JP2006307100A - Thermoelastomer composition and sealing member with low stiffness using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelastomer composition being superior in sealing property and showing a superior chemical resistivity (solvent resistance) using for a long term and to provide a low stiffness sealing member superior for a sealing liquid containing a chemical substance which especially generates a solvent crack. <P>SOLUTION: The thermoelastomer composition is made by dynamically cross-linking a polymer mixture containing (a) an olefinic resin, (b) an oil extended ethylenic copolymer rubber containing an ethylenic copolymer rubber with an intrinsic viscosity [η] of 4.3-6.8 dl/g determined in a decalin solvent at 135°C and a mineral oil type softener in the presence of a cross-linking agent and having a hardness of 10-50 determined in accordance with JIS K 6031(A) type standard. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermoplastic elastomer composition and a low hardness seal member using the same. More specifically, the present invention relates to a low-hardness seal member that is excellent in sealing properties and exhibits excellent chemical resistance (solvent resistance) even in long-term use, and particularly excellent for liquid sealing containing chemical substances that cause solvent cracks.

In recent years, electronic devices such as computers and printers have become more sophisticated and smaller in size and have a complicated circuit configuration, and even a small amount of dust can cause damage, increasing the need for dust protection in practice. Normally, a gasket is sandwiched between the box-shaped body containing these electronic devices and the cover, and the cover is integrated with a mounting bolt, etc. In order to simplify the handling, a cover-integrated gasket in which a gasket and a cover are integrated is often used (see, for example, Patent Documents 1 and 2).
Further, there is an increasing demand for chemical resistance depending on the use of the seal member, and a technique of a seal material using a fluorine-based rubber such as a fluoropolyether-based rubber is disclosed (for example, see Patent Documents 3 and 4). ). These fluorine-based rubbers have a sufficient effect on chemical resistance, but are special rubbers and are expensive. Therefore, they use general-purpose materials and have a low hardness sealing member (liquid) with excellent chemical resistance (solvent resistance). There was an increasing need for sealing members.
Usually, thermoplastic elastomers such as styrene-ethylene / butylene-styrene triblock copolymer (SEBS) and styrene-ethylene / propylene-styrene triblock copolymer (SEPS) used for low hardness rubber seal members are used. In such a case, the chemical resistance of the seal member is still not sufficient.
In particular, there is a strong demand for low-hardness seal members for liquids that contain chemical substances that cause solvent cracks.

JP 2004-36739 A JP 2002-349712 A JP 2004-168881 A JP-A-7-53821

  The present invention provides a low-hardness seal member that is excellent in liquid sealing containing a chemical substance that exhibits excellent chemical resistance (solvent resistance) and long-term use, as well as chemical substances that cause solvent cracks. Objective.

As a result of intensive studies to achieve the above object, the present inventor has dynamically crosslinked a specific olefin resin and a specific oil-extended ethylene copolymer rubber in the presence of a crosslinking agent. It has been found that an obtained thermoplastic elastomer composition and a seal member using the same can achieve the above object. The present invention has been completed based on such findings.
That is, the present invention
(1) (a) an olefin resin, and (b) an ethylene copolymer rubber and a mineral oil softener having an intrinsic viscosity [η] measured at 135 ° C. in a decalin solvent of 4.3 to 6.8 dl / g. The hardness obtained by dynamically cross-linking a polymer mixture containing an oil-extended ethylene-based copolymer rubber in the presence of a cross-linking agent and in accordance with JIS K6031 (A) type is 10 to 10. 50, a thermoplastic elastomer composition,
(2) The mass ratio (a) / (b ′) of the olefin resin of component (a) and the ethylene copolymer rubber in component (b) is 10/90 to 90/10. A thermoplastic elastomer composition,
(3) The component (a) olefin resin is an ethylene homopolymer, a crystalline ethylene copolymer containing 90 mol% or more of ethylene units, a crystalline propylene homopolymer, and 90 mol of propylene units. % Of the thermoplastic elastomer composition according to (1) or (2), which is at least one selected from crystalline propylene copolymers containing at least%,
(4) The heat of (1) to (3) above, wherein the oil-extended ethylene copolymer rubber of component (b) contains 20 to 300 parts by mass of a mineral oil softener with respect to 100 parts by mass of the ethylene copolymer rubber. A plastic elastomer composition,
(5) The low-hardness sealing member characterized by using the thermoplastic elastomer composition of (1) to (4) above, and (6) for a liquid containing a chemical substance that generates a solvent crack (5) ) Low hardness seal member,
Is to provide.

