Additive manufacturing method of a 3D printed gypsum-based decorative panel

Abstract

The application discloses an additive preparation method of a 3D printing gypsum-based decorative plate and relates to the technical field of additive preparation. The method comprises the following steps: mixing alpha-hemihydrate gypsum and beta-hemihydrate gypsum to form an initial powder, adding a chopped carbon fiber reinforcement, and adopting a spiral type of alternately spraying a binder and laying the powder to construct a blank. The mixed dual-phase gypsum is complementary in high strength of the alpha phase and suitable setting characteristics of the beta phase, preliminarily balances the performance short board of a single gypsum phase, the chopped carbon fiber disperses in the matrix to form a three-dimensional reinforcing network, preliminarily improves the toughness to inhibit the fracture, the spiral type of spraying the binder is opposite in direction between adjacent layers, the binder is evenly distributed in a staggered penetration shape, and the close powder laying is matched layer by layer, so that the water content gradient in the blank is ensured to be uniform, the water is evaporated synchronously from each layer during drying, the shrinkage stress difference is reduced, the blank deformation is effectively controlled, and the size precision is ensured.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and more particularly to an additive manufacturing method for 3D printed gypsum-based decorative panels. Background Technology

[0002] Gypsum, as a traditional inorganic cementitious material, has long been used in architectural decoration and cultural and creative fields due to its environmental friendliness, non-toxicity, light weight, low cost, and high plasticity, especially suitable for the production of complex shaped components. With the development of 3D printing technology towards personalized customization and efficient molding, the combination of gypsum's properties and additive manufacturing has become an important area of ​​exploration in the field of green building materials. Its application potential in decorative panels, art installations, and architectural models is gradually emerging, aiming to break through the bottlenecks of traditional gypsum processing in terms of fine structures and mass customization.

[0003] In existing technologies, plaster 3D printing mostly employs binder jetting processes. Typically, single-phase plaster powder is used as the printing material, with some additives to improve flowability. The binder is usually a water-soluble polymer solution such as polyvinyl alcohol or starch, selectively sprayed onto the surface of the laid plaster powder layer through a nozzle along a preset path, causing the powder in the contact area to bond and solidify. This process of layering and jetting is then repeated to form a preform, which is finally dried to remove moisture and obtain the finished product. Some technologies attempt to adjust powder particle size or binder concentration to optimize strength, but the core process remains primarily based on single-phase plaster, unidirectional binder jetting, and simple powder laying.

[0004] The existing gypsum 3D printing technology has the following defects: First, the selection of a single gypsum phase leads to an imbalance in performance. For example, although α-hemihydrate gypsum has high strength, it sets too quickly and is prone to cracking, while β-hemihydrate gypsum sets more slowly but has lower strength, making it difficult to balance strength and construction adaptability. Second, during the drying process, due to the single direction of binder spraying, uneven bonding between powder layers, and large differences in moisture evaporation rate, non-uniform shrinkage stress is generated inside the blank, which often causes warping and deformation. Dimensional accuracy is difficult to control, affecting the flatness and installation compatibility of the decorative panel, thus restricting the practical application and promotion of the product.

[0005] Therefore, it is necessary to improve the existing plaster 3D printing technology to solve the above problems. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and provides an additive manufacturing method for 3D printed gypsum-based decorative panels.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: an additive manufacturing method for 3D printed gypsum-based decorative panels, comprising the following steps:

[0008] S1: Mix α-hemihydrate gypsum powder and β-hemihydrate gypsum powder to obtain initial gypsum powder; mix the initial gypsum powder with chopped carbon fibers to obtain printing powder; dissolve polyvinyl alcohol in water to obtain a binder;

[0009] S2: Apply adhesive to the gypsum-based fiberboard by spraying along a preset spiral trajectory; then lay the printing powder in the area where the adhesive is sprayed.

[0010] S3: Repeat the spraying of the adhesive and the laying of the printing powder in S2 until a decorative panel blank is obtained; the rotation directions of the spraying spiral trajectories of adjacent layers of adhesive are opposite;

[0011] S4: Dry the decorative panel blank to obtain a 3D printed gypsum-based decorative panel.

[0012] In a preferred embodiment of the present invention, the particle size of the α-hemihydrate gypsum powder is 50-100 μm, and the particle size of the β-hemihydrate gypsum powder is 10-30 μm.

[0013] In a preferred embodiment of the present invention, the mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 4:6-5:5.

[0014] In a preferred embodiment of the present invention, the length of the chopped carbon fiber is 0.08-0.12 mm and the diameter is 7-10 μm; the chopped carbon fiber is soaked in 0.5 wt% silane coupling agent KH550 at a temperature of 60-80°C for 2-3 hours.

[0015] In a preferred embodiment of the present invention, the short-cut carbon fibers in the printing powder account for 0.3-0.5% of the mass of the initial gypsum powder.

[0016] In a preferred embodiment of the present invention, the injection starting point in S2 is the center point of the substrate, the pitch is 0.1-0.15mm, and the height of the nozzle outlet of the injection head from the printing plane is 0.1-0.3mm.

[0017] In a preferred embodiment of the present invention, the adhesive spraying speed is 5-10 mm / s, the adhesive droplets are 10-15 pL, and the droplet spacing is 0.1-0.15 mm.

[0018] In a preferred embodiment of the present invention, the thickness of each layer of printing powder is 0.2-0.3 mm.

