A kind of intelligent pressure sensing elastic foam material

Abstract

The present invention discloses an intelligent pressure sensing elastomer foam material, the foam material contains the following components: 1 to 30 parts by mass of polyolefin resin, 70 to 99 parts by mass of thermoplastic elastomer, 0.01 to 3 parts by mass of dispersant, 0.01 to 2 parts by mass of nucleating agent and a conductive agent whose mass content does not exceed its conductive threshold, the conductive agent is one or a mixture of conductive carbon material, conductive polymer material and metal nanomaterial. The product made of the intelligent pressure sensing elastomer foam material can release different electrical signals under different external forces, and can be used to prepare high-end flexible electronic devices such as sensors and detectors, and used in intelligent sensing devices such as intelligent mechanical arms, grabbing arms, robots, and intelligent wearable devices.

Description

Technical Field

[0001] The invention relates to an intelligent pressure-sensing elastic foam material, belongs to the field of intelligent materials, and specifically relates to an elastic foam material that exhibits different electrical signals under the action of different external forces. Background Art

[0002] With the advancement of science and technology, various types of smart polymer materials are emerging continuously. Smart polymer materials can produce unique feedback under the stimulation of different external signals: for example, under the stimulation of different factors such as light, electric field, magnetic field, external force, the material produces a certain degree of deformation or color change; after the external stimulation stops, the material returns to its original state. The smart sensing materials we are familiar with use the above principle. Because smart materials have the ability to feedback external factors such as light, electricity, magnetism, and force, they can be used to prepare high-end electronic devices such as sensors and detectors, and used in smart sensing devices such as smart robotic arms, grabber arms and robots.

[0003] The biggest features of foamed polymer materials are lightweight, elasticity, cushioning, and excellent sound insulation performance, but there is almost no research and application of foamed polymer materials combined with intelligent characteristics. Traditional rigid structure manipulators (including mechanical clamps and mechanical forceps) have problems such as high replacement cost and complex control algorithms. Especially when grasping fragile and fragile special-shaped objects, due to the lack of effective and sensitive force feedback, it is easy to break and damage the grasped objects. In this scenario, if a foamed material with the ability to sense external forces can be used to prepare a flexible manipulator, this problem can be solved. Intelligent foam materials will generate different electrical signals and feed back to the central controller at the same time according to the pressure generated by the manipulator on the grasped object; the central controller will then calculate based on the electrical signal and output the appropriate gripping force, while improving the accuracy of the manipulator's adhesion to the grasped object, reducing the risk of damaging the grasped object due to excessive gripping force. For example, in order to achieve better results, track and field, basketball, and football players have higher and higher requirements for the performance of sports shoes. Insoles made of this type of intelligent sensing elastomer foam material can measure the different pressures generated by different parts of the soles of different athletes during running and jumping, and output them to the data processor in the form of electrical signals. Based on the received signals, the data processor can model and analyze the appropriate cushioning and resilience required for different parts of the soles (left / right forefoot, midfoot, heel, etc.), thereby providing a data basis for sports shoe designers to design personalized, differentiated and high-performance sports shoes.

[0004] Therefore, it is very important to develop intelligent pressure-sensing foam materials. Summary of the invention

[0005] The present invention provides an intelligent pressure-sensing elastomeric foam material. The foam material can release different electrical signals under different external pressures. When the external pressure increases, the electrical signal increases; conversely, when the external pressure decreases or disappears, the electrical signal also weakens or disappears. The intelligent pressure-sensing foam material can be used as a pressure sensor, and can also be used to prepare flexible manipulators, intelligent robots, and intelligent wearable devices.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solution: an intelligent pressure-sensing elastomer foam material, comprising the following components: 1 to 30 parts by mass of a polyolefin resin, 70 to 99 parts by mass of a thermoplastic elastomer, 0.01 to 3 parts by mass of a dispersant, 0.01 to 2 parts by mass of a nucleating agent, and a conductive agent whose mass content does not exceed its conductive threshold, wherein the conductive agent is one or a mixture of conductive carbon materials, conductive polymer materials, and metal nanomaterials.

