Annular sealing material and manufacturing method

Abstract

To provide an annular seal material that comprises a center core and an outside layer, where a crack in the outside layer and flash of the center core from the outside layer are suppressed, and to provide a method for manufacturing the same.SOLUTION: An annular seal material includes: a center core; and an outside layer covering a periphery of the center core. The outside layer includes a thick film part and a non-thick film part at a cross section in a peripheral length direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to annular sealing materials, and more particularly to a method for manufacturing them. [Background technology]

[0002] Annular (O-ring shaped) sealing materials are known as sealing materials (gaskets, packings, etc.) used in various applications. Annular sealing materials are often manufactured by, for example, placing the material in a mold and press-molding it while heating it.

[0003] Patent Document 1 describes a method for manufacturing a composite O-ring, which involves cutting a composite structural material made by inserting a string-shaped inner layer into the internal space of a tubular outer layer, setting it in an O-ring mold, and then setting a string-shaped piece of material to be used for the outer layer into the gap between the cut surfaces of the composite structural material, and then pressurizing and heating it.

[0004] Patent Document 2 describes a method for manufacturing a composite O-ring structure in which two covering materials are pre-formed using a core material and a core material of approximately the same shape, the core material is removed, and a supercritical extraction-treated O-ring-shaped rubber core material is inserted into the resulting cavity and integrally molded together with the covering material.

[0005] Patent Document 3 describes a method for manufacturing a two-layer O-ring, characterized by extruding a string-like body composed of an outer layer and an inner layer, and simultaneously vulcanizing the inner and outer layers by heat pressing.

[0006] Patent Document 4 describes a method for manufacturing an O-ring having a two-layer structure, which involves wrapping an outer layer material containing a perfluoroelastomer in a ribbon shape around a core material and then heating and pressurizing it, and a method in which the outer layer material is freeze-pulverized to form particles, which are then attached to the core material and then heated and pressurized. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 4148493 [Patent Document 2] Japanese Patent Publication No. 10-323847 [Patent Document 3] Japanese Patent Application Publication No. 10-52885 [Patent Document 4] Japanese Patent Publication No. 10-329271 [Overview of the project] [Problems that the invention aims to solve]

[0008] In the manufacturing method described in Patent Document 1, the outer layer material may rupture when the outer layer is inflated. Furthermore, because a connecting member made of the outer layer material is placed at the joint, the joint does not have a two-layer structure. Moreover, the process is complex and costly.

[0009] In the manufacturing method described in Patent Document 2, the core material may protrude from the gap between the upper and lower outer layers during integral molding in the mold.

[0010] In the manufacturing method described in Patent Document 3, the inner layer may protrude from the seam during molding with a mold.

[0011] In the manufacturing method described in Patent Document 4, simply wrapping the material in a ribbon shape makes it difficult to insert the material into the mold because wrinkles form in the curved part of the inner diameter of the O-ring. Furthermore, there is a high possibility that the core material will protrude through the gaps in the ribbon, and it is difficult to take countermeasures against this. Moreover, when the outer layer material is freeze-dried and pulverized to form particles, and these particles are then attached to the core material, the particles do not adhere to the core material, making it difficult to completely cover the core.

[0012] Thus, in annular sealing materials composed of a core and an outer layer, cracks often appear in the outer layer or the core protrudes from the outer layer.

[0013] An object of the present invention is to provide an annular sealing material composed of a core and an outer layer, and a method for manufacturing the same, in which cracking in the outer layer and protrusion of the core from the outer layer are suppressed.

Means for Solving the Problems

[0014] The present invention provides the following annular sealing material and a method for manufacturing the same. [1] An annular sealing material including a core and an outer layer covering the periphery of the core, wherein the outer layer has a thick film portion and a non-thick film portion in a cross-section in the circumferential direction, the annular sealing material. [2] The annular sealing material according to [1], wherein an average ratio of the thickness of the outer layer of the thick film portion to the thickness of the outer layer of the non-thick film portion is 1.05 or more and 1.20 or less. [3] The annular sealing material according to [1] or [2], wherein the annular sealing material has a difference in diameter of a cross-section of 0.01 mm or less near the boundary between the thick film portion and the non-thick film portion. [4] The annular sealing material according to any one of [1] to [4], wherein the thick film portion has a width in the circumferential direction of 1 mm or more and 100 mm or less. [5] The outer layer includes at least one cross-linked product selected from the group consisting of perfluoroelastomer and fluororubber, and the core includes at least one cross-linked product selected from the group consisting of perfluoroelastomer, fluororubber, silicone rubber, and fluorosilicone rubber, the annular sealing material according to any one of [1] to [4]. [6] A method for manufacturing the annular sealing material according to any one of [1] to [5], a preliminary forming step of preparing one or two or more rope-shaped preforms including an uncross-linked core made of a cross-linkable rubber composition for the core and an uncross-linked outer layer made of a cross-linkable rubber composition for covering the periphery of the uncross-linked core, a hot press step of bringing two ends of the rope-shaped preform into contact with each other, installing them in a mold, and performing hot press molding including, a method for manufacturing an annular sealing material. [7] The preforming step includes an extrusion molding step using the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer, and is the method for producing the annular sealing material according to [6]. [8] In the hot press step, before being placed in the mold, the method further includes a step of winding an uncrosslinked thin film layer around the joint of the two ends of the rope-shaped preform that have been brought into contact, and the material constituting the uncrosslinked thin film layer uses the crosslinkable rubber composition for the outer layer, and is the method for producing the annular sealing material according to [6] or [7]. [9] Before the hot press step, the method further includes a step of removing the uncrosslinked core from the two ends of the rope-shaped preform, and is the method for producing the annular sealing material according to any one of [6] to [8].

