Low specific gravity rubber composition floating on water

Abstract

To provide a rubber composition of low density floatable on water (specific gravity less than 1.00), the rubber composition having tensile strength at room temperature and at elevated temperature sufficient for practical application.SOLUTION: A rubber composition includes: (1) 100 pts.mass of a base agent comprising non-oil-extended EPDM, oil-extended EPDM, carbon black, and process oil; and (2) compounding ingredients including zinc oxide, stearic acid, antioxidant, polyethylene glycol, sulfur, and vulcanization accelerator (the content of each compounding ingredient being 0.2 to 2 pts.mass).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a low-specific-gravity rubber composition that floats on water, and more specifically to a low-specific-gravity rubber composition that uses "oil-extended ethylene-propylene-non-conjugated diene copolymer rubber" (hereinafter referred to as EPDM) as a base polymer and is suitable as a material for exterior parts of wire harnesses for automobiles (particularly for electric automobiles). [Background technology]

[0002] Grommets used as exterior components of automotive wiring harnesses have traditionally been made from rubber compositions containing EPDM as the base polymer, to which 30 to 100 parts by mass of carbon black, a white filler, and process oil have been added per 100 parts by mass of the base polymer. Such compositions have a specific gravity of approximately 1.15 or higher, and sink in water. In recent years, there has been a demand for lighter automobiles in consideration of environmental measures, etc., and progress has been made in reducing the weight of the materials used in automotive wire harnesses. In addition, there is also a demand for quieter automobiles to improve ride comfort, and as a result, the shapes of grommets are becoming more complex in order to improve sound insulation.

[0003] Patent Document 1 discloses a low-specific-gravity rubber composition containing 100 parts by mass of EPDM, 10 to 70 parts by mass of ethylene-vinyl acetate copolymer, low-density polyethylene or amorphous ethylene-α-olefin copolymer, 10 to 50 parts by mass of carbon black, and 10 to 50 parts by mass of process oil. However, this low-specific-gravity rubber composition has the drawback of having an excessively large compression set. Patent Document 2 discloses a rubber composition containing 100 parts by mass of EPDM (copolymer rubber mass equivalent) and 0.1 to 10 parts by mass (per compounding agent) of at least one compounding agent selected from the group consisting of ethylene-vinyl acetate copolymer, low-density polyethylene, carbon black, and process oil, and having a specific gravity of less than 1. However, the composition has the drawback of having low tensile strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 57-177039 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-319465 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber composition that has a low specific gravity so that it floats on water (specific gravity less than 1.00) and has tensile strength at room temperature and high temperature that is sufficient for practical use. [Means for solving the problem]

[0006] Thus, the problems are solved by the rubber composition according to the present invention, which contains (1) 100 parts by mass of a base agent containing non-oil-extended ethylene-propylene-non-conjugated diene copolymer rubber (EPDM), oil-extended EPDM, carbon black, and process oil, and (2) 0.3 to 3.8 parts by mass (per compounding agent) of a compounding agent containing zinc oxide, stearic acid, an antioxidant, polyethylene glycol, sulfur, and a vulcanization accelerator. In this case, the blending ratio of the base agent is preferably 65-75 parts by mass of non-oil-extended EPDM, 50-55 parts by mass of oil-extended EPDM, 40-50 parts by mass of carbon black, and 55-65 parts by mass of process oil. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a rubber composition which has a low specific gravity, floats on water, and has tensile strength at room temperature and at high temperature sufficient for practical use. DETAILED DESCRIPTION OF THE INVENTION

[0008] Next, embodiments of the present invention will be described with reference to tables. However, the technical scope of the present invention is not limited to these embodiments, and the invention can be embodied in various forms without changing the gist of the invention. EPDM has excellent heat resistance, weather resistance, and ozone resistance, and its specific gravity of approximately 0.87 is the lowest among synthetic rubbers. Oil-extended EPDM is a composition in which process oil is blended with EPDM. The amount of process oil contained in oil-extended EPDM is 13 to 50 mass% of the EPDM, but it can also contain less or more process oil. Commercially available oil-extended EPDMs include EP96 (oil-extended amount 50), EP501EC (oil-extended amount 40), EP98 (oil-extended amount 75), and EP104E (oil-extended amount 30), manufactured by ENEOS Materials Corporation.

[0009] Oil-extended EPDM has a relatively high Mooney viscosity and also high green strength. By combining two or more different grades of oil-extended EPDM, it is possible to achieve a molecular weight distribution that meets the processability, physical properties, and other characteristics required of the rubber composition.

[0010] The rubber composition of the present invention contains (1) 100 parts by mass of a base agent containing un-oil-extended EPDM, oil-extended EPDM, carbon black, and process oil, and (2) 0.2 to 2 parts by mass (per compounding agent) of compounding agents containing zinc oxide, stearic acid, antioxidant, polyethylene glycol, sulfur, vulcanization accelerator, and processing aid. The zinc oxide, stearic acid, antioxidant, polyethylene glycol, sulfur, vulcanization accelerator, and processing aid are all known compounding agents. The amount of each compounding agent is 0.2 to 2 parts by mass per 100 parts by mass of the base agent. If the amount of each compounding agent is less than 0.2 parts by mass, the effect of adding each compounding agent will not be exerted, which is not preferable.

