Preparation method of photo-orientation heat-conducting anisotropic side-chain type liquid crystal photosensitive resin monomer and application thereof in 3D printing

Abstract

This invention discloses a method for preparing a side-chain liquid crystal photosensitive resin monomer with photo-oriented and thermally anisotropic properties and its application in 3D printing. Using 2,2-di(hydroxymethyl)propionic acid, isophorone diisocyanate, and hydroxyethyl methacrylate as raw materials, a side-chain liquid crystal photosensitive resin monomer is prepared and applied to 3D printing resin. Under the action of a 3D printing laser, the liquid crystal units in the side-chain liquid crystal photosensitive resin monomer of this invention form an oriented structure in the laser direction, allowing heat flow to be conducted along the oriented structure and effectively suppressing phonon scattering, thus exhibiting thermal anisotropy. Simultaneously, the side-chain liquid crystal photosensitive resin monomer with photo-oriented and thermally anisotropic properties of this invention exhibits good mechanical properties after 3D printing.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a method for preparing a side-chain type liquid crystal photosensitive resin monomer with light-absorbing and thermally conductive anisotropic properties and its application in 3D printing. Background Technology

[0002] With the development of modern artificial intelligence, the requirements for electronic devices are becoming increasingly stringent, among which thermal management has become a crucial factor affecting the performance of electronic devices. Polymer materials are widely used for the protection and encapsulation of electronic devices due to their lightweight, ease of processing, chemical resistance, and low cost; however, their inherently poor thermal conductivity often limits the extent of their application.

[0003] Photosensitive resins are widely used in insulation applications such as electrical equipment due to their excellent adhesion, electrical insulation, corrosion resistance, and processing performance. However, photosensitive resins also have low thermal conductivity, making them unsuitable for the heat dissipation requirements of insulation encapsulation in high-power, ultra-high-frequency microelectronic devices and high-voltage electrical equipment. Currently, like other common polymers, research on the thermal conductivity of photosensitive resins mainly focuses on two aspects: first, preparing filled photosensitive resins by adding a large number of thermally conductive particles; and second, synthesizing intrinsically thermally conductive polymers with high thermal conductivity. While the method of filling with thermally conductive particles is simple and effective, for photosensitive resins, achieving high thermal conductivity requires the amount of thermally conductive filler to reach a certain percolation threshold. However, a high filler content affects the 3D printing performance of photosensitive resins. Therefore, the second method of preparing intrinsically thermally conductive photosensitive resins can, to some extent, synergistically improve the thermal conductivity of photosensitive resin materials with the first method.

[0004] Liquid crystal molecules readily form highly ordered crystalline structures due to their molecular orientation, greatly increasing the phonon transport path of freedom and reducing phonon scattering, thus exhibiting excellent thermal conductivity. Therefore, introducing liquid crystal unit structures is an effective method to improve the thermal conductivity of polymers. Gu Junwei et al. prepared an intrinsically high thermal conductivity epoxy resin with a liquid crystal unit structure, which significantly improved the thermal conductivity of the epoxy resin (CN 113234042 A). In addition, there are many patent applications concerning the use of liquid crystal units to improve the thermal conductivity and strength of resins (CN 113881006B, CN 114058155 B, CN 113604007 B, CN 108409689 B, and CN 111205249 B, etc.). Our research team previously studied the influence of liquid crystal structures on the performance of photosensitive resins for 3D printing and discovered that liquid crystal units can be oriented according to light in 3D printing, forming anisotropic structures, and the 3D printed products exhibit anisotropic characteristics (CN 117551238 A). Patent application CN 116969840 A describes the preparation of an acrylic resin liquid crystal monomer, which is oriented under the action of an electric field and shaped under photopolymerization to obtain an intrinsically high thermal conductivity liquid crystal material in the lateral direction. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a side-chain type liquid crystal photosensitive resin monomer with light-absorbing and thermally conductive anisotropic properties and its application in 3D printing.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The light-absorbing, thermally conductive, anisotropic side-chain liquid crystal photosensitive resin monomer has the structure shown in Formula I:

[0008]

[0009] The preparation steps of the side-chain type liquid crystal photosensitive resin monomer are as follows:

[0010] (1) Dissolve 2,2-di(hydroxymethyl)propionic acid and 2,2-dimethoxypropane in acetone, then add p-toluenesulfonic acid to the above solution. The resulting mixture is stirred at room temperature for 12-18 hours. Then triethylamine is added and reacted for 5-10 minutes. Finally, acetone is removed by rotary evaporation at 75-85°C. The residue is dissolved in dichloromethane and then washed with Na2CO3 and distilled water respectively. The organic phase is dried with anhydrous Na2SO4 and then dichloromethane is removed by rotary evaporation to obtain white solid product 1.

