A method for realizing color continuous gradient transition by using DLP light curing 3D printing

Abstract

The application provides a method for realizing color continuous gradient transition by using DLP light curing 3D printing, and belongs to the technical field of additive manufacturing. The steps comprise: providing a dual-wavelength DLP light curing printing device, adjusting a printing focal plane, segmenting and slicing a three-dimensional digital model, setting dual-wavelength exposure parameters, preparing a photosensitive resin slurry containing components such as pH responsive dyes and photoacid generators, completing layer-by-layer printing through reciprocating dynamic switching of visible light curing forming and ultraviolet light color regulation, and obtaining a target workpiece after post-processing. The method realizes high-resolution, continuous gradient integrated forming of multi-color materials through single-light-machine dual-wavelength (365nm ultraviolet light and 460nm visible light) ultra-high-speed dynamic switching combined with a specific formula of photosensitive resin slurry.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a method for achieving a continuous color gradient transition using DLP photopolymerization 3D printing. Background Technology

[0002] Against the backdrop of continuously growing demand for personalized manufacturing, integrated functional and aesthetic devices, color-coded structures, and biomimetic appearance parts, additive manufacturing based on surface projection photopolymerization (such as DLP) has been widely used for rapid prototyping of complex structures due to its high precision and efficiency. However, as applications evolve from "single-material forming" to "multi-color, multi-performance integrated forming," existing surface projection photopolymerization technologies have revealed significant limitations in the synergistic integration of materials and appearance.

[0003] Existing multicolor photopolymerization manufacturing routes, such as multi-tank switching, multi-channel mixing and feeding, spray / coating coloring and curing, and dual-photon multi-wavelength curing, face a series of common bottlenecks in achieving high resolution, high saturation of multiple colors, continuous gradation, and synergistic control of material properties:

[0004] 1. Multicolor expression is "discretized", making it difficult to achieve continuous gradation with high saturation: Existing multicolor manufacturing usually relies on "material change / color change" or "fixed ratio color mixing", which easily forms discrete colors in layers or zones. Due to limitations such as layer thickness and color change granularity, continuous gradation is prone to problems such as abrupt transitions, blurred color boundaries, and insufficient saturation, making it difficult to achieve fine "bionic / realistic" color gradations.

[0005] 2. The multi-slot switching / mixing feeding process is complex, inefficient and prone to cross-contamination: When relying on multi-slot switching or online mixing, frequent material discharge, material replacement and cleaning are required, which leads to multiple interruptions in the printing process, reduced efficiency, and difficulty in completely removing residual resin, which can easily cause color mixing and cross-contamination. It may also disturb the formed structure and introduce dimensional errors or surface defects.

[0006] 3. Multicolor is often accompanied by "multi-formulation / multi-component", and the interface bonding and internal stress problems are prominent: In multicolor material systems, different pigment systems, resin matrices or functional components coexist. When heterogeneous regions are connected, the molecular interpenetration / chemical coupling at the interface is insufficient, the bonding strength is unstable, and the differences in curing kinetics and polymerization shrinkage in different regions will cause residual internal stress, resulting in warping, deformation, cracking or delamination, which affects the reliability and life of the parts.

[0007] 4. Existing multi-wavelength curing solutions have complex hardware and difficulty in ensuring synchronization accuracy: Existing multi-wavelength selective curing solutions often adopt dual-optical-mechanism or multi-optical-path structures, which are complex in system structure, high in cost, difficult to calibrate and maintain. The spatial alignment and time synchronization of multiple optical paths are difficult to maintain stability over a long period of time, which can easily lead to exposure mismatch and may also cause problems such as blurred color boundaries and gradient distortion, making it difficult to meet the requirements of high-speed and fine color change.

[0008] Taking complete denture manufacturing as a typical application scenario, traditional complete denture fabrication relies on manual processes, which are cumbersome, time-consuming (usually 1-2 weeks), and highly dependent on the technician's experience, making it difficult to guarantee accuracy and long-term comfort. DLP technology, as a type of photopolymer 3D printing, has been introduced into the complete denture manufacturing process due to its high printing accuracy (usually reaching the micron level) and relatively fast printing speed. It digitizes the denture manufacturing process, forming denture bases or even integrated dentures by curing photosensitive resin (such as PMMA-based materials) layer by layer, significantly shortening the treatment cycle (reducing to 2-3 visits) and providing patients with shorter treatment periods and a more comfortable experience.

[0009] To achieve integrated printing of denture bases and gingival-colored resin, or to manufacture integrated dentures with different mechanical properties, researchers have proposed a multi-slot switching method for printing complete dentures (ZL202411996939.8 - 3D printing method and equipment and 3D printing data processing method and device; ZL202511092764.2: A method and system for controlling the morphology of 3D printed parts based on support structure morphology compensation; ZL201811112654.8: A method for integrated fabrication of complete dentures based on DLP photopolymerization 3D printing). This series of patents, in the field of DLP photopolymerization 3D printing, significantly improves the structural density, bonding strength between different materials, and overall mechanical reliability of complete dentures through integrated fabrication processes, optimized printing paths and motion control. The innovative introduction of biomimetic diffusion structures and machine learning prediction models enables directional wetting and controllable fusion of resin at multi-material interfaces, greatly reducing the number of slot switching and cleaning steps during printing. This significantly improves printing efficiency and reduces the risk of material cross-contamination while ensuring interface quality. Based on an intelligent support-based active morphology compensation mechanism, the flow and curing morphology of resin are controlled by designing micro-nano structures, effectively overcoming surface collapse and dimensional distortion caused by factors such as gravity, and achieving high-precision, high-fidelity printing of complex three-dimensional morphologies. These technologies together constitute an efficient, accurate, and reliable multi-material photopolymerization printing solution for complete dentures. However, for applications requiring continuous gradients of highly saturated colors, fundamentally solving the interfacial stress problem caused by differences in material shrinkage rates remains a significant challenge for current technologies.

