JP2004176048A - Inner liner for use in pneumatic tire, and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide such an inner liner for use in a pneumatic tire, excellent in gas barrier properties and flexing resistance. <P>SOLUTION: The inner liner for use in the pneumatic tires comprises a modified ethylene-vinyl alcohol copolymer (C) which is obtained by reacting 100 pts.wt. of an ethylene-vinyl alcohol copolymer (A) having an ethylene content of 25-50mol% with 1-50 pts.wt. of an epoxy compound (B). The pneumatic tire using the above inner liner permits a large improvement in the internal pressure maintenance in a new tire and that after running without increase in the tire weight. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to an inner liner for a pneumatic tire having excellent gas barrier properties and bending resistance. The present invention also relates to a pneumatic tire using the inner liner, and relates to a technique for improving internal pressure retention at the time of a new product and after traveling without increasing the tire weight.

  Conventionally, butyl rubber, halogenated butyl rubber, or the like has been used as a main raw material of an inner liner as an air barrier layer to maintain the internal pressure of a tire. However, in the rubber composition containing these, the thickness of the inner liner was required to be about 1 mm because of its low air barrier property. Therefore, the weight of the inner liner in the tire is about 5%, which is an obstacle to reducing the weight of the tire and improving the fuel efficiency of the vehicle.

  On the other hand, it is known that an ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as EVOH) has excellent gas barrier properties. Since EVOH has an air permeability of 1/100 or less of the butyl-based inner liner rubber composition, even at a thickness of 50 μm or less, EVOH can significantly improve the internal pressure retention and reduce the weight of the tire. It is possible. Although there are many resins having lower air permeability than butyl rubber, when the air permeability is about one-tenth of that of the butyl-based inner liner, unless the thickness exceeds 100 μm, the effect of improving the internal pressure retention is small. When the thickness exceeds the above range, the effect of reducing the tire weight is small, and the inner liner is broken or cracked due to deformation at the time of bending of the tire, so that it is difficult to maintain the barrier property. On the other hand, since EVOH can be used at a thickness of 50 μm or less, breakage or cracking hardly occurs due to bending deformation during rolling of the tire. From this, it can be said that it is effective to use EVOH for the tire inner liner in order to improve the air permeability of the pneumatic tire. For example, as a pneumatic tire having a tire inner liner made of EVOH, a technique disclosed in JP-A-6-40207 (Patent Document 1) is disclosed.

  When ordinary EVOH is used as the inner liner, the effect of improving the internal pressure retention is great, but the elastic modulus is much higher than that of the rubber normally used for tires. There was something. For this reason, when the inner liner made of EVOH is used, although the internal pressure retention before use of the tire is greatly improved, the internal pressure retention of the used tire subjected to bending deformation during rolling of the tire is higher than before use. It could be lower. In order to solve this problem, a resin composition comprising 60 to 99% by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 20 to 70% by mole and a saponification degree of 85% or more and a hydrophobic plasticizer of 1 to 40% by weight. An inner liner for a tire inner surface is disclosed (Japanese Patent Application Laid-Open No. 2002-52904: Patent Document 2).

JP-A-6-40207 (page 2) JP-A-2002-52904 (page 2)

  However, in recent years, there has been a demand for an inner liner having higher flex resistance while maintaining gas barrier properties as compared with a conventional tire inner liner made of EVOH, and further technical improvements are desired. I was An object of the present invention is to provide an inner liner for a pneumatic tire which is excellent in both gas barrier properties and bending resistance. It is another object of the present invention to provide a pneumatic tire in which the internal pressure holding technology of an inner liner or the like is improved to greatly improve the internal pressure holding ability at the time of a new product and after traveling.

  The object is to provide a modified ethylene-vinyl obtained by reacting 1 to 50 parts by weight of an epoxy compound (B) with 100 parts by weight of an ethylene-vinyl alcohol copolymer (A) having an ethylene content of 25 to 50 mol%. The problem is solved by an inner liner for a pneumatic tire comprising the alcohol copolymer (C).

  In a preferred embodiment, the epoxy compound (B) is glycidol or epoxypropane.

  In a preferred embodiment, the degree of saponification of the ethylene-vinyl alcohol copolymer (A) is 90% or more.

In a preferred embodiment, the layer made of the modified ethylene-vinyl alcohol copolymer (C) has an oxygen transmission rate at 20 ° C. and 65 RH% of 3.0 × 10 ⁻¹² cm ³ · cm / cm ² · sec · cmHg or less. It is.

  In a preferred embodiment, the modified ethylene-vinyl alcohol copolymer (C) is crosslinked in the inner liner for a pneumatic tire.

  In a preferred embodiment, the layer made of the modified ethylene-vinyl alcohol copolymer (C) has a thickness of 50 μm or less.

  In a preferred embodiment, the inner liner for a pneumatic tire includes an auxiliary layer (D) made of an elastomer adjacent to a layer made of the modified ethylene-vinyl alcohol copolymer (C).

  In a preferred embodiment, the inner liner for a pneumatic tire includes a layer made of the modified ethylene-vinyl alcohol copolymer (C) and an auxiliary layer (D) made of an elastomer via at least one adhesive layer. Can be attached.

In a preferred embodiment, the auxiliary layer (D) made of an elastomer has an oxygen permeability at 20 ° C. and 65 RH% of 3.0 × 10 ⁻⁹ cm ³ · cm / cm ² · sec · cmHg or less.

  In a preferred embodiment, butyl rubber or halogenated butyl rubber is used for the auxiliary layer (D) made of an elastomer.

  In a preferred embodiment, a diene elastomer is used for the auxiliary layer (D) made of an elastomer.

  In a preferred embodiment, a thermoplastic urethane-based elastomer is used for the auxiliary layer (D) made of an elastomer.

