Impact cushioning structure and method of making same

Abstract

This application discloses an impact buffer structure, which includes an inner support, a buffer layer, and a paint layer. The buffer layer is disposed on the outer surface of the inner support, and the paint layer is disposed on the outer surface of the buffer layer. The buffer layer contains a mesh and multiple layers of carbon fiber balls. This application can improve the buffering capacity of the impact buffer structure and increase its service life.

Description

Technical Field

[0001] This application relates to the field of impact buffer structures, and in particular to anti-collision structures and their preparation methods. Background Technology

[0002] Collisions frequently occur during vehicle movement. Minor collisions often cause paint to peel off, while major collisions often cause the anti-collision structure to break. How to improve the anti-fracture capability of the anti-collision structure and extend its service life has always been a problem. Summary of the Invention

[0003] To address the problems existing in the prior art, this application discloses an impact buffer structure, which includes an inner support, a buffer layer, and a paint layer. The buffer layer is disposed on the outer surface of the inner support, and the paint layer is disposed on the outer surface of the buffer layer.

[0004] The buffer layer contains a mesh and multiple layers of carbon fiber balls.

[0005] An adhesive is provided between the carbon fiber spheres in the buffer layer. At least three layers of carbon fiber spheres are provided within the buffer layer. One side of the mesh is provided with the carbon fiber sphere layer, and the other side of the mesh is provided on the surface of the inner support. Carbon fiber is mainly composed of carbon elements and can be made from acrylic fiber and viscose fiber through high-temperature oxidation and carbonization. It possesses high-temperature resistance, friction resistance, thermal conductivity, and corrosion resistance. Carbon fiber is fibrous and flexible. Due to its graphite microcrystalline structure preferentially oriented along the fiber axis, it has high strength and modulus along the fiber axis. In addition, carbon fiber also includes multi-walled carbon nanotubes. Experiments have shown that multi-walled carbon nanotubes have better spheroidization performance during spray granulation. The diameter of the carbon fiber is 100nm-10µm, and the diameter of the carbon fiber spheres is 5-50µm. The diameter of the carbon fiber spheres can be adjusted according to the solution concentration (the content of carbon fiber in the solution) and the nozzle size of the spray gun during the spray granulation process. Because carbon fiber... The carbon fiber balls have a porous structure and high toughness, which can buffer impact stress when a minor impact occurs. When the impact force increases, they can break through the paint layer and cause the carbon fiber balls to shift, further buffering the impact stress through the shift of the carbon fiber balls. As long as the inner support is not broken, the surface scratches caused by the break can be repaired by spraying a carbon fiber ball solution containing adhesive and drying it, which is convenient and equivalent to improving the service life of the impact protection structure. Compared with some existing technologies that use foam to protect the impact protection structure, the chemical stability of foam is much lower than that of carbon fiber, so the impact buffer structure of this application has a longer service life. In addition, compared with the buffer layer being a solid fiber layer, the fiber layer cannot form the carbon fiber ball displacement function, so the fiber layer is prone to stress concentration at the most severely impacted position during the impact, which can easily cause the support below (or behind) the buffer layer to break.

[0006] A method for fabricating an impact buffer structure, the method comprising the following steps:

[0007] Step P1: Prepare carbon fiber spheres;

[0008] Step P2: Place carbon fiber spheres on the surface of the inner support.

[0009] Step P3: Apply a coating to the surface of the carbon fiber ball.

[0010] Step P1 includes the following steps:

[0011] Step F1: Mixing. Place the carbon fiber and soluble salt solution in a mixing container and ultrasonically stir until homogeneous.

[0012] Step F2: Spray granulation. The liquid in the mixed solution is spray-dried using a spray drying device to obtain the first carbon fiber ball. The spray drying process is as follows: the spray drying device adsorbs the mixed solution through a pipe to a high-temperature nozzle. The high-temperature nozzle has many tiny nozzles. The mixed solution in the high-temperature nozzle is sprayed out through the tiny nozzles under high pressure to form salt water droplets. The salt water droplets contain carbon fibers and soluble salts. An air supply device is installed outside the high-temperature nozzle. After passing through the air supply device and high-temperature and high-pressure spraying, the water in the salt water droplets is rapidly evaporated. At the same time, the carbon fibers in the salt water droplets agglomerate into carbon fiber balls and the soluble salts precipitate out to form soluble salt balls. Due to the blocking effect of the carbon fibers, the soluble salts precipitate out in the form of soluble salt balls between the carbon fibers inside the first carbon fiber ball.

