A modified graphene material and its preparation method

Abstract

This invention relates to the field of graphene materials technology, and discloses a modified graphene material and its preparation method. The preparation method includes: modifying graphene oxide with sodium lignosulfonate through π-π stacking to prepare an aqueous stable dispersion; introducing saponified rosin acid to attach the rosin acid tricyclic hydrophobic framework to the graphene surface; compounding tung oil emulsion, utilizing the α-tung acid conjugated triene double bond to form a film through free radical oxidation polymerization at room temperature (15-35℃), and covalently bonding graphene into the organic film-forming system through phenolic radical coupling; adding zinc borate, where zinc ions catalyze curing and promote the formation of zinc rosin acid, and borate ions form an inorganic borate ester crosslinking network with the hydroxyl groups of sodium lignosulfonate; adjusting the solid content and grinding to obtain the finished product. The conductive ink prepared by this invention self-cures at room temperature, and the cured coating has excellent water resistance and conductivity stability, making it suitable for heat-sensitive flexible substrates.

Description

Technical Field

[0001] This invention relates to the field of graphene materials technology, and more specifically, to a modified graphene material and its preparation method. Background Technology

[0002] Graphene, with its excellent conductivity and two-dimensional sheet-like morphology, is an ideal carbon-based material for preparing conductive inks and has been widely used in printed electronics, flexible sensors, and RFID tags. Currently, water-based graphene conductive inks typically use synthetic surfactants (such as sodium dodecylbenzenesulfonate and polyoxyethylene surfactants) to disperse graphene in the aqueous phase, and synthetic resins such as acrylate emulsions and alkyd resins as film-forming base materials, followed by high-temperature baking to complete film formation and curing.

[0003] However, existing water-based graphene conductive inks have significant technical defects: synthetic surfactants migrate and accumulate between graphene sheets during the curing process, forming an insulating residue layer that leads to a significant decrease in the conductivity of the cured coating; the synthetic resin film-forming system requires high-temperature baking and curing above 120°C, which far exceeds the temperature resistance limit of heat-sensitive flexible substrates such as PET film (approximately 80°C), paper, and fabrics, making it unsuitable for these substrates; and there is a lack of chemical bonding between the synthetic resin and graphene, causing graphene to migrate and re-aggregate after the coating comes into contact with water, resulting in the breakage of the conductive network and a sharp decrease in conductivity, which cannot meet the requirements for use in high humidity and outdoor environments. Summary of the Invention

[0004] This invention provides a modified graphene material and its preparation method, solving the technical problems of residual synthetic surfactants in existing water-based graphene conductive inks that damage the conductivity of the cured coating, the need for high-temperature baking to form the film which limits its applicability to heat-sensitive flexible substrates, and the poor water resistance of the cured coating.

[0005] A method for preparing a modified graphene material includes the following steps:

[0006] Step 1: Mix and stir sodium lignosulfonate with graphene oxide aqueous dispersion. The benzene ring of the phenylpropane unit of sodium lignosulfonate is adsorbed onto the graphene oxide substrate through π-π stacking. The sulfonic acid group provides electrostatic repulsion, thus obtaining sodium lignosulfonate modified graphene oxide aqueous dispersion.

[0007] Step 2: Saponify rosin acid with sodium hydroxide to prepare sodium rosinate solution, add it to the dispersion obtained in step 1 and mix evenly. Rosin acid ions are attached to the surface of graphene oxide with a tricyclic phenanthrene hydrophobic framework.

[0008] Step 3: Add the aqueous tung oil emulsion to the dispersion obtained in Step 2 and mix evenly; the conjugated triene double bond of α-tung acid in tung oil causes the finished product to undergo free radical oxidation polymerization and self-drying curing after being coated and exposed to air at room temperature of 15-35℃. During the curing process, the phenolic hydroxyl groups of sodium lignosulfonate are oxidized to phenolic oxygen free radicals and coupled with carbon free radicals of tung oil, embedding graphene into the organic film-forming system through carbon-oxygen covalent bonds;

[0009] Step 4: Add zinc borate, stir and disperse. Zinc ions metathesis with sodium rosinate to form zinc rosinate, and borate ions form covalent cross-linked bonds of borate ester with the aliphatic hydroxyl groups of sodium lignin sulfonate segments. Adjust the solid content and disperse by grinding to obtain modified graphene conductive ink material.

[0010] Preferably, based on 1 part by weight of graphene oxide, the amount of sodium lignosulfonate is 2 to 4 parts by weight, the amount of rosin acid is 0.5 to 1.5 parts by weight, the amount of tung oil is 3 to 6 parts by weight, and the amount of zinc borate is 0.2 to 0.6 parts by weight.

[0011] Preferably, the graphene oxide has a sheet diameter of 1–20 μm and a C / O atomic ratio of 2:1–4:1; the sodium lignosulfonate has a sulfonic acid group content of 6%–14% (mass fraction).

[0012] Preferably, in step 1, graphene oxide is dispersed in deionized water and treated with ultrasound at a power of 200-400 W for 30-60 min to prepare an aqueous dispersion with a concentration of 2-5 mg / mL; sodium lignosulfonate is prepared into an aqueous solution with a mass concentration of 5%-15% and then mixed with the graphene oxide aqueous dispersion, and stirred at 200-500 r / min at 15-35℃ for 1-2 hours.

[0013] Preferably, in step 2, the molar ratio of sodium hydroxide to rosin acid is 1.05:1 to 1.1:1, the saponification reaction temperature is 50 to 70°C, and the time is 30 to 60 min; after the sodium rosin acid solution is cooled to room temperature, it is added to the dispersion obtained in step 1 and stirred at 200 to 400 r / min for 20 to 40 min.

