Magnetic ink for RFID (Radio Frequency Identification Device) electronic tag and preparation method of magnetic ink

Abstract

The invention relates to the technical field of RFID equipment manufacturing, novel magnetic ink and the like, and provides magnetic ink for an RFID equipment electronic tag and a preparation method of the magnetic ink. The magnetic ink is prepared from a bisphenol A epoxy acrylate prepolymer, modified polyester resin, polyamide-imide resin, nanoscale soft magnetic ferrite powder, silver-coated flaky copper powder, a low-polymerization-degree polyurethane compatibilizer, a gamma-glycidyl ether oxypropyl triethoxy silane coupling agent, a photoinitiator, an antioxidant, a flatting agent and an active diluting monomer. The D50 of the ferrite powder is 0.1-0.3 m, the surface of the ferrite powder is subjected to phosphate-silane dual coating treatment, the magnetic conductivity after ultraviolet curing is 20-60, and the loss tangent value is smaller than or equal to 0.05. The printing ink has excellent magnetic performance, conductivity and flexibility, can effectively improve the electromagnetic response, crack resistance and printing precision of labels, and is suitable for printing high-Q-value narrow-linewidth antenna patterns.

Description

Technical Field

[0001] The present invention relates to the technical fields of RFID equipment manufacturing, new magnetic inks, and the like, and in particular to a magnetic ink for electronic tags of RFID equipment and a preparation method thereof. Background Art

[0002] In the process of manufacturing electronic tags for RFID devices, it is necessary to cover the back of a PET film sheet with metal foil (copper or aluminum), and then print magnetic ink on the antenna pattern area of the metal foil on the back to optimize the electromagnetic performance of the antenna and improve the reliability and adaptability of the tag. However, existing magnetic ink formulas mostly use micron-sized ferrite powders with a wide particle size distribution. They are prone to hysteresis loss due to agglomeration, resulting in low magnetic permeability (µʹ<15) in RFID operating frequency bands such as 13.56MHz and 860-960MHz. This leads to insufficient magnetic permeability and high frequency loss. Moreover, in order to obtain a medium viscosity suitable for silk screen or gravure printing, a large amount of low-viscosity active diluent monomers needs to be added to the existing formula. This causes the PET and metal foil composite substrate to be easily torn when the shrinkage rate after UV curing is greater than 7%, reducing the label's reliability in resisting bending and dropping. In addition, the resin system in the existing magnetic ink formula has insufficient adhesion to the metal foil interface, which is prone to curling or cracking. In addition, the hiding power of existing formulas relies on high content of carbon black or magnetic pigments, which causes the viscosity of the system to soar and the minimum printable line width to be too large (>100µm), making it difficult to meet the printing process requirements of high-Q value fine antenna patterns with narrow line width (<100µm line width).

[0003] In summary, the existing technology has technical problems such as insufficient magnetic permeability of electronic tags, high frequency loss, low bending and falling reliability of tags, easy curling or cracking, large minimum printable line width, and difficulty in meeting the printing process requirements of narrow line width of high-Q value fine antenna patterns. Summary of the Invention

[0004] In response to the shortcomings of the above-mentioned prior art, the present invention provides a magnetic ink for RFID device electronic tags and a preparation method thereof, so as to improve the magnetic permeability of the electronic tags, the bending and falling reliability, reduce the frequency loss of the tags, avoid curling or cracking, reduce the minimum printable line width, and meet the printing process requirements of high-Q value fine antenna patterns with narrow line width.

[0005] In a first aspect, the present invention provides a magnetic ink for an electronic tag of an RFID device, comprising, by weight percentage: 20-40% bisphenol A epoxy acrylate prepolymer, 5-20% modified polyester resin, 3-15% polyamide-imide resin, 15-35% nano-scale soft magnetic ferrite powder, 2-10% silver-coated flaky copper powder, 1-8% low-polymerization degree polyurethane compatibilizer, 0.2-2% γ-glycidyloxypropyl triethoxysilane coupling agent, 0.5-5% bis(2,4-dimethylbenzoyl)diphenylphosphine oxide photoinitiator, 0.1-1% hindered phenol antioxidant, 0.1-1% polyether modified acrylate leveling agent, and 5-15% tripropylene glycol diacrylate active diluent monomer; wherein the D of the nano-scale soft magnetic ferrite powder is 0. 50 The thickness of the magnetic field is 0.1-0.3µm, and the surface is double-coated with phosphate-silane. After UV curing, it provides an initial magnetic permeability of 20-60 and maintains a loss tangent value of ≤0.05 in the 13.56MHz frequency band.

