JP4186511B2 - Hard disk drive cover integrated gasket - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cover-integrated gasket for a hard disk drive. More specifically, the present invention relates to a cover-integrated gasket for a hard disk drive that is easy to manufacture and has improved low outgassing properties.
[0002]
[Prior art]
In recent years, with the miniaturization and high performance of electronic device products, it has been required to make the components small and thin. From the viewpoint of reducing the assembly workability in the manufacturing process if the component parts are made smaller, it is required to integrate and combine various parts. At the same time, there is a demand for improved performance of required characteristics such as outgassing and sealing properties.
[0003]
Of the electronic storage devices, especially for gaskets that are installed as hard disk drive covers that prevent intrusion of water and dust and require low outgassing properties, rubber covers and polyurethane foam sheets are covered with metal covers such as stainless steel and aluminum. It has been proposed to improve the assembly work by joining a metal cover such as stainless steel and a rubber material such as fluoro rubber with an adhesive and integrating them (see FIG. (Patent No. 2,517,797).
[0004]
However, in this method, gasket-shaped rubber is vulcanized and formed in a separate process in advance, and later joined to the metal cover with an adhesive, and the process is long and complicated. In fact, the gasket vulcanization process takes a few minutes, and the vulcanized gasket is easy to tear and torn off. A simplified method was desired.
[0005]
In order to solve such problems, a gasket material made of an elastomer made of a polystyrene block copolymer has been proposed, which can simplify the process without requiring a vulcanization process as compared with a rubber material, and can recycle the material and reduce the cost. (Patent No. 2,961,068).
[0006]
Since this material is thin, soft, and easy to adhere, unless the gasket material is fixed in advance by some method, the workability of the hard disk drive assembling work becomes very poor. As a countermeasure, a polystyrene block copolymer elastomer gasket is prepared in advance for what is called a frame, and then assembled and integrated between a box and lid of a hard disk drive or the like. You need other parts, such as a body.
[0007]
In recent years, due to the high performance of hard disk drives, gaskets attached to hard disk drive covers tend to be exposed to temperatures as high as 100 ° C or higher. Under these circumstances, these polystyrene-based thermoplastic elastomers have a performance. Was not enough.
[0008]
In particular, gaskets attached to hard disk drive covers have severe requirements for sealing properties, clean properties, and heat resistance.
[0009]
Speaking of sealability, three material properties that influence this are hardness, compression set, and water permeability. The hardness (JIS durometer type A) is preferably 60 or less, and if it is harder than this, when assembled as a product, there will be a gap due to the reaction force and sealing will not be possible. A material with inferior compression set loses its tightness during long-time assembly and cannot be sealed, and cannot be used when this value is 100% or more. Further, since there is water vapor (humidity) in addition to dust, dust and the like in the sealed object, the gasket needs to have low water permeability. Also, if there is water vapor in the hard disk drive, it will also cause rust.
[0010]
Regarding cleanliness, there are three factors related to this: outgas, contained components, and fillers that easily fall off. If outgas generated from the material adheres to the disk, it will cause a crash. In addition, chlorine, silicone, sulfur, sulfuric acid, nitric acid, acrylic acid esters (including the case where they exist as ions) may corrode the hard disk drive. Furthermore, if it contains a large amount of filler and it is incompatible with the polymer, the particles will fall off and still cause a crash if they enter the hard disk drive.
[0011]
Speaking of heat resistance, hard disk drives that are conventionally used in personal computers are basically used indoors, and the usage environment is about 0 to 60 ° C. Even it is around 80 ° C maximum. However, when a hard disk drive is used in a car navigator, etc., it is installed in a car and can move immediately even if left in a cold area (up to -40 ° C), or left in a sealed car exposed to direct sunlight. Even if it is (up to about 100 ° C), it is necessary to maintain its performance. Conventional thermoplastic elastomers that are mainstream materials have a glass transition temperature (Tg) of the hard segment of about 100 ° C., and heat resistance beyond this is basically impossible.
[0012]
[Problems to be solved by the invention]
An object of the present invention is to provide a gasket for a hard disk drive that is easy to manufacture and excellent in low outgassing properties, low hardness, high temperature sealing properties, and the like.
