Magnetic ink for RFID electronic tags and its preparation method

Abstract

This invention relates to the technical fields of RFID equipment manufacturing and novel magnetic inks, providing a magnetic ink for RFID electronic tags and its preparation method. The magnetic ink comprises bisphenol A epoxy acrylate prepolymer, modified polyester resin, polyamide-imide resin, nano-scale soft magnetic ferrite powder, silver-coated flake copper powder, low-polymerization-degree polyurethane compatibilizer, γ-glycidyl etheroxypropyltriethoxysilane coupling agent, photoinitiator, antioxidant, leveling agent, and reactive diluent monomer. The ferrite powder has a D50 of 0.1-0.3µm and its surface is treated with a phosphate ester-silane double coating. After UV curing, its magnetic permeability is 20-60, and its loss tangent is ≤0.05. This invention's ink possesses excellent magnetic properties, conductivity, and flexibility, effectively improving the tag's electromagnetic response, crack resistance, and printing accuracy. It is suitable for printing high-Q value narrow-linewidth antenna patterns.

Description

Technical Field

[0001] This invention relates to the technical fields of RFID equipment manufacturing and novel magnetic inks, and in particular to a magnetic ink for electronic tags of RFID equipment and its preparation method. Background Technology

[0002] In the manufacturing process of RFID electronic tags, a metal foil (copper or aluminum) needs to be coated on the back of a PET film sheet. Magnetic ink is then printed on the antenna pattern area of ​​the metal foil on the back to optimize the antenna's electromagnetic performance and improve the tag's reliability and adaptability. However, existing magnetic ink formulations mostly use micron-sized ferrite powder with a wide particle size distribution, which is prone to agglomeration and hysteresis loss. This results in low permeability (µʹ<15) in RFID operating frequency bands such as 13.56MHz and 860-960MHz, leading to insufficient permeability and high frequency loss. Furthermore, to obtain a medium viscosity suitable for screen printing or gravure printing, existing formulations require the addition of a large amount of low-viscosity reactive diluent monomers. This causes the PET and metal foil composite substrate to crack when the shrinkage rate after UV curing exceeds 7%, reducing the tag's bending and drop resistance reliability. Additionally, the resin system in existing magnetic ink formulations has insufficient adhesion to the metal foil interface, easily leading to edge curling or cracking. In addition, the opacity of existing formulations relies on high carbon black or magnetic pigment content, which causes the system viscosity to soar and the minimum printable linewidth to be too large (>100µm), making it difficult to meet the printing process requirements of narrow linewidth (<100µm linewidth) for high Q value micro antenna patterns.

[0003] In summary, existing technologies suffer from several technical problems, including insufficient magnetic permeability of electronic tags, high frequency loss, low reliability in bending and drop resistance, susceptibility to edge curling or cracking, excessively large minimum printable linewidth, and difficulty in meeting the printing process requirements for narrow linewidths of high-Q micro-antenna patterns. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention provides a magnetic ink for RFID electronic tags and its preparation method, thereby improving the magnetic permeability of the electronic tags, enhancing their resistance to bending and drop, reducing tag frequency loss, preventing edge curling or cracking, reducing the minimum printable linewidth, and meeting the printing process requirements for narrow linewidths of high-Q micro-antenna patterns.

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

[0006] Secondly, the present invention provides a method for preparing magnetic ink for electronic tags of RFID devices, comprising:

[0007] Raw material pretreatment steps: The nano-sized soft magnetic ferrite powder and silver-coated flake copper powder were dried at 60℃ and 40%RH for 2 hours respectively, and then cooled to 25℃ and placed in an inert nitrogen box for later use.

[0008] Coupling activation step: Add 0.5-1.5wt% γ-glycidyl etheroxypropyltriethoxysilane to 40wt% bisphenol A epoxy acrylate prepolymer-tripropylene glycol diacrylate premix and react at 45℃ for 30min to form an epoxy-active interface layer.

[0009] High-efficiency dispersion step: A nano-bead mill is used with a rotor linear speed of 12 ms. -1 The powder mixture obtained in the pretreatment step and the interface layer mixture obtained in the coupling activation step are ground for 20 minutes to reduce the D of the nano-scale soft magnetic ferrite powder. 50 D is a 0.1-0.3µm, silver-coated flake copper powder. 50 ≤8µm, and the variance of the dispersed particle size ≤0.1;

[0010] Resin compatibilization-rheology regulation steps: Modified polyester resin, polyamide-imide resin and low-polymerization-degree polyurethane compatibilizer are added sequentially at 30-40℃. The mixture is degassed for 15 minutes using a double planetary vacuum mixer at -0.09MPa, and the viscosity of the system is adjusted to 4±0.5Pa·s.

