JP2000230167A - Gasket material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gasket material having desired properties such as excellent rubber elasticity, good oil retention, low hardness and small compression set and suitable for dustproofing and waterproofing applications to hard disks and car lump fittings, and the like. SOLUTION: This gasket material is composed of (a) 100 pts.wt. hydrogenated black copolymer having >=150,000 average degree of polymerization, obtained by hydrogenation of a block copolymer consisting of at least one polymer block mainly comprising a vinylaromatic compound and at least one polymer block mainly comprising a conjugated diene compound, (b) 50-200 pts.wt. nonaromatic rubber softener having >=300 mm2s-1 dynamic viscosity at 40 deg.C and (c) 5-50 pts.wt. polyolefin-based resin mainly composed of polypropylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gasket material, and more particularly, to a gasket material having desired properties such as excellent rubber elasticity, good oil retention, low hardness, and small compression set. The present invention relates to a gasket material suitable for dustproof and waterproof applications such as hard disk drives, mobile phones, information communication devices such as computers, home appliances such as refrigerators and vacuum cleaners, and automobile parts such as automobile lighting.

[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. Sex is growing. For example, conventionally, in order to prevent dust, the hard disk itself was housed in a case and sealed with an elastomer, but since heat generated by the rotation of the hard disk is accumulated inside the case and failure occurs, in recent years, the purpose of dust prevention has been As a gasket material, urethane foam is widely used because of good set properties and simplicity. However, the urethane foam has a hardness of about 50 ° in JIS-A hardness, has a certain tightening force as a dust-proof gasket material, and has an adhesive tape for attaching to a hard disk storage case. Needed the adhesive means. Increasing the tightening force causes sag of the gasket material, resulting in reduced dustproofing. Also,
The foam also has process problems such as difficulty in cleaning and drying to remove dust before assembly. For this reason, there has been a demand for a gasket material that can reduce the tightening force and that can form a packing having low hardness and excellent set characteristics. Furthermore, in recent years, the performance of lamps for automobiles and the like has been improved, the weight thereof has been reduced, and the use of complicated mechanical structures and plastic composite materials has been increasing. Therefore, the need for a gasket that can be easily formed with low hardness and that is excellent in dustproofness and waterproofness is increasing. Conventionally, gaskets using vulcanized rubber and mechanisms that do not require a gasket have been developed for dust prevention and waterproofing.However, gaskets using vulcanized rubber can provide materials with low hardness. Since it is difficult, the fastening force at the time of installing the gasket has to be increased, and as a result, the plastic member constituting the lamp may be greatly distorted or damaged. Further, even if a gasket is made of a vulcanized rubber of low hardness ignoring manufacturing difficulties, it is extremely difficult to install the gasket on a lamp later. Even in a mechanism that does not require a gasket, the design of the lamp is greatly restricted, and the plastic material that can be used is often limited. For this reason, there has been a demand for a gasket material having low hardness, which can be integrally formed at the time of molding a lamp, and which is excellent in dustproofness and waterproofness.

[0003]

SUMMARY OF THE INVENTION The present invention provides a rubber composition having excellent rubber elasticity, good oil retention, low hardness, excellent settability, and small compression set under such circumstances. By using a material having characteristics, it is possible to provide a gasket material suitable for dust prevention of a hard disk or the like, which can easily perform adhesion to a case lid or the like, and can further facilitate production of a gasket. It is the purpose.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that a gasket material composed of a material containing a thermoplastic elastomer composed of a specific block copolymer is used. It was found that the purpose could be achieved. The present invention has been completed based on such findings. That is, the present invention provides (a) hydrogenating a block copolymer consisting of at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound by hydrogenation. 100 parts by weight of the obtained hydrogenated block copolymer having a weight average molecular weight of 150,000 or more, and (b) a kinematic viscosity at 40 ° C. of 300 mm ² s ^−1.
A gasket material comprising a material comprising 50 to 200 parts by weight of the above softener for non-aromatic rubber and (c) 5 to 50 parts by weight of a polyolefin resin containing polypropylene as a main component. Is provided.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the gasket material of the present invention, (a) at least one of a polymer block mainly composed of a vinyl aromatic compound and at least one of a polymer block mainly composed of a conjugated diene compound are used. (B) 40 parts by weight of a hydrogenated block copolymer obtained by hydrogenating one block copolymer, wherein the weight-average molecular weight is 150,000 or more;
50 to 200 parts by weight of a softener for a non-aromatic rubber having a kinematic viscosity at 300 ° C. of 300 mm ² s ⁻¹ or more, and (c) a polyolefin-based resin 5 to 5 containing polypropylene as a main component.
What consists of 0 weight part (henceforth a thermoplastic material) is used.