[0013]
[Means for Solving the Problems]
An object of the present invention is to provide a gasket in which a packing material is integrated with a metal cover via an adhesive layer, and 100 parts by weight of a blend of EPDM and a polystyrene-based thermoplastic elastomer as a packing material, This is achieved by a cover-integrated gasket for a hard disk drive using a molding from a mixture of 150 parts by weight, 20 to 130 parts by weight of a plasticizer and 0.1 to 10 parts by weight of an organic peroxide crosslinking agent.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
As EPDM, an ethylene-propylene-diene copolymer rubber obtained by copolymerizing various diene monomers can be used. EPDM can form a polyolefin-based thermoplastic elastomer as a blend type by mechanical blending with a polypropylene resin, and since a crosslinking agent is present, a partially crosslinked blend type obtained by partially crosslinking EPDM or polypropylene is used. It is considered that any of a completely crosslinked blend type composed of a composite having a continuous phase and a completely crosslinked EPDM as a dispersed phase can be formed.
[0015]
Therefore, it can be considered that a mixture of EPDM and polypropylene resin (and cross-linking agent) forms a polyolefin-based thermoplastic elastomer, and instead of using these components as a mixture, it is defined here. Commercially available polyolefin-based thermoplastic elastomers in which these components are already mixed in a certain ratio, such as series products such as Mitsui Chemicals Miralastomer, AES Santoprene, etc., can be used as they are.
[0016]
These polyolefin-based thermoplastic elastomers are excellent in heat resistance because the softening temperature of polypropylene, which is a hard segment, is about 130 to 150 ° C., and also have good outgassing properties, but the hardness is slightly higher. used as a blend thereof with a polystyrene-based thermoplastic elastomer to reduce the hardness.
[0017]
As described above, when the cover is attached to the main body when the hardness is high, the cover is warped due to the reaction force of the gasket and cannot be sealed. On the other hand, if the hardness is as low as 10 or less, it becomes easy to stick or the strength is lost and it is easy to tear off. However, from the viewpoint of performance as a gasket, if the gasket shape is made finer, the reaction force will be lowered, and a higher hardness can be used accordingly.
[0018]
From this point of view, a packing material having a hardness (JIS durometer type A) of 20 to 60, preferably 30 to 50, is required. For this reason, EPDM, which is the main component of polyolefin-based thermoplastic elastomer, has a polystyrene content of 20 % by weight or more. -Based thermoplastic elastomer is used in a proportion of 80 % by weight or less , that is, polyolefin-based thermoplastic elastomer is used as a blend with polystyrene-based thermoplastic elastomer, and since these are non-polar, they have the property of being difficult to permeate water vapor. ing.
[0019]
In particular, when EPDM, which is the main component of a polyolefin-based thermoplastic elastomer, is used in a proportion of 30 to 70 % by weight, the sealing property indicated by the compression set value after heat treatment at a high temperature of about 80 to 100 ° C. Marked improvement. On the other hand, when the blend ratio of the polystyrene-based thermoplastic elastomer is increased, the holding power of the plasticizer can be increased, and the hardness can be easily optimized. On the other hand, when a polystyrene-based thermoplastic elastomer is used alone, the compression set resistance at high temperatures is deteriorated, and the sealing performance for a long time cannot be secured.
[0020]
Polystyrene-based thermoplastic elastomers include polystyrene-poly (ethylene-propylene) -polystyrene triblock copolymer [SEPS], polystyrene-poly (ethylene / ethylene-propylene) -polystyrene triblock copolymer [SEEPS], etc. Is used. SEPS is obtained by hydrogenating a polystyrene-polyisoprene-polystyrene block copolymer, and SEEPS is obtained by hydrogenating a polystyrene- (butadiene-isoprene) random copolymer-polystyrene block copolymer. It is done.
[0021]
These polystyrene thermoplastic elastomers preferably have a number average molecular weight Mn of 50,000 or more. If this number average molecular weight Mn is less than this, the bleed of the plasticizer increases, the compression set also increases, and there may be a problem that the actual use cannot be endured. On the other hand, the upper limit of the number average molecular weight Mn is not particularly limited, but is usually about 400000. The content of the amorphous styrene block in the polystyrene-based thermoplastic elastomer is preferably 10 to 70% by weight, and preferably 15 to 60% by weight. The glass transition temperature (Tg) of the amorphous styrene block portion is 60 ° C. or higher, preferably 80 ° C. or higher. Furthermore, the polymer at the portion connecting the amorphous styrene blocks at both ends is preferably amorphous. The polystyrene-based thermoplastic elastomer is mainly used alone, but two or more kinds may be blended and used. In practice, Kuraray products Septon 2006 [SEPS], Septon 4055 [SEEPS] and the like that satisfy these conditions are used.
