Method for preparing suspended structure silicone rubber radiation shielding composite material by wax support assisted 3D printing

Abstract

The present invention discloses a method for preparing a silicone rubber radiation shielding composite material with a suspended structure by wax support-assisted 3D printing, which relates to the technical field of radiation shielding materials. The composite material uses two-component liquid silicone rubber as a flexible matrix material, hydrophilic fumed silica as a thickener, boron carbide, bismuth oxide, etc. as radiation shielding fillers, and 80# microcrystalline wax as a support material. The type and amount of the shielding filler and the geometric shape of the radiation shielding composite material are determined according to the distribution of the radiation field. Then, a geometric model of the shielding material and the support material is established, and parameters are selected for slicing to obtain a 3D printing slicing file. The slicing is performed using a multi-head 3D printer. Finally, heating and curing are performed to remove the wax block support to obtain the silicone rubber radiation shielding composite material with a suspended structure. The method can be applied to neutron and gamma ray protection of special-shaped components such as pipelines, and has the advantages of good conformability, light weight, small size, and high radiation shielding efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of radiation shielding materials, and in particular to a method for preparing a silicone rubber radiation shielding composite material with a suspended structure by wax-supported 3D printing. Background Art

[0002] Flexible radiation shielding (neutron, gamma ray, etc.) materials have become key materials for the protection of special-shaped components in the nuclear field due to their outstanding advantages such as good conformability and compact structure. Rubber-based composite materials are one of the representative flexible radiation shielding materials. There are two typical processing and preparation processes: (1) For solid rubber raw materials, solid rubber is mixed with various functional fillers and processing aids, and then molded and vulcanized to prepare rubber-based composite materials; (2) For liquid rubber raw materials, liquid rubber is mixed with various fillers and curing agents, cast in a specific mold, and prepared through heat curing or room temperature curing process. Both processing and molding methods require molds, and the diversity of special-shaped components determines the need for processing different types of molds. This not only increases manufacturing costs, but also cannot immediately meet the rapid manufacturing needs of radiation shielding materials.

[0003] 3D printing technology has advantages such as moldless manufacturing, high design freedom, and high efficiency. In particular, direct ink writing (DIW) 3D printing technology also has the advantages of low equipment requirements and low cost, which complements traditional processing technology. Some researchers used polysiloxane as a flexible matrix and elemental bismuth powder and boron-10 powder as radiation shielding functional fillers to prepare flexible gamma shielding and neutron shielding materials through direct writing 3D printing (Radiation Physics and Chemistry, 2021, 188: 109616). However, it is limited to the preparation of regular shaped materials such as flat plates. In contrast, special-shaped components such as curved pipes and multiple right-angled shapes are more widely used in actual applications. They require the use of radiation shielding materials with suspended structures to compact and integrate them for protection. However, during the printing process of suspended structure materials, the polymer slurry is difficult to maintain its shape after deposition, causing the structure to collapse. Therefore, existing printing technology cannot meet the protection needs of special-shaped parts such as bent pipes in nuclear radiation protection.

[0004] In the 3D printing process of ordinary materials, it is possible to prepare suspended structural materials by adding support materials, such as polyvinyl alcohol water-soluble support, wax support, etc. Some researchers have used a multi-material jet 3D printer, using a photocurable material as the main material and wax as the support material to prepare rigid plastic samples with suspended structural characteristics (Virtual and Physical Prototyping, 2017, 12(1):95-103.). However, in 3D printing technologies based on photocuring or fused deposition, the rigid polymer material is solidified and formed simultaneously after injection or extrusion, so the support material plays a temporary supporting role and only needs to meet the requirements of printability and easy removal after printing, and no other performance requirements are required. In 3D printing radiation shielding material technology based on DIW, the flexible polymer material cannot be formed immediately after extrusion deposition and needs to be further heated to solidify it. Therefore, the support material is required to have a long-term stable support function to avoid structural collapse of the flexible material before solidification. This places extremely high demands on the thermal and mechanical properties of the support material itself and its matching with the thermal / mechanical properties of the main material. In particular, in 3D printing of radiation shielding materials, to enhance their radiation shielding effectiveness, it is necessary to add radiation shielding fillers to the matrix material. This, in turn, impacts the performance of the main material, increasing the technical difficulty of implementation. Therefore, how to use 3D printing to prepare suspended silicone rubber radiation shielding composite materials remains a technical challenge that needs to be urgently addressed in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing. Through the coordination of structural design and material preparation process, using wax blocks as support and a direct writing 3D printing method, a suspended structure flexible radiation shielding composite material that meets the requirements of practical applications is prepared.