  In a preferred embodiment, in the auxiliary layer (D) made of an elastomer, different auxiliary layers are bonded via at least one or more adhesive layers.

  In a preferred embodiment, the total thickness of the auxiliary layer (D) made of an elastomer is 50 to 1500 µm.

  Further, the above-mentioned problem is solved by a pneumatic tire provided with the inner liner for a pneumatic tire.

  In a preferred embodiment, the pneumatic tire comprises a bead, a side, a tread, a carcass, and a belt.

  In a preferred embodiment, the part of the auxiliary layer (D) made of an elastomer is equivalent to a radial width of at least 30 mm in a region from each belt end to the bead part. This is a state where the thickness of the auxiliary layer (D) corresponding to the lower part of the belt of (D) is 0.2 mm or more.

  The inner liner for a pneumatic tire of the present invention is excellent in gas barrier properties and flex resistance. Further, the pneumatic tire using the inner liner can significantly improve the internal pressure retention at the time of a new product and after traveling without increasing the tire weight.

  The inner liner for a pneumatic tire of the present invention includes a layer composed of a modified ethylene-vinyl alcohol copolymer (C) obtained by reacting an epoxy compound (B) with an ethylene-vinyl alcohol copolymer (A). By the modification using the epoxy compound (B) in the present invention, the modulus of elasticity of the ethylene-vinyl alcohol copolymer can be significantly reduced, and the breakability at bending and the degree of crack generation can be improved.

  The ethylene-vinyl alcohol copolymer (A) used in the present invention needs to have an ethylene content of 25 to 50 mol%. From the viewpoint of obtaining good bending resistance and fatigue resistance, the lower limit of the ethylene content is more preferably 30 mol% or more, and still more preferably 35 mol% or more. In addition, from the viewpoint of gas barrier properties, the upper limit of the ethylene content is more preferably 48 mol% or less, and still more preferably 45 mol% or less. If the ethylene content is less than 25 mol%, the bending resistance and the fatigue resistance may deteriorate, and the melt moldability may deteriorate. If it exceeds 50 mol%, the gas barrier properties may be insufficient.

  Further, the degree of saponification of the ethylene-vinyl alcohol copolymer (A) used in the present invention is preferably 90% or more. The degree of saponification is more preferably at least 95%, even more preferably at least 98%, and most preferably at least 99%. If the saponification degree is less than 90%, the gas barrier properties and the thermal stability at the time of forming the inner liner for a pneumatic tire may be insufficient.

  The preferred melt flow rate (MFR) of the ethylene-vinyl alcohol copolymer (A) used in the present invention (at 190 ° C. under a load of 2160 g) is 0.1 to 30 g / 10 minutes, more preferably 0.1 to 30 g / 10 minutes. 3 to 25 g / 10 min. However, when the melting point of the ethylene-vinyl alcohol copolymer (A) is around 190 ° C. or exceeds 190 ° C., it is measured under a load of 2160 g at a plurality of temperatures equal to or higher than the melting point. , And the logarithm of MFR are plotted on the vertical axis, and represented by values extrapolated to 190 ° C.

  The inner liner for a pneumatic tire of the present invention is a modified ethylene-vinyl alcohol copolymer obtained by reacting 1 to 50 parts by weight of an epoxy compound (B) with 100 parts by weight of an ethylene-vinyl alcohol copolymer (A). It consists of a polymer (C). More preferably, the mixing ratio of (A) and (B) is from 2 to 40 parts by weight of (B) to 100 parts by weight of (A), and still more preferably from 100 to 100 parts by weight of (A). (B) 5 to 35 parts by weight.

  The method for producing the modified ethylene-vinyl alcohol copolymer (C) by reacting the ethylene-vinyl alcohol copolymer (A) with the epoxy compound (B) is not particularly limited. A preferred method is a production method in which A) and the epoxy compound (B) are reacted in a solution.

  In the production method by a solution reaction, a modified ethylene-vinyl alcohol copolymer (C) is produced by reacting a solution of the ethylene-vinyl alcohol copolymer (A) with an epoxy compound (B) in the presence of an acid catalyst or an alkali catalyst. can get. As the reaction solvent, a polar aprotic solvent which is a good solvent for the ethylene-vinyl alcohol copolymer (A) such as dimethylsulfoxide, dimethylformamide, dimethylacetamide and N-methylpyrrolidone is preferred. Examples of the reaction catalyst include acid catalysts such as p-toluenesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, sulfuric acid, and boron trifluoride, and alkali catalysts such as sodium hydroxide, potassium hydroxide, lithium hydroxide, and sodium methoxide. Is mentioned. Of these, it is preferable to use an acid catalyst. An appropriate amount of the catalyst is about 0.0001 to 10 parts by weight based on 100 parts by weight of the ethylene-vinyl alcohol copolymer (A). The modified ethylene-vinyl alcohol copolymer (C) can also be produced by dissolving the ethylene-vinyl alcohol copolymer (A) and the epoxy compound (B) in a reaction solvent and performing a heat treatment.

  The epoxy compound (B) used in the present invention is not particularly limited, but is preferably a monovalent epoxy compound. When the epoxy compound is a divalent or higher valent epoxy compound, a cross-linking reaction with the ethylene-vinyl alcohol copolymer (A) occurs, and the quality of the inner liner for a pneumatic tire may be degraded due to the generation of gels, bumps and the like. From the viewpoints of easiness of production of the modified ethylene-vinyl alcohol copolymer (C), gas barrier properties, flex resistance and fatigue resistance, preferred monohydric epoxy compounds include glycidol and epoxy propane.

