Sealing material

Abstract

Provided is a novel sealing material which exhibits excellent adhesion (sealing properties) at a low surface pressure.　The sealing material is characterized by comprising an elastic layer including a foamed rubber layer and pressure-sensitive adhesive layers respectively disposed on both main surfaces of the elastic layer, and is further characterized in that: the foamed rubber layer is a foamed object formed from an unfoamed rubber layer comprising an ethylene / propylene / diene terpolymer (EPDM) which is a rubber component, a crosslinking agent, a crosslinking accelerator, and a blowing agent; and the crosslinking agent is a phenolic-resin crosslinking agent and the crosslinking accelerator is an organic sulfonic acid compound.

Description

sealing material

[0001] The present invention relates to a sealing material.

[0002] Rubber foams have traditionally been used as sealing materials for the purposes of dust prevention, heat insulation, soundproofing, vibration damping, cushioning, watertightness, and airtightness in various industrial products such as automobiles, vehicles, ships, and various electrical and electronic devices. For example, in the automotive field, there has been a rapid increase in demand for sealing materials used in electrical component protective cases and the like in housing locations for various electrical and electronic devices that make up hybrid automobiles and electric automobiles. Examples of sealing materials used in locations configured by fastening a pair of low-rigidity flanges with small bolts, such as the above-mentioned electrical component protective cases, include those made of rubber foam having foam rubber layers on one or both sides of a substrate made of a metal plate or the like (see Patent Documents 1 and 2).

[0003] Patent No. 4814895 Patent No. 5852470

[0004] In a part such as the electrical component protection case described above, where a pair of low-rigidity flanges are fastened together with small bolts, sufficient sealing performance is required due to the low tightening surface pressure generated between the bolts due to the undulations of the flanges.

[0005] However, when a foamed rubber sealing material having a foamed rubber layer on a substrate made of a metal plate or the like as described above is used, there are cases where the fluid to be sealed penetrates between the metal plate substrate and the foamed rubber layer, reducing the adhesion between the two and reducing the sealing ability.

[0006] On the other hand, if the clamping load of the flange is increased in order to increase the clamping surface pressure, the components may be damaged if vibrations or shocks are applied during clamping or during operation after clamping.

[0007] For this reason, there has been a growing demand for sealing materials used in protective cases for electrical components that exhibit excellent sealing properties at low surface pressure.

[0008] Another known sealing material is a waterproof seal provided inside an automobile door. The waterproof seal is disposed in a compressed state inside the automobile door and is susceptible to intermittent shocks caused by vibrations when the door is opened and closed or when the vehicle is being driven. For this reason, there has been a demand for a waterproof seal provided inside the automobile door that exhibits excellent sealing properties at low surface pressure.

[0009] Furthermore, as a sealing material, a waterproof sealing material provided in various electronic devices, such as mobile terminals (e.g., mobile phones and tablets) and in-vehicle electronic devices, is known. The above-mentioned sealing material is disposed in a compressed state inside the electronic device, and is therefore susceptible to intermittent shocks due to vibrations during use or operation. For this reason, there has been a demand for a waterproof sealing material provided inside the electronic device that exhibits excellent sealing properties at low surface pressure.

[0010] Under these circumstances, an object of the present invention is to provide a novel sealing material that exhibits high adhesion (sealing properties) at low surface pressure.

[0011] In order to achieve the above object, the present inventors have conducted extensive research and have found that the above technical problems can be solved by a sealing material having an elastic layer made of a specific foamed rubber layer and pressure-sensitive adhesive layers laminated on both main surfaces of the elastic layer, and have completed the present invention based on this finding.