[0010] Firstly, traditional processes based on multi-material system switching and heterogeneous interface integration limit the achievement of high saturation and continuous color gradation (due to layer thickness limitations), such as the clear boundary between teeth (white) and gums (pink). Achieving continuous color gradation (such as a transition from deep red to light pink) theoretically still requires frequent switching of resin tanks with different color ratios, or reliance on more complex multi-channel mixing and feeding systems. Secondly, traditional multi-material printing does not completely solve the inherent challenges of interface bonding between "heterogeneous materials." The intermolecular chemical bonds at the interface of photosensitive resins with different components may still be weak or exhibit differences in polymerization shrinkage, generating internal stress. This stress can cause warping, deformation, or even cracking at the interface during later use. Therefore, the interface area remains a potential weak point under continuous stress loading. Finally, balancing process complexity and precision control is difficult. After switching material tanks, the interface of the printed portion must be thoroughly cleaned to remove residual resin. Improper handling in this step can easily lead to contamination or damage to the printed fine structure, significantly increasing the complexity of the process. Furthermore, it requires strict control over the curing depth and uniformity; improper handling can affect the performance and quality stability of the final product. Therefore, there is an urgent need for a comprehensive printing solution with a material gradient transition to simultaneously meet the color and mechanical performance requirements of different parts of the complete denture. Summary of the Invention

[0011] The purpose of this invention is to provide a method for achieving a continuous color gradient transition using DLP photopolymerization 3D printing, in order to solve the above-mentioned technical problems.

[0012] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0013] This invention provides a method for achieving a continuous color gradient transition using DLP photopolymerization 3D printing, comprising the following steps:

[0014] S1: Provide a dual-wavelength DLP photopolymerization printing device: The DLP optomechanical system light source of the device can switch between two wavelengths, 365nm ultraviolet light and 460nm visible light, and is output through the same digital micromirror device projection system to ensure high overlap and high-precision alignment of the two lights in space;

[0015] S2: Adjust the printing focal plane: According to the printing material and layer thickness requirements, the optical engine is focused and calibrated so that the projection surface is at a certain height of the resin mixture surface, ensuring that the beam of each layer is clearly focused and the size is accurate;

[0016] S3: Digital Model Processing and Slicing

[0017] S301: Construct a three-dimensional digital model of the gradient material to be printed, and divide different regions in the model based on color to form continuous or discontinuous regions A and B.

[0018] S302: The three-dimensional digital model is sliced ​​using slicing software to obtain projection slice patterns X1, X2, X3, ..., Xn;

[0019] S303: Perform secondary segmentation on each slice image: extract pixels containing region A in slice pattern X1 and generate a new projection pattern X1A; extract pixels containing region B in slice pattern X1 and generate a new projection pattern X1B, and so on, until all slice patterns are processed to obtain X1A,…,XnA,X1B,…,XnB, where slice patterns XnA and XnB are grayscale images and are positive and negative films for each other, n=1,2,3,…n;

[0020] S4: Set printing parameters:

[0021] S401: Set the exposure parameters for ultraviolet and visible light respectively, including the exposure intensity, exposure time, switching delay and sequence of the two light sources, release method and speed for each layer;

[0022] S402: Classify X1A~XnA as Group A projection mask images and classify X1B~XnB as Group B projection mask images. Input them into the DMD optical engine in the order of X1A, X1B, X2A, X2B...XnA, XnB, and synchronously coordinate with the ultra-high-speed dynamic switching of ultraviolet and visible light sources for sequential curing exposure under ultraviolet or visible light, respectively. The exposure order can be adjusted as needed.

[0023] S403: For a certain curing layer, the switching delay time between XnA and XnB is 100~1000μs, and the exposure time between XnA and XnB is 500~10000μs; by matching color-power-time multi-dimensional parameters, long-term exposure of ultraviolet light is given to the area to be color-changed to control the color, and short-term exposure of visible light is given to the area to be cured to form it, thereby achieving gradient curing of colors at different locations;

[0024] S5: Preparation of photosensitive resin slurry: Weigh each component according to the formula to prepare a resin mixture;

[0025] S6: Printing: The printing program is started, and the equipment performs layer-by-layer exposure molding according to the set sequence. For each layer, a visible light positive film pattern is first projected onto the resin surface and exposed for a predetermined time, allowing the resin in the corresponding area to fully cure and form the polymer part of that layer. Then, the system switches to ultraviolet light and projects a negative film pattern, irradiating the area that was initially cross-linked, and reactivating the photoacid generator to produce a small amount of acid, which becomes the color-changing part. At the same time, the system dynamically switches to ultraviolet light at ultra-high speed and projects a negative film pattern, irradiating the preset color-changing area, and activating the photoacid generator to produce acid to adjust the color change. Through the repeated dynamic switching between visible light and ultraviolet light, the molding area is fully cured, and the corresponding area of ​​the negative film only produces acid, becoming the color-changing part. The above steps are performed alternately, layer by layer, to integrally mold a functional graded material part.

