High-performance composite resin for inducing liquid crystal orientation through 3D printing technology and preparation method of high-performance composite resin

Abstract

According to the high-performance composite resin for inducing liquid crystal orientation through the 3D printing technology and the preparation method of the high-performance composite resin, liquid crystal is added into a resin matrix, the molecular orientation characteristic of the liquid crystal is utilized, and in the SLA process, under the condition that no photon is absorbed, the liquid crystal molecular orientation in the printing process is changed through a photoelectric field provided by a laser beam, and therefore the liquid crystal orientation is improved. And inducing a polymer chain to enter the same orientation to prepare the high-performance composite resin material. By controlling the 3D printing mode, the printing resolution and the liquid crystal content, the composite resin with tensile strength, elongation at break, bending strength, bending modulus, impact strength and other mechanical properties superior to those of commercial ink can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulating materials, and particularly relates to a high-performance composite resin with liquid crystal orientation induced by 3D printing technology and a preparation method thereof. Background Art

[0002] Additive manufacturing technology is different from traditional material-equal and material-reducing manufacturing methods, and it can quickly and easily produce materials of various designs. 3D printing has become one of the main ways to develop future product processing methods. Among them, stereolithography (SLA) technology is a rapid prototyping process that uses a laser beam to scan a liquid photosensitive resin point by point to cure it. Because of its high precision and the ability to induce photopolymerization with only one light source, it has become one of the most widely used technologies. In addition, this method has low energy consumption and less environmental pollution, and SLA is the only light-curing 3D printing technology that can print large models. However, the application potential of 3D-printed polymer components is still limited, mainly because of their weak mechanical properties. For further industrial development, it is crucial to develop high-performance composite resin materials for 3D printing.

[0003] Currently, three methods for improving the comprehensive performance of composite resin materials have been proposed in domestic and foreign research: using different monomers, adding inert fillers or additives, and adopting an epoxy acrylate hybrid system. Among these methods, adding inert fillers or additives, such as silica fillers, calcium sulfate whisker fillers, graphene oxide fillers, polysiloxane core-shell nanoparticles, carbon-based nanoparticles, polyimide, and liquid crystal (LC) resins, is the most convenient and commonly used method. Using such fillers or additives reduces the volume shrinkage after material forming and improves the mechanical properties of the obtained structure.

[0004] The DongLin team at Purdue University combined graphene oxide nanofillers with stereolithography to study the enhancement of photosensitive polymer components. The team added 0.2% graphene oxide to the SLA precursor, which increased the tensile strength and ductility of the printed composite material. However, the improvement of the tensile strength and ductility of composite resin materials by traditional fillers such as graphene oxide is extremely limited. Due to the strong interaction between graphene oxide sheets, they are prone to agglomeration in epoxy resins, reducing their dispersibility and uniformity in composite materials, which is not conducive to further enhancing the comprehensive performance of composite resin materials. At the same time, the addition of graphene oxide may increase the brittleness of composite materials, especially in the case of high filler content, limiting its use in applications that require high toughness. And when the polymer is oriented, its mechanical properties will be greatly improved, and traditional fillers do not have the function of regulating the photo-orientation of 3D-printed polymers.

[0005] Liquid crystal is an intermediate phase between the solid and liquid states of matter, exhibiting strong non-linear optical effects. Liquid crystals have the molecular orientation characteristics of solid crystals but change shape like liquids. During the phase separation process, liquid crystals and polymers are mixed into a common solution. Subsequently, the mixture is sprayed, and the liquid crystal molecules separate from the polymer and remain in the medium as unique LC droplets. By controlling the microstructure of the liquid crystal / polymer composite, polymer-stabilized liquid crystal (PSLC) and polymer-dispersed liquid crystal (PDLC) systems with specific properties can be produced. The PDLC film is obtained by dispersing liquid crystal droplets in a polymer matrix and then initiating polymerization through methods such as thermal curing and ultraviolet irradiation. However, when using this method, the solubility of the liquid crystal in the polymer matrix decreases, resulting in phase separation and the formation of a micro-phase separation structure.

