A conductive paste, its preparation method and application

Abstract

This invention discloses a conductive paste, its preparation method, and its application, relating to the field of medical materials technology. The conductive paste comprises the following components in parts by weight: 0.5-6 parts of a composite thixotropic system; 45-85 parts of a solvent-water-retaining system; and 0.8-10 parts of a conductive electrolyte system. The composite thixotropic system includes 0.2-2 parts of cross-linked polyacrylic acid microgel, 0.2-3 parts of hydrophobically modified cellulose, and 0.05-1.5 parts of chitosan derivatives. The solvent-water-retaining system includes deionized water and polyols. The conductive electrolyte system includes organic electrolyte salts and inorganic salts. This invention yields a low-chloride conductive paste suitable for hair-covered scalp, which can be rapidly prepared, shear-thinned, and rapidly recovers upon standing. The conductive paste of this invention can be prepared within minutes and is ready to use immediately, overcoming the shortcomings of existing conductive pastes in terms of hair-scalp penetration and spread, long-term impedance stability, and complex preparation processes.

Description

Technical Field

[0001] This invention relates to the field of medical materials technology, and in particular to a conductive paste, its preparation method, and its application. Background Technology

[0002] Electroencephalography (EEG) and other bioelectrical signal acquisition typically employs silver / silver chloride (Ag / AgCl) cup or disc electrodes in contact with the scalp. To obtain stable, low-noise signals, a continuous ion-conducting interface needs to be formed between the electrode and the skin, and the electrode-skin contact impedance should be minimized. Conductive ointments are widely used in clinical and research settings as "wet electrode media." These media are usually aqueous systems, providing ionic conductivity through electrolyte salts, and are combined with thickeners, humectants, surfactants, inorganic thixotropic fillers, and preservatives to achieve spreadability, adhesion, and anti-drying properties. For example, Ten20 conductive ointment, commonly used in the EEG field, contains water, glycerin, 1,2-propanediol, sodium chloride, potassium chloride, and is formulated with montmorillonite and calcium carbonate to form the ointment.

[0003] However, in practical applications, scalp hair forms a "hair barrier," making it difficult for conductive paste to quickly reach the scalp and establish a continuous interface between the hair, resulting in increased contact resistance and decreased stability. Existing research has proposed solutions such as coatable / applyable biogels for long-term EEG records of hair and scalp, and compared them with commercial EEG conductive pastes in terms of electrode-scalp impedance, indicating that this problem is widespread.

[0004] To reduce interfacial impedance and improve adhesion stability, existing EEG conductive pastes mainly follow two technical routes: 1. Commercially available EEG conductive paste For example, the formulation framework of Ten20 (WEAVER and COMPANY) includes water, glycerin, 1,2-propanediol, sodium chloride, potassium chloride, and structural components such as montmorillonite (e.g., Gelwhite) and calcium carbonate. Its instructions for use typically recommend a light skin scrub pretreatment and, if necessary, use gauze or tape to secure the electrodes to ensure adhesion and conductivity. Another example is AC Cream, a conductive paste disclosed by the FDA 510(k), which is a water-based, salt-containing conductive medium. It discloses technical similarities to control products in aspects such as "using salt as a conductive material and thickeners / moisturizers to form the paste," and provides impedance data at 10 Hz and over time. Furthermore, EEG / EMG (electromyography) conductive pastes such as Elefix V Paste (Nihon Kohden) also use an aqueous system with sodium chloride as the main conductive material, and are compounded with emulsifiers, moisturizers, and preservatives.

[0005] 2. Conductive paste in the published patent For example, the conductive paste embodiment in CN113663091A includes components such as potassium chloride / sodium chloride, glycerin, 1,2-propanediol, sodium carboxymethyl cellulose, and chitosan, and employs hour-level stirring to achieve thickener swelling and uniform dispersion of additives. CN103550795A discloses a scheme using natural polymers such as sodium carboxymethyl cellulose, hydroxyethyl cellulose, and xanthan gum as thickening systems, potassium chloride / sodium chloride as conductive components, and lubricating and moisturizing agents to form a conductive paste. CN108904819A points out in the background art that the use of high inorganic salt content in ordinary conductive pastes may cause skin irritation and electrode corrosion problems. At the same time, polymer thickeners are not easy to disperse, often requiring increased stirring intensity, extended stirring time, or heating. Its solution improves dispersion and skin compatibility by first dispersing modified cellulose in polyol and controlling the inorganic salt content, but still provides process conditions of stirring at room temperature for 1-3 hours.

