A DLP-printable ion-conductive polyurethane acrylate resin composition, its preparation method and application

Abstract

This invention discloses a DLP-printable ion-conductive polyurethane acrylate resin composition, its preparation method, and its applications. The resin composition comprises polyurethane acrylate, polyethylene glycol diacrylate, acrylic acid, lithium bis(trifluoromethanesulfonyl)imide, and a photoinitiator. The preparation method includes basic resin mixing, lithium salt dispersion, photoinitiator addition, vacuum degassing, and DLP photocuring printing steps. This resin composition exhibits good flowability, photocurability, flexibility, and ion conductivity, enabling DLP printing of microstructure arrays such as inverted pyramids, cylinders, and hemisphericals. Furthermore, the geometric parameters of different microstructures have a modulating effect on sensing performance, with small hemisphericals showing the best performance in low-pressure sensitivity and pressure resolution. Compared with existing technologies, the resin system preparation method of this invention is simple, has good printing adaptability, and is suitable for the construction of ion-conductive elastomer structures, flexible functional materials, and microstructure arrays.

Description

Technical Field

[0001] This invention relates to the field of photocurable resin materials technology, specifically to a DLP-printable ion-conductive polyurethane acrylate resin composition, its preparation method, and its application. Background Technology

[0002] Digital Light Processing (DLP) photopolymerization printing technology boasts advantages such as high forming accuracy, fast forming speed, and high degree of freedom in structural design, showing promising application prospects in fields such as flexible functional structures, microstructure arrays, and photopolymerization additive manufacturing. Compared with traditional molding and casting methods, DLP printing is more suitable for constructing complex geometric structures and high-resolution microstructure arrays, but it also places higher demands on the viscosity, light transmittance, photopolymerization response, and post-curing mechanical properties of the resin system.

[0003] Polyurethane acrylate resins combine the flexibility of polyurethane segments with the photocurability of acrylate groups, making them an important class of photocurable resin materials. However, existing polyurethane acrylate resins used in DLP printing typically suffer from the following problems: First, it is difficult to simultaneously achieve good printability and maintain post-curing flexibility and mechanical properties; second, while introducing ionicly conductive components can improve the material's conductivity, it often results in decreased system flowability, structural instability, or reduced flexibility; third, there are relatively few ionicly conductive polyurethane acrylate resin compositions suitable for DLP printing, especially resin systems that combine ionic conductivity, flexibility, and printability.

[0004] Therefore, developing a polyurethane acrylate resin composition that is suitable for DLP printing and has good ionic conductivity and flexibility, as well as its preparation method, is of practical significance. Summary of the Invention

[0005] The purpose of this invention is to provide a DLP-printable ion-conductive polyurethane acrylate resin composition and its preparation method, so as to solve the problems of insufficient printing adaptability and difficulty in balancing flexibility and conductivity of ion-conductive resins in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a DLP-printable ion-conductive polyurethane acrylate resin composition comprising the following components:

[0008] The base resin system includes: polyurethane acrylate (PUA), polyethylene glycol diacrylate (PEGDA), and acrylic acid (AA).

[0009] Lithium salt, added in an amount of 30 wt% to 40 wt% of the total mass of the base resin system;

[0010] The photoinitiator is added at a rate of 0.5 to 2 wt% of the total mass of the base resin system.

[0011] Wherein, the polyethylene glycol diacrylate is polyethylene glycol diacrylate 1000, the mass ratio of the polyurethane acrylate to the polyethylene glycol diacrylate 1000 is 6:4 to 5:3; and the acrylic acid accounts for 10 wt% to 20 wt% of the total mass of the base resin system.

[0012] Preferably, the amount of acrylic acid added is 20 wt%.

[0013] Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, and the amount added is 30 wt%.

[0014] Preferably, the photoinitiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0015] Preferably, the amount of photoinitiator added is 1 wt%.

