JP2011162745A - Conductive rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive rubber composition excellent in processability such that conductive rubber does not adhere to each other even in the uncrosslinked state. <P>SOLUTION: In conductive rubber obtained by adding a conductivity imparting agent to base rubber having Mooney viscosity (ML) of 40 or less, an ethylene-α-olefin copolymer is added to the base rubber so that the ethylene-α-olefin copolymer is 5-40 pts.mass based on the total 100 pts.mass thereof. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a conductive rubber composition used for a conductive member such as a cord switch.

As a conductive rubber used for an electromagnetic wave shield, an antistatic, an electrode of a pressure sensitive switch, or the like, a type in which a conductivity imparting agent such as carbon is added to a base rubber is used. For example, there are those obtained by adding carbon as a conductivity imparting agent to acrylonitrile butadiene rubber (NBR) (Patent Document 1) and those obtained by adding carbon to silicone rubber (Patent Document 2). The conductive rubber has a low viscosity with a Mooney viscosity ML _{1 + 4} (100 ° C.) of 40 or less because the viscosity increases when carbon is added and the processing becomes difficult.

  And methods for crosslinking the conductive rubber include sulfur crosslinking, peroxide crosslinking, electron beam irradiation crosslinking, and the like. Among these, since sulfur crosslinking and peroxide crosslinking are crosslinked by using heat as a trigger, it is necessary to perform extrusion or the like at a temperature at which crosslinking does not proceed when a sheet or the like is extruded. In contrast, electron beam irradiation cross-linking involves cross-linking by irradiating a molded body with an electron beam, so that even if molding such as extrusion at a high temperature, cross-linking occurs in an apparatus such as an extruder, resulting in poor molding. There is a feature that high temperature molding is possible.

  In particular, when it is desired to reduce the volume resistance of the conductive rubber, it is necessary to add a large amount of a conductivity-imparting agent such as carbon. Therefore, electron beam irradiation cross-linking that can be molded by reducing the viscosity at high temperature is effective as a method for cross-linking low-resistance conductive rubber.

JP-A-7-126439 Japanese Patent Laid-Open No. 10-30059

However, in the case of electron beam irradiation cross-linking, electron beam irradiation cross-linking is often performed in a separate step after molding or extrusion molding. This is because the electron beam irradiation apparatus is very expensive and difficult to incorporate into the molding process. For this reason, when moving compacts, such as an uncrosslinked sheet, to the next electron beam cross-linking step, the compacts may be overlapped or wound several times around the bobbin from the viewpoint of handling. However, since the conductive rubber is uncrosslinked at this time, there is a problem that the molded bodies stick to each other. Furthermore, when the Mooney viscosity ML _{1 + 4} (100 ° C.) of the base rubber is a low viscosity of 40 or less, there is a problem that sticking becomes remarkable.

  Accordingly, an object of the present invention is to provide a conductive rubber composition which is excellent in processability without causing the conductive rubbers to stick to each other even in an uncrosslinked state in the conductive rubber subjected to electron beam irradiation crosslinking.

  In order to achieve the above object, the invention according to claim 1 is a conductive rubber in which a conductivity-imparting agent is added to a base rubber having a Mooney viscosity ML of 40 or less, and an ethylene-α-olefin copolymer is added to the base rubber in a total of 100. The conductive rubber composition is characterized in that the ethylene-α-olefin copolymer is added so as to be 5 to 40 parts by mass with respect to parts by mass.

  The invention according to claim 2 is the conductive rubber composition according to claim 1, wherein the ethylene-α-olefin copolymer has a rubber hardness of 60 to 95.

  The invention according to claim 3 is the conductive rubber composition according to claim 1 or 2, wherein the ethylene-α-olefin copolymer has a melt flow rate of 5 or more.

  The invention according to claim 4 is the conductive rubber composition according to any one of claims 1 to 3, wherein the conductivity imparting agent is carbon.

  According to the present invention, in a conductive rubber that undergoes electron beam irradiation crosslinking, a conductive rubber composition having excellent processability can be obtained without the conductive rubber sticking even in an uncrosslinked state.

It is a schematic diagram which shows the preparation methods of the sticking strength measurement sample of an Example and a comparative example in this invention. It is a schematic diagram which shows the tension test method for measuring the adhesive strength of an Example and a comparative example in this invention.

  Hereinafter, a preferred embodiment of the present invention will be described in detail.

  The conductive rubber composition of the present invention comprises a base rubber, a conductivity imparting agent, and an ethylene-α olefin copolymer.

