JP2001316561A - Method for producing gasket for hard disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing the subject gasket as an injection molded form easily releasable from a mold when made from an adhesive thermoplastic elastomer composition, therefore with no need of coating the mold with a releasant at every injection molding operation. SOLUTION: This method for producing the subject gasket comprises placing a metallic cover or the like on a mold and subjecting an adhesive thermoplastic elastomer composition as gasket material to injection molding on the metallic cover or the like to effect integration of the resultant gasket with the cover or the like; wherein the mold to be used is such that its inner surface is coated with a fluororesin, and the thermoplastic elastomer composition to be used, for example, comprises 100 pts.wt. of a styrene-based thermoplastic elastomer as a block copolymer, 3-50 pts.wt. of an ethylene-(meth)acrylic acid copolymer 5-45 wt.% in (meth)acrylic acid content, and 50-170 pts.wt. of a paraffin-based oil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a gasket for a hard disk drive in which a metal cover or a metal frame and a gasket made of an adhesive thermoplastic elastomer composition are integrated. Injecting the thermoplastic elastomer composition into a metal cover body or the like, and removing the molded body (gasket) from the mold, the molded body can be easily released from the mold, and The present invention relates to a method for manufacturing a gasket for a hard disk drive, which does not require applying a release agent to a mold each time injection molding is performed.

[0002]

2. Description of the Related Art Conventionally, low-hardness elastomers are frequently used as gasket materials for hard disk drives. The low-hardness elastomer is integrated with a metal cover or a metal frame and used as a form of a gasket with a cover or a gasket with a frame. Thus, there is an advantage that the characteristics of the low hardness elastomer are sufficiently exhibited. Conventionally, to integrate a low-hardness elastomer and a metal, use an adhesive, use an acid-modified styrene-based thermoplastic elastomer as the low-hardness elastomer, process the metal, and physically combine the metal with the low-hardness elastomer. For example, such a method as to be integrated integrally is used. However, the above-described method requires an adhesive application step, and requires step management such as application and drying of the adhesive, which is troublesome, and has a problem that impurities such as volatile components are generated from the adhesive. is there. The above methods have a problem that various properties of the low-hardness elastomer, particularly compression set, are reduced because the polymer is modified, and impurities such as catalyst residues and unreacted substances are generated due to the modification. In the above-mentioned method, there is a problem that the metal and the low-hardness elastomer cannot be integrated because the processing of the metal is troublesome, and the processing for integration cannot be performed with fine parts. Therefore, using a thermoplastic elastomer composition having adhesiveness as a gasket material, and injecting the composition into a metal cover body or a metal frame body, the metal cover body and the like and the gasket are integrated. Has been proposed. In this case, in order to improve the releasability between the injection molded body and the mold, a process of applying a release agent to the inner surface of the mold is performed.
Since the effect of the release agent is not maintained, it is necessary to apply the release agent almost every time injection molding is performed, so that the manufacturing process becomes complicated. Further, since the release agent component is transferred to and adheres to the gasket, and the release agent component acts as an impurity component in the gasket, there is a problem that the release agent component cannot be used as a gasket for electric parts or electronic parts.

[0003]

DISCLOSURE OF THE INVENTION The present invention relates to a method of injection molding a thermoplastic elastomer composition having an adhesive property into a metal cover or the like, and removing the molded body from the mold when removing the molded body from the mold. It is an object of the present invention to provide a method of manufacturing a gasket for a hard disk drive, which can be easily released from a mold, and does not need to apply a release agent to a mold each time injection molding is performed.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve such an object, and as a result, have found that a mold for injection-molding a thermoplastic elastomer composition having an adhesive property is required. It has been found that the purpose can be achieved by coating the surface with a fluororesin. The present invention has been completed based on such findings. That is, the present invention, by placing a metal cover or metal frame on a mold, by injection molding a thermoplastic elastomer composition having an adhesive property as a gasket material on the cover or frame, In a method of manufacturing a gasket for a hard disk in which a cover body or a frame body and a gasket are integrated, a mold whose inner surface is coated with a fluororesin is used as the mold, and the thermoplastic elastomer composition is (a1) 100 parts by weight of a styrene-based thermoplastic elastomer composed of a block copolymer, and (b1) ethylene having a (meth) acrylic acid content of 5 to 45% by weight.
3 to 50 parts by weight of (meth) acrylic acid copolymer or ethylene / (meth) acrylate copolymer and (c1)
Thermoplastic elastomer composition (I) comprising 50 to 170 parts by weight of paraffinic oil or styrene thermoplastic elastomer 10 comprising (a2) block copolymer
0 parts by weight, (b2) 1 to 15 parts by weight of maleic anhydride-grafted polyolefin, and (c2) paraffinic oil 3
An object of the present invention is to provide a method for producing a gasket for a hard disk drive, comprising using a thermoplastic elastomer composition (II) comprising 0 to 170 parts by weight.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The metal forming the cover or frame of the gasket for a hard disk drive according to the present invention is as follows.
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.

