Preparation method of flexible circuit substrate based on room-temperature self-repairing elastomer

Abstract

The invention provides a preparation method of a flexible circuit substrate based on a room-temperature self-repairing elastomer, and belongs to the technical field of flexible electronics. According to the method, amino-modified multi-walled carbon nanotubes (AMWCNT), amino-modified polydimethylsiloxane (APDMS) and terephthalaldehyde (DFB) are selected as reactants, a room-temperature self-repairing elastomer with reversible imine bonds is formed through a Schiff base reaction, and then the flexible circuit substrate is prepared based on the room-temperature self-repairing elastomer. The tensile strength of the prepared elastomer can reach 132.3 kPa, when the elastomer is damaged, the elastomer is placed at room temperature for 24 h, the mechanical property can be restored to 99.87% of the previous mechanical property, and the application range of the self-repairing elastomer can be expanded. The flexible circuit substrate prepared based on the self-repairing elastomer also has excellent self-repairing capability and mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the field of flexible electronic technology, and in particular relates to a method for preparing a flexible circuit substrate based on a room temperature self-healing elastomer. Background Art

[0002] Flexible circuit boards are widely used due to their advantages such as light weight, thin thickness, free bending and folding. They usually use polyester film or polyimide as the substrate, with high reliability and excellent flexibility. By embedding the circuit design into a thin and flexible material, flexible circuit boards can accommodate a large number of precision components in a small space to form a flexible circuit structure. This design is not only small in size and light in weight, but also has good heat dissipation and convenient installation, breaking through the limitations of traditional interconnection technology. However, flexible circuit boards are often affected by mechanical stress such as bending, folding and scratching in actual applications, which may cause circuit breakage or performance degradation. Giving flexible circuit boards the ability to self-repair can improve their durability and reliability, increase their service life, and maintain stable performance in various complex environments.

[0003] Self-healing materials are a type of material that can self-diagnose and repair damage, thereby restoring the original function. In recent years, they have attracted widespread attention due to their unique properties. Self-healing materials can be divided into two categories: one is achieved by adding microcapsules or microvessels embedded with repair agents into the matrix, that is, external aid self-repair. When the material is damaged, the microcapsules or microvessels will rupture, and the liquid repair agent will flow to the damaged part and react with the catalyst in the matrix to achieve repair. The other is achieved through reversible physical and chemical effects in the material system, that is, intrinsic self-repair. Reversible covalent bonds (such as imine bonds, acylhydrazone bonds, Diels-Alder reactions, etc.) or reversible non-covalent bonds (such as π-π stacking bonds, hydrogen bonds, metal coordination bonds, etc.) are introduced into the material. When the material is damaged, the reversible chemical bonds break and then recombine, thereby achieving material repair. The interaction between non-covalent bonds is weak, so it is challenging to balance mechanical properties and self-healing properties. In contrast, covalent bonds can provide superior mechanical properties due to their stronger bonding force.

