Seal structure and closure

Abstract

A seal structure for a housing with an opening for introduction of a cable, the seal structure comprising a first seal rubber and a second seal rubber arranged at the opening, the first seal rubber and the second seal rubber each having a hollow cylindrical shape, the second seal rubber being arranged on an axially outer side of the first seal rubber with respect to the housing, the housing having a rib in contact with an outer face of the first seal rubber, the first seal rubber having a hardness of 10 or less, and the second seal rubber having chemical resistance greater than that of the first seal rubber.

Description

Seal Structures and Closures

[0001] This application claims priority to Japanese Patent Application No. 2022-137973, filed on August 31, 2022, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Document 1 discloses a sealing material using a low elastic modulus rubber composition.

[0003] Japanese Patent Application Publication No. 2001-253983

[0004] The sealing structure of the present disclosure is a sealing structure for a housing having an opening for introducing a cable, the sealing structure including a first sealing rubber and a second sealing rubber arranged in the opening, the first sealing rubber and the second sealing rubber both having a hollow cylindrical shape, the second sealing rubber being arranged axially outside the first sealing rubber with respect to the housing, the housing having a rib in contact with the outer surface of the first sealing rubber, the first sealing rubber having a hardness of 10 degrees or less, and the second sealing rubber having higher chemical resistance than the first sealing rubber.

[0005] The closure of the present disclosure comprises the seal structure of the present disclosure.

[0006] Fig. 1 is a diagram illustrating an example of a seal structure according to an embodiment of the present disclosure, and Fig. 2 is a diagram illustrating a cable entry portion of the seal structure with a cable entered.

[0007] [Problem to be Solved by the Present Disclosure] Closures and the like used to house branching and splicing sections of optical cables have a highly airtight seal structure to protect the cables and components inside. In such seal structures, a soft, low-hardness rubber is used as a seal material placed at the section where the cable is introduced into the closure housing to accommodate cables of various shapes and cables with a wide range of outer diameters. Closures may be required by national standards to have a certain level of chemical resistance (e.g., gasoline resistance). However, low-hardness rubber generally has poor chemical resistance. Therefore, it has been difficult to achieve both airtightness and chemical resistance with conventional seal structures.

[0008] The present disclosure aims to provide a seal structure and closure that has high airtightness and chemical resistance.

[0009] [Advantages of the Present Disclosure] According to the present disclosure, it is possible to provide a seal structure and a closure that have high airtightness and chemical resistance.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. A seal structure according to one embodiment of the present disclosure includes: (1) a seal structure for a housing having an opening for introducing a cable, the seal structure including a first seal rubber and a second seal rubber disposed in the opening, the first seal rubber and the second seal rubber both having a hollow cylindrical shape, the second seal rubber being disposed axially outward of the first seal rubber with respect to the housing, the housing having a rib in contact with an outer surface of the first seal rubber, the first seal rubber having a hardness of 10 degrees or less, and the second seal rubber having higher chemical resistance than the first seal rubber.

[0011] The seal structure according to this embodiment places a second seal rubber (highly chemical-resistant seal rubber) on the outside of a first seal rubber (low-hardness rubber), thereby preventing chemicals from coming into contact with the first seal rubber and preventing the first seal rubber from being deteriorated by chemicals. Furthermore, if chemicals come into contact with the first seal rubber, the first seal rubber may swell. By placing the second seal rubber on the outside of the first seal rubber, even if chemicals do come into contact with the first seal rubber, swelling is suppressed, preventing deterioration of the first seal rubber. This results in a seal structure with excellent airtightness and high chemical resistance.

[0012] (2) In the above (1), the second seal rubber may be nitrile butadiene rubber.

[0013] Nitrile butadiene rubber has excellent chemical resistance, so by using nitrile butadiene rubber as the second seal rubber, a seal structure with particularly excellent chemical resistance can be obtained.

[0014] (3) In the above (1) or (2), the first seal rubber may be ethylene propylene diene rubber.

