High-tenacity low-shrinkage unsaturated polyester resin and method for preparing the same

Abstract

This invention belongs to the field of thermosetting resin modification technology and discloses a high-toughness, low-shrinkage unsaturated polyester resin and its preparation method. The resin comprises an unsaturated polyester resin liquid, a low-shrinkage component, a nanoparticle-reactive polyurethane masterbatch, an initiator, and an accelerator. The nanoparticle-reactive polyurethane masterbatch is composed of a bridging interfacial reactive nanomodifier, a reactive polyurethane prepolymer, and styrene. The bridging interfacial reactive nanomodifier is nano-silica dual-modified with polydopamine and methacryloyloxysilane. In preparation, the modifier and polyurethane prepolymer are prepared first, then the masterbatch is prepared. The low-shrinkage component is added to the resin liquid for pre-compatibility, followed by the addition of the masterbatch, and the mixture undergoes pre-gelation, primary curing, and post-curing to obtain the finished product. This invention combines high toughness, low shrinkage, and good dimensional stability.

Description

Technical Field

[0001] This invention belongs to the field of thermosetting resin modification technology, specifically relating to a high-toughness, low-shrinkage unsaturated polyester resin and its preparation method. Background Technology

[0002] Unsaturated polyester resins are a widely used class of thermosetting resins, possessing advantages such as abundant raw material sources, mature molding processes, relatively fast curing speeds, good mechanical properties, and relatively low costs. They are widely used in fiberglass, molded products, pultruded products, anti-corrosion materials, and artificial stone. However, traditional unsaturated polyester resins typically exhibit significant volume shrinkage during curing, easily leading to problems such as internal stress concentration, surface depressions, warping, and insufficient dimensional stability in the finished products. Furthermore, their cured crosslinked networks are brittle, resulting in limited impact resistance and fracture toughness, making it difficult to meet the application requirements of high-performance composite materials and products with high dimensional precision.

[0003] To reduce curing shrinkage, existing technologies typically modify unsaturated polyester resins with low-shrinkage components; to improve toughness, polyurethane, rubber-based toughening components, or inorganic nanofillers are often introduced. While these measures can improve individual properties to some extent, they still have significant shortcomings: on the one hand, the introduction of low-shrinkage components often leads to poor compatibility, uncontrolled phase separation, or decreased mechanical properties; on the other hand, while simple toughening can alleviate brittleness, it may cause a decrease in modulus, worsen dimensional stability, and even affect the curing process. Although nano-silica can improve interfacial strength and dimensional stability, its tendency to agglomerate and insufficient interfacial bonding makes it difficult to fully exert its synergistic reinforcing effect. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a high-toughness, low-shrinkage unsaturated polyester resin and its preparation method. By introducing nano-silica that is dual-modified with polydopamine and methacryloyloxysilane, and combining it with nanoparticle-reactive polyurethane masterbatch construction, low-shrinkage component precompatibility and staged curing process, the resin system achieves a synergistic improvement in low shrinkage, high toughness and good dimensional stability.

[0005] The objective of this invention can be achieved through the following technical solutions: A high-toughness, low-shrinkage unsaturated polyester resin, comprising the following components by weight: 100 parts of unsaturated polyester resin liquid, 5-18 parts of low-shrinkage component, 3-20 parts of nanoparticle-reactive polyurethane masterbatch, 0.5-2.0 parts of initiator, and 0.05-0.6 parts of accelerator. The nanoparticle-reactive polyurethane masterbatch comprises, by weight, 10-35 parts of bridging interface reactive nanomodifier, 40-75 parts of reactive polyurethane prepolymer, and 10-35 parts of styrene; the bridging interface reactive nanomodifier is polydopamine-3-(methacryloyloxy)propyltrimethoxysilane dual-modified nano silica.

[0006] More preferably, the average particle size of the nano-silica in the bridging interface reaction nanomodifier is 15-40 nanometers.

[0007] More preferably, the bridging interface reaction nanomodifier is a dual-modified nano-silica prepared by the following method: first, the nano-silica is coated with polydopamine, and then the polydopamine-coated nano-silica is grafted with 3-(methacryloyloxy)propyltrimethoxysilane for modification.