[10] Before the hot press step, the method further includes a step of heating the two ends of the rope-shaped preform, and is the method for producing the annular sealing material according to any one of [6] to [9].

[11] In the hot press step, the method further includes a step of arranging a connecting member between the two ends of the rope-shaped preform and placing it in the mold, The connecting member includes an uncrosslinked core made of the crosslinkable rubber composition for the core and an uncrosslinked outer layer made of the crosslinkable rubber composition for the outer layer covering the periphery of the uncrosslinked core, and the uncrosslinked outer layer of the connecting member is thicker than the uncrosslinked outer layer of the rope-shaped preform, and is the method for producing the annular sealing material according to any one of [6] to

[10] .

[12] In the hot press step, connecting two or more of the rope-shaped preforms, and is the method for producing the annular sealing material according to any one of [6] to

[11] .

Advantages of the Invention

[0015] According to the present invention, in the annular sealing material composed of a core and an outer layer, it is possible to provide an annular sealing material in which cracking in the outer layer and protrusion of the core from the outer layer are suppressed, and a method for producing the same.

Brief Description of the Drawings

[0016] [Figure 1] Shows a schematic cross-sectional view of the annular sealing material. [Figure 2] A schematic cross-sectional view of the annular sealing material in the circumferential direction is shown. [Figure 3] A schematic cross-sectional view of the annular sealing material in the circumferential direction is shown. [Figure 4] This diagram shows a schematic cross-sectional view of an annular seal material in the circumferential direction, illustrating one step in the manufacturing process of the annular seal material. [Figure 5] This diagram shows a schematic cross-sectional view of the annular seal material in the circumferential direction, illustrating another step in the manufacturing process of the annular seal material. [Figure 6] This diagram shows a schematic cross-sectional view of the annular seal material in the circumferential direction, illustrating another step in the manufacturing process of the annular seal material. [Figure 7] This diagram shows a schematic cross-sectional view of the annular seal material in the circumferential direction, illustrating yet another step in the manufacturing process of the annular seal material. [Figure 8] This shows a cross-section of the annular sealing material prepared in Example 1 in the circumferential direction. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following embodiments. In all the following drawings, the scale has been adjusted as appropriate to make each component easier to understand, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

[0018] <Annular sealing material> The annular sealing material of the present invention is an annular sealing material comprising a core and an outer layer covering the periphery of the core, wherein the outer layer has a thick film portion and a non-thick film portion in cross-section in the circumferential direction.

[0019] Figure 1 shows a cross-section of an annular sealant. The annular sealant 1 shown in Figure 1(a) includes a core 2 and an outer layer 3 that surrounds the core 2. As shown in Figure 1(a), the annular sealant 1 preferably has a circular cross-sectional shape, but may have other cross-sectional shapes depending on the application. In Figure 1, the diameter of the cross-section of the annular sealant 1 is the maximum dimension D in the cross-sectional shape of the annular sealant 1, and the thickness of the outer layer 3 is dimension T [Figure 1(b)].

[0020] The annular sealant 1 preferably has an average ratio of the thickness of the outer layer 3 to the total thickness in the cross-section (hereinafter also referred to as the average ratio) of 1 / 50 to 1 / 3, and more preferably 1 / 35 to 1 / 4. The average ratio is the average of the ratios measured at two or more randomly selected cross-sections other than the joints in the annular sealant. The ratio is, for example, in Figure 2, the ratio T / D of the thickness T of the outer layer 3, which is the largest thickness in the cross-section of the annular sealant 1, and the diameter D of the cross-section of the annular sealant 1 that includes that thickness.

[0021] The thickness T of the outer layer 3 may be, for example, 0.1 to 10 mm, and preferably 0.2 to 3 mm. The diameter D of the cross-section of the sealing material 1 may be, for example, 3 to 50 mm, and preferably 3 to 15 mm.

[0022] The thick-film and non-thick-film sections will be explained with reference to Figure 2. Figure 2 is a cross-sectional view of the annular sealant 1 in the circumferential direction. The annular sealant 1 shown in Figure 2 has a thick-film section A and a non-thick-film section B in its outer layer. The outer layer of the thick-film section A has a greater thickness than the outer layer of the non-thick-film section B. The annular sealant 1 tends to suppress cracking in the outer layer and protrusion of the core from the outer layer by having a thick-film section A and a non-thick-film section B in its outer layer. There can be no step at the boundary between the thick-film section A and the non-thick-film section B, and they can be smoothly connected.

[0023] The average ratio of the thickness of the outer layer of the thick film portion A to the thickness of the outer layer of the non-thick film portion B may be, for example, 1.05 or more and 10 or less, preferably 1.5 or more and 8 or less. When the average ratio of the thickness of the outer layer of the thick film portion A to the thickness of the outer layer of the non-thick film portion B is within the above range, cracking in the outer layer and protrusion of the core from the outer layer tend to be suppressed. The average ratio of the thickness of the outer layer of the thick film portion A to the thickness of the outer layer of the non-thick film portion B is the average of the ratios of the outer layer thicknesses at two or more randomly selected locations in the thick film portion A and the non-thick film portion B, respectively. The annular sealing material 1 may have one thick film portion A and one non-thick film portion B, or it may have two or more. When the annular sealing material 1 has multiple thick film portion A and non-thick film portion B, the average ratio of each will be within the above range.

[0024] The annular sealing material 1 may have a difference in the cross-sectional diameter near the boundary between the thick film portion A and the non-thick film portion B, for example, 0.05 mm or less, and preferably 0 mm.

