JP4589615B2 - Inner liner for pneumatic tire and pneumatic tire - Google Patents

Description

  The present invention relates to an inner liner for a pneumatic tire excellent in 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 when new and after running without increasing the tire weight.

  Conventionally, butyl rubber, halogenated butyl rubber, or the like has been used as a main raw material for an inner liner as an air barrier layer in order to maintain the internal pressure of a tire. However, in the rubber composition containing these, since the air barrier property is low, the thickness of the inner liner is required to be about 1 mm. For this reason, 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 consumption of the vehicle.

  On the other hand, it is known that an ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as EVOH) is excellent in gas barrier properties. EVOH has an air permeation amount that is 1/100 or less of that of a butyl-based inner liner rubber composition. Therefore, even when the thickness is 50 μm or less, internal pressure retention can be greatly improved, and the weight of the tire can be reduced. It is possible. There are many resins that have a smaller air permeability than butyl rubber, but if the air permeability is about one-tenth that of a butyl inner liner, the effect of improving internal pressure retention is small unless the thickness exceeds 100 μm, and 100 μm If the thickness exceeds the range, the effect of reducing the tire weight is small, and the inner liner breaks or cracks due to deformation during bending of the tire, making it difficult to maintain barrier properties. On the other hand, since EVOH can be used at a thickness of 50 μm or less, it is less likely to break or crack 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 Japanese Patent Laid-Open No. 6-40207 (Patent Document 1) is disclosed.

  When normal EVOH is used as an inner liner, the effect of improving internal pressure retention is great, but because the elastic modulus is significantly higher than that of rubber used in normal tires, breakage or cracking occurs due to deformation during bending. There was a thing. For this reason, when using an inner liner made of EVOH, the internal pressure retention before use of the tire is greatly improved, but the internal pressure retention of the tire after use subjected to bending deformation at the time of tire rolling is higher than that before use. There was a decline. In order to solve this problem, a resin composition comprising an ethylene content of 20 to 70 mol%, an ethylene-vinyl alcohol copolymer having a saponification degree of 85% or more and 60 to 99 wt% and a hydrophobic plasticizer of 1 to 40 wt%. An inner liner for a tire inner surface made of a product is disclosed (Japanese Patent Laid-Open No. 2002-52904: Patent Document 2).

Japanese Patent Laid-Open No. 6-40207 (2nd page) JP 2002-52904 A (page 2)

  However, in recent years, as compared with conventional tire inner liners made of EVOH, inner liners having higher bending resistance while maintaining gas barrier properties have been demanded, and further technical improvements are desired. It was. An object of the present invention is to provide an inner liner for a pneumatic tire that is excellent in both gas barrier properties and bending resistance. Another object of the present invention is to provide a pneumatic tire that is improved in internal pressure retention technology such as an inner liner, and that greatly improves internal pressure retention when new and after running.

Above-mentioned problems, an ethylene content of 25 to 50 mole% ethylene - vinyl alcohol copolymer (A) with respect to 100 parts by weight, from reacting the monovalent epoxy compound (B) 1 to 50 parts by weight, unreacted This is solved by an inner liner for a pneumatic tire comprising a modified ethylene-vinyl alcohol copolymer (C) obtained by removing the reaction epoxy compound (B) . At this time, it is preferable to react the epoxy compound (B) with the ethylene-vinyl alcohol copolymer (A) in the presence of an acid catalyst or an alkali catalyst. It is more preferable that it is 0.0001-10 weight part with respect to 100 weight part of polymers (A).

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

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

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

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

  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 the layer made of the modified ethylene-vinyl alcohol copolymer (C).

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

In a preferred embodiment, the auxiliary layer (D) made of an elastomer has an oxygen permeation amount at 20 ° C. and 65 RH% of 3.0 × 10 ⁻⁹ cm ³ · 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 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 together via at least one adhesive layer.

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

  Moreover, the subject mentioned above is solved by the pneumatic tire provided with the said inner liner for pneumatic tires.

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

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

  The inner liner for a pneumatic tire of the present invention is excellent in gas barrier properties and bending resistance. In addition, the pneumatic tire using the inner liner can greatly improve the internal pressure retention when new and after running without increasing the tire weight.