[0006] In a second aspect, the present invention provides a method for preparing a magnetic ink for an electronic tag of an RFID device, comprising: Raw material pretreatment steps: Nano-scale soft ferrite powder and silver-coated flaky copper powder were dried at 60°C and 40% RH for 2 h, cooled to 25°C, and placed in an inert nitrogen box for standby use; Coupling activation step: adding 0.5-1.5 wt% of γ-glycidyloxypropyltriethoxysilane to a 40 wt% premix of bisphenol A epoxy acrylate prepolymer and tripropylene glycol diacrylate, and reacting at 45°C for 30 minutes to form an epoxy-active interface layer; Efficient dispersion step: using nano-bead mill, rotor linear speed 12ms -1 The powder in the raw material pretreatment step and the interface layer mixed slurry obtained in the coupling activation step were ground for 20 minutes to make the D of the nano-scale soft ferrite powder 50 D of 0.1-0.3µm, silver-coated flake copper powder 50 ≤8µm, and the dispersion particle size variance ≤0.1; Resin compatibilization and rheological control steps: Modified polyester resin, polyamide-imide resin, and low-polymerization degree polyurethane compatibilizer were added in sequence at 30-40°C. Degassing was performed using a dual planetary vacuum mixer at -0.09 MPa for 15 minutes to adjust the system viscosity to 4±0.5 Pa·s. Functional additive fine-tuning steps: adding a photoinitiator, a hindered phenol antioxidant, and a leveling agent under slow stirring at room temperature, standing in vacuum for 30 minutes to remove residual bubbles, filtering with a 0.2µm stainless steel filter, and packaging with nitrogen to obtain the finished magnetic ink.

[0007] Compared with the prior art, the present invention has the following beneficial effects: The invention provides a magnetic ink for an electronic tag of an RFID device and a preparation method thereof. The magnetic ink comprises, by weight percentage, 20-40% of bisphenol A epoxy acrylate prepolymer, 5-20% of modified polyester resin, 3-15% of polyamide-imide resin, 15-35% of nano-scale soft magnetic ferrite powder, 2-10% of silver-coated flaky copper powder, 1-8% of a low-polymerization-degree polyurethane compatibilizer, 0.2-2% of a γ-glycidyloxypropyl triethoxysilane coupling agent, 0.5-5% of a bis(2,4-dimethylbenzoyl)diphenylphosphine oxide photoinitiator, 0.1-1% of a hindered phenol antioxidant, 0.1-1% of a polyether-modified acrylate leveling agent, and 5-15% of a tripropylene glycol diacrylate active diluent monomer; wherein the D of the nano-scale soft magnetic ferrite powder is 0. 50 The magnetic ink is 0.1-0.3µm thick and has a double phosphate-silane coating. After UV curing, it provides an initial magnetic permeability of 20-60% and maintains a loss tangent of ≤0.05 in the 13.56MHz frequency band. This magnetic ink improves the electronic tag's magnetic permeability, improves its reliability against bending and drops, reduces frequency loss, prevents curling or cracking, and reduces the minimum printable line width, meeting the printing process requirements for high-Q fine antenna patterns with narrow line widths. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute an undue limitation of the present invention. Some specific embodiments of the present invention will be described in detail in an illustrative and non-restrictive manner with reference to the drawings. The same reference numerals in the drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 The present invention is a flow chart of a method for preparing magnetic ink for electronic tags of RFID devices according to an embodiment of the present invention. DETAILED DESCRIPTION

[0009] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0010] Example 1 See also Figure 1The present embodiment provides a magnetic ink for RFID device electronic tags, which comprises, by weight percentage: 20-40% bisphenol A epoxy acrylate prepolymer, 5-20% modified polyester resin, 3-15% polyamide-imide resin, 15-35% nano-scale soft magnetic ferrite powder, 2-10% silver-coated flaky copper powder, 1-8% low-polymerization degree polyurethane compatibilizer, 0.2-2% γ-glycidyloxypropyl triethoxysilane coupling agent, 0.5-5% bis(2,4-dimethylbenzoyl)diphenylphosphine oxide photoinitiator, 0.1-1% hindered phenol antioxidant, 0.1-1% polyether modified acrylate leveling agent and 5-15% tripropylene glycol diacrylate active diluent monomer; wherein the D of the nano-scale soft magnetic ferrite powder is 0. 50 The thickness of the magnetic field is 0.1-0.3µm, and the surface is double-coated with phosphate-silane. After UV curing, it provides an initial magnetic permeability of 20-60 and maintains a loss tangent value of ≤0.05 in the 13.56MHz frequency band.