[0006] The gasket in the gasket for a hard disk drive according to the present invention is formed of the thermoplastic elastomer composition (I) having adhesive property or the thermoplastic elastomer composition (II) having adhesive property. As the component (a1) of the thermoplastic elastomer composition (I), a styrene-based thermoplastic elastomer composed of a block copolymer is used. Specifically, a block copolymer of crystalline polyethylene and an ethylene / butylene-styrene random copolymer obtained by hydrogenating a block copolymer of polybutadiene and a butadiene-styrene random copolymer, polybutadiene and polystyrene And a block copolymer of polyisoprene and polystyrene, or obtained by hydrogenating a block copolymer of polybutadiene or an ethylene-butadiene random copolymer and polystyrene, for example, crystalline Diblock copolymer of polyethylene and polystyrene, styrene
Ethylene / butylene-styrene triblock copolymer (SEBS), styrene-ethylene / propylene-styrene triblock copolymer (SEPS), among others, styrene-ethylene / butylene-styrene block copolymer or styrene-ethylene / A-A type copolymer such as propylene / styrene block copolymer. In the present invention, these elastomers may be used alone or in combination of two or more.

[0007] (b) of the thermoplastic elastomer composition (I)
1) As a component, the content of (meth) acrylic acid is 5 to 45.
% By weight of an ethylene / (meth) acrylic acid copolymer or an ethylene / (meth) acrylic acid ester copolymer. Here, (meth) acrylic acid means acrylic acid or methacrylic acid. In the case of an ethylene / (meth) acrylic acid ester copolymer, the (meth) acrylic acid content means the content of (meth) acrylic acid ester converted to (meth) acrylic acid. When the (meth) acrylic acid content in the ethylene / (meth) acrylic acid copolymer or the ethylene / (meth) acrylate copolymer is less than 5% by weight, the adhesiveness of the resin composition is reduced, If the content of (meth) acrylic acid exceeds 45% by weight, the flexibility and heat resistance of the resin composition decrease. ethylene·
The (meth) acrylic acid content in the (meth) acrylic acid copolymer is preferably from 5 to 20% by weight, particularly preferably from 8 to 18% by weight. In addition, ethylene
(Meth) in (meth) acrylate copolymer
The acrylic acid content is preferably from 25 to 45% by weight, particularly preferably from 28 to 40% by weight.

The (meth) acrylate in the ethylene / (meth) acrylate copolymer includes:
C1-C10 alkyl esters are preferred, and specific examples include methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, and the like. In the present invention, a copolymer of an ester of acrylic acid having 1 to 4 carbon atoms is particularly preferred.
The ethylene / (meth) acrylic acid copolymer or ethylene / (meth) acrylic acid ester copolymer has a temperature of 19
The melt flow rate (MFR) at 0 ° C. and a load of 2.16 kgf (21.2 N) is preferably from 0.1 to 50 g / 10 min, particularly preferably from 0.5 to 30 g / 10 min. In the ethylene / (meth) acrylic acid ester copolymer, the MFR is particularly preferably 1 to 30 g / 10 min, and more preferably 5 to 25 g / 10 min. The MFR is based on JIS K7210
It is a value measured in accordance with. The blending amount of the component (b1) is 100% of the styrene thermoplastic elastomer 100 of the component (a1).
It is 3 to 50 parts by weight, preferably 4 to 40 parts by weight based on parts by weight. If the blending amount of the component (b1) is less than 3 parts by weight, the adhesiveness of the resin composition will decrease, and if the blending amount of the component (b1) exceeds 50 parts by weight, compression set and heat resistance will decrease. , The hardness will increase.

The paraffinic oil as the component (c1) is blended for the purpose of lowering the hardness of the thermoplastic elastomer composition (I), and the blending amount thereof is (a)
The amount is 50 to 170 parts by weight based on 100 parts by weight of the styrene-based thermoplastic elastomer of the component (1).
Parts by weight are preferred. If the compounding amount is less than 50 parts by weight, it is not possible to achieve a sufficiently low hardness, and the flexibility of the injection molded product becomes insufficient. If it exceeds 170 parts by weight, the mechanical strength of the injection molded product is reduced. The paraffinic oil preferably has a kinematic viscosity at 40 ° C. of 100 mm ² / sec or more, particularly 100 to 10000 mm ² / s.
ec, and more preferably 200 to 5000 mm ² / sec. The paraffin oil preferably has a weight average molecular weight of 450 to 5,000.

