A water-based polyurethane for robotic flexible skin, its preparation method and application

Abstract

This invention relates to the field of flexible materials for robotic functional coatings, particularly waterborne polyurethane for robotic flexible skin, its preparation method, and its application. By compounding polytetrahydrofuran diol (PTD) and polycaprolactone diol (PCD), the high flexibility, low Tg, weak ether bond polarity, and high degree of rotational freedom of PTD are utilized. PTD serves as the main soft segment in the waterborne polyurethane system, reducing overall intermolecular forces and the system's Tg, thus establishing a low modulus. The weak hydrogen bonds of PCD further enhance the rapid recovery ability of the chain segments after the removal of external forces, achieving a complementary advantage between the two components. This achieves a synergistic balance between low modulus and high resilience without relying on increasing the proportion of hard segments or crosslinking density, meeting the elasticity requirements of robotic flexible skin during repeated movements, while avoiding problems such as material hardening and decreased flexibility that may result from increasing the proportion of hard segments or crosslinking density.

Description

Technical Field

[0001] This invention relates to the field of flexible materials for robot functional coating, specifically to a waterborne polyurethane for robot flexible skin, its preparation method, and its application. Background Technology

[0002] With the rapid development of robotics technology towards greater flexibility and biomimicry, robots are increasingly being used in fields such as human-computer interaction, medical rehabilitation, precision manufacturing, and specialized operations. This widespread application of robots in these areas places increasingly higher demands on flexible robot skin. Flexible robot skin not only needs to possess good flexibility and elasticity to adapt to the complex movements of robots, but also needs to meet low modulus requirements to ensure safety and fit when in contact with the human body or precision workpieces. Furthermore, to meet the needs of large-scale production, flexible robot skin should also be environmentally friendly and easy to process and mold. Therefore, developing a flexible robot skin material that meets these requirements is of great significance for the application and development of robotics technology.

[0003] Waterborne polyurethane, a polymer material with unique properties, uses water as a dispersion medium and boasts advantages such as environmental friendliness, non-pollution, and a certain degree of elasticity, making it a highly anticipated candidate material for developing flexible skin for robots. The elasticity of waterborne polyurethane derives from the soft and hard segments in its molecular structure. The soft segments, typically composed of polyethers or polyester polyols, impart flexibility and elasticity; the hard segments, composed of isocyanates and small-molecule chain extenders, provide mechanical strength and hardness. By adjusting the ratio of soft and hard segments and the molecular structure, the performance of waterborne polyurethane materials can be controlled to a certain extent to meet different application requirements. In the development of flexible skin for robots, researchers aim to optimize the formulation and preparation process of waterborne polyurethane to achieve better flexibility and elasticity while reducing the material's modulus, thus meeting the requirements for use in flexible robotic skin. However, in the pursuit of mechanical strength, the formulation design of existing technologies tends to favor high cross-linking, resulting in high material modulus and insufficient flexibility and elasticity, making it difficult to meet the synergistic requirements of "high elasticity" and "low modulus". At the same time, some waterborne polyurethanes have problems such as poor bending fatigue resistance and insufficient low-temperature toughness, which cannot directly meet the requirements for the use of flexible skin in robots. Summary of the Invention

[0004] To address the problem that existing waterborne polyurethanes cannot simultaneously meet the requirements of high elasticity and low modulus, this invention provides a waterborne polyurethane for robotic flexible skin, its preparation method, and its application.

[0005] To achieve the above objectives, the present invention employs the following technical solution: This invention provides an aqueous polyurethane for robotic flexible skin, comprising the following raw material components by weight: 70-100 parts of polyether polyol, 1-30 parts of polyester polyol, 20-25 parts of isocyanate, 3-4 parts of hydrophilic chain extender and 1.5-2.5 parts of small molecule chain extender; The polyether-type polyol includes at least polytetrahydrofuran diol, and the polyester-type polyol includes at least polycaprolactone diol.

[0006] Optionally, the molecular weight of both the polyether polyol and the polyester polyol is 2000.

[0007] Optionally, it also includes 14-42 parts of MXene aqueous dispersion.

[0008] Optionally, the MXene aqueous dispersion is a Ti3C2MXene aqueous dispersion with a concentration of 8-12 mg / mL.