  A thermoplastic elastomer composition that has excellent sealing properties and excellent chemical resistance (solvent resistance) even for long-term use, and low hardness that is excellent for liquid sealing, including chemical substances that cause solvent cracks. A seal member can be provided.

  The thermoplastic elastomer composition of the present invention comprises (a) an olefin resin and (b) an ethylene copolymer having an intrinsic viscosity [η] measured at 135 ° C. in a decalin solvent of 4.3 to 6.8 dl / g. A polymer mixture containing an oil-extended ethylene copolymer rubber containing a rubber and a mineral oil softener is dynamically cross-linked in the presence of a cross-linking agent, and obtained in accordance with JIS K6031 (A) type. The required hardness is required to be 10-50.

The olefin-based resin that is the component (a) used in the thermoplastic elastomer composition of the present invention is not particularly limited. For example, ethylene homopolymer, crystalline ethylene containing 90 mol% or more of ethylene units. A copolymer, a crystalline propylene homopolymer, and a crystalline propylene copolymer containing 90 mol% or more of propylene units are preferable, and a crystalline propylene homopolymer is particularly preferable.
Specifically, crystalline ethylene polymers such as high density polyethylene, low density polyethylene, ethylene / 1-butene copolymer, ethylene / 1-hexene copolymer, ethylene / 1-octene copolymer; isotactic Polypropylene, propylene / ethylene copolymer, propylene / 1-butene copolymer, propylene / 1-pentene copolymer, propylene / 3-methyl-1-butene copolymer, propylene / 1-hexene copolymer, propylene / 3-methyl-1-pentene copolymer, propylene / 4-methyl-1-pentene copolymer, propylene / 3-ethyl-1-pentene copolymer, propylene / 1-octene copolymer, propylene / 1 -Decene copolymer, propylene / 1-undecene copolymer, propylene / 1-butene / ethylene terpolymer, pro Examples thereof include crystalline propylene polymers whose main component is a propylene component such as len / 1-hexene / 1-octene terpolymer and propylene / 1-hexene / 4-methyl-1-pentene terpolymer. .

  Moreover, it is preferable that the number average molecular weight of (a) component olefin resin is 10,000-1,000,000, More preferably, it is 50,000-500,000. (A) By making the number average molecular weight of a component into the said range, while ensuring the low hardness of a sealing member, it is preferable for durability of a sealing member.

  Next, the oil-extended ethylene copolymer rubber which is the component (b) of the thermoplastic elastomer composition of the present invention has an intrinsic viscosity [η] measured at 135 ° C. in a decalin solvent of 4.3 to 6.8 dl. / G of ethylene copolymer rubber and mineral oil softener.

Examples of the ethylene copolymer rubber include a random copolymer obtained by copolymerizing ethylene, an α-olefin having 3 or more carbon atoms, preferably 3 to 8 carbon atoms, and a non-conjugated diene. Examples of the α-olefin having 3 or more carbon atoms copolymerized with ethylene include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene and 1-decene. The α-olefin can be used alone or in combination of two or more.
Non-conjugated dienes to be copolymerized include dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylene norbornene, ethylidene norbornene, 5-methyl-1,4-hexadiene, 4-methyl-1,4- Examples include hexadiene, 6-methyl-1,5-heptadiene, and methyl-1,6-octadiene. It is also possible to give a branched structure to the ethylene random copolymer by a known method. Preferred dienes for imparting a branched structure include 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene, norbornadiene and the like. These non-conjugated dienes may be used alone or in combination of two or more.
From the viewpoint of maintaining the mechanical strength and flexibility of the ethylene random copolymer rubber, these ethylene random copolymers preferably have an ethylene / α-olefin molar ratio of 50/50 to 95/5, More preferably, it is copolymerized at 40 to 90/10. The content of non-conjugated diene is preferably 12% by mass or less, and more preferably 1 to 10% by mass.

  The intrinsic viscosity of the ethylene copolymer rubber is 4.3 to 6.8 dl / g, preferably 4.3 to 6.0 dl / g, more preferably as a value measured at a temperature of 135 ° C. in a decalin solvent. 4.4 to 5.7 dl / g. By setting the intrinsic viscosity within the above range, excellent elastic recovery and processability at the time of molding can be obtained.