[0004] The use of self-healing elastomers to prepare flexible circuit substrates will undoubtedly bring revolutionary progress to the field of flexible electronics. Wang Peng et al. (Wang, P.; Yang, L.; Dai, B.; Yang, Z, H.; Guo, S.; Gao, G.; Xu, L, G.; Sun, M, Q.; Yao, K, L.; Zhu, J, Q., A self-healing transparent polydimethylsiloxane elastomer based on imine bonds. EUR POLYM J, 2020, 123.) used amino-modified polydimethylsiloxane and terephthalaldehyde as raw materials to synthesize an elastomer with self-healing ability. The tensile strength of the obtained elastomer was 40.92 kPa. After 6 hours of self-healing at room temperature, the tensile strength was 97% of the original. By introducing nanomaterials into self-healing elastomers, the tensile strength of the matrix can be effectively improved. For example, Wu Tongfei et al. (Wu, T. F.; Chen, B. Q., Synthesis of Multiwalled Carbon Nanotube-Reinforced Polyborosiloxane Nanocomposites with Mechanically Adaptive and Self-Healing Capabilities for Flexible Conductors, ACS Appl. Mater, 2016, 8, 24071-24078.) used hydroxyl-modified polydimethylsiloxane and boric acid as raw materials to synthesize a polyborosiloxane elastomer with self-healing ability, and doped it with multi-walled carbon nanotubes (MWCNTs). The doping of MWC NTs significantly enhanced the mechanical properties of the elastomer, but when doped with 3.0 wt% MWCNTs, the self-healing efficiency of the elastomer at room temperature for 10 minutes decreased from 99.6% to 39.5%. This is because the doping of nanomaterials hinders the flow of macromolecular segments, resulting in a decrease in self-healing efficiency.Chen Xiaoliang et al. (Chen, X. L.; Sun, P.; Tian, ​​H. M.; Li, X. M.; Wang, C. H.; Duan, J. K.; Luo, S. Y.; Li, S.; Chen, X. M.; Shao, J. Y., Self-healing and stretchable conductor based on embedded liquid metal patterns within imprintable dy namic covalent elastomer, J Mater Chem C. 2022, 10, 1039-1047.) used amino-modified polydimethylsiloxane, amino-modified multi-walled carbon nanotubes and trimesic acid as raw materials to synthesize a substrate with self-healing ability, and used liquid metal gallium to prepare a conductive path on the substrate, thereby obtaining a stretchable and self-healable circuit, but the low melting point of liquid metal gallium will limit the application of such flexible circuits.

[0005] Therefore, how to prepare a self-healing substrate that can balance tensile strength and self-healing ability, and use the substrate to prepare a flexible circuit substrate, has become a research focus. Summary of the invention

[0006] In view of the problems existing in the background technology, the purpose of the present invention is to provide a method for preparing a flexible circuit substrate based on a room temperature self-healing elastomer. The method uses amino-modified multi-walled carbon nanotubes (AMWCNT), amino-modified polydimethylsiloxane (APDMS) and terephthalaldehyde (DFB) as reactants, forms a room temperature self-healing elastomer with a reversible imine bond through a Schiff base reaction, and then prepares a flexible circuit substrate based on the room temperature self-healing elastomer; the finally obtained flexible circuit substrate has excellent self-healing ability and mechanical properties.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for preparing a flexible circuit substrate based on a room temperature self-healing elastomer comprises the following steps:

[0009] S1. Preparing a mixed solution of APDMS and AMWCNT: adding AMWCNT and APDMS to a first organic solvent, and then stirring at room temperature to make them uniformly dispersed; wherein AMWCNT accounts for 6wt%-9wt% of the mass of APDMS;

[0010] S2. Preparing a crosslinker solution: adding the crosslinker to the second organic solvent and stirring at room temperature until completely dissolved, wherein the crosslinker accounts for 1.5wt%-3.0wt% of the mass of APDMS;

[0011] S3. The crosslinking agent solution obtained in S2 is added to the mixed solution obtained in S1 to obtain a reaction solution, and then stirred at 25-70° C. for 1-6 hours;

[0012] S4. After the reaction is completed, the mixture is dried at room temperature for 12-24 hours, then placed in a mold, and hot-pressed at 70-90°C and 10-20MPa for 20-30 minutes to obtain a self-healing elastomer of the desired shape;

[0013] S5. Preparation of flexible circuit substrate by metallization of elastomer surface: Use insulating tape to cover the surface of the self-healing elastomer prepared in S4, leaving a copper-plated area, and then use chemical plating to prepare a circuit with the required pattern on the surface of the self-healing elastomer to obtain the required flexible circuit substrate.

[0014] Furthermore, the nitrogen content of APDMS in S1 is 0.32-0.42%, and the viscosity is 800-5000 cPs. The viscosity is too high, and its fluidity is poor, making it difficult to process and mix. The outer diameter of AMWCNT is 8-15 nm, the inner diameter is 3-5 nm, the length is 10-50 μm, and the nitrogen content is less than 0.21%.

