JP2002088219A - Gasket material and gasket for hard disk apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gasket material which is excellent in properties required of a gasket material, such as low hardness and low compression set, and gives a gasket having a low permeability to a low-mol.-wt. siloxane, etc. SOLUTION: This gasket material comprises (a) 100 pts.wt. thermoplastic styrene elastomer having a styrene unit content of 20-35 wt.% and a wt. average mol.wt. of 250,000 or higher, (b) 50-200 pts.wt. polyisobutylene having a wt. average mol.wt. of 500-20,000, and (c) 10-50 pts.wt. polyethylene or polypropylene modified with acrylic acid, methacrylic acid, maleic anhydride or maleic acid or copolymer of ethylene or propylene with acrylic acid, methacrylic acid, maleic anhydride or maleic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gasket material which provides a gasket having a low hardness and a small compression set, which is excellent in performance required as a gasket material, and which has a low permeability of low molecular weight siloxane and the like. The present invention relates to a gasket for a hard disk drive formed by molding the gasket material.

[0002]

2. Description of the Related Art In recent years, electronic devices such as computers have been improved in performance and miniaturization, and have complicated circuit structures. Even small amounts of dust can cause obstacles. The use of gaskets to prevent dust intrusion is common practice. Conventionally, low-hardness elastomers have been widely used as gasket materials for hard disk drives, and when the low-hardness elastomer is integrated with a metal cover or metal frame and used as a form of a gasket with a cover or a gasket with a frame, a low-hardness elastomer is used. There is an advantage that the characteristic of is fully exhibited. In a gasket for a hard disk device, in addition to preventing dust from entering, it is required that the permeability of a substance such as water vapor or a low molecular weight siloxane, which easily hinders the maintenance of the function of the hard disk device, be low. The low molecular weight siloxane is contained in, for example, a hair spray, and the inconvenience that the hard disk device malfunctions when the low molecular weight siloxane in the hair spray adhering to the head vaporizes and penetrates through the gasket into the hard disk device. Occurs.

[0003]

Under such circumstances, the present invention is excellent in performance required as a gasket material, such as low hardness and small compression set, and has low molecular weight siloxane and the like. It is an object of the present invention to provide a gasket material that provides a gasket having low performance.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, it has been found that a specific styrene-based thermoplastic elastomer has polyisobutylene having a weight average molecular weight in a specific range and It has been found that a gasket material containing a specific amount of a specific modified polyethylene or a specific modified polypropylene can achieve the object. The present invention has been completed based on such findings.

That is, the present invention relates to (a) 100 parts by weight of a styrene-based thermoplastic elastomer having a styrene unit content of 20 to 35% by weight and a weight average molecular weight of 250,000 or more;
(B) 50 to 200 parts by weight of polyisobutylene having a weight average molecular weight of 500 to 20,000 and (c) modified polyethylene or polypropylene modified with acrylic acid, methacrylic acid, maleic anhydride or maleic acid, or acrylic acid or methacrylic acid Acid, a gasket material comprising 10 to 50 parts by weight of a copolymer of maleic anhydride or maleic acid and ethylene or propylene, a gasket for a hard disk device formed by molding the gasket material into a metal cover or a metal frame. To provide.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As the component (a) of the gasket material of the present invention, the styrene unit content is 20 to 35% by weight,
A styrene-based thermoplastic elastomer having a weight average molecular weight of 250,000 or more is used. Specifically, a block copolymer of polybutadiene and polystyrene, and a block copolymer of polyisoprene and polystyrene, or a block copolymer of polybutadiene or an ethylene-butadiene random copolymer and polystyrene are hydrogenated. For example, styrene-ethylene / butylene-styrene triblock copolymer (SEBS), styrene-ethylene / propylene-styrene triblock copolymer (SEPS), etc. A such as a block copolymer or a styrene-ethylene / propylene-styrene block copolymer,
-BA type copolymer can be mentioned. In the present invention, these elastomers may be used alone,
Two or more kinds may be used in combination. If the styrene unit content of the styrene-based thermoplastic elastomer is less than 20% by weight, the heat resistance is inferior, and the disadvantage that sag at high temperatures is increased. If it exceeds 35% by weight, the hardness increases, It becomes difficult to obtain a desired low hardness gasket material. On the other hand, if the weight average molecular weight of the styrene-based thermoplastic elastomer is less than 250,000, the holding performance of the softener and oil is inferior, and the softener bleeds under compression. The upper limit of the weight average molecular weight of the styrene-based thermoplastic elastomer is not particularly limited,
Usually, it is about one million.

