3D printing structural color ink, and preparation method and application thereof

Abstract

The application discloses 3D printing structural color ink and a preparation method and application thereof, and relates to the field of 3D printing ink. The ink comprises a prepolymer and an organic solvent B in a mass ratio of 100:(9-15), and the prepolymer comprises an acrylate nematic liquid crystal monomer, a chiral dopant, a chain extender, a photoinitiator and a catalyst. The 3D printing structural color ink of the application has proper rheological properties and shear thinning characteristics by introducing the volatile organic solvent B, is suitable for extrusion type 3D printing technology, has high printing precision, has a large available resolution range, and the obtained formed part has excellent mechanical properties and bright angle-dependent structural color; the color can be adjusted by the content of the chiral dopant, and the 3D printing structural color ink can be used in the fields of multi-color printing, information storage and bionic coating, etc.

Description

Technical Field

[0001] This invention relates to the field of 3D printing inks, and more particularly to a 3D printing structural color ink, its preparation method, and its application. Background Technology

[0002] Color plays an indispensable role in both nature and human society. It can originate from the selective absorption of light by dye molecules or the selective reflection of light by micro / nano structures. Structural coloring, exemplified by chameleons, butterfly wings, and bird feathers, utilizes the photonic band gap generated by Bragg scattering of light in periodic nanostructures, rather than relying on the chemical properties of individual pigment molecules. Inspired by plants and animals in nature, researchers have developed various artificial coloring methods based on ordered nanostructures to present more stable, durable, and customizable structural colors, which are applied in fields such as anti-counterfeiting labels, color printing, pattern encryption, and visual sensing. Based on the artificial nanostructures used, commonly used structural color materials can be classified into the following categories: 1) self-assembled colloidal crystals; 2) cholesteric liquid crystals; 3) gratings; and 4) block copolymers.

[0003] Existing structural color manufacturing methods often rely on templates formed by the self-assembly of nanomaterials, resulting in planar and simplified structures that are not conducive to further applications. 3D printing technology is a bottom-up, layer-by-layer deposition method that uses a discrete-stacking process to accumulate materials point-by-point and layer-by-layer to form a three-dimensional solid structure. Currently, extrusion-based structural color 3D printing based on bottle-brush block copolymers and colloidal crystal inks has been achieved, and grating structures have also been printed using high-resolution two-photon printing technology. Recently, cholesteric liquid crystal elastomers have been successfully printed using heated nozzles, and their optical properties have been programmable by adjusting the printing direction, printing speed, and substrate temperature, further expanding the application range of cholesteric liquid crystal elastomers. However, due to limitations in equipment requirements and ink performance, the manufacture of small-sized, high-precision, and high-mechanical-performance structural color materials remains a significant challenge. Summary of the Invention

[0004] This invention provides a 3D printing structural color ink, its preparation method, and its application, to solve the problems of poor precision and low mechanical properties of cholesteric liquid crystal elastomer inks in 3D printing. The ink has good rheological properties and obvious shear thinning behavior, making it suitable for high-precision 3D printing equipment. The resulting molded parts have excellent mechanical properties and bright angle-dependent structural colors.

[0005] To address the aforementioned technical problems, one objective of this invention is to provide a 3D printing structural color ink, comprising a prepolymer and an organic solvent B in a mass ratio of 100:(9-15). The prepolymer comprises an acrylate-based nematic liquid crystal monomer, a chiral dopant, a chain extender, a photoinitiator, a catalyst, and an organic solvent A.

[0006] As a preferred embodiment, the mass ratio of the acrylate-based nematic liquid crystal monomer to the chiral dopant is 100:(4.5-7.5).

[0007] By adopting the above scheme, the content of chiral dopant can determine the color of the 3D printing structural color ink after curing. By continuously changing the amount of chiral dopant within the above ratio range, the color of the 3D printing structural color ink after curing can cover the entire visible light band.

[0008] As a preferred embodiment, the mass ratio of the acrylate nematic liquid crystal monomer to the chain extender is 100:(20-35), preferably 100:(23-35).

[0009] By adopting the above scheme, the addition of chain extender is beneficial to improving the flexibility of 3D printing structural color ink after curing. Limiting the above proportion of chain extender can effectively improve tensile strength and elongation at break, so that the model has both strength and flexibility.

[0010] As a preferred embodiment, the mass ratio of the acrylate nematic liquid crystal monomer to the photoinitiator is 100:(0.5-1.5); the catalyst accounts for 5wt%-20wt% of the total volume of the prepolymer system.

