Annular seal material and manufacturing method

Abstract

To provide a manufacturing method capable of mass-producing an annular seal material composed of a middle core and an outer layer, at low cost.SOLUTION: A method for manufacturing an annular seal material comprising a middle core and an outer layer surrounding the middle core, comprises: a preforming step of preparing one or more rope-like preforms composed of an uncrosslinked middle core made of a crosslinkable rubber composition for a middle core, and an uncrosslinked outer layer made of a crosslinkable rubber composition for an outer layer that covers the periphery of the uncrosslinked middle core; a first hot press step of installing the rope-like preform in a first mold, and hot press-molding a portion of the rope-like preform other than its end part; and a second heat press step of installing two end parts of the rope-like preforms in contact with each other in a second mold, and hot press-molding them.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] Patent Document 1 describes a method for manufacturing a composite structure O-ring, in which a composite structural material is produced by inserting a string-shaped inner layer into the internal space of a tubular outer layer, cutting the composite structural material, setting it in an O-ring mold, and then setting a string-shaped piece of material used for the outer layer in the gap between the cut surfaces of the composite structural material, and molding it under pressure and heat.

[0003] Patent Document 2 describes a method for manufacturing a composite structure O-ring, in which two covering materials are preformed using a core of approximately the same shape as the core material, the core is removed, and then a supercritically extracted O-ring-shaped rubber core material is inserted into the hollow space and molded integrally with the covering materials.

[0004] Patent Document 3 describes a method for manufacturing an O-ring with a two-layer structure, characterized in that a string-like body consisting of an outer layer and an inner layer is extruded and hot-pressed to simultaneously vulcanize the inner and outer layers.

[0005] Patent Document 4 describes two methods for manufacturing O-rings having a two-layer structure: one method in which an outer layer material containing a perfluoroelastomer is wound in the form of a ribbon around a core material and then heated and pressurized; and another method in which the outer layer material is frozen and crushed to form particles, which are then attached to a core material and then heated and pressurized. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4148493 [Patent Document 2] Japanese Patent Publication No. 10-323847 [Patent Document 3] Japanese Patent Publication No. 10-52885 [Patent Document 4] Japanese Patent Application Publication No. 10-329271 Summary of the Invention [Problem to be solved by the invention]

[0007] In the manufacturing method described in Patent Document 1, the outer layer material may break when the outer layer is inflated. Furthermore, because a connecting member made of the outer layer material is placed at the seam, the layer structure at the seam does not have a two-layer structure. Furthermore, the process is complicated and costly.

[0008] 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 a mold.

[0009] In the manufacturing method described in Patent Document 3, the inner layer portion may protrude from the joint during molding in a mold.

[0010] 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 a mold because wrinkles form on the curved portion of the inner diameter of the O-ring. Also, there is a high possibility that the core material will protrude from the gaps in the ribbon, making it difficult to prevent this. Furthermore, when the outer layer material is frozen and crushed into particles and then attached to the core material, it is difficult to completely cover the core because the particles alone do not adhere to the core material.

[0011] As described above, a manufacturing method that can mass-produce annular sealing materials composed of a core and an outer layer at low cost has not yet been established.

[0012] An object of the present invention is to provide a method for mass-producing annular sealing materials each composed of a core and an outer layer at low cost. Another object of the present invention is to provide a method for manufacturing an annular sealing material consisting of a core and an outer layer, which can suppress cracking of the outer layer and protrusion of the core at the joint. [Means for solving the problem]