  The inner liner for a pneumatic tire of the present invention includes a layer made 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 elastic modulus of the ethylene-vinyl alcohol copolymer can be greatly lowered, and the breakability at the time of bending and the occurrence of cracks can be improved.

  As ethylene-vinyl alcohol copolymer (A) used for this invention, ethylene content needs to be 25-50 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 even more preferably 35 mol% or more. From the viewpoint of gas barrier properties, the upper limit of the ethylene content is more preferably 48 mol% or less, and even more preferably 45 mol% or less. When the ethylene content is less than 25 mol%, flex resistance and fatigue resistance may be deteriorated, and melt moldability may be deteriorated. Moreover, when it exceeds 50 mol%, there exists a possibility that gas-barrier property may be insufficient.

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

  The preferred melt flow rate (MFR) (under 190 ° C. and 2160 g load) of the ethylene-vinyl alcohol copolymer (A) used in the present invention is 0.1 to 30 g / 10 min, more preferably 0.8. 3-25 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 at a plurality of temperatures above the melting point under a load of 2160 g, and the horizontal axis indicates the reciprocal absolute temperature in a semi-logarithmic graph. The logarithm of MFR is plotted on the vertical axis and expressed as a value 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 (B) 2 to 40 parts by weight with respect to (A) 100 parts by weight, and more preferably (A) with respect to 100 parts by weight. (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, but the ethylene-vinyl alcohol copolymer ( A suitable method is a production method in which A) and the epoxy compound (B) are reacted in a solution.

  In the production method by solution reaction, the modified ethylene-vinyl alcohol copolymer (C) is obtained by reacting the epoxy compound (B) with the solution of the ethylene-vinyl alcohol copolymer (A) in the presence of an acid catalyst or an alkali catalyst. can get. The reaction solvent is preferably a polar aprotic solvent which is a good solvent for the ethylene-vinyl alcohol copolymer (A) such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide and N-methylpyrrolidone. Reaction catalysts 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. As a catalyst amount, about 0.0001-10 weight part is suitable with respect to 100 weight part of ethylene-vinyl alcohol copolymers (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 divalent or higher, 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 deteriorated due to generation of gels, blisters and the like. From the viewpoint of ease of production of the modified ethylene-vinyl alcohol copolymer (C), gas barrier properties, flex resistance and fatigue resistance, preferred monovalent epoxy compounds include glycidol and epoxypropane.

  The melt flow rate (MFR) (under 190 ° C. and 2160 g load) of the modified ethylene-vinyl alcohol copolymer (C) used in the present invention is not particularly limited, but has good gas barrier properties, flex resistance and fatigue resistance. From the viewpoint of obtaining, the melt flow rate (MFR) of the modified ethylene-vinyl alcohol copolymer (C) is preferably 0.1 to 30 g / 10 minutes, and preferably 0.3 to 25 g / 10 minutes. More preferably, it is more preferably 0.5 to 20 g / 10 minutes. However, when the melting point of the modified EVOH is around 190 ° C. or exceeds 190 ° C., it is measured under a load of 2160 g and at a plurality of temperatures higher than the melting point. The value is plotted and 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 amount of 3.0 × 10 ⁻¹² cm ³ · cm / cm ² · at 20 ° C. and 65 RH%. It is preferably 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. -More preferably, it is below sec-cmHg.

  The modified ethylene-vinyl alcohol copolymer (C) used in the present invention is formed into a film, sheet or the like by melt molding in order to be used as an inner liner for a pneumatic tire. Moreover, extrusion molding etc. are mentioned as melt molding methods, such as a film and a sheet | seat. 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, but is preferably about 150 to 270 ° C.

  In the inner liner for a pneumatic tire of the present invention, the layer of the modified ethylene-vinyl alcohol copolymer (C) made of the modified ethylene-vinyl alcohol copolymer (C) is preferably crosslinked. When the modified ethylene-vinyl alcohol copolymer (C) is not crosslinked, the layer made of the modified ethylene-vinyl alcohol copolymer (C) is significantly deformed and uniform in the vulcanization process for producing a pneumatic tire. The layer cannot be retained, and the gas barrier property, flex 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 energy rays. Examples of the energy rays include ionizing radiation such as ultraviolet rays, electron beams, X-rays, α rays, and γ rays, and electron beams are preferable.

