Preparation method of lignin carbon quantum dot luminescent ink, ink and application thereof

Abstract

This invention discloses a method for preparing lignin-carbon quantum dot luminescent ink, the ink itself, and its applications. This ink possesses excellent fluorescence properties, printability, and environmental friendliness. 0.07-0.15 parts by weight of lignin and 0.4-0.8 parts by weight of ethylenediamine are dissolved in 10-15 parts by weight of deionized water. After stirring and ultrasonic dispersion, the mixture is subjected to a hydrothermal reaction at 140-160°C for 6-8 hours. After cooling, the supernatant is collected to obtain a lignin-carbon quantum dot (LCQD) dispersion. This dispersion is mixed with an aqueous photocurable resin and a photoinitiator, stirred until homogeneous, and the viscosity is adjusted to obtain a photocurable 3D-printable luminescent ink. After being printed using digital light processing (DLP) or other photocurable 3D printing technologies, this ink can produce complex decorative logos with stable luminescence effects. Under ultraviolet light excitation, it exhibits bright blue fluorescence and has application potential in personalized decoration, smart signage, and artistic design.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of functional nanomaterials and advanced manufacturing technology. Specifically, it is a lignin carbon quantum dot luminescent ink, an ink preparation method, and the application of the ink in the manufacture of personalized and intelligent 3D printed luminescent decorative signage products. Background Technology

[0002] Decorative signage is widely used in commercial spaces, cultural venues, and home environments, with its materials and forms increasingly pursuing personalization, artistry, and intelligence. Traditional signage manufacturing processes (such as engraving and spraying) have limitations in achieving complex three-dimensional structures, dynamic lighting effects, and rapid customization. 3D printing technology, especially photopolymer 3D printing, provides a revolutionary means for the free forming of complex structures. However, current resin materials available for photopolymer 3D printing are functionally limited and lack built-in, stable optical functions, such as self-illuminating properties.

[0003] Carbon quantum dots (CQDs), as an emerging carbon-based fluorescent nanomaterial, possess advantages such as tunable emission color, good biocompatibility, and wide availability of raw materials. Currently, research on CQDs is largely focused on fields such as sensing and bioimaging; research on their deep integration as functional fillers with 3D printing technology for the direct manufacture of end-product decorative materials with bulk luminescence properties is still insufficient. Furthermore, the preparation of most CQDs relies on refined chemicals, resulting in high costs and environmental concerns.

[0004] Lignin is the most abundant renewable aromatic polymer in nature, mainly derived from a byproduct of the paper industry, and is often treated as waste. Using lignin as a carbon source to prepare carbon quantum dots can achieve high-value utilization of waste biomass, aligning with the concept of green and sustainable development. However, how to stably and efficiently integrate lignin carbon quantum dots (LCQDs) into a photopolymerization 3D printing system and realize their aesthetic and functional expression in decorative signage remains a pressing technical problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a lignin-carbon quantum dot luminescent ink and its preparation method that are made from environmentally friendly raw materials, are low in cost, have a simple and efficient process, and exhibit excellent performance. Another objective of this invention is to provide a successful application solution for the above-mentioned ink in photopolymerization 3D printing technology, particularly for integrated, direct molding of decorative signage products with complex three-dimensional structures and stable self-luminescence, thereby providing innovative material and manufacturing solutions for personalized decoration, smart signage, and artistic design.

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

[0007] A lignin-carbon quantum dot luminescent ink is composed of a lignin-carbon quantum dot (LCQD) dispersion, an aqueous photocurable resin, and a photoinitiator, wherein the weight ratio of each component is as follows:

[0008] 8-12 parts of the lignin carbon quantum dot (LCQD) dispersion;

[0009] 86-90 parts of water-based UV-curable resin;

[0010] Photoinitiator 1.5-3.5 parts;

[0011] The lignin carbon quantum dot (LCQDs) dispersion is prepared by hydrothermal reaction of the following raw materials in parts by weight: 0.07-0.15 parts alkali lignin, 0.4-0.8 parts ethylenediamine, and 10-15 parts deionized water.

