WO2023249010A1

WO2023249010A1 - Seal ring

Info

Publication number: WO2023249010A1
Application number: PCT/JP2023/022747
Authority: WO
Inventors: 真也小田
Original assignee: Ntn株式会社
Priority date: 2022-06-21
Filing date: 2023-06-20
Publication date: 2023-12-28
Also published as: JP2024000928A

Abstract

Provided is a seal ring having improved resistance when assembled into an annular groove even if the seal ring is a small-diameter PPS seal ring. This seal ring 1 is a molded article of a polyphenylene sulfide resin composition and has a joint 5 in one location. The seal ring 1 also has, on both sides of a joint-opposing part 5F, thin-walled parts 6 where the radial-direction thickness of the ring is reduced at a ring inner peripheral surface 3, the thin-walled parts having a bending elastic modulus of 10,000 Mpa or less and a bending strain exceeding 2.0%. The radial-direction thickness of the thin-walled parts is 50-70% of the radial-direction thickness of the joint-opposing part 5F.

Description

Seal ring

The present invention is intended for sealing fluid in devices that utilize the fluid pressure of fluids such as hydraulic oil, such as automatic transmissions (hereinafter referred to as AT) and continuously variable transmissions (hereinafter referred to as CVT). Concerning the seal ring used.

In equipment such as ATs and CVTs, seal rings are installed at key points to seal hydraulic oil. For example, the seal ring is attached to a pair of spaced apart annular grooves provided on the rotating shaft that is inserted into the shaft hole of the housing, and the hydraulic oil supplied from the oil passage between the two annular grooves is supplied to the side and inner peripheral surfaces of both seal rings. The side wall of the annular groove and the inner circumferential surface of the housing are sealed by the opposite side surface and outer circumferential surface. Each sealing surface of the seal ring is in sliding contact with the side wall of the annular groove and the inner circumferential surface of the housing, respectively, and maintains the hydraulic pressure of the hydraulic oil between both seal rings.
When assembling the seal ring into the annular groove, it is necessary to expand the inner diameter of the seal ring to be larger than the outer diameter of the rotating shaft by widening the abutment of the seal ring. When the diameter of the seal ring is expanded, stress may be concentrated at the position facing the abutment.

In recent years, as equipment has become smaller, seal rings have tended to become smaller in diameter. Regarding small-diameter seal rings, for example, Patent Document 1 describes a seal ring that suppresses problems due to diameter expansion when assembling the small-diameter ring to a rotating shaft by providing a thin-walled portion on the inner diameter portion of the seal ring. There is.

Patent No. 4500007

In recent years, seal rings made of polyphenylene sulfide (hereinafter referred to as "PPS") resin, which has excellent wear resistance, have been adopted in locations where the limiting PV value (product of circumferential speed (V) and surface pressure (P)) is low. is increasing. For example, in the case of a small-diameter seal ring with an outer diameter of 30 mm or less, even if a relatively flexible (low elastic) material is used, the resistance is poorer than that of a seal ring with an outer diameter of more than 30 mm. Therefore, a small-diameter seal ring made of PPS resin, which is a relatively highly elastic resin material (hereinafter referred to as a small-diameter PPS seal ring), is required to further improve its resistance to diameter expansion.

The present invention has been made to address such problems, and an object of the present invention is to provide a seal ring with improved durability when incorporated into an annular groove, even if it is a small diameter PPS seal ring.

The seal ring of the present invention is a seal ring having one joint, which is a molded product of a polyphenylene sulfide resin composition, and has a bending modulus of elasticity of 10,000 MPa or less and a bending strain of more than 2.0%. It has a thin wall portion that reduces the radial thickness of the ring on both sides of the inner circumferential surface of the ring at a position facing the abutment, and the radial thickness of the thin wall portion is equal to It is characterized by being 50% to 70% of the radial thickness. Here, the thin-walled portions on both sides of the position facing the abutment are formed in areas separated from each other.

The seal ring is characterized in that it has a bending modulus of elasticity of 8500 MPa or less and a bending strain of 2.5% or more.

The above seal ring is characterized in that its outer diameter is φ30 mm or less.

The seal ring is an injection molded product, and is characterized by having gate marks during injection molding at a position opposite to the abutment.

