JP4715362B2 - Inner liner for tire and pneumatic tire using the same - Google Patents

Description

  The present invention relates to an inner liner for a tire and a pneumatic tire using the same, and more particularly to an inner liner for a tire having a balanced air permeability and durability and a pneumatic tire using the same.

  A technique has been developed in which a gas permeation prevention layer (or inner liner) made of a thermoplastic resin or a thermoplastic resin elastomer composition is provided inside a pneumatic tire (see, for example, Patent Document 1). However, a material such as a resin having a high elastic modulus has a problem that its durability is not sufficient for use in a dynamic environment such as a tire even if it has low air permeability.

Japanese Patent Laid-Open No. 10-25375

  Accordingly, an object of the present invention is to develop an inner liner that is excellent in air permeation resistance and durability and can be reduced in weight while eliminating the problems of the conventional tire inner liner.

According to the present invention, (i) the dynamic elastic modulus E ′ of −20 ° C. to 60 ° C. is 1000 MPa or less, (ii) the 50% modulus of the molded product of −20 ° C. to 60 ° C. is 30 MPa or less, (iii ) The ratio of the tire width direction / circumferential direction of the breaking strength TB and the breaking elongation EB of the molded product at −20 ° C. to 60 ° C. is 0.75 to 1.3, respectively, and (iv) the air permeability coefficient at 30 ° C. Provided are a tire inner liner that is 50 × 10 ⁻¹² cm ³ · cm / cm ² · sec · cmHg or less, and a pneumatic tire using the same.

  According to the present invention, a material having a high modulus and a low gas permeability can be obtained by optimizing the thickness of the molded article of the inner liner for a pneumatic tire, the breaking strength / breaking elongation ratio of the line / inverse line. It can be used as a material for a tire inner liner, and the weight reduction of the tire can be achieved while improving the internal pressure holding performance of the tire.

  As is well known, the inner liner of a pneumatic tire is required to have a function of maintaining the air pressure inside the tire. For this purpose, the resin is generally used as a material having low air permeability. However, since a pneumatic tire is used in a dynamic environment where an automobile runs, a material such as a resin having a high elastic modulus is used as an inner liner. When used for, there is a problem in terms of durability. Also, the largest strain on the inner liner is applied to the shoulder portion of the tire, but the main strain direction of this portion is about 45 ° from the width direction and the circumferential direction of the tire, so the material is oriented in one direction. If the air permeability is low enough even with a material with high elastic modulus, the transmittance and rigidity can be reduced by reducing the thickness of the molded product (film). Can be balanced. The present inventors have succeeded in achieving an optimal balance between these factors from this viewpoint. In addition, since the use environment of a tire changes with climates, it is necessary for an inner liner to obtain | require the balance of the said characteristic over the range of -20 degreeC-60 degreeC.

  In the present invention, the dynamic elastic modulus E ′ is obtained by cutting a part of the inner liner molded product (film) into a strip and using an extension type viscoelasticity measuring device in a temperature range of −20 ° C. to 60 ° C. The value measured under the conditions of 0.1% and a frequency of 20 Hz is used. The tensile test is performed by cutting out JIS No. 3 dumbbells from the tire circumferential direction and the width direction of the inner liner molded product (film). The value measured according to JIS K6251 in the temperature range.

  The material used for the inner liner according to the present invention is a material that satisfies the above-mentioned requirements (i) to (iv), and is not limited to these as described in, for example, JP-A-8-259741. However, it can be obtained by molding so as to satisfy the requirements (i) to (iv) using, for example, a thermoplastic resin or a thermoplastic elastomer composition. Specifically, polyamide resins (for example, nylon 6, nylon 66, nylon 11, nylon 12, nylon 610, nylon 612, nylon 6/66 copolymer, etc.), polyester resins (polybutylene terephthalate, polyethylene terephthalate, etc.), Thermoplastic resins such as polynitrile resins as well as these thermoplastic resins as a continuous phase (matrix), and an elastomer component (for example, diene rubber, olefin rubber, thermoplastic elastomer, etc.), if necessary, at least partially A thermoplastic elastomer composition that is dynamically vulcanized to form a dispersed phase can be used.

