Annular seal material and manufacturing method

Abstract

To provide an annular seal material having a parting line with improved visibility and a manufacturing method of the same.SOLUTION: An annular seal material comprises a middle core, and an outer layer surrounding the middle core. The outer layer of the annular seal material has a parting line on an outer diameter side and an inner diameter side. In the annular seal material, a thickness of at least a part of a portion of the outer layer where the parting line exists is smaller than a thickness of a portion of the outer layer where the parting line does not exist.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an annular sealing material and also to a method for manufacturing the same. [Background technology]

[0002] BACKGROUND ART As a method for manufacturing sealing materials such as gaskets and packings used for various purposes, a method is known in which a material is placed in a mold and subjected to hot press molding (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 08-151450 Summary of the Invention [Problem to be solved by the invention]

[0004] Annular sealing materials manufactured by hot press molding often have a linear parting line formed on the surface along the joint of the mold. Attaching the annular sealing material to a device or the like can sometimes be done accurately and easily by visually checking whether the parting line is twisted or slackened. However, it is desirable that the parting line be as small as possible in order to ensure airtightness when the annular sealing material is attached to an apparatus or the like, and it may be difficult to visually recognize the parting line.

[0005] An object of the present invention is to provide an annular sealing material having a parting line with improved visibility, and a method for manufacturing the same. [Means for solving the problem]

[0006] The present invention provides the following annular sealing material and a method for producing the same. [1] An annular sealing material including a core and an outer layer surrounding the core, wherein the annular sealing material has parting lines on the outer diameter side and the inner diameter side, and the thickness of at least a portion of the outer layer where the parting line exists is smaller than the thickness of the outer layer where the parting line does not exist. [2] The annular sealing material according to claim 1, wherein the ratio of the thickness of the outer layer at a portion where the parting line is present to the thickness of the portion where the parting line is not present is 1.05 to 40. [3] The annular sealing material according to [1] or [2], wherein the core contains a colorant. [4] The annular sealing material according to any one of [1] to [3], wherein the outer layer contains at least one crosslinked material selected from the group consisting of perfluoroelastomers and fluororubbers, and the core contains at least one crosslinked material selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers. [5] A method for producing the annular sealing material according to any one of [1] to [4], a preforming step of preparing one or more rope-shaped preforms including an uncrosslinked core made of a crosslinkable rubber composition for a core and an uncrosslinked outer layer made of a crosslinkable rubber composition for an outer layer that covers the periphery of the uncrosslinked core; a heat press molding step in which the two ends of the rope-shaped preform are brought into contact with each other and placed in a mold, and heat press molding is performed; A method for manufacturing an annular sealing material, comprising: [6] The method for producing an annular sealing material according to [5], wherein the step of preparing the preform includes a step of extrusion molding using the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an annular sealing material having a parting line with improved visibility and a method for manufacturing the same. [Brief explanation of the drawings]

[0008] [Figure 1] 1 shows a schematic cross-sectional view of an annular sealing material. [Figure 2] 1 shows a schematic cross-sectional view of an annular sealing material. [Figure 3] 1A and 1B are schematic cross-sectional views of an annular sealing material in the circumferential direction, illustrating one step of a method for manufacturing the annular sealing material; [Figure 4] 10A and 10B are schematic cross-sectional views in the circumferential direction of the annular sealing material, illustrating another step of the method for manufacturing the annular sealing material. [Figure 5] 10A and 10B are schematic cross-sectional views in the circumferential direction of the annular sealing material, illustrating another step in the method for manufacturing the annular sealing material. [Figure 6] 10 is a schematic cross-sectional view in the circumferential direction of the annular sealing material, illustrating yet another step in the method for manufacturing the annular sealing material. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In all of the drawings, the scales of the components are appropriately adjusted to make them easier to understand, and the scales of the components shown in the drawings do not necessarily match the scales of the actual components.

[0010] <Annular seal material> The annular sealing material of the present invention comprises a core and an outer layer surrounding the core, has parting lines on the outer diameter side and the inner diameter side, and is characterized in that the thickness of at least a portion of the outer layer where the parting line is present is smaller than the thickness of the outer layer where the parting line is not present.

[0011] Figure 1(a) shows the shape of the annular sealing material in a plan view. In Figure 1(a), the annular sealing material 1 is indicated by the shaded area. The annular sealing material 1 has an outer diameter D1, which is the diameter of the outer periphery, and an inner diameter D2, which is the diameter of the inner periphery. The outer and inner peripheries are the outer and inner circumferences, respectively, when viewed from the plan view of the annular sealing material 1. The plan view refers to a view from the thickness direction of the annular sealing material 1.