[0014] Preferably, in step 3, the preparation of the aqueous tung oil emulsion uses an emulsifier that is a mixture of Tween-80 and Spande-80 in a mass ratio of 6:4. The amount of emulsifier is 3% to 5% of the mass of tung oil. The high-speed shear emulsification speed is 6000 to 10000 r / min and the time is 10 to 20 min. The solid content of the tung oil emulsion is 40% to 60%.

[0015] Preferably, in step 3, the aqueous tung oil emulsion is mixed with the dispersion obtained in step 2 and stirred at 200-400 r / min for 20-40 min; based on solid content, tung oil accounts for 40%-55% of the total solid content of each component.

[0016] Preferably: In step 4, the chemical formula of zinc borate is It accounts for 4% to 8% (mass fraction) of the total solid content of each component; after addition, stir at 200 to 400 r / min for 20 to 40 min.

[0017] Preferably, the solid content is adjusted to 20%–35% (mass fraction) with deionized water, wherein graphene accounts for no less than 10% of the solid content by mass fraction; and the particles are ground and dispersed so that the particle size D50 of each component is no greater than 5 μm.

[0018] A modified graphene material, wherein the material is a conductive ink prepared by the above preparation method, with a solid content of 20% to 35% (mass fraction), graphene oxide accounting for not less than 10% of the solid content by mass fraction, and the particle size D50 of each component not greater than 5 μm; the conductive ink is coated at room temperature of 15 to 35°C and exposed to air for 8 to 36 hours to complete self-drying curing, the cured coating contains both tung oil free radical oxidized polymer crosslinking network and borate ester crosslinking network, and sodium lignosulfonate modified graphene is embedded in the tung oil free radical oxidized polymer by carbon-oxygen covalent bonds.

[0019] The beneficial effects of this invention are as follows: This invention uses sodium lignosulfonate instead of synthetic surfactants to disperse graphene oxide. Sodium lignosulfonate is fixed to the graphene surface through π-π stacking of phenylpropane units, and does not migrate or migrate during the curing process, thus avoiding the formation of an insulating residual layer between graphene sheets and effectively improving the conductivity of the cured coating. Using tung oil as the film-forming base material, it utilizes the conjugated triene double bonds of α-tung acid for self-drying curing at room temperature (15-35℃) without high-temperature baking, broadening its applicability to heat-sensitive flexible substrates (PET film, paper, fabrics, etc.). The synergistic effect of the tung oil free radical oxidative polymer crosslinking network and the inorganic borate ester crosslinking network, combined with the rosin acid tricyclic hydrophobic layer, endows the cured coating with excellent water resistance. Graphene is embedded in the organic film-forming system through carbon-oxygen covalent bonds, maintaining long-term stability of the conductive network under bending and water immersion conditions, meeting the requirements for outdoor and high-humidity applications. Attached Figure Description

[0020] Figure 1 This is a comparative bar chart showing the effect of different dispersants on the sheet resistance of the modified graphene curing coating.

[0021] Figure 2 This is a graph showing the change in sheet resistance with curing time during the curing process at 25°C according to an embodiment of the present invention.

[0022] Figure 3 This is a comparison curve of the sheet resistance of the cured coating of this invention and the control group after immersion in deionized water at 25°C for 336 hours as a function of time.

[0023] Figure 4 This is the SEM morphology of sample B in experimental group B of this embodiment of the invention. Detailed Implementation

[0024] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0025] Example 1

[0026] This embodiment discloses a method for preparing modified graphene materials, which includes the following steps:

[0027] Step 1: Dissolve 3 parts by mass of sodium lignosulfonate (10% by mass of sulfonic acid groups) in deionized water to prepare a 10% sodium lignosulfonate aqueous solution. Disperse 1 part by mass of graphene oxide (5-10 μm in diameter, C / O atomic ratio 3:1) in an appropriate amount of deionized water and treat with ultrasound at 300 W for 45 min to prepare a homogeneous aqueous dispersion of graphene oxide with a concentration of 3 mg / mL. Mix the sodium lignosulfonate aqueous solution with the graphene oxide aqueous dispersion and stir at 300 r / min for 1.5 hours at 25°C to obtain a sodium lignosulfonate-modified graphene oxide aqueous dispersion.

[0028] Step 2: Add 1 part by mass of rosin acid to a 6% sodium hydroxide aqueous solution, with a molar ratio of sodium hydroxide to rosin acid of 1.07:1. Stir at 60°C for 45 min to completely saponify the rosin acid, obtaining an aqueous solution of sodium rosinate (rosin soap). After cooling the rosin soap aqueous solution to room temperature, add it to the dispersion obtained in Step 1, and stir at 300 r / min for 30 min until homogeneous, obtaining an aqueous dispersion of modified graphene containing rosin soap.

[0029] Step 3: Add 4 parts by mass of tung oil to deionized water containing a mixture of Tween-80 and Spin-80 at a mass ratio of 6:4 (total emulsifier amount is 4% of the tung oil mass). Emulsify at 8000 r / min for 15 min to prepare an aqueous tung oil emulsion with a solid content of 50%. Add the aqueous tung oil emulsion to the dispersion obtained in Step 2 and stir at 300 r / min for 30 min until homogeneous to obtain a modified graphene composite dispersion containing tung oil emulsion; the solid content of tung oil accounts for 42.1% of the total solid content of all components.

[0030] Step 4: Add zinc borate ( 0.5 parts by mass (5.3% of the total solid content of each component) were added to the dispersion obtained in step 3, and stirred at 300 r / min for 30 min to fully disperse it, thus obtaining a modified graphene composite dispersion containing all functional components.

