Preparation method of environment-friendly multifunctional printing ink based on excimer UV curing

Abstract

The invention relates to a preparation method of environment-friendly multifunctional printing ink based on excimer UV curing, and belongs to the field of printing ink preparation. The preparation method comprises the following steps: compounding a hydroxyl-containing aliphatic polyurethane acrylate prepolymer and a carboxyl-containing epoxy acrylate oligomer according to a specific ratio; and adding a compound photoinitiator, a modified nano silicon dioxide filler and other components, and carrying out secondary sanding, vacuum defoaming and other processes to obtain the ink. According to the method, the adhesive force of a base material is improved through a hydroxyl-carboxyl synergistic effect, the wear resistance and hardness of a film layer are enhanced through nanofiller modification and a gradient grinding process, and efficient curing under 172nm excimer ultraviolet light is realized by compounding a photoinitiator. The curing time of the prepared ink is less than or equal to 1.5 seconds (the film thickness is 10 microns), the pencil hardness is more than or equal to 3H, the acetone wiping resistance is more than or equal to 50 times, the solid content is 65-75%, no VOC (Volatile Organic Compounds) is discharged, the problems that the traditional UV ink is slow in curing and unbalanced in performance are solved, and the ink is suitable for the fields of high-speed printing, high-end packaging, electronic circuits and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of printing ink preparation, and in particular to a method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing. Background Art

[0002] As a key material for conveying graphic information, the performance of printing inks directly impacts print quality and its scope of application. With increasing environmental protection requirements and advancements in printing technology, excimer UV curing technology, with its advantages such as fast curing speed, low energy consumption, and zero volatile organic compound (VOC) emissions, is gaining increasing popularity in packaging printing, electronic circuits, and other fields. However, existing excimer UV curing printing inks still face several challenges in practical application. Firstly, traditional formulations often utilize a single prepolymer, resulting in a struggle to balance adhesion, flexibility, and abrasion resistance after curing. This is particularly true on non-absorbent substrates such as plastics and metals, where peeling and cracking are common. Secondly, the inefficient photoinitiator system results in slow curing speeds under 172nm excimer UV light, making it difficult to meet the demands of high-speed printing lines. Furthermore, issues such as poor filler dispersion and unstable viscosity control also affect the ink's application performance and final film quality. Summary of the Invention

[0003] The main purpose of the present invention is to provide a method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing, which can significantly improve the curing efficiency, improve the comprehensive performance of the film layer and make the process controllable.

[0004] To achieve the above object, the present invention provides a method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing, comprising the following steps: Add hydroxyl-containing aliphatic polyurethane acrylate prepolymer, carboxyl-containing epoxy acrylate oligomer, difunctional propylene glycol methyl ether acrylate reactive diluent, and trimethylolpropane triacrylate functional monomer in a mass ratio of 40-50:20-30:15-25:10-15 into a reactor, and stir at a low speed at 50-60°C for 30-45 minutes until they are completely dissolved in each other; Add 0.8-1.5% of the total mass of the system of α-hydroxycyclohexyl phenyl ketone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide compound photoinitiator, 0.3-0.8% of organic silicon leveling agent, and 1-2% of nano-silica wear-resistant filler, raise the temperature to 65-75°C and disperse at high speed for 60-90 minutes to form a homogeneous mixture; The mixture was transferred to a sand mill, and zirconia beads with a diameter of 0.3-0.5 mm were used as the grinding medium. The grinding pressure was controlled at 0.4-0.6 MPa, and the mixture was cyclically ground until the slurry fineness was ≤15 μm. Add deionized water to the ground slurry to adjust the system viscosity to 80-120mPa s, degassing for 15-20 minutes at a vacuum degree of -0.08 to -0.06 MPa, and finally preparing a printing ink with a solid content of 65-75%.

[0005] Furthermore, the hydroxyl-containing aliphatic polyurethane acrylate prepolymer has a hydroxyl value of 50-80 mgKOH / g, a number average molecular weight of 2000-3000 Da, and contains a hexamethylene diisocyanate-derived segment in its molecular structure.

[0006] Furthermore, the carboxyl content of the carboxyl-containing epoxy acrylate oligomer is 1.5-2.5 mmol / g, and it is prepared by a ring-opening esterification reaction of bisphenol A epoxy resin and acrylic acid, and the acid value is controlled at 30-50 mgKOH / g.

[0007] Furthermore, the mass ratio of α-hydroxycyclohexyl phenyl ketone to 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in the composite photoinitiator is 2:1-3:1, wherein the phosphorus content of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide is ≥10wt%.

[0008] Furthermore, the organosilicon leveling agent is polyether-modified polydimethylsiloxane with a molecular weight of 8000-12000 Da, and needs to be vacuum-dried at 50° C. for 2 hours to remove adsorbed water before addition.

[0009] Furthermore, the nano-silica wear-resistant filler has an average particle size of 50-80 nm, and its surface is modified with γ-methacryloxypropyltrimethoxysilane, with the amount of the modifier being 3-5% of the filler mass.

[0010] Furthermore, the sand mill adopts a two-stage series process during grinding, with a first-stage grinding pressure of 0.6 MPa, a second-stage grinding pressure of 0.4 MPa, and a cycle number of not less than 3 times.

[0011] Furthermore, the conductivity of the deionized water is ≤10 μS / cm, and when adjusting the viscosity, low-speed stirring of 300-500 rpm is adopted and the reading of the rotational viscometer is detected simultaneously.

[0012] Furthermore, during the vacuum degassing process, the temperature in the kettle is maintained at 40-50° C. and controlled by an external circulating water system, and 0.1-0.3% of 2,6-di-tert-butyl-p-cresol is added as a stabilizer 5 minutes before the end of the degassing.