[0006] Therefore, using 3D printing technology to induce liquid crystal orientation can regulate the orientation properties of composite resin materials under the action of light during the printing process, and preparing high-performance electrical resin insulation materials with excellent mechanical properties will be of great significance for the development of electrical insulation. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section, as well as in the abstract and title of the specification of this application, to avoid obscuring the purpose of this section, the abstract, and the title, and such simplifications or omissions shall not be used to limit the scope of the present invention.

[0008] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0009] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a high-performance composite resin with liquid crystal orientation induced by 3D printing technology.

[0010] To solve the above technical problems, the present invention provides the following technical solutions:

[0011] Under light-shielded conditions, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide is added to an acrylate prepolymer to obtain a resin matrix;

[0012] 4-Cyano-4'-pentylbiphenyl liquid crystal is added to the resin matrix, stirred evenly, and degassed under vacuum to obtain a 4-cyano-4'-pentylbiphenyl liquid crystal / photosensitive resin composite;

[0013] The composite material is introduced into the 3D printer feed trough for printing to print out a composite resin product;

[0014] Among them, the acrylate prepolymer is composed of tripropylene glycol diacrylate, glycidyl methacrylate, and trimethylolpropane triacrylate.

[0015] As a preferred embodiment of the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology according to the present invention, wherein: the mass ratio of tripropylene glycol diacrylate, glycidyl methacrylate, and trimethylolpropane triacrylate is 5-6:2-3:1.

[0016] As a preferred embodiment of the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology according to the present invention, wherein: the addition amount of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide relative to the acrylate prepolymer is 0.4-0.6 wt%.

[0017] As a preferred embodiment of the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology according to the present invention, wherein: the addition amount of 4-cyano-4'-pentylbiphenyl liquid crystal relative to the resin matrix is 2.7-7.3 wt%.

[0018] As a preferred embodiment of the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology according to the present invention, wherein: the addition amount of 4-cyano-4'-pentylbiphenyl liquid crystal relative to the resin matrix is 2.7-3.3 wt%.

[0019] As a preferred embodiment of the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology according to the present invention, wherein: the printing direction includes one of vertical printing and parallel printing.

[0020] As a preferred embodiment of the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology according to the present invention, wherein: the printing direction is vertical printing.

[0021] As a preferred embodiment of the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology according to the present invention, wherein: the printing resolution is 25-50 μm.

[0022] As a preferred embodiment of the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology according to the present invention, wherein: the printing resolution is 25 μm.

[0023] Another object of the present invention is to overcome the deficiencies in the prior art and provide a high-performance composite resin prepared by the preparation method of the high-performance composite resin with liquid crystal orientation induced by 3D printing technology.

[0024] Advantages of the present invention:

[0025] (1) The PR-5CB resin obtained by blending 4'-pentyl-4-cyanobiphenyl (5CB) with a photosensitive acrylic resin in the present invention has well-dispersed rod-shaped LC molecules in the resin matrix, which can effectively bind to the resin matrix. By adding an appropriate amount of 5CB, the viscosity of the system under high-speed shearing conditions is lower than that of commercial inks, providing the possibility for large-scale production using 3D printing.

[0026] (2) By controlling the 3D printing method, printing resolution, and 5CB content, the mechanical properties of 3D printed products can be effectively improved. When the addition amount of 5CB is 3wt%, under the vertical printing method, and the printing resolution is 25μm, the mechanical properties such as tensile strength, elongation at break, flexural strength, flexural modulus, and impact strength of the composite resin products are all improved compared with commercial inks.