[0015] Furthermore, the mass volume ratio of APDMS to the first organic solvent in S1 is 1 g:(0.5-1) mL; preferably 1 g:1 mL.

[0016] Furthermore, the mass ratio of APDMS to AMWCNT in S1 is preferably 1:0.06.

[0017] Furthermore, the cross-linking agent is preferably terephthalaldehyde (DFB) or trimesaldehyde (TFB).

[0018] Furthermore, the mass volume ratio of DFB to the second organic solvent in S2 is 1 g:(40-60) mL; preferably 1 g:50 mL.

[0019] Furthermore, the mass ratio of APDMS to the cross-linking agent in S3 is preferably 1:0.028.

[0020] Furthermore, the first organic solvent and the second organic solvent are the same or different, and are preferably toluene, tetrahydrofuran or N,N-dimethylformamide.

[0021] Furthermore, the specific process of chemical plating in S5 is: the self-healing elastomer covered with insulating tape is ultrasonically cleaned (degreasing), dried, and then plasma treated (to increase surface roughness and promote the formation of a mechanical locking structure between the copper circuit and the substrate), and then immersed in 3-aminopropyltriethoxysilane (amino silanization of the substrate surface), rinsed after immersion, and then immersed in a sensitizing solution (to adsorb Sn on the substrate) in turn. 2+ ), deionized water (to make the substrate surface adsorb gel) and activation solution (Sn 2+ Reduction of Pb 2+ The flexible circuit substrate is immersed in a metal Pb for a period of time, rinsed after immersion, and chemically plated with copper in a chemical copper plating solution. After the chemical plating is completed, the desired flexible circuit substrate can be obtained.

[0022] Furthermore, the sensitizing solution includes SnCl2·2H2O and HCl, and the activating solution includes PdCl2 and HCl.

[0023] The mechanism of the present invention is:

[0024] The amino groups in both APDMS and AMWCNT react with the aldehyde groups in the cross-linking agent through a Schiff base reaction to form a reversible imine bond. When the elastomer is subjected to an external force (such as stretching or scratching, etc.), causing the imine bond structure to be destroyed, the imine bond will be re-formed after a certain period of time. The self-repairing process can be achieved at room temperature without any external stimulation. The cross-linking agent provides a dynamic reversible site for the self-repairing process, and AMWCNTs with a larger aspect ratio are added therein as reinforcing nanomaterials, entangled and overlapped with each other, effectively improving the mechanical properties of the self-repairing elastomer. The presence of amino groups in AMWCNT enhances the affinity with APDMS, allowing it to be evenly dispersed in the matrix. Therefore, the room temperature self-repairing elastomer obtained by the present invention effectively balances the self-repairing ability and mechanical properties, and the flexible substrate prepared based on the self-repairing elastomer also has excellent self-repairing properties and mechanical properties.

[0025] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0026] (1) Although traditional self-healing elastomers have high self-healing efficiency, their mechanical properties are poor. Filling the self-healing elastomer with nano-reinforced material AMWCNT can effectively balance the mechanical properties and self-healing efficiency of the self-healing elastomer. The tensile strength of the elastomer prepared by the present invention can reach 132.3 kPa. When the elastomer is damaged, the mechanical properties can be restored to 99.87% of the previous value after being placed at room temperature for 24 hours, which is conducive to expanding the application range of self-healing elastomers.

[0027] (2) AMWCNT not only acts as a filling material, but also participates in the cross-linking process. The amino groups on the surface react with the aldehyde groups in the cross-linking agent to generate reversible imine bonds, which participate in the self-repair process. When 6wt% of AMWCNT and multi-walled carbon nanotubes (MWCNT) are added, the self-repair efficiency of AMWCNT can be effectively improved by 46.89% compared with MWCNT under the condition of room temperature repair for 24h.