[0012] As a further improvement of the present invention, the photoinitiator is selected from at least one of Irgacure 819, TPO, or 1173. The viscosity of the ink can be adjusted to 500-2000 mPa·s by adding deionized water or a thickener to adapt to photopolymerization 3D printing equipment with different precision requirements.

[0013] To achieve the above-mentioned technical objectives, another technical solution adopted by the present invention is as follows:

[0014] A method for preparing a lignin-carbon quantum dot luminescent ink includes the following steps:

[0015] (1) Preparation of lignin carbon quantum dot (LCQD) dispersion: Weigh 0.07-0.15 parts of alkali lignin, 0.4-0.8 parts of ethylenediamine and 10-15 parts of deionized water according to the proportion, mix and stir and ultrasonically disperse to obtain a precursor mixture; place the precursor mixture in a closed reaction vessel and carry out hydrothermal reaction at 140-160℃ for 6-8 hours; after the reaction is completed, cool to room temperature, collect the supernatant by static precipitation or low-speed centrifugation to obtain lignin carbon quantum dot (LCQD) dispersion;

[0016] (2) Preparation of printing ink: Take 8-12 parts of the lignin carbon quantum dot (LCQD) dispersion obtained in step (1), 86-90 parts of water-based photocurable resin, and 1.5-3.5 parts of photoinitiator according to the proportion. First, mix the lignin carbon quantum dot (LCQD) dispersion with the water-based photocurable resin and stir thoroughly until uniform. Then, add the photoinitiator under light-protected conditions and continue stirring until completely uniform to obtain the lignin carbon quantum dot luminescent ink.

[0017] As a further improvement of the present invention, in step (1), the hydrothermal reaction is carried out at 150°C for 7 hours.

[0018] As a further improved technical solution of the present invention, in step (2), the weight ratio of the lignin carbon quantum dot (LCQD) dispersion, the aqueous photocurable resin and the photoinitiator is 10:88:2.

[0019] As a further improvement of the present invention, step (2) further includes: adjusting the viscosity of the ink to 500-2000 mPa·s by adding deionized water or a thickener.

[0020] The core of this invention lies in the direct preparation of fluorescent carbon quantum dots from lignin using a hydrothermal method. The resulting dispersion is then directly compounded with commercially available photocurable resin without complex purification treatment to form a "ready-to-use" functional printing ink. This ink system is stable and can be rapidly cured under ultraviolet light. Furthermore, the cured product emits strong blue fluorescence when excited by light of a specific wavelength (such as 365 nm ultraviolet light).

[0021] To achieve the above-mentioned technical objectives, another technical solution adopted by the present invention is as follows:

[0022] An application of a lignin-carbon quantum dot luminescent ink, or a lignin-carbon quantum dot luminescent ink prepared by the aforementioned method, in the fabrication of 3D printed luminescent decorative signs. This ink is suitable for photopolymerization 3D printing processes such as DLP and SLA, and can precisely manufacture entities with complex geometric shapes and fine surface textures. The printed signs exhibit the original color of the substrate or a semi-transparent effect under natural light, while displaying a preset luminescent pattern and effect under ultraviolet light excitation in a dark environment, thus creating a unique visual experience and interactive possibilities.

[0023] As a further improvement of the present invention, the 3D printing is a photopolymerization-based printing process, specifically a digital light processing (DLP) or stereolithography (SLA) process; during the printing process, the recommended process parameters are: a printing layer thickness of 0.05-0.1 mm and an exposure time of 5-15 seconds per layer.

[0024] To achieve the above-mentioned technical objectives, another technical solution adopted by the present invention is as follows:

[0025] A method for preparing a 3D printed luminous decorative sign includes the following steps:

[0026] Provide lignin-carbon quantum dot luminescent ink, or lignin-carbon quantum dot luminescent ink prepared according to the preparation method, as a printing material;

[0027] Based on the three-dimensional digital model of the target decorative mark, a photopolymer 3D printer is used to print and cure the ink layer by layer.