[0007] Since it is necessary to ensure that the material produces different conductivity under different external pressures, the amount of conductive agent added should be slightly less than or equal to the conductive threshold of the material (i.e., the minimum amount of conductive agent added when the material is conductive without applying external force). For example, when there is no external pressure, the foaming material does not deform, the conductive agents do not (or very little) contact each other, do not (or very little) form a "conductive path", and have no (or weak) conductivity; when pressure begins to act on the foaming material, the material begins to deform, more conductive agents contact each other, the foaming material has a certain conductivity and generates a corresponding electrical signal; when the external pressure continues to increase, the deformation of the foaming material further increases, the number of conductive agents in contact with each other further increases, the conductivity of the material is further enhanced and can output a strong electrical signal; finally, when the external pressure is removed, the deformation of the material disappears due to the good resilience of the foaming material itself, the conductive agent returns to the original non-contact (or very little) contact state, and the material shows insulation (or weak conductivity) properties again. In addition, the amount of conductive agent added cannot be too much, otherwise the material will still have good conductivity without external pressure. When the external force increases and the deformation of the material increases, the conductivity of the material cannot be further increased, and it cannot output differentiated electrical signals, making the material unable to "sense" the size of the external force.

[0008] Furthermore, the conductive carbon material is one or a mixture of conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and multi-branched carbon nanotubes (CNS); the conductive polymer material is one or a mixture of polyacetylene, polythiophene, polypyrrole, polyaniline, and polyphenylene; and the metal nanomaterial is one or a mixture of gold nanoparticles, gold nanorods, silver nanoparticles, silver nanorods, and stainless steel nanofibers.

[0009] Furthermore, the conductive agent is preferably a multi-branched carbon nanotube (CNS). CNS has a "tree-like" multi-branched structure of carbon nanotubes. Common conductive agents such as conductive carbon black, straight tubular carbon nanotubes, conductive polymer materials, and metal nanomaterials need to be added in relatively large amounts to ensure that they are in contact with each other, forming a closed "conductive path" in the polymer matrix, so that electrons can move freely in the "conductive path"; CNS, due to its own special "tree trunk-tree branch" structure, can form a complete "conductive path" through the interconnection of "branch-branch", "branch-trunk", and "trunk-trunk" when added in small amounts, increasing the probability of contact points, so that the material has conductive properties.

[0010] Furthermore, the polyolefin resin is one or more of homopolymer polypropylene, polyethylene, ethylene-propylene copolymer, propylene-butylene copolymer. To ensure that the foamed material has the necessary mechanical strength and excellent elasticity, polyethylene or ethylene-propylene copolymer is preferred, with an elastic modulus of ≤700MPa and a notched impact strength of ≥3.5kJ / m 2 (23℃), the difference between the melting point and the Vicat softening point does not exceed 60℃.

[0011] Further, the thermoplastic elastomer is one or more of ethylene-vinyl acetate copolymer elastomer, polyamide elastomer (including C6 and C12 polyamide elastomer), polyester-based elastomer, polystyrene-based elastomer, ethylene-propylene random or block copolymer elastomer, ethylene-octene random or block copolymer elastomer. Preferably, ethylene-octene random or block copolymer elastomer. Compared with other elastomeric materials, ethylene-octene random or block copolymer elastomer and polyethylene-based substrate have good compatibility because they both contain repeating units of ethylene segments; more importantly, ethylene-octene random or block copolymer elastomer has good elastic deformation and recovery, and in the process of repeated application of external force, the irreversible permanent compression deformation produced is less, and the service life is longer.

[0012] Furthermore, the dispersant is a maleic anhydride grafted polymer. One end of the maleic anhydride grafted polymer is affinity to CNS, and the other end is affinity to organic polymer bodies. This can improve the dispersibility of CNS in the polymer matrix, reduce agglomeration, and improve the conductivity when a small amount of conductive agent is added.

