A method for preparing 3D printed photosensitive foam elastomers using a dynamic bond synergistic emulsion template method

Abstract

This invention discloses a method for preparing 3D-printed photosensitive foam elastomers using a dynamic bond synergistic emulsion template method. The resin uses a polyurethane acrylate oligomer containing dynamically hindered urea bonds as the continuous phase and deionized water as the dispersed phase. A stable water-in-oil high-internal-phase emulsion is formed through high-speed emulsification, which is then compounded with a thermally latent curing agent, an active diluent, and a photoinitiator. During printing, UV light cures the acrylate groups to form a temporary cross-linked network, fixing the aqueous droplets as a "pore template." During post-processing heating, the dynamically hindered urea bonds reversibly dissociate, reducing the cross-linking density. Simultaneously, the thermally latent curing agent activates and initiates cross-linking of epoxy groups, forming a permanent network. After the aqueous phase evaporates, a uniform closed-cell foam material is obtained. This invention requires no additional foaming agent, has a controllable foaming ratio, uniform cell size, low product density, and high compression resilience, combining high-precision printing with lightweight performance. It is suitable for applications such as footwear materials, cushioning packaging, and biological scaffolds.

Description

Technical Field

[0001] This invention relates to the field of photopolymer 3D printing materials technology, and in particular to a method for preparing 3D printed photosensitive foam elastomers using a dynamic bond synergistic emulsion template method. Background Technology

[0002] Photopolymer 3D printing technology boasts significant advantages in personalized customization and complex structure manufacturing due to its fast forming speed, high precision, and adjustable material properties. However, currently commercially available photosensitive resins are mostly dense, highly cross-linked materials with low elongation and high brittleness, making it difficult to meet the specific requirements of lightweight and high elasticity in applications such as shoe midsoles, cushioning packaging, and flexible sensors. Existing photopolymer 3D printing foam material technologies mostly employ post-processing foaming strategies. For example, the supercritical fluid foaming method uses high-pressure equipment to dissolve inert gas in the printed preform, and then induces nucleation and foaming through heating or depressurization. This method involves large equipment investment, long process cycles, and difficulty in precisely controlling the macroscopic dimensional changes caused by foaming. Another example is the thermal expansion microsphere foaming method, which pre-disperses microspheres in resin. During post-heating, the outer shell of the microspheres softens, and the internal low-boiling-point hydrocarbons vaporize and expand, achieving foaming. However, due to the constraint of the rigid photocrosslinking network, the free expansion space of the microspheres is limited, resulting in insufficient foaming ratio and poor cell uniformity.

[0003] High internal phase emulsion template method is a material preparation technique that uses aqueous droplets as in-situ pore templates, with an internal phase volume fraction exceeding approximately 75%. However, during photocuring, the rapid polymerization of acrylates in resins containing high internal phase emulsions causes significant tensile stress on the pore walls due to the intense volume shrinkage, leading to pore wall cracking. This structural defect severely degrades the mechanical integrity of the material, and this problem is a key bottleneck in the preparation of 3D printed foam materials using the emulsion template method. Dynamically hindered urea bonds are a type of dynamic covalent bond formed by the reaction of bulky amines (such as tert-butylamino) with isocyanates. These bonds can undergo reversible dissociation in the moderate temperature range of 60-100℃, temporarily severing the crosslinking network and reducing the crosslinking density, and then rebonding after cooling. Existing research has introduced dynamically hindered urea bonds into photocurable material systems, achieving recyclability, self-healing, or stress relaxation functions through post-heating dissociation. However, such research focuses more on the adaptive properties imparted to the bulk material by dynamic bonds, and has not yet been shown to be used in conjunction with the high internal phase emulsion template method to solve the pore wall cracking problem. Summary of the Invention

[0004] The purpose of this invention is to disclose a new technical approach, providing a method for preparing 3D printed photosensitive foam elastomers using a dynamic bond synergistic emulsion template method. This method organically combines the temperature responsiveness of dynamically hindered urea bonds, the in-situ pore-forming characteristics of the high internal phase emulsion template method, and the network building ability of photothermal two-stage curing, fundamentally solving the contradiction between printing accuracy and cell integrity, and preparing foam elastomers with both high resilience and lightweight.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing 3D-printed photosensitive foam elastomers using a dynamic bond-synergistic emulsion template method includes the following steps:

[0007] (1) Using polyether polyol, diisocyanate and acrylate end-capping agent containing tert-butylamino as raw materials, a polyurethane acrylate oligomer containing dynamic hindered urea bonds is synthesized by step-by-step polymerization reaction. This step introduces dynamic hindered urea bonds and photosensitive acrylate double bonds into the polymer backbone at the same time.