The mineral oil-based softener contained in the component (b) oil-extended ethylene-based copolymer rubber is used for imparting moldability and flexibility and improving the appearance of the product. Examples of the mineral oil softener include aromatic, naphthenic, and paraffinic ones. Of these, paraffinic and naphthenic ones are preferable. The blending amount of the mineral oil-based softener is usually 20 to 100 parts by mass of the ethylene copolymer rubber in consideration of the balance of molding processability, flexibility, heat resistance, and strength of the low hardness seal member of the present invention. 300 parts by mass, preferably 30 to 200 parts by mass, more preferably 50 to 150 parts by mass, and most preferably 80 to 150 parts by mass.
These softeners may be used alone or in combination of two or more as long as they are compatible with each other. Further, the blending amount of the softening agent is preferably selected within the above range depending on the molecular weight of the ethylene copolymer rubber and the type of other components added to the ethylene copolymer rubber.

The oil-extended ethylene copolymer rubber which is the component (b) of the present invention can be prepared by removing the solvent from a mixed solution containing the ethylene copolymer rubber and the mineral oil softener. The method is not particularly limited, but as a preferred method, a predetermined amount of a mineral oil softener is added to and mixed with the ethylene copolymer rubber mixture obtained by polymerization, and then a steam stripping method, a flash method, etc. Examples of the method include desolvation by a method.
After polymerization, the resulting ethylene copolymer rubber is uniformly dissolved in a good solvent such as a hydrocarbon solvent such as benzene, toluene, xylene, hexane, heptane, cyclohexane, or a halogenated hydrocarbon solvent such as chlorobenzene, and None, after adding and mixing a predetermined amount of a mineral oil softener, the solvent may be removed by a method such as a steam stripping method or a flash method. Moreover, the oil expansion of ethylene copolymer rubber can also be performed using the apparatus used for oil expansion of normal rubber, such as a Banbury mixer, a pressure kneader, or a roll. However, since the molecular weight of the rubber before the oil exhibition is high, it is difficult in terms of operation to uniformly disperse the mineral oil softener in the ethylene copolymer rubber.

When a mineral oil softener is added to the mixed solution of ethylene copolymer rubber as described above, the softener is sufficiently uniformly dispersed in the rubber so that the softener bleeds out from the surface of the molded product. This is preferable.
Ethylene copolymer rubber can be polymerized by a known polymerization method, for example, in the presence of a vanadium-based, titanium-based, or metallocene-based catalyst. Is practically preferred.

The ethylene copolymer rubber can be used alone or in combination of two or more. Further, as ethylene copolymer rubber, halogenated ethylene copolymer rubber in which some of hydrogen atoms of ethylene copolymer rubber are substituted with halogen atoms such as chlorine atom and bromine atom, vinyl chloride, vinyl acetate, ( (Meth) acrylic acid or derivatives thereof (eg methyl (meth) acrylate, glycidyl (meth) acrylate, (meth) acrylamide etc.), maleic acid or derivatives thereof (eg maleic anhydride, maleimide, dimethyl maleate etc.), conjugated dienes ( For example, a graft-modified ethylene copolymer obtained by graft polymerization of an unsaturated monomer such as butadiene, isoprene, or chloroprene can also be used. The shape of the component (b) oil-extended ethylene copolymer rubber may be any shape such as a bale, crumb or pellet.
Such an oil-extended ethylene copolymer rubber as component (b) is preferably amorphous or low crystalline from the viewpoint of flexibility and elastic recovery of the resulting composition. The crystallinity is related to the density, and in general, the crystallinity can be substituted with the density more easily.
In the oil-extended ethylene copolymer rubber of the component (b) of the present invention, the density is preferably 0.89 g / cm ³ or less.

In addition, the mass ratio (a) / (b ′) of the olefin resin of the component (a) and the ethylene copolymer rubber in the component (b) is usually 90/10 to 10/90, preferably 70 / 30 to 10/90, more preferably 50/50 to 10/90. (A) The ratio of the olefin-based resin and the ethylene-based copolymer rubber in the component (b) is in the above range, so that the thermoplastic elastomer composition of the present invention has an excellent balance between flexibility and moldability, The product appearance can also be improved.
Moreover, the hardness measured based on JIS K6031 (A) type | mold of the thermoplastic elastomer composition of this invention needs to be 10-50, More preferably, it is 20-40. By setting it as the above range, excellent liquid sealing performance can be obtained when used as a sealing member with excellent flexibility.