The seal ring has an outer diameter of φ30 mm or less, a bending modulus of elasticity of 8,500 MPa or less, and a bending strain of 2.5% or more, and is an injection molded product, and the gate marks from injection molding are removed from the abutment. It is characterized in that it is located at opposing positions.

The seal ring of the present invention is a seal ring having one joint, which is a molded product of a polyphenylene sulfide resin composition, and has a bending modulus of elasticity of 10,000 MPa or less and a bending strain of more than 2.0%. Therefore, it has excellent toughness. In addition, there is a thin part that reduces the radial thickness of the ring on the inner peripheral surface of the ring on both sides of the position facing the joint (hereinafter referred to as the joint facing part), and the radial thickness of the thin part is Since it is 50% to 70% of the radial thickness of the mouth-facing portion, stress easily escapes to the thin-walled portion when the ring diameter is expanded. Thereby, even if the PPS seal ring has a small diameter, it is possible to improve the durability when assembling it into the annular groove.

Since the seal ring has an outer diameter of φ30 mm or less, it can be applied to smaller devices.

The seal ring is an injection molded product, and even if it has gate marks from injection molding on the part facing the abutment, it is difficult for force to concentrate around the gate marks, which are weak in strength, when the ring diameter is expanded. It is possible to suppress the concentration of force around the gate mark due to the diameter expansion of the ring during assembly. Moreover, a seal ring with good molding balance can be obtained.

FIG. 2 is a plan view showing an example of a seal ring of the present invention. FIG. 2 is an enlarged view of part A of the seal ring in FIG. 1; FIG. 2 is a perspective view of the seal ring of FIG. 1; FIG. 2 is a side view of an assembly jig and a schematic diagram of a jig passing test. It is a top view which shows the shape of the seal ring after heat setting.

An example of the seal ring of the present invention will be explained based on FIGS. 1 and 2. FIG. 1 is a plan view of the seal ring, and FIG. 2 is an enlarged view of portion A in FIG. The seal ring 1 shown in FIG. 1 is an annular body having a perfect circular outer diameter and a substantially rectangular cross section. The ring outer peripheral surface 2 and the ring inner peripheral surface 3 are surfaces parallel to the axial direction of the seal ring 1. The corners of the ring inner circumferential surface 3 and the ring side surfaces 4 (both side surfaces) may be chamfered in a straight or curved manner.

The seal ring 1 is a cut-type PPS resin ring having one abutment 5 in which both ends in the circumferential direction face each other, and is expanded in diameter by elastic deformation and is installed in an annular groove of a rotating shaft. . The seal ring 1 is set to have approximately the same outer diameter as the sealing surface (inner wall of the housing) in a free state without being subjected to external force, and is brought into close contact with the sealing surface by the pressure of the sealing fluid. Although the shape of the joint 5 can be a straight cut shape, an angle cut shape, etc., it is preferable to adopt the compound step cut shape shown in FIG. 1 because it has excellent sealing properties for the sealing fluid.

The seal ring 1 is provided with a plurality of V-shaped recesses 4a along the ring circumferential direction at the inner diameter side ends of both side surfaces 4 of the ring. In the seal ring 1, one of the ring side surfaces 4 is a sliding surface with the side wall surface of the annular groove, and the V-shaped recess 4a formed in the ring side surface 4 (sliding surface) is a non-contact part with the side wall surface. becomes. By providing the recess 4a, fluid can appropriately flow out to the sliding surface through the recess. Specifically, the boundary between the sliding surface X between adjacent recesses 4a and the recess 4a has a continuous shape, and the boundary between the sliding surface Y on the outer diameter side of the recess 4a and the recess 4a has a continuous shape. Because of the discontinuous shape (steps), fluid easily flows out to the sliding surface X, and fluid flows out less easily to the sliding surface Y compared to the sliding surface X. When the fluid flows out onto the sliding surfaces X and Y, a fluid film such as an oil film is formed on the sliding surfaces, thereby reducing rotational torque and wear. Moreover, by suppressing the outflow to the sliding surface Y, it leads to low leakage performance. This recess can be formed on one or both sides of the ring, as required. Note that the shape of the recess may be other than the above shape.

