Damping process and damping material for electronic part fixing device

Abstract

The invention relates to the field of electronic part damping processing, and particularly discloses an electronic part fixing device damping process and a damping material. An electronic part fixing device damping technology comprises the following steps that S1, a damping material, a fixing device plastic material and a mute plug pin are prepared, and the damping material and the fixing device plastic material are dried; s2, a fixing device plastic material is molten and injected into an injection mold, cooling and shaping are conducted, and a fixing device semi-finished product is obtained; and S3, the mute plug pin is put into an injection mold and placed corresponding to the mounting hole of the fixing device semi-finished product, then a damping material is melted and injected into the area, corresponding to the mounting hole, of the mute plug pin, pressure maintaining and cooling forming are conducted, and the integrally-formed fixing device is manufactured. The damping material, the mute plug pin and the fixing device plastic material are integrally formed step by step, the manufactured electronic part fixing device has a good damping effect and is not prone to loosening or damage after being used for a long time, and the reliability and stability of an electronic product are improved.

Description

Technical Field

[0001] The present application relates to the field of shock-absorbing processing of electronic parts, and more specifically, to a shock-absorbing process and shock-absorbing material for an electronic component fixing device. Background Art

[0002] Electronic component fixtures are generally used in electronic products such as computers and tablets to fix and support electronic components such as hard disks. They generally include fixing brackets, etc. In order to protect electronic components such as hard disks from external shocks and vibrations and ensure data security and long-term stable operation of hard disks, it is necessary to install shock-absorbing structures on electronic fixtures.

[0003] Current shock-absorbing components are generally silent pins and soft silicone. The soft silicone is attached to the silent pins, and the silent pins are installed in the mounting holes of the electronic fixtures, so that the electronic components are shock-absorbing through the silent pins. Although such shock-absorbing components can achieve a certain shock-absorbing effect, the silent pins are prone to loosening during long-term operation of the electronic components, which reduces the shock-absorbing effect of the electronic fixtures and affects the stability of the electronic products. Summary of the invention

[0004] In order to solve the problem that the mute pins of conventional electronic component fixing devices are easily loosened, thereby reducing the shock absorbing effect of the electronic component fixing device, the present application provides a shock absorbing process and a shock absorbing material for an electronic fixing device.

[0005] In a first aspect, the present application provides a vibration reduction process for an electronic fixture, which adopts the following technical solution: A vibration reduction process for an electronic fixture comprises the following steps: S1. Prepare shock-absorbing materials, plastic materials for fixing devices and silent latches, and dry the shock-absorbing materials and plastic materials for fixing devices; S2, melting the plastic material of the fixture and injecting it into the injection mold, cooling and shaping it, and obtaining a semi-finished fixture; S3. Put the silent plug into the injection mold and place it at the installation hole position of the semi-finished fixture. Then melt the shock-absorbing material and inject it into the area corresponding to the installation hole of the silent plug. Then maintain the pressure and cool it to form an integrated electronic component fixture.

[0006] By adopting the above technical scheme, the shock-absorbing material and the plastic material of the fixture are first dried to remove the moisture in the material and reduce the influence of moisture on the subsequent injection molding process; then the plastic material of the fixture is first melt-injected and cooled in the injection mold to obtain a semi-finished fixture that has been initially finalized. The cooling molding process allows the obtained semi-finished fixture to have good fitting stability with the shock-absorbing material in the subsequent process while maintaining the shape of the fixture; then the silent plug is fixedly placed in the installation position corresponding to the semi-finished fixture, and then the shock-absorbing material is melt-injected to stably fit the shock-absorbing material and the semi-finished fixture, and the silent plug is covered and fixed to further improve the installation stability of the silent plug and the fixture. The silent plug, shock-absorbing material and fixture of the electronic component fixture obtained by this application are integrally formed, have a stable shock-absorbing effect, and are used in the support of electronic product accessories such as hard disks. It can reduce the amplitude of electronic product accessories, is not easy to loosen or damage during long-term operation, and can improve the reliability and stability of electronic products.

[0007] Preferably, the male mold temperature of the injection mold is 85-95° C., the female mold temperature is 62-72° C., and the injection pressure is 90-110 bar.

