameter of 1220 mm.

(24) Successively, the bubble was made in a flat form by using a nip-roll through a flat support, and both sides were cut with a knife-edge to make into two flat films. Then, both sides of each film were cut and wound on a winder to obtain a flat base film having a thickness of 30 μm.

(25) (2) Coating of Adhesive

(26) Resorcinol and formaldehyde were mixed at a molar ratio of 1:2.5, and then subjected to a condensation reaction to obtain a condensate of resorcinol and formaldehyde. 22 wt % of the condensate of resorcinol and formaldehyde and 78 wt % of styrene/butadiene-1,3/vinylpyridine latex were mixed to obtain a resorcinol-formalin-latex (RFL)-based adhesive with a concentration of 30%.

(27) Then, the resorcinol-formalin-latex (RFL)-based adhesive was coated onto both sides of the base film using a gravure coater, dried at 150° C. for 1.5 minutes, and reacted to form adhesive layers each having a thickness of 10 μm on both sides.

Example 5

(28) (1) Preparation of Base Film

(29) A polyamide-based resin (nylon 6) with a relative viscosity (96% sulfuric acid solution) of 3.8 prepared from ϵ-caprolactam, a copolymer resin with a weight average molecular weight of about 137,000 (synthesized using 16 wt % of polyether-based segments having an amine terminal group-containing polytetramethylene oxide as a main chain and 84 wt % of polyamide-based segments derived from ϵ-caprolactam), and an ethylene-propylene copolymer grafted with maleic anhydride (0.8 wt %) (density: 0.910 g/cm.sup.3) were mixed at a weight ratio of 8:70:22, and 0.2 parts by weight of an oxazoline-based compound and 1.0 part by weight of a heat resistance agent [a mixture of copper iodide and potassium iodide—the content of copper (Cu) in the mixture: 7 wt %] were added relative to 100 parts by weight of the mixture to prepare a mixture for manufacturing a base film.

(30) Then, the mixture was extruded at a temperature of 230° C. through a circular die (die gap—2.2 mm, die diameter 600 mm) while maintaining uniform flow of molten resin, and the temperature inside the bubble was adjusted to 45° C. by using an air ring and inner bubble cooler (IBC). By adjusting the air volume and the discharge volume of the blower, the blow-up ratio (BUR) of the bubble was set to 1.83 and the draw-down ratio (DDR) was set to 5.7, thereby forming a bubble with a diameter of 1100 mm.

(31) Successively, the bubble was made in a flat form by using a nip-roll through a flat support, and both sides were cut with a knife-edge to make two flat films. Then, both sides of each film were cut and wound on a winder to obtain a flat base film having a thickness of 210 μm.

(32) (2) Coating of Adhesive

(33) An adhesive layer was formed in the same manner as in Example 4, except that the adhesive layer with a thickness of 1 μm was formed on both sides of the base film.

Comparative Example: Preparation of Polymer Film

(34) (1) Preparation of Base Film

(35) A polyamide-based resin (nylon 6) with a relative viscosity (96% sulfuric acid solution) of 3.8 prepared from ϵ-caprolactam, and a copolymer resin with a weight average molecular weight of about 137,000 (synthesized using 16 wt % of polyether-based segments having an amine terminal group-containing polytetramethylene oxide as a main chain and 84 wt % of polyamide-based segments derived from ϵ-caprolactam) were mixed at a weight ratio of 90:10 to prepare a mixture for manufacturing a base film.

(36) Then, the mixture was extruded at a temperature of 255° C. through a T-type die (die gap—1.2 mm) while maintaining uniform flow of molten resin, and the molten resin was cooled and solidified in the shape of a film with uniform thickness using an air knife on the surface of a cooling roll that was controlled to 20° C. Then, a base film having a thickness of 100 μm was obtained at a speed of 10 m/min without passing through stretching and heating sections.

(37) (2) Coating of Adhesive

(38) A resorcinol-formalin-latex (RFL)-based adhesive was coated onto both sides of the base film using a gravure coater in the same manner as in Example 1, and dried and reacted at 150° C. for 1 minute to form adhesive layers each having a thickness of 3 μm on both sides.