  The melt flow rate (MFR) (at 190 ° C. under a load of 2160 g) of the modified ethylene-vinyl alcohol copolymer (C) used in the present invention is not particularly limited, but good gas barrier properties, flex resistance and fatigue resistance are required. From the viewpoint of obtaining, the modified ethylene-vinyl alcohol copolymer (C) preferably has a melt flow rate (MFR) of 0.1 to 30 g / 10 min, and more preferably 0.3 to 25 g / 10 min. More preferably, it is more preferably 0.5 to 20 g / 10 minutes. However, the modified EVOH having a melting point of around 190 ° C. or exceeding 190 ° C. was measured under a load of 2160 g at a plurality of temperatures equal to or higher than the melting point. Plotted and expressed as a value extrapolated to 190 ° C.

The layer made of the modified ethylene-vinyl alcohol copolymer (C) in the inner liner for a pneumatic tire of the present invention has an oxygen transmission rate at 20 ° C. and 65 RH% of 3.0 × 10 ⁻¹² cm ³ .cm / cm ^2. sec · cmHg or less, more preferably 1.0 × 10 ⁻¹² cm ³ · cm / cm ² · sec · cmHg or less, and 5.0 × 10 ⁻¹³ cm ³ · cm / cm ^2. · Sec · cmHg or less is more preferable.

  The modified ethylene-vinyl alcohol copolymer (C) used in the present invention is formed into a film, a sheet, or the like by melt molding for use as an inner liner for a pneumatic tire. Extrusion molding and the like can be given as a method for melt-molding a film, a sheet or the like. The method of extrusion molding is not particularly limited, and examples thereof include a T-die method and an inflation method. The melting temperature varies depending on the melting point of the copolymer and the like, but is preferably about 150 to 270 ° C.

  In the inner liner for a pneumatic tire of the present invention, it is preferable that the modified ethylene-vinyl alcohol copolymer (C) in the layer composed of the modified ethylene-vinyl alcohol copolymer (C) is crosslinked. When the modified ethylene-vinyl alcohol copolymer (C) is not crosslinked, the layer comprising the modified ethylene-vinyl alcohol copolymer (C) is significantly deformed in the vulcanization step for producing a pneumatic tire, and the uniformity is obtained. The layer cannot be retained, and the gas barrier property, bending resistance, and fatigue resistance of the inner liner may be deteriorated.

  The method for forming a crosslinked structure in the modified ethylene-vinyl alcohol copolymer (C) is not particularly limited, but a preferable method is a method of irradiating an energy ray. Examples of energy rays include ionizing radiation such as ultraviolet rays, electron beams, X-rays, α-rays, and γ-rays, and preferably include electron beams.

  Regarding the method of irradiating an electron beam, there is a method in which, after processing a film or a sheet by extrusion molding, a molded body is introduced into an electron beam irradiation apparatus and irradiated with an electron beam. The dose of the electron beam is not particularly limited, but is preferably in the range of 10 to 60 Mrad. When the irradiation electron dose is lower than 10 Mrad, the crosslinking is difficult to proceed. On the other hand, when the electron dose to be irradiated exceeds 60 Mrad, the deterioration of the molded body is apt to progress. More preferably, the range of electron dose is between 20 and 50 Mrad.

  The inner liner for a pneumatic tire of the present invention has a multilayer structure including at least one layer made of a modified ethylene-vinyl alcohol copolymer (C), in addition to being provided to the pneumatic tire as a single-layer molded product. It can be offered for pneumatic tires. In the present invention, the inner liner for a pneumatic tire preferably includes an auxiliary layer (D) made of an elastomer, adjacent to the layer made of the modified ethylene-vinyl alcohol copolymer (C).

  Further, in the inner liner for a pneumatic tire of the present invention, the layer made of the modified ethylene-vinyl alcohol copolymer (C) is attached to the auxiliary layer (D) made of an elastomer via at least one adhesive layer. Can be adapted.

  Since the ethylene-vinyl alcohol copolymer has an —OH group, it is relatively easy to secure adhesion to rubber. For example, if a chlorinated rubber / isocyanate-based adhesive is used for the adhesive layer, adhesion to the rubber composition used for the tire can be ensured.

  As the layer structure of the multilayer structure, the layer composed of the modified ethylene-vinyl alcohol copolymer (C) of the present invention is represented by C, the auxiliary layer (D) composed of an elastomer is represented by D1, D2, and the adhesive layer is represented by Ad. , C / D1, D1 / C / D1, C / Ad / D1, D1 / Ad / C / Ad / D1, D1 / C / D1 / D2, D1 / C / D1 / Ad / D2, and the like. It is not limited to this. D1 and D2 each represent an auxiliary layer made of a different elastomer. Each layer may be a single layer, or may be a multilayer in some cases. Further, the modified ethylene-vinyl alcohol copolymer (C), the elastomer and the adhesive layer used may be of one type or may be of various types depending on the case.

  The method for producing the above-described multilayer structure is not particularly limited. For example, a method in which an elastomer and an adhesive layer are melt-extruded on a molded article (film, sheet, etc.) made of the modified ethylene-vinyl alcohol copolymer (C), and conversely, a modified ethylene-vinyl alcohol copolymer ( C) and a method of melt-extruding an adhesive layer, a method of co-extrusion of a modified ethylene-vinyl alcohol copolymer (C) and an auxiliary layer (D) (and an adhesive layer if necessary), a modified ethylene-vinyl alcohol A method of laminating a molded product obtained from the copolymer (C) with an elastomer film or sheet using an adhesive layer, and further, on a drum at the time of tire molding, from a modified ethylene-vinyl alcohol copolymer (C). A method of laminating the obtained molded product and the auxiliary layer (D) (and the adhesive layer as necessary) is exemplified.