[0019] In a preferred embodiment of the present invention, after each layer of printing powder is laid, wait 2-4 minutes before spraying the next layer of adhesive.

[0020] In a preferred embodiment of the present invention, the drying process includes a first drying process and a second drying process. The first drying process has a temperature of 30-40°C, a humidity of 50-60%RH, and a time of 12-24h. The second drying process has a temperature of 24-26°C, a humidity of 30-40%RH, and a time of 24-72h.

[0021] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0022] (1) This invention provides an additive manufacturing method for 3D printed gypsum-based decorative panels. The method involves mixing α-hemihydrate gypsum and β-hemihydrate gypsum to form an initial powder, adding short-cut carbon fiber reinforcement, and constructing a blank by spirally alternating spraying of binder and laying powder. The mixed biphase gypsum complements the high strength of the α phase and the suitable coagulation characteristics of the β phase, thus initially balancing the performance shortcomings of the single gypsum phase. The short-cut carbon fiber disperses in the matrix to form a three-dimensional reinforcement network, which initially improves toughness to suppress fracture. When the binder is spirally sprayed, the directions of adjacent layers are opposite, so that the binder is evenly distributed in an interlaced and permeable manner. Compared with the prior art, the method is combined with layer-by-layer tight powder laying to ensure a consistent moisture gradient inside the blank. During drying, the moisture evaporates synchronously from each layer, reducing the shrinkage stress difference, thereby effectively controlling the deformation of the blank and ensuring dimensional accuracy.

[0023] (2) In this invention, the particle size of α-hemihydrate gypsum is set to 50-100μm and the particle size of β-hemihydrate gypsum is set to 10-30μm with a mass ratio of 4:6-5:5. The larger particle size of the α phase forms a skeleton support structure, and the smaller particle size of the β phase fills the pores between the particles. The gradient distribution of the two reduces the packing voids and increases the powder packing density. The mass ratio of 4:6-5:5 makes the high strength of the α phase and the slow setting characteristics of the β phase work together. Compared with the prior art, the gypsum performance is balanced by the particle size gradient and the ratio, avoiding the cracking or insufficient strength of the single phase due to excessively fast solidification. The comprehensive mechanical properties of the material are optimized from the microstructure, laying a dense and uniform powder foundation for subsequent printing.

[0024] (3) In this invention, the adhesive is sprayed in a spiral manner, and the spraying directions of adjacent layers are opposite. The spiral trajectory makes the adhesive penetrate in a continuous ring shape, avoiding blind spots or overlaps in the bonding. The opposite directions of adjacent layers make the adhesive interweave between layers to form a network bonding structure. Compared with the prior art, the adhesive is evenly distributed and the interlayer bonding is enhanced, which strengthens the interlayer shear force. At the same time, it creates channels for the uniform evaporation of moisture during drying and reduces local stress concentration.

[0025] (4) In this invention, α-hemihydrate gypsum and β-hemihydrate gypsum are mixed to form a two-phase initial powder, and the green body is constructed by using a reverse spiral method with opposite directions of the adhesive spraying spirals of adjacent layers. The rapid hydration of α-hemihydrate gypsum provides immediate interfacial bonding strength, while the slow hydration of β-hemihydrate gypsum allows the crystals to interweave with each other at the microscale to form a continuous network. The interlaced adhesive channels formed by the reverse spiral spraying constitute an asymmetric capillary network, which allows the water in the α-phase region to migrate preferentially along the β-phase gaps, avoiding the α-phase from drying shrinkage cracks due to rapid water loss. At the same time, it promotes the uniform growth of β-phase crystals and guides the water to evaporate synchronously in each layer, effectively reducing the difference in shrinkage stress. It also promotes the synergistic growth of α-hemihydrate gypsum crystal nuclei and β-hemihydrate gypsum crystals at the interlayer interface, eliminates weak interfacial areas, and achieves improved interlayer bonding strength and uniform shrinkage stress, thereby significantly reducing the deformation of the green body and achieving dual optimization of material mechanical properties and dimensional accuracy. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart illustrating the method steps of a preferred embodiment of the present invention. Detailed Implementation

[0028] 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.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0030] Application Overview:

[0031] Plaster 3D printing typically uses single-phase plaster powder as the main material, such as using only α-hemihydrate plaster or β-hemihydrate plaster. After mixing it with a small amount of water-based binder, the powder is laid layer by layer through a powder spreading device. Then, the binder is sprayed through a nozzle or plaster slurry is extruded to achieve interlayer bonding. Finally, the layers are stacked into a blank and then dried and cured to obtain the finished product.

[0032] When only α-hemihydrate gypsum is used, its rapid hydration leads to excessively fast interlayer shrinkage, and the stress peak exceeds the tensile strength of the material, causing micro-cracks and easy breakage; when only β-hemihydrate gypsum is used, the slow hydration results in insufficient penetration of the binder and insufficient crystal growth rate, leading to loss of dimensional accuracy.