[0008] By adopting the above technical scheme, when the plastic material of the fixture is injected into the injection mold, the plastic material of the fixture shrinks and hardens from the surface to the inside under the cooling action of the injection mold, and internal stress will be generated during the shrinkage process; if the temperature of the mother mold is too high, excessive internal stress will be generated inside the hardened fixture, making the fixture prone to shrinkage and deformation or even cracking. Therefore, the present application controls the temperature of the mother mold and the male mold of the injection mold, and makes the temperature of the mother mold lower than the temperature of the male mold, which helps to control the cooling speed and shrinkage rate of the fixture and further reduce the generation of internal stress; the better injection pressure can make the plastic material of the fixture evenly and stably filled into the injection mold, further reducing the problem of the fixture being prone to shrinkage and deformation.

[0009] Preferably, the cooling and shaping time in step S2 is 8-15s.

[0010] By adopting the above technical scheme, the optimal cooling and shaping time can make the semi-finished product of the fixing device maintain its shape while having good bonding stability with the shock-absorbing material in the subsequent process, further improving the shock-absorbing stability of the electronic component fixing frame; when the cooling and shaping time is too short, the shaping effect of the semi-finished product of the fixing device is not good, and when the cooling and shaping time is too long, the semi-finished product of the fixing device has been completely solidified and formed, reducing the bonding stability with the shock-absorbing material.

[0011] Preferably, the holding pressure in the step S3 is 110-120 bar, the holding time is 20-30 s, and the cooling molding time is 25-35 s.

[0012] By adopting the above technical scheme, the better holding pressure and holding time can make the shock-absorbing material, the plastic material of the fixing device and the silent pin fit stably, while reducing the shrinkage rate of the manufactured electronic component fixing device and improving the dimensional stability; the better cooling molding time can make the shock-absorbing material and the plastic material of the fixing device solidify stably, improving the solidification uniformity and stability between the manufactured electronic component fixings.

[0013] Preferably, the shock-absorbing material is TPU, and the plastic material of the fixing device is ABS and / or PC.

[0014] By adopting the above technical solution, TPU is a thermoplastic polyurethane elastomer, which has better elasticity and temperature resistance than silicone, and can enhance the shock absorbing effect of the fixing device; the fixing device is made of ABS and / or PC, which has good strength, impact resistance and wear resistance, is not easy to be damaged, and has good stability in use.

[0015] In a second aspect, the present application provides a shock absorbing material, which adopts the following technical solution: A shock absorbing material, which is used in the above-mentioned shock absorbing process of the electronic component fixing device, and is made of the following raw materials in parts by weight: Thermoplastic polyurethane elastomer 100-120 parts Polyolefin elastomer 20-30 parts Thickener 12-18 parts Stabilizer 10-15 parts 1-3 parts of antioxidants.

[0016] By adopting the above technical scheme, those skilled in the art know that the shock-absorbing material generally used in the prior art is silicone, but silicone tends to turn yellow during long-term use, and silicone has low elasticity. When used in the present application, electronic products will generate heat during long-term operation, which can easily cause aging of the silicone and reduce the shock-absorbing effect on the accessories of the electronic products. Therefore, the present application further optimizes and improves the shock-absorbing material used.

[0017] The present application uses a compound of thermoplastic polyurethane elastomer and polyolefin elastomer in an optimal amount as the main raw material of the shock-absorbing material, and further compounds it with a tackifier and a stabilizer. The obtained shock-absorbing material has good temperature resistance, resilience and mechanical properties, and can be stably bonded to the semi-finished product of the fixing device during the injection molding process, further improving the temperature resistance and resilience of the obtained electronic component fixing device, improving the shock-absorbing effect, and is not prone to aging, loosening and damage after long-term use.

[0018] Preferably, the tackifier is composed of 2-octenylsuccinic anhydride and tetramethyltetravinylcyclotetrasiloxane in a weight ratio of 1:(0.5-1.5).

[0019] By adopting the above technical scheme, using 2-octenylsuccinic anhydride and tetramethyltetravinylcyclotetrasiloxane in a relatively optimal dosage ratio as a thickener, the interface compatibility between the shock-absorbing material and the plastic material of the fixture can be improved, thereby improving the fitting stability between the shock-absorbing material and the semi-finished product of the fixture; at the same time, the thickener can be further evenly dispersed with the thermoplastic polyurethane elastomer and the polyolefin elastomer, thereby improving the resilience and temperature resistance of the obtained shock-absorbing material.