[0012] 1(b) and (c) show cross-sectional views perpendicular to the plane of the annular sealing material 1. The annular sealing material 1 includes a core 2 and an outer layer 3 that surrounds the core 2. As shown in FIG. 1(a), the annular sealing material 1 preferably has a circular cross-sectional shape, but may have other cross-sectional shapes depending on the application. The annular sealing material 1 has a cross-sectional diameter D3 and a thickness T of the outer layer 3.

[0013] Although not shown in Fig. 1, the annular sealing material 1 has parting lines on the outer diameter side and inner diameter side. The parting lines can be traces of the seams between two dies that appear on the surface of the outer layer 3 during the hot press molding process, or traces left by removing burrs. The annular sealing material 1 has parting lines formed on the surface of the outer layer 3 along the outer and inner circumferences.

[0014] As shown in Figure 2, the parting line may be formed so as to convex outward in the cross section of the annular sealing material 1. In the annular sealing material 1, the outer layer 3 has a thickness T1 of at least a portion where the parting line is present that is smaller than a thickness T2 of a portion where the parting line is not present. Because the thickness T1 of at least a portion where the parting line is present in the outer layer 3 is smaller than the thickness T2 of a portion where the parting line is not present, the core 2 becomes easier to see through the outer layer 3 on the parting line, which tends to improve the visibility of the parting line. The outer layer 3 of the annular sealing material 1 may have thickness T1 in a portion where the parting line is present, or may have thickness T1 throughout the entire portion where the parting line is present.

[0015] The ratio T2 / T1 of the thickness T2 of the part without the parting line to the thickness T1 of the part with the parting line of the outer layer 3 is 1.05 to 40, and from the viewpoint of making the core 2 easily visible through the outer layer 3, is preferably 1.2 to 20.

[0016] From the viewpoint of making the core 2 (parting line) more easily visible, the core 2 preferably contains a colorant. The outer layer 3 may or may not contain a colorant. If the outer layer 3 contains a colorant, it preferably contains a colorant different from the colorant contained in the core 2. From the viewpoint of visibility of the core 2 (parting line), it is more preferable that the outer layer 3 does not contain a colorant.

[0017] From the viewpoint of reducing material costs, the annular sealing material 1 may preferably have an average ratio (hereinafter also referred to as average ratio) of the thickness T of the outer layer 3 to the cross-sectional diameter D3 of, for example, 1 / 35 or more and 1 / 4 or less, and preferably 1 / 20 or more and 1 / 5 or less. The average ratio is the average of ratios measured at five randomly selected cross sections of the annular sealing material 1. The ratio is expressed, for example, as the ratio T / D3 of the largest thickness T of the outer layer 3 in the cross section of the annular sealing material 1 to the cross-sectional diameter D3 including that thickness.

[0018] The thickness T of the outer layer 3 and the thickness T2 of the parting line-free portion may be, for example, 0.3 mm to 10 mm, and preferably 0.5 mm to 3 mm. The thickness T1 of the parting line-free portion of the outer layer 3 may be, for example, 0.1 mm to 5 mm, and preferably 0.2 mm to 1.5 mm. The diameter D3 of the cross section of the annular sealing material 1 may be, for example, 3 mm or more and 50 mm or less, and preferably 3 mm or more and 15 mm or less.

[0019] The core 2 and the outer layer 3 can contain a cross-linked product of a cross-linkable rubber composition. Hereinafter, the cross-linkable rubber composition forming the core 2 will be referred to as a core cross-linkable rubber composition, the cross-linkable rubber composition forming the outer layer 3 will be referred to as an outer layer cross-linkable rubber composition, and the cross-linkable rubber composition will be referred to as a cross-linkable rubber composition when referring to both the core cross-linkable rubber composition and the outer layer cross-linkable rubber composition.

[0020] The 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 a crosslinkable moiety such as a carbon-carbon unsaturated group, a nitrile group, a hydroxyl group, an amino group, a carbonyl group, or a halogen group.

[0021] Specific examples of cross-linkable rubber components include perfluoroelastomers (FFKM), fluororubbers (FKM), silicone rubbers, fluorosilicone rubbers, ethylene-propylene rubbers (EPM), ethylene-propylene-diene rubbers (EPDM), nitrile rubbers (NBR; acrylonitrile butadiene rubbers), hydrogenated nitrile rubbers (HNBR; hydrogenated acrylonitrile butadiene rubbers), butyl rubbers (IIR), and acrylic rubbers. Among these, perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers are preferred. In the cross-linkable rubber composition, only one type of cross-linkable rubber component may be used, or two or more types may be used in combination.