[0009] Optionally, the isocyanate includes isophorone diisocyanate and / or hexamethylene diisocyanate.

[0010] Optionally, the hydrophilic chain extender comprises sodium 2-(diethanolamine)ethanesulfonate and / or sodium 1,2-propanediol-3-sulfonate.

[0011] Optionally, the small molecule chain extender includes one or more of ethylene glycol, propylene glycol, and 1,4-butanediol.

[0012] The present invention also provides a method for preparing the above-described robotic flexible skin using water-based polyurethane, comprising: Dehydration treatment of polyether polyols and polyester polyols; Under inert gas protection, dehydrated polyether polyol and polyester polyol are mixed with isocyanate and subjected to prepolymerization reaction under the action of catalyst to obtain the first prepolymer. A hydrophilic chain extender and a small molecule chain extender were added to the first prepolymer to carry out a chain extension reaction, thereby obtaining the WPU prepolymer. Water was added to the WPU prepolymer and emulsified to obtain an aqueous polyurethane emulsion. Aqueous polyurethane emulsion is molded and dried to obtain aqueous polyurethane for robotic flexible skin.

[0013] Optionally, after emulsifying the WPU prepolymer with water, the process further includes adding MXene aqueous dispersion to the emulsified WPU prepolymer and conducting a constant-temperature reaction; the amount of MXene aqueous dispersion added is 14-42 parts; the constant-temperature reaction temperature is room temperature, and the reaction time is 1-3 hours.

[0014] The above describes the application of water-based polyurethane in robotic flexible skin.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides an aqueous polyurethane for robotic flexible skin. The aqueous polyurethane for robotic flexible skin uses polyether-type polyol containing polytetrahydrofuran diol with high flexibility and low glass transition temperature (Tg) as the main soft segment. Its ether bond polarity is weak and the molecular chain rotational freedom is high, which can effectively reduce the overall intermolecular forces and the Tg of the system, making the chain segments easy to slide and stretch under external force, laying the foundation for low modulus, and making the material more likely to deform under stress, which meets the requirement of soft and close fit for robotic flexible skin. By combining an appropriate amount of polyester-type polyol soft segments containing polycaprolactone diol with strong chain regularity, the ester carbonyl groups can form weak intermolecular hydrogen bonds. These weak hydrogen bonds are much weaker than those in hard segments and will not significantly increase the intermolecular forces and thus raise the modulus. At the same time, the regular chain structure can suppress the permanent deformation of the soft segments after being subjected to force, and it can also work with the hydrogen bonds in the hard segments to form a hierarchical support structure, which helps to improve the rapid recovery ability of the chain segments after the external force is removed. The two are complementary and compatible. They will not increase the modulus due to excessive intermolecular forces caused by slightly higher polarity, and they can work with polytetrahydrofuran diol to improve the rapid recovery ability of the chain segments after the external force is removed. Without relying on increasing the proportion of hard segments or crosslinking density, a synergistic balance between low modulus and high resilience is achieved, which meets the elasticity requirements of the robot's flexible skin during repeated movements, while avoiding the problems of material hardening and decreased flexibility that may be caused by increasing the proportion of hard segments or crosslinking density.

[0016] MXene possesses extremely high conductivity and a large specific surface area. When combined with polyurethane, MXene forms a continuous conductive network within the polyurethane matrix. When the material is subjected to external forces such as tension or bending, the structure of this conductive network changes, leading to a regular change in the material's resistance. By detecting these changes in resistance, mechanical deformation can be sensed. This material meets the core requirements of flexible robotic skin for flexible fit, resistance to deformation fatigue, and accurate perception of mechanical signals, and has significant application value in the field of intelligent interaction in biomimetic robots.

[0017] This invention also provides a method for preparing the aforementioned waterborne polyurethane for robotic flexible skin. This method involves dehydration of the polyol, prepolymerization with isocyanate, subsequent chain extension reaction, emulsification, molding, and drying to achieve the preparation of the aforementioned waterborne polyurethane for robotic flexible skin. From raw material processing to final product molding, the various steps are closely linked and the operation is relatively simple. Compared to some complex preparation processes, this method does not require complex equipment or cumbersome operating procedures, which is beneficial for large-scale industrial production.

