An in-situ foaming material for 3D printing and its preparation method

Abstract

This invention belongs to the field of 3D printing technology and relates to an in-situ foaming material for 3D printing and its preparation method. The raw materials for preparing the in-situ foaming material include acrylate oligomers, acrylate monomers, and a photoinitiator. The acrylate oligomers are monofunctional polyurethane acrylates, and the acrylate monomers are monofunctional acrylate monomers without active hydrogen. The monofunctional polyurethane acrylate has an acrylate group at one end and an isocyanate group at the other end, and the isocyanate group is foamed in situ under hydrothermal conditions. The in-situ foaming material provided by this invention significantly reduces material density while maintaining good mechanical properties and functionality, and also meets the requirements of green and environmentally friendly production.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing technology, and relates to a foaming material, particularly to an in-situ foaming material for 3D printing and its preparation method. Background Technology

[0002] 3D printing foam material is a novel material that combines additive manufacturing (3D printing) technology with foaming technology, featuring lightweight, porous, high strength, and high elasticity. This material significantly reduces density while maintaining good mechanical properties and functionality by introducing gas during or after printing to form a complex internal foam structure.

[0003] Due to their lightweight and high strength, 3D-printed foam materials have shown broad application potential in multiple fields. For example, in the aerospace industry, these materials can be used to manufacture lightweight structural components; in the automotive industry, they can be used to produce shock-absorbing parts; and in the field of sports equipment, such as footwear manufacturing, they can achieve lighter weight and better cushioning and shock absorption. Furthermore, foam materials are also used in building insulation, medical stents, and biomedical engineering.

[0004] Currently, the foaming methods for 3D printed foam materials mainly include physical foaming and chemical foaming. Physical foaming typically uses supercritical CO2 as a foaming agent, encapsulating the gas within the material under high pressure and then releasing it at lower pressure, causing the material to expand and form a foam structure. However, commonly used foaming agents have low solubility in certain situations, which can easily have adverse environmental impacts. Chemical foaming relies on the decomposition products of the foaming agent to generate gas, but this method usually involves the use of toxic substances and does not meet the requirements of green and environmentally friendly production.

[0005] In addition, although foamed materials have a lower density, their mechanical strength and durability after foaming are usually lower than those of solid materials, especially under high temperature or high load conditions, in which case the materials are prone to deformation or failure.

[0006] Therefore, it is evident that how to provide a 3D printing foam material that can significantly reduce material density while maintaining good mechanical properties and functionality, and also meet the requirements of green and environmentally friendly production, has become an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an in-situ foaming material for 3D printing and its preparation method. The in-situ foaming material significantly reduces material density while maintaining good mechanical properties and functionality, and also meets the requirements of green and environmentally friendly production.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides an in-situ foaming material for 3D printing, wherein the raw materials for preparing the in-situ foaming material include acrylate oligomers, acrylate monomers and photoinitiators, wherein the acrylate oligomers are monofunctional polyurethane acrylates and the acrylate monomers are monofunctional acrylate monomers that do not contain active hydrogen.

[0010] The monofunctional polyurethane acrylate has an acrylate group at one end and an isocyanate group at the other end, and the isocyanate group is foamed in situ under hydrothermal conditions.

[0011] The in-situ foaming material provided by this invention uses monofunctional polyurethane acrylate and monofunctional acrylate monomers without active hydrogen as raw materials. After photocuring, this monofunctional material forms a chain structure, which is beneficial for foaming expansion. This avoids the three-dimensional network structure formed by multifunctional materials after photocuring, which hinders the full expansion of bubbles and effectively improves the foaming performance of the material.

[0012] Furthermore, the monofunctional polyurethane acrylate used in this invention has an acrylate group at one end, which is responsible for photocuring, and an isocyanate group at the other end, which is responsible for in-situ foaming under hydrothermal conditions, thereby further crosslinking and curing, significantly enhancing the mechanical strength and durability of the foamed material. This in-situ foaming characteristic avoids the use of foaming agents and meets the requirements of green and environmentally friendly production.

