Selective foaming multilayer flexible composite material and preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a selective foaming multilayer flexible composite material and a preparation method and application thereof. According to the invention, the flexible elastomer is used as a matrix and is respectively blended with different conductive fillers to form a flexible matrix blending system with different conductive fillers, because the conductive fillers have different influences on the mechanical strength of the system, after compounding is carried out in a layer-by-layer pouring or hot pressing mode, foaming is carried out by using a high-pressure fluid foaming method, and the flexible elastomer is prepared. A flexible composite material having a cellular structure only in part of the layers can be obtained. When the composite material is made into a three-layer structure, the obtained composite material can be used as an integrated sensor, and is good in cohesiveness, not prone to layering and good in stability.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a selectively foamed multi-layer flexible composite material and a preparation method and application thereof. Background Art

[0002] With the development of social science and technology, highly sensitive, highly flexible and lightweight flexible sensors can be used to detect human motion, robot electronic skin, soft fixtures, health monitoring, etc. Polyurethane foam materials are widely used as flexible sensing materials due to their light weight, good durability and high flexibility. However, the electrode layer and dielectric layer of traditional capacitive foam sensors are usually packaged by multi-layer composite methods such as bonding. The sensor layers prepared in this way have obvious interfaces between the layers, and the interface defects between the layers affect the mechanical response and working stability of the sensor.

[0003] In the existing technology, when preparing sensors with integrated electrode layers and functional layers, conductive fillers of different contents or types are mainly bonded and layered to the electrode layers and functional layers of the foam sensor. The conductive fillers of the integrated sensors prepared in this way fall off after repeated use, which seriously affects the durability and sensing stability of the sensors. Summary of the invention

[0004] The present invention aims to solve the packaging problem of the sensor multi-layer structure composite, the problem of mechanical mismatch between the electrode layer and the functional layer of the sensor, and complete the integrated preparation 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, which comprises the following steps:

[0006] (1) blending a flexible matrix with a first conductive filler and a second conductive filler respectively to obtain a first blend and a second blend, wherein the first conductive filler is a filler capable of increasing the mechanical strength of the flexible matrix blend system and the second conductive filler is a filler capable of toughening 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) compounding the first blend and the second blend together by layer-by-layer casting or hot pressing to obtain a foamed body;

[0008] (3) injecting a gas used as a foaming agent into the foamed body under closed conditions, performing a saturation treatment until the dissolution of the foaming agent gas in the foamed body reaches a saturated state, and then rapidly releasing the pressure to obtain a selectively foamed multi-layer flexible composite material in which only the layer formed by casting the second blend is foamed.

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

[0010] Furthermore, the flexible substrate 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 metal conductive fillers or carbon-based conductive fillers.

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

[0013] Furthermore, the carbon-based conductive filler includes graphite, carbon nanotubes (such as 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 plays a role in increasing the conductive properties of the blend system, so the amount of the first conductive filler added is sufficient as long as it can build 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 ionic liquid.

[0016] Further, the imidazolium ionic liquid can be selected from, for example, at least one of 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, but the blend must ensure a certain mechanical strength, so there is no special requirement 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 the 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, for example, it can be selected from one or more of NN dimethylformamide, NN 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 the solvent at 50-80° C. until the flexible matrix is ​​completely dissolved in the solvent, and then adding the first or second conductive filler and magnetically stirring to obtain a blended dispersion of the flexible matrix and the conductive filler.

[0023] Further, 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, in the process of pouring layer by layer, after pouring the previous layer, the solvent is dried to 65-75%, preferably 70%, and then the next layer is poured.

[0025] Furthermore, after pouring, it is preferred to first stand at room temperature, for example, for 12-36 hours, and then dry the solvent.

[0026] Furthermore, the solvent drying temperature may be about half of the solvent boiling point, such as 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] Further, the temperature of the saturation treatment 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 according to the thickness of the foamed body. Preferably, the saturation treatment time is proportional to the thickness of the foamed body, such as saturation treatment of a 1 mm thick foamed body for 1 hour.

[0031] Furthermore, the pressure relief speed 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 two layers, three layers 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) comprises laminating 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 different layers are the same or different, ie contain the same or different first conductive fillers.

[0034] In other aspects, the present invention also provides a selectively foamed multi-layer flexible composite material prepared according to the method described herein.

[0035] In other aspects, the present invention also provides applications of the selectively foamed multi-layer flexible composite material described herein in flexible sensing, electromagnetic shielding, and impact protection.

[0036] In other aspects, the present invention also provides the use of the selectively foamed multi-layer flexible composite material described herein in preparing a foam sensor with an integrated electrode layer and a functional layer.

[0037] In other aspects, the present invention also provides the use of the selectively foamed multi-layer flexible composite material described herein as a foam sensor integrating an electrode layer and a functional layer.

[0038] Preferably, the selectively foamed multi-layer flexible composite material used as or for preparing a foam sensor with an integrated electrode layer and a functional layer is a three-layer material formed by laminating a first blend and a second blend in the order of first blend-second blend-first blend as described herein, wherein the first blends of different layers are the same or different, that is, contain the same or different first conductive fillers.