[0006] In general, the aforementioned existing technologies are improved mainly in the following directions: 1. Using inorganic salts such as NaCl / KCl as the main source of conductivity, compounded with polyols and thickening / thixotropic components, a pre-made conductive paste is formed. 2. Adhesion, anti-drying properties, or cleanability can be improved by using polymer thickening systems such as cellulose / natural gums and additives, but the preparation often depends on a long dispersion and swelling time.

[0007] Although existing patents have proposed various formulations and processes for conductive pastes, there are still three main shortcomings in meeting the needs for long-term stable EEG monitoring and rapid deployment on hair-covered scalps: (1) The salt system as the main component brings a trade-off between skin tolerance and electrode corrosion, making it difficult to balance low impedance and mildness: Commercial EEG conductive pastes generally use inorganic salts such as NaCl / KCl as the conductivity source (Ten20, AC Cream, Elefix V, etc. all belong to this technical route). Meanwhile, CN108904819A explicitly points out in its background technology that the use of high inorganic salt content in ordinary conductive pastes can lead to skin irritation and corrosion of the electrode metal parts, and identifies this as a defect in existing technology that needs improvement. Therefore, traditional "chloride salt-based" conductive pastes often require trade-offs between conductivity, skin tolerance, and material compatibility, and there is still room for optimization in scenarios involving long-term wear or sensitive individuals.

[0008] (2) Lack of "ready-to-use" rapid configuration capability: Currently, most published patents rely on complex dispersion / swelling processes that take hours to complete, making it difficult to meet the needs of rapid on-site deployment and individualized formulation. In these patents, to ensure sufficient swelling of the thickener, uniform dispersion of the additives, and to prevent sedimentation, prolonged stirring is often employed: Example CN113663091A shows multiple stages of stirring, including 2h, 6h, 8h, and a subsequent 1-2h dispersion; CN108904819A also provides process conditions of 1-3h stirring at room temperature, noting in the background that polymeric thickeners are difficult to disperse in water, often requiring extended stirring time / increased stirring intensity or special processes such as heating. This type of process is not conducive to achieving the rapid formulation goal of "forming a usable paste in about 1 minute after weighing and mixing, and immediately applying it to the scalp," nor is it conducive to individualized on-site adjustments based on different hair densities, perspiration levels, and environmental humidity.

[0009] (3) The low impedance and long-term stability need to be further improved: In long-term (especially ≥24h) EEG monitoring, traditional wet electrode conductive pastes, including Ten20 and Elefix V, as aqueous ionic conductive media, typically dry out over time, accompanied by changes in the hair-scalp interface (such as being squeezed out, diffused / carried away along the hair, or partially detached). This leads to a gradual increase or fluctuation in electrode-skin (scalp) contact impedance, increasing the risk of electrode loosening, slippage, or even detachment. These problems are amplified under dynamic activity or sweating conditions. Literature also indicates that for recordings requiring ≥24h, the likelihood of signal quality or contact impedance quality deterioration increases after the conductive paste dries. Furthermore, in extended dynamic EEG monitoring, electrode-related problems often arise when using conductive paste to fix electrodes, and in some scenarios, additional fixation or stronger adhesion methods are required to ensure long-term stability. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a conductive paste, its preparation method, and its application. This invention constructs a low-chloride conductive paste suitable for hair-covered scalps, capable of rapid preparation, shear thinning, and rapid recovery upon standing. The conductive paste can be prepared within minutes and is ready to use immediately, thus addressing the shortcomings of existing conductive pastes in terms of hair-scalp penetration and spread, long-term impedance stability, and complex preparation processes.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a conductive paste, which, based on 100 parts by weight, comprises the following components in parts by weight: Composite thixotropic system: 0.5-6.0 parts; solvent-based water-retaining system: 45-85 parts; conductive electrolyte system: 0.8-10 parts; additives: 0-10 parts; The composite thixotropic system comprises 0.2 to 2.0 parts of cross-linked polyacrylic acid microgel, 0.2 to 3.0 parts of hydrophobically modified cellulose, and 0.05 to 1.5 parts of chitosan derivative; The solvent-based water-retaining system includes deionized water and polyols; The conductive electrolyte system includes organic electrolyte salts and inorganic salts.