[0013] Step F3, water washing: The first carbon fiber ball formed in step F2 is washed with water. During the water washing process, soluble salts dissolve, thereby forming sacrificial pores at the original soluble salt ball positions, thereby increasing the internal space of the carbon fiber ball and improving the buffering capacity.

[0014] Step F4: Drying. The first carbon fiber ball that has passed through step F3 is dried to obtain the second carbon fiber ball.

[0015] The soluble salt in the soluble salt solution of step F1 includes sodium chloride, and the solvent is water. Sodium chloride and water are readily available and will not cause pollution to the environment.

[0016] The carbon fiber used in step F1 includes multi-walled carbon nanotubes.

[0017] Step P2 includes the following process:

[0018] Step S1: Laying the attached mesh on the metal platform;

[0019] Step S2: Coating and drying. The solution containing the carbon fiber balls and adhesive is sprayed onto the upper surface of the attachment mesh through a coating gun and then dried. After the drying process, the solvent in the solution is evaporated, resulting in a carbon fiber ball and adhesive coating adhering to the upper surface of the attachment mesh.

[0020] Step S3: Separate by shovel, separating the attached mesh from the metal platform.

[0021] The surface of the metal stage is smooth, which means that the surface roughness Ra value is less than 0.02. Since the mesh is a porous structure, the coating solution will penetrate into the metal stage through the mesh. The smooth surface of the metal stage is required to reduce the adhesion between the coating and the surface of the metal stage after coating and drying, so as to facilitate separation and obtain a complete coating.

[0022] The solvent used in step S2 is water, and the binder is polyvinylidene fluoride. The mass ratio of the binder to the carbon fiber balls in the coating is 0.2-0.4. When the mass ratio is less than 0.2, powder is easily shed during the process of attaching the mesh and carbon fiber balls to the surface of the inner support and during the painting process, which does not meet the product quality requirements. When the mass ratio is greater than 0.4, a large amount of binder will fill the gaps between the carbon fiber balls and the voids inside the carbon fiber balls, reducing the deformation ability and slippage ability of the carbon fiber balls, thus making the impact buffering ability not meet the quality requirements.

[0023] The bottom of the metal platform is equipped with rollers, which are equipped with locking devices. During the coating process in step S2, the rollers are locked. During the transfer to the drying oven after coating in step S2, the rollers are unlocked to facilitate pushing the metal platform and thus the attached mesh above the metal platform and the mixed layer coated and dried on the surface of the attached mesh. Since the mixed layer has a high solvent content at this time, the mixed layer is easy to flow, which increases the difficulty of transferring it to the drying process after coating. By moving the metal platform synchronously, the problem of insufficient coating uniformity caused by the flow of the mixed chamber is reduced. During the drying process, the rollers are locked.

[0024] In step S3, a metal spatula is used to pull the mesh or coating along the contact surface between the mesh and the metal platform. While holding the mesh, the metal spatula is slid along the surface of the metal platform to remove the mesh or coating from the surface of the metal platform. Compared with directly peeling off the mesh with coating on the surface of the metal platform, the spatula separation method reduces the adhesion between the coating and the metal platform caused by the adhesive, and makes it easier to obtain a complete coating structure.

[0025] Step P2 further includes the following step: rolling the composite structure of the attached mesh and coating obtained in step S3. After rolling, the carbon fiber balls can be more tightly connected, preventing the carbon fiber balls from falling off during the painting process. The thickness difference of the composite structure of the attached mesh and coating before and after rolling can be adjusted according to the thickness of the buffer layer, the porosity of the carbon fiber balls, the number of layers of carbon fiber balls, and the target buffer stress.

