Resin composition containing novel photocuring initiator system as well as preparation method and application of resin composition

Abstract

The invention relates to the technical field of organic polymers, in particular to a resin composition containing a novel photocuring initiator system as well as a preparation method and application of the resin composition. The composition comprises an epoxy acrylate prepolymer, a polyurethane acrylate prepolymer, a reactive diluent, bisphenol A epoxy resin, sulfydryl-terminated liquid polysulfide and a photocuring initiator system. The initiator system is composed of an initiator mother solution and an initiating nano auxiliary agent according to a specific ratio, and the initiating nano auxiliary agent is obtained by grafting a photosensitive unit to silicon dioxide wrapped by polydopamine and then reacting with sulfydryl-terminated liquid polysulfide. The resin composition provided by the invention has excellent photocuring performance under a 405nm LED light source, can effectively expand a printing window, improve deep curing, significantly reduce polymerization shrinkage and improve interlayer bonding strength and dimensional precision, and is especially suitable for three-dimensional photocuring 3D printing with high precision requirements.

Description

Technical Field

[0001] This invention relates to the field of organic polymer technology, and in particular to a resin composition containing a novel photocurable initiator system, its preparation method, and its application. Background Technology

[0002] Photopolymer 3D printing technology, as an important branch of rapid prototyping, has been widely used in industrial manufacturing, biomedicine, and electronic devices in recent years. This technology primarily relies on photosensitive resins undergoing polymerization reactions under the irradiation of a specific wavelength light source to achieve layer-by-layer deposition. However, traditional photosensitive resins mostly employ ultraviolet light initiation systems. With the widespread adoption of visible light LED light sources, especially the extensive use of 405nm wavelengths, the compatibility of existing resins has become increasingly limited. Commonly used single visible light initiators or simple two-component systems suffer from low light absorption efficiency and insufficient initiation activity, resulting in limited curing depth. This is particularly problematic when printing high aspect ratio structures or deep cavity parts, where insufficient curing of the bottom layer can easily lead to uncured residues or structural collapse.

[0003] The simplified design of the initiator system also leads to the drawback of an excessively narrow printing window. Due to the excessively fast or slow photopolymerization reaction rate, it is difficult to precisely control the curing process, resulting in decreased bonding strength between layers. In multi-layer printing, short curing times for each layer lead to weak interfacial adhesion, while long curing times cause excessive shrinkage, thus affecting the overall mechanical properties of the molded part. Furthermore, the simple initiation system lacks the ability to regulate polymerization kinetics, allowing free radical polymerization or cationic polymerization to proceed singly, failing to form an interpenetrating network structure and further exacerbating internal stress accumulation.

[0004] Polymerization shrinkage is an inherent challenge of photocurable resins, particularly prominent in visible light curing. Traditional resins, produced through free radical polymerization of acrylate monomers, exhibit high volume shrinkage rates, often leading to dimensional deviations, warping, or cracking in molded parts. While some studies have attempted to suppress shrinkage by adding inorganic fillers or modifying prepolymers, uneven filler dispersion or poor compatibility can introduce new defects, such as enhanced light scattering and increased haze, affecting the application of transparent parts. Furthermore, shrinkage stress is concentrated and released at interlayer interfaces, weakening interlayer adhesion and limiting the resin's use in the manufacture of precision parts.

[0005] Inaccurate control of deep curing is another key bottleneck. While 405nm LED light sources offer energy-saving and environmental advantages, their photon energy is relatively low, and their penetration ability is weaker than that of ultraviolet light. Existing resin photoinitiators do not absorb enough light in deep regions, resulting in significant curing gradients and large differences in performance between upper and lower layers. Especially for microstructures or complex geometries, light scattering and shading effects lead to incomplete local curing and reduced surface detail resolution. Furthermore, simple two-component initiation systems lack synergistic effects; for example, an improper ratio of photosensitizer to co-initiator further reduces light energy utilization.

[0006] While some existing technologies attempt to improve performance through nanomaterials or multiple initiation mechanisms, they often focus on improving a single metric, such as simply increasing hardness or reducing shrinkage, failing to systematically address the contradictions between deep curing, interlayer bonding, and dimensional accuracy. For example, while introducing nano-silica can improve strength, it may sacrifice light transmittance; adding chain transfer agents improves toughness but slows down the curing rate. This lack of synergistic design makes it difficult for the overall performance of the resin to meet the demands of high-end applications, such as the manufacture of medical devices or optical components. Summary of the Invention

[0007] In view of this, the purpose of this invention is to propose a resin composition containing a novel photocuring initiator system, its preparation method and application, in order to solve the problems of existing photocuring 3D printing resins, which suffer from narrow printing windows, insufficient deep curing and large polymerization shrinkage due to the single initiation system, resulting in weak interlayer bonding and poor dimensional accuracy of the molded parts, making it difficult to meet the requirements of high-precision microstructure manufacturing.