[0033] An unexpected discovery revealed that the uniform porous matrix formed by the compound gypsum provides an ideal channel for binder penetration. Carbon fibers dispersed in the matrix inhibit crack propagation by bridging microcracks, while the binder sprayed in a reverse spiral forms a cross-linked liquid film network in adjacent layers, mechanically interlocking with the bonded areas of the lower layer like a mortise and tenon structure. This interlocking structure works synergistically with the fiber-reinforced matrix, eliminating the interlayer weaknesses that are easily generated by unidirectional spiral spraying, and distributing external forces through stress transfer at the fiber-gypsum interface. At the same time, the close packing of particles of different sizes in the compound gypsum reduces drying shrinkage, and gradient drying controls uniform moisture evaporation. Ultimately, this achieves a simultaneous improvement in interlayer bonding strength, overall flexural strength, and dimensional stability, fundamentally overcoming the performance limitations of single materials and unidirectional processes.

[0034] like Figure 1 As shown, an additive manufacturing method for 3D printed gypsum-based decorative panels includes the following steps:

[0035] S1: Mix α-hemihydrate gypsum powder and β-hemihydrate gypsum powder to obtain initial gypsum powder, mix the initial gypsum powder with short-cut carbon fibers to obtain printing powder; dissolve polyvinyl alcohol in water to obtain binder; this step aims to prepare composite powder materials suitable for 3D printing and to configure a matching binder.

[0036] S2: On a gypsum-based fiberboard, adhesive is applied via jetting along a pre-defined spiral path; printing powder is then laid in the adhesive jetting area. This step demonstrates the basic method of 3D printing. Using a gypsum-based fiberboard as the substrate provides high flatness and moderate moisture absorption, preventing warping of the blank due to substrate deformation in the early stages of printing.

[0037] S3: Repeat the spraying of adhesive and laying of printing powder in S2 until the decorative panel blank is obtained; the rotation direction of the spraying spiral trajectory of the adhesive of adjacent layers is opposite; this step achieves the layer-by-layer forming of the decorative panel blank through the alternating operation of spiral spraying of adhesive and laying of printing powder.

[0038] S4: Dry the decorative panel blank to obtain a 3D printed gypsum-based decorative panel.

[0039] In step S1:

[0040] The particle size of α-hemihydrate gypsum powder is 50-100 μm, and the particle size of β-hemihydrate gypsum powder is 10-30 μm. The mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 4:6-5:5.

[0041] The chopped carbon fibers have a length of 0.08-0.12 mm and a diameter of 7-10 μm. The chopped carbon fibers are soaked in 0.5 wt% silane coupling agent KH550 at 60-80℃ for 2-3 hours. The chopped carbon fibers account for 0.3-0.5% of the initial gypsum powder mass in the printing powder.

[0042] Specifically, α-hemihydrate gypsum powder and β-hemihydrate gypsum powder are mixed at a mass ratio of 4:6-5:5 to form initial gypsum powder. The particle size of the α-hemihydrate gypsum powder is controlled at 50-100 μm, and the particle size of the β-hemihydrate gypsum powder is 10-30 μm.

[0043] This particle size range is set based on two considerations: α-hemihydrate gypsum, as a high-strength phase, requires a larger particle size to ensure the strength of the material's skeleton, while β-hemihydrate gypsum, as a fast-setting phase, requires a smaller particle size to improve slurry flowability and filling density. The combination of the two leverages both the hardened strength advantage of α-hemihydrate gypsum and the rapid setting characteristics of β-hemihydrate gypsum, resulting in tighter interlayer bonding during printing while avoiding the cracking risk caused by differences in shrinkage rates in single-phase gypsum.

[0044] Subsequently, short-cut carbon fibers are added to the initial plaster powder to form printing powder. The short-cut carbon fibers need to be pre-treated by immersing them in an aqueous solution containing 0.5 wt% silane coupling agent KH550 at a temperature of 60-80°C for 2-3 hours.

[0045] The purpose of this treatment is to form an organic coating layer on the fiber surface using a silane coupling agent, thereby enhancing the interfacial bonding between the fiber and the gypsum matrix, reducing fiber agglomeration during printing, and improving the crack resistance and toughness of the composite material. The treated carbon fibers have a length of 0.08-0.12 mm and a diameter of 7-10 μm. This range effectively leverages the reinforcing effect of the fibers while avoiding printhead clogging or uneven distribution due to excessive fiber length.

[0046] In a preferred embodiment, the amount of chopped carbon fibers added to the printing powder is 0.3-0.5% of the initial gypsum powder mass. An appropriate amount of fiber can improve the flexural strength of the board by bridging cracks and inhibiting the propagation of microcracks without significantly increasing the material density. However, if the amount is too high, it will lead to a decrease in powder flowability, affecting the uniformity of the printed layer thickness. Furthermore, excessive fiber may cause localized stress concentration, thus reducing the overall performance of the material.

[0047] Specifically, the binder is a polyvinyl alcohol aqueous solution, the concentration of which needs to be adjusted according to the ambient humidity and printing speed. Generally, the solid content is controlled at 5-8 wt% to ensure that the binder can quickly wet the gypsum powder particles after spraying, forming a continuous three-dimensional network structure, which provides a foundation for subsequent interlayer bonding.

[0048] In step S2:

[0049] The spraying starting point is the center point of the substrate, the pitch is 0.1-0.15mm, and the height of the nozzle exit of the spray head from the printing plane is 0.1-0.3mm. The adhesive spraying moving speed is 5-10mm / s, the adhesive droplet size is 10-15pL, and the droplet spacing is 0.1-0.15mm.

