Surface treatment method for improving wettability of PMMA 3D printing powder

Abstract

The invention discloses a surface treatment method for improving wettability of PMMA 3D printing powder. The method comprises the following steps: firstly, carrying out low-temperature dehydration and plasma activation treatment on PMMA powder to enhance the surface activity, and then uniformly coating and depositing a SiOfilm on the surface of the PMMA powder by taking a silane precursor and an oxidant as reaction sources under the low-temperature condition of 30-80 DEG C through a rotation-assisted atomic layer deposition technology, so as to obtain the PMMA / SiOM composite material. And finally, annealing the PMMA powder to enhance the binding force of the film. According to the method, the wettability of the PMMA powder is remarkably improved, and the method is suitable for high-resolution additive manufacturing and multi-material composite printing. The thermal degradation limitation of a traditional modification process is broken through, and the prepared SiO-coated PMMA powder has no agglomeration phenomenon after being stored for 30 days in an environment with the humidity larger than or equal to 75% and shows excellent interface bonding force and forming quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface modification and additive manufacturing of polymer materials, and particularly relates to a surface treatment method for improving the wettability of PMMA 3D printing powder. Background Art

[0002] Polymethyl methacrylate (PMMA) is regarded as an ideal 3D printing material due to its excellent light transmittance, low density, and easy processability. However, its application in jet bonding (such as binder jetting) technology is severely restricted. The main reasons are as follows: 1. Stable surface properties and poor wettability: The PMMA powder has strong surface chemical inertness and low surface energy (usually <40 mN / m), resulting in poor wettability with polar binders (such as water-based or alcohol-based binders), insufficient interfacial bonding force, and easy delamination or strength defects in the formed parts. 2. High thermal sensitivity: The glass transition temperature (Tg) of PMMA is about 90 °C. Traditional surface modification technologies (such as high-temperature plasma treatment, melt coating, etc.) need to be carried out at high temperatures (>100 °C), which easily leads to powder softening, caking, and even thermal degradation, damaging the fluidity and printing accuracy of the powder. 3. Limitations of traditional modification technologies: Existing surface coating methods (such as mechanical mixing coating, solution impregnation) are difficult to achieve nanoscale uniform coating, and are prone to introducing impurities or damaging the powder morphology, resulting in unstable modification effects.

[0003] In view of the above problems, the present invention proposes a low-temperature surface treatment process based on atomic layer deposition, which significantly improves the wettability by precisely regulating the surface chemical composition and microstructure of PMMA powder without affecting its thermal stability. Summary of the Invention

[0004] The purpose of the present invention is to provide a surface treatment method for improving the wettability of PMMA 3D printing powder. In view of the problems of poor wettability and low surface activity of PMMA powder, the present invention proposes a low-temperature surface treatment method based on atomic layer deposition (ALD) technology. By coating a nanoscale dense SiO2 film on the surface of PMMA powder, its wettability and 3D printing performance are significantly improved.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A surface treatment method for improving the wettability of PMMA 3D printing powder, comprising the following steps:

[0007] 1) Low-temperature dehydration: Place the PMMA powder (particle size range 1-100 μm) in a vacuum drying device and treat it at 40-60 °C for 1-3 hours to remove the water adsorbed on the powder surface and part of the embedded moisture, so as to ensure that the subsequent film deposition process is not interfered by water molecules.

[0008] 2) Surface activation: The dehydrated PMMA powder is surface - modified by oxygen plasma with a power range of 50 - 200 W and a treatment time of 1 - 10 minutes. This step removes surface contaminants through mild etching and introduces oxygen - containing functional groups (such as hydroxyl groups) at the same time, significantly improving the adsorption ability of the powder surface to the deposition precursor.

[0009] 3) Perform ALD coating deposition: Using silane - based precursors and oxidants as reaction sources, a 1 - 10 nm gradient - dense SiO2 thin film (surface roughness less than 1 nm) is uniformly coated and deposited on the surface of PMMA powder by rotating - chamber - assisted atomic layer deposition. The deposition conditions are as follows:

[0010] Temperature control: The thin - film deposition process is carried out in the range of 30 - 80 °C (preferably 60 - 70 °C) to avoid thermal decomposition of PMMA powder.