[0016] In a second aspect, the present invention provides a method for preparing the above-mentioned resin composition, comprising the following steps:

[0017] Step (1) Mix polyurethane acrylate, polyethylene glycol diacrylate 1000 and acrylic acid to obtain a base resin mixture;

[0018] Step (2) Add lithium bis(trifluoromethanesulfonyl)imide to the base resin mixture and stir until homogeneous;

[0019] Step (3) Add a photoinitiator and continue mixing to obtain an ion-conducting resin;

[0020] Step (4) The obtained ion-conducting resin is degassed under vacuum to obtain the resin composition.

[0021] Preferably, the mixing temperature in step (1) is 70°C to 90°C, more preferably 80°C.

[0022] Preferably, the vacuum degassing time in step (4) is 5 h to 7 h.

[0023] Thirdly, the present invention provides the application of the above-described resin composition in DLP photopolymerization printing.

[0024] Preferably, the resin composition is used to print inverted pyramid arrays, cylindrical arrays, large hemispherical arrays, or small hemispherical array structures.

[0025] All four arrays can achieve good printability and produce stable electrical responses to external pressure stimuli. Different structures exhibit significant differences in sensitivity, dynamic response, and multi-level pressure resolution. The sensitivity in the low-pressure region follows the order: small hemispherical array > large hemispherical array > inverted pyramid array > cylindrical array. The inverted pyramid array has relatively fast response / recovery characteristics, the cylindrical array provides more stable output, while the hemispherical array, especially the proportionally scaled-down small hemispherical array, performs best in low-pressure sensitivity and pressure resolution.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] (1) The present invention combines polyurethane acrylate, polyethylene glycol diacrylate, acrylic acid and lithium bis(trifluoromethanesulfonyl)imide to make the resin system have good flowability, photocurability and ionic conductivity.

[0028] (2) The resin described in this invention has a certain ionic conductivity while maintaining good flexibility, and can be used to construct ionic conductive elastomer structures.

[0029] (3) The resin composition of the present invention is suitable for DLP photopolymerization 3D printing to construct four array structures: inverted pyramid, cylinder, large hemisphere and small hemisphere. The system reveals the regulation of sensing performance by microstructure geometric parameters. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the preparation and DLP printing process of the ion-conductive polyurethane acrylate resin composition described in this invention.

[0031] Figure 2 The X-ray photoelectron spectroscopy (XPS) results of the resin composition described in this invention are shown below, where (a) is the C 1s spectrum, (b) is the O 1s spectrum, (c) is the N 1s spectrum, (d) is the Li 1s spectrum, and (e) is the full spectrum.

[0032] Figure 3 The conductivity results are shown in the graph for cured samples of resin compositions with different contents of lithium bis(trifluoromethanesulfonyl)imide.

[0033] Figure 4 Stress-strain curves of cured samples of resin compositions with different contents of lithium bis(trifluoromethanesulfonyl)imide.

[0034] Figure 5 The present invention provides the storage modulus G′ and loss modulus G″ of the 30 wt% lithium bis(trifluoromethanesulfonyl)imide resin composition under 405 nm illumination as a function of time.

[0035] Figure 6The diagram shows a comparison of the conductivity of the example sample and the comparative sample after curing. The comparative sample is a resin system without polyurethane acrylate and polyethylene glycol diacrylate 1000 in a mass ratio of 5:3.

[0036] Figure 7 The diagram shows a microstructure array formed by printing with the resin composition described in this invention, and a representative microstructure array sample obtained by printing with the resin composition described in this invention.

[0037] Figure 8 The figures show the pressure-electric response test results of different microstructure array samples printed with the resin composition of the present invention, where (a) is a cylindrical array sample, (b) is a pyramid array sample, (c) is a large hemispherical array sample, and (d) is a small hemispherical array sample. Detailed Implementation

[0038] The present invention will be further described below through specific embodiments, but the present invention is not limited to the following embodiments.