[0050] Precise pitch control ensures a moderate overlap between adjacent droplets, guaranteeing continuous adhesive coverage while preventing excessive droplet fusion and localized overwetting. During spraying, the adhesive droplet volume is controlled at 10-15 pL, and the droplet spacing is 0.1-0.15 mm. This parameter combination is achieved through a precision piezoelectric nozzle, ensuring a droplet landing accuracy of ±0.05 mm on the substrate, thus meeting the precision requirements of the decorative panel surface pattern.

[0051] In step S3;

[0052] Each layer of printing powder is 0.2-0.3mm thick, with a total of 400-1000 layers. After each layer of printing powder is laid, wait 2-4 minutes before spraying the next layer of adhesive. The total number of layers specifically refers to the sum of the number of printing powder layers.

[0053] Furthermore, immediately after the binder is sprayed, printing powder is laid down, with the thickness of each powder layer strictly controlled between 0.2-0.3 mm. This layer thickness design is key to balancing printing efficiency and accuracy: too thin a layer increases the number of printing layers and prolongs the production cycle; too thick a layer results in the powder not being fully penetrated by the binder, forming internal pores. After powder laying, the mixture needs to stand for 2-4 minutes to allow the powder to settle naturally under gravity, while simultaneously allowing the binder to initially penetrate the powder gaps, creating stable interface conditions for the next layer spraying.

[0054] Specifically, the opposite direction of the spraying spirals of adjacent adhesive layers means that odd-numbered layers use a clockwise spiral, and even-numbered layers use a counter-clockwise spiral. This alternating spiral spraying breaks up the weak interlayer surfaces created by unidirectional liquid flow, allowing the upper and lower adhesive layers to interlock in the intersection area, forming a mechanical interlock similar to a tenon and mortise structure, significantly improving interlayer shear strength.

[0055] In step S4:

[0056] The drying process includes a first drying process and a second drying process. The first drying process has a temperature of 30-40℃, a humidity of 50-60%RH, and a time of 12-24h. The second drying process has a temperature of 24-26℃, a humidity of 30-40%RH, and a time of 24-72h.

[0057] In detail, after the green body is formed, it needs to be dried to remove free moisture and obtain a stable structure. The drying process is divided into two stages:

[0058] The first stage is the first drying process, with the temperature controlled at 30-40℃ and the relative humidity at 50-60%RH, lasting for 12-24 hours. This stage employs a low-temperature, high-humidity environment to slowly evaporate the surface moisture of the gypsum board, preventing stress cracking due to excessive temperature differences between the inside and outside. Research shows that under these conditions, the growth rate of gypsum crystals matches the moisture diffusion rate, resulting in a uniform calcium sulfate dihydrate crystal structure that provides initial strength to the slab.

[0059] The second stage is the second drying process, where the temperature is lowered to 24-26℃ and the relative humidity is 30-40%RH, continuing drying for 24-72 hours. The low-temperature environment further reduces drying stress, while extending the drying time ensures that the core moisture is completely removed. The final moisture content of the board is controlled below 0.5wt%, at which point the gypsum crystals have fully hardened, and the board's dimensional stability reaches its optimal state.

[0060] Sodium sulfate and dodecyltrimethylammonium bromide were dissolved together in water at a mass ratio of 50-80:1 to prepare an aqueous solution with a total concentration of 5-15 wt%. The solution was then dried at 80-120℃ to obtain a composite modifier. The composite modifier was then added at an amount of 0.1-1.0% relative to the dry weight of phosphogypsum and mixed with water at a solid-liquid mass ratio of 1:4-1:6 to prepare a solution. Phosphogypsum powder was then added and stirred evenly. Finally, the mixture was placed in a reaction vessel and reacted at 120-150℃ and 0.2-0.4 MPa for 2-4 hours. After the reaction was completed, the mixture was filtered, washed, and dried at 60-80℃ to obtain α-hemihydrate gypsum.

[0061] Using phosphogypsum as raw material, it is dried at 150-200℃ until the moisture content is less than 5%, then crushed and calcined in a fluidized bed furnace at 160-190℃ for 1.5-3 hours; the calcined clinker is then ground and passed through a sieve to finally obtain β-hemihydrate gypsum powder.

[0062] Example 1:

[0063] This embodiment provides an additive manufacturing method for 3D printing gypsum-based decorative panels, including the following steps:

[0064] S1: Mix α-hemihydrate gypsum powder and β-hemihydrate gypsum powder to obtain initial gypsum powder; mix the initial gypsum powder with short-cut carbon fibers to obtain printing powder; dissolve polyvinyl alcohol in water to obtain binder;

[0065] The α-hemihydrate gypsum powder has a particle size of 60 μm, and the β-hemihydrate gypsum powder has a particle size of 20 μm. The mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 4:6. The chopped carbon fibers have a length of 0.1 mm and a diameter of 8 μm; the chopped carbon fibers are soaked in 0.5 wt% silane coupling agent KH550 at 70 °C for 2.5 h. The chopped carbon fibers account for 0.4% of the mass of the initial gypsum powder in the printing powder.

[0066] S2: On a gypsum-based fiberboard, adhesive is applied via spraying along a preset spiral trajectory; printing powder is then laid in the adhesive spraying area; the spraying starting point is the center point of the substrate, the pitch is 0.1mm, and the nozzle exit height of the spray head is 0.2mm above the printing plane. The adhesive spraying speed is 8mm / s, the adhesive droplet size is 12pL, and the droplet spacing is 0.1mm.