[0008] To achieve the above objectives, the present invention provides a resin composition containing a novel photocurable initiator system, comprising, by weight, the following components: 360-440 parts of epoxy acrylate prepolymer; 230-270 parts of polyurethane acrylate prepolymer; an active diluent comprising 110-130 parts of 2-phenoxyethyl acrylate and 70-90 parts of N-vinylcaprolactam; 70-90 parts of bisphenol A type epoxy resin; 8-16 parts of terminal thiol liquid polysulfide; and a photocurable initiator system comprising 24-36 parts of initiator stock solution and 3-5 parts of initiation nano-auxiliaries.

[0009] Furthermore, the initiator stock solution is prepared by dissolving 4-isopropylthioxanthrone, diphenyliodonium hexafluorophosphate, and ethyl p-dimethylaminobenzoate in 2-phenoxyethyl acrylate; the mass ratio of 4-isopropylthioxanthrone, diphenyliodonium hexafluorophosphate, ethyl p-dimethylaminobenzoate, and 2-phenoxyethyl acrylate is 9:18:9:50.

[0010] Furthermore, the initiating nano-auxiliary agent is obtained by coupling 2-[(9-oxo-9H-thiooxanthracene-2-yl)oxy]acetic acid with polydopamine-coated silica to obtain a photosensitive unit grafted with polydopamine-coated silica, and then reacting the photosensitive unit grafted with polydopamine-coated silica with a terminal mercapto liquid polysulfide; the mass ratio of 2-[(9-oxo-9H-thiooxanthracene-2-yl)oxy]acetic acid to polydopamine-coated silica is 1.2-2:3-5; the mass ratio of the photosensitive unit grafted with polydopamine-coated silica to the terminal mercapto liquid polysulfide is 2-3:3-5.

[0011] Preferably, the type of bisphenol A epoxy resin is EPON 828.

[0012] Preferably, in the reactive diluent, the mass ratio of 2-phenoxyethyl acrylate to N-vinylcaprolactam is 1.2-1.9:1.

[0013] Preferably, the type of the terminal thiol liquid polysulfide is Thioplast G112.

[0014] Preferably, the initiator mother liquor is filtered through a 0.45μm filter membrane and then stored in a light-proof, sealed container.

[0015] Preferably, the epoxy acrylate prepolymer is obtained by reacting bisphenol A type epoxy resin and acrylic acid under triphenylphosphine catalysis and p-methoxyphenol inhibition conditions at a temperature not exceeding 90°C until the acid value is 5 mg KOH / g; the mass ratio of bisphenol A type epoxy resin to acrylic acid is 200:72.

[0016] Preferably, the polyurethane acrylate prepolymer is prepared by reacting polytetrahydrofurandiol, isophorone diisocyanate and hydroxyethyl methacrylate at 60-70°C under the catalysis of dibutyltin dilaurate; the mass ratio of polytetrahydrofurandiol, isophorone diisocyanate and hydroxyethyl methacrylate is 100:26:26.

[0017] Preferably, the number-average molecular weight of the polytetrahydrofuran diol is 800-1200.

[0018] Preferably, the polydopamine-coated silica is prepared by hydrolyzing tetraethoxysilane in an alcohol-water-ammonia system to obtain silica, and then forming a polydopamine coating layer by dopamine self-polymerization in Tris buffer.

[0019] The present invention further provides a method for preparing a resin composition containing a novel photocurable initiator system, comprising the following steps: mixing epoxy acrylate prepolymer, polyurethane acrylate prepolymer, reactive diluent and bisphenol A type epoxy resin at 60°C and degassing at -0.08MPa for 10 min according to the specified ratio; adding initiator mother liquor and initiation nano-auxiliary agent; ultrasonically dispersing for 5 min; and degassing again at -0.08MPa for 5 min to obtain the resin composition.

[0020] The present invention further provides an application of a resin composition containing a novel photocuring initiator system for stereolithography 3D printing under a 405nm LED light source.