[0013] Preferably, the structural formula of the monofunctional polyurethane acrylate is:

[0014] Structural Formula A:

[0015] and / or;

[0016] Structural formula B:

[0017] Wherein, R1 refers to H and / or CH3, R2 refers to the remaining structure of isocyanate after removing the -NCO group, and R3 refers to the remaining structure of polyol after removing the terminal H atom.

[0018] Preferably, the isocyanate includes isophorone diisocyanate and / or toluene diisocyanate.

[0019] Preferably, the monofunctional acrylate monomer that does not contain active hydrogen includes any one or a combination of at least two of the following: cyclotrimethylolpropane methyl acetal acrylate, acrylmorpholine, tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, laurate acrylate, laurate methacrylate, 3,3,5-trimethylcyclohexyl acrylate, tert-butylcyclohexyl acrylate, ethoxyethoxyethyl acrylate, isobornyl acrylate, or isobornyl methacrylate.

[0020] Preferably, the photoinitiator comprises any one or a combination of at least two of α-dialkoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, or diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide, and more preferably diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide.

[0021] Preferably, the raw materials for preparing the in-situ foaming material, by weight, include: 30-80 parts of monofunctional polyurethane acrylate; 20-65 parts of monofunctional acrylate monomer without active hydrogen; and 0.5-8 parts of photoinitiator.

[0022] Preferably, the source of water in the hydrothermal conditions includes water vapor and / or water of crystallization.

[0023] The water of crystallization is derived from adding a compound containing water of crystallization to the raw materials.

[0024] In a second aspect, the present invention provides a method for preparing an in-situ foamed material for 3D printing as described in the first aspect, the method comprising the following steps:

[0025] (1) Preparation of monofunctional polyurethane acrylate by addition reaction;

[0026] (2) Mix monofunctional polyurethane acrylate, monofunctional acrylate monomers without active hydrogen and photoinitiator for 3D printing, and obtain solid material after photocuring.

[0027] (3) The solid material is foamed in situ under hydrothermal conditions to obtain in situ foamed material.

[0028] Preferably, when the monofunctional polyurethane acrylate has structural formula A, the addition reaction method in step (1) is as follows:

[0029] Hydroxyethyl acrylate and difunctional isocyanate were mixed in a molar ratio of 1:(1-1.05) and reacted at 40-60℃ for 4-6 hours to obtain monofunctional polyurethane acrylate.

[0030] Alternatively, hydroxyethyl methacrylate and difunctional isocyanate are mixed in a molar ratio of 1:(1-1.05) and reacted at 40-60℃ for 4-6 hours to obtain monofunctional polyurethane acrylate.

[0031] Preferably, when the monofunctional polyurethane acrylate has structural formula B, the addition reaction method in step (1) is as follows:

[0032] A difunctional polyol and a difunctional isocyanate are mixed at a molar ratio of 1:(2-2.05) and reacted at 50-70℃ for 2-4 hours. The temperature is then lowered to 40-60℃, and hydroxyethyl acrylate or hydroxyethyl methacrylate is added. The reaction is continued at 40-60℃ for 4-6 hours to obtain a monofunctional polyurethane acrylate.

[0033] The amount of hydroxyethyl acrylate or hydroxyethyl methacrylate added is 0.95-1 times the molar amount of the bifunctional polyol.

[0034] Preferably, the photocuring in step (2) uses ultraviolet light, and the energy density of the ultraviolet light is 10-200 mW / cm². 2 .

[0035] Preferably, the photocuring time in step (2) is 5-60 min.

[0036] Preferably, the temperature of the hydrothermal conditions in step (3) is 100-180℃.

[0037] Preferably, the in-situ foaming time in step (3) is 30-60 minutes.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The in-situ foaming material provided by the present invention uses monofunctional polyurethane acrylate and monofunctional acrylate monomers without active hydrogen as raw materials. After photocuring, this monofunctional material forms a chain structure, which is conducive to foaming expansion. This avoids the three-dimensional network structure formed by multifunctional materials after photocuring from hindering the full expansion of bubbles, and effectively improves the foaming performance of the material.

