JP2001114976A - Thermoplastic elastomer composition and gasket material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic elastomer composition which is excellent in sealing properties, is prevented from generating a gas such as a volatile low-mol.wt. component, and is suitable as a gasket material, especially as a gasket material for a hard disk unit. SOLUTION: This composition comprises (A) 100 pts.wt. hydrogenated block copolymer prepared by hydrogenating a block copolymer comprising at least one polymer block formed mainly from an aromatic vinyl compound and at least one polymer block formed mainly from a conjugated diene compound, (B) 50-1,000 pts.wt. nonaromatic softener having a kinematic viscosity (at 40 deg.C) of 100 mm2/sec or higher, and (C) 1-100 pts.wt. polymer which is a propylene homopolymer and/or a propylene copolymer formed mainly from propylene and which does not contain a lubricant or has been thermally treated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic elastomer composition and a gasket material using the same. In particular, the present invention relates to a thermoplastic elastomer composition and a gasket material suitable for use as a member of an electronic device.

[0002]

2. Description of the Related Art In recent years, the development of electronic devices has been remarkable. These electronic devices use an integrated circuit using a semiconductor and are printed and wired on a substrate.
The weight has been reduced. These electronic devices dislike moisture and dust. Therefore, the sealing performance of the gasket that seals the joint surface between the box-shaped main body and the cover body containing these integrated circuits depends on the performance and durability of the electronic devices. Is an important factor for For this reason, usually, a gasket is sandwiched between the joining surfaces of the box body and the lid body containing these integrated circuits and the like, and they are integrated by fastening with mounting bolts or the like. Urethane foam material was used. This urethane foam material is obtained by cutting urethane foam into a thin sheet, and is often used by sticking an adhesive tape to the sheet and punching it into a desired shape. In addition, a method has been proposed in which a frame made of stainless steel or rigid resin is inserted into a mold and then an elastomer is injection-molded (Japanese Patent Application Laid-Open No. 8-283698).

[0003] However, both gaskets made of urethane foam material and gaskets made of elastomer often generate gas that contaminates the magnetic disk when the temperature inside the electronic device body rises to 40 to 50 ° C during actual use. The generated gaseous components may accumulate on a disk such as a hard disk device, which may make the hard disk device unreadable. In order to solve such inconveniences, a mechanism for adsorbing the generated gas is provided (Japanese Patent Laid-Open No. 6-302178). This problem is dealt with by providing a gas adsorbent in the breathing hole (JP-A-6-36548).
However, generation of gas from the gasket has been for a long time, and the inconvenience of always generating gas when using an electronic device cannot be avoided.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermoplastic elastomer composition which is excellent in sealing properties in such a situation and which prevents generation of gas such as volatile low molecular components. It is assumed that. Another object of the present invention is to provide a gasket material, particularly a gasket material for a hard disk drive, in which the above-mentioned problem is solved, particularly when used as a member of an electronic device.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have found that the object can be achieved by using a specific thermoplastic elastomer composition. Was. The present invention has been completed based on such findings. That is, the present invention provides (a)
A hydrogenated block copolymer 100 obtained by hydrogenating a block copolymer composed of at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. (B) 50 to 1000 parts by weight of a non-aromatic softener having a kinematic viscosity at 40 ° C. of 100 mm ² / sec or more, and (c) a propylene homopolymer and / or propylene containing no lubricant. Propylene copolymer 1 to 100
It is intended to provide a thermoplastic elastomer composition consisting of parts by weight. Further, the present invention provides a method wherein (a) a block copolymer comprising at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound is hydrogenated. 100 parts by weight of the obtained hydrogenated block copolymer, (b) 50 to 1000 parts by weight of a non-aromatic softener having a kinematic viscosity at 40 ° C. of 100 mm ² / sec or more, and (c ′) heat-treated propylene alone An object of the present invention is to provide a thermoplastic elastomer composition comprising 1 to 100 parts by weight of a propylene copolymer mainly composed of a polymer and / or propylene. The present invention further provides a gasket material comprising the above-mentioned thermoplastic elastomer composition, particularly a gasket material for a hard disk drive.