[0022] The outer layer 3 preferably contains at least one crosslinked material selected from the group consisting of perfluoroelastomers and fluororubbers, and the core 2 preferably contains at least one crosslinked material selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers. 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 fluororubbers, 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, fluororubbers, silicone rubbers, and fluorosilicone rubbers. From the viewpoint of radical resistance, the outer layer 3 advantageously contains a crosslinked material of a perfluoroelastomer. From the viewpoint of material cost, the core 2 advantageously contains at least one crosslinked material selected from the group consisting of fluororubbers, silicone rubbers, and fluorosilicone rubbers.

[0023] The perfluoroelastomer is not particularly limited, and examples thereof 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 perfluoromonomers. A perfluoroelastomer composition containing a perfluoroelastomer can have improved 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 may contain two or more types.

[0024] The perfluoro(alkyl vinyl ether) forming the tetrafluoroethylene (TFE)-perfluoro(alkyl vinyl ether) copolymer may have an alkyl group with 1 to 5 carbon atoms, such as perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), etc. Perfluoro(methyl vinyl ether) is preferred.

[0025] The perfluoro(alkoxyalkyl vinyl ether) forming the TFE-perfluoro(alkoxyalkyl vinyl ether) copolymer may have 3 to 12 carbon atoms in the group bonded to the vinyl ether group (CF2=CFO-), for example. 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.

[0026] The perfluoroelastomer preferably has crosslinkability, and more specifically, it is preferably a copolymer of a crosslinking site monomer (a copolymer further containing a structural unit derived from a crosslinking site monomer). The crosslinking site means a site capable of crosslinking reaction. Examples of the crosslinking site include a nitrile group, a halogen group (e.g., an I group, a Br group, etc.), a perfluorophenyl group, etc.

[0027] An example of a crosslinking site monomer having a nitrile group as a 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 to 4) The following can be mentioned:

[0028] An example of a crosslinking moiety monomer having a halogen group as a crosslinking moiety is a halogen group-containing perfluorovinyl ether, such as the above-mentioned specific example of a nitrile group-containing perfluorovinyl ether, in which the nitrile group is replaced with a halogen group.

[0029] The crosslinkable perfluoroelastomer may have a crosslinked structure that crosslinks two main chains.

[0030] The molar ratio of TFE-derived structural units / perfluoro(alkyl vinyl ether) or perfluoro(alkoxyalkyl vinyl ether)-derived structural units / crosslinking site monomer-derived structural units in the perfluoroelastomer is usually 50-79.6% / 20-49.8% / 0.2-5%, and preferably 60-74.8% / 25-39.5% / 0.5-2%. The crosslinkable rubber composition may contain two or more perfluoroelastomers having different ratios of the above structural units.

[0031] Examples of fluororubbers 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, vinylidene fluoride / tetrafluoroethylene / propylene copolymers, tetrafluoroethylene / propylene copolymers, ethylene / tetrafluoroethylene / perfluoromethyl vinyl ether copolymers, thermoplastic fluororubbers, and liquid fluororubbers with a perfluoropolyether skeleton (for example, "SIFEL (registered trademark)" manufactured by Shin-Etsu Chemical Co., Ltd.). One type of fluororubber may be used alone, or two or more types may be used in combination.

[0032] The fluororubber may contain a functional group. The functional group can be introduced, for example, by copolymerizing a crosslinking site monomer having the functional group. The crosslinking site monomer can be a halogen group-containing monomer.

[0033] The crosslinkable rubber composition may contain a crosslinking agent according to the crosslinking system of the crosslinkable rubber component, optionally 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 rubbers and tetrafluoroethylene-propylene rubbers include peroxide crosslinking systems, polyamine crosslinking systems, and polyol crosslinking systems. The crosslinkable rubber composition may be crosslinked with any one type of crosslinking system, or with two or more types of crosslinking systems.