The hydrogenated block copolymer (a) has two polymer blocks mainly composed of a vinyl aromatic compound, and the polymer blocks are located at both ends of the hydrogenated block copolymer. The hydrogenated block copolymer is preferably located, and the polymer block mainly composed of a vinyl aromatic compound is preferably polystyrene. For example, hydrogenated block copolymer of polybutadiene and polystyrene, and block copolymer of polyisoprene and polystyrene, or block copolymer of polybutadiene or ethylene-butadiene random copolymer and polystyrene can be obtained. Styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, or hydrogenated block copolymer obtained by hydrogenating styrene-butadiene / isoprene-styrene block copolymer Is preferred. Specific examples of the hydrogenated block copolymer (a) in the present invention include a diblock copolymer of crystalline polyethylene and polystyrene, and a triblock copolymer of styrene-ethylene / butylene-styrene (SEBS). Styrene-ethylene / propylene-styrene triblock copolymer (SEPS), styrene-ethylene propylene / ethylene butylene-styrene block copolymer, etc., among which SEBS, SEPS or styrene-ethylene propylene / ethylene Butylene-styrene block copolymers are preferred.

The weight average molecular weight of these hydrogenated block copolymers is 150,000 or more. When the number average molecular weight is less than 150,000, there is a problem that the bleeding of the softener is remarkable, the compression set is large, and the material cannot withstand practical use. The weight average molecular weight is not particularly limited, but is usually about 400,000 to 700,000. The content of the amorphous styrene block in the hydrogenated block copolymer is 10 to 70% by weight, preferably 15 to 60% by weight, and more preferably 20 to 40% by weight.
It is desirable to have a range of weight%. Further, the glass transition temperature (Tg) of the amorphous styrene block portion is 60 ° C. or more,
Preferably, the temperature is 80 ° C. or higher. As the polymer at the portion connecting the amorphous styrene blocks at both ends, an amorphous polymer is also preferable. For example, hydrogenated products such as ethylene-butylene copolymer, butadiene polymer, and isoprene polymer are preferable. And a block or random copolymer thereof. In addition, these hydrogenated block copolymers are mainly used alone, but two or more kinds may be blended and used. The fluidity during molding can be improved by blending two or more copolymers having different molecular weights and different amounts of styrene. These hydrogenated block copolymers are commercially available, such as Septon (trade name) manufactured by Kuraray Co., Ltd., Clayton G (trade name) manufactured by Shell Chemical Co., Ltd., and Tuftec (trade name) manufactured by Asahi Kasei Corporation. It is easily available from.