[0006] Specifically, the above invention object is achieved through the following solutions:

[0007] A method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing comprises the following steps:

[0008] 1) Based on the neutron or gamma-ray dose rate at the target protection object and the environmental radiation dose rate limit, liquid silicone rubber is used as the flexible base material, and a neutron shielding filler or gamma-ray shielding filler with a large effective cross-section is selected. The radiation shielding filler content, ratio, and thickness of the radiation shielding material (preferably 2 mm) are determined according to the attenuation coefficient calculation formula and the ray intensity attenuation calculation formula.

[0009] 2) Designing the shape of the silicone rubber radiation shielding composite material into a geometric shape complementary to the target protection object, and the material thickness is the same as in step 1); adding wax supports to the hollow structure or suspended structure of the silicone rubber radiation shielding composite material so that the composite material can maintain a stable geometric shape during the 3D printing process; using geometric modeling software (such as SolidWorks) to establish a three-dimensional geometric model of the composite material and the wax support, and then importing it into slicing software (such as Simplify3D) for discretization, converting it into a code recognizable by a 3D printer, and obtaining a slicing file recognizable by the 3D printer.

[0010] The method of converting the target shape modeling into a code recognizable by a 3D printer in this step is a conventional technology in this field, as disclosed in the reference book "Yan Chunze et al. 3D Printing Materials Series - 3D Printing Polymer Materials [M]. 1st Edition, Beijing: Chemical Industry Press, 2020."

[0011] 3) Mixing the materials using a planetary stirring degassing machine: First, according to the parameters obtained in step 1), add a sieved (110 mesh) radiation shielding filler to the liquid silicone rubber base, stir and mix evenly, and obtain a mixed solution I; then, add hydrophilic fumed silica to the mixed solution I in portions, stir and mix evenly, and obtain a mixed solution II; finally, add a curing agent compatible with the liquid silicone rubber base to the mixed solution II, stir and mix evenly, and obtain a mixed solution III; transfer the mixed solution III to the plastic barrel of the 3D printer, place it in a centrifuge and centrifuge to remove bubbles generated during the loading process.

[0012] 4) The wax block is loaded into a metal barrel and heated uniformly from room temperature to 100°C by an electric heating device to completely melt the wax block and maintain the temperature for 30 minutes; then the temperature is uniformly lowered to 40°C and maintained there to allow the wax material to condense and deposit at the bottom of the barrel.

[0013] The original wax block loaded in the metal barrel is composed of many wax blocks of different sizes, with large gaps between them. If it is heated directly after loading, continuous filament production cannot be achieved, making continuous 3D printing difficult. This step first heats and melts it and then cools it down to condense and deposit it, which can form a dense whole of the originally scattered wax blocks in the metal barrel to facilitate subsequent continuous 3D printing. The printability of the wax material itself is highly dependent on temperature. After many experiments, this application finally determined that 40°C is the optimal temperature to ensure its 3D printing and compatibility with the slurry.

[0014] 5) Initiate the 3D printing process using the multi-material 3D printer: Connect the air compressor to the 3D printer after pressurization, load the barrel onto the 3D printer, and level and calibrate the 3D printer; Select the slicing file from step 2) and simultaneously print the silicone rubber radiation shielding composite material and the wax support material; After printing, heat and cure in an oven and remove the wax support.

[0015] The neutron shielding filler in step 1) is boron carbide, and the gamma radiation shielding filler is bismuth oxide. The particle size range of the neutron shielding filler and the gamma radiation shielding filler is 1 to 3 μm.