[0018] The aforementioned application of waterborne polyurethane in robotic flexible skin leverages its low modulus to ensure a tight fit to the robot's surface, while its high resilience prevents detachment or damage during robot movement. Combined with its precise mechanical signal sensing capabilities, the robot can react accordingly to the external forces sensed by the flexible skin, achieving more natural and intelligent interaction. This enhances the overall performance and user experience of bionic robots, demonstrating significant application value in the field of intelligent interaction for bionic robots. Furthermore, because the waterborne polyurethane achieves a synergistic balance between low modulus and high resilience, the material can easily deform under repeated external forces and quickly return to its original position after the forces are removed. This prevents fatigue damage during long-term use, maintains good performance stability, extends the lifespan of the robotic flexible skin, reduces the frequency of replacement and maintenance, and lowers operating costs. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation method of a waterborne polyurethane for a robotic flexible skin according to the present invention.

[0020] Figure 2 The image shows a finger bending signal of the flexible electronic skin prepared using the robotic flexible skin made of water-based polyurethane according to Example 5 of the present invention.

[0021] Figure 3 The image shows the vocal signal of the throat of the flexible electronic skin prepared using the robotic flexible skin prepared in Example 5 of this invention, which is made of water-based polyurethane. Detailed Implementation

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0024] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0025] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0026] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0029] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0030] This invention discloses an aqueous polyurethane for robotic flexible skin, comprising the following raw material components by weight: The composition comprises 70-100 parts of polyether polyol, 1-30 parts of polyester polyol, 20-25 parts of isocyanate, 3-4 parts of hydrophilic chain extender, and 1.5-2.5 parts of small molecule chain extender; wherein the polyether polyol includes at least polytetrahydrofuran diol, and the polyester polyol includes at least polycaprolactone diol; preferably, the molecular weight of both the polyether polyol and the polyester polyol is 2000. The isocyanate includes isophorone diisocyanate and / or hexamethylene diisocyanate; the main soft segment is polytetrahydrofuran diol with high flexibility and low Tg, whose ether bonds are weakly polar and the molecular chain has high rotational freedom, which can effectively reduce the overall intermolecular forces and the system Tg, making the chain segments easy to slide and stretch under external forces, laying the foundation for low modulus; an appropriate amount of polycaprolactone diol soft segment with strong chain regularity is compounded, and the ester carbonyl group can form weak intermolecular hydrogen bonds. The weak hydrogen bond force is much weaker than the hydrogen bond of the hard segment and will not significantly increase the intermolecular forces and pull the chain. It has a high modulus and can suppress permanent deformation of soft segments under stress by means of regular chain structure. It can also work with hard segments to form a hierarchical support structure through hydrogen bonds, which helps to improve the rapid recovery ability of chain segments after the removal of external force. The two are complementary and compatible. It will not increase the modulus due to excessive increase in intermolecular forces caused by slightly higher polarity. It can also work with polytetrahydrofuran diol to improve the rapid recovery ability of chain segments after the removal of external force. The two complement each other and achieve a synergistic balance between low modulus and high resilience without relying on increasing the proportion of hard segments or crosslinking density.

[0031] The hydrophilic chain extender includes sodium 2-(diethanolamino)ethanesulfonate and / or sodium 1,2-propanediol-3-sulfonate; the small molecule chain extender includes one or more of ethylene glycol, propylene glycol and 1,4-butanediol. Preferably, the material further includes 14-42 parts of an MXene aqueous dispersion, wherein the MXene aqueous dispersion is a Ti3C2MXene aqueous dispersion with a concentration of 8-12 mg / mL. MXene has extremely high conductivity and a large specific surface area. When combined with polyurethane, MXene forms a continuous conductive network within the polyurethane matrix. When the material is subjected to external forces such as tension or bending, the structure of the conductive network changes, leading to a regular change in the material's resistance. By detecting the change in resistance, the mechanical deformation can be sensed.

[0032] By combining the above components, the water-based polyurethane of this robot's flexible skin can meet the core requirements of flexible skin for flexible fit, resistance to deformation fatigue, and accurate perception of mechanical signals, and has important application value in the field of bionic robot intelligent interaction.

