Isotropic high-strength photocuring 3D printing resin and preparation method thereof

Abstract

The invention relates to isotropic high-strength photocuring 3D printing resin and a preparation method thereof. The preparation method of the dynamically dissociated isocyanate cross-linking agent in the resin system comprises the step of synthesizing the dynamically dissociated isocyanate cross-linking agent by taking tert-butylaminoethyl methacrylate and isophorone diisocyanate as raw materials. The dynamically dissociated isocyanate cross-linking agent prepared by the invention can be used as a photo-cross-linking agent in a photo-curing 3D printing process, so that the shape retention of 3D printing is improved, and isocyanate groups can be released in a thermocuring process, so that a secondary cross-linked network is formed between layers. On the premise of ensuring the printability, the mechanical strength of a printing material is improved, and meanwhile, the anisotropy of a printed product is eliminated, so that the wide application of photocuring 3D printing is favorably realized.

Description

TECHNICAL FIELD

[0001] The present application relates to an isotropic high-strength light-cured 3D printing resin and a preparation method thereof, and belongs to the technical field of chemical industry and polymer materials. BACKGROUND

[0002] Additive manufacturing, commonly known as 3D printing, is a new manufacturing technology that has attracted much attention in recent years. Its manufacturing method is to stack materials layer by layer. Compared with traditional forming manufacturing process, additive manufacturing directly forms complex structures through digital model, not only breaks through the geometric shackles of equal material manufacturing mold design, but also avoids the material waste caused by subtractive manufacturing, showing the characteristics of high integration, high efficiency and speed, intelligence and customization. Therefore, it has great development potential in the fields of biological medicine, electronic devices, aerospace, etc. The 3D printing based on light curing technology has been favored by researchers due to its fast speed, high precision and other advantages.

[0003] The existing photo-curable 3D printing technology mainly includes stereo lithography (SLA), digital light processing (DLP), continuous liquid interface production (CLIP) and liquid crystal display (LCD) and the like. Among them, the most widely used photosensitive resin is acrylate monomer / oligomer, which is a free radical type photosensitive resin system, and has the advantage of fast polymerization speed. The preparation of 3D structure is based on digital model, which is sliced and projected on the predetermined position of the printing platform, and the liquid monomer / oligomer is photo-polymerized, one plane is formed at a time, and the target structure is obtained by layer-by-layer stacking. After the ultraviolet light cures a layer of resin on the printing platform, the platform will move a layer of thickness, and the liquid resin will quickly fill to cure the next layer. However, this forming process inevitably produces a solid-liquid interface, and the compatibility of the upper cured resin and the lower liquid resin decreases, and the chemical bonding between the layers cannot be effectively carried out, so that the interlayer bonding force is weaker than the intra-layer. That is, the solid-liquid interface in the printing process leads to the "delamination" phenomenon of the printed product. Moreover, the mechanical properties of the printed part will change with the direction of the external load, that is, anisotropy. When the external load directly acts on the weak interface, the interlayer will produce cracks before the external force reaches the overall bearing capacity, forming local defects, and then expanding to cause the printed part to break. The anisotropy of the mechanical properties of the photo-curable 3D printed product leads to the fact that the application field of the photo-curable 3D printing acrylate resin mainly concentrates in model products, and it cannot be really used as a structural part. Therefore, improving the interlayer bonding force of the photo-curable 3D printed structure, reducing or even eliminating the anisotropy of its mechanical strength, is the basis for the wide application of the photo-curable 3D printed product.