[0011] By adopting the above scheme and the limited photoinitiator addition ratio, the rapid curing of the 3D printed sample can be guaranteed, while avoiding yellowing of the sample and affecting the structural color effect; the added catalyst can ensure that the prepolymer can be synthesized at room temperature without heating, avoiding uncontrolled thermal polymerization of monomers caused by heating.

[0012] As a preferred option, at least one of the following a)-f) is satisfied:

[0013] a) The nematic liquid crystal monomer of the acrylate class is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene and / or 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, and the structural formula of the 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene is: The structural formula of the 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene is:

[0014] b) The chiral dopant is (3R,3aR,6S,6aR)-hexahydrofurano[3,2-b]furan-3,6-dimethylbis(4-((4-((((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoate), and its structural formula is:

[0015] c) The chain extender is a thiol and / or amine chain extender, which has better compatibility with nematic liquid crystal monomers of acrylates;

[0016] d) The photoinitiator is an oil-soluble photoinitiator, which has better compatibility with acrylate-based nematic liquid crystal monomers;

[0017] e) Organic solvent A and organic solvent B are each independently selected from at least one of dichloromethane, toluene, and acetone;

[0018] f) The catalyst is triethylamine.

[0019] As a preferred embodiment, the chain extender is 3,6-dioxa-1,8-octanedithiol and / or n-butylamine; the photoinitiator is at least one of 2,2-dimethoxy-2-phenylacetophenone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, and α-hydroxyisobutyroxene.

[0020] To address the aforementioned technical problems, a second objective of this invention is to provide a method for preparing 3D printing structural color ink, comprising the following steps:

[0021] (1) Add nematic liquid crystal monomer, chiral dopant, chain extender and photoinitiator to sample vial, add organic solvent A, and stir magnetically at room temperature to mix the mixture evenly to form a transparent precursor solution.

[0022] (2) Add a catalyst to the above precursor solution and carry out the Michael addition reaction at room temperature while stirring.

[0023] (3) Wash the above solution with dilute hydrochloric acid, extract it with organic solvent A, wash it with water and saturated brine, dry it with anhydrous sodium sulfate, and finally heat the solution to remove organic solvent A to obtain the prepolymer.

[0024] (4) Weigh the prepolymer and place it in a sample bottle. Add organic solvent B, mix it evenly and remove the air bubbles to obtain 3D printing structural color ink.

[0025] As a preferred embodiment, in step (1), the amount of organic solvent A added accounts for 50 wt% or more of the transparent precursor solution.

[0026] As a preferred option, in step (2), the Michael addition reaction temperature is 20-30℃ and the reaction time is 12-48h.

[0027] To address the aforementioned technical problems, a third objective of this invention is to provide an application of 3D printing structural color ink in the fields of 3D printing, multicolor printing, information storage, or biomimetic coatings.

[0028] As a preferred option, additive manufacturing using 3D printing equipment is employed when preparing 3D structural color models.

[0029] As a preferred embodiment, the additive manufacturing method is an ink-direct writing 3D printing system. Ink-direct writing printing is a 3D printing or additive manufacturing technology based on viscoelastic ink extrusion and deposition. It requires ink to have shear-thinning properties, a wide range of usable materials, and a wide range of usable resolutions. It can perform planar printing as well as printing of multi-material, multi-layer, and multi-dimensional three-dimensional structures.

[0030] As a preferred option, the distribution pressure is 175kPa-1050kPa, the printing speed is 0.5mm / s-4mm / s, and the needle diameter is 0.025mm-0.41mm.

[0031] As a preferred option, the pressure distributed during 3D printing of 3D structural color models is 525kPa-1050kPa.

[0032] As a preferred option, the printed model is evaporated to remove organic solvent B and then cured under 365nm ultraviolet light for 5-30 minutes.

[0033] As a preferred option, the printed model is evaporated at 60°C or room temperature to remove organic solvent B for 2-8 hours.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The 3D printing structural color ink of this application firstly synthesizes oligomers by Michael addition of nematic liquid crystal monomers, chiral dopants, and chain extenders in a solvent via a catalyst. This aims to extend the chains of liquid crystal molecules to improve the elasticity and flexibility of the final product. Subsequently, a very small amount of volatile organic solvent B is introduced to reduce the viscosity of the oligomers while maintaining shape retention, thus assisting the self-assembly of liquid crystal molecules. This results in the 3D printing structural color ink having appropriate rheological properties and shear thinning characteristics, making it suitable for extrusion 3D printing technology. It offers high printing precision, a wide range of usable resolutions, and produces parts with excellent mechanical properties and vibrant angle-dependent structural colors, while effectively avoiding needle clogging during printing. The color of this 3D printing structural color ink can be adjusted by the content of the chiral dopant, and it can also be used in multicolor printing, information storage, and biomimetic coatings.

