JPH0349932B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a hard rubber composition, particularly a hard rubber composition suitable for bead apex or clinch apex, and more specifically, it relates to a hard rubber composition suitable for bead apex or clinch apex. The present invention relates to a hard rubber composition containing a thermosetting resin and a curing agent. Generally, in radial tires, the carcass ply cords are arranged parallel to each other at almost right angles to the tire equatorial plane, and both ends are folded back around the bead wire, and the folded ends of the ply and the inner side surrounded by the carcass are A bead apex is disposed extending in the direction of the wall, and a clinch apex is disposed in an area adjacent to the rim flange outside the fold of the ply. Tires with a radial structure like this have a step in stiffness at the folded end of the ply, which is prone to damage, and because it is a radial structure, it inherently has poor lateral stiffness. Bead apexes or clinch apex having particularly high hardness (or dynamic elastic modulus) have been proposed. (Unexamined Japanese Patent Publication 1973)
−4059). Therefore, in order to create a vulcanized rubber with high hardness (dynamic modulus), it is necessary to increase the amount of thermosetting resin or carbon, or to increase the crosslinking density by using large amounts of sulfur or vulcanization accelerator. It is being done. However, when the former rubber is kneaded in a Banbury mixer, it generates a lot of heat, which causes the rubber to scorch, and the composition itself has a high viscosity, which causes an excessive load during kneading and extrusion. In addition, the latter has the problem that sulfur blooms during processing of the composition, impairing the tackiness of the rubber and deteriorating the physical properties of the vulcanized rubber. The present invention aims to solve these problems, and proposes a rubber composition that has extremely high hardness without problems such as workability. The present invention provides at least one diene rubber 100
This is a hard rubber composition characterized by containing 1 to 30 parts by weight of aromatic polyamide pulp. The aromatic polyamide pulp used in the present invention can be manufactured from aromatic polyamide fibers or can be manufactured at the stage of synthesizing the aromatic polyamide polymer, but this pulp usually has a diameter of 0.1 to
It has fibrils with a diameter of 1μ and a length of 3 to 1000μ. Since this aromatic polyamide pulp has fine branches, it can be mixed with rubber at the molecular level by kneading it into rubber, achieving more effective reinforcement than when mixing fiber cords or short fibers. . If the diameter is less than 0.1μ or the length is less than 3μ, it will be difficult to incorporate into rubber, and it will not be possible to secure the necessary rigidity when used in bead apex. Furthermore, if the diameter exceeds 1μ or the length exceeds 1000μ, poor dispersion in the rubber will occur. It is necessary to blend aromatic polyamide pulp in an amount of 1 to 30 parts by weight, preferably 5 to 20 parts by weight; if it is less than 1 part by weight, the reinforcing effect will not be sufficient, and if it exceeds 30 parts by weight, it will be difficult to knead and extrude. Workability deteriorates. Next, in the present invention, a thermosetting resin and a curing agent can be blended. Here, thermosetting resins are phenolic resins, cresol resins, or modified resins thereof, such as cashew varnish modified resins, oil-modified resins modified with oils such as linoleic acid, linolenic acid, and oleic acid, and resins modified with alkylbenzenes such as xylene. Resins that harden by heat, such as alkylbenzene-modified phenols, epoxy-modified resins, aniline-modified resins, and melamine-modified resins, can be used alone or in combination of two or more in any proportion. This thermosetting resin is blended in an amount of 2 to 40 parts by weight, preferably 10 to 20 parts by weight, per 100 parts by weight of the rubber component. If it is less than 2 parts by weight, the reinforcing effect will not be sufficient, and if it exceeds 40 parts by weight, the kneading workability will be significantly impaired. Next, the curing agent used in the present invention is one that cures the thermosetting resin, and is a compound that donates methylene groups when vulcanized at 40 to 200°C, especially under normal vulcanization conditions, so-called methylene donor. It is the body. Examples include hexamethylenetetramine, polyvalent methylolmelamine derivatives, oxazolidine, bis(1,3 oxazolidine), bis(1,3 oxazolidine) derivatives, and the like. The amount of this curing agent needs to be adjusted depending on the amount of thermosetting resin, but it is blended in an amount of 0.5 to 7 parts by weight per 100 parts by weight of the rubber component. Note that by using a thermosetting resin and a curing agent together with the aromatic polyamide pulp, the hardness (dynamic modulus) of the vulcanized rubber can be further increased. The diene rubber used in the present invention is natural rubber, cis 1,4 polyisoprene rubber, cis 1,4
Polybutadiene rubber, styrene-butadiene copolymer rubber, etc. can be used alone or in a blend of two or more. Furthermore, it goes without saying that the composition of the present invention may appropriately contain commonly used compounding agents such as fillers such as carbon and silica, as well as softeners, anti-aging agents, vulcanization accelerators, plasticizers, and the like. However, by vulcanizing the rubber composition according to the present invention by a conventional method, properties such as kneading workability and extrusion processability can be further improved while maintaining properties such as flex crack resistance, low heat build-up, and high hardness. becomes possible. Example 1 Various rubber compositions for bead apex shown in Table 1 were vulcanized at 150°C for 30 minutes, and their modulus, hardness, complex modulus, etc. were measured, and the results are shown in Table 2. It is recognized that all the properties are improved by blending the aromatic polyamide pulp, and in particular, they are further improved by the combined use of the aromatic polyamide pulp and the phenolic resin (Example 5).

【table】

【table】

Claims (1)

[Scope of Claims] 1. A bead characterized in that 1 to 30 parts by weight of aromatic polyamide pulp fibrils having a diameter of 0.1 to 1 μm and a length of 3 to 1000 μm are blended with 100 parts by weight of at least one type of diene rubber. Hard rubber composition for Apex. 2 100 parts by weight of at least one type of diene rubber, 1 to 30 parts by weight of aromatic polyamide pulp fibrils with a diameter of 0.1 to 1μ and a length of 3 to 1000μ, 2 to 40 parts by weight of a thermosetting resin, and a curing agent. A hard rubber composition for bead apex, characterized in that it contains 1 to 20 parts by weight of. 3. The hard rubber composition for bead apex according to claim 2, wherein the thermosetting resin is a phenolic resin, a cresol resin, or a modified resin thereof. 4. The hard rubber composition for bead apex according to claim 2, wherein the curing agent is derived from oxazolidine. 5. The hard rubber composition for bead apex according to claim 2, wherein the curing agent is hexamethylenetetraamine.