[0034] Examples of peroxide crosslinking agents include 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (commercially available products include NOF Corporation's "Perhexa 25B" and "Perhexa 25B-40"); dicumyl peroxide (commercially available products include NOF Corporation's "Percumyl D"); 2,4-dichlorobenzoyl peroxide; di-t-butyl peroxide; t-butyldicumyl peroxide; benzoyl peroxide (commercially available products include NOF Corporation's "Niper B"); 2,5-dimethyl-2,5-(t-butylperoxy)hexyne-3 (commercially available products include NOF Corporation's "Perhexyne 25B"); 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; α,α'-bis(t-butylperoxy-m-isopropyl)benzene (commercially available products include NOF Corporation's "Perbutyl P"); t-butylperoxyisopropyl carbonate; and parachlorobenzoyl peroxide. The peroxide crosslinking agent may be used alone or in combination of two or more kinds.

[0035] Examples of co-crosslinking agents used in peroxide crosslinking systems include compounds (unsaturated polyfunctional compounds) capable of radical co-crosslinking, such as triallyl isocyanurate (a commercially available product example is "TAIC" manufactured by Mitsubishi Chemical Corporation); triallyl cyanurate; triallyl formal; triallyl trimellitate; N,N'-m-phenylene bismaleimide; dipropargyl terephthalate; diallyl phthalate; and tetraallyl terephthalamide. Only one type of co-crosslinking agent may be used, or two or more types may be used in combination. Among the above, from the viewpoints of reactivity and heat resistance (compression set properties), it is preferable that the co-crosslinking agent contains triallyl isocyanurate.

[0036] In the triazine crosslinking system, a crosslinking catalyst such as an organotin compound, an onium salt such as a quaternary phosphonium salt or a quaternary ammonium salt, urea, or silicon nitride is used.

[0037] Examples of crosslinking agents used in the oxazole crosslinking system include 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 preferably used.

[0038] The crosslinking agent used in the imidazole crosslinking system and the thiazole crosslinking system may be a conventionally known crosslinking agent, such as 3,3',4,4'-tetraaminobenzophenone or 3,3'-diaminobenzidine.

[0039] The content of the crosslinking agent (the total amount when 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, relative to 100 parts by mass of the total amount of the crosslinkable rubber components.

[0040] The content of the co-crosslinking agent (the total amount when two or more types are used) in the crosslinkable rubber composition is, for example, 0.5 to 10 parts by mass relative to 100 parts by mass of the total amount of the crosslinkable rubber components, and from the viewpoint of improving heat resistance, it is preferably 1 to 8 parts by mass.

[0041] The crosslinkable rubber composition may contain additives such as antioxidants, antioxidants, vulcanization accelerators, processing aids (such as stearic acid), stabilizers, tackifiers, silane coupling agents, plasticizers, flame retardants, mold release agents, waxes, and lubricants, as needed, for the purpose of improving processability and adjusting physical properties. Another example of an additive is a tackiness reducer (preventer) such as fluorine-based oil (such as perfluoroether). One type of additive may be used alone, or two or more types may be used in combination.

[0042] However, when the annular sealing material is used in a high-temperature environment, etc., there is a risk of volatilization, elution, or precipitation. Therefore, it is preferable that the amount of additives be 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 per 100 parts by mass of the total amount of the crosslinkable rubber component), and it is desirable that no additives are contained.

[0043] Furthermore, the crosslinkable rubber composition may contain at least one selected from the group consisting of a colorant and a filler, as needed. The colorant and the filler may each be used alone or in combination of two or more.

[0044] The colorant may be at least one selected from the group consisting of inorganic pigments and organic pigments. Examples of inorganic pigments include white pigments (e.g., silica, zinc oxide, white lead, lithopone, titanium dioxide, precipitated barium sulfate, and baryte powder), red pigments (e.g., red lead, iron oxide red), yellow pigments (e.g., yellow lead, zinc yellow), blue pigments (e.g., ultramarine blue, Prussian blue, YInMn blue), and black pigments (e.g., carbon black). Examples of organic pigments include azo pigments (azo lake pigments, insoluble azo pigments, condensed azo pigments, etc.); anthraquinone pigments, thioindigo pigments, perinone pigments, perylene pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, dioxazine pigments, quinophthalone pigments, and polycyclic pigments such as diketopyrrolopyrrole pigments; and phthalocyanine pigments. Organic pigments classified as pigments in the Color Index can be used. The pigment preferably used is an organic pigment that does not contain metal elements, because the organic pigment does not cause the scattering of substances derived from metal elements even when the sealing material is used in a severe ozone environment, such as for semiconductor applications, and the annular sealing material is etched.

[0045] The content of the colorant in the crosslinkable rubber composition (the total amount when two or more types are used) may be, for example, 0.01 parts by mass or more and less than 2 parts by mass, preferably 0.05 parts by mass or more and 1.5 parts by mass or less, and more preferably 0.1 parts by mass or more and 1 part by mass or less, per 100 parts by mass of the crosslinkable rubber component.