[0031] Step 5: The dispersion obtained in Step 4 is concentrated by rotary evaporation at 50℃ and reduced pressure of -0.085 MPa to a solid content of over 18%. The solid content is then adjusted to 28% (mass fraction) with deionized water. The mixture is then milled and dispersed using a three-roll mill until the particle size D50 of each component is 2 μm, yielding the modified graphene conductive ink. This finished product is coated onto a 125 μm thick PET film substrate and allowed to air-dry for 12 hours at 25℃ to complete self-curing. The resulting cured coating has a pencil hardness of 2H and a sheet resistance of approximately 350 Ω.

[0032] Example 2

[0033] This embodiment discloses a method for preparing modified graphene materials, which includes the following steps:

[0034] Step 1: Dissolve 2 parts by mass of sodium lignosulfonate (6% by mass of sulfonic acid groups) in deionized water to prepare a 5% sodium lignosulfonate aqueous solution. Disperse 1 part by mass of graphene oxide (1-5 μm in diameter, C / O atomic ratio 2:1) in an appropriate amount of deionized water and treat with ultrasound at 200 W for 60 min to prepare a uniform aqueous dispersion of graphene oxide with a concentration of 2 mg / mL. Mix the sodium lignosulfonate aqueous solution with the graphene oxide aqueous dispersion and stir at 200 r / min for 2 hours at 15℃ to obtain a sodium lignosulfonate-modified graphene oxide aqueous dispersion.

[0035] Step 2: Add 0.5 parts by mass of rosin acid to a 5% sodium hydroxide aqueous solution, with a molar ratio of sodium hydroxide to rosin acid of 1.05:1. Stir at 50°C for 60 min to completely saponify the rosin acid, obtaining a sodium abirate aqueous solution. After cooling the sodium abirate solution to room temperature, add it to the dispersion obtained in Step 1, and stir at 200 r / min for 40 min until homogeneous.

[0036] Step 3: Add 3 parts by mass of tung oil to deionized water containing a mixture of Tween-80 and Spin-80 at a mass ratio of 6:4 (total emulsifier amount is 3% of the tung oil mass). Emulsify at 6000 r / min for 20 min to prepare an aqueous tung oil emulsion with a solid content of 40%. Add the aqueous tung oil emulsion to the dispersion obtained in Step 2 and stir at 200 r / min for 40 min until homogeneous; the solid content of tung oil accounts for 44.1% of the total solid content of all components.

[0037] Step 4: Add zinc borate ( 0.3 parts by mass (4.4% of the total solid content of each component) were added to the dispersion obtained in step 3, and stirred at 200 r / min for 40 min to ensure thorough dispersion.

[0038] Step 5: The dispersion obtained in Step 4 is concentrated by rotary evaporation under reduced pressure conditions of 40℃ and -0.080 MPa to a solid content of over 18%. The solid content is then adjusted to 20% (mass fraction) with deionized water. The mixture is then milled and dispersed using a sand mill until the particle size D50 of each component is 5 μm, yielding the modified graphene conductive ink. This finished product is coated onto coated paper (230 g / m²) substrate and allowed to self-cur at 15℃ for 36 hours.

[0039] Example 3

[0040] This embodiment discloses a method for preparing modified graphene materials, which includes the following steps:

[0041] Step 1: Dissolve 4 parts by mass of sodium lignosulfonate (14% by mass of sulfonic acid groups) in deionized water to prepare a 15% sodium lignosulfonate aqueous solution. Disperse 1 part by mass of graphene oxide (10-20 μm in diameter, C / O atomic ratio 4:1) in an appropriate amount of deionized water and treat with ultrasound at 400 W for 30 min to prepare a uniform aqueous dispersion of graphene oxide with a concentration of 5 mg / mL. Mix the sodium lignosulfonate aqueous solution with the graphene oxide aqueous dispersion and stir at 500 r / min for 1 hour at 35℃ to obtain a sodium lignosulfonate-modified graphene oxide aqueous dispersion.

[0042] Step 2: Add 1.5 parts by mass of rosin acid to an 8% sodium hydroxide aqueous solution, with a molar ratio of sodium hydroxide to rosin acid of 1.10:1. Stir at 70°C for 30 min to completely saponify the rosin acid, obtaining a sodium abirate aqueous solution. After cooling the sodium abirate solution to room temperature, add it to the dispersion obtained in Step 1, and stir at 400 r / min for 20 min until homogeneous.

[0043] Step 3: Add 6 parts by mass of tung oil to deionized water containing a mixture of Tween-80 and Spin-80 at a mass ratio of 6:4 (total emulsifier amount is 5% of the tung oil mass). Emulsify at 10,000 r / min for 10 min to prepare an aqueous tung oil emulsion with a solid content of 60%. Add the aqueous tung oil emulsion to the dispersion obtained in Step 2 and stir at 400 r / min for 20 min until homogeneous; the solid content of tung oil accounts for 45.8% of the total solid content of all components.

[0044] Step 4: Add zinc borate ( 0.6 parts by mass (4.6% of the total solid content of each component) were added to the dispersion obtained in step 3, and stirred at 400 r / min for 20 min to ensure thorough dispersion.

[0045] Step (5): The dispersion obtained in Step 4 is concentrated by rotary evaporation at 60℃ and reduced pressure of -0.090 MPa to a solid content of over 18%. The solid content is then adjusted to 35% (mass fraction) with deionized water. The mixture is then ground and dispersed using a three-roll mill until the particle size D50 of each component is 3 μm, thus obtaining the modified graphene conductive ink. The finished product is coated onto a cotton fabric substrate and allowed to air-dry for 8 hours at 35℃ to complete the self-curing process.