[0027] (3) In the present invention, liquid crystal is doped with a photosensitive resin matrix. Utilizing the molecular orientation characteristics of liquid crystal, in the SLA process, in the absence of photon absorption, the photoelectric field provided by the laser beam changes the orientation of liquid crystal molecules during printing, and then induces polymer chains to enter the same orientation, preparing a high-performance composite resin material. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. Among them:

[0029] Figure 1 It is a 3D printing process diagram using the SLA technology in Embodiment 1 of the present invention;

[0030] Figure 2 It is a schematic diagram of the printing direction in Embodiments 1 and 3 of the present invention;

[0031] Figure 3 It is a morphology diagram of the composite materials prepared in Embodiments 1-2 of the present invention under a polarized light microscope (POM);

[0032] Figure 4 It is a curve graph showing the change of the viscosity of the composite materials prepared in Embodiments 1-2 and Comparative Example 1 of the present invention with the shear rate;

[0033] Figure 5 It is a morphology diagram of the surface and cross-section of the resin products prepared in Embodiments 1 and 3 and Comparative Examples 1-2 of the present invention under a polarized light microscope (POM);

[0034] Figure 6XRD patterns of the surfaces and cross-sections of the resin products prepared in Example 1 and Example 3 of the present invention and Comparative Examples 1-2

[0035] Figure 7 Impact fracture morphology diagrams of the resin products prepared in Example 1 and Example 3 of the present invention and Comparative Examples 1-2

[0036] Figure 8 XRD patterns of the surfaces of the resin products prepared in Examples 1-2 of the present invention and Comparative Examples 1, 3, and 4

[0037] Figure 9 Morphology diagrams of the resin products prepared in Examples 1-2 of the present invention and Comparative Examples 1, 3, 4, and 6 under a polarized light microscope (POM) Detailed implementation manners

[0038] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the detailed implementation manners of the present invention in conjunction with the embodiments of the specification.

[0039] In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0040] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selectively exclusive embodiment from other embodiments.

[0041] The raw materials used in the present invention are commercially available without special instructions.

[0042] The method for testing the dispersibility of PR-5CB resin in the present invention during printing is as follows: Use a polarized light microscope to observe and test, and use POM to observe the dispersion state of the photosensitive resin and the orientation of the 3D printed film. Drop an appropriate amount of dispersion liquid between two cover glasses to form a thick solution, and observe its state.

[0043] The method for testing the rheological properties of PR-5CB resin in the present invention during printing is as follows: Use a mixing rheometer to measure the rheological behavior of the resin in the steady-state shear rate range of 1 to 1000 s -1

[0044] ​The method for testing the morphology of the printed sample in the present invention is as follows: Use a polarized light microscope to test the POM images of the surface and cross-sectional area of the 3D printed sample in the 0° and 45° directions, and observe the light and dark changes within the shooting field of view. Use Fourier transform polarized infrared spectroscopy to determine the arrangement mode of liquid crystal molecules. And use a scanning electron microscope (SEM) to observe the fracture morphology of the 3D printed part.

[0045] The method for testing the orientation degree of the printed sample in the present invention is as follows: Use an X-ray diffractometer to check the orientation degree of the 3D printed sample. This device uses a copper target, and the set parameters for the inspection include a tube voltage of 40 kV, a tube current of 40 mA, a scanning range of 7 - 80°, and a scanning speed of 10° / min. Use a 3D printer to print samples with a size of 12 mm × 12 mm × 12 mm, and adjust the printing direction and resolution. Subsequently, divide the sample into two identical squares. Carefully cut these samples into samples with a thickness of 1 - 2 mm using a knife, and then evenly polish the samples with sandpaper to ensure that the test surface is flat and polished.

[0046] The method for testing the tensile properties of the printed sample in the present invention is as follows: Use a universal material testing machine to conduct tensile property tests. The tensile test speed is 10 mm / min, and the average value is taken after each sample is repeatedly tested five times.

[0047] The method for testing the hardness of the printed product in the present invention is as follows: Use a D-type digital rubber hardness tester to conduct tests in accordance with the standards of GB / T531 - 99, GB / T2411 - 80, HG / T2489 - 93, and JJG304 - 003. The average value is taken after each sample is repeatedly tested five times.

[0048] The method for testing the notched impact properties of the printed sample in the present invention is as follows: Use a pendulum impact testing machine to conduct tests in accordance with the standard of GB / T1043 - 2008. The test sample size is 80 ± 2, 10 ± 0.2, 4 ± 0.2 mm, and the V-notch depth is 2 ± 0.1 mm. The average value is taken after each sample is repeatedly tested five times.