[0046] Examples of fillers that can be used include fluororesin, silica, alumina, zinc oxide, titanium oxide, 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 types can be used in combination. The content of the filler in the crosslinkable rubber composition (the total amount when two or more types are used) is, for example, 0.1 to 40 parts by mass per 100 parts by mass of the total amount of the crosslinkable rubber components. From the viewpoint of improving mechanical strength, the content is preferably 1 to 30 parts by mass, and more preferably more than 1 part by mass and 30 parts by mass. In this specification, the filler is distinguished from the organic pigments and inorganic pigments described above as colorants, and different types of fillers can be used.

[0047] When the crosslinkable rubber composition contains a fluororesin filler, the ozone resistance and mechanical strength of the crosslinked product can be further improved. The fluororesin can be contained in the crosslinkable rubber composition, for example, in the form of fluororesin particles.

[0048] The fluororesin used as a filler is a resin having fluorine atoms in the 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 (PVF), vinylidene fluoride-hexafluoropropylene copolymer (VDF-HFP copolymer), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE copolymer), etc. One type of fluororesin may be used alone, or two or more types may be used in combination.

[0049] Among the above, it is preferable to use fluororesins with a relatively high melting point, such as PFA and PTFE, from the viewpoint of preventing the resin from melting in a high-temperature environment and impairing properties such as compression set.

[0050] The fluororesin used as a filler may contain a functional group. The functional group can be introduced, for example, by copolymerizing a monomer having the functional group. When the above-mentioned crosslinking site monomer is copolymerized as the monomer having the functional group, crosslinking between the fluororesin and the perfluoroelastomer also proceeds with the crosslinking agent, thereby further increasing the mechanical strength of the crosslinked product of the perfluoroelastomer composition. An example of a fluororesin containing a functional group is nitrile group-containing polytetrafluoroethylene, as described in JP 2013-177631 A. The fluororesin may also be a modified fluororesin, such as "TFM-modified PTFE" (manufactured by Dyneon).

[0051] When the crosslinkable rubber composition contains a perfluoroelastomer and a fluororesin filler, for example, 1) a method of kneading a perfluoroelastomer powder and a fluororesin powder using a mixing roll, 2) a method of melt-kneading a perfluoroelastomer powder or pellets and a fluororesin powder or pellets using an apparatus such as a mixer or a twin-screw extruder, or 3) a method of adding a fluororesin at the stage of preparing the perfluoroelastomer, can be used to produce a perfluoroelastomer containing a fluororesin.

[0052] As the method 3) above, can be mentioned that the aqueous dispersion of perfluoroelastomer obtained by emulsion polymerization method and the aqueous dispersion of fluororesin are mixed, and then the mixture of perfluoroelastomer and fluororesin is obtained by co-coagulation.

[0053] The crosslinkable rubber composition can be prepared by uniformly kneading a crosslinkable rubber component, a colorant, a crosslinking agent, a co-crosslinking agent added as needed, a filler, and additives. Conventional kneaders such as a mixing roll, a pressure kneader, and an internal mixer (Banbury mixer) can be used as the kneader. The components may be mixed and kneaded at once, or they may be kneaded in multiple stages, such as first uniformly kneading the components excluding those that contribute to the crosslinking reaction (crosslinking accelerator, crosslinking retarder, crosslinking agent, etc.), and then kneading the components that contribute to the crosslinking reaction.

[0054] The method for manufacturing the annular sealing material 1 may include, for example, the following steps. A preforming process for preparing one or more rope-shaped preforms including 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 uncrosslinked core. The hot pressing process involves placing the two ends of the rope-shaped preform in contact with each other in a mold and then hot pressing the preform. The above explanation of the annular sealing material applies to the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer.

[0055] (Preforming process) The preforming step can include a step of extrusion molding a crosslinkable rubber composition for the core and a crosslinkable rubber composition for the outer layer. The rope-shaped preform 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 ribbon-shaped molded products, for example, with a width of 5 mm to 30 mm, using a cutter. The ribbon-shaped molded products of the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer are then placed in a screw-type extruder equipped with a crosshead and extruded into a rope-like shape, thereby obtaining a rope-shaped preform 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 the rope-like shape can be, for example, 100 mm / min to 1000 mm / min.