[0020] Preferably, the stabilizer is composed of ethylene-octene-glycidyl methacrylate and trimethylolpropane diallyl ether in a weight ratio of 1:(1-3).

[0021] By adopting the above technical scheme, ethylene-octene-methacrylate glycidyl ester and trimethylolpropane diallyl ether are compounded with a better dosage ratio, which can produce a good synergistic effect with the tackifier, and the soft branched chain segments can be interwoven and dispersed with the thermoplastic polyurethane elastomer and the polyolefin elastomer. The prepared shock-absorbing material has good compactness and good flexibility and resilience, thereby improving the temperature resistance and shock absorption of the prepared shock-absorbing material.

[0022] Preferably, the antioxidant is antioxidant 1010 and / or antioxidant 168.

[0023] By adopting the above technical solution, the above antioxidant can improve the aging resistance of the prepared shock-absorbing material, thereby improving the service life of the fixing device.

[0024] Preferably, the shock-absorbing material is prepared by the following steps: mixing a thermoplastic elastomer, a polyolefin elastomer, a tackifier, a stabilizer and an antioxidant, melt-extruding, cooling and granulating to obtain the shock-absorbing material.

[0025] By adopting the above technical solution, a uniformly dispersed shock-absorbing material is prepared by a melt extrusion process, which is easy to be processed by injection molding.

[0026] In summary, this application has the following beneficial effects: 1. The shock-absorbing process for the electronic component fixing device of the present application is to firstly inject the plastic material of the fixing device and cool it to shape, then put in a silent latch and inject the shock-absorbing material at the silent latch installation position, maintain the pressure and cool it to form, so as to obtain an integrally formed electronic component fixing device with stable shock-absorbing effect. It is used in the support of electronic product accessories such as hard disks, can reduce the amplitude of electronic product accessories, is not easy to loosen or be damaged during long-term operation, and can improve the reliability and stability of electronic products.

[0027] 2. The shock-absorbing material of the present application is made of a thermoplastic polyurethane elastomer, a polyolefin elastomer, a tackifier, a stabilizer and an antioxidant. The tackifier is composed of 2-octenylsuccinic anhydride and tetramethyltetravinylcyclotetrasiloxane, and the stabilizer is composed of ethylene-octene-methacrylate glycidyl ester and trimethylolpropane diallyl ether. The tackifier, stabilizer, thermoplastic polyurethane elastomer and polyolefin elastomer play a good synergistic role. The prepared shock-absorbing material has good temperature resistance and resilience, is not easy to age after long-term use, and has good shock-absorbing stability. DETAILED DESCRIPTION

[0028] The present application is further described in detail below in conjunction with embodiments.

[0029] The following are the sources and specifications of some raw materials of this application. The raw materials used in the preparation examples and embodiments of this application can be obtained from the market, including but not limited to the raw materials of the following models and manufacturers. Raw materials with equivalent performance can be used: 1. Thermoplastic polyurethane elastomer: BASF C75AHPM; 2. Polyolefin elastomer: Dow POE8450; 3. 2-Octenylsuccinic anhydride: Kemik, CAS No. 26680-54-6, content 99%; 4. Ethylene-octene-glycidyl methacrylate: Jiayirong, SOG-02; 5. Trimethylolpropane diallyl ether: CAS No. 682-09-7, content 99%; 6. Maleic anhydride grafted styrene copolymer: Jiayirong SAM-020; 7. Styrene acrylonitrile copolymer: Jiayirong EMI-100.

[0030] Preparation example of shock absorbing material Preparation Example 1 Preparation Example 1 discloses a shock-absorbing material, which is prepared by the following steps: 10 kg of thermoplastic elastomer, 3 kg of polyolefin elastomer, 1.2 kg of tackifier (composed of maleic anhydride and vinyl trimethoxy silane in a weight ratio of 1:1), 1.5 kg of styrene acrylonitrile copolymer as a stabilizer and 0.1 kg of antioxidant (composed of antioxidant 1010 and antioxidant 168 in a weight ratio of 1:1) are mixed, and melt-extruded using a twin-screw extruder, the screw speed is controlled to be 300 r / min, and the temperatures of the six temperature zones are as follows: the temperature of the first zone is 190°C, the second zone is 200°C, the third zone is 210°C, the fourth zone is 220°C, the fifth zone is 210°C, and the sixth zone is 200°C. After melt-extrusion, the shock-absorbing material is water-cooled, air-dried and granulated.

