A photocurable bio-based 3D printing resin and a preparation method thereof

Abstract

This invention belongs to the field of polymer materials and 3D printing technology, and particularly relates to a photocurable 3D printing bio-based resin, its preparation method, and its applications. By weight, the resin is mainly composed of 50-70 parts of a photosensitive resin prepolymer matrix, 30-50 parts of the reactive diluent hydroxyethyl methacrylate (HEMA), and 1-5 parts of a photoinitiator. The prepolymer matrix is ​​prepared by ring-opening esterification of malic acid and citric acid with glycidyl methacrylate (GMA) through a specific step-temperature controlled process, followed by the compounding of precisely synthesized photosensitive malic acid monomer (MG) and photosensitive citric acid crosslinking agent (CG). This invention utilizes HEMA to effectively break the large molecular hydrogen bond network between prepolymers, achieving an effective reduction in resin viscosity while maintaining a high bio-based content. The resin of this invention exhibits low viscosity, rapid photoresponse, high double bond conversion rate, and excellent curing heat stability, making it highly suitable for stereolithography (SLA), digital light processing (DLP), and applications in electronic packaging and electromagnetic shielding.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and 3D printing technology, specifically relating to a bio-based photocurable 3D printing resin based on malic acid and citric acid and its preparation method. Background Technology

[0002] Photopolymer 3D printing technology (including stereolithography (SLA) and digital light processing (DLP)) has shown great application potential in precision electronic packaging, integrated circuit insulation filling, and the precision manufacturing of complex electromagnetic shielding components due to its high processing precision, fast forming speed, and strong ability to manufacture complex three-dimensional structures. Especially in the field of electronic packaging, high-density chip integration requires packaging materials to possess excellent heat resistance, low shrinkage, and good mechanical isotropy. However, currently, commercially available photopolymer resins used in electronic packaging and electromagnetic shielding substrates (such as bisphenol A epoxy acrylates and polyurethane acrylates) are almost entirely dependent on non-renewable petrochemical resources and generally suffer from strong skin irritation, high biotoxicity, and difficulty in achieving harmless degradation, which is inconsistent with the industrialization trend of green, low-carbon, and sustainable development. Therefore, developing low-toxicity, renewable, and high-bio-based photocurable resins has become a research hotspot in both academia and industry. Malic acid (MA) and citric acid (CA), as naturally occurring aliphatic polycarboxylic acids, are widely available, inexpensive, non-toxic, and highly biocompatible. Their molecular structures contain multiple highly reactive carboxyl groups (-COOH) and hydroxyl groups (-OH), making them ideal platform compounds for synthesizing bio-based photosensitive prepolymers. However, developing high-performance photocurable resins for 3D printing suitable for electronic packaging or electromagnetic shielding directly from polybasic acids faces the following key technical bottlenecks in practical applications: 1. High viscosity and low processability: The backbones of malic acid and citric acid are extremely polar. After modification to introduce photosensitive unsaturated double bonds, a dense and strong hydrogen bond association network exists between the prepolymer molecules. This extremely strong intermolecular interaction results in the prepolymer exhibiting extremely high viscosity at room temperature (even in a semi-solid, non-flowing state), which greatly limits the resin leveling properties during the 3D printing process and makes it unsuitable for direct use in SLA or DLP printing. 2. Low Double Bond Conversion Rate Due to High Crosslinking: Citric acid has a triangular symmetrical multi-component network structure, which is prone to rapid premature crosslinking in the early stages of curing, leading to rapid glass transition of the system. The highly polar hydrogen bond network after glass transition greatly restricts the diffusion of residual double bonds and monomers, resulting in a generally low double bond conversion rate (DC) of the final cured product. Unreacted free low-molecular-weight monomers remain in the system, causing small molecule migration and spillage during the later heating and operation of electronic components, severely damaging the insulation performance and thermal stability of electronic packaging materials. 3. Insufficient thermal stability of cured materials: Conventional bio-based materials generally have low thermal decomposition temperatures due to the aliphatic characteristics of their molecular chain segments and uneven cross-linking density. However, in electronic packaging and high-frequency electromagnetic shielding applications, materials often need to withstand the instantaneous high temperatures generated during chip operation. If the thermal resistance of the resin matrix is ​​substandard, it can easily lead to device packaging failure or deformation of shielding components. In summary, the key challenge for the application of bio-based photocurable resins based on polybasic acids in electronic packaging and electromagnetic shielding is to significantly increase the bio-based content of the resin while effectively breaking down its stubborn strong hydrogen bond association network, reducing its rheological viscosity, and achieving ultra-high free radical double bond conversion rate and excellent curing heat resistance without premature glass transition. Summary of the Invention

