Method for preparing nylon material for selective laser sintering through thermally induced phase separation

Abstract

The invention discloses a method for preparing a nylon material for selective laser sintering by thermally induced phase separation in the technical field of high polymer material preparation and additive manufacturing. The method comprises the following steps: S1, preparing a homogeneous modified prepolymer solution; s2, performing programmed cooling to induce liquid-liquid phase separation and powder prototype formation; s3, curing, separating and post-processing; s4, drying; the introduction of a chemical modifier and the physical forming process of thermally induced phase separation are fused at the source, and a functional modifier is added at the initial homogeneous solution stage of TIPS, so that the functional modifier uniformly and deeply interacts with a nylon 6 molecular chain in the subsequent phase separation and curing crystallization process; therefore, the nylon 6 powder which has excellent spherical morphology and is adaptive to the SLS process and has the characteristics of low melting point and wide window is directly prepared by a one-step method. The method has the advantages that the process is simplified, uniform modification of the body is achieved, the shape and the property are synchronously and accurately regulated and controlled, the comprehensive performance of the powder is good, and the recoverability of the material is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer material preparation and additive manufacturing technology, in particular to a method for preparing a polymer powder for a selective laser sintering (SLS) process, and more particularly to a method for preparing a spherical nylon 6 (PA6) powder with a low melting point and a wide sintering window by thermally induced phase separation (TIPS) technology combined with in-situ chemical modification. BACKGROUND

[0002] Selective laser sintering (SLS) is a technology that uses an infrared laser as a power source and uses powder materials as modeling materials. The SLS technology has strict requirements on the morphology, particle size distribution, thermal properties and fluidity of the powder materials. Nylon 12 (PA12) is the most widely used material in the SLS field due to its excellent comprehensive performance, but its raw material cost is high.

[0003] Nylon 6 (PA6) is the most widely used general-purpose engineering plastic with the largest output and lower cost, and has excellent mechanical properties, but its direct application in SLS faces two major bottlenecks:

[0004] First, the melting point is high (~220℃), which exceeds the powder bed heating limit (usually ≤200℃) of many commercial SLS devices;

[0005] Second, the crystallization speed is fast, the sintering window is narrow, which leads to easy warping during the molding process and difficult process control.

[0006] In order to prepare a polymer powder suitable for SLS, the existing technologies mainly include:

[0007] Solvent precipitation method: complex process, high temperature and high pressure, high energy consumption, and limited solvent system suitable for high melting point and strong polar materials such as PA6.

[0008] Deep cooling grinding method: huge energy consumption, irregular powder morphology (mostly angular or flaky), poor fluidity, affecting powder uniformity and part accuracy.

[0009] Therefore, the present application designs a method for preparing a nylon material for selective laser sintering by thermally induced phase separation to solve the above problems. SUMMARY

[0010] The application aims to provide a method for preparing nylon material for selective laser sintering by thermally induced phase separation, which combines the introduction of chemical modifiers with the physical forming process of thermally induced phase separation at the source, adds functional modifiers in the initial homogeneous solution stage of TIPS, and makes the modifiers interact with nylon 6 molecular chains uniformly and deeply in the subsequent phase separation and solidification and crystallization process, so as to directly prepare nylon 6 powder with excellent spherical morphology, low melting point and wide window characteristics suitable for SLS process in one step, thereby solving the problems in the background art.

[0011] To achieve the above-mentioned purpose, the application provides the following technical scheme:

[0012] A method for preparing nylon material for selective laser sintering by thermally induced phase separation, which adopts one-step in-situ modification of thermally induced phase separation process and comprises the following steps:

[0013] S1, preparing a homogeneous modified prepolymer solution

[0014] Nylon 6 resin, metal salt modifier and mixed diluent are added to a reaction container in proportion, the mixture is heated to 170-210 DEG C under the protection of inert atmosphere, and stirring is continued at the temperature for 1.5-3.5 hours until the nylon 6 resin is completely dissolved, the metal salt is fully dispersed and dissociated, and preliminary interaction occurs between the metal salt and the amide groups on the nylon 6 molecular chain to form a transparent and uniform modified prepolymer solution, which ensures uniform dispersion of the modifier at the molecular level;

