JP2002105436A - Rubber composition for gasket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber material for a gasket excellent in electromagnetic wave-shielding property without detriment to sealing property. SOLUTION: The rubber composition for a gasket contains 5-15 vol.% of ketchen black in the rubber composition having incorporated thereinto various kinds of ingredients.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a rubber composition for a gasket. More specifically, it relates to a rubber composition for a gasket having an electromagnetic wave shielding property.

[0002]

2. Description of the Related Art As electronic devices have become more sophisticated, each device has been operated with a very small current. Electromagnetic waves whose signals are disturbed by electromagnetic waves generated from the device itself and interference waves from other devices. There are many obstacles. In order to operate electronic devices normally, it is necessary to shield electromagnetic waves that enter from outside the devices.

As a method of shielding electromagnetic waves, a method of covering an electronic device with a conductive material is generally used. Specifically, a casing is made of conductive plastic, or a conductive surface treatment is performed. There is a method of covering the surface of the housing with a used material or conductive paint, or making or covering the housing with a metal material.

On the other hand, when the electronic device is not integrated with the housing, it is necessary to shield the electromagnetic wave also at the joint. The components used in this case are required to have a sealing performance that prevents dust, dirt, oil, grease, liquid, and the like from entering the inside of the electronic device from the outside, and a material excellent in such performance is a rubber material.

[0005] As the rubber material for shielding electromagnetic waves, 8 to 100 parts by weight of a conductive rubber material to which a conductive filler is added are used.
Although an electromagnetic wave shielding material to which 16 parts by weight of sulfur has been added has been proposed (JP-A-10-298355), a large amount of acetylene black, furnace black, carbon fiber, etc. is blended as a conductive filler. Even if such a shielding material is used for a sealing material, excellent sealing performance is not exhibited there.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a rubber material for a gasket which has an excellent electromagnetic wave shielding property and does not impair the sealing property.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
This is achieved by a rubber composition for a gasket containing 5 to 15% by volume of Ketjen Black in a rubber composition containing various compounding agents.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As a rubber material, a material which is favorably required as a gasket material is suitable, and specifically, fluorine rubber, acrylic rubber, ethyl acrylate-ethylene copolymer, nitrile rubber, hydrogenated nitrile Rubber, chlorinated polyethylene, chloroprene rubber, chlorosulfonated polyethylene, ethylene-propylene-diene terpolymer, ethylene-propylene copolymer, epichlorohydrin rubber, vinyl methyl silicone rubber, fluoroalkyl vinyl methyl silicone rubber, butyl rubber , Polyester urethane, polyether urethane and the like. Among them, ethylene-propylene-diene terpolymer (EPDM), which has a good balance of weather resistance, heat resistance, sealing properties, cost, etc., is preferably used.

As EPDM, a terpolymer rubber having a weight ratio of ethylene to propylene of 90:10 to 10:90 and a non-conjugated diene is used. In general, dicyclopentadiene, methyltetrahydroindene, methylenenorbornene, ethylidene norbornene, 1,4-hexadiene and the like are used as the non-conjugated diene, and those obtained by copolymerizing ethylidene norbornene or dicyclopentadiene are used in the present invention. Particularly suitable.

In these rubber materials, Ketjen black is used in an amount of 5 to 15% by volume, preferably 8 to 12% by volume in a rubber composition containing various compounding agents. Ketjen black has so-called hollow shell-like particles, such as thin graphite crystals gathered on the outside.If Ketjen black is used at a lower ratio, the tensile strength and electromagnetic wave When the shielding effect is reduced, the elongation at break and the compression set are significantly deteriorated when used at a higher ratio.

[0011] In the rubber composition containing the above components as essential components, a plasticizer, an antioxidant, an acid acceptor, a cross-linking agent, a vulcanization accelerator or a cross-linking auxiliary, etc. are compounded as necessary. Used.