[0022]
The polypropylene resin and the plasticizer are used in consideration of the moldability and hardness of the packing material obtained by molding. Polypropylene resin affects the moldability, and the plasticizer adjusts the hardness. From such a viewpoint, the addition ratio of the polypropylene resin and the plasticizer is selected.
[0023]
Examples of the polypropylene resin include a crystalline polymer which is a homopolymer of propylene or a copolymer of propylene and a small amount of α-olefin (for example, ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, etc.). Coalescence is used. Polypropylene resin, blend 10 to 100 parts by weight per 100 parts by weight of EPDM and polystyrene-based thermoplastic elastomer preferably used in a ratio of 20 to 80 parts by weight. When the blending amount is larger than this, the hardness is increased, whereas when the blending amount is smaller than this, the fluidity is deteriorated and the injection molding becomes difficult.
[0024]
The plasticizer is not particularly limited as long as it is used for ordinary rubbers and thermoplastic elastomers. For example, petroleum softeners such as process oil, lubricating oil, paraffinic oil, castor oil, linseed oil, rapeseed oil Fatty oil-based softeners such as coconut oil, ester plasticizers such as dibutyl phthalate, dioctyl phthalate, dioctyl adipate, and dioctyl sebacate are used, and paraffin oil is preferably used. These plasticizers are used in an amount of 20 to 130 parts by weight, preferably 50 to 120 parts by weight, per 100 parts by weight of EPDM or a blend of the thermoplastic thermoplastic elastomer and EPDM. When the blending amount is larger than this, outgas increases, and when the blending amount is less than this, the sealing property is deteriorated.
[0025]
The crosslinking agent is preferably an organic peroxide such as dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di- (t-butylperoxy) hexane, t -Butylcumyl peroxide is used. These organic peroxide cross-linking agent is a blend of 0.1 to 10 parts by weight per 100 parts by weight of EPDM, preferably used 1 to 5 parts by weight, that such proportion that proportion is commonly used be able to.
[0026]
In the mixture containing the above components as essential components, a powdery solid filler (for example, various metal powders, glass powders, ceramic powders, granular or powder polymers) usually blended with rubber or thermoplastic elastomer as necessary. Etc.), antioxidants (eg amines and derivatives thereof, imidazoles, phenols and derivatives thereof), waxes, stabilizers, tackifiers, release agents, pigments, flame retardants, lubricants, etc. Used.
[0027]
In addition, a small amount of thermoplastic resin or rubber can be added to improve wear and moldability. Furthermore, a short fiber etc. can also be added for the improvement of intensity | strength and rigidity.
[0028]
These mixtures are melt-kneaded using a heat kneader, such as a single screw extruder, twin screw extruder, roll, Banbury mixer, brabender, kneader, high shear mixer, etc., and a crosslinking aid, etc. if necessary. Or by mixing these necessary ingredients at the same time, heating and melting and kneading. Prepare a thermoplastic material kneaded with a polymer organic material and a plasticizer, and use this material here. It can also be used in combination with one or more high molecular organic materials of the same type or different types.
[0029]
Thus obtained, blends of EPDM and polystyrene-based thermoplastic elastomer, polypropylene resin, a mixture consisting of plasticizer and crosslinking agent, injected into the mold which is inserted a metal cover coated with adhesive By doing so, it is integrally formed as a packing material. As metal covers, aluminum plates, aluminum plates plated, stainless steel plates, stainless steel damping plates, etc., and adhesives include maleic anhydride, acrylic acid, etc. on the side chains of polyolefin resins Those modified by grafting polar groups of the above are dissolved in an aromatic or aliphatic organic solvent and liquefied, dispersed, or styrene-butadiene copolymer rubber is aromatic or aliphatic. Those dissolved in an organic solvent and liquefied are used. In addition, when an adhesive is not used, peeling occurs at the time of molding, and integral molding cannot be performed. As the method for applying the adhesive, an optimum method such as dip coating, spray coating, screen printing, brush coating, or stamp method is selected as necessary.
[0030]
The hardness (JIS durometer type A) of the molded packing material rubber material is 20 to 60, preferably 20 to 50, by balancing the amount of polypropylene resin and the amount of plasticizer within the specified range. The compression set at 100 ° C. for 72 hours (based on JIS K6262) is adjusted to 50% or less. When the hardness is higher than this, the reaction force when the cover-integrated gasket is assembled to the main body is increased, the cover is deformed and the like cannot be completely sealed, and the sealing performance as a gasket is deteriorated. On the other hand, if the hardness is less than this, care must be taken in handling, such as the gasket being easily torn or sticking. On the other hand, if the compression set is larger than this, it is impossible to ensure a long-term sealing performance at high temperatures. The shape of the molded packing material is determined in accordance with the shape of the hard disk drive cover in which it is integrated.