[0028] After printing, the molded product is cleaned and post-cured to obtain the luminous decorative logo.

[0029] As a further improvement of the present invention, the post-curing process involves irradiating the product with an ultraviolet light source of wavelength 365-405 nm for 5-15 minutes to obtain a final decorative signage product with a complete structure and stable luminescent performance.

[0030] The beneficial effects of this invention are as follows:

[0031] Using lignin, a waste product from papermaking, as the main raw material, this invention achieves high-value utilization of biomass resources, reduces raw material costs, and is environmentally friendly throughout the entire preparation process. A short-process strategy of "hydrothermal synthesis - purification-free - direct compounding" is adopted. This eliminates time-consuming steps such as traditional dialysis and freeze-drying of carbon quantum dots, avoids agglomeration problems that may occur during drying, simplifies the conversion path from material to application product, and improves efficiency. The invention successfully combines the fluorescent properties of lignin carbon quantum dots with the molding freedom of 3D printing, enabling the integrated manufacture of decorative signs with complex internal or surface luminescent structures that are difficult to achieve with traditional processes, exhibiting uniform and stable luminous efficacy. The luminescent decorative signs obtained by this invention can be widely used in brand display, spatial decoration, art installations, luminous indicators, personalized gifts, and other fields, providing designers and manufacturers with a new material and means of expression that combines artistic value and practical function.

[0032] Compared with existing technologies, the core advantage of this invention lies in its first-ever construction of a complete and short-process technology chain encompassing "biomass waste resource utilization—green preparation of nano-fluorescent materials—integrated digital functional structure molding." Specifically, existing research either focuses on the synthesis and properties of carbon quantum dots or is limited to the development of general-purpose 3D printing materials, often resulting in a disconnect between the two. This invention, however, creatively uses lignin, a byproduct of the papermaking industry, as the sole carbon source, directly preparing carbon quantum dots with stable fluorescence via a one-step hydrothermal method. Furthermore, it innovatively employs a "purification-free" strategy, efficiently compounding the original solution with photocurable resin to successfully develop luminescent inks that can be directly used in high-precision photocurable 3D printing. This not only upgrades waste biomass into high-value-added functional materials but also bypasses the cumbersome and energy-intensive separation and drying process that traditional nanomaterials must undergo before application, thus ensuring the greenness and economy of the material at the source and simplifying and improving the process. Ultimately, this technology makes it possible to obtain customized decorative signs with complex structures and built-in uniform and stable light emission functions through a single printing job. It solves the technical bottleneck of traditional decorative processes that make it difficult to deeply integrate light emission functions with complex three-dimensional forms, and provides a brand-new material solution and design freedom for the fields of smart home, personalized display and interactive design. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the preparation process of the lignin-carbon quantum dot luminescent ink of this invention and its application in 3D printing. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0035] Example of LCQDs dispersion preparation:

[0036] Example D1:

[0037] Weigh 0.07 g of alkali lignin, 0.40 g of EDA, and 10.0 g of deionized water. After magnetic stirring for 30 minutes and ultrasonic treatment for 30 minutes, the mixture is transferred to a 50 mL high-pressure reactor and hydrothermally reacted at 140 °C for 6 hours. After cooling to room temperature and standing, the supernatant is collected to obtain a lignin carbon quantum dot (LCQD) dispersion.

[0038] Example D2:

[0039] Weigh 0.15 g of alkali lignin, 0.80 g of EDA, and 15.0 g of deionized water. After magnetic stirring for 30 minutes and ultrasonic treatment for 30 minutes, the mixture is transferred to a 50 mL high-pressure reactor and hydrothermally reacted at 160 °C for 8 hours. After cooling to room temperature and standing, the supernatant is collected to obtain a lignin carbon quantum dot (LCQD) dispersion.