  With respect to the electron beam irradiation method, a method of introducing a molded body into an electron beam irradiation apparatus after film or sheet processing by extrusion molding and irradiating the electron beam can be mentioned. Although it does not specifically limit regarding the dose of an electron beam, Preferably it exists in the range of 10-60 Mrad. When the electron dose to irradiate is lower than 10 Mrad, it becomes difficult to crosslink. On the other hand, when the electron dose to be irradiated exceeds 60 Mrad, the molded body tends to deteriorate. More preferably, the electron dose range is 20 to 50 Mrad.

  The inner liner for a pneumatic tire according to the present invention is a multilayer structure including at least one layer made of a modified ethylene-vinyl alcohol copolymer (C), in addition to being used as a single-layer molded product for a pneumatic tire. Can be used 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).

  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 ensure adhesion with rubber. For example, if a chlorinated rubber / isocyanate adhesive is used for the adhesive layer, adhesion to the rubber composition used in the tire can be ensured.

  As the layer structure of the multilayer structure, a layer made of the modified ethylene-vinyl alcohol copolymer (C) of the present invention is represented by C, an auxiliary layer (D) made of an elastomer is represented by D1, D2, and an 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, etc. It is not limited to this. D1 and D2 denote auxiliary layers made of different elastomers. Each layer may be a single layer or may be a multilayer according to circumstances. Further, the modified ethylene-vinyl alcohol copolymer (C), the elastomer and the adhesive layer used may be of one type or may be many types depending on the case.

  The method for producing the multilayer structure shown above is not particularly limited. For example, a method in which an elastomer and an adhesive layer are melt-extruded into a molded product (film, sheet, etc.) made of a modified ethylene-vinyl alcohol copolymer (C), and conversely, a modified ethylene-vinyl alcohol copolymer ( C) and a method of melt-extruding the adhesive layer, a method of co-extrusion of the modified ethylene-vinyl alcohol copolymer (C) and the auxiliary layer (D) (and an adhesive layer as required), a modified ethylene-vinyl alcohol From the modified ethylene-vinyl alcohol copolymer (C), a method of laminating a molded product obtained from the copolymer (C) with an elastomer film and sheet using an adhesive layer, and further on a drum during tire molding. Examples include a method of bonding the obtained molded product and the auxiliary layer (D) (and an adhesive layer as necessary).

  In the inner liner for a pneumatic tire of the present invention, the layer made of the modified ethylene-vinyl alcohol copolymer (C) preferably has a thickness of 50 μm or less. When it exceeds 50 μm, the merit of weight reduction becomes smaller than the inner liner using butyl rubber, halogenated butyl rubber or the like currently used. Furthermore, the bending resistance and fatigue resistance of the layer made of the modified ethylene-vinyl alcohol copolymer (C) are reduced, and the bending deformation at the time of rolling of the tire is likely to cause breakage and cracking, and the crack is easy to extend. Therefore, the internal pressure retention after use of the tire may be lower than before use. On the other hand, it is preferable that it is 0.1 micrometer or more from a viewpoint of the gas barrier property of the inner liner for pneumatic tires. From the viewpoint of gas barrier properties, flex resistance, and fatigue resistance, the thickness of the layer made of the modified ethylene-vinyl alcohol copolymer (C) is more preferably 1 to 40 μm, and even more preferably 5 to 30 μm.

  As described above, in the layer made of the modified ethylene-vinyl alcohol copolymer (C), bending resistance and fatigue resistance are improved by use at 50 μm or less, and breakage and cracking occur due to bending deformation during rolling of the tire. It becomes difficult. In addition, even if it breaks, 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 difficult to extend. No breakage or cracks occur. In addition, even if it occurs, the auxiliary layer (D) compensates for the gas barrier properties of the fractures and cracks generated in the layer made of the modified ethylene-vinyl alcohol copolymer (C), so that good internal pressure retention is maintained even after use of the tire. Is possible.