[0012] That is, the present invention provides: (1) a sealing material having an elastic layer including a foamed rubber layer and pressure-sensitive adhesive layers laminated and disposed on both main surfaces of the elastic layer, wherein the foamed rubber layer is made of a foamed unfoamed rubber layer containing ethylene-propylene-diene terpolymer (EPDM) as a rubber component, a phenolic resin crosslinking agent, a crosslinking accelerator, and a foaming agent, and the crosslinking accelerator is an organic sulfonic acid compound; (2) the sealing material according to (1) above, wherein the content of the phenolic resin crosslinking agent in the unfoamed rubber layer is 2.0 to 20.0 mass % in terms of solid content; (3) the sealing material according to (1) or (2) above, wherein the elastic layer consists of only the foamed rubber layer, or consists of a laminated integral product in which the foamed rubber layers are laminated and disposed on both main surfaces of a substrate layer made of a metal plate or a resin plate; (4) the sealing material according to any of (1) to (3) above, wherein the diene content of the ethylene-propylene-diene terpolymer (EPDM) is 1 to 20 mass %; (5) The sealing material according to any one of (1) to (4) above, wherein the foamed rubber layer is a foam having an expansion ratio of 1.5 times or more that of the unfoamed rubber layer; (6) The sealing material according to any one of (1) to (5) above, wherein the pressure-sensitive adhesive layer contains, as a pressure-sensitive adhesive, at least one selected from urethane resin, natural rubber, butadiene rubber, isoprene rubber, styrene butadiene, nitrile rubber, ethylene-propylene-diene terpolymer, butyl rubber, chloroprene rubber, thermoplastic elastomer, and any of these with water additives; (7) The sealing material according to (6) above, wherein the thermoplastic elastomer is at least one selected from styrene-based elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, ester-based thermoplastic elastomers, and amide-based thermoplastic elastomers.

[0013] According to the present invention, it is possible to provide a novel sealing material that exhibits high adhesion (sealing properties) at low surface pressure.

[0014] 1 is a diagram schematically illustrating a vertical cross section of an example of a sealing material according to the present invention, and FIG. 2 is a diagram schematically illustrating a vertical cross section of an example of a sealing material according to the present invention.

[0015] The sealing material according to the present invention comprises an elastic layer including a foamed rubber layer, and pressure-sensitive adhesive layers laminated on both main surfaces of the elastic layer, wherein the foamed rubber layer is made of a foamed unfoamed rubber layer containing an ethylene-propylene-diene terpolymer (EPDM) as a rubber component, a phenolic resin crosslinking agent, a crosslinking accelerator, and a foaming agent, and the crosslinking accelerator is an organic sulfonic acid compound.

[0016] The sealing material according to the present invention has a laminated structure including an elastic layer and pressure-sensitive adhesive layers laminated on both main surfaces of the elastic layer.

[0017] In the sealing material according to the present invention, the elastic layer includes a foamed rubber layer.

[0018] In the sealing material according to the present invention, the elastic layer may have a configuration consisting of only a foamed rubber layer (hereinafter referred to as the first configuration), or may have a configuration consisting of a laminated integrated product in which foamed rubber layers are laminated on both main surfaces of a base layer made of a metal plate or a resin plate (hereinafter referred to as the second configuration).

[0019] Fig. 1 is a schematic diagram of a vertical cross section of one embodiment of the sealing material according to the present invention, showing an example in which the elastic layer adopts a first form. In the embodiment shown in Fig. 1, the sealing material 1 includes an elastic layer i consisting only of a foamed rubber layer r, and pressure-sensitive adhesive layers s, s laminated on both main surfaces of the elastic layer i.

[0020] 2 is a schematic vertical cross-sectional view of another embodiment of the sealing material according to the present invention, showing an embodiment in which the elastic layer adopts the second form. In Fig. 2, the sealing material 1 includes an elastic layer i consisting of a base layer b made of a metal plate or a resin plate and foamed rubber layers r, r laminated and arranged on both main surfaces of the base layer, and pressure-sensitive adhesive layers s, s laminated and arranged on both main surfaces of the elastic layer i.

[0021] In the sealing material according to the present invention, the elastic layer preferably has a thickness of 300 to 800 μm, more preferably 400 to 700 μm.

[0022] The thickness of the elastic layer means the arithmetic mean value when the thickness is measured at 10 points using a dial gauge.

[0023] In the sealing material of the present invention, by having the thickness of the elastic layer within the above range, it is possible to easily provide a sealing material that has the desired density, the desired flexibility, and excellent adhesion (sealing properties).