[0025] The thick film portion A may have a width W in the circumferential direction of, for example, 1 mm or more and 100 mm or less, preferably 3 mm or more and 50 mm or less.

[0026] The outer layer 3 may have a multilayer structure in the thick film portion A. The outer layer of the thick film portion A shown in Figure 3 has a two-layer structure composed of a first layer A1 and a second layer A2. The first layer A1 and the second layer A2 may be formed from the same type of material, or they may be formed from different types of materials. The second layer A2 is preferably formed on the surface opposite to the core 2 of the first layer A1, which is formed continuously from the outer layer 3 of the non-thick film portion B. The thickness of the first layer A1 may be the same as the thickness T of the outer layer 3, for example, 0.1 mm or more and 10 mm or less, and preferably 0.2 mm or more and 3 mm or less. The thickness of the second layer A2 may be, for example, 0.05 mm or more and 5 mm or less, and preferably 0.1 mm or more and 3 mm or less.

[0027] The core 2 and the outer layer 3 may contain crosslinked material of the crosslinkable rubber composition. Hereinafter, the crosslinkable rubber composition forming the core 2 will also be referred to as the core crosslinkable rubber composition, the crosslinkable rubber composition forming the outer layer 3 will also be referred to as the outer layer crosslinkable rubber composition, and the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer will also be referred to as the crosslinkable rubber composition.

[0028] A crosslinkable rubber composition may contain a crosslinkable rubber component. The crosslinkable rubber component can form an elastomer (crosslinked rubber) having a crosslinked structure through a crosslinking reaction. The crosslinkable rubber component may have crosslinkable sites such as carbon-carbon unsaturated groups, nitrile groups, hydroxyl groups, amino groups, carbonyl groups, and halogen groups.

[0029] 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 rubber (NBR; acrylonitrile butadiene rubber), hydrogenated nitrile rubber (HNBR; hydrogenated acrylonitrile butadiene rubber), butyl rubber (IIR), and acrylic rubber. Among these, perfluoroelastomers, fluororubber, silicone rubber, and fluorosilicone rubber are preferably used. In a crosslinkable rubber composition, only one type of crosslinkable rubber component may be used, or two or more types may be used in combination.

[0030] The outer layer 3 preferably contains at least one crosslinked material selected from the group consisting of perfluoroelastomers and fluororubber, and the core 2 preferably contains at least one crosslinked material selected from the group consisting of perfluoroelastomers, fluororubber, silicone rubber, and fluorosilicone rubber. Therefore, the crosslinkable rubber component in the crosslinkable rubber composition for the outer layer is preferably at least one selected from the group consisting of perfluoroelastomers and fluororubber, and more preferably a perfluoroelastomer. The crosslinkable rubber component in the crosslinkable rubber composition for the core is preferably at least one selected from the group consisting of perfluoroelastomers, fluororubber, silicone rubber, and fluorosilicone rubber. The outer layer 3 preferably contains a crosslinked perfluoroelastomer from the viewpoint of radical resistance. The core 2 preferably contains at least one crosslinked material selected from the group consisting of fluororubber, silicone rubber, and fluorosilicone rubber from the viewpoint of material cost.

[0031] The perfluoroelastomer is not particularly limited, and examples include tetrafluoroethylene (TFE)-perfluoro(alkyl vinyl ether) copolymers and TFE-perfluoro(alkoxyalkyl vinyl ether) copolymers. These copolymers may further contain constituent units derived from other perfluoro monomers. A perfluoroelastomer composition containing a perfluoroelastomer can provide higher ozone resistance compared to a crosslinkable rubber composition containing a hydrogen atom-containing fluorine elastomer. The crosslinkable rubber composition may contain only one type of perfluoroelastomer or two or more types.

[0032] The perfluoro(alkyl vinyl ether) that forms the tetrafluoroethylene (TFE)-perfluoro(alkyl vinyl ether) copolymer can have 1 to 5 carbon atoms in the alkyl group, and can be, for example, perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), etc. Preferably, it is perfluoro(methyl vinyl ether).

[0033] The perfluoro(alkoxyalkyl vinyl ether) that forms a TFE-perfluoro(alkoxyalkyl vinyl ether) copolymer can have 3 to 12 carbon atoms in the group bonded to the vinyl ether group (CF2=CFO-), for example CF2=CFOCF2CF(CF3)OC , m , 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 can be. In the above formula, n is, for example, 1 to 5, and m is, for example, 1 to 3.

[0034] The perfluoroelastomer preferably has crosslinkability, and more specifically, it is preferably one obtained by further copolymerizing a crosslinking site monomer (one further containing a structural unit derived from the crosslinking site monomer). The crosslinking site means a site capable of a crosslinking reaction. Examples of the crosslinking site include a nitrile group, a halogen group (e.g., I group, Br group, etc.), a perfluorophenyl group, and the like.

[0035] An example of a crosslinking site monomer having a nitrile group as the crosslinking site is a nitrile group-containing perfluorovinyl ether. Examples of the nitrile group-containing perfluorovinyl ether 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, for example, 2, m is, for example, 1 to 5), CF2 = CFO[CF2CF(CF3)O] m (CF2) n CN(n is, for example, 1 to 4, m is, for example, 1 to 2), CF2 = CFO[CF2CF(CF3)O] n CF2CF(CF3)CN(n is, for example, 0-4) Examples include:

[0036] An example of a crosslinking monomer having a halogen group as the crosslinking site is a halogen-containing perfluorovinyl ether. An example of a halogen-containing perfluorovinyl ether is the one described above, where the nitrile group is replaced with a halogen group.

[0037] A crosslinkable perfluoroelastomer may have a crosslinking structure that crosslinks two main chains.