[0046] Example 4

[0047] This embodiment discloses a method for preparing modified graphene materials, which includes the following steps:

[0048] Step 1: Dissolve 2.5 parts by mass of sodium lignosulfonate (8% by mass of sulfonic acid groups) in deionized water to prepare an 8% sodium lignosulfonate aqueous solution. Disperse 1 part by mass of graphene oxide (3-8 μm in diameter, C / O atomic ratio 2.5:1) in an appropriate amount of deionized water and treat with ultrasound at 350 W for 40 min to prepare a uniform aqueous dispersion of graphene oxide with a concentration of 4 mg / mL. Mix the sodium lignosulfonate aqueous solution with the graphene oxide aqueous dispersion and stir at 400 r / min at 20℃ for 1.5 hours to obtain a sodium lignosulfonate-modified graphene oxide aqueous dispersion.

[0049] Step 2: Add 0.8 parts by mass of rosin acid to a 7% sodium hydroxide aqueous solution, with a molar ratio of sodium hydroxide to rosin acid of 1.08:1. Stir at 55°C for 50 min to completely saponify the rosin acid, obtaining a sodium abirate aqueous solution. After cooling the sodium abirate solution to room temperature, add it to the dispersion obtained in Step 1, and stir at 350 r / min for 25 min until homogeneous.

[0050] Step 3: Add 5 parts by mass of tung oil to deionized water containing a mixture of Tween-80 and Spandex-80 at a mass ratio of 6:4 (total emulsifier amount is 4.5% of the tung oil mass). Emulsify at 9000 r / min for 12 min to prepare an aqueous tung oil emulsion with a solid content of 55%. Add the aqueous tung oil emulsion to the dispersion obtained in Step 2 and stir at 350 r / min for 25 min until homogeneous; the solid content of tung oil accounts for 51.5% of the total solid content of all components.

[0051] Step 4: Add zinc borate ( 0.4 parts by mass (4.1% of the total solid content of each component) were added to the dispersion obtained in step 3, and stirred at 350 r / min for 25 min to ensure thorough dispersion.

[0052] Step 5: The dispersion obtained in Step 4 is concentrated by rotary evaporation at 45℃ and reduced pressure of -0.085 MPa to a solid content of over 18%. The solid content is then adjusted to 30% (mass fraction) with deionized water. The mixture is then milled and dispersed using a three-roll mill until the particle size D50 of each component is 2.5 μm, yielding the modified graphene conductive ink. This finished product is coated onto an epoxy glass cloth (FR4) substrate and allowed to self-cur at 28℃ for 20 hours.

[0053] Example 5

[0054] This embodiment discloses a method for preparing modified graphene materials, including the following specific implementation steps:

[0055] Step 1: Modification treatment of graphene oxide by sodium lignosulfonate

[0056] Sodium lignosulfonate (3 parts by mass, 10% sulfonic acid group content) was dissolved in deionized water to prepare a 10% sodium lignosulfonate aqueous solution. Graphene oxide (1 part by mass, sheet diameter 5–10 μm, C / O atomic ratio 3:1) was dispersed in an appropriate amount of deionized water and ultrasonically treated (300 W, 45 min) to prepare a homogeneous aqueous dispersion of graphene oxide with a concentration of 3 mg / mL. The sodium lignosulfonate aqueous solution and the graphene oxide aqueous dispersion were mixed and stirred at 300 r / min for 1.5 hours at 25°C to obtain a sodium lignosulfonate-modified graphene oxide aqueous dispersion.

[0057] Sodium lignosulfonate is a byproduct extracted from the sulfite pulping wastewater of the papermaking industry. Its molecules are composed of repeating phenylpropane units polymerized via ether or carbon-carbon bonds, with each phenylpropane unit containing a benzene ring (a 6π-electron aromatic system). Graphene oxide is prepared by chemically oxidizing and exfoliating graphite, and some regions on its sheet surface still retain an aromatic six-membered carbon ring network (a large π-conjugated system on the graphene basal surface). The π-π stacking adsorption between the benzene ring π-electron system in sodium lignosulfonate and the large π-electron system on the graphene basal surface allows sodium lignosulfonate to firmly adhere to the graphene surface via non-covalent bonds; after attachment, the sulfonic acid groups (… The strong electronegativity of graphene (which completely dissociates into anions in neutral aqueous solution) generates a continuous electrostatic repulsion between adjacent graphene sheets, isolating the sheets from each other and preventing them from agglomerating and settling. This allows for the stable dispersion of graphene in aqueous media without the use of synthetic surfactants.

[0058] Step 2: Saponification of rosin acid and establishment of a hydrophobic layer on the graphene surface

[0059] A rosin acid (1 part by mass) was added to a 6% sodium hydroxide aqueous solution, with a molar ratio of sodium hydroxide to rosin acid of 1.07:1. The mixture was stirred at 60°C for 45 min to completely saponify the rosin acid, yielding an aqueous solution of sodium rosinate (rosin soap). After cooling the rosin soap aqueous solution to room temperature, it was added to the sodium lignosulfonate-modified graphene oxide aqueous dispersion obtained in step 1. The mixture was stirred at 300 r / min for 30 min at room temperature until homogeneous, yielding an aqueous dispersion of modified graphene containing rosin soap.

