Annular seal, preform, and manufacturing method

Abstract

The present disclosure relates to an annular seal comprising a central core and an outer layer covering a periphery of the central core. The ring-shaped seal has parting lines on the outer diameter side and the inner diameter side, and in a cross-section of the ring-shaped seal, one end of a straight line connecting the parting line on the outer diameter side and the parting line on the inner diameter side is set to a position where a central angle centered on the midpoint of the straight line is 0 DEG. When the thickness of the outer layer at a position where the central angle is 90 degrees is set as T90 and the thickness of the outer layer at a position where the central angle is 45 degrees is set as T45 in at least one direction from one side end of the straight line, the following formula (1) is satisfied: T45 > T90.

Description

Technical Field

[0001] This invention relates to annular seals, and further to preforms for manufacturing annular seals and methods for manufacturing annular seals. Background Technology

[0002] Japanese Patent No. 4148493 (Patent Document 1) describes a method for manufacturing a composite O-ring. The method involves cutting a composite material made by inserting a cord-shaped inner layer into the internal space of a tubular outer layer, placing the cut material in an O-ring mold, and then placing a cord-shaped substance made from the material used for the outer layer into the gap between the cut surfaces of the composite material, followed by pressure heating to form the O-ring.

[0003] Japanese Patent Application Publication No. 10-323847 (Patent Document 2) discloses a method for manufacturing a composite O-ring, which uses a core of approximately the same shape as the core material to pre-form two covering materials. After removing the core, an O-ring-shaped rubber core material that has undergone supercritical extraction is inserted into its cavity and integrally formed together with the covering materials.

[0004] Japanese Patent Application Publication No. 10-52885 (Patent Document 3) discloses a method for manufacturing a two-layer O-ring, characterized by extruding and hot-pressing a cord-like body composed of an outer layer and an inner layer, thereby simultaneously vulcanizing the inner and outer layers.

[0005] In Japanese Patent Application Publication No. 10-329271 (Patent Document 4), as a method for manufacturing an O-ring with a two-layer structure, a method is described in which an outer layer material containing a perfluoroelastomer is formed into a ribbon and wound around a core material and then heated and pressurized, and a method is described in which the outer layer material is frozen, crushed, and granulated, then attached to the core material and heated and pressurized.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 4148493

[0009] Patent Document 2: Japanese Patent Application Publication No. 10-323847

[0010] Patent Document 3: Japanese Patent Application Publication No. 10-52885

[0011] Patent Document 4: Japanese Patent Application Publication No. 10-329271 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] In the manufacturing method described in Patent Document 1, the outer layer material may break when the outer layer is expanded. Furthermore, since the connecting member made of the outer layer material is positioned at the joint, the joint does not have a two-layer structure. Consequently, the process is complex and costly.

[0014] In the manufacturing method described in Patent Document 2, when the core material is integrally formed in a mold, it may sometimes be exposed from the gap between the upper and lower outer layers.

[0015] In the manufacturing method described in Patent Document 3, the inner layer sometimes protrudes from the parting line during molding in the mold.

[0016] In the manufacturing method described in Patent Document 4, if only a strip is wound, wrinkles easily form at the curved portion of the inner diameter of the O-ring when it is placed into the mold, making material placement difficult. Furthermore, the core material is highly likely to be exposed through gaps in the strip, making countermeasures difficult. Moreover, even when the outer layer material is cryogenically pulverized and granulated to adhere to the core material, granulation alone is insufficient for bonding, making complete coverage of the core difficult.

[0017] When manufacturing annular seals with a two-layer structure consisting of a core and an outer layer, the core is often exposed from the outer layer at the parting line.

[0018] The object of the present invention is to provide an annular seal, a preform thereof, and a method thereof for manufacturing the same, which suppresses the exposure of the core from the outer layer at the parting line when manufacturing an annular seal having a two-layer structure consisting of a core and an outer layer.

[0019] Solution for solving the problem

[0020] The present invention provides the following annular seal, preform, and manufacturing method.

[0021] [1] An annular seal includes a core and an outer layer covering the periphery of the core. The annular seal has parting lines on the outer diameter side and the inner diameter side. In the cross section of the annular seal, when one end of the straight line connecting the parting line on the outer diameter side and the parting line on the inner diameter side is set at a position with a central angle of 0° centered on the midpoint of the straight line, when the thickness of the outer layer at the position with a central angle of 90° is set to T90 and the thickness of the outer layer at the position with a central angle of 45° is set to T45, the following equation (1) is satisfied: (1) T45 > T90.

[0022] [2] According to the annular seal described in [1], wherein the following formula (2) is satisfied: (2) 1.1≤T45 / T90≤25.

[0023] [3] The core contains a colorant, and the annular seal described in [1] or [2].

[0024] [4] The annular seal according to any one of [1] to [3], wherein the outer layer comprises at least one crosslinking material selected from the group consisting of perfluoroelastomers and fluororubbers, and the inner core comprises at least one crosslinking material selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers and fluorosilicone rubbers.

[0025] [5] A rope-like preform for manufacturing an annular seal as described in any one of [1] to [4], the rope-like preform comprising: an uncrosslinked core comprising a crosslinked rubber composition for the core; and an uncrosslinked outer layer comprising a crosslinked rubber composition for the outer layer covering the periphery of the uncrosslinked core, wherein the uncrosslinked core is elliptical or rounded square in cross-section of the rope-like preform.

[0026] [6] According to [5], the rope-shaped preform has a circular cross-sectional shape.

[0027] [7] The rope-like preform according to [5] or [6], wherein the uncrosslinked outer layer has a thin portion and a linear protrusion on the outer surface of the thin portion.

[0028] [8] A method for manufacturing an annular seal, which uses a rope-shaped preform as described in any one of [5] to [7].

[0029] [9] The manufacturing method of the annular seal according to [8] includes: a preforming step, in which the rope-shaped preform is obtained by extrusion molding using a cross-linked rubber composition for the core and a cross-linked rubber composition for the outer layer; and a hot pressing step, in which the two ends of the rope-shaped preform are brought into contact and disposed in a mold for hot pressing molding, wherein the uncross-linked outer layer of the rope-shaped preform has a thin portion, and in the hot pressing step, the rope-shaped preform is disposed in the mold with the thin portion of the uncross-linked outer layer facing upward.

[0030]

[10] In the manufacturing method of the annular seal according to [9], in the preforming process, a linear protrusion is formed on the outer surface of the thin portion of the uncrosslinked outer layer.

[0031]

[11] In the manufacturing method of the annular seal according to

[10] , the rope-shaped preform is placed in the mold with the linear protrusion facing upward in the hot pressing process.

[0032] Invention Effects

[0033] According to the present invention, an annular seal having a two-layer structure consisting of a core and an outer layer is provided, which suppresses the core from protruding from the outer layer at the parting line when manufacturing an annular seal, a preform for manufacturing the annular seal, and a method for manufacturing the annular seal are provided. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of an annular seal.