[0015] S2, programmed temperature reduction to induce liquid-liquid phase separation and powder formation

[0016] The homogeneous modified prepolymer solution obtained in step S1 is programmed to reduce the temperature to a phase separation temperature interval of 100-130 DEG C at a rate of 0.5-3 DEG C / min, and after reaching the target temperature, the temperature is kept constant in the interval for 1-3 hours;

[0017] In this process, the system undergoes thermally induced liquid-liquid phase separation, and the polymer phase rich in modified nylon 6 is precipitated and grown in the form of microspherical droplets from the continuous diluent phase. The presence of the modifier changes the solubility and crystallization kinetics of the polymer chain, thereby affecting the formation and coarsening process of the droplets;

[0018] S3, solidification, separation and post-treatment

[0019] After completing the constant temperature phase separation, the system is naturally cooled or controlled to room temperature, and in the cooling process, the nylon 6 is crystallized and solidified inside the microspherical droplets, and the metal salt modifier is fixed in the nylon matrix to form stable solid powder particles; the solid-liquid separation is carried out by filtration or centrifugation, and the obtained solid is washed with ethanol and deionized water in sequence to completely remove the residual diluent and unreacted free metal ions.

[0020] S4, Drying

[0021] The washed wet powder was placed in a vacuum oven at 60°C to 80°C and dried for 12 to 36 hours to obtain dry, loose, free-flowing spherical nylon 6 powder.

[0022] Preferably, the metal salt modifier is calcium stearate, and its addition amount is 1.0 wt% to 8.0 wt% of the mass of nylon 6 resin.

[0023] Preferably, the amount of the metal salt modifier added is 3.0 wt% to 5.0 wt% of the mass of nylon 6 resin.

[0024] Preferably, the mixed diluent consists of a good solvent and a non-solvent, with the mass ratio of the good solvent to the non-solvent being 70:30 to 85:15.

[0025] Preferably, the good solvent is one or more of N,N-dimethylacetamide (DMAC), formic acid, and m-cresol.

[0026] Preferably, the non-solvent is one or more of polyethylene glycol 400 (PEG400), ethanol, and glycerin.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. Simplified process: The powder morphology construction and performance modification are integrated into a single continuous process. Compared with the traditional two-step method of "first powder preparation and then modification", the process flow is significantly shortened and the equipment complexity, energy consumption and production costs are reduced.

[0029] 2. Achieve uniform bulk modification: Since the modifier is introduced into the polymer molecular chain in a dissolved state and is "locked" in the polymer matrix during subsequent phase separation and curing, the modification effect is ensured to achieve uniform distribution at the molecular level within the powder particles, resulting in thorough and stable performance improvement.

[0030] 3. Simultaneous and precise control of "shape" and "properties": It not only inherits the TIPS method's ability to precisely control the sphericity, particle size and distribution of powder, but also directly intervenes in and optimizes the thermodynamic behavior of nylon 6 during powder formation through in-situ modification, which greatly broadens the sintering window and enables PA6 powder to be compatible with standard SLS equipment.

[0031] 4. Good overall powder properties: The obtained powder has high sphericity, narrow particle size distribution, excellent flowability and high bulk density, and its thermal properties fully meet the thermal performance requirements of the SLS process.

[0032] 5. Improved material recyclability: The uniform modified structure helps to suppress the post-condensation reaction of nylon end groups in the high-temperature powder bed, slows down powder aging, and improves the recycling rate of unsintered powder, resulting in significant economic and environmental benefits. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments 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 drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a SEM image of the spherical nylon 6 powder of the present invention with a Mag value of 100×.

[0035] Figure 2 This is a SEM image of the spherical nylon 6 powder of the present invention with a Mag value of 300×.

[0036] Figure 3 This is a schematic diagram of the thermal properties of the material of the present invention. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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.

[0038] Example 1

[0039] A method for preparing nylon materials for selective laser sintering by thermally induced phase separation, the details of which are as follows:

[0040] (1) Formula:

[0041] 100g of PA6 resin (intrinsic viscosity 2.5), 4g of calcium stearate (4wt%), and a mixed diluent consisting of 750g of DMAC and 250g of PEG400 (mass ratio 75:25).