[0038] In perfluoroelastomers, the ratio of TFE-derived constituent units / perfluoro(alkyl vinyl ether) or perfluoro(alkoxyalkyl vinyl ether)-derived constituent units / crosslinking site monomer-derived constituent units is typically 50-79.6% / 20-49.8% / 0.2-5% in molar ratio, and preferably 60-74.8% / 25-39.5% / 0.5-2%. The crosslinkable rubber composition may also contain two or more perfluoroelastomers with different ratios of the above constituent units.

[0039] Examples of fluororubbers include binary vinylidene fluoride rubbers such as vinylidene fluoride / hexafluoropropylene copolymer, ternary vinylidene fluoride rubbers such as vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, vinylidene fluoride / tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, vinylidene fluoride / tetrafluoroethylene / propylene copolymer, tetrafluoroethylene / propylene copolymer, ethylene / tetrafluoroethylene / perfluoromethyl vinyl ether copolymer, thermoplastic fluororubber, and liquid fluororubber with a perfluoropolyether backbone (for example, "SIFEL®" manufactured by Shin-Etsu Chemical Co., Ltd.). Fluororubber may be used individually or in combination of two or more types.

[0040] Fluororubber may contain functional groups. Functional groups can be introduced, for example, by copolymerizing a crosslinked monomer having the functional group. The crosslinked monomer may be a halogen-containing monomer.

[0041] The crosslinkable rubber composition may optionally contain a crosslinking agent, depending on the crosslinking system of the crosslinkable rubber component, together with a co-crosslinking agent (crosslinking aid). 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 rubber and tetrafluoroethylene-propylene rubber include peroxide crosslinking systems, polyamine crosslinking systems, and polyol crosslinking systems. The crosslinkable rubber composition may be crosslinked with one of these crosslinking systems, or with two or more crosslinking systems.

[0042] Examples of peroxide crosslinking agents include 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (examples of commercially available products: NOF Corporation's "Perhexa 25B" and "Perhexa 25B-40"), dicumyl peroxide (example of commercially available product: NOF Corporation's "Permil D"), 2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide, t-butyldicumyl peroxide, benzoyl peroxide (example of commercially available product: NOF Corporation's "Nipper B"), 2,5-dimethyl-2,5-(t-butylperoxy)hexyn-3 (example of commercially available product: NOF Corporation's "Perhexyn 25B"), 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene (example of commercially available product: NOF Corporation's "Perbutyl P"), t-butylperoxyisopropyl carbonate, and parachlorobenzoyl peroxide. Peroxide crosslinking agents may be used individually or in combination of two or more types.

[0043] Examples of co-crosslinking agents used in peroxide crosslinking systems include compounds (unsaturated polyfunctional compounds) that can be co-crosslinked by radicals, such as triallyl isocyanurate (example of a commercially available product: "TAIC" manufactured by Mitsubishi Chemical Corporation); triallyl cyanurate; triallyl formal; triallyl trimellitate; N,N'-m-phenylene bismaleimide; dipropagyl terephthalate; diallyl phthalate; and tetraallyl terephthalamide. One co-crosslinking agent may be used alone, or two or more may be used in combination. Among the above, from the viewpoint of reactivity and heat resistance (compression set characteristics), it is preferable that the co-crosslinking agent includes triallyl isocyanurate.

[0044] In triazine crosslinking systems, crosslinking catalysts such as organotin compounds, onium salts such as quaternary phosphonium salts and quaternary ammonium salts, urea, and silicon nitride are used.

[0045] Examples of crosslinking agents used in oxazol crosslinking systems include 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BOAP), 4,4'-sulfonylbis(2-aminophenol), and 9,9-bis(3-amino-4-hydroxyphenyl)fluorene. Preferably, BOAP is used.

[0046] Conventionally known crosslinking agents can be used in imidazole crosslinking systems and thiazole crosslinking systems. Examples of crosslinking agents used in imidazole crosslinking systems include 3,3',4,4'-tetraaminobenzophenone and 3,3'-diaminobenzidine.

[0047] The amount of crosslinking agent (total amount if two or more types are used) in the crosslinkable rubber composition 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, per 100 parts by mass of the total amount of crosslinkable rubber components.

[0048] The content of co-crosslinking agents (total amount if two or more are used) in the crosslinkable rubber composition is, for example, 0.5 to 10 parts by mass per 100 parts by mass of the total amount of crosslinkable rubber components, and preferably 1 to 8 parts by mass from the viewpoint of improving heat resistance.

[0049] The crosslinkable rubber composition may contain additives such as antioxidants, antioxidants, vulcanization accelerators, processing aids (e.g., stearic acid), stabilizers, tackifiers, silane coupling agents, plasticizers, flame retardants, mold release agents, waxes, and lubricants, as needed, for purposes such as improving processability and adjusting physical properties. Other examples of additives include tackiness reducing (preventing) agents such as fluorinated oils (e.g., perfluoroethers). Only one additive may be used, or two or more may be used in combination.

[0050] However, when the annular sealing material is used in a high-temperature environment, there is a risk of volatilization, leaching, or precipitation, so it is preferable to use as little additive 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, per 100 parts by mass of the total amount of crosslinkable rubber components), and it is desirable to use no additive at all.

[0051] Furthermore, the crosslinkable rubber composition may optionally contain colorants (e.g., inorganic pigments, organic pigments, etc.) and fillers (e.g., 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 powders, glass powders, ceramic powders, etc.). Only one type of filler may be used, or two or more types may be used in combination. The filler content in the crosslinkable rubber composition (total amount if two or more types are used) is, for example, 0.1 parts by mass or more than 40 parts by mass per 100 parts by mass of the total amount of the crosslinkable rubber component, preferably 1 part by mass or more than 30 parts by mass, and more preferably more than 1 part by mass and 30 parts by mass or less, from the viewpoint of improving mechanical strength. In this specification, fillers are distinguished from the organic pigments and inorganic pigments used as colorants, and different types of fillers can be used.

