Radiation refrigeration composite powder material for ink-jet 3D printing and preparation method of radiation refrigeration composite powder material

Abstract

The invention discloses a radiation refrigeration composite powder material for inkjet 3D printing and a preparation method of the radiation refrigeration composite powder material. The radiation refrigeration composite powder material comprises 75-95 parts of a polymer matrix material, 5-20 parts of a radiation refrigerant, 0.1-1 part of a flow modifier and 0.1-5 parts of other fillers. The material can be processed and prepared by one or more of a mechanical blending method, a solution coating method, a solution blending method and a melt blending method. The radiation refrigeration composite material prepared by the invention can spontaneously radiate heat to the surrounding space to realize self-cooling after being excited by the wavelength of a near-infrared region, so that the purposes of increasing the temperature difference between an ink-jet region and a non-ink-jet region and improving the dimensional precision are achieved. Besides, due to the interaction between the cellulose and the polymer, under the condition that the addition amount is large, a printed piece does not shrink or warp, and the printing cost is reduced; and through cellulose modification, hydrogen bond interaction is enhanced, so that the mechanical strength of a printed piece can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing materials, and in particular to a radiation cooling composite powder material for inkjet 3D printing and a preparation method thereof. Background Art

[0002] Powder bed fusion (PBF) is one of the seven different types of additive manufacturing (AM) technologies in the ASTM standard. It fuses powder particles layer by layer into a three-dimensional structure by applying different heat sources (such as laser, infrared light, thermal print head, etc.) to selected powder areas on the powder bed. Compared with many other additive manufacturing processes, the unmelted powder in PBF technology can act as a support structure, which allows printing to manufacture parts with complex structures without support materials. In polymer powder bed fusion, the most widely used technology is selective laser sintering (SLS). SLS technology uses a high-energy laser beam to scan a layer of powder, and the sintered material layers are fused together to form a complex 3D structure. However, in laser sintering, the cross-section of each layer of the part is raster scanned from "point to point", the sintering speed is slow, and the cost of carbon dioxide lasers is relatively high, which is not conducive to large-scale industrial applications.

[0003] In recent years, inkjet 3D printing has attracted widespread attention due to its use of low-energy near-infrared light. Compared with the point-by-point sintering method of selective laser sintering, inkjet 3D printing technology can quickly sinter the entire surface. Its printing speed is several times or even dozens of times that of traditional selective laser sintering, and it is an important development direction in the current polymer 3D printing field. The inkjet 3D printing process includes: designing a three-dimensional model, layering the model through software and storing it as corresponding processing information, and then the printer roller spreads a certain thickness of powder on the workbench; then the substrate preheats the powder deposition layer as a whole, and the print head sprays ink on the polymer powder according to the model selection area. The ink can convert the absorbed infrared radiation into heat energy; infrared light irradiates the powder bed, and the polymer powder in the ink spraying area sinters and solidifies due to the absorption of more heat, and the area without radiation absorbing material does not absorb enough heat and fails to sinter; through layer-by-layer sintering and accumulation, the corresponding three-dimensional entity is finally obtained.

[0004] Although the surface scanning mode used in inkjet 3D printing has a much greater advantage in molding speed than the point scanning mode of laser sintering, new problems also arise: the inkjet part of the powder absorbs infrared energy to reach above the melting point for sintering, but the un-inkjet part of the powder will also absorb some heat to reach the phase transition temperature point, causing the powder morphology to change. For example, the commonly used elastomer materials on the market are widely used due to their excellent impact strength and flexibility. But at the same time, it has unique thermal properties, and its powder will stick together when the temperature reaches above the softening point. In the process of inkjet 3D printing, the un-inkjet part of the powder is easy to reach due to its low softening point, which makes the powder easy to agglomerate, making it difficult to peel off the printed product. In addition, the temperature difference between the non-sintered area and the sintered area is small, resulting in poor dimensional accuracy of the product. How to reduce the temperature of the unsintered area and widen the temperature difference between the sintered area and the non-sintered area is very important.