[0031]
【The invention's effect】
By using the hard disk drive cover-integrated gasket according to the present invention, it is excellent in sealing properties at low hardness and high temperature, low outgas, low water permeability, adhesiveness, moldability, etc., and has high dust resistance. A gasket material can be easily produced .
[0032]
【Example】
Next, the present invention will be described with reference to examples.
[0033]
Example 1
EPDM ( Mitsui Chemicals Mitsui EPT3045) 50 parts by weight Polystyrene thermoplastic lastomer 50 50
(Kuraray Product Septon 2006 [SEPS])
Polypropylene resin ( Idemitsu Kosan product J700GP) 25 〃
Paraffin oil (Diana Process Oil PW380) 100 〃
Cross-linking agent ( Nippon Oil Products Park Mill D) 2
The mixture was extruded with a twin screw extruder (Hyper KTX46 manufactured by Kobe Steel) at a set temperature of 210 to 180 ° C. and a rotation speed of 150 rpm.
[0034]
Using this compound, a test sheet (150 x 150 x 2 mm) is molded using an injection molding machine (KM-80 manufactured by Kawaguchi Tekko) at a set temperature of 210 to 180 ° C, an injection speed of 0.5 sec, an injection pressure of 100 MPa, and a cycle time of 30 seconds. And used for tests of hardness, high temperature compression set, outgas, and water permeability. In addition, a part in which a modified olefin resin adhesive (Sotec product skip # 66) is applied to an aluminum plate (electroless nickel plating 2 to 5 μm treatment) pre-molded in a cover shape is inserted into the mold, Similarly, a gasket was molded on the cover at an injection speed of 0.5 seconds, an injection pressure of 30 MPa, and a cycle time of 30 seconds. Using a cover-integrated gasket, a sealability test, an adhesion test, and a moldability evaluation were performed.
[0035]
Example 2
In Example 1 , the EPDM amount was changed to 70 parts by weight, and the polystyrene-based thermoplastic elastomer [SEPS] amount was changed to 30 parts by weight.
[0036]
Example 3
In Example 1 , the EPDM amount was changed to 30 parts by weight, and the polystyrene-based thermoplastic elastomer [SEPS] amount was changed to 70 parts by weight.
[0037]
Example 4
In Example 1 , in place of the polystyrene-based thermoplastic elastomer [SEPS], the same amount of other polystyrene-based thermoplastic elastomer (Kuraray product Septon 4055 [SEEPS]) was used.
[0038]
Example 5
In Example 1 , a styrene / butadiene copolymer rubber adhesive (Nogawa Chemical product Diabond DA3188) was used in place of the modified olefin resin adhesive.
[0039]
Using the test sheet obtained in each of the above examples and a gasket integrated with the cover, the following items were measured.
Hardness: JIS K6253 compliant (3 test sheets stacked)
High-temperature compression set test: Compliant with JIS K6262 , measuring compression set rate after 72 hours at 100 ° C Outgas test: Heat-extracted strip test sheet of 50 × 3 × 2mm at 120 ° C for 1 hour, then outgas amount , And those that show an outgas amount of less than 50 μg / g are evaluated as ◯, those that show an outgas amount of 50 μg / g or more are evaluated as × (those that show an outgas amount of 50 μg / g or more require high performance) (It is not preferable as a gasket for hard disks in servers, etc.)