[0067] S3: Repeat the adhesive spraying and powder application process in S2 until the decorative panel blank is obtained; the rotation directions of the spraying spiral trajectories of adjacent adhesive layers are opposite; the thickness of each powder layer is 0.2mm, and the total number of layers is 630. After each powder layer is applied, wait 3 minutes before spraying the next layer of adhesive.

[0068] S4: Dry the decorative panel blank to obtain a 3D printed gypsum-based decorative panel.

[0069] The drying process includes a first drying process and a second drying process. The first drying process has a temperature of 35℃, a humidity of 60%RH, and a time of 18h. The second drying process has a temperature of 25℃, a humidity of 35%RH, and a time of 60h.

[0070] Example 2:

[0071] The difference between this embodiment and Embodiment 1 is that the mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 4.5:5.5, while the rest are the same.

[0072] Example 3:

[0073] The difference between this embodiment and Embodiment 1 is that the mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 5:5, while the rest are the same.

[0074] Example 4:

[0075] The difference between this embodiment and Embodiment 2 is that the thickness of each layer of printed powder is 0.25 mm, and the total number of layers is 504; otherwise, they are the same.

[0076] Example 5:

[0077] The difference between this embodiment and Embodiment 2 is that the thickness of each layer of printed powder is 0.3 mm, and the total number of layers is 420; otherwise, they are the same.

[0078] Comparative Example 1:

[0079] This comparative example provides an additive manufacturing method for 3D printing gypsum-based decorative panels, including the following steps:

[0080] S1: Mix α-hemihydrate gypsum powder and β-hemihydrate gypsum powder to obtain initial gypsum powder; mix the initial gypsum powder with short-cut carbon fibers to obtain printing powder; dissolve polyvinyl alcohol in water to obtain binder;

[0081] The α-hemihydrate gypsum powder has a particle size of 60 μm, and the β-hemihydrate gypsum powder has a particle size of 20 μm. The mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 3.5:6.5. The chopped carbon fibers have a length of 0.1 mm and a diameter of 8 μm; the chopped carbon fibers are soaked in 0.5 wt% silane coupling agent KH550 at 70 °C for 2.5 h. The chopped carbon fibers account for 0.4% of the mass of the initial gypsum powder in the printing powder.

[0082] S2: On a gypsum-based fiberboard, adhesive is applied via spraying along a preset spiral trajectory; printing powder is then laid in the adhesive spraying area; the spraying starting point is the center point of the substrate, the pitch is 0.1mm, and the nozzle exit height of the spray head is 0.2mm above the printing plane. The adhesive spraying speed is 8mm / s, the adhesive droplet size is 12pL, and the droplet spacing is 0.1mm.

[0083] S3: Repeat the adhesive spraying and powder application process in S2 until the decorative panel blank is obtained; the spraying spiral trajectories of adjacent adhesive layers rotate in opposite directions; the thickness of each powder layer is 0.2 mm, and the total number of layers is 600. After each powder layer is applied, wait 3 minutes before spraying the next adhesive layer.

[0084] S4: Dry the decorative panel blank to obtain a 3D printed gypsum-based decorative panel.

[0085] The drying process includes a first drying process and a second drying process. The first drying process has a temperature of 35℃, a humidity of 60%RH, and a time of 18h. The second drying process has a temperature of 25℃, a humidity of 35%RH, and a time of 60h.

[0086] Comparative Example 2:

[0087] This comparative example provides an additive manufacturing method for 3D printing gypsum-based decorative panels, including the following steps:

[0088] S1: Mix α-hemihydrate gypsum powder and β-hemihydrate gypsum powder to obtain initial gypsum powder; mix the initial gypsum powder with short-cut carbon fibers to obtain printing powder; dissolve polyvinyl alcohol in water to obtain binder;

[0089] The α-hemihydrate gypsum powder has a particle size of 60 μm, and the β-hemihydrate gypsum powder has a particle size of 20 μm. The mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 5.5:4.5. The chopped carbon fibers have a length of 0.1 mm and a diameter of 8 μm; the chopped carbon fibers are soaked in 0.5 wt% silane coupling agent KH550 at 70 °C for 2.5 h. The chopped carbon fibers account for 0.4% of the mass of the initial gypsum powder in the printing powder.

[0090] S2: On a gypsum-based fiberboard, adhesive is applied via spraying along a preset spiral trajectory; printing powder is then laid in the adhesive spraying area; the spraying starting point is the center point of the substrate, the pitch is 0.1mm, and the nozzle exit height of the spray head is 0.2mm above the printing plane. The adhesive spraying speed is 8mm / s, the adhesive droplet size is 12pL, and the droplet spacing is 0.1mm.

[0091] S3: Repeat the adhesive spraying and powder application process in S2 until the decorative panel blank is obtained; the spraying spiral trajectories of adjacent adhesive layers rotate in opposite directions; the thickness of each powder layer is 0.2 mm, and the total number of layers is 600. After each powder layer is applied, wait 3 minutes before spraying the next adhesive layer.

[0092] S4: Dry the decorative panel blank to obtain a 3D printed gypsum-based decorative panel.

[0093] The drying process includes a first drying process and a second drying process. The first drying process has a temperature of 35℃, a humidity of 60%RH, and a time of 18h. The second drying process has a temperature of 25℃, a humidity of 35%RH, and a time of 60h.