[0011] It should be noted that, in this embodiment, nano-scale soft ferrite powder (D 50 =0.1-0.3µm), significantly improving magnetic permeability (reaching 20-60) and reducing frequency loss (tanδ ≤ 0.05). Simultaneously, the nanoscale soft ferrite powder is double-coated with phosphate and silane to enhance its dispersion stability and interfacial adhesion in the resin system. The resin system incorporates a synergistic film-forming structure of bisphenol A epoxy acrylate, polyester resin, and polyamide-imide resin, enhancing flexibility and adhesion while maintaining film strength after UV curing. Silver-coated flaky copper powder, with its excellent conductivity and flaky structure, creates a complementary magnetic conductivity path, improving the high-frequency response of the antenna pattern. Furthermore, a low-polymerization polyurethane compatibilizer, photoinitiator, antioxidant, leveling agent, and reactive diluent monomer regulate and enhance ink viscosity, cure shrinkage, and environmental stability. The overall formulation closely matches the process requirements of the PET + metal foil composite substrate, resulting in a highly adaptable and reliable magnetic functional ink.

[0012] Example 1: This example prepares a magnetic ink for RFID electronic tags. The components are as follows by weight: bisphenol A epoxy acrylate prepolymer: 32%; modified polyester resin: 10%; polyamide-imide resin: 5%; nano-scale soft magnetic ferrite powder (Ni 0.5 Zn 0.5 Fe2O4, D 50=0.2µm, surface coated with phosphate-silane): 25%; silver-coated flake copper powder (flake diameter 10µm, aspect ratio 80): 5%; low-polymerization degree polyurethane compatibilizer (Mn=1000): 5%; γ-glycidyloxypropyltriethoxysilane: 1%; bis(2,4-dimethylbenzoyl)diphenylphosphine oxide photoinitiator: 3%; hindered phenol antioxidant (IRGANOX 1010): 0.5%; polyether-modified acrylate leveling agent: 0.5%; tripropylene glycol diacrylate reactive diluent: 13%. The above ink samples were screen-printed onto a PET+copper foil substrate with a film thickness of approximately 10µm. After curing under 395nm LED UV light for 2 seconds, the test results showed: initial magnetic permeability µ': 45 (13.56MHz, HP 4291B); loss tangent tanδ: 0.035; Q value: 31; minimum line width of the printed pattern: 70µm; and resistance change of <5% after 2000 180° bends.

[0013] Example 2: This example prepares a magnetic ink for RFID electronic tags. The components are as follows by weight: bisphenol A epoxy acrylate prepolymer: 28%; modified polyester resin: 15%; polyamide-imide resin: 4%; nano-scale soft magnetic ferrite powder (D 50 =0.1µm): 22%; silver-coated copper flake powder (8µm diameter): 6%; low-polymerization polyurethane compatibilizer: 7%; γ-glycidyloxypropyltriethoxysilane: 1%; bis(2,4-dimethylbenzoyl)diphenylphosphine oxide photoinitiator: 3%; hindered phenol antioxidant: 0.5%; polyether-modified acrylate leveling agent: 0.5%; tripropylene glycol diacrylate reactive diluent monomer: 13%. An 8µm thick film printed on an aluminum foil-PET substrate was tested after curing: room temperature elongation: 8.4%; no cracks were observed after thermal cycling (−40°C to 85°C, 100 cycles); resistance change after 10,000 flex cycles: 7.2%; and adhesion (100-grid method) was grade 0 (the highest grade).

[0014] Example 3: This example prepares a magnetic ink for RFID electronic tags. The components are calculated by weight as follows: bisphenol A epoxy acrylate prepolymer: 35%; modified polyester resin: 5%; polyamide-imide resin: 5%; nano-scale soft ferrite powder (D50=0.3µm): 20%; silver-coated flake copper powder (flake diameter 15µm): 7%; low-polymerization degree polyurethane compatibilizer: 6%; γ-glycidyloxypropyltriethoxysilane: 1%; bis(2,4-dimethylbenzoyl)diphenylphosphine oxide photoinitiator: 2.5%; hindered phenol antioxidant: 0.5%; polyether-modified acrylate leveling agent: 0.5%; tripropylene glycol diacrylate active diluent monomer: 12.5%. The sample thickness is 12µm, and the electromagnetic properties after curing are as follows: magnetic permeability µ' (13.56MHz): 39; tanδ: 0.029; high-frequency resonance efficiency (860-960MHz, S11 test) increased by 16% relative to the blank film layer; environmental reliability (85℃ / 85%RH, 168h): peel strength decreased by <8%, and no edge warping was observed.

[0015] Preferably, the modified polyester resin has a carboxyl content of 0.4-0.6mmolg -1 The linear saturated polyester is modified with bisphenol S epoxy acrylate end groups, and the glass transition temperature Tg is controlled at -10-5°C, so that the cured film layer can be cycled at -40-85°C for 500 times without kinking or cracking. It should be noted that in this embodiment, by introducing a carboxyl content of 0.4-0.6mmolg -1 The linear saturated polyester resin is end-group modified with bisphenol S epoxy acrylate to regulate its molecular chain flexibility and reactivity, resulting in a low-temperature, flexible film with a glass transition temperature (Tg) of -10-5°C. The synergistic reaction between this modified polyester resin and bisphenol A epoxy acrylate allows it to maintain crack-free flexibility after 500 cycles of hot and cold cycling between -40°C and 85°C. This improves the mechanical fatigue resistance of the ink on PET and metal foil composite films, effectively preventing curling and cracking after curing.