[0004] The most direct way to improve the interlayer adhesion of photocured 3D printed structures is to optimize the printing process, that is, to select appropriate printing parameters such as layer thickness, printing speed, and curing time by continuous adjustment. Although it can have some effect, it cannot completely eliminate anisotropy and is time-consuming, labor-intensive, and material-consuming, and cannot be used as an effective means. In addition, after printing is completed, the printed product is subjected to post-curing treatment using ultraviolet light, which allows the residual monomers that have not fully reacted during the printing process to further cross-link between layers. However, due to the limited penetration of ultraviolet light, the residual monomers in the deep structure cannot be completely cross-linked, and internal defects in the printed product still exist, that is, the simple ultraviolet post-treatment process does not significantly improve the interlayer adhesion. Therefore, research on improving interlayer adhesion focuses on establishing new connections at the layer interface through physical action or chemical cross-linking. For example, Miao et al. prepared a modified carbon fiber (CF-amine) reinforced photosensitive acrylate printing system, which established a bridge between layers through the action of carbon fibers, strengthened the weak connection between layers, and increased the tensile strength of the original resin matrix by 44.7%, and the anisotropy of the tensile strength in the horizontal and vertical printing directions decreased from 40.6% to 3.3%, and the anisotropy of the elongation at break also decreased from 37.1% to 1.9% (see literature: Miao J-T.; Yang B.; Sang X.; Liu R. Composites Communications 2025, 55, 102315.). Zhu et al. proposed a universal strategy, that is, adding a small amount of linear polymers such as polycaprolactone (PCL), polyethylene glycol (PEG), and polyisobornyl acrylate (PIBOA) to the mature commercial DLP printing resin, and by heating the linear polymer to melt it, it can diffuse or rearrange at the interface between the printed layers, thereby connecting the printed layers, and the mechanical strength of the printed product increases with the increase of the content of linear polymers. When the content of PCL added to the commercial resin is 4.7%, the tensile strength of the resin reaches a maximum value, and compared with the resin without PCL, the anisotropy of the y-axis and z-axis compared with the x-axis decreases from 14% and 24% to 5% and 7%, respectively (see literature: Zhu, G.; Hou, Y.; Xu, J.; Zhao, N. Macromolecular Rapid Communications 2022, 43 (9), 2200053.).Li et al. added a core-shell particle (CSP) containing epoxy groups to an epoxy / acrylate hybrid system, and established chemical cross-linking between the solid resin cured on the upper layer and the liquid resin not cured on the lower layer through the polymerization of epoxy groups. When the content of CSP was 7%, the anisotropy of tensile strength in the horizontal and vertical directions decreased from 42.1% to 0.3%, but the elongation at break still had anisotropy of 56.1% (see document: Li, Y.; Peng, S.; Miao, J.-T.; Zheng, L.; Zhong, J.; Wu, L.; Weng, Z. Chemical Engineering Journal 2020, 394, 124873.). Wang et al. synthesized acrylate containing disulfide bond (DSDA), and added it to the photosensitive resin printing system. During printing, the UV-induced disulfide bond metathesis and rearranged the disulfide bond crosslinking network, and transferred the interlayer crosslinking to the interlayer. The tensile strength of the printing system with 10% DSDA content achieved isotropy of 98.4% in the z-axis to the x-axis, but the elongation at break had anisotropy of 25% (see document: Wang, S.; Yin, J.; Huang, W.; Ye, J.; Deng, H.; Huang, J.; Wang, S.; Liu, X.; Xiang, H. Additive Manufacturing 2022, 59, 103085.). These research methods can effectively improve the interlayer bonding force and reduce the anisotropy to a certain extent, but still have some shortcomings, such as not completely eliminating the anisotropy, and the mechanical strength of the obtained material is low. Therefore, it is of great significance to improve the interlayer bonding force by a simple method and obtain isotropic high-mechanical-strength photocurable 3D printing resin.

[0005] Epoxy acrylate is a kind of commonly used free radical type photocuring 3D printing resin system, which is rich in hydroxyl after photocuring. By using this structural advantage, a crosslinking agent which can further react with hydroxyl after photocuring is added to the system to establish interlayer crosslinking, so as to improve the interlayer bonding force and reduce or even eliminate anisotropy. Isocyanate is a compound with NCO group, which can react with hydroxyl to obtain polyurethane with high plasticity and high mechanical strength. By using the synthesis characteristics of polyurethane, isocyanate groups are introduced into the epoxy acrylate system, and further reaction is carried out through thermal curing after photocuring to establish interlayer crosslinking, so that the layers are welded into a uniform and dense whole, and a truly isotropic photocuring 3D printing product is obtained. In the previous research of the research group, hexamethylene diisocyanate-based polyisocyanate trimer (PHDI) is directly added to the epoxy acrylate system, the interlayer crosslinking is increased by light and heat double curing strategy, a double crosslinking network is formed, and the interlayer and intralayer bonding force is also strengthened, so that the layers are fused into a whole, thereby realizing the isotropy of mechanical properties. However, we ignored the slow reaction between NCO and hydroxyl at room temperature, which led to poor storage of the double curing 3D printing system, and the viscosity of the printing resin solution increased with time. Although the viscosity increase has no effect on the printing area, it seriously limits the long-term storage of the printing solution. SUMMARY

[0006] To improve the above technical problems, the present application provides a dynamic dissociation isocyanate crosslinking agent, which is an important component of an isotropic high-strength photocuring 3D printing resin composition, The first object of the present application is to provide a dynamic dissociation isocyanate crosslinking agent, the crosslinking agent being 2-((1-((tert-butyl)-3-((5-(3-(tert-butyl ester)-3-(2-(methacryloyloxy)ethyl)ureido)-1,3,3-trimethylcyclohexyl) methyl) ureido ethyl) methacrylate, the structural formula being shown as formula I: Formula I In the formula, O represents oxygen, N represents nitrogen, and H represents hydrogen.