  In the inner liner for a pneumatic tire of the present invention, the thickness of the layer made of the modified ethylene-vinyl alcohol copolymer (C) is preferably 50 μm or less. If it exceeds 50 μm, the merit of weight reduction is smaller than that of the currently used inner liner using butyl rubber, halogenated butyl rubber or the like. Furthermore, the layer made of the modified ethylene-vinyl alcohol copolymer (C) has reduced flex resistance and fatigue resistance, and is liable to break or crack due to bending deformation during rolling of the tire, and it is easy for the crack to extend. Therefore, the internal pressure retention after use of the tire may be lower than before use. On the other hand, the thickness is preferably 0.1 μm or more from the viewpoint of the gas barrier properties of the inner liner for a pneumatic tire. The thickness of the layer made of the modified ethylene-vinyl alcohol copolymer (C) is more preferably 1 to 40 μm, and still more preferably 5 to 30 μm, from the viewpoints of gas barrier properties, flex resistance, and fatigue resistance.

  As described above, in the layer made of the modified ethylene-vinyl alcohol copolymer (C), the use of 50 μm or less improves the bending resistance and fatigue resistance, and causes breakage and cracks due to bending deformation during rolling of the tire. It becomes difficult. Further, even if the layer is broken, the layer made of the modified ethylene-vinyl alcohol copolymer (C) has good adhesion to the auxiliary layer (D) made of an elastomer, so that it is difficult to peel off, and the crack is hard to spread, so that it is large. No breaks and cracks occur. In addition, even when it occurs, the auxiliary layer (D) compensates for the gas barrier property of the rupture and crack portions generated in the layer made of the modified ethylene-vinyl alcohol copolymer (C), so that the internal pressure can be maintained even after using the tire. Becomes possible.

  That is, even if the layer is made of the modified ethylene-vinyl alcohol copolymer (C) having a thickness of 50 μm or less, pinholes and cracks may be formed. By arranging the auxiliary layer (D) made of an elastomer between the ply layers to be formed, crack growth can be suppressed. Even if cracks occur, the layer composed of the modified ethylene-vinyl alcohol copolymer (C) is firmly adhered to the surface of the auxiliary layer (D), so that the surface is almost covered with the film, By using an elastomer (butyl rubber, halogenated butyl rubber) having a low air permeability for the layer (D), it is possible to suppress the air leakage from the crack portion.

The auxiliary layer (D) made of the elastomer of the inner liner for a pneumatic tire of the present invention has an oxygen permeation amount at 20 ° C. and 65 RH% of 3.0 × 10 ⁻⁹ cm ³ · cm / cm ² · sec · cmHg or less. This is preferable from the viewpoint of the gas barrier properties of the inner liner. More preferably, it is 1.0 × 10 ⁻⁹ cm ³ · cm / cm ² · sec · cmHg or less.

  Preferred examples of the elastomer laminated as the auxiliary layer (D) of the inner liner for a pneumatic tire according to the present invention include butyl rubber and diene elastomer. Suitable examples of the diene-based elastomer include natural rubber and butadiene rubber. From the viewpoint of gas barrier properties, it is preferable to use butyl rubber as the elastomer, and it is more preferable to use halogenated butyl rubber. Further, from the viewpoint of suppressing the extension of the crack after the crack has occurred in the auxiliary layer (D) made of the elastomer, it is preferable to use a composition made of butyl rubber and a diene-based elastomer as the elastomer. By using such a composition as the elastomer, even if a small crack occurs in the auxiliary layer (D) made of the elastomer, the internal pressure retention of the pneumatic tire after running can be kept high.

  Further, as the elastomer laminated as the auxiliary layer (D) of the inner liner for a pneumatic tire of the present invention, a thermoplastic urethane-based elastomer is also exemplified as a suitable one. It is preferable to use a thermoplastic urethane-based elastomer from the viewpoint of reducing the thickness of the auxiliary layer (D) and suppressing the generation of cracks and extension.

  As the elastomer laminated as the auxiliary layer (D) of the inner liner for a pneumatic tire of the present invention, the auxiliary layer (D) composed of a thermoplastic urethane elastomer and the auxiliary layer (D) composed of a composition composed of butyl rubber and a diene elastomer are used. ) Is more preferably multi-layered.

  In the inner liner for a pneumatic tire of the present invention, the total thickness of the auxiliary layer (D) made of an elastomer is preferably 50 to 1500 µm. When the total thickness of the auxiliary layer (D) made of an elastomer is less than 50 μm, the bending resistance and fatigue resistance of the inner liner are reduced, and the inner liner is easily broken or cracked by bending deformation during rolling of the tire. Since the cracks are easily extended, the internal pressure retention after use of the tire may be significantly reduced as compared with before the use. Further, it is difficult to make the total thickness of the auxiliary rubber layer at the lower part of the belt less than 50 μm in the production of the tire.

  On the other hand, when the total thickness of the auxiliary layer (D) made of an elastomer exceeds 1500 μm, the merit of weight reduction is smaller than that of a currently used pneumatic tire. The total thickness of the auxiliary layer (D) made of an elastomer is more preferably 100 to 1000 μm, and further preferably 300 to 800 μm, from the viewpoints of gas barrier properties, flex resistance, fatigue resistance, and weight reduction of the pneumatic tire of the inner liner. preferable.

  Further, the above-mentioned fracture, crack, and crack are generated mainly in the side portion largely deformed by bending. Therefore, by increasing the thickness of the auxiliary layer only at the side portions, it is possible to achieve both the internal pressure retention after running and the reduction in tire weight.

  In the inner liner for a pneumatic tire according to the present invention, the auxiliary layer (D) made of an elastomer preferably has a 300% modulus of 10 MPa or less in order to suppress the generation and growth of cracks. When the 300% modulus exceeds 10 MPa, the bending resistance and the fatigue resistance of the inner liner decrease. The 300% modulus of the auxiliary layer (D) made of an elastomer is more preferably 8 MPa or less, and even more preferably 7 MPa or less.