[0040] (2) The monofunctional polyurethane acrylate used in this invention has an acrylate group at one end, which is responsible for photocuring and molding, and an isocyanate group at the other end, which is responsible for in-situ foaming under hydrothermal conditions, thereby further crosslinking and curing, which significantly enhances the mechanical strength and durability of the foamed material. This in-situ foaming characteristic avoids the use of foaming agents and meets the requirements of green and environmentally friendly production. Attached Figure Description

[0041] Figure 1The image shows the HNMR spectrum of the monofunctional polyurethane acrylate (structural formula A) provided in Example 1.

[0042] Figure 2 These are photographs of the physical materials provided in Example 1;

[0043] Figure 3 This is a photograph of the in-situ foaming material provided in Example 1. Detailed Implementation

[0044] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0045] One embodiment of the present invention provides an in-situ foaming material for 3D printing. The raw materials for preparing the in-situ foaming material include acrylate oligomers, acrylate monomers and photoinitiators. The acrylate oligomers are monofunctional polyurethane acrylates, and the acrylate monomers are monofunctional acrylate monomers that do not contain active hydrogen.

[0046] The monofunctional polyurethane acrylate has an acrylate group at one end and an isocyanate group at the other end, and the isocyanate group is foamed in situ under hydrothermal conditions.

[0047] The in-situ foaming material provided by this invention uses monofunctional polyurethane acrylate and monofunctional acrylate monomers without active hydrogen as raw materials. After photocuring, this monofunctional material forms a chain structure, which is beneficial for foaming expansion. This avoids the three-dimensional network structure formed by multifunctional materials after photocuring, which hinders the full expansion of bubbles and effectively improves the foaming performance of the material.

[0048] Furthermore, the monofunctional polyurethane acrylate used in this invention has an acrylate group at one end, which is responsible for photocuring, and an isocyanate group at the other end, which is responsible for in-situ foaming under hydrothermal conditions, thereby further crosslinking and curing, significantly enhancing the mechanical strength and durability of the foamed material. This in-situ foaming characteristic avoids the use of foaming agents and meets the requirements of green and environmentally friendly production.

[0049] In some embodiments, the structural formula of the monofunctional polyurethane acrylate is:

[0050] Structural Formula A:

[0051] and / or;

[0052] Structural formula B:

[0053] Wherein, R1 refers to H and / or CH3, R2 refers to the remaining structure of isocyanate after removing the -NCO group, and R3 refers to the remaining structure of polyol after removing the terminal H atom.

[0054] Specifically, R2 refers to the remaining structure of the isocyanate after removing the -NCO group, such as isophorone, hexamethylene, dicyclohexylmethane, toluene, or diphenylmethane, etc., and the isocyanate is more preferably isophorone diisocyanate and / or toluene diisocyanate; R3 refers to the remaining structure of the polyol after removing the terminal H atom, and the polyol can be polypropylene glycol, polytetrahydrofuran ether glycol, poly1,3-propylene glycol, polycaprolactone polyol, polycarbonate polyol, polyethylene adipate polyol, or polybutylene adipate polyol, etc.

[0055] As can be seen from the above structural formulas, structural formula A is relatively simple, while structural formula B contains polyols, making its molecular structure more complex, resulting in longer polymer chains and more branched structures. On the one hand, structural formula A, due to its simple structure, is easier to control during synthesis, and its high isocyanate content leads to higher foaming ratio and mechanical strength. On the other hand, structural formula B, due to its complex structure, has longer molecular chains and more branches, which helps to improve the toughness and durability of the material, and the complex structure also brings better chemical and thermal stability.

[0056] It is evident that the present invention, through the synergistic combination of structural formula A and structural formula B, effectively balances the comprehensive performance and cost control of the resulting foamed material.

