A selectively foamed multilayer flexible composite material and methods of making and using the same

Abstract

This invention belongs to the field of polymer materials technology, specifically relating to a selectively foamed multilayer flexible composite material, its preparation method, and its applications. The invention uses a flexible elastomer as a matrix, blending it with different conductive fillers to form flexible matrix blend systems with different conductive fillers. Since the conductive fillers have varying effects on the mechanical strength of the system, after layer-by-layer casting or hot pressing, high-pressure fluid foaming is used to obtain a flexible composite material with a cellular structure in only some layers. When made into a three-layer structure, the resulting composite material can be used as an integrated sensor, exhibiting excellent adhesion, resistance to delamination, and high stability.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a selectively foamed multilayer flexible composite material, its preparation method, and its application. Background Technology

[0002] With the development of social technology, highly sensitive, highly flexible, and lightweight flexible sensors can be used for detecting human motion, robotic electronic skin, soft grippers, health monitoring, and more. Polyurethane foam materials are widely used in flexible sensing materials due to their light weight, durability, and high flexibility. However, the electrode layer and dielectric layer of traditional capacitive foam sensors are usually encapsulated through multi-layer composite methods such as bonding. This method results in obvious interfaces between sensor layers, and the interface defects between these layers affect the sensor's mechanical response and operational stability.

[0003] Current technologies for fabricating sensors with integrated electrode and functional layers primarily involve bonding and layering conductive fillers of varying amounts or types onto the electrode and functional layers of a foam sensor. However, integrated sensors fabricated in this way often experience filler detachment after repeated use, severely impacting the sensor's durability and sensing stability. Summary of the Invention

[0004] This invention aims to address the packaging problem of multi-layer composite sensor structures, solve the mechanical mismatch between the electrode layer and the functional layer of the sensor, and complete the integrated fabrication of the electrode layer and the functional layer of the foam sensor.

[0005] Specifically, in one aspect, the present invention provides a method for preparing a selectively foamed multilayer flexible composite material, comprising the following steps:

[0006] (1) The flexible matrix is ​​blended with the first conductive filler and the second conductive filler to obtain the first blend and the second blend, wherein the first conductive filler is a filler that can increase the mechanical strength of the flexible matrix blend system and the second conductive filler is a filler that can toughen the flexible matrix blend system, so that the melt strength of the first blend is greater than the melt strength of the second blend.

[0007] (2) The first blend and the second blend are combined by layer-by-layer casting or hot pressing to obtain a foamed preform;

[0008] (3) Inject the gas used as a foaming agent into the foamed preform under closed conditions and perform saturation treatment until the dissolution of the foaming agent gas in the foamed preform reaches saturation. Then, quickly depressurize to obtain a selectively foamed multilayer flexible composite material in which only the second blend is cast and foamed.

[0009] Furthermore, the hardness of the flexible substrate is 60-80A.

[0010] Furthermore, the flexible matrix is ​​selected from one or more of polyurethane, thermoplastic polyurethane, polydimethylsiloxane, and silicone rubber, but is not limited thereto.

[0011] Furthermore, the first conductive filler is selected from metallic conductive fillers or carbon-based conductive fillers.

[0012] Furthermore, the metallic conductive filler includes metallic nanowires or metallic powders, etc.

[0013] Furthermore, carbon-based conductive fillers include graphite, carbon nanotubes (e.g., multi-walled carbon nanotubes), or carbon black.

[0014] Furthermore, in addition to increasing the mechanical strength of the blend system, the first conductive filler mainly serves to increase the conductivity of the blend system. Therefore, the amount of the first conductive filler added only needs to be sufficient to construct a complete conductive network in the blend system. For example, the amount of the first conductive filler added is 9 to 13% of the total mass of the first blend.

[0015] Furthermore, the second conductive filler is an imidazole-based ionic liquid.

[0016] Furthermore, the imidazole ionic liquid may be selected from at least one of, for example, 1-butyl-3-methylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-dodecyl-3-methylimidazolium hexafluorophosphate, 1-benzyl-3-methylimidazolium hexafluorophosphate, 1-allyl-3-methylimidazolium hexafluorophosphate, 1-vinyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-vinyl hexafluorophosphate, 1-benzyl-3-vinyl hexafluorophosphate, and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate.