[0052] When a crosslinkable rubber composition contains a fluororesin filler, the ozone resistance and mechanical strength of the crosslinked material can be further improved. The fluororesin can be included in the crosslinkable rubber composition, for example, as fluororesin particles.

[0053] The fluororesin used as a filler is a resin having fluorine atoms in its molecule, and can be, for example, 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), polyvinyl fluoride-hexafluoropropylene copolymer (PVF), vinylidene fluoride-hexafluoropropylene copolymer (VDF-HFP copolymer), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE copolymer), etc. A single fluororesin may be used alone, or two or more may be used in combination.

[0054] Among the above, it is preferable to use fluororesins such as PFA and PTFE, which have relatively high melting points, from the viewpoint of preventing the resin from melting in a high-temperature environment and impairing properties such as compression set.

[0055] The fluororesin used as a filler may contain functional groups. Functional groups can be introduced, for example, by copolymerizing monomers having such functional groups. When the above-mentioned crosslinking site monomers are copolymerized as monomers having functional groups, the crosslinking between the fluororesin and the perfluoroelastomer also proceeds due to the crosslinking agent, which can further enhance the mechanical strength of the crosslinked product of the perfluoroelastomer composition. An example of a fluororesin containing functional groups is the nitrile group-containing polytetrafluoroethylene described 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).

[0056] When a crosslinkable rubber composition contains a perfluoroelastomer and a fluororesin filler, for example, a fluororesin-containing perfluoroelastomer can be used, produced by 1) kneading perfluoroelastomer powder and fluororesin powder using a mixing roll, 2) melt-kneading perfluoroelastomer powder or pellets and fluororesin powder or pellets using equipment such as a mixer or twin-screw extruder, or 3) adding fluororesin during the perfluoroelastomer preparation stage.

[0057] The method described in 3) above includes a method in which an aqueous dispersion of perfluoroelastomer obtained by emulsion polymerization is mixed with an aqueous dispersion of fluororesin, and then a mixture of perfluoroelastomer and fluororesin is obtained by co-coagulation.

[0058] A crosslinkable rubber composition can be prepared by uniformly mixing a crosslinkable rubber component, a colorant, a crosslinking agent, a co-crosslinking agent (if necessary), a filler, and additives. Conventional mixing machines such as mixing rolls, pressure kneaders, and internal mixers (Banbury mixers) can be used. Each component may be mixed and kneaded all at once, or the components may be mixed in stages, such as first uniformly mixing the components excluding those that contribute to the crosslinking reaction (crosslinking accelerators, crosslinking retarders, crosslinking agents, etc.), and then mixing in the components that contribute to the crosslinking reaction.

[0059] <Method for manufacturing ring-shaped sealing material> A method for manufacturing an annular sealing material may include, for example, the following steps. A pre-molding step of preparing one or more rope-shaped pre-molded bodies, each comprising an uncrosslinked core made of a crosslinkable rubber composition for the core and an uncrosslinked outer layer made of a crosslinkable rubber composition for the outer layer that covers the periphery of the uncrosslinked core. A hot press molding process in which a rope-shaped preform is placed in a mold with its two ends in contact, and then hot press molding is performed.

[0060] The above-described explanation for the annular sealing material applies to the annular sealing material, the crosslinkable rubber composition for the core, and the crosslinkable rubber composition for the outer layer.

[0061] (Pre-molding process) The pre-molding process may include a step of extruding using a crosslinkable rubber composition for the core and a crosslinkable rubber composition for the outer layer. A rope-shaped pre-molded body can be produced, for example, as follows: First, the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer are formed into a sheet using a roll to produce a sheet-shaped molded product. The thickness of the sheet-shaped molded product may be, for example, 1 mm to 5 mm. Next, the sheet-shaped molded product is cut into a ribbon-shaped molded product, for example, with a width of 5 mm to 30 mm, using a cutting machine. Then, the ribbon-shaped molded products of the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer are fed into a screw-type extruder equipped with a crosshead and extruded into a rope shape to obtain a rope-shaped pre-molded body having a two-layer structure in which the outer layer is made of the crosslinkable rubber composition for the outer layer and the core is made of the crosslinkable rubber composition for the core. The extrusion speed into a rope shape can be, for example, 100 mm / min to 1000 mm / min.

[0062] The diameter of the cross-section of the rope-shaped preform may be, for example, 3 to 50 mm, preferably 3 to 15 mm. The outer layer thickness of the rope-shaped preform may be, for example, 0.1 to 10 mm, preferably 0.2 to 3 mm. The length of the rope-shaped preform may be, for example, 100 to 5000 mm.

[0063] Ribbon-shaped molded products can also be produced by feeding a crosslinkable rubber composition for the core and a crosslinkable rubber composition for the outer layer into a plunger-type extruder and extruding them into a ribbon shape, without having to produce the sheet-shaped molded product described above.

[0064] The number of rope-like pre-molded bodies to be prepared may be one, two or more, for example, three to ten, and can be adjusted according to the inner and / or outer diameter of the annular sealing material.

[0065] (Hot pressing process) In the hot pressing process, an annular sealing material consisting of a core and an outer layer containing a crosslinked product of a crosslinkable rubber composition can be obtained by press molding while heating the uncrosslinked core and uncrosslinked outer layer. The heating temperature in the hot pressing process may be, for example, around 110°C to 220°C.

