Conductive liquid as well as preparation method and application thereof

Abstract

The embodiment of the invention provides conductive liquid as well as a preparation method and application thereof. The conductive liquid comprises carbon nanotubes, a combined dispersant, matrix resin, nitrile rubber and water, wherein the combined dispersing agent comprises polyvinylpyrrolidone and polyethylene glycol; the matrix resin comprises polyurethane resin and polyurethane epoxy resin. According to the conductive liquid as well as the preparation method and the application thereof provided by the embodiment of the invention, the problems of non-uniform dispersion, poor mechanical property and pollution of a traditional conductive liquid are systematically solved through the advantages of efficient dispersion of CNTs, rigid-flexible synergy of a resin matrix and environmental protection of a water-based system. Through adsorption-steric hindrance dispersion, interpenetrating network construction, interface optimization and other mechanisms, the unification of conductivity, durability and environmental friendliness is realized, and the composite material is suitable for the field of high-precision electronic packaging.

Description

Technical Field

[0001] This application belongs to the technical field of conductive liquids, and particularly relates to a conductive liquid, a preparation method thereof, and an application thereof. Background Art

[0002] A carrier tape is a strip-shaped carrier used for the encapsulation, transportation, and automated mounting of electronic components (such as chips, resistors, capacitors, etc.), and is widely used in the electronics manufacturing industry (such as SMT surface mount technology). Its core function is to protect precision electronic components from physical damage, electrostatic damage, and environmental pollution during transportation, storage, and mounting. The conductive film layer is a conductive coating covering the surface or specific areas of the carrier tape for electrostatic protection.

[0003] Currently, the materials used to prepare the conductive film layer may use a single resin, resulting in insufficient mechanical properties of the finally formed conductive film layer, such as high brittleness, poor flexibility, easy cracking or peeling, especially in the application of cover tapes / carrier tapes that require bending. Summary of the Invention

[0004] In view of this, embodiments of this application provide a conductive liquid, a preparation method thereof, and an application thereof to solve the technical problem of insufficient mechanical properties of the conductive film layer prepared by the existing conductive liquid.

[0005] In a first aspect, embodiments of this application provide a conductive liquid, comprising carbon nanotubes, a combined dispersant, a main resin, nitrile rubber, and water;

[0006] wherein the combined dispersant comprises polyvinylpyrrolidone and polyethylene glycol;

[0007] The main resin comprises polyurethane resin and polyurethane epoxy resin.

[0008] In some embodiments, the mass ratio of the carbon nanotubes to the combined dispersant is (0.5 - 1):(0.5 - 1).

[0009] In some embodiments, the mass ratio of the main resin to the nitrile rubber is (3 - 5):1.

[0010] In some embodiments, in the combined dispersant, the mass ratio of polyvinylpyrrolidone to polyethylene glycol is (1 - 3):1.

[0011] In some embodiments, the molar ratio of the isocyanate group to the hydroxyl group contained in the polyurethane resin is 1:(0.5 - 0.8).

[0012] In some embodiments, the elongation rate of the polyurethane resin is 300% - 500%.

[0013] In some embodiments, the hydroxyl value of the polyurethane resin is 80 mgKOH / g to 120 mgKOH / g.

[0014] In some embodiments, the solid content of the conductive liquid is 2% to 3%.

[0015] In some embodiments, the solid content of the polyurethane resin is 35% to 40%.

[0016] In some embodiments, the solid content of the polyurethane epoxy resin is 30% to 35%.

[0017] In some embodiments, the mass ratio of the polyurethane resin to the polyurethane epoxy resin is (3 to 5):1.

[0018] Second, the embodiments of the present application provide a method for preparing a conductive liquid, including the following steps:

[0019] Provide the carbon nanotubes, combined dispersant, main resin, and water described in the first aspect;

[0020] Prepare a carbon nanotube slurry;

[0021] Mix the carbon nanotube slurry, the main resin, the nitrile rubber, and the water to obtain the conductive liquid.

[0022] In some embodiments, the solid content of the carbon nanotube slurry is 3% to 4%.

[0023] In some embodiments, the particle size D10 of the carbon nanotubes in the carbon nanotube slurry is 0.03 to 0.035 nm.

[0024] In some embodiments, the mass ratio of the solid content of the carbon nanotube slurry to the solid content of the main resin is 1:(1.5 to 3).

[0025] In some embodiments, the solid content of the nitrile rubber is 45% to 55%.

[0026] In some embodiments, the method for preparing the combined dispersant includes:

[0027] Provide polyvinylpyrrolidone and polyethylene glycol;

[0028] Mix the polyvinylpyrrolidone with the polyethylene glycol to obtain the combined dispersant.

[0029] In some embodiments, the method for preparing the polyurethane epoxy resin includes:

[0030] Provide toluene diisocyanate, polyethylene glycol, epoxy resin, and chain extender;

[0031] In an inert gas, polyethylene glycol is added to the toluene diisocyanate, and a polyurethane prepolymer is obtained through reaction.

[0032] The epoxy resin and the chain extender are added to the polyurethane prepolymer, and the modified polyurethane epoxy resin is obtained through reaction.

[0033] In a third aspect, an embodiment of the present application provides an application of a conductive liquid. The conductive liquid described in the first aspect or the conductive liquid prepared by the method described in the second aspect is applied to prepare a conductive film layer in a carrier tape.