[0007] The second object of the present application is to provide a method for preparing the dynamic dissociation isocyanate crosslinking agent as described above, comprising the following steps: (1) dissolving tert-butyl aminoethyl methacrylate TBEMA and isophorone diisocyanate IPDI in an organic solvent respectively to obtain TBEMA solution and IPDI solution; (2) adding the IPDI solution dropwise into the TBEMA solution, stirring and reacting; (3) after the reaction is completed, removing the organic solvent to obtain the dynamic dissociation isocyanate crosslinking agent.

[0008] A third object of the present application is to provide a resin composition comprising the dynamic dissociation isocyanate crosslinking agent as described above.

[0009] A fourth object of the present application is to provide a method for preparing the resin composition as described above, comprising the following steps: mixing an acrylate monomer, a dynamic dissociation isocyanate crosslinking agent, and a photoinitiator to obtain an isotropic high-strength photocuring 3D printing resin composition.

[0010] A fifth object of the present application is to provide the use of the resin composition as described above in photocuring 3D printing.

[0011] Advantages The present application has the following advantages: 1. The dynamic dissociation isocyanate crosslinking agent synthesized in the present application can be used as a photocrosslinking agent in the photocuring 3D printing process, improving the shape retention of 3D printing, and can release isocyanate groups in the thermal curing process to form a secondary crosslinking network. Under the premise of ensuring the printing property, the mechanical strength of the printing material is improved, and the anisotropy of the printed product is eliminated, thereby facilitating the wide application of photocuring 3D printing.

[0012] 2. The resin used in 3D printing needs to meet a certain viscosity range, so a diluent is usually added to the 3D printing resin to obtain a resin suitable for 3D printing (with a viscosity of less than 1.3 Pa·s). However, the addition of the diluent will reduce the crosslinking density of the resin and deteriorate the comprehensive performance of the material. The isotropic high-strength photocuring 3D printing resin provided in the present application can be directly used for 3D printing without adding a diluent, thereby avoiding the adverse effects of the addition of the diluent on the performance of the material.

[0013] 3. The isotropic photocuring 3D printing resin composition provided in the present application is directly used as an excellent 3D printing resin material and applied to the 3D printing process. The printing speed is fast, the efficiency is high, and the precision is high, which is conducive to overcoming the defects of traditional photocuring reaction materials (especially systems requiring fillers) that cannot be applied to rapid prototyping of large products due to low photocuring activity. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is the synthesis route (reaction formula) of the crosslinking agent provided in Example 1 and Comparative Example 1 of the present application; Figure 2 is the nuclear magnetic resonance hydrogen spectrum of the dynamic dissociation isocyanate crosslinking agent provided in Example 1 of the present application; Figure 3 is the high-resolution mass spectrum of the dynamic dissociation isocyanate crosslinking agent provided in Example 1 of the present application; Figure 4is the 3D complex structure provided by embodiment 1 of the present application; Figure 5 is the morphology of the 3D complex structure provided by embodiment 1 of the present application after the interlayer welding process is completed; Figure 6 is the excellent mechanical property of the 3D printing resin composition provided by embodiment 1 of the present application; Figure 7 is the effect of the interlayer welding provided by embodiment 1 and comparative example 1 of the present application at the micro interface; Figure 8 is the principle schematic diagram of the embodiment of the present application; Figure 9 is the reaction flow schematic diagram of the embodiment of the present application; Figure 10 is the good storage stability of the 3D printing resin composition provided by embodiment 1 and embodiment 2 of the present application; Figure 11 is the application example of the interlayer welding provided by embodiment 1 of the present application. DETAILED DESCRIPTION

[0015] The present application relates to a kind of preparation method of dynamic dissociation isocyanate crosslinking agent, and as important component group constitutes a isotropic high-strength photocuring 3D printing resin composition.The preparation method of isotropic photocuring 3D printing resin includes: (1) with tertiary butyl aminoethyl methacrylate and isophorone diisocyanate as raw material, dynamic dissociation isocyanate crosslinking agent is synthesized; (2) acrylic ester monomer, dynamic dissociation isocyanate crosslinking agent, photo initiator are mixed, and the photocuring 3D printing resin composition with good storage stability is obtained; (3) by photocuring 3D printing and interlayer welding heat treatment process, isotropic high-strength photocuring 3D printing product is obtained.