[0006]

DETAILED DESCRIPTION OF THE INVENTION In the thermoplastic elastomer composition of the present invention, at least one of a polymer block mainly composed of a vinyl aromatic compound and a polymer block mainly composed of a conjugated diene compound are used as component (a). A hydrogenated block copolymer obtained by hydrogenating a block copolymer composed of at least one of the following is used. As the hydrogenated block copolymer, for example, a polystyrene / polybutadiene / polystyrene block copolymer or a polystyrene / polyisoprene / polystyrene block copolymer obtained by hydrogenation, for example, styrene-ethylene / butylene -Triblock copolymer of styrene (SE
BS) and a triblock copolymer of styrene-ethylene / propylene-styrene (SEPS). The number average molecular weight of these hydrogenated block copolymers is preferably 60,000 or more. When the number average molecular weight is less than 60,000, the bleeding of the softener increases, the compression set becomes large, and there may be a disadvantage that it cannot withstand actual use. The upper limit of the number average molecular weight is not particularly limited, but is usually about 400,000.

The content of the amorphous styrene block in the hydrogenated block copolymer is desirably in the range of 10 to 70% by weight, preferably 15 to 60% by weight. The glass transition temperature (Tg) of the amorphous styrene block portion is 6
Those having a temperature of 0 ° C. or higher, preferably 80 ° C. or higher are desirable. Also, the polymer at the portion connecting the amorphous styrene blocks at both ends is preferably amorphous. In addition, these hydrogenated block copolymers are mainly used alone, but two or more kinds may be blended and used.

In the thermoplastic elastomer composition of the present invention, the kinematic viscosity at 40 ° C. is 100 mm ² / sec or more at 40 ° C. for the purpose of lowering the hardness of the thermoplastic elastomer (a). It is necessary to compound a non-aromatic softener which is If the kinematic viscosity at 40 ° C. of the softener is less than 100 mm ² / sec, the composition loses weight and bleeds significantly due to volatilization, which causes inconvenience that it cannot withstand actual use. The kinematic viscosity is 100 to 10000 mm ^{2 at} 40 ° C. in terms of practical use and production.
/ S, preferably 200 to 5000 mm
² / sec is preferred. Further, from the viewpoint of the molecular weight, those having a weight average molecular weight of less than 20,000, particularly 10,000 or less, especially 5,000 or less are preferred. As such a softening agent, usually, a liquid or liquid at room temperature is suitably used. Further, both hydrophilic and hydrophobic softeners can be used. The softener having such properties can be appropriately selected from various softeners for non-aromatic rubbers such as mineral oils, vegetable oils, and synthetic oils. Here, the mineral oils include naphthenic and paraffinic process oils, and the vegetable oils include
Castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, sardine oil, peanut oil, wood wax, pine oil, olive oil, and the like. Of these, one or more selected from mineral oil-based paraffinic oils, naphthenic oils, and synthetic polyisobutylene-based oils, and those having a weight average molecular weight of 450 to 5000 are preferred.

These softeners may be used alone or in a combination of two or more. The mixing amount of these softeners is 50 to 1000 parts by weight, preferably 55 to 1000 parts by weight, per 100 parts by weight of the component (a).
300 parts by weight. If the amount is less than 50 parts by weight, a sufficiently low hardness cannot be attained and the flexibility of the thermoplastic elastomer composition becomes insufficient. If the amount exceeds 1000 parts by weight, the softener tends to bleed and the thermoplastic elastomer This causes a decrease in the mechanical strength of the composition. The amount of the softener is appropriately selected from the above range according to the molecular weight of the hydrogenated block copolymer of the component (a) and the type of other components added to the hydrogenated block copolymer. Is preferred.