[0056] The cross-sectional diameter of the rope-shaped preform may be, for example, 3 mm to 50 mm, preferably 3 mm to 15 mm. The outer layer thickness of the rope-shaped preform may be, for example, 0.1 mm to 10 mm, preferably 0.2 mm to 3 mm. The length of the rope-shaped preform may be, for example, 100 mm to 5000 mm.

[0057] The ribbon-shaped molded product can also be produced by putting the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer into a plunger-type extruder and extruding them into a ribbon shape, without producing the above-mentioned sheet-shaped molded product.

[0058] The number of rope-shaped preforms to be prepared may be one, or two or more, for example, 3 to 10, and can be adjusted depending on the inner diameter and / or outer diameter of the annular sealing material.

[0059] (heat press process) In the heat press process, the uncrosslinked core and the uncrosslinked outer layer are press-molded while being heated to obtain an annular sealing material 1 consisting of a core 2 containing a crosslinked product of the crosslinkable rubber composition and an outer layer 3. The heating temperature in the heat press molding may be, for example, about 110°C or higher and 220°C or lower.

[0060] In the annular sealing material 1, one method for making the thickness T1 of at least a portion of the parting line of the outer layer 3 smaller than the thickness T2 of the portion without the parting line is to adjust the shape of the mouthpiece of the crosshead to prepare a rope-shaped preform in which the thickness of the outer layer is smaller at the 0° and 180° positions in the rope cross section, and then to place the rope-shaped preform in a mold so that the 0° and 180° positions become the parting lines. Another method is to adjust the amount of material input so that more flash is produced from the parting line.

[0061] In the heat-pressing process, the two ends of the rope-shaped preform may be brought into contact with each other using a mold with an annular cavity, followed by heat-pressing to produce an annular sealing material. Alternatively, a mold with a linear or arc-shaped cavity may be used to first heat-press the rope-shaped preform except for the ends to obtain a linear or arc-shaped body, and then the two ends of this linear or arc-shaped body are brought into contact at the joint, where they are heat-pressed to produce an annular sealing material. The embodiment 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 circumferential length of the joint may be, for example, 100 mm or more and 1200 mm or less. Feed-press molding will be described later.

[0062] In order to prevent cracking of the outer layer or protrusion of the core from the outer layer at the joint connecting the ends of the rope-like preform, the heat pressing process may further include a step (hereinafter also referred to as step a) of wrapping an uncrosslinked thin film layer 30 around the joint between the two ends of the contacted rope-like preform 11, as shown in Figure 3, before placing it in a mold having an annular cavity, or, if feed press molding is performed, before the second heat pressing process described below (before placing it in a mold having a linear or arc-shaped cavity).

[0063] 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 steps on the periphery of the rope-like preform 11.

[0064] The material constituting the uncrosslinked thin film layer 30 may be the above-mentioned outer layer crosslinkable rubber composition, and is preferably the same type of outer layer crosslinkable rubber composition as the outer layer crosslinkable rubber composition constituting the outer layer 12 of the rope-shaped preform 11.

[0065] The uncrosslinked thin film layer 30 can be obtained by forming the crosslinkable rubber composition for the outer layer into a sheet using a roll, cutting it into a ribbon-like molded product having a width of, for example, about 5 mm to 100 mm using a cutter, and further cutting it according to the length to be wound around the joint of the rope-like preform 11. Alternatively, the rope-like preform from which the core material has been removed can also be used as the uncrosslinked thin film layer 30.

[0066] In step a, the uncrosslinked thin film layer 30 may be wound one or more times around the joint of the rope-like preform 11. From the viewpoint of reducing the step on the outer periphery of the rope-like preform 11, it is preferable to wind the uncrosslinked thin film layer 30 one to two times around the joint of the rope-like preform 11.

[0067] In order to prevent the core from protruding from the joint, the method for producing the annular sealing material of the present invention can 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 preform 11, as shown in Figure 4a), before the heat pressing step or before the second heat pressing step described below.As shown in Figure 4b), by placing the two ends (outer layer 12) from which the uncrosslinked core has been removed in contact with each other in a mold and performing heat press molding, it is possible to more easily prevent the core from protruding from the joint.

[0068] Step b may be performed before the heat pressing step, and when feed press molding is performed, it may be performed before the first heat pressing step described below, or between the first heat pressing step and the second heat pressing step.

[0069] The uncrosslinked core 14 to be removed can be, for example, in the 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, nippers, or the like.