[0024] In the sealing material according to the present invention, when the elastic layer is in the first form, i.e., when it is made of (only) a foamed rubber layer, the thickness of the elastic layer corresponds to the thickness of the foamed rubber layer. In the sealing material according to the present invention, when the elastic layer is in the second form, i.e., when it is made of a laminated integrated product in which foamed rubber layers are laminated on both main surfaces of a base layer made of a metal plate or a resin plate, the thickness of the elastic layer corresponds to the sum of the thickness of the base layer made of a metal plate or a resin plate and the thickness of the foamed rubber layer.

[0025] In the sealing material according to the present invention, the foamed rubber layer constituting the elastic layer is made of a foamed product of the unfoamed rubber layer.

[0026] In the sealing material according to the present invention, the foamed rubber layer is preferably a foam having an expansion ratio of 1.5 times or more that of the unfoamed rubber layer, more preferably a foam having an expansion ratio of 2.0 times or more, and even more preferably a foam having an expansion ratio of 2.5 times or more. There is no particular upper limit to the expansion ratio of the unfoamed rubber layer, but the expansion ratio of the unfoamed rubber is usually 6.0 times or less.

[0027] In the sealing material according to the present invention, the foaming ratio of the unfoamed rubber layer is 1.5 times or more, so that excellent adhesion (sealing properties) can be easily exhibited even when the surface pressure is low.

[0028] In the present application, the foaming ratio means a value calculated by the following formula: Foaming ratio = Thickness of foamed rubber layer / Thickness of unfoamed rubber layer (where the thickness of the foamed rubber layer means the arithmetic mean value when the thickness is measured at 10 points using a dial gauge, and the thickness of the unfoamed rubber layer also means the arithmetic mean value when the thickness is measured at 10 points using a dial gauge.)

[0029] In the sealing material according to the present invention, the foamed rubber layer is made of a foam of the unfoamed rubber layer, which contains an ethylene-propylene-diene terpolymer (EPDM) as a rubber component, a phenolic resin crosslinking agent, a crosslinking accelerator, and a foaming agent.

[0030] The ethylene-propylene-diene terpolymer (EPDM) preferably contains 1 to 20% by mass of diene, more preferably 5 to 15% by mass of diene.

[0031] When the amount of diene constituting the EPDM is within the above range, the foamed rubber layer can be easily imparted with the desired resistance to settling.

[0032] When the unfoamed rubber layer contains ethylene-propylene-diene terpolymer (EPDM) as a rubber component, a foamed rubber layer having desired properties can be easily obtained.

[0033] The unfoamed rubber layer preferably contains 10 to 90% by mass, more preferably 30 to 70% by mass, of ethylene-propylene-diene terpolymer (EPDM) in terms of solid content.

[0034] When the unfoamed rubber layer contains the ethylene-propylene-diene terpolymer (EPDM) in the above proportion, a sealing material excellent in adhesion (sealing properties) and recovery can be easily provided.

[0035] In the sealing material according to the present invention, the unfoamed rubber layer contains a phenol resin crosslinking agent as a crosslinking agent.

[0036] The unfoamed rubber layer preferably contains 2.0 to 20.0 mass % of the phenol resin crosslinking agent, and more preferably 2.6 to 17.5 mass %, calculated as solid content.

[0037] When the unfoamed rubber layer contains the phenolic resin crosslinking agent in the above proportion, the flexibility of the foamed rubber layer can be easily controlled, and a sealing material with excellent adhesion (sealing properties) and recovery properties can be easily provided.

[0038] In the sealing material according to the present invention, the unfoamed rubber layer contains an organic sulfonic acid compound as a crosslinking accelerator, such as methanesulfonic acid (MSA), benzenesulfonic acid (BSA), trifluoromethanesulfonic acid (TFMSA), p-toluenesulfonic acid (PTSA), heptafluoropropanesulfonic acid, heptadecafluorooctanesulfonic acid, naphthalenesulfonic acid (NSA), naphthalenedisulfonic acid (NDSA), methanedisulfonic acid (MDSA), ethanedisulfonic acid (EDSA), nonafluorobutanesulfonic acid (FBSA), or bis(nonafluorobutanesulfonyl)imide. (BFBSI), dinonylnaphthalenesulfonic acid (DNNSA), dinonylnaphthalenedisulfonic acid (DNNDSA), dodecylbenzenesulfonic acid (DDBSA), ethanesulfonic acid (ESA), propanesulfonic acid (PSA), butanesulfonic acid (BSA), dodecanesulfonic acid (DDSA), cumenesulfonic acid (IPBSA), camphorsulfonic acid (CSA), hydroxyethanesulfonic acid (HESA), hydroxyethanedisulfonic acid (HEDSA), and the like.