[0010] The (a) of the thermoplastic elastomer composition (II)
The component (2) is the same as the component (a1). As the component (b2) of the thermoplastic elastomer composition (II),
A maleic anhydride grafted polyolefin is used.
The maleic anhydride modification degree of the maleic anhydride-grafted polyolefin is preferably from 3 to 15%, particularly preferably from 4 to 12%. Here, the maleic acid modification degree (%) means a numerical value calculated by [(maleic acid site molecular weight of graft) / (total molecular weight of maleic anhydride)] × 100. If the degree of maleic acid modification is less than 3%, it may not be possible to obtain a sufficient adhesive strength with metal when injection-molded.
If it exceeds 5%, the physical properties (compression set, breakage properties, etc.) of the obtained resin composition are reduced, and it may not be possible to obtain practically sufficient properties. Examples of the maleic anhydride-grafted polyolefin include maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polybutylene, and the like. Acid-grafted polypropylene is preferred.
The weight average molecular weight of the polypropylene in the maleic anhydride grafted polypropylene is preferably 10,000 to 150,000,
Particularly preferably, it is 20,000 to 100,000.

The amount of the component (b2) is 1 to 100 parts by weight of the styrene thermoplastic elastomer of the component (a2).
-15 parts by weight, preferably 2-13 parts by weight.
If the blending amount of the component (b2) is less than 3 parts by weight, the adhesiveness of the gasket material will decrease, and if the blending amount of the component (b2) exceeds 50 parts by weight, compression set and heat resistance will decrease, Hardness increases.

The paraffinic oil of the component (c2) is blended for the purpose of lowering the hardness of the thermoplastic elastomer composition (II), and the blending amount thereof is (a)
2) It is 30 to 170 parts by weight based on 100 parts by weight of the styrene-based thermoplastic elastomer of the component, but is 35 to 160 parts by weight.
Parts by weight are preferred. If the amount is less than 30 parts by weight, a sufficiently low hardness cannot be attained, and the flexibility of the injection molded product becomes insufficient. If the amount exceeds 170 parts by weight, the mechanical strength of the injection molded product decreases. The paraffinic oil preferably has a kinematic viscosity at 40 ° C. of 100 mm ² / sec or more, particularly 100 to 10000 mm ² / s.
ec, and more preferably 200 to 5000 mm ² / sec. The paraffin oil preferably has a weight average molecular weight of 450 to 5,000.

The method for producing the thermoplastic elastomer composition (I) or (II) used in the present invention is not particularly limited, and a known method can be applied. For example, (a1)-
The component (c1) or the components (a2) to (c2) and optionally used additive components are mixed with a heat kneader, for example, a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer,
It can be easily manufactured by melt-kneading using a lavender, kneader, high shear mixer, or the like. The thus obtained thermoplastic elastomer composition (I) or (II) is injection-molded into a metal cover or a metal frame, whereby an integrated type in which the gasket and the cover or the frame are integrated. A gasket can be obtained. Injection molding can be performed at a mold temperature of 30 ° C. or higher, preferably 40 to 90 ° C., and a resin temperature of 170 to 90 ° C.
250 ° C, preferably 180-230 ° C, injection speed is 1
00 to 10 ⁵ sec ⁻¹ , preferably 1000 to ⁵ × 10
It can be set to ⁴ sec ^-1 .

Examples of the fluororesin for coating the mold include FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (perfluoroalkoxy fluororesin), and PTFE (polytetrafluoroethylene). One kind may be used alone, or two or more kinds may be used in combination. The method of coating the inner surface of the mold with a fluororesin is not particularly limited, but usually, a coating liquid obtained by dissolving or dispersing a fluororesin, an organic binder resin and various additives is dipped or roll-coated. After being applied to the inner surface of the mold by a doctor blade method, a spray method, or the like, it is dried at room temperature or at a temperature of about 50 to 170 ° C., and crosslinked and cured to form a coating film. It is preferable to perform such a coating treatment twice or more from the viewpoint of forming a strong film. Commercially available products can also be used as the coating liquid. For example, a modified coating containing a fluororesin and an organic binder resin (manufactured by DuPont, 959-
205) can be used. The thickness of the coating film is not particularly limited, but if the coating film is too thin, the release effect is not sufficient, and the durability is particularly poor. If the coating film is too thick, the thickness varies. Is preferably 5 to 50 μm, and more preferably 10 to 30 μm.
Is particularly preferred. Before the mold is coated with fluororesin, the inner surface is sandblasted,
It is preferable to perform a treatment such as a resin blast treatment from the viewpoint of the adhesion of the coating film to the mold. Also,
The material of the mold is not particularly limited.