In the thermoplastic material according to the present invention,
The purpose of reducing the hardness of the thermoplastic elastomer (a)
The kinematic viscosity at 40 ° C. is 300 mm as the component (b).
^Twos ^-1The above softener for non-aromatic rubber is blended.
The kinematic viscosity at 40 ° C. of this softener is 300 mm^Twos^-1
If it is less than the above, the composition loses weight or bleeds due to volatilization.
Significantly, there is an inconvenience that it cannot withstand actual use.
This kinematic viscosity is set at 40 ° C for practical and manufacturing reasons.
300 ~ 10000mm^Twos^-1Preferably
And especially 300-5000mm^Twos^-1Is preferred. Ma
In addition, from the viewpoint of molecular weight, the weight average molecular weight is 20,000.
Less than 10,000, especially less than 5000
Are preferred. As such a softener, usually,
A liquid or liquid at room temperature is suitably used. this
Examples of the softener having such properties include mineral oils,
Softening agents for various non-aromatic rubbers such as vegetable oils and synthetics
It can be appropriately selected from among them. Where mineral oil
As a result, process oils such as naphthenic and paraffinic
Vegetable oils include castor oil, cottonseed oil and linseed oil.
Oil, rapeseed oil, soybean oil, palm oil, nagiko oil, peanut
Oil, wood wax, pine oil, olive oil, etc.
You. In particular, mineral oil paraffin oil,
Futen oil or synthetic polyisobutylene oil
One or two or more selected from
Those having a molecular weight of 450 to 5000 are preferred.

These softeners may be used alone or as a mixture of two or more as long as they have good compatibility with each other. The compounding amount of these softeners is 50 to 200 parts by weight, preferably 100 to 200 parts by weight, particularly preferably 100 to 150 parts by weight based on 100 parts by weight of the component (a). If the amount is less than 50 parts by weight, it is not possible to achieve a sufficiently low hardness, and the flexibility of the thermoplastic material may be insufficient. If the amount exceeds 200 parts by weight, the softener tends to bleed, and This causes the mechanical strength of the plastic material to decrease. The amount of the softener is appropriately selected from the above range according to the molecular weight of the hydrogenated block copolymer of the component (a) and the type of other components added to the hydrogenated block copolymer. Is preferred. These softeners include Diana Process Oil Series (trade name) manufactured by Idemitsu Kosan Co., Ltd., Sambar Series (trade name) and Sunsen Series (trade name) manufactured by Nippon Sun Oil Co., Ltd., and Lucant manufactured by Mitsui Chemicals, Inc. It can be easily obtained from those commercially available as a series (product name).

In order to improve the processability and heat resistance of the thermoplastic material according to the present invention, a polyolefin-based hydrocarbon resin containing polypropylene as a main component can be added as the component (c). Examples of the resin include isotactic polypropylene, a copolymer of propylene and a small amount of other α-olefin (for example, a propylene-ethylene copolymer, a propylene / 4-methyl-1-pentene copolymer), and the like. be able to. Further, if a material obtained by grafting maleic anhydride or acrylic acid to polypropylene or by copolymerization is used, familiarity with the base material is improved, and more effective gasket performance can be exhibited. When a copolymer of isotactic polypropylene is used as the polyolefin resin,
FR (Based on JIS K7210, 230 ° C, 2.16k
(under a g load) of 0.1 g / 10 min or more, especially 0.5 g / 10 min or more can be suitably used. The amount of the component (c) is 5 to 50 parts by weight based on 100 parts by weight of the component (a).
The amount is preferably 5 to 30 parts by weight. If the amount is more than 50 parts by weight, the hardness of the obtained thermoplastic material becomes too high, which is not preferable.

In the thermoplastic material according to the present invention, in order to improve the processability and heat resistance of the material, (c)
A polystyrene resin can be used in combination as a component. As the polystyrene resin, any one obtained by a radical polymerization method or an ionic polymerization method can be suitably used as long as it is obtained by a known production method. The number average molecular weight of the polystyrene resin can be preferably selected from the range of 5,000 to 500,000, more preferably 10,000 to 200,000, and the molecular weight distribution [ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (Mw / Mn)] ] Is preferably 5 or less. Examples of the polystyrene resin include polystyrene, a styrene-butadiene block copolymer having a styrene unit content of 60% by weight or more, rubber-reinforced polystyrene, poly α-methyl styrene, poly pt-butyl styrene, and the like. May be used alone or in combination of two or more. Further, a copolymer obtained by polymerizing a mixture of monomers constituting these polymers can also be used. In the thermoplastic material according to the present invention,
When the polystyrene resin is used in combination with the component (c), the hardness of the obtained material tends to be higher than when the polystyrene resin is not used together. Therefore, the hardness of the obtained thermoplastic material can be adjusted by selecting these compounding ratios. In this case, the ratio of polyolefin resin / polystyrene resin is 95/5 to 5/95.
It is preferable to select from the range of (weight ratio).