[0012] In this invention, the composite thixotropic system is used to achieve the key rheological properties of "high shear easy flow and hair penetration, and rapid recovery and stable adhesion after static placement"; the solvent water-retaining system is used to provide the ion conduction medium and anti-water loss capability for the wet electrode; and the conductive electrolyte system is used to provide a stable ion conduction pathway.

[0013] Preferably, the cross-linked polyacrylic acid microgel includes at least one of carbomer and polycarbophil.

[0014] Preferably, the hydrophobically modified cellulose includes at least one of hydrophobically modified hydroxyethyl cellulose (HMHEC) and hydrophobically modified ethyl hydroxyethyl cellulose (HMEHEC).

[0015] Preferably, the chitosan derivative includes at least one of carboxymethyl chitosan, carboxychitosan, and their derivatives, used to improve wetting, structural recovery, and interfacial stability. Carboxymethyl chitosan / carboxychitosan has better water solubility and wettability, can be uniformly dispersed under short-time mixing, and provides more stable hydrogen bonding / electrostatic interactions at the hair-scalp interface, helping to reduce microslip and impedance drift.

[0016] In the composite thixotropic system, the amount of the cross-linked polyacrylic acid microgel is 0.2 to 2.0 parts, for example, it can be 0.2 parts, 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.6 parts, 1.8 parts, 2.0 parts, or any two of these values.

[0017] The amount of the hydrophobically modified cellulose is 0.2 to 3.0 parts, for example, it can be 0.2 parts, 0.5 parts, 0.8 parts, 1 part, 1.2 parts, 1.6 parts, 1.8 parts, 2 parts, 2.5 parts, 3.0 parts, or any two of these values.

[0018] The amount of the chitosan derivative is 0.05 to 1.5 parts, for example, it can be 0.05 parts, 0.1 parts, 0.2 parts, 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts or any two of these values.

[0019] Preferably, the polyol includes at least one of glycerol and propylene glycol. The amount of glycerol used is preferably 8-25 parts, and the amount of propylene glycol used is preferably 2-15 parts.

[0020] Preferably, the polyol further includes sorbitol and polyethylene glycol to further improve the resistance to drying and the coating properties.

[0021] Preferably, the molecular weight of the polyethylene glycol is 200-1000.

[0022] Preferably, the amount of deionized water used in the solvent water-retaining system is 20 to 55 parts, for example, it can be 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts or any two of these values.

[0023] Preferably, the amount of polyol used in the solvent water-retaining system is 10 to 40 parts, for example, it can be 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts or any two of these values.

[0024] Preferably, the solvent-water-retaining system further includes 0-3 parts of a wetting and dispersing agent to improve the spreadability and coating properties of hair and scalp.

[0025] Preferably, the wetting and dispersing agent includes at least one of Turkish red oil (sulfated castor oil) and polyethylene glycol hydrogenated castor oil. The amount of Turkish red oil used is preferably 0.05 to 1.0 parts, and the amount of polyethylene glycol hydrogenated castor oil used is preferably 0.05 to 1.0 parts.

[0026] Preferably, the amount of organic electrolyte salt in the conductive electrolyte system is 0.8 to 8 parts, for example, it can be 0.8 parts, 1.0 parts, 2.0 parts, 3.0 parts, 4.0 parts, 5.0 parts, 6.0 parts, 7.0 parts, 8.0 parts, or any two of these values.

[0027] Preferably, the amount of inorganic salt in the conductive electrolyte system is 0.05 to 1.5 parts, for example, it can be 0.05 parts, 0.1 parts, 0.2 parts, 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, or any two of these values.

[0028] Preferably, the organic electrolyte salt includes at least one of lactate, citrate, and acetate.

[0029] More preferably, the organic electrolyte salt includes at least one of sodium lactate, potassium lactate, sodium citrate, potassium citrate, sodium acetate, and potassium acetate.

[0030] Preferably, the inorganic salt includes at least one of NaCl and KCl, wherein the amount of NaCl is preferably 0.05 to 1.0 parts, and the amount of KCl is preferably 0 to 0.8 parts.