[0049] The method for conducting dynamic mechanical analysis (DMA) on the printed sample in the present invention is as follows: Use a dynamic thermomechanical analyzer, with a temperature range of 30 - 300 °C, a heating rate of 3 °C / min, a frequency of 1 Hz, and a sample size of 35.0 mm × 10.0 mm × 3.0 mm.

[0050] Example 1

[0051] This example provides a preparation method for a high-performance composite resin with liquid crystal orientation induced by 3D printing technology, specifically as follows:

[0052] (1) Under light - shielding conditions, stir trimethylolpropane triacrylate (TPGDA), glycidyl methacrylate (GMA), and tris(2 - hydroxyethyl)isocyanurate triacrylate (TMPTA) evenly in a mass ratio of 6:3:1 to obtain an acrylate prepolymer. Subsequently, add 0.5 wt% of bis(2,4,6 - trimethylbenzoyl)phenylphosphine oxide (BAPO) as a photo - initiator to obtain a resin matrix;

[0053] (2) Add 3 wt% of 4 - cyano - 4'-pentylbiphenyl liquid crystal (5CB) to the resin matrix, stir evenly, and remove air bubbles under vacuum to obtain a 5CB / photosensitive resin composite, namely PR - 5CB - 3;

[0054] (3) Introduce PR - 5CB - 3 into the 3D printer's material tank, and use a laser intensity of 103 W / cm 2 to perform printing. Control the printing direction to be vertical printing, with a printing resolution of 25 μm, and print out a composite resin product, namely PR - 5CB - 3 / / (25μm).

[0055] Example 2

[0056] This example provides a preparation method of a high - performance composite resin with liquid crystal orientation induced by 3D printing technology. Adjust the dosage of 5CB in step (2) of Example 1 to 5 wt% and 7 wt% respectively to obtain PR - 5CB - 5 and PR - 5CB - 7. The remaining preparation processes are the same as those in Example 1, and composite resin products, namely PR - 5CB - 5 / / (25μm) and PR - 5CB - 7 / / (25μm), are prepared.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that the dosage of 5CB in step (2) is adjusted to 0 wt% to obtain PR - 5CB - 0, and the remaining preparation processes are the same as those in Example 1, and a resin product, namely PR - 5CB - 0 / / (25μm), is prepared.

[0059] Analyze the dispersibility and fluidity of the resin products prepared in Examples 1 - 2 and Comparative Example 1. The results are as Figures 3 - 4 shown. Among them, Figure 3 are the micrographs of PR - 5CB - 3, PR - 5CB - 5, and PR - 5CB - 7 composites under a polarized light microscope (POM) to analyze the dispersibility of liquid crystal molecules in the resin matrix, Figure 4 is the curve of the viscosity of PR - 5CB - 0, PR - 5CB - 3, PR - 5CB - 5, and PR - 5CB - 7 composites varying with the shear rate, which is used for the analysis of flow performance.

[0060] As Figure 3As shown in the figure, it was observed under a polarized light microscope (POM) that the rod-like liquid crystal (LC) molecules in each composite material were well dispersed in the resin matrix, indicating the feasibility of obtaining high-performance 3D printed products from 5CB / photosensitive resin composites. According to Figure 4 It can be seen that adding 5CB increases the system viscosity, and as the shear rate increases, the overall viscosity of the system decreases significantly, indicating that the 5CB / photosensitive resin composite has good fluidity, which helps to level or fully scrape the resin before each layer of raw material solidifies during 3D printing.

[0061] The mechanical properties of the resin products prepared in Examples 1-2 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0062] Table 1 Influence of 5CB dosage on the mechanical properties of composite resins

[0063]

[0064] It can be seen from Table 1 that the composite resin with a 5CB addition of 3wt% has the best mechanical properties, while when the addition of 5CB is too high, reaching 5wt% and 7wt%, the mechanical properties of the printed products will gradually decrease, indicating that an appropriate 5CB addition can improve the mechanical properties of the composite resin products.