[0013] Furthermore, the curing performance of the printing ink satisfies the following requirements: under 172nm excimer ultraviolet lamp irradiation, the curing time is ≤1.5 seconds when the film thickness is 10 μm, the pencil hardness is ≥3H, and the number of acetone wiping resistance is ≥50 times.

[0014] The preparation method of the environmentally friendly multifunctional printing ink based on excimer UV curing provided by the present invention has the following beneficial effects: (1) By compounding a hydroxyl-containing aliphatic polyurethane acrylate prepolymer with a carboxyl-containing epoxy acrylate oligomer, the synergistic effect of hydroxyl and carboxyl groups is utilized to significantly improve the adhesion between the ink and the substrate and the flexibility of the cured film layer, thus solving the problem of unbalanced performance of the traditional single prepolymer system; (2) After being modified with silane, the nano-silica filler has excellent compatibility with the resin matrix. Combined with a specific sand mill grinding process, the filler is evenly dispersed in the ink, effectively improving the wear resistance and hardness of the film layer while avoiding performance degradation caused by agglomeration.

[0015] (3) α-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide are used as a composite photoinitiator. The complementary absorption wavelength characteristics of different initiators are utilized to greatly improve the initiation efficiency under excimer ultraviolet light, and the ink is quickly cured within 1.5 seconds, meeting the production requirements of high-speed printing. In addition, no harmful solvents are added during the entire preparation process, and the solid content is controlled at 65-75%, which is in line with the development trend of environmentally friendly inks. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 1 is a schematic flow chart of a method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to one embodiment of the present invention; Figure 2 This is a molecular diagram of α-hydroxycyclohexyl phenyl ketone in a method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing in one embodiment of the present invention; Figure 3 This is a molecular diagram of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in a method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing in one embodiment of the present invention; Figure 4 This is one of the microscopic images of the printing ink in the method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing in one embodiment of the present invention; Figure 5 This is a second microscopic image of the printing ink in the method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing in one embodiment of the present invention; Figure 6 This is a diagram of the actual application scenario of the printing ink in the preparation method of the environmentally friendly multifunctional printing ink based on excimer UV curing in one embodiment of the present invention.

[0017] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] Reference Figure 1-6 The following is a process flow diagram, molecular diagram, microscopic image diagram, and actual application scenario diagram of a method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing proposed by the present invention. The process method includes the following steps: S100, adding a hydroxyl-containing aliphatic polyurethane acrylate prepolymer, a carboxyl-containing epoxy acrylate oligomer, a difunctional propylene glycol methyl ether acrylate reactive diluent, and a trimethylolpropane triacrylate functional monomer in a mass ratio of 40-50:20-30:15-25:10-15 into a reaction kettle, and stirring at a low speed at 50-60° C. for 30-45 minutes until they are completely dissolved in each other; S200, add 0.8-1.5% of the total mass of the system of α-hydroxycyclohexyl phenyl ketone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide compound photoinitiator, 0.3-0.8% of organic silicone leveling agent, 1-2% of nano-silica wear-resistant filler, heat to 65-75 ° C and disperse at high speed for 60-90 minutes to form a homogeneous mixture; S300, the mixture is transferred to a sand mill, and zirconia beads with a diameter of 0.3-0.5 mm are used as grinding media. The grinding pressure is controlled at 0.4-0.6 MPa, and the mixture is cyclically ground until the slurry fineness is ≤15 μm; S400, add deionized water to the ground slurry to adjust the system viscosity to 80-120mPa s, degassing for 15-20 minutes at a vacuum degree of -0.08 to -0.06 MPa, and finally preparing a printing ink with a solid content of 65-75%.

[0020] Step S100 is a fundamental step in the entire preparation process. A hydroxyl-containing aliphatic urethane acrylate prepolymer, a carboxyl-containing epoxy acrylate oligomer, a difunctional propylene glycol methyl ether acrylate reactive diluent, and a trimethylolpropane triacrylate functional monomer are added to a reactor in a specific mass ratio and stirred under controlled conditions. The hydroxyl-containing aliphatic urethane acrylate prepolymer, as one of the main resins, has hydroxyl groups in its molecular structure that can form hydrogen bonds with polar groups on substrate surfaces (such as metals and plastics), significantly improving the ink's adhesion to non-absorbent substrates. The introduction of aliphatic segments imparts excellent flexibility and low-temperature resistance to the cured film. The carboxyl-containing epoxy acrylate oligomer is produced by the ring-opening esterification of bisphenol A epoxy resin with acrylic acid. The carboxyl groups can form hydrogen bonds with the hydroxyl groups in the prepolymer, enhancing compatibility between the resins. Furthermore, the epoxy acrylate segments in its molecular structure are highly reactive, forming a dense cross-linked network during the excimer UV curing process, improving the film's hardness and chemical resistance. The difunctional propylene glycol methyl ether acrylate reactive diluent serves the dual purpose of diluting the system's viscosity and participating in the crosslinking reaction. The methoxy structure in its molecule improves the wettability of the resin and filler, while the difunctional structure connects different prepolymer molecules during curing to form a uniform network. Trimethylolpropane triacrylate, a multifunctional crosslinker, rapidly initiates free radical polymerization with its three acrylate groups under photoinitiation, increasing the system's crosslinking density and thus improving the ink's curing speed and the film's mechanical strength. The reaction temperature is controlled at 50-60°C and low-speed stirring is employed to promote swelling and diffusion between the components through moderate molecular thermal motion while avoiding high-temperature decomposition of the prepolymer. This ensures that the components are fully miscible within a mass ratio range of 40-50:20-30:15-25:10-15, forming a stable, uniform preliminary mixture.