[0021] The beneficial effects of this invention are: This invention significantly improves photocuring performance by introducing a novel photocuring initiator system, achieving a multi-component synergistic effect in the resin composition. The following beneficial effects are based on the specific substances and component combinations of the solution and are manifested through the inherent correlation of technical features: The resin composition provided by this invention incorporates polydopamine-encapsulated silica as a carrier within the initiating nano-agent, and achieves interfacial anchoring through grafting with photosensitive units. This allows for the uniform distribution and efficient utilization of photoinitiating active species during the curing process. This structure facilitates the simultaneous occurrence of free radical and cationic reactions under visible light conditions, effectively broadening the kinetic window of the photocuring reaction and avoiding stress concentration problems caused by excessively rapid local polymerization. Simultaneously, the terminal thiol-containing liquid polysulfide acts as a chain transfer agent, introducing flexible segments into the crosslinking network and alleviating the internal stress generated by polymerization shrinkage, resulting in significantly improved dimensional stability of the molded parts.

[0022] This invention utilizes a ternary initiator stock solution composed of a thioxanthone derivative, diphenyliodonium salt, and an amine co-initiator. This system exhibits excellent light absorption efficiency and photosensitivity under a 405nm LED light source. This ternary initiation system not only accelerates the surface curing rate but also promotes photopolymerization in deep regions through an energy transfer mechanism, overcoming the insufficient light penetration of traditional single initiators in deep cavities or microstructures. Furthermore, the introduction of polydopamine enhances the compatibility between the nano-auxiliaries and the resin matrix, reduces phase separation, and thus improves the continuity and density of the cured network.

[0023] The synergistic use of epoxy acrylate prepolymer and polyurethane acrylate prepolymer in the resin composition provided by this invention imparts a good balance of mechanical strength and toughness to the cured material. Epoxy acrylate provides a rigid framework, while polyurethane acrylate introduces elastic segments. Combined with reactive diluents such as N-vinylcaprolactam, this allows the crosslinked network to maintain high hardness while possessing a certain degree of ductility. This molecular design reduces volume shrinkage during curing and improves interlayer bonding strength, preventing delamination or warping in the printed parts.

[0024] This invention further optimizes the chemical structure of the cured network through the synergistic effect of terminal thiol-containing liquid polysulfides and cationic ring-opening components. The polysulfides delay the gelation process and reduce network defects through sulfide chain transfer reactions, while the cationic polymerization initiated by diphenyliodonium salt compensates for the deficiencies of the free radical reaction, achieving a dual curing mechanism. This design allows the resin to maintain reactivity in the later curing stages, improving conversion efficiency and thus enhancing the material's chemical resistance and durability.

[0025] The light scattering control effect of the nano-additives in this invention matches the light transmittance of the resin matrix, enabling the cured material to maintain high light transmittance while effectively suppressing haze. This is due to the nanoscale effect and surface functionalization of polydopamine-encapsulated silica, which avoids excessive light scattering during transmission, making it suitable for applications with high optical performance requirements, such as microstructure printing. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0027] Example 1: (1) Add 300g of anhydrous ethanol, 30g of deionized water and 15g of ammonia (concentration 28wt%) to a beaker, stir for 10min, then add 30g of tetraethoxysilane, stir at room temperature for 120min, centrifuge, wash and dry at 60℃ for 12h to obtain silica powder; then place 100g of Tris buffer (10mmol / L, pH 8.5) in a three-necked flask, disperse 4g of silica powder, add 0.8g of dopamine hydrochloride, stir at room temperature for 12h, centrifuge, wash three times with water, and vacuum dry at 50℃ for 6h to obtain polydopamine-coated silica; (2) Add 40g N,N-dimethylformamide and 4g deionized water to a flask, dissolve 1.2g 2-[(9-oxo-9H-thiooxanthracene-2-yl)oxy]acetic acid, add 1.2g 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 0.6g N-hydroxysuccinimide, activate at room temperature for 30min, add 3g polydopamine-coated silica, stir for 6h, centrifuge, wash three times each with deionized water and anhydrous ethanol, and vacuum dry at 50℃ for 6h to obtain photosensitive unit-grafted polydopamine-coated silica; then disperse 2.0g photosensitive unit-grafted polydopamine-coated silica in 40g anhydrous ethanol / deionized water (volume ratio 8:2), add 3g thiol-terminated liquid polysulfide (Thioplast) G112), the pH was adjusted to 8.5 with ammonia (28wt%), stirred at 40℃ for 4h, centrifuged, washed 3 times each with deionized water and anhydrous ethanol, and vacuum dried at 50℃ for 6h to obtain the initiating nano-auxiliary agent. (3) Add 50g of 2-phenoxyethyl acrylate to a brown bottle, dissolve 9g of 4-isopropylthioxanthone, add 18g of diphenyliodonium hexafluorophosphate and 9g of p-dimethylaminobenzoate, stir for 30min, filter through a 0.45μm filter membrane, seal in the dark, and obtain the initiator mother liquor; (4) Add 200g of bisphenol A epoxy resin (EPON 828), 1g of p-methoxyphenol and 1g of triphenylphosphine to a four-necked flask, stir at 80°C, add 72g of acrylic acid dropwise over 60min, maintain the reaction temperature below 90°C, and continue the reaction until the acid value is titrated to 5mgKOH / g. After cooling to 60°C, remove trace amounts of volatiles under vacuum to obtain epoxy acrylate prepolymer. (5) Add 100g of polytetrahydrofuran diol (number average molecular weight 1000), 26g of isophorone diisocyanate and 1g of dibutyltin dilaurate to a four-necked flask, stir and react at 60°C for 2h, add 26g of hydroxyethyl methacrylate and 1g of p-methoxyphenol, react at 70°C for 2h to obtain polyurethane acrylate prepolymer; (6) 360g of epoxy acrylate prepolymer, 230g of polyurethane acrylate prepolymer, 110g of 2-phenoxyethyl acrylate, 70g of N-vinylcaprolactam, 70g of bisphenol A epoxy resin (EPON 828) and 8g of terminal thiol liquid polysulfide (Thioplast G112) were added sequentially to a stirred tank. The mixture was stirred at 60°C for 30 min and degassed at -0.08MPa for 10 min. Then, 24g of initiator mother liquor and 3g of initiating nano-auxiliary agent were added. The mixture was ultrasonically dispersed for 5 min (100W) and then degassed at -0.08MPa for 5 min to obtain a resin composition containing a novel photocurable initiator system.