[0039] By including the crosslinking accelerator in the unfoamed rubber layer, it is possible to easily control the flexibility of the foamed rubber layer and provide a sealing material that is excellent in adhesion (sealing properties) and recovery properties.

[0040] The foaming agent constituting the unfoamed rubber layer is not particularly limited, but is preferably a microcapsule in which a volatile liquid foaming agent is encapsulated in a thermoplastic shell polymer with gas barrier properties. When the microcapsule is heated, the outer shell of the capsule softens and the liquid foaming agent encapsulated in the capsule vaporizes, increasing the internal pressure. This action causes the capsule to expand, generating hollow spherical particles, which form voids in the foamed rubber layer.

[0041] Examples of the volatile liquid blowing agent that constitutes the microcapsules include hydrocarbons with low boiling points such as isopentane, isobutane, and isopropane.

[0042] Examples of the thermoplastic shell polymer constituting the microcapsules include one or more selected from polyacrylonitrile, vinylidene chloride-acrylonitrile copolymer, vinylidene chloride-methyl methacrylate copolymer, vinylidene chloride-ethyl methacrylate, acrylonitrile-methyl methacrylate copolymer, acrylonitrile-ethyl methacrylate, and the like.

[0043] By including the microcapsules as a foaming agent in the unfoamed rubber layer, the foamability of the unfoamed rubber layer can be easily controlled, a foamed rubber layer with suitable flexibility can be easily formed, and a sealing material that exhibits excellent adhesion (sealing properties) even when the surface pressure is low can be easily provided.

[0044] The unfoamed rubber layer preferably contains 1.0 to 10.0 mass % of a foaming agent, and more preferably 2.0 to 8.0 mass %, calculated as solid content.

[0045] By including a foaming agent in the unfoamed rubber layer in the above-mentioned ratio, it is possible to easily control the flexibility of the foamed rubber layer and provide a sealing material with excellent adhesion (sealing properties).

[0046] In the sealing material according to the present invention, when the elastic layer takes the second form, the elastic layer is made of a laminated integrated product in which foamed rubber layers are laminated on both main surfaces of a base layer made of a metal plate or a resin plate.

[0047] In this application, a laminated integral product means that adjacent layers are chemically or physically fixed together.

[0048] In the sealing material according to the present invention, the metal plate or resin plate constituting the base layer is not particularly limited.

[0049] The metal plate constituting the substrate layer is not particularly limited, but examples thereof include plates made of stainless steel (ferritic, martensitic, austenitic, etc.), iron, plated materials, aluminum, etc., and examples thereof include plate-shaped articles made of one or more metals selected from stainless steel, iron, etc. The metal plate constituting the substrate layer may be a plurality of metal plates joined together by bonding, etc., and preferred examples of such metal plates are joined stainless steel plates and iron plates.

[0050] Examples of the resin plate constituting the base layer include plates made of one or more resins selected from polyethylene (PE)-based resins, polypropylene (PP)-based resins, polyethylene terephthalate (PET)-based resins, polyethylene naphthalate (PEN)-based resins, polyvinyl chloride (PVC)-based resins, polystyrene (PS)-based resins, acrylic resins (PMMA), polycarbonate (PC)-based resins, polyphenylene sulfide (PPS)-based resins, polytetrafluoroethylene (PTFE)-based resins, polyether ether ketone (PEEK)-based resins, polyethersulfone (PES)-based resins, polyamide (PA)-based resins, polyimide (PI)-based resins, and the like. As the resin plate constituting the base layer, of the above-mentioned plate-like materials, a plate-like material made of one or more resins selected from polyethylene terephthalate (PET)-based resins, polyethylene naphthalate (PEN)-based resins, polystyrene (PS)-based resins, polyphenylene sulfide (PPS)-based resins, polyethersulfone (PES)-based resins, etc. is preferred.