[0016] The sieving process in step 3) refers to sieving using a sieve of not less than 110 meshes.

[0017] The specific surface area of ​​the hydrophilic fumed silica in step 3) is 150 m 2 / g.

[0018] In the step 3), the amount of shielding filler used is 20 to 100 phr (measured in parts by mass, with 100 phr of liquid silicone rubber base as the measurement basis), the amount of hydrophilic fumed silica used is 18 to 20 phr (this amount ensures that the rheological properties of the mixed solution III meet the requirements of direct writing 3D printing, that is, the "storage modulus-shear stress" and "loss modulus-shear stress" curves of the mixed solution III have an intersection), and the amount of curing agent used is 10 phr.

[0019] The centrifugation in step 3) refers to centrifugation at a speed of 4000-5000 rpm for more than 5 minutes.

[0020] The temperature for heating, curing, and removing the wax support in step 5) is 80°C for 1 hour. In this application, the wax block used is 80# microcrystalline wax. After temperature treatment based on this application, its rheological properties meet the requirements of direct-write 3D printing, and its compressive strength is greater than the weight of the composite material of this application, and its melting temperature is no higher than the curing temperature of the composite material.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are:

[0022] (1) The introduction of wax support in direct-write 3D printing enables precise molding of suspended silicone rubber radiation shielding composite materials. The shielding material has good conformability and reduces redundant shielding, thus achieving lightweight, small size and high shielding effectiveness.

[0023] (2) The wax support used can be recycled after being removed by heating and can be reused repeatedly, which can not only reduce the manufacturing cost of radiation shielding materials but also be environmentally friendly;

[0024] (3) This application uses specific fillers and ratios, has low requirements for 3D printing equipment, and the preparation method is compatible with commercially available multi-head direct-writing 3D printers. The method is simple and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flowchart of a method for preparing a suspended structure of silicone rubber radiation shielding composite material for wax support-assisted 3D printing;

[0026] Among them, 1-use a multi-head 3D printer to print wax support; 2-print silicone rubber radiation shielding material; 3-repeatedly print wax support and shielding material layer by layer; 4-3D print layer by layer to the desired geometric shape; 5-heat and remove the wax support to obtain a suspended structure silicone rubber radiation shielding composite material.

[0027] Figure 2 This is a structural diagram of the protective rubber material used in Example 1.

[0028] Figure 3 This is a structural diagram of the wax support material used in Example 1.

[0029] Figure 4 Schematic diagram of a multi-head 3D printer.

[0030] Figure 5 This is a physical picture of the silicone rubber radiation shielding composite material with a suspended structure prepared by 3D printing in Example 1;

[0031] Among them, (a) is before removing the wax support, and (b) is after heating to remove the wax support and solidifying the molding.

[0032] Figure 6 This is a structural diagram of the protective rubber material used in Example 2.

[0033] Figure 7 This is a structural diagram of the wax support material used in Example 2. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical solutions of the present invention in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0035] The liquid silicone rubber used in the examples was Dow Corning Sylgard 184 two-component silicone rubber (containing a base rubber and a curing agent, the main component of which was polydimethylsiloxane, and its supporting curing agent was dimethylvinylated and trimethylated silica, CAS: 68988-89-6), purchased from The Dow Chemical Company; the wax block was 80# microcrystalline wax, purchased from Shanghai Chenjun Industrial Co., Ltd.; and hydrophilic fumed silica (specific surface area of ​​150 m 2 / g), bismuth oxide was purchased from Shanghai Aladdin Co., Ltd.; boron carbide was purchased from Naiyat Alloy Co., Ltd.; planetary stirring degassing machine model was SIE-C200, purchased from Guangzhou Schnoss Technology Co., Ltd.

