JP2001279013A - Gasket for hdd having low moisture permeability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gasket for a hard disk drive(HDD) capable of starting up with an extremely short leading time when producing a new model, free from gas generation, a dimensional problem or the like and having low moisture permeability. SOLUTION: The gasket for HDD having the low moisture permeability is an HDD gasket comprising punching a predetermined shape in an elastic sheet comprising a crosslinked rubber having a hydrocarbon backbone, and has features comprising properties consisting of (1) less than two times of expansion ratio, (2) 10-85 of Ascar C hardness, (3) 1% or less of water absorption rate at 70 deg.C, (4) from +0 to -1% of rate of heat weight change at 120 deg.C and (5) 1 gf/g or more of frictional coefficient of surface of the gasket.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gasket interposed between a case body and a cover of a hard disk drive and used for sealing the inside of the case body.

[0002]

2. Description of the Related Art With the miniaturization of computers and the increase in storage capacity, the performance required of hard disk drives (HDDs) has been increasing and becoming severer. The required performance of gaskets used in HDDs has also been increasing accordingly.
Conventionally, a gasket interposed between an HDD main body and a cover has been used by being punched into a predetermined shape from a cross-linked rubber-like elastic sheet material such as foamed rubber or high-density urethane foam. Although it is highly airtight, it has been found that moisture easily penetrates into the inside through a gasket and seriously impairs the HDD function. On the other hand, a non-foamed rubber product or a product formed by forming a gasket by adhering a thin stainless steel plate to both sides of a thin stainless steel plate is also used. These have disadvantages in that the manufacturing process is complicated and therefore the cost is high. Further, a mold for rubber and a mold for manufacturing stainless steel are required to make a product, and these take a long time to manufacture. HDD-related products are a field in which technological progress is remarkable, and the frequency of newly developed products is extremely high, so that it is required that the lead time for product startup be short. There is a disadvantage that rubber molded products cannot sufficiently meet such demands.

On the other hand, by providing a gasket made of a urethane foam using a hydrophobic polyol as a crosslinked rubber-like elastic body and having improved moisture permeability by giving specific physical property values, a HDD of a certain level is provided. Was able to respond. However, with recent demands for HDD performance improvement, low moisture permeability and low gas generation for gaskets (reducing the amount of gas generated based on volatile components of the material itself),
The required quality of cleanliness (no contamination, etc.) has further increased. In order to reduce the amount of gas generation, although improvements are made by examining the selection and amount of the materials and compounding agents, it has become essential to perform a heat treatment called baking. This baking process is also becoming hotter and longer for years. In addition, there has been an increasing demand for cleaning gaskets with water in order to increase the degree of cleanliness.

Although it is easy to think of improving the material by increasing the hydrophobicity of the material in order to obtain a gasket having a low moisture permeability, this method only lowers the water absorption rate only, but the baking process is difficult. The material may deform, shrink,
It does not expand or its moisture permeability and gas generation properties are not easily reduced. For example, when silicone rubber is selected to increase the hydrophobicity, the water absorption is extremely reduced, but the moisture permeability is extremely high. Further, if natural rubber, isoprene rubber, or butadiene rubber is selected as the rubber material, a certain degree of low moisture permeability can be achieved. However, in these vulcanization processes, sulfur, a vulcanization accelerator and the like are compounded. These agents are harmful to HDDs and are unacceptable in small amounts. Even if these rubbers are crosslinked without using these chemicals, these rubbers contain many double bonds, and the materials deteriorate due to baking at high temperatures, so that the amount of gas generation further increases and shrinkage due to heating Therefore, the dimensions do not match at the time of assembly, which causes inconvenience.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a HDD gasket which can shorten the lead time at the start of a new model as described above, has no gas generation property, has no problems in dimensions, and has a further reduced moisture permeability. It is to provide. Further, the present invention provides a gasket which can be washed with water and has a short drying time. The low moisture permeability of the present invention refers to a material having a moisture permeability of 0.20% or less according to a moisture permeability measuring method described later.