  That is, even a layer made of the modified ethylene-vinyl alcohol copolymer (C) having a thickness of 50 μm or less may cause pinholes, cracks, etc., but in such a case, the film layer is located on the outside of the film layer. By arranging the auxiliary layer (D) made of an elastomer between the ply layers to be cracked, the growth of cracks can be suppressed. Even if cracks occur, the layer made of the modified ethylene-vinyl alcohol copolymer (C) is firmly adhered to the surface of the auxiliary layer (D), so the surface is almost covered with a film. By using an elastomer (butyl rubber, halogenated butyl rubber) having low air permeability for the layer (D), it is possible to suppress 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 of 3.0 × 10 ⁻⁹ cm ³ · cm / cm ² · sec · cmHg or less at 20 ° C. and 65 RH%. It is preferable from the viewpoint of 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 of the present invention include butyl rubber and diene elastomer. Suitable examples of the diene elastomer include natural rubber and butadiene rubber. From the viewpoint of gas barrier properties, butyl rubber is preferably used as the elastomer, and halogenated butyl rubber is more preferably used. Further, from the viewpoint of suppressing the extension of the crack after the auxiliary layer (D) made of the elastomer has cracked, it is preferable to use a composition made of butyl rubber and a diene elastomer as the elastomer. By using such a composition as an elastomer, even when a minute crack is generated in the auxiliary layer (D) made of the elastomer, the internal pressure retention of the pneumatic tire after traveling can be kept high.

  Moreover, a thermoplastic urethane-type elastomer is also illustrated as a suitable thing as an elastomer laminated | stacked as an auxiliary | assistant layer (D) of the inner liner for pneumatic tires of this invention. From the viewpoint of thinning the auxiliary layer (D), generation of cracks, and suppression of extension, it is preferable to use a thermoplastic urethane-based elastomer.

  As an elastomer laminated as an auxiliary layer (D) of the inner liner for a pneumatic tire of the present invention, an auxiliary layer (D) made of a thermoplastic urethane elastomer and an auxiliary layer (D) made of a composition consisting of butyl rubber and a diene elastomer ) Is more preferably multilayered.

  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 elastomer is less than 50 μm, the inner liner's bending resistance and fatigue resistance are reduced, and bending and deformation at the time of tire rolling tend to cause breakage and cracking. Since cracks tend to extend, there is a risk that the internal pressure retention after use of the tire will be significantly reduced compared to before use. Furthermore, it is difficult to manufacture the tire to make the total thickness of the auxiliary rubber layers below the belt less than 50 μm.

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

  In addition, the above-described breakage, cracks, and cracks are generated mainly on the side portions that are largely deformed by bending. Therefore, by increasing the thickness of the auxiliary layer only at the side portion, it is possible to achieve both internal pressure retention after running and reduction in tire weight.

  In the inner liner for a pneumatic tire of the present invention, the 300% modulus of the auxiliary layer (D) made of an elastomer is preferably 10 MPa or less in order to suppress generation and growth of cracks. When the 300% modulus exceeds 10 MPa, the bending resistance and fatigue resistance of the inner liner deteriorate. The 300% modulus of the auxiliary layer (D) made of an elastomer is more preferably 8 MPa or less, and further 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-described 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 of the present invention, the auxiliary layer (D) made of an elastomer has a portion of the auxiliary layer (D) corresponding to a radial width of at least 30 mm in the region from each belt end to the bead portion. The thickness of the auxiliary layer (D) corresponding to the lower part of the belt of the layer (D) is preferably 0.2 mm or more.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all 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 the spectrum obtained by ¹ H-NMR (nuclear magnetic resonance) measurement (using “JNM-GX-500 type” manufactured by JEOL Ltd.) using deuterated dimethyl sulfoxide as a solvent.