[0051] In the sealing material according to the present invention, the thickness of the metal plate or resin plate constituting the substrate layer is not particularly limited, but is usually 1 to 500 μm.

[0052] In the present application, the thickness of the metal plate or resin plate refers to the arithmetic mean value when the thickness is measured at 10 points using a dial gauge.

[0053] In the sealing material of the present invention, when the elastic layer takes the second form, the elastic layer has a base layer made of a metal plate or a resin plate, which makes it possible to easily improve the handleability of the sealing material.

[0054] In the sealing material according to the present invention, the elastic layer consisting of a foamed rubber layer can be formed by dissolving a rubber compound containing desired amounts of ethylene-propylene-diene terpolymer (EPDM), a phenolic resin crosslinking agent, a crosslinking accelerator, a foaming agent, etc. in an organic solvent to form a coating liquid, which is then applied to the main surface of a suitable substrate and fixed to form an unfoamed rubber layer, which is then heated at a predetermined temperature for a predetermined time to foam.

[0055] The expansion ratio can be easily controlled by adjusting the types and compounding ratios of the rubber component constituting the rubber compound, the phenolic resin crosslinking agent, the crosslinking accelerator and the foaming agent, and in particular, by adjusting the crosslinking rate of the EPDM rubber component.

[0056] If the crosslinking rate is increased, crosslinking will proceed before the rubber component is expanded and deformed by the foaming gas, making it easier to suppress the expansion ratio. Conversely, if the crosslinking rate is decreased, deformation of the rubber component by the foaming gas will take precedence over the hardening rate of the rubber due to crosslinking, making it easier to increase the expansion ratio.

[0057] In the sealing material according to the present invention, when the elastic layer consisting of a foamed rubber layer takes the first form, i.e., a form consisting only of a foamed rubber layer, the coating liquid is applied to the main surface of a suitable substrate such as a metal plate or a resin plate, and fixed to form an unfoamed rubber layer, which is then foamed to form a foamed rubber layer, and the foamed rubber layer is then peeled off from the substrate layer to obtain the desired elastic layer (elastic layer consisting only of a foamed rubber layer).

[0058] In the sealing material according to the present invention, when the elastic layer consisting of a foamed rubber layer takes the second form, i.e., a form consisting of a laminated integrated product in which foamed rubber layers are laminated on both main surfaces of a base layer consisting of a metal plate or a resin plate, the coating liquid is applied to both main surfaces of the base layer consisting of a metal plate or a resin plate, fixed to form unfoamed rubber layers, and then foamed to form foamed rubber layers, thereby obtaining the desired elastic layer (an elastic layer consisting of a laminated integrated product in which foamed rubber layers are laminated on both main surfaces of a base layer consisting of a metal plate or a resin plate).

[0059] The sealing material according to the present invention comprises the elastic layer and a pressure-sensitive adhesive layer laminated on each of the two main surfaces thereof. In the sealing material according to the present invention, the pressure-sensitive adhesive layer is formed by the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer adhering to the main surfaces of the elastic layer by its adhesive force.

[0060] The thickness of each of the pressure-sensitive adhesive layers is preferably 1 to 100 μm, more preferably 5 to 70 μm, and even more preferably 10 to 60 μm. The thicknesses of the pressure-sensitive adhesive layers formed on both main surfaces of the elastic layer may be the same or different.

[0061] In the sealing material according to the present invention, when the thickness of the pressure-sensitive adhesive layer is within the above range, the desired adhesiveness (sealing property) can be easily exhibited.

[0062] The thickness of the pressure-sensitive adhesive layer refers to the arithmetic mean value when the thickness is measured at 10 points using a dial gauge. In the sealing material according to the present invention, when the thickness of the pressure-sensitive adhesive layer is within the above range, the desired adhesion (sealing property) can be easily imparted to the sealing material.

[0063] In the sealing material according to the present invention, the pressure-sensitive adhesive layer preferably contains, as a pressure-sensitive adhesive, at least one selected from urethane resin, natural rubber (NR), butadiene rubber (BR), isoprene rubber (IR), styrene butadiene (SBR), nitrile rubber (NBR), ethylene-propylene-diene terpolymer (EPDM), butyl rubber (IIR), chloroprene rubber (CR), thermoplastic elastomer, and any of the above water additives.