[0066] In the hot pressing process, an annular sealing material may be produced by using a die having an annular cavity to bring the two ends of a rope-shaped preform into contact and performing hot pressing. Alternatively, a feed press forming method may be used in which a die having a straight or arc-shaped cavity is used to first hot press form the parts of the rope-shaped preform other than the ends to obtain a straight or arc-shaped molded body, and then the joint where the two ends of this straight or arc-shaped molded body are brought into contact is hot press formed to produce an annular sealing material. The configuration in which the two ends are brought into contact includes a state in which the two end faces of the rope-shaped preform are in contact. The length in the circumferential direction of the joint may be, for example, 100 mm or more and 1200 mm or less. Feed press forming will be described later.

[0067] The hot pressing process may further include a step (hereinafter also referred to as step a) in which, from the viewpoint of preventing cracking of the outer layer and protrusion of the core from the outer layer at the joint where the ends of the rope-shaped preform are connected, an uncrosslinked thin film layer 30 is wrapped around the joint of the two ends of the rope-shaped preform 11 that are in contact, as shown in Figure 4, before being placed in a mold having an annular cavity, or, in the case of feed press molding, before the second hot pressing process described later (before being placed in a mold having a linear or arc-shaped cavity).

[0068] The thickness of the uncrosslinked thin film layer 30 may be, for example, 0.05 mm or more and 5 mm or less, and is preferably 0.1 mm or more and 1 mm or less from the viewpoint of reducing the step on the outer circumference of the rope-shaped preformed body 11.

[0069] The material constituting the uncrosslinked thin film layer 30 is the crosslinkable rubber composition for the outer layer described above, preferably the same type of crosslinkable rubber composition for the outer layer that constitutes the outer layer 12 of the rope-shaped premolded body 11.

[0070] The uncrosslinked thin film layer 30 is obtained by forming the crosslinkable rubber composition for the outer layer into a sheet using a roll, cutting it into a ribbon-shaped molded product with a width of, for example, 5 mm to 100 mm using a cutting machine, and then cutting it further according to the length to be wrapped around the joint of the rope-shaped pre-molded body 11. Alternatively, the uncrosslinked thin film layer 30 can also be used as the rope-shaped pre-molded body from which the core material has been removed.

[0071] In step a, the uncrosslinked thin film layer 30 may be wrapped around the joint of the rope-shaped preformed body 11 once, or it may be wrapped around two or more times. From the viewpoint of reducing the step on the outer circumference of the rope-shaped preformed body 11, it is preferable to wrap the uncrosslinked thin film layer 30 around the joint of the rope-shaped preformed body 11 once or twice.

[0072] The uncrosslinked thin film layer 30 may become integrated with the outer layer after the hot pressing process, or it may become a second layer A2 that constitutes a multi-stage structure in the thick film portion, as shown in Figure 3.

[0073] The method for manufacturing the annular sealing material of the present invention may further include a step (hereinafter also referred to as step b) of removing the uncrosslinked core 14 from the two ends of the rope-shaped preformed body 11, as shown in Figure 5a), before the hot pressing step or before the second hot pressing step described later, from the viewpoint of preventing the core from protruding at the joint. As shown in Figure 5b), by bringing the two ends (outer layer 12) from which the uncrosslinked core has been removed into contact and placing them in a mold for hot pressing, it is possible to easily prevent the core from protruding at the joint.

[0074] Step b may be performed before the hot pressing step, and if feed press forming is performed, it may be performed before the first hot pressing step described later, or between the first hot pressing step and the second hot pressing step.

[0075] The uncrosslinked core 14 to be removed can be, for example, in a range of 0.1 mm to 20 mm inward from the end face. The uncrosslinked core 14 can be removed using, for example, scissors, a scalpel, or pliers.

[0076] The method for manufacturing the annular sealing material of the present invention may further include a step (hereinafter also referred to as step c) of heating the two ends of the rope-shaped preform before the hot pressing step, or, in the case of feed press molding, before the second hot pressing step described later, from the viewpoint of improving the jointability between the ends. After step c, by bringing the two ends of the rope-shaped preform into contact and placing it in the mold for hot press molding, the jointability between the ends can be strengthened and the protrusion of the core can be prevented.

[0077] In step c), as shown in Figure 6a), a heater 20 is placed between the two ends of the rope-shaped preformed body 11, the end faces are heated and melted, and then, as shown in Figure 6b), the molten ends can be brought into contact with each other.

[0078] The method for manufacturing the annular sealing material of the present invention may further include, from the viewpoint of preventing the core from protruding at the joint, a step (hereinafter also referred to as step d) of placing a connecting member 40 between the two ends of a rope-shaped preformed body 11 to be placed in the mold and installing it in the mold, as shown in Figure 7, during the hot pressing process or, when performing feed press molding, during the second hot pressing process described later. If the uncrosslinked outer layer 42 of the connecting member 40 is thicker than the uncrosslinked outer layer 12 of the rope-shaped preformed body 11, it is easier to prevent the core from protruding at the joint during hot pressing.

[0079] 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, 1.1 to 10. The length of the connecting member 40 in the circumferential direction can be, for example, 5 mm to 100 mm.

[0080] From the viewpoint of reducing the step height on the outer circumference of the annular sealing material, it is preferable that the diameter of the cross-section of the connecting member 40 be the same as, approximately the same as, or larger than, the diameter of the cross-section of the rope-shaped pre-molded body 11.