(2) Melt flow rate of ethylene-vinyl alcohol copolymer (A):
The ethylene-vinyl alcohol copolymer (A) as a sample was filled in a cylinder with an inner diameter of 9.55 mm and a length of 162 mm of a melt indexer L244 (manufactured by Takara Kogyo Co., Ltd.), and melted at 190 ° C. The load was evenly applied using a 2160 g, 9.48 mm diameter plunger. The amount of resin extruded per unit time (g / 10 minutes) from an orifice with a diameter of 2.1 mm provided in the center of the cylinder was measured, and this was used as the 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 at a plurality of temperatures above the melting point under a load of 2160 g, and the horizontal axis indicates the reciprocal absolute temperature in a semi-logarithmic graph. The logarithm of MFR is plotted on the vertical axis and expressed as a value extrapolated to 190 ° C.

<Synthesis of modified ethylene-vinyl alcohol copolymer (C)>
Synthesis example 1
2 wt% ethylene-vinyl alcohol copolymer (A) (MFR: 5.5 g / 10 min (190 ° C., 2160 g load)) having an ethylene content of 44 mol% and a saponification degree of 99.9% in a pressurized reaction vessel And 8 parts by weight of N-methyl-2-pyrrolidone were charged and stirred at 120 ° C. for 2 hours to completely dissolve the ethylene-vinyl alcohol copolymer (A). To this was added 0.4 part by weight of glycidol as an epoxy compound (B), and then heated at 160 ° C. for 4 hours. After the heating, it 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). . Further, the modified ethylene-vinyl alcohol copolymer (C) thus obtained was fined to a particle size of about 2 mm with a pulverizer, and then sufficiently washed with a large amount of distilled water again. The washed particles were vacuum-dried at room temperature for 8 hours, and then melted at 200 ° C. using a twin-screw extruder and pelletized.

Synthesis example 2
2 wt% ethylene-vinyl alcohol copolymer (A) (MFR: 5.5 g / 10 min (190 ° C., 2160 g load)) having an ethylene content of 44 mol% and a saponification degree of 99.9% in a pressurized reaction vessel And 8 parts by weight of N-methyl-2-pyrrolidone were charged and stirred at 120 ° C. for 2 hours to completely dissolve the ethylene-vinyl alcohol copolymer (A). To this was added 0.3 part by weight of glycidol as an epoxy compound (B), followed by heating at 160 ° C. for 4 hours. After the heating, it 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). . Further, the modified ethylene-vinyl alcohol copolymer (C) thus obtained was fined to a particle size of about 2 mm with a pulverizer, and then sufficiently washed with a large amount of distilled water again. The washed particles were vacuum-dried at room temperature for 8 hours, and then melted at 200 ° C. using a twin-screw extruder and pelletized.

Synthesis example 3
2 wt% ethylene-vinyl alcohol copolymer (A) (MFR: 5.5 g / 10 min (190 ° C., 2160 g load)) having an ethylene content of 44 mol% and a saponification degree of 99.9% in a pressurized reaction vessel And 8 parts by weight of N-methyl-2-pyrrolidone were charged and stirred at 120 ° C. for 2 hours to completely dissolve the ethylene-vinyl alcohol copolymer (A). To this was added 0.4 parts by weight of epoxypropane as an epoxy compound (B), and then heated at 160 ° C. for 4 hours. After the heating, it 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). It was. Further, the modified ethylene-vinyl alcohol copolymer (C) thus obtained was fined to a particle size of about 2 mm with a pulverizer, and then sufficiently washed with a large amount of distilled water again. The washed particles were vacuum-dried at room temperature for 8 hours, and then melted at 200 ° C. using a twin-screw extruder and pelletized.

<Preparation of layer made of modified ethylene-vinyl alcohol copolymer (C)>
Film 1
Using pellets of the modified ethylene-vinyl alcohol copolymer (C) obtained in Synthesis Example 1, a 40 mmφ extruder (PLABOR GT-40-A manufactured by Plastics Engineering Laboratory) and a T-die film forming machine were used. 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-row full flight type, surface nitrided steel Screw rotation speed: 40rpm
Die: 550 mm wide coat hanger die Lip gap: 0.3 mm
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 the film 1 except that the pellets of the modified ethylene-vinyl alcohol copolymer (C) obtained in Synthesis Example 2 were used.