[0064] In the sealing material according to the present invention, the thermoplastic elastomer is preferably at least one selected from a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, a vinyl chloride-based thermoplastic elastomer, an ester-based thermoplastic elastomer, and an amide-based thermoplastic elastomer.

[0065] In the sealing material according to the present invention, the styrene-based thermoplastic elastomer may be at least one selected from α-methylstyrene-ethylene-butylene-α-methylstyrene copolymers, styrene-butadiene-styrene triblock copolymers, styrene-butadiene random copolymers, styrene-isobutylene-styrene block copolymers, hydrogenated products in which part or all of the carbon-carbon double bonds of these copolymers such as styrene-butadiene-styrene (SBS) are hydrogenated, maleic anhydride-modified styrene-isoprene-styrene block copolymers, maleic anhydride-modified styrene-butadiene-styrene block copolymers (MAH-SBS), and the like. Examples of hydrogenated copolymers in which part or all of the carbon-carbon double bonds of copolymers such as styrene-butadiene-styrene (SBS) have been hydrogenated include one or more selected from styrene-(ethylene / propylene)-styrene block copolymers (SEPS; hydrogenated SIS), styrene-(ethylene / butylene)-styrene block copolymers (SEBS; hydrogenated SBS), styrene-ethylene-(ethylene / propylene)-styrene block copolymers (SEEPS; hydrogenated styrene-butadiene / isoprene-styrene block copolymers), styrene-isobutylene-styrene block copolymers (SIBS), hydrogenated styrene butadiene (hydrogenated SBR), maleic anhydride-modified styrene-(ethylene / butylene)-styrene block copolymers (MAH-SEBS), maleic anhydride-modified styrene-(ethylene / propylene)-styrene block copolymers (MAH-SEPS), and the like.

[0066] In the sealing material according to the present invention, the adhesive layer contains a thermoplastic elastomer as an adhesive, so that it can easily exhibit good sealing properties compared to a case where no adhesive layer is present.

[0067] In the sealing material according to the present invention, the pressure-sensitive adhesive layer preferably contains 50 to 100% by mass, more preferably 60 to 90% by mass, of the thermoplastic elastomer in terms of solid content.

[0068] In the sealing material according to the present invention, the pressure-sensitive adhesive layer contains the thermoplastic elastomer in the above-mentioned ratio, so that it can easily exhibit good sealing properties.

[0069] In the sealing material according to the present invention, the adhesive layer can be formed, for example, by applying an adhesive-containing liquid containing a thermoplastic elastomer onto the main surface of the elastic layer obtained by the method described above.

[0070] According to the present invention, it is possible to provide a sealing material that exhibits high adhesion (sealing properties) at low surface pressure.

[0071] Next, the present invention will be described in more detail with reference to examples, but these are merely illustrative and do not limit the present invention.

[0072] Example 1 (1) Preparation of Elastic Material As shown in Table 1, a rubber compound containing ethylene-propylene-diene terpolymer (EPDM) as a rubber component, a filler, a phenolic resin crosslinking agent, a foaming agent, and an organic sulfonic acid as a crosslinking accelerator was kneaded so that the phenolic resin crosslinking agent content was 2.6% by mass. A hydrocarbon solvent was then dissolved in the rubber compound to obtain a liquid unfoamed rubber composition. The resulting liquid unfoamed rubber composition was applied to a predetermined thickness using a coater and then dried in a drying oven at 60°C to obtain an unfoamed rubber molded body with a thickness of 0.3 mm. The unfoamed rubber molded body obtained by the drying process was then heat-treated in an oven at 180°C to crosslink and foam, producing a foamed elastic material with an expansion ratio of 2.7. The production conditions are shown in Table 1. Furthermore, the above rubber compound was prepared without containing a foaming agent, and the obtained rubber compound was used to mold an uncrosslinked rubber molded article having a thickness of 3 mm. The torque change of the molded article was measured by a moving die rheometer (MDR) using the following method. The results are shown in Table 1.