[0065] Example 3

[0066] This example provides a preparation method for a high-performance composite material with liquid crystal orientation induced by 3D printing technology. The vertical printing in step (3) of Example 1 was adjusted to parallel printing, and the rest of the preparation processes were the same as those in Example 1, obtaining a composite resin product, namely PR-5CB-3⊥(25μm).

[0067] Comparative Example 2

[0068] The difference between this comparative example and Comparative Example 1 is that the vertical printing in step (3) was adjusted to parallel printing, and the rest of the preparation processes were the same as those in Comparative Example 1, obtaining a composite resin product, namely PR-5CB-0⊥(25μm).

[0069] The orientation analysis of the resin products prepared in Examples 1 and 3 and Comparative Examples 1-2 was carried out, and the results are as Figure 5 shown.

[0070] From Figure 5 it can be seen that for the composite resin product without 5CB, under both printing directions, the surface and cross-section are always dark under POM, indicating that the product is isotropic whether printed in the vertical or horizontal direction.

[0071] The composite resin product containing 3 wt% 5CB and printed vertically shows dark and bright images at 0° and 45° respectively on the surface observed using POM, while the cross-section remains dark, indicating that PR-5CB-3 / / (25μm) is anisotropic. For the composite resin product containing 3 wt% 5CB and printed horizontally, it is observed using POM that the surface remains dark while the cross-section shows dark and bright images at 0° and 45° respectively, indicating that PR-5CB-3⊥(25μm) is also anisotropic.

[0072] XRD tests were conducted on the surfaces and cross-sections of the resin products prepared in Examples 1 and 3 and Comparative Examples 1-2, and the results are as Figure 6 shown.

[0073] Comparing Figure 6 the samples without 5CB in two printing directions, it was found that the XRD peaks of the surface and cross-section were the same, indicating that the aggregation state of the polymer without 5CB was hardly affected by the printing direction, and the samples were not anisotropic.

[0074] For the composite resin product containing 3 wt% 5CB and printed vertically, PR-5CB-3 / / (25μm), the XRD peak of the surface was significantly higher than that of the cross-section, indicating that the crystallinity of the aggregates on the surface and cross-section was different, that is, the aggregation states were different. For the composite resin product containing 3 wt% 5CB and printed horizontally, PR-5CB-3⊥(25μm), the XRD peak of the cross-section was significantly higher than that of the surface. Both showed that the crystallinity along the UV irradiation direction was higher than that in other directions, indicating that the orientation of the polymer was along the UV irradiation direction.

[0075] Tensile property tests were conducted on the resin products prepared in Examples 1 and 3 and Comparative Examples 1-2, and the results are shown in Table 2.

[0076] Table 2 Comparison of Tensile Properties of Resins Containing 3 wt% Liquid Crystal and Resins without Liquid Crystal

[0077]

[0078] According to Table 2, the tensile strength and elongation at break of the 3D printed products containing 3 wt% 5CB were both higher than those of the 3D printed products without 5CB liquid crystal, and the tensile strength and elongation at break of PC-5CB-3 / / were both higher than those of PC-5CB-3⊥, that is, the mechanical properties of the composite resin product printed along the layer stacking direction were better than those printed along the cross-section stacking direction, indicating that the liquid crystal was arranged orderly along the layer stacking direction, and the long-range ordered liquid crystal improved the strength of the material. For the printed products without liquid crystal, different printing methods had little effect on their tensile properties. This shows that the composite material was oriented, and the orientation had an impact on the tensile properties of the material.

[0079] The resin products prepared in Example 1 and 3 and Comparative Examples 1-2 were subjected to bending, impact strength, hardness tests and dynamic mechanical analysis, and the results are shown in Table 3.

[0080] Table 3 Performance comparison of resins containing 3wt% liquid crystal and resins without liquid crystal

[0081]

[0082]

[0083] According to Table 3, the bending strength, bending modulus and impact strength of the composite resin containing 3wt% liquid crystal are higher than those of the resin without liquid crystal, and the hardness of all resin samples changes little. The storage modulus and Tg values of PC-5CB-3 / / and PC-5CB-3⊥ are higher than those of PC-5CB-0 / / and PC5CB-0⊥, and all the properties of the vertically printed resin are better than those of the horizontally printed resin, indicating that the addition of 5CB improves the strength and toughness of the resin. This is mainly due to the similarity between the orientation of 5CB and the direction of light irradiation during the curing process.