[0017] Furthermore, the second conductive filler mainly serves to increase the dielectric constant of the system and toughen the flexible matrix. However, the blend must also ensure a certain mechanical strength, so there are no special requirements for its addition amount. For example, the addition amount of the second conductive filler is 0 to 50% of the total mass of the second blend. Preferably, the addition amount of the second conductive filler is greater than zero.

[0018] Furthermore, the blending includes solution blending or melt blending.

[0019] Furthermore, the solution blending includes dissolving the flexible matrix in a solvent, and then adding a first or second conductive filler for blending to obtain a blended dispersion of the flexible matrix and the conductive filler.

[0020] Furthermore, the solvent should be selected to be compatible with the first conductive filler, the second conductive filler, and the flexible matrix, and may be selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and tetrahydrofuran.

[0021] Furthermore, the solution blending is carried out at 50-80°C.

[0022] Furthermore, the solution blending includes magnetically stirring the flexible matrix and solvent at 50-80°C until the flexible matrix is ​​completely dissolved in the solvent, followed by adding a first or second conductive filler and magnetically stirring to obtain a blended dispersion of the flexible matrix and the conductive filler.

[0023] Furthermore, in the case of solution blending, layer-by-layer casting is used in step (2), or in the case of melt blending, hot pressing is used in step (2).

[0024] Furthermore, during the layer-by-layer pouring process, after pouring the previous layer, the solvent is dried to 65-75%, preferably 70%, before pouring the next layer.

[0025] Furthermore, after casting, it is preferable to let it stand at room temperature for 12-36 hours before drying the solvent.

[0026] Furthermore, the solvent drying temperature can be about half the solvent boiling point, for example, 70-90°C.

[0027] Furthermore, the gas used as a foaming agent is at least one of carbon dioxide and nitrogen.

[0028] Furthermore, the pressure of the saturation treatment is 8-15 MPa, preferably 10 MPa.

[0029] Furthermore, the saturation treatment temperature is lower than the optimal foaming temperature of the first blend and within the optimal foaming temperature range of the second blend. Preferably, the saturation temperature is 80-90°C.

[0030] Furthermore, the saturation treatment time can be selected by those skilled in the art based on the thickness of the foamed preform. Preferably, the saturation treatment time is proportional to the thickness of the foamed preform, such as 1 hour for saturation treatment of a 1 mm thick foamed preform.

[0031] Furthermore, the depressurization rate is not less than 5 MPa / s.

[0032] Further, step (2) includes stacking the first blend and the second blend together in any order to form a double, triple or more layers, wherein the first blends of different layers are the same or different, i.e., contain the same or different first conductive fillers, and the second blends of different layers are the same or different, i.e., contain the same or different second conductive fillers.

[0033] Preferably, step (2) includes stacking the first blend and the second blend together in the order of first blend-second blend-first blend to form three layers, wherein the first blends of the different layers are the same or different, i.e., contain the same or different first conductive fillers.

[0034] In other respects, the present invention also provides selectively foamed multilayer flexible composite materials prepared according to the methods described herein.

[0035] In other respects, the present invention also provides the application of the selectively foamed multilayer flexible composite material described herein in flexible sensing, electromagnetic shielding, and impact protection.

[0036] In other respects, the present invention also provides the application of the selectively foamed multilayer flexible composite material described herein in the fabrication of a foam sensor with an integrated electrode layer and functional layer.

[0037] In other respects, the present invention also provides the application of the selectively foamed multilayer flexible composite material described herein as a foam sensor integrating the electrode layer and the functional layer.

[0038] Preferably, the selectively foamed multilayer flexible composite material used for or in the preparation of a foam sensor integrating electrode layers and functional layers is, as described herein, a three-layer material formed by stacking a first blend and a second blend together in the order of first blend-second blend-first blend, wherein the first blends of the different layers are the same or different, i.e., containing the same or different first conductive fillers.

[0039] The beneficial effects of this invention are:

[0040] (1) The preparation method of this invention is simple and controllable, and the gaseous foaming agent is green and environmentally friendly. The foaming process reduces the density and flexibility of the material. This foam material has a wide range of applications, such as flexible sensing, electromagnetic shielding, and impact protection.

[0041] (2) The present invention achieves foaming of the material control area by adjusting the foaming window of different areas of the material.

[0042] (3) When the foam material of the present invention is made into a three-layer structure, it can be used as an integrated sensor for flexible sensing. It has good adhesion, is not easy to delaminate, has good stability, and has good structural properties under the condition of good sensitivity. It has high sensitivity in a wide detection range of 0-2000KPa, and the sensitivity in 0-700KPa reaches S1=1.2nF / KPa. Attached Figure Description

[0043] Figure 1 This is a cross-sectional scanning electron microscope image of the thermoplastic polyurethane foam sensing composite material of Example 1.