[0094] Comparative Example 3:

[0095] This comparative example provides an additive manufacturing method for 3D printing gypsum-based decorative panels, including the following steps:

[0096] S1: Mix α-hemihydrate gypsum powder and β-hemihydrate gypsum powder to obtain initial gypsum powder; mix the initial gypsum powder with short-cut carbon fibers to obtain printing powder; dissolve polyvinyl alcohol in water to obtain binder;

[0097] The α-hemihydrate gypsum powder has a particle size of 60 μm, and the β-hemihydrate gypsum powder has a particle size of 20 μm. The mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 4.5:5.5. The chopped carbon fibers have a length of 0.1 mm and a diameter of 8 μm; the chopped carbon fibers are soaked in 0.5 wt% silane coupling agent KH550 at 70 °C for 2.5 h. The chopped carbon fibers account for 0.4% of the mass of the initial gypsum powder in the printing powder.

[0098] S2: On a gypsum-based fiberboard, adhesive is applied via spraying along a preset spiral trajectory; printing powder is then laid in the adhesive spraying area; the spraying starting point is the center point of the substrate, the pitch is 0.1mm, and the nozzle exit height of the spray head is 0.2mm above the printing plane. The adhesive spraying speed is 8mm / s, the adhesive droplet size is 12pL, and the droplet spacing is 0.1mm.

[0099] S3: Repeat the adhesive spraying and powder application process in S2 until the decorative panel blank is obtained; the rotation directions of the spraying spiral trajectories of adjacent adhesive layers are opposite; the thickness of each powder layer is 0.15mm, and the total number of layers is 840. After each powder layer is applied, wait 3 minutes before spraying the next adhesive layer.

[0100] S4: Dry the decorative panel blank to obtain a 3D printed gypsum-based decorative panel.

[0101] The drying process includes a first drying process and a second drying process. The first drying process has a temperature of 35℃, a humidity of 60%RH, and a time of 18h. The second drying process has a temperature of 25℃, a humidity of 35%RH, and a time of 60h.

[0102] Comparative Example 4:

[0103] This comparative example provides an additive manufacturing method for 3D printing gypsum-based decorative panels, including the following steps:

[0104] S1: Mix α-hemihydrate gypsum powder and β-hemihydrate gypsum powder to obtain initial gypsum powder; mix the initial gypsum powder with short-cut carbon fibers to obtain printing powder; dissolve polyvinyl alcohol in water to obtain binder;

[0105] The α-hemihydrate gypsum powder has a particle size of 60 μm, and the β-hemihydrate gypsum powder has a particle size of 20 μm. The mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 4.5:5.5. The chopped carbon fibers have a length of 0.1 mm and a diameter of 8 μm; the chopped carbon fibers are soaked in 0.5 wt% silane coupling agent KH550 at 70 °C for 2.5 h. The chopped carbon fibers account for 0.4% of the mass of the initial gypsum powder in the printing powder.

[0106] S2: On a gypsum-based fiberboard, adhesive is applied via spraying along a preset spiral trajectory; printing powder is then laid in the adhesive spraying area; the spraying starting point is the center point of the substrate, the pitch is 0.1mm, and the nozzle exit height of the spray head is 0.2mm above the printing plane. The adhesive spraying speed is 8mm / s, the adhesive droplet size is 12pL, and the droplet spacing is 0.1mm.

[0107] S3: Repeat the adhesive spraying and powder application process in S2 until the decorative panel blank is obtained; the rotation directions of the spraying spiral trajectories of adjacent adhesive layers are opposite; the thickness of each powder layer is 0.35mm, and the total number of layers is 360. After each powder layer is applied, wait 3 minutes before spraying the next adhesive layer.

[0108] S4: Dry the decorative panel blank to obtain a 3D printed gypsum-based decorative panel.

[0109] The drying process includes a first drying process and a second drying process. The first drying process has a temperature of 35℃, a humidity of 60%RH, and a time of 18h. The second drying process has a temperature of 25℃, a humidity of 35%RH, and a time of 60h.

[0110] Comparative Example 5:

[0111] This comparative example provides an additive manufacturing method for 3D printing gypsum-based decorative panels, the steps of which are as follows:

[0112] β-hemihydrate gypsum powder with a particle size range of 30μm was used as the main material, without any added reinforcing fibers. The binder was a polyvinyl alcohol aqueous solution with a solid content controlled at 10wt%, prepared using a simple dissolution method. Regarding process parameters, the printing substrate was a regular wooden flat plate. An Archimedes spiral spraying method was used, with a pitch of 0.5mm, a droplet volume of 20pL, a droplet spacing of 0.2mm, and a spraying speed of 8mm / s. The spraying spiral direction of adjacent layers was opposite, i.e., odd-numbered layers were clockwise, and even-numbered layers were counterclockwise. Each layer was pure β-hemihydrate gypsum powder, 0.5mm thick, with a total of 252 layers. After laying each layer, a 1-minute waiting period was observed before spraying the next layer. Drying was a single-stage process at 50℃ with no humidity control for 12 hours, ultimately yielding a gypsum-based blank.