[0035] Figure 2 This is a schematic cross-sectional view of the annular seal.

[0036] Figure 3 This is a schematic cross-sectional view of the rope-shaped preform.

[0037] Figure 4 This is a schematic cross-sectional view along the circumference of an annular seal, illustrating one step in the manufacturing method of the annular seal.

[0038] Figure 5 This is a schematic cross-sectional view along the circumference of the annular seal, illustrating another step in the manufacturing method of the annular seal.

[0039] Figure 6 This is a schematic cross-sectional view along the circumference of the annular seal, illustrating another step in the manufacturing method of the annular seal.

[0040] Figure 7 This is a schematic cross-sectional view of the annular seal along its circumference, illustrating another step in the manufacturing process of the annular seal.

[0041] Figure 8 This is a schematic diagram illustrating the first hot pressing process in the pressing and molding process.

[0042] Figure 9 This is another schematic diagram illustrating the first hot pressing process in the pressing and molding process. Detailed Implementation

[0043] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, etc., but the present invention is not limited to the following embodiments. In all the following drawings, the scale has been appropriately adjusted for ease of understanding of each component element, and the scale of each component element shown in the drawings may not be consistent with the actual scale of the component elements.

[0044] <Annular Seal>

[0045] The annular seal of the present invention is an annular seal comprising a core and an outer layer covering the periphery of the core. The annular seal has parting lines on the outer diameter side and the inner diameter side. In the cross section of the annular seal, when one end of the straight line connecting the parting line on the outer diameter side and the parting line on the inner diameter side is set to a position with a central angle of 0° centered on the midpoint of the straight line, when the thickness of the outer layer at a position with a central angle of 90° is set to T90 and the thickness of the outer layer at a position with a central angle of 45° is set to T45 in at least one direction from one end of the straight line, the following equation (1) is satisfied: (1) T45 > T90.

[0046] Figure 1 Image (a) shows the shape of the annular seal in top view. Figure 1 In (a), the annular seal 1 is indicated by a slanted line. The annular seal 1 has an outer diameter D1 as its outer circumference diameter and an inner diameter D2 as its inner circumference diameter. The outer circumference and the inner circumference are the outer and inner circumferences of the annular seal 1, respectively, when viewed from above. Viewed from above means viewed in the thickness direction of the annular seal 1.

[0047] Figure 1 (b) and Figure 1 Image (c) shows a cross-sectional view perpendicular to the plane of the annular seal 1. The annular seal 1 includes a core 2 and an outer layer 3 covering the periphery of the core 2. Figure 1 As shown in (a), the cross-sectional shape of the annular seal 1 is preferably circular, but it may have other cross-sectional shapes depending on the application. The annular seal 1 has a cross-sectional diameter D3 and a thickness T of the outer layer 3.

[0048] Although Figure 1 Not shown, but the annular seal 1 has parting lines on both the outer and inner diameter sides. The parting lines can be traces of the mold seam between the two molds produced on the surface of the outer layer 3 during the hot pressing process, or traces after removing flash. The annular seal 1 has parting lines formed along the outer and inner circumferences on the surface of the outer layer 3.

[0049] Figure 2 (b) is Figure 2 A schematic cross-sectional view of the annular seal 1 shown in (a) at point A-A'. Figure 2As shown in (b), in the cross-sectional shape of the annular seal 1, when one end of the straight line L connecting the parting line Po on the outer diameter side and the parting line Pi on the inner diameter side is set at a position with a central angle of 0° centered at the midpoint C of the straight line L, when the thickness of the outer layer 3 at a position with a central angle of 90° in at least one direction from one end of the straight line L is set to T90 and the thickness of the outer layer 3 at a position with a central angle of 45° is set to T45, equation (1) is satisfied: (1) T45 > T90. The annular seal 1 may satisfy the above equation (1) in all parts or only in part. By satisfying equation (1), the annular seal 1 can easily suppress the core from being exposed from the outer layer at the parting line. It should be noted that when the annular seal 1 has the linear protrusion described later, T90 is the thickness excluding the linear protrusion. As a means of realizing formula (1), for example, methods such as setting the shape of the core of the rope-shaped preform used to manufacture the annular seal 1 to be elliptical or rounded square, and increasing the thickness of the part that becomes the uncrosslinked outer layer, as described below.

[0050] Figure 2 (b) shows Figure 2 The cross-sectional shape of the annular seal 1 at A-A' shown in (a). Figure 2 As shown in (b), the shape of the core 2 can be elliptical, or, although not shown, a rounded square. Furthermore, during thermoforming, the core 2 tends to expand outwards at the parting lines Pi and Po. Therefore, as... Figure 2 As shown in (c), the outer side of the core 2 at the parting lines Pi and Po can also be expanded.

[0051] From the viewpoint of preventing the core 2 from being exposed from the outer layer 3 at the parting line, T90 is preferably less than the thickness of the outer layer 3 in the part where the parting line is located. Although T45 can be less than or greater than the thickness of the outer layer 3 in the part where the parting line is located, from the viewpoint of preventing the core 2 from being exposed from the outer layer 3 at the parting line, it is preferable to be less than the thickness of the outer layer 3 in the part where the parting line is located.

[0052] From the viewpoint of preventing the core 2 from being exposed from the outer layer 3 at the parting line, the annular seal 1 preferably satisfies equation (2): (2) 1.1≤T45 / T90≤25. The left side of equation (2) is preferably 1.2, more preferably 1.3. The right side of equation (2) is preferably 15, more preferably 10.

[0053] T45 can be, for example, 0.3 mm or more and 10 mm or less, preferably 0.5 mm or more and 3 mm or less.

[0054] T90 can be, for example, 0.1 mm or more and 5 mm or less, preferably 0.2 mm or more and 1.5 mm or less.

[0055] The diameter D3 of the cross section of the annular seal 1 can be, for example, 2 mm or more and 50 mm or less, preferably 3 mm or more and 15 mm or less.

[0056] From the perspective of reducing material costs, the average ratio (hereinafter also referred to as the average ratio) of the thickness T of the outer layer 3 of the annular seal 1 to the diameter D3 of the cross section can be, for example, more than 1 / 35 and less than 1 / 4, preferably more than 1 / 20 and less than 1 / 5. The average ratio is the average of the ratios measured at five randomly selected cross sections in the annular seal 1. The ratio is expressed, for example, as the ratio T / D3 of the thickness T of the outer layer 3 with the largest thickness in the cross section of the annular seal 1 to the diameter D3 of the cross section including that thickness.

[0057] The area ratio of the core 2 to the outer layer 3 in the cross-section of the annular seal 1 is 0.4 or more, preferably 0.7 or more, and more preferably 1.0 or more and 4.0 or less.