[0057] In some embodiments, the monofunctional acrylate monomer that does not contain active hydrogen includes any one or a combination of at least two of the following: cyclotrimethylolpropane methyl acetal acrylate, acrylmorpholine, tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, laurate acrylate, laurate methacrylate, 3,3,5-trimethylcyclohexyl acrylate, tert-butylcyclohexyl acrylate, ethoxyethoxyethyl acrylate, isobornyl acrylate, or isobornyl methacrylate.

[0058] This invention strictly limits the specific types of monofunctional acrylate monomers. Because each monomer molecule contains only one reactive group during the photocuring process, the conversion rate is high. This means that during the 3D printing process, more monomer molecules can participate in the photocuring reaction, thereby forming a stable polymer network and ultimately improving the curing efficiency of the material and the performance of the resulting product.

[0059] In addition, since monofunctional acrylate monomers form a lower crosslinking density during photocuring, their volume shrinkage rate is also relatively low, which helps to reduce the stress and deformation caused by volume changes during photocuring, ensuring the dimensional accuracy and structural stability of 3D printed parts.

[0060] Furthermore, monofunctional acrylate monomers typically have lower viscosity, which helps improve the flowability and coatability of materials during 3D printing, making the printing process smoother, fully filling the gaps between printed layers, and improving the surface quality and uniformity of the internal structure of the printed parts.

[0061] In some embodiments, the photoinitiator comprises any one or a combination of at least two of α-dialkoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, or diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide. Typical but non-limiting combinations include combinations of α-dialkoxyacetophenone and 2-hydroxy-2-methyl-1-phenylpropanone, combinations of 2-hydroxy-2-methyl-1-phenylpropanone and 1-hydroxycyclohexylphenyl ketone, or combinations of 1-hydroxycyclohexylphenyl ketone and diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide, more preferably diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide.

[0062] In some embodiments, the raw materials for preparing the in-situ foaming material, by weight, include: 30-80 parts of monofunctional polyurethane acrylate, for example, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80 parts; 20-65 parts of monofunctional acrylate monomers without active hydrogen, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, or 65 parts; and 0.5-8 parts of photoinitiator, for example, 0.5, 1, 2, 3, 4, 5, 6, 7, or 8 parts, but not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0063] In some embodiments, the source of water in the hydrothermal conditions includes water vapor and / or water of crystallization.

[0064] The water of crystallization is obtained by adding a compound containing water of crystallization to the raw materials, such as calcium sulfate dihydrate, potassium aluminum sulfate dodecahydrate (commonly known as alum), or zinc sulfate heptahydrate.

[0065] In this invention, the compound containing water of crystallization is dehydrated in a high-temperature environment, and the resulting water is then foamed in situ with isocyanate groups.

[0066] One embodiment of the present invention provides a method for preparing an in-situ foamed material for 3D printing as described in any of the above embodiments, the preparation method comprising the following steps:

[0067] (1) Preparation of monofunctional polyurethane acrylate by addition reaction;

[0068] (2) Mix monofunctional polyurethane acrylate, monofunctional acrylate monomers without active hydrogen and photoinitiator for 3D printing, and obtain solid material after photocuring.

[0069] (3) The solid material is foamed in situ under hydrothermal conditions to obtain in situ foamed material.

[0070] In some embodiments, the raw materials for the addition reaction in step (1) are hydroxyethyl acrylate and isocyanate, or hydroxyethyl acrylate, isocyanate and polyol.

[0071] As previously mentioned, the monofunctional polyurethane acrylate has two structural formulas. When it is structural formula A, hydroxyethyl acrylate and isocyanate are used as raw materials for the addition reaction. The specific reaction formula is as follows:

[0072]

[0073] In the above situation, the method for the addition reaction in step (1) is as follows:

[0074] Hydroxyethyl acrylate and difunctional isocyanate were mixed in a molar ratio of 1:(1-1.05) and reacted at 40-60℃ for 4-6 hours to obtain monofunctional polyurethane acrylate.

[0075] Alternatively, hydroxyethyl methacrylate and difunctional isocyanate are mixed in a molar ratio of 1:(1-1.05) and reacted at 40-60℃ for 4-6 hours to obtain monofunctional polyurethane acrylate.