In order to manufacture a gasket for a hard disk drive using such a mold, a metal cover or frame is placed in the mold, and then the thermoplastic elastomer composition is injected with an injection molding machine. The molded body (gasket) of the thermoplastic elastomer composition is formed on a part of the cover body or the frame body by melt injection molding, and is taken out of the mold. Removal from the mold is easy because the inner surface of the mold is coated with a fluororesin. In this manner, a gasket with a cover or a gasket with a frame in which the cover or the frame and the gasket are integrally integrated is obtained.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 (1) Triblock copolymer of styrene-ethylene / propylene-styrene [manufactured by Kuraray Co., Ltd., trade name: Septon 4077] (number average molecular weight: 280,000 and styrene content: 30
(2%) methacrylic acid-modified polyethylene [Mitsui DuPont Polychemical Co., Ltd.]
(Trade name: Nucrel N1525) (temperature 190 ° C,
MFR under a load of 2.16 kgf is 25 g / 10 min.) 4
0 parts by weight and (3) a kinematic viscosity at 40 ° C. of 2200 m
A thermoplastic elastomer composition was prepared by kneading 150 parts by weight of a paraffinic oil [manufactured by Mitsui Chemicals, Inc., trade name: Lucant HC-150] (weight average molecular weight 1500) having a m ² / sec. The thermoplastic elastomer composition had a JIS-A hardness of 35 degrees and was subjected to sandblasting on the inner surface of a stainless steel mold used for injection molding, and a modified paint containing a fluororesin and an organic binder resin on the surface. (Dupont, 9
59-205) by a spray method, and dried.
By baking at a temperature of 400 ° C., a coating film was formed on the inner surface of the mold. Such application, drying and baking were repeated once again to form a coating film having a thickness of 20 μm. DC made by Nissei Plastic Industry Co., Ltd. as a molding machine
Using a 60E5ASE machine, mold temperature 85 ° C, resin temperature 2
Under conditions of 10 ° C. and an injection speed of 3 × 10 ⁴ sec ⁻¹ , the above thermoplastic elastomer composition was 0.5 mm thick and 2.0 m wide on a nickel-plated aluminum cover body.
m, and a gasket with a cover in which the cover 1 and the gasket 2 were integrated as shown in FIG. 1 was produced.
In the gasket with the cover, there was no sink mark and no burrs, and the adhesiveness between the gasket and the metal was sufficient. For a sheet-like sample prepared under the same conditions as the above injection conditions, the strain measured at 70 ° C. for 22 hours under 25% compression was 35% when measured according to JIS K6206. When the gasket with the cover thus manufactured was used in a hard disk device of a computer, no failure of the hard disk device occurred for a long period of time, and sufficient sealing properties were maintained for a long period of time. Further, the above-mentioned mold exhibited sufficient releasability even after being used 10,000 times.

Example 2 (1) Triblock copolymer of styrene-ethylene / propylene-styrene [Septon 4077, trade name, manufactured by Kuraray Co., Ltd.] (number average molecular weight 280,000 and styrene content 30
(2) maleic acid-modified polypropylene (manufactured by Sanyo Chemical Co., Ltd., trade name: Umex 1001) (melt viscosity at 160 ° C. is about 16% by weight).
000 mPa · s) 8 parts by weight and (3) a paraffinic oil having a kinematic viscosity at 40 ° C. of 380 mm ² / sec [manufactured by Idemitsu Kosan Co., Ltd., trade name: Diana Process Oil PW380] (weight average molecular weight 750) 120 weight parts By kneading the parts, a thermoplastic elastomer composition was prepared. JIS- of this thermoplastic elastomer composition
The mold used in Example 1 was used as a mold having an A hardness of 26 degrees, and the molding machine was manufactured by Nissei Plastic Industry Co., Ltd.
Using a C60E5ASE machine, mold temperature 50 ° C., resin temperature 210 ° C., injection speed 3 × 10 ⁴ sec ⁻¹ , the above-mentioned thermoplastic elastomer composition was thickened on a nickel-plated aluminum cover body. 0.5mm in width, 2.0 in width
Injection molding was performed to obtain a gasket with a cover in which the cover body 1 and the gasket 2 were integrated as shown in FIG. In the gasket with the cover, there was no sink mark and no burrs, and the adhesiveness between the gasket and the metal was sufficient. With respect to a sheet-like sample produced under the same conditions as the above-mentioned injection conditions, the strain measured at 70 ° C. for 22 hours under 25% compression was 30% as measured according to JIS K6206. When the gasket with the cover thus manufactured was used in a hard disk drive of a computer, no failure of the hard disk drive occurred for a long period of time, and sufficient sealing properties were maintained for a long period of time.