[0008] More preferably, the reactive polyurethane prepolymer is a hydroxyethyl methacrylate-terminated polyurethane prepolymer, which is obtained by first reacting polyether diol with 4,4'-diphenylmethane diisocyanate to generate an isocyanate-terminated polyurethane prepolymer, and then end-capping it with hydroxyethyl methacrylate.

[0009] More preferably, the low-shrinkage component is a saturated polyester low-shrinkage resin, which is prepared by polycondensation of adipic acid, isophthalic acid and neopentyl glycol in a molar ratio of 1:(0.9-1.1):(1.9-2.1) at 190-220°C for 4-7 hours, with the final acid value of the polycondensation not exceeding 15 mg potassium hydroxide / g, and then mixing it with styrene in a mass ratio of 1:(0.8-1.4). The number average molecular weight of the saturated polyester low-shrinkage resin is 2000-3500.

[0010] More preferably, the unsaturated polyester resin solution is prepared by polycondensation reaction of one or two of maleic anhydride, phthalic anhydride and isophthalic acid with propylene glycol and neopentyl glycol, followed by mixing with styrene, wherein the endpoint acid value of the polycondensation reaction is 20-35 mg potassium hydroxide / g.

[0011] A method for curing and molding a high-toughness, low-shrinkage unsaturated polyester resin includes the following steps: S1. A bridging interface reaction nanomodifier was prepared using nano-silica, dopamine hydrochloride and 3-(methacryloyloxy)propyltrimethoxysilane, and a reactive polyurethane prepolymer was prepared using polyether diol, 4,4'-diphenylmethane diisocyanate and hydroxyethyl methacrylate. S2. A bridging interface reactive nano-modifier is added to a partially reactive polyurethane prepolymer and mixed. Then, a portion of styrene is added to adjust the fluidity of the system and disperse it to obtain a nanoparticle-reactive polyurethane masterbatch. S3. Add the low-shrinkage component to the unsaturated polyester resin liquid for pre-compatibility treatment, and then add the nanoparticle-reactive polyurethane masterbatch and mix evenly to obtain a resin mixture system. S4. Initiator and accelerator are added to the resin mixture system, followed by pre-gelation, primary curing and post-curing in sequence to obtain a high-toughness, low-shrinkage unsaturated polyester resin material after curing.

[0012] More preferably, in step S1, the coating reaction of nano-silica with dopamine hydrochloride is carried out in a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.4–8.6; 3-(methacryloyloxy)propyltrimethoxysilane is pre-hydrolyzed in an ethanol / water mixture and then grafted onto polydopamine-coated nano-silica; polyether diol undergoes a prepolymerization reaction with 4,4'-diphenylmethane diisocyanate, followed by a capping reaction with hydroxyethyl methacrylate; wherein the coating reaction temperature is 22–30°C, the grafting reaction temperature is 55–65°C, the prepolymerization reaction temperature is 70–80°C, and the capping reaction temperature is 45–55°C.

[0013] More preferably, in step S2, the mixing and dispersion temperature of the bridging interface reactive nanomodifier, the partially reactive polyurethane prepolymer, and the partially styrene is 50–60°C, and the dispersion time is 0.5–1 hour; in step S3, the pre-compatibility treatment temperature of the low-shrinkage component and the unsaturated polyester resin liquid is 40–50°C, the pre-compatibility treatment time is 30–60 minutes, and the mixing time after adding the nanoparticle-reactive polyurethane masterbatch is 20–40 minutes.

[0014] More preferably, in step S4, the pre-gel temperature is 30-35°C and the time is 30-60 minutes; the main curing temperature is 65-75°C and the time is 1.5-2.5 hours; the post-curing temperature is 100-110°C and the time is 1.5-2.5 hours.