[0026] S7: Post-processing and inspection: After printing, lift the part to allow the remaining liquid to drip off, and use a scraper to remove the uncured resin remaining on the surface; take out the part and rinse it in isopropanol solution to remove the adhering paste, and then blow dry or air dry the surface to obtain the desired color-changing material part.

[0027] Furthermore, the resin mixture formulation, by weight percentage, comprises: 92.00-94.00 wt% bifunctional acrylate monomer, 0.01-0.02 wt% pH-responsive dye, 0.19-0.21 wt% photoinitiator, 0.50-0.70 wt% co-initiator ethyl 4-dimethylaminobenzoate, 3.00-4.00 wt% photoacid generator, 0.19-0.21 wt% hydroquinone light stabilizer, 2.00-3.00 wt% 1.2M sodium hydroxide solution, and 0.50-4 wt% solvent.

[0028] Furthermore, the pH-responsive dye is bromocresol green and / or methyl red, the photoacid generator is one or more of triarylsulfonium hexafluorophosphate, sulfonium salt of 4-(9'-phenylanthryl)phenyltrifluoromethanesulfonate, and sulfonium salt of 4-(4'-N,N-diethyl-1'-styryl)phenyltrifluoromethanesulfonate, the solvent is dimethyl sulfoxide, and the photoinitiator is camphorquinone.

[0029] Furthermore, in step S401, the exposure parameters for the ultraviolet light are: light intensity of 35~50mW / cm². 2 The exposure time is 400~800s.

[0030] Furthermore, in step S401, the visible light exposure parameters are: light intensity of 30~40mW / cm². 2 The exposure time is 400~800s.

[0031] Furthermore, in step S2, the layer thickness is 10~200μm, and the height from the surface of the resin mixture is 1000~5000μm.

[0032] The beneficial effects of this invention are:

[0033] This invention achieves precise control of the spatial gradient of the crosslinking density of photosensitive resin by employing a dual-wavelength optical programming-based ultra-high-speed dynamic synergistic control strategy. This technology can construct a color transition region with continuously changing characteristics between the functional color-changing region and the main molding region. This gradient structure based on continuous changes in composition and properties can effectively suppress the stress concentration effect caused by abrupt changes in performance at the interfaces of different materials. As a result, under external loads, the stress in various regions within the part can be smoothly transitioned and redistributed, thereby avoiding the risk of failure due to excessive local stress.

[0034] In practical applications of dental prostheses, this invention enables denture bases to exhibit natural and aesthetically pleasing color gradients. This biomimetic design concept achieves an optimized match between material performance and aesthetic requirements. Clinical benefits include: patients wearing gradient denture bases prepared using this technology not only experience a more realistic visual effect of color transitions, but also see a significant improvement in the comfort and safety of their prostheses during long-term use due to structural optimization. Attached Figure Description

[0035] Figure 1 This is a digital model processing and slice diagram of the present invention;

[0036] Figure 2 This is a comparison image of the 4-pixel printed gradient color-changing material in Embodiment 1 of the present invention;

[0037] Figure 3 This is a comparison image of the 9-pixel printed gradient color-changing material in Embodiment 2 of the present invention;

[0038] Figure 4 This is a comparison image of the 56-pixel printed gradient color-changing material in Embodiment 3 of the present invention;

[0039] Figure 5 This is a photograph of a gradient color-changing denture sample printed according to Embodiment 4 of the present invention. Detailed Implementation

[0040] This invention provides a method for achieving a continuous color gradient transition using DLP photopolymerization 3D printing, comprising the following steps:

[0041] S1: Provide a dual-wavelength DLP photopolymerization printing device: The DLP optomechanical system light source of the device can switch between two wavelengths, 365nm ultraviolet light and 460nm visible light, and is output through the same digital micromirror device projection system to ensure high overlap and high-precision alignment of the two lights in space;

[0042] S2: Adjust the printing focal plane: According to the printing material and layer thickness requirements, the optical engine is focused and calibrated so that the projection surface is at a certain height of the resin mixture surface, ensuring that the beam of each layer is clearly focused and the size is accurate;

[0043] S3: Digital Model Processing and Slicing

[0044] S301: Construct a three-dimensional digital model of the gradient material to be printed, and divide different regions in the model based on color to form continuous or discontinuous regions A and B.

[0045] S302: The three-dimensional digital model is sliced ​​using slicing software to obtain projection slice patterns X1, X2, X3, ..., Xn;

[0046] S303: Perform secondary segmentation on each slice image: extract pixels containing region A in slice pattern X1 and generate a new projection pattern X1A; extract pixels containing region B in slice pattern X1 and generate a new projection pattern X1B, and so on, until all slice patterns are processed to obtain X1A,…,XnA,X1B,…,XnB, where slice patterns XnA and XnB are grayscale images and are positive and negative films for each other, n=1,2,3,…n;

[0047] S4: Set printing parameters:

[0048] S401: Set the exposure parameters for ultraviolet and visible light respectively, including the exposure intensity, exposure time, switching delay and sequence of the two light sources, release method and speed for each layer;

[0049] S402: Classify X1A~XnA as Group A projection mask images and classify X1B~XnB as Group B projection mask images. Input them into the DMD optical engine in the order of X1A, X1B, X2A, X2B...XnA, XnB, and synchronously coordinate with the ultra-high-speed dynamic switching of ultraviolet and visible light sources for sequential curing exposure under ultraviolet or visible light, respectively. The exposure order can be adjusted as needed.