  The crosslinking agent used in the present invention is usually used for crosslinking of ethylene copolymer rubber such as EPM or EPDM, for example, sulfur, sulfur compound, organic peroxide, phenol resin crosslinking agent, quinoid crosslinking agent. Acrylic acid metal salt crosslinking agent, bismaleimide crosslinking agent and the like are used. Hereinafter, these crosslinking agents will be described.

(I) Sulfur and sulfur compounds As the sulfur and sulfur compounds used in the present invention, those generally manufactured and sold for vulcanization of rubber can be used. Examples of sulfur include powdered sulfur, sulfur white, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur. In addition, as sulfur compounds, sulfur chloride; sulfur dichloride; morihorn disulfide; alkylphenol disulfide; thioureas such as dibutylthiourea; mercaptobenzothiazole, dibenzothiazyl disulfide, 2- (4-morpholinodithio) benzothiazole, etc. And dithiocarbamates such as zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate and sodium dimethyldithiocarbamate.

(B) Organic peroxide Examples of the organic peroxide include dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, and 2,5-dimethyl- Di (tert-butylperoxy) hexyne-3, 1,3-bis (tert-butylperoxyisopropyl) benzene, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane, n-butyl- 4,4-bis (tert-butylperoxy) valeride, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butylperoxybenzoate, tert-butylperoxyisopropyl carbonate, diacetyl peroxide, lauroyl peroxide Tert-butyl peroxide, etc. It is.
Among these organic peroxides, those in which the decomposition reaction is gentle and the crosslinking reaction proceeds after the rubber and the resin component are more uniformly mixed are preferable. An organic peroxide having a mild decomposition reaction can be expressed, for example, using a 1-minute half-life temperature as an index, and the one-minute half-life temperature is sufficiently high, and those having a temperature of 150 ° C. or higher are preferable. Examples of such organic peroxides include 2,5-dimethyl-2,5-di (tert-butylperoxy) -hexyne-3, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane. 1,3-bis (tert-butylperoxyisopropyl) benzene. In particular, the use of 2,5-dimethyl-2,5-di (tert-butylperoxy) -hexyne-3 having a high decomposition temperature is most preferable.

  When an appropriate crosslinking aid is present together with an organic peroxide as a crosslinking agent, a uniform and mild crosslinking reaction can be expected. Examples of crosslinking aids include sulfur, p-quinone dioxime, p, p′-dibenzoylquinone dioxime, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene dimethacrylate, polyethylene glycol dimethacrylate, Trimethylolpropane trimethacrylate, diaryl phthalate, diaryl phthalate, tetraaryloxyethane, triaryl cyanurate, diaryl phthalate, tetraaryloxyethane, triaryl cyanurate, N, Nm-phenylenebismaleimide, maleic anhydride, Divinylbenzene, zinc di (meth) acrylate, aluminum tri (meth) acrylate, magnesium di (meth) acrylate, and the like are used. Among these, N, Nm-phenylene bismaleimide, p, p′-dibenzoylquinone dioxime, and divinylbenzene are preferable. These can be used alone or in combination of two or more.

The blending ratio of these organic peroxides is based on 100 parts by mass of the total amount of the olefin resin as the component (a) and the ethylene copolymer rubber component as the component (b) from the viewpoint of uniform and moderate partial crosslinking. The amount is preferably 0.02 to 1.5 parts by mass, and more preferably 0.05 to 1.0 parts by mass. The blending ratio of the crosslinking aid is preferably 3 parts by mass or less, more preferably 0 with respect to 100 parts by mass of the total amount of the olefin resin as the component (a) and the ethylene copolymer rubber component as the component (b). .2 to 2 parts by mass.
When the blending ratio is within this range, the thermoplastic elastomer composition of the present invention maintains the uniformity of the phase structure (sea-island structure) and the molding processability associated therewith.
In addition, excessive use may remain in the thermoplastic elastomer composition as an unreacted monomer, and may cause a change in physical properties due to a thermal history during molding.

(C) Phenol resin cross-linking agent A preferred phenol resin cross-linking agent is a compound represented by the following general formula.

