Ion gel for stretchable circuit and stretchable circuit board based thereon

Abstract

The present invention discloses an ion gel for a stretchable circuit and a stretchable circuit board based thereon. The ion gel is prepared by physical cross-linking an ionic liquid and gelatin in proportion. The cations in the ionic liquid are one or more of 1-butyl-3-methylimidazole, 1-ethyl-3-methylimidazole, 1-n-octyl-3-methylimidazole, 1-n-dodecyl-3-methylimidazole, 1-butyl-2,3-dimethylimidazole, 1-butyl-methylpyrrolidinyl, and 1-methylpropylpyrrolidinyl, and the anions are one or more of bromide, chloride, boron tetrafluoride, ethyl sulfate, phosphorus hexafluoride, dicyanamide, and bistrifluoromethanesulfonimide. The present invention precisely controls the conductivity, morphology, and viscosity of the ion gel by selecting the ionic liquid in the ion gel and the mass ratio of the ionic liquid to gelatin, making it easy to adapt to diverse application scenarios.

Description

Technical Field

[0001] The present invention relates to the technical field of stretchable circuits, and in particular to an ion gel for stretchable circuits and a stretchable circuit board based thereon. Background Art

[0002] With the development of wearable electronic devices, flexible and stretchable circuits that can conform to the human body have emerged. Traditional circuit conductive materials, primarily metal / alloy conductors, liquid metals, and conductive plastics / rubbers, can be difficult to bend and stretch, or experience unstable signal transmission after bending or stretching. Furthermore, polymer conductive materials obtained through structural doping or composite processes also suffer from poor stability, processability, and mechanical properties.

[0003] Ion gel is a network structure with encapsulated ionic liquids (ILs) as the dispersion medium. It is a solid mixture with ionic conductivity, formed by self-assembly / bonding (physical or chemical). It has been widely studied for its conductive ability and excellent stretchable conductivity, but the application of ion gel in stretchable circuit boards has rarely been seen.

[0004] Stretchable circuit boards that combine ion gels with high-performance elastomers can significantly expand their application areas, finding widespread application in green and sustainable chemistry, electronics, medical devices, aerospace, and machinery. These stretchable circuit boards, with their unique advantages, play a vital role in new flexible electronics, electronic connecting pieces, and on-skin electronics. These emerging industries are placing new demands on the conductive and packaging materials used in the development and application of stretchable circuit boards. Summary of the Invention

[0005] After continuous exploration, the present invention proposes an ion gel for stretchable circuits and a stretchable circuit board based thereon.

[0006] The present invention protects an ion gel for stretchable circuits, which is prepared by physical cross-linking of ionic liquid and gelatin in proportion, wherein the cations in the ionic liquid are one or more of 1-butyl-3-methylimidazole, 1-ethyl-3-methylimidazole, 1-n-octyl-3-methylimidazole, 1-n-dodecyl-3-methylimidazole, 1-butyl-2,3-dimethylimidazole, 1-butyl-methylpyrrolidino, and 1-methylpropylpyrrolidino, and the anions are one or more of bromide, chloride, boron tetrafluoride, ethyl sulfate, phosphorus hexafluoride, dicyanamide, and bistrifluoromethanesulfonimide.

[0007] Preferably, the ionic liquid combination is one of 1-butyl-3-methylimidazolium bromide, 1-butyl-2,3-dimethylimidazolium chloride, and 1-butyl-3-methylimidazolium dicyanamide.

[0008] The preparation method of the above-mentioned ion gel for stretchable circuits is to stir and react ionic liquid and gelatin in water at a temperature of 35 to 55°C. After the gelatin is completely melted, it is quickly placed at room temperature to be completely cooled to obtain the ion gel; wherein the mass ratio of ionic liquid to gelatin is 1:1 to 7:1, and the mass fraction of water is less than 22%.

[0009] The present invention also protects a stretchable circuit board, which is composed of two thermoplastic elastomers with grooves etched therein, which are bonded together and the interior of the grooves is filled with the ion gel described in claim 1.

[0010] Preferably, the trenches are etched by laser etching or photolithography, wherein the blackbody etching power of the laser etching is 30% to 80%.

[0011] Preferably, the ion gel is filled by blade coating, spin coating, slit extrusion, injection or 3D printing.

