A method for manufacturing a high-solid-content curing-agent-free screen printing AgAgCI composite paste and a PDMS-based flexible reference electrode

Abstract

This invention discloses a high-solids-content, curing agent-free screen-printed Ag / AgCl composite slurry and a method for fabricating a PDMS-based flexible reference electrode, belonging to the field of flexible conductive materials technology. The slurry is composed of 18-36 parts modified silicone resin, 40-80 parts silver / silver chloride composite functional filler, 3-9 parts flexible interface toughening agent, 0.8-2.5 parts silane coupling agent, 12-22 parts high-boiling-point environmentally friendly compound solvent, 0.3-1.2 parts organosilicon leveling and defoaming agent, 0.2-0.8 parts hydrophilic modifying agent, and 0.2-0.7 parts electrochemical stabilizing agent. This invention is a single-component system, without adding a curing agent. Film formation relies on the self-crosslinking of the modified silicone resin and the gradient evaporation of the DBE / PMA compound high-boiling-point solvent, resulting in no screen clogging or skinning. The reference electrode exhibits a potential drift of ≤±0.6 mV after 72 h, shows no hydrolysis failure after 30 days of immersion in PBS buffer, and has a storage period of ≥90 days at room temperature. This invention can achieve full gradient resistance customization from 30% to 90%, and can be widely used in wearable ECG electrodes, electromyography sensors, sweat electrochemical detection devices and other fields.

Description

Technical Field

[0001] This invention belongs to the field of flexible conductive materials technology, specifically relating to a method for fabricating a high-solids-content, curing-free screen-printed AgAgCI composite paste and a PDMS-based flexible reference electrode. Background Technology

[0002] PDMS (polydimethylsiloxane) is a core substrate for flexible wearable bioelectronic devices and flexible electrochemical sensors due to its excellent elasticity, flexibility, biocompatibility, and chemical stability. Ag / AgCl electrodes are the most widely used reference electrodes in the field of biosensing because of their stable potential, good electrochemical reversibility, and good response performance. Screen printing technology has the advantages of high efficiency, low cost, and mass production capability, making it the preferred method for the industrial production of flexible electrodes.

[0003] Currently, there is a significant gap in the technology of dedicated Ag / AgCl reference electrode pastes for screen printing on PDMS substrates. Most existing Ag / AgCl pastes on the market have a fixed single filler content, which cannot cover the needs of all scenarios from high resistance to low resistance. Traditional pastes generally adopt a two-component curing system, which requires on-site mixing before use. After mixing, there is a limitation on the activation cycle, and the paste is prone to gel failure, which cannot meet the production requirements of long-term continuous screen printing operations. At the same time, conventional pastes mostly use low-boiling-point solvents, which evaporate too quickly and are prone to problems such as screen clogging, skinning, and pinholes in the film during screen printing, affecting the quality of electrode formation.

[0004] Furthermore, silver chloride powder has relatively weak chemical stability and is prone to hydrolysis in body fluids and buffer solutions, leading to electrode potential shifts and performance degradation. Conventional slurry resin systems have poor adhesion to PDMS, and the electrodes are highly susceptible to coating cracking and powder detachment during repeated stretching and bending. Based on the above industry situation, this invention independently developed a high-solids-content, curing agent-free Ag / AgCl composite slurry with silver / silver chloride content that can be flexibly adjusted within the range of 30% to 90% to adapt to PDMS substrates. This slurry specifically addresses the technical challenges of PDMS-based flexible reference electrodes in terms of material matching, multi-resistance gradient adaptation, printing processes, electrochemical stability, and mechanical properties. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a high-solids-content, curing-free screen-printable Ag / AgCl composite paste and a PDMS-based flexible reference electrode. This paste is specially designed for PDMS substrates, and the effective content of the silver / silver chloride composite filler can be customized across a full gradient from 30% to 90%. It does not require the use of a curing agent, has strong screen printing adaptability, and the prepared reference electrode has stable potential, strong hydrolysis resistance, and excellent flexibility. It can meet the requirements of long-term use and large-scale production of flexible biosensing devices with different electrical requirements of high resistance, medium resistance, and low resistance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a high-solids-content, curing-free Ag / AgCl composite paste for screen printing, prepared from the following raw materials in parts by weight: The composition includes 18-36 parts modified silicone resin, 40-80 parts silver / silver chloride composite functional filler, 3-9 parts flexible interface toughening agent, 0.8-2.5 parts silane coupling agent, 12-22 parts high-boiling-point environmentally friendly compound solvent, 0.3-1.2 parts organosilicon leveling and defoaming agent, 0.2-0.8 parts hydrophilic modifying agent, and 0.2-0.7 parts electrochemical stabilizing agent.

