Poorly air-permeable rubber laminate composed of poorly air-permeable resin and rubber composition, and method for production thereof

#The present invention relates to a low air permeable rubber laminate and a method for producing the same, more specifically relates to a low air permeable rubber laminate having a superior air barrier property and durability comprised of a layer of a rubber composition on which a low air permeable resin layer having an average thickness greater than 0.05 μm and less than 5 μm is laminated, a method for producing the same and a product obtained therefrom.

#It has been known in the past to cover a layer of a rubber composition with a layer (or film) of a thermoplastic (or thermosetting) resin to obtain a laminate having functions derived from that resin. As an example, various attempts have been made to coat a rubber composition with a film having a low air permeability and to use this as an inner liner layer of a pneumatic tire. Recently, for example, Japanese Patent Publication (A) No. 2002-79804 proposes the use of an electron beam cross-linked polyvinyl alcohol, ethylene-vinyl alcohol copolymer, etc. as a gas barrier layer, which is then laminated on an elastomer auxiliary layer. The resultant laminate is used as the inner liner layer of a pneumatic tire. The thickness of this gas barrier layer is defined as being 30 μm or less, but the examples only describe the case of a thickness of EVOH of 20 μm. EVOH is an extremely hard resin having a tensile modulus of elasticity of 2 to 3 GPa, and therefore, in the case of a thickness of 20 μm, if stretched, necking deformation occurs and, due to stress concentration, easy breakage occurs. For this reason, due to repeated dynamic strain, cracks easily occur, peeling occurs from cracks, and other problems arise. Further, Japanese Patent. Publication (A) No. 20.04-255937 describes a support, and a pneumatic run flat tire, using a single layer of an electron beam cross-linked polyvinyl alcohol or ethylene-vinyl alcohol copolymer having a thickness of 5 to 100 μm, as a gas barrier layer.

#Note that, as a method of coating a thin film of a low air permeable rein (A) on a rubber composition layer, there is the method of coating a solution or emulsion of the resin (A) on the rubber composition layer. This method has no problems when coating a relatively thick film of such as, for example, 10 μm or more, but it is difficult to control the uniformity of a thin film having a thickness of, for example, thinner than 5 μm, more particularly 3 μm or less. Further, there is the problem that the number of steps such as coating a primer for imparting bondability with the rubber composition layer, drying of the solvent, etc. is, increased. Further, when, a rubber composition requiring a vulcanization step is coated, in, order to give the separability from the bladder rubber, it is necessary to coat the laminate surface with a release agent, followed by vulcanizing the same. At this time, the coating layer is liable to break. Therefore, there is the problem that it is not possible to impart a sufficient gas barrier property.

#The singular form a (“a”, “an”, and “the”) used in the Description and attached Claims should be understood as including the plural form except when otherwise clear from the context.

#The inventors engaged in research to solve the above problems and, as a result, found that, by laminating and vulcanizing a two- or three-layer coextruded laminate (D) of a thermoplastic resin composition (B)/low air permeability resin (A)/optional adhesive (C) with a layer of a rubber composition (E), then peeling off the thermoplastic resin composition (B) layer, it is possible to uniformly coat a thin film of the low air permeable resin (A) layer having a thickness of less than 5 μm on the layer of the rubber composition (E), found that this low air permeable rubber laminate (F) has superior properties (e.g., gas barrier, property and dynamic properties), whereby the present invention has been completed.

#If the thickness of the low permeable resin (A) layer having an air permeation coefficient of 1.0×10−12 cc·cm/cm2·sec·cmHg or less (determined according JIS K7126 (test gas: air; (N2:O2=8:2), 30° C.), the same hereinbelow) is less than 5 μm, preferably 1 to 3 μm, it is possible to remarkably improve the gas barrier property such as oxygen, ozone, without sacrificing the dynamic properties (e.g., elongation at break, tensile and compressive set, etc.) of the rubber. For this reason, since the oxidation degradation of the rubber is remarkably decreased, the invention can be suitably applied to the side rubber etc. of tires, in addition to the inner liner. Further, a thin film of a low air permeable resin having a thickness of less than 5 μm has flexing fatigue resistance, and, therefore, the low permeable rubber laminate (E) can be suitably used, even as one layer of, for example, an inner layer, intermediate layer and outer layer of a hose, where flexing fatigue resistance and gas barrier property are essential.