[0003] This invention utilizes a temperature-step controlled process to enable efficient and side-reaction-free ring-opening esterification reactions between the epoxy groups on glycidyl methacrylate and the dicarboxyl groups of malic acid and the tricarboxyl groups of citric acid, respectively, to construct photosensitive malic acid monomers (MG) with both flexible segments and bifunctionality, and photosensitive citric acid crosslinking agents (CG) with high symmetry and high crosslinking activity. The core design of this invention lies in compounding MG and CG and introducing hydroxyethyl methacrylate (HEMA), an active diluent with a specific chemical structure. The scientific mechanism by which it synergistically regulates and overcomes the aforementioned technical bottlenecks is as follows: 1. A high-density three-dimensional network is constructed by using MG (bifunctional flexible monomer) and CG (triangular star rigid crosslinking agent) to achieve a balance between rigidity and toughness and dimensional stability. 2. The introduction of small molecule HEMA generates a "hydrogen bond breaking" effect, which breaks the strong hydrogen bond association between prepolymers, causing a sharp decrease in rheological viscosity and improving crosslinking uniformity and processability. 3. HEMA, as a solvation medium, promotes the free diffusion of double bonds, endowing the system with high conversion rate and no residue. The resulting dense ester bond network locks the carbon chain skeleton, significantly improving the heat resistance stability of the cured product and meeting the high-temperature application requirements of electronic packaging. Detailed implementation method: The technical solution adopted by this invention to solve its technical problem is as follows: This invention provides a photocurable 3D printing bio-based resin based on malic acid and citric acid derivatives, comprising the following components by weight: Photosensitive resin prepolymer matrix: 50-70 parts; Reactive diluent: 30-50 parts; Photoinitiator: 1 to 5 parts; Specifically, the photosensitive resin prepolymer matrix is ​​composed of photosensitive malic acid monomer (MG) and photosensitive citric acid crosslinking agent (CG) in a mass ratio of 1:0.05; Specifically, the active diluent is hydroxyethyl methacrylate (HEMA). Specifically, the preparation method of the photocurable bio-based resin is carried out according to the following steps: (1) Stepwise temperature-controlled synthesis of photosensitive malic acid monomer In a 250 mL three-necked round-bottom flask equipped with an all-glass reflux condenser, mechanical stirrer, and precision thermometer, 28.4 g glycidyl methacrylate (GMA, 0.20 mol), 0.04 g polymerization inhibitor p-hydroxyanisole (MEHQ, 0.10 wt% of GMA), 0.04 g antioxidant 1010 (0.10 wt% of GMA), and 1.24 g catalyst triphenylphosphine (TPP, 3.0 wt% of GMA) were added sequentially. Mechanical stirring was started, and after all components in the flask were thoroughly mixed and dissolved, the system temperature was raised to 60 °C. Then, 13.4 g of dry malic acid (MA) powder (0.10 mol) was added in a single batch. Stirring was continued until the malic acid powder was completely dissolved and the system was clear. The ring-opening esterification reaction was then carried out using a stepped temperature control program: first, the temperature was raised to 95 °C and held for 3 hours; then, the temperature was increased to 105 °C and held for 2 hours; finally, the