[0033] See Figure 1 The present invention also provides a method for preparing the above-described robotic flexible skin using water-based polyurethane, comprising: S1: The polyether polyol and polyester polyol are dehydrated, specifically as follows: Under vacuum conditions, polyether polyols and polyester polyols are mixed and vacuum dehydrated at 100-120℃ for 1-2 hours to remove water from the polyether polyols and polyester polyols, avoid side reactions, ensure the purity and performance stability of the raw materials, and lay the foundation for the preparation of high-quality waterborne polyurethane.

[0034] S2: Under inert gas protection, dehydrated polyether polyol and polyester polyol are mixed with isocyanate, and a prepolymerization reaction is carried out in the presence of a catalyst to obtain the first prepolymer, specifically: Under the protection of an inert gas (usually nitrogen), the catalyst and isocyanate are added to the dehydrated polyether polyol and polyester polyol and mixed. The mixture is then subjected to a prepolymerization reaction at 75-90°C for 1.5-3 hours to obtain the first prepolymer. The catalyst is dibutyltin dilaurate, and the amount of catalyst added is 0.01-0.03 parts, preferably 0.02 parts.

[0035] S3: Add a hydrophilic chain extender and a small molecule chain extender to the first prepolymer to carry out a chain extension reaction, thereby obtaining the WPU prepolymer, specifically as follows: At 75-90℃, a hydrophilic chain extender and a small molecule chain extender are added to the first prepolymer, and the chain extension reaction is carried out for 1-1.5h to obtain the WPU prepolymer.

[0036] S4: Add water to the WPU prepolymer for emulsification to obtain an aqueous polyurethane emulsion, specifically: Cool the WPU prepolymer to 30-40℃, add water to the WPU prepolymer for emulsification, and add 14-42 parts of MXene aqueous dispersion to the WPU prepolymer after installation by stirring and dripping. Continue the reaction for 1-3 hours to obtain an aqueous polyurethane emulsion, denoted as MXene / WPU emulsion; wherein, the amount of water added during the water emulsification process is 150-200 parts.

[0037] S5: The aqueous polyurethane emulsion is molded and dried to obtain the robotic flexible skin using aqueous polyurethane, specifically: Aqueous polyurethane emulsion was poured into a polytetrafluoroethylene mold and allowed to dry naturally at room temperature to obtain aqueous polyurethane for robotic flexible skin.

[0038] This method is simple to operate, has mild reaction conditions, requires no complex equipment, has low investment costs, is suitable for industrialization, and the prepared robotic flexible skin using water-based polyurethane can meet the core requirements of robotic flexible skin for flexible fit, resistance to deformation fatigue, and accurate perception of mechanical signals.

[0039] The aforementioned application of waterborne polyurethane in robotic flexible skin leverages its low modulus to ensure a tight fit to the robot's surface, while its high resilience prevents detachment or damage during robot movement. Combined with its precise mechanical signal sensing capabilities, the robot can react accordingly to the external forces sensed by the flexible skin, achieving more natural and intelligent interaction. This enhances the overall performance and user experience of bionic robots, demonstrating significant application value in the field of intelligent interaction for bionic robots. Furthermore, because the waterborne polyurethane achieves a synergistic balance between low modulus and high resilience, the material can easily deform under repeated external forces and quickly return to its original position after the forces are removed. This prevents fatigue damage during long-term use, maintains good performance stability, extends the lifespan of the robotic flexible skin, reduces the frequency of replacement and maintenance, and lowers operating costs.

[0040] Example 1 Weigh 90g of polytetrahydrofuran diol and 10g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 100°C for 1 hour.

[0041] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another 1h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 14g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48h to obtain waterborne polyurethane for robotic flexible skin.

[0042] Example 2 Weigh 80g of polytetrahydrofuran diol and 20g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 110°C for 2 hours.

[0043] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another 1h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 14g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48h to obtain waterborne polyurethane for robotic flexible skin.

[0044] Example 3 Weigh 70g of polytetrahydrofuran diol and 30g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 120°C for 1 hour.

[0045] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another 1h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 14g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48h to obtain waterborne polyurethane for robotic flexible skin.

[0046] Example 4 Weigh 70g of polytetrahydrofuran diol and 30g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 100°C for 1 hour.

[0047] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another 1h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 22g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48h to obtain waterborne polyurethane for robotic flexible skin.