[0011] (2) Dissolve the above white solid product 1 and 4-phenylphenol in tetrahydrofuran to obtain a solution, cool to 0-5°C, dissolve dicyclohexylcarbodiimide and 4-dimethylaminopyridine in tetrahydrofuran and slowly add to the above solution, react the resulting mixture with stirring for 12-18 h, then remove tetrahydrofuran by rotary evaporation, dissolve the obtained residue in dichloromethane, then wash the mixture with NaHCO3 and distilled water respectively, dry the organic phase with anhydrous Na2SO4, and then remove dichloromethane by rotary evaporation to obtain white solid product 2;

[0012] (3) Dissolve product 2 in methanol, add ion exchange resin, react at room temperature for 12-18 h, filter off the ion exchange resin, remove methanol by rotary evaporation, and obtain transparent liquid product 3.

[0013] (4) The transparent liquid product 3 was diluted with tetrahydrofuran, isophorone diisocyanate was added, and dibutyltin dilaurate was added as a catalyst. The reaction was carried out at 75-85°C for 5-9 hours. The tetrahydrofuran was removed by rotary evaporation to obtain a pale yellow viscous liquid. The obtained pale yellow viscous liquid was dissolved in ethyl acetate, hydroxyethyl methacrylate was added, and dibutyltin dilaurate was added as a catalyst. The reaction was carried out at 85-95°C for 5-8 hours. The ethyl acetate solvent was removed by rotary evaporation to obtain a pale yellow viscous side-chain type liquid crystal photosensitive resin monomer.

[0014] The molar ratio of 2,2-bis(hydroxymethyl)propionic acid and 2,2-dimethoxypropane is 1:(1 to 1.5).

[0015] The molar ratio of product 1 to 4-phenylphenol is 1:(1 to 1.2).

[0016] The molar ratio of product 2 to ion exchange resin is 1:(1 to 1.2).

[0017] The molar ratio of product 3 to IPDI (isophorone diisocyanate) is 1:(2-2.4).

[0018] The molar ratio of product 3 to HEMA (hydroxyethyl methacrylate) is 1:(2-2.4).

[0019] This invention also provides an intrinsically high thermal conductivity liquid crystal photosensitive resin material, comprising the aforementioned side-chain type liquid crystal photosensitive resin monomer, diluent DMAA (N,N-dimethylacrylamide), photoinitiator TPO (trimethylbenzoyl-diphenylphosphine oxide), and photoinitiator 184 (1-hydroxycyclohexylphenylacetone), the formulation of which is as follows by weight:

[0020]

[0021] The intrinsically high thermal conductivity liquid crystal photosensitive resin material is applied to the 3D printing process as follows: N,N-dimethylacrylamide and side-chain liquid crystal photosensitive resin monomers are mixed evenly under high-speed stirring, and then 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone are added. The mixture is stirred until it is clear and then poured into the resin tank of the photosensitive resin 3D printer for photocuring 3D printing. The wavelength of the light is preferably 405nm and the illumination time is preferably 6-12s.

[0022] To utilize the property of liquid crystal cells aligning under light, this invention introduces liquid crystal cells as side chains into the photosensitive resin structure, preparing a side-chain type liquid crystal photosensitive resin monomer for application in 3D printing. Compared with existing technologies, this invention has the following advantages:

[0023] 1. The side-chain liquid crystal structure is oriented under the action of 3D printing laser, forming a highly ordered crystalline structure. It exhibits good thermal conductivity in the orientation direction, which makes the 3D printed product have anisotropic thermal conductivity.