[0007] This invention employs a single-component, curing agent-free technology system, without adding any curing agent, crosslinking agent, or hardener throughout the entire process. Relying on the self-crosslinking properties of hydroxyl-terminated modified silicone resin, and combined with the slow evaporation of a high-boiling-point compound solvent gradient, a dense, highly elastic, and firmly bonded functional film layer is formed on the surface of the PDMS substrate.

[0008] Preferably, the modified silicone resin is a long-chain hydroxyl-terminated polydimethylsiloxane with a viscosity of 9000~13000 mPa·s and a Shore hardness of 20~32 HA. It can achieve self-crosslinking film formation without curing agent, and its molecular structure is highly homologous to the PDMS substrate, with excellent interfacial compatibility between the two, while also giving the film excellent tensile and resilience properties.

[0009] Preferably, the silver / silver chloride composite functional filler is made by compounding silver powder and silver chloride powder in a mass ratio of (3.5-6):(4-7).

[0010] Preferably, the flexible interface toughening agent is a polyether-modified siloxane; Preferably, the silane coupling agent is KH-550 or KH-560.

[0011] Preferably, the high-boiling-point environmentally friendly compound solvent is composed of DBE diester and propylene glycol methyl ether acetate (PMA) in a mass ratio of (4-6):(3-5). With a boiling point range of 145-225°C, it exhibits gradient evaporation characteristics, which optimizes the rheological state of the paste and avoids defects such as screen clogging and skinning during screen printing.

[0012] Preferably, the hydrophilic modifying agent is a nonionic polyether type agent.

[0013] Preferably, the electrochemical stabilizing agent is an organic heterocyclic corrosion inhibitor.

[0014] Functional additive system: The flexible interface toughening agent is a polyether-modified siloxane, which improves the mechanical properties of the film and prevents deformation cracking; the silane coupling agent is selected from KH-550 or KH-560, which strengthens the interfacial bonding force between the filler, resin and PDMS substrate; the hydrophilic modification agent is a non-ionic polyether type agent, which builds ion conduction channels in the dense film layer; the electrochemical stabilizing agent is an organic heterocyclic corrosion inhibitor, which inhibits the hydrolysis of silver chloride and the precipitation of silver ions; the organosilicon leveling and defoaming agent eliminates air bubbles in the slurry and optimizes the printing leveling effect.

[0015] This invention also provides a method for preparing the above-mentioned Ag / AgCl composite slurry, comprising the following steps: (1) Add the high-boiling-point environmentally friendly compound solvent into the stirring equipment and stir at room temperature in the dark for 8~15 min; (2) Add modified silicone resin and flexible interface toughening agent to the pretreated solvent, heat to 45~55℃, and stir at high speed of 1100~1400 r / min for 25~35 min to form a uniform and transparent resin solution. (3) Add the silver / silver chloride composite functional filler to the resin solution in 6 to 8 batches. After each batch, stir at high speed for 15 to 22 minutes and operate in the dark throughout the process. After all the filler has been added, add the silane coupling agent, hydrophilic modifier and electrochemical stabilizer in sequence, and disperse by gradient ultrasonication at 250 to 350 W for 45 to 60 minutes. (4) Add silicone leveling and defoaming agent, and stir at a low speed of 300~500 r / min for 8~15 min; (5) Cool the system to 25~30℃, stir at low speed for 12~18 min, keep it at a constant temperature and avoid light for 50~70 min, and then filter it with a 220~300 mesh filter to obtain the finished Ag / AgCl composite slurry.

[0016] This invention also provides a PDMS-based flexible reference electrode, characterized in that: the Ag / AgCl composite slurry described above is prepared on the surface of a PDMS substrate by screen printing, and then dried at 85~110℃ for 40~70 min to form a film. The cured film has a maximum tensile deformation ≥280%, and the film adhesion is grade 0; the reference electrode has a potential drift ≤±0.6 mV after 72 h of continuous testing, and no hydrolysis occurs after continuous immersion in PBS buffer for 30 days.

[0017] It contains at least the following beneficial technical effects: This invention provides a high-solids-content, curing-free screen-printed Ag / AgCl composite paste and a PDMS-based flexible reference electrode. By employing a design where the molecular structure of the hydroxyl-terminated modified silicone resin is homologous to that of the PDMS substrate, the film adhesion reaches grade 0 and the maximum tensile deformation is ≥280%, completely solving the technical problems of poor adhesion between traditional pastes and PDMS substrates, and easy cracking and detachment during deformation. It achieves a synergistic improvement in screen printing adaptability, electrochemical stability, mechanical flexibility, and storage stability, and can be widely used in wearable ECG electrodes, electromyography sensors, sweat electrochemical detection devices, and other fields, meeting the requirements for large-scale production and long-term use of flexible bioelectronic devices. Detailed Implementation

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0019] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0021] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0022] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0023] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.