[0008] (2) The oligomer obtained in step (1) is mixed with epoxy resin, latent amine curing agent, reactive diluent, dehydrating agent, photoinitiator, emulsifier, and hydrophobic light absorber as the oil phase; deionized water is mixed with hydrophilic light absorber as the aqueous phase; the aqueous phase is added dropwise to the oil phase under high-speed stirring and ultrasonic action to prepare a stable water-in-oil emulsion with a high internal phase volume fraction of about 75%;

[0009] (3) Place the emulsion obtained in step (2) into a DLP or LCD type 3D printer for photopolymerization and print layer by layer to obtain a water-containing green body;

[0010] (4) The green part obtained in step (3) is first kept at 80-100℃ to dissociate the dynamically hindered urea bonds and release stress, while activating the latent amine curing agent to carry out chain extension reaction; then the temperature is raised to 100-130℃ to complete the crosslinking of epoxy groups, and the moisture is removed by drying to obtain photosensitive foam elastomer.

[0011] As a further embodiment of the present invention, the polyether polyol in step (1) is one or more of polytetramethylene ether glycol, polypropylene glycol, and polyethylene glycol, with a molecular weight of 1000-3000; the diisocyanate is one or more of isophorone diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, and dicyclohexylmethane diisocyanate; and the acrylate end-capping agent containing tert-butylamino is one or more of 2-(tert-butylamino)ethyl methacrylate and 2-(tert-butylamino)ethyl acrylate.

[0012] As a further embodiment of the present invention, in step (1), the mass molar ratio of polyether polyol, diisocyanate and acrylate end-capping agent containing tert-butylamino is 1:1.8-2.2:1.6-2.4, the reaction temperature is 60-85℃, organotin catalyst is used as catalyst, phenolic compound is used as polymerization inhibitor, and the reaction endpoint is determined by the disappearance of the isocyanate group characteristic peak at 2260-2280 cm-1 by infrared spectroscopy monitoring or by the method specified in national standard GB 12009.4-89.

[0013] As a further embodiment of the present invention, the latent amine curing agent in step (2) is one or more of the ketimine and aldehyde imine thermal latent curing agents, and its dosage is 2-10 wt% of the total mass of the oil phase.

[0014] As a further embodiment of the present invention, the epoxy resin in step (2) is one or more of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenolic type epoxy resin, and aliphatic epoxy resin, with an epoxy equivalent of 160-250 g / eq and an amount of 5-30 wt% of the total mass of the oil phase.

[0015] As a further embodiment of the present invention, the active diluent in step (2) is one or more of the following: isobornyl acrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, and 4-acryloylmorpholine, and its amount is 15-40 wt% of the total mass of the oil phase.

[0016] As a further embodiment of the present invention, the photoinitiator in step (2) is one or more of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl 2,4,6-trimethylbenzoylphosphonate, and 2-hydroxy-2-methyl-1-phenyl-1-propanone; the emulsifier is a high molecular weight nonionic polymeric surfactant; the hydrophobic light absorber is one or more of β-carotene and oil-soluble yellow; and the hydrophilic light absorber is one or more of tartrazine and tartrazine.

[0017] As a further embodiment of the present invention, the dehydrating agent in step (2) is one or more of type 3A, type 4A, and type 5A molecular sieves, and the amount used is 0.5-5 wt% of the total mass of the oil phase.

[0018] As a further embodiment of the present invention, in step (3), the printing layer thickness is 0.02-0.2 mm, the ultraviolet light wavelength is 385-405 nm, and the single-layer exposure time is 2-10 s.