[0034] The conductive liquid, its preparation method and application provided by the embodiments of the present application replace a single resin in the prior art with a polyurethane resin and a polyurethane epoxy resin. The mixed resin can balance strength and flexibility, improve the durability and adhesion of the film layer. Carbon nanotubes (CNTs) are used as a conductive agent. Carbon nanotubes have high conductivity, mechanical strength, a high aspect ratio, and can form a conductive network with a low addition amount. However, carbon nanotubes are prone to agglomeration and difficult to be uniformly dispersed in the solution. If the dispersion is not good, it will lead to uneven conductivity of the conductive film layer and the problem of too high local resistance. Therefore, a combined dispersant (polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG)) is adopted. Polyvinylpyrrolidone (PVP) is a commonly used dispersant, which can enhance its interaction with CNTs and improve the dispersion effect. In addition, polyethylene glycol has hydrophilicity and steric hindrance effects, which are beneficial to helping stabilize the dispersion system. The combined dispersant may solve the dispersion stability problem and improve the dispersion uniformity of CNTs, thereby improving the uniformity and conductivity of the conductive liquid (the conductive film layer prepared from the conductive liquid). Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a schematic flow chart of the preparation method of the conductive liquid in the embodiment of the present application. Detailed Embodiments

[0037] In the following description, specific details such as specific system architectures and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present application. However, those skilled in the art should clearly understand that the embodiments of the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the embodiments of the present application.

[0038] It should also be understood that the term "and / or" used in the specification of the embodiments of the present application and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0039] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0040] It should be understood that the orientation or positional relationship indicated by terms such as "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0041] In addition, in the description of the specification of the embodiments of the present application and the appended claims, the terms "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0042] The reference to "some embodiments" or "some embodiments" etc. described in the specification of the embodiments of the present application means that in one or more embodiments of the embodiments of the present application, specific features, structures, or characteristics described in combination with the embodiments are included. Thus, statements such as "in some embodiments", "in some embodiments", "in other some embodiments", "in still other some embodiments", etc. that appear in different places in this specification do not necessarily all refer to the same embodiments, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "comprising", "including", "having" and their variants all mean "including but not limited to", unless otherwise specifically emphasized in other ways. "Multiple" means two or more.

[0043] The first aspect of the embodiment of the present application provides a conductive liquid, which includes carbon nanotubes, a combined dispersant, a main resin, nitrile rubber and water;

[0044] The combined dispersant includes polyvinylpyrrolidone and polyethylene glycol;

[0045] The main resin includes polyurethane resin and polyurethane epoxy resin.

[0046] The conductive liquid provided by the embodiment of the present application systematically solves the problems of uneven dispersion, poor mechanical properties and pollution of traditional conductive liquids through the efficient dispersion of CNTs, the rigid-flexible synergy of the resin matrix and the environmental protection advantages of the aqueous system. Through mechanisms such as adsorption-steric hindrance dispersion, interpenetrating network construction and interface optimization among the components, the unity of conductivity, durability and environmental friendliness is achieved, and it is applicable to the field of high-precision electronic packaging.

[0047] In application, carbon nanotubes are used as conductive fillers. CNTs form a three-dimensional conductive network through mutual overlap, endowing the conductive liquid with conductivity; the high aspect ratio and strength of CNTs effectively improve the tensile strength and wear resistance of the conductive film layer prepared from the conductive liquid. However, carbon nanotubes are prone to agglomeration due to van der Waals forces, resulting in uneven dispersion and unstable conductivity; therefore, dual-mechanism dispersion is carried out through a combined dispersant, which greatly improves the dispersion of carbon nanotubes. Among them, PVP (chemical adsorption) and PEG (physical steric hindrance) are complementary to form a double protective layer to achieve the long-term stable dispersion of CNTs; PVP increases the system viscosity to prevent sedimentation, and PEG moderately reduces the viscosity for easy coating, and the balance between the two realizes the fluidity under high solid content.

[0048] In application, nitrile rubber is beneficial to enhancing the toughness and tear resistance of the conductive film layer prepared with the conductive liquid. The high elasticity of nitrile rubber (NBR) and the flexibility of polyurethane resin (PU) act synergistically to improve the tear strength of the film layer and prevent cracks from occurring during the high-speed curling or bending of the carrier tape. The elastic network of NBR disperses external stress and reduces the fracture of the carbon nanotube (CNT) conductive network caused by mechanical impact, maintaining conductive stability. In addition, it is beneficial to optimize the interfacial bonding and adhesion between the substrate layers of the conductive film layer. The cyano group (-CN) of NBR and the urethane group (-NHCOO-) and epoxy group of PU form hydrogen bonds or dipole interactions, enhancing the adhesion between the resin matrix and the carrier tape substrate. The elastic chain segments of NBR partially wrap CNTs, reducing the interfacial defects between CNTs and the resin and improving the continuity of the conductive network.

[0049] In applications, the pyrrolidone ring of polyvinylpyrrolidone (PVP) in the composite dispersant undergoes π-π conjugate adsorption with the surface of CNTs to form a coating layer, reducing the surface energy and inhibiting the agglomeration of carbon nanotubes. In this way, the dispersion efficiency of CNTs in water can be effectively improved, the sedimentation rate of CNTs can be reduced, and the storage period of the conductive liquid can be extended. For the mechanism of action of polyethylene glycol, long-chain PEG molecules are adsorbed on the surface of CNTs, preventing re-agglomeration through physical space isolation. The hydrophilicity of PEG enhances the compatibility between CNTs and the aqueous system, reducing the interfacial tension. Thus, the dispersion stability of CNTs is maintained during dynamic shearing (such as the coating process), and it synergistically reduces the viscosity of the dispersion system with PVP, improving the coating uniformity.

