Preparation method of anti-shrinkage shock-absorbing gasket and shock-absorbing gasket thereof

Abstract

The application relates to a preparation method of an anti-shrinkage shock-absorbing gasket and the shock-absorbing gasket, and the preparation method comprises the following steps of S1: mixing and stirring 95-105 parts of polystyrene particles with 1-3 parts of polyvinyl alcohol particles or polycarbonate particles according to weight parts to form mixed particles; S2: heating the mixed particles until melting to form molten materials; S3: after the molten materials are cooled and formed at least once, sheet blank is formed, an insulating sheet is arranged between two pieces of the sheet blank, and the two pieces of the sheet blank are connected to each other to form a three-layer sheet, the three-layer sheet is extrusion formed to form a smooth sheet, and the smooth sheet is dried; S4: the dried smooth sheet is extrusion formed again to form a textured sheet; and S5: the textured sheet is cut to obtain the anti-shrinkage shock-absorbing gasket. The anti-shrinkage shock-absorbing gasket can improve the resilience of the gasket, thereby improving the utilization rate of the gasket, and the gasket has high anti-shrinkage.

Description

Technical Field

[0001] This invention relates to the field of gasket technology, and in particular to a method for preparing an anti-shrinkage damping gasket and the damping gasket thereof. Background Technology

[0002] Vibration occurs during the transportation or storage of precision electronic components, which can damage them. Therefore, shock-absorbing pads are placed under the electronic components to reduce the damage caused by vibration and impact. Existing shock-absorbing pads are typically made of foam or thin-walled materials. Foam materials are easily deformed and have weak resilience after deformation, and are usually for single use, resulting in low utilization. Thin-walled materials tend to shrink inwards at the corners in cold weather, causing thin electronic components to deform due to loss of support at the corners. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing an anti-shrinkage damping pad and the damping pad thereon, which can improve the resilience of the pad, thereby improving the utilization rate of the pad, and the pad has strong anti-shrinkage properties.

[0004] To solve the above-mentioned technical problems, the present invention provides a method for preparing an anti-shrinkage damping gasket, comprising: S1: mixing and stirring 95-105 parts by weight of polystyrene particles with 1-3 parts by weight of polyvinyl alcohol particles or polycarbonate particles to form mixed particles; S2: heating the mixed particles until they melt to form a molten material; S3: after the molten material is cooled and shaped at least once to form a sheet blank, placing an insulating sheet between two sheets blanks and connecting them to form a three-layer sheet, extruding the three-layer sheet to form a smooth sheet, and drying the smooth sheet; S4: extruding the dried smooth sheet again to form a textured sheet; S5: cutting the textured sheet to obtain the anti-shrinkage damping gasket. The anti-shrinkage damping gasket can improve the resilience of the gasket, thereby improving the utilization rate of the gasket, and the gasket has strong anti-shrinkage properties.

[0005] In one embodiment of the present invention, after step S5 is completed, static electricity on the surface of the anti-shrinkage damping pad is removed.

[0006] In one embodiment of the present invention, the mixed particles are heated in a barrel until they melt, and the temperature at which the mixed particles melt in the barrel is controlled at 240-300°C.

[0007] In one embodiment of the present invention, the molten material is extruded from the barrel into the mold, the temperature inside the mold is controlled at 210-230°C, a cooling system is provided at the outlet of the mold, and the molten material forms a sheet blank after passing through the cooling system.

[0008] In one embodiment of the present invention, the molten material is extruded into the mold by a screw rotating inside the barrel, and the screw extrusion pressure is controlled at 65-100 MPa.

[0009] In one embodiment of the present invention, the three-layer sheet is extruded by a smooth roller, and the dried smooth sheet is extruded again by a textured roller. The smooth roller and the textured roller are preheated to 55-65°C before extrusion.

[0010] In one embodiment of the present invention, the three-layer sheet is extruded by a smooth roller, the smooth sheet is dried in a drying oven, the smooth sheet is left to stand in the drying oven for 25 to 35 minutes, and the temperature in the drying oven is controlled at 25 to 35°C.