[0081] The connecting member 40 may include an uncrosslinked core 41 made of a crosslinkable rubber composition for the core described later, and an uncrosslinked outer layer 42 made of a crosslinkable rubber composition for the outer layer described later that surrounds the uncrosslinked core 41. The material constituting the uncrosslinked core 41 is preferably the same type of crosslinkable rubber composition for the core as the one constituting the uncrosslinked core 13 of the rope-shaped premolded body 11. The material constituting the uncrosslinked outer layer 42 is preferably the same type of crosslinkable rubber composition for the outer layer as the one constituting the uncrosslinked outer layer 12 of the rope-shaped premolded body 11.

[0082] A hot pressing process including at least one of process a and process d tends to easily yield an annular sealing material comprising a core and an outer layer covering the periphery of the core, wherein the outer layer has a thick film portion and a non-thick film portion in cross-section in the circumferential direction.

[0083] The method for manufacturing annular sealing material may further include a secondary crosslinking step after the hot pressing step to promote crosslinking of uncrosslinked or insufficiently crosslinked portions. The heating temperature in the secondary crosslinking step may be, for example, between 150°C and 310°C.

[0084] (Feed press forming) When feed press forming is performed in a hot pressing process, the feed press forming may include the following steps. A first hot pressing step involves placing a rope-shaped preform into a first mold and hot-pressing the portion of the rope-shaped preform other than the ends. The second hot press process involves bringing the two ends of a rope-shaped preform into contact and placing it in the second mold, then performing hot press molding.

[0085] In the first hot pressing step, the portion of the rope-shaped preform other than the ends can be made into a cross-linked state. The first mold in which the rope-shaped preform is placed in the first hot pressing step can have a linear or arc-shaped cavity. After being placed in the first mold, the rope-shaped preform can be pressed while being heated by a C-type press. The temperature of the hot pressing in the first hot pressing step may be, for example, around 110°C to 220°C.

[0086] A method for hot-press molding a portion of a rope-shaped preform other than its end is to cool the portion of the rope-shaped preform corresponding to the end of the first mold using a cooling device or the like. The length of the portion to be cooled can be the length in the circumferential direction of the end of the rope-shaped preform that is in an unbridged or insufficiently bridged state, and may be, for example, 1 mm to 600 mm.

[0087] In the second hot pressing process, the two ends of the rope-shaped preform are brought into contact and placed in the second mold, and the ends of the rope-shaped preform can be joined in a bridging state by performing hot pressing. By repeatedly joining the ends of two or more rope-shaped preforms, or by joining the ends of a single rope-shaped preform, an annular sealing material can be obtained.

[0088] The second mold, which houses the two ends of the rope-like preform, may have a linear or arc-shaped cavity. The two ends of the rope-like preform placed in the second mold may each have a width in the circumferential direction of, for example, 50 mm or more and 600 mm or less. The two ends may be both ends of a single rope-like preform, or they may be one end of each of two rope-like preforms.

[0089] The temperature of the hot press molding in the second hot press process may be, for example, around 110°C to 220°C. From the viewpoint of preventing cracking at the joint and protrusion of the core, the temperature of the hot press molding in the second hot press process is preferably lower than the temperature of the hot press molding in the first hot press process, and more preferably 5°C to 20°C lower than the temperature of the hot press molding in the first hot press process. [Examples]

[0090] The present invention will be described in more detail below with reference to examples. In the examples, "%" and "parts" refer to mass%, and parts, respectively, unless otherwise specified.

[0091] <Example 1> A crosslinkable rubber composition for the outer layer was prepared by mixing perfluoroelastomer with 1 part by mass of a crosslinking agent (Perhexa 25B) and 2 parts by mass of a crosslinking aid (TAIC) per 100 parts by mass of perfluoroelastomer and kneading it using a kneader. Next, a crosslinkable rubber composition for the core was prepared by mixing fluororubber with 1 part by mass of a crosslinking agent (Perhexa 25B) and 3 parts by mass of a crosslinking aid (TAIC) per 100 parts by mass of fluororubber and kneading it using a kneader. Next, the crosslinkable rubber composition for the outer layer and the crosslinkable rubber composition for the core were formed into sheets using a roll to a thickness of approximately 3 mm, and then cut into ribbons with a width of approximately 15 mm using a cutting machine. A ribbon-shaped crosslinkable rubber composition for the outer layer and a crosslinkable rubber composition for the core were fed into a screw-type extruder equipped with a crosshead to produce five rope-like pre-molded bodies having a two-layer structure, with the outer layer being the crosslinkable rubber composition for the outer layer and the core being the crosslinkable rubber composition for the core. The cross-sectional diameter of the rope-like pre-molded bodies was approximately 7 mm, the outer layer thickness was approximately 1 mm, and the length was 800 mm. Using the above-mentioned crosslinkable rubber composition for the outer layer, a sheet was formed using a roll to a thickness of approximately 0.5 mm, and then cut into pieces with a width of 15 mm and a length of 26 mm to produce sheet-like molded products for the uncrosslinked thin film layer.

[0092] Next, each of the five rope-like preforms was placed in a first mold of a straight type (length 800 mm, cavity dimension 7 mm), and while cooling both ends (width 100 mm at one end) so that the ends remained uncrosslinked, the rest of the preforms were hot-pressed at a temperature of 165°C using a C-type press.