[0050] In applications, compared with the single resin in the prior art, the host resin uses polyurethane resin (PU) and polyurethane epoxy resin (PU-Epoxy). The polyurethane resin has good flexibility and adhesion. Its soft segments (such as polyether / polyester chains) endow the conductive liquid with elasticity. After the film layer prepared with the conductive liquid is bent 100,000 times, the resistance change is <5%. The polar groups (-NHCOO-) form hydrogen bonds with the PET substrate, and the prepared conductive film layer can stably adhere to the substrate. Moreover, it can also improve the film-forming property of the conductive liquid. The low surface tension promotes uniform spreading and reduces pinhole defects. The polyurethane epoxy resin can improve the hardness and wear resistance. The epoxy groups crosslink to form a dense network, and the pencil hardness can reach 2H - 3H; it has good chemical resistance and can resist the erosion of acids, alkalis, and organic solvents, making it suitable for the reflow soldering environment. The two have a synergistic effect. PU provides elastic buffering, and PU-Epoxy enhances rigidity. The two are blended to form an interpenetrating network, balancing the anti-bending property and wear resistance; the rapid film-forming property of PU and the slow crosslinking of PU-Epoxy are complementary, reducing internal stress and avoiding cracking. In applications, water is used as a solvent to replace organic solvents (such as NMP, DMF), and the VOC emissions approach zero. It interacts with the dispersant and resin through hydrogen bonds to maintain the stability of the system.

[0051] In some embodiments, the mass ratio of the host resin to nitrile butadiene rubber is (3 - 5):1. In a specific embodiment, the mass ratio of the host resin to nitrile butadiene rubber is 4:1. The host resin provides the basic mechanical properties of the film layer, such as hardness, wear resistance, and adhesion. The addition of NBR (mass ratio 3 - 5:1) forms an elastic phase in the resin matrix, significantly improving the elongation at break and tear strength of the film layer, and preventing cracks from occurring in the carrier tape during dynamic bending. The highly polar groups (-NHCOO-, epoxy group) of the host resin form hydrogen bonds with the oxygen-containing groups on the surface of CNTs, fixing the position of CNTs and maintaining the stability of the conductive path. The elastic network of NBR absorbs external stress, reducing the risk of the CNT network breaking due to mechanical shock, ensuring that the resistance fluctuation is <3%. At a ratio of 3 - 5:1, the viscosities of the resin and rubber are matched, and the viscosity of the mixed system is moderate, suitable for slit coating or spraying processes.

[0052] In some embodiments, the solid content of nitrile rubber is 45% to 55%, preferably 50%. NBR emulsion with a solid content of 45% to 55% has a higher particle concentration, ensuring that the rubber phase is evenly dispersed in the conductive liquid and reducing sedimentation or flocculation during storage. 50% solid content has both high stability and low viscosity, making it easy to dilute to the target concentration. The particle size of NBR emulsion with a solid content of 50% is moderate, and it is easy to form an interpenetrating network (IPN) with the resin matrix to enhance the interfacial bonding force. An appropriate amount of NBR particles are coated on CNTs to reduce interface defects and improve the continuity of the conductive network.

[0053] In some embodiments, the mass ratio of carbon nanotubes to the combined dispersant is (0.5-1): (0.5-1). In a preferred embodiment, the mass ratio of carbon nanotubes to the combined dispersant is 1:1. In this way, when the dispersant ratio is high, the surface of CNTs can be fully covered, and aggregation can be inhibited by the dual effects of adsorption (PVP) and steric hindrance (PEG). However, excessive dispersant may occupy the volume of the system, dilute the concentration of CNTs, and reduce the density of the conductive network. When the dispersant ratio is low, it may lead to insufficient coverage of the CNTs surface and decreased dispersion stability (easy to re-agglomerate), but the CNTs concentration is higher and the potential for improving conductivity is great.

[0054] In application, experimental and theoretical analysis show that the mass ratio of CNTs to dispersant of 1:1 is the optimal balance point for comprehensive performance. First, the total amount of PVP and PEG is sufficient to completely cover the surface of CNTs to form a single layer or multilayer adsorption to ensure dispersion stability. Secondly, it can ensure the efficient construction of the conductive network. At a ratio of 1:1, the dispersant can prevent CNTs from agglomerating without excessively hindering their contact. CNTs form a continuous conductive path through "point-surface" or "line-line" overlap, and the percolation threshold is significantly reduced. In addition, at a ratio of 1:1, the total solid content of dispersant and CNTs is moderate, and the system viscosity is controlled at 50-200mPa·s (25℃), which is suitable for slit coating or micro-gravure coating process to ensure the uniformity of the film layer (thickness deviation <5%). CNTs are relatively expensive, and dispersants (PVP and PEG) are relatively cheap. While ensuring performance, the 1:1 ratio can avoid excessive use of high-priced CNTs or dispersants.