[0013] The present invention provides the following annular sealing material and a method for producing the same. [1] A method for manufacturing an annular sealing material including a core and an outer layer covering the periphery of the core, 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 first heat pressing step of placing the rope-shaped preform in a first mold and heat-pressing the rope-shaped preform except for its end portions; a second heat pressing step in which the two ends of the rope-shaped preform are placed in a second mold in contact with each other and heat-pressed; A method for manufacturing an annular sealing material, comprising the steps of: [2] The method for producing an annular sealing material according to [1], wherein the preforming step includes a step of extrusion molding the core crosslinkable rubber composition and the outer layer crosslinkable rubber composition. [3] A method for manufacturing an annular sealing material described in [1] or [2], wherein the ratio of the diameter of the cavity of the second mold to the diameter of the cavity of the first mold in the cross section of the first mold and the second mold is 1.004 or more and 1.10 or less. [4] The method for producing an annular sealing material according to any one of [1] to [3], wherein the temperature of the heat press molding in the second heat press step is lower than the temperature of the heat press molding in the first heat press step. [5] A method for producing an annular sealing material according to any one of [1] to [4], further comprising a step of removing the uncrosslinked core from the two ends of the rope-shaped preform before the second heat pressing step. [6] The method for producing an annular sealing material according to any one of [1] to [5], further comprising a step of heating two ends of the rope-shaped preform before the second heat pressing step. [7] A method for producing an annular sealing material according to any one of [1] to [6], further comprising a step of wrapping an uncrosslinked thin film layer around the seam of the two ends of the rope-shaped preform that are in contact with each other before placing the rope-shaped preform in the second mold in the second hot pressing step, and a crosslinkable rubber composition for an outer layer is used as a material for constituting the uncrosslinked thin film layer. [8] The second hot pressing step further includes a step of placing a connecting member between two ends of the rope-shaped preform and placing the rope-shaped preform in a second mold; The method for manufacturing an annular sealing material described in any one of [1] to [7], wherein 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 that covers the uncrosslinked core, and the uncrosslinked outer layer of the connecting member is thicker than the uncrosslinked outer layer of the rope-shaped preform. [9] A method for manufacturing an annular sealing material described in any one of [1] to [8], wherein in the second hot pressing process, the two ends of the rope-shaped preform placed in the second mold each have a width in the circumferential direction of 50 mm or more and 600 mm or more.

[10] The method for producing an annular sealing material according to any one of [1] to [9], wherein two or more of the rope-shaped preforms are connected in the second hot pressing step.

[11] The method for producing an annular sealing material according to any one of [1] to

[10] , wherein the crosslinkable rubber composition for the outer layer contains at least one selected from the group consisting of perfluoroelastomers and fluororubbers, and the core contains at least one selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers.

[12] An annular sealing material that is a heat-pressed product of two or more rope-shaped preforms, The two or more rope-shaped preforms have a joint portion, An annular sealing material, wherein the ratio of the cross-sectional diameter of the joint portion to the cross-sectional diameter of the portion other than the joint portion is 1.004 or more and 1.10 or less. [Effects of the Invention]

[0014] According to the present invention, there is provided a method for manufacturing an annular sealing material composed of a core and an outer layer, which can suppress cracking of the outer layer and protrusion of the core at the joint. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows a schematic cross-sectional view of an annular sealing material. [Figure 2] 3A and 3B are schematic plan views of the annular sealing material in the circumferential direction at a joint portion and a portion other than the joint portion of the 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

[0016] 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.

[0017] <Method of manufacturing annular sealing material> The method for manufacturing an annular sealing material of the present invention is a method for manufacturing an annular sealing material comprising a core and an outer layer covering the periphery of the core, and comprises, in this order: a pre-molding step for preparing one or more rope-shaped preforms 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 covering the periphery of the uncrosslinked core; a first heat-pressing step for placing the rope-shaped preform in a first mold and heat-pressing the portion other than the ends of the rope-shaped preform; and a second heat-pressing step for placing the two ends of the rope-shaped preform in contact with each other and placing it in a second mold and heat-pressing.

[0018] The annular sealing material includes a core and an outer layer that covers the periphery of the core, and the core and outer layer include crosslinked products of crosslinkable rubber compositions that have different colors after heat pressing or secondary crosslinking.