[0058] From the viewpoint of easily visually confirming that the core 2 is exposed from the outer layer 3 at the parting line, the core 2 of the annular seal 1 preferably contains a colorant. The outer layer 3 may or may not contain a colorant. If the outer layer 3 contains a colorant, it is preferable to contain a colorant different from the colorant contained in the core 2. From the viewpoint of visual confirmation of the core 2 (parting line), the outer layer 3 is more preferably free of colorant.

[0059] The core 2 and the outer layer 3 may contain crosslinks of the crosslinked rubber composition. Hereinafter, the crosslinked rubber composition forming the core 2 will be referred to as the crosslinked rubber composition for the core, and the crosslinked rubber composition forming the outer layer 3 will be referred to as the crosslinked rubber composition for the outer layer. When both the crosslinked rubber composition for the core and the crosslinked rubber composition for the outer layer are referred to, they will also be collectively referred to as the crosslinked rubber composition.

[0060] Crosslinked rubber compositions may contain crosslinked rubber components. These components can form elastomers (crosslinked rubber) with crosslinked structures through a crosslinking reaction. The crosslinked rubber components may have crosslinking sites such as carbon-carbon unsaturated groups, nitrile groups, hydroxyl groups, amino groups, carbonyl groups, and halogen groups.

[0061] Specific examples of crosslinkable rubber components include perfluoroelastomers (FFKM), fluororubber (FKM), silicone rubber, fluorosilicone rubber, ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), nitrile butadiene rubber (NBR; acrylonitrile butadiene rubber), hydrogenated nitrile butadiene rubber (HNBR; hydrogenated acrylonitrile butadiene rubber), butyl rubber (IIR), and acrylic rubber. Among these, perfluoroelastomers, fluororubber, silicone rubber, and fluorosilicone rubber are preferred. In the crosslinkable rubber composition, only one crosslinkable rubber component may be used, or two or more may be used in combination.

[0062] Preferably, the outer layer 3 comprises at least one crosslinked material selected from the group consisting of perfluoroelastomers and fluororubbers, and the core 2 comprises at least one crosslinked material selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers. Therefore, the crosslinked rubber component in the crosslinked rubber composition for the outer layer is preferably at least one selected from the group consisting of perfluoroelastomers and fluororubbers, more preferably a perfluoroelastomer. The crosslinked rubber component in the crosslinked rubber composition for the core is preferably at least one selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers. From the viewpoint of free radical resistance, it is advantageous that the outer layer 3 comprises a crosslinked material of a perfluoroelastomer. From the viewpoint of material cost, it is advantageous that the core 2 comprises at least one crosslinked material selected from the group consisting of fluororubbers, silicone rubbers, and fluorosilicone rubbers.

[0063] There are no particular limitations on perfluoroelastomers; examples include tetrafluoroethylene (TFE)-perfluoro(alkyl vinyl ether) copolymers and TFE-perfluoro(alkoxyalkyl vinyl ether) copolymers. These copolymers may further contain structural units derived from other perfluoro monomers. According to perfluoroelastomer compositions containing perfluoroelastomers, ozone resistance can be further improved compared to crosslinked rubber compositions containing hydrogen-containing fluoroelastomers. Crosslinked rubber compositions may contain only one type of perfluoroelastomer or may contain two or more types.

[0064] Regarding the perfluoro(alkyl vinyl ether) forming the tetrafluoroethylene (TFE)-perfluoro(alkyl vinyl ether) copolymer, the number of carbon atoms in the alkyl group can be 1 to 5, for example, it can be perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), etc. Perfluoro(methyl vinyl ether) is preferred.

[0065] For the perfluoro(alkoxyalkyl vinyl ether) forming the TFE-perfluoro(alkoxyalkyl vinyl ether) copolymer, the number of carbon atoms in the group bonded to the vinyl ether group (CF2=CFO-) can be 3 to 12, for example, it can also be: CF2=CFOCF2CF(CF3)OC n F 2n+1 CF2 = CFO(CF2)3OC n F 2n+ 1. CF2=CFOCF2CF(CF3)O(CF2O) m C n F 2n+1 Or CF2 = CFO(CF2)2OC n F 2n+ 1. In the above formula, n is, for example, 1 to 5, and m is, for example, 1 to 3.

[0066] Perfluorinated elastomers are preferably crosslinkable, and more specifically, are preferably substances formed by further copolymerizing monomers at the crosslinking sites (further comprising structural units derived from the monomers at the crosslinking sites). The crosslinking site refers to a site capable of undergoing a crosslinking reaction. Examples of crosslinking sites include nitrile groups, halogen groups (e.g., I-group, Br-group, etc.), and perfluorophenyl groups.

[0067] An example of a crosslinking monomer having a nitrile group as a crosslinking site is a perfluorovinyl ether containing a nitrile group. Examples of perfluorovinyl ethers containing a nitrile group include: CF2=CFO(CF2). n OCF(CF3)CN (n is, for example, 2 to 4), CF2 = CFO(CF2) n CN (n is, for example, 2 to 12), CF2 = CFO[CF2CF(CF3)O] m (CF2) n CN (n is 2 for example, m is 1~5 for example), CF2 = CFO[CF2CF(CF3)O] m (CF2) n CN (n is 1-4 for example, m is 1-2 for example), CF2 = CFO[CF2CF(CF3)O] n CF2CF(CF3)CN (n is, for example, 0 to 4), etc.

[0068] An example of a crosslinking monomer having a halogen group as a crosslinking site is a perfluorovinyl ether containing a halogen group. Examples of perfluorovinyl ethers containing halogen groups include substances formed by replacing the nitrile groups with halogen groups in the specific examples of perfluorovinyl ethers containing nitrile groups described above.

[0069] Crosslinked perfluoroelastomers can also have crosslinked structures that crosslink the two main chains.

[0070] The molar ratio of structural units derived from TFE in the perfluoroelastomer to structural units derived from perfluoro(alkyl vinyl ether) or perfluoro(alkoxyalkyl vinyl ether) to structural units derived from the crosslinking site monomer is typically 50–79.6% / 20–49.8% / 0.2–5%, preferably 60–74.8% / 25–39.5% / 0.5–2%. The crosslinked rubber composition may also contain two or more perfluoroelastomers with different ratios of the aforementioned structural units.

[0071] Regarding fluororubber, examples include: binary vinylidene fluoride rubbers such as vinylidene fluoride / hexafluoropropylene copolymers; ternary vinylidene fluoride rubbers such as vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, vinylidene fluoride / tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers, and vinylidene fluoride / tetrafluoroethylene / propylene copolymers; tetrafluoroethylene / propylene copolymers; ethylene / tetrafluoroethylene / perfluoromethyl vinyl ether copolymers; thermoplastic fluororubbers; and liquid fluororubbers with a perfluoropolyether backbone (e.g., "SIFEL (registered trademark)" manufactured by Shin-Etsu Chemical Industry Co., Ltd.). Fluororubbers can be used alone or in combination with two or more types.

[0072] Fluororubber can also contain functional groups. These functional groups can be introduced, for example, by copolymerizing a crosslinking site monomer containing that functional group. The crosslinking site monomer can be a monomer containing a halogen group.