[0006]

SUMMARY OF THE INVENTION The above objects are achieved by providing an HDD gasket having the following characteristics. That is, a low-moisture permeable HDD gasket punched into a predetermined shape from a crosslinked rubber-like elastic sheet having a hydrocarbon skeleton, 1) foaming ratio is less than 2 times 2) Asker C hardness is 10 to 85 3) 70 ° C 4) The rate of increase or decrease in weight at 120 ° C. is +0 to −1%. 5) A low-moisture permeable HDD gasket characterized by having a friction coefficient of 1 gf / g or more on the gasket surface. .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The material of the low humidity HDD gasket according to the present invention is a crosslinked rubber-like elastic body having a hydrocarbon skeleton. The composition is, for example, a synthetic rubber-based elastic body such as EPDM or SEBS, or the like. There is a hydrophobic urethane-based elastic body. The hydrocarbon skeleton refers to those having a total content of carbon and hydrogen in the composition of 80% or more. Further, these values are preferably about 83% or more. These crosslinked rubber-like elastic bodies are
It is necessary to crosslink by a chemical crosslinking agent or a physical crosslinking method such as electron beam or ultraviolet ray. The chemical cross-linking includes a method of mixing a cross-linking agent called dynamic cross-linking and performing continuous partial cross-linking with an extruder or the like. As described above, by being cross-linked and having other constitutional requirements of the present invention, resilience is assured, and the shape can be maintained even in the baking step. In the present invention, the above-mentioned crosslinked rubber-like elastic sheet-shaped article is stamped and used in a predetermined shape. Such a sheet-like article may be a continuously produced article or a discontinuously produced article. A sheet-like article provided with an adhesive layer on one side is also included. As a method of punching a sheet-shaped product into a predetermined shape, for example, a simple die manufactured with a Thomson blade is used and punching is performed with low pressure. These are suitable because they are low-cost, have a very short lead time of several days, and start up quickly.

The rubber-like elastic material used in the present invention may or may not be foamed. The foam needs to be closed cells to increase airtightness. Although a high expansion ratio has a soft merit, it is generally poor in airtightness and easy to permeate, so that the expansion ratio is less than 2 times. Further, from the viewpoint of moisture permeability and hardness, the best expansion ratio is 1 to 1.5 times. The gasket of the present invention must have an Asker C hardness of 10 to 85. HDDs have been reduced in size and weight, and the cover strength is low. If the hardness of the gasket is high, the cover itself is deformed and it is not possible to maintain airtightness. It is possible to use a gasket with a certain degree of hardness by reducing the width of the gasket. However, when the width, height, and height of the gasket are less than a certain value, there is a problem in that when the gasket is pressed, the material is not satisfactorily collapsed and the airtightness cannot be maintained. The most preferred hardness is between 20 and 65. When the gasket has such hardness, it satisfies airtightness, does not apply too much load to the cover,
The assembly properties are also good. In order to achieve such low hardness, it is easier to use a foam, but if the foaming ratio of the foam is too high, the water absorption and moisture permeability increase, which is not preferable. The material of the present invention needs to have a water absorption at 70 ° C. of 1.0% or less. Even if the water absorption at room temperature is low, the water absorption at high temperature is not always low or the moisture permeability is not always low. For example, silicone rubber has a low water absorption but a high moisture permeability, and rubber or urethane resin treated with a silicone-based or fluorine-based surfactant has a relatively low water absorption at room temperature, but a high-temperature water absorption. High, high moisture permeability. On the other hand, in the case of a rubber-like elastic body having a hydrocarbon skeleton, the water absorption at room temperature to 70 ° C. is low and the moisture permeability is low.

The material of the present invention needs to have a heating weight increase / decrease at 120 ° C. of +0 to −1%. With the increase in capacity of HDDs, there has been an increasing demand for lowering the amount of gas generated from gaskets, and gasket materials have been subjected to heat treatment called baking. The process of baking exposes the material from 100 ° C to 150 ° C for a certain time,
It vaporizes low volatile components contained in the material. Thus, the material must not stretch, shrink, or degrade at that temperature. In short, it has become necessary to increase the heat resistance of the material itself. The material of the present invention has no problem in terms of dimensions and gas generation as long as the heating increase / decrease rate at 120 ° C. is from + 0% to −1%. In the case of a material exceeding -1%, problems such as curling of the sheet material, inability to perform positioning when setting the HDD cover with an adhesive, and an increase in the amount of gas generated due to deterioration of the material occur. Those with + 0% or more increase in weight and are oxidatively deteriorated. For this reason, the material of the present invention needs to be a crosslinked rubber-like elastic body, and the material composition is not so large, for example, as a rubber material, the content of unsaturated groups or ether groups which are easily oxidized and degraded in the molecule. Thing. It is preferable not to mix low-molecular-weight substances that easily volatilize, such as process oils and plasticizers.