[0024] 2. The rigid liquid crystal cells endow the photosensitive resin with excellent mechanical properties and temperature resistance. Therefore, the side-chain type liquid crystal photosensitive resin monomer with light-emitting and thermally conductive anisotropic properties of the present invention exhibits good mechanical properties after 3D printing. Attached Figure Description

[0025] Figure 1 This is the 1H NMR spectrum of the chain-type liquid crystal photosensitive resin monomer of the present invention.

[0026] Figure 2 These are polarizing microscope (POM) images of the side-chain type liquid crystal photosensitive resin monomer of the present invention at different temperatures. Detailed Implementation

[0027] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0028] Example 1

[0029] 1 mol of 2,2-di(hydroxymethyl)propionic acid and 1.2 mol of 2,2-dimethoxypropane were dissolved in acetone by molar amounts. Then, 0.01 mol of p-toluenesulfonic acid was added to the solution, and the mixture was reacted at room temperature with stirring for 9 h. Next, 0.01 mol of triethylamine was added, and after reacting for 5 min, the acetone was removed by rotary evaporation. The residue was dissolved in dichloromethane, and the mixture was washed with Na₂CO₃ and distilled water, respectively. The organic phase was dried with anhydrous Na₂SO₄, and then the dichloromethane was removed by rotary evaporation to obtain hydroxyl-terminated 2,2-di(hydroxymethyl)propionic acid.

[0030] 1 mol of hydroxyl-terminated 2,2-di(hydroxymethyl)propionic acid and 1.1 mol of 4-phenylphenol were dissolved in tetrahydrofuran. The mixture was cooled to 0 °C, and a tetrahydrofuran solution containing 0.005 mol of dicyclohexylcarbodiimide and 0.005 mol of 4-dimethylaminopyridine was slowly added. The reaction was carried out with stirring for 12 h. The tetrahydrofuran and dicyclohexylcarbodiimide were removed by rotary evaporation. The residue was dissolved in dichloromethane, and the mixture was washed with NaHCO3 and distilled water, respectively. The organic phase was dried with anhydrous Na2SO4, and then the dichloromethane was removed by rotary evaporation to obtain a hydroxyl-terminated side-chain liquid crystal product.

[0031] One mol of hydroxyl-terminated side-chain liquid crystal was dissolved in methanol, and ion exchange resin AmberliteIR-120 was added. After reacting at room temperature for 12 h, the ion exchange resin was filtered, and methanol was removed by rotary evaporation to obtain the hydroxyl-terminated side-chain liquid crystal product.

[0032] 1 mol of the hydroxyl-terminated liquid crystal product was dissolved in tetrahydrofuran. 2.2 mol of isophorone diisocyanate and 0.001 mol of dibutyltin dilaurate catalyst were added to the solution. The mixture was reacted at 75 °C for 6 h. The tetrahydrofuran was removed by rotary evaporation to obtain a pale yellow viscous liquid. The obtained pale yellow viscous liquid was dissolved in ethyl acetate. 2.3 mol of hydroxyethyl methacrylate and 0.001 mol of dibutyltin dilaurate catalyst were added. The mixture was reacted at 90 °C for 6 h. The tetrahydrofuran was removed by rotary evaporation to obtain a pale yellow side-chain type liquid crystal photosensitive resin monomer.

[0033] By weight, 60 parts of side-chain liquid crystal photosensitive resin monomer, 40 parts of N,N-dimethylacrylamide, 4 parts of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 1 part of photoinitiator 1-hydroxycyclohexylphenyl ketone were stirred until the mixture became clear. The mixture was then poured into the resin tank of a photosensitive resin 3D printer for photocuring 3D printing. The wavelength of the light was 405 nm, and the illumination time was 9 seconds. Samples for thermal conductivity testing and mechanical properties were printed using both longitudinal and transverse methods.

[0034] Example 2

[0035] Side-chain type liquid crystal photosensitive resin monomers were prepared according to the method shown in Example 1.

[0036] By weight, 70 parts of side-chain liquid crystal photosensitive resin monomer, 30 parts of N,N-dimethylacrylamide, 4 parts of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 1 part of photoinitiator 1-hydroxycyclohexylphenyl ketone were stirred until the mixture became clear. The resulting clear mixture was then poured into the resin tank of a photosensitive resin 3D printer for photocuring 3D printing. The wavelength of the light was 405 nm, and the illumination time was 9 seconds. Samples for thermal conductivity testing and mechanical properties were printed using both longitudinal and transverse methods.