[0028] Example 2: (1) Add 300g of anhydrous ethanol, 30g of deionized water and 15g of ammonia (concentration 28wt%) to a beaker, stir for 10min, then add 30g of tetraethoxysilane, stir at room temperature for 120min, centrifuge, wash and dry at 60℃ for 12h to obtain silica powder; then place 100g of Tris buffer (10mmol / L, pH 8.5) in a three-necked flask, disperse 4g of silica powder, add 0.8g of dopamine hydrochloride, stir at room temperature for 12h, centrifuge, wash three times with water, and vacuum dry at 50℃ for 6h to obtain polydopamine-coated silica; (2) Add 40g N,N-dimethylformamide and 4g deionized water to a flask, dissolve 1.6g 2-[(9-oxo-9H-thiooxanthracene-2-yl)oxy]acetic acid, add 1.6g 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 0.8g N-hydroxysuccinimide, activate at room temperature for 30min, add 4g polydopamine-coated silica, stir for 6h, centrifuge, wash three times each with deionized water and anhydrous ethanol, and vacuum dry at 50℃ for 6h to obtain photosensitive unit-grafted polydopamine-coated silica; then disperse 2.5g photosensitive unit-grafted polydopamine-coated silica in 40g anhydrous ethanol / deionized water (volume ratio 8:2), add 4g thiol-terminated liquid polysulfide (Thioplast) G112), the pH was adjusted to 8.5 with ammonia (28wt%), stirred at 40℃ for 4h, centrifuged, washed 3 times each with deionized water and anhydrous ethanol, and vacuum dried at 50℃ for 6h to obtain the initiating nano-auxiliary agent. (3) Add 50g of 2-phenoxyethyl acrylate to a brown bottle, dissolve 9g of 4-isopropylthioxanthone, add 18g of diphenyliodonium hexafluorophosphate and 9g of p-dimethylaminobenzoate, stir for 30min, filter through a 0.45μm filter membrane, seal in the dark, and obtain the initiator mother liquor; (4) Add 200g of bisphenol A epoxy resin (EPON 828), 1g of p-methoxyphenol and 1g of triphenylphosphine to a four-necked flask, stir at 80°C, add 72g of acrylic acid dropwise over 60min, maintain the reaction temperature below 90°C, and continue the reaction until the acid value is titrated to 5mgKOH / g. After cooling to 60°C, remove trace amounts of volatiles under vacuum to obtain epoxy acrylate prepolymer. (5) Add 100g of polytetrahydrofuran diol (number average molecular weight 1000), 26g of isophorone diisocyanate and 1g of dibutyltin dilaurate to a four-necked flask, stir and react at 60°C for 2h, add 26g of hydroxyethyl methacrylate and 1g of p-methoxyphenol, react at 70°C for 2h to obtain polyurethane acrylate prepolymer; (6) 400g of epoxy acrylate prepolymer, 250g of polyurethane acrylate prepolymer, 120g of 2-phenoxyethyl acrylate, 80g of N-vinylcaprolactam, 80g of bisphenol A epoxy resin (EPON 828) and 12g of terminal thiol liquid polysulfide (Thioplast G112) were added sequentially to a stirred tank. The mixture was stirred at 60°C for 30 min and degassed at -0.08 MPa for 10 min. Then, 30g of initiator mother liquor and 4g of initiating nano-auxiliary agent were added. The mixture was ultrasonically dispersed for 5 min (100W) and then degassed at -0.08 MPa for 5 min to obtain a resin composition containing a novel photocurable initiator system.