[0048] Example 5 Weigh 70g of polytetrahydrofuran diol and 30g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 100°C for 1 hour.

[0049] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another 1h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 32g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48h to obtain waterborne polyurethane for robotic flexible skin.

[0050] Example 6 Weigh 70g of polytetrahydrofuran diol and 30g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 100°C for 1 hour.

[0051] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another 1h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 42g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48h to obtain waterborne polyurethane for robotic flexible skin.

[0052] Example 7 Weigh 70g of polytetrahydrofuran diol and 30g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 120°C for 1 hour.

[0053] Subsequently, under a nitrogen atmosphere and at 75°C, 25g of hexamethylene diisocyanate and 0.03g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 75°C for 3 hours. Then, 3g of sodium 1,2-propanediol-3-sulfonate and 2.5g of propylene glycol were added sequentially, and the reaction was continued at 80°C for 1 hour. After the reaction was completed, the temperature was lowered to below 30°C, and 180g of water was added for emulsification to obtain a WPU emulsion. Then, 32g of Ti3C2MXene aqueous dispersion with a concentration of 8mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2 hours with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48 hours to obtain waterborne polyurethane for robotic flexible skin.

[0054] Example 8 Weigh 70g of polytetrahydrofuran diol and 30g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 100°C for 1 hour.

[0055] Subsequently, under a nitrogen atmosphere and at 90°C, 23g of hexamethylene diisocyanate and 0.01g of dibutyltin dilaurate catalyst were added. After reacting at a constant temperature of 90°C for 1.5h, 1g of sodium 1,2-propanediol-3-sulfonate, 2g of sodium 2-(diethanolamine)ethanesulfonate, and 2g of ethylene glycol were added sequentially, and the reaction was continued at 75°C for another 1.5h. After the reaction was completed, the temperature was lowered to below 30°C, and 180g of water was added for emulsification to obtain a WPU emulsion. Then, 16g of Ti3C2MXene aqueous dispersion with a concentration of 12mg / mL was added dropwise to the WPU emulsion, and the mixture was reacted in a water bath at room temperature for 2h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and allowed to dry naturally at room temperature for 48h to obtain waterborne polyurethane for robotic flexible skin.

[0056] Example 9 Weigh 70g of polytetrahydrofuran diol and 30g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 100°C for 1 hour.

[0057] Subsequently, under a nitrogen atmosphere and at 85°C, 24g of hexamethylene diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 85°C for 2 hours. Then, 4g of sodium 1,2-propanediol-3-sulfonate, 0.5g of 1,4-butanediol, and 2g of ethylene glycol were added sequentially, and the reaction was continued at 85°C for another 2 hours. After the reaction was completed, the temperature was lowered to below 30°C, and 200g of water was added for emulsification to obtain a WPU emulsion. Then, 20g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2 hours with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48 hours to obtain waterborne polyurethane for robotic flexible skin.

[0058] Example 10 Weigh 99g of polytetrahydrofuran diol and 1g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 100°C for 1 hour.

[0059] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5 h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 14g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2 h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48 h to obtain waterborne polyurethane for robotic flexible skin.

[0060] Comparative Example 1 Weigh 100g of polycaprolactone diol and add it to a four-necked flask. Dehydrate under vacuum at 100 °C for 1 h.

[0061] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5 h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 14g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2 h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48 h to obtain waterborne polyurethane for robotic flexible skin.

[0062] Comparative Example 2 Weigh 70 g of polytetrahydrofuran diol and 30 g of polycaprolactone diol and add them to a four-necked flask. Dehydrate under vacuum at 100°C for 1 h.

[0063] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another 1h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. The product was poured into a polytetrafluoroethylene mold and allowed to dry naturally at room temperature for 48h to obtain waterborne polyurethane for robotic flexible skin.

[0064] Comparative Example 3 Weigh 100g of polytetrahydrofuran diol and add it to a four-necked flask. Dehydrate under vacuum at 100°C for 1 hour.