[0012] Beneficial effects of the present invention:

[0013] 1. The preparation of ion gel only requires ionic liquid and gelatin, which is simple and convenient to operate and does not require other solvents;

[0014] 2. The circuit is formed by ion gel, which will not cause leakage accidents due to damage of packaging materials;

[0015] 3. The channel is carved by laser etching or photolithography, which does not require a vacuum environment and greatly reduces production costs;

[0016] 4. The stretchable circuit board prepared by combining ion gel and thermoplastic elastomer can ensure the excellent properties of the elastomer such as high mechanical properties, high temperature resistance, and solvent resistance, while the electrical signal transmission is more stable, which can achieve low-cost and high-efficiency applications, thereby expanding its actual industrial application scenarios.

[0017] 5. Through the selection of ionic liquid in the ion gel and the mass ratio of ionic liquid to gelatin, the conductivity, morphology and viscosity of the ion gel can be precisely controlled, and circuit packaging can be achieved through hot pressing bonding and other methods, making it easy to adapt to diverse application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the stretchable circuit board structure disclosed in the present invention. DETAILED DESCRIPTION

[0019] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for purposes of illustration and description and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments are chosen and described to better illustrate the principles of the invention and its practical application, and to enable those skilled in the art to understand the invention and design various embodiments with various modifications suitable for specific applications.

[0020] Example 1

[0021] The stretchable circuit board disclosed in the present invention is as follows: Figure 1 As shown, it is formed by two pieces of thermoplastic elastomer A and ion gel circuit B using a sandwich packaging structure.

[0022] The ionic liquid combination used in this example is 1-butyl-3-methylimidazolium bromide ([BMIM][Br]). 3 parts of ionic liquid and 1 part of gelatin are mixed in 1.5 parts of water and stirred at 50°C and 20 rpm for 40 minutes. After the gelatin is completely melted, it is quickly cooled at room temperature for 30 minutes to obtain a [BMIM][Br] ion gel.

[0023] The ion gel forms a circuit structure, which requires engraving channels on the thermoplastic elastomer. In this embodiment, the elastomer is placed in a carbon dioxide laser etching device, and the circuit is etched at 50% black body power.

[0024] After the channel etching is completed, the ion gel is filled into the etched elastomer channel by scraping, and then the surface is covered with the same elastomer in the form of a sandwich and placed in a hot press. At a temperature of 120°C and a pressure of 0.1MPa, hot pressing and bonding are performed for 40 minutes. The printed circuit board is taken out and cooled at room temperature for 2 hours to obtain a stretchable circuit board encapsulating the ion gel circuit.

[0025] In this example, [BMIM][Br] ionic liquid was used to prepare the ion gel, with a mass ratio of ionic liquid to gelatin set at 3:1. This is because the [BMIM][Br] ion gel prepared at this ratio has high viscosity and a certain degree of fluidity. When this ratio is too high, the ion gel tends to be liquid, with strong fluidity and ductility; when this ratio is too low, the ion gel tends to be solid, with poor fluidity and ductility. In short, for the [BMIM][Br] ion gel, a mass ratio of ionic liquid to gelatin greater than or less than 3:1 will adversely affect the resulting stretchable circuit board. At a mass ratio of ionic liquid to gelatin of 3:1, the resulting stretchable circuit board can maintain smooth circuitry and stable performance during stretching.

[0026] Example 2

[0027] Different from Example 1, the ionic liquid combination selected in this example is 1-butyl 2,3-dimethylimidazolium chloride ([BDMIM][Cl]). One part of ion gel and one part of gelatin are mixed in one part of water, stirred at 60°C and 30 rpm for 35 minutes. After the gelatin is completely melted, it is quickly placed at room temperature and cooled for 40 minutes to obtain [BDMIM][Cl] ion gel.

[0028] The elastomer is placed in a carbon dioxide laser etching device to carve a channel. In this embodiment, the circuit is etched at a black body power of 60%.

[0029] After the channel etching is completed, the ion gel is filled into the etched elastomer channel by scraping, and then the surface is covered with the same elastomer in the form of a sandwich and placed in a hot press. At a temperature of 115°C and a pressure of 0.3MPa, hot pressing and bonding are performed for 35 minutes. The printed circuit board is taken out and cooled at room temperature for 2 hours to obtain a stretchable circuit board encapsulating the ion gel circuit.

[0030] Different from Example 1 in which [BMIM][Br] ion gel is selected and the mass ratio of ionic liquid to gelatin is set to 3:1, this embodiment selects [BDMIM][Cl] and, correspondingly, the mass ratio of ionic liquid to gelatin is set to 1:1, so that the prepared [BDMIM][Cl] ion gel has a larger viscosity and a certain fluidity, further enabling the formed stretchable circuit board to maintain smooth circuit and stable performance during the stretching process.