temperature was further raised to 115 °C for 1 hour of ripening. After the reaction was complete, the system was allowed to cool naturally to room temperature, and a light brown transparent liquid was discharged, which was the target photosensitive malic acid monomer (MG). (2) Stepwise temperature-controlled synthesis of photosensitive citric acid monomer In a 250 mL three-necked round-bottom flask equipped with an all-glass reflux condenser, mechanical stirrer, and precision thermometer, 42.6 g glycidyl methacrylate (GMA, 0.30 mol), 0.06 g polymerization inhibitor p-hydroxyanisole (MEHQ, 0.10 wt% of GMA), 0.06 g antioxidant 1010 (0.10 wt% of GMA), and 1.91 g catalyst triphenylphosphine (TPP, 3.0 wt% of GMA) were added sequentially. Mechanical stirring was started, and after all components in the flask were thoroughly mixed and dissolved, the system temperature was raised to 60 °C. Then, 19.2 g of dry citric acid (CA) powder (0.10 mol) was added in a single batch. Stirring was continued until the citric acid powder was completely dissolved and the system was clear. The ring-opening esterification reaction was then carried out using a stepped temperature control program: first, the temperature was raised to 90 °C and held for 2 hours; then, the temperature was increased to 105 °C and held for 0.5 hours; finally, the temperature was further raised to 115 °C for aging for 0.5 hours. After the reaction was complete, the system was allowed to cool naturally to room temperature, and a pale yellow transparent liquid was discharged, which was the target photosensitive citric acid crosslinking agent (CG). (3) Preparation of photocurable bio-based resin The photosensitive malic acid monomer (MG) obtained in step (1) and the photosensitive citric acid crosslinking agent (CG) obtained in step (2) are mixed at a mass ratio of 1:0.05. The mixture is mechanically stirred at room temperature (300~500 rpm) for 20~30 min to ensure uniform mixing and obtain photocurable bio-based resin. Subsequently, the photosensitive resin prepolymer matrix and the reactive diluent hydroxyethyl methacrylate (HEMA) are mixed at a preset mass ratio (e.g., 1:1, 3:2, or 7:3), and a photoinitiator of 1wt% to 5wt% of the total mass of the system is added. Under completely dark conditions, the mixture is stirred at 500 to 1000 rpm for 15 to 30 minutes. After the components are completely miscible and clear, the mixture is placed in a vacuum drying oven or ultrasonic cleaner for degassing for 5 to 10 minutes to remove internal micro-bubbles, thus obtaining a photocurable bio-based resin (ink) suitable for 3D printing. (4) Photocurable 3D printing of photocurable bio-based resin Pour any of the resin inks obtained in step (3) into the SLA printer slot and allow it to stand to level and remove bubbles. Import a CAD model of the electromagnetic shielding component with dimensions of 25*15*2 mm into the control terminal, and set the slice layer thickness to 0.05 mm. Set the printing parameters for a 405 nm (or 365 nm) light source according to the ink specifications: Sample A (1:1): Printed at room temperature, bottom exposure for 30 s, normal layer exposure for 10 s; Sample B (3:2): Printed at room temperature, bottom exposure for 30 s, normal layer exposure for 10 s; Sample C (7:3): Printed at room temperature, bottom exposure for 30 s, normal layer exposure for 10 s; The printer prints layer by layer. After completion, the component is removed, cleaned in anhydrous ethanol for 2-3 minutes, and then