  The pneumatic tire of the present invention is provided using an inner liner including a layer made of the above-mentioned modified ethylene-vinyl alcohol copolymer (C).

  In the pneumatic tire of the present invention, the pneumatic tire preferably includes a bead portion, a side portion, a tread portion, a carcass, and a belt.

  In the pneumatic tire according to the present invention, the auxiliary layer (D) made of an elastomer has a portion corresponding to a radial width of at least 30 mm in a region from each belt end to a bead portion. It is preferable that the thickness of the auxiliary layer (D) corresponding to the lower part of the layer (D) be 0.2 mm or more.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by these Examples.

<Measurement of characteristic value of ethylene-vinyl alcohol copolymer (A)>
(1) Ethylene content and saponification degree of ethylene-vinyl alcohol copolymer (A):
It was calculated from a spectrum obtained by ¹ H-NMR (nuclear magnetic resonance) measurement using deuterated dimethyl sulfoxide as a solvent (using “JNM-GX-500” manufactured by JEOL Ltd.).

(2) Melt flow rate of ethylene-vinyl alcohol copolymer (A):
The ethylene-vinyl alcohol copolymer (A) as a sample was filled into a cylinder having an inner diameter of 9.55 mm and a length of 162 mm of a melt indexer L244 (manufactured by Takara Kogyo Co., Ltd.), melted at 190 ° C., and weighed. A 2160 g, 9.48 mm diameter plunger was used to evenly load. The amount (g / 10 minutes) of resin extruded per unit time from an orifice having a diameter of 2.1 mm provided at the center of the cylinder was measured, and this was defined as a melt flow rate. However, when the melting point of the ethylene-vinyl alcohol copolymer (A) is around 190 ° C. or exceeds 190 ° C., it is measured under a load of 2160 g at a plurality of temperatures equal to or higher than the melting point. , And the logarithm of MFR are plotted on the vertical axis, and represented by values extrapolated to 190 ° C.

<Synthesis of modified ethylene-vinyl alcohol copolymer (C)>
Synthesis Example 1
2 weight of ethylene-vinyl alcohol copolymer (A) having an ethylene content of 44 mol% and a saponification degree of 99.9% (MFR: 5.5 g / 10 min (190 ° C., under a load of 2160 g)) in a pressurized reaction tank And 8 parts by weight of N-methyl-2-pyrrolidone, and the mixture was heated and stirred at 120 ° C. for 2 hours to completely dissolve the ethylene-vinyl alcohol copolymer (A). After adding 0.4 parts by weight of glycidol as the epoxy compound (B), the mixture was heated at 160 ° C. for 4 hours. After the heating, the precipitate was precipitated in 100 parts by weight of distilled water, and N-methyl-2-pyrrolidone and unreacted glycidol were sufficiently washed with a large amount of distilled water to obtain a modified ethylene-vinyl alcohol copolymer (C). . Furthermore, the obtained modified ethylene-vinyl alcohol copolymer (C) was pulverized to a particle diameter of about 2 mm with a pulverizer, and then sufficiently washed again with a large amount of distilled water. The particles after washing were vacuum-dried at room temperature for 8 hours, then melted at 200 ° C. using a twin-screw extruder, and pelletized.

Synthesis Example 2
2 weight of ethylene-vinyl alcohol copolymer (A) having an ethylene content of 44 mol% and a saponification degree of 99.9% (MFR: 5.5 g / 10 min (190 ° C., under a load of 2160 g)) in a pressurized reaction tank And 8 parts by weight of N-methyl-2-pyrrolidone, and the mixture was heated and stirred at 120 ° C. for 2 hours to completely dissolve the ethylene-vinyl alcohol copolymer (A). After adding 0.3 parts by weight of glycidol as the epoxy compound (B), the mixture was heated at 160 ° C. for 4 hours. After the heating, the precipitate was precipitated in 100 parts by weight of distilled water, and N-methyl-2-pyrrolidone and unreacted glycidol were sufficiently washed with a large amount of distilled water to obtain a modified ethylene-vinyl alcohol copolymer (C). . Furthermore, the obtained modified ethylene-vinyl alcohol copolymer (C) was pulverized to a particle diameter of about 2 mm with a pulverizer, and then sufficiently washed again with a large amount of distilled water. The particles after washing were vacuum-dried at room temperature for 8 hours, then melted at 200 ° C. using a twin-screw extruder, and pelletized.

Synthesis Example 3
2 weight of ethylene-vinyl alcohol copolymer (A) having an ethylene content of 44 mol% and a saponification degree of 99.9% (MFR: 5.5 g / 10 min (190 ° C., under a load of 2160 g)) in a pressurized reaction tank And 8 parts by weight of N-methyl-2-pyrrolidone, and the mixture was heated and stirred at 120 ° C. for 2 hours to completely dissolve the ethylene-vinyl alcohol copolymer (A). After adding 0.4 parts by weight of epoxypropane as the epoxy compound (B), the mixture was heated at 160 ° C. for 4 hours. After heating, the precipitate is precipitated in 100 parts by weight of distilled water, and N-methyl-2-pyrrolidone and unreacted epoxypropane are sufficiently washed with a large amount of distilled water to obtain a modified ethylene-vinyl alcohol copolymer (C). Was. Furthermore, the obtained modified ethylene-vinyl alcohol copolymer (C) was pulverized to a particle diameter of about 2 mm with a pulverizer, and then sufficiently washed again with a large amount of distilled water. The particles after washing were vacuum-dried at room temperature for 8 hours, then melted at 200 ° C. using a twin-screw extruder, and pelletized.