[0011] In one embodiment of the present invention, 1 to 3 parts of SBS toughening agent or 1 to 3 parts of polyolefin anti-aging agent may be added to S1.

[0012] The present invention also provides a shock-absorbing pad, which is prepared by the same method for preparing anti-shrinkage shock-absorbing pads.

[0013] A shock-absorbing pad includes an insulating layer and plastic layers disposed on the upper and lower sides of the insulating layer, wherein the outer side of at least one side of the plastic layer is provided with a plurality of parallel and elastic protrusions.

[0014] The technical solution of the present invention has the following advantages compared with the prior art:

[0015] This invention discloses a method for preparing an anti-shrinkage damping pad and the pad itself. Using polystyrene as the raw material, the anti-shrinkage damping pad is elastic, effectively damping shocks. It exhibits good resilience, is not easily deformed, has high utilization rate, and is resistant to expansion and contraction, with minimal dimensional changes due to thermal expansion and contraction. An insulating sheet is used in the middle, and antistatic auxiliary particles are added to give the pad antistatic properties. Structurally, it employs parallel and elastic protrusions, which not only provide shock absorption and cushioning but also increase the overall strength of the anti-shrinkage damping pad. Attached Figure Description

[0016] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0017] Figure 1 This is a schematic diagram of the cross-ribbed roller extrusion process in the present invention, which describes an anti-shrinkage and shock-absorbing pad and its preparation method.

[0018] Figure 2 This is a schematic diagram of vertical grooved roller extrusion;

[0019] Figure 3 This is a schematic diagram of the texture shape of the textured sheet material;

[0020] Figure 4 This is a side view of the textured sheet material;

[0021] Figure 5 This is a cross-sectional view of the shock-absorbing pad;

[0022] Figure 6 This is a diagram illustrating how to use shock-absorbing pads.

[0023] Explanation of reference numerals in the accompanying drawings: 1. Textured sheet; 2. Vertical grooved roller; 3. Horizontal grooved roller; 4. Insulation layer; 5. Plastic layer; 6. Product; 7. Shock-absorbing pad; 11. Triangular textured sheet; 12. Trapezoidal textured sheet; 13. Semi-circular textured sheet; 14. Single-sided textured sheet; 15. Double-sided textured sheet. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0025] The present invention discloses a method for preparing an anti-shrinkage damping pad, comprising:

[0026] S1: Mix 95-105 parts by weight of polystyrene particles with 1-3 parts by weight of polyvinyl alcohol particles or polycarbonate particles to form mixed particles;

[0027] S2: Heat the mixed particles until they melt to form a molten material;

[0028] S3: After the melted material is cooled and shaped at least once, a sheet blank is formed. An insulating sheet is placed between two sheets and connected to each other to form a three-layer sheet. The three-layer sheet is extruded to form a smooth sheet. The smooth sheet is then dried.

[0029] S4: The dried smooth sheet is extruded again to form a textured sheet;

[0030] S5: Cut the textured sheet to obtain an anti-shrinkage and shock-absorbing pad.

[0031] This invention discloses a method for preparing an anti-shrinkage damping pad. By using polystyrene as the raw material, the anti-shrinkage damping pad is made elastic, which can play a role in damping shock. It has good resilience, is not easily deformed, and has a high utilization rate. It can resist expansion and contraction, and the change in size due to thermal expansion and contraction is small. An insulating sheet is used in the middle, and antistatic auxiliary particles are added to make the pad have antistatic ability.

[0032] S1: 95-105 parts by weight of polystyrene particles and 1-3 parts by weight of polyvinyl alcohol particles or polycarbonate particles are mixed in a mixer until homogeneous, forming a mixed particle. Polystyrene is characterized by low cost, non-absorbency, corrosion resistance, and high insulation, and it is also elastic. The antistatic auxiliary particles are one or more of polyvinyl alcohol particles and polycarbonate. Polyvinyl alcohol has good antistatic ability and chemical stability, and will not cause agglomeration when mixed with polystyrene particles, and it is low in cost. Polycarbonate has high strength and heat resistance, and strong antistatic ability. 1-3 parts by weight of SBS toughening agent can also be added to the raw materials. SBS is a block copolymer of styrene and butadiene, which can improve the toughness, flexural strength, and low-temperature resistance of polystyrene, and has good compatibility with polystyrene. 1-3 parts by weight of polyolefin anti-aging agent can also be added to the raw materials. Polyolefin has good resistance to thermal oxidative degradation, which can improve the anti-yellowing and anti-aging properties of polystyrene, and extend its service life.