dried. Finally, it is placed in a 100-200 W UV oven for 2-5 minutes to eliminate internal stress, resulting in a high-precision, high-density electromagnetically shielded bio-based three-dimensional solid component. Attached image description: Figure 1 For the preparation route of MG; Figure 2 For CG preparation route; Figure 3 Infrared spectra of MG and CG; Figure 4 The 1H NMR spectra of MG and CG are shown. Figure 5 Image of a photocurable bio-based resin; Figure 6 A graph showing the conversion rate of photocured double bonds in photocurable bio-based resins; Figure 7 Thermogravimetric analysis (TGA) results for photocurable bio-based resin printed parts; Example: Example 1: Preparation of photocurable bio-based resin (CM / HEMA 1:1 by mass ratio) (1) Matrix compounding: Weigh 47.62 g of MG obtained in step (1) and 2.38 g of CG obtained in step (2) (i.e., the mass ratio of MG to CG is 1:0.05), mix and stir evenly to obtain 50.0 g of photosensitive resin prepolymer matrix; (2) Ink compounding: Add 50.0 g of reactive diluent HEMA to the above matrix (so that the mass ratio of prepolymer matrix to reactive diluent is 1:1). Then add 2.0 g of photoinitiator TPO (accounting for 2.0 wt% of the total mass of the system); (3) Mixing and degassing: Under light-protected conditions, the mixture was stirred at 1000 rpm for 15 min using a high-speed mechanical stirrer until the system was completely clear and miscible. Then, it was ultrasonically degassed for 5 min to obtain a photocurable bio-based resin ink sample (CM / HEMA 1:1). Example 2: Preparation of photocurable bio-based resin (CM / HEMA 3:2) at a mass ratio of 3:2 (1) Matrix compounding: Weigh 57.14 g of MG obtained in step (1) and 2.86 g of CG obtained in step (2) (MG:CG = 1:0.05), mix and stir evenly to obtain 60.0 g of photosensitive resin prepolymer matrix; (2) Ink compounding: Add 40.0 g of reactive diluent HEMA to the above matrix (so that the mass ratio of prepolymer matrix to reactive diluent is 3:2). Then add 2.0 g of photoinitiator TPO (accounting for 2.0 wt% of the total mass of the system); (3) Mixing and degassing: The process is the same as in Example 1. Stirring at high speed in the dark for 15 min and ultrasonic degassing are performed to obtain a photocurable bio-based resin ink sample (CM / HEMA 3:2). Example 3: Preparation of photocurable bio-based resin (CM / HEMA 7:3 by mass ratio) (1) Matrix compounding: Weigh 66.67 g of MG obtained in step (1) and 3.33 g of CG obtained in step (2) (MG:CG = 1:0.05), mix and stir evenly to obtain 70.0 g of photosensitive resin prepolymer matrix; (2) Ink compounding: Add 30.0 g of reactive diluent HEMA to the above matrix (so that the mass ratio of prepolymer matrix to reactive diluent is 7:3). Then add 2.0 g of photoinitiator TPO (accounting for 2.0 wt% of the total mass of the system); (3) Mixing and degassing: The process is the same as in Example 1. Stirring at high speed in the dark for 15 min and ultrasonic degassing are performed to obtain a photocurable bio-based resin ink sample (CM / HEMA 7:3). Performance testing (1) Take the samples from embodiments (1) and (2) and perform infrared spectroscopy tests; (2) Dissolve the samples from embodiments (1) and (2) in deuterated chloroform for 1H NMR spectroscopy. (3) Take samples from Examples (1), (2), and (3) and perform real-time infrared testing; (4) Take the printed parts of Examples (1), (2) and (3) for thermogravimetric testing. The heating rate is 20℃ / min and the temperature range is 40-600 degrees.