  The tire inner liner according to the present invention needs to satisfy the requirements (i) to (iv). First, the dynamic elastic modulus E 'must be 1000 MPa or less, preferably 600 MPa or less in the temperature range of -20 ° C to 60 ° C. If E 'is too high, the durability performance during running of the tire is poor, which is not preferable.

  In the tire inner liner of the present invention, the 50% modulus (M50) of the molded product (film) must be 30 MPa or less, preferably 2 to 20 MPa in the range of -20 ° C to 60 ° C. Since the durability performance at the time is inferior, it is not preferable.

  In the tire inner liner of the present invention, the ratio of the tire width direction / the tire circumferential direction of each of TB and EB is 0.00 when the breaking strength TB and breaking elongation EB of the molded product (film) are in the temperature range of −20 ° C. to 60 ° C. It should be in the range of 75 to 1.3, preferably 0.85 to 1.15. If this ratio is small, cracks in the circumferential direction are likely to occur during tire travel. Since cracks in the direction tend to occur, it is not preferable.

The tire inner liner of the present invention has an air permeability coefficient of 50 × 10 ⁻¹² cm ³ · cm ² · sec · cm · Hg or less, preferably 25 × 10 ⁻¹² cm ³ · cm / cm ² · sec, because of its function. -It must be below cmHg, and this value mainly depends on the material used.

  In order to satisfy the requirements (i) to (iv), particularly (i) to (iii), a given material can be obtained by molding under the following conditions. That is, in blow molding or inflation molding, the physical property ratio in the vertical and horizontal directions can be adjusted by adjusting the ratio of the discharge amount / take-off speed and the blow ratio. For example, to obtain a homogeneous film with a diameter of 400 mm using a thermoplastic elastomer, a film having a small difference in physical properties in length and width can be obtained by setting the discharge rate / take-off speed to about 167 g / m and the blow ratio to about 4.0. be able to. The discharge amount can be adjusted by the number of revolutions of the extruder, and the blow ratio can be adjusted by changing the size of the die lip.

  The material used for the tire inner liner according to the present invention includes, in addition to the above-described essential components, other reinforcing agents (fillers) such as carbon black and silica, vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, Various additives that are generally blended for tires such as oils, anti-aging agents, and plasticizers, and other general rubbers can be blended, and these additives are kneaded by a general method to form a composition. Can be used for vulcanization or crosslinking. The blending amounts of these additives may be conventional conventional blending amounts as long as the object of the present invention is not adversely affected.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, it cannot be overemphasized that the scope of the present invention is not limited to these Examples.

Examples 1-2 and Comparative Examples 1-4
The dynamic elastic modulus E ′, breaking strength (TB) and elongation at break (EB), 50% modulus (M50), air permeability and durability of the film of the material shown in Table I were measured by the following methods. The results are shown in Table I.

Physical property evaluation test method Dynamic elastic modulus (20 ° C.): A part of the inner liner molded product is cut into a strip, and after using a stretch type viscoelasticity measuring device, a static strain of 10% is applied, a dynamic strain is 0.1%, and a frequency is 20 Hz. Measured with
Tensile test (25 ° C.): In accordance with JIS K6251, the tire width direction and tire circumferential direction TB (breaking strength) and EB (breaking elongation) of the inner liner molded product were measured, and the ratio was determined.
50% modulus (20 ° C.): A modulus at 50% elongation when a tensile test was performed according to JIS K6251 was determined.

  Air permeability (30 ° C.): Measured according to JIS K7126.

  Durability: 195 / 65R15 size tires were made using the materials described in each example, installed in a vehicle with an air pressure of 200 KPa and a displacement of 2000 cc class, run in a cold region for 30000 km in winter, and then the tires after running The inner liner was observed, and those with no cracks were judged good and those with cracks were judged as bad.