[0031] Preparation Example 2-3 The difference between Preparation Example 2-3 and Preparation Example 1 is that the amount of raw materials used and the preparation conditions are different, see Table 1 below for details.

[0032] Table 1 Raw material dosage and preparation conditions of Preparation Examples 1-3 Preparation Example 4 The difference between Preparation Example 4 and Preparation Example 1 is that the tackifier is different. The tackifier in Preparation Example 4 is composed of 2-octenylsuccinic anhydride and tetramethyltetravinylcyclotetrasiloxane. The amount of 2-octenylsuccinic anhydride is 0.8 kg, and the amount of tetramethylvinylcyclotetrasiloxane is 0.4 kg. The rest is the same as Preparation Example 1.

[0033] Preparation Example 5 The difference between Preparation Example 5 and Preparation Example 1 is that the tackifier consists of 2-octenyl succinic anhydride and tetramethyltetravinylcyclotetrasiloxane, the amount of 2-octenyl succinic anhydride used is 0.48 kg, the amount of tetramethylvinylcyclotetrasiloxane used is 0.72 kg, and the rest is the same as Preparation Example 1.

[0034] Preparation Example 6 The difference between Preparation Example 6 and Preparation Example 4 is that the stabilizer is different. The stabilizer in Preparation Example 6 is composed of ethylene-octene-methacrylate glycidyl ester and trimethylolpropane diallyl ether. The amount of ethylene-octene-methacrylate glycidyl ester is 0.75 kg, and the amount of trimethylolpropane diallyl ether is 0.75 kg. The rest is the same as Preparation Example 4.

[0035] Preparation Example 7 The difference between Preparation Example 7 and Preparation Example 4 is that the stabilizer consists of ethylene-octene-methacrylate glycidyl ester and trimethylolpropane diallyl ether, the amount of ethylene-octene-methacrylate glycidyl ester is 0.375 kg, the amount of trimethylolpropane diallyl ether is 1.125 kg, and the rest is the same as Preparation Example 4.

[0036] Preparation Example 8 The difference between Preparation Example 8 and Preparation Example 6 is that the stabilizer consists of ethylene-octene-methacrylate glycidyl ester and isooctyl phthalate, the amount of ethylene-octene-methacrylate glycidyl ester is 0.375 kg, the amount of isooctyl phthalate is 1.125 kg, and the rest is the same as Preparation Example 6. Example

[0037] Example 1 Embodiment 1 discloses a vibration reduction process for an electronic component fixing device, comprising the following steps: S1. Select TPU as the shock-absorbing material and PC as the plastic material of the fixture, prepare the shock-absorbing material, the plastic material of the fixture and the silent latch, and place the shock-absorbing material and the plastic material of the fixture in an oven, adjust the oven temperature to 80°C, and bake for 2 hours, wherein the TPU is BASF C75AHPM and the PC is commercially available Mitsubishi LGH2230M; S2, melt the plastic material of the fixture at a temperature of 230° C.; then adjust the female mold temperature of the injection mold of the injection molding machine to 62° C., the male mold temperature to 85° C., and the injection pressure to 90 bar, and then inject it into the injection mold. After the injection is completed, cool and shape for 8 seconds to obtain a semi-finished fixture; S3. Place the silent latch into the injection mold and position it at the mounting hole of the semi-finished fixture. Then, melt the shock-absorbing material at a temperature of 210°C and inject it into the area of ​​the silent latch corresponding to the mounting hole. Then, maintain the pressure at a holding pressure of 110 bar for 20 seconds. Then, cool and mold for 25 seconds to obtain an integrally molded fixture.

[0038] Example 2 The difference between Example 2 and Example 1 is that the preparation process parameters are different, see Table 2 below for details.

[0039] Table 2 Preparation process parameters of Example 1-2 Example 3 The difference between Example 3 and Example 2 is that the temperature of the female mold of the injection mold is 90° C., and the temperature of the male mold is 60° C., and the rest is the same as Example 2.