[0011] Reaction atmosphere: Inert gas atmosphere, using a slightly negative - pressure environment, without high - vacuum conditions.

[0012] Precursor selection: Alternately introduce silane - based precursors (such as silicon tetrachloride SiCl4 or TEOS) and oxidants (such as water vapor or ozone), and use inert gases (such as nitrogen or argon) as carrier gases and purge gases.

[0013] Pulse parameters: The pulse - time ratio of silane - based precursors to oxidants is 1:2 - 1:3. After each pulse, a 15 - 60 - second purge is carried out, and the total number of cycles is 5 - 40 times.

[0014] Rotating - chamber rotation speed: 20 - 100 rpm to ensure uniform dispersion of powder particles, avoid accumulation and coverage dead - angles.

[0015] This step uses a rotating atomic layer deposition device to perform surface treatment on the powder. The rotating chamber continuously rotates to uniformly disperse PMMA powder particles in the reaction chamber, avoiding particle accumulation and ensuring sufficient contact between the precursor gas and the surface of each particle. The rotational motion can also effectively prevent adhesion between particles, further improving the uniformity and coverage integrity of the thin film. The gas flow in the chamber is precisely controlled in terms of flow rate and pressure to ensure a high degree of consistency in the thin - film deposition thickness.

[0016] 4) Post - treatment: Under the protection of inert gas, the PMMA powder coated with SiO2 is subjected to low - temperature annealing treatment at 30 - 60 °C for 10 - 30 minutes to eliminate the residual stress inside the thin film and further enhance the bonding strength between the SiO2 thin film and the PMMA powder surface.

[0017] The PPMMA powder obtained by the surface treatment method of the present invention shows higher coating uniformity and interfacial bonding strength when applied to the 3D printing process.

[0018] The present invention adopts the above technical solutions, performs low-temperature dehydration and plasma activation treatment on PMMA powder to enhance surface activity, develops pulse timing feedback control technology (the pulse time ratio of precursor / oxidant is 1:2 - 1:3), realizes three-dimensional full coverage of the inner surface of micro-nano pores by ALD coating (coverage rate > 99.6%), and finally performs annealing treatment on the coated PMMA powder to enhance the film bonding force. This method significantly improves the wettability of PMMA powder. After the coating treatment, the water contact angle of the powder decreases by ≤ 50%, which is suitable for high-resolution additive manufacturing and multi-material composite printing. The present invention breaks through the thermal degradation limitation of traditional modification processes. The prepared SiO2-coated PMMA powder shows no agglomeration phenomenon after being stored in an environment with a humidity ≥ 75% for 30 days, and exhibits excellent interfacial bonding force and molding quality.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) The present invention forms a continuous and dense SiO2 film on the surface of PMMA powder through the ALD process, introduces polar Si-O bonds, and improves its wettability with water or polar solvents.

[0021] (2) After the surface of PMMA powder is coated with a SiO2 film, the surface energy of PMMA powder is homogenized, the agglomeration phenomenon between powders is reduced, and its fluidity is improved.

[0022] (3) The presence of the SiO2 film significantly improves the interfacial bonding force between PMMA powder and the binder or other materials, which is suitable for multi-material composite printing. Description of the Drawings

[0023] Figure 1 TEM characterization diagram of PMMA particles coated for 10 cycles; where, a: HRTEM bright field image; b: local magnification; c: HAADF-STEM dark field image; d: EDS element content diagram; (e) - (h) TEM-EDS surface scan images.

[0024] Figure 2 TEM characterization diagram of PMMA particles coated for 20 cycles; where, a: HRTEM bright field image; b: local magnification; c: EDS element content diagram; (d) - (g) TEM-EDS surface scan images.