[0073] Crosslinkable rubber compositions may, along with co-crosslinking agents (crosslinking aids), optionally contain a crosslinking agent corresponding to the crosslinking system of the crosslinkable rubber component. Examples of crosslinking systems for perfluoroelastomers include: peroxide crosslinking systems, triazine crosslinking systems, oxazole crosslinking systems, imidazole crosslinking systems, thiazole crosslinking systems, and bisphenol crosslinking systems. Examples of crosslinking systems for vinylidene fluoride rubbers and tetrafluoroethylene-propylene rubbers include: peroxide crosslinking systems, polyamine crosslinking systems, and polyol crosslinking systems. Crosslinkable rubber compositions can be crosslinked using any one crosslinking system, or using two or more crosslinking systems.

[0074] Peroxide crosslinking agents can be, for example, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (commercial examples: PERHEXA 25B, PERHEXA 25B-40 manufactured by Nippon Oil Co., Ltd.); dicumyl peroxide (commercial example: Percumyl D manufactured by Nippon Oil Co., Ltd.); 2,4-dichlorobenzoyl peroxide; di-tert-butyl peroxide; tert-butyldicumyl peroxide; benzoyl peroxide (commercial example: Nyper B manufactured by Nippon Oil Co., Ltd.); 2,5-dimethyl-2,5-(tert-butylperoxy)hexyne-3 (commercial example: PERHEXYNE manufactured by Nippon Oil Co., Ltd.) 25B”); 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; α,α'-bis(tert-butylperoxym-isopropyl)benzene (example of commercially available products: "PERBUTYL P" manufactured by Nippon Oil Co., Ltd.); tert-butylperoxyisopropyl carbonate; p-chlorobenzoyl peroxide, etc. One peroxide crosslinking agent may be used alone, or two or more may be used in combination.

[0075] Examples of co-crosslinking agents used in peroxide crosslinking systems include: triallyl isocyanurate (commercially available examples: "TAIC" manufactured by Mitsubishi Chemical Corporation); triallyl cyanurate; triallyl formaldehyde; triallyl trimellitate; N,N'-m-phenylene bismaleimide; diacetylacetate; diallyl phthalate; tetraallyl terephthalamide, and other compounds capable of co-crosslinking via free radicals (unsaturated multifunctional compounds). Only one co-crosslinking agent can be used, or two or more can be used in combination. From the viewpoint of reactivity and heat resistance (compression set properties), triallyl isocyanurate is preferably included as a co-crosslinking agent.

[0076] In triazine crosslinking systems, crosslinking catalysts such as organotin compounds, onium salts such as quaternary phosphonium salts or quaternary ammonium salts, urea, and silicon nitride can be used.

[0077] Crosslinking agents used in the oxazole crosslinking system include, for example, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BOAP), 4,4'-sulfonylbis(2-aminophenol), and 9,9-bis(3-amino-4-hydroxyphenyl)fluorene. BOAP is preferred.

[0078] As the crosslinking agent used in the imidazole crosslinking system and the thiazole crosslinking system, conventionally known crosslinking agents can be used. Examples of crosslinking agents used in the imidazole crosslinking system include 3,3',4,4'-tetraaminobenzophenone and 3,3'-diaminobenzidine.

[0079] Regarding the content of crosslinking agent (the total amount when two or more are used) in the crosslinked rubber composition, it is, for example, 0.1 to 10 parts by mass, preferably 0.2 to 5 parts by mass, and more preferably 0.3 to 3 parts by mass, relative to 100 parts by mass of the total crosslinked rubber component.

[0080] Regarding the content of crosslinking agent (the total amount when two or more are used) in the crosslinked rubber composition, it is, for example, 0.5 to 10 parts by mass relative to 100 parts by mass of the total crosslinked rubber component, and preferably 1 to 8 parts by mass from the viewpoint of improving heat resistance.

[0081] Crosslinked rubber compositions, intended to improve processability and adjust physical properties, may contain additives such as anti-aging agents, antioxidants, vulcanization accelerators, processing aids (stearic acid, etc.), stabilizers, tackifiers, silane coupling agents, plasticizers, flame retardants, mold release agents, waxes, and lubricants, as needed. Other examples of additives include fluorinated oils (such as perfluoroethers) as viscosity reducers (anti-sticking agents). Additives may be used individually or in combination of two or more.

[0082] However, in situations such as using annular seals at high temperatures, volatilization, dissolution, or precipitation may occur. Therefore, the amount of additives is preferably as small as possible (for example, 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less, relative to the total amount of crosslinked rubber components of 100 parts by mass), and ideally, no additives are required.

[0083] Furthermore, the crosslinked rubber composition may, as needed, contain at least one selected from the group consisting of colorants and fillers. Colorants and fillers may each be used individually or in combination of two or more.

[0084] Examples of colorants include, for example, at least one selected from the group consisting of inorganic and organic pigments. Examples of inorganic pigments include, for example, white pigments (e.g., silica, zinc white, lead white, zinc barium white, titanium dioxide, precipitated barium sulfate, and barite powder), red pigments (e.g., red lead, iron oxide red), yellow pigments (e.g., chrome yellow, zinc yellow), blue pigments (e.g., ultramarine blue, Prussian blue, yttrium indium manganese blue), and black pigments (e.g., carbon black). Examples of organic pigments include, for example, azo pigments (azo lake pigments, insoluble azo pigments, condensed azo pigments, etc.); anthraquinone pigments, thioindole pigments, perinone pigments, perylene pigments, quinacridone pigments, isoindoline pigments, isoindoline pigments, dioxazine pigments, quinoline pigments, diketopyrrolopyrrole pigments, and other polycyclic pigments, phthalocyanine pigments, etc. As organic pigments, organic pigments classified as pigments in the color index can be used. Preferably, the pigments used are organic pigments that do not contain metal elements. If organic pigments that do not contain metal elements are used, there is no concern about the dispersion of substances originating from metal elements, even if the seal is sometimes used in harsh ozone environments such as those used in semiconductor applications, resulting in the etching of the annular seal.

[0085] The content of colorant in the crosslinked rubber composition (the total amount when two or more are used) may, for example, be more than 0.01 parts by mass and less than 2 parts by mass relative to 100 parts by mass of the crosslinked rubber component, preferably more than 0.05 parts by mass and less than 1.5 parts by mass, and more preferably more than 0.1 parts by mass and less than 1 part by mass.

