Preparation method of low-refractive composite powder and application thereof

Abstract

The application discloses a preparation method of a low-refractive composite powder and application thereof. The preparation method of the low-refractive composite powder comprises the following steps: mixing submicron powder with a mixture containing tetraethyl orthosilicate, heating, and reacting under an acidic condition to obtain a first sol slurry; mixing and stirring the first slurry with a binder to obtain a second slurry; and performing spray granulation and calcination on the second slurry to obtain a low-refractive core-shell structure composite powder. According to the technical scheme, the high-refractive or high-absorbance submicron powder, which is not suitable for or cannot be used for 3D printing, is covered with the silicon dioxide nanoparticles formed by the reaction of the mixture containing tetraethyl orthosilicate on the surface of the submicron powder, so that the refractive index or the absorbance of the submicron powder is reduced, the refractive index difference between the ceramic powder material which is difficult to solidify or cannot be solidified and the photosensitive resin is reduced, and the solidification performance of the ceramic material is improved.

Description

A method for preparing a low-refractive-index composite powder and its application. Technical Field

[0001] This invention relates to the field of ceramic 3D printing, specifically to a method for preparing a low-refractive-index composite powder and its application. Background Technology

[0002] Current research on photopolymerization printing of ceramics mainly focuses on light-colored ceramic materials such as white and gray, primarily oxide ceramics such as alumina and zirconium oxide, bioceramics such as hydroxyapatite and tricalcium phosphate, and a small amount of non-oxide materials such as SiC and Si3N4. However, materials with slightly darker colors, such as SiC and Si3N4, are difficult to cure directly in 3D printing because photopolymerization printing primarily uses ultraviolet light with shorter wavelengths. For example, green nickel oxide powder, due to its high refractive index and high absorbance, cannot be directly photopolymerized. Research on darker ceramics with higher refractive indices and high absorbance is still insufficient, especially on the photopolymerization printing of colored ceramic materials. This remains a difficult industry challenge to overcome. For instance, green NiO has almost zero curing performance and cannot be directly photopolymerized for printing.

[0003] Therefore, there is an urgent need to develop a new preparation method so that these dark-colored, high-refractive-index and high-absorbency materials can be applied to the field of 3D printing, thus broadening the range of materials used in photopolymerization printing. Summary of the Invention

[0004] The main objective of this invention is to propose a method for preparing low-refractive-index composite powder and its application, aiming to solve the problem that dark-colored ceramic materials, due to their high refractive index and high light absorption, have almost zero curing performance during 3D photopolymerization printing, making them unsuitable for direct photopolymerization printing.

[0005] To achieve the above objectives, this invention proposes a method for preparing a low-refractive-index composite powder, the method comprising the following steps:

[0006] S10. Mix the submicron powder with a mixture containing tetraethyl orthosilicate, heat, and react under acidic conditions to obtain the first slurry;

[0007] S20. Mix the first slurry with the binder to obtain the second slurry;

[0008] S30. The second slurry is spray-granulated and calcined to obtain a composite powder with low refractive index.

[0009] Optionally, in step S10, the mixture containing tetraethyl orthosilicate includes tetraethyl orthosilicate, ethanol, water, and acetic acid.

[0010] Optionally, the mass ratio of the tetraethyl orthosilicate, the ethanol, the water, and the acetic acid is (5-10):(53-66):(1.5-2.5):(0.5-1.5).

[0011] Optionally, in step S10, the material of the submicron powder includes zirconium oxide, nickel oxide, or silicon carbide.

[0012] Optionally, in step S10, the heating temperature is 45–60°C; and / or the heating time is 24–48 hours; and / or, under the acidic conditions, the pH value is 3–5.

[0013] Optionally, in step S20, the binder includes at least one of PVP, PEG2000, and PVA, wherein the mass of the binder added is 1 to 3% of the mass of the submicron powder.

[0014] Optionally, in step S30, the calcination temperature is 600–800°C; and / or the calcination time is 250–350 min.

[0015] Optionally, in step S30, the parameters of the spray granulation include: an inlet temperature of 150–210°C and an outlet temperature of 60–90°C.

[0016] The present invention also provides a photocurable 3D printing material, wherein the photocurable 3D printing material is a low-refractive-index composite powder prepared by the low-refractive-index composite powder preparation method described above.