The friction coefficient of the gasket surface of the present invention is 1 g.
f / g or more, preferably 1 gf / g to 10 gf / g. The moisture permeability of the gasket is the sum of the moisture passing through the inside of the material and the moisture passing from the interface between the HDD body and the cover and the gasket. Therefore, even if the material itself does not transmit moisture, if the transmission from the interface is large, a large moisture permeability results. In order to reduce such interface permeation, it is necessary to regulate the surface condition of the gasket. The adhesion between the gasket and the HDD main body is related to the hardness and surface condition of the gasket. It is the coefficient of friction that defines this surface condition. If the coefficient of friction is too high, blocking and stickiness of the materials will occur, resulting in poor workability and adhesion of dust, which is not preferable in terms of HDD function. As a method of controlling the surface state of the gasket, for example, by casting and curing a liquid material on a piece of paper or a mold, the surface state of the paper or mold can be transferred to a product. If it is a solid raw material, the press surface or mold surface during vulcanization can be transferred to the product.

The material of the present invention is a crosslinked rubber elastic body having a hydrocarbon skeleton. Therefore, although polyethylene and polypropylene are hydrocarbon skeletons, they have high crystallinity and are not called rubber elastics. That is, the rubber is essentially non-crystalline. The term "rubber having a hydrocarbon skeleton" includes, for example, chloroprene, chlorinated polyethylene, chlorsulfonated polyethylene, epichlorohydrin rubber and the like, which do not contain a large amount of halogen, sulfur, oxygen or the like in the molecule thereof.

As mentioned above, rubbers containing few double bonds, such as EPDM, are preferred as the material of the present invention. vice versa,
Rubbers having a large amount of double bonds, such as natural rubber, polybutadiene rubber, and polyisoprene rubber, have a high heat shrinkage and an increase in outgassing due to thermal deterioration, which is not preferable as the material of the present invention. However, rubbers having these double bonds may be added to EPDM or the like as long as the essential performance is not deteriorated. When a crosslinked rubber elastic body is obtained from an unvulcanized rubber such as an EPDM rubber, a peroxide is preferably used as a crosslinking agent. Since sulfur is easily corroded as a crosslinking agent,
It cannot be used for DD. In addition, many inorganic fillers, process oils, and the like should be refrained from being used because they cause generation of dust and gas generation from gaskets. Also,
To foam these, azodicarbonamide (ADC)
It is desirable to use a foaming agent such as A). Also, EPDM
It is also preferable to obtain a crosslinked rubber elastic body by using a mixture of an olefinic rubber such as olefinic resin and an olefinic resin such as polyethylene and polypropylene and crosslinking the mixture with a peroxide or an electron beam. Of course, also in this case, a foam can be obtained by using a foaming agent in combination.

As the crosslinked rubber elastic body having a hydrocarbon skeleton used in the present invention, an olefin rubber can be mentioned. Preferred examples include α-olefins such as ethylene, propylene and butene and copolymers such as dicyclopentadiene and ethylidene norbornene. In addition, SEBS (hydrogenated styrene / butadiene / styrene block copolymer), SEPS (hydrogenated styrene / isoprene / styrene block copolymer), and partially hydrogenated polymers thereof are also included.