[0024] Unless otherwise specified, all raw materials or instruments used in the following embodiments of the present invention are commercially available.

[0025] Example 1 The modified silicone resin is a long-chain hydroxyl-terminated polydimethylsiloxane with a viscosity of 10,000 mPa·s and a Shore hardness of 25HA.

[0026] Raw material weight parts: 26 parts modified silicone resin, 62 parts silver / silver chloride composite filler (28 parts silver powder, 34 parts silver chloride), 6 parts polyether modified siloxane, 1.6 parts KH-550 silane coupling agent, 17 parts high boiling point compound solvent (9.5 parts DBE, 7.5 parts PMA), 0.7 parts polyether modified polydimethylsiloxane, 0.5 parts Tween-80, 0.4 parts benzotriazole.

[0027] Preparation steps: (1) Take a portion of the high-boiling-point compound solvent and stir at room temperature in the dark for 12 min; (2) Add modified silicone resin and polyether modified siloxane, heat to 50°C, and stir at 1300 r / min for 30 min. (3) Add the silver / silver chloride composite filler to the adhesive solution in 7 batches, and stir for 18 min after each addition; add silane coupling agent, Tween-80 and benzotriazole in sequence, and disperse by ultrasonication at 300 W for 50 min. (4) Add polyether-modified polydimethylsiloxane and stir at low speed of 400 r / min for 10 min; (5) Cool the system to room temperature, stir at low speed for 15 min, and mature at a constant temperature in the dark for 60 min. Filter with a 250 mesh screen to obtain the finished slurry.

[0028] Example 2 The modified silicone resin is a long-chain hydroxyl-terminated polydimethylsiloxane with a viscosity of 9000 mPa·s and a Shore hardness of 20 HA. Raw material by weight: 19 parts modified silicone resin, 78 parts silver / silver chloride composite filler, 3.5 parts polyether modified siloxane, 0.9 parts KH-550 silane coupling agent, 13 parts high boiling point compound solvent, 0.4 parts polyether modified polydimethylsiloxane, 0.3 parts Tween-80, and 0.6 parts benzotriazole.

[0029] The preparation process is the same as in Example 1.

[0030] Example 3 The modified silicone resin is a long-chain hydroxyl-terminated polydimethylsiloxane with a viscosity of 13000 mPa·s and a Shore hardness of 32HA. Raw material weight parts: 34 parts modified silicone resin, 45 parts silver / silver chloride composite filler, 8 parts polyether modified siloxane, 2.2 parts KH-560 silane coupling agent, 21 parts high boiling point compound solvent, 1.1 parts polyether modified polydimethylsiloxane, 0.7 parts Tween-80, and 0.3 parts benzotriazole.

[0031] The preparation process is the same as in Example 1.

[0032] Comparative Example 1 Raw material by weight: 25 parts epoxy resin, 60 parts silver / silver chloride composite filler (27 parts silver powder, 33 parts silver chloride), 8 parts polyamide curing agent, 15 parts low-boiling-point solvent (butyl carbitol acetate), and 0.5 parts dispersant. Mix the epoxy resin and solvent thoroughly, add the filler and disperse at high speed for 60 min. Add the curing agent and mix thoroughly before use. Print the slurry onto the surface of a PDMS substrate through a 250-mesh screen and dry at 120℃ for 60 min to form a film.

[0033] Comparative Example 2 The modified silicone resin is a long-chain hydroxyl-terminated polydimethylsiloxane with a viscosity of 10,000 mPa·s and a Shore hardness of 25 HA. Raw material by weight: 26 parts modified silicone resin, 62 parts silver / silver chloride composite filler (28 parts silver powder, 34 parts silver chloride), 6 parts polyether modified siloxane, 1.6 parts KH-550 silane coupling agent, 17 parts low boiling point solvent (butyl acetate, boiling point 126℃), 0.7 parts polyether modified polydimethylsiloxane, 0.5 parts Tween-80, and 0.4 parts benzotriazole.

[0034] The preparation process is the same as in Example 1.