[0036] Example 1

[0037] This embodiment provides a method for preparing a wax-supported 3D-printed suspended structure silicone rubber radiation shielding composite material for thermal neutron shielding and applied to arc-shaped pipeline protection. The preparation process is as follows: Figure 1 As shown, the following steps are included:

[0038] 1) In this embodiment, the target protection object is an arc-shaped pipeline, the radiation type is thermal neutrons, and the protection requirement is determined to be a thermal neutron shielding rate of more than 80%. Combined with the use environment, the thickness of the composite material is further determined to be 2 mm, the type of shielding filler is boron carbide, and the addition amount is 100 phr (in parts by mass).

[0039] 2) According to the shape of the arc-shaped pipe of the target protection object, the shape of the silicone rubber radiation shielding composite material is designed as follows Figure 2 The hollow elbow structure shown in the figure is designed with the shape of wax support material. Figure 3 As shown, Figure 3 In the figure, A is a schematic diagram of the shape used to support the external silicone rubber radiation shielding composite material, and B is a schematic diagram of the shape used to support the internal silicone rubber radiation shielding composite material. Both A and B are solid structures. A 3D geometric model of the composite material and wax support was created using the geometry modeling software SolidWorks. This model was then imported into Simplify3D software for slicing, generating a slice file that can be read by a 3D printer.

[0040] 3) Using a planetary stirring degassing machine, the materials were mixed at a speed of 5000 rpm: first, 100 phr of boron carbide (3 μm) sieved through a 110-mesh sieve was added to 100 phr of liquid silicone rubber base (Dow Corning 184 base), and stirred for 1 min until the mixture was uniform to obtain a mixed solution I; then, a silica gel with a specific surface area of ​​150 m was added to the mixed solution I in four portions; 2 / g of hydrophilic fumed silica (5 phr each time, totaling 20 phr) was added and stirred for 3 min until uniformly mixed to obtain a mixed solution II; finally, 10 phr of a curing agent was added to the mixed solution II and stirred for 1 min until uniformly mixed to obtain a mixed solution III; the mixed solution III was transferred to a printing barrel and placed in a centrifuge and centrifuged at 4000 rpm for 5 min to remove bubbles generated during the loading process.

[0041] 4) A block of 80# microcrystalline wax was loaded into a stainless steel barrel (25 mm outer diameter, 23 mm inner diameter). An electric heating film with temperature feedback regulation function was attached to the surface of the stainless steel barrel. The barrel was heated to 100°C and maintained for 30 min to completely melt the wax block into liquid and sink to the bottom; then the temperature was lowered to 40°C and maintained for 30 min to allow the wax material to condense and deposit at the bottom of the barrel.

[0042] 5) Use a multi-head printer (EFL BP6602 extrusion 3D printer) for 3D printing, the structure of which is as follows Figure 4 As shown; after the air compressor is loaded to 0.6MPa, it is connected to the printer, the barrel is loaded on the printer, and the printer is leveled and calibrated; the slicing file in step 1) is selected, and the corresponding air pressure is adjusted through the pipe switch and air valve connected to the barrel, and the support material and rubber material are printed at the same time; after printing, it is placed in an 80℃ oven for curing for 1 hour, and the wax support is removed to obtain a curved tube-shaped radiation protection silicone rubber that is highly consistent with the designed shape, as shown Figure 5 As shown, the actual pictures before and after removing the wax support are as follows Figure 5 As shown in (a) and (b).

[0043] The thermal neutron shielding performance of the obtained silicone rubber composite material was tested using an Am-Be neutron source (moderated) and a He-3 detector (Beijing Beilifu Electronic Technology Co., Ltd.). The test showed that the thermal neutron shielding rate of the obtained material was 81.37%, which has good thermal neutron protection performance and meets the required thermal neutron shielding requirements.

[0044] Example 2

[0045] This embodiment provides a method for preparing a silicone rubber radiation shielding composite material with a wax support-assisted 3D printing suspended structure for low-energy gamma ray shielding and applied to the protection of equipment with multiple right-angled surfaces, including the following steps:

[0046] 1) The target protection object of this embodiment is a multi-rectangular shape, and the radiation type is low-energy gamma rays. The protection requirement is determined to be a 39keV gamma ray shielding rate of more than 75%. Combined with the use environment, the thickness of the composite material is further determined to be 2mm, and the type of shielding filler is determined to be bismuth oxide, and the addition amount is determined to be 100phr.