[0005] The concept of radiative cooling was proposed in 1828. Such materials achieve energy-free cooling by spontaneously radiating heat into the cold outer space. This cooling method does not rely on air convection or material conduction, but rather utilizes the relationship between the temperature of an object and the intensity of the infrared radiation it emits. In recent years, with the maturity of the basic principles of radiative cooling and the development of technology, radiative cooling technology has been developed and applied to various fields, including architecture, photovoltaic cooling, condensate collection, and personal thermal management. However, so far, it has not been used in 3D printing. Cellulose, as one of the most abundant biological resources in nature, has a large number of hydroxyl functional groups and carbon-oxygen links. The molecular vibration of cellulose gives it the characteristics of high infrared emissivity in the atmospheric window, and it can be directly used as a radiative cooling material. In addition, cellulose crystals are composed of hard, tightly arranged extended cellulose chains, and the intermolecular forces are so strong that its Young's modulus in the chain direction exceeds 100GPa. And due to the strong hydrogen bonding, it has good adhesion in the polar interface area of ​​the material. Cellulose and its modified derivatives added to polymer materials can play a role in strengthening and toughening. Since it is added to the polymer as a radiation refrigerant, it can effectively improve the mechanical properties of the material.

[0006] In Additive Manufacturing 91(2024)104331, the printing method of Multi Jet Fusion (MJF) is explained and its advantages are described. The printing process can be described as: a radiation-absorbing liquid (also known as a melt) is sprayed into the printing area of ​​the polymer powder bed, and a refiner is sprayed to cool the non-printing area. After the spraying is completed, an infrared lamp is used to irradiate so that the part sprayed with the melt is fused, and the area sprayed with the refiner is not fused. In the MJF manufacturing process, the refiner is selectively deposited in the non-printing area to further reduce heat accumulation and avoid fusion of the non-printing area, thereby improving the dimensional accuracy of the part. In Additive Manufacturing 30(2019)100879, the so-called capillary effect is studied. The capillary effect originates from the interaction between the details and the melt in the layer-based part construction process, which determines the deviation of the upper plane geometry when approaching the boundary edge between the molten material and the powder bed. This technology reduces the energy absorption of the heat source by spraying refiners in non-printing areas, but has the following disadvantages: ① The size deviation of the printed sample is caused by the curved liquid surface caused by capillary action. For example, near the edge of the molten pool or the adjacent fusion area, the curved liquid surface formed by the capillary action of liquid molten alloy and other materials will cause the actual distribution boundary of the material to exceed the expected design boundary range. For example, if you want to print a thin-walled structure with precise size requirements, the width of the original designed wall is fixed, but the capillary action causes the material at the curved liquid surface to spread to the periphery, so that the width of the thin wall finally printed increases, and the overall shape and dimensional accuracy cannot meet the design requirements, resulting in the possibility that it may not be accurately assembled with other matching parts in the future. ② It affects the recycling of powder materials. Recycling powder sprayed with refiners and printing again will spray the melting agent again. The cross-contamination of the two liquids produced may affect the chemical composition of the powder, thereby negatively affecting the subsequent layering and construction quality. Poor interlayer adhesion, increased porosity, and reduced tensile strength and fracture deformation were observed in parts printed with 100% recycled powder materials.

[0007] CN112322110A discloses a near-infrared reflective composite material for inkjet 3D printing, which has a near-infrared reflective effect and can be directly applied to inkjet 3D printing using near-infrared as a processing energy source. The temperature difference between the inkjet part and the non-inkjet part during printing can be increased, and while the inkjet part is kept at a high temperature to fully melt the powder to obtain a printed product with good strength, the non-inkjet part is kept at a low temperature without producing bonding and agglomeration. The invention increases the temperature difference between the inkjet and non-inkjet areas by adding a near-infrared reflective inorganic filler. However, the content of the inorganic filler cannot be too high, otherwise it will lead to an increase in the crystal nuclei in the material and an increase in the crystallinity, thereby causing the printed product to warp, so the improvement effect is very limited. Summary of the invention

[0008] In view of the problem that the temperature difference between the inkjet and non-inkjet areas in the prior art, especially the materials with elastomer as the polymer matrix, is small during inkjet 3D printing, which leads to difficulty in peeling the parts and poor dimensional accuracy. At the same time, for the purpose of improving printing strength and reducing costs, the present invention has developed a radiation cooling composite material for inkjet 3D printing for the first time. When the infrared lamp irradiates the powder bed, the inkjet area absorbs radiation and heats up due to the radiation absorption of the ink, and the non-inkjet area can spontaneously radiate heat to the surrounding space to achieve self-cooling due to the enhancement of radiation cooling, after being excited by the wavelength of the near-infrared region, thereby achieving the purpose of increasing the temperature difference between the inkjet and non-inkjet areas during printing and improving dimensional accuracy. In addition, due to the interaction between cellulose and polymer, when the addition amount is large, the printed parts will not shrink or warp, reducing the printing cost; and through cellulose modification, the mechanical strength of the printed parts is effectively improved.