[0031] Preferably, the mass ratio of the organic electrolyte salt to the inorganic salt is (2~30):1, for example, it can be 2:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1 or any two of these values.

[0032] This invention, by controlling the mass ratio of organic electrolyte salts to inorganic salts, can ensure conductivity while reducing the irritation and compatibility pressure caused by the high proportion of chloride salts.

[0033] Preferably, the adjuvant comprises 0 to 5 parts of an adhesion-enhancing component, used to improve interfacial adhesion and anti-slip ability in sweat / sebum and hair / scalp environments. For example, it can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, or any two of these values.

[0034] Preferably, the adhesion-enhancing component includes 0.02 to 1.0 parts of a polyphenol / catechin adhesion component, preferably tannic acid, gallic acid and its derivatives, catechin functionalized polymers or their salts (such as catechinized chitosan derivatives or dopamine-modified PEG).

[0035] Preferably, the adhesion-enhancing component further includes 0.05 to 2.0 parts of a polyhydroxy or polyphosphate complex, preferably phytic acid or its salt.

[0036] Preferably, the adjuvant includes 0-2 parts of an antiseptic and antibacterial system for storage stability, such as a phenoxyethanol system or a similar acceptable preservative.

[0037] Secondly, the present invention also provides a method for preparing conductive paste, comprising the following steps: Mix the components for 30-90 seconds, then let stand for 10-120 seconds to obtain conductive paste.

[0038] The preparation process described in this invention does not require swelling and curing, and can achieve the formation of conductive paste in minutes - ready to use.

[0039] The conductive paste described in this invention possesses the following rheological properties at 25°C: (1) Low shear apparent viscosity η(1 s) -1 ): 20~200 Pa·s; (2) High shear apparent viscosity η(100 s) -1 0.2~5 Pa·s; (3) Shear thinning factor η(1) / η(100): ≥30; (4) The structural recovery rate is ≥70% within 30~60 s after shearing stops.

[0040] Thirdly, the present invention also provides an application of conductive paste in electroencephalogram (EEG) monitoring.

[0041] Specifically, the conductive paste is applied to the hair-covered scalp area using methods such as scraping, brushing, syringe extrusion, or targeted application. During application, the conductive paste is in a shear-thinning window: its viscosity decreases significantly under external shear force, allowing it to penetrate the hair gaps and wet the scalp surface, while simultaneously filling micro-folds and local depressions in the skin to form a continuous ionic conductive interface. After application is complete and shearing ceases, the conductive paste enters a restorative window: its structure rapidly recovers and generates a certain yield strength and adhesion, thereby inhibiting the paste from flowing and spreading along the hair surface and reducing the risk of relative slippage at the electrode-scalp interface. Subsequently, Ag / AgCl cup-shaped or disc-shaped electrodes are pressed onto the coated area to form a stable electrode-conductive paste-scalp sandwich interface structure.

[0042] When the conductive paste is applied to the scalp covered with hair, it can penetrate the gaps between hairs during the application process by shear thinning / shear fluidity and quickly fix after standing, thereby forming a stable electrode-conductive paste-skin conductive interface with the Ag / AgCl electrode or gold electrode; the electrode-scalp contact impedance is ≤10 kΩ at 10 Hz, and the increase in contact impedance is ≤30% after 24 hours of continuous wear in daily wear mode, thereby realizing continuous monitoring of EEG signals and maintaining signal stability during daily wear.

[0043] The conductive paste and its preparation method described in this invention have the following advantages: 1. It combines shear thinning and rapid structural recovery properties, significantly improving the spreadability and adhesion stability of hair covering the scalp: This invention constructs a composite thixotropic system consisting of cross-linked polyacrylic acid microgel, hydrophobically modified cellulose, and chitosan derivatives, which significantly enhances the fluidity of the conductive cream under high shear conditions, enabling it to quickly penetrate the hair follicles and wet the scalp (spreading area / scalp reach time: 1 cm). 2 ( / 5 s); after shearing stops, the structure recovers to more than 70% of its initial strength within 30~60 s, forming a stable yield strength and adhesion. This design achieves controllable rheological behavior of "easy flow under shearing and stable shape upon resting", thus taking into account hair penetration, interfacial continuity and long-term stable adhesion performance.