[0029] Example 3: (1) Add 300g of anhydrous ethanol, 30g of deionized water and 15g of ammonia (concentration 28wt%) to a beaker, stir for 10min, then add 30g of tetraethoxysilane, stir at room temperature for 120min, centrifuge, wash and dry at 60℃ for 12h to obtain silica powder; then place 100g of Tris buffer (10mmol / L, pH 8.5) in a three-necked flask, disperse 4g of silica powder, add 0.8g of dopamine hydrochloride, stir at room temperature for 12h, centrifuge, wash three times with water, and vacuum dry at 50℃ for 6h to obtain polydopamine-coated silica; (2) Add 40g N,N-dimethylformamide and 4g deionized water to a flask, dissolve 2.0g 2-[(9-oxo-9H-thiooxanthracene-2-yl)oxy]acetic acid, add 2.0g 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.0g N-hydroxysuccinimide, activate at room temperature for 30min, add 5g polydopamine-coated silica, stir for 6h, centrifuge, wash three times each with deionized water and anhydrous ethanol, and vacuum dry at 50℃ for 6h to obtain photosensitive unit-grafted polydopamine-coated silica; then disperse 3.0g photosensitive unit-grafted polydopamine-coated silica in 40g anhydrous ethanol / deionized water (volume ratio 8:2), add 5g thiol-terminated liquid polysulfide (Thioplast) G112), the pH was adjusted to 8.5 with ammonia (28wt%), stirred at 40℃ for 4h, centrifuged, washed 3 times each with deionized water and anhydrous ethanol, and vacuum dried at 50℃ for 6h to obtain the initiating nano-auxiliary agent. (3) Add 50g of 2-phenoxyethyl acrylate to a brown bottle, dissolve 9g of 4-isopropylthioxanthone, add 18g of diphenyliodonium hexafluorophosphate and 9g of p-dimethylaminobenzoate, stir for 30min, filter through a 0.45μm filter membrane, seal in the dark, and obtain the initiator mother liquor; (4) Add 200g of bisphenol A epoxy resin (EPON 828), 1g of p-methoxyphenol and 1g of triphenylphosphine to a four-necked flask, stir at 80°C, add 72g of acrylic acid dropwise over 60min, maintain the reaction temperature below 90°C, and continue the reaction until the acid value is titrated to 5mgKOH / g. After cooling to 60°C, remove trace amounts of volatiles under vacuum to obtain epoxy acrylate prepolymer. (5) Add 100g of polytetrahydrofuran diol (number average molecular weight 1000), 26g of isophorone diisocyanate and 1g of dibutyltin dilaurate to a four-necked flask, stir and react at 60°C for 2h, add 26g of hydroxyethyl methacrylate and 1g of p-methoxyphenol, react at 70°C for 2h to obtain polyurethane acrylate prepolymer; (6) 440g of epoxy acrylate prepolymer, 270g of polyurethane acrylate prepolymer, 130g of 2-phenoxyethyl acrylate, 90g of N-vinylcaprolactam, 90g of bisphenol A epoxy resin (EPON 828) and 16g of terminal thiol liquid polysulfide (Thioplast G112) were added sequentially to a stirred tank. The mixture was stirred at 60°C for 30 min and degassed at -0.08MPa for 10 min. Then, 36g of initiator mother liquor and 5g of initiating nano-auxiliary agent were added. The mixture was ultrasonically dispersed for 5 min (100W) and then degassed at -0.08MPa for 5 min to obtain a resin composition containing a novel photocurable initiator system.

[0030] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that no initiating nano-additive is added in step (6), while the other conditions are the same as in Example 2.