[0060] Abietic acid (with abietic acid as the main component, molecular formula) This is a solid resin acid, insoluble in water, and must be saponified with sodium hydroxide to form a water-soluble sodium rosinate before it can be introduced into an aqueous system; the saponification reaction is as follows: Rosin tannin ( The molecular skeleton of the compound is a tricyclic phenanthrene structure (composed of three fused six-membered carbon rings). This tricyclic skeleton is highly hydrophobic and adheres to the graphene oxide substrate modified with sodium lignosulfonate through hydrophobic interactions, establishing a hydrophobic coating layer on the graphene surface. This reduces the affinity of the graphene surface for water molecules, laying the foundation for the water resistance of the cured coating. When zinc borate is added in step 4, the zinc borate releases… A metathesis reaction occurs with rosin acid to generate zinc rosinate, thereby immobilizing rosin acid in the film-forming system through chemical bonding.

[0061] Step 3: Formulation of tung oil emulsion and establishment of a room-temperature self-drying cross-linking film-forming system

[0062] Tung oil (4 parts by mass) was added to deionized water containing a composite emulsifier (4% by mass of tung oil) of Tween-80 (polysorbate-80) and Span-80 (sorbitan monooleate) in a mass ratio of 6:4. The mixture was then emulsified under high-speed shear (8000 r / min, emulsification time 15 min) to prepare an aqueous tung oil emulsion with a solid content of 50% (mass fraction). The aqueous tung oil emulsion was added to the modified graphene aqueous dispersion containing rosin soap obtained in step 2, and stirred at 300 r / min for 30 min until homogeneous. Based on solid content, tung oil accounted for approximately 43% (mass fraction) of the total solid content of all components, resulting in a modified graphene composite dispersion containing tung oil emulsion.

[0063] Tung oil is a natural plant oil extracted from the seeds of the tung tree (Vernicia fordii). Its main component, α-tunglicic acid (accounting for approximately 80% of the total tung oil content), is 9,11,13-octadecanoic acid, containing three sequentially conjugated carbon-carbon double bonds, i.e., a (9Z,11E,13E) conjugated triene configuration. These conjugated triene double bonds are highly sensitive to air oxidation; when the finished product is coated onto a substrate and exposed to oxygen in the air at room temperature (15–35°C), a free radical chain oxidation polymerization reaction is initiated, resulting in a high-molecular-weight three-dimensional cross-linked polymer with C-C bonds as the main connecting bonds. In the above-mentioned free radical oxidative polymerization process, the phenolic hydroxyl groups attached to the benzene ring of the sodium lignosulfonate chain are oxidized to phenolic oxygen free radicals under the hydrogen abstraction action of free radicals present in the system. Then, they undergo free radical coupling reaction with the carbon free radicals on the tung oil polymer chain, embedding the sodium lignosulfonate-graphene composite unit into the tung oil crosslinked polymer chain through carbon-oxygen covalent bonds (CO bonds), so that the graphene is fixed in the organic film-forming system in a covalent bond manner.

[0064] Step 4: Addition of zinc borate and establishment of the double cross-linked network

[0065] Zinc borate ( Add 0.3 parts by mass to the modified graphene composite dispersion containing tung oil emulsion obtained in step 3, and stir at 300 r / min for 30 min at room temperature to fully disperse the zinc borate particles in the system, thereby obtaining a modified graphene composite dispersion containing all functional components.

[0066] Zinc borate hydrolyzes in an aqueous medium, releasing zinc ions ( ) and borate ions ( ). By coordinating with the peroxide intermediates and oxygen-containing groups generated during the auto-oxidation of tung oil via Lewis acid, the activation energy for further cross-linking reactions of the oxidative polymerization intermediates is reduced, accelerating the formation rate of the cross-linked network of the tung oil oxidative polymer, and shortening the self-drying curing time of the finished product at 15–35°C to 8–36 hours; simultaneously… With the sodium rosinate introduced in step 2 ( Double displacement reaction occurs: This generates zinc rosinate, which is poorly soluble in water, enhancing the adhesion and hydrophobicity of the cured coating. An esterification reaction occurs with the aliphatic hydroxyl groups on the sodium lignosulfonate chain segments, generating BOC borate covalent crosslinks, thus establishing an inorganic borate crosslink network between the sodium lignosulfonate-graphene composite units. After coating and curing, the coating contains both a tung oil free radical oxidizing polymer crosslink network (with C-C bonds as the main nodes) and an inorganic borate crosslink network (with BOC bonds as nodes). The two work together to solidify the sodium lignosulfonate-modified graphene, ensuring that the conductive network of the cured coating does not break under water immersion conditions.

[0067] Step 5: Finished Product Preparation

[0068] The modified graphene composite dispersion containing all functional components obtained in step 4 is concentrated by rotary evaporation under reduced pressure conditions of 50°C and -0.085 MPa until the solid content reaches more than 18%. The solid content is then finely adjusted to 28% (mass fraction) with deionized water, with graphene accounting for no less than 10% of the solid content by mass. The dispersion is then milled and dispersed using a three-roll mill until the particle size D50 of each component is no greater than 3 μm, yielding the modified graphene conductive ink. This finished product is coated onto a substrate (such as PET film, paper, or fabric) and allowed to self-cur within 12 hours at room temperature (25°C). The resulting cured coating has a pencil hardness of 2H and a sheet resistance of approximately 350 Ω, making it suitable for printing conductive circuits, electromagnetic shielding coatings, or conductive layers for flexible sensors.

[0069] Experimental verification

[0070] Experiment 1: Comparison of Conductivity of Cured Coatings

[0071] 1. Experimental Objective

[0072] The effect of replacing synthetic surfactants (sodium dodecyl sulfate, Triton X-100) with sodium lignosulfonate (LS) on the sheet resistance of the cured coating was verified, demonstrating that the π-π conjugated adsorption mechanism of LS can eliminate the residual surfactant insulating layer and significantly improve conductivity.