[0050] S403: For a certain curing layer, the switching delay time between XnA and XnB is 100~1000μs, and the exposure time between XnA and XnB is 500~10000μs; by matching color-power-time multi-dimensional parameters, long-term exposure of ultraviolet light is given to the area to be color-changed to control the color, and short-term exposure of visible light is given to the area to be cured to form it, thereby achieving gradient curing of colors at different locations;

[0051] S5: Preparation of photosensitive resin slurry: Weigh each component according to the formula to prepare a resin mixture;

[0052] S6: Printing: The printing program is started, and the equipment performs layer-by-layer exposure molding according to the set sequence. For each layer, a visible light positive film pattern is first projected onto the resin surface and exposed for a predetermined time, allowing the resin in the corresponding area to fully cure and form the polymer part of that layer. Then, the system switches to ultraviolet light and projects a negative film pattern, irradiating the area that was initially cross-linked, and reactivating the photoacid generator to produce a small amount of acid, which becomes the color-changing part. At the same time, the system dynamically switches to ultraviolet light at ultra-high speed and projects a negative film pattern, irradiating the preset color-changing area, and activating the photoacid generator to produce acid to adjust the color change. Through the repeated dynamic switching between visible light and ultraviolet light, the molding area is fully cured, and the corresponding area of ​​the negative film only produces acid, becoming the color-changing part. The above steps are performed alternately, layer by layer, to integrally mold a functional graded material part.

[0053] S7: Post-processing and inspection: After printing, lift the part to allow the remaining liquid to drip off, and use a scraper to remove the uncured resin remaining on the surface; take out the part and rinse it in isopropanol solution to remove the adhering paste, and then blow dry or air dry the surface to obtain the desired color-changing material part.

[0054] In this invention, a photoacid generator (PAG, triarylthionium salt) and pH-responsive dyes (bromocresol green and methyl red) are simultaneously introduced into the resin formulation. PAG is irradiated with 365nm ultraviolet light to generate acid, thereby altering the protonation state and color of the dye. This completely separates the chemical principles of object structure forming (460nm visible light curing) from color control (UV photoacid generation), enabling the acquisition of multiple colors from a single material, rather than relying on changing the resin or mixing materials of different colors. By using dyes with different pH response ranges (such as bromocresol green from blue-green-yellow to methyl red from yellow-orange-red), and by mixing multiple dyes, color palettes can be expanded and customized. Through calibration, complex multicolor patterns can be precisely "drawn" on printed objects using differences in UV irradiation dose (grayscale value). Unlike traditional manufacturing processes that require dual optical paths and two different initiator systems, this invention utilizes a single-optical-engine ultra-high-speed dynamic projection to achieve dual-wavelength specific absorption photochemical reactions, thereby controlling the "color change" and "curing" processes in the material separately. The dual-wavelength dynamic switching rate reaches the micrometer level (250 μs), avoiding problems such as slow printing speed and material cross-contamination. Based on this principle, software controls the intensity and exposure time of different lights at each pixel in the projected slice pattern, achieving precise adjustment of the final curing degree of each voxel. Therefore, the material's color and transparency can achieve a continuous and smooth pixel-level gradient transition in three-dimensional space. Compared to directly replacing different materials, the gradient transition interface effectively avoids interface stress concentration caused by abrupt material changes. Traditional multi-material printing often results in stress concentration, delamination, or cracking at the interfaces between different materials due to abrupt changes in chemical composition and differences in curing shrinkage. This invention, however, establishes a continuous transition zone between different color areas, dispersing and releasing interface stress, achieving a strong chemical bond and seamless connection, significantly improving the durability and reliability of the manufactured parts.

[0055] In this invention, through mask separation and ultra-high-speed dynamic switching of projection slice patterns, different positions on the same layer can be irradiated with different wavelengths and for different times, resulting in significantly different degrees of curing, thereby allowing for large-scale and precise control of the color of the sample to be printed.

[0056] In this invention, during the printing process, no material changes or interruptions are required, and functional graded material parts are integrally formed.

[0057] This invention can print complete color-changing structural samples, and allows for dimensional measurement and performance evaluation. For printed samples in different areas, a structured light scanner can be used to measure their dimensional accuracy, characterizing the aesthetic performance of the soft-hard transition of the color-changing material. This invention achieves the fabrication of structures with continuous color-changing transitions in a single printing process.

[0058] In this invention, the resin mixture comprises, by weight percentage: 92.00-94.00 wt% bifunctional acrylate monomer, 0.01-0.02 wt% pH-responsive dye, 0.19-0.21 wt% photoinitiator, 0.50-0.70 wt% co-initiator ethyl 4-dimethylaminobenzoate, 3.00-4.00 wt% photoacid generator, 0.19-0.21 wt% hydroquinone light stabilizer, 2.00-3.00 wt% 1.2M sodium hydroxide solution, and 0.50-4 wt% solvent.

[0059] Preferably, the resin mixture comprises, by weight percentage: 92.00 wt% bifunctional acrylate monomer, 0.01 wt% pH-responsive dye, 0.20 wt% photoinitiator, 0.60 wt% co-initiator ethyl 4-dimethylaminobenzoate, 3.00 wt% photoacid generator, 0.19 wt% hydroquinone light stabilizer, 2.00 wt% 1.2 M sodium hydroxide solution, and 2.00 wt% solvent.