[0086] Examples of fillers that can be used include fluororesins, silica, alumina, zinc oxide, titanium dioxide, clay, talc, diatomaceous earth, barium sulfate, calcium carbonate, magnesium carbonate, calcium oxide, mica, graphite, aluminum hydroxide, aluminum silicate, hydrotalcite, metal powder, glass powder, and ceramic powder. Only one type of filler can be used, or two or more can be used in combination. Regarding the filler content in the crosslinked rubber composition (the total amount when two or more are used), relative to 100 parts by mass of the total crosslinked rubber component, it is, for example, 0.1 parts by mass or more and 40 parts by mass or less. From the viewpoint of improving mechanical strength, it is preferably 1 part by mass or more and 30 parts by mass or less, more preferably more than 1 part by mass and 30 parts by mass or less. In this specification, the filler is different from the organic and inorganic pigments used as colorants mentioned above; substances of a different type than organic and inorganic pigments can be used.

[0087] When a crosslinked rubber composition contains a fluoropolymer filler, the ozone resistance and mechanical strength of the crosslinked compound can be further improved. The fluoropolymer can be contained in the crosslinked rubber composition, for example, in the form of fluoropolymer particles.

[0088] Fluoropolymers used as fillers are resins containing fluorine atoms within their molecules. Examples include: polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride (PVF), vinylidene fluoride-hexafluoropropylene copolymer (VDF-HFP copolymer), and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE copolymer). Fluoropolymers can be used alone or in combination with two or more types.

[0089] Among the above, from the viewpoint of preventing the resin from melting under high temperature conditions and thus damaging its properties such as compression set, it is preferable to use fluoropolymers with relatively high melting points such as PFA and PTFE.

[0090] The fluororesin used as a filler can also be a fluororesin containing functional groups. Functional groups can be introduced, for example, by copolymerizing a monomer having that functional group. When the aforementioned crosslinking site monomer is copolymerized as a monomer having a functional group, the crosslinking of the fluororesin and the perfluoroelastomer is also carried out by the aforementioned crosslinking agent, thus further improving the mechanical strength of the crosslinked perfluoroelastomer composition. Examples of fluororesins containing functional groups include the nitrile-containing polytetrafluoroethylene disclosed in Japanese Patent Application Publication No. 2013-177631. Furthermore, the fluororesin can also be a modified fluororesin, such as "TFM-modified PTFE" (manufactured by Dyneon Corporation).

[0091] When a crosslinked rubber composition contains a perfluoroelastomer and a fluororesin filler, a perfluoroelastomer containing a fluororesin, for example, can be used by: 1) a method of mixing perfluoroelastomer powder and fluororesin powder using a mixing roller; 2) a method of melt-mixing perfluoroelastomer powder or granules with fluororesin powder or granules using a mixer or a biaxial extruder; and 3) a method of adding fluororesin during the preparation stage of the perfluoroelastomer.

[0092] As an example of the method described in 3) above, the following method can be listed: after mixing an aqueous dispersion of perfluoroelastomer obtained by emulsion polymerization with an aqueous dispersion of fluororesin, a mixture of perfluoroelastomer and fluororesin is obtained by co-condensation.

[0093] Crosslinkable rubber compositions can be prepared by uniformly mixing crosslinkable rubber components, colorants, crosslinking agents, co-crosslinking agents added as needed, fillers, and additives. Conventional mixing machines, such as mixing rollers, pressure kneaders, and internal mixers (Banbury mixers), can be used. The components can be mixed in one step, or the mixture can be divided into multiple stages, such as first uniformly mixing the components other than those that contribute to the crosslinking reaction (crosslinking accelerators, crosslinking delayers, crosslinking agents, etc.), and then mixing the components that contribute to the crosslinking reaction.

[0094] <Rope-shaped preform>

[0095] The annular seal 1 can be manufactured using a rope-like preform. Another aspect of the invention is a rope-like preform for manufacturing the annular seal.

[0096] The rope-like preform comprises: an uncrosslinked core comprising a crosslinked rubber composition for the core; and an uncrosslinked outer layer comprising a crosslinked rubber composition for the outer layer, covering the periphery of the uncrosslinked core. The uncrosslinked outer layer comprises a crosslinked rubber composition for the outer layer. The description of the crosslinked rubber composition for the core and the crosslinked rubber composition for the outer layer applies to the above-described annular seal.

[0097] In the cross-section of the rope-like preform, the core is elliptical or rounded square. Figure 3 (b) shows Figure 3 The cross-sectional shape of the rope-shaped preform 4 at B-B' shown in (a). Figure 3In the rope-like preform 4 shown in (b), the uncrosslinked core 5 has a rounded square shape. Although not shown, the shape of the uncrosslinked core 5 in the cross-section of the rope-like preform 4 can also be elliptical. In this specification, a rounded square can be a quadrilateral with rounded corners, such as a rounded square, rounded rectangle, rounded rhombus, rounded parallelogram, etc., and the sides constituting the quadrilateral can also be curved. Figure 3 The cross-sectional shape of the rope-shaped preform 4 shown in (b) is circular.

[0098] The rope-like preform 4 has a portion with a small thickness of the uncrosslinked outer layer 6. The thickness Ts of the small portion of the uncrosslinked outer layer 6 can be the minimum thickness in the cross section of the rope-like preform 4. Ts can be, for example, 0.1 mm or more and 5 mm or less, preferably 0.2 mm or more and 1.5 mm or less.

[0099] The rope-like preform 4 has a portion that is thicker than the portion with a smaller thickness relative to the uncrosslinked outer layer 6. The thickness Tb of the thicker portion of the uncrosslinked outer layer 6 can be the maximum thickness in the cross section of the rope-like preform 4. Tb can be, for example, 0.3 mm or more and 10 mm or less, preferably 0.5 mm or more and 3 mm or less.

[0100] Tb / Ts can be, for example, 1.1 to 25, preferably 1.2 to 15.

[0101] like Figure 3 As shown in (a), the outer surface of the rope-like preform 4 has linear protrusions 7. Figure 3 As shown in (b), the rope-like preform 4 has linear protrusions 7 on the outer surface of the thinner portion. When the rope-like preform 4 has linear protrusions 7, in the hot pressing process described later, by placing the rope-like preform 4 in the mold with the linear protrusions 7 facing upwards, it is possible to avoid the formation of parting lines in the thinner portion of the uncrosslinked outer layer 6, thus easily suppressing the core 2 from protruding from the outer layer 3 at the parting line. The linear protrusions 7 can, for example, have a height of 0.05 to 1.0 mm.

[0102] The linear protrusion 7 can be like Figure 3 As shown in (b), it can be formed only on any one of the portions with small thickness, or as... Figure 3 As shown in (c), it is formed in the thinner portions.

[0103] In the cross-section of the rope-shaped preform 4, the area ratio of the uncrosslinked core 5 to the uncrosslinked outer layer 6 is, for example, 0.4 or more, preferably 0.7 or more, and more preferably 1.0 or more and 4.0 or less.

[0104] When the cross-sectional shape of the rope-shaped preform 4 is circular, the diameter (excluding the linear protrusion 7) can be, for example, 2 mm or more and 50 mm or less, preferably 3 mm or more and 15 mm or less.