[0011] Functional additive fine-tuning steps: Add photoinitiator, hindered phenolic antioxidant and leveling agent under slow stirring at room temperature, let stand under vacuum for 30 minutes to remove residual air bubbles, filter through a 0.2µm stainless steel filter, and encapsulate with nitrogen to obtain the finished magnetic ink.

[0012] Compared with the prior art, the beneficial effects of this invention are as follows:

[0013] This invention provides a magnetic ink for RFID electronic tags and its preparation method. The magnetic ink, by weight percentage, comprises: 20-40% bisphenol A epoxy acrylate prepolymer, 5-20% modified polyester resin, 3-15% polyamide-imide resin, 15-35% nano-sized soft magnetic ferrite powder, 2-10% silver-coated flake copper powder, 1-8% low-polymerization-degree polyurethane compatibilizer, 0.2-2% γ-glycidyl etheroxypropyltriethoxysilane coupling agent, 0.5-5% bis(2,4-dimethylbenzoyl)diphenylphosphine photoinitiator, 0.1-1% hindered phenolic antioxidant, 0.1-1% polyether-modified acrylate leveling agent, and 5-15% tripropylene glycol diacrylate reactive diluent monomer; wherein the nano-sized soft magnetic ferrite powder contains D... 50 With a thickness of 0.1-0.3µm, the surface is treated with a double coating of phosphate ester and silane. After UV curing, it provides an initial permeability of 20-60 and maintains a loss tangent of ≤0.05 in the 13.56MHz frequency band. This magnetic ink improves the permeability of electronic tags, enhances their resistance to bending and drop, reduces tag frequency loss, prevents edge curling or cracking, and reduces the minimum printable linewidth, meeting the printing process requirements of narrow linewidths for high-Q micro-antenna patterns. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. Some specific embodiments of the invention will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings designate the same or similar parts or components. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings:

[0015] Figure 1 This is a schematic flowchart of a method for preparing magnetic ink for electronic tags of RFID devices according to an embodiment of the present invention. Detailed Implementation

[0016] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0017] Example 1

[0018] See Figure 1 This embodiment provides a magnetic ink for RFID device electronic tags, comprising, by weight percentage: 20-40% bisphenol A epoxy acrylate prepolymer, 5-20% modified polyester resin, 3-15% polyamide-imide resin, 15-35% nano-sized soft magnetic ferrite powder, 2-10% silver-coated flake copper powder, 1-8% low-polymerization-degree polyurethane compatibilizer, 0.2-2% γ-glycidyl etheroxypropyltriethoxysilane coupling agent, 0.5-5% bis(2,4-dimethylbenzoyl)diphenylphosphine photoinitiator, 0.1-1% hindered phenolic antioxidant, 0.1-1% polyether-modified acrylate leveling agent, and 5-15% tripropylene glycol diacrylate reactive diluent monomer; wherein the nano-sized soft magnetic ferrite powder D 50 The thickness is 0.1-0.3µm, and the surface is treated with phosphate ester-silane double coating. After UV curing, it provides an initial permeability of 20-60 and maintains a loss tangent of ≤0.05 in the 13.56MHz frequency band.

[0019] It should be noted that in this embodiment, nanoscale soft magnetic ferrite powder (D...) is used. 50 =0.1-0.3µm), thus significantly improving magnetic permeability (reaching 20-60) and reducing frequency loss (tanδ≤0.05). Simultaneously, the surface of the nano-scale soft magnetic ferrite powder is enhanced by phosphate ester-silane double coating, improving its dispersion stability and interfacial adhesion in the resin system. The resin system incorporates three synergistic film-forming structures: bisphenol A epoxy acrylate, polyester resin, and polyamide-imide resin, improving flexibility and adhesion while ensuring film strength after UV curing. Furthermore, silver-coated flake copper powder with excellent conductivity and flake structure constructs a magnetically complementary path, improving the high-frequency response of the antenna pattern. In addition, low-polymerization-degree polyurethane compatibilizers, photoinitiators, antioxidants, leveling agents, and reactive diluents play a regulating and enhancing role in ink viscosity, curing shrinkage, and environmental stability. The overall formulation closely matches the process requirements of the PET+metal foil composite substrate, forming a highly adaptable and reliable magnetic functional ink.