[0039] Example 1 Preparation of Resin Composition

[0040] like Figure 1 As shown, the ion-conductive polyurethane acrylate resin composition is prepared according to the following procedure:

[0041] Weigh 5.00 g of polyurethane acrylate and 3.00 g of polyethylene glycol diacrylate 1000, making the mass ratio of polyurethane acrylate to polyethylene glycol diacrylate 1000 5:3, and the total mass of the two components accounting for 80 wt% of the base resin system. Then add 2.00 g of acrylic acid, making the acrylic acid account for 20 wt% of the base resin system, to obtain the base resin system. Place the above components in a brown reagent bottle and stir and mix at 80 °C for 30 min to obtain the base resin mixture.

[0042] 4.29 g of lithium bis(trifluoromethanesulfonyl)imide was added to the obtained base resin mixture, making the mass ratio of the base resin system to lithium bis(trifluoromethanesulfonyl)imide 7:3, i.e., lithium bis(trifluoromethanesulfonyl)imide accounted for 30 wt% of the total mass of the base resin system and lithium bis(trifluoromethanesulfonyl)imide. The mixture was stirred for 2 h to ensure uniform dispersion of the lithium salt in the system. After the system cooled to room temperature, 0.1 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide was added, and stirring was continued for 1 h. Subsequently, the obtained resin system was subjected to vacuum degassing under the following conditions: temperature 25 ℃, vacuum gauge pressure -0.1 MPa, and degassing time 6 h. After degassing, an ion-conductive polyurethane acrylate resin composition suitable for DLP printing was obtained.

[0043] XPS of the obtained resin composition as follows Figure 2As shown, elemental signals such as C, O, N, and Li were detected in the XPS spectrum of the sample, indicating that LiTFSI has been successfully introduced into the polymer system. Figure 2 As shown, in the C 1s high-resolution spectrum, the main peak can be attributed to the C–C / C–H bonds in the polymer backbone, while the peaks at higher binding energies mainly correspond to oxygen-containing functional groups such as C–O and C=O / O–C=O, which is consistent with the ether, ester, and carbonyl structures in the PEGDA, PUA, and AA systems. The O 1s spectrum further indicates the simultaneous presence of carbonyl oxygen and ether oxygen environments in the sample, suggesting that the crosslinked network retains abundant polar oxygen-containing sites. The N 1s characteristic peak can be attributed to the nitrogen-containing chemical environment in the anionic structure of LiTFSI, which is one of the important pieces of evidence for the successful incorporation of lithium salt into the system; at the same time, the appearance of the Li 1s signal further proves that Li + Presence in the cured sample.

[0044] Example 2 Preparation of resin compositions with different lithium salt contents

[0045] The basic resin system was prepared according to the method in Example 1. Specifically, 5.00 g of polyurethane acrylate, 3.00 g of polyethylene glycol diacrylate 1000, and 2.00 g of acrylic acid were weighed, wherein the mass ratio of polyurethane acrylate to polyethylene glycol diacrylate 1000 was 5:3, and the two together accounted for 80 wt% of the mass of the basic resin system, and the acrylic acid accounted for 20 wt% of the mass of the basic resin system. The above components were placed in a brown reagent bottle and stirred and mixed at 80 °C for 30 min to obtain the basic resin mixture.

[0046] Subsequently, 4.29 g, 6.67 g, 10.00 g, and 15.00 g of lithium bis(trifluoromethanesulfonyl)imide were added to the obtained base resin mixture, respectively, so that the mass ratio of the base resin system to lithium bis(trifluoromethanesulfonyl)imide was 7:3, 6:4, 5:5, and 4:6, respectively, corresponding to lithium bis(trifluoromethanesulfonyl)imide accounting for 30 wt%, 40 wt%, 50 wt%, and 60 wt% of the total mass of the base resin system and the total mass of lithium bis(trifluoromethanesulfonyl)imide. After the system cooled to room temperature, 0.10 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide was added, and stirring was continued for 1 h. The remaining stirring, vacuum degassing, and photocuring conditions were kept consistent, resulting in ion-conducting resin compositions with different lithium salt contents.

[0047] like Figure 3 As shown, the results indicate that as the lithium bis(trifluoromethanesulfonyl)imide content increases from 30 wt% to 60 wt%, the conductivity of the resulting material increases from 2.80 × 10⁻⁶. -8 S·cm -1 Increased to 2.93×10 -5 S·cm -1While higher lithium salt content is beneficial for improving ionic conductivity, excessive lithium salt content may affect the flexibility, molding stability, and adaptability of the resin system for DLP printing.