As the component (b) of the gasket material of the present invention, polyisobutylene having a weight average molecular weight of 500 to 20,000 is used. This polyisobutylene functions as a softener, but if the weight average molecular weight is less than 500, a large amount of gas is generated from the gasket, which may cause malfunction in the hard disk drive. If the weight average molecular weight exceeds 20,000, the polyisobutylene becomes rubbery, which makes it difficult to knead the gasket when producing the gasket, and also increases the compression set of the gasket. As a result, practically sufficient characteristics cannot be obtained. The amount of the component (b) is from 50 to 200 parts by weight, preferably from 100 to 180 parts by weight, per 100 parts by weight of the styrene thermoplastic elastomer of the component (a). If the blending amount of the component (b) is less than 50 parts by weight, a low-hardness body cannot be obtained, and if the blending amount of the component (b) exceeds 200 parts by weight, gas generated from the gasket increases, This causes a malfunction in the hard disk device.

As the component (c) of the gasket material of the present invention, modified polyethylene or modified polypropylene modified with acrylic acid, methacrylic acid, maleic anhydride or maleic acid, or acrylic acid, methacrylic acid, maleic anhydride or maleic acid A copolymer of ethylene and propylene is used. Modification rate or copolymerization rate (% by weight:
The modifier or the copolymer used in 100 parts by weight of polyethylene or polypropylene is 10 to 10 parts by weight from the viewpoint of obtaining an adhesive force to a metal cover or a metal frame.
20% by weight is preferred. The amount of the component (c) is from 10 to 50 parts by weight, preferably from 20 to 30 parts by weight, per 100 parts by weight of the styrene thermoplastic elastomer of the component (a). When the amount of the component (c) is less than 10 parts by weight, the adhesive strength is significantly reduced. When the amount of the component (c) exceeds 50 parts by weight, a desired low-hardness body can be easily obtained. Can not be done.

The gasket material of the present invention may contain a non-aromatic softener other than the component (b) as long as the effects of the present invention are not impaired.
It is preferably from 0 to 10,000 mm ² / sec.
Those having 0 mm ² / sec are particularly preferred. From the viewpoint of 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. The softener having such properties can be appropriately selected from various softeners for non-aromatic rubbers such as mineral oils and synthetics. here,
Mineral oils include naphthenic and paraffinic process oils. Of these, one or more selected from mineral oil-based paraffinic oil, naphthenic oil or synthetic polyisobutylene-based oil, and those having a weight average molecular weight of 450 to 1,000 are preferred.

The method for producing the gasket material of the present invention is not particularly limited, and a known method can be applied. For example, the components (a) to (c) and optional additives are mixed by a heating kneader such as a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer, a pravender, a kneader, and a high-shear mixer. It can be easily manufactured by melt-kneading using. By injection-molding the gasket material thus obtained into a metal cover or metal frame, an integrated gasket in which the gasket and the cover or frame are integrated can be obtained. The injection molding can be performed at a mold temperature of 30 ° C. or higher, preferably 50 to 100 ° C., and a resin temperature of 17 ° C.
0 to 250 ° C., preferably 180 to 230 ° C., the injection speed is 100 to 105 sec ⁻¹ , preferably 1000 to ⁵ ×.
It can be 10 ⁴ sec ⁻¹ .