The seal ring 1 has a plurality of thin portions 6 on the inner peripheral surface side of the ring to reduce the radial thickness (hereinafter also simply referred to as "thickness") of the ring. The thin portion 6 is formed by reducing the radial thickness while maintaining the outer diameter of the seal ring 1. The radial thickness of the portion other than the thin portion 6 is a non-thin portion 7 which is thicker than the thin portion 6. The abutment facing portion 5F of the seal ring 1 is a non-thin portion 7, and thin portions 6 are formed on both sides in the circumferential direction. The non-thin portions 7 are formed between the thin portions 6 adjacent to each other in the circumferential direction, and are formed in the same number or approximately the same number as the thin portions 6. The thin portions 6 and the non-thin portions 7 are provided alternately along the ring circumferential direction. Note that the number of thin portions 6 and non-thin portions 7 is not limited to the configuration shown in FIG. 1 . In FIG. 1, the side surface of the stepped portion 71 of the non-thin portion 7 is formed at a lower position (thinner width) than the ring side surface 4, but it may be an extension surface of the ring side surface 4. When the non-thin portion 7 is formed to have a small width in the axial direction, the non-thin portion 7 is configured not to come into contact with the side wall surface of the annular groove. Further, this may be used as a protruding surface during injection molding of the seal ring 1. In the seal ring 1 of FIG. 1, the thickness of the thin portion 6 and the thickness of the non-thin portion 7 are each constant.

Note that the thickness of the thin portion 6 and the thickness of the non-thin portion 7 may not be constant. In this specification, when the thickness of one thin portion 6 is not constant, the thickness of the thin portion 6 is defined as the thickness of the region where the thickness of the thin portion 6 is the smallest. When the thickness of one non-thin part 7 is not constant, the thickness of the non-thin part 7 is the thickness of the region where the non-thin part 7 has the largest thickness. Note that the center point of the outer diameter of the seal ring 1 and the center point of the inner diameter of the non-thin portion 7 are the same.

As mentioned above, the thickness of the seal ring 1 is partially reduced while maintaining the outer diameter. In other words, only the inner diameter of the seal ring 1 is enlarged and the thickness is partially reduced, so that the inner circumferential surface of the housing can maintain adhesion with the material, and sealing performance is less likely to deteriorate. Furthermore, since the amount of strain generated in the thin portion is reduced, resistance to diameter expansion can be improved.

As shown in FIG. 2, in the seal ring of the present invention, the thickness B of the thin portion 6 is 50% to 70% of the thickness C of the non-thin portion 7. By setting the ratio of these thicknesses within a predetermined numerical range, it is possible to improve resistance to diameter expansion, as shown in Examples described later. Further, the thickness B of the thin portion 6 is preferably 55% to 70% of the thickness C of the non-thin portion 7, and more preferably 55% to 65%. Further, the thickness B of the thin portion 6 is specifically 0.9 mm to 2.3 mm.

The step portion 71 located in the non-thin portion 7 on the inner peripheral side of the virtual curved surface obtained by extending the ring inner peripheral surface 3 of the thin portion 6 will be described. The stepped portion 71 has an upper curved surface 71a disposed on the inner circumferential side and a lower curved surface 71b disposed on the outer circumferential side at one end in the circumferential direction, and similarly has an upper curved surface 71a at the other end. A lower curved surface 71b is formed. At each end, the upper curved surface 71a and the lower curved surface 71b are connected via a plane. Note that the upper curved surface 71a and the lower curved surface 71b may be directly connected to each other without using a plane. Further, one end portion and the other end portion of the stepped portion 71 may be formed only of a flat surface instead of a curved surface.

The axial width of the stepped portion will be explained based on FIG. 3. 3(a) is a perspective view of the seal ring shown in FIG. 1, and FIG. 3(b) is an enlarged view of portion D in FIG. 3(a). As shown in FIG. 3(b), the side surface 71c of the stepped portion 71 in the non-thin portion 7 is a concave surface formed lower than the ring side surface 4 by a depth E. As shown in FIG. Since both side surfaces of the stepped portion 71 are formed to be lower than the ring side surface 4 by a depth E, the width of the stepped portion 71 is smaller than the width of the thin portion 6 by 2E. Note that the two

side surfaces

71c, 71c of the stepped portion 71 may be formed to have different depths from the ring side surface 4, and only one side surface may be a concave surface and the other side surface may be an extension surface of the ring side surface 4. . Further, it is not necessary to form concave surfaces on both side surfaces.