[0026] The method disclosed in this application has the following advantages:

[0027] Because carbon fiber balls have a porous structure and high toughness, they can buffer impact stress when minor impacts occur. When the impact force increases, they can break the paint layer or cause the carbon fiber balls to shift, further buffering the impact stress through the shift of the carbon fiber balls. As long as the inner support is not broken, surface scratches caused by the breakage can be repaired by spraying a carbon fiber ball solution containing adhesive and drying it, making repair convenient and effectively increasing the service life of the anti-collision structure. Compared with some existing technologies that use foam to protect the anti-collision structure, the chemical stability of foam is much lower than that of carbon fiber, resulting in a lower service life than the impact buffer structure of this application. In addition, compared with a single fiber layer as the buffer layer, the fiber layer cannot facilitate the shifting of carbon fiber balls, making it easy for stress concentration to form at the most severely impacted location during impact, which can easily cause the support below (or behind) the buffer layer to break. However, the carbon fiber balls can shift during impact, which is equivalent to causing the impacting object to slide, thus buffering the stress concentration.

[0028] Meanwhile, by pre-forming a composite structure between the attached mesh and the coating containing carbon fiber balls, and then using the composite structure to wrap around the inner support, the bonding process between the composite structure and the inner support is simplified. By setting a carbon fiber ball layer on one side of the attached mesh and wrapping the inner support on the other side of the attached mesh, the presence of the attached mesh is equivalent to increasing the surface roughness of the inner support, thereby increasing the bonding force between the carbon fiber balls and the surface of the inner support, thus solving the problem of low bonding force between the carbon fiber balls and the surface of the inner support. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0030] Figure 1 This is a schematic diagram of the overall impact buffer structure and a schematic diagram of the AA section location in this application.

[0031] Figure 2 This application Figure 1 The diagram shows the cross-section of section AA and the enlarged view of section E.

[0032] Figure 3 This application Figure 2Enlarged view of the position of E in the middle.

[0033] Figure 4 This is an overall flowchart of the method for preparing the impact buffer structure of this application.

[0034] Figure 5 This is a schematic diagram of the mixing state in step P1 of this application.

[0035] Figure 6 This is a schematic diagram of the brine droplet structure during the spray granulation process in step P1 of this application.

[0036] Figure 7 This is a schematic diagram of the structure of the first carbon fiber ball after the spray granulation process in step P1 of this application.

[0037] Figure 8 This is a schematic diagram of the structure of the second carbon fiber ball after water washing and drying in step P1 of this application.

[0038] Figure 9 This is a schematic diagram of step P1 of this application.

[0039] Figure 10 This is a schematic diagram of the process of spraying a solution containing carbon fiber balls onto the surface of the attached mesh.

[0040] Figure 11 This is a schematic diagram of step S1 of this application.

[0041] Figure 12 This is a schematic diagram of step S2 of this application.

[0042] Figure 13 This is a schematic diagram of step S3 of this application.

[0043] Figure 14 This is a schematic diagram of the overall process of step P2 in this application.

[0044] 1 Impact buffer structure 11 Internal support 12 Buffer layer 121 carbon fiber ball 1211 First carbon fiber ball 1212 Second carbon fiber ball 13 paint layer 14 Attached network 21 Mixing container 23 carbon fiber 25 soluble salt solution 26 Soluble salt balls 260 Sacrifice Hole 27 Saltwater droplets 41 metal table 42 Coating gun AA Figure 1 Schematic position of cross section E Figure 2 Enlarged schematic position Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention;

[0046] like Figure 1-14 As shown, in order to solve the problems existing in the prior art, this application discloses an impact buffer structure 1, which includes an inner support 11, a buffer layer 12, and a paint layer 13. The buffer layer 12 is disposed on the outer surface of the inner support 11, and the paint layer 13 is disposed on the outer surface of the buffer layer 12.

[0047] The buffer layer 12 is provided with a mesh 14 and multiple carbon fiber balls 121.