[0040] Example D3:

[0041] Weigh 0.10 g of alkali lignin, 0.60 g of EDA, and 12.0 g of deionized water. After magnetic stirring for 30 minutes and ultrasonic treatment for 30 minutes, the mixture is transferred to a 50 mL high-pressure reactor and hydrothermally reacted at 150 °C for 7 hours. After cooling to room temperature and standing, the supernatant is collected to obtain a lignin carbon quantum dot (LCQD) dispersion.

[0042] Example of printing ink formulation:

[0043] Example I1:

[0044] Take 8 g of LCQDs dispersion, 90 g of aqueous photocurable resin, and 2.0 g of photoinitiator Irgacure 819. First, mix the dispersion and resin and stir for 30 minutes, then add the photoinitiator and stir for 60 minutes in the dark to obtain the ink.

[0045] Example I2:

[0046] Take 12 g of LCQDs dispersion, 86 g of aqueous photocurable resin, and 2.0 g of photoinitiator Irgacure 819. First, mix the dispersion and resin and stir for 30 minutes, then add the photoinitiator and stir for 60 minutes in the dark to obtain the ink.

[0047] Example I3:

[0048] Take 10 g of LCQDs dispersion, 88 g of aqueous photocurable resin, and 2.0 g of photoinitiator Irgacure 819. First, mix the dispersion and resin and stir for 30 minutes, then add the photoinitiator and stir for 60 minutes in the dark to obtain the ink.

[0049] Example I4:

[0050] Take 10 g of LCQDs dispersion, 88 g of resin, and 1.5 g of photoinitiator Irgacure 819. First, mix the dispersion and resin and stir for 30 minutes, then add the photoinitiator and stir for 60 minutes in the dark to obtain the ink.

[0051] Example I5:

[0052] Take 10 g of LCQDs dispersion, 88 g of resin, and 3.5 g of photoinitiator TPO. First, mix the dispersion and resin and stir for 30 minutes, then add the photoinitiator and stir for 60 minutes in the dark to obtain the ink.

[0053] Example of printing parameters:

[0054] Example P1:

[0055] Using the ink prepared in one of the above embodiments, a DLP printer was used to print standard test strips and identification samples with a layer thickness of 0.05 mm and an exposure time of 15 seconds per layer.

[0056] Example P2:

[0057] The ink prepared using one of the above embodiments had a layer thickness of 0.10 mm and an exposure time of 5 seconds per layer. Standard test strips and marking samples were printed using a DLP photopolymerization 3D printer.

[0058] Example P3:

[0059] The ink prepared using one of the above embodiments had a layer thickness of 0.075 mm and an exposure time of 10 seconds per layer. Standard test strips and label samples were printed using a DLP photopolymerization 3D printer.

[0060] Combined Implementation Example:

[0061] Example 1:

[0062] Dispersion: D1 (0.07 g lignin), Ink: I1 (8 g LCQDs dispersion + 90 g aqueous photocurable resin + 2 g photoinitiator), Printing: P1 (0.05 mm, 15 seconds).

[0063] Example 2:

[0064] Dispersion: D2 (0.15 g lignin); Ink: I2 (12 g LCQDs dispersion + 86 g aqueous UV-curable resin + 2 g photoinitiator); Printing: P2 (0.10 mm, 5 seconds).

[0065] Example 3:

[0066] Dispersion: D3 (0.10 g lignin); Ink: I3 (10 g LCQDs dispersion + 88 g aqueous UV-curable resin + 2 g photoinitiator); Printing: P3 (0.075 mm, 10 seconds).

[0067] Example 4:

[0068] Dispersion: D3; Ink: I4 (10 g LCQDs dispersion + 88 g aqueous UV-curable resin + 1.5 g photoinitiator); Printing: P3 (0.075 mm, 10 seconds).

[0069] Example 5:

[0070] Dispersion: D3; Ink: I5 (10 g LCQDs dispersion + 88 g aqueous UV-curable resin + 3.5 g photoinitiator); Printing: P3 (0.075 mm, 8 seconds, adjusted for initiator activity).