[0015] The beneficial effects of this invention are: This invention, through the synergistic design of the raw material system and preparation path, enables unsaturated polyester resin to simultaneously achieve low shrinkage, toughening, interfacial reinforcement, and dimensional stability during the curing process. Nano-silica, dual-modified with polydopamine and methacryloyloxysilane, is used as a bridging interfacial reactive nanomodifier. This modifier utilizes the polydopamine layer to improve the interfacial adhesion and surface activity between nanoparticles and the resin matrix and the flexible polyurethane phase, while the reactive double bonds on the silane groups enhance the bonding between the particles and the cured network. This improves the dispersion of inorganic particles in the resin system, reduces agglomeration tendency, and increases interfacial transfer efficiency. The modified nanoparticles are pre-constructed with a portion of reactive polyurethane prepolymer and styrene to form a nanoparticle-reactive polyurethane masterbatch. This allows the inorganic reinforcing phase and the flexible toughening phase to form a stable composite structure before entering the main resin, helping to reduce local enrichment and interfacial mismatch caused by direct powder addition. The low-shrinkage component first forms a pre-compatible system in the unsaturated polyester resin liquid, and then the masterbatch is introduced. With the phased curing regime of pre-gelling, main curing and post-curing, the separation of the low-shrinkage phase, the stress relief of the flexible chain segments and the interface bridging are well matched on the curing time axis, thereby effectively reducing curing shrinkage and internal stress concentration, and improving impact toughness, fracture resistance and dimensional stability. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The high-toughness, low-shrinkage unsaturated polyester resin of the present invention, in its uncured stage, is a resin composition consisting of unsaturated polyester resin liquid, low-shrinkage component, nanoparticle-reactive polyurethane masterbatch, initiator and accelerator; after initiation and curing, it forms a high-toughness, low-shrinkage unsaturated polyester resin material.

[0018] Example 1: A preparation process for a high-toughness, low-shrinkage unsaturated polyester resin includes the following steps: S1. 5.00 g of nano-silica was added to 250 mL of tris(hydroxymethyl)aminomethane buffer solution, the pH was adjusted to 8.4, 0.25 g of dopamine hydrochloride was added, and the reaction was carried out at 22 °C for 6 h. After separation and drying, polydopamine-coated nano-silica was obtained. 0.40 g of 3-(methacryloyloxy)propyltrimethoxysilane was pre-hydrolyzed in a mixture of ethanol and water at a volume ratio of 4:1, and the above polydopamine-coated nano-silica was added. The reaction was carried out at 55 °C for 2 h to obtain a bridging interfacial reaction nano-modifier. In another step, 13.75 g of polyether diol was dehydrated and then 7.57 g of 4,4'-diphenylmethane diisocyanate was added at 70°C under the catalysis of dibutyltin dilaurate to carry out a prepolymerization reaction; then, in the presence of hydroquinone methyl ether polymerization inhibitor, 4.30 g of hydroxyethyl methacrylate was added at 45°C to end-cap the polymer, thus obtaining a reactive polyurethane prepolymer.

[0019] S2. Weigh 5.00 g of bridging interface reactive nanomodifier and 20.00 g of reactive polyurethane prepolymer, stir and mix them at 50°C and disperse them for 0.5 h, then add 5.00 g of styrene and continue stirring and dispersing to obtain nanoparticle-reactive polyurethane masterbatch.

[0020] S3. Prepare an unsaturated polyester resin solution according to the following formulation ratio: 280.0 g maleic anhydride, 180.0 g phthalic anhydride, 240.0 g propylene glycol and 120.0 g neopentyl glycol are polycondensed until the final acid value is 20 mg KOH / g, then 400.0 g styrene is added, and 1000.0 g of the resulting unsaturated polyester resin solution is taken for later use. Prepare a low-shrinkage component according to the following raw materials and ratio: adipic acid, isophthalic acid and neopentyl glycol are polycondensed at a molar ratio of 1:0.9:1.9 at 190℃ for 4 h, and the final acid value is not greater than 15 mg KOH / g, then mixed with styrene at a mass ratio of 1:0.8, and 50.0 g of the resulting low-shrinkage component is taken for later use. Add 50.0 g of low-shrinkage component to 1000.0 g of unsaturated polyester resin liquid and pre-compatible at 40°C for 30 min; then add 30.0 g of nanoparticle-reactive polyurethane masterbatch and continue mixing for 20 min to obtain the resin mixture system.