[0037] Example 3

[0038] The side-chain type liquid crystal photosensitive resin monomer was prepared according to the method shown in Example 1.

[0039] By weight, 80 parts of side-chain liquid crystal photosensitive resin monomer, 20 parts of N,N-dimethylacrylamide, 4 parts of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 1 part of photoinitiator 1-hydroxycyclohexylphenyl ketone were stirred until the mixture became clear. The mixture was then poured into the resin tank of a photosensitive resin 3D printer for photocuring 3D printing. The wavelength of the light was 405 nm, and the illumination time was 9 seconds. Samples for thermal conductivity testing and mechanical properties were printed using both longitudinal and transverse methods.

[0040] Example 4

[0041] Side-chain type liquid crystal photosensitive resin monomers were prepared according to the method shown in Example 1.

[0042] By weight, 90 parts of side-chain liquid crystal photosensitive resin monomer, 10 parts of N,N-dimethylacrylamide, 4 parts of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 1 part of photoinitiator 1-hydroxycyclohexylphenyl ketone were stirred until the mixture became clear. The mixture was then poured into the resin tank of a photosensitive resin 3D printer for photocuring 3D printing. The wavelength of the light was 405 nm, and the illumination time was 9 seconds. Samples for thermal conductivity testing and mechanical properties were printed using both longitudinal and transverse methods.

[0043] Comparative Example 1

[0044] By weight, 100 parts of bisphenol A epoxy resin, 3 parts of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 1 part of photoinitiator 1-hydroxycyclohexylphenyl ketone were stirred until the mixture became clear. The mixture was then poured into the resin tank of a photosensitive resin 3D printer for photocuring 3D printing. The wavelength of the light was preferably 405 nm, and the illumination time was 9 seconds. Samples for thermal conductivity testing and mechanical properties were printed using both longitudinal and transverse methods.

[0045] Comparative Example 2

[0046] By weight, 100 parts of commercially available acrylic photosensitive resin, 3 parts of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 1 part of photoinitiator 1-hydroxycyclohexylphenyl ketone were stirred until the mixture became clear. The mixture was then poured into the resin tank of a photosensitive resin 3D printer for photocuring 3D printing. The wavelength of the light was 405 nm, and the illumination time was 9 seconds. Samples for thermal conductivity testing and mechanical properties were printed using both longitudinal and transverse methods.

[0047] Following the national testing standard GB / T 1040.1-2018, corresponding tensile test specimens were printed using a Form 2 3D printer. Tensile tests were performed using an LD24 electronic universal testing machine; the loading rate during the tensile test was set to 10 mm / min. The thermal conductivity of the intrinsically high thermal conductivity liquid crystal photosensitive resin material was tested using a Xiangtan Xiangyi DRL-III thermal conductivity tester, in accordance with the internationally recognized thermal conductivity testing standard ASTM-D5470.

[0048] Table 1 Thermal conductivity and tensile strength of printed products

[0049]

[0050] As shown in Table 1, the thermal conductivity of the 3D photocurable product is improved with the introduction of side-chain liquid crystal structures. Specifically, the thermal conductivity in the thickness direction of the lateral printed product increases significantly with the increase in the content of side-chain liquid crystal structures. The lateral printed product in Example 4 has a thermal conductivity of 0.281 W / (m·K), which is about 50% higher than that of Comparative Examples 1 and 2 without side-chain liquid crystal structures. This is because the highly ordered arrangement of liquid crystal molecules during photocuring can form local crystalline structures, allowing heat flow to propagate along the ordered molecular chains and effectively suppressing phonon scattering, thereby greatly improving the thermal conductivity of the photosensitive resin. Simultaneously, it can be observed that the introduction of side-chain liquid crystal structures has a similar trend in the tensile strength of the 3D printed product, indicating the enhancing effect of the side-chain liquid crystal structures.