[0021] In step S200, adding a specific ratio of a composite photoinitiator, a silicone leveling agent, and a nano-silica wear-resistant filler to the pre-mixed resin system, and controlling the heating and dispersion conditions, is a key step in achieving the multifunctionality of the ink. The composite photoinitiator consists of α-hydroxycyclohexyl phenyl ketone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in a mass ratio of 2:1-3:1, accounting for 0.8-1.5% of the total mass of the system. α-hydroxycyclohexyl phenyl ketone has high light absorption efficiency under 172nm excimer ultraviolet light, which can quickly generate primary free radicals to initiate polymerization. 2,4,6-trimethylbenzoyl-diphenylphosphine oxide acts as a highly efficient co-initiator. The phosphoryl group in its molecular structure can capture hydrogen atoms in the system, generating more active free radicals. The synergistic effect of the two creates a complementary wavelength absorption range and a superposition of initiation efficiencies, ensuring that the curing reaction is initiated and completed in a very short time. The silicone leveling agent uses polyether-modified polydimethylsiloxane with a molecular weight of 8,000-12,000 Da. It is vacuum-dried at 50°C before addition to remove adsorbed water, thus preventing surface defects caused by moisture. The polyether segments in the molecule are highly compatible with the resin matrix, while the siloxane segments effectively reduce the surface tension of the ink, promoting even ink spreading across the substrate and eliminating coating defects such as craters and orange peel. An addition level of 0.3-0.8% achieves a balance between leveling and anti-crater performance. The wear-resistant nanosilica filler has an average particle size of 50-80 nm and is modified with γ-methacryloxypropyltrimethoxysilane (3-5% of the filler mass). The double bonds grafted onto the surface copolymerize with the acrylate groups in the resin, significantly improving the interfacial bonding between the filler and the resin matrix. A 1-2% addition enhances film hardness and wear resistance through the rigid support provided by the nanoparticles while avoiding the sudden increase in system viscosity or difficulty in dispersion caused by excessive filler. The temperature is raised to 65-75°C and high-speed dispersion is used for 60-90 minutes in order to improve the fluidity of the material while fully dispersing the fillers and additives through mechanical shear force. This temperature range not only ensures the chemical stability of the photoinitiator and leveling agent, but also enables the modified nano-silica to deagglomerate in the resin melt. The shear force generated during the high-speed dispersion process can destroy the weak interactions between the filler particles, causing them to be evenly distributed in the system in a monodisperse state, ultimately forming a mixture with uniform optical and mechanical properties.

[0022] In step S300, the preliminarily mixed materials are transferred to a sand mill for fine grinding. This is a critical process for ensuring sufficient dispersion of the solid particles in the ink, improving system stability, and enhancing film quality. Zirconia beads with a diameter of 0.3-0.5 mm are selected as the grinding medium. Due to their high hardness (Mohs hardness 8.5-9), low abrasion rate (≤0.1‰), and chemical inertness, they prevent the medium from abrading and introducing impurities during the grinding process while effectively shearing and breaking up any aggregates of nano-silica filler and additives. Beads in this particle size range provide sufficient surface area for contact with the material while forming a dense collision and dispersion zone within the turbulent flow of the sand mill chamber, meeting the dispersion requirements of fillers with particle sizes of 50-80 nm.

[0023] The grinding pressure is controlled at 0.4-0.6MPa by adjusting the feed pump pressure of the sand mill: the lower pressure (0.4MPa) is suitable for the initial cycle grinding to avoid excessive shear force that causes damage to the filler surface modification layer or breakage of the prepolymer molecular chain; as the number of cycles increases, it is gradually increased to 0.6MPa to enhance the grinding effect and ensure that the agglomerated particles are effectively peeled off. A cyclic grinding process (the specific implementation of the two-stage series process described in claim 7) is adopted. Through the synergistic effect of different pressure gradients in the multi-stage grinding chamber (first stage 0.6MPa coarse grinding, second stage 0.4MPa fine grinding), the slurry undergoes at least 3 cycles of shear, collision and friction inside the chamber, and finally achieves the control target of slurry fineness ≤15μm. This fineness index ensures that the filler is evenly distributed in the resin matrix in the form of monodisperse or small aggregates, avoiding problems such as printing screen blocking and rough film surface caused by coarse particles, while providing a homogeneous system with good fluidity for the subsequent degassing process. During the grinding process, the mechanical energy generated by the high-speed movement of the zirconia beads is converted into shear energy of the material, which not only promotes the dispersion of the filler, but also further enhances the compatibility between the components, allowing functional additives such as photoinitiators and leveling agents to form stable intermolecular interactions with the resin matrix.

[0024] In step S400, deionized water is added to the ground slurry and vacuum degassing is performed. This is a key step in achieving ink application performance control and ensuring the quality of the finished product. First, the conductivity of the deionized water is controlled at ≤10μS / cm to prevent ionic impurities in the water from adversely affecting the stability of the resin system and the curing reaction. The system viscosity is precisely adjusted to 80-120mPa by simultaneously monitoring the reading of the rotational viscometer through low-speed stirring (300-500rpm). s. This viscosity range meets the ink fluidity requirements of common processes such as screen printing and flexographic printing, ensuring even transfer of the ink to the substrate surface during printing and avoiding screen blocking or poor conformal properties caused by excessive viscosity. During the water addition process, deionized water forms weak hydrogen bonds with polar groups (such as hydroxyl and carboxyl) in the resin system, optimizing viscosity without compatibility issues. This also keeps the solids content within a range of 65-75%, balancing the ink's environmental friendliness (low VOC emissions) and film-forming efficiency (high solids content ensures a thick film is formed in one go).