[0105] When the uncrosslinked core 5 is elliptical in shape, the major axis diameter of the ellipse can be, for example, 2 mm or more and 40 mm or less, preferably 2.5 mm or more and 14 mm or less, and the minor axis diameter of the ellipse can be, for example, 1 mm or more and 30 mm or less, preferably 2 mm or more and 25 mm or less. When the uncrosslinked core 5 is rounded square in shape, the longer side of the interval between the two opposite sides can be, for example, 2 mm or more and 40 mm or less, preferably 2.5 mm or more and 14 mm or less; the shorter side can be, for example, 1 mm or more and 30 mm or less, preferably 2 mm or more and 25 mm or less.

[0106] The length of the rope-shaped preform 4 can be, for example, more than 100 mm and less than 5000 mm.

[0107] The rope-shaped preform 4 can be manufactured by the preforming process in the manufacturing method of the annular seal 1 described later.

[0108] <Manufacturing Method of Annular Seals>

[0109] Another aspect of the present invention is a method for manufacturing an annular seal using a rope-like preform. The method for manufacturing the annular seal may include the following steps.

[0110] The preforming process involves extruding a rope-like preform using a cross-linked rubber composition for the core and a cross-linked rubber composition for the outer layer; and the hot pressing process involves placing the two ends of the rope-like preform into contact within a mold for hot pressing.

[0111] In the preforming process, the above description applies to the cross-linked rubber composition for the core, the cross-linked rubber composition for the outer layer, and the rope-like preform. Specifically, the rope-like preform can be produced as follows: First, the cross-linked rubber composition for the core and the cross-linked rubber composition for the outer layer are formed into a sheet using rollers to produce a sheet-like molded article. The thickness of the sheet-like molded article can be, for example, 1 mm or more and 5 mm or less. Next, the sheet-like molded article is cut into a strip-like molded article, for example, 5 mm or more and 30 mm or less wide, using a cutting machine. Then, the strip-like molded article of the cross-linked rubber composition for the core and the cross-linked rubber composition for the outer layer is fed into a screw extruder with a crosshead and extruded into a rope shape, thereby obtaining a rope-like preform with a two-layer structure, wherein the uncross-linked outer layer is composed of the cross-linked rubber composition for the outer layer, and the uncross-linked core is composed of the cross-linked rubber composition for the core. The extrusion speed into the rope shape can be, for example, 100 mm / min or more and 1000 mm / min or less.

[0112] In the cross-section of the rope-like preform, in order to set the shape of the uncrosslinked core to an ellipse or a rounded square, the die shape of the crosslinked rubber composition for extruding the core can be set to an ellipse or a rounded square. In order to make the annular seal 1 satisfy the above formula (1), the dimensions of the die shape of the crosslinked rubber composition for extruding the core and the die shape of the crosslinked rubber composition for extruding the outer layer can be adjusted.

[0113] When extruded into a rope shape, linear protrusions can be formed on the outer surface of the thinner portion of the uncrosslinked outer layer. These linear protrusions can be formed by providing a cut in the die of the extruded outer layer using a crosslinked rubber composition for forming the linear protrusions.

[0114] The strip-shaped article can also be produced by placing the cross-linked rubber composition for the core and the cross-linked rubber composition for the outer layer into a plunger extruder and extruding them into a strip without producing the sheet-shaped article described above.

[0115] The number of rope-shaped preforms prepared in the preforming process can be one or more, such as three to ten, and can be adjusted according to the inner diameter and / or outer diameter of the annular seal.

[0116] In the hot pressing process, the two ends of the rope-like preform are brought into contact and placed in a mold. While heating the uncrosslinked core and the uncrosslinked outer layer, pressing is performed to obtain an annular seal 1 composed of a core 2 (containing a crosslinked rubber composition) and an outer layer 3. When the two ends of the rope-like preform are brought into contact and placed in the mold, by placing the rope-like preform in the mold with the thinner portion of the uncrosslinked outer layer facing upwards, it is easy to prevent the core from protruding from the outer layer at the parting line. When the rope-like preform has the aforementioned linear protrusions, by placing the rope-like preform in the mold with the linear protrusions facing upwards, it is easy to place the thinner portion of the uncrosslinked outer layer in the mold with its thinner portion facing upwards.

[0117] The heating temperature in hot pressing can be, for example, above 110°C and below 220°C.

[0118] In the hot pressing process, a mold with an annular cavity can be used to heat-press the two ends of the rope-like preform to create an annular seal. Alternatively, in the hot pressing process, feed-in pressing can be performed: using a mold with a straight or arc-shaped cavity, the portion of the rope-like preform except for the ends is first heat-pressed to obtain a straight or arc-shaped molded body. Then, the joint formed by bringing the two ends of the straight or arc-shaped molded body into contact is heat-pressed to create an annular seal. Alternatively, in the hot pressing process, feed-in pressing can be performed: using a mold with a circular cavity, a portion of the rope-like preform is first heat-pressed to obtain a circular molded body of the rope-like preform. Then, the uncrosslinked portion of the circular molded body is cut off, and the joint formed by bringing the two ends into contact is heat-pressed to create an annular seal. The method of bringing the two ends into contact includes having the two end faces of the rope-like preform in contact. The length of the joint in the circumferential direction can be, for example, more than 100 mm and less than 1200 mm. Feeding and pressing will be explained later.

[0119] In the hot pressing process, from the viewpoint of preventing cracking of the outer layer and exposure of the core at the joint where the ends of the rope-like preform are connected, before placing it in a mold with an annular cavity, or in the case of feed pressing, before the second hot pressing process described later (before placing it in a mold with a straight or arc-shaped cavity), the following steps can be further included: Figure 4 As shown, an uncrosslinked film layer 30 is wrapped around the mold seam at both ends of the rope-shaped preform 11 after it comes into contact (hereinafter also referred to as process a).

[0120] The thickness of the uncrosslinked film layer 30 can be, for example, 0.05 mm or more and 5 mm or less, but from the viewpoint of reducing the steps on the outer periphery of the rope-like preform 11, it is preferably 0.1 mm or more and 1 mm or less.

[0121] The material constituting the uncrosslinked film layer 30 can be the above-mentioned crosslinked rubber composition for outer layer, preferably the same type of crosslinked rubber composition for outer layer as the uncrosslinked outer layer 12 constituting the rope-like preform 11.

[0122] The uncrosslinked film layer 30 can be obtained by: molding the outer layer of the crosslinked rubber composition into a sheet using a roller, cutting it into a strip shape, for example, with a width of 5 mm or more and about 100 mm or less, using a cutting machine, and further cutting it according to the length of the mold seam wound around the rope-like preform 11. Alternatively, the portion obtained by removing the core material from the rope-like preform can also be used as the uncrosslinked film layer 30.

[0123] In step a, the uncrosslinked film layer 30 may be wound once or more around the mold joint of the rope-like preform 11. From the viewpoint of reducing the steps on the outer periphery of the rope-like preform 11, the uncrosslinked film layer 30 is preferably wound once or twice around the mold joint of the rope-like preform 11.