[0013] Furthermore, the nucleating agent is one or a mixture of calcium carbonate, montmorillonite, sodium chloride, potassium chloride, zinc borate, glass fiber, etc. The nucleating agent can act as a bubble nucleus during the foaming process of the material to play a role in heterogeneous nucleation, effectively reducing the foaming pressure while making the size of the pores more uniform.

[0014] Furthermore, the foaming material also contains 0.01 to 3 parts by mass of a lubricant, which is one or a mixture of small molecule polyethylene wax, white oil, erucic acid amide, oleic acid amide, talcum powder, etc. The lubricant can improve the extrusion processing flowability of the material. A colorant, flame retardant, and other additives can also be added according to actual needs.

[0015] A method for preparing an intelligent pressure-sensing elastic foam material comprises the following steps:

[0016] Step 1: After the formulated amount of polyolefin resin, thermoplastic elastomer, dispersant, nucleating agent and conductive agent are fully mixed and uniformly, the mixture is put into an extruder for granulation;

[0017] Step 2: Disperse the microparticles obtained in step 1 into deionized water and add the water into a closed high-pressure foaming kettle with a stirring function;

[0018] Step 3: Heat the high-pressure foaming kettle, and at the same time, slowly introduce carbon dioxide gas into the high-pressure foaming kettle, and continue to stir the material to make the material fully contact with the carbon dioxide;

[0019] Step 4: After the temperature and pressure rise to the set value, isothermal and isobaric conditions are maintained for a certain period of time to allow the particles and carbon dioxide to form a homogeneous state. Subsequently, the particles in the high-pressure foaming kettle are instantly discharged to a normal temperature and pressure environment for foaming. Due to the instantaneous huge pressure difference, carbon dioxide and particles are phase separated, and pores are generated and grow inside the particles. At the same time, the particles are gradually cooled and solidified. After the pores grow to a certain size, they are cooled and shaped, thereby obtaining foamed beads;

[0020] Step 5: Allow the above-mentioned foamed beads to stand still in a normal temperature and pressure environment until the internal and external pressures of the foamed beads are balanced, then add them to a steam compression molding machine and introduce an appropriate amount of hot steam for molding. At this time, the foamed beads are melted and bonded to each other on the surface, but the internal pore structure is still intact. Then, cold water is introduced to cool the foamed parts and the mold is opened to demold them, thereby obtaining an intelligent pressure-sensing elastomer foam material.

[0021] Furthermore, the preparation method may also include step six: placing the intelligent pressure sensing elastomer foam material obtained in step five in a drying room at a temperature of 60 to 80° C. for 6 to 12 hours to stabilize the external dimensions of the foamed product and reduce dimensional deviations caused by shrinkage.

[0022] Furthermore, the extrusion temperature of step 1 is 160-260° C., the screw speed is 300-1000 r / min, the length of the extruded particles is 2.0-4.0 mm, and the unit weight is 1.0-3.0 mg.

[0023] Furthermore, in step 4, according to the required foaming ratio and density, the temperature setting value is 120-170° C., and the pressure setting value is 2-5 MPa. After reaching the foaming setting temperature and pressure, isothermal and isobaric conditions are maintained for 3-30 minutes.

[0024] Furthermore, depending on the size and shape complexity of the mold used in the steam molding machine, during molding in step five, the steam pressure used is 0.2 to 4 kg, the time for the steam to act on the foamed beads is 2 to 20 seconds, and the water cooling time is 60 to 200 seconds.

[0025] The beneficial effects of the present invention are:

[0026] The intelligent pressure-sensitive elastic foam material of the present invention has the ability to generate different electrical signal feedbacks to external pressures: when there is no external pressure, the intelligent elastic foam material has no conductivity (or has poor conductivity) and does not generate (or generates weak) electrical signals; when different pressures act on the intelligent elastic foam material, the material has different conductivity and outputs electrical signals of different strengths; when the external pressure is removed, the intelligent elastic foam material can return to an insulating (weakly conductive) state. At the same time, the conductive properties of the material in different states can be adjusted to generate different electrical signal feedbacks to different pressures.