[0031] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that in step (2), polydopamine-coated silica was directly replaced with polydopamine-coated silica grafted onto the photosensitive unit, while the other conditions were the same as in Example 2.

[0032] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that: in step (3) when preparing the initiator mother liquor, diphenyliodonium hexafluorophosphate is not added, and the other components and their mass remain unchanged. In step (6), the mass of the initiator mother liquor added is still 30g, and the other conditions are the same as in Example 2.

[0033] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that the mass of 4-isopropylthioxanthraquinone was adjusted from 9g to 3g when preparing the initiator mother liquor in step (3), while the other conditions were the same as in Example 2.

[0034] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that ethyl p-dimethylaminobenzoate is not added when preparing the initiator stock solution in step (3), and the other conditions are the same as in Example 2.

[0035] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that: step (6) does not involve the addition of terminal thiol liquid polysulfide; the other conditions are the same as in Example 2.

[0036] Comparative Example 7: The difference between Comparative Example 7 and Example 2 is that in step (6), 12g of terminal thiol liquid polysulfide was replaced with 12g of ethyl p-dimethylaminobenzoate, and the other conditions were the same as in Example 2.

[0037] Comparative Example 8: The difference between Comparative Example 8 and Example 2 is that in step (6), no initiator stock solution is added, and the other conditions are the same as in Example 2.

[0038] Performance testing: Coating sample preparation: A wet film was prepared on a clean glass plate using a 100 μm blade coater, using a 405 nm LED light source (irradiance 10 mW·cm). -2 Irradiation was performed on both sides for 60 seconds, followed by a 30-second interval between flipping, resulting in a dry film thickness of (60±5) μm. The film was then cured in a 60℃ oven for 30 minutes. For mechanical testing of bulk samples: Resin was injected into a polytetrafluoroethylene mold (80mm×10mm×2mm) and cured at 405nm and 10mW·cm⁻¹. -2 Under the given conditions, the samples were irradiated in layers for 60 seconds each, with a 10-second interval between layers, for a total thickness of 2 mm. After demolding, the samples were cured at 60°C for 60 minutes. All samples were conditioned for 24 hours at (23±2)°C and (50±5)% relative humidity before testing.

[0039] Non-volatile content: Weigh 1.0000g of resin composition into an aluminum dish according to GB / T 1725-2007, place it in an oven at 105℃ for 60min, remove it and cool it to room temperature in a desiccator, weigh it, and calculate the non-volatile mass fraction (%). Each sample was tested in triplicate and the average value was taken and reported to 0.1%. The results are shown in Table 1.

[0040] Rotational viscosity (25℃): According to GB / T 2794-2022, a rotational viscometer was selected (the rotor number and speed were selected according to the standard to ensure that the torque was within 10%-90% of the measurement range). The viscosity (mPa·s) was read under constant temperature conditions of 25.0℃. Each sample was measured 3 times and the average value was taken. The results are shown in Table 1.

[0041] Volume shrinkage rate: According to GB / T 24148.9-2014, the volume shrinkage rate (%) was calculated after the material was injected into the standard volume mold cavity, cured and stabilized for 24 hours, and retained to two decimal places. The results are shown in Table 1.

[0042] Tensile properties: According to GB / T 1040.2-2006, using a universal testing machine with a fixture spacing of 50 mm and a testing speed of 5 mm·min. -1 The tensile strength (MPa) and elongation at break (%) of the strip samples were tested; at least 5 samples were taken in each group and the average value was taken. The results are shown in Table 1.

[0043] Adhesion (cross-cut test): According to GB / T 9286-2021, a six-blade cross-cut tester was used with a spacing of 1mm. After cross-cutting, 3M tape was applied and quickly peeled off at 90°. The test was rated from 0 to 5. The same test board was tested 3 times at different locations. The results are shown in Table 1.

[0044] Pencil hardness: According to GB / T 6739-2022, the pencil lead is sharpened into a semi-circle with a 5mm exposed lead length, the clamp angle is 45°, and it is applied at a 5mm·s under a 750g load. -1 The highest hardness level (6B-9H sequence) that did not produce scratches was recorded by pushing at a constant speed. The results are shown in Table 1.

[0045] Transmittance and haze: According to GB / T 2410-2008, a plate with a thickness of 2 mm was prepared, and the total transmittance (%) and haze (%) were determined by haze meter method (method A). The results are shown in Table 1.