[0042] (2) Process:

[0043] S1: Put the above materials into a high-pressure reactor, purge with nitrogen, heat to 185°C and stir for 2.5 hours to form a transparent homogeneous liquid;

[0044] S2: Cool down to 115℃ at a rate of 2℃ / min and hold at 115℃ for 2 hours;

[0045] S3: Cool naturally to room temperature, filter, wash successively with hot ethanol and deionized water, and vacuum dry at 75°C for 24 hours.

[0046] (3) Morphology and physical properties: Scanning electron microscopy (SEM) showed that the powder was in the form of regular spherical shapes, such as... Figure 1 , Figure 2 As shown, the laser particle size analyzer measured D50 = 52.3 μm and Span = 0.89.

[0047] (4) Thermal properties (DSC, 10℃ / min): Melting peak temperature (Tm) = 201.7℃, crystallization peak temperature (Tc) = 156.7℃, the calculated sintering window ΔT = 45℃, as follows Figure 3 As shown.

[0048] Comparative Example 1 (Traditional TIPS method, unmodified):

[0049] Referring to Example 1, but without adding calcium stearate, pure PA6 powder sample B was prepared using only PA6 resin and the same diluent under the same TIPS conditions.

[0050] Performance characterization: The powder morphology is similar, D50=50.8μm, Span=0.94.

[0051] The DSC display shows: Tm = 221.7℃; Tc = 187.7℃; ΔT = 34℃. Figure 3 As shown.

[0052] Comparative Example 2 (Two-step post-processing modification):

[0053] Take 50g of pure PA6 powder B prepared in Comparative Example 1, immerse it in 200mL of ethanol solution containing 2g of calcium stearate, reflux and stir at 70℃ for 4 hours, filter, wash and dry to obtain post-treated modified powder sample C.

[0054] Performance characterization: The powder surface is slightly sticky.

[0055] DSC display shows: Tm-onset=208.5℃, Tc-onset=165.2℃, ΔT=43.3℃.

[0056] The melting point decreased, but the decrease was much smaller than that in Example 1, and the DSC curve showed broadening or shoulders, indicating that the modification was not uniform.

[0057] Comparison conclusion:

[0058] The one-step method of this invention (Sample A) successfully reduced the melting onset temperature of PA6 powder from ~221℃ to ~201℃ in a single process, while maintaining a wide sintering window of up to 45℃ and excellent powder physical properties. Compared with the two-step method (Sample C), the modification effect of this invention is more significant and uniform, and the process flow is greatly simplified.

[0059] Example 2 (Effect of different amounts of calcium stearate)

[0060] Referring to Example 1, only the amount of calcium stearate added was changed to 2g (2wt%, sample A2) and 6g (6wt%, sample A6).

[0061] Results: The Tm-onset of sample A2 was 203.6℃ and the Tc-onset was 162.8℃; the Tm-onset of sample A6 was 193.5℃ and the Tc-onset was 151.4℃.

[0062] This indicates that within a certain range, increasing the amount of modifier can further reduce the melting point and crystallization temperature of the powder, providing a flexible means to adjust the thermal properties of the powder; however, excessive addition (such as 6%) may lead to a slight increase in the particle size of the powder.

[0063] SLS molding verification:

[0064] The powder A obtained in Example 1 was tested for printing on a commercial SLS device with the powder bed temperature set at 175°C.

[0065] The molding process was smooth, the powder was evenly spread, and the fusion bonding was good after laser scanning. The surface of the obtained sample was smooth and there was no visible warping. The tensile strength and elongation at break were tested and reached or exceeded the level of commercial PA12SLS parts.

[0066] The above embodiments fully demonstrate that the one-step in-situ modified thermally induced phase separation method provided by the present invention is an effective, efficient, and high-performance innovative solution to solve the bottleneck of Nylon 6 material applied to selective laser sintering technology, and can produce the following synergistic gain technical effects:

[0067] 1. Simplified process: Integrating powder morphology construction and performance modification into a single continuous process significantly shortens the process flow and reduces equipment complexity, energy consumption and production costs compared to the traditional two-step method of "powder preparation first and then modification".