[0048] Example 3 Tensile Test

[0049] To further investigate the effect of lithium bis(trifluoromethanesulfonyl)imide content on the mechanical properties of cured samples, resin compositions with different lithium salt contents were prepared according to the method in Example 1, based on the aforementioned conductivity test. Specifically, 5.00 g of polyurethane acrylate, 3.00 g of polyethylene glycol diacrylate 1000, and 2.00 g of acrylic acid were weighed to obtain the basic resin system. The mass ratio of polyurethane acrylate to polyethylene glycol diacrylate 1000 was 5:3, with the two accounting for 80 wt% of the total mass of the basic resin system, and acrylic acid accounting for 20 wt% of the total mass of the basic resin system.

[0050] Subsequently, 1.11 g, 2.50 g, 4.29 g, 6.67 g, and 10.00 g of lithium bis(trifluoromethanesulfonyl)imide were added to the aforementioned base resin system, respectively, to achieve mass ratios of 9:1, 8:2, 7:3, 6:4, and 5:5, corresponding to lithium bis(trifluoromethanesulfonyl)imide comprising 10 wt%, 20 wt%, 30 wt%, 40 wt%, and 50 wt% of the total mass of the base resin system and lithium bis(trifluoromethanesulfonyl)imide. The addition method of acrylic acid and photoinitiator, stirring conditions, vacuum degassing conditions, and photocuring conditions remained consistent with those in Example 1. After photocuring and molding the obtained resin composition, tensile tests were performed to obtain stress-strain curves.

[0051] like Figure 4 As shown, with the increase of lithium bis(trifluoromethanesulfonyl)imide content, the fracture strain and tensile strength of the cured sample generally showed a decreasing trend, indicating that the increase of lithium salt content weakens the mechanical load-bearing capacity and ductility of the cured resin network to a certain extent. Combined with... Figure 3 The conductivity results show that a higher lithium salt content is beneficial for improving the ionic conductivity of the material, but it has an adverse effect on the material's flexibility and mechanical strength. Compared with the 40 wt% and 50 wt% lithium salt samples, the 30 wt% lithium bis(trifluoromethanesulfonyl)imide sample maintains measurable ionic conductivity while still exhibiting good fracture strain, tensile strength, and structural integrity, and can meet the molding requirements of DLP-printed microstructure arrays. Therefore, 30 wt% lithium bis(trifluoromethanesulfonyl)imide is the optimal addition ratio in the system of this invention that balances conductivity, flexibility, and printability.

[0052] Example 4: Photocurable dynamic rheological test

[0053] To further evaluate the photocurability and DLP printing adaptability of the resin composition of the present invention, a photocurable dynamic rheological test was conducted using the resin composition obtained in Example 1. The amount of lithium bis(trifluoromethanesulfonyl)imide added to the resin composition was 30 wt% of the total mass of the final resin composition.

[0054] Before testing, the resin composition was thoroughly stirred and degassed under vacuum. An appropriate amount was placed on the rheometer testing platform, ensuring the sample was evenly spread within the testing area. The testing temperature was room temperature (25 °C). During the test, the initial storage modulus of the resin composition was first recorded under non-illuminated conditions. Subsequently, an in-situ photocuring test was performed using a 405 nm light source, and the change in storage modulus G′ with illumination time was recorded. Throughout the test, the sample thickness, illumination conditions, and rheological testing parameters remained consistent.

[0055] like Figure 5 As shown, the photocuring dynamic rheological test results indicate that the resin composition containing 30 wt% lithium bis(trifluoromethanesulfonyl)imide has a low storage modulus before light irradiation, indicating that it has low elastic resistance in the uncured state, which is beneficial for resin spreading and interlayer renewal during DLP printing. After irradiation with 405 nm light, the storage modulus G′ of the resin composition increases rapidly with irradiation time, indicating that the acrylate groups in the system can undergo photopolymerization and gradually form a stable crosslinked network.