As the polyurethane-based crosslinked rubber elastic material used in the present invention, the polyol has a hydrocarbon skeleton. As these polyols, dimer acid and short-chain diol, dimer acid ester obtained from short-chain triol, dimer diol obtained by hydrogenating dimer acid and long-chain glycol such as α-olefin glycol and adipic acid, Long chain fatty esters obtained from dibasic acids such as sebacic acid, castor oil and transesterified products of castor oil with fatty acids and glycols may also be used. Also included are hydrogenated products of polybutadiene polyol and polyisoprene polyol, and styrene and acrylonitrile copolymers of these polyols. The polyurethane may be produced by a general-purpose method such as a general one-shot method or a prepolymer method. These hydrophobic polyols are TDI, MDI
And a catalyst, and if necessary, a foam stabilizer, a crosslinking agent, and the like, to form a polyurethane rubber elastic body. The method of crosslinking may be any of a method using two or more functional crosslinking agents, and a method of mixing isocyanate in an equivalent amount or more. In the present invention, a crosslinked rubber-like sheet product may be used in a single layer, but it may be laminated with a resin film to increase the rigidity of the sheet product, or may be manufactured integrally with a resin film with a single-sided adhesive when manufacturing the sheet product. You can do it. Further, when the sheet product of the present invention is laminated on the front and back of the resin film, a gasket having extremely excellent airtightness is obtained.

[0015]

Examples and Comparative Examples Examples and comparative examples are shown below.
The present invention will be described more specifically. Unless otherwise stated, parts in the examples are parts by weight. The method for measuring the performance of the products obtained in the examples and comparative examples will be specifically described as follows. a. The weight and thickness (average value of 9 points) of the foamed product test pieces punched to an expansion ratio of 100 × 100 mm are measured. The density is determined by the following equation. Density g / cm ³ = weight g / volume cm ³ The density of the unfoamed product is determined in the same manner as described above. The expansion ratio is calculated by the following equation. Expansion ratio = density of unfoamed product / density of foamed product

B. Asker C hardness Physical test method for Japanese rubber association standard standard SRISO101 expanded rubber Measured by spring hardness test. Specifically, this is performed as follows. A test specimen punched out to 30 × 30 mm is laminated to about 10 mm. The Asker C-type hardness tester is pressed vertically with a load of about 1 kg, and the maximum value is read. c. Water absorption at 70 ° C. Measured by a method according to a physical test method of a physical test method for expanded rubber of Japan Rubber Association Standard SRISO101. Specifically, the test piece size, water temperature, and immersion time are changed as follows. A 200 × 25 × 2 mm test piece was immersed in water 150 mm below the water surface for 96 hours at a water temperature of 70 ° C., and the weight increase was measured. The rate of this weight increase is expressed based on the initial weight. Water absorption% = (weight after immersion−weight before immersion) / weight before immersion × 100

D. Weight change rate at 120 ° C. A test piece of 200 × 25 × 2 mm was placed in an oven at 120 ° C. for 24 hours, and the weight change was measured. The rate of this change was expressed based on the initial weight. Weight change rate% = (weight after heating−weight before heating) / weight before heating × 100 e. A test piece having a coefficient of static friction of 63 × 25 mm (thickness: 2 mm) is attached to a smooth stainless plate (200 g) with a double-sided tape, and the weight is measured. This was set on a textured PET film (trade name “Emblet Sandmat SM”, manufactured by Unitika Ltd., center line average roughness Ra = 0.451 μm), and Tensilon (CT-500, manufactured by Orientec) At, pull horizontally at a pulling speed of 150 mm / min.
Slide on film. The obtained initial load is divided by the above-mentioned weight to obtain a coefficient of static friction. Static friction coefficient gf / g = initial load gf / (test piece + stainless steel plate) weight g Here, the center line average roughness Ra representing the surface roughness of the PET film is defined by the definition and display of JIS B0601 surface roughness.・ Measured value.

F. Moisture Permeability This measurement method was partially modified to measure the moisture permeability of a gasket-shaped material based on the JIS Z 0208 moisture permeability test method for a moisture-proof packaging material (cup method). Briefly, at a temperature of 70 ° C., the measurement material is a boundary line, and the air on one side is a relative humidity of 95%,
When the air on the other side is kept dry by a desiccant (dry silica gel), the mass of water vapor passing through this boundary within a certain period of time is measured by the weight increase of the desiccant. Hereinafter, the method will be specifically described. A ring-shaped test piece having an outer diameter of 54φ, an inner diameter of 50φ, and a thickness of 1 mm is sandwiched between upper and lower acrylic plates.
At this time, a spacer with a height of 0.8 mm was inserted, and the compression ratio was 8
0%. Drill a hole in the center of this bottom acrylic plate,
The structure is such that the glass container can be attached and detached via packing. About 30 g of the dried silica gel is precisely weighed, placed in a glass container, and set on an acrylic plate. The material thus prepared is placed in a state of 70 ° C. and 95% RH for 5 days. When finished, weigh the silica gel. At the same time, a blank in which the upper and lower acrylic plates are completely bonded with an acrylic adhesive is prepared, and the increase in silica gel weight is measured. The moisture permeability is
It is calculated by the following formula. Moisture permeability% = (weight after weight−weight before weight) / weight before weight × 100−blank% In this method, the moisture permeability of a conventionally used urethane foam gasket is about 1%. In the present invention, this is set to 0.2% or less, more preferably 0.15% or less.