[0076] In some embodiments, the molar ratio described above may be 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04 or 1:1.05, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0077] When it has structural formula B, hydroxyethyl acrylate, isocyanate, and polyol are used as raw materials for the addition reaction. The specific reaction formula is as follows:

[0078]

[0079] In the above situation, the method for the addition reaction in step (1) is as follows:

[0080] A difunctional polyol and a difunctional isocyanate are mixed at a molar ratio of 1:(2-2.05) and reacted at 50-70℃ for 2-4 hours. The temperature is then lowered to 40-60℃, and hydroxyethyl acrylate or hydroxyethyl methacrylate is added. The reaction is continued at 40-60℃ for 4-6 hours to obtain a monofunctional polyurethane acrylate.

[0081] In some embodiments, the molar ratio described above may be 1:2, 1:2.01, 1:2.02, 1:2.03, 1:2.04 or 1:2.05, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0082] In some embodiments, the amount of hydroxyethyl acrylate or hydroxyethyl methacrylate added is 0.95-1 times the molar amount of the bifunctional polyol, for example, it can be 0.95 times, 0.96 times, 0.97 times, 0.98 times, 0.99 times or 1 times, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0083] In some embodiments, the photocuring in step (2) uses ultraviolet light, and the energy density of the ultraviolet light is 10-200 mW / cm². 2 For example, it could be 10mW / cm 2 20mW / cm 2 40mW / cm 2 60mW / cm 2 80mW / cm 2 100mW / cm 2 120mW / cm 2 140mW / cm 2 160mW / cm 2 180mW / cm 2 Or 200mW / cm 2 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0084] In some embodiments, the photocuring time in step (2) is 5-60 min, for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0085] Specifically, during the photocuring process, the reaction formulas between the various materials are as follows:

[0086]

[0087] or;

[0088]

[0089] or;

[0090]

[0091] In some embodiments, the temperature of the hydrothermal conditions in step (3) is 100-180°C, for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C or 180°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0092] In some embodiments, the in-situ foaming time in step (3) is 30-60 min, for example, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0093] Specifically, the reaction that occurs in the solid material during in-situ foaming is as follows:

[0094]

[0095] or;

[0096]

[0097] or;

[0098]

[0099] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0100] Example 1

[0101] This embodiment provides an in-situ foaming material for 3D printing and its preparation method, the preparation method including the following steps:

[0102] (1) Preparation of monofunctional polyurethane acrylates by addition reaction, specifically:

[0103] (1.1) Add 1.02 mol of isophorone diisocyanate to a three-necked flask, heat to 40°C, then slowly add 1 mol of hydroxyethyl acrylate dropwise, controlling the reaction temperature not to exceed 50°C; after the hydroxyethyl acrylate is completely added, continue the reaction at 50°C for 5 hours to obtain a monofunctional polyurethane acrylate with structural formula A and a content of more than 95 wt% (H NMR spectrum shown in [reference needed]). Figure 1 The relevant chemical formulas are as follows:

[0104]

[0105] (1.2) Add 1 mol of polycaprolactone (molecular weight 1000) and 2.02 mol of isophorone diisocyanate to a three-necked flask, and continue the reaction at 60°C for 3 h. Then, cool down to 50°C and slowly add 0.98 mol of hydroxyethyl acrylate, controlling the reaction temperature to not exceed 50°C. After the hydroxyethyl acrylate has been added, continue the reaction at 50°C for 5 h to obtain a monofunctional polyurethane acrylate with structural formula B and a content of more than 95 wt%. The relevant chemical formula is as follows:

[0106]

[0107]

[0108] In the above formula, R1 specifically refers to H, R2 specifically refers to isophorone, and R3 specifically refers to polycaprolactone.

[0109] (2) The monofunctional polyurethane acrylate (30 parts of structure A and 30 parts of structure B) obtained in step (1), the monofunctional acrylate monomer without active hydrogen (36 parts of isobornyl acrylate), and the photoinitiator (4 parts of diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide) were mixed and 3D printed (printer model TAPS200). After removing the model, it was cleaned and subjected to an energy density of 100mW / cm². 2 The material was cured under ultraviolet light for 30 minutes to obtain a solid material (see...). Figure 2 ).