[0124] From the viewpoint of preventing the core from being exposed at the joint, the method for manufacturing the annular seal of the present invention may further include, before the hot pressing process or before the second hot pressing process described later, as follows: Figure 5 The process shown in (a) of removing the uncrosslinked core 14 from both ends of the rope-like preform 11 (hereinafter also referred to as process b). Figure 5 As shown in (b), by hot pressing the two ends (uncrosslinked outer layer 12) that have had the uncrosslinked core removed into contact within the mold, it is easy to prevent the core from being exposed at the joint.

[0125] Step b can be performed before the hot pressing step. In the case of feeding and pressing molding, it can be performed before the first hot pressing step described later, or between the first hot pressing step and the second hot pressing step.

[0126] The uncrosslinked core 14 to be removed can be, for example, 0.1 mm or more and 20 mm or less from the end face to the inside. The uncrosslinked core 14 can be removed using, for example, scissors, a knife, pliers, etc.

[0127] From the viewpoint of improving the engagement between the ends, the manufacturing method of the annular seal of the present invention may further include a step of heating the two ends of the rope-like preform (hereinafter also referred to as step c) before the hot pressing step, or before the second hot pressing step described later, in the case of feed pressing. After step c, by bringing the two ends of the rope-like preform into contact and placing them in the mold for hot pressing, the engagement between the ends can be strengthened, and the core can be prevented from being exposed.

[0128] In process c, such as Figure 6 As shown in (a), the heater 20 is clamped between the two ends of the rope-shaped preform 11, and the end faces are heated to melt them. Then, as shown in (a), Figure 6 As shown in (b), the molten ends can be brought into contact with each other.

[0129] From the viewpoint of preventing the core from being exposed at the joint, the manufacturing method of the annular seal of the present invention can, in the case of feed pressing, further include, as described later, the following in the second hot pressing process: Figure 7 As shown, the process of arranging a connecting member 40 between the two ends of a rope-like preform 11 disposed within a mold (hereinafter also referred to as process d) is described. Since the uncrosslinked outer layer 42 of the connecting member 40 is thicker than the uncrosslinked outer layer 12 of the rope-like preform 11, it is easier to prevent the core from being exposed at the joint during hot pressing.

[0130] The ratio of the thickness of the uncrosslinked outer layer 42 of the connecting member 40 to the thickness of the uncrosslinked outer layer 12 can be, for example, about 1.1 or more and about 10 or less. The length of the connecting member 40 in the circumferential direction can be, for example, about 5 mm or more and about 100 mm or less.

[0131] From the viewpoint of reducing the steps on the outer periphery of the annular seal, the diameter of the cross section of the connecting member 40 is preferably the same as or approximately the same as, or larger than, the diameter of the cross section of the rope-shaped preform 11.

[0132] The connecting member 40 may include: an uncrosslinked core 41, composed of a crosslinked rubber composition for a core (described later); and an uncrosslinked outer layer 42, composed of a crosslinked rubber composition for an outer layer (described later), covering the periphery of the uncrosslinked core 41. The material constituting the uncrosslinked core 41 is preferably the same type of crosslinked rubber composition for a core as the crosslinked rubber composition for a core constituting the uncrosslinked core 13 of the rope-like preform 11. The material constituting the uncrosslinked outer layer 42 is preferably the same type of crosslinked rubber composition for an outer layer as the crosslinked rubber composition for an outer layer constituting the uncrosslinked outer layer 12 of the rope-like preform 11.

[0133] In the manufacturing method of annular seals, after the hot pressing process, a secondary cross-linking process may be further included to promote cross-linking of uncross-linked or insufficiently cross-linked portions. The heating temperature in the secondary cross-linking process may be, for example, above 150°C and below approximately 310°C.

[0134] (Feed into pressing and molding)

[0135] When feeding and pressing are performed in a hot pressing process, feeding and pressing may include the following steps.

[0136] In the first hot pressing process, the rope-shaped preform is placed in the first mold, and the part of the rope-shaped preform except for the ends is hot pressed.

[0137] In the second hot pressing process, the two ends of the rope-shaped preform are brought into contact and placed in the second mold for hot pressing.

[0138] In the first hot pressing process, the portion of the rope-like preform, excluding the ends, can be cross-linked. The first mold used to set the rope-like preform in the first hot pressing process can have a straight, arc-shaped, or circular cavity. After the rope-like preform is placed into the first mold, it can be pressurized while being heated using a C-type press. The hot pressing temperature in the first hot pressing process can be, for example, between approximately 110°C and 220°C.

[0139] A method for hot-pressing the portion of a rope-like preform other than its ends includes, for example, cooling the portion of the rope-like preform in a first mold corresponding to the ends using a cooling device, and hot-pressing the portion other than the ends using a hot press plate. The length of the cooled portion can be set as the circumferential length of the end of the rope-like preform in an uncrosslinked or insufficiently crosslinked state, for example, it can be 1 mm or more and 600 mm or less.

[0140] like Figure 8 As shown in (a), when using a first mold 51 with a straight cavity, the portion of the rope-shaped preform in the first mold 51, on which the rope-shaped preform is provided, corresponding to the portion other than the end, is hot-pressed by a hot press plate 50, and the portion of the rope-shaped preform in the first mold 51 corresponding to the end is cooled, thereby forming uncrosslinked and crosslinked portions. Furthermore, as... Figure 8 As shown in (b), when using a first mold 52 with an arc-shaped cavity, the portion of the rope-shaped preform of the first mold 52 on which the rope-shaped preform is provided is hot-pressed by a hot press plate 50, and the portion of the rope-shaped preform in the first mold 52 on which the rope-shaped preform is provided is cooled, and uncrosslinked portions and crosslinked portions can also be formed.

[0141] Furthermore, such as Figure 9 As shown, when using a first mold 53 with a circular cavity, a portion of the first mold 53 on which the rope-shaped preform is provided is hot-pressed by a hot press plate 50, and the remaining portion is cooled to perform hot pressing molding. Then, the circular molded body 54 of the rope-shaped preform taken out from the first mold 53 is cut to form a rope-shaped preform 11 having an uncrosslinked portion and a crosslinked portion.

[0142] In the second hot pressing process, by bringing the two ends of the rope-shaped preform into contact and placing them in the second mold for hot pressing, the ends of the rope-shaped preform can be joined in a cross-linked state. By repeatedly joining the ends of two or more rope-shaped preforms, or by joining the ends of one rope-shaped preform to each other, an annular seal can be obtained.

[0143] The second mold for setting the two ends of the rope-like preform can have a straight or arc-shaped cavity. The width of the two ends of the rope-like preform set in the second mold in the circumferential direction can be, for example, more than 50 mm and less than 600 mm. The two ends can be the two ends of a single rope-like preform, or the ends of two rope-like preforms on one side of each.