[0017] In the technical solution provided by this invention, submicron powder and a mixture containing tetraethyl orthosilicate are used as polymer coating agents and mechanically stirred until uniformly mixed. Simultaneously, when heated to a certain temperature in a water bath, the mixture containing tetraethyl orthosilicate undergoes a chemical reaction to form silica sol. During this process, as the reaction proceeds, more nano-silica sol particles accumulate and adhere to the submicron powder, forming a first slurry. After the reaction reaches a certain extent, a binder is added to improve the adhesion between particles, making them less prone to loosening. After mixing and stirring with the binder to form a second slurry, the second slurry is spray-granulated to form spherical particles, simultaneously improving adhesion. After calcination, the density of the polymer particles is further improved. Simultaneously, the silica sol particles adsorbed on the powder surface form a silica nanoparticle layer after calcination. This silica nanoparticle layer coats the atomized and dried submicron powder, not only improving density but also obtaining a low-refractive-index silica nanoparticle layer, resulting in a low-refractive-index composite powder, significantly improving the curing performance of the powder. Attached Figure Description

[0018] 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 of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 is a schematic diagram of the structure of a low-refractive-index composite powder prepared by an embodiment of the preparation method provided by the present invention.

[0020] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. 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.

[0022] Current research on photopolymerization printing of ceramics mainly focuses on light-colored ceramic materials such as white and gray, primarily oxide ceramics such as alumina and zirconium oxide, bioceramics such as hydroxyapatite and tricalcium phosphate, and a small amount of non-oxide materials such as SiC and Si3N4. However, materials with slightly darker colors, such as SiC and Si3N4, are difficult to cure directly in 3D printing because photopolymerization printing primarily uses ultraviolet light with shorter wavelengths. For example, green nickel oxide powder, due to its high refractive index and high absorbance, cannot be directly photopolymerized. Research on darker ceramics with higher refractive indices and high absorbance is still insufficient, especially on the photopolymerization printing of colored ceramic materials. This remains a difficult industry challenge to overcome. For instance, green NiO has almost zero curing performance and cannot be directly photopolymerized for printing.

[0023] In view of this, the present invention proposes a low-refractive-index composite powder, the preparation method of which includes the following steps:

[0024] S10. Mix the submicron powder with a mixture containing tetraethyl orthosilicate, heat, and react under acidic conditions to obtain the first slurry;

[0025] S20. Mix the first slurry with the binder to obtain the second slurry;

[0026] S30. The second slurry is spray-granulated and calcined to obtain a composite powder with low refractive index.

[0027] In the preparation method of this application, submicron powder and a mixture containing tetraethyl orthosilicate are used as polymer coating agents and mechanically stirred until uniformly mixed. Simultaneously, when heated to a certain temperature in a water bath, the mixture containing tetraethyl orthosilicate undergoes alcoholysis and hydrolysis chemical reactions. Due to the presence of powder particles, the reacted substances use the powder as a nucleating agent to form silica sol on the surface of the powder particles. During this process, as the reaction proceeds, more nano-silica sol particles accumulate on the powder surface, adhering to the entire surface of the submicron powder particles. At this point, a first slurry of new chemically reacted substances (powder and nano-silica sol particles) is formed. After the chemical reaction reaches its maximum extent, a binder is added to improve the adhesion between particles, making them less prone to loosening. After forming the second slurry, the second slurry is spray-granulated to form spherical particles. The sol particle layer adsorbed on the particle surface forms a gel layer through spray drying, which improves the adhesion of the powder particles. After calcination, the density of the agglomerated particles is further improved. At the same time, the silica sol particles adsorbed on the powder surface will generate silica nanoparticles under high-temperature calcination, forming a silica nanoparticle film layer covering the entire particle surface of the submicron powder. The silica nanoparticle film layer completely covers the atomized and dried submicron powder, which not only improves the density but also obtains a low-refractive-index silica nanoparticle layer, resulting in a low-refractive-index composite powder, which greatly improves the curing performance of the powder.

[0028] In some embodiments, in step S10, the mixture containing tetraethyl orthosilicate includes tetraethyl orthosilicate, ethanol, water, and acetic acid.

[0029] It should be noted that mixtures containing tetraethyl orthosilicate can undergo both alcoholysis and hydrolysis. Depending on the acid and alkaline conditions, the final particle size of the silica will vary.