[0027] When this intelligent elastomer foam material is combined with a data processor, it can be prepared into an intelligent detection and control device. Such equipment has the ability to generate different feedback response measures for different external pressures: such as intelligent flexible mechanical grasping arms, bionic sensor feedback intelligent equipment, adaptive control equipment, etc., which will play an important role in the future intelligent manufacturing, high-end equipment and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 It is a schematic diagram of the intelligent pressure sensing elastic foam material of the present invention generating an electrical signal when subjected to an external force. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Embodiment 1:

[0032] 30 parts by weight of polyethylene (PE), 70 parts by weight of thermoplastic elastomer (POE), 2 parts by weight of CNS, 2 parts by weight of maleic anhydride grafted polyethylene (MAH-g-PE), 0.5 parts by weight of polyethylene wax, and 0.01 parts by weight of calcium carbonate were added to a twin-screw extruder, and extrusion granulation was performed at 180-220° C. to obtain small elastomer particles with a length of 2.0-4.0 mm and a unit weight of 1.0-3.0 mg.

[0033] 100 parts by mass of the elastic particles, 300 parts by mass of deionized water, 0.5 parts by mass of kaolin and 0.3 parts by mass of butter are added to a high-pressure foaming kettle and stirred with increasing temperature and pressure. When the temperature and pressure are increased to 120-170°C and 2-5MPa, the pressure is rapidly released after isothermal and isobaric treatment for 10 minutes to obtain an elastic foaming bead material.

[0034] The prepared elastic body foaming bead material is molded in a steam molding device to obtain an intelligent elastic body foaming material with an electric feedback effect.

[0035] The main components and test results of Examples 1-4 (E1-E4) and Comparative Examples 1-5 (C1-C5) are shown in Table 1. Among them, the conductive agent materials used in E1-E4 are different, and the surface resistance of the obtained smart elastomer foam material when the deformation is 20% and 40% is the same, the conductive agent of E1 is CNS, the conductive agent of E2 is conductive carbon black, the conductive agent of E3 is multi-walled carbon nanotubes, and the conductive agent of E4 is nano silver rods; the CNS content of C1 and C2 is different from that of E1, the content of maleic anhydride grafted polyethylene compatibilizer of C3 and C4 is different from that of E1, and C5 is a foam material without thermoplastic elastomer.

[0036] Table 1

[0037]

[0038]

[0039] In Example 1, the foaming conditions of 124°C and 3.6 MPa can obtain elastomer beads with a density of 74 g / L. After the foamed elastomer beads are formed, when they are not subjected to external pressure and are not deformed, the surface resistance is 10 8～9 Ω / m 2 When the external pressure causes the material to deform by 20% (compressed by 20% in the thickness direction), the surface resistance is 10 5～6 Ω / m 2 When the pressure is further increased and the compression deformation of the material is 40%, the surface resistance is reduced to 10 4～5 Ω / m 2The compression deformation of the material caused by external force increases the concentration of CNS per unit volume, creates more "conductive pathways", increases the conductivity of the material, changes the output electrical signal, and ultimately enables the material to sense the size of the external force.

[0040] As can be seen from Table 1, in Examples 1 to 4, when the same conductivity needs to be achieved (i.e., the surface resistance of the obtained smart elastomer foam material is the same when the deformation is 20% and 40%), the amount of conductive carbon black added is the largest, followed by multi-walled carbon nanotubes and nanosilver rods, and the amount of CNS added is the smallest. It can be predicted that if CNS is mixed with other conductive agents, when the same conductivity is achieved, the amount of mixed conductive agent added is between CNS and other conductive agents. In addition, excessive addition of inorganic conductive agents will affect the welding performance of the foamed beads during molding, resulting in poor mechanical strength. Therefore, in order to ensure that the mechanical properties of the material are not affected too much while having good electrical sensitivity, CNS is preferred.

[0041] In order to make the foamed elastomer material have sensitive external force perception ability, the added conductive CNS should be appropriate: if too little is added (Comparative Example 1), even if a larger external force causes the material to produce a larger elastic deformation, the surface resistance of the material is infinite and there is no electrical signal output; if too much is added (Comparative Example 2), the "conductive path" inside the material is too perfect, and when different elastic deformations are produced under different external forces, the material shows the same surface resistance value, which means that the ability to identify different external forces is lost, and the material cannot achieve the intelligent effect.