[0047] 2) According to the multi-rectangular shape of the target protection object surface, the shape of the silicone rubber radiation shielding composite material is designed as follows Figure 6 The structure shown in the figure is designed to have a shape of wax support material. Figure 7 As shown in the figure, a three-dimensional geometric model of the composite material and wax support is created using the geometric modeling software SolidWorks, which is then imported into the Simplify3D software for slicing to obtain a slice file that can be recognized by the 3D printer.

[0048] 3) Using a planetary stirring degassing machine, the materials were mixed at a speed of 4000 rpm: first, 100 phr of bismuth oxide (1 μm) sieved through a 110-mesh sieve was added to 100 phr of liquid silicone rubber base (Dow Corning 184 base), and stirred for 1 min until the mixture was uniform to obtain a mixed solution I; then, a 150 m3 / s bismuth oxide with a specific surface area of ​​150 m3 / s was added to the mixed solution I in four portions; 2 / g of hydrophilic fumed silica (5 phr added each time, a total of 20 phr added), stirred for 3 minutes until mixed uniformly to obtain a mixed solution II; finally, 10 phr of a curing agent was added to the mixed solution II, and stirred for 1 minute until mixed uniformly to obtain a mixed solution III; the mixed solution III was transferred to a printing material cylinder, and placed in a centrifuge at a speed of 4000 rpm for 5 minutes to remove bubbles generated during the loading process;

[0049] 4) A block of 80# microcrystalline wax was loaded into a stainless steel barrel (25 mm outer diameter, 23 mm inner diameter). An electric heating film with temperature feedback regulation function was attached to the surface of the stainless steel barrel. The barrel was heated to 100°C and maintained for 30 min to completely melt the wax block into liquid and sink to the bottom; then the temperature was lowered to 40°C and maintained for 30 min to allow the wax material to condense and deposit at the bottom of the barrel.

[0050] 5) Use Figure 4 3D printing was performed using the multi-head printer (EFL BP6602 extrusion 3D printer) shown in FIG. After the air compressor was loaded to a pressure of 0.6 MPa, it was connected to the printer, the barrel was loaded on the printer, and the printer was leveled and calibrated. The slicing file in step 1) was selected, and the corresponding air pressure was adjusted through the pipe switch and air valve connected to the barrel to print the support material and rubber material simultaneously. After printing, the material was placed in an 80°C oven for curing for 1 hour, and the wax support was removed to obtain a multi-rectangular radiation protection silicone rubber that highly conformed to the designed shape.

[0051] use 152 The gamma-ray shielding performance of the obtained silicone rubber was tested using a Eu (39keV) source and a HPGe detector (Ortec). The test showed that the low-energy gamma-ray shielding rate of the obtained material was 77.36%, which has good gamma-ray protection performance and meets the required low-energy gamma-ray shielding requirements.

[0052] Both Example 1 and Example 2 show that the preparation method disclosed in the present invention can prepare a suspended structure silicone rubber radiation shielding composite material that has good conformity to the surface of the target protection object and has the advantage of high radiation shielding effectiveness.

[0053] Comparative Example 1

[0054] Except that the cooling temperature in step 4) is 55° C. and maintained at 55° C., the remaining steps are the same as those in Example 1.

[0055] In this comparative example, the wax material cannot solidify after 3D printing extrusion and cannot play an effective supporting role, and the silicone rubber radiation shielding composite material structure is severely deformed.

[0056] Comparative Example 2

[0057] Except that the boron carbide is not screened in step 3), the remaining steps are the same as those in Example 1.

[0058] In this comparative example, since the particle size distribution of boron carbide does not meet the requirements, wire breakage and clogging of the 3D printing nozzle occur during the 3D printing process, and the silicone rubber radiation shielding composite material cannot be obtained.

[0059] Comparative Example 3

[0060] Considering the conservatism of radiation protection, the amount of bismuth oxide used in step 3) is 22 g, and the remaining steps are the same as in Example 2.