[0016] The dynamic dissociation isocyanate crosslinking agent prepared by the present application can be used as a photocrosslinking agent during photocuring 3D printing, improving the shape retention of 3D printing, and releasing isocyanate groups during thermal curing to form a secondary crosslinking network. Under the premise of ensuring the printing property, the mechanical strength of the printing material is improved, and the anisotropy of the printing product is eliminated, thereby facilitating the wide application of photocuring 3D printing.

[0017] On the one hand, the present application proposes a kind of dynamic dissociation isocyanate crosslinking agent, and the crosslinking agent is 2-(1-(tert-butyl)-3-((5-(3-(tert-butyl ester)-3-(2-(methyl acryloyl oxy) ethyl) urea group)-1,3,3-trimethylcyclohexyl) methyl) urea group ethyl methacrylate, and the structure formula is as shown in formula I: Formula I wherein, O represents oxygen, N represents nitrogen, and H represents hydrogen.

[0018] In another aspect, the present application provides a method for preparing the dynamic dissociation isocyanate crosslinking agent as described above, comprising the following steps: (1) dissolving t-butyl aminoethyl methacrylate TBEMA and isophorone diisocyanate IPDI in organic solvents respectively, to obtain TBEMA solution and IPDI solution respectively; (2) adding the IPDI solution dropwise into the TBEMA solution, stirring and reacting; (3) after the reaction is completed, removing the organic solvent to obtain the dynamic dissociation isocyanate crosslinking agent.

[0019] According to an embodiment of the present application, in step (1), the molar ratio of t-butyl aminoethyl methacrylate and isophorone diisocyanate is 2:1.

[0020] According to an embodiment of the present application, in step (1), the organic solvent independently includes any one or more of dichloromethane, trichloromethane, ethyl acetate, methanol, petroleum ether, and n-butanol.

[0021] According to an embodiment of the present application, in step (2), the temperature of the reaction is 30-80 ℃.

[0022] According to an embodiment of the present application, in step (2), the time of the reaction is 1-8 h. In another aspect, the present application provides a resin composition comprising the dynamic dissociation isocyanate crosslinking agent as described above.

[0023] According to an embodiment of the present application, the resin composition comprises the following components by mass fraction: 100 parts of an acrylate monomer, 5-50 parts of the dynamic dissociation isocyanate crosslinking agent, and 0.1-10 parts of a photoinitiator.

[0024] According to an embodiment of the present application, the mass ratio of the acrylate monomer, the dynamic dissociation isocyanate crosslinking agent, and the photoinitiator is 100:(5-50):(2.1-3), and more preferably 100:(10-30):(2.2-2.6).

[0025] According to an embodiment of the present application, the acrylate monomer includes at least one of 2-acrylic acid-2-hydroxy-3-phenoxypropyl ester, methacrylic acid-2-hydroxyethyl ester, acrylic acid-2-hydroxyethyl ester, and acrylic acid-2-hydroxypropyl ester.

[0026] According to an embodiment of the present application, the photoinitiator comprises at least one of 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, 2,4,6-trimethylbenzoyl-ethoxy-phenyl phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenyl phosphine oxide, 2,2-dimethoxy-1,2-diphenylacetophenone, 2-ethyloctyl-4-dimethylaminobenzoate, 4-p-tolyl 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone.

[0027] Dynamic dissociation Dynamic dissociation Dynamic dissociation Dynamic dissociation In another aspect, the present application provides a method for preparing the resin composition as described in any of the above, comprising the following steps: mixing the acrylate monomer, the dynamic dissociation isocyanate crosslinking agent, and the photoinitiator to obtain the isotropic high-strength light-cured 3D printing resin composition.

[0028] The present application also provides that the resin composition has good storage stability.

[0029] According to an embodiment of the present application, the resin composition has an anisotropy in tensile strength of no more than 1.0%, further no more than 0.5%, and more further 0.1-0.5%, and more further 0.1-0.4%. According to an embodiment of the present application, the viscosity of the resin composition has no significant change within 200 days of storage, meeting the requirements of 3D printing (viscosity less than 1.3 Pa·s).

[0030] In another aspect, the present application further provides the use of the resin composition in light-cured 3D printing.

[0031] The technical solutions of the present application will be further described in detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology implemented based on the above description of the present application is covered within the scope of protection intended by the present application.