[0065] Subsequently, under a nitrogen atmosphere and at 80°C, 20g of isoflurane diisocyanate and 0.02g of dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 1.5 h. Then, 4g of sodium 2-(diethanolamine)ethanesulfonate and 1.5g of 1,4-butanediol were added sequentially, and the reaction was continued at 80°C for another h. After the reaction was completed, the temperature was lowered to below 30°C, and 150g of water was added for emulsification to obtain a WPU emulsion. Then, 14g of Ti3C2MXene aqueous dispersion with a concentration of 10mg / mL was added dropwise to the WPU emulsion, and the reaction was carried out in a water bath at room temperature for 2 h with continuous stirring. After the reaction was completed, the product was poured into a polytetrafluoroethylene mold and dried naturally at room temperature for 48 h to obtain waterborne polyurethane for robotic flexible skin.

[0066] The water-based polyurethane films for robotic flexible skin prepared in Examples 1-6 and Comparative Examples 1-3 were uniformly thickened to 0.2 mm using a template-limited hot-pressing process, and then subjected to a series of performance tests. Mechanical properties were tested according to GB / T 228.1-2021, hardness according to ASTM D2240, and resilience according to GB / T 1681-2018 standard for determination of permanent deformation at a given elongation. Resilience retention at 100% and 300% elongation was tested. Volume resistivity and volume conductivity were measured according to GBT-1410-2006. The test results are shown in the table below: Tensile strength (MPa) Young's modulus (MPa) 100% springback retention 300% springback retention Shore A hardness Example 1 13.27 1.23 97% 93% 28 Example 2 13.56 1.87 98% 94% 31 Example 3 14.83 2.36 99% 98% 34 Example 4 14.72 2.29 99% 97% 36 Example 5 15.01 2.54 99% 97% 35 Example 6 14.98 2.43 99% 97% 35 Comparative Example 1 17.33 5.73 99% 98% 67 Comparative Example 2 14.68 2.64 99% 97% 35 Comparative Example 3 12.44 0.98 95% 89% 26 It is evident that the Young's modulus of Examples 1-3, Comparative Examples 2 and 3 is significantly lower than that of Comparative Example 1. In Examples 1-3 and Comparative Example 3, the Young's modulus gradually increases with the increase of polyester polyol content, and remains within the low modulus range. Resilience performance tests show that in Examples 1-3, Comparative Examples 3 and Comparative Example 1, the increase of polyester polyol content leads to a simultaneous increase in the 100% and 300% constant elongation resilience retention rates of the samples. Comparative Example 1 exhibits the best resilience retention rate. Furthermore, when the ratio of polyether polyol to polyester polyol is 7:3, the sample also demonstrates excellent resilience. Simultaneously, the Shore A hardness of Examples 1-5, Comparative Examples 3 and 2 is significantly lower than that of Comparative Example 1. This is mainly because the ether bonds of polyether polyols are weakly polar, there are no hydrogen bonds between molecules, and the chain segments are flexible and easy to slide, which can effectively reduce the modulus and hardness. Polyester polyols contain ester carbonyl groups, which can form weak intermolecular hydrogen bonds and have excellent chain segment regularity. Increasing the content can strengthen the constraints between molecular chains, resulting in a slight increase in modulus and hardness and a significant improvement in resilience. Moreover, the present invention does not cause a significant increase in modulus and hardness under the limited ratio. In contrast, Comparative Example 1, due to the excessive amount of polyester polyol and the low proportion of polyether polyol, resulted in a large accumulation of hydrogen bonds in the system and a sharp increase in the intermolecular forces, causing a sharp increase in Young's modulus and Shore A hardness. Although the resilience performance was excellent, it could not meet the requirements for low modulus.

[0067] Therefore, based on the above test results, when the content of polyether polyol and polyester polyol is 3:7, the low modulus and high resilience are optimal, meeting the basic requirements for robotic flexible skin applications.