[0011] Metals forming the cover body and the frame body include:
For example, nickel-plated aluminum, nickel-plated steel, cold-rolled steel, galvanized steel, aluminum / zinc alloy-plated steel, stainless steel, aluminum, aluminum alloy, magnesium, magnesium alloy, etc. Can be appropriately selected and used. Further, a product obtained by injection-molding magnesium can also be used. From the viewpoint of corrosion resistance, a metal subjected to electroless nickel plating is preferable, and in the present invention,
Nickel plated aluminum and nickel plated steel are preferred. As the electroless nickel plating method, known methods conventionally applied to metal materials, for example, pH 4.0 to 5.0 containing nickel sulfate, sodium hypophosphite, lactic acid, propionic acid, and the like at an appropriate ratio. For example, a method of immersing a metal plate in an electroless nickel plating bath composed of an aqueous solution having a temperature of about 85 to 95 ° C. can be used. The gasket material of the present invention has a diameter of 8 mm and a thickness of 2 mm.
mm gasket material with a siloxane concentration of 200
It has a siloxane permeability of 0.4 μg or less when left at 60 ° C. for 15 hours in an atmosphere of 0 ppm, and is suitable as a gasket material for a hard disk drive.

[0012]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The evaluation of physical properties in the following Examples and Comparative Examples was performed by the following methods.

(1) Hardness Measured with a type A durometer according to JIS K6253. (2) Compression set In accordance with JIS K6262, 70 ° C under 25% compression,
After standing for 22 hours, the compression set was measured. (3) Siloxane permeation amount Each gasket material was converted to DC60 manufactured by Nissei Plastic Industry Co., Ltd.
The sheet was molded at a molding resin temperature of 180 ° C. using an E5ASE machine to produce a sheet having a thickness of 2 mm. The sheet is punched into a circle having a diameter slightly smaller than the inner diameter of the vial lid, and the circular sheet is subjected to ultrasonic cleaning using an ultrasonic cleaner.
Wash with warm water of 0 ° C for about 5 minutes to remove surface dirt,
After washing, it was air-dried to obtain a test sheet. The vial lid is provided with a hole having a diameter of 8 mm substantially at the center thereof, and is sufficiently washed. The vial used has a volume of 20 milliliters, and has been subjected to a drying treatment at 300 ° C. for 10 minutes or more. 0.05 g of an adsorbent (Tenax-TA, manufactured by GL Sciences Co., Ltd., product having passed through 60 to 80 mesh) which had been subjected to a drying treatment at 300 ° C. for 30 minutes or more was weighed, placed in a plate made of aluminum foil, and put in this state. The adsorbent is placed on the dried vial, the test sheet is placed on the mouth of the vial, and the lid is closed. When closing the lid, observe the test sheet from the outside of the vial and make sure that the test sheet is not deformed. After closing the lid, a Teflon tape is wrapped around the side of the vial and the side of the lid so that the side of the vial and the gap between the vial and the lid are not visible from the outside, and a transmission measurement system is provided. The treatment with Teflon tape is performed in order to prevent the adsorption of siloxane because the siloxane is easily adsorbed on the glass, and to absorb the siloxane only from the test sheet.

A sealable container made of stainless steel having an internal volume of 10 liters is prepared. In the container, the above-mentioned permeation measurement system and a tetramer of cyclic siloxane (2,000 ppm relative to the volume of the container) are prepared. The bottle with the liquid) is placed and sealed. The sealed container is left for 15 hours in a thermostatic chamber adjusted to 60 ° C., and is allowed to permeate the test sheet and adsorb the cyclic siloxane in the adsorbent in the vial. After 15 hours have elapsed, the sealed container is taken out of the thermostat and left at room temperature. After confirming that the sealed container has reached room temperature, the sealed container is opened and the transmission measurement system is taken out. The adsorbent is taken out by opening the permeation measurement system taken out, and the amount of the cyclic siloxane tetramer adsorbed on the adsorbent is determined by dynamic HS.
-Measured with a GC-MS (Dynamic Gas Chromatograph Mass Spectrometer) measuring instrument, and quantified based on a pentadecane calibration curve prepared by measuring separately. The measuring instruments and the like used are as follows.