[0040] Example 4 The difference between Example 4 and Example 2 is that the cooling and shaping time in step S2 is 40s, and the rest is the same as Example 2.

[0041] Example 5 The difference between Example 5 and Example 2 is that the holding pressure in step S3 is 80 bar and the holding time is 40 s, and the rest is the same as Example 2.

[0042] Embodiment 6-13 The difference between Examples 6-13 and Example 2 is that the sources of the shock absorbing materials are different, see Table 3 below for details.

[0043] Table 3 Sources of shock absorbing materials of Examples 6-13 Example Sources of shock-absorbing materials Example 6 Preparation Example 1 Example 7 Preparation Example 2 Example 8 Preparation Example 3 Example 9 Preparation Example 4 Example 10 Preparation Example 5 Embodiment 11 Preparation Example 6 Example 12 Preparation Example 7 Embodiment 13 Preparation Example 8 Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that the preparation processes are different. In Comparative Example 1, TPU is directly injection molded at a temperature of 210° C. to obtain a shock-absorbing material; the shock-absorbing material is adhered to the silent latch, and then the silent latch is fixedly installed on a fixing device to obtain an electronic component fixing device.

[0044] Performance testing 1. The performance of the shock absorbing materials prepared in Preparation Examples 1-8 was tested as follows. The shock absorbing materials prepared in Preparation Examples 1-8 were injection molded at 210° C. to prepare test pieces with a thickness of 2 mm: 1) Elasticity test: According to the test method in ASTM D1054, the resilience of the test piece is tested and the test results are recorded in terms of rebound rate (unit: %); 2) High temperature resistance test: According to the test method in ASTM D624, the tear strength of the test piece is tested, which is recorded as the tear strength before heat resistance (unit: KN / m). Then the test piece is placed in a constant temperature and humidity test box with a temperature of 85°C and a humidity of 85%. After the test for 7 days, the tear strength of the test piece is tested, which is recorded as the tear strength after heat resistance (unit: KN / m). The test results are tested and recorded. The following are the performance test data of the shock-absorbing materials prepared in Preparation Examples 1-8, see Table 4 below for details.

[0045] Table 4 Performance data of the shock absorbing materials of Preparation Examples 1-8 Combining Preparation Examples 1-3 and Preparation Examples 4-5 and Table 4, it can be concluded that the use of 2-octenylsuccinic anhydride and tetramethyltetravinylcyclotetrasiloxane in the preferred dosage ratio of the present application as a tackifier can improve the resilience and temperature resistance of the prepared shock-absorbing material; Compared with Example 1, the rebound rate of Preparation Example 4-5 is increased by 6.9%, the tear strength before the heat resistance test is increased by 4.5 KN / m, and the tear strength after the heat resistance test is increased by 6.4 KN / m. It can be seen that the shock-absorbing material prepared in Preparation Example 4-5 has good resilience and temperature resistance.

[0046] Combining Preparation Example 4 and Preparation Examples 6-8 and Table 4, it can be seen that the use of ethylene-octene-methacrylate glycidyl ester and trimethylolpropane diallyl ether in the preferred dosage ratio of the present application as stabilizers can further improve the resilience and temperature resistance of the prepared shock-absorbing material. Compared with Preparation Example 4, Preparation Examples 6-7 have a rebound rate of 7.1%, a tear strength before the heat resistance test of 4.2 KN / m, and a tear strength after the heat resistance test of 6.3 KN / m. In Preparation Example 8, ethylene-octene-methacrylate glycidyl ester and isooctyl phthalate are used as stabilizers, and the resilience and tear resistance of the prepared shock-absorbing material are reduced; it can be seen that ethylene-octene-methacrylate glycidyl ester and trimethylolpropane diallyl ether as stabilizers have a good synergistic effect.

[0047] 2. The following shock absorption test is performed on the electronic component fixtures prepared in Examples 1-6, Example 12 and Comparative Example 1: In an anechoic chamber, a vibration tester is used to mount a hard disk on the electronic component fixture. The vibration frequency of the vibration tester is adjusted to 1 KHz, and a vibration test is performed on the hard disk. The A-weighted measurement method is used, and the distance from the hard disk is 0.5 m. The noise (unit: dB) generated by the hard disk during vibration is tested and recorded, and the test results are tested and recorded; The following are the noise detection data of the electronic component fixing devices prepared in Examples 1-6, Example 12 and Comparative Example 1, see Table 5 below for details.