In the gasket material of the present invention, in order to obtain a thermoplastic material containing a large amount of a softening agent and a smaller amount of a high-molecular-weight organic material, it is necessary to use a softening agent to be used and a conjugate constituting a hydrogenated block copolymer. Solubility parameter value δ = (ΔE /
V) ^1/2 (ΔE = molar evaporation energy, V = molar volume)
It is preferable to select both materials so that the difference between them is 3.0 or less, preferably 2.5 or less, and more preferably 1.0 or less. If this difference exceeds 3.0, it is difficult to maintain a large amount of the softening agent due to the compatibility of the two materials, which hinders the lowering of the hardness of the obtained thermoplastic material, and bleeding of the softening agent is liable to occur. Is not preferred. Further, the thermoplastic material according to the present invention may optionally contain a polyphenylene ether resin for the purpose of improving the compression set of the material. The polyphenylene ether resin used here is a homopolymer composed of a repeating unit represented by the following general formula or a copolymer containing the repeating unit.

[0013]

Embedded image

(In the formula, R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, a halogen atom or a hydrocarbon group.) As the polyphenylene ether resin, known ones can be used. Specifically, poly (2,6-dimethyl-1,4-phenylene ether), poly (2-methyl-6-ethyl-1,4-phenylene ether), poly (2,6-diphenyl-1, 4-phenylene ether), poly (2-methyl-6-phenyl-1,4-phenylene ether), poly (2,6-dichloro-1,4-
Phenylene ether), and 2,6-
Dimethylphenol and monovalent phenols (for example,
2,3,6-trimethylphenol or 2-methyl-6
A polyphenylene ether copolymer such as a copolymer with (butylphenol) can also be used. Above all, poly (2,6-dimethyl-1,4-phenylene ether)
And a copolymer of 2,6-dimethylphenol and 2,3,6-trimethylphenol, and more preferably poly (2,6-dimethyl-1,4-phenylene ether).

The blending amount of the polyphenylene ether resin is as follows:
It can be suitably selected in the range of 10 to 250 parts by weight based on 100 parts by weight of the thermoplastic material. If this blending amount is 2
If the amount is more than 50 parts by weight, the hardness of the thermoplastic material may be increased. If the amount is less than 10 parts by weight, the effect of improving the compression set obtained by blending is not sufficient. The thermoplastic material according to the present invention includes clay, diatomaceous earth, talc, barium sulfate, calcium carbonate,
Scaly inorganic additives such as magnesium carbonate, metal oxides, mica, graphite, aluminum hydroxide,
Various metal powders, glass powders, ceramic powders, granular or powdery solid fillers such as granular or powdered polymers, and other various natural or artificial short fibers and long fibers (eg, glass fibers, metal fibers, various other Polymer fiber).

Further, a hollow filler, for example, an inorganic hollow filler such as a glass balloon, polyvinylidene fluoride,
The weight can be reduced by blending an organic hollow filler composed of a polyvinylidene fluoride copolymer or the like. Further, in order to improve various physical properties such as weight reduction, it is possible to mix various foaming agents, and it is also possible to mechanically mix gas during mixing or the like.

Further, as other additives, if necessary,
Various tackifiers such as flame retardants, antibacterial agents, hindered amine light stabilizers, ultraviolet absorbers, antioxidants, coloring agents, coumarone resins, coumarone-indene resins, phenol terpene resins, petroleum hydrocarbons, rosin derivatives, etc. Fire), Rheosummer B (trade name: manufactured by Riken Vinyl Co., Ltd.)
Various adhesive elastomers, such as HYBRA (trade name: Kuraray Co., a block copolymer in which polystyrene blocks are linked to both ends of a vinyl-polyisoprene block), Norex (trade name, manufactured by Zeon Corporation, norbornene) Other thermoplastic elastomers or resins such as polynorbornene obtained by ring-opening polymerization can be used in combination.