[0025] The vacuum degassing process is performed at a vacuum of -0.08 to -0.06 MPa for 15-20 minutes. Meanwhile, the kettle temperature is maintained at 40-50°C via an external circulating water system. This effectively reduces the surface tension of bubbles within the system, encouraging the rise and collapse of tiny bubbles introduced during grinding and stirring. Under vacuum, the boiling point of the liquid is lowered, increasing the kinetic energy of gas molecules dissolved in the ink and facilitating their escape from the system. Temperature control prevents premature decomposition of the photoinitiator or oxidation of the resin caused by excessive heating. Five minutes before the end of the degassing process, 0.1-0.3% of 2,6-di-tert-butyl-p-cresol (BHT) is added. Its phenolic hydroxyl group traps free radicals in the system, inhibiting potential oxidative degradation during storage and extending the ink's shelf life. This process optimizes both application performance (viscosity and rheology) and storage stability. Its solids content meets the trend for environmentally friendly UV-curable inks, avoiding the volatile contamination associated with traditional solvent-based inks.

[0026] In Example 1, the hydroxyl-containing aliphatic polyurethane acrylate prepolymer has a hydroxyl value of 50-80 mgKOH / g, a number average molecular weight of 2000-3000 Da, and contains a hexamethylene diisocyanate-derived segment in its molecular structure.

[0027] In this Example 1, the hydroxyl-containing aliphatic polyurethane acrylate prepolymer is prepared by the following method: using hexamethylene diisocyanate (HDI), polytetramethylene ether glycol (PTMG, molecular weight 1000Da), and dimethylol propionic acid (DMPA) as raw materials, a prepolymerization reaction is carried out at 80°C under nitrogen protection, and then end-capping with hydroxyethyl acrylate to obtain a series of prepolymers having hydroxyl values of 50mgKOH / g, 65mgKOH / g, and 80mgKOH / g, respectively, and number average molecular weights (measured by GPC) of 2000Da, 2500Da, and 3000Da, respectively. The proportion of HDI-derived chain segments in the molecular structure of the prepolymers was verified to be 35-45mol% by infrared spectroscopy (FT-IR).

[0028] Based on the above basic formula, a prepolymer (45 parts by mass), a carboxyl-containing epoxy acrylate oligomer (25 parts by mass), propylene glycol methyl ether acrylate (20 parts by mass), and trimethylolpropane triacrylate (10 parts by mass) were weighed. Two control groups were then set up: Comparative Example 1: a prepolymer with a hydroxyl value of 30 mgKOH / g and a molecular weight of 1500 Da was used; and Comparative Example 2: an aromatic polyurethane acrylate prepolymer (without an HDI-derived segment) was used. The experimental data are shown in Table 1:

[0029] Table 1

[0030] Influence of hydroxyl value: When the hydroxyl value of Examples 1-1 to 1-3 is in the range of 50-80 mgKOH / g, the hydroxyl groups form strong hydrogen bonds with the polar groups on the surface of the substrate, and the adhesion reaches level 0, which is significantly better than that of Comparative Example 1 (the insufficient hydroxyl value leads to low hydrogen bond density, and the adhesion drops to level 2).

[0031] Molecular weight effect: When the number average molecular weight is 2000-3000Da, the flexibility of the prepolymer chain segment is balanced with the cross-linking density, and there is no cracking in the T-bend test (T0 level). In comparative example 1, due to the low molecular weight (1500Da), the chain segment is too short, resulting in increased brittleness of the film layer, and T2 level cracking occurs after bending.

[0032] Advantages of the chain segment structure: The weather resistance of the example containing the HDI-derived chain segment is ΔE ≤ 1.3, which is much better than that of Comparative Example 2 (the aromatic chain segment is easily damaged by UV light due to the benzene ring structure, and the ΔE = 3.5 exceeds the standard), proving that the aliphatic structure significantly improves weather resistance.

[0033] In Example 2, the carboxyl content of the carboxyl-containing epoxy acrylate oligomer is 1.5-2.5 mmol / g, and the epoxy acrylate oligomer is prepared by a ring-opening esterification reaction of bisphenol A epoxy resin and acrylic acid, and the acid value is controlled at 30-50 mgKOH / g.

[0034] Specifically, bisphenol A epoxy resin (E-51, epoxy value 0.51eq / 100g) and acrylic acid (AA) are used as raw materials, and the epoxy group to carboxyl group molar ratio is 1:1.2. 0.5% p-toluenesulfonic acid (catalyst) and 1% hydroquinone (inhibitor) are added. The temperature is raised to 120°C under nitrogen protection, and the reaction is carried out for 4-6 hours. The reaction end point is controlled by real-time monitoring of the acid value (potentiometric titration method), and oligomers (denoted as Oligomer-1, Oligomer-2, and Oligomer-3) with carboxyl group contents of 1.5mmol / g, 2.0mmol / g, and 2.5mmol / g, respectively, and acid values of 30mgKOH / g, 40mgKOH / g, and 50mgKOH / g, respectively, are obtained.

[0035] Using a basic formulation, the prepolymer (45 parts by mass), reactive diluent (20 parts by mass), and functional monomer (10 parts by mass) were fixed, and oligomers with different carboxyl group contents (25 parts by mass) were substituted. Comparative Example 1 was used with a carboxyl group content of 1.0 mmol / g and an acid value of 20 mgKOH / g; Comparative Example 2 was used with a carboxyl group content of 3.0 mmol / g and an acid value of 60 mgKOH / g; and Comparative Example 3 used unmodified bisphenol A epoxy resin. The experimental data are shown in Table 2.