The PPS resin composition forming the seal ring of the present invention has a bending elastic modulus of 10,000 MPa or less and a bending strain of more than 2.0%. By having such bending characteristics, the seal ring can be elastically deformed when assembled, and durability can be improved. From the viewpoint of durability, the flexural modulus is preferably 8,500 MPa or less, more preferably 7,000 MPa or less, and even more preferably 5,500 MPa or less. On the other hand, the bending elastic modulus is preferably 3500 MPa or more.

Furthermore, from the viewpoint of durability, the bending strain is preferably 2.5% or more, more preferably 3.0% or more, and even more preferably 3.5% or more. On the other hand, the bending strain is preferably 5.0% or less.

The bending elastic modulus and bending strain were determined by a three-point bending test using a test piece (127 mm x 12.7 mm x thickness 3.1 mm) based on ASTM D790, with a distance between fulcrums of 50 mm, and a crosshead speed of 1.3 mm/min. It can be measured by In addition, in this specification, the bending elastic modulus and bending strain mean values obtained by a test at room temperature (23° C.).

Here, we will consider the reason why a small diameter seal ring, for example, an outer diameter of φ30 mm or less, has lower resistance during diameter expansion than a seal ring with an outer diameter of more than φ30 mm. When the outer diameter of the seal ring is a small diameter of φ30 mm or less, the ratio of the diameter expansion amount to the outer diameter dimension when the seal ring is assembled is likely to be larger than that of a seal ring whose outer diameter exceeds φ30 mm. Therefore, it is thought that a seal ring with a small diameter tends to have a large amount of strain when the diameter is expanded, and has low resistance when the diameter is expanded. For example, a seal ring with a diameter of about 50 mm has a diameter expansion rate of 110% or less, a seal ring with a diameter of about 40 mm has a diameter expansion rate of 115% or less, but a seal ring with a diameter of 30 mm or less has a diameter expansion rate of 110% or less. 120% or more, and the resistance during diameter expansion becomes low.

In the seal ring of the present invention, when the thickness of the thin part is 70% or less of the thickness of the non-thin part, the surface pressure applied to the side surface of the seal ring does not become excessive and abnormal wear is less likely to occur. In addition, a predetermined sealing area can be secured and the sealing performance is excellent (small leakage). On the other hand, when the thickness of the thin wall portion is 50% or more of the thickness of the non-thin wall portion, stress tends to escape to the thin wall portion, and the amount of strain is difficult to increase in the thin wall portion. As a result, even if the seal ring of the present invention is a small-diameter PPS seal ring with a diameter expansion ratio of 120% or more, the seal ring has improved durability when assembled into an annular groove of a rotating shaft or the like.

The outer diameter of the seal ring can be freely set, and from the viewpoint of application to small hydraulic equipment, etc., it is preferably φ30 mm or less, more preferably φ25 mm or less, and even more preferably φ20 mm or less. In view of durability, the outer diameter of the seal ring is preferably φ15 mm to 30 mm, more preferably φ15 mm to 25 mm, and even more preferably φ15 mm to 20 mm. By providing a thin wall portion, the seal ring of the present invention can be applied to smaller hydraulic equipment, etc., which is difficult to apply to molded bodies of PPS resin compositions used in conventional seal rings.

The seal ring of the present invention is an injection molded product of a resin composition, and the gate marks 8 are formed at the gate positions where molten resin is injected during injection molding (see FIG. 1). Although the position of the gate mark is not particularly limited, it is preferably formed on the inner peripheral side of the ring from the viewpoint of ensuring sealing performance and eliminating the need for post-processing. Further, as shown in FIG. 1, from the viewpoint of flow balance in injection molding, it is preferable to have the seal ring at the center of the developed length of the seal ring 1 on the ring inner circumferential surface 3. Specifically, gate marks 8 are formed on the inner circumferential surface of the abutment facing portion 5F. Since the abutment facing portion 5F is a non-thin wall portion 7, it is preferable from the viewpoint of durability.

In this way, by having the gate mark in the non-thin part at the center of the expanded length of the seal ring, it becomes difficult for force to concentrate around the gate mark, which is weak in strength, when the ring diameter is expanded. This makes it possible to prevent force from being concentrated especially around the gate mark due to the diameter expansion of the ring during assembly.

Note that the gate mark 8 may be provided at a position other than the center of the developed length of the seal ring 1. Further, the gate mark 8 may be provided in the thin portion 6.