EXPERIMENTAL EXAMPLE

Experimental Example 1: Oxygen Permeability Test

(39) For the base films obtained in the examples and comparative example, oxygen permeability was measured under the conditions of 25° C. and 60 RH % using a gas transmission rate tester (Model BR-1/BT-2, manufactured by Toyoseiki Seisaku-Sho Company) according to ASTM D 1434.

Experimental Example 2: Modulus Balance at 25% Elongation

(40) The base films obtained in the examples and comparative example were left for 24 hours under the conditions of 23° C. and 50% relative humidity, one side end of the base film layer was suspended in a hot air oven at 170° C. and then left (heat-treated) in a no-load and no-contact state for 30 minutes. Immediately thereafter, the value of the strength was measured ten times at 25% elongation in the machine direction (MD) and the transverse direction (TD) by setting a sample length to 30 mm, a sample width to 30 mm, and a tensile speed to 300 mm/min using a universal tensile test machine (Instron Inc.). Modulus values at 25% elongation at high temperature (170° C.) in the machine direction (MD) and the transverse direction (TD) were determined as an average value of eight values excluding the maximum value and the minimum value.

(41) With the ratio of the modulus values at 25% elongation and high temperature (170° C.) in the machine direction (MD) and the transverse direction (TD) measured by the above-mentioned method, modulus balance could be confirmed, and was calculated as shown in the following Equation 1.
Modulus Balance=Machine Direction (MD) Modulus/Transverse Direction (TD) Modulus  <Equation 1>

Experimental Example 3: Heat Resistant Impact Strength Ratio (MD/TD)

(42) Heat resistant impact strength of the base films obtained in the examples and comparative example were measured as follows.

(43) Heat resistant impact strength was measured using ISO 8256 Method A, and for the machine direction (MD) and the transverse direction (TD) of the base film, each of 10 specimens for evaluation were taken using a cutting device ISO 8256 Type 4.

(44) Here, the specimen was cut such that the shape of the specimen for evaluation (specimen length×shoulder width×parallel specimen length×specimen width) became 60 mm×10 mm×25 mm×3 mm according to ISO 8256 Type 4, and the specimen for evaluation cut according to the standard was left under the conditions of 23° C. and 50% relative humidity for 24 hours, and then heat-treated in a hot air oven at 170° C. for 1 hour, and immediately thereafter, heat resistant impact strengths in the machine direction (MD) and the transverse direction (TD) of the heat treated base film were measured 10 times under a temperature of 23° C. and relative humidity of 50% using a Pendulum Impact Tester, Zwick/Roell Company, Model HIT 5.5P according to ISO 8256 Method A, and the mean values of 8 values excluding the maximum and minimum were calculated.

(45) When measuring the heat resistant impact strength, in order to minimize a deviation due to the external environment, the specimens for evaluation were cut to a size required for measurement before heat treatment, and in order to minimize a change in physical properties, measurement was completed within 15 minutes after heat treatment.

(46) The heat resistant impact strengths for the machine direction (MD) and the transverse direction (TD) of the base film were calculated according to the following Equation 2.
Heat Resistant Impact Strength (kJ/m.sup.2)=Impact Energy (kJ)/[Film Thickness (m)×Specimen Width (0.003 m)]  <Equation 2>

(47) (Herein, the width of the specimen for evaluation was fixed to 3 mm)

(48) In addition, the ratio of heat resistant impact strengths was calculated according to the following Equation 3.
Ratio of Heat Resistant Impact Strengths=(Heat Resistant Impact Strength for Machine Direction)/(Heat Resistant Impact Strength for Transverse Direction)  <Equation 3>

Experimental Example 4: Determination of Moldability

(49) Using the base films of the examples and comparative example as inner liners, each of 100 tires were manufactured with a standard of 205R/65R16.

(50) During the tire manufacturing process, the manufacturability and appearance were evaluated after preparing a green tire, and the final appearance of a tire was examined after vulcanization.

(51) Here, when there was no crushing of the green tire or the vulcanized tire and the standard deviation of the diameter was within 5%, it was evaluated as ‘good’.