[0056] The above results demonstrate that even after adding 30 wt% lithium bis(trifluoromethanesulfonyl)imide, the resin composition of this invention still maintains good photocuring response and can achieve rapid web formation and curing under 405 nm illumination. Combined with the molding results of the DLP-printed microstructure array in the examples, it can be proven that this resin composition possesses ionic conductivity, photocuring capability, and DLP printing adaptability, making it suitable for preparing ionicly conductive microstructure elastomers and flexible sensing structures.

[0057] Example 5: Conductivity test of comparative resin compositions

[0058] To verify the effect of the specific mass ratio of polyurethane acrylate to polyethylene glycol diacrylate 1000 on the ionic conductivity of the present invention, a comparative sample was prepared that did not use the 5:3 composite ratio of the present invention, and compared with the resin composition obtained in Example 1.

[0059] In Comparative Example 1, 8.00 g of polyurethane acrylate and 2.00 g of acrylic acid were weighed to obtain a basic resin system, wherein the polyurethane acrylate accounted for 80 wt% of the mass of the basic resin system and the acrylic acid accounted for 20 wt% of the mass of the basic resin system. Subsequently, 4.29 g of lithium bis(trifluoromethanesulfonyl)imide was added, so that lithium bis(trifluoromethanesulfonyl)imide accounted for 30 wt% of the total mass of the basic resin system and the lithium bis(trifluoromethanesulfonyl)imide.

[0060] In Comparative Example 2, 8.00 g of polyethylene glycol diacrylate 1000 and 2.00 g of acrylic acid were weighed to obtain a basic resin system, wherein polyethylene glycol diacrylate 1000 accounted for 80 wt% of the mass of the basic resin system, and acrylic acid accounted for 20 wt% of the mass of the basic resin system. Subsequently, 4.29 g of lithium bis(trifluoromethanesulfonyl)imide was added, so that lithium bis(trifluoromethanesulfonyl)imide accounted for 30 wt% of the total mass of the basic resin system and lithium bis(trifluoromethanesulfonyl)imide.

[0061] The type and amount of photoinitiator, stirring conditions, vacuum degassing conditions, and photocuring conditions in Comparative Examples 1 and 2 were consistent with those in Example 1. The resulting resin compositions were photocured and then subjected to resistance testing.

[0062] Test results are as follows Figure 6 As shown, in 4×10 4 Under the Ω resistance range, both Comparative Example 1 and Comparative Example 2 cured samples showed over-range performance and failed to obtain an effective conductive response. However, in Example 1, when a composite matrix of polyurethane acrylate and polyethylene glycol diacrylate 1000 in a mass ratio of 5:3 was used, measurable ionic conductivity was obtained under the same lithium salt content conditions. This result indicates that using polyurethane acrylate or polyethylene glycol diacrylate 1000 alone as the main resin, even with the addition of the same amount of acrylic acid and lithium bis(trifluoromethanesulfonyl)imide, it is difficult to form an effective conductive path after curing. The polyurethane acrylate / polyethylene glycol diacrylate 1000 composite matrix with a specific mass ratio in this invention has a synergistic effect with acrylic acid and lithium bis(trifluoromethanesulfonyl)imide, giving the resulting cured material both DLP photocurable properties and ionic conductivity.

[0063] Example 7: DLP Printing

[0064] The resin composition obtained in Example 1 or Example 2 was added to the resin tank of a DLP printing device and cured layer by layer under a 405 nm light source. The resin composition of Example 2, with a lithium bis(trifluoromethanesulfonyl)imide content of 30 wt%, was added to the resin tank of a DLP printing device and cured layer by layer under a 405 nm light source. During printing, the light intensity was 3500 μW / cm². 2 The exposure time for each layer is 20 seconds. The printed models include inverted pyramid arrays, cylindrical arrays, large hemispherical arrays, and small hemispherical arrays. For example... Figure 7 As shown, the printing results indicate that the resin composition with 30 wt% lithium bis(trifluoromethanesulfonyl)imide can achieve DLP molding of the above-mentioned microstructure array. The resulting printed sample has a complete structure and clear outline, indicating that the resin composition has good DLP printing adaptability under the above-mentioned photocuring conditions.