[0071] Example 6:

[0072] Dispersion: D3; Ink: I3 (10 g LCQDs dispersion + 88 g aqueous UV-curable resin + 2 g photoinitiator); Printing: 0.05 mm, 8 seconds (between P1 and P3).

[0073] Example 7:

[0074] Dispersion: D3; Ink: I3 (10 g LCQDs dispersion + 88 g aqueous UV-curable resin + 2 g photoinitiator); Printing: 0.10 mm, 12 seconds (between P2 and P3).

[0075] Comparative Example 1 (pure resin):

[0076] 100g of the same water-based photocurable resin as in the example was used directly, and 2g of photoinitiator Irgacure 819 was added. After mixing evenly, 3D printing was performed under exactly the same parameters.

[0077] Performance testing:

[0078] The inks prepared in Examples 1-5 and Comparative Example 1 were printed into standard test strips (for mechanical testing) and flat samples of uniform size (for optical testing). Testing was conducted according to the following standards:

[0079] Fluorescence intensity: The maximum fluorescence emission peak intensity of the sample was measured using a fluorescence spectrophotometer at an excitation wavelength of 365 nm.

[0080] Printing accuracy: A high-precision 3D scanner is used to measure the deviation between the dimensions of the printed sample and the design model, and the average absolute error is taken.

[0081] Interlayer bonding / surface quality: Visually inspect the surface of the printed sample to see if it is smooth, whether there is delamination or defects, and rate it (Excellent / Good / Medium / Poor).

[0082] Impact toughness: The impact strength of the simply supported beam of the printed strip was tested according to GB / T 1843-2008 standard.

[0083] The test results are shown in Table 1 below.

[0084] Table 1 shows the test results:

[0085] sample Lignin (g) Dispersion (g) Initiator (g) Layer thickness (mm) Exposure (seconds) Fluorescence intensity (au) Printing size error (μm) Surface quality Impact strength (kJ / m²) Example 1 0.07 8 2.0 0.05 15 65 ±38 good 10.2 Example 2 0.15 12 2.0 0.1 5 125 ±52 middle 8.8 Example 3 0.1 10 2.0 0.075 10 105 ±30 excellent 9.9 Example 4 0.1 10 1.5 0.075 10 95 ±65 middle 9.0 Example 5 0.1 10 3.5 0.075 8 100 ±32 good 9.5 Example 6 0.1 10 2.0 0.05 8 102 ±34 good 9.8 Example 7 0.1 10 2.0 0.1 12 104 ±45 middle 9.2 Comparative Example 1 none 0 2.0 0.075 10 0 ±28 excellent 10.5

[0086] Test conclusions and analysis:

[0087] Test results and analysis show that the introduction of lignin carbon quantum dots significantly improves the fluorescence performance of the ink. The fluorescence intensity is positively correlated with the amount of lignin used. Example 2 (0.15 g lignin) achieved the highest fluorescence intensity of 125 au, while Comparative Example 1 showed no fluorescence. Printing accuracy and surface quality are influenced by the ink ratio and printing parameters. Example 3 (0.10 g lignin, 10 g dispersion, 88 g resin, 2 g initiator, 0.075 mm layer thickness, 10 seconds exposure) showed the best performance in terms of dimensional error (±30 μm) and surface quality, indicating that this ratio achieves the best balance in terms of fluidity, curing speed, and interlayer bonding. Too low an initiator amount (Example 4, 1.5 g) leads to incomplete curing and increased error, while too high an amount (Example 5, 3.5 g) slightly affects mechanical properties. Layer thickness and exposure time need to be matched; thin layers (0.05 mm) are suitable for 8-15 seconds of exposure, while thick layers (0.10 g lignin, 10 g dispersion, 88 g resin, 2 g initiator, 0.075 mm layer thickness, 10 seconds exposure) are suitable for 10 seconds of exposure. (mm) It is recommended that the exposure time be no less than 10 seconds to ensure interlayer bonding; considering all performance aspects, Example 3 is the best implementation method, achieving the optimal balance between fluorescence intensity, printing accuracy, surface quality and mechanical properties, and is suitable for manufacturing high-precision, high-performance luminous decorative signs.