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

Film 4
As a gas barrier material, an ethylene-vinyl alcohol copolymer (A) having an unmodified ethylene content of 44 mol%, a saponification degree of 99.9%, and MFR = 5.5 g / 10 min (under 190 ° C. and 2160 g load) is used. A single-layer film having a thickness of 20 μm was obtained in the same manner as the film 1 except that it 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 (Kuraray Co., Ltd. Kuramylon 3190) as an elastomer, using a two-kind three-layer coextrusion device, under the following coextrusion molding conditions: A three-layer film (thermoplastic polyurethane layer / modified EVOH (C) layer / thermoplastic polyurethane layer) was produced. The thickness of each layer is 20 μm for both the modified EVOH (C) layer and the thermoplastic polyurethane layer.

The coextrusion 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 (manufactured by Osaka Seiki Co., Ltd.)
Modified EVOH (C):
20mmφ Extruder Lab Machine ME Type CO-EXT (Toyo Seiki Co., Ltd.)
T-die specification:
500mm width for 2 types and 3 layers (Plastic Engineering Laboratory Co., Ltd.)
Cooling roll temperature: 50 ° C
Pickup speed: 4m / min

<Evaluation of layer made of modified ethylene-vinyl alcohol copolymer (C)>
According to the method shown below, the produced films 1 to 5 were evaluated for oxygen permeation amount and bending resistance.

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

Evaluation of bending resistance:
50 sheets of the above-prepared films cut to 21 cm × 30 cm were prepared. Each film was conditioned at 20 ° C.-65% RH for 5 days, and then Rigaku Kogyo Co., Ltd. according to ASTM F 392-74. Using a gelboflex tester manufactured, the number of flexing times is 50, 75, 100, 125, 150, 175, 200, 225, 250, 300, 400, 500, 600, After bending 700 times, 800 times, 1000 times and 1500 times, the number of pinholes was measured. In each bending number, the measurement was performed 5 times, and the average value was defined as the number of pinholes. Taking the number of bends (P) on the horizontal axis and the number of pinholes (N) on the vertical axis, plotting the above measurement results, and obtaining the number of bends (Np1) when the number of pinholes is one by extrapolation. Two digits were used. However, for a film in which no pinhole was observed after 1500 bending, the number of bending was increased every 500 times, and the number of bending where a pinhole was observed was 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, Np1 was 500 times, indicating 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-described method, Np1 was 100 times, indicating 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 excellent gas barrier properties were exhibited. Moreover, when the bending resistance of the film 3 was evaluated according to the above-mentioned method, Np1 was 500 times, indicating 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 an excellent gas barrier property was exhibited. Moreover, 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-described method, Np1 was 5000 times, indicating extremely excellent bending resistance.

<Composition of rubber composition and production of rubber inner liner and auxiliary layer>
A rubber composition was prepared according to the following blending amount, vulcanized at 145 ° C. for 40 minutes, and then 300% modulus was measured by a method according to JIS K6301. Moreover, the oxygen transmission rate was measured by the same method as the measurement of the oxygen transmission rate 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 (Nihon Sun Oil Co., Ltd.): 7
Stearic acid (Asahi Denka Kogyo Co., Ltd.): 1
NOCCELER DM (Ouchi Shinsei Chemical Co., Ltd.): 1.3
Zinc oxide (manufactured by Hakusui Chemical Co., Ltd.): 3
Sulfur (manufactured by Karuizawa Refinery): 0.5
300% modulus: 6.5Mpa
Oxygen permeation: 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 (Nihon Sun Oil Co., Ltd.): 7
Stearic acid (Asahi Denka Kogyo Co., Ltd.): 1
NOCCELER DM (Ouchi Shinsei Chemical Co., Ltd.): 1.3
Zinc oxide (manufactured by Hakusui Chemical Co., Ltd.): 3
Sulfur (manufactured by Karuizawa Refinery): 0.5
300% modulus: 6.0Mpa
Oxygen transmission rate: 3.0 × 10 ^-10 cm ³ · cm / cm ² · sec · cmHg