[0044] Figure 2 The results show the sensing performance test results of the thermoplastic polyurethane foam sensing composite material in Example 1.

[0045] Figure 3 This is a cross-sectional scanning electron microscope image of the polydimethylsiloxane foam sensing composite material of Example 2.

[0046] Figure 4 The results show the sensing performance test results of the polydimethylsiloxane foam sensing composite material in Example 2.

[0047] Figure 5 This is a cross-sectional scanning electron microscope image of the thermoplastic polyurethane foam sensing composite material of Example 3.

[0048] Figure 6 The results are the sensing performance test results of the thermoplastic polyurethane foam sensing composite material in Example 3. Detailed Implementation

[0049] The technical solution of this invention includes: using a flexible elastomer as a matrix, and blending it with different conductive fillers to form flexible composite materials with different conductive fillers. Since the conductive fillers have different effects on the mechanical strength of the system, the top and bottom layers of the three-layer material obtained after layer-by-layer casting have better melt strength, while the middle layer has weaker melt strength. By using a high-pressure fluid foaming method to foam this structure, a flexible sensing composite material in which only the middle layer has a cellular structure can be obtained.

[0050] More specifically, the technical solution of the present invention includes:

[0051] (1) Preparation of foamed preform

[0052] A flexible matrix is ​​mixed with a first conductive filler and a second conductive filler in a solvent to obtain a blended dispersion. First, the blended dispersion containing the first conductive filler is poured. After the solvent dries, the blended dispersion containing the second conductive filler is poured. After the solvent dries, the blended dispersion containing the first conductive filler is poured. The solvent is then dried.

[0053] (2) Foaming

[0054] The foamed preform prepared above is placed in a high-pressure device, and then a gas that can be used as a foaming agent is introduced. The preform is saturated with high temperature and high pressure in the foaming agent until the foaming gas dissolves in the foamed preform to a saturated state. Then the pressure is quickly released to obtain a flexible sensing composite material with only the intermediate layer material foamed.

[0055] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0056] Example 1

[0057] Steps for preparing polyurethane foam sensing composite materials with only the middle layer foamed:

[0058] (1) Preparation of foamed preform

[0059] The flexible matrix was selected as thermoplastic polyurethane with a hardness of 70A. The first conductive filler was multi-walled carbon nanotubes, the second conductive filler was 1-butyl-3-methylimidazolium hexafluorophosphate, and the solvent was N,N-dimethylformamide.

[0060] Thermoplastic polyurethane was added to N,N-dimethylformamide and magnetically stirred for 1 hour in an oil bath at 80°C. Multi-walled carbon nanotubes were then added and magnetically stirred for another 1 hour to obtain a blended dispersion. The content of multi-walled carbon nanotubes was 9 wt.%.

[0061] Thermoplastic polyurethane was added to N,N-dimethylformamide and magnetically stirred for 1 hour in an oil bath at 80°C. Then, an ionic liquid was added and magnetically stirred for another 1 hour to obtain a blended dispersion. The content of the ionic liquid was 20 wt.%.

[0062] The blended dispersion containing multi-walled carbon nanotubes was poured into a mold and the solvent was dried at 80°C.

[0063] When the solvent in the previous step is about 70% dry, pour the blended dispersion containing ionic liquid into the mold layer by layer, let it stand at room temperature for 24 hours, and then dry the solvent at 80°C.

[0064] When the solvent in the previous step is dried to about 70%, the blended dispersion containing multi-walled carbon nanotubes is poured into the mold layer by layer, left to stand at room temperature for 24 hours, and the solvent is dried at 80°C to obtain the foamed preform.

[0065] (2) Foaming intermediate layer

[0066] The prepared foamed preform was placed in a high-pressure autoclave for foaming. The foaming agent gas was carbon dioxide, the foaming temperature was 90℃, the foaming pressure was 10MPa, the foaming time was 1h, and the pressure was released at 5MPa / s.

[0067] The foamed material was cut into sections with a blade, and the cell structure was observed using a scanning electron microscope. For example... Figure 1 As shown, the material was found to have a porous structure only in the middle layer region.

[0068] The sensing performance of the foamed flexible sensing composite material was tested, and the test results are as follows: Figure 2 As shown.