Comparative Example 1 A gasket with a cover was prepared in the same manner as in Example 1 except that no coating treatment was performed, using the same mold as in Example 1, and a molded article (gasket) of the thermoplastic elastomer composition was obtained. Because part is glued to the mold,
The gasket with the cover could not be removed from the mold. When this was forcibly taken out of the mold, the gasket was peeled off from the cover body, resulting in a defective product. Comparative Example 2 A gasket with a cover was prepared in the same manner as in Example 1 except that a mold sprayed with a silicone release agent was used instead of performing the coating treatment. It could be taken out of the mold. However, in order to maintain the mold release effect in the mold, it is necessary to spray the mold release agent each time injection molding is performed, and the operation becomes complicated, which is unsuitable for mass production. Was done. In addition, a release agent component (silicone component) adheres to the obtained gasket with a cover, and this component causes a failure of the hard disk device. Therefore, the gasket is not suitable as a gasket for a hard disk device. Was.

[0019]

According to the present invention, the thermoplastic elastomer composition, which is a gasket material, is injection-molded into a metal cover or the like, and when the molded body (gasket) is taken out of the mold, the molded body is made of metal. It can be easily released from the mold,
In addition, a gasket for a hard disk drive can be manufactured without applying a release agent to a mold each time injection molding is performed.

[Brief description of the drawings]

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

[Explanation of symbols]

 1: Cover body 2: Gasket

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 25/04 101 G11B 25/04 101J 33/12 303 33/12 303Z // (C08L 53/00 (C08L) 53/00 23:04 23:04 91:00 91:00 23:26) 23:26) B29K 19:00 B29K 19:00 F term (reference) 4F202 AA45 AH13 AH38 AJ03 AJ05 AJ09 CA11 CB01 CK43 CK53 CK90 4H017 AA03 AA23 AA31 AB01 AB07 AB17 AC02 AD03 AE04 AE05 4J002 AE053 BB072 BB082 BB212 BP011 GJ02 GS00

Claims (9)

[Claims] A cover is prepared by placing a metal cover or a metal frame on a mold and injection-molding a thermoplastic elastomer composition having a gasket material on the cover or the frame. In a method of manufacturing a gasket for a hard disk in which a body or a frame and a gasket are integrated, a mold whose inner surface is coated with a fluororesin is used as the mold, and (a1) a block is used as the thermoplastic elastomer composition. 100 parts by weight of a styrene-based thermoplastic elastomer made of a copolymer, and (b1) ethylene-containing (meth) acrylic acid having a content of 5 to 45% by weight.
3 to 50 parts by weight of (meth) acrylic acid copolymer or ethylene / (meth) acrylate copolymer and (c1)
Thermoplastic elastomer composition (I) comprising 50 to 170 parts by weight of paraffinic oil or styrene thermoplastic elastomer 10 comprising (a2) block copolymer
0 parts by weight, (b2) 1 to 15 parts by weight of maleic anhydride-grafted polyolefin, and (c2) paraffinic oil 3
A method for producing a gasket for a hard disk drive, comprising using a thermoplastic elastomer composition (II) comprising 0 to 170 parts by weight. 2. The method according to claim 1, wherein the metal cover or the metal frame is made of nickel-plated aluminum, nickel-plated steel, aluminum or stainless steel. 3. The styrene-based thermoplastic elastomer comprising a block copolymer is a styrene-ethylene / butylene-styrene block copolymer and / or a styrene-ethylene / propylene-styrene block copolymer. The manufacturing method as described. 4. The method according to claim 1, wherein the ethylene / (meth) acrylic acid copolymer has a (meth) acrylic acid content of 5 to 20% by weight. 5. The method according to claim 1, wherein the ethylene / (meth) acrylate copolymer has a (meth) acrylic acid content of 25 to 45% by weight. 6. The method according to claim 1, wherein the maleic anhydride-grafted polyolefin has a degree of maleic acid modification of the graft of 3 to 15%. 7. The method according to claim 1, wherein the maleic anhydride-grafted polyolefin is maleic anhydride-grafted polypropylene. 8. The method according to claim 7, wherein the maleic anhydride-grafted polypropylene has a weight average molecular weight of 10,000 to 150,000. 9. The fluororesin for coating a mold,
9. One or two or more selected from FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (perfluoroalkoxy fluororesin) and PTFE (polytetrafluoroethylene).
The method according to any one of the above.