[0036] Table 2

[0037] The key role of carboxyl content: When the carboxyl content of Examples 2-1 to 2-3 ranged from 1.5 to 2.5 mmol / g, the carboxyl groups formed hydrogen bonds with the prepolymer hydroxyl groups, resulting in homogeneous resin compatibility. Furthermore, Tg increased with increasing carboxyl content (62°C → 70°C), indicating a higher crosslink density. In Comparative Example 1, insufficient carboxyl groups weakened hydrogen bonding, resulting in reduced compatibility and a low crosslink density (Tg = 50°C). In Comparative Example 2, excessive carboxyl groups enhanced intermolecular electrostatic repulsion, causing gel precipitation and, in turn, reducing the number of effective crosslinking points.

[0038] Balance between acid value and reactivity: An acid value of 30-50 mgKOH / g corresponds to a moderate degree of esterification, retaining sufficient carboxyl groups for hydrogen bonding while avoiding storage stability issues caused by residual unreacted acrylic acid. Comparative Example 1, with an acid value too low (20 mgKOH / g), exhibited incomplete esterification, with residual hydroxyl groups susceptible to reaction with the photoinitiator, resulting in an acetone-resistant rub count of only 35. Comparative Example 2, with an acid value too high (60 mgKOH / g), exhibited excessive carboxyl groups, leading to interchain repulsion and increased film brittleness, resulting in a rub count drop of only 45.

[0039] Synergistic effect with prepolymer: When comparative example 3 uses carboxyl-free epoxy resin, due to the lack of interaction between polar groups, the resin is "heterogeneous" after mixing, the cured film is not fully cross-linked, and the acetone wiping resistance is only 20 times, which is significantly lower than the example containing carboxyl oligomer.

[0040] In Example 3, the mass ratio of α-hydroxycyclohexyl phenyl ketone to 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in the composite photoinitiator is 2:1-3:1, wherein the phosphorus content of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide is ≥10wt%.

[0041] HCPK and TPO-L (phosphorus content 12 wt%) were weighed in a mass ratio of 2:1, 2.5:1, and 3:1, and magnetically stirred at 50°C for 30 minutes until completely dissolved to prepare a series of composite initiators (denoted as I-1, I-2, and I-3).

[0042] Comparative Example 1: mass ratio 1:1; Comparative Example 2: mass ratio 4:1; Comparative Example 3: using a single HCPK (without TPO-L); Comparative Example 4: TPO-L with a phosphorus content of 8 wt% was used.

[0043] Experimental data refer to Table 3:

[0044] Table 3

[0045] Synergistic Effect of the Mixing Ratio: In Examples 3-1 to 3-3, when the ratio was between 2:1 and 3:1, HCPK (primary absorption at 172nm) and TPO-L (assisting in the generation of active phosphorus free radicals) formed complementary absorption and synergistic free radical generation, increasing the absorption coefficient ε to over 0.85, achieving a curing time of ≤1.3 seconds and a degree of cure of ≥98%. In Comparative Example 1 (1:1), insufficient TPO-L resulted in low free radical generation, extending the curing time to 2.0 seconds and reducing the acetone rub count to 40. In Comparative Example 2 (4:1), excessive HCPK saturated the initiator's absorption capacity, resulting in a light-shielding effect from the excess molecules, which reduced curing efficiency.

[0046] The key role of the phosphorus content in TPO-L: When comparative example 4 used TPO-L with a phosphorus content of 8wt%, although the compounding ratio was appropriate (2.5:1), the insufficient phosphorus content resulted in a low concentration of phosphoryl groups, a decrease in hydrogen atom capture efficiency, a curing degree of only 95%, and a pencil hardness of 2H, proving that a phosphorus content of ≥10wt% is a necessary condition to ensure efficient free radical generation.

[0047] Limitations of a single initiator: When using a single HCPK in Comparative Example 3, due to the lack of TPO-L's co-initiation effect, the curing time is as long as 3.5 seconds, the curing degree is only 85%, and the film hardness and solvent resistance are significantly reduced, highlighting the necessity of a compound system.

[0048] In Example 4, the organosilicon leveling agent is polyether-modified polydimethylsiloxane with a molecular weight of 8000-12000 Da. Before addition, it needs to be vacuum-dried at 50° C. for 2 hours to remove adsorbed water.

[0049] Example samples: polyether-modified siloxanes with molecular weights of 8000Da (denoted as FL-1), 10000Da (FL-2), and 12000Da (FL-3), with the polyether segment being PEG-1000 (accounting for 30 mol%); Comparative Example 1: molecular weight 6000Da (below the range); Comparative Example 2: molecular weight 14000 Da (above the range); Comparative Example 3: No drying treatment (water content 0.5wt%); Comparative Example 4: Unmodified polydimethylsiloxane (without polyether segment) was used.

[0050] Experimental data refer to Table 4:

[0051]

[0052] Table 4

[0053] The key influence of molecular weight: When the molecular weight of Examples 4-1 to 4-3 was between 8000 and 12000 Da, the ratio of polyether segments to siloxane segments was well-matched, and the surface tension was controlled at 23.8-24.5 mN / m, significantly lower than that of the substrate (PET surface tension of 38 mN / m). The initial contact angle was ≤35°, rapidly spreading to 25-28° within 30 seconds, and achieving a leveling grade of 10 (no defects). Comparative Example 1 (6000 Da) had a short polyether segment, which reduced compatibility, increased surface tension to 26.8 mN / m, and increased contact angle, resulting in a leveling grade of 7. Comparative Example 2 (14000 Da), despite its low surface tension (22.5 mN / m), had an overly long siloxane segment, causing slight incompatibility and a leveling grade of 8 (slight cratering at the edges).