The method for producing a thermoplastic material according to the present invention comprises:
There is no particular limitation, and a known method can be applied.
For example, the above components and optionally used additive components are mixed with a heat kneader, for example, a single screw extruder, a twin screw extruder,
Melt and knead using a roll, Banbury mixer, pravender, kneader, high-shear mixer, etc., and further add a cross-linking agent such as an organic peroxide, a cross-linking assistant, etc., if necessary, or these necessary components. Can be easily manufactured by simultaneously mixing and kneading under heating and melting. Also, a thermoplastic material prepared by kneading a high-molecular organic material and a softening agent is prepared in advance, and this material is further mixed with one or more high-molecular organic materials of the same type or different types used here. It can also be manufactured. Furthermore, in the thermoplastic material according to the present invention,
Crosslinking can also be performed by adding a crosslinking agent such as an organic peroxide, a crosslinking aid, or the like.

The crosslinking agent that can be added for partial crosslinking is preferably an organic peroxide. Specifically, for example, 2,5-dimethyl-2,5-di (t
-Butylperoxy) -hexane; 2,5-dimethyl-
2,5-di (benzoylperoxy) -hexane; t-
Butylperoxybenzoate; dicumyl peroxide; t-butylcumyl peroxide; diisopropylbenzohydroperoxide; 1,3-bis- (t-
Butylperoxyisopropyl) -benzene; benzoyl peroxide; 1,1-di (t-butylperoxy) -3,3,5-trimethylcyclohexane and the like, and useful crosslinking aids include, for example, Divinylbenzene, trimethylolpropane triacrylate, ethylene dimethacrylate, diallyl phthalate,
Quinone dioxime, phenylene bismaleimide, polyethylene glycol dimethacrylate and the like.
These organic peroxides and crosslinking assistants can be used arbitrarily to adjust the degree of crosslinking in the range of 0.1 to 5 parts by weight, based on 100 parts by weight of the whole compounding material. These organic peroxides and crosslinking assistants may be used in combination of two or more, if necessary. When an unsaturated silane compound is used as a crosslinking aid,
Further, crosslinking can be promoted by contact with water in the presence of a silanol condensation catalyst.

The thermoplastic material thus obtained according to the present invention can be molded into a desired shape by a known method, for example, injection molding or extrusion molding, and used as a gasket material. The gasket material of the present invention is particularly preferably used as a gasket material for a hard disk drive that requires high dustproofing properties. Any of them can be suitably used.

[0021]

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) Oil Retentivity A sheet-like sample of 10 mm × 10 mm and a thickness of 2 mm was sandwiched between graph papers, and a load of 1 kg / cm ² was applied to the sample at 60 ° C.
For 24 hours, and oil seepage was observed.
A sample without oil seepage was indicated by “○”, and a sample with oil seepage was indicated by “×”. (3) Compression set In accordance with JIS K6262, 70 ° C under 25% compression,
After standing for 22 hours, the compression set was measured. In addition,
The number average molecular weight of the copolymer was measured by gel permeation chromatography [apparatus: HLC-8020 (TOS
O), column: GMHXL-L × 2 + G1000HX
L + pre-column (manufactured by TOSO), flow rate: 1.0 ml / min (solvent: tetrahydrofuran)], and using a differential refractive index (RI) in terms of polystyrene using monodisperse polystyrene as a standard. The kinematic viscosity was measured according to JIS K2283, using a B-type viscometer [Co., Ltd.].
Tokimec].

Examples 1 and 2 and Comparative Examples 1 to 4 (1) Preparation of Thermoplastic Material Samples of the thermoplastic material were prepared by sufficiently kneading the components having the formulations shown in Table 1 and An evaluation was performed.
As a result, as is clear from Table 1, the thermoplastic materials of Examples 1 and 2 had good oil retention, but the thermoplastic materials of Comparative Examples 1 to 4 showed oil bleed.