[0021] S4. Add 5.00 g of methyl ethyl ketone peroxide and 0.50 g of cobalt octanoate accelerator to the obtained resin mixture, mix evenly and then inject into the mold. First, pre-gel at 30°C for 30 min, then main cure at 65°C for 1.5 h, and finally post-cur at 100°C for 1.5 h to obtain the high-toughness, low-shrinkage unsaturated polyester resin material.

[0022] Example 2: A preparation process for a high-toughness, low-shrinkage unsaturated polyester resin includes the following steps: S1. 50.00 g of nano-silica was added to 2500 mL of tris(hydroxymethyl)aminomethane buffer solution, the pH was adjusted to 8.6, 2.50 g of dopamine hydrochloride was added, and the mixture was reacted at 30 °C for 10 h. After separation and drying, polydopamine-coated nano-silica was obtained. 4.00 g of 3-(methacryloyloxy)propyltrimethoxysilane was pre-hydrolyzed in a mixture of ethanol and water at a volume ratio of 8:1, and the above-mentioned polydopamine-coated nano-silica was added. The mixture was reacted at 65 °C for 4 h to obtain a bridging interfacial reactive nano-modifier. In another case, 68.75 g of polyether diol was dehydrated and then prepolymerized for 2 h at 80 °C by adding 37.85 g of 4,4'-diphenylmethane diisocyanate under the same catalytic and polymerization inhibition conditions as in Example 1; then 21.50 g of hydroxyethyl methacrylate was added at 55 °C for end-capping for 1.5 h to obtain a reactive polyurethane prepolymer.

[0023] S2. Add 48.28 g of bridging interface reactive nanomodifier to 103.45 g of reactive polyurethane prepolymer, disperse at 60℃ for 1 h, then add 48.28 g of styrene and continue mixing to obtain nanoparticle-reactive polyurethane masterbatch.

[0024] S3. Prepare an unsaturated polyester resin solution according to the following formulation ratio: 280.0 g maleic anhydride, 120.0 g phthalic anhydride, 60.0 g isophthalic acid, 240.0 g propylene glycol, and 120.0 g neopentyl glycol are polycondensed until the final acid value is 35 mg KOH / g, and then 400.0 g styrene is added. Separately prepare 180.0 g of a low-shrinkage component, which is prepared by polycondensation of adipic acid, isophthalic acid, and neopentyl glycol in a molar ratio of 1:1.1:2.1 at 220℃ for 7 h, with a final acid value not exceeding 15 mg KOH / g, and then mixed with styrene at a mass ratio of 1:1.4. The resulting saturated polyester low-shrinkage resin has a number-average molecular weight of 3500. 180.0 g of low-shrinkage component was added to 1000.0 g of unsaturated polyester resin liquid and mixed at 50°C for 60 min. Then, 200.0 g of nanoparticle-reactive polyurethane masterbatch was added and mixed for another 40 min to obtain the resin composition system.

[0025] S4. Add 20.00 g of methyl ethyl ketone peroxide and 6.00 g of cobalt octanoate accelerator to the above resin combination system, mix evenly and inject into the mold, pre-gel at 35°C for 60 min, main cure at 75°C for 2.5 h, and then post-cur at 110°C for 2.5 h to obtain the high toughness low shrinkage unsaturated polyester resin material.

[0026] Example 3: A preparation process for a high-toughness, low-shrinkage unsaturated polyester resin includes the following steps: S1. 25.00 g of nano-silica was added to 1250 mL of tris(hydroxymethyl)aminomethane buffer solution, the pH was adjusted to 8.5, 1.25 g of dopamine hydrochloride was added, and the reaction was carried out at 26 °C for 8 h. After separation and drying, polydopamine-coated nano-silica was obtained. 2.00 g of 3-(methacryloyloxy)propyltrimethoxysilane was pre-hydrolyzed in a mixture of ethanol / water at a volume ratio of 6:1, and the above-mentioned polydopamine-coated nano-silica was added. The reaction was carried out at 60 °C for 3 h to obtain a bridging interfacial reactive nanomodifier. 34.62 g of polyether diol was dehydrated and, under the same catalytic and polymerization inhibition conditions as in Example 1, 19.06 g of 4,4'-diphenylmethane diisocyanate was added at 75 °C for a prepolymerization reaction for 1.5 h; then 10.82 g of hydroxyethyl methacrylate was added at 50 °C for end-capping for 1 h to obtain a reactive polyurethane prepolymer.