[0084] The impact fracture surfaces of the resin products prepared in Example 1 and 3 and Comparative Examples 1-2 were observed, and the results are as Figure 7 shown.

[0085] As Figure 7 shown, in the PR-5CB-0 system, due to the poor molecular motion ability of the cured product, the cross-section is smooth, the direction of microcracks is single, it is not easy to produce yield deformation, and the microcracks are basically unobstructed during the propagation process, which is a typical manifestation of brittle damage. When the content of 5CB is 3wt%, the cross-section of PR-5CB-3 shows a higher roughness and a river-like cross-section. The surface of the cross-section area of PR-5CB-3⊥ has clearer granularity and also shows a river-like appearance. This is mainly because 5CB generates a one-dimensional orientation during the printing process, and the PR-5CB-3 / / specimen cracks under impact because the impact direction is perpendicular to the orientation direction of 5CB and the polymer, resulting in the formation of a bridging zone in the fracture area, which prevents crack propagation and improves the impact strength of the material. Without the addition of 5CB, the difference in the printing direction has little effect on the morphology of the cross-section fracture surface. The addition of 5CB effectively enhances the ductile fracture of the 3D printed composite resin product, and the change in the printing direction will affect the surface morphology of the fracture surface.

[0086] Comparative Example 3

[0087] The difference between this comparative example and Example 1 is that the printing resolutions in step (3) were adjusted to 50μm and 100μm respectively, and the rest of the preparation processes were the same as those in Example 1, obtaining composite resin products, namely PR-5CB-3 / / (50μm) and PR-5CB-3 / / (100μm).

[0088] Comparative Example 4

[0089] The difference between this comparative example and Comparative Example 1 is that the printing resolutions in step (3) are adjusted to 50 μm and 100 μm respectively, and the remaining preparation processes are the same as those in Example 1, obtaining resin products, namely PR-5CB-0 / / (50 μm) and PR-5CB-0 / / (100 μm).

[0090] XRD tests were performed on the surface sections of the resin products prepared in Examples 1-2 and Comparative Examples 1, 3, and 4, and the results are as Figure 8 shown.

[0091] As can be seen from Figure 8 , the XRD peaks of the PR-5CB-0 composite resin products vary little at different printing resolutions. When the printing resolution is 25 μm, the XRD peak of PR-5CB-3 / / is higher than that of PR-5CB-0 / / . This is because the thickness of the PR-5CB-3 / / sample is approximately the same as the length of the rod-like liquid crystal, and the printing time is shorter, and the liquid crystal aligns the surrounding photosensitive resin in the direction of light irradiation. When the photosensitive resin polymerizes, it fixes the 5CB liquid crystal in one direction, resulting in the polymer showing anisotropy.

[0092] Increasing the printing resolution of PR-5CB-3 / / to 50 μm will cause a slight decrease in the XRD peak because the thickness of the polymer is slightly greater than the length of the liquid crystal rod, and during the light-induced orientation process, the liquid crystal is also basically aligned with the surrounding photosensitive resin. When the printing resolution is increased to 100 μm, the height of the XRD peak decreases significantly. This is because the excessive amount of photosensitive resin makes the orientation incomplete, and the 5CB liquid crystal is surrounded by the photosensitive resin. Due to the dispersion of the photosensitive resin during the photocuring process due to the inability to be oriented, the polymer cannot be oriented.

[0093] Comparing the XRD curves of PR-5CB-3 / / (25 μm), PR-5CB-5 / / (25 μm), and PR-5CB-7 / / (25 μm), it is found that as the content of 5CB increases, the height of the XRD peak decreases. When the content of 5CB reaches 7 wt%, the height of the XRD peak drops sharply, which means that the increase in the content of 5CB will cause the aggregation of liquid crystal molecules, making it difficult for the liquid crystal molecules and the photosensitive resin to be oriented under light irradiation. Therefore, selecting appropriate printing accuracy and liquid crystal content is extremely important for improving the performance of the resin sample.