[0028] (3) The raw materials of the present invention are cheap, the synthesis route is simple, and it can be produced in large quantities and quickly. The surface of the self-healing elastomer can be metallized by chemical plating to prepare a flexible substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a reaction principle diagram of the self-healing elastomer of the present invention.

[0030] Figure 2 This is a picture showing the self-healing process of the self-healing elastomer of the present invention.

[0031] Figure 3 These are SEM images of the self-healing elastomer of the present invention before and after self-healing.

[0032] Figure 4 This is a SEM image of the surface of the self-healing elastomer of the present invention after copper plating.

[0033] Figure 5 This is a picture of the self-repair process of the flexible wire prepared by the present invention. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation modes and the accompanying drawings.

[0035] Example 1

[0036] A method for preparing a flexible circuit substrate based on a room temperature self-healing elastomer, using APDMS as a substrate and DFB as a crosslinking agent, and generating crosslinks in a toluene solution, comprising the following steps:

[0037] S1. Preparation of a mixed solution of amino-modified polydimethylsiloxane and amino-modified multi-walled carbon nanotubes: 0.6 g AMWCNT was added to 10 g APDMS, dissolved in 10 mL toluene solution, and stirred at room temperature to disperse evenly;

[0038] S2. Prepare DFB solution: add 14 mL of toluene solution to 0.28 g of DFB and stir at room temperature until completely dissolved;

[0039] S3. The DFB solution obtained in S2 was added to the mixed solution obtained in S1 to obtain a reaction solution, and then the reaction was stirred at 70° C. for 6 h;

[0040] S4. After the reaction is completed, the mixture is dried at room temperature for 24 hours, then placed in a polytetrafluoroethylene mold, and hot-pressed at 90°C and 20 MPa for 30 minutes to obtain a self-healing elastomer of the desired shape;

[0041] S5. Preparation of flexible circuit substrate by metallization of elastomer surface: Use insulating tape to cover the surface of the self-healing elastomer prepared in S4, leaving a copper-plated area, and then use chemical plating to prepare a circuit with the required pattern on the surface of the self-healing elastomer to obtain the required flexible circuit substrate.

[0042] The reaction principle diagram of the self-healing elastomer prepared by the method of the present invention is as follows Figure 1 As shown. The amino groups of APDMS and AMWCNT react with the aldehyde groups in DFB through Schiff base to form reversible dynamic imine bonds. DFB acts as a cross-linking agent to provide cross-linking sites for the reaction.

[0043] The self-healing elastomer prepared in step S4 was cut and the self-healing performance was studied at room temperature. Figure 2 As shown, from Figure 2 It can be seen that after being placed at room temperature for 24 hours, the cut fracture can repair itself.

[0044] SEM was used to characterize the fracture state before and after self-repair. The characterization results are as follows: Figure 3 As shown, the crack was obvious at first, and it almost completely disappeared after 24 hours, confirming that the elastomer can rebond and achieve self-repair at room temperature without any external stimulation. This is due to the movement of the broken polymer molecular chains, which promotes the reorganization and combination of the broken chemical bonds.

[0045] Example 2

[0046] The flexible circuit substrate was prepared according to the steps of Example 1, except that the content of AMWCNT in step S1 was adjusted to 0.7 g, and the other steps remained unchanged.

[0047] Example 3

[0048] The flexible circuit substrate was prepared according to the steps of Example 1, except that the content of DFB in step S2 was adjusted to 0.2 g, and the other steps remained unchanged.

[0049] Comparative Example 1

[0050] The flexible circuit substrate was prepared according to the steps of Example 1, except that the content of AMWCNT in step S1 was adjusted to 0, and the other steps remained unchanged.

[0051] Comparative Example 2

[0052] The flexible circuit substrate was prepared according to the steps of Example 1, except that the content of AMWCNT in step S1 was adjusted to 1.5 g, and the other steps remained unchanged.