[0069] Example 2

[0070] Steps for preparing polydimethylsiloxane foam sensing composite materials with only the middle layer foamed:

[0071] (1) Preparation of foamed preform

[0072] The flexible matrix was selected as polydimethylsiloxane (base material: curing agent = 10:1). The first conductive filler was multi-walled carbon nanotubes, the second conductive filler was 1-butyl-3-methylimidazolium hexafluorophosphate, and the solvent was N,N-dimethylformamide.

[0073] Polydimethylsiloxane was added to N,N-dimethylformamide and magnetically stirred for 1 hour in an oil bath at 80°C. Multi-walled carbon nanotubes were then added and magnetically stirred for another 1 hour to obtain a blended dispersion. The content of multi-walled carbon nanotubes was 9 wt.%.

[0074] Polydimethylsiloxane was added to N,N-dimethylformamide and magnetically stirred for 1 hour in an oil bath at 80°C. Then, an ionic liquid was added and magnetically stirred for another 1 hour to obtain a co-dispersed solution. The content of the ionic liquid was 20 wt.%.

[0075] The blended dispersion containing multi-walled carbon nanotubes was poured into a mold and the solvent was dried at 80°C.

[0076] When the solvent in the previous step is about 70% dry, pour the blended dispersion containing ionic liquid into the mold layer by layer, let it stand at room temperature for 24 hours, and then dry the solvent at 80°C.

[0077] When the solvent in the previous step is dried to about 70%, the blended dispersion containing multi-walled carbon nanotubes is poured into the mold layer by layer, left to stand at room temperature for 24 hours, and the solvent is dried at 80°C to obtain the foamed preform.

[0078] (2) Foaming intermediate layer

[0079] The prepared foamed preform was placed in a high-pressure autoclave for foaming. The foaming agent gas was carbon dioxide, the foaming temperature was 90℃, the foaming pressure was 10MPa, the foaming time was 1h, and the pressure was released at 5MPa / s.

[0080] The foamed material was cut into sections with a blade, and the cell structure was observed using a scanning electron microscope. For example... Figure 3 As shown, the material was found to have a porous structure only in the middle layer region.

[0081] The sensing performance of the foamed flexible sensing composite material was tested, and the test results are as follows: Figure 4 As shown.

[0082] Example 3

[0083] Steps for preparing polyurethane foam sensing composite materials with only the middle layer foamed:

[0084] (1) Preparation of foamed preform

[0085] The flexible matrix was selected as thermoplastic polyurethane with a hardness of 70A. The first conductive filler was multi-walled carbon nanotubes, the second conductive filler was multi-walled carbon nanotubes, and the solvent was N,N-dimethylformamide.

[0086] Thermoplastic polyurethane was added to N,N-dimethylformamide and magnetically stirred for 1 hour in an oil bath at 80°C. Multi-walled carbon nanotubes were then added and magnetically stirred for another 1 hour to obtain a blended dispersion. The content of multi-walled carbon nanotubes was 9 wt.%.

[0087] Thermoplastic polyurethane was added to N,N-dimethylformamide and magnetically stirred for 1 hour in an oil bath at 80°C. Multi-walled carbon nanotubes were then added and magnetically stirred for another 1 hour to obtain a blended dispersion. The content of multi-walled carbon nanotubes was 3 wt.%.

[0088] A blended dispersion containing 9 wt.% multi-walled carbon nanotubes was poured into a mold and the solvent was dried at 80°C.

[0089] When the solvent in the previous step is dried to about 70%, pour the blended dispersion of multi-walled carbon nanotubes with a content of 3wt% into the mold layer by layer, let it stand at room temperature for 24 hours, and then dry the solvent at 80℃.

[0090] When the solvent in the previous step is dried to about 70%, the blended dispersion containing 9 wt.% multi-walled carbon nanotubes is poured layer by layer into the mold, left to stand at room temperature for 24 hours, and the solvent is dried at 80°C to obtain the foamed preform.

[0091] (2) Foaming intermediate layer

[0092] The prepared foamed preform was placed in a high-pressure autoclave for foaming. The foaming agent gas was carbon dioxide, the foaming temperature was 90℃, the foaming pressure was 10MPa, the foaming time was 1h, and the pressure was released at 5MPa / s.

[0093] The foamed material was cut into sections with a blade, and the cell structure was observed using a scanning electron microscope. For example... Figure 5 As shown, the material was found to have a porous structure only in the middle layer region.