[0094] Comparative Example 5

[0095] The difference between this comparative example and Example 1 is that in step (2), 5CB is adjusted to SiO2, calcium sulfate whiskers, graphene oxide, multi-walled carbon, and polyimide respectively, and the remaining preparation processes are the same as those in Example 1, obtaining composite resin products.

[0096] The tensile properties of the composite resin product prepared in Comparative Example 5 were tested, and the results are shown in Table 4.

[0097] Table 4 Comparison of tensile properties of different composite resin products

[0098]

[0099] As can be seen from Table 4, using SiO2, calcium sulfate whiskers, graphene oxide, multi-walled carbon, and polyimide as fillers to compound with the resin matrix has limited effect on improving the tensile strength of the resin and will cause a decrease in toughness. While using the 5CB liquid crystal in the present invention can greatly improve the tensile strength of the resin and also improve the toughness, showing excellent comprehensive properties.

[0100] Comparative Example 6

[0101] The difference between this comparative example and Example 2 is that the printing resolutions in step (3) were adjusted to 50 μm and 100 μm respectively, and the remaining preparation processes were the same as those in Example 2. Finally, the resin products of this comparative example were prepared, namely PR-5CB-5 / / (50 μm), PR-5CB-5 / / (100 μm), PR-5CB-7 / / (50 μm), and PR-5CB-7 / / (100 μm).

[0102] The surfaces of the resin products prepared in Examples 1-2 and Comparative Examples 1, 3, 4, and 6 were observed, and the results are as Figure 9 shown.

[0103] From Figure 9 it can be seen that during the entire 360° rotation of the stage, the POM images of the surface of the 3D printed composite resin product PR-5CB-0 / / are all dark, indicating that the surface is isotropic at different printing resolutions. For printing resolutions of 25 μm and 50 μm, when the carrier stage is rotated 360°, their POM images at 0° and 45° show a dark image and a bright image respectively, indicating that the PR-5CB-3 / / and PR-5CB-5 / / composite resin products exhibit optical anisotropy similar to that of liquid crystals, and the photosensitive resin polymerizes along the orientation direction of the small liquid crystals during the polymerization process. While at a printing resolution of 100 μm, during the 360° rotation of the PR-5CB-3 / / and PR-5CB-5 / / composite resin products on the carrier stage, their POM images are always bright, indicating the presence of cryptocrystalline or microcrystalline aggregates on their surfaces. For the PR-5CB-7 / / composite resin product, the POM images are always bright, and even when the printing resolution changes from 25 μm to 100 μm, some spherical aggregates can be observed on the surface.

[0104] The mechanical properties of the resin products prepared in Examples 1 and 2 and Comparative Examples 1, 3, 4, and 6 were tested, and the results are shown in Table 5.

[0105] Table 5 Influence of Printing Resolution on the Mechanical Properties of Resin Materials

[0106]

[0107]

[0108] As can be seen from Table 5, for the resin PR-5CB-0 / / without liquid crystal, its mechanical properties are almost independent of the printing resolution. For the composite resin with 3 wt% 5CB added, the mechanical properties of the 3D printed products can be effectively improved by controlling the printing resolution. When the printing resolution is 25 μm, all mechanical indexes of the PB-5CB-3 / / (25 μm) composite resin product are more than doubled compared with the corresponding values of PB-5CB-0 / / (25 μm). Therefore, when the printing resolution is 25 μm, adding 3 wt% 5CB can effectively improve the strength and toughness of the resin product. However, when the printing resolution reaches 50 μm and 100 μm, the mechanical properties decline, and when the printing resolution is 100 μm, the mechanical properties are lower than those of the samples printed with PB-5CB-0 / / resin, indicating that the printing resolution needs to be controlled when the addition amount of 5CB is appropriate to effectively improve the performance of the resin product.