(1) Model name Dynamic HS: (TDS / CIS system, manufactured by GERSTES) GC: HP6890 MS: HP5973 (2) Analysis conditions Dynamic HS TDS Flow mode: Solvent venting TDS Sample mode: Standard CIS Injection mode: Solvent venting Sample heating temperature, time: 30 ° C (heating rate; 60 ° C / min)-100 ° C (hold for 10 minutes) Trap temperature: -100 ° C Desorption temperature, time: 130 ° C, 5 minutes Transfer line temperature: 130 GC separation column: HP-5MS 30 m 0.25 mm I.C. D. (Film 0.25 μm) Temperature condition: 50 ° C. (hold for 1 minute) to 300 ° C. (heating rate; 15 ° C./min) MS Measurement mass range: 35 to 500 Threshold: 150 Samples: 3 scans / sec: 1.63

(3) Data processing method 28 which is a fragment ion of a cyclic siloxane tetramer
The area is calculated from the ion chromatogram of No. 1 and the amount of siloxane is determined from the following calibration curve. (4) Preparation of standard sample for calibration curve n-pentadecane (Kanto Chemical Co., special grade reagent) is diluted with acetone (Kanto Chemical Co., special grade reagent) to prepare a standard solution. Place 1 microliter of the standard solution in the sample tube and use it as the standard sample. Prepare three or more standard samples with different concentrations,
Prepare a calibration curve. Using the area value calculated in (3) above, the amount of siloxane in terms of n-pentadecane is determined from this calibration curve.

Examples 1 to 9 and Comparative Examples 1 and 2 Each component having the composition shown in Table 1 was sufficiently kneaded to prepare a gasket material, and the physical properties were evaluated. First result
Shown in the table. The siloxane permeation amount of each of the gasket materials of the examples was 0.4 μg or less, which indicates that the gasket material is suitable as a gasket material for a hard disk drive.

[0018]

[Table 1]

[0019]

[Table 2]

(Note) (Styrene-based thermoplastic elastomer) a-1: Septon 4077 manufactured by Kuraray Co., Ltd. (Sulfon having a weight average molecular weight of 350,000 and a styrene unit content of 30% by weight)
EPS) a-2: Septon 4055 manufactured by Kuraray Co., Ltd. (S with a weight average molecular weight of 290,000 and a styrene unit content of 30% by weight)
EPS) (softening agent) b-1: Nippon Petrochemical Co., Ltd., Nisseki Polybutene HV3
5 (weight average molecular weight 750) b-2: Nippon Petrochemical Co., Ltd., Nisseki polybutene HV1
5 (weight average molecular weight 630) b-3: Nippon Petrochemical Co., Ltd., Nisseki polybutene HV5
0 (weight average molecular weight 800) b-4: Nippon Petrochemical Co., Ltd., Nisseki Polybutene HV1
00 (weight average molecular weight: 1000) b-5: Idemitsu Polybutene 15H, manufactured by Idemitsu Petrochemical Co., Ltd.
(Weight average molecular weight 750) b-6: Idemitsu Polybutene 100 manufactured by Idemitsu Petrochemical Co., Ltd.
H (weight average molecular weight: 960) b-7: Idemitsu Polybutene 300 manufactured by Idemitsu Petrochemical Co., Ltd.
H (weight average molecular weight 1500) b-8: Idemitsu Polybutene 35R, manufactured by Idemitsu Petrochemical Co., Ltd.
(Weight average molecular weight 720) b-9: Diana Process Oil P manufactured by Idemitsu Kosan Co., Ltd.
W380 (weight average molecular weight 750) b-10: manufactured by Mitsui Chemicals, Inc., Lucant HC150
(Weight average molecular weight: 4000) (modified polyethylene or modified polypropylene) c-1: manufactured by Mitsui Dupont Polychemical Co., Ltd., Nucrel AN4312C (ethylene-acrylic acid copolymer) c-2: manufactured by Mitsui Dupont Polychemical Co., Ltd. Nucrel N1050H (ethylene-acrylic acid copolymer) c-3: manufactured by Mitsui Dupont Polychemicals Co., Ltd., Nucrel N2050H (ethylene-acrylic acid copolymer) c-4: manufactured by Sanyo Chemical Co., Ltd., Umex 1010 (anhydrous Maleic acid-modified polypropylene) c-1: Sanyo Kasei Co., Ltd., Umex 1001 (maleic anhydride-modified polypropylene)