[0068] The conductivity of the robotic flexible skins prepared in Examples 1-6 and Comparative Examples 1-3 using waterborne polyurethane was tested, and the results are shown in the table below: Volume resistivity (kΩ) Volumetric conductivity (S / m) Example 1 114 44 Example 2 125 40 Example 3 130 34 Example 4 102 50 Example 5 10 240 Example 6 10000 8 Comparative Example 1 129 35 Comparative Example 2 1000 0 Comparative Example 3 128 37 Test results show that in Examples 2-6, the volumetric conductivity of the material first increases and then decreases with the increase of MXene addition. The volumetric conductivity reaches its peak when the MXene addition is 20wt%, and drops sharply to 8S / m when it is increased to 25wt%. At low addition levels, insufficient MXene content prevents the construction of a continuous conductive network within the polyurethane matrix, resulting in a discrete distribution and consequently, high volume resistivity and low volume conductivity. When the MXene addition reaches 20 wt%, the conductive percolation threshold is reached. At this point, the abundant hydroxyl groups on the Ti3C2MXene surface covalently graft with the isocyanate groups of the polyurethane prepolymer, achieving uniform dispersion of MXene in the matrix. This effectively avoids the agglomeration and shedding problems caused by physical blending. Simultaneously, its two-dimensional layered structure synergistically forms a stable network-like structure with the polyurethane matrix, ensuring rapid and smooth electron transport while maintaining the integrity of the material structure. This results in excellent conductivity, with a volume conductivity of 240 S / m and a volume resistivity of only 10 kΩ. When the MXene addition is further increased to 25 wt%, excessive MXene undergoes severe agglomeration, disrupting the continuity of the conductive network. The current transport path is blocked and dispersed by the agglomerates, leading to a significant decrease in conductivity. Therefore, the membrane exhibits optimal conductivity at an MXene addition level of 20 wt%.

[0069] Because the thin film of Example 5 has the best volume conductivity, it was fabricated into an electronic skin sensor to detect signals when different parts of the human body move. Figure 2 and Figure 3 The display shows that all signals are short and stable, and the signal output exhibits a reciprocating cycle during movement, indicating that the thin film has good sensing stability.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A waterborne polyurethane for a robot flexible skin, characterized by, By mass, it includes the following raw material components: 70-100 parts of polyether polyol, 1-30 parts of polyester polyol, 20-25 parts of isocyanate, 3-4 parts of hydrophilic chain extender and 1.5-2.5 parts of small molecule chain extender; The polyether-type polyol includes at least polytetrahydrofuran diol, and the polyester-type polyol includes at least polycaprolactone diol.

2. The aqueous polyurethane for robotic flexible skin according to claim 1, characterized in that, The molecular weights of the polyether polyol and the polyester polyol are both 2000.

3. The aqueous polyurethane for robotic flexible skin according to claim 1, wherein, It also includes 14-42 parts of MXene aqueous dispersion.

4. The aqueous polyurethane for robotic flexible skin according to claim 3, characterized in that, The MXene aqueous dispersion is a Ti3C2MXene aqueous dispersion with a concentration of 8-12 mg / mL.

5. The aqueous polyurethane for robotic flexible skin according to claim 1, wherein, The isocyanate includes isophorone diisocyanate and / or hexamethylene diisocyanate.

6. The aqueous polyurethane for robotic flexible skin according to claim 1, characterized in that, The hydrophilic chain extender includes sodium 2-(diethanolamine)ethanesulfonate and / or sodium 1,2-propanediol-3-sulfonate.

7. The robotic flexible skin waterborne polyurethane of claim 1, wherein, The small molecule chain extender includes one or more of ethylene glycol, propylene glycol, and 1,4-butanediol.

8. A process for the preparation of a waterborne polyurethane for robotic flexible skin as claimed in any one of claims 1 to 7, characterized in that, include: Dehydration treatment of polyether polyols and polyester polyols; Under inert gas protection, dehydrated polyether polyol and polyester polyol are mixed with isocyanate and subjected to prepolymerization reaction under the action of catalyst to obtain the first prepolymer. A hydrophilic chain extender and a small molecule chain extender were added to the first prepolymer to carry out a chain extension reaction, thereby obtaining the WPU prepolymer. Water was added to the WPU prepolymer and emulsified to obtain an aqueous polyurethane emulsion. Aqueous polyurethane emulsion is molded and dried to obtain aqueous polyurethane for robotic flexible skin.

9. The method for preparing the aqueous polyurethane for robotic flexible skin according to claim 8, characterized in that, After emulsifying the WPU prepolymer with water, the process also includes adding MXene aqueous dispersion to the emulsified WPU prepolymer and reacting at a constant temperature; the amount of MXene aqueous dispersion added is 14-42 parts; the temperature of the constant temperature reaction is room temperature, and the reaction time is 1-3 hours.

10. The application of the aqueous polyurethane for robotic flexible skin according to any one of claims 1-7 in a robot.

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