[0073] 2. Sample preparation

[0074] According to the complete preparation method of this invention, three groups of modified graphene conductive inks were prepared respectively. The only difference between the three groups of preparation methods is the type of dispersant used in step 1; the other steps and parameters are exactly the same.

[0075] Control group A1: Sodium dodecyl sulfate (SDS, 3 parts by mass) was used to replace sodium lignosulfonate to disperse graphene oxide (GO, 1 part by mass, sheet diameter 5-10 μm, C / O atomic ratio 3:1). The dosage and preparation steps of the remaining components (1 part by mass of rosin acid, 4 parts by mass of tung oil emulsion (solid content 50%), 0.5 parts by mass of zinc borate) were the same as those of experimental group B, but the solid content was adjusted to 28%.

[0076] Control group A2: Triton X-100 (3 parts by mass) was used to replace sodium lignosulfonate dispersed graphene oxide (GO, 1 part by mass, sheet diameter 5-10 μm, C / O atomic ratio 3:1). The dosage and preparation steps of the remaining components (1 part by mass of rosin acid, 4 parts by mass of tung oil emulsion (solid content 50%), 0.5 parts by mass of zinc borate) were the same as those of experimental group B, but the solid content was adjusted to 28%.

[0077] Experimental Group B: Modified graphene conductive ink was prepared according to the preparation method of Example 1 using graphene oxide (GO, 1 part by mass, sheet diameter 5-10 μm, C / O atomic ratio 3:1), sodium lignosulfonate (LS, 3 parts by mass, sulfonic acid content 10%), rosin acid (1 part by mass), tung oil (4 parts by mass, emulsion solid content 50%), and zinc borate (0.5 parts by mass), with the solid content adjusted to 28%.

[0078] All three groups of samples were coated on PET film (125 μm thick) using a wire bar coater. The wet film thickness was about 80 μm. The samples were then naturally dried at 25℃ and 55% relative humidity for 24 hours. The dry film thickness of the cured coating was measured to be about 17 μm.

[0079] 3. Testing Methods

[0080] Sheet resistance The four-probe method (probe spacing 1 mm) was used for measurement. Five different locations were measured for each sample group, and the average value was taken. The degree of curing was characterized by the pencil hardness test (GB / T 6739). All three groups of samples were cured for 24 h under the same conditions (25℃, relative humidity 55%±5%, natural contact with air). The pencil hardness test was performed after 24 h of curing to confirm that the degree of curing of the three groups was comparable and to eliminate the interference of different curing degrees on conductivity.

[0081] 4. Experimental Results

[0082] Table 1. Effect of different dispersants on the sheet resistance of the cured coating

[0083]

[0084] Compared with group A1 (SDS), the sheet resistance of experimental group B decreased by 87.5%; compared with group A2 (Triton X-100), it decreased by 84.1%. The pencil hardness of all three groups of samples was 2H (consistent with the results obtained by experimental group C in Table 2 after curing at 25℃ for 24 h), indicating that the degree of curing was similar, and the difference in conductivity was due to the type of dispersant rather than the degree of curing.

[0085] 5. Results Analysis

[0086] SDS and Triton X-100 are physically adsorbed onto the graphene sheet surface. Their hydrocarbon segments and hydrophilic head groups remain at the contact points of the conductive network after curing, forming an insulating spacer layer and significantly increasing contact resistance. Sodium lignosulfonate's phenylpropane backbone forms a strong conjugated adsorption with the graphene aromatic plane through π-π stacking. During free radical oxidative polymerization, the phenolic hydroxyl groups of LS are oxidized to phenoxy radicals, which then couple with tung oil carbon radicals, covalently embedding into the tung oil polymer network. After curing, these radicals cannot migrate freely and do not form an insulating layer between the graphene sheets, thus having minimal interference with the conductive network of the coating. Figure 1 It can be seen that the standard deviation of the sheet resistance of experimental group B (28 Ω) is significantly smaller than that of the control group (183, 154 Ω), indicating that the LS modified system has better conductivity uniformity.

[0087] The SEM morphology of sample B in experimental group B is shown below. Figure 4 The LS-rGO sheets are flat and uniformly stacked, while ordinary rGO shows obvious agglomeration, which is consistent with the results of this experiment showing that the LS group has better conductivity uniformity (smaller standard deviation).

[0088] Experiment 2: Verification of self-curing performance at room temperature and suitability for heat-sensitive flexible substrates

[0089] 1. Experimental Objective

[0090] The purpose of this invention is to verify whether the conductive ink of the present invention can be cured by free radical oxidative polymerization of the tung oil conjugated triene system at room temperature of 15-35°C, and to evaluate its applicability to heat-sensitive PET substrates by comparing it with traditional epoxy conductive inks that require high-temperature baking (120°C).

[0091] 2. Sample preparation

[0092] Experimental Group C (Invention): Modified graphene conductive ink was prepared according to the preparation method of Example 1 using graphene oxide (1 part by mass, sheet diameter 5-10 μm, C / O atomic ratio 3:1), sodium lignosulfonate (3 parts by mass, sulfonic acid content 10%), rosin acid (1 part by mass), tung oil (4 parts by mass, emulsion solid content 50%), and zinc borate (0.5 parts by mass), with the solid content adjusted to 28%.

[0093] Control group D (traditional high-temperature curing system): The amounts of graphene (1 part by mass, sheet diameter 5-10 μm, C / O atomic ratio 3:1), sodium lignosulfonate (3 parts by mass, sulfonic acid content 10%), rosin acid (1 part by mass), and zinc borate (0.5 parts by mass) were the same as in experimental group C. Aqueous epoxy emulsion (48% solid content, 4 parts by mass, equivalent to the solid content of tung oil) was used instead of tung oil emulsion. Aqueous fatty amine curing agent was added at a mass ratio of epoxy resin to curing agent of 5:1. Conductive ink was prepared according to the formula with a solid content of 28%. It required baking at 120℃ for 30 min to achieve complete cross-linking and curing. This group differed only in the film-forming resin system (tung oil air-drying at room temperature → epoxy high-temperature baking); all other components were completely identical to experimental group C, ensuring single-variable control.