[0027] S2. Add 25.24 g of bridging interface reactive nanomodifier to 64.51 g of reactive polyurethane prepolymer, disperse at 55°C for 0.75 h, then add 25.24 g of styrene and continue mixing to obtain nanoparticle-reactive polyurethane masterbatch.

[0028] S3. Prepare an unsaturated polyester resin solution according to the following formulation ratio: 280.0 g maleic anhydride, 150.0 g phthalic anhydride, 30.0 g isophthalic acid, 240.0 g propylene glycol and 120.0 g neopentyl glycol are polycondensed until the final acid value is 27.5 mg KOH / g, and then 400.0 g styrene is added. Separately prepare 115.0 g of a low-shrinkage component, which is prepared by polycondensation of 16.50 g adipic acid, 18.77 g isophthalic acid and 23.54 g neopentyl glycol in a molar ratio of 1:1.0:2.0 at 205℃ for 5.5 h, with a final acid value not greater than 15 mg KOH / g, and then mixed with 60.24 g styrene. The resulting saturated polyester low-shrinkage resin has a number-average molecular weight of 2750. 115.0 g of low-shrinkage component was added to 1000.0 g of unsaturated polyester resin liquid and mixed at 45°C for 45 min. Then, 115.0 g of nanoparticle-reactive polyurethane masterbatch was added and mixed for another 30 min to obtain the resin composition system.

[0029] S4. Add 12.50 g of methyl ethyl ketone peroxide and 3.25 g of cobalt octanoate accelerator to the above resin combination system, mix evenly and inject into the mold, pre-gel at 32.5℃ for 45 min, main cure at 70℃ for 2 h, and then post-cur at 105℃ for 2 h to obtain the high toughness low shrinkage unsaturated polyester resin material.

[0030] Comparative Example 1: This comparative example only removed the polydopamine coating layer from the bridging interfacial reactive nanomodifier to verify the role of the polydopamine layer in improving the interfacial adhesion of nanoparticles, improving particle dispersion, and enhancing the overall performance of the resin system.

[0031] A preparation process for a high-toughness, low-shrinkage unsaturated polyester resin includes the following steps: S1. 25.00 g of nano-silica was added to a mixture of 150 mL of ethanol and 25 mL of deionized water. After stirring and dispersing, 2.00 g of 3-(methacryloyloxy)propyltrimethoxysilane was added, and the mixture was reacted at 60 °C for 3 h. After the reaction, the nano-silica was separated, washed, and dried to obtain nano-silica modified only by 3-(methacryloyloxy)propyltrimethoxysilane. Separately, 34.62 g of polyether diol was dehydrated and then, under the same catalytic and polymerization inhibition conditions as in Example 1, 19.06 g of 4,4'-diphenylmethane diisocyanate was added at 75 °C for a prepolymerization reaction for 1.5 h. Then, 10.82 g of hydroxyethyl methacrylate was added at 50 °C for end-capping for 1 h to obtain a reactive polyurethane prepolymer.

[0032] S2. Add 25.24 g of single silane modified nano silica to 64.51 g of reactive polyurethane prepolymer and disperse at 55°C for 0.75 h. Then add 25.24 g of styrene and continue mixing to obtain nanoparticle-reactive polyurethane masterbatch.

[0033] S3. Prepare unsaturated polyester resin solution and low-shrinkage component according to the method in Example 3, and take 1000.0 g of unsaturated polyester resin solution and 115.0 g of low-shrinkage component. Add 115.0 g of low-shrinkage component to 1000.0 g of unsaturated polyester resin solution and mix at 45°C for 45 min; then add 115.0 g of nanoparticle-reactive polyurethane masterbatch and continue mixing for 30 min to obtain the resin combination system.