(52) Also, when the green tire or the vulcanized tire was crushed, and thus a tire was not properly manufactured, or the inner liner inside the tire was melted or torn and damaged, or when the standard deviation of the diameter was greater than 5%, it was evaluated as ‘poor’.

(53) For the 100 tires manufactured using the base films of the examples and comparative example as tire inner liners, the number of tires having good appearance was confirmed to evaluate moldability, wherein the moldability was calculated by the following Equation 4.
Moldability (%)=Number of Tires Evaluated as ‘Good’/100 (Number of Manufactured Tires)×100(%)  <Equation 4>

Experimental Example 5: Measurement of Tire Durability

(54) The durability of the tire manufactured in Experimental Example 4 was tested and evaluated while increasing a load, according to the FMVSS139 tire durability measuring method.

(55) The measurement of durability was conducted by two methods of an endurance test which increases load by step loading and a high speed test which increases speed, and it was confirmed whether or not a crack was generated inside a tire, and it was indicated as ‘good’ when there was no crack, and as ‘poor’ when a crack was generated.

(56) The final appearance of tires was evaluated by the method of Experimental Example 4, and 20 tires with ‘good’ appearance were selected, and the endurance test and the high speed test were progressed for each of 10 tires to confirm whether or not a crack was generated. Further, after measuring durability for 10 tires, the durability of tires according to the endurance test and the high speed test was calculated by the following Equation 5, using the number of ‘good’ tires without crack generation.
Durability of Tires (%)=Number of ‘Good’ Tires/10 (Number of Evaluated Tires)×100(%)  <Equation 5>

Experimental Example 6: Measurement of Internal Pressure Retention

(57) For the tires manufactured in Experimental Example 4, 90-day internal pressure retention was measured at a temperature of 21° C. under pressure of 101.3 kPa according to ASTM F1112-06, as shown in the following Equation 6.
Internal Pressure Retention (%)={1−(Internal Pressure of Tire at First Evaluation−Internal Pressure of Tire After Being Left for 90 Days)/(Internal Pressure of Tire at First Evaluation)}×100  <Equation 6>
The results of Experimental Examples 1 to 6 are shown in the following Table 1

(58) TABLE-US-00001 TABLE 1 Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example Oxygen permeability 156 118 183 74 106 18 [cm.sup.3/(m.sup.2 .Math. 24 h .Math. atm)] Modulus balance (MD/TD) 0.98 0.85 1.13 1.17 1.01 1.42 Impact strength balance 1.03 0.83 1.09 1.19 1.04 1.67 (MD/TD) Moldability (%) 100 100 100 98 100 31 Tire durability Endurance 100 100 100 90 100 0 (%) Test High Speed 100 100 100 100 100 50 Test Internal pressure retention 96.9 97.8 96.4 98.4 97.1 98.7 (%)

(59) As shown in Table 1, it was confirmed that the inflation films manufactured in the examples exhibit physical properties that are uniform and excellent in all directions, and have low modulus while having a relatively high tensile strength and impact strength, and specifically, the ratio of the machine direction modulus of the base film to the transverse direction modulus of the base film at 25% elongation, after heat-treating the base film at 170° C. for 30 minutes, is in the range of 0.85 to 1.17, so that the modulus along the direction was uniform and the stress applied to the film during the molding process and the vulcanization process of a tire can be uniformly dispersed.

(60) In addition, it was confirmed that, in the inflation films manufactured in the examples, the ratio of impact strength for the machine direction of the base film to impact strength for the transverse direction of the base film, after heat-treating the base film at 170° C. for 1 hour, is 0.83 to 1.19, so that the pneumatic tire provided with the inflation film easily disperses the stress applied from the outside during running of the automobile, thereby reducing the occurrence of cracks due to stress concentration.

(61) Finally, it was confirmed that in the inflation films manufactured in the examples exhibit oxygen permeability of 183 cm.sup.3/(m.sup.2.Math.24 h.Math.atm) or less even at a thickness of 30 μm to 210 μm, and thus, can realize an excellent gas barrier property even with a thin thickness, and can secure high durability when applied to a tire as well as excellent moldability.