[0031] Example 3

[0032] Different from Example 1, the ionic liquid combination selected in this example is 1-butyl-3-methylimidazolium dicyanamide ([BMIM][[N(CN)2]). Two parts of ion gel and one part of gelatin are mixed in two parts of water, stirred at 50°C and 20 rpm for 30 minutes. After the gelatin is completely melted, it is quickly placed at room temperature and cooled for 30 minutes to obtain [BMIM][[N(CN)2] ion gel.

[0033] The elastomer is placed in a carbon dioxide laser etching device to carve a channel. In this embodiment, the circuit is etched at a black body power of 40%.

[0034] After the channel etching is completed, the ion gel is filled into the etched elastomer channel by scraping, and then the surface is covered with the same elastomer in the form of a sandwich and placed in a hot press. At a temperature of 115°C and a pressure of 0.3MPa, hot pressing and bonding are performed for 35 minutes. The printed circuit board is taken out and cooled at room temperature for 2 hours to obtain a stretchable circuit board encapsulating the ion gel circuit.

[0035] Different from Example 1 in which [BMIM][Br] ion gel is selected and the mass ratio of ionic liquid to gelatin is set to 3:1, this embodiment selects [BMIM][[N(CN)2] ion gel, and correspondingly, the mass ratio of ionic liquid to gelatin is set to 2:1, so that the prepared [BMIM][[N(CN)2] ion gel has a larger viscosity and a certain fluidity, further enabling the formed stretchable circuit board to maintain smooth circuit and stable performance during the stretching process.

[0036] The static conductivity and elongation of the ion gel in Examples 1-3 were compared with those of two traditional conductive materials, metal wire and conductive rubber, as shown in Table 1 below.

[0037] Table 1

[0038] Serial number category Components <![CDATA[Conductivity / S·m -1 > Elongation 1 Ion gel [BMIM][Br] ion gel 2.6 ＞200％ 2 Ion gel [BDMIM][Cl] ion gel 2.4 ＞200％ 3 Ion gel <![CDATA[[BMIM][[N(CN)2] ionic gel]]> 2.3 ＞200％ 4 Metal wire copper <![CDATA[5.8*10 7 ]]> ＜20％ 5 Conductive rubber Glass-coated silver-filled highly conductive silicone rubber 1.67 ＜150％

[0039] As can be seen in Table 1, while copper has the highest electrical conductivity, its elongation is relatively poor, typically around 13%. Exceeding this limit can easily lead to breakage, potentially causing circuit boards to malfunction. While glass-coated silver-filled highly conductive silicone rubber exhibits acceptable elongation, its conductivity is significantly lower than the ion gel disclosed in this invention. Based on material property analysis, the ion gels provided in Examples 1-3 achieve elongations of up to 300%, significantly exceeding those of glass-coated silver-filled highly conductive silicone rubber.

[0040] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made according to the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A stretchable circuit board, characterized in that: It is composed of two pieces of thermoplastic elastomer with grooves etched in them, and the grooves are filled with ion gel; The ion gel is prepared by physical cross-linking of an ionic liquid and gelatin in proportion, wherein the cation in the ionic liquid is one or more of 1-butyl-3-methylimidazole, 1-ethyl-3-methylimidazole, 1-n-octyl-3-methylimidazole, 1-n-dodecyl-3-methylimidazole, 1-butyl-2,3-dimethylimidazole, 1-butyl-methylpyrrolidinyl, and 1-methylpropylpyrrolidinyl, and the anion is one or more of bromide, chloride, boron tetrafluoride, ethyl sulfate, phosphorus hexafluoride, dicyanamide, and bistrifluoromethanesulfonimide; The preparation method of the ion gel comprises the following steps: reacting an ionic liquid and gelatin in water at a temperature of 35 to 55° C. by stirring; after the gelatin is completely melted, the reaction is quickly placed at room temperature for complete cooling to obtain the ion gel; wherein the mass ratio of the ionic liquid to the gelatin is 1:1 to 3:1, and the mass fraction of water is less than 22%.

2. The stretchable circuit board according to claim 1, wherein: The ionic liquid combination is one of 1-butyl-3-methylimidazolium bromide, 1-butyl-2,3-dimethylimidazolium chloride and 1-butyl-3-methylimidazolium dicyanamide.

3. The stretchable circuit board according to claim 1, wherein: The trenches are etched using laser etching or photoetching, wherein the blackbody etching power of the laser etching is 30% to 80%.

4. The stretchable circuit board according to claim 1, wherein: The ion gel is filled by blade coating, spin coating, slit extrusion, injection or 3D printing.

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