[0020] Example 1: This example prepares a magnetic ink for RFID electronic tags. The components, by weight percentage, are: bisphenol A epoxy acrylate prepolymer: 32%; modified polyester resin: 10%; polyamide-imide resin: 5%; nano-sized soft magnetic ferrite powder (Ni 0.5 Zn 0.5 Fe2O4, D 50 =0.2µm, surface coated with phosphate ester-silane): 25%; Silver-coated flake copper powder (flake diameter 10µm, aspect ratio 80): 5%; Low-polymerization degree polyurethane compatibilizer (Mn=1000): 5%; γ-glycidyl etheroxypropyltriethoxysilane: 1%; Bis(2,4-dimethylbenzoyl)diphenylphosphine photoinitiator: 3%; Hindered phenolic antioxidant (IRGANOX 1010): 0.5%; Polyether modified acrylate leveling agent: 0.5%; Tripropylene glycol diacrylate reactive diluent monomer: 13%. The above ink samples were screen printed onto the surface of a PET+copper foil substrate using a screen printing process, with a film thickness of approximately 10µm. After curing under 395nm LED ultraviolet light for 2 seconds, the following tests were conducted: initial permeability µ': 45 (13.56MHz, HP 4291B); loss tangent tanδ: 0.035; Q value: 31; minimum linewidth of printed pattern: 70µm; resistance change <5% after 2000 180° bends.

[0021] Example 2: This example prepares a magnetic ink for RFID electronic tags. The components, by weight percentage, are: bisphenol A epoxy acrylate prepolymer: 28%; modified polyester resin: 15%; polyamide-imide resin: 4%; nano-sized soft magnetic ferrite powder (D... 50 =0.1µm): 22%; Silver-coated flake copper powder (8µm diameter): 6%; Low-polymerization degree polyurethane compatibilizer: 7%; γ-glycidyl etheroxypropyltriethoxysilane: 1%; Bis(2,4-dimethylbenzoyl)diphenylphosphine photoinitiator: 3%; Hindered phenolic antioxidant: 0.5%; Polyether-modified acrylate leveling agent: 0.5%; Tripropylene glycol diacrylate reactive diluent monomer: 13%. An 8µm thick film was printed on an aluminum foil-PET substrate. After curing, the following tests were conducted: Elongation at room temperature: 8.4%; No cracks in the film after 100 cycles of thermal cycling (−40~85℃); Resistance change rate after 10,000 bends: 7.2%; Adhesion test (100-cross cross-cut test): Grade 0 (highest grade).

[0022] Example 3: This example prepares a magnetic ink for RFID electronic tags. The components, by weight percentage, are as follows: Bisphenol A epoxy acrylate prepolymer: 35%; Modified polyester resin: 5%; Polyamide-imide resin: 5%; Nanoscale soft magnetic ferrite powder (D50=0.3µm): 20%; Silver-coated flake copper powder (flake diameter 15µm): 7%; Low-polymerization-degree polyurethane compatibilizer: 6%; γ-glycidyl etheroxypropyltriethoxysilane: 1%; Bis(2,4-dimethylbenzoyl)diphenylphosphine photoinitiator: 2.5%; Hindered phenolic antioxidant: 0.5%; Polyether-modified acrylate leveling agent: 0.5%; Tripropylene glycol diacrylate reactive diluent monomer: 12.5%. The sample thickness was 12µm. The electromagnetic properties after curing were as follows: magnetic permeability µ' (13.56MHz): 39; tanδ: 0.029; high-frequency resonant efficiency (860-960MHz, S11 test) increased by 16% compared to the blank film; environmental reliability (85℃ / 85%RH, 168h): peel strength decreased by <8%, and no edge lifting was observed.

[0023] Preferably, the modified polyester resin has a carboxyl content of 0.4-0.6 mmol / g. -1 Linear saturated polyester was obtained by end-group modification with bisphenol S epoxy acrylate, and the glass transition temperature (Tg) was controlled at −10⁻⁵℃, so that the cured film layer remained crack-free after 500 cycles at −40–85℃. It should be noted that in this embodiment, a carboxyl group content of 0.4–0.6 mmol / g was introduced. -1 The linear saturated polyester base is modified with bisphenol A epoxy acrylate end groups, which can control the flexibility and reactivity of its molecular chain, thereby forming a low-temperature flexible film layer with a glass transition temperature (Tg) of −10⁻⁵℃. After the modified polyester resin reacts synergistically with bisphenol A epoxy acrylate, it can maintain crack-free flexibility after 500 cycles of thermal cycling at −40℃-85℃, thereby improving the mechanical fatigue adaptability of the ink on PET and metal foil composite film materials and effectively solving the problems of curling and cracking after curing.