[0019] As a further embodiment of the present invention, the two-stage gradient thermosetting process in step (4) involves heating to 80-100℃ at a rate of 1-10℃ / min and holding for 10-60 minutes, and heating to 100-130℃ at a rate of 1-10℃ / min and holding for 0.5-3 hours. The resulting photosensitive foam elastomer has a density of 0.2-0.8 g / cm3, a cell size of 30-300 μm, and a compression resilience of ≥70%.

[0020] Compared with existing technologies, this invention has the following advantages: it synergistically integrates dynamic hindered urea bonds with a high internal phase emulsion template method. The reversible dissociation of dynamic bonds at 80-100℃ effectively releases photopolymerization shrinkage stress, eliminating pore wall cracking at its source and producing a closed-cell foam elastomer with crack-free and high resilience. The product has a compression resilience of ≥75% and a density as low as 0.3 g / cm3, combining lightweight and excellent mechanical properties.

[0021] By introducing latent amine curing agents, the active amines generated by the decongestion of latent amines bridge the polyurethane acrylate network and the epoxy network, fundamentally solving the interface separation problem of physically blended interpenetrating networks and further improving the modulus and toughness of the material.

[0022] The entire process requires no external foaming agent or high-pressure equipment. The pore structure is fixed during the printing stage, resulting in high printing accuracy and a simple process. The foam density and pore structure can be flexibly customized by adjusting the internal phase volume fraction. Attached Figure Description

[0023] Figure 1 A schematic diagram of the synthetic route for polyurethane acrylate oligomers containing dynamically hindered urea bonds according to the present invention.

[0024] Figure 2 The images show the physical images of the high internal phase emulsion, the SEM images of the photocurable polyurethane acrylate oligomer mixed high internal phase emulsion, and the SEM images of the foam elastomer obtained after curing. Among them, (a) is the physical image of the high internal phase emulsion, (b) is the SEM image of the high internal phase emulsion, (c) is the SEM image of the photocurable polyurethane acrylate oligomer mixed high internal phase emulsion, (d) is the SEM image of the foam obtained in Case 1, (e) is the SEM image of the foam material obtained in Comparative Example 1, and (f) is the SEM image of the foam material obtained in Comparative Example 2.

[0025] Figure 3 The cyclic compression stress-strain curve of the foam elastomer prepared for the example is shown.

[0026] Figure 4 Infrared peak diagram of dynamic bond dissociation when heated to 90℃. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] (1) Synthesis of polyurethane acrylate oligomers containing dynamically hindered urea bonds:

[0030] 400.0 g of polypropylene glycol (PPG2000) was added to a reaction flask and dehydrated under vacuum at 110 °C and -0.095 MPa for 2 hours. After cooling to 50 °C, 89 g of isophorone diisocyanate (IPDI) and 0.16 g of dibutyltin dilaurate were added. Under nitrogen protection, the mixture was reacted at 50 °C for 30 minutes with mechanical stirring, followed by a reaction at 80 °C for 2 hours. The NCO content was measured, and after decreasing to the theoretical value, the temperature was lowered to 60-65 °C. 77.2 g of 2-(tert-butylamino)ethyl methacrylate (TBEMA) (with 0.26 g of p-hydroxyanisole pre-dissolved in the capping agent) was slowly added dropwise, maintaining a temperature not exceeding 70 °C, and the reaction continued for 1-2 hours. Infrared spectroscopy was monitored until the NCO characteristic peak at 2270 cm⁻¹ completely disappeared, yielding a polyurethane acrylate oligomer containing dynamically hindered urea bonds.

[0031] (2) Preparation of high internal phase emulsion resin:

[0032] First, prepare the oil phase: Take 180 g of oligomer from step (1), 45 g of bisphenol A type epoxy resin E51, 12 g of ketimine latent curing agent, 60 g of reactive diluent (IBOA and PEG600DA mixed at a mass ratio of 2:1), 6 g of TPO photoinitiator, 15 g of Hypermer B246 emulsifier, 0.3 g of β-carotene, and 6 g of 4A type molecular sieve powder, and stir evenly.

[0033] Aqueous phase: Add an appropriate amount of deionized water and dissolve 0.2 wt% lemon yellow.

[0034] The emulsification process begins with adding the aqueous phase dropwise to the oil phase using a high-speed mixer at 1000 rpm for 5 minutes to form a crude emulsion. The crude emulsion is then ultrasonically treated in an ultrasonic homogenizer for 10 minutes, with the total aqueous phase volume fraction being 70%. After emulsification, the emulsion is degassed under vacuum for 10 minutes at room temperature using a vacuum pump.