[0036] (2) The introduction of volatile organic solvent B allows 3D printing structural color inks to be printed at room temperature, avoiding the loss of printing accuracy and uniformity caused by using heating equipment.

[0037] (3) After printing, the capillary force during the evaporation of organic solvent helps to induce the self-assembly of liquid crystal molecules and obtain a higher degree of orientation. Attached Figure Description

[0038] Figure 1 : The viscosity of the 3D printing structural color ink prepared in Examples 1, 10 and Comparative Examples 1-2 of this invention is shown as a function of shear rate.

[0039] Figure 2 : Optical microscope observation results of filaments printed with the 3D printing structural color ink prepared in Example 1 of the present invention at different printing pressures and speeds;

[0040] Figure 3 The visible light reflectance spectrum of the 3D printing structural color ink prepared in Examples 1-5 of this invention after 3D printing and curing.

[0041] Figure 4 : The uniaxial tensile stress-strain curve of the sample after 3D printing curing of the 3D printing structural color ink prepared in Example 1 of the present invention;

[0042] Figure 5 The part is a 3D printed structural color ink prepared in Example 1 of the present invention after being cured by 3D printing. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Table 1 below shows the sources of raw materials in the embodiments and comparative examples of this application. Unless otherwise specified, the nematic liquid crystal monomers, chiral dopants, chain extenders and photoinitiators are all obtained commercially, and the same nematic liquid crystal monomers, chiral dopants, chain extenders and photoinitiators are used in parallel experiments.

[0045] Table 1 - Sources and types of raw materials used in the embodiments and comparative examples of this application

[0046]

[0047] Examples 1-7

[0048] A 3D printing structural color ink, the components and contents of which are shown in Table 2 below, includes a prepolymer with a mass ratio of 100:9 and an organic solvent B dichloromethane. The prepolymer includes an acrylate-based nematic liquid crystal monomer RM257, a chiral dopant LC756, a chain extender, an oil-soluble photoinitiator I-651, and a catalyst triethylamine. Its preparation method includes the following steps:

[0049] (1) Add nematic liquid crystal monomer RM 257, chiral dopant LC 756, chain extender and photoinitiator I-651 to a 20mL sample bottle, add 8mL of organic solvent A dichloromethane, and stir magnetically at room temperature for 10min to mix the mixture evenly and form a transparent precursor solution.

[0050] (2) Add the catalyst triethylamine to the above precursor solution and keep stirring to react at room temperature for 24 h;

[0051] (3) The above solution was washed with dilute hydrochloric acid, then extracted with organic solvent A dichloromethane, then washed with distilled water and saturated brine, and dried with anhydrous sodium sulfate. Finally, the solution was dried at 60°C to remove dichloromethane and obtain the prepolymer.

[0052] (4) Weigh 2g of prepolymer into a 10mL sample bottle, add 0.18g of organic solvent B dichloromethane, mix it evenly and remove bubbles using a mixer. Set the parameters as follows: mixing mode 5min, debubbling mode 1min, repeat mixing three times to obtain 3D printing structural color ink.

[0053] Table 2 - Components and content of prepolymer in step (3) of 3D printing structural color ink in Examples 1-7 of this application

[0054]

[0055]

[0056] Example 8

[0057] A 3D printing structural color ink, the preparation method and the processes and reagents used in each step are the same as those in Example 1, the difference being that the amount of chain extender added is 0.766g.

[0058] Example 9

[0059] A 3D printing structural color ink, the preparation method and the processes and reagents used in each step are the same as those in Example 1, the difference being that the amount of chain extender added is 0.51g.

[0060] Example 10

[0061] A 3D printing structural color ink, the preparation method and the processes and reagents used in each step are the same as those in Example 1. The difference is that in step (4), the amount of dichloromethane added is 0.3g.

[0062] Comparative Example 1

[0063] A 3D printing structural color ink, the preparation method and the processes and reagents used in each step are the same as those in Example 1. The difference is that in step (4), 2g of prepolymer is weighed and placed in a 10mL sample bottle, and the air bubbles are removed using a mixer. The parameters are set as follows: degassing mode for 1min, repeated three times, to obtain the 3D printing structural color ink.

[0064] Comparative Example 2

[0065] A 3D printing structural color ink, the preparation method and the processes and reagents used in each step are the same as those in Example 1. The difference is that in step (4), the amount of dichloromethane added is 0.12g.

[0066] Comparative Example 3

[0067] A 3D printing structural color ink, the preparation method and the processes and reagents used in each step are the same as those in Example 1, the difference being that the nematic liquid crystal monomer RM257 is replaced by 4'-pentyl-4-biphenylacetonitrile.