[0051] In summary, this invention prepares photosensitive resin monomers by introducing side-chain liquid crystal structures, and applies them to liquid photosensitive resin 3D printing. Due to the directional alignment of the side-chain liquid crystal structures under the action of laser in 3D printing, forming local crystalline structures, the 3D printed products have significantly improved thermal conductivity and tensile strength in the directions of these crystal orientations, and exhibit anisotropic characteristics.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A side-chain type liquid crystal photosensitive resin monomer with light-absorbing, thermally conductive, and anisotropic properties, characterized in that, Its structural formula is as follows:

2. The method for preparing a side-chain type liquid crystal photosensitive resin monomer with light-absorbing and thermally conductive anisotropic properties as described in claim 1, characterized in that, It includes the following steps: (1) Dissolve 2,2-di(hydroxymethyl)propionic acid and 2,2-dimethoxypropane in acetone, then add p-toluenesulfonic acid to the above solution. The resulting mixture is stirred at room temperature for 12-18 hours, then triethylamine is added and reacted for 5-10 minutes. Finally, acetone is removed by rotary evaporation at 75-85℃. The residue is dissolved in dichloromethane, and then the mixture is washed with Na2CO3 and distilled water respectively. The organic phase is dried with anhydrous Na2SO4, and then dichloromethane is removed by rotary evaporation to obtain product 1. (2) Dissolve product 1 and 4-phenylphenol in tetrahydrofuran to obtain a solution, cool to 0-5°C, dissolve dicyclohexylcarbodiimide and 4-dimethylaminopyridine in tetrahydrofuran and slowly add them to the above solution, react the resulting mixture with stirring for 12-18 h, then remove tetrahydrofuran by rotary evaporation, dissolve the obtained residue in dichloromethane, then wash the mixture with NaHCO3 and distilled water respectively, dry the organic phase with anhydrous Na2SO4, and then remove dichloromethane by rotary evaporation to obtain product 2; (3) Dissolve product 2 in methanol, add ion exchange resin, react at room temperature for 12-18 h, filter off the ion exchange resin, remove methanol by rotary evaporation, and obtain product 3. (4) The transparent liquid product 3 was diluted with tetrahydrofuran, isophorone diisocyanate was added, and dibutyltin dilaurate was added as a catalyst. The reaction was carried out at 75-85°C for 5-9 hours. The tetrahydrofuran was removed by rotary evaporation to obtain a liquid. The obtained liquid was dissolved in ethyl acetate, hydroxyethyl methacrylate was added, and dibutyltin dilaurate was added as a catalyst. The reaction was carried out at 85-95°C for 5-8 hours. The ethyl acetate solvent was removed by rotary evaporation to obtain a side-chain type liquid crystal photosensitive resin monomer.

3. The method for preparing a side-chain type liquid crystal photosensitive resin monomer with light-absorbing and thermally conductive anisotropic properties according to claim 2, characterized in that, The molar ratio of 2,2-bis(hydroxymethyl)propionic acid and 2,2-dimethoxypropane is 1:1 to 1.

5.

4. The method for preparing a side-chain type liquid crystal photosensitive resin monomer with light-absorbing and thermally conductive anisotropic properties according to claim 2, characterized in that, The molar ratio of product 1 to 4-phenylphenol is 1:1 to 1.

2.

5. The method for preparing a side-chain type liquid crystal photosensitive resin monomer with light-absorbing and thermally conductive anisotropic properties according to claim 2, characterized in that, The molar ratio of product 2 to ion exchange resin is 1:1 to 1.

2.

6. The method for preparing a side-chain type liquid crystal photosensitive resin monomer with light-absorbing and thermally conductive anisotropic properties according to claim 2, characterized in that, The molar ratio of product 3, isophorone diisocyanate, and hydroxyethyl methacrylate is 1:2-2.4:2-2.

4.

7. An intrinsically high thermal conductivity liquid crystal photosensitive resin material, characterized in that, It is composed of the following raw materials in parts by weight: The structural formula of the side-chain type liquid crystal photosensitive resin monomer is as follows:

8. The application of an intrinsically high thermal conductivity liquid crystal photosensitive resin material as described in claim 7 in 3D printing, characterized in that, N,N-dimethylacrylamide and side-chain liquid crystal photosensitive resin monomers were mixed evenly under high-speed stirring. Then, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone were added and stirred until the mixture was clear. The mixture was then poured into the resin tank of a photosensitive resin 3D printer for photocuring 3D printing.

9. The application according to claim 8, characterized in that, The wavelength of light used in the photopolymerization 3D printing process is 405nm, and the illumination time is 6-12s.

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