[0054] Necessity of drying treatment: When comparative example 3 was not dried, the water content of 0.5wt% caused the surface tension to rise sharply to 28.3mN / m, the contact angle was 50° and did not change, and the leveling grade was only level 5 (dense shrinkage holes). The reason was that the water formed hydrogen bonds with the polar resin, hindering the migration of siloxane to the surface; the water resistance test showed that the undried sample turned white after immersion (residual water caused the film layer to swell), while the water resistance of the dried samples was all level 0.

[0055] Effect of polyether modification: When unmodified siloxane was used in Comparative Example 4, although the surface tension was low (21.0 mN / m), the lack of polyether segments resulted in poor compatibility with the resin. After coating, "fisheye" defects appeared (leveling grade 6) and water resistance decreased (grade 3), demonstrating that the polyether segments are key to balancing compatibility and surface activity.

[0056] In Example 5, the nano-silica wear-resistant filler has an average particle size of 50-80 nm, and its surface is modified with γ-methacryloxypropyltrimethoxysilane, with the amount of the modifier being 3-5% of the filler mass.

[0057] Nano-SiO2 was dispersed in an ethanol / water (8:2) solution (solid content 10%), and KH-570 silane coupling agent (dosage was 2%, 3%, 4%, 5%, 6% of the filler mass) was added. Ultrasonic dispersion was performed at 50°C for 30 minutes, pH was adjusted to 4-5 for hydrolysis for 30 minutes, the temperature was raised to 80°C for reaction for 2 hours, and after centrifugal washing, the modified filler with double bonds grafted on the surface (denoted as m-SiO2) was obtained.

[0058] According to the process, other components are fixed, the addition amount of nano-SiO2 is 1.5% (accounting for the total mass of the system), and fillers with different particle sizes and modification conditions are used to set up a comparison group: Example 5-1: 50 nm, 3% modifier; Example 5-2: 65 nm, 4% modifier; Example 5-3: 80 nm, 5% modifier; Comparative Example 1: 30 nm, 4% modifier (particle size is too small); Comparative Example 2: 100 nm, 4% modifier (particle size is too large); Comparative Example 3: 65nm, 2% modifier (insufficient dosage); Comparative Example 4: 65nm, 6% modifier (excessive dosage); Comparative Example 5: 65 nm, unmodified (without KH-570).

[0059] The experimental data are shown in Table 5:

[0060] Table 5

[0061] Effect of Particle Size on Dispersibility and Wear Resistance: For Examples 5-1 to 5-3, when the particle size was 50-80 nm, the filler specific surface area and surface energy were balanced. After ultrasonic dispersion, the aggregate size was ≤200 nm and uniformly distributed in the resin. The wear-resistant mass loss was only 6.5-8.2 mg (≤10 mg is considered high quality), and the pencil hardness was ≥3H. For Comparative Example 1 (30 nm), due to its large specific surface area and high surface energy, strong hydrogen bonding agglomerates (agglomerates >800 nm) were easily formed, resulting in an increased wear-resistant loss of 15.3 mg and a decrease in hardness. For Comparative Example 2 (100 nm), due to its excessively large particle size, the filler and resin interface was weak, resulting in easy detachment during wear, resulting in a mass loss of 12.1 mg and a mere 10% elongation at break (resulting in a brittle film).

[0062] The key role of modifier dosage: In Example 5-2 (4% modifier), the silanol groups generated by KH-570 hydrolysis condense with the surface hydroxyl groups of SiO2, and the grafted double bonds copolymerize with the resin acrylate groups, forming a covalent interfacial bond. This results in optimal dispersion (agglomerates ≤ 150nm), a wear loss of only 6.5mg, and an elongation at break of 20% (a balance between flexibility and strength). In Comparative Example 3 (2%), insufficient modifier resulted in only partial grafting of the filler surface, resulting in weak interfacial bonding and poor dispersion (agglomerates > 500nm). In Comparative Example 4 (6%), excessive modifier resulted in multiple layers of silane physically adsorbed on the filler surface, hindering chemical bonding with the resin. This reduced dispersion (agglomerates 300-400nm) and inferior wear resistance compared to the examples.

[0063] Limitations of unmodified fillers: Comparative Example 5 (unmodified) has a hydroxyl-rich surface and a significant polarity difference with the resin, resulting in "filler-resin" interface defects (agglomerates > 1000 nm). It exhibits a wear loss of up to 20.1 mg, a pencil hardness of only H, and an elongation at break of 8%, demonstrating that surface modification is necessary to improve the compatibility of fillers with resins.

[0064] In one embodiment, the sand mill adopts a two-stage series process during grinding, with a first-stage grinding pressure of 0.6 MPa, a second-stage grinding pressure of 0.4 MPa, and a cycle number of not less than 3 times.