[0060] In this invention, the bifunctional acrylate monomer is one or more of polyethylene glycol diacrylate (PEGDA), bisphenol A dimethicone glycidyl acrylate (Bis-GMA), bisphenol A ethoxylated dimethacrylate (Bis-EMA), urethane dimethacrylate (UDMA), and triethylene glycol dimethacrylate (TEGDMA), preferably Bis-EMA.

[0061] In this invention, the pH-responsive dye is bromocresol green and / or methyl red; the photoacid generator is one or more of triarylsulfonium hexafluorophosphate, sulfonium 4-(9'-phenylanthryl)phenyltrifluoromethanesulfonate, and sulfonium 4-(4'-N,N-diethyl-1'-styryl)phenyltrifluoromethanesulfonate, preferably triarylsulfonium hexafluorophosphate; the solvent is dimethyl sulfoxide; and the photoinitiator is camphorquinone.

[0062] In this invention, the resin mixture is prepared by mixing the components together and then shaking or stirring at high speed for 30 seconds to fully dissolve and uniformly disperse camphorquinone and triarylsulfonium hexafluorophosphate in the resin. Then, the mixed slurry is poured into the resin tank of the DLP printer.

[0063] In this invention, in step S401, the exposure parameters for ultraviolet light are: light intensity of 35~50 mW / cm². 2 The preferred value is 40~45W / cm. 2 Further optimized to 42W / cm 2 The exposure time is 400~800s, preferably 500~600s.

[0064] In this invention, in step S401, the exposure parameters for visible light are: light intensity of 30~40 mW / cm². 2 The preferred value is 35W / cm. 2 The exposure time is 400~800s, preferably 500~600s.

[0065] In this invention, in step S2, the layer thickness is 10~200μm, preferably 20~100μm; the height from the surface of the resin mixture is 1000~5000μm, preferably 2000~3000μm.

[0066] The key to this invention lies in utilizing two wavelengths to project slice patterns via ultra-high-speed dynamic switching (microsecond level) through a single optical mask (DMD). Through synergistic triggering and polymerization / inhibition effects, it achieves integrated, precise, and rapid forming of gradient color-changing materials. The core advantage of the single-optical-engine dynamic switching scheme is that its color change is mainly achieved by rapidly altering optical properties through an electrical signal-driven modulator. This is a physical switching process with speeds easily reaching microsecond or even nanosecond levels. Furthermore, because the single-optical-engine relies on high-speed and precise electrical control or photoelectric effects, it can achieve very clear feature boundaries and complex real-time dynamic patterns.

[0067] This invention uses different negative and positive film slices and grayscale image inputs. The negative image corresponds to a 365nm exposure slice, and the positive image corresponds to a 460nm exposure slice. Through the cooperation between the slices, overlapping / complementary exposure is performed in different areas. The 365nm wavelength excites the photoacid generator TAS to produce acid, which acts on the pH-responsive dye, causing the dye to change color. The 460nm wavelength blue light is used for polymerization and molding.

[0068] This invention features integrated molding without the need to change material tanks: Compared to processes requiring multiple material tanks and repeated material changes, the method described in this invention only requires a single mixed resin to achieve printing of multiple performance regions. During the printing process, two types of light alternately act on the same resin tank, eliminating the need to interrupt printing or change materials, avoiding cross-contamination between different resins, and significantly improving printing efficiency. This integrated molding capability makes it possible to mass-produce gradient color-changing material devices, reducing production costs and process complexity.

[0069] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0070] Example 1: Testing the effect of 4-pixel color-changing printing

[0071] A method for achieving a continuous color gradient transition using DLP photopolymerization 3D printing includes the following steps:

[0072] S1: Provide a dual-wavelength DLP photopolymerization printing device: The DLP optomechanical system light source of the device can switch between two wavelengths, 365nm ultraviolet light and 460nm visible light, and is output through the same digital micromirror device projection system to ensure high overlap and high-precision alignment of the two lights in space;

[0073] S2: Adjust the printing focal plane: According to the printing material and layer thickness requirements, the optical engine is focused and calibrated so that the projection surface is at a certain height of the resin mixture surface, ensuring that the beam of each layer is clearly focused and the size is accurate;

[0074] S3: Digital Model Processing and Slicing

[0075] S301: Construct a three-dimensional digital model of the gradient material to be printed, and divide different regions in the model based on color to form continuous or discontinuous regions A and B.

[0076] S302: The three-dimensional digital model is sliced ​​using slicing software to obtain projection slice patterns X1, X2, X3, ..., Xn;

[0077] S303: Perform secondary segmentation on each slice image: extract pixels containing region A in slice pattern X1 and generate a new projection pattern X1A; extract pixels containing region B in slice pattern X1 and generate a new projection pattern X1B, and so on, until all slice patterns are processed to obtain X1A,…,XnA,X1B,…,XnB, where slice patterns XnA and XnB are grayscale images and are positive and negative films for each other, n=1,2,3,…n;

[0078] S4: Set printing parameters:

[0079] S401: Set the exposure parameters for ultraviolet and visible light respectively, including the exposure intensity, exposure time, switching delay and sequence of the two light sources, release method and speed for each layer;

[0080] S402: Classify X1A~XnA as Group A projection mask images and classify X1B~XnB as Group B projection mask images. Input them into the DMD optical engine in the order of X1A, X1B, X2A, X2B...XnA, XnB, and synchronously coordinate with the ultra-high-speed dynamic switching of ultraviolet and visible light sources for sequential curing exposure under ultraviolet or visible light, respectively. The exposure order can be adjusted as needed.