The seal ring of the present invention is a molded article of a PPS resin composition containing PPS resin as a main component, and may contain components other than PPS resin. PPS resin is a crystalline thermoplastic resin having a polymer structure shown in the following formula (1) in which benzene rings are connected at para positions by sulfur bonds. PPS resin has a melting point of about 280° C. and has excellent chemical resistance, so it can be used even when the temperature of the hydraulic oil to be sealed is high. In addition, PPS resins include crosslinked PPS resins and semi-crosslinked PPS resins obtained by oxidative crosslinking of low molecular weight ones, and linear PPS resins that do not have a crosslinked structure. It can be used without being limited to. Since the diameter is expanded when it is incorporated into the annular groove, it is preferable to use a linear PPS resin that has excellent toughness. Examples of the PPS resin that can be used in the present invention include MA-520 and T-4AG (trade name of DIC Corporation).

The resin component of the PPS resin composition may be a PPS resin alone or may contain other resins. The PPS resin composition can include, for example, an elastomer. The elastomer may be either a thermosetting elastomer or a thermoplastic elastomer, but a thermoplastic elastomer that can increase the toughness of the PPS resin is preferred. Examples of the thermoplastic elastomer include polyamide elastomer, polyurethane elastomer, polyester elastomer, polystyrene elastomer, and olefin elastomer. Note that it is preferable that the decomposition start temperature of the elastomer is equal to or higher than the molding temperature of the PPS resin (280 to 320° C.). However, decomposition of low molecular weight components during seal ring molding shall be allowed.

If necessary, fibrous reinforcing materials such as carbon fiber, glass fiber, and aramid fiber, spherical fillers such as spherical silica and spherical carbon, scaly reinforcing materials such as mica and talc, potassium titanate whiskers, etc. are added to the PPS resin composition as necessary. can be blended with microfiber reinforcing material. In addition, solid lubricants such as PTFE resin, graphite, tungsten disulfide, molybdenum disulfide, and boron nitride, sliding reinforcement materials such as calcium phosphate and calcium sulfate, and coloring agents such as carbon powder, iron oxide, and titanium oxide can be added. . These can be blended alone or in combination.

The bending elastic modulus and bending strain of the seal ring of the present invention are appropriately set depending on the type and amount of the PPS resin, the type and amount of components (elastomer, fibrous reinforcing material, etc.) added to the PPS resin, and the like.

The means for mixing and kneading the above raw materials is not particularly limited. For example, a PPS resin alone may be used, and carbon fibers, glass fibers, etc. may be side-fed and kneaded using a twin-screw extruder or the like. In addition, only the powder raw materials are dry mixed using a Henschel mixer, ball mixer, ribbon blender, Ledige mixer, Ultra Henschel mixer, etc., and then melt-kneaded using a melt extruder such as a twin-screw extruder to obtain pellets for molding. You can. As the molding method, it is preferable to employ injection molding because it is easy to form a complicated joint shape and a recess on the side surface of the ring. Note that a treatment such as annealing treatment may be applied to the molded article in order to improve its physical properties.

The raw materials for the resin compositions used in Examples and Comparative Examples are listed below.
(1) PPS resin [PPS]
(2) Glass fiber [GF]

The above raw materials were melt-kneaded using a twin-screw extruder to produce pellets for injection molding. The glass fibers of Examples 1 to 3 and Comparative Examples 1 and 2 were 30% by mass, and the glass fibers of Comparative Example 3 were 40% by mass.

(1) Bending test A test piece (127 mm x 12.7 mm x thickness 3.1 mm) compliant with ASTM D790 was created using the above pellet, and using this, the distance between fulcrums was 50 mm, and the crosshead speed was 1.3 mm/min. A three-point bending test was conducted using the following methods, and the bending elastic modulus and bending strain were measured. Table 1 shows the raw material composition, flexural modulus, and flexural strain of each test piece.

(2) Assembly jig passing test (seal ring diameter expansion test)
The assembly jig passing test will be explained using FIG. 4. FIG. 4(a) is a side view of an assembly jig (tapered jig), and FIG. 4(b) is a schematic diagram of a seal ring assembly jig passing test.