[0048] Table 5 Noise data of electronic component fixing devices of Examples 1-6, Example 12 and Comparative Example 1 By combining Examples 1-2, Examples 3-5 and Comparative Example 1 and Table 5, it can be concluded that the electronic component fixing device prepared using the shock-absorbing process of the present application has significantly improved shock-absorbing effect on the hard disk. Compared with Comparative Example 1, the noise of Examples 1-2 is reduced by 10.6dB; by changing the process parameters in Examples 3-5, the shock-absorbing effect of the electronic component fixing device on the hard disk is reduced, indicating that controlling the optimal injection molding temperature, cooling and setting time, holding pressure and holding time can improve the stability of the preparation of the electronic component fixing device and further improve the shock-absorbing effect.

[0049] Combining Example 2, Example 6, Example 12 and Table 5, it can be concluded that the shock-absorbing material, fixing device plastic material and silent pin of the present application are further used for integrated injection molding. The shock-absorbing material has good resilience and can further enhance the shock-absorbing effect of the electronic component fixing device on the hard disk. Compared with Example 6, the noise of Example 12 is reduced by 5.2dB.

[0050] It can be seen from the above that by optimizing the shock-absorbing process and process parameters of the present application and using the shock-absorbing material prepared by the present application, the shock-absorbing effect of the prepared electronic component fixing device can be significantly improved.

[0051] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A shock absorbing process for an electronic component fixing device, characterized in that: The following steps are involved: S1. Prepare shock-absorbing materials, plastic materials for fixing devices and silent latches, and dry the shock-absorbing materials and plastic materials for fixing devices; S2, melting the plastic material of the fixture and injecting it into the injection mold, cooling and shaping it, and obtaining a semi-finished fixture; S3. Put the silent plug into the injection mold and place it at the installation hole position of the semi-finished fixture. Then melt the shock-absorbing material and inject it into the area corresponding to the installation hole of the silent plug. Then maintain the pressure and cool it to form an integrated electronic component fixture.

2. The vibration reduction process for an electronic component fixing device according to claim 1, characterized in that: The male mold temperature of the injection mold is 85-95° C., the female mold temperature is 62-72° C., and the injection pressure is 90-110 bar.

3. The vibration reduction process for an electronic component fixing device according to claim 1, characterized in that: The cooling and shaping time in the step S2 is 8-15s.

4. The vibration reduction process for an electronic component fixing device according to claim 1, characterized in that: The holding pressure in the step S3 is 110-120 bar, the holding time is 20-30 s, and the cooling molding time is 25-35 s.

5. A vibration reduction process for an electronic component fixing device according to any one of claims 1 to 4, characterized in that: The shock-absorbing material is TPU, and the plastic material of the fixing device is ABS and / or PC.

6. A shock absorbing material used in the shock absorbing process of the electronic component fixing device according to any one of claims 1 to 5, characterized in that: The shock absorbing material is prepared from the following raw materials in parts by weight: Thermoplastic polyurethane elastomer 100-120 parts Polyolefin elastomer 20-30 parts Thickener 12-18 parts Stabilizer 10-15 parts 1-3 parts of antioxidants.

7. A shock absorbing material according to claim 6, characterized in that: The tackifier is composed of 2-octenyl succinic anhydride and tetramethyltetravinylcyclotetrasiloxane in a weight ratio of 1:(0.5-1.5).

8. A shock absorbing material according to claim 6, characterized in that: The stabilizer is composed of ethylene-octene-methacrylate glycidyl ester and trimethylolpropane diallyl ether in a weight ratio of 1:(1-3).

9. A shock absorbing material according to claim 6, characterized in that: The antioxidant is antioxidant 1010 and / or antioxidant 168.

10. A shock absorbing material according to claim 6, characterized in that: The shock-absorbing material is prepared by the following steps: mixing, melting, extruding, cooling and granulating a thermoplastic elastomer, a polyolefin elastomer, a tackifier, a stabilizer and an antioxidant to obtain the shock-absorbing material.

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