[0009] The present invention is achieved by the following technical means:

[0010] The present invention first discloses a radiation cooling composite material for inkjet 3D printing, comprising the following components in parts by weight:

[0011] 75-95 parts of polymer matrix material, 5-20 parts of radiation refrigerant, 0.1-1 parts of flow modifier, and 0.1-5 parts of other fillers.

[0012] Furthermore, the polymer matrix material is selected from: one or more of thermoplastic polyurethane, dynamically cross-linked polyurethane elastomer, nylon elastomer, polystyrene, polypropylene, polyetheretherketone, polyethylene terephthalate, and polydimethylsiloxane.

[0013] Furthermore, the radiation refrigerant is selected from any one of cellulose nanocrystals, microcrystalline cellulose, carboxylated cellulose nanofibers, and hydroxypropyl methylcellulose.

[0014] Furthermore, the flow modifier is one or both of silicon dioxide and silicone powder.

[0015] Furthermore, the other fillers are selected from one or more of calcium carbonate, talcum powder, mica powder and barium sulfate.

[0016] Furthermore, the particle size of the polymer matrix material is ≤200um, the particle size of the flow modifier is ≤150um, and the particle size of the other fillers is ≤150um.

[0017] The radiation refrigerant is used to enhance the radiation of the printed material to the surrounding space to achieve cooling when the material is excited by certain wavelengths. Modified cellulose is a cellulose modified product that can enhance the interaction with the corresponding polymer.

[0018] The present invention also discloses a method for preparing any of the above-mentioned radiation cooling composite materials for inkjet 3D printing, comprising:

[0019] One or more of mechanical blending, solution coating, solution blending and melt blending.

[0020] Further, the mechanical blending method comprises:

[0021] 75-95 parts of polymer elastomer, 5-20 parts of radiation refrigerant, 0.1-1 part of flow modifier and 0.1-5 parts of other fillers are placed in a high-speed mechanical blending mixer, mixed at a speed of 100-12000 rpm, and stirred 3-10 times, each time for 10-60 seconds, with an interval of 10-30 seconds.

[0022] Further, the solution coating method comprises:

[0023] Disperse 75-95 parts of polymer elastomer in ethanol by stirring for 1 hour, add 5-20 parts of radiation refrigerant and continue stirring for 2 hours. Due to electrostatic interaction, the two polymer powders will adsorb each other. After filtering and drying, mechanically blend with 0.1-1 parts of flow modifier and 0.1-5 parts of other fillers according to the proportion.

[0024] Further, the solution blending method comprises:

[0025] 75-95 parts of polymer matrix material are mixed with solvent until the material is dissolved, and then stirred and mixed with 5-20 parts of radiation refrigerant dispersed in the same solvent. After mixing evenly, it is cast into a tetrafluoroethylene mold to dry the solvent to form a block material, which is deep-cryogenically crushed to form a composite powder, and then mixed with 0.1-1 parts of flow modifier and 0.1-5 parts of other fillers by mechanical blending.

[0026] Furthermore, the solvent is selected from 1,4-dioxane or tetrahydrofuran.

[0027] Further, the melt blending method comprises:

[0028] 75-95 parts of polymer elastomer, 5-20 parts of radiation refrigerant, 0.1-1 parts of flow modifier and 0.1-5 parts of other fillers are extruded into granules by a screw extruder and then cryogenically crushed to obtain composite powder.

[0029] The beneficial effects of the present invention are:

[0030] 1. In the existing inkjet printing technology, the temperature difference between the inkjet and non-inkjet areas is small, which makes it difficult to peel off the parts and has poor dimensional accuracy. At the same time, it is also for the purpose of improving printing strength and reducing costs. The radiation cooling composite material used in this technology can spontaneously radiate heat to the surrounding space after being excited by the wavelength in the near-infrared region to achieve self-cooling, thereby achieving the purpose of increasing the temperature difference between the inkjet and non-inkjet areas and improving dimensional accuracy.

[0031] 2. In addition, due to the interaction between cellulose and polymer, when a large amount is added, the printed parts will not shrink or warp, reducing the printing cost; and by modifying cellulose and enhancing the hydrogen bond interaction, the mechanical strength of the printed parts can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the temperature difference between the non-inkjet area of ​​comparative example 1 and the temperature of embodiment 1 under the same printing conditions, wherein the temperature of comparative example 1 is always greater than that of embodiment 1.

[0033] Figure 2 The following are the samples printed using the materials of Example 2 and Comparative Example 2.