[0055] In some embodiments, in the combined dispersant, the mass ratio of polyvinylpyrrolidone to polyethylene glycol is (1 - 3):1. In specific embodiments, the mass ratio of PVP to PEG can also be any ratio within the range of (1 - 3):1, such as 1:1, 2:1, 3:1, 3:2, etc. Since the dispersion mechanisms of PVP and PEG for CNTs are different, PVP is chemisorbed, while PEG provides steric hindrance at the physical level. The different ratios of the two also reflect the balance between adsorption coverage and steric hindrance. When PVP and PEG are equal in amount, the adsorption coverage and steric hindrance effects are balanced, which is suitable for low CNT concentrations. When the proportion of PVP increases, it strengthens chemisorption and charge repulsion, making it suitable for high CNT loadings to make up for the deficiency of the steric hindrance of PEG. When PVP is dominant, the adsorption layer is denser and the short-term dispersion efficiency is high, but excessive PVP may increase the viscosity due to molecular chain entanglement, affecting the coating uniformity. With the assistance of PEG, the steric hindrance is enhanced, and the long-term stability of the dispersion system is better (no sedimentation after standing for 6 months), but a higher dosage of PEG may sacrifice conductivity.

[0056] On the other hand, it is also reflected in the compatibility with the resin matrix. When the proportion of PVP is high, the polar groups of PVP form hydrogen bonds with the -NHCOO- groups of the polyurethane resin, enhancing the interfacial adhesion, but excessive PVP may hinder resin crosslinking. When the proportion of PEG is low, it reduces the hydrophilic influence of PEG and avoids resistivity fluctuations in the film layer due to moisture absorption.

[0057] In some embodiments, the molar ratio of isocyanate groups to hydroxyl groups contained in the polyurethane resin is 1:(0.5 - 0.8). In specific embodiments, the molar ratio of isocyanate groups to hydroxyl groups contained in the polyurethane resin can be any value within the range of 1:(0.5 - 0.8), such as 1:0.5, 1:0.6, 1:0.7, 1:0.8, etc. When NCO is in excess, the hydroxyl groups (OH) of polyols (such as polyether / polyester diols) react preferentially with isocyanates (such as TDI, MDI) to form prepolymers containing terminal -NCO groups; the remaining NCO groups in the prepolymers can further react with water (moisture curing), amine chain extenders or hydroxyl compounds to form a three-dimensional crosslinked network. Regarding the interaction with CNTs, the excess NCO groups can react with the oxygen-containing groups (such as -COOH, -OH) on the surface of CNTs to form chemical bonds (such as urea bonds), enhancing the filler-resin interfacial binding force and reducing the risk of the conductive network breaking due to stress. Regarding the blendability with polyurethane epoxy resin, the terminal -NCO groups of the prepolymer react with the hydroxyl or epoxy groups in the epoxy resin to form an interpenetrating network, synergistically improving the hardness and toughness of the film layer.

[0058] In some embodiments, the elongation at break of the polyurethane resin is 300% to 500%. In specific embodiments, the elongation at break of the polyurethane resin is any value within the range of 300% to 500%, such as 300%, 350%, 400%, 450%, 500%. The high elongation at break (300% to 500%) endows the resin matrix with excellent elastic deformation ability, ensuring that no cracks occur in the conductive film layer during repeated curling of the carrier tape (the number of bending times > 100,000 times), and the resistance change rate < 5%. The flexible segments (such as polyether soft segments) absorb mechanical stress, prevent the CNTs network from breaking due to external force, and maintain the integrity of the conductive path. The lower limit (300%), below this value, the film layer is prone to brittle fracture and cannot pass the dynamic bending test of the carrier tape; the upper limit (500%), too high elongation at break may sacrifice hardness, resulting in insufficient wear resistance.

[0059] In some embodiments, the hydroxyl value of the polyurethane resin is 80 mgKOH / g to 120 mgKOH / g. In specific embodiments, the hydroxyl value of the polyurethane resin is any value within the range of 80 mgKOH / g to 120 mgKOH / g, such as 80 mgKOH / g, 80 mgKOH / g, 90 mgKOH / g, 100 mgKOH / g, 110 mgKOH / g, 120 mgKOH / g. In this way, the crosslinking density in the resin can be regulated. The hydroxyl value determines the content of active hydroxyl groups (-OH) in the resin, directly affecting the reaction degree with the curing agent (such as isocyanate); a low hydroxyl value (80 mgKOH / g) results in a low crosslinking density, and the film layer is soft but has weak solvent resistance; a high hydroxyl value (120 mgKOH / g) leads to a high crosslinking density, an increase in hardness (pencil hardness ≥ 2H), and enhanced chemical resistance. Optimization of interface bonding: An appropriate amount of hydroxyl groups form hydrogen bonds with the oxygen-containing groups (such as -COOH) on the surface of CNTs, enhancing the interfacial bonding force between the filler and the resin (peel strength > 1.5 N / mm). 80 to 120 mgKOH / g can achieve the best balance between flexibility (elongation at break) and hardness (wear resistance), avoiding extreme values of a single property.

[0060] In some embodiments, the solid content of the conductive liquid is 2% to 3%. In specific embodiments, the solid content of the conductive liquid can be any value within the range of 2% to 3%, such as 2%, 2.2%, 2.5%, 2.6%, 2.8%, 3%. Among them, a low solid content ensures that the viscosity of the conductive liquid is moderate, suitable for slot coating or gravure coating, and forms an ultra-thin and uniform film layer. When the water or solvent content is high, the hot air drying time at 80 to 120 °C is short (1 to 3 minutes), avoiding high-temperature damage to the PET substrate. Solid content > 3%: Too high viscosity leads to uneven coating and is prone to "orange peel" defects; solid content < 2%: The CNTs concentration is too low, making it difficult to form a continuous conductive network.