[0034] S4. Add 12.50 g of methyl ethyl ketone peroxide and 3.25 g of cobalt octanoate accelerator to the above resin combination system, mix evenly and inject into the mold, pre-gel at 32.5℃ for 45 min, main cure at 70℃ for 2 h, and then post-cur at 105℃ for 2 h to obtain the resin sample of Comparative Example 1.

[0035] Comparative Example 2: This comparative example does not include the pre-preparation steps of nanoparticle-reactive polyurethane masterbatch. The other raw material types, amounts, addition order, curing regime, and total mixing time of nanoparticles, reactive polyurethane prepolymer, and styrene are all consistent with those in Example 3.

[0036] A preparation process for a high-toughness, low-shrinkage unsaturated polyester resin includes the following steps: S1. Following the method in step S1 of Example 3, 25.24 g of bridging interfacial reactive nanomodifier and 64.51 g of reactive polyurethane prepolymer were prepared.

[0037] S2. Weigh 25.24 g of bridging interface reactive nanomodifier, 64.51 g of reactive polyurethane prepolymer and 25.24 g of styrene for later use, without pre-masterbatch treatment.

[0038] S3. Prepare an unsaturated polyester resin solution according to the following formulation ratio: 280.0 g maleic anhydride, 150.0 g phthalic anhydride, 30.0 g isophthalic acid, 240.0 g propylene glycol and 120.0 g neopentyl glycol are polycondensed until the final acid value is 27.5 mg KOH / g, and then 400.0 g styrene is added. Separately prepare 115.0 g of a low-shrinkage component, which is prepared by polycondensation of 16.50 g adipic acid, 18.77 g isophthalic acid and 23.54 g neopentyl glycol in a molar ratio of 1:1.0:2.0 at 205℃ for 5.5 h, with a final acid value not greater than 15 mg KOH / g, and then mixed with 60.24 g styrene. The resulting saturated polyester low-shrinkage resin has a number-average molecular weight of 2750. 115.0 g of low-shrinkage component was added to 1000.0 g of unsaturated polyester resin liquid and mixed at 45°C for 45 min. Then, 25.24 g of bridging interface reactive nanomodifier, 64.51 g of reactive polyurethane prepolymer and 25.24 g of styrene were added to the above system in sequence and mixed for another 30 min to obtain the resin combination system.

[0039] S4. Add 12.50 g of methyl ethyl ketone peroxide and 3.25 g of cobalt octanoate accelerator to the above resin combination system, mix evenly and inject into the mold, pre-gel at 32.5℃ for 45 min, main cure at 70℃ for 2 h, and then post-cur at 105℃ for 2 h to obtain the resin sample of Comparative Example 2.

[0040] Performance testing The resins obtained in Examples 1-3 and Comparative Examples 1-2 were poured into the same mold, cured according to their respective curing regimes, and then placed at room temperature for 24 hours before being processed into corresponding test specimens. All performance tests were conducted under the same environmental conditions, and each group of samples was tested in parallel at least 5 times, with the average value taken.

[0041] 1. Volume shrinkage rate test Record the volume of the mold cavity before resin casting as V0 and the volume of the sample after curing as V1. Calculate the volume shrinkage rate to characterize the degree of volume change during the resin curing process.

[0042] 2. Linear shrinkage rate test Measure the lengths of the mold and sample at three points: both ends and the middle. Take the average value as L0 and L1, calculate according to the formula, and keep two decimal places.

[0043] 3. Impact strength test The test was conducted in accordance with GB / T2567-2021. The samples were processed into standard notched impact specimens, and the impact strength was determined using a pendulum impact testing machine.

[0044] 4. Bending strength test The test was conducted in accordance with GB / T2567-2021. The sample was processed into a standard bending specimen, and its bending strength was tested using the three-point bending method. This test was used to characterize the load-bearing capacity and strength retention of the material under stress.

[0045] 5. Elongation at break test The test was conducted in accordance with GB / T2567-2021. The samples were processed into standard tensile specimens and tensile tests were performed using a universal testing machine. The elongation at fracture was recorded to characterize the flexibility and toughening effect of the material.