Here, m is an integer of 0 to 10, and X and Y are hydroxyl groups or halogen atoms, which may be the same or different. R is a saturated hydrocarbon group having 1 to 15 carbon atoms. Phenolic resin crosslinking agents are commonly used as rubber crosslinking agents, as described, for example, in US Pat. Nos. 3,287,440 and 3,709,840. And this crosslinking agent can be manufactured by polycondensing a substituted phenol and an aldehyde in presence of an alkali catalyst.
The blending ratio of the phenol-based crosslinking agent is such that the degree of partial crosslinking of the thermoplastic elastomer composition of the present invention is appropriate, and in order to improve oil resistance, shape recovery, and flexibility, The total amount of the ethylene copolymer rubber component (b) is preferably 100 to 10 parts by mass, more preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and still more preferably 0.4 to 2 parts. Part by mass. The phenolic crosslinking agent can be used alone, but can also be used in combination with a crosslinking accelerator in order to adjust the crosslinking rate.
As the crosslinking accelerator, organic halides such as stannous chloride and ferric chloride metal halides, chlorinated polypropylene, brominated polypropylene, brominated butyl rubber and chloroprene rubber can be used. Further, a metal oxide such as zinc oxide or a dispersant such as stearic acid may be used in combination.

(D) Quinoid type cross-linking agent Preferable quinoid type cross-linking agents include p-quinone dioxime derivatives. Specifically, p-benzoquinone dioxime, p-dibenzoylquinone diamide, and the like. The mixing ratio of the quinoid crosslinking agent is the same as that of the phenol crosslinking agent described above, and the total amount of the olefin resin as the component (a) and the ethylene copolymer rubber component as the component (b) is 100 parts by mass. On the other hand, it is preferably 0.2 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and still more preferably 0.8 to 3 parts by mass. The crosslinking agent can be used alone, but a crosslinking accelerator can be used in combination in order to adjust the crosslinking rate. As the crosslinking accelerator, oxidizing agents such as red lead, dibenzothiazoyl sulfide, and tetrachlorobenzoquinone can be used. Further, a metal oxide such as zinc oxide or a dispersant such as stearic acid may be used.

(E) Acrylic acid metal salt-based crosslinking agent An acrylic acid metal salt-based crosslinking agent is a metal salt such as zinc or calcium such as acrylic acid or methacrylic acid. Usually, it is obtained, for example, by reaction of zinc oxide or zinc carbonate with methacrylic acid.
Specifically, zinc dimethacrylate, calcium dimethacrylate, magnesium dimethacrylate, monohydroxyaluminum dimethacrylate, aluminum trimethacrylate, calcium diacrylate, magnesium diacrylate, monohydroxyaluminum diacrylate, aluminum triacrylate, etc. It is.
When the heat treatment is carried out dynamically with the metal acrylate crosslinker as the main component, the preferred amount of the metal acrylate crosslinker used is the olefin resin (a) and the ethylene copolymer (b). Preferably it is 1-20 mass parts with respect to 100 mass parts of total amounts of a rubber component, More preferably, it is 4-12 mass parts.

(F) Bismaleimide-based cross-linking agent A commonly used bismaleimide-based cross-linking agent is N, N′-m-phenylene bismaleimide. A bismaleimide-based crosslinking agent is usually used as a crosslinking aid for organic peroxide crosslinking, but it is known that a crosslinking reaction occurs even when used alone. The preferred blending ratio of the bismaleimide crosslinking agent is 0.05 to 10 parts by weight with respect to 100 parts by weight of the total amount of the olefin resin of the component (a) and the ethylene copolymer rubber component of the component (b). Preferably it is 0.1-5 mass parts, More preferably, it is 0.2-2 mass parts.

  The thermoplastic elastomer composition of the present invention includes an antioxidant, an antistatic agent, a weathering stabilizer, an ultraviolet absorber, a lubricant, and a blocking agent in an amount that does not substantially impair the characteristics of the composition depending on the application. Inhibitors, sealability improvers, crystal nucleating agents, flame retardants, fungicides, fungicides, tackifiers, softeners, plasticizers, colorants (titanium oxide, carbon black, etc.), fillers (glass Fiber, carbon fiber, metal fiber, aramid fiber, glass bead, mica, calcium carbonate, potassium titanate whisker, talc, barium sulfate, glass flake, fluororesin, and the like) can be appropriately blended. In addition, polymers such as rubbery polymers (such as butyl rubber and NBR), thermoplastic resins, and thermoplastic elastomers (such as low crystalline propylene-based polymers and hydrogenated diene-based polymers) can be appropriately blended. These polymers may be blended when the component (a) and the component (b) are dynamically crosslinked in the presence of a crosslinking agent, and the component (a) and the component (b) are mixed with the crosslinking agent. You may mix | blend after bridge | crosslinking dynamically in presence of this. It is less than 30 parts by mass with respect to 100 parts by mass of the total amount of the olefin resin as the component (a) and the ethylene copolymer rubber component as the component (b). In addition, the above-described mineral oil-based softening agent may be further added to the thermoplastic elastomer composition of the present invention, for example, at the stage of dynamically crosslinking within a range not causing bleed.