[0039] Beneficial effects of the present invention:

[0040] (1) The preparation of the present invention is simple and controllable, the gas foaming agent is green and environmentally friendly, and the density and flexibility of the material are reduced by foaming. The foam material has a wide range of applications, such as flexible sensing, electromagnetic shielding, impact protection, etc.

[0041] (2) The present invention achieves foaming in a controlled area of ​​the material by regulating the foaming windows in 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 excellence under the condition of good sensitivity. It has high sensitivity in a wide detection range of 0-2000KPa, and the sensitivity of 0-700KPa reaches S1=1.2nF / KPa. BRIEF DESCRIPTION OF THE DRAWINGS

[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 sensing performance test results of the thermoplastic polyurethane foam sensing composite material of Example 1 are shown.

[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 sensing performance test results of the polydimethylsiloxane foam sensing composite material of 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 These are the sensing performance test results of the thermoplastic polyurethane foam sensing composite material of Example 3. DETAILED DESCRIPTION

[0049] The technical scheme of the present invention includes: taking a flexible elastomer as a matrix, respectively blending with different conductive fillers to form a flexible composite material with different conductive fillers. Since the conductive fillers have different effects on the mechanical strength of the system, the upper and lower layers of the three-layer material obtained after layer-by-layer casting have good melt strength, and the middle layer material has a weak melt strength. The structure is foamed by a high-pressure fluid foaming method to obtain a flexible sensing composite material with only the middle layer material having a cellular structure.

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

[0051] (1) Preparation of foamed body

[0052] Take a flexible substrate and add a first conductive filler and a second conductive filler respectively, and blend them in a solvent to obtain a blended dispersion; first cast the blended dispersion containing the first conductive filler, wait for the solvent to dry, then cast the blended dispersion containing the second conductive filler, and after the solvent is dried, cast the blended dispersion containing the first conductive filler, and dry the solvent.

[0053] (2) Foaming

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

[0055] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0056] Example 1

[0057] Steps for preparing polyurethane foam sensing composite material with only middle layer foaming:

[0058] (1) Preparation of foamed body

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

[0060] Thermoplastic polyurethane was added to N,N-dimethylformamide, heated in an oil bath at 80°C with magnetic stirring for 1 hour, and then multi-walled carbon nanotubes were added and magnetic stirring was performed for 1 hour to obtain a blended dispersion, wherein the content of the multi-walled carbon nanotubes was 9 wt.%.

[0061] Thermoplastic polyurethane was added to N,N-dimethylformamide, heated in an oil bath at 80°C with magnetic stirring for 1 hour, and then ionic liquid was added and magnetic stirring was performed for 1 hour to obtain a blended dispersion, wherein the content of the ionic liquid was 20 wt.%.

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

[0063] When the solvent in the previous step is dried by about 70%, the blended dispersion containing the ionic liquid 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.

[0064] When the solvent in the previous step is dried by about 70%, the blended dispersion containing 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 a foamed body.

[0065] (2) Foaming middle layer

[0066] The prepared foamed body was placed in an autoclave for foaming. The foaming agent gas was carbon dioxide, the foaming temperature was 90°C, the foaming pressure was 10MPa, the foaming time was 1h, and the pressure relief was 5MPa / s.

[0067] The foamed material was cut into sections with a blade and the cell structure was observed using a scanning electron microscope. Figure 1 As shown, it is found that the material has a cellular structure only in the middle layer region.

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

[0069] Example 2

[0070] Steps for preparing polydimethylsiloxane foam sensing composite material with only middle layer foaming:

[0071] (1) Preparation of foamed body

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

[0073] Polydimethylsiloxane was added to N,N-dimethylformamide, and magnetically stirred for 1 hour under 80°C oil bath heating, and then multi-walled carbon nanotubes were added and magnetically stirred for 1 hour to obtain a blended dispersion, wherein the content of the multi-walled carbon nanotubes was 9 wt.%.

[0074] Polydimethylsiloxane was added to N,N-dimethylformamide, and magnetically stirred for 1 hour under 80°C oil bath heating, and then ionic liquid was added and magnetically stirred for 1 hour to obtain a blended dispersion, wherein the content of the ionic liquid was 20 wt.%.

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

[0076] When the solvent in the previous step is dried by about 70%, the blended dispersion containing the ionic liquid 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.

[0077] When the solvent in the previous step is dried by about 70%, the blended dispersion containing 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 a foamed body.

[0078] (2) Foaming middle layer

[0079] The prepared foamed body was placed in an autoclave for foaming. The foaming agent gas was carbon dioxide, the foaming temperature was 90°C, the foaming pressure was 10MPa, the foaming time was 1h, and the pressure relief was 5MPa / s.

[0080] The foamed material was cut into sections with a blade and the cell structure was observed using a scanning electron microscope. Figure 3 As shown, it is found that the material has a cellular structure only in the middle layer region.