[0024] Preferably, the polyamide-imide resin has an imidization degree between 15-35%, and its main chain incorporates a rigid o-hydroxybenzoyl-p-phenylene structure. Through synergistic effects of hydrogen bonding and the epoxy acrylate crosslinking network, the peel strength decreases by no more than 10% after 1000 hours at 85°C / 85%RH. It should be noted that in this embodiment, controlling the imidization degree of the polyamide-imide resin to 15-35% can improve the resin's stability under high temperature and humidity conditions while maintaining solubility and film-forming properties. The introduction of the rigid o-hydroxybenzoyl-p-phenylene structure provides excellent intramolecular hydrogen bonding, forming a multi-point entanglement network after crosslinking and curing. This synergistically enhances the adhesion strength and anti-delamination performance of the film layer, thereby ensuring that the peel strength decreases by no more than 10% after aging at 85°C / 85%RH for 1000 hours, solving the problem of severe peeling in high humidity and heat environments.

[0025] Preferably, the nanoscale soft magnetic ferrite powder is Ni. 0.5 Zn 0.5 Fe2O4 was prepared by a two-step sintering process using thiourea-citric acid co-precipitation combined with an inert atmosphere, achieving a saturation magnetization Ms ≥ 70 emu. -1 The relative reversible permeability µᵣ ≥ 2.5 under a 100 mT magnetic field. It should be noted that in this embodiment, the nanoscale soft magnetic ferrite powder is Ni. 0.5 Zn 0.5 Fe2O4, a ferrite type, possesses excellent high-frequency permeability and low-loss characteristics, making it suitable for RFID frequency bands (13.56MHz and 860-960MHz). High-purity, highly dispersible magnetic powder is obtained through a thiourea-citric acid co-precipitation method combined with two-step sintering under an inert atmosphere. The saturation magnetization Ms ≥ 70 emu / g can achieve a high µᵣ ≥ 2.5 under a weak field of 100mT, effectively improving the magnetic response performance of the ink and suppressing the problem of insufficient permeability.

[0026] Preferably, the surface coating layer of the nanoscale soft magnetic ferrite powder is a gradient composite film of 3-methacryloyloxypropyltrimethoxysilane and zirconium dodecyl phosphate with a relative concentration of 3:1, which forms a nanoscale interwoven resin-loving layer after vacuum heat treatment at 110°C for 2 hours. It should be noted that in this embodiment, by coating the surface of the nanoscale soft magnetic ferrite powder with a gradient composite film (a combination of 3-methacryloyloxypropyltrimethoxysilane and zirconium dodecyl phosphate in a 3:1 ratio) and forming a nanoscale network resin-loving layer after vacuum heat treatment at 110°C, a strong chemical adhesion interface is formed between the magnetic powder and the resin. This improves the interfacial compatibility and filler stability between the powder and the resin, reduces sedimentation and agglomeration, enhances film uniformity and magneto-electric synergy, and effectively solves the problem of performance degradation caused by magnetic powder agglomeration.

[0027] Preferably, the silver-coated flake copper powder has an aspect ratio of 40-120 and a flake diameter of 5-20µm. A continuous and dense silver shell is obtained through cyanide-free silver-palladium bimetallic autocatalytic replacement, with a bulk resistivity ≤1.5×10⁻⁶. -5 The resistivity is Ω·cm, and after UV curing, it is used to construct a conductive-magnetic complementary microstructure network with nano-ferrite. It should be noted that sheet-like copper powder with an aspect ratio of 40-120 is used and subjected to cyanide-free silver-palladium bimetallic substitution to form a dense silver shell layer, resulting in silver-coated sheet-like copper powder with good conductivity (volume resistivity ≤1.5×10⁻⁻⁻⁶). 5 (Ω·cm) not only provides a lateral conductive path, but also uses its large specific surface area to construct a conductive-magnetic complementary network with nano-ferrite, thereby enhancing electromagnetic response synergy, improving antenna performance, optimizing electromagnetic parameter matching, and effectively solving the problem of linewidth enlargement caused by high carbon black or magnetic pigment masking.

[0028] 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, which can improve 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 fine ink system, improve printing accuracy and the ability to print narrow line widths, and solve the problem of the inability to print fine lines due to the contradiction between hiding power and viscosity.