[0034] Figure 3 The dimensional accuracy of the splines printed using the materials of Example 2 and Comparative Example 2 in the Z-axis direction. DETAILED DESCRIPTION

[0035] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Embodiment 1:

[0037] A radiation cooling composite material for inkjet 3D printing, comprising the following powder components in parts by weight:

[0038] Weigh 85 parts of polydimethylsiloxane, 20 parts of carboxylated cellulose nanofibers, 0.2 parts of silicon dioxide, and 0.2 parts of talc respectively according to weight;

[0039] The preparation method of the composite material is as follows:

[0040] 85 parts of polydimethylsiloxane powder were dispersed in ethanol by stirring for 1 hour, and 20 parts of carboxylated cellulose nanofibers were added and stirred for 2 hours. The two polymer powders will adsorb each other, and after filtering and drying, a uniformly coated composite powder can be obtained.

[0041] The composite powder, 0.2 parts of silicon dioxide and 0.2 parts of talcum powder were placed in a high-speed mechanical blending mixer and mixed at a speed of 1000 rpm. The mixture was stirred 10 times, each time for 20 seconds, with an interval of 30 seconds.

[0042] Screening with a 120-mesh sieve gave a radiation cooling composite material with an average particle size of less than 125 μm, which can be directly used for inkjet 3D printing.

[0043] Embodiment 2:

[0044] A radiation cooling composite material for inkjet 3D printing, comprising the following powder components in parts by weight:

[0045] Weigh 89 parts of thermoplastic polyurethane, 10 parts of carboxylated cellulose nanofibers, 0.2 parts of silicon dioxide, 0.5 parts of silicone powder, and 1 part of mica powder respectively according to weight parts;

[0046] The preparation method of the composite material is as follows:

[0047] All the weighed powder materials were placed in a high-speed mechanical blending mixer and mixed at a speed of 1000 rpm for 5 times, each time for 30 seconds with an interval of 20 seconds.

[0048] Screening with a 160-mesh sieve gave a radiation cooling composite material with an average particle size of less than 100 μm, which can be directly used for inkjet 3D printing.

[0049] Embodiment 3:

[0050] Prepared by combining solution blending and mechanical blending

[0051] A radiation cooling composite material for inkjet 3D printing, comprising the following powder components in parts by weight:

[0052] Weigh 89 parts of dynamically cross-linked polyurethane, 5 parts of cellulose, 0.2 parts of silicon dioxide, and 0.2 parts of talc respectively according to weight parts;

[0053] The preparation method of the composite material is as follows:

[0054] Add 5 parts of cellulose dispersed in 1,4-dioxane to the dynamic polyurethane solution that has not been completely cross-linked, mix evenly at 80°C, cast into a tetrafluoroethylene mold to dry the solvent, form a block material, and perform deep cold crushing to make a composite powder. Then, mix it with 0.2 parts of silicon dioxide and 0.2 parts of talc by mechanical blending.

[0055] Screening with a 120-mesh sieve gave a radiation cooling composite material with an average particle size of less than 125 μm, which can be directly used for inkjet 3D printing.

[0056] Comparative Example 1:

[0057] A composite material for inkjet 3D printing, comprising the following powder components in parts by weight:

[0058] Weigh 100 parts of polydimethylsiloxane, 0.2 parts of silicon dioxide, and 0.2 parts of talc respectively according to weight parts;

[0059] The preparation method of the composite material is as follows:

[0060] All the weighed powder materials were placed in a high-speed mechanical blending mixer and mixed at a speed of 1000 rpm for 10 times, each time for 20 seconds with an interval of 30 seconds.

[0061] The composite powder with an average particle size of less than 125 μm was screened with a 120-mesh sieve for inkjet 3D printing.

[0062] Test: The composite materials of Example 1 and Comparative Example 1 were respectively subjected to inkjet printing. During the printing process, the powder bed temperature at the same position of each layer without inkjet printing was measured and compared. The results are as follows: Figure 2 ΔT is the difference between the measurement result of comparative example 1 and the measurement result of embodiment 1.

[0063] like Figure 1 As shown, it can be seen that under the same printing conditions, the temperature of the non-inkjetted area of ​​Example 1 is always 2-5°C lower than that of Comparative Example 1. This is the result of the radiation refrigerant, and the printed product is easier to peel off.

[0064] Comparative Example 2:

[0065] A composite material for inkjet 3D printing, comprising the following powder components in parts by weight:

[0066] Weigh 99 parts of thermoplastic polyurethane, 0.2 parts of silicon dioxide, 0.5 parts of silicone powder, and 1 part of mica powder respectively according to weight;

[0067] The preparation method of the composite material is as follows:

[0068] All the weighed powder materials were placed in a high-speed mechanical blending mixer and mixed at a speed of 1000 rpm for 5 times, each time for 30 seconds with an interval of 20 seconds.