[0032] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0033] Example 1 1) Preparation of dynamic dissociation isocyanate crosslinking agent methyl methacrylate 2-(1-(tert-butyl)-3-((5-(3-(tert-butyl ester)-3-(2-(methacryloyloxy)ethyl)ureido)-1,3,3-trimethylcyclohexyl) methyl) ureido ethyl ester 22.2 g IPDI was added into 30 ml dichloromethane, mixed well to get IPDI solution, 37.1 g TBEMA and 50 ml dichloromethane were mixed well in a three-necked round bottom flask equipped with a mechanical stirrer and a condenser reflux device to get TBEMA solution.

[0034] The IPDI solution was added dropwise into the TBEMA solution at room temperature, and the dropping was completed in 20 min. Then the mixture was slowly heated to 50°C for 3 h.

[0035] After the reaction was completed, dichloromethane was removed by rotary evaporation to obtain a colorless transparent liquid, which was a dynamic dissociation isocyanate crosslinking agent.

[0036] 2) Preparation of isotropic high-strength photocurable 3D printing resin composition 2-hydroxy-3-phenoxypropyl acrylate (100 g), the dynamic dissociation isocyanate crosslinking agent prepared in step 1) (20 g), phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide (2.4 g) were mixed well at 70°C for 20 min to obtain a clear liquid, and the obtained liquid was placed into a 405 nm digital light processing (DLP) 3D printer for 3D printing molding. The printed 3D printed structure was placed into an ultraviolet curing box for curing for 5 min.

[0037] 3) Interlayer welding heat treatment process The 3D printed structure after complete ultraviolet light curing in step (2) was placed into a hot oven at 120°C for 1 h of preheating, then heated to 180°C for 2 h of heat curing, and then naturally cooled to room temperature after the end of the process, to complete the interlayer welding. At this time, the printed layers were welded together as a whole to obtain an isotropic photocured 3D printed product.

[0038] 4) Effect of interlayer welding at the interface between layers The isotropic high-strength photocurable 3D printing resin composition in step (2) was placed into a 405 nm digital light processing (DLP) 3D printer, a cuboid model with dimensions of 50 mm x 10 mm x 1 mm was set, and 3D printing molding was performed to prepare two cuboid samples. The printed samples were placed into an ultraviolet curing box for curing for 5 min. After complete photocuring, the two samples were placed in cross-over with an overlapping area of 20 mm, and then the interlayer welding heat treatment process in step (3) was performed. After heat curing, a layer-welded sample was obtained. The sample was placed on a universal testing machine for tensile testing, and the maximum tensile fracture force was measured to be 369 N. Then the tensile fracture section was placed under a scanning electron microscope to take a cross-sectional morphology, and it was found that the cross-section was smooth and flat without gaps (see FIG. 6). Figure 7

[0039] ​In the present embodiment, the synthesis reaction formula, 1H NMR spectrum and high resolution mass spectrum of the dynamic dissociation isocyanate crosslinking agent are shown in Figs. 1, 2 and 3, respectively. Figure 1 , 2 and 3.

[0040] Fig. 1 is a synthesis flowchart (reaction formula) of the dynamic dissociation isocyanate crosslinking agent provided in Embodiment 1 of the present application, which is a nucleophilic addition reaction of isocyanate group and amino group. Figure 1

[0041] Fig. 2 is a 1H NMR spectrum of the dynamic dissociation isocyanate crosslinking agent provided in Embodiment 1 of the present application. Figure 2

[0042] Fig. 3 is a high resolution mass spectrum of the dynamic dissociation isocyanate crosslinking agent provided in Embodiment 1 of the present application, as shown in the figure, the experimental value of [M+Na + ] is 615.4094, which is consistent with the theoretical value 615.4098. Together with Fig. 2, it indicates that the crosslinking agent has been successfully synthesized. Figure 3 Figure 2 Fig. 4 is a 3D complex structure provided in Embodiment 1 of the present application, which indicates that the isotropic high-strength photocuring 3D printing resin composition can be used for DLP 3D printing.

[0043] Fig. 5 is the morphology of the 3D complex structure provided in Embodiment 1 of the present application after interlayer welding heat treatment process, which indicates that the process will not cause damage to the 3D printed product. Figure 4 Fig. 6 is the tensile test result of the 3D printed tensile sample provided in Embodiment 1 of the present application, which indicates that the anisotropy between the horizontal printing and the vertical printing sample is eliminated, and has excellent mechanical properties.

[0044] Figure 5 Fig. 7 is the electron microscope morphology of the interlayer welding sample at the tensile fracture section provided in Embodiment 1 and Comparative Example 1 of the present application, which indicates that the isocyanate is released in the interlayer welding heat treatment process, and further reacts with the epoxy acrylate crosslinking network to form a secondary crosslinking network, filling the pores of the interlayer interface, thereby improving the interlayer bonding force and eliminating the anisotropy of mechanical properties.