[0011] In addition to the above compounding agents, other compounding agents that are commonly used in rubber products can also be added to the rubber composition of the present invention. However, it is preferable to use compounding agents with a high specific gravity, such as white fillers (calcium carbonate, etc.), in as small an amount as possible. The rubber composition of the present invention can be produced by mixing and kneading the above components using a conventional rubber kneading machine (such as a Banbury mixer, kneader, or open roll) at a temperature ranging from room temperature to 200° C. The resulting rubber composition can be molded into a desired shape by a conventional molding method (such as molding, injection molding, or extrusion molding).

[0012] <Example> Next, the present invention will be described in more detail with reference to examples and comparative examples. Using a Banbury mixer, the components shown in Table 1 (Comparative Examples 1 to 4) and Table 2 (Examples 1 and 2) were kneaded in the proportions (parts by mass) shown in the tables, and then sulfur and a vulcanization accelerator were added using a two-roll kneader. Note that for Comparative Examples 1 to 4, the same components as those used in "Examples 1 to 3 and Comparative Example 1" of Patent Document 2 were used. The resulting rubber composition was molded into a predetermined shape suitable for physical property testing, and press-vulcanized at 160°C for 20 minutes to prepare a test sample.

[0013] [Table 1]

[0014] In Table 1, (Note 1) refers to Keltan 708x15 (process oil content 13% by mass) manufactured by Idemitsu DSM Co., Ltd., (Note 2) Keltan 512x50 (process oil content 25% by mass) manufactured by Idemitsu DSM Co., Ltd., (Note 3) Keltan 509x100 (process oil content 50% by mass) manufactured by Idemitsu DSM Co., Ltd., (Note 4) Sumikathene C-215 manufactured by Sumitomo Chemical Co., Ltd., (Note 5) Seast SO manufactured by Tokai Carbon Co., Ltd., (Note 6) Diana PW-380 manufactured by Idemitsu Kosan Co., Ltd., (Note 7) polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (manufactured by Kawaguchi Chemical Co., Ltd.), (Note 8) PEG #4000 manufactured by Wako Pure Chemical Industries, Ltd., and (Note 9) a mixture containing thiuram dithiocarbamate (ACCELEM-33 manufactured by Kawaguchi Chemical Co., Ltd.).

[0015] [Table 2]

[0016] For each test sample, room temperature physical properties (tensile strength, elongation at break) and high temperature (170°C) physical properties (tensile strength, elongation at break) were measured in accordance with JIS K6301. The specific gravity, hardness, and compression set of the vulcanized rubber composition were also measured. The evaluation criteria were: a specific gravity of less than 1.0 (floating on water) was considered acceptable; a room temperature tensile strength of 15 MPa or more; and a high temperature tensile strength of 10 MPa or more. The results are shown in Table 3.

[0017] [Table 3]

[0018] As shown in Table 3, Comparative Examples 1 to 3 had specific gravities of less than 1.0, but had weak tensile strength at room temperature and high temperature, and were considered to be of poor practical use. In contrast, Examples 1 and 2 both had specific gravities of less than 1.0, floated on water, and had tensile strength at room temperature and high temperature that was sufficient for practical use. Although not shown in detail, when the blending ratios (parts by mass) of the base agent were appropriately changed within the range of 65-75 for non-oil-extended EPDM, 50-55 for oil-extended EPDM, 40-50 for carbon black, and 55-65 for process oil, and when the blending ratios of zinc oxide to 2.7-3.3, stearic acid to 0.9-1.1, antioxidant to 1.8-2.2, polyethylene glycol to 0.9-1.1, sulfur to 0.37-0.44, vulcanization accelerator to 2.5-3.3, and processing aid to 3.0-3.8 were appropriately changed, the same effects as in Examples 1 and 2 were observed. As described above, according to this embodiment, a rubber composition was provided which has a low specific gravity, floats on water (specific gravity less than 1.00), and has tensile strength at room temperature and high temperature sufficient for practical use.

Claims

1. A rubber composition comprising: (1) 100 parts by mass of a base agent containing non-oil-extended ethylene-propylene-non-conjugated diene copolymer rubber (non-oil-extended EPDM), oil-extended ethylene-propylene-non-conjugated diene copolymer rubber (oil-extended EPDM), carbon black, and process oil; and (2) 0.3 to 3.8 parts by mass (per compounding agent) of a compounding agent containing zinc oxide, stearic acid, an antioxidant, polyethylene glycol, sulfur, and a vulcanization accelerator.

2. 2. The rubber composition according to claim 1, wherein the blending ratio of the base agent is 65 to 75 parts by mass of non-oil-extended EPDM, 50 to 55 parts by mass of oil-extended EPDM, 40 to 50 parts by mass of carbon black, and 55 to 65 parts by mass of process oil.

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