[0015] Since ethylene propylene diene rubber has low hardness, by using ethylene propylene diene rubber as the first seal rubber, a seal structure with particularly excellent airtightness can be obtained.

[0016] (4) In any one of the above (1) to (3), the first seal rubber and the second seal rubber may be integrally molded.

[0017] By integrally molding the first and second seal rubbers, swelling of the first seal rubber due to chemicals is limited, resulting in a seal structure with excellent chemical resistance. In addition, the number of parts can be reduced, leading to lower management costs.

[0018] (5) In any one of the above (1) to (4), the length of the first seal rubber along the axial direction may be greater than the length of the second seal rubber along the axial direction.

[0019] Even if the axial length of the second seal rubber is small, the seal structure has excellent chemical resistance. When the overall dimensions of the seal rubber are set to a predetermined value, a seal structure with particularly excellent airtightness can be obtained by making the length of the first seal rubber longer than that of the second seal rubber.

[0020] (6) A closure according to one embodiment of the present disclosure includes a seal structure according to any one of (1) to (5) above.

[0021] According to the above configuration, a closure having excellent airtightness and chemical resistance can be obtained.

[0022] [Details of the embodiment of the present disclosure] Specific examples of the seal structure according to the embodiment of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0023] (Sealing structure) Fig. 1 is a diagram showing an example of a sealing structure 1 according to this embodiment. As shown in Fig. 1, the sealing structure 1 is a sealing structure for a housing 2 having an opening 23 for introducing a cable 5 into the housing 2. The sealing structure 1 includes a first sealing rubber 3 and a second sealing rubber 4.

[0024] The housing 2 is a housing for accommodating the cable 5 therein. The housing 2 has an upper portion 21 and a lower portion 22, which are separable from each other. The upper portion 21 and the lower portion 22 are configured such that, when they are combined, an opening 23 is formed for introducing the cable 5. The opening 23 is formed by a semi-cylindrical portion 25 provided in the upper portion 21 and a semi-cylindrical portion 26 provided in the lower portion 22.

[0025] The first seal rubber 3 and the second seal rubber 4 are both seal rubbers arranged in the opening 23. The first seal rubber 3 and the second seal rubber 4 both have a hollow cylindrical shape and have hollow holes 31 and 41 that penetrate axially at their radial centers, respectively. The cable 5 can be introduced into the housing 2 by passing it through the hollow hole 31 of the first seal rubber 3 and the hollow hole 41 of the second seal rubber 4. The second seal rubber 4 is arranged axially outward of the first seal rubber 3 with respect to the housing 2.

[0026] The housing 2 has an arc-shaped rib 24 provided on the periphery of the opening 23 (the inner peripheral surface of the semi-cylindrical portion 25 of the upper portion 21 and the inner peripheral surface of the semi-cylindrical portion 26 of the lower portion 22). The rib 24 is provided so as to come into contact with the first seal rubber 3 when the cable 5 is introduced and the upper portion 21 and the lower portion 22 are combined.

[0027] Next, we will explain how the seal structure 1 seals when the cable 5 is introduced into the housing 2. Fig. 2 is a diagram showing the cable introduction portion of the seal structure 1 with the cable 5 introduced, as seen from the outside in the axial direction of the cable 5 relative to the housing 2. As shown in Fig. 2, the gap between the cable 5 and the second seal rubber 4 and the gap between the second seal rubber 4 and the housing 2 are each sealed. The gap between the cable 5 and the first seal rubber 3 and the gap between the first seal rubber 3 and the housing 2 are also each sealed.

[0028] Before the cable 5 is introduced, the inner diameters of the first seal rubber 3 and the second seal rubber 4 are smaller than the outer diameter of the cable 5. As a result, when the cable 5 is introduced, each seal rubber expands in the radial direction, and the elastic force of each seal rubber seals the gap between each seal rubber and the cable 5.