[0030] In some embodiments, the mixture containing tetraethyl orthosilicate is prepared under acidic conditions with the addition of acetic acid. This results in smaller polymer particles, smaller gaps between particles, and higher density. Simultaneously, in conjunction with ethanol, tetraethyl orthosilicate undergoes an alcoholysis reaction to obtain a silicon-oxygen structure film layer. This film layer can be used to coat submicron powders, forming a nano-sized silica nanoparticle film layer on the surface of the submicron powder. This silica nanoparticle film layer is formed using a sol-gel method and chemical reaction, with the powder as a nucleating agent, to form very uniform nano-sol particles on the entire surface of the particles. The sol particle layer adsorbed on the particle surface is spray-dried to form a gel layer, and then calcined at high temperature to convert the sol particles into silica nanoparticles, thereby transforming the gel film layer into a silica nanoparticle film layer. This process enables the preparation of a nano-film layer on the powder surface, achieving the goal of fully coating the entire powder particle, forming a fully coated core-shell structure powder, thus improving curing performance.

[0031] In some embodiments, the mass ratio of tetraethyl orthosilicate, ethanol, water, and acetic acid is (5-10):(53-66):(1.5-2.5):(0.5-1.5), for example, 5:60:2:1, 10:65:2.5:1.5, 7:60:2:1, etc. By controlling the proportions of tetraethyl orthosilicate, ethanol, water, and acetic acid to meet the above range, the core-shell structure can be better controlled, the film thickness can be better controlled, and the size and particle distribution of the low-refractive-index composite powder can be adjusted, resulting in a denser particle distribution.

[0032] In some embodiments, in step S10, the material of the submicron powder includes zirconium oxide, nickel oxide, or silicon carbide.

[0033] It should be noted that the submicron powder material in this embodiment can be any material that can be used for 3D printing. For example, although silicon carbide has a high refractive index, its refractive index can be reduced by coating it with tetraethyl orthosilicate, thus making it applicable to 3D printing and broadening the range of material applications.

[0034] In some embodiments, in step S10, the heating temperature is 45–60°C; and / or the heating time is 24–48 hours; and / or, under the acidic conditions, the pH value is 3–5. In this invention, the heating method can be water bath heating, the heating temperature can be 45°C, 50°C, 55°C, or 60°C, etc., and the heating time can be 24 hours, 30 hours, 35 hours, or 48 hours. Under the acidic conditions, a pH value of 3, 4, or 5 is preferred. Within this range, the submicron powder can react fully with the mixture containing tetraethyl orthosilicate, and the reaction efficiency can be improved.

[0035] In some embodiments, the binder includes at least one of PVP, PEG2000, and PVA, wherein the mass of the binder added is 1 to 3% of the mass of the submicron powder.

[0036] It should be noted that the binder is added to improve the adhesion between particles. The binder can be any one of PVP, PEG2000 or PVA, or any two at the same time. Furthermore, the added and prepared composite powder particles have better density and improved curing performance. The mass of the binder added is 1 to 3% of the mass of the submicron powder, which can be 1%, 2% or 3%. Within this range, the curing effect is better.

[0037] In step S30, the calcination temperature is 600–800°C; and / or the calcination time is 250–350 min.

[0038] It should be noted that the calcination temperature can be 600℃, 650℃, 700℃ or 800℃, and the calcination time can be 250min, 280min, 300min or 350min respectively. Within this range, calcination is sufficient and the bonding force between particles is improved, making the prepared particles more compact and further improving the density.

[0039] In step S30, the parameters of the spray granulation include: inlet temperature of 150-210°C and outlet temperature of 60-90°C.

[0040] Furthermore, in order to achieve better granulation effect of composite powder, the parameters of spray granulation can be controlled. The inlet temperature can be set to 150℃, 180℃ or 210℃, and the outlet temperature can be set to 60℃, 80℃ or 90℃. Within the above range, the spray granulation effect is better, resulting in a denser spherical shape formed between particles.

[0041] The present invention also provides a 3D printing material, wherein the photocurable 3D printing material is a low-refractive-index composite powder prepared by the preparation method of the low-refractive-index composite powder as described above. Therefore, it includes all the beneficial effects of the above preparation method, and will not be described in detail.

[0042] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0043] Example 1

[0044] A method for preparing a low-refractive-index composite powder includes the following steps:

[0045] 1) 40g of submicron zirconia powder (particle size 0.5μm) was mixed with 5g of tetraethyl orthosilicate, 53g of ethanol, 1.5g of water and 0.5g of acetic acid in a reaction vessel while being heated to 45℃. After stirring for 24 hours, the first slurry was obtained.

[0046] 2) Add 0.4g of PVP binder to the first slurry, continue heating and mechanical stirring for a period of time to obtain the mixed second slurry;

[0047] 3) The second slurry is spray-dried and granulated. The inlet temperature is 150℃ and the outlet temperature is 60℃ to obtain SiOn coated spherical core-shell structure powder A.