[0023]

[Table 1]

Polymer A: Septon 4077 (styrene-ethylene propylene / ethylene butylene-styrene block copolymer) manufactured by Kuraray Co., Ltd. having a weight average molecular weight of 150,000 or more Polymer B: Styrene having a weight average molecular weight of 50,000 30 wt% SEBS oil A: kinematic viscosity at 40 ° C. is 380 mm ² s ⁻¹
Paraffinic oil [manufactured by Idemitsu Kosan Co., Ltd., trade name: Diana Process Oil PW380] (number average molecular weight 75
0) Oil B: a paraffinic oil having a kinematic viscosity at 40 ° C. of 30 mm ² s ⁻¹ [manufactured by Idemitsu Kosan Co., Ltd., trade name: Diana Process Oil PW32] (number average molecular weight 400) Oil C: kinematic viscosity at 40 ° C. Is 1300mm ² s
^-1 paraffinic oil [Mitsui Chemicals Co., Ltd., trade name:
Lucant HC100] (number average molecular weight 1450)

(2) Molding of Thermoplastic Material (Manufacture of Gasket) FIG. 1 is a perspective view showing a gasket with a lid for a case for accommodating a hard disk drive, which is an embodiment of the gasket according to the present invention (FIG. 1). This figure is a view of the gasket material with the lid viewed from the sealing surface side.) Gasket 1
Is in close contact with the surface of the aluminum lid 2, and the lid 2
Is a lid of the hard disk drive storage case. Devices such as a magnetic disk, a magnetic head, and an actuator are disposed on the box side of the hard disk drive device storage case in the center gap portion of the gasket with the lid, and these devices are connected to a metal box (not shown). It is closed with a gasket with a lid and stored in a hard disk drive device storage case. Such a gasket with a lid was used as a lid of a hard disk drive device storage case, that is, the gasket was placed in the hard disk drive device, and after 30 days of use, the gasket was visually observed. As a result, a thermoplastic material was used in Examples. In that case, no settling of the gasket is allowed,
Also, the dustproof property during use was good. On the other hand, when the thermoplastic material of the comparative example was used, settling of the gasket and oil bleeding occurred. As is clear from the evaluation results, the gasket with the lid according to the present invention can be easily manufactured and the gasket has good adhesion between the lid and the lid. When used as a gasket, the dustproof property was good, and the gasket was made of a material of low hardness, so that it was not deformed even after being used for a long time.

[0026]

The gasket material of the present invention is made of a material having characteristics such as excellent rubber elasticity, good oil retention, low hardness, and low compression set. Can be easily bonded, and gasket can be easily manufactured.
It is suitable for dust prevention of hard disks and the like.

[Brief description of the drawings]

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

[Explanation of symbols]

 1: Gasket 2: Hard disk drive case lid

Claims (6)

[Claims] 1. A method comprising hydrogenating a block copolymer comprising (a) at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. A hydrogenated block copolymer having a weight average molecular weight of 150,000 or more, 100 parts by weight of a hydrogenated block copolymer, and (b) a kinematic viscosity at 40 ° C. of 300 mm ² s ⁻¹ or more. A gasket material comprising: 50 to 200 parts by weight of a softening agent for a system rubber; and (c) 5 to 50 parts by weight of a polyolefin resin containing polypropylene as a main component. 2. The hydrogenated block copolymer has two polymer blocks mainly composed of a vinyl aromatic compound, and the polymer blocks are located at both ends of the hydrogenated block copolymer. The gasket material according to claim 1, which is a hydrogenated block copolymer. 3. The gasket material according to claim 2, wherein the polymer block mainly composed of a vinyl aromatic compound is polystyrene. 4. The weight ratio of polystyrene is from 20 to 40.
%, And the gasket material according to claim 3. 5. The gasket material according to claim 1, wherein the hardness of the material is 50 ° or less with a type A durometer in accordance with JIS K6253. 6. The material according to claim 1, wherein the material has a compression set of 50% or less after standing at 70 ° C. for 22 hours under 25% compression measured in accordance with JIS K6262. Gasket material.