[0093] After bringing one end of each of the two rope-like preforms, which had been hot-press molded, into contact, a sheet-like molded material for the uncrosslinked thin film layer was wrapped around the joint of the two ends 1.5 times. Then, it was placed in a second mold for the joint, and the joint was hot-press molded at a temperature of 160°C. The same procedure was performed on the ends of the remaining rope-like preforms, and an annular seal material was obtained by joining five rope-like preforms. The obtained annular seal material was subjected to secondary crosslinking at a temperature of 200°C. It was confirmed that there was no overhang from the outer layer of the core at the joint of the obtained annular seal material. In the obtained annular seal material, the thick film portion (the part wrapped with the uncrosslinked thin film layer) had an outer layer thickness of 1.6 mm, a cross-sectional diameter of 7.1 mm, and a width of 10 mm, while the non-thick film portion had an outer layer thickness of 1 mm and a cross-sectional diameter of 7.1 mm. The average ratio of the outer layer thickness of the thick-film portion to the outer layer thickness of the non-thick-film portion was 1.6, and the difference in the cross-sectional diameter of the annular sealing material near the boundary between the thick-film and non-thick-film portions was 0.05 mm or less. Figure 8 shows the cross-section of the fabricated annular sealing material in the circumferential direction. [Explanation of symbols]

[0094] 1.50 Annular sealing material, 2 Core, 3.53 Outer layer, 11 Rope-shaped pre-molded body, 12 Uncrosslinked outer layer, 13 Uncrosslinked core, 14 Uncrosslinked core to be removed, 20 Heater, 30 Uncrosslinked thin film layer, 40 Connecting member, 41 Uncrosslinked core, 42 Uncrosslinked outer layer, 51 First part, 52 Second part, A Thick film part, A1 First layer, A2 Second layer, B Non-thick film part, T Thickness of the outer layer, D Diameter of the cross-section, W Width of the thick film part.

Claims

1. A method for manufacturing an annular sealing material, The annular sealing material includes a core and an outer layer that covers the periphery of the core. The outer layer has a thick film portion and a non-thick film portion in a cross-section in the circumferential direction. A pre-molding step of preparing one or more rope-shaped pre-molded bodies, each comprising an uncrosslinked core made of a crosslinkable rubber composition for the core and an uncrosslinked outer layer made of a crosslinkable rubber composition for the outer layer that covers the periphery of the uncrosslinked core, A hot press process is performed in which the two ends of the rope-shaped preform are brought into contact and placed in a mold, and hot press molding is carried out. Prior to the aforementioned hot pressing process, a step is taken to remove the uncrosslinked core from the two ends of the rope-shaped preformed body, A method for manufacturing an annular sealing material, including [the specified element].

2. A method for manufacturing an annular sealing material, The annular sealing material includes a core and an outer layer that covers the periphery of the core. The outer layer has a thick film portion and a non-thick film portion in a cross-section in the circumferential direction. A pre-molding step of preparing one or more rope-shaped pre-molded bodies, each comprising an uncrosslinked core made of a crosslinkable rubber composition for the core and an uncrosslinked outer layer made of a crosslinkable rubber composition for the outer layer that covers the periphery of the uncrosslinked core, A hot press process is performed in which the two ends of the rope-shaped preform are brought into contact and placed in a mold, and hot press molding is carried out. Prior to the aforementioned hot pressing process, a step is taken to heat the two ends of the rope-shaped preformed body, A method for manufacturing an annular sealing material, including [the specified element].

3. A method for manufacturing an annular sealing material, The annular sealing material includes a core and an outer layer that covers the periphery of the core. The outer layer has a thick film portion and a non-thick film portion in a cross-section in the circumferential direction. A pre-molding step of preparing one or more rope-shaped pre-molded bodies, each comprising an uncrosslinked core made of a crosslinkable rubber composition for the core and an uncrosslinked outer layer made of a crosslinkable rubber composition for the outer layer that covers the periphery of the uncrosslinked core, A hot press process is performed in which the two ends of the rope-shaped preform are brought into contact and placed in a mold, and hot press molding is carried out. In the aforementioned hot pressing process, the process includes placing a connecting member between the two ends of the rope-shaped preform and installing it in the mold, Includes, A method for manufacturing an annular sealing material, wherein the connecting member comprises an uncrosslinked core made of the crosslinkable rubber composition for the core and an uncrosslinked outer layer made of the crosslinkable rubber composition for the outer layer that covers the periphery of the uncrosslinked core, and the uncrosslinked outer layer of the connecting member is thicker than the uncrosslinked outer layer of the rope-shaped premolded body.

4. The method for manufacturing an annular sealing material according to any one of claims 1 to 3, wherein the average ratio of the thickness of the outer layer of the thick film portion to the thickness of the outer layer of the non-thick film portion is 1.05 or more and 10 or less.

5. The method for manufacturing an annular sealing material according to any one of claims 1 to 4, wherein the difference in the diameter of the cross-section of the annular sealing material near the boundary between the thick film portion and the non-thick film portion is 0.05 mm or less.

6. The method for manufacturing an annular sealing material according to any one of claims 1 to 5, wherein the thick film portion has a width of 1 mm or more and 100 mm or less in the circumferential direction.

7. A method for manufacturing an annular sealing material according to any one of claims 1 to 6, wherein the outer layer comprises at least one crosslinked material selected from the group consisting of perfluoroelastomer and fluororubber, and the core comprises at least one crosslinked material selected from the group consisting of perfluoroelastomer, fluororubber, silicone rubber and fluorosilicone rubber.

8. The method for manufacturing an annular seal material according to any one of claims 1 to 7, wherein the pre-molding step includes a step of extruding using the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer.

9. A method for manufacturing an annular sealing material according to any one of claims 1 to 8, further comprising the step of wrapping an uncrosslinked thin film layer around the joint of the two ends of the rope-shaped premolded body that have been brought into contact, before being placed in the mold, wherein the material constituting the uncrosslinked thin film layer is a crosslinkable rubber composition for outer layers.

10. A method for manufacturing an annular sealing material according to any one of claims 1 to 9, wherein in the hot pressing step, two or more rope-shaped preformed bodies are connected.

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