[0046] Table 1 Performance Test Results

[0047] Data Analysis: As can be seen from the data in Examples 1-3 in Table 1, the formulation of this invention achieves a balance between low shrinkage, mechanical strength, and surface hardness by adjusting the grafting amount of photosensitive units, the gradient of terminal thiol liquid polysulfide, and the initiator mother liquor. The system in these examples utilizes the synergistic photosensitivity of a thioanthracene derivative-diphenyliodonium salt-ethyl p-dimethylaminobenzoate to achieve deep initiation under visible light conditions. The terminal thiol liquid polysulfide provides chain transfer and stress retardation, and combined with the interfacial anchoring of polydopamine-coated silica, the crosslinked network becomes more continuous and dense between layers and at the interface. Consequently, tensile strength and adhesion are simultaneously improved while volume shrinkage is suppressed, and pencil hardness and light transmittance-haze are maintained within the acceptable range for optical applications, demonstrating the comprehensive advantages of deep curing, low stress, and high toughness.

[0048] As can be seen from the data in Example 2 and Comparative Example 1 in Table 1, the lack of initiating nano-additives restricts deep curing and interlayer penetration, leading to increased shrinkage, decreased adhesion, and a slight increase in light transmittance. The main reason is that the interface localization-electron donor-acid source enhancement micro-region is weakened, resulting in insufficient dark reaction propagation and network unevenness. Therefore, nano-additives have a significant synergistic effect in improving deep curing and interfacial adhesion.

[0049] As can be seen from the data in Example 2 and Comparative Example 2 in Table 1, when the photosensitive unit was not anchored to the polydopamine-coated silica surface, the deep curing and adhesion of the coating decreased simultaneously. The main reason is that the photosensitive unit is easily migrated and its local energy utilization rate decreases, resulting in insufficient free radical / acid source density at the interface. Therefore, it is evident that interface immobilization of the photosensitive unit helps improve photochemical efficiency and adhesion stability.

[0050] As can be seen from the data in Example 2 and Comparative Example 3 in Table 1, after removing diphenyliodonium hexafluorophosphate, the cationic ring-opening process was difficult to advance, resulting in decreased strength and hardness and increased shrinkage. The main reason is that the free radical-dominated network is more prone to generating polymerization stress and unconverted end groups, and the missing acid source also weakens interfacial bonding. Therefore, free radical-promoted cationic dual curing has an unexpected synergistic effect in reducing stress and increasing density.

[0051] As can be seen from the data in Example 2 and Comparative Example 4 in Table 1, when the photosensitizer dosage is reduced, the initial efficiency and deep curing are slightly affected, resulting in a slight decrease in strength and adhesion, but a slight improvement in optical properties. This is mainly because the reduced absorption / scattering brings an advantage in light transmission, but the network integrity is limited due to the reduction in photoactive species. Therefore, there is an optimization window for the photosensitizer content that balances optical performance and curing efficiency.

[0052] As can be seen from the data in Example 2 and Comparative Example 5 in Table 1, the absence of ethyl p-dimethylaminobenzoate hinders the initiation chain transfer, leading to a decrease in curing conversion rate and network unevenness, manifested as simultaneous deterioration in strength, elongation, and adhesion. The main reason is the lack of an efficient hydrogen donor, which inhibits free radical generation under visible light. Therefore, amine co-initiators play a crucial role in initiation efficiency under visible light conditions.

[0053] As can be seen from the data in Example 2 and Comparative Example 6 in Table 1, after removing the terminal thiol liquid polysulfide, the system hardness increased while elongation and adhesion decreased significantly, and shrinkage also increased. The main reason is that chain transfer and stress relaxation channels were weakened, the network tended to become brittle, and internal stress accumulated at the interface. Therefore, it is evident that the terminal thiol polysulfide exhibits a synergistic effect with cation ring-opening in inhibiting shrinkage and improving toughness, with a synergistic effect of 1+1>2.

[0054] As can be seen from the data in Table 1 for Example 2 and Comparative Example 7, replacing terminal thiol polysulfides with a large amount of amines increases elongation but decreases strength, hardness, and optical stability. The main reason is that the plasticizing and yellowing tendency of amines increases the local free volume fraction of the internal phase, but fails to provide effective stress retardation and interfacial chemical anchoring. Therefore, the compatibility of polysulfides with the ternary initiation system is superior to simply increasing the amine content.