<Preparation of layer composed of modified ethylene-vinyl alcohol copolymer (C)>
Film 1
Using the modified ethylene-vinyl alcohol copolymer (C) pellets obtained in Synthesis Example 1, using a 40 mmφ extruder (PLABOR GT-40-A manufactured by Plastics Engineering Laboratory) and a film forming machine including a T-die. Then, a film was formed under the following extrusion conditions to obtain a single-layer film having a thickness of 20 μm.
Type: Single screw extruder (non-vent type)
L / D: 24
Diameter: 40mmφ
Screw: Single full flight type, surface nitrided steel Screw rotation speed: 40 rpm
Die: 550mm width coat hanger die Lip gap: 0.3mm
Cylinder / die temperature setting: C1 / C2 / C3 / adapter / die = 180/200/210/210/210 (° C)

Film 2
A single-layer film having a thickness of 20 μm was obtained in the same manner as in Film 1, except that pellets of the modified ethylene-vinyl alcohol copolymer (C) obtained in Synthesis Example 2 were used.

Film 3
A monolayer film having a thickness of 20 μm was obtained in the same manner as in Film 1, except that pellets of the modified ethylene-vinyl alcohol copolymer (C) obtained in Synthesis Example 3 were used.

Film 4
As a gas barrier material, unmodified ethylene-vinyl alcohol copolymer (A) having an ethylene content of 44 mol%, a saponification degree of 99.9%, and an MFR of 5.5 g / 10 min (at 190 ° C. under a load of 2160 g) was used. A monolayer film having a thickness of 20 μm was obtained in the same manner as in Film 1, except that the modified ethylene-vinyl alcohol copolymer (C) was used instead of the modified ethylene-vinyl alcohol copolymer (C).

Film 5
Using the modified EVOH (C) obtained in Synthesis Example 3 and thermoplastic polyurethane (Kuramylon 3190 manufactured by Kuraray Co., Ltd.) as an elastomer, using a two-type three-layer coextrusion apparatus under the following coextrusion molding conditions: A three-layer film (thermoplastic polyurethane layer / modified EVOH (C) layer / thermoplastic polyurethane layer) was prepared. The thickness of each layer is 20 μm for both the modified EVOH (C) layer and the thermoplastic polyurethane layer.

The co-extrusion molding conditions are as follows.
Layer structure:
Thermoplastic polyurethane / modified EVOH (C) / thermoplastic polyurethane (thickness 20/20/20: unit is μm)
Extrusion temperature of each resin:
C1 / C2 / C3 / die = 170/170/220/220 ° C
Extruder specifications for each resin:
Thermoplastic polyurethane:
25mmφ extruder P25-18AC (Osaka Seiki Co., Ltd.)
Modified EVOH (C):
20mmφ extruder Laboratory machine ME type CO-EXT (Toyo Seiki Co., Ltd.)
T-die specification:
For 500mm width 2 types 3 layers (Plastic Engineering Laboratory Co., Ltd.)
Cooling roll temperature: 50 ° C
Pickup speed: 4m / min

<Evaluation of layer composed of modified ethylene-vinyl alcohol copolymer (C)>
The films 1 to 5 prepared above were evaluated for the amount of oxygen permeation and the bending resistance according to the methods described below.

Measurement of oxygen permeability of film:
The film prepared above was conditioned at 20 ° C.-65% RH for 5 days. According to the method described in JIS K7126 (isobaric method) under the conditions of 20 ° C. and 65% RH using the MOCON OX-TRAN 2/20 type manufactured by Modern Control Co., Ltd. Then, the oxygen permeation amount was measured, and the average value was obtained.

Evaluation of bending resistance:
Fifty pieces of the above-prepared films cut into a size of 21 cm × 30 cm were prepared, and each film was conditioned at 20 ° C.-65% RH for 5 days. Then, according to ASTM F392-74, Rigaku Kogyo Co., Ltd. Using a gelboflex tester manufactured, the number of bending times 50 times, 75 times, 100 times, 125 times, 150 times, 175 times, 200 times, 225 times, 250 times, 300 times, 400 times, 500 times, 600 times, After bending 700 times, 800 times, 1000 times, and 1500 times, the number of pinholes was measured. At each bending number, measurement was performed 5 times, and the average value was defined as the number of pinholes. The number of bends (P) is plotted on the horizontal axis, the number of pinholes (N) is plotted on the vertical axis, and the above measurement results are plotted. Number was two digits. However, for a film in which a pinhole was not observed after being bent 1500 times, the number of times of bending was increased every 500 times thereafter, and the number of times of bending in which a pinhole was observed was defined as Np1.

The oxygen permeation amount of the film 1 was 3.0 × 10 ⁻¹³ cm ³ · cm / cm ² · sec · cmHg, and showed excellent gas barrier properties. Moreover, when the bending resistance of the film 1 was evaluated according to the above-mentioned method, the Np1 was 500 times, showing extremely excellent bending resistance.

The oxygen permeation amount of the film 2 was 1.0 × 10 ⁻¹³ cm ³ · cm / cm ² · sec · cmHg, and showed excellent gas barrier properties. Moreover, when the bending resistance of the film 2 was evaluated according to the above-mentioned method, Np1 was 100 times, showing extremely excellent bending resistance.

The oxygen permeation amount of the film 3 was 4.0 × 10 ⁻¹³ cm ³ · cm / cm ² · sec · cmHg, and showed excellent gas barrier properties. Moreover, when the bending resistance of the film 3 was evaluated according to the above-mentioned method, Np1 was 500 times, showing extremely excellent bending resistance.

The oxygen permeation amount of the film 4 was 4.6 × 10 ⁻¹⁴ cm ³ · cm / cm ² · sec · cmHg, and showed excellent gas barrier properties. In addition, when the bending resistance of the film 4 was evaluated according to the above method, Np1 was 47 times.