[0033] S2: The mixed particles are injected into the barrel through the feeding system. A heater inside the barrel heats the mixed particles until they melt, causing them to transform from a solid to a viscous flow state, forming molten material. The molten material is extruded from the barrel into the die. Specifically, the molten material is extruded through a rotating screw inside the barrel and injected into the die through a nozzle at the end of the barrel. The screw extrusion pressure is controlled at 65–100 MPa. The temperature inside the die is lower than the temperature inside the barrel; the temperature of the molten mixed particles inside the barrel is controlled at 240–300℃, while the temperature inside the die is controlled at 210–230℃.

[0034] S3: After the molten material passes through the cooling system at the mold exit, it forms a sheet blank. Specifically, because the temperature inside the mold is lower than the temperature inside the barrel, the molten material undergoes a first cooling process within the mold to form a sheet. A water circulation cooling system is installed at the mold exit to perform a second cooling process on the molten material, thus forming the sheet blank, which is 0.5mm thick. An insulating sheet is placed between two sheet blanks and connected to each other with adhesive to form a three-layer sheet. Specifically, the insulating sheet is 0.2mm thick and is composed of polyphthalamide, which has antistatic properties, high hardness, high strength, and chemical corrosion resistance. The adhesive used is high-impact polystyrene adhesive, which is easy to use, has high bonding strength, and cures at room temperature. Three-layer sheets are extruded using smooth rollers to form a smooth sheet consisting of two plastic layers on the top and bottom, and an insulating layer in the middle. Specifically, the smooth sheet is 1mm thick. The smooth rollers are preheated to 55-65℃ before extrusion to prevent cracking of the three-layer sheet due to cold compression. The smooth sheet is then dried in a drying oven for 25-35 minutes at a temperature controlled between 25-35℃. This releases internal stress and allows the adhesive to fully solidify. Depending on the application requirements, the die exit size can be adjusted to create sheet blanks of different thicknesses, thus producing anti-shrinkage and shock-absorbing pads of varying thicknesses.

[0035] S4: Reference Figure 1 and Figure 2As shown, the dried smooth sheet is extruded through textured rollers to form textured sheet 1. Specifically, the maximum thickness of textured sheet 1 is 1.2–1.3 mm. The textured rollers are preheated to 55–65°C before extrusion to prevent the smooth sheet from cracking due to cold when the textured rollers extrude it. The textured rollers can be divided into horizontal textured rollers 3 and vertical textured rollers 2. The textures on the rollers are machine-engraved. When manufacturing vertical textured rollers 2, because the textures are vertical, the roller needs to rotate once for each engraved texture, and the rotation speed cannot be too fast. Therefore, repeating this process until the entire roller is engraved takes a long time. However, when the vertical textured rollers 2 rotate and extrude the smooth sheet, the protrusions on the surface of the smooth sheet are simultaneously formed under force. During extrusion, the raised parts of the texture remain in contact with the texture of the roller. Therefore, the vertical textured rollers 2 have higher precision when extruding the smooth sheet, and the elasticity of each area is the same. When manufacturing the horizontally textured roller 3, since the texture is horizontal, the engraving process is horizontal, which is faster. Each engraved texture only requires the roller to rotate a certain angle, thus completing the entire roller engraving process is shorter. However, when the horizontally textured roller 3 rotates and extrudes the smooth sheet, only one texture can be formed at a time. When extruding one texture, the raised portion of the previous texture no longer adheres to the roller's texture, causing a certain degree of bending deformation. Rollers with different textures can be selected based on manufacturing time and processing quality. When manufacturing the texture on the roller, different textures can be engraved according to the shape of the product 6 and usage requirements, thus processing the smooth sheet into textures of different shapes. For example, refer to... Figure 3 As shown, it can be processed into triangular textured sheet 11, trapezoidal textured sheet 12, or semi-circular textured sheet 13. (Refer to...) Figure 4 As shown, single-sided textured sheet 14 and double-sided textured sheet 15 can be manufactured. During manufacturing, double-sided textured sheet 15 can be formed by setting two rollers, one above the other, and pressing the smooth sheet between the two textured rollers.