[0029] Preferably, the photoinitiator is a 3:2 mixture of bis(2,4-dimethylbenzoyl)diphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone, with 0.05-0.2 wt% of a catalytic tertiary amine synergist added. Under 395 nm narrow-band UV-LED irradiation for 1.5 s, bimodal free radical-cation coupling curing is achieved, with a curing shrinkage rate controlled ≤4%. It should be noted that the photoinitiator, a 3:2 mixture of bis(2,4-dimethylbenzoyl)diphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone, supplemented with 0.05-0.2 wt% of a catalytic tertiary amine synergist, effectively broadens the free radical generation band and improves the initiation rate. Under 395 nm UV-LED irradiation, a bimodal curing reaction can be achieved in 1.5 seconds, with a curing shrinkage rate controlled ≤4%. This meets the dual requirements of high-speed production lines for rapid curing and low shrinkage, improving the overall quality and interfacial compatibility of the film layer and avoiding the problem of easily tearing PET+metal foil composite substrates.

[0030] Preferably, the leveling agent is a hydrophilic-hydrophobic two-segment polyether-modified acrylate with an HLB value of 11-13. It should be noted that using a two-segment polyether-modified acrylate leveling agent with an HLB value of 11-13, which possesses both hydrophilic and oleophilic properties, can improve the spreadability and film uniformity of the ink during the printing process, suppress surface defects such as Bénard swirls and pinholes, contribute to the stable printing of high-precision antenna patterns, and enhance the pattern integrity in microstructure areas.

[0031] Preferably, the reactive diluent monomer is a mixture of tripropylene glycol diacrylate and 1,6-hexanediol diacrylate in a 7:3 mass ratio, with an apparent viscosity of 0.09 Pa·s and a double bond density of 6.5 mmol / g. -1 It should be noted that the tripropylene glycol diacrylate and 1,6-hexanediol diacrylate are blended in a 7:3 ratio to form an reactive 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 overall rheological properties of the system and adapts to different printing process requirements (screen printing, gravure printing). At the same time, the network density after curing is reasonable, avoiding brittle failure caused by high crosslinking.

[0032] Preferably, the hindered phenolic antioxidant is 3-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)-2,2-dimethylpropionic acid triol ester, with an oxidation induction time >900s. It should be noted that the hindered phenolic antioxidant, 3-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)-2,2-dimethylpropionic acid triol ester, possesses high-temperature thermal stability and UV shielding capabilities, which can delay resin yellowing and filler oxidation, improve the stability of ink formulations during transportation, storage, and printing, and has an oxidation induction time greater than 900s, far exceeding conventional industrial requirements, ensuring the long-term outdoor stability of RFID tags.

[0033] Preferably, the total solid content of the nano-scale soft magnetic ferrite powder and resin is controlled at 65-78 wt%, and the dielectric constant εʹ of the ink in the 0.01-10MHz range is 6-9, and the dielectric loss tangent tanδ ≤ 0.06. It should be noted that controlling the total solid content of the soft magnetic powder and resin system (65-78 wt%) and achieving low-loss characteristics with a dielectric constant of 6-9 and tanδ ≤ 0.06 in the 0.01-10MHz frequency band covers the main operating frequency band of RFID, enabling good electromagnetic matching and antenna resonance characteristics, and improving signal transmission efficiency and identification sensitivity.

[0034] Example 2

[0035] See Figure 1To obtain the magnetic ink in the above embodiments, this embodiment provides a method for preparing magnetic ink for RFID device electronic tags, comprising:

[0036] Raw material pretreatment steps: The nano-sized soft magnetic ferrite powder and silver-coated flake copper powder were dried at 60℃ and 40%RH for 2 hours respectively, and then cooled to 25℃ and placed in an inert nitrogen box for later use.

[0037] Coupling activation step: Add 0.5-1.5wt% γ-glycidyl etheroxypropyltriethoxysilane to 40wt% bisphenol A epoxy acrylate prepolymer-tripropylene glycol diacrylate premix and react at 45℃ for 30min to form an epoxy-active interface layer.

[0038] High-efficiency dispersion step: A nano-bead mill is used with a rotor linear speed of 12 ms. -1 The powder mixture obtained in the pretreatment step and the interface layer mixture obtained in the coupling activation step are ground for 20 minutes to reduce the D of the nano-scale soft magnetic ferrite powder. 50 D is a 0.1-0.3µm, silver-coated flake copper powder. 50 ≤8µm, and the variance of the dispersed particle size ≤0.1;

[0039] Resin compatibilization-rheology regulation steps: Modified polyester resin, polyamide-imide resin and low-polymerization-degree polyurethane compatibilizer are added sequentially at 30-40℃. The mixture is degassed for 15 minutes using a double planetary vacuum mixer at -0.09MPa, and the viscosity of the system is adjusted to 4±0.5Pa·s.