[0045] Fig. 8 is a 3D complex structure provided in Embodiment 1 of the present application, which indicates that the isotropic high-strength photocuring 3D printing resin composition can be used for DLP 3D printing. Figure 6 Fig. 9 is the morphology of the 3D complex structure provided in Embodiment 1 of the present application after interlayer welding heat treatment process, which indicates that the process will not cause damage to the 3D printed product.

[0046] Figure 7 Fig. 10 is the tensile test result of the 3D printed tensile sample provided in Embodiment 1 of the present application, which indicates that the anisotropy between the horizontal printing and the vertical printing sample is eliminated, and has excellent mechanical properties.

[0047] Fig. 11 is the electron microscope morphology of the interlayer welding sample at the tensile fracture section provided in Embodiment 1 and Comparative Example 1 of the present application, which indicates that the isocyanate is released in the interlayer welding heat treatment process, and further reacts with the epoxy acrylate crosslinking network to form a secondary crosslinking network, filling the pores of the interlayer interface, thereby improving the interlayer bonding force and eliminating the anisotropy of mechanical properties. Figure 8 Figure 9 ​​​​​​It is the interlayer welding mechanism diagram provided by the embodiment 1 of the present application, the dynamic dissociation of the steric hindrance urea bond releases the -NCO group, the -NCO reacts with the -OH of the epoxy acrylate during the heating process, and the stable urethane bond is obtained, the chemical bond connection between the reinforcement layer and the layer is realized, and the interlayer welding is realized.

[0048] Referring to the accompanying drawings Figure 10 It is the viscosity of the isotropic high-strength photocurable 3D printing resin composition provided by the embodiment 1 and the embodiment 2 of the present application without obvious change within 200 days, which indicates that the resin composition has good storage stability.

[0049] Referring to the accompanying drawings Figure 11 It is an interlayer welding application example provided by the embodiment 1 of the present application. Two hollow diamond structures are welded into a whole through heat treatment and can be used as a bearing structure to lift a 5kg weight without falling off. The model shows the effect of interlayer welding more intuitively.

[0050] Referring to Table 1, the tensile strength of the horizontal printing and vertical printing tensile test samples of the obtained isotropic high-performance photocurable 3D printing resin composition is 84.2±2.5MPa and 84.0±2.7MPa respectively. It can be seen that the isotropic epoxy acrylate 3D printing resin composition has 0.1% anisotropy in tensile strength. Less than 5% is considered to eliminate anisotropy and achieve isotropy.

[0051] Embodiment 2 Except for step 2), it is the same as embodiment 1. Specifically, the difference from embodiment 1 is that the amount of dynamic dissociation isocyanate crosslinking agent in the resin composition is different.

[0052] 2) Preparation of isotropic high-strength photocurable 3D printing resin composition 2-hydroxy-3-phenoxypropyl acrylate (100g), dynamic dissociation isocyanate crosslinking agent (30g), phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide (2.6g) were mixed uniformly at 70°C for 20min to obtain a clear liquid, and the obtained liquid was put into a 405nm digital light processing DLP 3D printer for 3D printing molding. The printed 3D printing structure was put into a ultraviolet curing box for curing for 5min.

[0053] Referring to Table 1, the tensile strength of the horizontal printing and vertical printing tensile test samples of the obtained isotropic high-performance photocurable 3D printing resin composition is 77.3±2.8MPa and 77.0±2.3MPa respectively. It can be seen that the isotropic epoxy acrylate 3D printing resin composition has 0.4% anisotropy in tensile strength. Less than 5% is considered to eliminate anisotropy and achieve isotropy.

[0054] Table 1 Comparative Example 1 1) Preparation of non-dynamic dissociation isocyanate crosslinker 2-((((5-(((2- (methacryloyloxy)ethoxy)carbonyl)amino)-1,3,3-trimethylcyclohexyl)methyl)amino- carbonyl)oxy)methyl methacrylate The difference between this comparative example and Example 1 is that TBEMA is replaced by HEMA.

[0055] 22.2 g of IPDI was added into 30 ml of dichloromethane, mixed uniformly to obtain an IPDI solution, 26.0 g of HEMA and 50 ml of dichloromethane were mixed uniformly in a three-necked round-bottom flask equipped with a mechanical stirrer and a condensation reflux device to obtain a HEMA solution.