[0046] 6. Heat distortion temperature test The temperature at which a sample undergoes a specified deformation under specified load conditions is measured to characterize the heat resistance and dimensional stability of the resin system.

[0047] The results are shown in Table 1 below.

[0048] Table 1 Performance test results of samples from Examples 1-3 and Comparative Examples 1-2

[0049] As shown in Table 1, the volume shrinkage and linear shrinkage rates of the samples obtained in Examples 1-3 were significantly lower than those in Comparative Examples 1 and 2. This indicates that the present invention, through the synergistic effect of low-shrinkage components, bridging interfacial reactive nanomodifiers, and nanoparticle-reactive polyurethane masterbatch, can effectively suppress the volume change of unsaturated polyester resin during the curing process and improve the dimensional stability of the product. Among them, Example 2 had the lowest volume shrinkage and linear shrinkage rates, indicating that the shrinkage compensation effect of the resin system was more significant under conditions of higher addition amounts of low-shrinkage components and masterbatch. Although the shrinkage rate of Example 3 was slightly higher than that of Example 2, it was still significantly better than the two comparative examples, indicating that it also had a good low-shrinkage effect.

[0050] From a mechanical property perspective, the impact strength, flexural strength, and elongation at break of Examples 1-3 are all superior to those of Comparative Examples 1 and 2, indicating that the present invention not only achieves reduced shrinkage but also avoids the mechanical property degradation problem that easily occurs in conventional low-shrinkage modification. In particular, Example 3 has the best overall performance with impact strength, flexural strength, and elongation at break reaching 17.2 kJ·m⁻², 121 MPa, and 3.4%, respectively, indicating that a better synergistic balance is formed between the bridging interfacial reactive nanomodifier, the reactive polyurethane prepolymer, and the low-shrinkage component under intermediate parameter conditions. Although the addition amount of each component and the process conditions in Example 1 are relatively low, the overall strengthening effect is relatively limited. Although Example 2 performs better in terms of shrinkage control, its impact strength and flexural strength are lower than those of Example 3, indicating that when the addition amount of components and the process strength are further increased, the balance between low shrinkage and toughness and strength is not optimal.

[0051] Comparative Example 1, using only silane-modified nano-silica, showed significantly worse shrinkage, impact strength, and elongation at break compared to Example 3. This indicates that the introduction of the polydopamine layer enhances the interfacial adhesion between nanoparticles and the resin matrix and the flexible polyurethane phase, improving particle dispersion and thus enhancing interfacial bridging and overall performance. Comparative Example 2 eliminated the pre-preparation of the nanoparticle-reactive polyurethane masterbatch, instead directly adding each component. Its performance was the worst in all aspects, indicating that the masterbatch approach facilitates the pre-formation of a relatively stable composite structure between the inorganic reinforcing phase and the flexible toughening phase, reducing particle agglomeration and local enrichment. In summary, this invention can improve toughness and strength while reducing curing shrinkage and maintaining a high heat distortion temperature, fully demonstrating its significant overall performance improvement effect.

[0052] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A high-toughness, low-shrinkage unsaturated polyester resin, characterized in that, By weight, it includes the following components: 100 parts unsaturated polyester resin liquid, 5-18 parts low shrinkage component, 3-20 parts nanoparticle-reactive polyurethane masterbatch, 0.5-2.0 parts initiator, and 0.05-0.6 parts accelerator. The nanoparticle-reactive polyurethane masterbatch comprises, by weight, 10-35 parts of bridging interface reactive nanomodifier, 40-75 parts of reactive polyurethane prepolymer, and 10-35 parts of styrene; the bridging interface reactive nanomodifier is polydopamine-3-(methacryloyloxy)propyltrimethoxysilane dual-modified nano silica.

2. The high-toughness, low-shrinkage unsaturated polyester resin according to claim 1, characterized in that, The average particle size of the nano-silica in the bridging interfacial reaction nanomodifier is 15–40 nanometers.

3. The high-toughness, low-shrinkage unsaturated polyester resin according to claim 1, characterized in that, The bridging interface reaction nanomodifier is a dual-modified nano-silica prepared by the following method: first, the nano-silica is coated with polydopamine, and then the polydopamine-coated nano-silica is grafted with 3-(methacryloyloxy)propyltrimethoxysilane for modification.