[0065] The sand mill adopts a two-stage tandem grinding process (first-stage grinding pressure of 0.6MPa, second-stage grinding pressure of 0.4MPa, and the number of cycles is not less than 3). The core is to achieve efficient dispersion of nano-scale fillers and precise regulation of ink system uniformity through gradient pressure control and multiple cycles of "coarse grinding-fine grinding". The first-stage grinding is set at a higher pressure of 0.6MPa. The high-speed turbulence generated by the zirconia beads under high pressure generates strong shear force and collision energy. It "coarsely crushes" the large nano-silica agglomerates (initial particle size 50-80nm, agglomerates can reach hundreds of nanometers) that may remain after high-speed dispersion, and quickly disassembles them into submicron particles. The second-stage grinding is reduced to a lower pressure of 0.4MPa. At this time, the material has been initially dispersed. Reducing the pressure can avoid damage to the filler surface modification layer caused by excessive shear (such as the cleavage of double bonds grafted by γ-methacryloxypropyltrimethoxysilane) or breakage of resin molecular chains, while achieving "fine dispersion" through gentler medium movement. , which promotes the uniform distribution of fillers in the resin in the form of monodisperse or small aggregates; the number of cycles is not less than 3 times, which is the key to ensure sufficient dispersion. In the first cycle, the material enters the second fine grinding after the first coarse grinding, and the particle size is significantly reduced but there is still local unevenness; in the second cycle, the particles that are not completely dispersed undergo the coarse grinding-fine grinding process again, and the dispersion uniformity is further improved; in the third and above cycles, the system reaches a "dynamic equilibrium", the particle size is no longer significantly reduced, but the distribution is narrower and the dispersion is more uniform, and finally the slurry fineness ≤15μm is met. The control target; through the synergistic effect of pressure gradient and cycle number, this process not only efficiently disperses the nanofiller, but also protects the integrity of the filler surface modification layer and the resin molecular structure, ensures the interface bonding force between the filler and the resin (through covalent bonds or hydrogen bonds), and avoids sedimentation or stratification caused by interface separation during storage; at the same time, the slurry with a fineness of ≤15μm has good fluidity and is adjusted with subsequent deionized water to adjust the viscosity (80-120mPa s) process synergy ensures that the ink can be evenly transferred to the substrate surface during printing, avoiding defects such as network blocking or rough film surface caused by coarse particles, and ultimately achieving high dispersibility, high stability and high-quality printability of the ink.

[0066] In one embodiment, the conductivity of the deionized water is ≤10 μS / cm, and the viscosity is adjusted by stirring at a low speed of 300-500 rpm and simultaneously detecting the reading of a rotational viscometer.

[0067] The conductivity of deionized water is limited to ≤10μS / cm and viscosity is adjusted by using 300-500rpm low-speed stirring and synchronous detection of viscometer readings to ensure the precise control of chemical stability and rheological properties of the ink system. Deionized water with a conductivity of ≤10μS / cm has a high conductivity due to ionic impurities (such as Ca Mg The content of Cl⁻, etc. is extremely low, which can avoid ionic reactions with polar groups such as hydroxyl and carboxyl groups in the resin (such as metal ions forming complexes with carboxyl groups, resulting in resin precipitation) or interfering with the free radical generation of the photoinitiator (such as chloride ions capturing free radicals and reducing curing efficiency), thereby ensuring the chemical stability and reactivity of the various components of the ink (prepolymer, oligomer, photoinitiator, etc.); when adjusting the viscosity, low-speed stirring of 300-500rpm is used to reduce the damage of mechanical shear force to the dispersion state of nano-silica filler (avoiding the re-agglomeration of dispersed single particles due to high shear), while reducing the entrapment of air during stirring (reducing the burden of subsequent degassing steps), and the simultaneous detection of the rotational viscometer reading can monitor the corresponding relationship between the amount of deionized water added and the viscosity of the system in real time, ensuring that the viscosity is accurately adjusted to 80-120mPa. s target range (this range not only meets the ink fluidity requirements of processes such as screen printing and flexographic printing, but also avoids problems such as insufficient film thickness or screen blocking caused by too low viscosity); through the synergistic effect of conductivity control and low-speed stirring-real-time detection, the ionic purity, dispersion stability and uniformity of the ink system are ultimately achieved, providing key guarantees for the uniform transfer of the film layer during the printing process, the mechanical properties after curing, and the long-term storage stability.

[0068] In one embodiment, the temperature in the kettle is maintained at 40-50° C. during the vacuum degassing process and is controlled by an external circulating water system. 0.1-0.3% of 2,6-di-tert-butyl-p-cresol is added as a stabilizer 5 minutes before the end of the degassing.

[0069] During the vacuum degassing process, the temperature in the kettle is controlled at 40-50°C through an external circulating water system, and 0.1-0.3% of 2,6-di-tert-butyl-p-cresol (BHT) is added as a stabilizer 5 minutes before the end of degassing. This is based on a comprehensive consideration of bubble removal efficiency, system chemical stability and ink storage life; the temperature range of 40-50°C can not only reduce the viscosity of the ink (increase the bubble migration speed) and promote the escape of dissolved gases, but also avoid the thermal decomposition of photoinitiators (such as α-hydroxycyclohexyl phenyl ketone) or oxidative cross-linking of the resin matrix due to excessive temperature (>50°C). The external circulating water system ensures temperature uniformity in the kettle through precise temperature control to avoid local overheating causing component failure; BHT is added 5 minutes before the end of degassing to use its phenolic hydroxyl structure to capture possible The existing free radicals (such as primary free radicals generated by mechanical shear during grinding and stirring) inhibit the degradation of the resin caused by oxygen contact or slow thermal oxidation during storage. A dosage of 0.1-0.3% can not only form an effective antioxidant protective layer, but also avoid compatibility problems caused by excessive addition (such as stabilizer precipitation affecting film transparency). Through the synergistic effect of temperature control and stabilizer addition, this process accelerates the bursting and escape of bubbles in a vacuum environment (vacuum degree -0.08 to -0.06MPa) while ensuring the chemical integrity of the ink components. The final ink not only has a low bubble content (avoiding defects such as pinholes and pits in the printed film layer), but also has excellent storage stability (the shelf life is extended to more than 6 months without delamination or abnormal viscosity changes).

[0070] In one embodiment, the curing performance of the printing ink satisfies the following requirements: under 172nm excimer ultraviolet lamp irradiation, the curing time is ≤1.5 seconds when the film thickness is 10 μm, the pencil hardness is ≥3H, and the number of acetone wiping resistance is ≥50 times.