[0048] Powder A was placed in a sintering furnace and calcined at 600°C for 250 minutes to obtain a composite powder with low refractive index.

[0049] The difference between Examples 2-15 and Example 1 lies in the changes in preparation parameters, as detailed in Table 1.

[0050] Table 1

[0051]

[0052]

[0053] Comparative Example 1

[0054] Using existing zirconium oxide powder, the tetraethyl orthosilicate mixture in step 1) was removed, and the rest was the same as in Example 1.

[0055] Comparative Example 2

[0056] Using existing nickel oxide powder, except for the tetraethyl orthosilicate mixture in step 1), the rest is the same as in Example 6.

[0057] Comparative Example 3

[0058] Using existing silicon carbide powder, except for step 1) of the tetraethyl orthosilicate mixture, the rest is the same as in Example 11.

[0059] Results Analysis

[0060] The high-gloss-curing ceramic slurries prepared in Examples 1-15 and Comparative Examples 1-3 were subjected to curing performance tests, and the experimental results are shown in Table 2.

[0061] Table 2

[0062] Example Curing Depth (μm) Example 1 264 Example 2 268 Example 3 263 Example 4 275 Example 5 271 Example 6 231 Example 7 243 Example 8 229 Example 9 235 Example 10 238 Example 11 245 Example 12 249 Example 13 238 Example 14 241 Example 15 244 Comparative Example 130 Comparative Example 20 Comparative Example 320 surface

[0063] Table 2 shows that, for different powders—zirconia, nickel oxide, and silicon carbide—the curing depth was tested after removing and adding the coating agent. Nickel oxide powder, according to existing technology, cannot cure, therefore the curing depth is 0. After adding the tetraethyl orthosilicate mixture, the curing depth increased from 0 to 229–243 μm. For zirconia powder coated with the tetraethyl orthosilicate mixture, the curing depth also increased from 30 μm to 263–275 μm. For silicon carbide coated with the tetraethyl orthosilicate mixture, the curing depth also increased from 20 μm to 238–249 μm. This indicates that using the tetraethyl orthosilicate mixture of this application for coating… After coating, tetraethyl orthosilicate undergoes hydrolysis and alcoholysis to obtain a silicon-oxygen structure film layer, which can be used to coat submicron powders. A nano-sized silica nanoparticle film layer is formed on the surface of the submicron powder, forming a silica nanoparticle film layer on the shell of the original uncurable or poorly cured nanocomposite powder. The low refractive index of this film layer reduces the refractive index difference between the powder and the curing material during subsequent curing, thereby improving printing efficiency and overall curing depth. This avoids the problem of poor curing effect or even failure to cure caused by directly using the high refractive index of nanoparticles and the high refractive index difference between the powder and the curing material.

[0064] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A method for preparing a low-refractive-index composite powder, characterized in that, The preparation method of the low refractive index composite powder includes the following steps: S10, mixing submicron powder with a mixture containing tetraethyl orthosilicate, heating, and reacting under acidic conditions to obtain a first slurry; S20, mixing and stirring the first slurry with a binder to obtain a second slurry; S30, spray granulating and calcining the second slurry to obtain a low refractive index composite powder, wherein the mixture containing tetraethyl orthosilicate includes tetraethyl orthosilicate, ethanol, water, and acetic acid, and the mass ratio of tetraethyl orthosilicate, ethanol, water, and acetic acid is (5~10):(53~66):(1.5~2.5):(0.5~1.5), in step S10, the material of the submicron powder includes zirconium oxide, nickel oxide, or silicon carbide, and in step S30, the calcination temperature is 600~800℃, and the calcination time is 250~350 min.

2. The method for preparing the low-refractive-index composite powder as described in claim 1, characterized in that, In step S10: the heating temperature is 45~60℃; and / or the heating time is 24~48 hours; and / or, under the acidic conditions, the pH value is 3~5.

3. The method for preparing the low-refractive-index composite powder as described in claim 1, characterized in that, In step S20: the binder includes at least one of PVP, PEG2000, and PVA; and / or, the mass of the binder added is 1 to 3% of the mass of the submicron powder.

4. The method for preparing the low-refractive-index composite powder as described in claim 1, characterized in that, In step S30: the parameters of the spray granulation include: the inlet temperature is 150~210℃ and the outlet temperature is 60~90℃.

5. A photopolymerizable 3D printing material, characterized in that, The photopolymer 3D printing material is a low-refractive-index composite powder prepared by the method for preparing low-refractive-index composite powder as described in any one of claims 1 to 4.

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