[0053] Comparative Example 3

[0054] The flexible circuit substrate was prepared according to the steps of Example 1, except that the AMWCNT in step S1 was changed to MWCNT, and the other steps remained unchanged.

[0055] The self-healing efficiency test method of this experiment is as follows: the sample is made into a standard dumbbell-shaped spline, the spline is cut in half from the middle with a sharp blade, the sample cut surface is contacted at room temperature, and kept for 24 hours to conduct a self-healing experiment. Then the healed sample is subjected to a uniaxial tensile test. The mechanical healing efficiency η is calculated based on the ratio of the tensile strength of the healed sample to the tensile strength of the original sample. The test data of the tensile strength, elongation at break, and self-healing rate η of the materials obtained in this comparative example and embodiment are shown in Table 1.

[0056] Table 1

[0057] Test samples Tensile strength(kPa) Elongation at break (%) 24h mechanical healing efficiency η(%) Example 1 132.32 107.53 99.87 Example 2 206.53 98.13 87.97 Example 3 143.24 95.37 73.34 Comparative Example 1 57.22 77.83 99.99 Comparative Example 2 447.86 71.36 8.53 Comparative Example 3 302.38 158.94 58.98

[0058] It can be seen from the data of Example 1 and Comparative Example 1 that doping AMW CNT in the prepared self-healing elastomer substrate can effectively improve the tensile strength of the elastomer substrate, while the 24h self-healing efficiency will not be greatly affected. The AMWCNTs in the self-healing elastomer substrate are entangled with each other, which can effectively enhance the tensile strength of the elastomer. Within a certain range, the tensile strength of the elastomer increases with the increase of the doping amount of AMWCNT. It can be seen from the data of Example 1 and Comparative Example 2 that if too much AMWCNT is doped, it will hinder the movement of the elastomer molecular chain, thereby weakening its self-healing ability.

[0059] Compared with Example 3, if MWCNTs are doped in the prepared self-healing elastomer substrate, although the mechanical properties of the elastomer substrate can be improved, the self-healing performance will be significantly reduced. This is because compared with MWCNTs, AMWCNTs improve the interfacial interaction and enhance the compatibility with the polymer substrate. The amino groups in AMWCNTs react with the excess aldehyde groups in DFB to form imine bonds to assist the self-healing of the elastomer substrate. That is, adding AMWCNTs to the elastomer not only improves the mechanical strength, but also effectively reduces the significant decline in self-healing ability.

[0060] In Examples 1-3, DFB is used as a cross-linking agent to provide cross-linking sites for the reaction. Therefore, the concentration of DFB is crucial to the reaction rate and self-healing performance. Within a certain range, the self-healing efficiency of the elastomer substrate increases with the increase of DFB concentration, because high concentrations of DFB increase the possibility of reaction between aldehyde groups and amino groups, thereby increasing the possibility of Schiff base reaction. However, too high a concentration will reduce the number and length of cross-linked chains, thereby reducing the tensile strength of the material. At the same time, with the increase in the amount of AMWCNT added, more AMWCNTs in the elastomer are entangled with each other, thereby effectively enhancing the mechanical properties of the elastomer. However, too much AMWCNT will hinder the movement of the elastomer molecular chain, thereby weakening the self-healing ability of the elastomer. If the amount added is too much, the self-healing efficiency is too low, and it loses its significance as a self-healing elastomer substrate. Therefore, the amount of AMWCNT added and the amount of DFB added need to meet a specific range in order to achieve the prepared substrate having excellent mechanical properties and self-healing efficiency at the same time.

[0061] The copper metallization results on the surface of the elastomer substrate are as follows Figure 4 As shown in the figure, copper particles can be observed to be deposited on the surface of the elastomer substrate in a dense island shape. By connecting the copper circuit in series with the light-emitting diode and connecting it to a power source, the light-emitting diode can be successfully lit up. When the circuit is damaged and the light-emitting diode is extinguished, the damaged part is left at room temperature for 24 hours, and the self-healing ability of the substrate can make the circuit conductive again. This process is shown in the figure. Figure 5 shown.