[0044] 2. The low chloride content and synergistic system with organic electrolytes ensures conductivity while significantly reducing irritation and impedance drift: This invention employs organic electrolyte salts, primarily lactate, citrate, or acetate, supplemented with a small amount of inorganic salts (NaCl / KCl), to construct a low-chloride mixed electrolyte system. This system balances ion mobility and buffering capacity, maintaining the low-impedance conductive pathway required for EEG monitoring while effectively inhibiting chloride ion corrosion of the skin and Ag / AgCl electrodes. Compared to existing high-chloride systems, this invention significantly improves skin compatibility and electrode interface stability, offering advantages such as low irritation, low corrosion, and low drift.

[0045] 3. Minute-level preparation process, enabling rapid preparation, immediate use, and high repeatability: To address the problems of long swelling and curing times, cumbersome on-site mixing processes, and poor batch consistency in traditional conductive pastes, this invention employs a minute-level preparation process of "one-time weighing and direct mixing": At the point of use, all components are weighed according to the formula ratio and added to a mixing container. Under room temperature conditions, the mixture is rapidly mixed for 30-90 seconds using a handheld or planetary stirrer to obtain a homogeneous, directly applicable conductive paste. This process eliminates the need for pre-packaging, prolonged swelling or curing, and vacuum degassing, achieving the convenient "minute-level preparation - immediate use" operation. By rapidly establishing and achieving a stable thixotropic state in the key thickening network and electrolyte system within a short time, this invention significantly improves the timeliness and portability of conductive paste preparation, while reducing operational errors and improving batch consistency and repeatability, thus facilitating rapid deployment and large-scale application in clinical settings.

[0046] 4. Stable structure, low impedance, and stable signal, suitable for long-term and dynamic EEG monitoring: The conductive paste described in this invention forms a semi-solid structure with yield stress after static recovery, allowing it to adhere stably to hair and sebum environments, preventing flow and electrode slippage. Its thixotropic viscoelastic network absorbs micro-motion energy during dynamic motion, exhibiting mechanical low-pass filtering characteristics and effectively suppressing step frequency and harmonic artifacts. Tests show that at 10 Hz, the initial impedance is ≤10 kΩ, and after 24 hours of continuous monitoring, the impedance increase is less than 30%, with a signal-to-noise ratio significantly better than the control conductive paste, demonstrating excellent long-term stability and anti-motion artifact performance.

[0047] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention can reduce the risks of skin tolerance and electrode compatibility caused by chloride inorganic salts while ensuring the ionic conductivity required for EEG acquisition. It enables the conductive medium to balance low interfacial impedance and long-term wear gentleness, thereby solving the compatibility problem between the electrolyte system and the skin / electrode.

[0048] (2) The present invention can achieve rapid penetration and gap filling of conductive medium on hair-covered scalp, and quickly restore structural strength and adhesion stability after application is stopped, so as to suppress diffusion, micro-slippage and the resulting impedance fluctuations and motion artifacts, thereby obtaining a repeatable and consistent interface, thus solving the problem of interface establishment and anti-micro-motion on hair-covered scalp.

[0049] (3) The present invention can avoid the burden of complex dispersion / swelling / curing processes that are common in the currently disclosed solutions, realize the on-the-spot preparation of conductive media in clinical / research sites (e.g., minute-level ointment preparation), and support rapid and controllable individualized preparation for different hair density, degree of sweating, wearing time and other conditions, thereby solving the problems of rapid deployment and individualized preparation on site.

[0050] (4) The present invention can maintain a low and stable contact impedance at the electrode-scalp interface under long-term wear (especially ≥24h) and under conditions of sweat / sebum and dynamic disturbance, and reduce the risk of impedance increase caused by the loss of water and drying of conductive medium over time, performance degradation, and failure such as electrode loosening and slippage, thereby solving the current problem of low impedance and long-term stability for ≥24h. Detailed Implementation

[0051] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the scope of protection and implementation of the present invention are not limited thereto.

[0052] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0053] Example 1 This embodiment discloses a conductive paste, which, based on 100 parts by weight, comprises the following components in parts by weight: 5.5 parts of composite thixotropic system; 85 parts of solvent-based water-retaining system; 9.5 parts of conductive electrolyte system; The composite thixotropic system comprises 1.5 parts of cross-linked polyacrylic acid microgel (Carbomer 940), 2.5 parts of hydrophobically modified cellulose (HMHEC), and 1.5 parts of chitosan derivative (carboxymethyl chitosan). The solvent-based water-retaining system comprises 55 parts deionized water and 30 parts glycerin; The conductive electrolyte system comprises 8 parts of an organic electrolyte salt (sodium lactate) and 1.5 parts of an inorganic salt (NaCl).