The dimensions of the taper jig 12 used in the test are as follows, and the inner diameter of the seal ring is expanded by 1.25 times (diameter expansion rate: 125%) (see FIG. 4(a)).
L: 147.0mm
Dl: 27.6mm
Ds: 21.0mm

Seal rings used in Examples and Comparative Examples were manufactured by injection molding using the above pellets, and the outer diameter was adjusted to φ26 mm by heat setting. The shape of the seal ring after heat setting is the shape shown in Fig. 5, which is 26 mm in outer diameter x 22 mm in inner diameter x 1.9 mm in width, and has a radial length of 0.3 mm and a depth of 0.3 mm on the inner peripheral surface. It has a step part on both sides), and the joint is a compound step cut. The inner peripheral surface of this seal ring was additionally machined to create a thinner part using a milling machine, and 100 seal rings were manufactured for each example and comparative example. Note that the shape of the seal ring after additional machining and the position of the non-thin wall portion correspond to those in FIG. Using the taper jig 12, as shown in FIG. 4(b), 100 seal rings 11 of each example and comparative example were inserted into the taper jig 12 at a speed of 1 mm/s, and the presence or absence of resistance and resistance were determined. The presence/absence of these was evaluated. Table 2 shows the test results and the ratio of the thickness of the thin part to the thickness of the non-thin part (ratio of the thin part).

As shown in Table 2, Examples 1 to 3 in which the ratio of the thin wall portion (thickness of the thin wall portion/thickness of the non-thin wall portion x 100) is 50% to 70% have a bending elastic modulus of 8300 MPa and a bending strain of 2.5. %, and the number of samples without resistance was 0. On the other hand, both Comparative Examples 1 and 2, in which the ratio of thin-walled parts is greater than 70%, had a bending elastic modulus of 8300 MPa and a bending strain of 2.5%, similar to Examples 1 to 3, but were samples with no resistance. The numbers were 4 and 9, respectively. In addition, in Comparative Example 3, the ratio of thin wall portions was 50% as in Example 1, but the bending elastic modulus was 11,600 MPa, the bending strain was 2.0%, and the number of samples with no resistance was 7. Ta.

From the results in Table 2, when the bending elastic modulus is 8300 MPa, the bending strain is 2.5%, and the ratio of thin wall parts is 50% to 70%, even a small diameter PPS seal ring has resistance when assembled into an annular groove. That's what I found out. Furthermore, even with a bending modulus of elasticity of 8300 MPa and a bending strain of 2.5%, it was found that the small-diameter PPS seal ring lacks resistance when assembled into an annular groove when the ratio of the thin wall portion is greater than 70%. In this way, by combining the bending characteristics and the ratio of the thin wall portion in a suitable range in the seal ring, it is possible to improve the durability when assembled into the annular groove.

The seal ring of the present invention has improved resistance when assembled into an annular groove even if it is a small diameter PPS seal ring, so it is particularly suitable as a seal ring for sealing hydraulic oil in an annular passage of small hydraulic equipment, etc. available for use. Moreover, it can be suitably used not only for hydraulic equipment but also for seal rings having abutment and attached to an annular groove with an enlarged diameter.

1, 11 Seal ring 2 Ring outer circumferential surface 3 Ring inner circumferential surface 4 Ring side surface 4a Recessed portion 5 Abutment 5F Opposing part (Abutment opposing part)
6 Thin wall portion 7 Non-thin wall portion 71 Step portion 71a Upper curved surface 71b Lower curved surface 71c Side surface 8 Gate mark 12 Taper jig

Claims

A seal ring having one joint,
The seal ring is a molded body of a polyphenylene sulfide resin composition, has a bending modulus of elasticity of 10,000 MPa or less, and a bending strain of more than 2.0%. It has a thin part on the inner peripheral surface side of the ring in the area where the ring is thinned in the radial direction,
A seal ring characterized in that the radial thickness of the thin portion is 50% to 70% of the radial thickness at a position facing the abutment.
The seal ring according to claim 1, wherein the seal ring has a bending elastic modulus of 8500 MPa or less and a bending strain of 2.5% or more.
The seal ring according to claim 1, wherein the seal ring has an outer diameter of 30 mm or less.
2. The seal ring according to claim 1, wherein the seal ring is an injection molded product and has gate marks during injection molding at a position facing the abutment.
The seal ring has an outer diameter of 30 mm or less, a bending modulus of elasticity of 8,500 MPa or less, and a bending strain of 2.5% or more, and is an injection molded product, with gate marks from injection molding on the joint. The seal ring according to claim 1, characterized in that the seal rings are provided at opposing positions.