[0048] An adhesive is provided between the carbon fiber balls 121 in the buffer layer 12. At least three layers of carbon fiber balls 121 are provided in the buffer layer 12. One side of the attached mesh 14 is provided with the carbon fiber ball 121 layer, and the other side of the attached mesh 14 is provided on the surface of the inner support 11. The carbon fiber 23 is mainly composed of carbon elements and can be made from acrylic fiber and viscose fiber as raw materials, and is produced by high-temperature oxidation and carbonization. It has the characteristics of high temperature resistance, friction resistance, thermal conductivity and corrosion resistance. The carbon fiber 23 is fibrous and soft. Due to its graphite microcrystalline structure preferentially oriented along the fiber axis, it has high strength and modulus along the fiber axis. In addition, the carbon fiber 23 also includes multi-walled carbon nanotubes. It has been found through experiments that multi-walled carbon nanotubes have better spheroidization performance in the spray granulation process. The diameter of the carbon fiber 23 is 100nm-10um, and the diameter of the carbon fiber ball 121 is 5-50um. The diameter of the carbon fiber ball 121 can be adjusted according to the solution concentration (the content of carbon fiber 23 in the solution) and the nozzle size of the spray gun in the spray granulation process. Because the carbon fiber balls 121 have a porous structure and high toughness, they can buffer impact stress when a minor impact occurs. When the impact force increases, they can break the paint layer 13 and cause the carbon fiber balls 121 to shift, further buffering the impact stress through the shift of the carbon fiber balls 121. As long as the inner support 11 is not broken, the surface scratches caused by the breakage can be repaired by spraying a carbon fiber ball 121 solution containing adhesive and drying it, which is convenient for repair and equivalent to improving the service life of the anti-collision structure. Compared with some existing technologies that use foam to protect the anti-collision structure, the chemical stability of foam is much lower than that of carbon fiber 23, so it does not have a longer service life than the impact buffer structure 1 of this application. In addition, compared with the buffer layer 12 being a solid fiber layer, the fiber layer cannot form the function of shifting carbon fiber balls 121, so the fiber layer is prone to stress concentration at the most severe impact position during the impact, which can easily cause the support below (or behind) the buffer layer 12 to break.

[0049] A method for preparing an impact buffer structure 1, the method comprising the following steps:

[0050] Step P1: Prepare carbon fiber spheres 121;

[0051] Step P2: Place the carbon fiber ball 121 on the surface of the inner support 11;

[0052] Step P3: Apply paint layer 13 to the surface of carbon fiber ball 121.

[0053] Step P1 includes the following steps:

[0054] Step F1, mixing: carbon fiber 23 and soluble salt solution 25 are placed in mixing container 21 and ultrasonically stirred until homogeneous;

[0055] Step F2: Spray granulation. The liquid in the mixed solution is spray-dried using a spray drying device to obtain the first carbon fiber ball 1211. The spray drying process is as follows: the spray drying device adsorbs the mixed solution through a pipe to a high-temperature nozzle. The high-temperature nozzle has many small nozzles. The mixed solution in the high-temperature nozzle is sprayed out through the small nozzles under high pressure to form salt water droplets 27. The salt water droplets 27 contain carbon fibers 23 and soluble salts. An air supply device is installed outside the high-temperature nozzle. After passing through the air supply device and high-temperature and high-pressure spraying, the water in the salt water droplets 27 is rapidly evaporated. At the same time, the carbon fibers 23 in the salt water droplets 27 agglomerate into carbon fiber balls 121 and soluble salts precipitate out to form soluble salt balls 26. Due to the blocking effect of carbon fibers 23, soluble salts precipitate out in the form of soluble salt balls 26 between the carbon fibers 23 inside the first carbon fiber ball 1211.

[0056] Step F3, water washing: The first carbon fiber ball 1211 formed in step F2 is washed with water. During the water washing process, soluble salts dissolve, thereby forming sacrificial holes 260 at the original soluble salt ball 26 position, thereby increasing the internal space of the carbon fiber ball 121 and improving the buffering capacity.

[0057] Step F4: Drying. The first carbon fiber ball 1211, which has passed through step F3, is dried to obtain the second carbon fiber ball 1212.

[0058] The soluble salt in the soluble salt solution of step F1 includes sodium chloride, and the solvent is water. Sodium chloride and water are readily available and will not cause pollution to the environment.

[0059] The carbon fiber 23 used in step F1 includes multi-walled carbon nanotubes.

[0060] Step P2 includes the following process:

[0061] Step S1: Lay the auxiliary net 14 on the metal platform 41.

[0062] Step S2: Coating and drying. The solution containing the carbon fiber balls 121 and the adhesive is sprayed onto the upper surface of the attachment 14 through the coating gun 42 and dried. After the drying process, the solvent in the solution is evaporated, and a coating of carbon fiber balls 121 and adhesive is obtained on the upper surface of the attachment 14.

[0063] Step S3: Separate by shovel, separating the attached net 14 from the metal platform 41.