[0073] <Measurement of Torque Change Using a Moving Die Rheometer (MDR)> The torque change over time of the uncrosslinked rubber molded body was measured using a moving die rheometer (MDR) in accordance with the provisions of JIS K6300-2. The results are shown in Table 1. The M shown in Table 1 is the torque value measured by the above method 15 minutes after the start of vulcanization. Since the torque increases as the crosslinking of the uncrosslinked rubber molded body progresses, the M value serves as an index of the degree of crosslinking. A higher M indicates a crosslinked rubber molded body with a higher crosslink density. This means that even in an elastic material obtained by crosslinking and foaming an unfoamed rubber molded body having the same composition as the uncrosslinked rubber molded body except for the inclusion of a foaming agent, the crosslink density of the foamed rubber constituting the elastic material is increased, which means that when used as a sealing material, stress relaxation is more easily reduced and excellent sealing properties are exhibited.

[0074] (2) Application of adhesive: A predetermined amount of thermoplastic elastomer adhesive liquid was applied to both main surfaces of the foamed rubber elastic material obtained in (1) using a coater, and then dried in a drying oven to form adhesive layers on both main surfaces of the elastic material, thereby obtaining the desired sealing material. The stress relaxation rate and gas leakage property of the obtained sealing material were measured using the following methods. The results are shown in Table 1.

[0075] <Measurement of Stress Relaxation Rate> The obtained sealing material was punched into a doughnut-shaped sample with an inner diameter of 10 mm and an outer diameter of 20 mm. The obtained sample was sandwiched between upper and lower flanges using a commercially available compression and tensile testing machine (Autograph AG50kGN, manufactured by Shimadzu Corporation), compressed at an initial contact pressure of 1.0 MPa, and maintained at 25°C for 3.5 hours. The contact pressure was then measured 3.5 hours after the start of compression. The stress relaxation rate was then calculated using the following formula: Stress relaxation rate = (initial contact pressure - contact pressure 3.5 hours after the start of compression) ÷ initial contact pressure × 100 (%). The stress relaxation rate is an index of the sealing property of the sealing material, and indicates the rate of decrease in tightening contact pressure at a predetermined time after tightening when the sealing material is tightened at a predetermined tightening contact pressure. The smaller the stress relaxation rate of the sealing material, the less the deterioration in sealing property over time of the sealing material, indicating excellent sealing performance.

[0076] <Evaluation of Gas Leakage Property> Next, a sealing test was performed by injecting air gas so that a predetermined gas pressure (0.3 to 0.5 MPa) was applied to the doughnut-shaped sample sandwiched and compressed between the upper and lower flanges. The pressure (MPa) applied to the sealing material was confirmed with a pressure meter to check for the presence or absence of gas leakage, thereby evaluating the sealing property. The results are shown in Table 1.

[0077] (Examples 2 to 7, Comparative Examples 1 to 4) (1) Preparation of Elastic Materials In "(1) Preparation of Elastic Materials" of Example 1, except that the compounding ratio, calculated as solid content, of the phenolic resin crosslinking agent in the rubber compound and the type of crosslinking accelerator to be compounded were changed as shown in Table 1, unfoamed rubber molded bodies were obtained in the same manner as in Example 1, and then elastic materials were produced by crosslinking and foaming to the expansion ratio shown in Table 1. The production conditions are shown in Table 1. Furthermore, the torque values ​​(dN m) of the uncrosslinked rubber molded bodies produced in the same manner as in Example 1 were measured using a moving die rheometer (MDR) in the same manner as in Example 1. The results are shown in Table 1.

[0078] A predetermined amount of thermoplastic elastomer adhesive liquid, which was an adhesive, was applied to both main surfaces of each of the elastic materials made of foamed rubber obtained in Examples 2 to 7 and Comparative Examples 1 to 4 using a coater in the same manner as in Example 1 (2). The materials were then dried in a drying oven to form adhesive layers on both main surfaces of the elastic materials, thereby obtaining the desired sealing materials. In Comparative Example 1, the elastic material prepared in (1) above was used as the sealing material without being coated with an adhesive layer. The stress relaxation rate and gas leakage properties of the resulting sealing materials were measured using the same method as in Example 1. The results are shown in Table 1. The abbreviations for crosslinking accelerators in Table 1 refer to the following compounds: PTSA: p-toluenesulfonic acid DNNDSA: dinonylnaphthalenedisulfonic acid DDBSA: dodecylbenzenesulfonic acid DNNSA: dinonylnaphthalenesulfonic acid