[0010] The thermoplastic emerastomer composition of the present invention is intended to improve the processability and heat resistance of the composition,
In order to prevent gas generation such as volatile low molecular components,
As the component (c), it is necessary to add a propylene homopolymer containing no lubricant and / or a propylene copolymer mainly composed of propylene. Examples of the propylene polymer include a copolymer of propylene and a small amount of another α-olefin (for example, a propylene-ethylene copolymer or a propylene / 4-methyl-1-pentene copolymer). . Here, the polypropylene according to the present invention refers not to a polypropylene polymerized using a metallocene catalyst, but a general polypropylene, specifically, an isotactic polypropylene or an atactic polypropylene.
Obtained by polymerizing propylene in the presence of (system). Among copolymers, a random copolymer is obtained by coexisting a small amount of ethylene or another α-olefin during polymerization, and a block copolymer is obtained by polymerizing propylene homopolymer and then mainly polymerizing ethylene. A propylene homopolymer and / or a propylene-based propylene copolymer (hereinafter referred to as polypropylene, etc.) containing no lubricant as a gas generation source is 40 to 40%.
Since no gas is generated even in an environment of 50 ° C., even when the thermoplastic emullastomer composition containing propylene or the like containing no lubricant is used as a gasket material for a hard disk device for a long period of time, the disk performance is improved by gaseous volatile components. It will not be compromised. Here, the lubricant refers to an additive such as polypropylene which imparts lubricity necessary for facilitating molding processing, and specifically, a hydrocarbon-based lubricant such as paraffin and wax, and a fatty acid-based lubricant such as stearic acid. And metal soap-based lubricants such as calcium stearate, and fatty acid derivative-based lubricants such as fatty acid amides. It is preferable that the polypropylene or the like containing no lubricant further contains no additive that generates a gas at a temperature of 120 ° C. or lower. Examples of the gas-generating additives include various stabilizers such as phenol-substituted products, antioxidants such as aromatic amines, ultraviolet absorbers such as hindered amines and benzophenones, and DOP (dioctyl phthalate). Various additives such as a plasticizer such as a phthalic acid ester, a flame retardant using a halogen-based flame retardant, antimony oxide, and a phosphorus flame retardant alone or in combination thereof are exemplified. Further, even in the case of polypropylene or the like containing a lubricant or the like, since the contained gas can be removed by heat treatment, if the heat-treated polypropylene or the like is mixed with the thermoplastic elastomer composition, the gas can be removed even in an environment of 40 to 50 ° C. Does not occur. The heat treatment can be performed, for example, at a temperature of 80 to 150 ° C. for 1 to 48 hours, such as polypropylene before shaping into a gasket shape.
It is particularly preferable to carry out the reaction at 5 ° C. for 5 to 24 hours. The compounding amount of the component (c) or the component (c ′) is as described in the above (a).
1 to 100 parts by weight, based on 100 parts by weight of the component,
It is preferably 3 to 40 parts by weight, particularly preferably 5 to 30 parts by weight. If the amount is more than 100 parts by weight, the hardness of the obtained thermoplastic elastomer composition is too high.

The method for producing the thermoplastic elastomer composition of the present invention is not particularly limited, and a known method can be applied. For example, the above-mentioned components and optionally used additive components are melt-mixed using a heating kneader, for example, a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer, a pravender, a kneader, a high-shear mixer, or the like. Kneading, and further, if desired, adding a crosslinking agent such as an organic peroxide, a crosslinking aid, or the like, or by simultaneously mixing these necessary components, and heat-kneading,
It can be easily manufactured. Further, a thermoplastic elastomer composition obtained by kneading a high-molecular organic material and a softening agent is prepared in advance, and this composition is further added to one or more high-molecular organic materials of the same type or different types used here. It can also be manufactured by mixing.

Example 1 The following ingredients were mixed in a 220-screw extruder using a twin-screw extruder.
The mixture was kneaded at ℃, extruded into strands, and then cut into pellets. Ingredients (1) Triblock copolymer of styrene-ethylene / propylene-styrene [manufactured by Kuraray Co., Ltd., trade name: Septon] (SEPS having a number average molecular weight of 120,000 and a styrene content of 30% by weight) 100 parts by weight ( 2) 100 parts by weight of paraffin-based oil having a kinematic viscosity at 40 ° C. of 380 mm ² / sec [trade name: Diana Process Oil PW380 manufactured by Idemitsu Kosan Co., Ltd.] (weight average molecular weight: 750) (3) Excluding lubricant 25 parts by weight of polypropylene (trade name: CF3001 manufactured by Chisso Corp.) Next, the thermoplastic elastomer material thus obtained was used as an injection molding machine in a DC manufactured by Nissei Plastics Co., Ltd.
Using a 60E5ASE machine at a molding temperature of 180 ° C and a thickness of 1
mm sheet was prepared. The obtained sheet (0.1 g) was cut into small pieces, held in a sample tube of a thermal tesorption cold trap device, and heated at 100 ° C. for 30 minutes.
The generated gas is -13 at a He gas flow rate of 10 m1 / min.
After trapping in the trap portion cooled to 0 ° C., the trap portion was rapidly heated to 150 ° C. and the desorbed gas was subjected to GC-MS
Was measured. The detector used was a secondary electron multiplier equipped with a post-acceleration detector and an atomic emission detector. As a result, it was confirmed that the detected gas was a trace amount of saturated hydrocarbon.