Examples of the plasticizer include those used for ordinary rubber, for example, petroleum softeners such as process oils and lubricating oils, and fatty oil softeners such as castor oil, linseed oil, rapeseed oil, and coconut oil. Ester plasticizers such as dibutyl phthalate, dioctyl phthalate, dioctyl adipate, and dioctyl sebacate are used in an amount of about 10 to 150 parts by weight based on 100 parts by weight of rubber.
Parts by weight, preferably about 20 to 100 parts by weight.

As the anti-aging agent, those used for ordinary rubbers include amines or derivatives thereof, imidazoles, phenols or derivatives thereof, and waxes. As the acid acceptor, a metal compound (oxide or hydroxide) or a carboxylate, a silicate, or a carbonate that provides stability of a crosslinked product and an appropriate crosslinking rate, such as magnesium oxide and magnesium hydroxide , Barium hydroxide, magnesium carbonate, calcium hydroxide, calcium oxide,
Calcium carbonate, zinc white and the like are used.

As the crosslinking agent, sulfur, peroxides, thioureas, metal salts of dithiocarbamic acid, thiurams, trimercaptotriazines and the like can be used. Specific examples of peroxides include bis
(Tert-butylperoxy) trimethylcyclohexane, dicumyl peroxide and the like. These crosslinking agents are used in an amount of about 0.5 to 10 parts by weight, preferably about 1 to 5 parts by weight, based on 100 parts by weight of rubber.

Examples of the vulcanization accelerator include thiazoles, sulfamine amides, dicyclohexylamine salts, N,
N'-dicyclohexylsulfamine amides, dithiocarbamates and the like are used in an amount of about 0.5 to 10 parts by weight, preferably about 1 to 5 parts by weight, per 100 parts by weight of rubber. The crosslinking aid is effective when peroxides are used as a crosslinking agent, and polyfunctional monomers are preferably used. Specific examples thereof include triallyl isocyanate, triallyl cyanurate, ethylene glycol dimethacrylate, and trimethylolpropane. Trimethacrylate or the like is used in an amount of about 1 to 15 parts by weight, preferably about 2 to 10 parts by weight, per 100 parts by weight of rubber.

The rubber composition of the present invention may further contain various compounding agents usually compounded in rubber, for example, stabilizers, lubricants, tackifiers, internal release agents, pigments, flame retardants and the like. Can also. Further, a small amount of thermoplastic resin or rubber may be added to improve abrasion, moldability and the like, and short fibers may be added to improve strength and rigidity.

The composition comprising these components can be mixed with a usual rubber kneading machine such as a roll, kneader, intermix and the like, and the crosslinking thereof is performed by a press or an injection molding machine to obtain a molded product. be able to. Crosslinking conditions are about 12
The reaction can be appropriately performed at 0 to 220 ° C. for 1 minute to 1 hour. In addition, if necessary, these may be further heated to about 120 to 220 ° C.
The secondary vulcanization may be performed for about 0.5 to 24 hours.

[0018]

The gasket obtained from the rubber composition for a gasket according to the present invention has the following features at the same time. (1) The electromagnetic wave effect at 1 GHz is 15 dB or more, which is excellent in electromagnetic wave shielding. (2) Hardness (durometer A type) is in the range of 50 to 90, which is an appropriate range suitable for a gasket material. (3) Tensile strength of 10 MPa or more, which is excellent as a gasket material. (4) The elongation at break is 250% or more, which is excellent as a gasket material. (5) The compression set (70 ° C., 24 hours) is 50% or less, and has excellent compression set resistance as a gasket material. (6) Good moldability.

The rubber composition for a gasket of the present invention having such characteristics can be effectively used as a molding material for electronic equipment parts, automobile parts, etc., which are required to shield electromagnetic waves and also have sealing properties.

[0020]

Next, the present invention will be described with reference to examples.

Example 1 EPDM (Mitsui Chemicals EPT3070) 100 parts by weight Ketjen Black (Lion product EC600JD) 30 〃 Stearic acid 1 可塑 Plasticizer (Idemitsu Kosan Diana Process Oil PW-380) 120 亜 鉛 Zinc oxide 5 老 Aging Inhibitor (Ouchi Emerging Chemicals Nocrack White) 2 〃 Sulfur 2 〃 Vulcanization accelerator (Ouchi Emerging Chemicals Noxeller CZ) 2 を After kneading the above ingredients with a kneader for 10 minutes,
Dough kneaded with a roll for 3 minutes (carbon black content 6
% By volume) at 180 ° C. for 10 minutes and then at 150 ° C.
Secondary vulcanization was performed for 15 hours.