[0071] The setting of the printing ink curing performance index (curing time ≤ 1.5 seconds when the film thickness is 10 μm under 172nm excimer ultraviolet lamp, pencil hardness ≥ 3H, and acetone wiping resistance ≥ 50 times) is a quantitative definition of the core function of the ink, and its realization depends on the coordinated optimization of formula design and preparation process; the achievement of curing time ≤ 1.5 seconds is due to the high curing time of the composite photoinitiator (α-hydroxycyclohexyl phenyl ketone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in a ratio of 2:1-3:1) in claim 1 at a wavelength of 172nm. The effective light absorption and free radical generation capabilities, combined with the high reactivity of trimethylolpropane triacrylate multifunctional monomer and carboxyl-containing epoxy acrylate oligomer, quickly initiate free radical polymerization under excimer ultraviolet light to form a dense cross-linked network. At the same time, the secondary grinding process of claim 7 ensures the uniform dispersion of the photoinitiator, avoiding the curing delay caused by local initiation efficiency differences; the performance of pencil hardness ≥3H and acetone wiping resistance ≥50 times is due to the surface modified nano-silica filler (50-80nm particle size, 3-5% silane modifier) in claim 6. ) is uniformly dispersed in the resin matrix (grinded to a fineness of ≤15μm by the sand mill of claim 7), the rigid support of the nanoparticles and the covalent bond between the filler and the resin interface (grafted by γ-methacryloxypropyltrimethoxysilane) significantly improve the hardness of the film layer, and the hydrogen bond association between the hydroxyl-containing aliphatic polyurethane acrylate prepolymer and the carboxyl-containing epoxy acrylate oligomer in claims 2 and 3 enhances the density and solvent erosion resistance of the cross-linked network, making the cured film less susceptible to damage when repeatedly wiped with acetone solvent; the above performance indicators not only meet the requirements of high-speed The printing production line has strict requirements on curing speed (curing within 1.5 seconds can match printing speeds of more than 50m / min), and through the coordinated optimization of hardness and solvent resistance, it is suitable for scenarios such as packaging printing, electronic circuits, etc. that have high requirements for film reliability. Compared with the common problems of similar inks in the existing technology, such as slow curing speed (>2 seconds), insufficient hardness (≤2H), and wipe resistance of less than 30 times, the present invention has achieved a breakthrough improvement in curing performance through the triple innovation of raw material molecular structure design, component compounding ratio control and preparation process parameter optimization.

[0072] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing, characterized in that: The following steps are involved: Add hydroxyl-containing aliphatic polyurethane acrylate prepolymer, carboxyl-containing epoxy acrylate oligomer, difunctional propylene glycol methyl ether acrylate reactive diluent, and trimethylolpropane triacrylate functional monomer in a mass ratio of 40-50:20-30:15-25:10-15 into a reactor, and stir at a low speed at 50-60°C for 30-45 minutes until they are completely dissolved in each other; Add 0.8-1.5% of the total mass of the system of α-hydroxycyclohexyl phenyl ketone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide compound photoinitiator, 0.3-0.8% of organic silicon leveling agent, and 1-2% of nano-silica wear-resistant filler, raise the temperature to 65-75°C and disperse at high speed for 60-90 minutes to form a homogeneous mixture; The mixture was transferred to a sand mill, and zirconia beads with a diameter of 0.3-0.5 mm were used as the grinding medium. The grinding pressure was controlled at 0.4-0.6 MPa, and the mixture was cyclically ground until the slurry fineness was ≤15 μm. Add deionized water to the ground slurry to adjust the system viscosity to 80-120mPa s, degassing for 15-20 minutes at a vacuum degree of -0.08 to -0.06 MPa, and finally preparing a printing ink with a solid content of 65-75%.

2. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: The hydroxyl-containing aliphatic polyurethane acrylate prepolymer has a hydroxyl value of 50-80 mgKOH / g, a number average molecular weight of 2000-3000 Da, and contains a hexamethylene diisocyanate-derived chain segment in its molecular structure.

3. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: The carboxyl content of the carboxyl-containing epoxy acrylate oligomer is 1.5-2.5 mmol / g, and the epoxy acrylate oligomer is prepared by ring-opening esterification reaction of bisphenol A epoxy resin and acrylic acid, and the acid value is controlled at 30-50 mgKOH / g.

4. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: The mass ratio of α-hydroxycyclohexyl phenyl ketone to 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in the composite photoinitiator is 2:1-3:1, wherein the phosphorus content of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide is greater than or equal to 10 wt %.

5. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: The organosilicon leveling agent is polyether-modified polydimethylsiloxane with a molecular weight of 8000-12000 Da. Before addition, it needs to be vacuum-dried at 50° C. for 2 hours to remove adsorbed water.

6. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: The nano-silica wear-resistant filler has an average particle size of 50-80 nm, and its surface is modified with γ-methacryloxypropyltrimethoxysilane, with the amount of the modifier being 3-5% of the filler mass.

7. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: The sand mill adopts a two-stage series process during grinding, with a first-stage grinding pressure of 0.6 MPa, a second-stage grinding pressure of 0.4 MPa, and a cycle number of not less than 3 times.

8. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: The conductivity of the deionized water is ≤10 μS / cm. When adjusting the viscosity, low-speed stirring of 300-500 rpm is adopted and the reading of the rotational viscometer is detected simultaneously.

9. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: During the vacuum degassing process, the temperature in the kettle is maintained at 40-50° C. and controlled by an external circulating water system. 0.1-0.3% of 2,6-di-tert-butyl-p-cresol is added as a stabilizer 5 minutes before the end of the degassing.

10. The method for preparing an environmentally friendly multifunctional printing ink based on excimer UV curing according to claim 1, characterized in that: The curing performance of the printing ink meets the following requirements: under 172nm excimer ultraviolet lamp irradiation, the curing time is ≤1.5 seconds when the film thickness is 10 μm, the pencil hardness is ≥3H, and the number of acetone wiping resistance is ≥50 times.

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