[0068] 2. Achieve uniform bulk modification: Since the modifier is introduced into the polymer molecular chain in a dissolved state and is "locked" in the polymer matrix during subsequent phase separation and curing, the modification effect is ensured to achieve uniform distribution at the molecular level within the powder particles, resulting in thorough and stable performance improvement.

[0069] 3. Simultaneous and Precise Control of "Shape" and "Properties": This invention not only inherits the precise control capabilities of the TIPS method for powder sphericity, particle size, and distribution (Span value), but also directly intervenes in and optimizes the thermodynamic behavior of nylon 6 during powder formation through in-situ modification. The complexation of metal ions (such as Ca²⁺) with amide groups effectively disrupts the regular hydrogen bond network of nylon 6, significantly reducing its crystallization temperature (Tc) and melting temperature (Tm), thereby greatly widening the sintering window (ΔT) and enabling PA6 powder to be compatible with standard SLS equipment.

[0070] 4. Excellent overall powder properties: The obtained powder exhibits high sphericity, narrow particle size distribution, excellent flowability, and high bulk density. Its thermal properties are as follows: melting temperature is 201℃, crystallization initiation temperature (Tc-onset) is significantly reduced, and sintering window (ΔT) is 45℃, fully meeting the thermal performance requirements of the SLS process.

[0071] 5. Improved material recyclability: The uniform modified structure helps to suppress the post-condensation reaction of nylon end groups in the high-temperature powder bed, slows down powder aging, and improves the recycling rate of unsintered powder, resulting in significant economic and environmental benefits.

[0072] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0073] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing nylon materials for selective laser sintering by thermally induced phase separation, characterized in that, The one-step in-situ modified thermally induced phase separation process includes the following steps: S1. Preparation of homogeneous modified prepolymer liquid Nylon 6 resin, metal salt modifier and mixed diluent are added to the reaction vessel in proportion. Under the protection of an inert atmosphere, the mixture is heated to 170°C to 210°C and stirred continuously at this temperature for 1.5 to 3.5 hours until the nylon 6 resin is completely dissolved, the metal salt is fully dispersed and dissociated, and it initially interacts with the amide groups on the nylon 6 molecular chain to form a transparent and uniform modified prepolymer liquid. S2. Programmed cooling induces liquid-liquid phase separation and powder prototyping. The homogeneous modified prepolymer obtained in step S1 is cooled to a phase separation temperature range of 100°C to 130°C at a rate of 0.5°C / min to 3°C / min. After reaching the target temperature, it is kept at this temperature for 1 to 3 hours. S3, Curing, Separation and Post-treatment After isothermal phase separation is completed, the system is naturally cooled or controlled to room temperature, and solid-liquid separation is performed by filtration or centrifugation. The obtained solid is washed with ethanol and deionized water in sequence. S4, Drying The washed wet powder was placed in a vacuum oven at 60°C to 80°C and dried for 12 to 36 hours to obtain dry, loose, free-flowing spherical nylon 6 powder.

2. The method for preparing nylon materials for selective laser sintering by thermally induced phase separation according to claim 1, characterized in that: The metal salt modifier is calcium stearate, and its addition amount is 1.0 wt% to 8.0 wt% of the mass of nylon 6 resin.

3. The method for preparing nylon materials for selective laser sintering by thermally induced phase separation according to claim 3, characterized in that: The amount of the metal salt modifier added is 3.0 wt% to 5.0 wt% of the mass of nylon 6 resin.

4. The method for preparing nylon materials for selective laser sintering by thermally induced phase separation according to claim 1, characterized in that: The mixed diluent consists of a good solvent and a non-solvent, with a mass ratio of good solvent to non-solvent of 70:30 to 85:

15.

5. The method for preparing nylon materials for selective laser sintering by thermally induced phase separation according to claim 4, characterized in that: The good solvent is one or more of N,N-dimethylacetamide, formic acid, and m-cresol.

6. The method for preparing nylon materials for selective laser sintering by thermally induced phase separation according to claim 4, characterized in that: The non-solvent is one or more of polyethylene glycol 400, ethanol, and glycerin.

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