[0025] Figure 3 Contact angle comparison diagram; where, a: Curve of contact angle measured by the sessile drop method changing with time; b: Pictures of water droplets penetrating into the powder at different time intervals. Detailed Embodiments

[0026] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0027] Example 1

[0028] Coating SiO2 film on the surface of PMMA powder

[0029] 1) Low-temperature dehydration: Place PMMA powder (particle size range 10 - 50 μm) in a vacuum drying equipment and treat it at 50 °C for 2 hours to remove the moisture adsorbed on the powder surface and part of the embedded moisture.

[0030] 2) Surface activation: Perform surface modification on the dehydrated PMMA powder through oxygen plasma, with a power of 100 W and a treatment time of 5 minutes, to improve the surface activity by etching and introducing oxygen-containing functional groups.

[0031] 3) Perform ALD coating deposition: Use SiCl4 and water vapor as reaction sources, and adopt a rotary atomic layer deposition device to coat and deposit SiO2 film on the surface of PMMA powder. The deposition conditions are as follows:

[0032] Deposition temperature: 60 °C;

[0033] Precursor selection: Alternately introduce SiCl4 and water vapor, and use nitrogen as the carrier gas and purge gas;

[0034] Pulse parameters: The pulse time ratio of SiCl4 to water vapor is 1:2, the single purge time is 30 seconds, and the total number of cycles is 10 times;

[0035] Rotation speed of the rotary chamber: 50 rpm to ensure uniform dispersion of powder particles, avoid accumulation and coverage dead angles;

[0036] 4) Post-treatment: Under nitrogen protection, heat the powder to 50 °C at a heating rate of 5 °C / min and keep it warm for 20 minutes to eliminate the internal stress of the film and enhance the bonding force.

[0037] Dispersion and characterization: Ultrasonically disperse the annealed PMMA powder in deionized water for 10 minutes, then take samples, transfer them to the carbon support film of a transmission electron microscope (TEM), and use the electron microscope to observe and verify the thickness, uniformity, and surface morphology of the film. The results show that: as Figure 1 , in this example, a continuous SiO2 film with a thickness of 9.04 nm is obtained, the surface is uniform and defect-free, and no other impurity elements are detected in the original EDS distribution map, indicating that the reaction is a high-purity and high-selectivity process.

[0038] Water contact angle test:

[0039] As shown Figure 3 in a (black line), the initial contact angle of the uncoated PMMA powder was 119°, and then it only slightly decreased to 116° within 300 seconds. After coating, as shown Figure 3 in a (green line), after 201 seconds, the contact angle decreased from 96° at the beginning to 41°, showing a significant improvement in wettability; in contrast Figure 3 to b, for the PMMA powder without SiO2 coating, the water droplets almost remained spherical throughout the entire time period, and the change in the contact angle was not obvious. For the PMMA powder coated with 10 cycles, the change in the contact angle was obvious. After 201 s, the liquid droplet basically maintained at 43°. After storing for 30 days at 75% humidity, the integrity was maintained at 95%, and the powder did not agglomerate.

[0040] Example 2

[0041] Coating of SiO2 thin film on the surface of PMMA powder

[0042] 1) Low-temperature dehydration: Place the PMMA powder (particle size range 1 - 10 μm) in a vacuum drying equipment and treat it at 50 °C for 2 hours to remove the moisture adsorbed on the powder surface and part of the embedded moisture;

[0043] 2) Surface activation: Perform surface modification treatment on the dehydrated PMMA powder through oxygen plasma with a power of 100 W and a treatment time of 5 minutes to improve the surface activity by etching and introducing oxygen-containing functional groups;

[0044] 3) Perform ALD coating deposition: Use SiCl4 and ozone as reaction sources, and adopt a rotary atomic layer deposition device to coat and deposit SiO2 thin film on the surface of PMMA powder. The deposition conditions are as follows:

[0045] Deposition temperature: 40 °C;

[0046] Precursor selection: Alternately introduce SiCl4 and ozone, and use nitrogen as the carrier gas and purge gas;

[0047] Pulse parameters: The pulse time ratio of SiCl4 to ozone is 1:3, the single purge time is 20 seconds, and the total number of cycles is 20 times;

[0048] Rotation speed of the rotary chamber: 80 rpm to ensure the uniform dispersion of small-particle-size powder and the coating integrity;

[0049] 4) Post-treatment: Under nitrogen protection, heat the powder to 50 °C at a heating rate of 5 °C / min and keep it warm for 10 minutes to further improve the film bonding strength and stability.