[0040] Functional additive fine-tuning steps: Add photoinitiator, hindered phenolic antioxidant and leveling agent under slow stirring at room temperature, let stand under vacuum for 30 minutes to remove residual air bubbles, filter through a 0.2µm stainless steel filter, and encapsulate with nitrogen to obtain the finished magnetic ink.

[0041] It should be noted that in this embodiment, the powder is kept dry and pure through raw material pretreatment, the interface compatibility is ensured through coupling reaction, the microstructure uniformity is improved through bead milling dispersion, the rheological properties are controlled through low temperature compressibility enhancement, and finally, the printing defects such as bubbles are prevented through vacuum filtration and degassing, thereby forming a magnetic ink system that is compatible with various printing methods.

[0042] It should also be noted that in the raw material pretreatment step, the nano-sized soft magnetic ferrite powder and silver-coated flake copper powder are dried at 60℃ and 40%RH for 2 hours respectively, cooled to 25℃, and then placed in an inert nitrogen chamber for later use. This eliminates physically adsorbed water and trace organic residues in the powder, preventing bubbles or gel agglomeration during subsequent reactions with organic coupling agents and resins. It also controls ambient humidity to prevent oxidation of the silver-coated copper powder and ensures conductivity. Using an inert atmosphere (such as nitrogen) isolates the powder from air, reduces oxidation and moisture absorption rates, and improves the retention of powder activity. The dryness of the powder directly affects the efficiency of the coupling activation reaction and the uniformity of dispersion. If water residue is present, the silane coupling agent will hydrolyze and fail, resulting in weak bonding between the powder and resin. The raw material pretreatment step provides a clean and highly active starting point for the entire ink system, which is a prerequisite for ensuring subsequent performance. In the coupling activation step, 0.5-1.5 wt% of γ-glycidoxypropyltriethoxysilane is added to a premix consisting of 40 wt% bisphenol A epoxy acrylate prepolymer and tripropylene glycol diacrylate, and the mixture is reacted at 45°C for 30 minutes. In this way, γ-glycidoxypropyltriethoxysilane hydrolyzes in the solvent medium to form 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, constructing a covalent interfacial bridge structure between the powder, coupling agent, and resin. This enhances the interfacial bonding between the powder and the organic phase, improving the system's storage stability and shear resistance. The coupling reaction is carried out before dispersion, preventing the surface-coated magnetic powder from being damaged by mechanical shear during high-speed bead milling, thus improving stable dispersion efficiency and interfacial wettability, and reducing the risk of re-agglomeration after bead milling. In the efficient dispersion step, a nano-bead mill with a rotor linear speed of 12 m / s is used to grind the pretreated powder and coupling liquid for 20 minutes, resulting in a D-value of the nano-scale soft magnetic ferrite powder. 50 D is a 0.1-0.3µm, silver-coated flake copper powder. 50≤8µm, particle size variance ≤0.1. Nanoscale bead milling enables powder refinement and uniform particle size control. Simultaneously, it utilizes mechanical shearing to synergistically couple interfacial reactions, enhancing particle surface activation and ultimately forming a highly dispersed, narrowly distributed filler system. Controlling the particle size variance to ≤0.1 improves the edge clarity of printed patterns and ink stability, preventing screen clogging or pattern line breaks during subsequent printing. A stable nanoscale filler dispersion system lays the foundation for subsequent viscosity control, avoiding particle aggregation and system gelation during compatibilization, achieving simultaneous control of particle size and rheology. In the resin compatibilization-rheology control step, modified polyester resin, polyamide-imide resin, and low-polymerization-degree polyurethane compatibilizer are added at 30-40℃. Degassing is performed for 15 minutes at -0.09MPa using a dual planetary vacuum mixer, adjusting the system viscosity to 4±0.5Pa·s. In this way, resins with different structures participate in network formation: polyester resin provides flexibility, polyamide-imide enhances resistance to humid heat adhesion, and polyurethane compatibilizer improves compatibility and rheological properties. Vacuum degassing prevents air bubbles from entering the high-filler, high-viscosity system, improving ink density uniformity and the density of the printed film. Controlling the viscosity window adapts to screen printing, gravure printing, inkjet printing, and other processes, avoiding sagging or doctor blade residue in high-speed printing. The already highly uniform filler dispersion system is synergistically mixed with various functional resins in this step, ensuring the rheological and mechanical stability of the filler in the final ink, improving ink reproducibility and batch consistency. In the functional additive fine-tuning step, photoinitiators, antioxidants, and leveling agents are added. After standing for 30 minutes and venting, the mixture is filtered through a 0.2µm stainless steel filter and the finished product is sealed with nitrogen. The photoinitiator system ensures rapid curing of the ink under 395nm UV LED irradiation (1.5s), and low shrinkage (≤4%) prevents tearing of PET / metal foil. Antioxidants enhance storage stability, while leveling agents improve film surface quality and reduce pinholes and swirls. Static setting and fine filtration together ensure final ink particle size and cell control, avoiding microscopic defects. This step ensures that photoinitiator / leveling sensitive components are added only after the system's rheological properties are controlled, avoiding the risk of premature reaction or phase separation during film formation and improving compatibility with final application processes.