[0110] The reaction equations between the materials during the photocuring process are as follows:

[0111]

[0112] (3) The solid material obtained in step (2) is subjected to in-situ foaming under hydrothermal conditions of 150℃ water vapor for 45 minutes, and after cooling, the in-situ foamed material is obtained (see Figure 3 ).

[0113] The reaction that occurs in the solid material during in-situ foaming is as follows:

[0114]

[0115] Example 2

[0116] This embodiment provides an in-situ foaming material for 3D printing and its preparation method, the preparation method including the following steps:

[0117] (1) Preparation of monofunctional polyurethane acrylates by addition reaction, specifically:

[0118] 1.02 mol of toluene diisocyanate was added to a three-necked flask and heated to 40°C. Then, 1 mol of hydroxyethyl acrylate was slowly added dropwise, controlling the reaction temperature to not exceed 50°C. After the hydroxyethyl acrylate was completely added, the reaction was continued at 50°C for 5 hours to obtain a monofunctional polyurethane acrylate with structural formula A and a content of more than 95 wt%. The relevant chemical formula is as follows:

[0119]

[0120] In the above formula, R1 specifically refers to H, and R2 specifically refers to toluene.

[0121] (2) The monofunctional polyurethane acrylate (60 parts, structural formula A) obtained in step (1), the monofunctional acrylate monomer without active hydrogen (36 parts, cyclotrimethylolpropane methyl acetal acrylate), and the photoinitiator (4 parts, diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide) were mixed and 3D printed (printer model TAPS200). After removing the model, it was cleaned and subjected to an energy density of 100mW / cm². 2 The material is cured under ultraviolet light for 45 minutes to obtain a solid material.

[0122] The reaction equations between the materials during the photocuring process are as follows:

[0123]

[0124] (3) The solid material obtained in step (2) is foamed in situ for 60 minutes under the hydrothermal condition of 150℃ water vapor, and then cooled to obtain the in situ foamed material.

[0125] The reaction that occurs in the solid material during in-situ foaming is as follows:

[0126]

[0127] The morphology of the solid material and the in-situ foamed material obtained in this embodiment is similar to that in Embodiment 1, so it will not be described again here.

[0128] Example 3

[0129] This embodiment provides an in-situ foaming material for 3D printing and its preparation method, the preparation method including the following steps:

[0130] (1) Preparation of monofunctional polyurethane acrylates by addition reaction, specifically:

[0131] 1 mol of polypropylene glycol (molecular weight 2000) and 2.02 mol of isophorone diisocyanate were added to a three-necked flask, and the reaction was continued at 60°C for 3 hours. The temperature was then lowered to 50°C, and 0.98 mol of hydroxyethyl acrylate was slowly added dropwise, controlling the reaction temperature to not exceed 50°C. After the hydroxyethyl acrylate was completely added, the reaction was continued at 50°C for 5 hours to obtain a monofunctional polyurethane acrylate with structural formula B and a content of more than 95 wt%. The relevant chemical formula is as follows:

[0132]

[0133] In the above formula, R1 specifically refers to H, R2 specifically refers to isophorone, and R3 specifically refers to the remaining structure of polypropylene glycol after removing the terminal H atoms.

[0134] (2) The monofunctional polyurethane acrylate (60 parts, structural formula B) obtained in step (1), the monofunctional acrylate monomer without active hydrogen (36 parts, isobornyl acrylate), and the photoinitiator (4 parts, diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide) were mixed and 3D printed (printer model TAPS200). After removing the model, it was cleaned and subjected to an energy density of 100mW / cm². 2 The material is cured under ultraviolet light for 30 minutes to obtain a solid material.

[0135] The reaction equations between the materials during the photocuring process are as follows:

[0136]

[0137] (3) The solid material obtained in step (2) is foamed in situ for 30 minutes under the hydrothermal condition of 100°C water vapor, and then cooled to obtain the in situ foamed material.