<Production and Evaluation of Evaluation Tire>
Example 1
Using an electron beam irradiation device “Curetron EBC200-100 for production” manufactured by Nissin High Voltage Co., Ltd., film 1 was irradiated with an electron beam under the conditions of an acceleration voltage of 200 kV and an irradiation energy of 30 Mrad, and subjected to a crosslinking treatment. It used as a layer which consists of ethylene-vinyl alcohol copolymer (C). By applying Metallock R30M manufactured by Toyo Chemical Laboratories as an adhesive layer on one side of the obtained crosslinked film and pasting it with an auxiliary layer (D) having a thickness of 500 μm using rubber composition 1, a modified ethylene-vinyl alcohol copolymer is used. An inner liner composed of 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. A schematic cross-sectional view of the produced tire is shown in FIG. In the figure, 1 is a layer made of a modified ethylene-vinyl alcohol copolymer (C), and 2 is an auxiliary layer (D) made of an elastomer.

About the tire produced above, it was pressed with a load of 6 kN onto a drum having a rotational speed corresponding to a speed of 80 km / h at an air pressure of 140 kPa, and traveled 10,000 km. Using a non-running tire and a tire running under the above conditions, the internal pressure retention was evaluated under the following conditions. The internal pressure retention was evaluated by mounting the test tire on a 6JJ × 15 rim, filling the internal pressure with 240 kPa, and measuring the internal pressure after 3 months, and indexed by the following formula.
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 a normal rubber inner liner) described in Comparative Example 1 below.
The appearance of the inner liner of the tire after running the drum was visually observed to evaluate the presence or absence of cracks. The evaluation results are shown in Table 1.

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. The liner appearance was evaluated. The evaluation results are shown in Table 1.

Example 3
An inner liner and a pneumatic tire for a passenger car were produced in the same manner as in Example 1 except that the film 2 was used instead of the film 1, and the inner pressure retention and the appearance of the inner liner of the tire after running the drum were evaluated. It was. The evaluation results are shown in Table 1.

Example 4
An inner liner and a pneumatic tire for a passenger car are produced in the same manner as in Example 1 except that the film 3 is used instead of the film 1 and the inner pressure retention and the appearance of the inner liner of the tire after running the drum are evaluated. It was. The evaluation results are shown in Table 1.

Example 5
An inner liner and a pneumatic tire for a passenger car are produced in the same manner as in Example 1 except that the film 5 is used instead of the film 1, and the inner liner is maintained and the inner liner appearance of the tire after running the drum is evaluated. It was. The evaluation results are shown in Table 1.

Example 6
Using an electron beam irradiation device “Curetron EBC200-100 for production” manufactured by Nissin High Voltage Co., Ltd., film 1 was irradiated with an electron beam under the conditions of an acceleration voltage of 200 kV and an irradiation energy of 30 Mrad, and subjected to a crosslinking treatment. It used as a layer which consists of ethylene-vinyl alcohol copolymer (C). After applying Metallock R30M manufactured by Toyo Chemical Laboratory as an adhesive layer on one side of the resulting cross-linked film, the auxiliary layer (D) made of a rubber composition is not laminated and used as it is as an inner liner. A pneumatic tire for industrial use (195 / 65R15) was produced. Using the obtained tire, the internal pressure retention and the appearance of the inner liner of the tire after running the drum were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Comparative Example 1
For passenger cars having a 1500 μm thick inner liner using the rubber composition 2 used as a normal rubber inner liner and not having a layer made of a modified ethylene-vinyl alcohol copolymer (C) in the same manner as above. A pneumatic tire (195 / 65R15) was produced. Further, using the obtained tire, in the same manner as in Example 1, the internal pressure retention and the appearance of the inner liner of the tire after running the drum were evaluated. The evaluation results are shown in Table 1.