[0036] S5: The textured sheet is cut to obtain the anti-shrinkage damping pad. It can be cut into damping pads of different sizes according to the application requirements. After cutting, the static electricity on the surface of the anti-shrinkage damping pad can be removed by an ion fan.

[0037] Reference Figure 5 As shown, a shock-absorbing pad of the present invention includes an insulating layer 4 and plastic layers 5 disposed on the upper and lower sides of the insulating layer 4. At least one side of the plastic layer 5 has a plurality of parallel and elastic protrusions on its outer side. (Refer to...) Figure 6As shown, the shock-absorbing pad 7 can have a single-sided or double-sided texture. Double-sided textures are used when multiple products 6 are stacked. Depending on the shape of the product 6 and usage requirements, the texture of the shock-absorbing pad can also be triangular, trapezoidal, semi-circular, or other shapes. When using the shock-absorbing pad, the raised end of the pad contacts the product 6. When vibration occurs, the raised portion will tilt and deform to both sides. Due to the elasticity of the raised portion, it can act as a buffer. The raised portions can be parallel and equidistant, and all raised portions have the same height, thus ensuring stable and uniform shock absorption in all areas of the shock-absorbing pad, preventing damage to the product 6 in a certain area due to uneven stress caused by poor elasticity in one area. The raised portion acts like a reinforcing rib, increasing the overall strength of the shock-absorbing pad; reducing the changes in size due to thermal expansion and contraction, and enhancing the stability of the shock-absorbing pad. The end of the protrusion that contacts the product 6 can be roughened to enhance the friction between the protrusion and the product 6 and prevent the product 6 from shifting during storage or transportation.

[0038] The following specific embodiments further illustrate the preparation method of the anti-shrinkage damping pad of the present invention:

[0039] Example 1:

[0040] S1: Mix 1 kg of polystyrene particles with 10 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0041] S2: The mixed particles are injected into the feed cylinder through the feeding system. The heater inside the cylinder heats the mixed particles until they melt. The temperature of the melted mixed particles inside the cylinder is 260℃, forming molten material. The molten material is extruded by the rotating screw inside the cylinder and injected into the mold through the nozzle at the end of the cylinder. The screw extrusion pressure is 80MPa, and the temperature inside the mold is 220℃.

[0042] S3: The molten material undergoes a first cooling process within the mold to form a sheet. A water circulation cooling system at the mold exit further cools the molten material, forming a 0.5mm thick sheet blank. An insulating sheet is placed between two sheet blanks and connected with adhesive to form a three-layer sheet. The insulating sheet is 0.2mm thick and its main component is polyphthalamide. High-impact polystyrene adhesive is used. The three-layer sheet is then extruded using a smooth roller to form a smooth sheet, which is 1mm thick. The smooth sheet is then dried in a drying oven, where it is left to stand for 30 minutes at a temperature controlled at 30℃.

[0043] S4: The dried smooth sheet is extruded through a roller with vertical grooves to form a textured sheet, wherein the maximum thickness of the textured sheet is 1.2mm.

[0044] S5: The textured sheet is cut to obtain the anti-shrinkage damping pad, and the static electricity on the surface of the anti-shrinkage damping pad is removed by an ion fan.

[0045] Example 2:

[0046] S1: Mix 1 kg of polypropylene particles with 10 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0047] The remaining steps are the same as in Example 1, and will not be repeated here.

[0048] Example 3:

[0049] S1: Mix 1 kg of ABS material particles with 10 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0050] The remaining steps are the same as in Example 1, and will not be repeated here.