[0016] Preferably, the imidization degree of the polyamide-imide resin is between 15-35%, and the main chain thereof introduces an o-hydroxybenzoyl-p-phenylene rigid structure, which synergizes with the epoxy acrylate cross-linking network through hydrogen bonding, and the peel strength decreases by no more than 10% after 1000h under 85°C / 85%RH conditions. It should be noted that, in the present embodiment, the imidization degree of the polyamide-imide resin is controlled to be 15-35%, which can improve the stability of the resin under high temperature and humid heat conditions while maintaining solubility and film-forming properties. The introduction of the o-hydroxybenzoyl-p-phenylene rigid structure can provide good intramolecular hydrogen bonding, forming a multi-point entanglement network after cross-linking and curing, and cooperating with the epoxy acrylate system to enhance the adhesion strength and anti-delamination performance of the film layer, so that the peel strength decreases by no more than 10% after aging for 1000h under 85°C / 85%RH conditions, solving the problem of severe peeling in high humidity and heat environments.

[0017] Preferably, the nano-scale soft ferrite powder is Ni 0.5 Zn 0.5 Fe2O4, prepared by thiourea-citric acid co-precipitation combined with inert atmosphere two-step sintering process, saturation magnetization Ms ≥ 70emug -1 , under the condition of 100mT magnetic field, the relative reversible magnetic permeability µᵣ≥2.5. It should be noted that in this embodiment, the nano-scale soft magnetic ferrite powder is Ni 0.5 Zn 0.5 Fe2O4, a type of ferrite, offers excellent high-frequency permeability and low loss, making it suitable for RFID frequency bands (13.56 MHz and 860-960 MHz). A thiourea-citric acid co-precipitation method combined with a two-step sintering process under an inert atmosphere yields high-purity, highly dispersible magnetic powder with a saturation magnetization Ms ≥ 70 emu / g and a high µᵣ ≥ 2.5 at a weak field of 100 mT. This effectively improves the ink's magnetic response and mitigates the problem of insufficient magnetic permeability.

[0018] Preferably, the surface coating of the nano-scale soft ferrite powder is a gradient composite film of 3-methacryloxypropyltrimethoxysilane and zirconium dodecyl phosphate, with a relative concentration of 3:1, and a nano-scale interactive network resin-affinity layer is formed after vacuum heat treatment at 110°C for 2 hours. It should be noted that in this embodiment, by coating the surface of the nano-scale soft ferrite powder with a gradient composite film (a combination of 3-methacryloxypropyltrimethoxysilane and zirconium dodecyl phosphate, in a ratio of 3:1) and forming a nano-scale network resin-affinity layer after vacuum heat treatment at 110°C, a strong chemical adhesion interface is formed between the magnetic powder and the resin, improving the interfacial compatibility between the powder and the resin and the filler stability, reducing sedimentation and agglomeration, improving film formation uniformity and magneto-electric synergy, and effectively solving the problem of performance degradation caused by magnetic powder agglomeration.

[0019] Preferably, the silver-coated flaky copper powder has an aspect ratio of 40-120, a flake diameter of 5-20 μm, and a continuous and dense silver shell layer is obtained by cyanide-free silver-palladium bimetallic autocatalytic replacement, and its bulk resistance is ≤1.5×10 -5 Ω·cm, and after UV curing, it constructs a conductive-magnetic complementary microstructure network with nano-ferrite. It should be noted that the use of flaky copper powder with an aspect ratio of 40-120 and the application of cyanide-free silver-palladium bimetallic replacement to form a dense silver shell layer, to obtain silver-coated flaky copper powder with good conductivity (volume resistance ≤ 1.5×10⁻ 5 Ω·cm), not only provides a lateral conductive path, but also builds a conductive-magnetic complementary network with nano-ferrite by virtue of its large specific surface area, thereby enhancing the synergy of electromagnetic response, improving antenna performance, optimizing electromagnetic parameter matching, and effectively solving the problem of high content of carbon black or magnetic pigment covering and leading to line width amplification.

[0020] Preferably, the low-polymerization-degree polyurethane compatibilizer is an isocyanate-terminated polycaprolactone polyol with a molecular weight of 800-1200 Da and a dynamic viscosity of 0.15-0.25 Pa·s at 25°C. It should be noted that the low-polymerization-degree polyurethane compatibilizer (isocyanate-terminated polycaprolactone polyol, molecular weight 800-1200 Da) has good flexibility and viscoelastic properties, can enhance the compatibility within the resin system, improve the dispersibility of fillers such as magnetic powder and copper powder, and reduce the initial system viscosity to a reasonable screen printing window (0.15-0.25 Pa·s). This helps to form a uniform and delicate ink system, improve printing accuracy and the ability to print narrow line widths, and solve the problem of inability to print fine lines due to the conflict between hiding power and viscosity.