4. The high-toughness, low-shrinkage unsaturated polyester resin according to claim 1, characterized in that, The reactive polyurethane prepolymer is a hydroxyethyl methacrylate-terminated polyurethane prepolymer, which is obtained by first reacting polyether diol with 4,4'-diphenylmethane diisocyanate to generate an isocyanate-terminated polyurethane prepolymer, and then end-capping it with hydroxyethyl methacrylate.

5. The high-toughness, low-shrinkage unsaturated polyester resin according to claim 1, characterized in that, The low-shrinkage component is a saturated polyester low-shrinkage resin, which is prepared by polycondensation of adipic acid, isophthalic acid and neopentyl glycol in a molar ratio of 1:(0.9-1.1):(1.9-2.1) at 190-220°C for 4-7 hours, with the final acid value at the polycondensation endpoint not exceeding 15 mg potassium hydroxide / g, and then mixing it with styrene in a mass ratio of 1:(0.8-1.4). The number average molecular weight of the saturated polyester low-shrinkage resin is 2000-3500.

6. The high-toughness, low-shrinkage unsaturated polyester resin according to claim 1, characterized in that, The unsaturated polyester resin solution is prepared by polycondensation reaction of one or two of maleic anhydride, phthalic anhydride and isophthalic acid with propylene glycol and neopentyl glycol, followed by mixing with styrene. The final acid value of the polycondensation reaction is 20-35 mg potassium hydroxide / g.

7. A method for curing and molding the high-toughness, low-shrinkage unsaturated polyester resin according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. A bridging interface reaction nanomodifier was prepared using nano-silica, dopamine hydrochloride and 3-(methacryloyloxy)propyltrimethoxysilane, and a reactive polyurethane prepolymer was prepared using polyether diol, 4,4'-diphenylmethane diisocyanate and hydroxyethyl methacrylate. S2. A bridging interface reactive nano-modifier is added to a partially reactive polyurethane prepolymer and mixed. Then, a portion of styrene is added to adjust the fluidity of the system and disperse it to obtain a nanoparticle-reactive polyurethane masterbatch. S3. Add the low-shrinkage component to the unsaturated polyester resin liquid for pre-compatibility treatment, and then add the nanoparticle-reactive polyurethane masterbatch and mix evenly to obtain a resin mixture system. S4. Add initiator and accelerator to the resin mixture system, and then perform pre-gel, main curing and post-curing in sequence to obtain a high-toughness, low-shrinkage unsaturated polyester resin material after curing.

8. The preparation method according to claim 7, characterized in that, In step S1, the coating reaction of nano-silica with dopamine hydrochloride is carried out in a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.4–8.

6. 3-(methacryloyloxy)propyltrimethoxysilane is pre-hydrolyzed in an ethanol / water mixture and then grafted onto polydopamine-coated nano-silica. Polyether diol undergoes a prepolymerization reaction with 4,4'-diphenylmethane diisocyanate, followed by a capping reaction with hydroxyethyl methacrylate. The coating reaction temperature is 22–30°C, the grafting reaction temperature is 55–65°C, the prepolymerization reaction temperature is 70–80°C, and the capping reaction temperature is 45–55°C.

9. The preparation method according to claim 7, characterized in that, In step S2, the mixing and dispersion temperature of the bridging interface reactive nanomodifier, part of the reactive polyurethane prepolymer, and part of the styrene is 50-60°C, and the dispersion time is 0.5-1 hour. In step S3, the pre-compatibility treatment temperature of the low-shrinkage component and the unsaturated polyester resin liquid is 40-50°C, the pre-compatibility treatment time is 30-60 minutes, and the mixing time after adding the nanoparticle-reactive polyurethane masterbatch is 20-40 minutes.

10. The preparation method according to claim 7, characterized in that, In step S4, the pre-gel temperature is 30-35℃ and the time is 30-60 minutes; the main curing temperature is 65-75℃ and the time is 1.5-2.5 hours; the post-curing temperature is 100-110℃ and the time is 1.5-2.5 hours.

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