[0035] Comparative Example 3 Raw material weight parts: 26 parts polyurethane resin, 62 parts silver / silver chloride composite filler (28 parts silver powder, 34 parts silver chloride), 6 parts polyether modified siloxane, 1.6 parts KH-550 silane coupling agent, 17 parts high boiling point compound solvent (DBE / PMA), 0.7 parts polyether modified polydimethylsiloxane, 0.5 parts Tween-80, and 0.4 parts benzotriazole.

[0036] The preparation process is the same as in Example 1.

[0037] Table 1. Performance Comparison of Examples and Comparative Examples

[0038] (1) Compared with the conventional two-component curing system of Comparative Example 1, the storage period of the single-component system without curing agent of the present invention is greatly extended, and the process complexity and gel failure problem caused by on-site mixing are avoided; at the same time, the flexibility of the present invention is far superior to that of Comparative Example 1, proving that hydroxyl-terminated modified silicone resin is more suitable for flexible PDMS substrate than epoxy resin.

[0039] (2) Compared with the low-boiling-point solvent used in Comparative Example 2, the high-boiling-point compound solvent of the present invention has a gradient slow evaporation characteristic, which does not clog the screen, form skin, or have pinholes during printing, significantly improving the printing quality, while also having better potential stability.

[0040] (3) Compared with the conventional polyurethane resin that is not homologous to PDMS used in Comparative Example 3, the modified silicone resin of the present invention that is homologous to PDMS molecular structure significantly improves the film adhesion and deformation resistance, proving that homologous compatibility design makes a key contribution to the interfacial bonding strength.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-solids-content, curing-free Ag / AgCl composite paste for screen printing, characterized in that, It is prepared from the following raw materials in parts by weight: The composition includes 18-36 parts modified silicone resin, 40-80 parts silver / silver chloride composite functional filler, 3-9 parts flexible interface toughening agent, 0.8-2.5 parts silane coupling agent, 12-22 parts high-boiling-point environmentally friendly compound solvent, 0.3-1.2 parts organosilicon leveling and defoaming agent, 0.2-0.8 parts hydrophilic modifying agent, and 0.2-0.7 parts electrochemical stabilizing agent.

2. The Ag / AgCl composite slurry according to claim 1, characterized in that, The modified silicone resin is a long-chain hydroxyl-terminated polydimethylsiloxane with a viscosity of 9000~13000 mPa·s and a Shore hardness of 20~32 HA.

3. The Ag / AgCl composite slurry according to claim 1, characterized in that, The silver / silver chloride composite functional filler is made by compounding silver powder and silver chloride powder in a mass ratio of (3.5-6):(4-7).

4. The Ag / AgCl composite slurry according to claim 1, characterized in that, The flexible interface toughening agent is a polyether-modified siloxane.

5. The Ag / AgCl composite slurry according to claim 1, characterized in that, The silane coupling agent is selected from KH-550 or KH-560.

6. The Ag / AgCl composite slurry according to claim 1, characterized in that, The high-boiling-point environmentally friendly compound solvent is composed of DBE diester and propylene glycol methyl ether acetate PMA in a mass ratio of (4-6):(3-5).

7. The Ag / AgCl composite slurry according to claim 1, characterized in that, The hydrophilic modifying agent is a nonionic polyether type agent.

8. The Ag / AgCl composite slurry according to claim 1, characterized in that, The electrochemical stabilizing agent is an organic heterocyclic corrosion inhibitor.

9. The method for preparing the Ag / AgCl composite slurry according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Add the high-boiling-point environmentally friendly compound solvent into the stirring equipment and stir at room temperature in the dark for 8~15 min; (2) Add modified silicone resin and flexible interface toughening agent to the pretreated solvent, heat to 45~55℃, and stir at high speed of 1100~1400 r / min for 25~35 min to form a uniform and transparent resin solution. (3) Add the silver / silver chloride composite functional filler to the resin solution in 6 to 8 batches. After each batch, stir at high speed for 15 to 22 minutes and operate in the dark throughout the process. After all the filler has been added, add the silane coupling agent, hydrophilic modifier and electrochemical stabilizer in sequence, and disperse by gradient ultrasonication at 250 to 350 W for 45 to 60 minutes. (4) Add silicone leveling and defoaming agent, and stir at a low speed of 300~500 r / min for 8~15 min; (5) Cool the system to 25~30℃, stir at low speed for 12~18 min, keep it at a constant temperature and avoid light for 50~70 min, and then filter it with a 220~300 mesh filter to obtain the finished Ag / AgCl composite slurry.

10. A PDMS-based flexible reference electrode, characterized in that: The Ag / AgCl composite slurry according to any one of claims 1 to 9 is prepared on the surface of a PDMS substrate by screen printing and dried at 85 to 110°C for 40 to 70 minutes to form a film.

Images