Claims

1. A photocurable 3D printing bio-based resin based on malic acid and citric acid derivatives, characterized in that, Based on parts by weight, it is mainly prepared from the following raw material components: Photosensitive resin prepolymer matrix: 50-70 parts; Reactive diluent: 30-50 parts; Photoinitiator: 1 to 5 parts; The photosensitive resin prepolymer matrix is ​​composed of photosensitive malic acid monomer (MG) and photosensitive citric acid crosslinking agent (CG) in a mass ratio of 1:0.05; the reactive diluent is hydroxyethyl methacrylate (HEMA).

2. The photopolymerizable 3D printing bio-based resin according to claim 1, characterized in that, The mass ratio of the photosensitive resin prepolymer matrix to the reactive diluent (HEMA) is 1:1, 3:2, or 7:

3.

3. The photopolymerizable 3D printing bio-based resin according to claim 1, characterized in that, The photosensitive malic acid monomer (MG) is prepared by ring-opening esterification reaction of malic acid (MA) and glycidyl methacrylate (GMA) in the presence of triphenylphosphine (TPP) catalyst, p-hydroxyanisole (MEHQ) polymerization inhibitor and antioxidant 1010; wherein the molar ratio of malic acid (MA) to glycidyl methacrylate (GMA) is 1:

2.

4. The photopolymerizable 3D printing bio-based resin according to claim 1, characterized in that, The photosensitive citric acid crosslinking agent (CG) is prepared by citric acid (CA) and glycidyl methacrylate (GMA) through a ring-opening esterification reaction in the presence of the catalyst triphenylphosphine (TPP), the polymerization inhibitor p-hydroxyanisole (MEHQ), and the antioxidant 1010; wherein the molar ratio of citric acid (CA) to glycidyl methacrylate (GMA) is 1:

3.

5. The photopolymerizable 3D printing bio-based resin according to claim 1, characterized in that, The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO).

6. A method for preparing the photocurable 3D printing bio-based resin according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Stepwise temperature-controlled synthesis of photosensitive malic acid monomer (MG): Malic acid (MA) and glycidyl methacrylate (GMA) were mixed in a molar ratio of 1:2, and 0.10 wt% of p-hydroxyanisole (MEHQ), 0.10 wt% of antioxidant 1010, and 3.0 wt% of triphenylphosphine (TPP) were added. The mixture was first stirred at 60°C until the malic acid was completely dissolved, and then a stepwise temperature-controlled process was adopted: the reaction was carried out at 95°C for 3 h, then at 105°C for 2 h, and finally at 115°C for 1 h. After the reaction was completed, the mixture was cooled to room temperature to obtain a light brown transparent liquid MG. S2. Stepwise temperature-controlled synthesis of photosensitive citric acid crosslinking agent (CG): Citric acid (CA) and glycidyl methacrylate (GMA) were mixed in a molar ratio of 1:3, and 0.10 wt% of p-hydroxyanisole (MEHQ), 0.10 wt% of antioxidant 1010, and 3.0 wt% of triphenylphosphine (TPP) were added. The mixture was first stirred at 60°C until the citric acid was completely dissolved, and then a stepwise temperature-increasing process was adopted: the reaction was carried out at 90°C for 2 h, then at 105°C for 0.5 h, and finally at 115°C for 0.5 h. After the reaction was completed, the mixture was cooled to room temperature to obtain a pale yellow transparent liquid CG. S3. Blending of photocurable bio-based resin: The MG obtained in step S1 and the CG obtained in step S2 are blended at a mass ratio of 1:0.05 and stirred at room temperature for 20-30 min to obtain a photosensitive resin prepolymer matrix; then the photosensitive resin prepolymer matrix is ​​blended with the reactive diluent hydroxyethyl methacrylate (HEMA) and the photoinitiator is added. The mixture is stirred under light-protected conditions for 15-30 min. After complete miscibility, degassing is performed to obtain the photocurable 3D printing bio-based resin.

7. The method for preparing photocurable 3D printing bio-based resin according to claim 6, characterized in that: In step S3, the mass ratio of the photosensitive resin prepolymer matrix to the reactive diluent (HEMA) is 1:1, 3:2, or 7:3; the stirring speed is 500-1000 rpm; and the degassing treatment is to place the sample in a vacuum drying oven or ultrasonic cleaner for 5-10 minutes.

8. The application of the photopolymerizable 3D printing bio-based resin according to any one of claims 1-5 in stereolithography (SLA) 3D printing technology.

9. The application according to claim 8, characterized in that, The application is specifically used for the precision molding of electromagnetic shielding components or electronic packaging connectors.

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