[0109] In summary, for the PR-5CB resin obtained by blending 4'-pentyl-4-cyanobiphenyl (5CB) with acrylic photosensitive resin in the present invention, the rod-shaped LC molecules are well dispersed in the resin matrix and can effectively bind to the resin matrix. By adding an appropriate amount of 5CB, the viscosity of the system under high-speed shear conditions is lower than the ink viscosity (0.85 Pa·s) without addition, which provides the possibility for large-scale production using 3D printing.

[0110] By controlling the 3D printing method, printing resolution, and 5CB content, the mechanical properties of 3D printed products can be effectively improved. At the addition amount of 3 wt% 5CB and in the vertical printing mode, when the printing resolution is 25 μm, the mechanical properties such as tensile strength, elongation at break, flexural strength, flexural modulus, and impact strength of the composite resin product are all improved compared with those without adding 5CB, and they are 2.91 times, 1.80 times, 2.70 times, 2.12 times, and 2.75 times the corresponding values of the resin without adding liquid crystal, respectively.

[0111] In the present invention, liquid crystal is doped with a photosensitive resin matrix. By utilizing the molecular orientation characteristics of the liquid crystal, during the SLA process, in the absence of photon absorption, the photoelectric field provided by the laser beam causes the 5CB to change its molecular orientation under light driving, and then guides other acrylate prepolymers to orient in the same direction. Therefore, through POM observation, the entire fixed 3D printed product is anisotropic, and finally a high-performance composite resin material is prepared.

[0112] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a high-performance composite resin for inducing liquid crystal orientation using 3D printing technology, characterized in that: include, Adding phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide into acrylate prepolymer under light-proof conditions to obtain a resin matrix; Adding 4-cyano-4'-pentylbiphenyl liquid crystal into the resin matrix, stirring evenly and performing vacuum degassing to obtain a 4-cyano-4'-pentylbiphenyl liquid crystal / photosensitive resin composite material; The composite material is introduced into the 3D printer tank for printing to print out the composite resin product; The acrylate prepolymer is composed of tripropylene glycol diacrylate, glycidyl methacrylate and trimethylolpropane triacrylate.

2. The method for preparing a high-performance composite resin for inducing liquid crystal orientation by 3D printing technology as claimed in claim 1, characterized in that: The mass ratio of the tripropylene glycol diacrylate, glycidyl methacrylate and trimethylolpropane triacrylate is 5-6:2-3:

1.

3. The method for preparing a high-performance composite resin for inducing liquid crystal orientation by 3D printing technology as claimed in claim 1, characterized in that: The amount of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide added to the acrylate prepolymer is 0.4-0.6 wt %.

4. The method for preparing a high-performance composite resin for inducing liquid crystal orientation by 3D printing technology as claimed in claim 1, characterized in that: The amount of the 4-cyano-4'-pentylbiphenyl liquid crystal added to the resin matrix is ​​2.7-7.3 wt %.

5. The method for preparing a high-performance composite resin for inducing liquid crystal orientation by 3D printing technology as claimed in claim 4, characterized in that: The amount of the 4-cyano-4'-pentylbiphenyl liquid crystal added to the resin matrix is ​​2.7-3.3 wt %.

6. The method for preparing a high-performance composite resin for inducing liquid crystal orientation by 3D printing technology as claimed in claim 1, characterized in that: The printing direction includes one of vertical printing and parallel printing.

7. The method for preparing a high-performance composite resin for inducing liquid crystal orientation by 3D printing technology as claimed in claim 6, characterized in that: The printing direction is vertical printing.

8. The method for preparing a high-performance composite resin for inducing liquid crystal orientation by 3D printing technology as claimed in claim 1, characterized in that: The printing resolution is 25-50 μm.

9. The method for preparing a high-performance composite resin for inducing liquid crystal orientation by 3D printing technology as claimed in claim 8, characterized in that: The resolution of the printing was 25 μm.

10. A high-performance composite resin for inducing liquid crystal orientation using 3D printing technology, prepared by the preparation method according to any one of claims 1 to 9.

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