[0042] When no maleic anhydride grafted polyethylene is added (Comparative Example 3), CNS is poorly dispersed in the foamed elastomer, easily agglomerated, and cannot form an effective power grid path, resulting in poor conductivity and large surface resistance of the material. When too much maleic anhydride grafted polyethylene is added (Comparative Example 4), since CNS can be more evenly dispersed in the foamed elastomer, the surface resistance of the material is not much different.

[0043] The addition of thermoplastic elastomer in Example 1 can make the foam material have better toughness and resilience, ensuring that the material still has good shape recovery ability after long-term and repeated compression, and is more suitable for application in the fields of intelligent mechanical arms, sensors, etc. In Comparative Example 5, no thermoplastic elastomer is added, and the above-mentioned toughness, resilience and other properties cannot be achieved.

[0044] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An intelligent pressure sensing elastic foam material, characterized in that: The invention comprises the following components: 30 parts by weight of polyolefin resin, 70 parts by weight of thermoplastic elastomer, 0.01 to 3 parts by weight of dispersant, 0.01 to 2 parts by weight of nucleating agent and 2 parts by weight of multi-branched nano carbon bundle conductive agent; the density of the foaming beads used to prepare the foaming material is 74 g / L; the surface resistance of the foaming material is 10 8～9 Ω / m 2 ; When the external pressure causes the foam material to be compressed by 20% in the thickness direction, its surface resistance is 10 5～6 Ω / m 2 ; When the external pressure causes the foam material to be compressed by 40% in the thickness direction, its surface resistance is 10 4～5 Ω / m 2 The polyolefin resin is one or more of homopolypropylene, polyethylene, ethylene-propylene copolymer, and propylene-butene copolymer; the thermoplastic elastomer is one or more of ethylene-vinyl acetate copolymer elastomer, polyamide elastomer, polyester-based elastomer, polystyrene-based elastomer, ethylene-propylene random or block copolymer elastomer, and ethylene-octene random or block copolymer elastomer; the dispersant is a maleic anhydride grafted polymer.

2. The intelligent pressure sensing elastic foam material according to claim 1, characterized in that: The nucleating agent is one or a mixture of calcium carbonate, montmorillonite, sodium chloride, potassium chloride, zinc borate and glass fiber.

3. The intelligent pressure sensing elastic foam material according to claim 1, characterized in that: The foaming material further contains 0.01 to 3 parts by weight of a lubricant, which is one or a mixture of small molecule polyethylene wax, white oil, erucic acid amide, oleic acid amide and talcum powder.

4. The method for preparing an intelligent pressure sensing elastic foam material according to claim 1, characterized in that: The steps include: Step 1: After the formulated amount of polyolefin resin, thermoplastic elastomer, dispersant, nucleating agent and conductive agent are fully mixed and uniformly, the mixture is put into an extruder for granulation; Step 2: Disperse the microparticles obtained in step 1 into deionized water and add the water into a closed high-pressure foaming kettle with a stirring function; Step 3: Heat the high-pressure foaming kettle, and at the same time, slowly introduce carbon dioxide gas into the high-pressure foaming kettle, and continue to stir the material to make the material fully contact with the carbon dioxide; Step 4: After the temperature and pressure rise to the set value, isothermal and isobaric conditions are maintained for a certain period of time to allow the particles and carbon dioxide to form a homogeneous state, and then the particles in the high-pressure foaming kettle are instantly discharged to a normal temperature and pressure environment for foaming to obtain foamed beads; Step 5: Allow the foamed beads to stand at room temperature and pressure until the internal and external pressures of the foamed beads are balanced, add them to a steam compression molding machine for molding, and then cool and demold to obtain an intelligent pressure-sensing elastomer foam material.

5. Use of the intelligent pressure-sensing elastomer foam material according to any one of claims 1 to 4 for preparing pressure sensors, flexible manipulators, intelligent robots, and intelligent wearable devices.

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