[0113] Comparative Example 6:

[0114] This comparative example provides an additive manufacturing method for 3D printing gypsum-based decorative panels, the steps of which are as follows:

[0115] The mixture of α-hemihydrate gypsum powder and β-hemihydrate gypsum powder at a mass ratio of 3:7, with α-hemihydrate gypsum powder having a particle size of 100 μm and β-hemihydrate gypsum powder having a particle size of 30 μm, and no short-cut carbon fibers or other reinforcements added; the binder is a polyvinyl alcohol aqueous solution with a solid content of 6 wt%. The process parameters employ a standard powder-spreading method, where the mixed gypsum powder is first evenly spread on a worktable to a thickness of 0.4 mm, followed by overall spraying of the binder through a linear reciprocating nozzle with a droplet spacing of 0.3 mm, without spiral trajectory control. The binder is sprayed directly after each layer of powder is spread, without any settling time, for a total of 315 layers. Drying is a single-stage process at 45℃ for 24 hours, ultimately forming the decorative panel blank.

[0116] Shrinkage rate test, interlaminar bond test, planar deformation test, and toughness test were performed on the samples of the above embodiments and comparative examples, respectively. The shrinkage rate test standard was GB / T 17669.4-2010, the interlaminar bond test standard was ASTM D2344, the planar deformation test standard was GB / T 9775-2008, and the toughness test standard was GB / T 1043.1-2008. The test data are shown in Table 1.

[0117] The shrinkage rate test measures the change in length of the sample before and after drying and calculates the linear shrinkage rate, with the index being the linear shrinkage rate; the interlaminar bond test standard is to induce shear stress between the layers through three-point bending loading, record the failure load and calculate the strength, with the index being the strength; the planar deformation test measures the standard deviation of the height of points at the same horizontal height before and after drying of the sample, with the index being the standard deviation; the toughness test releases the pendulum, records the remaining energy of the pendulum after the sample breaks, and calculates the absorbed work, with the index being the absorbed work.

[0118] Table 1. Deformation and toughness test data for Examples 1-5 and Comparative Examples 1-6

[0119] Data source Linear shrinkage rate (%) Strength (MPa) Standard deviation (δ) Toughness absorption work (J) Example 1 0.39 1.3 0.5 1.3 Example 2 0.31 1.6 0.3 1.5 Example 3 0.40 1.7 0.4 1.4 Example 4 0.25 2.1 0.2 1.7 Example 5 0.42 1.8 0.4 1.6 Comparative Example 1 0.63 0.9 0.9 1.0 Comparative Example 2 0.59 1.0 0.7 1.1 Comparative Example 3 0.60 1.0 0.6 1.2 Comparative Example 4 0.65 0.9 0.8 1.3 Comparative Example 5 0.87 0.8 1.2 0.5 Comparative Example 6 0.83 0.7 1.4 0.4

[0120] As shown in Table 1, the linear shrinkage rate and standard deviation of Examples 1-5 are all smaller than those of Comparative Examples 1-6, and the interlaminar bond strength and toughness absorption work of Examples 1-5 are all greater than those of Comparative Examples 1-6. This solution has advantages.

[0121] In Examples 1-3 and Comparative Examples 1-2, as the proportion of α-hemihydrate gypsum powder in the mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder gradually increases, the linear shrinkage rate and standard deviation first decrease and then increase, while the interlayer bonding strength and toughness absorption work first increase and then decrease. This is because as the proportion of α-hemihydrate gypsum powder in the gypsum powder gradually increases within the mass ratio, the large-diameter particles of α-hemihydrate gypsum can construct a more stable skeleton structure, forming complementary filling with the small-diameter particles of β-hemihydrate gypsum, reducing the voids between particles. The large-diameter particles of α-hemihydrate gypsum and the small-diameter particles of β-hemihydrate gypsum form a skeleton-filler complementary structure. The increase in the proportion of α makes the skeleton more stable and the filling more dense, reducing the voids between particles. During hydration, the growth of dihydrate calcium sulfate crystals is more uniform, and the shrinkage stress difference is significantly reduced. Therefore, the linear shrinkage rate and standard deviation decrease accordingly. Simultaneously, the slow-setting characteristics of the α-phase and the fast-setting characteristics of the β-phase tend to balance, the setting time difference narrows, the binder can fully penetrate the composite matrix, and the interlayer mechanical interlocking formed by the reverse spiral spraying improves the interlayer bonding strength; the bridging effect of uniform hydration products and short-cut carbon fibers synergistically enhances the material's toughness, increasing the toughness absorption work. However, if the α-phase proportion is too high, its slow-setting characteristics dominate the hydration process, leading to a prolonged overall setting time and uneven reaction—an increase in large-diameter α-particles results in insufficient filling, increased porosity, disordered water migration paths, increased differences in crystal growth rates, a rebound in shrinkage stress difference, and a corresponding increase in linear shrinkage rate and standard deviation. Furthermore, slow setting leads to insufficient binder penetration, weak bonding of the lower powder layers, weakened mechanical interlocking effect of the reverse spiral, and decreased interlayer bonding strength; excessive α-phase exacerbates the imbalance between the setting rates of the α-phase and β-phase, widening the shrinkage difference between different regions during drying, reducing the interfacial stress transfer efficiency of the short-cut carbon fibers, and causing the material to shift from a strong-tough balance to a brittle-dominated state, reducing the toughness absorption work. The preferred embodiment is Example 2.