[0081] S403: For a certain curing layer, the switching delay time between XnA and XnB is 100~1000μs, and the exposure time between XnA and XnB is 500~10000μs; by matching color-power-time multi-dimensional parameters, long-term exposure of ultraviolet light is given to the area to be color-changed to control the color, and short-term exposure of visible light is given to the area to be cured to form it, thereby achieving gradient curing of colors at different locations;

[0082] S5: Preparation of photosensitive resin slurry: Weigh each component according to the formula to prepare a resin mixture;

[0083] S6: Printing: The printing program is started, and the equipment performs layer-by-layer exposure molding according to the set sequence. For each layer, a visible light positive film pattern is first projected onto the resin surface and exposed for a predetermined time, allowing the resin in the corresponding area to fully cure and form the polymer part of that layer. Then, the system switches to ultraviolet light and projects a negative film pattern, irradiating the area that was initially cross-linked, and reactivating the photoacid generator to produce a small amount of acid, which becomes the color-changing part. At the same time, the system dynamically switches to ultraviolet light at ultra-high speed and projects a negative film pattern, irradiating the preset color-changing area, and activating the photoacid generator to produce acid to adjust the color change. Through the repeated dynamic switching between visible light and ultraviolet light, the molding area is fully cured, and the corresponding area of ​​the negative film only produces acid, becoming the color-changing part. The above steps are performed alternately, layer by layer, to integrally mold a functional graded material part.

[0084] S7: Post-processing and inspection: After printing, lift the part to allow the remaining liquid to drip off, and use a scraper to remove the uncured resin remaining on the surface; take out the part and rinse it in isopropanol solution to remove the adhering paste, and then blow dry or air dry the surface to obtain the desired color-changing material part.

[0085] The gradient color-changing elastomer structure was printed using a CQ+TAS+EDAB initiation system. The resin formulation was as follows: 92% polyethylene glycol diacrylate monomer, 0.01wt% (2mg) of pH-responsive dye bromocresol green (BG) / methyl red (MR), 0.20wt% (40mg) of photoinitiator camphorquinone, 0.60wt% (120mg) of co-initiator ethyl 4-dimethylaminobenzoate (EDAB), 3.50wt% (0.8mL) of photoacid generator triarylsulfonium hexafluorophosphate (TAS), 0.20wt% (40mg) of light stabilizer hydroquinone (HQ), 2.50wt% (0.5mL) of 1.2M sodium hydroxide solution, and a small amount of DMSO solvent (0.99wt%) to help dissolve and disperse the initiator and dye. Printing was performed using this resin according to steps S1-S7: first, the printing focus was adjusted, and the slice pattern set of the printed sample was prepared using step S3. As shown in Table 1, the software sets the layer thickness to 100 μm and the blue light intensity at 460 nm to 35.00 mW / cm². 2The exposure time was 512 seconds, and the intensity of the 365nm violet light was close to 42.00mW / cm². 2 The exposure time was 512 seconds, with rapid alternating projection of green and purple light, switching between them 122,000 times within the total exposure time. During printing, blue and purple light were dynamically switched back and forth at ultra-high speed to solidify the color-changing / molding areas. This process was repeated to complete the printing of the entire piece, resulting in a sample with a continuous transition between the color-changing and molding areas. After printing, the sample was removed, cleaned, and dried. No delamination or cracks were observed, demonstrating a good bond between the two. The prepared gradient color-changing material is suitable for medical devices requiring aesthetically pleasing color transitions, such as complete dentures.

[0086] Table 1. 4-pixel color gradient printing parameter settings

[0087]

[0088] Example 2: 9-pixel printing color-changing effect.

[0089] The method is the same as in Example 1, except that a CQ+TAS+EDAB initiation system is used to print the gradient color-changing elastomer structure. The resin formulation is as follows: bisphenol A dimethacrylate glycidyl ester monomer accounts for 92%, pH-responsive dye bromocresol green BG / methyl red MR 0.01wt% (2mg), photoinitiator camphorquinone 0.20wt% (40mg), co-initiator ethyl 4-dimethylaminobenzoate (EDAB) 0.60wt% (120mg), photoacid generator sulfonium salt of 4-(9'-phenylanthrayl)phenyltrifluoromethanesulfonate 3.50wt% (0.8mL), light stabilizer hydroquinone HQ 0.20wt% (40mg), 1.2M sodium hydroxide solution 2.50wt% (0.5mL), and a small amount of DMSO solvent (0.99wt%) is added to help dissolve and disperse the above initiators and dyes. Printing is performed using this resin according to steps S1-S7: First, the printing focus is adjusted, and the slice pattern set of the printed sample is prepared using step S3. As shown in Table 2, the layer thickness is set to 100μm per layer and the 460nm blue light intensity is set to 35.00mW / cm² in the software. 2 The exposure time was 512 seconds, and the intensity of the 365nm violet light was close to 42.00mW / cm². 2 The exposure time was 512 seconds, with rapid alternating projection of green and purple light, switching between them 122,000 times within the total exposure time. During printing, blue and purple light were dynamically switched back and forth at ultra-high speed to solidify the color-changing / molding areas. This process was repeated to complete the printing of the entire piece, resulting in a sample with a continuous transition between the color-changing and molding areas. After printing, the sample was removed, cleaned, and dried. No delamination or cracks were observed, demonstrating a good bond between the two. The prepared gradient color-changing material is suitable for medical devices requiring aesthetically pleasing color transitions, such as complete dentures.