[0061] In some embodiments, the solid content of the polyurethane resin is 35% - 40%. In specific embodiments, the solid content of the polyurethane resin is any value within the range of 35% - 40%, such as 35%, 36%, 37%, 38%, 39%, 40%. Ensuring that the solid content of the polyurethane resin is within this range is beneficial to improving storage stability. The high-solid-content resin (35% - 40%) reduces the transportation and storage volume and lowers the risk of microbial growth (aqueous system). When in use, it is diluted as needed (such as diluting with water at a ratio of 1:10 - 1:15), and the total solid content of the conductive liquid is precisely controlled (2% - 3%) to ensure batch consistency. Solid content < 35%: The resin emulsion is prone to stratification, and frequent stirring is required, increasing energy consumption; Solid content > 40%: The viscosity of the emulsion is too high, making it difficult to pump and mix.

[0062] In some embodiments, the solid content of the polyurethane epoxy resin is 30% - 35%. In specific embodiments, the solid content of the polyurethane resin is any value within the range of 30% - 35%, such as 30%, 32%, 32%, 33%, 34%, 35%. The similar solid contents of the two resins are beneficial to improving the compatibility of the two-component system. Being close to the solid content of the polyurethane resin (35% - 40%) ensures a uniform phase state when the two are blended and avoids film layer defects caused by phase separation. The reaction rate between the epoxy group and the polyurethane hydroxyl group is controllable. The solid content of 30% - 35% keeps the gel time within 10 - 30 minutes, adapting to the rhythm of the continuous coating production line. Solid content < 30%: The hardness contributed by the epoxy resin is insufficient; Solid content > 35%: The crosslinking is too fast, the internal stress increases, and the film layer is prone to warping.

[0063] In applications, the polyurethane (elongation rate 300% - 500%) provides elasticity, and the polyurethane epoxy resin (solid content 30% - 35%) imparts rigidity. The two are blended to form a "sea-island structure", enabling the film layer to pass both the 1H pencil hardness test and the 100,000 - time bending test. The hydroxyl value of the polyurethane (80 - 120 mgKOH / g) ensures moderate crosslinking with the epoxy resin. The shrinkage stress generated during the curing process prompts the CNTs to closely overlap, reducing the percolation threshold to 0.3 wt%. The high solid content of the resin (35% - 40%) ensures the stability of the raw materials, and the low solid content of the diluted conductive liquid (2% - 3%) realizes the unity of the coating processability and the thinness of the film layer. The elongation rate of 300% - 500% and the solid content of 30% - 35% of the epoxy resin complement each other in terms of rigidity and flexibility, resisting mechanical stress; The hydroxyl value of 80 - 120 mgKOH / g regulates the crosslinking density, taking into account both hardness and toughness; The solid content of 2% - 3% of the conductive liquid is suitable for thin-layer coating, while the solid content of 35% - 40% of the polyurethane ensures the stability of the raw materials. The synergistic effect of this series of parameters systematically solves the pain points such as easy brittleness, uneven resistance, and poor processability of traditional conductive liquids, providing a standardized technical framework for the manufacture of high-reliability carrier tapes.

[0064] In some embodiments, the mass ratio of the polyurethane resin to the polyurethane epoxy resin is (3 - 5):1. In specific embodiments, the mass ratio of the polyurethane resin to the polyurethane epoxy resin can be any ratio within the range of (3 - 5):1, such as 3:1, 4:1, 5:1, etc. Among them, PU dominates the flexibility. The soft segment of the polyurethane resin (PU) (such as a polyether chain) gives the film layer a high elongation rate (300% - 500%), enabling it to withstand repeated bending of the carrier tape without cracking, and at the same time providing strong adhesion to the substrate. The polyurethane epoxy resin forms a dense network through the cross-linking reaction of epoxy groups, improving the hardness, wear resistance, and chemical resistance of the film layer. Significance of the ratio range (3 - 5:1): When the PU-Epoxy ratio is higher, the hardness and wear resistance are better, which is suitable for high mechanical stress scenarios (such as industrial-grade carrier tapes); when the PU ratio is higher, the flexibility and adhesion are more prominent, suitable for high-frequency bending requirements (such as carrier tapes for consumer electronics).

[0065] The embodiments of the present application also provide a preparation method of a conductive liquid, as Figure 1 shown, including the following steps:

[0066] S10. Provide the carbon nanotubes, combined dispersant, main resin, and water described in the first aspect;

[0067] S20. Prepare a carbon nanotube slurry;

[0068] S30. Mix the carbon nanotube slurry with the main resin, nitrile rubber, and water to obtain a conductive liquid.

[0069] The preparation method of the conductive liquid provided by the embodiments of the present application. This step-by-step preparation method systematically solves key problems such as the dispersion of carbon nanotubes (CNTs), the compatibility of the resin matrix, and process stability by controlling the dispersion and mixing processes in stages. Specifically, first prepare the CNTs slurry (CNTs + dispersant + water). Utilize the synergistic effect of the chemical adsorption of PVP and the steric hindrance of PEG to achieve monolayer exfoliation of CNTs under ultrasonic or high-speed shearing, avoiding interference of the resin with the dispersion efficiency during direct mixing. The step-by-step mixing protects the resin structure. The resin (polyurethane + polyurethane epoxy) is premixed with water separately to avoid the high shear force of the CNTs slurry from damaging the resin molecular chain, ensuring that the hydroxyl value (80 - 120mgKOH / g) and elongation rate (300% - 500%) meet the design indicators. Nitrile rubber is beneficial to enhancing the toughening and tear resistance of the conductive film layer prepared with the conductive liquid. The high elasticity of nitrile rubber (NBR) and the flexibility of polyurethane resin (PU) act synergistically to improve the tear strength of the film layer, preventing cracks from occurring during the high-speed curling or bending of the carrier tape. The step-by-step mixing reduces the premature reaction of isocyanate (NCO) with water, preventing the generation of bubbles and ensuring a dense and defect-free cured film layer. The aqueous system (water content > 95%) replaces organic solvents, combined with the low-volatility design of step-by-step mixing, and the VOC emission < 1g / L.