[0068] Comparative Example 4

[0069] A 3D printing structural color ink, the preparation method and the processes and reagents used in each step are the same as those in Example 1, the difference being that the amount of chain extender added is 0.

[0070] Performance testing

[0071] 1. Rheological property testing: The rheological properties of the 3D printing structural color inks prepared in Examples 1 and 10 and Comparative Examples 1 and 2 were tested using a rotational rheometer (MCR 302, Anton Paar). All samples were tested on a 25mm diameter plate, and the test temperature was maintained at 25±0.3℃. The ink temperature range was 0.001-1000s. -1 Steady-state rheological experiments were conducted within the range of shear rates to obtain the relationship between apparent viscosity and shear rate; at low shear rates, i.e., less than or equal to 10 s⁻¹, the relationship between apparent viscosity and shear rate was obtained. - 1. For 3D printing, the structural ink should have a high viscosity (10-1000 Pa·s) to ensure that the printed sample does not deform; and at high shear rates, i.e., greater than or equal to 100 s. -1The ink should have a low viscosity (<1 Pa·s) to facilitate extrusion through the needle. This low shear rate simulates the ink under natural conditions, while the high shear rate simulates the ink passing through a microneedle. The results are as follows: Figure 1 As shown in Table 3.

[0072] 2. Printability Analysis: The 3D printing structural ink prepared in Example 1 was transferred from the sample vial to a 3cc syringe. The syringe was sealed, and the ink was placed in a mixer for degassing for 30 seconds. Then, filament printing was performed. The structural ink was printed onto a clean glass slide using a 100μm needle. The printing pressure was 175-1050 kPa, and the printing speed was 0.5-4 mm / s. After printing, the sample was transferred to a 60℃ oven to remove organic solvents, and then cured under a 365nm UV curing lamp for 10 minutes to obtain the molded part. Images of the filaments obtained at different printing pressures and speeds were photographed using an optical microscope, and the linewidth was measured. The results are as follows: Figure 2 As shown.

[0073] 3. Visible Light Reflectance Spectroscopy Test: The 3D printing structural color inks prepared in Examples 1-5 were used to obtain 3D printed parts. Visible light reflectance spectra were then measured using a fiber optic spectrometer (DH-2000-BAL, Ocean Optics). The results are as follows: Figure 3 As shown.

[0074] 4. Tensile Performance Test: Using the 3D printing structural color inks from the examples and comparative examples, strip samples of 10mm × 20mm × 0.4mm were printed. After printing and curing, the samples were subjected to tensile performance tests on a universal testing machine (HZ1004B, Dongguan Lixian) to obtain the elongation at break and tensile strength. The samples were subjected to uniaxial tension along the long side at a tensile speed of 10mm / min. The results of Example 1 are as follows. Figure 4 As shown, the results of Examples 1-10 and Comparative Examples 3-4 are shown in Table 3 below.

[0075] Depend on Figure 1 It can be seen that as the shear rate increases from 10... -2 Increase to 10 3 s -1 All inks exhibited significant shear thinning. The apparent viscosity of Example 1 decreased from 758.86 Pa·s to 0.015 Pa·s, indicating a moderate viscosity suitable for ink-to-ink 3D printing and beneficial for improving printing accuracy. Comparative Example 1, at both low and high shear rates, showed solvent-free oligomers with viscosity reductions of 2.8 × 10⁻⁶ Pa·s. 4The high viscosity at Pa·s and 1.7 Pa·s, although with a higher initial viscosity, resulted in significant viscosity fluctuations at high shear rates. This may be due to uneven mixing caused by the reduction of solvent, which is not conducive to high-quality printing. This indicates that the addition of dichloromethane significantly reduces the viscosity of the system. At high shear rates, the viscosity of ink containing dichloromethane is reduced by 2-3 orders of magnitude compared to ink containing only oligomers. This is beneficial in preventing needle clogging when using small-sized extrusion needles.

[0076] Depend on Figure 2 It can be seen that the 3D printing structural color ink prepared in Example 1 has good printability. When the dispensing pressure is 525-1050 kPa and the printing speed is 0.5-4 mm / s, the printed filaments are straight with smooth edges, and their diameter is adjustable over a wide range, indicating that this 3D printing structural color ink has a large usable resolution range. Specifically, when the dispensing pressure is 525 kPa and the printing speed is 3 mm / s, the diameter of the printed filament is closest to the diameter of the needle tip, exhibiting good printing accuracy.