  The ethylene-α-olefin copolymer is a semi-crystalline resin, and even in an uncrosslinked state, the resins do not adhere to each other. Therefore, addition to the conductive rubber can prevent adhesion.

  As addition amount of an ethylene-alpha olefin copolymer, it is good to add 5-40 mass parts so that a sum total with a base rubber may be 100 mass parts. If it is less than 5 parts by mass, the effect of preventing the adhesion between the conductive rubbers is almost lost. When the amount is more than 40 parts by mass, characteristics as a conductive rubber are lost, for example, compression set becomes large.

  The rubber hardness (Shore A hardness) of the ethylene-α-olefin copolymer is preferably 60 to 95. If it is less than 60, the effect of preventing the adhesion between the conductive rubbers is almost lost. If it exceeds 95, the conductive rubber itself becomes too hard and loses flexibility.

  The melt flow rate of the ethylene-α olefin copolymer is preferably 5 or more. The melt flow rate is an index of flowability at the time of melting, and the larger the value, the better the flowability. When this value is less than 5, the viscosity at the time of processing the conductive rubber increases, and the processability becomes extremely poor.

  Examples of the α-olefin part resin of the ethylene-α-olefin copolymer include propylene and butene, but are not limited thereto.

Examples of the material of the base rubber include, but are not limited to, EPDM (ethylene-propylene-diene rubber), NBR (acrylonitrile butadiene rubber), SBR (styrene butadiene rubber), and the like. As the base rubber, a rubber having a Mooney viscosity ML _{1 + 4} (100 ° C.) at 100 ° C. of 40 or less is used.

  Carbon is used as the conductivity imparting agent.

  In addition, since the ethylene-α-olefin copolymer is a nonpolar resin, it is difficult to adhere to a metal and the mold releasability at the time of molding is improved. There is also an advantage that rubber peeling becomes easy.

  Next, the material constituting the conductive rubber composition is uniformly kneaded using various mixers, and molded or extruded to form a molded body such as a sheet. The molded body is moved to an electron beam irradiation step and crosslinked to form a crosslinked conductive rubber.

  In this invention, since the ethylene-alpha olefin copolymer is mix | blended, when moving a molded object to an electron beam irradiation process, even if a molded object is piled up, it does not stick.

  Hereinafter, Examples 1 to 6 and Comparative Examples 1 to 6 of the present invention will be described.

  First, Table 1 shows the physical properties of the ethylene-α olefin copolymers used in Examples 1 to 6 and Comparative Examples 1 to 6.

  Table 1 shows the rubber hardness (ASTM D2240) and the melt flow rate (230 ° C., ASTM D1238) of Shore A of the ethylene-α-olefin copolymer (trade name: TAFMER, manufactured by Mitsui Chemicals, Inc.) examined this time. It is a thing.

  Next, Table 2 shows the physical properties of the base rubbers used in Examples 1 to 6 and Comparative Examples 1 to 6.

Table 2 shows the Mooney viscosity ML _{1 + 4} (100 ° C.) (JIS K6300-1) of the base rubber (EP rubber, manufactured by Mitsui Chemicals, Inc.) examined this time.

  Table 3 shows the composition and characteristics of Examples 1 to 6 and Comparative Examples 1 to 6.

  EP rubber shown in Table 2 was used as the base rubber in Table 3, and Ketjen Black EC600JD manufactured by Ketjen Black International was used as the carbon. As the ethylene-α olefin copolymer, those having physical properties shown in Table 1 were used.

  The compounding materials of Examples 1 to 6 and Comparative Examples 1 to 6 were formed into 1 mm thick sheets at a temperature of 180 ° C. using a press (in an uncrosslinked state).

  In order to evaluate the adhesion between the conductive rubbers, as shown in FIG. 1, two sheets 1 and 1 ′ cut out to a width of 5 mm and a length of 20 mm are wrapped by 5 mm (the area of the adhesive surface 2 is 5 mm × 5 mm). A sample was prepared by placing a 1 kg weight 3 on the lapping surface and leaving it at 60 ° C. for 1 hour. Thereafter, as shown in FIG. 2, a tensile test was performed at a tensile speed of 50 mm / min to measure the sticking strength.

Moreover, the compound Mooney viscosity ML1 _{+ 4} (180 degreeC) (JIS K6300-1) which is a processability parameter | index about uncrosslinked electrically conductive rubber was measured.