[0035] (3) 3D printing molding;

[0036] Using Creality's HALOT-MAGE S LCD 3D printer, with a wavelength of 405 nm, a light intensity of 6 mW / cm2, a layer thickness of 20 μm, and a bottom layer exposure of 10 s, a water-containing green part was printed.

[0037] (4) Gradient thermosetting;

[0038] The green part is placed in an oven and heated to 90°C for 30 minutes; then heated to 120°C for 1.5 hours; then cooled and dried to remove moisture, resulting in a photosensitive foam elastomer.

[0039] Example 2

[0040] Referring to Example 1, the difference is that in step (2), the amount of water added makes the volume fraction of the internal phase reach 80%, and the rest are the same.

[0041] Example 3

[0042] Referring to Example 1, the difference is that in step (2), the amount of latent amine curing agent is adjusted to 18 g and the amount of epoxy resin E51 is adjusted to 60 g, while the rest are the same.

[0043] Comparative Example 1

[0044] Referring to Example 1, the difference is that TBEMA is not used in step (1), but instead an equimolar amount of hydroxyethyl methacrylate (HEMA) is used for end capping. The resulting oligomer molecular chain does not contain dynamically hindered urea bonds, and the other steps are the same.

[0045] Comparative Example 2

[0046] Referring to Example 1, the difference is that in step (2), no latent amine curing agent and epoxy resin are added, and only an emulsion containing a dynamic bond oligomer is used as a single resin component to prepare the emulsion and print and cure it.

[0047] Results and Data Analysis:

[0048] Figure 1 Example 1: Synthesis route diagram of photocurable polyurethane acrylate prepolymer;

[0049] Figure 2 The high internal phase emulsion and foam sponge structure synthesized in Example 1 are shown in the SEM images, characterized using a classic Hitachi S-4800 instrument. The results show that the foam obtained in Example 1 has a uniform pore structure and no obvious cracks. Figure 2 (d) In Comparative Example 1, which does not contain dynamic bonds, cracks appear in the pore structure due to stress concentration. Figure 2 (e) In Comparative Example 2, which does not contain latent amine curing agents or epoxy resin, the pore structure collapsed during the post-heat treatment stage. Figure 2 (f).

[0050] Table 1 shows the foam density and porosity data of Examples 1 and 2 under different internal phase volume fractions. The data were tested using a fully automated true density analyzer 3H-2000 from Best Instruments Technology (Beijing) Co., Ltd. The results also demonstrate that foam density and porosity can be controlled by adjusting the high internal phase emulsion.

[0051]

[0052] Table 1

[0053] Figure 3 The figures show the cyclic stress-strain curves of the foam elastomers prepared in Examples 1 and 3. It can be seen from the figures that under 60% compressive strain, Example 3 has higher compressive strength due to the addition of more epoxy crosslinking. The maximum stress retention rates of Example 1 and Comparative Example 3 after 50 cycles of compression are approximately 85% and 87%, respectively. This confirms the significant contribution of chemically bonded interpenetrating networks and dehydrating agents to mechanical properties.

[0054] Figure 4 Infrared images at different heating temperatures show no infrared peak at 2270 cm⁻¹ in the initial stage, but an infrared peak of NCO appears after heating to 90°C. This result confirms the dissociation of the dynamically hindered urea bonds in Example 1 during the 90°C heat preservation stage. Combined with SEM and mechanical property data, this effectively demonstrates that the solution of the present invention is the key mechanism for maintaining the shrinkage stress of the foam elastomer and eliminating pore wall cracking.

[0055] The above description represents a preferred embodiment of the present invention. For those skilled in the art, any changes, modifications, substitutions, and variations made to the implementation methods without departing from the principles and spirit of the present invention, based on the teachings of the present invention, still fall within the protection scope of the present invention.