  The thermoplastic elastomer composition of the present invention is obtained by dynamically crosslinking (a) the olefin resin of component (a) and (b) the oil-extended ethylene copolymer rubber in the presence of the crosslinking agent. In the present invention, dynamically crosslinking means that melt kneading / dispersing of component (a) and component (b) and crosslinking reaction of component (b) are performed simultaneously in the presence of a crosslinking agent. By performing such an operation, an olefinic thermoplastic elastomer composition having a sea-island structure in which the partially or completely crosslinked (b) component floats in the (a) component can be obtained. The temperature condition for dynamic crosslinking is preferably in the range of 150 ° C. to 250 ° C. in which the balance between the melting of the component (a) and the crosslinking reaction is good.

The apparatus used for the above-mentioned dynamic cross-linking is a batch kneader such as a pressure kneader, a banbury mixer, or a brabender, or a continuous kneader such as a single screw extruder, a twin screw extruder, a continuous kneader, or a feeder ruder. , And combinations of these devices. For example, the thermoplastic elastomer composition of the present invention can be obtained by the apparatus and method described in the following. The component (a) and the component (b) are kneaded by the batch kneader and set to a temperature at which the component (a) and the component (b) are sufficiently melted, and then dynamically crosslinked by adding a crosslinking agent. Using the batch kneader, the components (a) and (b) are sufficiently blended at a temperature at which the components (a) and (b) are sufficiently melted (first stage). Using a continuous kneader, the first-stage blend and the cross-linking agent are added to dynamically cross-link (second stage). The component (a), the component (b) and the crosslinking agent are charged into a continuous kneader and dynamically crosslinked. In the above, an additional mineral oil-based softener, various additives, etc. may be added at any stage, and dynamically crosslinks in the presence of a crosslinker in the state where component (a) and component (b) are melted. As long as the gist of the present invention is not exceeded, it is not limited to these methods.
The thermoplastic elastomer composition of the present invention thus obtained can be used as a low-hardness sealing member and can obtain excellent sealing properties, chemical resistance, solvent resistance and liquid sealing properties.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. Various measurements in each example and comparative example were performed as follows.
<Evaluation method>
(1) Material hardness It conformed to JIS K6301 (A type).
(2) Evaluation of chemical resistance (solvent resistance) A 2 mm thick sheet obtained by using a general-purpose injection molding machine for the evaluation materials shown in Table 1 was punched into a 1 cm vertical and 5 cm wide sample for evaluation. Got. The samples for evaluation were immersed in various liquids under the conditions shown in Table 2, and after one week, the presence or absence of changes such as breakage, cracks, dissolution, and shrinkage was confirmed.

<Synthesis of oil-extended ethylene / propylene / diene random copolymer rubber>
2 liters of dehydrated and purified n-hexane was charged into a separable flask with an internal volume of 3 liters that had been purged with nitrogen in advance, and flow rates of ethylene gas, propylene gas, and hydrogen gas purified through molecular sieves were 6/4/1 (volume ratio). The gas phase was fed at a ratio and dissolved at room temperature for 10 minutes with stirring. Next, the diene component (ethylidene norbornene), aluminum sesquichloride (AlEt _1.5 Cl _1.5 ) 5 mmol, and vanadium oxytrichloride (VOCl ₃ ) 0.1 mmol were charged to initiate polymerization. While the ethylene gas, propylene gas and hydrogen gas were fed in a gas phase, the reaction temperature was adjusted to 20 ° C., and the polymerization reaction was continued. Twenty minutes after the start of the polymerization, the catalyst was deactivated with isopropyl alcohol purified by molecular sieve to stop the polymerization. After blending a predetermined amount of paraffinic oil (trade name: PW-380, manufactured by Idemitsu Kosan Co., Ltd.) with the obtained copolymer solution, these components were added to methanol and precipitated, and then heated at 100 ° C. Drying with a roll gave an oil-extended copolymer rubber. The obtained polymer had a viscosity [η] of 4.9 (dl / g), a propylene content of 30% by mass, a diene content of 4.5% by mass, and an oil extended amount of 100 parts by mass.