[0054] This embodiment also discloses a method for preparing conductive paste, including the following steps: Weigh each component according to the formula and add it to the mixing container. Stir mechanically at room temperature for 60 seconds, then let stand for 30 seconds to obtain conductive paste.

[0055] Example 2 This embodiment discloses a conductive paste, which, based on 100 parts by weight, comprises the following components in parts by weight: Six parts of the composite thixotropic system; 84.5 parts of the solvent-water-retaining system; and 9.5 parts of the conductive electrolyte system. The composite thixotropic system comprises 2.0 parts of cross-linked polyacrylic acid microgel (Carbomer 940), 3.0 parts of hydrophobically modified cellulose (HMHEC), and 1.0 parts of chitosan derivative (carboxymethyl chitosan). The solvent-based water-retaining system comprises 55 parts deionized water and 29.5 parts glycerin; The conductive electrolyte system comprises 8 parts of an organic electrolyte salt (sodium lactate) and 1.5 parts of an inorganic salt (NaCl).

[0056] The preparation method of a conductive paste is the same as that in Example 1.

[0057] Example 3 This embodiment discloses a conductive paste, which, based on 100 parts by weight, comprises the following components in parts by weight: Six parts of the composite thixotropic system; 84.5 parts of the solvent-water-retaining system; and 9.5 parts of the conductive electrolyte system. The composite thixotropic system comprises 1.5 parts of cross-linked polyacrylic acid microgel (0.2 parts of Carbomer 940, 1.3 parts of Polycarbophil), 3.0 parts of hydrophobically modified cellulose (HMHEC), and 1.5 parts of chitosan derivative (carboxymethyl chitosan). The solvent-based water-retaining system comprises 55 parts deionized water and 29.5 parts glycerin; The conductive electrolyte system comprises 8 parts of an organic electrolyte salt (sodium lactate) and 1.5 parts of an inorganic salt (NaCl).

[0058] The preparation method of a conductive paste is the same as that in Example 1.

[0059] Example 4 The difference from Example 1 is that the mass ratio of organic electrolyte salt to inorganic salt in the conductive electrolyte system is 2:1.

[0060] Example 5 The difference from Example 1 is that the mass ratio of organic electrolyte salt to inorganic salt in the conductive electrolyte system is 30:1.

[0061] Example 6 The difference from Example 1 is that the conductive paste further includes 5 parts of an adhesion-enhancing component (tannic acid), wherein the amount of deionized water is 50 parts.

[0062] Comparative Example 1 The difference from Example 1 is that an equal mass of NaCl is used instead of sodium lactate in the conductive electrolyte system.

[0063] Comparative Example 2 The difference from Example 1 is that an equal mass of hydroxyethyl cellulose (HEC) (unmodified) is used instead of HMHEC in the conductive electrolyte system.

[0064] Comparative Example 3 The difference from Example 1 is that the composite thixotropic system uses an equal mass of deionized water instead of cross-linked polyacrylic acid microgels, that is, no cross-linked polyacrylic acid microgels are added.

[0065] Comparative Example 4 The difference from Example 1 is that, in the composite thixotropic system, an equal mass of chitosan (unmodified) is used instead of carboxymethyl chitosan.

[0066] Comparative Example 5 The difference from Example 1 is that a commercially available conductive paste (Ten20) is used.

[0067] Comparative Example 6 The difference from Example 1 is that the composite thixotropic system uses an equal mass of uncrosslinked polyacrylic acid instead of crosslinked polyacrylic acid microgels.

[0068] Comparative Example 7 The difference from Example 1 is that the amount of cross-linked polyacrylic acid microgel in the composite thixotropic system is 0.1 parts, the amount of HMHEC is 3.5 parts, and the amount of carboxymethyl chitosan is 1.9 parts.

[0069] Comparative Example 8 The difference from Example 1 is that the amount of cross-linked polyacrylic acid microgel in the composite thixotropic system is 3.5 parts, the amount of HMHEC is 0.5 parts, and the amount of carboxymethyl chitosan is 1.5 parts.