[0090] Table 2 9-pixel color gradient printing parameter settings

[0091]

[0092] Example 3: This example tests the pixel-level control of color-changing printing effect.

[0093] The method is the same as in Example 1, except that a CQ+TAS+EDAB initiation system is used to print the gradient color-changing elastomer structure. The resin formulation is as follows: 92% urethane dimethacrylate monomer, 0.01wt% (2mg) of pH-responsive dye bromocresol green BG / methyl red MR, 0.20wt% (40mg) of photoinitiator camphorquinone, 0.60wt% (120mg) of co-initiator ethyl 4-dimethylaminobenzoate (EDAB), 3.50wt% (0.8mL) of photoacid generator sulfonium salt of 4-(4'-N,N-diethyl-1'-styryl)phenyltrifluoromethanesulfonate, 0.20wt% (40mg) of light stabilizer hydroquinone HQ, 2.50wt% (0.5mL) of 1.2M sodium hydroxide solution, and a small amount of DMSO solvent (0.99wt%) is added to help dissolve and disperse the above initiators and dyes. Printing is performed using this resin according to steps S1-S7: First, the printing focus is adjusted, and the slice pattern set of the printed sample is prepared using step S3. As shown in Table 3, the layer thickness is set to 100 μm per layer and the 460 nm blue light intensity is set to 35.00 mW / cm² in the software. 2 The exposure time was 512 seconds, and the intensity of the 365nm violet light was close to 42.00mW / cm². 2 The exposure time was 512 seconds, with rapid alternating projection of green and purple light, switching between them 122,000 times within the total exposure time. During printing, blue and purple light were dynamically switched back and forth at ultra-high speed to solidify the color-changing / molding areas. This process was repeated to complete the printing of the entire piece, resulting in a sample with a continuous transition between the color-changing and molding areas. After printing, the sample was removed, cleaned, and dried. No delamination or cracks were observed, demonstrating a good bond between the two. The prepared gradient color-changing material is suitable for medical devices requiring aesthetically pleasing color transitions, such as complete dentures.

[0094] Table 3 Grayscale color gradient printing parameter settings

[0095]

[0096] Example 4 This example tests the printing effect of artificial tooth color change.

[0097] The method is the same as in Example 1, except that a CQ+TAS+EDAB initiation system is used to print the gradient color-changing elastomer structure. The resin formulation is as follows: triethylene glycol dimethacrylate monomer accounts for 92%, pH-responsive dye bromocresol green BG / methyl red MR 0.01wt% (2mg), photoinitiator camphorquinone 0.20wt% (40mg), co-initiator ethyl 4-dimethylaminobenzoate (EDAB) 0.60wt% (120mg), photoacid generator triarylsulfonium hexafluorophosphate TAS 3.50wt% (0.8mL), light stabilizer hydroquinone HQ 0.20wt% (40mg), 1.2M sodium hydroxide solution 2.50wt% (0.5mL), and a small amount of DMSO solvent (0.99wt%) is added to help dissolve and disperse the above initiators and dyes. Printing is performed using this resin according to steps S1-S7: First, the printing focus is adjusted, and the slice pattern set of the printed sample is prepared using step S3. As shown in Table 4, the layer thickness is set to 100μm per layer and the 460nm blue light intensity is set to 35.00mW / cm² in the software. 2 The exposure time was 512 seconds, and the intensity of the 365nm violet light was close to 42.00mW / cm². 2 The exposure time was 512 seconds, with rapid alternating projection of green and purple light, switching between them 122,000 times within the total exposure time. During printing, blue and purple light were dynamically switched back and forth at ultra-high speed to solidify the color-changing / molding areas. This process was repeated to complete the printing of the entire piece, resulting in a sample with a continuous transition between the color-changing and molding areas. After printing, the sample was removed, cleaned, and dried. No delamination or cracks were observed, demonstrating a good bond between the two. The prepared gradient color-changing material is suitable for medical devices requiring aesthetically pleasing color transitions, such as complete dentures.

[0098] Table 4. Parameter settings for printing artificial tooth + gingival color

[0099]

[0100] In summary, through the verification of the above embodiments, the method for manufacturing color-gradient materials using the dual-wavelength single-optical-mechanical ultra-high-speed dynamic projection photocuring process provided by this invention is feasible and effective. Samples with continuous color transitions were successfully produced under different formulations and process conditions. Application areas: The application of single-optical-mechanical dynamic high-speed switching technology in the field of oral medicine mainly focuses on achieving gradient changes in color and function within restorations through precise control of the photocuring process, thereby improving aesthetics and biocompatibility. Natural teeth exhibit natural color and transparency gradients from the cervical region to the incisal edge. Optomechanical dynamic high-speed switching technology can precisely control illumination parameters (such as intensity and exposure time) at the pixel level, achieving spatial gradient regulation of the crosslinking density of the restoration material in a single printing, thus replicating this complex color transition. For example, this technology can be used to manufacture crowns, veneers, or complete dentures with realistic color gradients, making them closer to natural teeth in color, transparency, and texture, achieving a high degree of aesthetic matching.