[0062] In summary, the present invention dopes AMWCNT into the elastomer substrate to effectively balance the mechanical properties and self-healing efficiency, and enhances the compatibility with the polymer substrate by improving the interfacial interaction between the nano-reinforced material and the elastomer substrate. Compared with ordinary self-healing elastomers, it has better mechanical properties, can be used as a flexible substrate, has good durability and reliability, can extend its service life, and maintain stable performance in various complex environments.

[0063] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for preparing a flexible circuit substrate based on a room temperature self-healing elastomer, characterized in that: The following steps are involved: S1. Preparing a mixed solution of APDMS and AMWCNT: adding AMWCNT and APDMS to a first organic solvent, and then stirring at room temperature to make them uniformly dispersed; wherein AMWCNT accounts for 6wt%-9wt% of the mass of APDMS; S2. Preparing a crosslinker solution: adding the crosslinker to the second organic solvent and stirring at room temperature until completely dissolved, wherein the crosslinker accounts for 1.5wt%-3.0wt% of the mass of APDMS; S3. The crosslinking agent solution obtained in S2 is added to the mixed solution obtained in S1 to obtain a reaction solution, and then stirred at 25-70° C. for 1-6 hours; S4. After the reaction is completed, the mixture is dried at room temperature for 12-24 hours, then placed in a mold, and hot-pressed at 70-90°C and 10-20MPa for 20-30 minutes to obtain a self-healing elastomer of the desired shape; S5. Preparation of flexible circuit substrate by metallization of elastomer surface: Use insulating tape to cover the surface of the self-healing elastomer prepared in S4, leaving a copper-plated area, and then use chemical plating to prepare a circuit with the required pattern on the surface of the self-healing elastomer to obtain the required flexible circuit substrate.

2. The method for preparing a flexible circuit substrate according to claim 1, wherein: The nitrogen content of APDMS in S1 is 0.32-0.42%, and the viscosity is 800-5000 cPs; the outer diameter of AMWCNT is 8-15 nm, the inner diameter is 3-5 nm, the length is 10-50 μm, and the nitrogen content is less than 0.21%.

3. The method for preparing a flexible circuit substrate according to claim 1, wherein: The mass volume ratio of APDMS to the first organic solvent in S1 is 1 g:(0.5-1) mL.

4. The method for preparing a flexible circuit substrate according to claim 1, wherein: The mass ratio of APDMS to AMWC NT in S1 is preferably 1:0.

06.

5. The method for preparing a flexible circuit substrate according to claim 1, wherein: The crosslinking agent is terephthalaldehyde or trimesaldehyde.

6. The method for preparing a flexible circuit substrate according to claim 1, wherein: The mass volume ratio of DFB to the second organic solvent in S2 is 1 g:(40-60) mL.

7. The method for preparing a flexible circuit substrate according to claim 1, wherein: The mass ratio of APDMS to the cross-linking agent in S3 is preferably 1:0.

028.

8. The method for preparing a flexible circuit substrate according to claim 1, wherein: The first organic solvent and the second organic solvent are the same or different.

9. The method for preparing a flexible circuit substrate according to claim 1, wherein: The specific process of chemical plating in S5 is: ultrasonically clean and dry the self-healing elastomer covered with insulating tape, then perform plasma treatment, soak it in 3-aminopropyltriethoxysilane, rinse it after soaking, soak it in sensitizing solution, deionized water and activation solution for a period of time respectively, rinse it after soaking, perform chemical copper plating in chemical copper plating solution, and the desired flexible circuit substrate can be obtained after the chemical plating is completed.

10. The method for preparing a flexible circuit substrate according to claim 9, wherein: The sensitizing solution includes SnCl2·2H2O and HCl, and the activating solution includes PdCl2 and HCl.

Images