[0043] Preferably, the pH value of the coupling activation reaction in the coupling activation step is controlled at 4-5, and the value is monitored at 915 cm⁻¹ by online Fourier transform infrared-ATR. -1 The degree of attenuation of the characteristic absorption peak of the epoxy group was used as the endpoint of the coupling reaction to ensure that the coupling agent fully coats the surface of the nano-sized soft magnetic ferrite powder and strengthens interfacial adhesion. It should be noted that by controlling the pH of the coupling reaction within the range of 4-5, the end group of γ-glycidyl etheroxypropyltriethoxysilane is activated, reacting with the hydroxyl groups on the ferrite surface to form a stable covalent bond. Simultaneously, Fourier transform infrared (ATR) monitoring showed that the epoxy group was located at 915 cm⁻¹. -1The characteristic absorption peak attenuation process can be observed to determine the reaction endpoint in real time, improve coupling efficiency and consistency, enhance the adhesion between magnetic powder and resin, and improve film-forming performance and interface reliability.

[0044] Preferably, immediately after grinding in the high-efficiency dispersion step, coarse particles are removed 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%, preventing screen clogging during subsequent printing. It should be noted that the high-speed centrifugation process at 5000 rpm after bead milling can effectively remove residual coarse particles and undispersed agglomerates. Combined with laser particle size analysis to precisely control the particle size distribution (controlling the volume fraction of particles larger than 1µm to ≤0.3%), this ensures that there is no risk of screen clogging in the printing of fine patterns, thereby improving printing consistency and pattern boundary clarity, and achieving narrow line printing of 70-100µm.

[0045] Preferably, the resin compatibilization-rheology regulation step employs dual-frequency ultrasonic synergistic planetary stirring at 25kHz and 40kHz to reduce the interfacial adhesion energy between the resin and nanoscale soft magnetic ferrite powder by 15%, thereby improving low-shear fluidity and thixotropic recovery rate, resulting in a viscosity increase of ≤7% after 6 months of storage at 25℃. It should be noted that the use of dual-frequency ultrasonic synergistic planetary stirring at 25kHz and 40kHz creates a macro- and micro-scale resonant cavitation effect, improving the interfacial wetting and adhesion energy between the resin and filler, enhancing the fluidity and thixotropy of the filler under low-shear conditions, and improving storage stability (viscosity change ≤7% after 6 months), thus solving the problem of easy layering and thickening of traditional magnetic inks after long-term storage.

[0046] It should be noted that the above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention, and the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A magnetic ink for electronic tags in RFID devices, characterized in that, The product comprises, by weight percentage: 20-40% bisphenol A epoxy acrylate prepolymer, 5-20% modified polyester resin, 3-15% polyamide-imide resin, 15-35% nano-sized soft magnetic ferrite powder, 2-10% silver-coated flake copper powder, 1-8% low-polymerization-degree polyurethane compatibilizer, 0.2-2% γ-glycidyl etheroxypropyltriethoxysilane coupling agent, 0.5-5% bis(2,4-dimethylbenzoyl)diphenylphosphine photoinitiator, 0.1-1% hindered phenolic antioxidant, 0.1-1% polyether-modified acrylate leveling agent, and 5-15% tripropylene glycol diacrylate reactive diluent monomer; wherein the nano-sized soft magnetic ferrite powder contains D 50 The thickness is 0.1-0.30 μm, and the surface is treated with phosphate ester-silane double coating. After UV curing, it provides an initial permeability of 20-60 and maintains a loss tangent of ≤0.05 in the 13.56 MHz frequency band. The modified polyester resin has a carboxyl content of 0.4-0.6 mmol / g. -1 The linear saturated polyester was modified with bisphenol S epoxy acrylate end groups, and the glass transition temperature Tg was controlled at -10-5℃, so that the cured film layer could still maintain its torsion without cracks after 500 cycles at -40-85℃. The polyamide-imide resin has an imidization degree between 15-35%, and its main chain introduces an o-hydroxybenzoyl-p-phenylene rigid structure. Through the synergistic effect of hydrogen bonding and epoxy acrylate crosslinking network, the peel strength decreases by no more than 10% under 1000h conditions at 85℃ / 85%RH. The nanoscale soft magnetic ferrite powder is Ni 0.5 Zn 0.5 Fe2O4 was prepared by a two-step sintering process using thiourea-citric acid co-precipitation combined with an inert atmosphere, achieving a saturation magnetization Ms ≥ 70 emu. -1 Under a magnetic field of 100 mT, the relative reversible permeability 0□≥2.5; The surface coating of the nanoscale soft magnetic ferrite powder is a gradient composite film of 3-methacryloyloxypropyltrimethoxysilane and zirconium dodecyl phosphate with a relative concentration of 3:

1. After vacuum heat treatment at 110℃ for 2 hours, a nanoscale interactive network resin-loving layer is formed. The silver-coated flake copper powder has an aspect ratio of 40-120 and a flake diameter of 5-200 μm. A continuous and dense silver shell is obtained through cyanide-free silver-palladium bimetallic autocatalytic replacement, with a bulk resistivity ≤1.5 × 10⁻⁶. -5 Ω·cm, and after UV curing, it forms a magnetic-conductivity complementary microstructure network with nano-ferrite; The photoinitiator is a mixture of bis(2,4-dimethylbenzoyl)diphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone in a 3:2 ratio, with the addition of 0.05-0.2 wt% of a catalytic tertiary amine synergist. Bimodal radical-cation coupling curing is achieved by irradiation with a narrow-spectrum 395 nm UV-LED for 1.5 s, and the curing shrinkage rate is controlled to ≤4%.

2. A method for preparing magnetic ink for RFID device electronic tags as described in claim 1, characterized in that, include: Raw material pretreatment steps: The nano-sized soft magnetic ferrite powder and silver-coated flake copper powder were dried at 60℃ and 40%RH for 2 hours respectively, and then cooled to 25℃ and placed in an inert nitrogen box for later use. Coupling activation step: Add 0.5-1.5 wt% γ-glycidyl etheroxypropyltriethoxysilane to 40 wt% bisphenol A epoxy acrylate prepolymer-tripropylene glycol diacrylate premix and react at 45°C for 30 min to form an epoxy-active interface layer. High-efficiency dispersion step: A nano-bead mill is used with a rotor linear speed of 12 ms. -1 The powder mixture obtained in the raw material pretreatment step and the interface layer mixture obtained in the coupling activation step are ground for 20 minutes to reduce the D of the nano-scale soft magnetic ferrite powder. 50 D, consisting of 0.1-0.30 μm silver-coated flake copper powder 50 ≤80m, and the variance of the dispersed particle size ≤0.1; Resin compatibilization-rheology regulation steps: Modified polyester resin, polyamide-imide resin and low-polymerization-degree polyurethane compatibilizer are added sequentially at 30-40℃. The mixture is degassed for 15 minutes using a double planetary vacuum mixer at -0.09MPa, and the viscosity of the system is adjusted to 4±0.5Pa·s. Functional additive fine-tuning steps: Add photoinitiator, hindered phenolic antioxidant and leveling agent under slow stirring at room temperature, let stand under vacuum for 30 minutes to remove residual air bubbles, filter through a 0.20m stainless steel filter, and encapsulate with nitrogen to obtain the finished magnetic ink.

3. The preparation method according to claim 2, characterized in that, In the coupling activation step, the pH value of the reaction is controlled at 4-5, and the value is monitored at 915 cm⁻¹ using online Fourier transform infrared spectroscopy-ATR. -1 The degree of reduction of the characteristic absorption peak of the epoxy group is used as the endpoint of the coupling reaction to ensure that the coupling agent fully coats the surface of the nanoscale soft magnetic ferrite powder and strengthens the interfacial adhesion.

4. The preparation method according to claim 3, characterized in that, After grinding in the high-efficiency dispersion step, coarse particles are removed immediately by centrifugation at 5000 rpm for 10 min. Laser particle size analysis is used to control the volume fraction of particles larger than 10 μm to ≤0.3% to prevent screen clogging during subsequent printing.

5. The preparation method according to claim 4, characterized in that, In the resin compatibilization-rheology regulation step, dual-frequency ultrasonic synergistic planetary stirring at 25kHz+40kHz is used to reduce the adhesion energy of the resin-nanoscale soft magnetic ferrite powder interface by 15%, improve low shear flowability and thixotropic recovery rate, and make the viscosity of the ink increase by ≤7% after 6 months of storage at 25℃.

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