[0019] FIG. 1 shows a cross section of an annular sealing material. The annular sealing material 1 shown in FIG. 1(a) 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 section, but may have other cross sections depending on the application. In the present invention, the cross-sectional diameter of the annular sealing material 1 is dimension D, and the thickness of the outer layer 3 is dimension T [FIG. 1(b)].

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

[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 thickness 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] (Preforming process) The rope-shaped preform can be produced by extrusion molding the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer (hereinafter, when referring to both, they are also referred to as the crosslinkable rubber composition) described below.

[0023] Extrusion molding can be performed, for example, as follows. First, the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer are each formed into a sheet using a roll to produce a sheet-like molded product. The thickness of the sheet-like molded product may be, for example, 1 mm to 5 mm. Next, the sheet-like molded product is cut into ribbon-like molded products, for example, with a width of 5 mm to 30 mm, using a cutter. Thereafter, the ribbon-like molded products of the crosslinkable rubber composition for the core and the crosslinkable rubber composition for the outer layer are placed in a screw-type extruder equipped with a crosshead and extruded, thereby obtaining a rope-like preform having a two-layer structure in which the outer layer is composed of the crosslinkable rubber composition for the outer layer and the core is composed of the crosslinkable rubber composition for the core. The extrusion speed can be, for example, about 100 mm / min to 1000 mm / min.

[0024] The cross-sectional diameter 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.

[0025] 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.

[0026] 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.

[0027] (First heat press process) 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.

[0028] 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.

[0029] (Second heat press process) In the second heat-pressing step, the rope-shaped preform is placed in a second mold with its two ends in contact and then heat-pressed, thereby joining the ends of the rope-shaped preform in a crosslinked state. An annular sealing material can be obtained by repeatedly joining the ends of two or more rope-shaped preforms, or by joining the ends of a single rope-shaped preform. The mode of bringing the two ends into contact includes a state in which the two end faces of the rope-shaped preform are in contact.

[0030] The second mold into which the two ends of the rope-like preform are placed can have a linear or arc-shaped cavity. Each of the two ends of the rope-like preform placed in the second mold can 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.

[0031] By making the cavity size (cavity diameter) of the second mold larger than that of the first mold, it becomes easier to suppress cracking of the outer layer and protrusion of the core at the joint formed by the two ends of the contacting rope-like preform (hereinafter also referred to as the joint).The ratio of the cavity size of the second mold to the cavity size of the first mold is preferably 1.004 or more and 1.10 or less, and more preferably 1.008 or more and 1.05 or less.

[0032] An annular sealing material manufactured using a second mold having a larger cavity size than a first mold tends to have a larger cross-sectional diameter at the joints formed by heat press molding using the second mold than at the other portions. The ratio of the cross-sectional diameter of the joints to the cross-sectional diameter of the other portions of the rope-shaped preform may be, for example, 1.004 or more and 1.10 or less, and preferably 1.008 or more and 1.05 or less. The annular sealing material may have one joint, or two or more. When there are multiple joints, the cross-sectional diameters of the joints and the other portions are the average of the cross-sectional diameters of the respective joints. The length in the circumferential direction of the joints may be, for example, 100 mm or more and 1200 mm or less.

[0033] Another aspect of the present invention is an annular sealing material that is a heat-pressed product of a rope-shaped preform, wherein the heat-pressed product has a joint of the rope-shaped preform, and the ratio of the cross-sectional diameter of the joint to the cross-sectional diameter of the parts other than the joint is 1.004 or more and 1.10 or less.

[0034] Fig. 2 is a schematic plan view showing a joint portion and a portion other than the joint portion of an annular sealing material. Annular sealing material 50 shown in Fig. 2 has joint portion 52 and portion 51 other than joint portion 52, which have different cross-sectional diameters. The ratio of the cross-sectional diameter of joint portion 52 to the cross-sectional diameter of portion 51 other than joint portion 52 is preferably 1.008 or more and 1.05 or less.