Claims

1. A method for preparing 3D-printed photosensitive foam elastomers using a dynamic bond synergistic emulsion template method, characterized in that, Includes the following steps: (1) Using polyether polyol, diisocyanate and acrylate end-capping agent containing tert-butylamino as raw materials, polyurethane acrylate oligomers containing dynamic hindered urea bonds are synthesized by stepwise polymerization reaction. (2) The polyurethane acrylate oligomer obtained in step (1) is mixed with epoxy resin, latent amine curing agent, reactive diluent, dehydrating agent, photoinitiator, emulsifier, and hydrophobic light absorber as the oil phase; deionized water is mixed with hydrophilic light absorber as the aqueous phase; the aqueous phase is added dropwise to the oil phase under high-speed stirring and ultrasonic action to prepare a stable water-in-oil emulsion with a high internal phase volume fraction of 75%. (3) Place the emulsion obtained in step (2) into a DLP or LCD type 3D printer for photopolymerization and print layer by layer to obtain a water-containing green body; (4) The green part obtained in step (3) is first kept at 80-100℃ to dissociate the dynamically hindered urea bonds and release stress, while activating the latent amine curing agent to carry out chain extension reaction; then the temperature is raised to 100-130℃ to complete the crosslinking of epoxy groups, and the moisture is removed by drying to obtain photosensitive foam elastomer.

2. The method according to claim 1, characterized in that, The polyether polyol mentioned in step (1) is one or more of the following: polytetramethylene ether glycol, polypropylene glycol, and polyethylene glycol, with a molecular weight of 1000-3000; the diisocyanate is one or more of the following: isophorone diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, and dicyclohexylmethane diisocyanate; and the tert-butylamino acrylate end-capping agent is one or more of the following: 2-(tert-butylamino)ethyl methacrylate and 2-(tert-butylamino)ethyl acrylate.

3. The method according to claim 1, characterized in that, In step (1), the mass molar ratio of polyether polyol, diisocyanate and acrylate end-capping agent containing tert-butylamino is 1:1.8-2.2:1.6-2.4, the reaction temperature is 60-85℃, organotin catalyst is used as catalyst, phenolic compound is used as polymerization inhibitor, and the reaction endpoint is determined by the disappearance of the characteristic peak of isocyanate group at 2260-2280cm-1 by infrared spectroscopy or by the method specified in national standard GB 12009.4-89.

4. The method according to claim 1, characterized in that, The latent amine curing agent mentioned in step (2) is one or more of the ketimine and aldehyde imine thermal latent curing agents, and its dosage is 2-10 wt% of the total mass of the oil phase.

5. The method according to claim 1, characterized in that, The epoxy resin mentioned in step (2) is one or more of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenolic type epoxy resin, and aliphatic epoxy resin. The epoxy equivalent is 160-250 g / eq, and its dosage is 5-30 wt% of the total mass of the oil phase.

6. The method according to claim 1, characterized in that, The active diluent mentioned in step (2) is one or more of the following: isobornyl acrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, and 4-acryloylmorpholine, and its amount is 15-40 wt% of the total mass of the oil phase.

7. The method according to claim 1, characterized in that, The photoinitiator in step (2) is one or more of the following: phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl 2,4,6-trimethylbenzoylphosphonate, and 2-hydroxy-2-methyl-1-phenyl-1-propanone; the emulsifier is a high molecular weight nonionic polymeric surfactant; the hydrophobic light absorber is one or more of β-carotene and oil-soluble yellow; and the hydrophilic light absorber is one or more of tartrazine and tartrazine.

8. The method according to claim 1, characterized in that, The dehydrating agent mentioned in step (2) is one or more of the molecular sieves of type 3A, type 4A, and type 5A, and the amount used is 0.5-5 wt% of the total mass of the oil phase.

9. The method according to claim 1, characterized in that, In step (3), the printing layer thickness is 0.02-0.2 mm, the ultraviolet light wavelength is 385-405 nm, and the single-layer exposure time is 2-10 s.

10. The method according to claim 1, characterized in that, In step (4), a two-stage gradient thermosetting process is used. The first stage involves heating to 80-100℃ at a rate of 1-10℃ / min and holding for 10-60 minutes. The second stage involves heating to 100-130℃ at a rate of 1-10℃ / min and holding for 0.5-3 hours. The resulting photosensitive foam elastomer has a density of 0.2-0.8 g / cm³. 3 The cell size is 30-300 μm, and the compression resilience is ≥70%.

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