[0094] Three substrates were selected: glass plate (high temperature resistant, used as a benchmark), PET film (125 μm, heat distortion temperature approximately 80℃, a thermosensitive substrate), and coated paper (230 g / m²). A wet film thickness of 80 μm was applied, and after curing at the required temperature and time for each system, pencil hardness and sheet resistance were measured.

[0095] 3. Monitoring of the curing process

[0096] In experimental group C (the present invention), samples were taken at 1, 2, 4, 6, 8, 10, 12 and 24 hours under the conditions of 25℃ and 55%±5% relative humidity. The curing process was characterized by pencil hardness and the integrity of the conductive network was measured by sheet resistance.

[0097] Table 2. Changes in pencil hardness and sheet resistance over time during room temperature curing in Experimental Group C (this invention).

[0098]

[0099] Figure 2 The curve showing the change of sheet resistance of experimental group C (the present invention) with curing time.

[0100] 4. Comparison of substrate applicability

[0101] Table 3. Comparison of comprehensive performance of experimental group C (this invention, cured at 25℃ for 12 h) and control group D (traditional system, cured at 120℃ for 30 min) on different substrates.

[0102]

[0103] 5. Results Analysis

[0104] Table 2 shows that the conductive ink of this invention achieves a pencil hardness of H after 8 hours of natural drying at 25℃, with a sheet resistance stable below 368 Ω; after 12 hours, the sheet resistance tends to stabilize at approximately 348 Ω, achieving a pencil hardness of 2H, meeting practical application requirements. Table 3 shows that the traditional high-temperature curing system (120℃, 30 min) causes irreversible thermal damage to PET film and coated paper substrates, making it completely unsuitable for heat-sensitive flexible substrates; the room-temperature curing system of this invention maintains substrate integrity and excellent adhesion on both PET and paper substrates. The sheet resistance of this invention on glass plates (348 Ω) is slightly higher than that of the traditional high-temperature system (280 Ω). This is because the 120℃ high-temperature baking helps the epoxy resin to fully cross-link, allowing the graphene sheets to form a tighter contact during curing and shrinkage; however, the usability of this invention on heat-sensitive flexible substrates (PET, paper) is something that the traditional high-temperature system simply cannot achieve, and its expanded application value far outweighs the impact of this difference in conductivity.

[0105] Experiment 3: Conductivity stability test of cured coating under water immersion conditions

[0106] 1. Experimental Objective

[0107] The invention's dual crosslinking network (synergistic crosslinking of tung oil free radical oxidative polymerization network and borate ester inorganic crosslinking network) was used to verify the conductive stability of the cured coating under long-term water immersion conditions. This was compared with conductive coatings based on a single water-based acrylic resin system, demonstrating the effectiveness of the water resistance mechanism.

[0108] 2. Sample preparation

[0109] Experimental Group E (Invention): Modified graphene conductive ink was prepared according to the preparation method of Example 4 using graphene oxide (1 part by mass, sheet diameter 3-8 μm, C / O atomic ratio 2.5:1), sodium lignosulfonate (2.5 parts by mass, sulfonic acid content 8%), rosin acid (0.8 parts by mass), tung oil (5 parts by mass, emulsion solid content 55%), and zinc borate (0.4 parts by mass), with the solid content adjusted to 30%. It was coated on epoxy glass cloth board (FR4, 1.6 mm thick) and cured at 25°C for 24 h, with a dry film thickness of about 8 μm.

[0110] Control group F (single aqueous acrylic system): The amounts of graphene (1 part by mass, sheet diameter 3-8 μm, C / O atomic ratio 2.5:1), sodium lignosulfonate (2.5 parts by mass, sulfonic acid content 8%), and rosin acid (0.8 parts by mass) were the same as those in experimental group E. Aqueous acrylic emulsion (solid content 48%, Tg about 20℃, minimum film-forming temperature about 15℃, 5 parts by mass, replacing tung oil emulsion in experimental group E) was used instead of tung oil emulsion as the film-forming resin. Zinc borate was not added. The formulation was prepared according to a solid content of 30%. The mixture was coated on the same type of FR4 board and dried at 25℃ for 48 h to form a film and cure. The dry film thickness was about 8 μm.

[0111] 3. Water immersion test conditions

[0112] Cut the cured sample into 5 cm × 5 cm pieces and immerse them completely in 25°C deionized water. Remove the pieces after immersion for 0 (before immersion), 24, 72, 168, and 336 hours, respectively. Quickly absorb the surface moisture with filter paper (without applying pressure) and immediately measure the sheet resistance using the four-probe method. After the measurement, put the pieces back into the immersion water and continue testing.

[0113] 4. Experimental Results

[0114] Table 4. Changes in block resistance with immersion time during water immersion test.

[0115]

[0116] 5. Results Analysis

[0117] From Table 4 and Figure 3 It can be seen that after 336 hours of continuous water immersion, the sheet resistance of experimental group E (the present invention) only increased from 350 Ω to 415 Ω, an increase of only 18.6%, and the conductivity remained basically stable. In contrast, the sheet resistance of control group F (a single water-based acrylic system) increased to 1250 Ω (an increase of 160.4%) after 24 hours of water immersion and to 18500 Ω after 336 hours, an increase of 3754.2%, indicating a severe deterioration in conductivity.