Comparative Example 1 Instead of the polypropylene used in Example 1, a polypropylene containing a metal soap salt lubricant [manufactured by Nippon Polychem Co., Ltd.
A sample was prepared in the same manner as in Example 1 except that trade name: EX6] was used, and the generated gas was measured in the same manner as in Example 1. As a result, the detected gas was found to be about 40 times the amount of saturated hydrocarbons in Example 1.

Example 2 Components composed of the following components were kneaded at 220 ° C. using a twin-screw extruder, extruded into strands, and then cut into pellets. Ingredients: (1) 100 parts by weight of triblock copolymer of styrene-ethylene / propylene-styrene (SEPS with a number average molecular weight of 50,000 and a styrene content of 30% by weight) (2) Paraffin oil [Idemitsu Kosan Co., Ltd. (Trade name: Diana Process Oil PW380) (weight average molecular weight 750) 125 parts by weight (3) Lubricant-free polypropylene (trade name: CF3001 manufactured by Chisso Corporation) 30 parts by weight A sheet was prepared from the elastomer material in the same manner as in Example 1, a sample was prepared from the sheet, and the gas generated in the same manner as in Example 1 was measured. As a result, the amount of detected gas was extremely small,
Was found to be about 1/20 of the saturated hydrocarbon.

Example 3 Injection molding was performed in the same manner as in Example 1 to produce a gasket with a lid for a case accommodating a hard disk drive as shown in FIG. 1 (this figure shows a gasket material with a lid). Is a view from the sealing surface side.) The gasket 1 is in close contact with the surface of a lid 2 made of aluminum, and the lid 2 serves as a lid of a hard disk drive device storage case. In the center gap of the gasket with lid, devices such as magnetic disk, magnetic head, actuator,
These devices are arranged on the box side of the hard disk drive storage case, and these devices are made of metal boxes (not shown).
And a gasket with a lid and closed in the hard disk drive device storage case. When such a gasket with a lid is used as a lid of a hard disk drive storage case, that is, a gasket is arranged in a hard disk drive and used, a failure considered to be caused by gas generated from the gasket occurs for a long time. Did not.

Example 4 The following components were mixed in a 220-screw extruder using a twin-screw extruder.
The mixture was kneaded at ℃, extruded into strands, and then cut into pellets. Ingredients (1) Triblock copolymer of styrene-ethylene / propylene-styrene [manufactured by Kuraray Co., Ltd., trade name: Septon] (SEPS having a number average molecular weight of 120,000 and a styrene content of 30% by weight) 100 parts by weight ( 2) 100 parts by weight of a paraffinic oil having a kinematic viscosity at 40 ° C. of 380 mm ² / sec [trade name: Diana Process Oil PW380 manufactured by Idemitsu Kosan Co., Ltd.] (weight average molecular weight: 750) (3) Polypropylene containing calcium stearate [Nippon Polychem Co., Ltd., trade name: MA03] heat-treated in an oven at 110 ° C. for 24 hours 25 parts by weight Next, the thermoplastic elastomer material thus obtained was used as an injection molding machine. DC manufactured by Nissei Plastic Industry Co., Ltd.
Using a 60E5ASE machine at a molding temperature of 180 ° C and a thickness of 1
mm sheet was prepared. The obtained sheet (0.1 g) was cut into small pieces, held in a sample tube of a thermal tesorption cold trap device, and heated at 100 ° C. for 30 minutes.
The generated gas is -13 at a He gas flow rate of 10 m1 / min.
After trapping in the trap portion cooled to 0 ° C., the trap portion was rapidly heated to 150 ° C. and the desorbed gas was subjected to GC-MS
Was measured. The detector used was a secondary electron multiplier equipped with a post-acceleration detector and an atomic emission detector. As a result, it was confirmed that the detected gas was a trace amount of saturated hydrocarbon.