[0138] The reaction that occurs in the solid material during in-situ foaming is as follows:

[0139]

[0140] The morphology of the solid material and the in-situ foamed material obtained in this embodiment is similar to that in Embodiment 1, so it will not be described again here.

[0141] Example 4

[0142] This embodiment provides an in-situ foaming material for 3D printing and its preparation method. Except that the hydrothermal conditions described in step (3) are changed to: 20 parts of calcium sulfate dihydrate are mixed in step (2), and water vapor is not introduced in step (3), but the in-situ foaming is carried out by direct heating. The other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0143] Example 5

[0144] This embodiment provides an in-situ foaming material for 3D printing and its preparation method. Except for replacing the monofunctional acrylate monomer without active hydrogen in step (2) with an equal weight of tert-butylcyclohexyl acrylate, the other steps and conditions are the same as in Example 1, so they will not be repeated here.

[0145] Example 6

[0146] This embodiment provides an in-situ foaming material for 3D printing and its preparation method. Except for replacing the photoinitiator in step (2) with an equal weight of 1-hydroxycyclohexylphenyl ketone, the other steps and conditions are the same as in Example 1, so they will not be described in detail here.

[0147] Comparative Example 1

[0148] This comparative example provides a foaming material for 3D printing and its preparation method, the preparation method comprising the following steps:

[0149] (1) A mixture of 60 parts polyurethane acrylate oligomer (brand name CN996), 36 parts acrylonitrile isobornyl ester, 4 parts diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide, and 8 parts azodicarbonamide was used for 3D printing (printer model TAPS200). After removing the model, it was cleaned and subjected to an energy density of 100 mW / cm². 2 The material is cured under ultraviolet light for 30 minutes to obtain a solid material.

[0150] (2) The solid material obtained in step (1) is foamed at 180°C for 45 minutes and then cooled to obtain foamed material.

[0151] Comparative Example 2

[0152] This comparative example provides a foaming material for 3D printing and its preparation method. Except for replacing the monofunctional acrylate monomer without active hydrogen in step (2) with an equal weight of difunctional acrylate monomer (bisphenol A dimethacrylate), the other steps and conditions are the same as in Example 1, so they will not be repeated here.

[0153] Comparative Example 3

[0154] This comparative example provides a foaming material for 3D printing and its preparation method. Except for replacing the monofunctional acrylate monomer without active hydrogen described in step (2) with an equal weight of trifunctional acrylate monomer (ethoxytrimethylolpropane triacrylate), the other steps and conditions are the same as in Example 1, so they will not be repeated here.

[0155] Performance testing

[0156] (1) Apparent density: Refer to the test method provided in GB / T 6343-2009;

[0157] (2) Tensile strength: Refer to the test method provided in GB / T 6344-2008;

[0158] (3) Rebound performance: Refer to the test method provided in GB / T 6670-2008.

[0159] The solid materials and foamed materials obtained in Examples 1-6 and Comparative Examples 1-3 were tested according to the above test methods, and the relevant test results are shown in Table 1 below.

[0160] Table 1

[0161]

[0162] Therefore, the in-situ foaming material provided by the present invention uses monofunctional polyurethane acrylate and monofunctional acrylate monomers without active hydrogen as raw materials. After photocuring, this monofunctional material forms a chain structure, which is conducive to foaming expansion. This avoids the three-dimensional network structure formed by multifunctional materials after photocuring, which hinders the full expansion of bubbles and effectively improves the foaming performance of the material.

[0163] Furthermore, the monofunctional polyurethane acrylate used in this invention has an acrylate group at one end, which is responsible for photocuring, and an isocyanate group at the other end, which is responsible for in-situ foaming under hydrothermal conditions, thereby further crosslinking and curing, significantly enhancing the mechanical strength and durability of the foamed material. This in-situ foaming characteristic avoids the use of foaming agents and meets the requirements of green and environmentally friendly production.