[0118] The superior water resistance of the coating of this invention stems from the synergistic effect of a triple protection mechanism: First, the free radical oxidative polymerization of tung oil forms a highly cross-linked C / C bond three-dimensional network, a pure hydrocarbon skeleton free of hydrolysis-sensitive groups such as ester and ether bonds. Water molecules have difficulty disrupting the polymer network structure, resulting in extremely low water absorption and swelling. Second, the borate ions generated from the hydrolysis of zinc borate undergo esterification with the aliphatic hydroxyl groups on the sodium lignosulfonate segments, forming a BOC inorganic borate ester cross-linked network. This further solidifies the conductive graphene sheets, blocking the path of water molecules penetrating through the gaps between the graphene sheets. Third, the large molecular skeleton of sodium lignosulfonate is covalently embedded in the tung oil polymer network and cannot migrate or dissolve from the network. Therefore, although the sulfonate groups absorb a small amount of water, they do not disrupt the macroscopic continuity of the conductive network. The combined effect of these three protection mechanisms ensures that the conductive coating of this invention maintains stable conductivity under water immersion conditions, meeting the requirements for outdoor and humid environments.

[0119] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for preparing a modified graphene conductive ink material, characterized in that, Includes the following steps: Step 1: Mix and stir sodium lignosulfonate with graphene oxide aqueous dispersion. The benzene ring of the phenylpropane unit of sodium lignosulfonate is adsorbed onto the graphene oxide substrate through π-π stacking. The sulfonic acid group provides electrostatic repulsion, thus obtaining sodium lignosulfonate modified graphene oxide aqueous dispersion. Step 2: Saponify rosin acid with sodium hydroxide to prepare sodium rosinate solution, add it to the dispersion obtained in step 1 and mix evenly. Rosin acid ions are attached to the surface of graphene oxide with a tricyclic phenanthrene hydrophobic framework. Step 3: Add the aqueous tung oil emulsion to the dispersion obtained in Step 2 and mix thoroughly; Step 4: Add zinc borate, stir and disperse. Zinc ions metathesis with sodium rosinate to form zinc rosinate, and borate ions form covalent cross-linked bonds of borate ester with the aliphatic hydroxyl groups of sodium lignin sulfonate segments. Adjust the solid content and disperse by grinding to obtain modified graphene conductive ink material.

2. The preparation method according to claim 1, characterized in that, Based on 1 part by mass of graphene oxide, the amount of sodium lignosulfonate is 2 to 4 parts by mass, the amount of rosin acid is 0.5 to 1.5 parts by mass, the amount of tung oil is 3 to 6 parts by mass, and the amount of zinc borate is 0.2 to 0.6 parts by mass.

3. The preparation method according to claim 2, characterized in that, The graphene oxide has a sheet diameter of 1–20 μm and a C / O atomic ratio of 2:1–4:1; the sodium lignosulfonate has a sulfonic acid group content of 6%–14%.

4. The preparation method according to claim 1, characterized in that, In step 1, graphene oxide is dispersed in deionized water and treated with ultrasound at a power of 200-400 W for 30-60 min to prepare an aqueous dispersion with a concentration of 2-5 mg / mL; sodium lignosulfonate is prepared into an aqueous solution with a mass concentration of 5%-15% and then mixed with the graphene oxide aqueous dispersion, and stirred at 15-35℃ and a speed of 200-500 r / min for 1-2 hours.

5. The preparation method according to claim 1, characterized in that, In step 2, the molar ratio of sodium hydroxide to rosin acid is 1.05:1 to 1.1:1, the saponification reaction temperature is 50 to 70°C, and the time is 30 to 60 min. After the sodium rosin acid solution is cooled to room temperature, it is added to the dispersion obtained in step 1 and stirred at 200 to 400 r / min for 20 to 40 min.

6. The preparation method according to claim 1, characterized in that, In step 3, the preparation of the aqueous tung oil emulsion uses an emulsifier made by compounding Tween-80 and Spande-80 at a mass ratio of 6:

4. The amount of emulsifier is 3% to 5% of the mass of tung oil. The high-speed shear emulsification speed is 6000 to 10000 r / min and the time is 10 to 20 min. The solid content of the tung oil emulsion is 40% to 60%.

7. The preparation method according to claim 1, characterized in that, In step 3, the aqueous tung oil emulsion is mixed with the dispersion obtained in step 2 and stirred at 200-400 r / min for 20-40 min; based on solid content, tung oil accounts for 40%-55% of the total solid content of each component.

8. The preparation method according to claim 1, characterized in that, In step 4, the chemical formula of zinc borate is: It accounts for 4% to 8% of the total solid content of each component; after addition, stir at 200 to 400 r / min for 20 to 40 min.

9. The preparation method according to claim 1, characterized in that, The solid content is adjusted to 20%–35% with deionized water, of which graphene accounts for no less than 10% of the solid content by mass; the particles are ground and dispersed so that the particle size D50 of each component is no greater than 5 μm.

10. A modified graphene conductive ink material, characterized in that, The modified graphene conductive ink material is prepared by the preparation method of any one of claims 1 to 9, with a solid content of 20% to 35%, and the mass fraction of graphene oxide in the solid content is not less than 10%, and the particle size D50 of each component is not greater than 5 μm; the modified graphene material is coated at room temperature of 15 to 35°C and exposed to air for 8 to 36 hours to complete self-drying curing. After curing, the coating contains both tung oil free radical oxidized polymer crosslinking network and borate ester crosslinking network, and sodium lignosulfonate modified graphene is embedded in the tung oil free radical oxidized polymer by carbon-oxygen covalent bonds.

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