[0029] Because the housing 2 has a rib 24 that contacts the outer surface of the first seal rubber 3, the gap between the first seal rubber 3 and the housing 2 is sealed with high airtightness. Although the gap between the second seal rubber 4 and the housing 2 is also sealed to a certain degree of airtightness, the airtightness of the gap between the seal rubber 3 and the housing 2 is primarily ensured by the first seal rubber 3 and the rib 24. The rib 24 contacts at least a portion of the outer surface of the first seal rubber 3. By contacting the first seal rubber 3, the rib 24 presses the first seal rubber 3 radially inward, thereby enhancing the airtightness between the housing 2 and the first seal rubber 3. Furthermore, by pressing the first seal rubber 3, the rib 24 restricts movement of the first seal rubber 3 so that the first seal rubber 3 is fixed relative to the opening 23. The rib 24 may be provided so as to be in continuous contact with the first seal rubber 3 along the entire outer surface of the first seal rubber 3.

[0030] The first seal rubber 3 is a low-hardness rubber having a hardness of 10 degrees or less. Because the first seal rubber 3 is a low-hardness rubber, high airtightness can be ensured for cables of various shapes and cables with a wide range of outer diameters. From the viewpoint of ensuring high airtightness, the hardness of the first seal rubber 3 may be 5 degrees or less, or may be 3 degrees or less. There is no particular limitation on the lower limit of the hardness of the first seal rubber 3, and it is 0 degrees or more. The hardness in this disclosure is the hardness measured using a Type A durometer in accordance with JIS K 6253-3:2012.

[0031] Various rubber compositions having a hardness of 10 degrees or less can be used as the material for the first seal rubber 3. Examples of such rubber compositions include silicone rubber and ethylene propylene diene rubber (EPDM). From the viewpoint of ensuring high airtightness, the first seal rubber 3 may be ethylene propylene diene rubber.

[0032] The second seal rubber 4 has higher chemical resistance than the first seal rubber 3. In the seal structure 1, the second seal rubber 4, which has higher chemical resistance than the first seal rubber 3, is arranged axially outward of the first seal rubber 3 with respect to the housing 2. This prevents chemicals such as gasoline from coming into contact with the first seal rubber 3. Therefore, even if chemicals such as gasoline are present outside the seal structure 1, the first seal rubber 3 can be prevented from being deteriorated by the chemicals. Furthermore, if the first seal rubber 3 comes into contact with a chemical, the first seal rubber 3 may swell. By arranging the second seal rubber 4 outside the first seal rubber 3, swelling is suppressed even if the first seal rubber 3 comes into contact with a chemical, and deterioration of the first seal rubber 3 can be prevented.

[0033] Chemical resistance in the present disclosure is evaluated by the following method. First, the rubber composition to be evaluated is immersed in a chemical mixture of isooctane and toluene in a ratio of 7:3 at room temperature (23°C) for 168 hours. Then, the ratio (W2 / W1) of the weight of the rubber composition after immersion (W2) to the weight of the rubber composition before immersion (W1) is calculated. A rubber composition with a smaller change in weight before and after immersion in the chemical, i.e., a rubber composition with a smaller value of W2 / W1, is evaluated to have higher chemical resistance.

[0034] Various rubber compositions having higher chemical resistance than the first seal rubber can be used as the material for the second seal rubber 4. An example of a rubber composition having high chemical resistance is nitrile butadiene rubber (NBR). From the viewpoint of obtaining high chemical resistance, the second seal rubber 4 may be nitrile butadiene rubber.

[0035] From the viewpoint of obtaining high chemical resistance, the weight change (W2 / W1) before and after immersion in a chemical in the above-described chemical resistance evaluation of the rubber composition used as the material for the second seal rubber 4 may be 150% or less, or may be 110% or less. The lower limit of W2 / W1 of the rubber composition used as the material for the second seal rubber 4 is not particularly limited, and is, for example, 100% or more.