[0079]

[0080] The sealing materials according to the present invention obtained in Examples 1 to 7 comprised an elastic material made of foamed rubber and pressure-sensitive adhesive layers laminated on both main surfaces of the elastic material, with the foamed rubber comprising a crosslinked and foamed unfoamed rubber molded article containing an ethylene-propylene-diene terpolymer (EPDM) rubber component, a phenolic resin crosslinking agent, a crosslinking accelerator made of an organic sulfonic acid compound, and a foaming agent. Therefore, as shown in Table 1, the uncrosslinked rubber molded articles produced in Examples 1 to 7 exhibited high torque values ​​M and high crosslink densities when torque change was measured using the MDR. Therefore, it was believed that the resulting elastic materials would exhibit excellent sealing properties that could reduce stress relaxation when used as sealing materials. Indeed, as shown in Table 1, the sealing materials according to the present invention obtained in Examples 1 to 7 exhibited low stress relaxation rates even at low surface pressures, and exhibited excellent adhesion (sealability) that prevented gas leakage when evaluated for gas leakage properties.

[0081] On the other hand, the sealing material obtained in Comparative Example 1 does not include an adhesive layer (it is made of only an elastic material). Therefore, as shown in Table 1, the sealing material obtained in Comparative Example 1 has a higher stress relaxation rate than the sealing material having an adhesive layer obtained in Example 1, and when gas leakage is evaluated, it is found to have poor adhesion (sealing properties) that cause gas leakage.

[0082] Furthermore, the sealing materials obtained in Comparative Examples 2 to 4 are found to have a higher stress relaxation rate than the sealing materials having pressure-sensitive adhesive layers obtained in Example 3 and Examples 5 to 7, since the foamed rubber constituting the elastic material is a crosslinked foam of an unfoamed rubber molding that does not contain a crosslinking accelerator made of an organic sulfonic acid compound. When gas leakage properties are evaluated, it is found that the sealing materials have poor adhesion (sealing properties) that cause gas leakage.

[0083] According to the present invention, it is possible to provide a sealing material that exhibits high adhesion (sealing properties) at low surface pressure.

[0084] 1 sealing material i elastic layer r foam rubber layer s adhesive layer b base material layer

Claims

1. A sealing material having an elastic layer including a foamed rubber layer, and pressure-sensitive adhesive layers laminated on both main surfaces of the elastic layer, wherein the foamed rubber layer is made of a foam of an unfoamed rubber layer containing an ethylene-propylene-diene terpolymer (EPDM) as a rubber component, a phenolic resin crosslinking agent, a crosslinking accelerator, and a foaming agent, and wherein the crosslinking accelerator is an organic sulfonic acid compound.

2. The sealing material according to claim 1, wherein the content of the phenol resin crosslinking agent in the unfoamed rubber layer is 2.0 to 20.0 mass % calculated as solid content.

3. A sealing material according to claim 1 or 2, wherein the elastic layer is made of only the foamed rubber layer, or is made of an integrated laminate in which the foamed rubber layer is laminated on each of the two main surfaces of a base layer made of a metal plate or a resin plate.

4. A sealing material according to claim 1 or 2, wherein the amount of diene constituting the ethylene-propylene-diene terpolymer (EPDM) is 1 to 20% by mass.

5. A sealing material according to claim 1 or 2, wherein the foamed rubber layer is a foam having a foaming ratio of 1.5 or more times that of the unfoamed rubber layer.

6. The sealing material according to claim 1 or 2, wherein the adhesive layer contains at least one adhesive selected from the group consisting of urethane resin, natural rubber, butadiene rubber, isoprene rubber, styrene butadiene, nitrile rubber, ethylene-propylene-diene terpolymer, butyl rubber, chloroprene rubber, thermoplastic elastomer, and water additives of any of these.

7. The sealing material according to claim 6, wherein the thermoplastic elastomer is at least one selected from the group consisting of styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, ester-based thermoplastic elastomers and amide-based thermoplastic elastomers.

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