[0050] Dispersion and Characterization: The annealed PMMA powder was ultrasonically dispersed in deionized water for 10 minutes, and then samples were taken, transferred onto the carbon support film of a transmission electron microscope (TEM), and the thickness, uniformity, and surface morphology of the film were observed and verified using the electron microscope. The results showed that: as Figure 2 In this example, a SiO2 film with a thickness of 35.2 nm was obtained, with a smooth and dense surface; no other impurity elements were detected in the original EDS distribution map, indicating that this reaction is a process with high purity and high selectivity.

[0051] Water Contact Angle Test: After coating, as Figure 3 a (yellow line), after 19 seconds, the contact angle decreased from the initial 78° to 35°, showing a significant improvement in wettability; compared with Figure 3 b, the water droplet of the PMMA powder without SiO2 coating remained almost spherical throughout the entire period, and the change in the contact angle was not obvious. For the PMMA powder coated 20 times, the change in the contact angle was obvious. After 19 s, the liquid droplet basically remained at 35°, and 95% of the integrity was maintained after storage at 75% humidity for 30 days, and the powder did not agglomerate.

[0052] As described above, the above are only specific embodiments of the present invention with relatively good creativity, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A surface treatment method for improving the wettability of PMMA 3D printing powder, characterized in that, It includes the following steps: 1) Low-temperature dehydration: Place the PMMA powder in a vacuum drying device and treat it at 40 - 60 °C for 1 - 3 hours to remove the moisture adsorbed on the powder surface and part of the embedded moisture; 2) Surface activation: Perform surface modification treatment on the dehydrated PMMA powder by oxygen plasma, with the power range of 50 - 200 W and the treatment time of 1 - 10 minutes; 3) ALD coating deposition: Use silane-based precursors and oxidants as reaction sources, and use inert gas as the carrier gas and purge gas. Adopt a rotating chamber-assisted atomic layer deposition to coat and deposit a 1 - 10 nm SiO2 thin film on the PMMA powder surface. The deposition temperature is 30 - 80 °C, and the pulse parameters are as follows: the pulse time ratio of the silane-based precursor to the oxidant is 1:2 - 1:3, and purge for 15 - 60 seconds after each pulse. The total number of cycles is 5 - 40 times; 4) Post-treatment: Under the protection of inert gas, perform low-temperature annealing treatment on the PMMA powder coated with SiO2 at 30 - 60 °C for 10 - 30 minutes.

2. The surface treatment method for improving the wettability of PMMA 3D printing powder according to claim 1, wherein, In step 1), the particle size of the PMMA powder is 1 - 100 μm.

3. A surface treatment method for improving the wettability of PMMA 3D printing powder according to claim 1, characterized in that In step 3), the silane-based precursor is silicon tetrachloride SiCl4 or TEOS, and the oxidant is water vapor or ozone.

4. A surface treatment method for improving the wettability of PMMA 3D printing powder according to claim 1, characterized in that In step 3), the rotation speed of the rotating chamber is 20 - 100 rpm.

5. The surface treatment method for improving the wettability of PMMA 3D printing powder according to claim 1, wherein The inert gas is nitrogen or argon.

6. A surface treatment method for improving the wettability of PMMA 3D printing powder according to claim 1, characterized in that In step 3), the thickness of the SiO2 thin film is 1 - 10 nm, and the surface roughness is less than 1 nm.

7. Application of the PPMMA powder obtained by the surface treatment method according to any one of claims 1 - 6 in 3D printing.

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