[0051] Example 4:

[0052] S1: Mix 1 kg of polyethylene particles with 10 g of polyvinyl alcohol particles using a mixer until they are evenly mixed to form a mixed particle.

[0053] The remaining steps are the same as in Example 1, and will not be repeated here.

[0054] Example 5:

[0055] S1: Mix 1 kg of polyvinyl chloride particles with 10 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0056] The remaining steps are the same as in Example 1, and will not be repeated here.

[0057] The performance of the anti-shrinkage damping pads prepared in Examples 1-5 was tested, and the test results are shown in Table 1:

[0058] Table 1: Performance Test Table for Shrink-Resistant Damping Gaskets

[0059] density Solution flow rate Shrinkage Tensile strength Example 1 <![CDATA[0.91g / cm 3 ]]> 3.65g / 10min 0.7％ 60MPa Example 2 0.96g / cm3 3.21g / 10min 1.8％ 30MPa Example 3 1.1g / cm3 2.2g / 10min 0.5％ 38MPa Example 4 0.97g / cm3 1.96g / 10min 2.3％ 20MPa Example 5 1.38g / cm3 1.1g / 10min 0.4％ 59MPa

[0060] When the material density is high, the anti-shrinkage damping pad is heavy, and it is not easy to handle large-sized anti-shrinkage damping pads. Therefore, materials with lower density should be selected.

[0061] When the melt flow rate is slow, the flowability is poor, the flow speed in the mold is slow, and the molding speed is slow. Therefore, materials with a faster melt flow rate should be selected.

[0062] When the shrinkage rate is too high, it is difficult to control the thickness and size of the anti-shrinkage damping pad, and it is also more sensitive to temperature, with large dimensional changes during thermal expansion and contraction; when the shrinkage rate is too low, the anti-shrinkage damping pad has high structural strength but poor toughness and elasticity, resulting in poor damping effect. Therefore, materials with a low shrinkage rate should be selected.

[0063] When the tensile strength is low, the anti-shrinkage damping pad is prone to cracking, so materials with higher tensile strength should be selected.

[0064] In conclusion, polystyrene is the preferred material.

[0065] Example 6:

[0066] S1: Mix 0.8 kg of polystyrene particles with 20 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0067] The remaining steps are the same as in Example 1, and will not be repeated here.

[0068] Example 7:

[0069] S1: Mix 0.95 kg of polystyrene particles with 20 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0070] The remaining steps are the same as in Example 1, and will not be repeated here.

[0071] Example 8:

[0072] S1: Mix 1.05 kg of polystyrene particles with 20 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0073] The remaining steps are the same as in Example 1, and will not be repeated here.

[0074] Example 9:

[0075] S1: Mix 1.2 kg of polystyrene particles with 20 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0076] The remaining steps are the same as in Example 1, and will not be repeated here.

[0077] Example 10:

[0078] S1: Mix 0.95 kg of polystyrene particles with 30 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0079] The remaining steps are the same as in Example 1, and will not be repeated here.

[0080] Example 11:

[0081] S1: Mix 1.05 kg of polystyrene particles with 10 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0082] The remaining steps are the same as in Example 1, and will not be repeated here.

[0083] Example 12:

[0084] S1: Mix 0.95 kg of polystyrene particles with 50 g of polyvinyl alcohol particles using a mixer until homogeneous to form mixed particles.

[0085] The remaining steps are the same as in Example 1, and will not be repeated here.