[0035] In the joint 52 of the annular sealing material 50 and the portion 51 other than the joint 52, the average ratio of the thickness of the outer layer to the total thickness in the cross section and the thickness of the outer layer can be within the ranges and preferred ranges exemplified above, respectively.

[0036] 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.

[0037] (Other processes) 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 a) of removing the uncrosslinked core 14 from the two ends of the rope-shaped preform 11, as shown in Figure 3a), before the second heat-pressing step.As shown in Figure 3b), the two ends (outer layer 12) from which the uncrosslinked core has been removed are brought into contact and placed in a second mold for heat-pressing, which makes it easier to prevent the core from protruding from the joint.

[0038] Step a may be carried out before the first heat pressing step or after the first heat pressing step.

[0039] 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.

[0040] The method for producing the annular sealing material of the present invention can further include a step of heating the two ends of the rope-shaped preform before the second heat-pressing step (hereinafter also referred to as step b), from the viewpoint of improving the bond between the ends. After step b, the two ends of the rope-shaped preform are brought into contact with each other and placed in a second mold for heat-pressing, thereby strengthening the bond between the ends and making it easier to prevent the core from protruding.

[0041] In step b, as shown in FIG. 4a), a heater 20 is sandwiched between the two ends of the rope-shaped preform 11 after the first heat pressing step, and the end faces are heated and melted, and then the melted ends can be joined together as shown in FIG. 4b).

[0042] In order to prevent cracking of the outer layer and protrusion of the core at the joint, the method for manufacturing the annular sealing material of the present invention can further include a step (hereinafter also referred to as step c) 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 5, before placing it in the second mold in the second hot pressing step.

[0043] 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.

[0044] The material constituting the uncrosslinked thin film layer 30 is a crosslinkable rubber composition for the outer layer described later, and is preferably the same type of crosslinkable rubber composition for the outer layer as the crosslinkable rubber composition for the outer layer constituting the outer layer 12 of the rope-shaped preform 11.

[0045] 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.

[0046] In step c), 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.

[0047] 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 second heat pressing step, a step (hereinafter also referred to as step d) of placing a connecting member 40 between two ends of the rope-like preform 11 placed in the second mold, as shown in Fig. 6. If the uncrosslinked outer layer 42 of the connecting member 40 is thicker than the uncrosslinked outer layer 12 of the rope-like preform 11, it can be easier to prevent the core from protruding from the joint during heat pressing.

[0048] 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 to 10. 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.

[0049] From the viewpoint of reducing the step, 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.

[0050] 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.

[0051] The method for producing the annular sealing material may further include a secondary crosslinking step after the second 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 to 310°C.

[0052] (Crosslinkable Rubber Composition) The crosslinkable rubber composition may contain a crosslinkable rubber component. The crosslinkable rubber component is capable of forming an elastomer (crosslinked rubber) having the above-mentioned 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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:

[0060] 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.

[0061] The crosslinkable perfluoroelastomer may have a crosslinked structure that crosslinks two main chains.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] Furthermore, the crosslinkable rubber composition may contain, as needed, a colorant (e.g., inorganic pigment, organic pigment, etc.) and a filler (e.g., 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, ceramic powder, etc.). Only one type of filler may be used, or two or more types may 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, it is preferably 1 to 30 parts by mass, and more preferably more than 1 part by mass and 30 parts by mass or less. In this specification, the filler is distinguished from the organic pigments and inorganic pigments described above as colorants, and a filler of a different type from the organic pigments and inorganic pigments can be used.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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).

[0080] 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.

[0081] 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.

[0082] 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. [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 a 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 the perfluoroelastomer and kneading the mixture using a kneader. Next, a crosslinkable rubber composition for the core was prepared by blending a 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 the 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 roll 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 mm, the outer layer thickness was approximately 1 mm, and the length was 800 mm.