As a molding machine, DC manufactured by Nissei Plastic Industry Co., Ltd.
Using a 60E5ASE machine, mold temperature 50 ° C, resin temperature 2
The gasket material of Example 1 was injection molded to a thickness of 0.5 mm and a width of 2.0 mm on a nickel-plated aluminum cover at 10 ° C. and an injection speed of 3 × 10 ⁴ sec ^-1. A gasket for a hard disk drive in which a gasket 1 and a cover 2 were integrated as shown in FIG. 1 was produced. In this gasket, the adhesion between the gasket material and the metal was sufficient.

[0022]

As described above, the gasket material of the present invention has a high dust-proofing property and has extremely low permeability to water vapor and low molecular weight siloxane, so that the function of the hard disk drive is not impaired by these substances. Further, since the gasket for a hard disk drive of the present invention is manufactured by injection-molding a gasket material on a metal frame or a metal cover, distortion may occur in the frame or the cover during the manufacturing process. And high pressure maintenance performance (high airtightness).

[Brief description of the drawings]

FIG. 1 is a perspective view of a cover with a gasket using a gasket material of the present invention as viewed from a sealing surface side.

[Explanation of symbols]

 1: Gasket material 2: Cover body

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09K 3/10 C09K 3/10 JE F16J 15/10 F16J 15/10 X 15/12 15/12 F G11B 33/14 501 G11B 33/14 501G 501J 503 503J // (C08L 53/02 (C08L 53/02 23:26) 23:26) B29K 9:06 B29K 9:06 23:00 23:00 B29L 31:00 B29L 31:00 (72) Inventor Tatsuhiko Hosokawa 3-3-9-203, Ogawa-Higashi-cho, Kodaira-shi, Tokyo (72) Inventor Shoson Shibata 903-9, Sekiya, Kamakura-shi, Kanagawa F term (reference) 3J040 AA01 AA12 BA01 EA15 EA17 EA48 FA02 FA06 HA09 HA15 HA30 4F071 AA12 AA12X AA15X AA20X AA21 AA22 AA22X AA32X AA36X AA75 AA78 AF13Y AF25Y AH14 BB05 BC03 BC06 4F206 AA03 AA13 AH13 JA07 JB12 AQ07 AB04 AD03 4J002 BB083 BB093 BB143 BB17X BB213 BP01W GJ02

Claims (6)

[Claims] (A) a styrene unit content of 20 to 35;
By weight, 100 parts by weight of a styrene thermoplastic elastomer having a weight average molecular weight of 250,000 or more, (b) 50 to 200 parts by weight of a polyisobutylene having a weight average molecular weight of 500 to 20,000, and (c) acrylic acid, methacrylic acid, A gasket material comprising 10 to 50 parts by weight of maleic anhydride or modified polyethylene or modified polypropylene modified with maleic acid, or acrylic acid, methacrylic acid, maleic anhydride or a copolymer of maleic acid and ethylene or propylene. 2. The gasket material according to claim 1, wherein the styrene-based thermoplastic elastomer is a triblock copolymer having polystyrene chains at both ends. 3. The modified polyethylene or modified polypropylene has a modification ratio of 10 to 20% by weight, and the copolymer with ethylene or propylene has a copolymerization ratio of 10 to 20% by weight. 3. The gasket material according to 2. 4. The gasket material has a hardness of JIS K
Compression set after standing at 70 ° C. for 22 hours under 25% compression measured at 50 ° or less with a type A durometer according to 6253 and 50% according to JIS K6262 is 50.
%. The gasket material according to claim 1, wherein the gasket material is less than or equal to%. 5. A gasket for a hard disk drive, wherein the gasket material according to claim 1 is injection-molded into a metal cover or a metal frame and integrated. 6. The gasket according to claim 5, wherein the metal cover or the metal frame is made of nickel-plated aluminum, nickel-plated steel or aluminum.