[0070] Performance testing The conductive pastes prepared in the above examples and comparative examples were subjected to the following performance tests.

[0071] 1. Contact resistance A three-electrode configuration was used, and the contact impedance on hair-covered scalp was measured using an electrochemical workstation. The electrode containing the conductive paste under test was used as the working electrode, and the conductive paste applied to the left and right ears served as the reference and counter electrodes. The impedance values ​​were read at 10 Hz. The contact impedance was tested again using the same method after 24 h.

[0072] 2. Shear thinning factor and recovery rate The shear thinning factor and recovery rate were obtained using a rheometer (Discovery HR-1 hybrid rheometer, TA Instruments, USA). Details are as follows: A flat plate (25 mm in diameter) was used. After loading the sample at a constant temperature of 25 °C, it was allowed to stand for 5 min to eliminate sample disturbance. Subsequently, the thixotropic reaction was measured according to a three-stage thixotropic procedure: Stage I was performed at a low shear rate of 1 s. -1 Maintain for 60 s and record the steady-state apparent viscosity η0; Stage II at a high shear rate of 100 s -1 Maintain for 60 s; in Phase III, immediately switch back to a low shear rate for 1 s. -1 The recovery process was recorded, and the apparent viscosity η(t) was read at a specified time point t (60 s). The shear thinning factor was calculated based on the steady-state two-point viscosity ratio: at 1 s... -1 With 100 s -1 Under constant shear for 60 s, the average apparent viscosity η(1 s) of each was taken in the last 10 s. -1 ) and η(100 s -1 ),calculate The recovery rate is calculated based on the viscosity recovery ratio during the low-shear recovery phase. .

[0073] 3. Adhesion performance Adhesion performance was tested using a 90° peel method. A tensile testing machine (ESM303 electric tensile / compression test stand, Mark-10 Corporation, USA) was used at a constant peel rate (20 mm / min) to record the force-displacement curves. The steady-state peel force F was recorded and calculated based on the sample width. Normalized calculation of interfacial toughness (peeling energy) .

[0074] 4. Signal-to-noise ratio This test only collected EEG signals during the initial wearing and after 24 hours of continuous wearing in a resting state. The power spectral density (PSD) was calculated using the Welch method, and the signal-to-noise ratio was calculated using the band-limited power ratio to evaluate the long-term signal stability of the conductive paste.

[0075] (1) Data collection time point Initially: Resting EEG was collected after the electrodes were stably attached; 24 h: After wearing the device continuously for 24 hours, EEG was collected again under the same resting conditions.

[0076] (2) Power spectrum calculation The PSD of the EEG signal was estimated using the Welch method to obtain the power distribution at different frequencies.

[0077] (3) SNR calculation Using 1.5-30 Hz as the total power of the EEG frequency band Using 25-30 Hz as the noise power (Used to characterize high-frequency interference / EMG noise, etc.), effective signal power is And calculate using the following formula: ; The initial and 24-hour SNR values ​​were obtained to compare the signal stability before and after long-term wear.

[0078] The test results are shown in Table 1.

[0079] Table 1 Note: N / A in Table 1 indicates that impedance and EEG signals could not be tested 24 hours after electrode detachment.

[0080] As can be seen from Examples 1-6, the present invention can keep the contact impedance of the electrode-scalp interface low and stable under long-term wear, and reduce the risk of impedance increase caused by the loss of water and drying of conductive medium over time, performance degradation, and failure such as electrode loosening and slippage, thereby solving the problems of low impedance and long-term wear stability.

[0081] Comparing Comparative Example 1 with Example 1, it can be seen that the conductive electrolyte system in Comparative Example 1 only added NaCl, with a higher proportion of inorganic salts and a lower initial contact impedance. However, it is easy to cause electrode polarization and increase interface noise, resulting in a significant decrease in signal quality after 24 hours, which leads to a decrease in long-term wearing stability.

[0082] Comparing Comparative Example 2 with Example 1, it can be seen that in Comparative Example 2, an equal mass of hydroxyethyl cellulose was used to replace the hydrophobically modified ethyl hydroxyethyl cellulose, meaning that the cellulose was not hydrophobically modified and could not synergize with cross-linked polyacrylic acid microgels and chitosan derivatives, resulting in increased impedance and decreased long-term wearing stability.