[0036] The first seal rubber 3 and the second seal rubber 4 may be integrally molded. In the case of integral molding, swelling of the first seal rubber 3 due to chemicals is limited, resulting in a seal structure 1 with excellent chemical resistance. In addition, the number of parts can be reduced, leading to reduced management costs, etc.

[0037] The axial length of the first seal rubber 3 may be greater than the axial length of the second seal rubber 4. Even if the axial length of the second seal rubber 4 is small, it is possible to prevent the intrusion of chemicals from the outside, and the seal structure 1 has excellent chemical resistance. Therefore, when the overall dimensions of the seal rubbers are set to a predetermined value, making the length of the first seal rubber 3 greater than that of the second seal rubber 4 results in a seal structure 1 with particularly excellent airtightness. The ratio (L1 / L2) of the axial length L1 of the first seal rubber 3 to the axial length L2 of the second seal rubber 4 may be greater than 1, 1.5 or greater, or 3 or greater. The upper limit of L1 / L2 is not particularly limited, but is, for example, 100 or less.

[0038] (Closure) The housing 2 is, for example, a housing for a closure. A closure is a device used to branch optical fibers from a trunk optical cable that contains hundreds to thousands of optical fibers and is installed aerial or underground to the user side, or to connect cables together. Optical cables have a coating layer to protect the built-in optical fibers, but the coating layer must be removed when branching or connecting the optical fibers. In order to protect the optical fibers from water and the like at branching or connecting points, the optical fibers are branched or connected inside the closure that houses the cable. A closure equipped with the seal structure of the present disclosure has excellent airtightness and chemical resistance.

[0039] In Figure 1, the upper part 21 of the housing 2, the first seal rubber 3 and the second seal rubber 4, and the lower part 22 of the housing 2 are shown separately, but "seal structure 1" refers to a structure in which the first seal rubber 3 and the second seal rubber 4 are arranged in the opening 23 formed by combining the upper part 21 and the lower part 22.

[0040] 1, the housing 2 can be separated into an upper part and a lower part, but the housing is not particularly limited as long as it allows cables to be introduced inside. For example, the housing may not be completely separated into an upper part and a lower part, but may be connected by a hinge so that it can be opened and closed, or the housing may be separated in the front-to-rear direction.

[0041] 2 shows a configuration in which the cable 5 is introduced into the housing 2 so as to be in direct contact with each seal rubber, but the present disclosure is not limited to this. For example, the cable may be introduced into the housing by passing a tube through which the cable can be passed through the hollow hole of each seal rubber and then passing the cable through the tube. In this case, the outer diameter of the tube is made smaller than the inner diameter of each seal rubber so that the gap between the tube and each seal rubber is sealed by the elastic force of the seal rubber.

[0042] REFERENCE SIGNS LIST 1 seal structure 2 housing 21 upper part 22 lower part 23 opening 24 rib 25, 26 semi-cylindrical part 3 first seal rubber 31 hollow hole 4 second seal rubber 41 hollow hole 5 cable

Claims

1. A seal structure for a housing having an opening for introducing a cable, the seal structure includes a first seal rubber and a second seal rubber disposed in the opening, the first seal rubber and the second seal rubber each have a hollow cylindrical shape, the second seal rubber is disposed axially outward of the first seal rubber with respect to the housing, the housing has a rib in contact with an outer surface of the first seal rubber, The first seal rubber has a hardness of 10 degrees or less, The second seal rubber has a higher chemical resistance than the first seal rubber.

2. The seal structure according to claim 1 , wherein the second seal rubber is a nitrile butadiene rubber.

3. The seal structure according to claim 1 , wherein the first seal rubber is an ethylene propylene diene rubber.

4. The seal structure according to claim 1 , wherein the first seal rubber and the second seal rubber are integrally formed.

5. The seal structure according to claim 1 , wherein a length along the axial direction of the first seal rubber is greater than a length along the axial direction of the second seal rubber.

6. A closure comprising the seal structure of claim 1.

7. A closure having the sealing structure described in claim 5.