[0070] From the viewpoint of improving the bonding strength between the ends, the method for producing the annular sealing material of the present invention can further include a step (hereinafter also referred to as step c) of heating the two ends of the rope-shaped preform before the heat pressing step, or before the second heat pressing step described below when feed press molding is performed. After step c, the two ends of the rope-shaped preform are placed in a mold in contact with each other and heat press molding is performed, thereby strengthening the bonding strength between the ends and preventing the core from protruding.

[0071] In step c, as shown in FIG. 5a), a heater 20 is sandwiched between the two ends of the rope-like preform 11, and the end faces are heated and melted, and then the melted ends can be brought into contact with each other as shown in FIG. 5b).

[0072] From the viewpoint of preventing the core from protruding from the joint, the method for producing the annular sealing material of the present invention can further include, in the heat pressing step, or in the second heat pressing step described below when feed press molding is performed, a step (hereinafter also referred to as step d) of placing a connecting member 40 between two ends of a rope-like preform 11 to be placed in a mold, as shown in Fig. 6. The uncrosslinked outer layer 42 of the connecting member 40 is thicker than the uncrosslinked outer layer 12 of the rope-like preform 11, which makes it easier to prevent the core from protruding from the joint during heat pressing.

[0073] 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 10 or less. The length of the connecting member 40 in the circumferential direction can be, for example, about 5 mm or more and 100 mm or less.

[0074] From the viewpoint of reducing the step on the outer periphery of the annular sealing material, it is preferable that the cross-sectional diameter of the connecting member 40 is the same as or approximately the same as, or larger than, the cross-sectional diameter of the rope-shaped preform 11.

[0075] The connecting member 40 can include an uncrosslinked core 41 made of a crosslinkable rubber composition for the core described below, and an uncrosslinked outer layer 42 made of a crosslinkable rubber composition for the outer layer described below that covers the periphery of the uncrosslinked core 41. The material that makes up the uncrosslinked core 41 is preferably the same type of crosslinkable rubber composition for the core as the crosslinkable rubber composition that makes up the uncrosslinked core 13 of the rope-shaped preform 11. The material that makes up the uncrosslinked outer layer 42 is preferably the same type of crosslinkable rubber composition for the outer layer as the crosslinkable rubber composition that makes up the uncrosslinked outer layer 12 of the rope-shaped preform 11.

[0076] The method for producing the annular sealing material may further include a secondary crosslinking step after the heat pressing step to promote crosslinking of uncrosslinked or insufficiently crosslinked portions. The heating temperature in the secondary crosslinking step may be, for example, about 150°C or higher and 310°C or lower.

[0077] (Feed press molding) When feed press molding is performed in the hot pressing step, the feed press molding can include the following steps. A first heat pressing step in which the rope-shaped preform is placed in a first mold and the portion other than the end of the rope-shaped preform is heat-pressed. A second heat pressing step in which the two ends of the rope-shaped preform are placed in contact with each other in a second mold and heat-pressed.

[0078] In the first heat-pressing step, the portions of the rope-shaped preform other than the ends can be crosslinked. The first mold into which the rope-shaped preform is placed in the first heat-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 using a C-type press. The heat-press molding temperature in the first heat-pressing step can be, for example, about 110°C or higher and 220°C or lower.

[0079] Examples of methods for hot press molding portions other than the ends of the rope-like preform include a method of cooling the portion of the first mold corresponding to the end of the rope-like preform using a cooling device, etc. The length of the portion to be cooled can be the length in the circumferential direction of the end of the rope-like preform that will be left in an uncrosslinked or insufficiently crosslinked state, and may be, for example, 1 mm or more and 600 mm or less.

[0080] In the second heat-pressing step, the two ends of the rope-shaped preform are placed in contact with each other in a second mold, and heat-press molding is performed, thereby joining the ends of the rope-shaped preform in a crosslinked state. 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.

[0081] The second mold into which the two ends of the rope-like preform are placed can have a linear, arc-shaped cavity. The two ends of the rope-like preform placed in the second mold can each have a circumferential width of, for example, 50 mm to 600 mm. The two ends can be both ends of a single rope-like preform, or one end of each of two rope-like preforms.

[0082] The temperature for the heat press molding in the second heat press step may be, for example, about 110° C. or higher and 220° C. or lower. From the viewpoint of preventing cracks at the joints and protrusion of the core, the temperature for the heat press molding in the second heat press step is preferably lower than the temperature for the heat press molding in the first heat press step, and more preferably 5° C. or higher and 20° C. or lower than the temperature for the heat press molding in the first heat press step. [Example]

[0083] The present invention will be described in more detail below with reference to examples. In the examples, "%" and "parts" are by mass % and mass parts unless otherwise specified.