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

[0082] Example 3

[0083] Steps for preparing polyurethane foam sensing composite material with only middle layer foaming:

[0084] (1) Preparation of foamed body

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

[0086] Thermoplastic polyurethane was added to N,N-dimethylformamide, heated in an oil bath at 80°C with magnetic stirring for 1 hour, and then multi-walled carbon nanotubes were added and magnetic stirring was performed for 1 hour to obtain a blended dispersion, wherein the content of the multi-walled carbon nanotubes was 9 wt.%.

[0087] Thermoplastic polyurethane was added to N,N-dimethylformamide, heated in an oil bath at 80°C with magnetic stirring for 1 hour, and then multi-walled carbon nanotubes were added and magnetic stirring was performed for 1 hour to obtain a blended dispersion, wherein the content of the multi-walled carbon nanotubes was 3 wt.%.

[0088] The blended dispersion containing 9 wt.% of 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 by about 70%, a blended dispersion of multi-walled carbon nanotubes with a content of 3 wt% 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.

[0090] When the solvent in the previous step is dried by about 70%, the blended dispersion containing 9 wt.% of 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 a foamed body.

[0091] (2) Foaming middle layer

[0092] The prepared foamed body was placed in an autoclave for foaming. The foaming agent gas was carbon dioxide, the foaming temperature was 90°C, the foaming pressure was 10MPa, the foaming time was 1h, and the pressure relief was 5MPa / s.

[0093] The foamed material was cut into sections with a blade and the cell structure was observed using a scanning electron microscope. Figure 5 As shown, it is found that the material has a cellular structure only in the middle layer region.

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

[0095] It should be noted that the preferred embodiments of the present invention are given in the specification of the present invention, but the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments are not intended to be additional limitations on the content of the present invention. The purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. In addition, the above-mentioned technical features continue to be combined with each other to form various embodiments not listed above, which are all considered to be within the scope of the present invention specification; further, for ordinary technicians in this field, they can be improved or transformed according to the above description, and all these improvements and transformations should belong to the protection scope of the claims attached to the present invention.

Claims

1. A method for preparing a selectively foamed multilayer flexible composite material, characterized in that: The following steps are involved: (1) blending a flexible matrix with a first conductive filler and a second conductive filler respectively to obtain a first blend and a second blend, wherein the first conductive filler is a filler capable of increasing the mechanical strength of the flexible matrix blend system and the second conductive filler is a filler capable of toughening the flexible matrix blend system, so that the melt strength of the first blend is greater than the melt strength of the second blend; (2) compounding the first blend and the second blend together by layer-by-layer casting or hot pressing to obtain a foamed body; (3) injecting a gas used as a foaming agent into the foamed body under closed conditions, performing a saturation treatment until the dissolution of the foaming agent gas in the foamed body reaches a saturated state, and then rapidly releasing the pressure to obtain a selectively foamed multi-layer flexible composite material in which only the layer formed by casting the second blend is foamed.

2. The preparation method according to claim 1, characterized in that: The hardness of the flexible substrate is 60-80A; Furthermore, 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 first conductive filler is selected from a metal conductive filler or a carbon conductive filler; Further, the metal conductive filler includes metal nanowires or metal powder; Further, the carbon-based conductive filler includes graphite, carbon nanotubes or carbon black; Furthermore, the addition amount of the first conductive filler is 9-13% of the total mass of the first blend.

4. The preparation method according to claim 1, characterized in that: The second conductive filler is an imidazole ionic liquid; Furthermore, the added amount of the second conductive filler 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, Furthermore, the solution blending includes dissolving the flexible matrix in a solvent, and then adding the first or second conductive filler for blending to obtain a blend of the flexible matrix and the conductive filler.

6. The preparation method according to claim 5, characterized in that: The solvent is selected from one or more of NN dimethylformamide, NN dimethylacetamide, and tetrahydrofuran; Further, the solution blending is carried out at 50-80°C; Furthermore, the solution blending includes magnetically stirring the flexible matrix and the solvent at 50-80° C. until the flexible matrix is ​​completely dissolved in the solvent, and then adding the first or second conductive filler and magnetically stirring to obtain a blend of the flexible matrix and the conductive filler.

7. 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; Furthermore, the pressure of the saturation treatment is 8-15 MPa; Further, the temperature of the saturation treatment is lower than the optimal foaming temperature of the first blend and within the optimal foaming temperature range of the second blend; Further, the saturation temperature is 80-90°C. Furthermore, the pressure relief speed is not less than 5 MPa / s.

8. The preparation method according to claim 1, characterized in that: Step (2) comprises laminating the first blend and the second blend together in any order to form two layers, three layers 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; Preferably, step (2) comprises laminating 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 different layers are the same or different, ie contain the same or different first conductive fillers.

9. A selectively foamed multi-layer flexible composite material prepared according to the method of any one of claims 1 to 8.

10. Application of the selectively foamed multilayer flexible composite material according to claim 9 in flexible sensing, electromagnetic shielding, and impact protection; Furthermore, the selectively foamed multilayer flexible composite material is used as or for preparing a foam sensor with an integrated electrode layer and a functional layer; Preferably, the selectively foamed multi-layer flexible composite material is a three-layer material formed by laminating a first blend and a second blend in the order of first blend-second blend-first blend.

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