[0065] Example 6 Conductivity Response Test of Different Microstructure Arrays

[0066] The resin composition obtained in Example 1 was used to print cylindrical arrays, pyramid arrays, large hemispherical arrays, and small hemispherical arrays, respectively. Pressure response tests were then conducted on the obtained samples under the same test conditions. The relative current change ΔI / I0 was used as the electrical response parameter. The test results are as follows: Figure 8 As shown.

[0067] Depend on Figure 7 It can be seen that the ΔI / I0 of all four microstructure array samples increases with increasing pressure, indicating that the obtained samples all have measurable pressure-electrical responses. The response sensitivities of different microstructure arrays vary significantly, with the cylindrical array, pyramid array, large hemispherical array, and small hemispherical array having sensitivities of 0.0137 kPa. -1 0.0218 kPa -1 0.06826 kPa -1 and 0.1065 kPa -1 The small hemispherical array sample exhibited the highest sensitivity, indicating that it showed a more significant change in electrical response under pressure.

[0068] The results demonstrate that the pressure-electric response performance of the sample can be controlled by the differences in the array structure after the resin composition of the present invention is formed into different microstructure arrays through DLP printing. Different array structures exhibit different deformation modes, effective contact areas, and changes in conductive paths during the pressure process, resulting in different response sensitivities. Therefore, the resin composition of the present invention is suitable for preparing flexible ion-conductive materials, pressure-responsive structures, and tactile sensing structures with tunable electrical responses.

Claims

1. A DLP-printable ion-conductive polyurethane acrylate resin composition, characterized in that, It includes the following components: The base resin system includes: polyurethane acrylate, polyethylene glycol diacrylate, and acrylic acid; Lithium salt, added in an amount of 30 wt% to 40 wt% of the total mass of the base resin system; The photoinitiator is added at an amount of 0.5~2 wt% of the total mass of the base resin system. Wherein, the polyethylene glycol diacrylate is polyethylene glycol diacrylate 1000, the mass ratio of the polyurethane acrylate to the polyethylene glycol diacrylate 1000 is 6:4 to 5:3; and the acrylic acid accounts for 10 wt% to 20 wt% of the total mass of the base resin system.

2. The DLP-printable ion-conductive polyurethane acrylate resin composition according to claim 1, characterized in that, The amount of acrylic acid added is 20 wt%.

3. The DLP-printable ion-conductive polyurethane acrylate resin composition according to claim 1, characterized in that, The lithium salt used is lithium bis(trifluoromethanesulfonyl)imide, and the amount added is 30 wt%.

4. The DLP-printable ion-conductive polyurethane acrylate resin composition according to claim 1, characterized in that, The photoinitiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and the amount added is 1 wt%.

5. A method for preparing a DLP-printable ion-conductive polyurethane acrylate resin composition as described in any one of claims 1-4, characterized in that, Includes the following steps: Step (1) Mix polyurethane acrylate, polyethylene glycol diacrylate 1000 and acrylic acid to obtain a base resin mixture; Step (2) Add lithium bis(trifluoromethanesulfonyl)imide to the base resin mixture and stir until homogeneous; Step (3) Add a photoinitiator and continue mixing to obtain an ion-conducting resin; Step (4) The obtained ion-conducting resin is degassed under vacuum to obtain the resin composition.

6. The preparation method according to claim 5, characterized in that, The mixing temperature in step (1) is 70℃~90℃.

7. The preparation method according to claim 5, characterized in that, The vacuum degassing time in step (4) is 5 h to 7 h.

8. The application of the DLP-printable ion-conductive polyurethane acrylate resin composition as described in any one of claims 1-4 in DLP photopolymerization printing.

9. The application according to claim 8, characterized in that, The resin composition is used to print inverted pyramid arrays, cylindrical arrays, large hemispherical arrays, or small hemispherical array structures.

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