Water permeability test: 10ml of distilled water is placed in a cylindrical SUS container (inner diameter 27mm, depth 50mm), a test sheet adjusted to 30mm in diameter and 1mm in thickness is sandwiched, and a SUS hollow lid (inner diameter of opening 27mm) ) And calculate the water permeability coefficient (g ・ mm / cm ²・ 24H) from the data after 100 hours at 70 ℃, and a value less than 5 × 10 ^-3 (g ・ mm / cm ²・ 24H) ○ indicates a value of 5 × 10 ^-3 (g · mm / cm ² · 24H) or higher, and is evaluated as × (those with a water permeability coefficient of 5 × 10 ^-3 or higher are for hard disks) It is not preferable as a gasket)
Sealability test: With the gasket integrally formed on the cover attached to the actual leak tester, after heat treatment at 80 ° C for 168 hours, return to room temperature, and continue to apply positive pressure of 5 kPa from the inside of the tester for 30 seconds The result was evaluated as ○ for those that did not leak after 15 seconds, and × for those that did not leak (leak if the gasket material is inferior in compression set or has a defective gasket shape)
Adhesion test: Create a through-peeler of approximately 1mm on the gasket adhesive surface integrated with the cover, pass a SUS wire through the part, apply a vertical tensile load, and measure the load when the peeler length increases to approximately 10mm. , And those with a peel load of 100 kPa or more evaluated as x (those with a peel load of 100 kPa or more have sufficient adhesive strength in the actual use environment)
Formability evaluation: In the injection molding of products, the failure to mold into a predetermined product shape does not result in defects such as deformation, sink marks, chipping, welds, short shots, burrs, etc. Evaluate those with such defects as x.
The results obtained in the above examples are shown in the following Table 1 .
Table 1
Example 1 2 3 4 5
[Test sheet]
Hardness (Durometer type A) 45 48 40 46 40
High temperature compression set (%) 45 42 47 45 45
Outgassing ○ ○ ○ ○ ○
Water permeability ○ ○ ○ ○ ○
〔gasket〕
Sealability ○ ○ ○ ○ ○
Adhesiveness ○ ○ ○ ○ ○
Formability ○ ○ ○ ○ ○
[0041]
Comparative Example 1
In Example 1, EPDM was not used, and a polystyrene-based thermoplastic elastomer (Septon 4055) was changed to 100 parts by weight .
[0042]
Comparative Example 2
In Comparative Example 1, the amount of paraffinic oil was changed to 120 parts by weight.
[0043]
Comparative Example 3
In Example 4 , EPDM was not used, and the amount of polystyrene-based thermoplastic elastomer [SEEPS] was changed to 100 parts by weight.
[0044]
Comparative Example 4
In Example 1 , the amount of paraffinic oil was changed to 5 parts by weight.
[0045]
Comparative Example 5
In Example 1 , paraffinic oil was used by changing to 150 parts by weight.
[0046]
Comparative Example 6
In Example 1 , the amount of polypropylene resin was changed to 5 parts by weight.
[0047]
Comparative Example 7
In Example 1 , the amount of polypropylene resin was changed to 120 parts by weight.
[0048]
Using the test sheet obtained in the above comparative example and the gasket integrated with the cover, each item was measured in the same manner as in the examples ( however, only the comparative examples 3 to 7 for high temperature compression set) , Measurements were taken ) . The results obtained are shown in Table 2 below.
Table 2
Comparative example 1 2 3 4 5 6 7
[Test sheet]
Hardness (Durometer Type A) 45 40 44 74 28 39 86
Hot compression set (%) − − 68 53 51 45 73
Outgassing × × ○ ○ × ○ ○
Water permeability ○ ○ ○ ○ ○ × ○
〔gasket〕
Sealability × × ○ × ○ ○ ×
Adhesiveness ○ ○ ○ ○ × ○ ○
Formability ○ ○ ○ ○ ○ × ○

Claims (6)

In gasket are integrated packing material through an adhesive layer to a metal cover, blend 100 parts by weight of EPDM and polystyrene-based thermoplastic elastomer as a packing material, polypropylene resin 10-150 parts by weight, plasticizer 20 A cover-integrated gasket for a hard disk drive using a molded product of a mixture of ~ 130 parts by weight and an organic peroxide crosslinking agent 0.1 to 10 parts by weight. EPDM 20 More than wt% and polystyrene-based thermoplastic elastomer 80 The cover-integrated gasket for a hard disk drive according to claim 1, wherein a blended material having a weight percent or less is used. The cover-integrated gasket for a hard disk drive according to claim 1, wherein the plasticizer is a paraffinic oil. Polystyrene thermoplastic elastomer is polystyrene-poly ( Ethylene-propylene ) The cover-integrated gasket for a hard disk drive according to claim 1, which is a polystyrene block copolymer. Polystyrene thermoplastic elastomer is polystyrene-poly ( Ethylene / ethylene-propylene ) The cover-integrated gasket for a hard disk drive according to claim 1, which is a polystyrene block copolymer. hardness (JIS Durometer type A) But 20 ~ 60 And compression set (JIS K6262 Conformity; 100 ℃, 72 time ) But 50 The hard disk drive cover-integrated gasket according to claim 1, wherein a packing material of not more than% is formed.