[0021] Preferably, the photoinitiator is a 3:2 mixture of bis(2,4-dimethylbenzoyl)diphenylphosphine oxide and 1-hydroxycyclohexyl phenyl ketone, with 0.05-0.2wt% of a catalytic tertiary amine added as a synergistic amine additive. Under 395nm narrow-spectrum UV-LED irradiation for 1.5s, bimodal free radical-cationic coupling curing is achieved, with curing shrinkage controlled to ≤4%. It should be noted that the photoinitiator uses a 3:2 mixture of bis(2,4-dimethylbenzoyl)diphenylphosphine oxide and 1-hydroxycyclohexyl phenyl ketone, supplemented with 0.05-0.2wt% of a catalytic tertiary amine additive, effectively broadening the free radical generation band and increasing the initiation rate. Under 395nm UV-LED irradiation, a bimodal curing reaction is achieved within 1.5s, with curing shrinkage controlled to ≤4%. This meets the dual requirements of fast curing and low shrinkage for high-speed production lines, improves the overall film quality and interfacial compatibility, and avoids the problem of easily cracking the PET+metal foil composite substrate.

[0022] Preferably, the leveling agent is a hydrophilic-hydrophobic dual-stage polyether-modified acrylate with an HLB value of 11-13. It should be noted that the use of a dual-stage polyether-modified acrylate leveling agent with an HLB value of 11-13, which exhibits both hydrophilic and lipophilic properties, can improve ink spreadability and film uniformity during printing, suppress surface defects such as Bénard vortices and pinholes, facilitate the stable printing of high-precision antenna patterns, and enhance pattern integrity in fine structure areas.

[0023] Preferably, the active diluent monomer is tripropylene glycol diacrylate and 1,6-hexanediol diacrylate in a mass ratio of 7:3, the apparent viscosity of the mixed system is 0.09 Pa·s, and the double bond density is 6.5 mmolg -1 It should be noted that tripropylene glycol diacrylate and 1,6-hexanediol diacrylate are compounded in a ratio of 7:3 to form an active diluent monomer system, providing moderate dilution capacity and crosslinking density (double bond density reaches 6.5 mmol / g). The viscosity of the mixed system is 0.09 Pa·s, which effectively adjusts the rheological properties of the overall system and adapts to the requirements of different printing processes (silk screen printing, gravure printing). At the same time, the network density after curing is reasonable, avoiding brittle failure caused by high crosslinking.

[0024] Preferably, the hindered phenol antioxidant is 3-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)-2,2-dimethylpropionic acid triol ester, and the oxidation induction time is greater than 900 seconds. It should be noted that the hindered phenol antioxidant is 3-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)-2,2-dimethylpropionic acid triol ester. This type of antioxidant has high-temperature thermal stability and UV shielding capabilities, which can delay resin yellowing and filler oxidation, and improve the stability of the ink formulation during transportation, storage, and printing. The oxidation induction time is greater than 900 seconds, which is far higher than conventional industrial requirements, ensuring the long-term outdoor stability of the RFID tag.

[0025] Preferably, the total solid content of the nanoscale soft ferrite powder and resin is controlled to 65-78wt%, and the ink has a dielectric constant εʹ of 6-9 and a dielectric loss tangent tanδ ≤ 0.06 in the 0.01-10MHz range. It should be noted that controlling the total solid content of the soft magnetic powder and resin system (65-78wt%) and achieving low-loss characteristics of a dielectric constant of 6-9 and tanδ ≤ 0.06 in the 0.01-10MHz frequency band, which covers the main RFID operating frequency band, can achieve good electromagnetic matching and antenna resonance characteristics, improving signal transmission efficiency and recognition sensitivity.