[0164] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An in-situ foaming material for 3D printing, the raw materials for preparing the in-situ foaming material comprising an acrylate oligomer, an acrylate monomer and a photoinitiator, characterized in that, The acrylate oligomer is a monofunctional polyurethane acrylate, and the acrylate monomer is a monofunctional acrylate monomer without active hydrogen; The monofunctional polyurethane acrylate has an acrylate group at one end and an isocyanate group at the other end, and the isocyanate group is in-situ foamed under hydrothermal conditions; The monofunctional polyurethane acrylate has the following structural formula: Structure formula A: ; and / or Structure formula B: ; wherein R1 represents H, R2 represents the remaining structure after removal of the -NCO group from the isocyanate, and R3 represents the remaining structure after removal of the terminal H atom from the polyol; The isocyanate includes isophorone diisocyanate and / or toluene diisocyanate, and the polyol includes polypropylene glycol or polycaprolactone polyol; The monofunctional acrylate monomer without active hydrogen includes any one or a combination of at least two of cyclo-trimethylolpropane formal acrylate, t-butylcyclohexyl acrylate, or isobornyl acrylate; The preparation raw materials of the in-situ foaming material include, in terms of weight parts, 30-80 parts of monofunctional polyurethane acrylate, 20-65 parts of monofunctional acrylate monomer without active hydrogen, and 0.5-8 parts of photoinitiator. The photoinitiator includes any one or a combination of at least two of α-dialkoxy-acetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, or diphenyl-(2,4,6-trimethylbenzoyl) phosphine oxide.

2. The in-situ foaming material for 3D printing according to claim 1, wherein, The source of water in the hydrothermal conditions includes water vapor and / or crystal water; 3. The in-situ foaming material for 3D printing of claim 1, wherein, The crystal water is derived from adding a crystal water-containing compound to the preparation raw materials. The preparation method includes the following steps:

4. A method for the preparation of in-situ foaming materials for 3D printing according to any one of claims 1-3, characterized in that, (1) preparing a monofunctional polyurethane acrylate by addition reaction; (2) mixing the monofunctional polyurethane acrylate, the monofunctional acrylate monomer without active hydrogen, and the photoinitiator for 3D printing, and obtaining a solid material after photocuring; (3) in-situ foaming the solid material under hydrothermal conditions to obtain an in-situ foaming material. When the monofunctional polyurethane acrylate is of structural formula A, the method of the addition reaction in step (1) is as follows:

5. The method for the preparation of in-situ foaming materials for 3D printing according to claim 4, characterized in that, Mixing hydroxyethyl acrylate and difunctional isocyanate at a molar ratio of 1:(1-1.05) and reacting at 40-60°C for 4-6h to obtain the monofunctional polyurethane acrylate; Alternatively, mixing hydroxyethyl methacrylate and difunctional isocyanate at a molar ratio of 1:(1-1.05) and reacting at 40-60°C for 4-6h to obtain the monofunctional polyurethane acrylate.

6. The preparation method of the in-situ foaming material for 3D printing according to claim 4, when the monofunctional polyurethane acrylate is of structural formula B, the method of the addition reaction in step (1) is as follows: Mixing difunctional polyol and difunctional isocyanate at a molar ratio of 1:(2-2.05) and reacting at 50-70°C for 2-4h, then cooling to 40-60°C, adding hydroxyethyl acrylate or hydroxyethyl methacrylate, and continuing to react at 40-60°C for 4-6h to obtain the monofunctional polyurethane acrylate; ​ wherein, The amount of the hydroxyethyl acrylate or hydroxyethyl methacrylate added is 0.95-1 times the molar amount of the difunctional polyol.

7. The method of claim 4, wherein the in-situ foaming material for 3D printing is prepared by the steps of: The photo-curing in step (2) uses ultraviolet light, and the energy density of the ultraviolet light is 10-200 mW / cm 2 ; And / or, the light curing time in step (2) is 5-60 min; And / or, the temperature of the hydrothermal condition in step (3) is 100-180℃; And / or, the time of the in-situ foaming in step (3) is 30-60 min.

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