[0101] 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 method for achieving a continuous color gradient transition using DLP photopolymerization 3D printing, characterized in that, Includes the following steps: S1: Provide a dual-wavelength DLP photopolymerization printing device: The DLP optomechanical system light source of the device can switch between two wavelengths, 365nm ultraviolet light and 460nm visible light, and is output through the same digital micromirror device projection system to ensure high overlap and high-precision alignment of the two lights in space; S2: Adjust the printing focal plane: According to the printing material and layer thickness requirements, the optical engine is focused and calibrated so that the projection surface is at a certain height of the resin mixture surface, ensuring that the beam of each layer is clearly focused and the size is accurate; S3: Digital Model Processing and Slicing S301: Construct a three-dimensional digital model of the gradient material to be printed, and divide different regions in the model based on color to form continuous or discontinuous regions A and B. S302: The three-dimensional digital model is sliced ​​using slicing software to obtain projection slice patterns X1, X2, X3, ..., Xn; S303: Perform secondary segmentation on each slice image: extract pixels containing region A in slice pattern X1 and generate a new projection pattern X1A; extract pixels containing region B in slice pattern X1 and generate a new projection pattern X1B, and so on, until all slice patterns are processed to obtain X1A,…,XnA,X1B,…,XnB, where slice patterns XnA and XnB are grayscale images and are positive and negative films for each other, n=1,2,3,…n; S4: Set printing parameters: S401: Set the exposure parameters for ultraviolet and visible light respectively, including the exposure intensity, exposure time, switching delay and sequence of the two light sources, release method and speed for each layer; S402: Classify X1A~XnA as Group A projection mask images and classify X1B~XnB as Group B projection mask images. Input them into the DMD optical engine in the order of X1A, X1B, X2A, X2B...XnA, XnB, and synchronously coordinate with the ultra-high-speed dynamic switching of ultraviolet and visible light sources for sequential curing exposure under ultraviolet or visible light, respectively. The exposure order can be adjusted as needed. S403: For a certain curing layer, the switching delay time between XnA and XnB is 100~1000μs, and the exposure time between XnA and XnB is 500~10000μs; by matching color-power-time multi-dimensional parameters, long-term exposure of ultraviolet light is given to the area to be color-changed to control the color, and short-term exposure of visible light is given to the area to be cured to form it, thereby achieving gradient curing of colors at different locations; S5: Preparation of photosensitive resin slurry: Weigh each component according to the formula to prepare a resin mixture; S6: Printing: The printing program is started, and the equipment performs layer-by-layer exposure molding according to the set sequence. For each layer, a visible light positive film pattern is first projected onto the resin surface and exposed for a predetermined time, allowing the resin in the corresponding area to fully cure and form the polymer part of that layer. Then, the system switches to ultraviolet light and projects a negative film pattern, irradiating the area that was initially cross-linked, and reactivating the photoacid generator to produce a small amount of acid, which becomes the color-changing part. At the same time, the system dynamically switches to ultraviolet light at ultra-high speed and projects a negative film pattern, irradiating the preset color-changing area, and activating the photoacid generator to produce acid to adjust the color change. Through the repeated dynamic switching between visible light and ultraviolet light, the molding area is fully cured, and the corresponding area of ​​the negative film only produces acid, becoming the color-changing part. The above steps are performed alternately, layer by layer, to integrally mold a functional graded material part. S7: Post-processing and inspection: After printing, lift the part to let the remaining liquid drip off, and use a scraper to remove the uncured resin remaining on the surface; take out the part and rinse it in isopropanol solution to remove the adhering paste, and then blow or air dry the surface to obtain the part with the desired color change material. The resin mixture comprises, by weight percentage: 92.00-94.00 wt% bifunctional acrylate monomer, 0.01-0.02 wt% pH-responsive dye, 0.19-0.21 wt% photoinitiator, 0.50-0.70 wt% co-initiator ethyl 4-dimethylaminobenzoate, 3.00-4.00 wt% photoacid generator, 0.19-0.21 wt% hydroquinone light stabilizer, 2.00-3.00 wt% 1.2M sodium hydroxide solution, and 0.50-4 wt% solvent.

2. The method for achieving continuous color gradient transition using DLP photopolymerization 3D printing according to claim 1, characterized in that, The pH-responsive dye is bromocresol green and / or methyl red, the photoacid generator is one or more of triarylsulfonium hexafluorophosphate, sulfonium salt of 4-(9'-phenylanthryl)phenyltrifluoromethanesulfonate, and sulfonium salt of 4-(4'-N,N-diethyl-1'-styryl)phenyltrifluoromethanesulfonate, the solvent is dimethyl sulfoxide, and the photoinitiator is camphorquinone.

3. The method for achieving a continuous color gradient transition using DLP photopolymerization 3D printing according to claim 1 or 2, characterized in that, In step S401, the exposure parameters for ultraviolet light are: light intensity of 35~50mW / cm². 2 The exposure time is 400~800s.

4. The method for achieving continuous color gradient transition using DLP photopolymerization 3D printing according to claim 1, characterized in that, In step S401, the exposure parameters for visible light are: light intensity of 30~40mW / cm². 2 The exposure time is 400~800s.

5. The method for achieving continuous color gradient transition using DLP photopolymerization 3D printing according to claim 1, characterized in that, In step S2, the layer thickness is 10~200μm, and the height from the surface of the resin mixture is 1000~5000μm.

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