[0069] The composite powder with an average particle size of less than 100 μm was obtained by sieving with a 160-mesh sieve, which can be directly used for inkjet 3D printing.

[0070] Test: The composite materials of Example 2 and Comparative Example 2 were used to print 2 mm thick specimens (such as Figure 2 ), conduct dimensional accuracy test in the Z-axis direction, record the difference between the Z-axis dimensions of the printed part and the model, and compare them. The results are as follows Figure 3It can be seen that under three different printing parameters (infrared lamp moving speed), after adding cellulose, its dimensional accuracy is significantly improved, more than twice.

[0071] Comparative Example 3:

[0072] A composite material for inkjet 3D printing, comprising the following powder components in parts by weight:

[0073] Weigh 89 parts of dynamically cross-linked polyurethane, 0.2 parts of silicon dioxide, and 0.2 parts of talc respectively according to weight parts;

[0074] The preparation method of the composite material is as follows:

[0075] The cross-linked dynamic polyurethane solution is cast into a tetrafluoroethylene mold to dry the solvent to form a block material, which is then cryogenically crushed to form a composite powder, and then mechanically blended with 0.2 parts of silicon dioxide and 0.2 parts of talcum powder.

[0076] Screening with a 120-mesh sieve gave a composite powder with an average particle size of less than 125 μm, which can be directly used for inkjet 3D printing.

[0077] Test: 2 mm thick specimens were printed using the conditions of Example 3 and Comparative Example 3 for mechanical property testing, and the time used in the processing was recorded for comparison. The results are shown in Table 1.

[0078] Table 1

[0079]

[0080] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A radiation cooling composite material for inkjet 3D printing, comprising: 75-95 parts of polymer matrix material, 5-20 parts of radiation refrigerant, 0.1-1 parts of flow modifier, and 0.1-5 parts of other fillers.

2. The radiative cooling composite material according to claim 1, wherein: The polymer matrix material is selected from: one or more of thermoplastic polyurethane, dynamically cross-linked polyurethane elastomer, nylon elastomer, polystyrene, polypropylene, polyetheretherketone, polyethylene terephthalate, and polydimethylsiloxane; the radiation refrigerant is selected from: any one of cellulose nanocrystals, microcrystalline cellulose, carboxylated cellulose nanofibers, and hydroxypropyl methylcellulose; The flow modifier is one or both of silicon dioxide and silicone powder; The other fillers are selected from one or more of calcium carbonate, talcum powder, mica powder and barium sulfate.

3. The radiative cooling composite material according to claim 2, wherein: The particle size of the polymer matrix material is ≤200um, the particle size of the flow modifier is ≤150um, and the particle size of the other fillers is ≤150um.

4. A method for preparing a radiation cooling composite material for inkjet 3D printing according to any one of claims 1 to 3, comprising: One or more of mechanical blending, solution coating, solution blending and melt blending.

5. The preparation method according to claim 4, wherein: The mechanical blending method comprises: 75-95 parts of polymer elastomer, 5-20 parts of radiation refrigerant, 0.1-1 part of flow modifier and 0.1-5 parts of other fillers are placed in a high-speed mechanical blending mixer, mixed at a speed of 100-12000 rpm, and stirred 3-10 times, each time for 10-60 seconds, with an interval of 10-30 seconds.

6. The preparation method according to claim 4, wherein: The solution coating method comprises: Disperse 75-95 parts of polymer elastomer in ethanol by stirring for 1 hour, add 5-20 parts of radiation refrigerant and continue stirring for 2 hours. Due to electrostatic interaction, the two polymer powders will adsorb each other. After filtering and drying, mechanically blend with 0.1-1 parts of flow modifier and 0.1-5 parts of other fillers.

7. The preparation method according to claim 4, wherein: The solution blending method comprises: 75-95 parts of polymer matrix material are mixed with solvent until the material is dissolved, and then stirred and mixed with 5-20 parts of radiation refrigerant dispersed in the same solvent. After mixing evenly, it is cast into a tetrafluoroethylene mold to dry the solvent to form a block material, which is deep-cryogenically crushed to form a composite powder, and then mixed with 0.1-1 parts of flow modifier and 0.1-5 parts of other fillers by mechanical blending.

8. The preparation method according to claim 7, wherein: The solvent is selected from 1,4-dioxane or tetrahydrofuran.

9. The preparation method according to claim 4, wherein: The melt blending method comprises: 75-95 parts of polymer elastomer, 5-20 parts of radiation refrigerant, 0.1-1 parts of flow modifier and 0.1-5 parts of other fillers are extruded into granules by a screw extruder and then cryogenically crushed to obtain composite powder.

Images