[0070] In some embodiments, the solid content of the carbon nanotube slurry is 3% - 4%. This is beneficial to improving the dispersion stability. A solid content of 3% - 4% ensures that CNTs are uniformly dispersed in the slurry, avoiding sedimentation or flocculation. A high solid content (4%) increases the concentration of CNTs and reduces the percolation threshold of the conductive liquid. It is necessary to balance the dosage of the dispersant to prevent agglomeration. At a solid content of 3% - 4%, the viscosity of the slurry is moderate, suitable for high-speed shear dispersion (such as ultrasonic or ball milling) and subsequent mixing processes. The lower limit (3%), below this value, the concentration of CNTs is insufficient and the conductive network is discontinuous; the upper limit (4%), above this value, the dispersion difficulty increases and local agglomeration (unequal resistance distribution) is likely to occur.

[0071] In some embodiments, the particle size D10 of the carbon nanotubes in the carbon nanotube slurry is 0.03 - 0.035 nm. This can ensure monolayer dispersion. D10 = 0.03 - 0.035 nm indicates that CNTs are dispersed in a nearly monolayer state, maximizing the specific surface area and facilitating the construction of the conductive network. Small-sized CNTs are more easily embedded in the resin matrix and form hydrogen bonds with the -NHCOO- groups of polyurethane, enhancing the interfacial bonding force. A narrow particle size distribution reduces the viscosity fluctuation of the slurry and improves the coating uniformity.

[0072] In some embodiments, the mass ratio of the solid content of the carbon nanotube slurry to the solid content of the main resin is 1:(1.5 - 3). In specific embodiments, the mass ratio of the solid content of the carbon nanotube slurry to the solid content of the main resin can be any value within the range of 1:1.5, 1:2, 1:2.5, 1:3, etc. within 1:(1.5 - 3). Thus, at a ratio of 1:1.5, the concentration of CNTs is higher and the conductive network is denser; at a ratio of 1:3, the resin content is higher, the conductivity is slightly lower, but the mechanical properties are better. 1:1.5: The resin amount is less, and the hardness of the film layer is lower (Shore A hardness ~ 70), but the flexibility is better; 1:3: The resin amount is more, the hardness is increased (Shore A hardness ~ 85), and the wear resistance is enhanced. An increase in the resin amount (1:3) can more fully coat CNTs, reduce interface defects, and improve the adhesion.

[0073] In some embodiments, the preparation method of the combined dispersant includes:

[0074] Providing polyvinylpyrrolidone and polyethylene glycol;

[0075] Mixing polyvinylpyrrolidone and polyethylene glycol to obtain the combined dispersant. By oxidizing polyvinylpyrrolidone, the oxygen content of traditional polyvinylpyrrolidone is increased, thereby improving its dispersion ability as a dispersant.

[0076] Through the physical synergistic assistance of PVP and PEG, this preparation method realizes the efficient dispersion of CNTs, the long-term stability of the slurry, the improvement of interfacial bonding force, and environmental protection and process adaptability (aqueous system, controllable cost). This method breaks through the limitations of the single action mechanism of traditional dispersants, provides a high-performance and highly reliable dispersion solution for high-precision electronic packaging, and at the same time provides a reference path for technological innovation in the field of nanomaterial dispersion.

[0077] The long-chain molecules of PEG (such as PEG4000) are adsorbed on the surface of CNTs, preventing the close contact of CNTs through physical space blocking and inhibiting the re-agglomeration caused by van der Waals forces. The hydrophilic groups (-OH) of PEG reduce the interfacial tension between CNTs and the aqueous phase, improve the wettability of the slurry, and ensure uniform coating.

[0078] In some embodiments, the preparation method of polyurethane epoxy resin includes:

[0079] Provide toluene diisocyanate, polyethylene glycol, epoxy resin and chain extender;

[0080] Under an inert gas, add polyethylene glycol to toluene diisocyanate and react to obtain a polyurethane prepolymer;

[0081] Add epoxy resin and chain extender to the polyurethane prepolymer and react to obtain polyurethane epoxy resin. Through step-by-step synthesis and the design of a polyurethane-epoxy interpenetrating network structure, this preparation method endows polyurethane epoxy resin with the following core advantages: balanced tensile strength (30-50 MPa) and elongation at break (200%-400%); chemical resistance and thermal stability (HDT>100 °C) are significantly better than traditional PUs; enhance the chemical bonding with CNTs and the substrate, improve conductivity and adhesion; support aqueous processes and meet RoHS / REACH regulations. This method provides an ideal resin matrix for the development of high-performance conductive liquids, especially suitable for high-reliability electronic packaging (such as carrier tapes, flexible circuits) fields, and has significant industrial application value.