[0077] Depend on Figure 3 As can be seen, with the increase of the chiral dopant content in Examples 1-5, the wavelength of the reflection peak in the reflection spectrum of the molded parts shifts towards shorter wavelengths. The reflection peak wavelength of molded part 1 is 634.06 nm, exhibiting red; the reflection peak wavelength of molded part 2 is 577.66 nm, exhibiting yellow; the reflection peak wavelength of molded part 3 is 534.27 nm, exhibiting cyan; the reflection peak wavelength of molded part 4 is 495.77 nm, exhibiting blue; and the reflection peak wavelength of molded part 5 is 434.5 nm, exhibiting purple. By continuously changing the amount of chiral dopant, the color of the cured 3D printing structural color ink can cover the entire visible light band.

[0078] Table 3 - Tensile properties of 3D printed structural color ink-molded parts in the examples and comparative examples

[0079]

[0080]

[0081] Depend on Figure 4 It can be seen that the 3D printing structural color ink prepared in Example 1, after being thermocured, has an elongation at break of 223.5%, a tensile strength of 8.04 MPa, and a tensile Young's modulus of 5.202 MPa. Combined with the test results of Examples 1-10 in Table 3, it can be seen that the 3D printing structural color ink prepared in this example has outstanding mechanical properties after printing-curing treatment.

[0082] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A 3D printing structural color ink, characterized in that, It includes a prepolymer in a mass ratio of 100:(9-15) and an organic solvent B, wherein the raw materials of the prepolymer include nematic liquid crystal monomers of acrylate, chiral dopants, chain extenders, photoinitiators, catalysts and organic solvent A; The acrylate-based nematic liquid crystal monomer is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene and / or 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene; The chiral dopant is (3R,3aR,6S,6aR)-hexahydrofurano[3,2-b]furan-3,6-dimethylbis(4-((4-((((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoate); The chain extender is a thiol chain extender.

2. The 3D printing structural color ink as described in claim 1, characterized in that, The mass ratio of the acrylate-based nematic liquid crystal monomer to the chiral dopant is 100:(4.5-7.5).

3. The 3D printing structural color ink as described in claim 1, characterized in that, The mass ratio of the acrylate-based nematic liquid crystal monomer to the chain extender is 100:(20-35).

4. The 3D printing structural color ink as described in claim 1, characterized in that, The mass ratio of the acrylate-based nematic liquid crystal monomer to the photoinitiator is 100:(0.5-1.5); the catalyst accounts for 5wt%-20wt% of the total volume of the prepolymer system.

5. A 3D printing structural color ink as described in claim 1, characterized in that, Satisfying at least one of the following a)-c): a) The photoinitiator is an oil-soluble photoinitiator; b) Organic solvent A and organic solvent B are each independently selected from at least one of dichloromethane, toluene, and acetone; c) The catalyst is triethylamine.

6. The 3D printing structural color ink as described in claim 5, characterized in that, The chain extender is 3,6-dioxa-1,8-octanedithiol; the photoinitiator is at least one of 2,2-dimethoxy-2-phenylacetophenone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, and α-hydroxyisobutyroxene.

7. A method for preparing 3D printing structural color ink as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Add the nematic liquid crystal monomer, chiral dopant, chain extender and photoinitiator to the sample vial, add organic solvent A, and stir magnetically at room temperature to mix the mixture evenly to form a transparent precursor solution; (2) Add the catalyst to the above precursor solution and carry out the Michael addition reaction at room temperature while stirring; (3) Wash the above solution with dilute hydrochloric acid, extract it with organic solvent A, wash it with water and saturated saline, dry it with anhydrous sodium sulfate, and finally heat the solution to remove organic solvent A to obtain the prepolymer. (4) Weigh the prepolymer and place it in a sample bottle. Add organic solvent B, mix it evenly and remove the air bubbles to obtain 3D printing structural color ink.

8. The method for preparing a 3D printing structural color ink as described in claim 7, characterized in that, In step (2), the Michael addition reaction temperature is 20-30℃ and the reaction time is 12-48h.

9. The application of a 3D printing structural color ink as described in any one of claims 1-8 in the fields of 3D printing, multicolor printing, information storage, or biomimetic coating.

10. The application of the 3D printing structural color ink as described in claim 9 in the fields of 3D printing, multicolor printing, information storage, or biomimetic coatings, characterized in that... When preparing 3D structural color models by 3D printing, the pressure is distributed at 175 kPa-1050 kPa, the printing speed is 0.5 mm / s to 4 mm / s, and the needle diameter is 0.025 mm to 0.41 mm. After printing, the model is evaporated to remove organic solvent B and cured under 365 nm ultraviolet light for 5-30 minutes.

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