[0055] As can be seen from the data in Example 2 and Comparative Example 8 in Table 1, the lack of initiator mother liquor resulted in insufficient curing and network discontinuity, leading to simultaneous deterioration of strength, elongation, and adhesion, as well as increased haze. The main reason for this is insufficient overall active species, which inhibits both dark propagation and interlayer penetration. Therefore, it is evident that initiator mother liquor and nano-adjuvants need to be synergistically formulated; relying solely on interface sensitization is insufficient to achieve stable performance.

[0056] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A resin composition containing a novel photocuring initiator system, characterized by comprising: comprising: 360-440 parts by mass of an epoxy acrylate prepolymer; 230-270 parts by mass of a polyurethane acrylate prepolymer; an active diluent comprising 110-130 parts by mass of 2-phenoxyethyl acrylate and 70-90 parts by mass of N-vinylcaprolactam; 70-90 parts by mass of a bisphenol A type epoxy resin; 8-16 parts by mass of a terminal mercapto liquid polysulfide; and a photocuring initiator system comprising 24-36 parts by mass of an initiator mother liquor and 3-5 parts by mass of an initiating nano adjuvant; the initiator mother liquor is prepared by dissolving 4-isopropylthioxanthone, diphenyliodonium hexafluorophosphate and p-dimethylaminoethyl benzoate in 2-phenoxyethyl acrylate; the mass ratio of the 4-isopropylthioxanthone, diphenyliodonium hexafluorophosphate, p-dimethylaminoethyl benzoate and 2-phenoxyethyl acryate is 9:18:9:50; the initiating nano adjuvant is obtained by coupling 2-[(9-oxo-9H-thioxanthen-2-yl)oxy]acetic acid and silica coated with polydopamine to obtain photosensitive unit grafted silica coated with polydopamine, and then reacting the photosensitive unit grafted silica coated with polydopamine with the terminal mercapto liquid polysulfide; the mass ratio of the 2-[(9-oxo-9H-thioxanthen-2-yl)oxy]acetic acid and silica coated with polydopamine is 1.2-2:3-5; the mass ratio of the photosensitive unit grafted silica coated with polydopamine and the terminal mercapto liquid polysulfide is 2-3:3-5.

2. The resin composition containing a novel photocuring initiator system according to claim 1, characterized by, The bisphenol A type epoxy resin is EPON 828.

3. The resin composition containing a novel photocuring initiator system according to claim 1, characterized by, In the active diluent, the mass ratio of the 2-phenoxyethyl acrylate and the N-vinylcaprolactam is 1.2-1.9:

1.

4. The resin composition containing a novel photocuring initiator system according to claim 1, characterized by, The terminal mercapto liquid polysulfide is Thioplast G112.

5. The resin composition containing a novel photocuring initiator system according to claim 1, characterized by, The initiator mother liquor is filtered through a 0.45 μm filter membrane and stored in the dark after sealing.

6. The resin composition containing a novel photocuring initiator system according to claim 1, characterized by, The epoxy acrylate prepolymer is obtained by reacting a bisphenol A type epoxy resin and acrylic acid at not higher than 90 DEG C under the catalysis of triphenylphosphine and the inhibition of p-methoxyphenol until the acid value is 5 mgKOH / g; the mass ratio of the bisphenol A type epoxy resin and the acrylic acid is 200:

72.

7. The resin composition containing a novel photocuring initiator system according to claim 1, characterized by, The polyurethane acrylate prepolymer is prepared by reacting polytetrahydrofuran glycol, isophorone diisocyanate and hydroxyethyl methacrylate at 60-70 DEG C under the catalysis of dibutyltin dilaurate; the mass ratio of the polytetrahydrofuran glycol, isophorone diisocyanate and hydroxyethyl methacrylate is 100:26:

26.

8. The resin composition containing a novel photocuring initiator system according to claim 1, characterized by, The silica coated with polydopamine is obtained by hydrolyzing and polycondensing tetraethoxysilane in an alcohol-water-ammonia system to obtain silica, and then forming a polydopamine coating layer in a Tris buffer.

9. A method for preparing a resin composition containing a novel photocuring initiator system according to any one of claims 1 to 8, characterized by, comprising: mixing the epoxy acrylate prepolymer, the polyurethane acrylate prepolymer, the active diluent and the bisphenol A type epoxy resin in a ratio at 60 DEG C and degassing under-0.08 MPa for 10 min, adding the initiator mother liquor and the initiating nano adjuvant, ultrasonic dispersing for 5 min and then degassing under-0.08 MPa for 5 min to obtain the resin composition.

10. Use of a resin composition containing a novel photoinitiator system according to any one of claims 1 to 8, characterized in that, For stereolithography 3D printing under 405 nm LED light source.

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