  The molded 1 mm thick sheet was subjected to electron beam irradiation crosslinking (irradiation amount: 18 Mrad) to obtain a crosslinked conductive rubber sheet. Thereafter, using this sheet, a compression set test (JIS K6262; 150 ° C., 25% compression, left for 22 hours), volume resistance measurement (JIS K7194; four-terminal four-deep needle method), rubber hardness measurement (ASTM D2240, Shore) A) was performed.

  In Examples 1 to 6, the blending amount of the ethylene-α-olefin copolymer is 5 to 40 parts by mass, the sticking strength is 15 N or less, the compression set is 50 or less, the compound Mooney viscosity is 120 or less, and the rubber hardness is 95 or less. is there.

  On the other hand, Comparative Example 1 uses the same ethylene-α olefin copolymer (Tuffmer A70090) as in Examples 1 to 3, but the blending amount is as small as 3 parts by mass, so in an uncrosslinked state. The sticking strength between the conductive rubbers of 19N exceeded 19N, which is the target (a level that causes no problem in practical use).

  Comparative Example 3 uses the same ethylene-α olefin copolymer (Toughmer A35070S) as in Examples 4 and 5, but the compounding amount is as small as 2.5 parts by mass, so that the conductivity in an uncrosslinked state is The sticking strength between the rubbers was 20 N, which exceeded the target of 15 N as in Comparative Example 1.

  Comparative Example 4 uses an ethylene-α olefin copolymer (Tuffmer A1050S) different from Comparative Examples 1 and 3. However, since the blending amount is as small as 3 parts by mass, conductivity in an uncrosslinked state is used. The sticking strength between the rubbers was 24 N, which exceeded the target 15 N as in Comparative Examples 1 and 3.

  Therefore, the blending amount of the ethylene-α olefin copolymer is preferably 5 parts by mass or more.

  Moreover, although the comparative example 2 uses the same ethylene-alpha olefin copolymer (Tuffmer A70090) as Examples 1-3, since a compounding quantity is as many as 50 mass parts, compression set is 56, The target of 50 was exceeded and there was a problem in practical use.

  Comparative Example 5 uses an ethylene-α olefin copolymer (BL4000) different from Comparative Example 2. However, since the blending amount is as large as 50 parts by mass, the compression set is 58 and the target 50 As in Comparative Example 2, there was a problem in practical use.

  Therefore, the blending amount of the ethylene-α olefin copolymer is preferably 40 parts by mass or less.

In Comparative Example 6, the same ethylene-α olefin copolymer (Tuffmer A70090) as in Example 2 was used in the same amount, but the Mooney viscosity ML _{1 + 4} (100 ° C.) of the base rubber was 45. Since a large EPT4045 was used, the compound Mooney viscosity became as large as 140, making it difficult to process. From this result, it is understood that the Mooney viscosity ML _{1 + 4} (100 ° C.) of the base rubber is preferably 40 or less.

  Further, when Comparative Example 1 and Comparative Example 4 are viewed, the blending amount of the ethylene-α olefin copolymer is the same at 3 parts by mass, but the Tuffmer A1050S of Comparative Example 4 has a low melt flow rate of 2.2. The compound Mooney viscosity is 126, which is larger than the target value (120 or less). Therefore, the melt flow rate is preferably 5 or more.

  Moreover, when the comparative example 2 and the comparative example 5 are seen, although the compounding quantity of an ethylene-alpha olefin copolymer is the same at 50 mass parts, since the Tuffmer BL4000 of the comparative example 5 has a large rubber hardness, it is bridge | crosslinking conductive. The rubber hardness of the rubber is 98, which is larger than the target value (60 to 95), and the flexibility is lost. From this result, the rubber hardness of the ethylene-α-olefin copolymer is preferably 60 to 95.

  From the above results, according to the present invention, in the conductive rubber subjected to electron beam irradiation crosslinking, there is no problem that the conductive rubbers stick to each other even in an uncrosslinked state, the processability is excellent, the compression set is small after crosslinking, the volume It can be seen that a conductive rubber having low resistance and flexibility can be obtained.

Claims (4)

  In a conductive rubber obtained by adding a conductivity-imparting agent to a base rubber having a Mooney viscosity ML of 40 or less, the ethylene-α olefin copolymer is added to the base rubber with respect to 100 parts by mass in total. Is added so as to be 5 to 40 parts by mass.   The conductive rubber composition according to claim 1, wherein the ethylene-α-olefin copolymer has a rubber hardness of 60 to 95.   The conductive rubber composition according to claim 1 or 2, wherein the ethylene-α-olefin copolymer has a melt flow rate of 5 or more.   The conductive rubber composition according to claim 1, wherein the conductivity imparting agent is carbon.

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