[0026] Example 2 See also Figure 1 To obtain the magnetic ink in the above embodiment, this embodiment provides a method for preparing the magnetic ink for RFID device electronic tags, comprising: Raw material pretreatment steps: Nano-scale soft ferrite powder and silver-coated flaky copper powder were dried at 60°C and 40% RH for 2 h, cooled to 25°C, and placed in an inert nitrogen box for standby use; Coupling activation step: adding 0.5-1.5 wt% of γ-glycidyloxypropyltriethoxysilane to a 40 wt% premix of bisphenol A epoxy acrylate prepolymer and tripropylene glycol diacrylate, and reacting at 45°C for 30 minutes to form an epoxy-active interface layer; Efficient dispersion step: using nano-bead mill, rotor linear speed 12ms -1 The powder in the raw material pretreatment step and the interface layer mixed slurry obtained in the coupling activation step were ground for 20 minutes to make the D of the nano-scale soft ferrite powder 50 D of 0.1-0.3µm, silver-coated flake copper powder 50 ≤8µm, and the dispersion particle size variance ≤0.1; Resin compatibilization and rheological control steps: Modified polyester resin, polyamide-imide resin, and low-polymerization degree polyurethane compatibilizer were added in sequence at 30-40°C. Degassing was performed using a dual planetary vacuum mixer at -0.09 MPa for 15 minutes to adjust the system viscosity to 4±0.5 Pa·s. Functional additive fine-tuning steps: adding a photoinitiator, a hindered phenol antioxidant, and a leveling agent under slow stirring at room temperature, standing in vacuum for 30 minutes to remove residual bubbles, filtering with a 0.2µm stainless steel filter, and packaging with nitrogen to obtain the finished magnetic ink.

[0027] It should be noted that in this embodiment, raw material pretreatment is used to ensure the dryness and purity of the powder, coupling reaction is used to ensure interface compatibility, bead milling dispersion is used to improve microscopic uniformity, low-temperature volume expansion is used to regulate rheological properties, and finally vacuum filtration and exhaust are used to prevent printing defects such as bubbles, thereby forming a magnetic ink system that is suitable for various printing methods.

[0028] It's also important to note that during the raw material pretreatment step, the nanoscale soft ferrite powder and silver-coated flake copper powder are dried at 60°C and 40% RH for 2 hours, cooled to 25°C, and placed in an inert nitrogen chamber for later use. This eliminates physically adsorbed water and trace organic residues in the powders, preventing bubbles or gel agglomeration during subsequent reactions with organic coupling agents and resins. Controlling the ambient humidity prevents oxidation of the silver-coated copper powder and ensures conductive properties. Using an inert atmosphere (such as nitrogen) isolates the powder from air, reduces oxidation and moisture absorption, and improves powder activity retention. Powder dryness directly affects the efficiency of the coupling activation reaction and dispersion uniformity. Residual water can hydrolyze and inactivate the silane coupling agent, resulting in weak powder-resin interfacial bonding. This raw material pretreatment step provides a clean, highly active starting point for the entire ink system and is a prerequisite for ensuring subsequent performance. During the coupling activation step, 0.5-1.5 wt% of γ-glycidyloxypropyltriethoxysilane is added to a premix of 40 wt% bisphenol A epoxy acrylate prepolymer and tripropylene glycol diacrylate, and the mixture is reacted at 45°C for 30 minutes. This hydrolysis of γ-glycidyloxypropyltriethoxysilane in the solvent medium forms trihydroxysilane, which bonds to the hydroxyl groups on the surface of the ferrite powder. Simultaneously, its epoxy end participates in the reaction or crosslinking of the prepolymer, forming a covalent interfacial bridge structure between the powder, coupling agent, and resin. This strengthens the interfacial bonding between the powder and the organic phase, improving the system's storage stability and resistance to shearing. The coupling reaction is performed before dispersion, preventing the surface-coated magnetic powder from being damaged by mechanical shear during high-speed bead milling, improving stable dispersion efficiency and interfacial wettability, and reducing the risk of reagglomeration after bead milling. In the efficient dispersion step, the pre-treated powder and the coupling liquid were ground for 20 minutes using a nano-bead mill with a rotor linear speed of 12 m / s to make the D of the nano-scale soft ferrite powder 50 D of 0.1-0.3µm, silver-coated flake copper powder 50≤8µm, with a particle size variance of ≤0.1. Nanoscale bead milling enables powder refinement and uniform particle size control. It also utilizes mechanical shear to synergistically couple interfacial reactions, enhancing the surface activation state of the particles and ultimately forming a highly dispersed, narrowly distributed filler system. Controlling the particle size variance to ≤0.1 improves edge definition and ink stability in printed patterns, preventing screen clogging or pattern breakage during subsequent printing. A stable nanoscale filler dispersion lays the foundation for subsequent system viscosity control, avoiding particle aggregation and system gelation during volume expansion, and achieving simultaneous control of particle size and rheology. During the resin volume expansion and rheology control step, modified polyester resin, polyamide-imide resin, and low-polymerization-degree polyurethane compatibilizer are added at 30-40°C. Degassing is then performed in a dual planetary vacuum mixer at -0.09 MPa for 15 minutes to adjust the system viscosity to 4±0.5 Pa·s. In this way, resins with different structures jointly participate in network formation: polyester resin provides flexibility, polyamide-imide enhances moisture-heat resistance and adhesion, and polyurethane compatibilizer improves compatibility and rheological properties. Vacuum degassing can prevent the incorporation of bubbles into high-filler, high-viscosity systems, improving ink density uniformity and the density of the film layer after printing. Controlling the viscosity window adapts to processes such as screen printing, gravure printing, and inkjet printing, avoiding sagging or scraper residue during high-speed printing. The already highly uniform filler dispersion system is synergistically mixed with various functional resins in this step to ensure the rheological and mechanical stability of the filler in the final ink, improving ink reproducibility and batch consistency. During the functional additive fine-tuning step, photoinitiators, antioxidants, and leveling agents are added. After standing for 30 minutes to degas, the product is filtered through a 0.2µm stainless steel filter and nitrogen-sealed. The photoinitiator system ensures rapid ink curing (1.5 seconds) under 395nm UV LED irradiation, with low shrinkage (≤4%) to prevent cracking of PET / metal foil. Antioxidants enhance storage stability, while leveling agents improve film surface quality, reducing pinholes and vortexes. Static filtration and fine filtration ensure control of the ink's final particle size and pore size, avoiding microscopic defects. This step ensures that sensitive photoinitiator / leveling components are added only after the system's rheological properties are fully controlled, preventing the risk of premature reaction or phase separation during film formation and improving compatibility with the final process.