The oxygen permeation amount of the film 5 was 3.5 × 10 ⁻¹³ cm ³ · cm / cm ² · sec · cmHg, and showed excellent gas barrier properties. Moreover, when the bending resistance of the film 5 was evaluated according to the above-mentioned method, the Np1 was 5,000 times, showing extremely excellent bending resistance.

<Blending of rubber composition and preparation of rubber inner liner and auxiliary layer>
A rubber composition was prepared according to the following compounding amount, and after vulcanization at 145 ° C. × 40 minutes, a 300% modulus was measured by a method according to JIS K6301. Further, the amount of oxygen permeation was measured by the same method as the measurement of the amount of oxygen permeation of the film.

Rubber composition 1 (compounding unit: parts by weight)
Natural rubber: 30
Br-IIR (Bromobutyl 2244 manufactured by JSR Corporation): 70
GPF carbon black (Asahi Carbon Co., Ltd. # 55): 60
SUNPAR2280 (manufactured by Nippon Sun Oil Co., Ltd.): 7
Stearic acid (Asahi Denka Kogyo Co., Ltd.): 1
NOCCELER DM (Ouchi Shinko Chemical Co., Ltd.): 1.3
Zinc oxide (manufactured by Hakusui Chemical Industry Co., Ltd.): 3
Sulfur (Karuizawa refinery): 0.5
300% modulus: 6.5Mpa
Oxygen transmission rate: 6.0 × 10 ^-10 cm ³・ cm / cm ²・ sec ・ cmHg

Rubber composition 2 (compounding unit: parts by weight)
Br-IIR (Bromobutyl 2244 manufactured by JSR Corporation): 100
GPF carbon black (Asahi Carbon Co., Ltd. # 55): 60
SUNPAR2280 (manufactured by Nippon Sun Oil Co., Ltd.): 7
Stearic acid (Asahi Denka Kogyo Co., Ltd.): 1
NOCCELER DM (Ouchi Shinko Chemical Co., Ltd.): 1.3
Zinc oxide (manufactured by Hakusui Chemical Industry Co., Ltd.): 3
Sulfur (Karuizawa refinery): 0.5
300% modulus: 6.0Mpa
Oxygen permeation amount: 3.0 × 10 ^-10 cm ³・ cm / cm ²・ sec ・ cmHg

<Production and evaluation of evaluation tire>
Example 1
The film 1 was irradiated with an electron beam under the conditions of an accelerating voltage of 200 kV and an irradiation energy of 30 Mrad using an electron beam irradiation apparatus manufactured by Nissin High Voltage Co., Ltd. “Curetron EBC200-100 for production”, and subjected to a cross-linking treatment. It was used as a layer composed of an ethylene-vinyl alcohol copolymer (C). Metallic R30M manufactured by Toyo Chemical Laboratories was applied as an adhesive layer to one surface of the obtained crosslinked film, and bonded to a 500 μm-thick auxiliary layer (D) using rubber composition 1 to obtain a modified ethylene-vinyl alcohol copolymer. An inner liner comprising the polymer (C) and the auxiliary layer (D) was produced. Using the obtained inner liner, a pneumatic tire for passenger cars (195 / 65R15) was produced by a conventional method. FIG. 1 shows a schematic sectional view of the manufactured tire. In the figure, 1 indicates a layer composed of a modified ethylene-vinyl alcohol copolymer (C), and 2 indicates an auxiliary layer (D) composed of an elastomer.

The tire thus manufactured was pressed at a load of 6 kN on a drum having an air pressure of 140 kPa and a rotation speed corresponding to a speed of 80 km / h, and traveled 10,000 km. The internal pressure retention was evaluated under the following conditions using an unrunnable tire and a tire running under the above conditions. The internal pressure retention was evaluated by mounting the test tire on a rim of 6JJ × 15, filling the internal pressure with 240 kPa, and measuring the internal pressure three months later.
Internal pressure retention = ((240−b) / (240−a)) × 100
In the formula, a and b are
a: Internal pressure after 3 months of test tire b: Internal pressure after 3 months of non-running tire (pneumatic tire using ordinary rubber inner liner) described in Comparative Example 1 below.
Further, the appearance of the inner liner of the tire after the above-mentioned drum running was visually observed to evaluate the presence or absence of cracks. Table 1 shows the evaluation results.

Example 2
An inner liner and a pneumatic tire for a passenger car were produced in the same manner as in Example 1, except that the thickness of the auxiliary layer using the rubber composition 1 was changed to 1000 μm, and the inner pressure retention and inner diameter of the tire after running the drum. The liner appearance was evaluated. Table 1 shows the evaluation results.

Example 3
An inner liner and a pneumatic tire for a passenger car were prepared in the same manner as in Example 1 except that Film 2 was used instead of Film 1, and the inner pressure retention and the inner liner appearance of the tire after running the drum were evaluated. Was. Table 1 shows the evaluation results.

Example 4
An inner liner and a pneumatic tire for a passenger car were prepared in the same manner as in Example 1 except that the film 3 was used instead of the film 1, and the inner pressure retention and the inner liner appearance of the tire after running the drum were evaluated. Was. Table 1 shows the evaluation results.

Example 5
An inner liner and a pneumatic tire for a passenger car were prepared in the same manner as in Example 1 except that the film 5 was used in place of the film 1, and the inner pressure retention and the inner liner appearance of the tire after running the drum were evaluated. Was. Table 1 shows the evaluation results.

Example 6
The film 1 was irradiated with an electron beam under the conditions of an accelerating voltage of 200 kV and an irradiation energy of 30 Mrad using an electron beam irradiation apparatus manufactured by Nissin High Voltage Co., Ltd. “Curetron EBC200-100 for production”, and subjected to a cross-linking treatment. It was used as a layer composed of an ethylene-vinyl alcohol copolymer (C). One side of the obtained cross-linked film was coated with Metaloc R30M manufactured by Toyo Chemical Laboratories as an adhesive layer, and then used as an inner liner without laminating an auxiliary layer (D) made of a rubber composition. A pneumatic tire for use (195 / 65R15) was produced. Using the obtained tire, the internal pressure retention and the inner liner appearance of the tire after running the drum were evaluated in the same manner as in Example 1. Table 1 shows the evaluation results.