[0056] The IPDI solution was added dropwise into the HEMA solution at room temperature, and the dropping was completed in 20 min. Then the above mixture was slowly heated to 50°C and reacted for 3 h.

[0057] After the reaction was completed, dichloromethane was removed by rotary evaporation to obtain a colorless transparent liquid, which was the comparative crosslinker with similar structure to the crosslinker of Example 1 (see the synthesis route in the attached figure Figure 1 ).

[0058] The stable carbamate bond in this crosslinker cannot be dissociated during heating, and the isocyanate group cannot be released during the interlayer welding heat treatment, so it cannot fill the lack of interlayer bonding force, and the models made in different printing directions have anisotropy.

[0059] 2) Preparation of anisotropic photocurable 3D printing resin composition 2-hydroxy-3-phenoxypropyl acrylate (100 g), the comparative crosslinker (20 g), phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide (2.4 g), were mixed uniformly at 70°C for 20 min to obtain a clear liquid, and the obtained liquid was put into a 405 nm digital light processing (DLP) 3D printer for 3D printing molding. The 3D printed structure after printing was placed in an ultraviolet curing box for curing for 5 min.

[0060] 3) The interlayer welding heat treatment process is the same as step 3) of Example 1 4) Preparation of interlayer welding sample The anisotropic photocured 3D printing resin (100 g) in step (1) was placed into a 405 nm digital light processing DLP 3D printer, a cuboid model with a size of 50 mm x 10 mm x 1 mm was set and 3D printing was performed to prepare two cuboid samples. After printing, the samples were placed in a UV curing box for post-curing for 5 min. After complete photocuring, the two samples were overlapped by 20 mm, and then interlayer welding heat treatment process was performed. Since the 3D printing resin cannot release isocyanate, no effective interlayer welding was performed during the heat treatment process, which was only used as a control group to show the effect of interlayer welding. The samples were placed on a universal testing machine for tensile testing, and the maximum tensile fracture force was measured to be 90 N, which was much smaller than that of the interlayer welded sample in Example 1. Then, the tensile fracture section was placed under a scanning electron microscope to take a cross-sectional morphology, and it was found that there was a clear gap in the center of the section (see FIG. 6). Figure 7 ).

[0061] Referring to Table 1, the tensile strengths of the horizontal and vertical printing tensile samples of the obtained anisotropic photocured 3D printing resin composition were 76.9 ± 0.2 MPa and 62.1 ± 3.2 MPa, respectively. It can be seen that the anisotropy of the anisotropic photocured 3D printing resin composition in tensile strength is 19%.

[0062] Through the comparison of Comparative Example 1, it is further shown that the isocyanate group further reacts with the hydroxyl group during the heat curing process to form a double crosslinking network, which fills the gap of the interlayer bonding force, eliminates the anisotropy, and also greatly improves the mechanical properties of the material.

[0063] Example 3 Except for step (2), it is the same as Example 1. Specifically, the difference from Example 1 is that the acrylic ester monomer selected in the resin composition is 2-hydroxyethyl methacrylate.

[0064] 2) Preparation of isotropic high-strength photocured 3D printing resin composition 2-hydroxyethyl methacrylate (100 g), dynamic dissociation isocyanate crosslinking agent (20 g), and phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide (2.4 g) were mixed uniformly at 70 °C for 20 min to obtain a clear liquid. The obtained liquid was placed into a 405 nm digital light processing DLP 3D printer for 3D printing.

[0065] Example 4 Except for step (2), it is the same as Example 1. Specifically, the difference from Example 1 is that the acrylic ester monomer selected in the resin composition is different, and the amount of initiator is different.

[0066] 2) Preparation of isotropic high-strength photocurable 3D printing resin composition 2-hydroxypropyl acrylate (100 g), dynamic dissociation isocyanate crosslinking agent (30 g), phenyl bis (2, 4, 6-trimethylbenzoyl) phosphine oxide (2.6 g), stirred at 70 ℃ for 20 min to obtain a clear liquid, the obtained liquid was put into 405 nm digital light processing DLP 3D printer, 3D printing forming. The printed 3D printing structure was put into the ultraviolet curing box for 5 min.

[0067] Example 5 Except for step (2), it is the same as example 1, specifically, the difference between example 1 is: the amount of dynamic dissociation isocyanate crosslinking agent and initiator in the resin composition is different.

[0068] 2) Preparation of isotropic high-strength photocurable 3D printing resin composition 2-hydroxy-3-phenoxypropyl acrylate (100 g), dynamic dissociation isocyanate crosslinking agent (30 g), 1-hydroxycyclohexyl phenyl ketone (2.6 g), stirred at 70 ℃ for 20 min to obtain a clear liquid, the obtained liquid was put into 405 nm digital light processing DLP 3D printer, 3D printing forming. The printed 3D printing structure was put into the ultraviolet curing box for 5 min.