[0085] Next, each of the five rope-shaped preforms was placed in a straight-type first mold (length 800 mm, cavity dimensions 7.1 mm). While cooling both ends (one end width 100 mm) so that they remained uncrosslinked, the remaining ends were hot-press molded using a C-type press at 165°C. The two hot-press molded rope-shaped preforms were then placed in a second joint mold (length 400 mm, cavity dimensions 7.2 mm) with one end of each in contact and hot-press molded at 155°C. The same procedure was performed on the remaining ends of the rope-shaped preforms, joining the five rope-shaped preforms to obtain an annular sealing material. The resulting annular sealing material was subjected to secondary crosslinking at 200°C. It was confirmed that the resulting annular sealing material did not protrude from the outer layer of the core at the joint. The resulting annular sealing material had a cross-sectional diameter of 7.1 mm at the joint and a cross-sectional diameter of 7.0 mm elsewhere. [Explanation of symbols]

[0086] 1,50 Annular sealing material, 2 Core, 3,53 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, 51 Portion other than joint, 52 Joint, T Thickness of outer layer, D Diameter of cross section.

Claims

1. A method for manufacturing an annular sealing material including a core and an outer layer covering the periphery of the core, 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 first heat pressing step of placing the rope-shaped preform in a first mold and heat-pressing the rope-shaped preform except for its end portions; a second heat pressing step in which the two ends of the rope-shaped preform are placed in a second mold in contact with each other and heat-pressed; A method for manufacturing an annular sealing material, comprising the steps of:

2. The method for producing an annular sealing material according to claim 1 , wherein the preforming step includes a step of extrusion molding the core crosslinkable rubber composition and the outer layer crosslinkable rubber composition.

3. 3. The method for manufacturing an annular sealing material according to claim 1, wherein the ratio of the diameter of the cavity of the second mold to the diameter of the cavity of the first mold in the cross sections of the first mold and the second mold is 1.004 or more and 1.10 or less.

4. The method for manufacturing an annular sealing material according to any one of claims 1 to 3, wherein a temperature of the heat press molding in the second heat press step is lower than a temperature of the heat press molding in the first heat press step.

5. The method for manufacturing an annular sealing material according to any one of claims 1 to 4, further comprising a step of removing the uncrosslinked core from two ends of the rope-shaped preform before the second heat pressing step.

6. The method for producing an annular sealing material according to any one of claims 1 to 5, further comprising a step of heating two ends of the rope-shaped preform before the second heat pressing step.

7. 7. The method for producing an annular sealing material according to claim 1, further comprising the step of winding an uncrosslinked thin film layer around the seam between the two ends of the rope-shaped preform that are in contact with each other before placing the rope-shaped preform in the second mold, and a crosslinkable rubber composition for an outer layer is used as a material for constituting the uncrosslinked thin film layer.

8. The second hot pressing step further includes a step of disposing a connecting member between two ends of the rope-shaped preform and placing the rope-shaped preform in a second mold; A method for manufacturing an annular sealing material described in any one of claims 1 to 7, wherein 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 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 preform.

9. A method for manufacturing an annular sealing material according to any one of claims 1 to 8, wherein in the second hot pressing step, the two ends of the rope-shaped preform placed in the second mold each have a width in the circumferential direction of 50 mm to 600 mm.

10. The method for producing an annular sealing material according to any one of claims 1 to 9, wherein two or more rope-shaped preforms are connected in the second hot pressing step.

11. The method for producing an annular sealing material according to any one of claims 1 to 10, wherein the cross-linkable rubber composition for the outer layer comprises at least one selected from the group consisting of perfluoroelastomers and fluororubbers, and the core comprises at least one selected from the group consisting of perfluoroelastomers, fluororubbers, silicone rubbers, and fluorosilicone rubbers.

12. An annular sealing material that is a hot press molded product of a rope-shaped preform, the hot-press molded product has a joint portion of the rope-shaped preform, An annular sealing material, wherein the ratio of the cross-sectional diameter of the joint portion to the cross-sectional diameter of the portion other than the joint portion is 1.004 or more and 1.10 or less.

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