[0061] The silicone rubber radiation shielding composite material obtained in this comparative example has bulges on its surface, and its gamma-ray shielding uniformity is lower than that in Example 2.

[0062] Comparative Example 4

[0063] Except that the oven temperature in step 5) is set to 60° C., the remaining steps are the same as those in Example 1.

[0064] In this comparative example, the silicone rubber radiation shielding composite material and the wax support are still bonded together as a whole, and the wax support is not removed.

[0065] Comparative Example 5

[0066] Except that the oven temperature in step 5) is set to 100° C., the remaining steps are the same as those in Example 2.

[0067] In this comparative example, the wax support melted prematurely and could not play a supporting role, causing the structure of the silicone rubber radiation shielding composite material to collapse severely.

[0068] It can be seen from the examples and comparative examples that the preparation of silicone rubber radiation shielding composite materials with suspended structures by wax support-assisted 3D printing has strict limitations on the preparation parameters (particle size, dosage, ratio of each raw material of the radiation shielding filler in the mixed solution, 3D printing temperature of wax support, processing temperature after 3D printing is completed, etc.). Only under specific parameter conditions can a silicone rubber radiation shielding composite material with a suspended structure that meets the requirements be obtained.

Claims

1. A method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support assisted 3D printing, characterized in that: The specific steps are as follows: 1) Determine the thickness of the silicone rubber radiation shielding composite material based on shielding requirements; design the shape of the silicone rubber radiation shielding composite material into a geometric shape that complements the target protection object, and add wax supports to the hollow structure or suspended structure of the silicone rubber radiation shielding composite material; Use geometric modeling software to create a three-dimensional geometric model of the silicone rubber radiation shielding composite material and wax support, then import it into slicing software to obtain a slice file that can be recognized by the 3D printer; 2) Place the liquid silicone rubber base in a planetary stirring degassing machine, add a radiation shielding filler, and stir and mix uniformly to obtain a mixed solution I; then, add hydrophilic fumed silica to the mixed solution I in portions, and stir and mix uniformly to obtain a mixed solution II; finally, add a curing agent to the mixed solution II, and stir and mix uniformly to obtain a mixed solution III; transfer the mixed solution III to the barrel of a 3D printer and centrifuge it; The radiation shielding filler includes a neutron shielding filler or a gamma ray shielding filler; 3) Load 80# microcrystalline wax block into the barrel, heat to 100°C and hold for 30 minutes; then cool to 40°C and hold; 4) After pressurizing the air compressor, connect it to the 3D printer, load the barrel onto the 3D printer, select the slice file from step 2), and print the silicone rubber radiation shielding composite and wax support material simultaneously; After printing is completed, it is placed in an oven for heating and curing and the wax support is removed to obtain a silicone rubber radiation shielding composite material for the suspended structure.

2. The method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing according to claim 1, characterized in that: In step 2), the neutron shielding filler is boron carbide, and the gamma radiation shielding filler is bismuth oxide; the particle size of the shielding filler is in the range of 1 to 3 μm.

3. The method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing according to claim 1, characterized in that: The liquid silicone rubber in step 2) is polydimethylsiloxane.

4. The method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing according to claim 1, characterized in that: The stirring refers to a rotation speed of 4000~5000rpm.

5. The method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing according to claim 1, characterized in that: Step 2) The radiation shielding filler is sieved using a sieve with a mesh size of not less than 110 meshes.

6. The method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing according to claim 1, characterized in that: Step 2) In parts by mass, the liquid silicone rubber base is 100 phr, the amount of shielding filler is 20-100 phr, the amount of hydrophilic fumed silica is 18-20 phr, and the amount of curing agent is 10 phr.

7. The method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing according to claim 1, characterized in that: Step 2) The centrifugation is performed at a speed of 4000-5000 rpm for more than 5 min.

8. The method for preparing a suspended structure silicone rubber radiation shielding composite material by wax support-assisted 3D printing according to claim 1, characterized in that: Step 4) The heating refers to heating at 80° C. for 1 h.

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