[0094] The sensing performance of the foamed flexible sensing composite material was tested, and the test results are as follows: Figure 6 As shown.

[0095] It should be noted that while the preferred embodiments of the present invention are provided in this specification, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are not intended to impose additional limitations on the content of the present invention; their purpose is to provide a more thorough and comprehensive understanding of the disclosure of the present invention. Furthermore, the above-described technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of the present invention. Moreover, those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a selectively foamed multilayer flexible composite material, characterized in that, Includes the following steps: (1) The flexible matrix is ​​blended with the first conductive filler and the second conductive filler to obtain the first blend and the second blend, wherein the first conductive filler is a filler that can increase the mechanical strength of the flexible matrix blend system and the second conductive filler is a filler that can toughen the flexible matrix blend system, such that the melt strength of the first blend is greater than the melt strength of the second blend, wherein the first conductive filler is selected from metal conductive fillers or carbon conductive fillers, and the second conductive filler is an imidazole ionic liquid; (2) The first blend and the second blend are combined by layer-by-layer casting or hot pressing to obtain a foamed preform; (3) Injecting gas used as a foaming agent into the foamed preform under closed conditions, and performing saturation treatment until the dissolution of the foaming agent gas in the foamed preform reaches saturation, and then rapidly depressurizing to obtain a selectively foamed multilayer flexible composite material in which only the second blend is cast and foamed, wherein the pressure of the saturation treatment is 8-15 MPa, the temperature is lower than the optimal foaming temperature of the first blend and within the optimal foaming temperature range of the second blend, and the depressurization rate is not less than 5 MPa / s.

2. The preparation method according to claim 1, characterized in that, The hardness of the flexible substrate is 60~80A; The flexible substrate is selected from one or more of polyurethane, thermoplastic polyurethane, polydimethylsiloxane, and silicone rubber.

3. The preparation method according to claim 1, characterized in that, The metal conductive filler includes metal nanowires or metal powder; The carbon-based conductive filler includes graphite, carbon nanotubes, or carbon black. The amount of the first conductive filler added is 9 to 13% of the total mass of the first blend.

4. The preparation method according to claim 1, characterized in that, The amount of the second conductive filler added is 0 to 50% of the total mass of the second blend.

5. The preparation method according to claim 1, characterized in that, The blending includes solution blending or melt blending.

6. The preparation method according to claim 5, characterized in that, The solution blending involves dissolving the flexible matrix in a solvent, followed by adding a first or second conductive filler for blending, to obtain a blend of the flexible matrix and the conductive filler.

7. The preparation method according to claim 6, characterized in that, The solvent is selected from one or more of N,N dimethylformamide, N,N dimethylacetamide, and tetrahydrofuran.

8. The preparation method according to claim 6, characterized in that, The solution blending was carried out at 50-80°C.

9. The preparation method according to claim 8, characterized in that, The solution blending process involves magnetically stirring the flexible matrix and solvent at 50-80°C until the flexible matrix is ​​completely dissolved in the solvent, followed by adding a first or second conductive filler and magnetically stirring to obtain a blend of the flexible matrix and the conductive filler.

10. The preparation method according to claim 1, characterized in that, The gas used as a foaming agent is at least one of carbon dioxide and nitrogen.

11. The preparation method according to claim 1, characterized in that, The saturation temperature is 80-90℃.

12. The preparation method according to claim 1, characterized in that, Step (2) includes stacking the first blend and the second blend together in any order to form a double, triple or more layers, wherein the first blends of different layers are the same or different, i.e., contain the same or different first conductive fillers, and the second blends of different layers are the same or different, i.e., contain the same or different second conductive fillers.

13. The preparation method according to claim 12, characterized in that, Step (2) involves stacking the first blend and the second blend together in the order of first blend-second blend-first blend to form three layers, wherein the first blends of the different layers are the same or different, i.e., contain the same or different first conductive fillers.

14. The selectively foamed multilayer flexible composite material prepared by the method according to any one of claims 1-13.

15. The application of the selectively foamed multilayer flexible composite material according to claim 14 in flexible sensing, electromagnetic shielding, and impact protection.

16. The application according to claim 15, characterized in that, The selectively foamed multilayer flexible composite material is used as, or used to prepare, an integrated foam sensor with an electrode layer and a functional layer.

17. The application according to claim 15, characterized in that, The selectively foamed multilayer flexible composite material is a three-layer material formed by stacking a first blend and a second blend together in the order of first blend-second blend-first blend.

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