Comparative Example 1
For a passenger car having no layer made of a modified ethylene-vinyl alcohol copolymer (C) in the same manner as described above, using an inner liner having a thickness of 1500 μm using a rubber composition 2 used as a normal rubber inner liner. A pneumatic tire (195 / 65R15) was produced. In addition, using the obtained tires, the internal pressure retention and the inner liner appearance of the tires after running the drum were evaluated in the same manner as in Example 1. Table 1 shows the evaluation results.

Comparative Example 2
The film 4 was irradiated with an electron beam under conditions of an acceleration voltage of 200 kV and an irradiation energy of 30 Mrad to perform a cross-linking treatment, and was used as a layer made of an unmodified ethylene-vinyl alcohol copolymer (A). One side of the obtained crosslinked film was coated with Metaloc R30M manufactured by Toyo Chemical Laboratories as an adhesive layer, and then used as an inner liner without laminating an auxiliary layer made of a rubber composition. A tire (195 / 65R15) was produced. Using the obtained tire, the internal pressure retention and the inner liner appearance of the tire after running the drum were evaluated in the same manner as in Example 1. Table 1 shows the evaluation results.

  From the results in Table 1, the pneumatic tire using the inner liner made of the modified ethylene-vinyl alcohol copolymer (C) described in Examples 1 to 5 was air-conditioned using the ordinary rubber inner liner described in Comparative Example 1. It can be seen that the tire has excellent internal pressure retention not only before running but also after running on a 10,000 km drum as compared to a tire with a tire. Also, in the evaluation of the inner liner appearance of the tire after running the drum, it can be seen that no crack has occurred and the tire has good fatigue resistance. On the other hand, in the pneumatic tire using the inner liner made of the unmodified ethylene-vinyl alcohol copolymer (A) described in Comparative Example 2, although the internal pressure retention before running was good, the inner running due to the drum running It can be seen that the liner is cracked and the internal pressure retention is extremely reduced.

1 is a schematic sectional view of a tire obtained in Example 1. FIG.

Explanation of reference numerals

1 Layer composed of modified ethylene-vinyl alcohol copolymer (C) 2 Auxiliary layer composed of elastomer (D)

Claims (18)

Modified ethylene-vinyl alcohol copolymer obtained by reacting 1 to 50 parts by weight of epoxy compound (B) with 100 parts by weight of ethylene-vinyl alcohol copolymer (A) having an ethylene content of 25 to 50 mol% An inner liner for a pneumatic tire comprising (C). The inner liner for a pneumatic tire according to claim 1, wherein the epoxy compound (B) is glycidol or epoxy propane. 3. The inner liner for a pneumatic tire according to claim 1, wherein the degree of saponification of the ethylene-vinyl alcohol copolymer (A) is 90% or more. The layer formed of the modified ethylene-vinyl alcohol copolymer (C) has an oxygen transmission rate at 20 ° C. and 65 RH% of 3.0 × 10 ⁻¹² cm ³ · cm / cm ² · sec · cmHg or less. 3. The inner liner for a pneumatic tire according to 2. The inner liner for a pneumatic tire according to claim 1 or 2, wherein the modified ethylene-vinyl alcohol copolymer (C) is crosslinked. The inner liner for a pneumatic tire according to claim 1 or 2, wherein the thickness of the layer made of the modified ethylene-vinyl alcohol copolymer (C) is 50 µm or less. The inner liner for a pneumatic tire according to claim 1 or 2, further comprising an auxiliary layer (D) made of an elastomer, adjacent to the layer made of the modified ethylene-vinyl alcohol copolymer (C). The pneumatic tire according to claim 7, wherein a layer made of the modified ethylene-vinyl alcohol copolymer (C) is bonded to an auxiliary layer (D) made of an elastomer via at least one adhesive layer. Inner liner. 20 ° C. auxiliary layer of elastomeric (D), pneumatic tire according to claim 7 oxygen permeability is ^{3.0 × 10 -9 cm 3 · cm} / cm 2 · sec · cmHg or less at 65 RH% Inner liner. The inner liner for a pneumatic tire according to claim 7, wherein butyl rubber or halogenated butyl rubber is used for the auxiliary layer (D) made of an elastomer. The inner liner for a pneumatic tire according to claim 7, wherein a diene elastomer is used for the auxiliary layer (D) made of an elastomer. The inner liner for a pneumatic tire according to claim 7, wherein a thermoplastic urethane-based elastomer is used for the auxiliary layer (D) made of an elastomer. The inner liner for a pneumatic tire according to claim 7, wherein in the auxiliary layer (D) made of an elastomer, different auxiliary layers are bonded together via at least one adhesive layer. The inner liner for a pneumatic tire according to claim 7, wherein the total thickness of the auxiliary layer (D) made of an elastomer is 50 to 1500 m. A pneumatic tire comprising the inner liner for a pneumatic tire according to claim 1 or 2. A pneumatic tire comprising the inner liner for a pneumatic tire according to claim 7. A pneumatic tire comprising the inner liner for a pneumatic tire according to claim 8. An auxiliary layer (D) made of an elastomer has a portion corresponding to at least a radial width of 30 mm in a region from the end of each belt to a bead portion, and a portion of the auxiliary layer (D) below the belt of the auxiliary layer (D). 18. The pneumatic tire according to claim 17, wherein the thickness of the pneumatic tire is at least 0.2 mm thicker than the corresponding part of the auxiliary layer (D).

Images