[0144] The hot pressing temperature in the second hot pressing process can be, for example, 110°C or higher and about 220°C or lower. From the viewpoint of preventing cracking at the joint and exposure of the core, the hot pressing temperature in the second hot pressing process is preferably lower than the hot pressing temperature in the first hot pressing process, and more preferably 5°C or higher and 20°C lower than the hot pressing temperature in the first hot pressing process.

[0145] Example

[0146] The present invention will be further described in detail below through examples. Unless otherwise specified, "%" and "parts" in the examples refer to mass percentage and mass parts, respectively.

[0147] <Example 1>

[0148] A crosslinked rubber composition for the outer layer is prepared by kneading a perfluoroelastomer, 1 part by weight of crosslinking agent (PERHEXA25B) relative to 100 parts by weight of the perfluoroelastomer, and 2 parts by weight of crosslinking aid (TAIC) using a kneader. Next, a crosslinked rubber composition for the core is prepared by kneading a fluororubber, 1 part by weight of crosslinking agent (PERHEXA 25B) relative to 100 parts by weight of the fluororubber, 3 parts by weight of crosslinking aid (TAIC), and 0.1 parts by weight of colorant (Cromphtal Violet D5700) using a kneader. Then, the crosslinked rubber composition for the outer layer and the crosslinked rubber composition for the core are respectively formed into sheets with a thickness of approximately 3 mm using rollers, and cut into strips with a width of approximately 15 mm using a cutting machine. In a screw extruder equipped with a cross-head die, a cross-linked rubber composition for the outer layer and a cross-linked rubber composition for the core, both shaped into strips, are fed in to produce five rope-like preforms with a double-layer structure. The uncross-linked outer layer is formed from the cross-linked rubber composition for the outer layer, and the uncross-linked core is formed from the cross-linked rubber composition for the core. The die for extruding the cross-linked rubber composition for the outer layer is circular, and the die for extruding the cross-linked rubber composition for the core is elliptical. The diameter of the cross-section of each rope-like preform is approximately 7.15 mm, the thickness of the uncross-linked outer layer is approximately 1.2 mm, and the length is 800 mm. The uncross-linked core in each rope-like preform is elliptical in shape. Furthermore, the rope-like preforms have lines on the outer surface of the thinner portion of the uncross-linked outer layer.

[0149] Next, five rope-like preforms are placed in a straight first mold (800mm in length and 7mm in cavity size). While cooling the two ends (100mm wide on one side) to keep them in an uncrosslinked state, the parts other than the two ends are hot-pressed at 165°C using a C-type press.

[0150] After bringing the ends of the two hot-pressed rope-shaped preforms together on one side, they are placed in a second mold for the joint, and the joint is hot-pressed at 160°C. The same operation is performed on the ends of the remaining rope-shaped preforms, and the five rope-shaped preforms are joined together. Then, a secondary cross-linking process is performed at 200°C to obtain an annular seal.

[0151] The resulting annular seal has parting lines on both the outer and inner diameter sides. Within a circle with the straight line connecting the outer and inner diameter partsing lines as its diameter, with the central angle at 0° centered at the midpoint of the diameter as one end of the diameter, the outer layer thickness T90 at a position with a central angle of 90° is 0.5 mm, and the outer layer thickness T45 at a position with a central angle of 45° is 1.0 mm, extending in at least one direction from one end of the diameter. No exposure of the annular seal's core was confirmed. Furthermore, using the aforementioned lines as markers, the annular seal can be easily installed in a device without causing twisting or loosening.

[0152] Explanation of reference numerals in the attached figures

[0153] 1: Annular seal; 2: Core; 3: Outer layer; 4, 11: Rope-like preform; 5, 13: Uncrosslinked core; 6, 12: Uncrosslinked outer layer; 7: Linear protrusion; 14: Uncrosslinked core to be removed; 20: Heater; 30: Uncrosslinked film layer; 40: Connecting member; 41: Uncrosslinked core; 42: Uncrosslinked outer layer; 50: Pressing plate; 51: First mold with a straight cavity; 52: First mold with an arc-shaped cavity; 53: First mold with a circular cavity; 54: Circular molded body; Pi: Parting line on the inner diameter side; Po: Parting line on the outer diameter side; L: Straight line; C: Midpoint; T, Ts, Tb: Thickness of outer layer; D1: Outer diameter; D2: Inner diameter; D3: Diameter of section.

Claims

1. An annular seal, wherein, The annular seal includes a central core and an outer layer covering the periphery of the central core. The annular seal has parting lines on both the outer and inner diameter sides. In the cross-section of the annular seal, if one end of the straight line connecting the parting line on the outer diameter side and the parting line on the inner diameter side is set to a position with a central angle of 0° centered on the midpoint of the straight line, and the thickness of the outer layer at the position with a central angle of 90° is set to T90 and the thickness of the outer layer at the position with a central angle of 45° is set to T45 in at least one direction from one end of the straight line, the following equation (1) is satisfied: (1) T45>T90.

2. The annular seal according to claim 1, wherein, The following equation (2) must be satisfied: (2) 1.1≤T45 / T90≤25.

3. The annular seal according to claim 1, wherein, The core contains a colorant.

4. The annular seal according to claim 1, wherein, The outer layer comprises at least one crosslinker selected from the group consisting of perfluoroelastomers and fluororubbers, and the core comprises at least one crosslinker selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers.

5. A rope-like preform, wherein, The rope-like preform is used to manufacture the annular seal as described in claim 1. The rope-like preform comprises: an uncrosslinked core comprising a crosslinked rubber composition for the core; and an uncrosslinked outer layer comprising a crosslinked rubber composition for the outer layer, covering the periphery of the uncrosslinked core. In the cross-section of the rope-like preform, the uncrosslinked core is elliptical or rounded square in shape.

6. The rope-like preform according to claim 5, wherein, The cross-sectional shape of the rope-shaped preform is circular.

7. The rope-like preform according to claim 5, wherein, The uncrosslinked outer layer has a thin portion, and the outer surface of the thin portion has linear protrusions.

8. A method for manufacturing an annular seal, wherein, The manufacturing method uses the rope-shaped preform as described in claim 5.

9. The method for manufacturing the annular seal according to claim 8, wherein, include: The rope-like preform is obtained by extrusion molding using a cross-linked rubber composition for the core and a cross-linked rubber composition for the outer layer. as well as In the hot pressing process, the two ends of the rope-shaped preform are brought into contact and placed inside a mold for hot pressing. The uncrosslinked outer layer of the rope-like preform has a thin portion. In the hot pressing process, the rope-shaped preform is placed on the mold with the thinner portion of the uncrosslinked outer layer facing upwards.

10. The method for manufacturing the annular seal according to claim 9, wherein, In the preforming process, linear protrusions are formed on the outer surface of the thinner portion of the uncrosslinked outer layer.

11. The method for manufacturing the annular seal according to claim 10, wherein, In the hot pressing process, the rope-shaped preform is placed on the mold with the linear protrusions facing upwards.

Images