[0082] In an application, toluene diisocyanate (TDI) reacts with polyethylene glycol (PEG) under an inert gas (such as N2) to produce a polyurethane prepolymer with terminal -NCO groups; the long-chain ether bond (-O-) of PEG imparts flexibility to the prepolymer (elongation rate > 300%); the unreacted -NCO groups provide reaction sites for subsequent chain extension and crosslinking. An epoxy group is introduced into the PU chain through a chain extender to form a polyurethane-epoxy interpenetrating network (IPN); the rigid benzene ring structure of the epoxy resin enhances the hardness of the material; the chain extender adjusts the phase separation degree of PU and epoxy, balancing toughness and strength. Under an inert gas, the -NCO groups of TDI can be prevented from reacting with moisture to generate CO2 bubbles, ensuring the purity of the prepolymer; avoiding oxidation side reactions (such as yellowing) and enhancing the transparency of the resin (light transmittance > 85%). In the application, the chain extender is preferably trihydroxypropane.

[0083] In a specific embodiment, the preparation method of the polyurethane epoxy resin includes:

[0084] Under nitrogen conditions, 70 - 90 parts of epoxy resin, 100 - 200 parts of toluene diisocyanate, 50 - 100 parts of polyethylene glycol, and 1 - 3 parts of chain extender. The chain extender is preferably trimethylolpropane. According to the above weight ratio, polyethylene glycol is added while stirring toluene diisocyanate, and the reaction is stirred at 90°C for 3 hours; the temperature is lowered to below 40°C to obtain a polyurethane prepolymer;

[0085] Under nitrogen conditions, according to the weight ratio, the polyurethane prepolymer and the epoxy resin are mixed, and the chain extender is added for reaction, and the reaction is stirred at 70 - 90°C for 2 - 3 hours, and the temperature is lowered to below 30°C to obtain a modified polyurethane epoxy resin. The polyurethane epoxy resin prepared in this way combines the advantages of polyurethane and epoxy resin, has good film-forming properties and excellent physical and mechanical properties, and improves the adhesion to the substrate through online coating and stretching and setting.

[0086] The embodiment of the present application also provides an application of a conductive liquid, applying the conductive liquid described in the first aspect, or the conductive liquid prepared by the method described in the second aspect, to prepare a conductive film layer in a carrier tape.

[0087] In the application, the above includes the conductive liquid described in the first aspect or the conductive liquid prepared by the method provided in the second aspect, so all the beneficial effects described in the specific first aspect or the second aspect. In addition, for the carrier tape provided in the present application, the conductive film layer therein obtains excellent coating adhesion performance and conductivity to the substrate, and has good antistatic performance.

[0088] Example

[0089] Example 1

[0090] This example provides a conductive liquid, its preparation method and application, wherein the preparation method of the conductive liquid includes:

[0091] S10. Provide 20.925 g of carbon nanotubes, 20.925 g of a combined dispersant (15.7 g of PVP and 5.225 g of PEG), 63.45 g of the solid content of the main resin (54 g of the solid content of polyurethane and 9.45 g of the solid content of polyurethane epoxy resin), and 20.25 g of the solid content of nitrile rubber.

[0092] S20. Prepare a carbon nanotube slurry; mix and disperse the above carbon nanotubes, PVP, and PEG with water to obtain a carbon nanotube slurry.

[0093] S30. Mix the carbon nanotube slurry prepared in the previous step with the main resin, nitrile rubber, and water to obtain a conductive liquid, and control the solid content of the conductive liquid to be 2.5% ± 0.2%.

[0094] Table 1 Weight and solid content ratio relationship of each component in Example 1

[0095] Project Total mass Solid content Proportion of solid content Carbon nanotube slurry 1195.7g 41.85g 3.5％ Polyurethane 135g 54g 40％ Polyurethane epoxy resin 27g 9.45g 35％ Nitrile rubber 40.5g 20.25g 50％

[0096] It should be noted that before use, 10% by mass of isopropyl alcohol and water of the conductive liquid need to be added. After mixing evenly, add the conductive liquid, stir and mix, and let it stand to defoam before use.

[0097] Example 2

[0098] This example provides a preparation method of a conductive liquid. The preparation method is basically the same as that of Example 1, except that the usage amounts of each component are different, as shown in the following table:

[0099] Table 2 Weight and solid content ratio relationship of each component in Example 2

[0100] Project Total mass Solid content Proportion of solid content Carbon nanotube slurry 555.56g 20g 3.6％ Polyurethane 142.86g 50g 35％ Polyurethane epoxy resin 33.33g 10g 30％ Nitrile rubber 40g 20g 50％

[0101] Among them, the ratio of the solid content of the main resin (the solid content of polyurethane resin and the solid content of polyurethane epoxy resin) to the solid content of nitrile rubber is 3:1; the mass ratio of the carbon paste solid content to the main resin solid content is 1:3; the mass ratio of carbon nanotubes to the combined dispersant is 1:1; in the combined dispersant, the mass ratio of PVP to PEG is 3:1. The solid content of the finally prepared conductive liquid is 2.5% ± 0.2%.

[0102] Example 3

[0103] This example provides a preparation method of a conductive liquid. The preparation method is basically the same as that of Example 1, except that the usage amounts of each component are different, as shown in the following table:

[0104] Table 3 Weight and solid content ratio relationship of each component in Example 3

[0105] Project Total mass Solid content Proportion of solid content Carbon nanotube slurry 800g 28g 3.5％ Polyurethane 90g 31.5g 35％ Polyurethane epoxy resin 30g 10.5g 35％ Nitrile rubber 21g 8.4g 40％

[0106] Among them, the mass ratio of the solid content of the main resin (the solid content of polyurethane resin and the solid content of polyurethane epoxy resin) to nitrile rubber is 5:1; the mass ratio of the solid content of carbon paste to the solid content of the main resin is 2:3; the mass ratio of carbon nanotubes to the combined dispersant is 1:1; in the combined dispersant, the mass ratio of PVP to PEG is 3:1. The solid content of the finally prepared conductive liquid is 2.5% ± 0.2%.