[0084] Example 1 A crosslinkable rubber composition for the outer layer was prepared by blending 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 the mixture using a kneader. Next, a crosslinkable rubber composition for the core was prepared by blending fluororubber with 1 part by mass of a crosslinking agent (Perhexa 25B), 3 parts by mass of a crosslinking aid (TAIC), and 0.1 parts by mass of a colorant (Cromphtal Violet D5700) per 100 parts by mass of fluororubber and kneading the mixture using a kneader. Next, the crosslinkable rubber composition for the outer layer and the crosslinkable rubber composition for the core were each formed into a sheet with a thickness of approximately 3 mm using a roller and cut into ribbons with a width of approximately 15 mm using a cutter. The cross-linkable rubber composition for the outer layer and the cross-linkable rubber composition for the core, both formed into ribbon shapes, were fed into a screw extruder equipped with a crosshead to produce five rope-shaped preforms having a two-layer structure consisting of an outer layer made of the cross-linkable rubber composition for the outer layer and a core made of the cross-linkable rubber composition for the core. The cross-sectional diameter of the rope-shaped preforms was approximately 7.15 mm, the outer layer thickness was approximately 1.2 mm, and the length was 800 mm.

[0085] Next, each of the five rope-shaped preforms was placed in a straight first mold (length 800 mm, cavity dimension 7 mm), and while cooling both ends (one end width 100 mm) so that they were in an uncrosslinked state, the rest was hot-press molded using a C-type press at a temperature of 165°C.

[0086] After the hot press molding, one end of each of the two rope-shaped preforms was brought into contact with the other, and then the two were placed in a second mold for joining, 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-shaped preforms, and five rope-shaped preforms were joined together. Then, secondary crosslinking was performed at a temperature of 200°C to obtain an annular sealing material.

[0087] The resulting annular sealing material had parting lines on the outer and inner peripheral sides, with the thickness of the outer layer where the parting lines were present being 200 μm and the thickness of the outer layer where there were no parting lines being 1200 μm, resulting in a ratio of the thickness of the outer layer where there were no parting lines to the thickness of the outer layer where there were no parting lines being 6 / 1. The resulting annular sealing material also had an outer diameter of 1194 mm in plan view, an inner diameter of 1180 mm, and a cross-sectional diameter of 7 mm. The annular sealing material's parting line was easily visible because the core could be seen through the outer layer at the parting line, and it could be easily installed in the device without twisting or sagging. [Explanation of symbols]

[0088] 1 Annular sealing material, 2 Core, 3 Outer layer, 11 Rope-shaped preform, 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, T Thickness of outer layer, T1 Thickness of part of outer layer where parting line is present, T2 Thickness of part of outer layer where parting line is not present, D1 Outer diameter, D2 Inner diameter, D3 Diameter of cross section.

Claims

1. An annular sealing material including a core and an outer layer covering the periphery of the core, the annular sealing material having parting lines on the outer diameter side and the inner diameter side, the thickness of the outer layer at least in a portion where the parting line exists is smaller than the thickness of the outer layer in a portion where the parting line does not exist, the core and the outer layer are made of a cross-linked product of a cross-linkable rubber composition, The annular sealing material, wherein the core contains an organic pigment.

2. The thickness of the outer layer and the thickness of the parting line-free portion are 0.3 mm or more and 3 mm or less, 2. The annular sealing material according to claim 1, wherein a thickness of the outer layer at a parting line is 0.1 mm or more and 1.5 mm or less.

3. 3. The annular sealing material according to claim 1, wherein the outer layer is made of a cross-linked product of a cross-linkable rubber composition containing at least one selected from the group consisting of perfluoroelastomers and fluororubbers, and the core is made of a cross-linked product of a cross-linkable rubber composition containing at least one selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers.

4. A method for manufacturing the annular sealing material according to any one of claims 1 to 3, a preforming step of preparing one or more rope-shaped preforms including an uncrosslinked core made of a crosslinkable rubber composition for a core and an uncrosslinked outer layer made of a crosslinkable rubber composition for an outer layer covering the periphery of the uncrosslinked core; a heat press molding step in which the two ends of the rope-shaped preform are brought into contact with each other and placed in a mold, and heat press molding is performed; A method for manufacturing an annular sealing material, comprising:

5. 5. The method for producing an annular sealing material according to claim 4, wherein the step of preparing the rope-shaped preform includes a step of extrusion molding the core crosslinkable rubber composition and the outer layer crosslinkable rubber composition.

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