[0064] The surface of the metal stage 41 is smooth, which means that the surface roughness Ra value is less than 0.02. Since the attachment mesh 14 is a porous structure, the coating solution will penetrate into the metal stage 41 through the attachment mesh 14. The requirement for the surface of the metal stage 41 to be smooth is to reduce the adhesion between the coating and the surface of the metal stage 41 after coating and drying, so as to facilitate separation and obtain a complete coating.

[0065] The solvent used in step S2 is water, and the binder is polyvinylidene fluoride. The mass ratio of the binder to the carbon fiber balls 121 in the coating is between 0.2 and 0.4. When the mass ratio is less than 0.2, powder is easily shed during the process of attaching the mesh 14 and the carbon fiber balls 121 to the surface of the inner support 11 and during the painting process, which does not meet the product quality requirements. When the mass ratio is greater than 0.4, a large amount of binder will fill the gaps between the carbon fiber balls 121 and the voids inside the carbon fiber balls 121, which reduces the deformation ability and sliding ability of the carbon fiber balls 121, thus making the impact buffering ability not meet the quality requirements.

[0066] The bottom of the metal platform 41 is equipped with rollers, which are equipped with locking devices. During the coating process in step S2, the rollers are locked. During the transfer to the drying oven after coating in step S2, the rollers are unlocked to facilitate pushing the metal platform 41 and thus the auxiliary mesh 14 above the metal platform 41 and the mixed layer coated and dried on the surface of the auxiliary mesh 14. Since the mixed layer has a high solvent content at this time, the mixed layer is easy to flow, which increases the difficulty of transferring it to the drying process after coating. By moving the metal platform 41 synchronously, the problem of insufficient coating uniformity caused by the flow of the mixing chamber is reduced. During the drying process, the rollers are locked.

[0067] In step S3, a metal shovel is used to pull the mesh 14 or coating along the contact surface with the metal platform 41. While holding the mesh 14, the metal shovel is slid along the surface of the metal platform 41 to remove the mesh 14 or coating from the surface of the metal platform 41. Compared with directly peeling off the mesh 14 with coating from the surface of the metal platform 41, the shovel separation method reduces the adhesion between the coating and the metal platform 41 caused by the adhesive, and makes it easier to obtain a complete coating structure.

[0068] Step P2 further includes the following step: rolling the attached mesh 14 and the coating composite structure obtained in step S3. After rolling, the carbon fiber balls 121 can be more tightly connected, preventing the carbon fiber balls 121 from falling off during the painting process. The thickness difference between the attached mesh 14 and the coating composite structure before and after rolling can be adjusted according to the thickness of the buffer layer 12, the porosity of the carbon fiber balls 121, the number of layers of carbon fiber balls 121, and the target buffer stress.

[0069] The method disclosed in this application has the following advantages:

[0070] Because the carbon fiber balls 121 have a porous structure and high toughness, they can buffer impact stress when a minor impact occurs. When the impact force increases, they can break the paint layer 13 and cause the carbon fiber balls 121 to shift, further buffering the impact stress through the shift of the carbon fiber balls 121. As long as the inner support 11 is not broken, the surface scratches caused by the breakage can be repaired by spraying a carbon fiber ball 121 solution containing adhesive and drying it, which is convenient for repair and equivalent to improving the service life of the anti-collision structure. Compared with some existing technologies that use foam to protect the anti-collision structure, the service life of the impact buffer structure 1 of this application is not as high because the chemical stability of foam is much lower than that of carbon fiber 23. In addition, compared with the buffer layer 12 being a solid fiber layer, the fiber layer cannot form the effect of shifting the carbon fiber balls 121, which makes it easy for the fiber layer to form stress concentration at the most severe impact position during the impact, thus making it easy for the support below (or behind) the buffer layer 12 to break. However, the carbon fiber balls 121 can shift during the impact, which is equivalent to causing the impacting object to slide, thereby buffering the stress concentration.

[0071] Meanwhile, by pre-forming a composite structure between the attached mesh 14 and the coating containing carbon fiber balls 121, and then using the composite structure to wrap around the inner support 11, the bonding process between the composite structure and the inner support 11 is simplified. By setting a layer of carbon fiber balls 121 on one side of the attached mesh 14 and wrapping the inner support 11 on the other side of the attached mesh 14, the presence of the attached mesh 14 is equivalent to increasing the surface roughness of the inner support 11, thereby increasing the bonding force between the carbon fiber balls 121 and the surface of the inner support 11, thus solving the problem of low bonding force between the carbon fiber balls 121 and the surface of the inner support 11.