G. Water washability Since the particles are washed with water, the material must be hardly wet with water and hardly absorb water. In particular,
Can be dried by the following cleaning method. 1) Ultrasonic cleaning 2) Bubbling cleaning 3) Hot air drying 80 ° C, 10 minutes 4) Vacuum drying 80 ° C, 7 minutes

H. Assemblability The assembly process from the baking process of the raw material, the shaping process, the process of setting the gasket on the lid of the HDD and pressing it to the main body, and the like are evaluated by performing tests. Specifically, the contents are as follows. -If the surface tack of the material is too large, the workability of the machining process and the assembly process is reduced. -If the dimensional stability against water and heat is low, it will not fit the lid due to dimensional changes after washing and drying after punching the material.・ If the material is too hard, it will not be possible to tighten the cover or the lid will be stiff. i. Gas generation Measure the gas generation of the baked material. Specifically, the purge and trap method is performed at 120 ° C. by GC / MS, and the total amount of generated gas is examined.

Example 1 100 parts of a dimer acid ester polyol (hereinafter abbreviated as DDEG, average molecular weight 1,400, hydroxyl value 80) obtained by reacting dimer acid and diethylene glycol, and diphenylmethane diisocyanate (hereinafter abbreviated as MDI, molecular weight 250) 1.3, NCO% 33.6) 19.6 parts (NCO /
OH1.10) was thoroughly mixed and stirred, then degassed with a vacuum pump, and the temperature was adjusted to 40 ° C. A small amount of catalyst (triethylenediamine, added amount 0.03 parts) was added to this mixture,
Stir gently and pour into tray. At this time, the bottom of the tray was a smooth PET film coated with silicon. Heat the tray in an oven (75 ° C for 2 minutes,
(At 120 ° C. for 3 minutes) and further at room temperature for 10 days to obtain a urethane elastomer. The physical properties of this elastomer are as shown in Table 1. The performance is HDD
It is suitable as a gasket.

Example 2 In Example 1, 0.01 part of water was added to DDEG,
After mixing with MDI, degassing was not performed (MDI equivalent ratio 1.10), catalyst (triethylenediamine, 0.3 part)
Was added and sanded up and down with a smooth PET film coated with silicon. The following heating conditions were the same as in Example 1 to obtain a sheet having an expansion ratio of 1.3. This foamed product is suitable as an HDD gasket. Comparative Example 1 Further, in Example 2, the number of added water was changed to 0.05 part (MDI equivalent ratio: 1.10) to obtain a sheet having a foaming ratio of 2.0. As shown in Table 1, this foamed product had f. In addition to having a high moisture permeability of 70% at 1%, g. It takes too much time for drying in the water washability, which is not preferable as an HDD gasket.

Example 3 In Example 1, a dimer acid ester polyol obtained by reacting dimer acid and ethylene glycol (hereinafter abbreviated as DEG, having an average molecular weight of 1,250,
Using a hydroxyl value of 90) (MDI equivalent ratio 1.10), a urethane elastomer was obtained in the same manner as in Example 1 below. This elastomer is suitable as an HDD gasket. Comparative Example 2 In Example 3 above, a urethane elastomer having a matte surface was prepared in place of the uneven PET film coated with silicon on the bottom of the tray. In this example, the adhesion at the interface was poor due to the unevenness of the surface, and as a result, e. Coefficient of static friction and f. The value at 70 ° C. was poor.