[0029] Preferably, the pH value of the coupling activation reaction in the coupling activation step is controlled at 4-5, and the reaction is monitored by online Fourier infrared-ATR at 915 cm -1 The degree of weakening of the characteristic absorption peak of the epoxy group is used as the end point of the coupling reaction to ensure that the coupling agent fully covers the surface of the nano-scale soft magnetic ferrite powder to strengthen the interface adhesion. It should be noted that by controlling the pH of the coupling reaction in the range of 4-5, the end group of γ-glycidyloxypropyltriethoxysilane is activated to react with the hydroxyl group on the surface of the ferrite to form a stable covalent bond. At the same time, the epoxy group is located at 915cm by Fourier transform infrared ATR monitoring. -1The characteristic absorption peak weakening process can be monitored to determine the reaction endpoint in real time, thereby improving coupling efficiency and consistency, enhancing the adhesion between magnetic powder and resin, and improving film-forming performance and interface reliability.

[0030] Preferably, coarse particles are removed immediately after milling in the efficient dispersion step by centrifugation at 5000 rpm for 10 minutes. Laser particle size analysis is used to control the volume fraction of particles larger than 1µm to ≤0.3% to prevent subsequent printing screen clogging. It should be noted that high-speed centrifugation at 5000 rpm after bead milling effectively removes residual coarse particles and undispersed agglomerates. Combined with laser particle size analysis, precise control of particle size distribution (controlling the volume fraction of particles larger than 1µm to ≤0.3%) ensures that the ink does not risk screen clogging during fine pattern printing, thereby improving printing consistency and pattern boundary clarity, and enabling printing of narrow lines of 70-100µm.

[0031] Preferably, the resin volume expansion and rheology control step uses dual-frequency ultrasound at 25kHz + 40kHz in conjunction with planetary stirring to reduce the interfacial adhesion energy between the resin and nano-scale soft ferrite powder by 15%, improve low-shear fluidity and thixotropic recovery rate, and ensure that the ink viscosity increases by ≤7% after 6 months of storage at 25°C. It should be noted that the use of dual-frequency ultrasound at 25kHz and 40kHz in conjunction with planetary stirring creates macro- and micro-scale resonant cavitation effects, improves the interfacial wetting and adhesion energy between the resin and filler, enhances the fluidity and thixotropy of the filler under low-shear conditions, and improves storage stability (viscosity change ≤7% over 6 months), thus resolving the problem of traditional magnetic inks prone to delamination and thickening after long-term storage.

[0032] It should be pointed out that the above embodiments are only preferred specific implementation methods of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. The protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A magnetic ink for RFID device electronic tags, characterized in that: The composition comprises, by weight percentage, 20-40% bisphenol A epoxy acrylate prepolymer, 5-20% modified polyester resin, 3-15% polyamide-imide resin, 15-35% nano-scale soft ferrite powder, 2-10% silver-coated flaky copper powder, 1-8% low-polymerization degree polyurethane compatibilizer, 0.2-2% γ-glycidyloxypropyl triethoxysilane coupling agent, 0.5-5% bis(2,4-dimethylbenzoyl)diphenylphosphine oxide photoinitiator, 0.1-1% hindered phenol antioxidant, 0.1-1% polyether modified acrylate leveling agent and 5-15% tripropylene glycol diacrylate active diluent monomer; wherein the D of the nano-scale soft ferrite powder is 0. 50 The thickness of the magnetic field is 0.1-0.3µm, and the surface is double-coated with phosphate-silane. After UV curing, it provides an initial magnetic permeability of 20-60 and maintains a loss tangent value of ≤0.05 in the 13.56MHz frequency band.