[0086] The performance of the anti-shrinkage damping pads prepared in Examples 6-12 was tested, and the test results are shown in Table 2:

[0087] Table 2: Performance Test Table for Shrink-Resistant Damping Gaskets

[0088] density melt flow rate Shrinkage Tensile strength Antistatic resistance value Example 6 0.98g / cm3 3.60g / 10min 0.65％ 50MPa <![CDATA[10 14 ]]> Example 7 0.93g / cm3 3.62g / 10min 0.71％ 58MPa <![CDATA[10 10 ]]> Example 8 0.95g / cm3 3.63g / 10min 0.73％ 56MPa <![CDATA[10 12 ]]> Example 9 1.02g / cm3 3.55g / 10min 0.75％ 50MPa <![CDATA[10 8 ]]> Example 10 1.03g / cm3 3.51g / 10min 0.69％ 58MPa <![CDATA[10 21 ]]> Example 11 0.92g / cm3 3.64g / 10min 0.63％ 58MPa <![CDATA[10 7 ]]> Example 12 1.03g / cm3 3.51g / 10min 0.71％ 48MPa <![CDATA[10 24 ]]>

[0089] In practical applications, the tensile strength should be above 55 MPa, and the antistatic resistance value should be above 10. 7 Therefore, the optimal choice is to use 95-105 parts by weight of polystyrene particles and 1-3 parts by weight of antistatic additives.

[0090] This invention discloses a method for preparing an anti-shrinkage shock-absorbing pad. Using polystyrene as the raw material, the pad exhibits elasticity, effectively damping shocks with good resilience, resistance to deformation, and high utilization rate. It also boasts a low shrinkage rate, resisting both expansion and contraction, and minimizing dimensional changes due to thermal expansion and contraction. Furthermore, its low density and lightweight nature make it easy to handle. The fast melt flow rate allows for rapid manufacturing. High tensile strength reduces the likelihood of cracking, enhancing adaptability and resulting in high utilization and a long service life. The use of an insulating sheet and the addition of antistatic additives further enhance the pad's antistatic properties. Structurally, the parallel and elastic protrusions provide both shock absorption and cushioning, while also increasing the overall strength of the anti-shrinkage shock-absorbing pad, reducing dimensional changes due to thermal expansion and contraction, and improving its stability.

[0091] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method of making an anti-shrinkage shock pad, characterized in that, It comprises: S1: mixing and stirring 95-105 parts of polystyrene particles with 1-3 parts of polyvinyl alcohol particles or polycarbonate particles by weight to form mixed particles; S2: heating the mixed particles until melting to form molten material; S3: after at least one cooling and molding of the molten material, a sheet blank is formed, an insulating sheet is placed between two sheet blanks and connected to each other to form a three-layer sheet, the three-layer sheet is extruded and molded to form a smooth sheet, and the smooth sheet is dried; S4: the dried smooth sheet is extruded and molded again to form a textured sheet; S5: cutting the textured sheet to obtain an anti-shrinkage shock pad.

2. The method of claim 1, wherein: After S5 is completed, the static electricity on the surface of the anti-shrinkage shock pad is removed.

3. The method of claim 1, wherein: The mixed particles are heated in the barrel until melting, and the temperature of the mixed particles in the barrel is controlled at 240-300℃.

4. The method of claim 3, wherein: The molten material is extruded from the barrel into a mold, the temperature in the mold is controlled at 210-230℃, the outlet position of the mold is provided with a cooling system, and the molten material forms a sheet blank after passing through the cooling system.

5. The method of claim 4, wherein: The molten material is extruded into the mold by the rotation of the screw in the barrel, and the extrusion pressure of the screw is controlled at 65-100MPa.

6. The method of claim 1, wherein: The three-layer sheet is extruded and molded by a smooth roller, the dried smooth sheet is extruded and molded again by a textured roller, and the smooth roller and the textured roller are preheated to 55-65℃ before extrusion and molding.

7. The method of claim 1, wherein: The smooth sheet is dried in a drying oven, the smooth sheet is placed in the drying oven for 25-35 minutes, and the temperature in the drying oven is controlled at 25-35℃.

8. The method of claim 1, wherein: 1-3 parts of SBS toughening agent or 1-3 parts of polyolefin anti-aging agent are added in S1.

9. A shock pad characterized in that, The anti-shrinkage shock pad is prepared by the method of any one of claims 1-8.

10. A shock pad according to claim 9, wherein, It comprises an insulating layer and plastic layers arranged on the upper and lower sides of the insulating layer, and a plurality of elastic protrusions are arranged on the outer side of at least one plastic layer.

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