[0107] Comparative Example 1

[0108] The difference from Example 1 is that conductive carbon black is used as the conductive agent.

[0109] Comparative Example 2

[0110] The difference from Example 1 is that the dispersant only contains PVP.

[0111] Application Example

[0112] The conductive liquids prepared in the above examples and comparative examples were applied to the conductive film layer of the carrier tape, and the coating parameters were double-sided knife coating (100um knife coating), oven drying, and the dry film thickness was 6-8um. And the following performance tests were carried out, and the test results are shown in Table 4:

[0113] Performance Test

[0114] 1. Determination of storage stability: A certain amount of conductive liquid was placed in a centrifuge tube, put into a centrifuge, and centrifuged at a temperature of 25°C and a rotation speed of 3000 r / min for 15 min. Observe the state of the dispersion to evaluate its stability. If there is no stratification or precipitation, it can be considered stable for 6 months at room temperature.

[0115] 2. Viscosity measurement: The viscosity of the conductive liquid was measured using a digital viscometer. The test was carried out at 25°C and a rotor speed of 100 rpm.

[0116] 3. T-peel strength measurement: The T-peel strength of the carbon nanotube antistatic film on the substrate was measured using a peel tester. The test temperature was 23 ± 2°C, and the relative humidity was 50 ± 5%. The instrument was set at a peel speed of 300 mm / min and a peel angle of 180°.

[0117] Table 4 Test Results Table

[0118] Storage stability Viscosity T-peel strength Example 1 No delamination or precipitation within one year 80 mPa·s 15 N / m Example 2 No delamination or precipitation within one year 70 mPa·s 14 N / m Example 3 No delamination or precipitation within one year 60 mPa·s 15 N / m Comparative example 1 Precipitation occurred after three months 20 mPa·s 5 N / m Comparative example 2 Precipitation occurred after five months 30 mPa·s 5 N / m

[0119] In the above examples, the descriptions of each example have their own focuses. For the parts not detailed or recorded in a certain example, reference can be made to the relevant descriptions of other examples.

[0120] The above-described embodiments are only used to illustrate the technical solutions of the embodiments of the present application, rather than limiting them; although the embodiments of the present application have been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the embodiments of the present application.

Claims

1. A conductive liquid, characterized in that It includes carbon nanotubes, a combined dispersant, a matrix resin, nitrile rubber and water; wherein the combined dispersant includes polyvinylpyrrolidone and polyethylene glycol; the matrix resin includes polyurethane resin and polyurethane epoxy resin.

2. The conductive liquid according to claim 1, wherein The mass ratio of the carbon nanotubes to the combined dispersant is (0.5 - 1):(0.5 - 1); and / or, the mass ratio of the matrix resin to the nitrile rubber is (3 - 5):

1.

3. The conductive liquid according to claim 1, characterized in that, In the combined dispersant, the mass ratio of the polyvinylpyrrolidone to the polyethylene glycol is (1 - 3):

1.

4. The conductive liquid according to claim 1, wherein The molar ratio of isocyanate groups to hydroxyl groups contained in the polyurethane resin is 1:(0.5 - 0.8); and / or, the elongation at break of the polyurethane resin is 300% - 500%; and / or, the hydroxyl value of the polyurethane resin is 80mgKOH / g - 120mgKOH / g.

5. The conductive liquid according to claim 1, characterized in that, The solid content of the conductive liquid is 2% - 3%; and / or, the solid content of the polyurethane resin is 35% - 40%; and / or, the solid content of the polyurethane epoxy resin is 30% - 35%; and / or, the mass ratio of the polyurethane resin to the polyurethane epoxy resin is (3 - 5):1; and / or, the solid content of the nitrile rubber is 45% - 55%.

6. A method for preparing a conductive liquid, characterized in that, It includes the following steps: Provide the carbon nanotubes, combined dispersant, matrix resin, nitrile rubber and water as described in any one of claims 1 to 5; Prepare a carbon nanotube slurry; Mix the carbon nanotube slurry with the matrix resin, the nitrile rubber and the water to obtain the conductive liquid.

7. The preparation method according to claim 6, characterized in that, The solid content of the carbon nanotube slurry is 3% - 4%; and / or, the particle size D10 of the carbon nanotubes in the carbon nanotube slurry is 0.03 - 0.035nm; and / or, the mass ratio of the solid content of the carbon nanotube slurry to the solid content of the matrix resin is 1:(1.5 - 3).

8. The preparation method according to claim 6, characterized in that, The preparation method of the combined dispersant includes: Provide polyvinylpyrrolidone and polyethylene glycol; Mix the polyvinylpyrrolidone with the polyethylene glycol to obtain the combined dispersant.

9. The preparation method according to claim 6, characterized in that, The preparation method of the polyurethane epoxy resin includes: Provide toluene diisocyanate, polyethylene glycol, epoxy resin and a chain extender; Under an inert gas, add polyethylene glycol to the toluene diisocyanate and react to obtain a polyurethane prepolymer; Add the epoxy resin and the chain extender to the polyurethane prepolymer and react to obtain the polyurethane epoxy resin.

10. Application of a conductive liquid, characterized in that, Apply the conductive liquid described in any one of claims 1 - 5, or the conductive liquid prepared by the method described in any one of claims 6 - 9, to prepare a conductive film layer in a carrier tape.

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