2. The magnetic ink for RFID device electronic tags according to claim 1, characterized in that: The modified polyester resin has a carboxyl content of 0.4-0.6 mmolg -1 The linear saturated polyester is modified with bisphenol S epoxy acrylate end groups, and the glass transition temperature Tg is controlled at -10-5℃, so that the cured film layer remains kink-free and crack-free after 500 cycles at -40-85℃.

3. The magnetic ink for RFID device electronic tags according to claim 2, characterized in that: The imidization degree of the polyamide-imide resin is between 15-35%, and its main chain introduces an o-hydroxybenzoyl-p-phenylene rigid structure, which synergizes with the epoxy acrylate cross-linking network through hydrogen bonds, and the peel strength decreases by no more than 10% after 1000 hours under 85°C / 85%RH conditions.

4. The magnetic ink for RFID device electronic tags according to claim 3, characterized in that: The nano-scale soft ferrite powder is Ni 0.5 Zn 0.5 Fe2O4, prepared by thiourea-citric acid co-precipitation combined with inert atmosphere two-step sintering process, saturation magnetization Ms ≥ 70emug -1 , the relative reversible magnetic permeability µᵣ≥2.5 under 100mT magnetic field conditions.

5. The magnetic ink for RFID device electronic tags according to claim 4, characterized in that: The surface coating layer of the nano-scale soft magnetic ferrite powder is a gradient composite film of 3-methacryloxypropyltrimethoxysilane and dodecyl zirconium phosphate with a relative concentration of 3:

1. After vacuum heat treatment at 110° C. for 2 hours, a nano-scale interactive network resin-affinity layer is formed.

6. The magnetic ink for RFID device electronic tags according to any one of claims 1 to 5, characterized in that: The silver-coated flaky copper powder has a thickness-to-diameter ratio of 40-120 and a flake diameter of 5-20 μm. A continuous and dense silver shell is obtained by cyanide-free silver-palladium bimetallic autocatalytic replacement, and its bulk resistance is ≤1.5×10 -5 Ω·cm, and after UV curing, it constructs a conductive-magnetic complementary microstructure network with nano-ferrite.

7. A method for preparing the magnetic ink for RFID device electronic tags according to any one of claims 1 to 6, characterized in that: include: Raw material pretreatment steps: Nano-scale soft ferrite powder and silver-coated flaky copper powder were dried at 60°C and 40% RH for 2 h, cooled to 25°C, and placed in an inert nitrogen box for standby use; Coupling activation step: adding 0.5-1.5 wt% of γ-glycidyloxypropyltriethoxysilane to a 40 wt% premix of bisphenol A epoxy acrylate prepolymer and tripropylene glycol diacrylate, and reacting at 45°C for 30 minutes to form an epoxy-active interface layer; Efficient dispersion step: using nano-bead mill, rotor linear speed 12ms -1 The powder in the raw material pretreatment step and the interface layer mixed slurry obtained in the coupling activation step were ground for 20 minutes to make the D of the nano-scale soft ferrite powder 50 D of 0.1-0.3µm, silver-coated flake copper powder 50 ≤8µm, and the dispersion particle size variance ≤0.1; Resin compatibilization and rheological control steps: Modified polyester resin, polyamide-imide resin, and low-polymerization degree polyurethane compatibilizer were added in sequence at 30-40°C. Degassing was performed using a dual planetary vacuum mixer at -0.09 MPa for 15 minutes to adjust the system viscosity to 4±0.5 Pa·s. Functional additive fine-tuning steps: adding a photoinitiator, a hindered phenol antioxidant, and a leveling agent under slow stirring at room temperature, standing in vacuum for 30 minutes to remove residual bubbles, filtering with a 0.2µm stainless steel filter, and packaging with nitrogen to obtain the finished magnetic ink.

8. The preparation method according to claim 7, characterized in that The pH value of the coupling activation reaction was controlled at 4-5 during the coupling activation step, and the reaction was monitored by online Fourier transform infrared-ATR at 915 cm -1 The degree of weakening of the characteristic absorption peak of the epoxy group is taken as the end point of the coupling reaction to ensure that the coupling agent fully covers the surface of the nano-scale soft ferrite powder to strengthen the interface adhesion.

9. The preparation method according to claim 7, characterized in that In the efficient dispersion step, coarse particles are immediately removed by centrifugation at 5000 rpm for 10 minutes after grinding. Laser particle size analysis is used to control the volume fraction of particles larger than 1 µm to ≤ 0.3% to prevent subsequent printing screen clogging.

10. The preparation method according to claim 7, characterized in that In the resin volume expansion and rheology control step, 25kHz+40kHz dual-frequency ultrasonic coordinated planetary stirring is used to reduce the resin-nanoscale soft ferrite powder interface adhesion energy by 15%, improve low-shear fluidity and thixotropic recovery rate, and make the ink viscosity increase by ≤7% after 6 months of storage at 25°C.

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