[0122] In Examples 2, 4, 5 and Comparative Examples 3-4, as the thickness of each printed powder layer gradually increases, the linear shrinkage rate and standard deviation first decrease and then increase, while the interlayer bonding strength and toughness absorption work first increase and then decrease. This is because, with moderate thickness, the powder layer provides more sufficient penetration space for the binder. The binder sprayed by the Archimedes spiral jet can form a more continuous three-dimensional network in the layer, promoting the synergistic hydration of α-hemihydrate gypsum and β-hemihydrate gypsum, resulting in more uniform growth of calcium sulfate dihydrate crystals and reducing the expansion differences caused by uneven local hydration. Therefore, the linear shrinkage rate and standard deviation decrease. At the same time, the total number of layers decreases with the increase of the thickness of a single layer, the number of interlayer interfaces decreases, and the superposition effect of shrinkage stress between adjacent layers weakens, further suppressing overall shrinkage and deformation unevenness. Regarding interlayer bonding strength, moderate thickness allows the binder to more uniformly cover the powder particles. Combined with the cross-interlocking structure of the reverse spiral spraying, the interlayer mechanical interlocking is tighter, and the bonding force is improved. Toughness absorption energy initially shows an increasing trend due to improved hydration uniformity and increased stress transfer efficiency at the interface between the fiber reinforcement and the gypsum matrix, enhancing the material's ability to absorb impact energy. However, when the thickness exceeds a critical value, the excessively thick powder layer makes it difficult for the binder to fully penetrate to the bottom layer. The lower powder layer, due to insufficient contact with the binder, suffers from inadequate bonding, forming internal pores. During hydration, the upper layer reacts faster than the lower layer, resulting in a significant increase in the difference in crystal growth rates, leading to a rebound in deformation, and consequently, an increase in linear shrinkage and standard deviation. In terms of interlayer bonding strength, excessive thickness weakens the bond between the lower powder layer and the upper binder, diminishes the mechanical interlocking effect of the reverse spiral, and makes the layers prone to delamination due to stress concentration, resulting in decreased bonding strength. The toughness absorption work decreases because the moisture evaporation path is prolonged in the thick layer, and the asynchronous drying shrinkage leads to local stress concentration. The bridging cracking effect of the short-cut carbon fibers is suppressed, and the material shifts from a strong-tough balance to a brittle-dominated state, thus weakening its ability to absorb impact energy. The preferred embodiment is Example 4.

[0123] In Comparative Example 5, although the two-component gypsum can reduce uneven hydration and shrinkage through the complementarity of the large-particle-size α-phase skeleton and the small-particle-size β-phase filler, it lacks the interlayer mechanical interlocking of the reverse spiral process. The interlayer bonding still relies on ordinary bonding, resulting in limited strength improvement. Moreover, without carbon fiber reinforcement, the toughness is easily limited by the brittleness of single gypsum.

[0124] In Comparative Example 6, although the interlayer bonding can be enhanced through spiral cross-interlocking, if the material is a single gypsum or a two-component material with an unoptimized ratio, it cannot solve the problems of large shrinkage stress and high standard deviation of planar deformation caused by the difference in hydration rate. In addition, there are no fiber bridging cracks, and it is difficult to improve the toughness absorption work.

[0125] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for additive manufacturing of 3D printed gypsum-based decorative panels, characterized in that, Includes the following steps: S1: Mix α-hemihydrate gypsum powder and β-hemihydrate gypsum powder to obtain initial gypsum powder; mix the initial gypsum powder with chopped carbon fibers to obtain printing powder; dissolve polyvinyl alcohol in water to obtain a binder; S2: Apply adhesive to the gypsum-based fiberboard by spraying along a preset spiral trajectory; then lay the printing powder in the area where the adhesive is sprayed. S3: Repeat the spraying of the adhesive and the laying of the printing powder in S2 until a decorative panel blank is obtained; the rotation directions of the spraying spiral trajectories of adjacent layers of adhesive are opposite; S4: Dry the decorative panel blank to obtain a 3D printed gypsum-based decorative panel.

2. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: The α-hemihydrate gypsum powder has a particle size of 50-100 μm, and the β-hemihydrate gypsum powder has a particle size of 10-30 μm.

3. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: The mass ratio of α-hemihydrate gypsum powder to β-hemihydrate gypsum powder in the initial gypsum powder is 4:6-5:

5.

4. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: The chopped carbon fibers have a length of 0.08-0.12 mm and a diameter of 7-10 μm; the chopped carbon fibers are soaked in 0.5 wt% silane coupling agent KH550 at a temperature of 60-80°C for 2-3 hours.

5. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: The short-cut carbon fibers in the printing powder account for 0.3-0.5% of the mass of the initial gypsum powder.

6. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: The injection starting point in S2 is the center point of the substrate, the pitch is 0.1-0.15mm, and the height of the nozzle outlet of the injection head from the printing plane is 0.1-0.3mm.

7. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: The adhesive spraying speed is 5-10 mm / s, the adhesive droplets are 10-15 pL, and the droplet spacing is 0.1-0.15 mm.

8. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: The thickness of each layer of the printed powder is 0.2-0.3 mm.

9. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: After each layer of printing powder is laid, wait 2-4 minutes before spraying the next layer of adhesive.

10. The additive manufacturing method for 3D printed gypsum-based decorative panels according to claim 1, characterized in that: The drying process includes a first drying process and a second drying process. The first drying process has a temperature of 30-40℃, a humidity of 50-60%RH, and a time of 12-24h. The second drying process has a temperature of 24-26℃, a humidity of 30-40%RH, and a time of 24-72h.

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