Comparative Example 2 In Example 4, a calcium stearate-containing polypropylene [manufactured by Nippon Polychem Co., Ltd., trade name: MA03]
A sample was prepared in the same manner as in Example 4 except that was used without heat treatment, and the generated gas was measured in the same manner as in Example 4. As a result, the detected gas was found to be about 40 times the amount of saturated hydrocarbons in Example 4.

Example 5 The following components were kneaded at 220 ° C. using a twin screw extruder, extruded into strands, and then cut into pellets. Ingredients: (1) 100 parts by weight of triblock copolymer of styrene-ethylene / propylene-styrene (SEPS with a number average molecular weight of 50,000 and a styrene content of 30% by weight) (2) Paraffin oil [Idemitsu Kosan Co., Ltd. (Trade name: Diana Process Oil PW380) (weight average molecular weight: 750) 125 parts by weight (3) Calcium stearate-containing polypropylene [manufactured by Nippon Polychem Co., Ltd., trade name: MA03] is heated in an oven at 110 ° C. for 24 hours. 30 parts by weight Next, a sheet was prepared from the obtained thermoplastic elastomer material in the same manner as in Example 1, a sample was prepared from the sheet, and the gas generated in the same manner as in Example 1 was measured. went. As a result, the amount of detected gas was extremely small,
Was found to be about 1/20 of the saturated hydrocarbon.

Example 6 Injection molding was performed in the same manner as in Example 4 to produce a gasket with a lid similar to that in Example 3. When this gasket with a lid was used as a lid of a hard disk drive storage case, that is, a gasket was placed in the hard disk drive and used, no failure that could be caused by gas generated from the gasket occurred for a long time. .

[0020]

The thermoplastic elastomer composition of the present invention has excellent sealing properties and prevents generation of a gas containing a volatile low-molecular component even when used for a long time. further,
Since the thermoplastic elastomer composition of the present invention hardly generates a volatile gas on a magnetic disk or the like under electronic device use conditions, the present invention is preferably used for a gasket material, especially for a gasket material for a hard disk device. Is done. Further, the present invention can be widely applied to the production of seal materials, vibration-proof materials, shock-absorbing materials, cover materials, cushioning materials and the like.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a gasket according to the present invention.

[Explanation of symbols]

 1: Gasket 2: Hard disk drive case lid

Claims (7)

[Claims] 1. A method comprising hydrogenating a block copolymer comprising (a) at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. (B) a non-aromatic softening agent having a kinematic viscosity at 40 ° C. of 100 mm ² / sec or more;
A thermoplastic elastomer composition comprising 000 parts by weight and (c) 1 to 100 parts by weight of a propylene homopolymer and / or a propylene copolymer containing propylene as a main component without a lubricant. 2. (c) The propylene homopolymer and / or propylene copolymer containing propylene as a lubricant does not contain an additive which generates gas at a temperature of 120 ° C. or lower. 2. The thermoplastic elastomer composition according to 1. 3. A gasket material comprising the thermoplastic elastomer composition according to claim 1. 4. A gasket material for a hard disk drive, comprising the thermoplastic elastomer composition according to claim 1. 5. A method comprising hydrogenating a block copolymer comprising (a) at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. (B) a non-aromatic softening agent having a kinematic viscosity at 40 ° C. of 100 mm ² / sec or more;
(C ′) a thermoplastic elastomer composition comprising 1 to 100 parts by weight of a heat-treated propylene homopolymer and / or a propylene-based propylene copolymer. 6. A gasket material comprising the thermoplastic elastomer composition according to claim 5. 7. A gasket material for a hard disk drive comprising the thermoplastic elastomer composition according to claim 5.