[note]
* 1, PP: Polypropylene [Product name: MA-03, manufactured by Nippon Polychem Co., Ltd.]
* 2, Oil-extended EPDM: The rubber obtained in the above synthesis is used. * 3, SEPS: [Kuraray's product name: SEPTON 2027]
* 4, Paraffin oil: [Idemitsu Kosan Co., Ltd., trade name: PW-380]
* 5, Crosslinker 1: 2,5-dimethyl-2,5-di (tert-butylperoxy) -hexyne-3 [Nippon Yushi Co., Ltd. trade name: perhexine 25B]
* 6, Cross-linking agent 2: N, Nm-phenylene bismaleimide (trade name: Balnock PM manufactured by Ouchi Shinsei)

［注］
＊７、浸漬液体ａ：イソプロピルアルコール
＊８、浸漬液体ｂ：アセトン
＊９、浸漬液体ｃ：非イオン系界面活性剤（グリセリン脂肪酸エステル〔花王社製、商品名：エキセル３００Ｖ〕）を３０％含有する水溶液

[note]
* 7, Immersion liquid a: Isopropyl alcohol * 8, Immersion liquid b: Acetone * 9, Immersion liquid c: Nonionic surfactant (glycerin fatty acid ester [product name: Excel 300V], 30%) Aqueous solution

Example 1
According to the formulation shown in Table 1, PP and oil-extended EPDM were charged as a polymer into a pressure type kneader whose temperature in the tank was set to 180 ° C., melted and mixed, and then discharged. The discharged composition was continuously extruded using a feeder ruder and cut into strands to prepare master batch pellets. A blend of the obtained master batch pellets and a crosslinking agent was dynamically and continuously crosslinked to obtain a thermoplastic elastomer composition. Table 3 shows the evaluation results regarding hardness and chemical resistance.

Comparative Example 1
According to the formulation shown in Table 1, PP and SEPS as a polymer and paraffin oil as a softening agent were added to a pressure type kneader whose temperature in the tank was set at 180 ° C., and melt-mixed to obtain a thermoplastic elastomer composition. Table 3 shows the evaluation results regarding hardness and chemical resistance.

Comparative Example 2
According to the formulation shown in Table 1, SEPS as a polymer and paraffin oil as a softening agent were put into a pressure type kneader having a tank internal temperature set to 180 ° C., and melt-mixed to obtain a thermoplastic elastomer composition. Table 3 shows the evaluation results regarding hardness and chemical resistance.

Table 3 shows the following.
The thermoplastic elastomer composition (Example 1) of the present invention is greatly improved in chemical resistance as compared with the compositions (Comparative Examples 1 and 2) in which the conventional hardness is set to the same value.

The thermoplastic elastomer composition of the present invention exhibits excellent chemical resistance (solvent resistance),
As a low-hardness seal member, it is suitably used as a liquid sealing member containing a gasket, a seal material, particularly a compound that generates a solvent crack.

Claims (6)

  (A) an olefin resin, and (b) an ethylene copolymer rubber having an intrinsic viscosity [η] measured in a decalin solvent at 135 ° C. of 4.3 to 6.8 dl / g and a mineral oil softener. A polymer mixture containing an oil-extended ethylene copolymer rubber is dynamically crosslinked in the presence of a crosslinking agent, and the hardness obtained in accordance with JIS K6031 (A) type is 10 to 50 A thermoplastic elastomer composition characterized by the above.   The thermoplastic elastomer according to claim 1, wherein the mass ratio (a) / (b ') of the olefin resin of component (a) and the ethylene copolymer rubber in component (b) is 10/90 to 90/10. Composition.   The component (a) olefin resin is an ethylene homopolymer, a crystalline ethylene copolymer containing 90 mol% or more of ethylene units, a crystalline propylene homopolymer, and 90 mol% or more of propylene units. The thermoplastic elastomer composition according to claim 1 or 2, which is at least one selected from crystalline propylene copolymers.   The oil-extended ethylene copolymer rubber of component (b) contains 20 to 300 parts by mass of a mineral oil softener with respect to 100 parts by mass of the ethylene copolymer rubber. Thermoplastic elastomer composition.   A low-hardness sealing member using the thermoplastic elastomer composition according to claim 1. The low-hardness seal member according to claim 5, which is for a liquid containing a chemical substance that causes a solvent crack.