[0069] Example 6 Except for step (2), it is the same as example 1, specifically, the difference between example 1 is: the type of initiator in the resin composition is different.

[0070] 2) Preparation of isotropic high-strength photocurable 3D printing resin composition 2-hydroxy-3-phenoxypropyl acrylate (100 g), dynamic dissociation isocyanate crosslinking agent (20 g), 2, 2-dimethoxy-1, 2-diphenyl ethanone (2.4 g), stirred at 70 ℃ for 20 min to obtain a clear liquid, the obtained liquid was put into 405 nm digital light processing DLP 3D printer, 3D printing forming. The printed 3D printing structure was put into the ultraviolet curing box for 5 min.

[0071] Example 7 Except for step (2), it is the same as example 1, specifically, the difference between example 1 is: the type and amount of dynamic dissociation isocyanate crosslinking agent and initiator in the resin composition is different.

[0072] 2) Preparation of isotropic high-strength photocurable 3D printing resin composition The 2-hydroxyethyl acrylate (100 g), dynamic dissociation isocyanate crosslinking agent (40 g), 4-p-tolyl 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone (2.8 g), were mixed homogeneously at 70 °C under stirring for 20 min to obtain a clear liquid, and the obtained liquid was put into a 405 nm digital light processing (DLP) 3D printer for 3D printing. The printed 3D structure was put into a UV curing box for curing for 5 min.

[0073] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A dynamically dissociating isocyanate crosslinking agent, characterized in that The crosslinking agent is 2-(1-(tert-butyl)-3-((5-(3-(tert-butyl)-3-(2-(methacryloyloxy)ethyl)ureido)-1,3,3-trimethylcyclohexyl)methyl)ureidoethyl methacrylate, and the structural formula is shown in Formula I: Formula I Among them, O represents oxygen, N represents nitrogen, and H represents hydrogen.

2. The method for preparing the dynamically dissociating isocyanate crosslinking agent according to claim 1, characterized in that: The following steps are involved: (1) Dissolving tert-butylaminoethyl methacrylate (TBEMA) and isophorone diisocyanate (IPDI) in an organic solvent to obtain a TBEMA solution and an IPDI solution, respectively; (2) Add IPDI solution dropwise to TBEMA solution, stir, and react; (3) After the reaction is completed, the organic solvent is removed to obtain a dynamically dissociated isocyanate crosslinker.

3. The method according to claim 2, characterized in that In step (1), the molar ratio of tert-butylaminoethyl methacrylate to isophorone diisocyanate is 2:

1.

4. The method according to claim 2, characterized in that In step (1), the organic solvent independently includes any one or more of dichloromethane, chloroform, ethyl acetate, methanol, petroleum ether, and n-butanol.

5. The method according to claim 2, characterized in that In step (2), the reaction temperature is 30-80°C; and / or In step (2), the reaction time is 1-8 h.

6. A resin composition, characterized in that Contains the dynamically dissociating isocyanate crosslinking agent as claimed in claim 1.

7. The resin composition according to claim 6, characterized in that The resin composition comprises the following components by mass: 100 parts of an acrylate monomer, 5-50 parts of a crosslinking agent, and 0.1-10 parts of a photoinitiator, wherein the crosslinking agent is the dynamically dissociated isocyanate crosslinking agent according to claim 1; Preferably, the mass ratio of the acrylate monomer, the dynamically dissociated isocyanate crosslinker and the photoinitiator is 100:(5-50):(2.1-3), and more preferably 100:(10-30):(2.2-2.6).

8. The resin composition according to claim 7, characterized in that The acrylate monomer includes at least one of 2-hydroxy-3-phenoxypropyl 2-acrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate; and / or The photoinitiator includes at least one of 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, 2,4,6-trimethylbenzoyl-ethoxy-phenyl phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenyl phosphine oxide, 2,2-dimethoxy-1,2-diphenylethanone, 2-ethyloctyl-4-dimethylaminobenzoate, and 4-toluene 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone.

9. A method for preparing a resin composition according to any one of claims 6 to 8, characterized in that: The method comprises the following steps: mixing an acrylate monomer, a dynamically dissociated isocyanate crosslinking agent, and a photoinitiator to obtain an isotropic high-intensity light-cured 3D printing resin composition.

10. Use of the resin composition according to any one of claims 6 to 8 in photocuring 3D printing.

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