In Example 1, a thermoplastic elastomer composed of a blend of isobutylene-paramethylstyrene bromide (Exxpro 89-4 manufactured by Exxon Mobile Chemical) and nylon 6 (UBE nylon 1030B manufactured by Ube Industries) (blend weight ratio = 55/45) was subjected to inflation. For molding, biaxial stretching is performed under the conditions of 240 ° C., discharge rate / take-off speed of 167 g / m, blow ratio of 4.0, and cutting is performed so that the molding direction is the tire width direction and the circumferential direction is the tire circumferential direction. It was. In Example 2, thermoplastic elastomer pellets made of a blend of brominated isobutylene-paramethylstyrene and nylon (blend weight ratio = 55/45) used in Example 1 were placed at 230 ° C. for 5 minutes, with a surface pressure of 80 kg / A film formed by press molding under the condition of cm ² was used.

  In Comparative Example 1, a thermoplastic elastomer composed of a brominated product of isobutylene-paramethylstyrene and nylon 6 (blend weight ratio = 55/45) used in Example 1 was applied to an extruder equipped with a T-shaped die. The film molded at 230 ° C. was cut and used so that the molding direction was the tire circumferential direction. In Comparative Example 2, a thermoplastic elastomer composed of a brominated product of isobutylene-paramethylstyrene and nylon 6 used in Example 1 (blend weight ratio = 55/45) was blown at 240 ° C. at a discharge amount / take-off. The film was stretched biaxially under conditions of a speed of 167 g / m and a blow ratio of 1.1, and was cut and used so that the molding direction was the tire width direction and the circumferential direction was the tire circumferential direction. Comparative Example 3 uses EVOH (Kuraray Eval L171B) with an ethylene content of 27%, which is cut at 220 ° C. by an extruder equipped with a T-shaped die so that the molding direction is the tire circumferential direction. It was. In Comparative Example 4, nylon 6 (Toray Amilan CM1061) was biaxially stretched by inflation molding under the conditions of 250 ° C., discharge rate / take-off speed of 167 g / m, and blow ratio of 4.0. It was cut and used so that the direction was the tire circumferential direction.

  As is apparent from the results in Table I, Example 1 is a biaxially stretched film of thermoplastic elastomer with a small physical property difference in the width direction / circumferential direction and a small modulus, so that it shows good durability in a tire durability test. . Example 2 is a press-molded film of the same thermoplastic elastomer, and this also has good durability because the difference in physical properties in the width direction / circumferential direction is small.

  On the other hand, Comparative Example 1 is a film formed by uniaxial stretching of the same thermoplastic elastomer, but cracks occurred in the tire durability test because the cracks easily developed in the stretching direction. In Comparative Example 2, the same thermoplastic elastomer was produced by biaxial stretching, but because the blow ratio was small, it was stretched greatly in the molding direction, and cracks occurred in the tire durability test. Comparative Example 3 is a film prepared by uniaxially stretching low permeability EVOH, but because of its very high modulus, many large cracks occurred in the tire durability test. Comparative Example 4 is a film made of low-permeability nylon 6 that is biaxially stretched so that there is no difference in physical properties in the width direction / circumferential direction. This also has a very high modulus, so large cracks occur in the tire durability test. did.

  As described above, according to the present invention, a tire inner liner excellent in air permeation resistance and durability can be obtained, which is very useful for use in various pneumatic tires for automobiles.

Claims (3)

(I) Dynamic elastic modulus E ′ at −20 ° C. to 60 ° C. is 1000 MPa or less, (ii) 50% modulus of the molded product at −20 ° C. to 60 ° C. is 30 MPa or less, (iii) −20 ° C. to 60 ° C. The ratio of the rupture strength TB and the rupture elongation EB of the molded product in the tire width direction / circumferential direction is 0.75 to 1.3, respectively, and (iv) the air permeability coefficient at 30 ° C. is 50 × 10 ⁻¹² cm ^3. Tire inner liner that is cm / cm ² · sec · cmHg or less.   The tire inner liner according to claim 1, wherein a material of the tire inner liner is a thermoplastic elastomer composed of a thermoplastic resin and an elastomer component.   A pneumatic tire comprising the tire inner liner according to claim 1.