[0088] The scope of protection of this invention includes, but is not limited to, the above embodiments. The scope of protection of this invention is defined by the claims. Any substitutions, modifications, or improvements to this technology that are easily conceived by those skilled in the art fall within the scope of protection of this invention.

Claims

1. A lignin carbon quantum dot light emitting ink, characterized by, It is composed of lignin carbon quantum dot (LCQD) dispersion, aqueous photocurable resin, and photoinitiator, wherein the weight ratio of each component is as follows: 8-12 parts of the lignin carbon quantum dot (LCQD) dispersion; 86-90 parts of water-based UV-curable resin; Photoinitiator 1.5-3.5 parts; The lignin carbon quantum dot (LCQDs) dispersion is prepared by hydrothermal reaction of the following raw materials in parts by weight: 0.07-0.15 parts alkali lignin, 0.4-0.8 parts ethylenediamine, and 10-15 parts deionized water.

2. The lignin carbon quantum dot light-emitting ink according to claim 1, characterized in that, The photoinitiator is selected from at least one of Irgacure 819, TPO, or 1173.

3. A method for preparing the lignin carbon quantum dot light-emitting ink according to claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of lignin carbon quantum dot (LCQD) dispersion: Weigh alkali lignin, ethylenediamine and deionized water according to the proportion, mix and stir and ultrasonically disperse to obtain precursor mixture; place the precursor mixture in a closed reaction vessel and carry out hydrothermal reaction at 140-160℃ for 6-8 hours; after the reaction is completed, cool and collect the supernatant to obtain lignin carbon quantum dot (LCQD) dispersion; (2) Preparation of printing ink: Take the lignin carbon quantum dot LCQDs dispersion, water-based photocurable resin and photoinitiator obtained in step (1) according to the proportion. First, mix the lignin carbon quantum dot LCQDs dispersion and water-based photocurable resin evenly, then add the photoinitiator and stir until completely uniform under light-proof conditions to obtain the lignin carbon quantum dot luminescent ink.

4. The preparation method according to claim 3, characterized in that, In step (1), the hydrothermal reaction is carried out at 150°C for 7 hours.

5. The preparation method according to claim 3, characterized in that, In step (2), the weight ratio of the lignin carbon quantum dot (LCQD) dispersion, the aqueous photocurable resin and the photoinitiator is 10:88:

2.

6. The preparation method according to claim 3, characterized in that, Step (2) further includes adjusting the viscosity of the ink to 500-2000 mPa·s by adding deionized water or a thickener.

7. The application of a lignin-carbon quantum dot luminescent ink as described in claim 1 or 2, or a lignin-carbon quantum dot luminescent ink prepared by any one of claims 3 to 6, in the preparation of 3D printed luminescent decorative signs.

8. The application according to claim 7, characterized in that, The 3D printing is a photopolymerization-based printing process, specifically digital light processing (DLP) or stereolithography (SLA); the printing layer thickness is 0.05-0.1 mm, and the exposure time for each layer is 5-15 seconds.

9. A method for preparing a 3D printed luminous decorative sign, characterized in that, Includes the following steps: Provide lignin-carbon quantum dot luminescent ink as described in claim 1 or 2, or lignin-carbon quantum dot luminescent ink prepared by any one of the preparation methods according to claims 3 to 6 as a printing material; Based on a preset three-dimensional digital model, a photopolymerization 3D printer is used to print and cure the ink layer by layer. After printing, the molded product undergoes post-curing treatment to obtain the luminous decorative logo.

10. The preparation method according to claim 9, characterized in that, The post-curing process involves irradiating the surface with an ultraviolet light source at a wavelength of 365-405nm for 5-15 minutes.

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