[0083] Comparing Comparative Example 3 with Example 1, it can be seen that Comparative Example 3 did not contain cross-linked polyacrylic acid microgels, and therefore could not be compounded with hydrophobically modified cellulose and chitosan derivatives, resulting in increased impedance and decreased long-term wear stability.

[0084] Comparing Comparative Example 4 with Example 1, it can be seen that in Comparative Example 4, chitosan of equal mass was used to replace carboxymethyl chitosan, that is, the chitosan was not modified and could not produce a synergistic effect with cross-linked polyacrylic acid microgels and hydrophobically modified cellulose, resulting in increased impedance and decreased long-term wearing stability.

[0085] Comparing Comparative Example 5 with Example 1, it can be seen that the commercially available Ten20 is a pre-made product, and it is impossible to achieve minute-level preparation of "one weighing-direct mixing for 30~90 seconds" on site. Long-term wear can easily dry out, leading to increased impedance and decreased stability.

[0086] Comparing Comparative Example 6 with Example 1, it can be seen that in Comparative Example 6, the use of uncrosslinked gel instead of crosslinked polyacrylic acid microgel resulted in increased impedance and decreased long-term wear stability. This indicates that uncrosslinked polyacrylic acid cannot replace crosslinked polyacrylic acid microgel, and the two are difficult to achieve the synergistic thixotropic effect described in this invention when combined with hydrophobically modified cellulose and chitosan derivatives.

[0087] Comparing Comparative Examples 7-8 with Example 1, it can be seen that by simultaneously controlling the amounts of cross-linked polyacrylic acid microgels, hydrophobically modified cellulose, and chitosan derivatives within the range defined by this invention, the present invention is beneficial to reducing contact resistance and improving long-term wearing stability.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A conductive paste, characterized in that, The conductive paste comprises the following components in parts by weight per 100 parts: Composite thixotropic system: 0.5-6.0 parts; solvent-based water-retaining system: 45-85 parts; conductive electrolyte system: 0.8-10 parts; additives: 0-10 parts; The composite thixotropic system comprises 0.2 to 2.0 parts of cross-linked polyacrylic acid microgel, 0.2 to 3.0 parts of hydrophobically modified cellulose, and 0.05 to 1.5 parts of chitosan derivative; The solvent-based water-retaining system includes deionized water and polyols; The conductive electrolyte system includes organic electrolyte salts and inorganic salts.

2. The conductive paste as described in claim 1, characterized in that, The cross-linked polyacrylic acid microgel includes at least one of carbomer and polycarbofil; And / or, the hydrophobically modified cellulose includes at least one of hydrophobically modified hydroxyethyl cellulose and hydrophobically modified ethyl hydroxyethyl cellulose; And / or, the chitosan derivative includes at least one of carboxymethyl chitosan, carboxychitosan and its derivatives.

3. The conductive paste as described in claim 1, characterized in that, The organic electrolyte salt includes at least one of lactate, citrate, and acetate; And / or, the inorganic salt includes at least one of NaCl and KCl.

4. The conductive paste as described in claim 1, characterized in that, The polyol includes at least one of glycerol, propylene glycol, sorbitol, and polyethylene glycol.

5. The conductive paste as described in claim 1, characterized in that, The amount of deionized water in the solvent-based water-retaining system is 20-55 parts, and the amount of polyol is 10-40 parts.

6. The conductive paste as described in claim 1, characterized in that, The amount of organic electrolyte salt in the conductive electrolyte system is 0.8 to 8.0 parts, and the amount of inorganic salt is 0.05 to 1.5 parts.

7. The conductive paste as described in claim 6, characterized in that, The mass ratio of the organic electrolyte salt to the inorganic salt is (2~30):

1.

8. The conductive paste as described in claim 1, characterized in that, The additives include 0-5 parts of an adhesion-enhancing component and 0-2 parts of an antiseptic and antibacterial system.

9. A method for preparing a conductive paste as described in any one of claims 1-8, characterized in that, Includes the following steps: Mix the components for 30-90 seconds, then let stand for 10-120 seconds to obtain conductive paste.

10. The application of the conductive paste as described in any one of claims 1-8 in electroencephalogram (EEG) monitoring.

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