Claims

1. A method for preparing an impact buffer structure, characterized in that, The method comprises the following steps: Step P1, preparing carbon fiber balls; Step P2, setting the carbon fiber balls on the surface of the inner support body; Step P3, setting a paint layer on the surface of the carbon fiber balls; The impact buffering structure prepared by the method comprises an inner support body, a buffering layer, and a paint layer, wherein the buffering layer is arranged on the outer surface of the inner support body; The buffering layer is provided with an auxiliary net and a plurality of layers of carbon fiber balls, the carbon fiber balls are provided with a bonding agent therebetween, and the buffering layer is provided with at least three layers of carbon fiber balls, one side of the auxiliary net is provided with a layer of carbon fiber balls, and the other side of the auxiliary net is arranged on the surface of the inner support body. The step P1 comprises the following steps: Step F1, mixing, the carbon fiber and the soluble salt solution are arranged in a mixing container and are uniformly stirred by ultrasonic; Step F2, spray granulation, the liquid in the mixed solution is spray dried by a spray drying device to obtain first carbon fiber balls, the spray drying process is as follows: the spray drying device absorbs the mixed solution through a pipeline to a high-temperature nozzle, the high-temperature nozzle has a plurality of small nozzles, the mixed solution in the high-temperature nozzle is sprayed out under high pressure through the small nozzles to form salt water droplets, the salt water droplets contain carbon fiber and soluble salt, a ventilation device is arranged outside the high-temperature nozzle, and the moisture in the salt water droplets is rapidly evaporated through the ventilation device and high-temperature high-pressure spraying, at the same time, the carbon fiber in the salt water droplets is aggregated into carbon fiber balls and the soluble salt is precipitated to form soluble salt balls, due to the blocking effect of the carbon fiber, the soluble salt is precipitated in the form of soluble salt balls between the carbon fiber in the first carbon fiber balls; Step F3, water washing, the first carbon fiber balls formed in the step F2 are subjected to a water washing process, in the water washing process, the soluble salt is dissolved, so that sacrifice holes are formed at the positions of the original soluble salt balls, thereby increasing the internal space of the carbon fiber balls and improving the buffering capacity; Step F4, drying, the first carbon fiber balls subjected to the step F3 are dried to obtain second carbon fiber balls, The soluble salt in the soluble salt solution of the step F1 comprises sodium chloride, and the solvent is water, The carbon fiber used in the step F1 comprises a multi-walled carbon tube.

2. The method of claim 1, wherein the method further comprises the step of: The step P2 comprises the following processes: Step S1, auxiliary net laying metal table, the auxiliary net is laid on the metal table; Step S2, coating and drying, a solution containing the carbon fiber balls and the bonding agent is sprayed onto the upper surface of the auxiliary net by a coating gun and is dried; Step S3, shovel separation, the auxiliary net is separated from the metal table.

3. A method of preparing a shock cushioning structure according to claim 2, wherein The surface of the metal table is smooth, and the surface smoothness means that the surface roughness Ra value is less than 0.02; The solvent of the solution used in the step S2 is water, the bonding agent is polyvinylidene fluoride, and the mass ratio of the bonding agent to the carbon fiber balls in the coating layer is 0.2-0.

4.

4. A method of preparing a shock cushioning structure according to claim 3, wherein The bottom of the metal table is provided with a roller, the roller is provided with a locking device, the roller is locked in the coating process of the step S2, and the roller is unlocked in the process of transferring to the oven after the coating of the step S2; In the step S3, a metal shovel is used along the contact surface of the auxiliary net or the coating layer and the metal table, the auxiliary net is pulled, and at the same time, the metal shovel is slid along the surface of the metal table, so that the auxiliary net or the coating layer on the surface of the metal table is removed.

5. A method of preparing a shock cushioning structure according to claim 4, wherein The step P2 further comprises the following step: rolling the web and coating composite structure obtained in the step S3. The step P2 further comprises the following step: rolling the web and coating composite structure obtained in the step S3.

Images