Comparative Example 2
The film 4 was irradiated with an electron beam under the conditions of an acceleration voltage of 200 kV and an irradiation energy of 30 Mrad, subjected to crosslinking treatment, and used as a layer made of an unmodified ethylene-vinyl alcohol copolymer (A). After applying Metallock R30M manufactured by Toyo Chemical Laboratory as an adhesive layer on one side of the resulting crosslinked film, it is used as an inner liner as it is 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 appearance of the inner liner of the tire after running the drum were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

  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 is air using the normal rubber inner liner described in Comparative Example 1. It can be seen that the inner pressure retention is excellent not only before traveling but also after traveling 10,000 km drum, as compared with the entering tire. In addition, in the evaluation of the appearance of the inner liner of the tire after running the drum, it can be seen that there is no crack and that 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, the inner pressure retention before running is good, but the inner tire is driven by drum running. It can be seen that the liner cracks and the internal pressure retention is extremely reduced.

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

Explanation of symbols

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

Claims (18)

After reacting 1 to 50 parts by weight of a monovalent epoxy compound (B) with respect to 100 parts by weight of an ethylene-vinyl alcohol copolymer (A) having an ethylene content of 25 to 50 mol% , an unreacted epoxy compound An inner liner for a pneumatic tire comprising a modified ethylene-vinyl alcohol copolymer (C) obtained by removing (B) . The inner liner for a pneumatic tire according to claim 1, wherein the epoxy compound (B) is reacted with the ethylene-vinyl alcohol copolymer (A) in the presence of an acid catalyst or an alkali catalyst. The inner liner for a pneumatic tire according to claim 2, wherein the catalyst amount is 0.0001 to 10 parts by weight with respect to 100 parts by weight of the ethylene-vinyl alcohol copolymer (A). The inner liner for a pneumatic tire according to any one of claims 1 to 3, wherein the epoxy compound (B) is glycidol or epoxypropane. The inner liner for a pneumatic tire according to any one of claims 1 to 4, wherein the saponification degree of the ethylene-vinyl alcohol copolymer (A) is 90% or more. Modified ethylene - vinyl alcohol copolymer (C) 20 ° C. layers of, claims 1 to oxygen permeability at 65 RH% is ^{3.0 × 10 -12 cm 3 · cm} / cm 2 · sec · cmHg or less The inner liner for a pneumatic tire according to any one of 5 . The inner liner for a pneumatic tire according to any one of claims 1 to 6, wherein the modified ethylene-vinyl alcohol copolymer (C) is crosslinked. The inner liner for a pneumatic tire according to any one of claims 1 to 7, wherein the layer made of the modified ethylene-vinyl alcohol copolymer (C) has a thickness of 50 µm or less. The inner liner for a pneumatic tire according to any one of claims 1 to 8, 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 9 , wherein the layer made of the modified ethylene-vinyl alcohol copolymer (C) is bonded to the auxiliary layer (D) made of an elastomer through at least one adhesive layer. Inner liner. The pneumatic layer according to claim 9 or 10 , wherein the auxiliary layer (D) made of an elastomer has an oxygen permeation amount of 3.0 x 10 ^-9 cm ³ · cm ² · sec · cmHg or less at 20 ° C and 65 RH%. Inner liner for tires. The inner liner for a pneumatic tire according to any one of claims 9 to 11 , 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 any one of claims 9 to 11, wherein a diene elastomer is used for the auxiliary layer (D) made of the elastomer. The inner liner for a pneumatic tire according to any one of claims 9 to 11, wherein a thermoplastic urethane elastomer is used for the auxiliary layer (D) made of an elastomer. The inner liner for a pneumatic tire according to any one of claims 9 to 14, wherein in the auxiliary layer (D) made of an elastomer, different auxiliary layers are bonded together through at least one adhesive layer. The inner liner for a pneumatic tire according to any one of claims 9 to 15, wherein the total thickness of the auxiliary layer (D) made of an elastomer is 50 to 1500 µm. The pneumatic tire provided with the inner liner for pneumatic tires in any one of Claims 1-16 . The auxiliary layer (D) made of an elastomer has a portion of the auxiliary layer (D) corresponding to a radial width of at least 30 mm in the region from each belt end to the bead portion. The pneumatic tire according to claim 17, wherein the pneumatic tire is 0.2 mm or more thicker than a corresponding portion of the auxiliary layer (D).

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