Example 4 Hydroxy-terminated polyisoprene hydrogenated product (hereinafter referred to as "HIP", trade name "Epol", manufactured by Idemitsu Petrochemical Co., Ltd., average molecular weight 2,500, hydroxyl group) was used in place of the polyol DEG in Example 1. Value 50.4). HIP1
12.4 parts of MDI (NCO / OH =
1.10), and a urethane elastomer was produced in the same manner as in Example 1. As shown in Table 2, this elastomer is suitable as an HDD gasket. Comparative Example 3 In place of the polyol DDEG in Example 1, a hydroxyl-terminated polybutadiene (hereinafter abbreviated as BD, manufactured by Idemitsu Petrochemical Co., Ltd., trade name “Poly bd”, average molecular weight 2,800, hydroxyl value 46.5) was used. used. BD10
0 parts, 11.4 parts of MDI (NCO / OH =
1.10), and a urethane elastomer was obtained in the same manner as in Example 1. As shown in Table 2, this elastomer was obtained from d. + 0.3% at 120 ° C weight change rate
In addition, since the hardness is increased by heating, the assembly property is poor, which is not preferable as a material of the HDD gasket.

Example 5, Example 6, Comparative Example 4 100 parts of EPT rubber (Mitsui EPT-4050), SRF
To a kneading roll, 35 parts of carbon black, 10 parts of zinc white, 1.0 part of stearic acid, 0.7 part of balachinone dioxime, and a composition in which the number of added foaming agents (azodicarbonamide) and foaming aid were changed were mixed. After press mixing, press-crosslinking was performed at 165 ° C. for 20 minutes. In this way, sheets having different expansion ratios were produced. The relationship between the expansion ratio and the examples / comparative examples is as follows: 1.0-fold and 1.2-fold products satisfy the performance, and 2.0-fold products satisfy f. Poor in moisture permeability at 70 ° C. Expansion ratio 1.0 → Example 5 Expansion ratio 1.2 → Example 6 Expansion ratio 2.0 → Comparative Example 4 Comparative Example 5 Natural rubber sheet (expansion ratio 1.0) High water absorption at 70 ° C, d. Since the weight change rate at 120 ° C. is large and other performances are inferior, it is not suitable as an HDD gasket.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

The low moisture permeability HDD gasket according to the present invention has the following effects. 1) In the production of a new HDD gasket model, a very short lead time can be achieved. 2) According to the present invention, the moisture permeating the inside of the material of the gasket and the interface can be reduced together, so that the moisture permeability can be extremely low. 3) Since the water can be washed at a high temperature, the cleanness of the gasket can be increased. Further, the drying time is shortened because the material itself does not easily absorb water. 4) Since the gasket material is not easily deformed or expanded or contracted in the baking process, it is easy to perform not only the baking operation but also the HDD assembly operation. Naturally, baking at a high temperature is also easy to perform, so that gas generation can be reduced accordingly.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08G 101: 00) C08G 101: 00) C08L 23:16 C08L 23:16 (72) Inventor Toshiaki Kimura Nagano 1170 No. Ako, Komagane 3 Fukui term (reference) 4F074 BA13 BA34 BB02 CA21 CC06X CC22X DA02 DA09 DA10 DA24 DA33 DA47 4J034 BA03 DA01 DB04 DB07 DC07 DC12 DC35 DC43 DC50 DF01 DF16 DF20 DF28 DP03 DP19 DP01 DP13 HA07 HA11 HC12 NA01 NA03 QB04 QB11 QB15 QC01 QC08 RA06 RA14

Claims (3)

[Claims] 1. A low-moisture permeable HDD gasket stamped out of a crosslinked rubber-like elastic sheet having a hydrocarbon skeleton into a predetermined shape, 1) having an expansion ratio of less than 2 times, and 2) having an Asker C hardness of 10 to 85 3. ) The water absorption rate at 70 ° C is 1% or less. 4) The heating weight change rate at 120 ° C is +0 to -1%. 5) The coefficient of friction of the gasket surface is 1 gf / g or more. Permeable HDD gasket. 2. The low-moisture permeable HDD gasket according to claim 1, wherein the crosslinked rubber-like elastic body is an α-olefin copolymer or / and a copolymer thereof and a non-conjugated diene, or a hydrophobic polyurethane-based elastic body. 3. The low-moisture permeable HDD gasket according to claim 1, wherein the polyurethane-based elastic body uses a dimer acid-based polyol or an olefin-based polyol.