The following items were measured for the obtained vulcanized sheet. Hardness (durometer A): compliant with JIS K-6253 Tensile strength: compliant with JIS K-6251 Elongation at break: compliant with JIS K-6251 Compression set: compliant with JIS K-6262 (70 ° C, 24 hours) Electromagnetic wave shielding: Plastic shield material evaluation device (TR17301A manufactured by Advantest) Measured at a frequency of 0 to 1GHz by the Advantest method. The electromagnetic wave shielding effect at 1GHz before and after sample mounting was demonstrated.

Example 2 In Example 1, the amount of Ketjen black was changed to 50 parts by weight (carbon black content: 10% by volume).

Example 3 In Example 1, the amount of Ketjen black was changed to 75 parts by weight (carbon black content: 14% by volume).

Example 4 In Example 1, the amount of the plasticizer was changed to 60 parts by weight, and the carbon black content was set to 8% by volume.

Example 5 In Example 4, 4 parts by weight of an organic peroxide (Nippon Oil & Fat Products, Parkmill D) was used in place of sulfur, and 2 parts by weight of trimethylolpropane trimethacrylate was used in place of the vulcanization accelerator. The carbon black content was 8% by volume.

Comparative Example 1 In Example 4, the amount of Ketjen black was changed to 15 parts by weight (carbon black content: 4% by volume).

Comparative Example 2 In Example 4, the amount of Ketjen black was changed to 80 parts by weight (carbon black content: 16% by volume).

Comparative Example 3 In Example 4, the same amount of FEF carbon black (Tokai Carbon Product Seast SO) was used in place of Ketjen Black.

Comparative Example 4 In Example 4, the same amount of acetylene black (Denka Black, an electrochemical product) was used in place of Ketjen Black.

Comparative Example 5 In Example 4, the same amount of MT carbon black (manufactured by CANCARB, N990) was used in place of Ketjen Black.

The measurement results in the above Examples and Comparative Examples are shown in the following table. Table Example Comparative Example Measurement items 1 2 3 4 5 1 2 3 4 5 Hardness (Durometer A) 51 66 84 70 70 40 91 50 55 45 Tensile strength (MPa) 19 20 20 23 18 12 25 14 17 12 Break Elongation at time (%) 950 860 690 710 300 850 300 600 650 400 Compression set (%) 18 24 30 22 6 15 45 15 18 12 Electromagnetic shielding effect 1 GHz (dB) 17 22 30 19 18 13 35 1 2 1

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H05K 9/00 H05K 9/00 EF term (Reference) 4H017 AA03 AA29 AB07 AC10 AC16 4J002 AC071 AC091 AC111 BB071 BB151 BB181 BB241 BB271 BD121 BG041 CH041 CK031 CK041 CP031 DA036 FD016 FD020 FD030 FD140 GJ02 5E321 AA03 BB44 BB60 GG05 GH07

Claims (4)

[Claims] 1. A rubber composition for a gasket comprising 5 to 15% by volume of Ketjen black in a rubber composition containing various compounding agents. 2. The rubber composition for a gasket according to claim 1, wherein EPDM is used as the rubber material. 3. The hardness (durometer A type) is 50 to 90, the tensile strength is 10 MPa or more, and the elongation at break is 250%.
The rubber composition for a gasket according to claim 1, which gives a gasket having a compression set (70 ° C, 24 hours) of 50% or less and an electromagnetic shielding property at 1 GHz of 15 dB or more. 4. Ketjen black contains 5 to 15% by volume, hardness (Durometer A type) is 50 to 90, tensile strength is 10 MPa or more, elongation at break is 250% or more, Compression set (70 ° C, 24 hours) is 50% or less, 1GHz
A gasket whose electromagnetic wave shielding performance is 15dB or more.