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

Abstract

The invention discloses a method for preparing a silicone rubber radiation shielding composite material with a suspended structure through wax support assisted 3D printing, and relates to the technical field of radiation shielding materials. According to the composite material, two-component liquid silicone rubber is used as a flexible base material, hydrophilic fumed silica is used as a thickening agent, boron carbide, bismuth oxide and the like are used as radiation shielding filler, and 80 # microcrystalline wax is used as a supporting material; according to the distribution condition of the radiation field, determining the type and dosage of the loaded shielding filler and the geometrical shape of the radiation shielding composite material; then, geometric models of a shielding material and a supporting material are established, and parameters are selected for slicing processing to obtain a 3D printing slice file; printing is conducted through a multi-head 3D printer; and finally, heating and curing to remove the wax block support to obtain the silicone rubber radiation shielding composite material with the suspended structure. The method can be applied to neutron and gamma ray protection of special-shaped components such as pipelines and the like, and has the advantages of good conformality, light weight, small size, high radiation shielding effectiveness and the like.

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. shielding) 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 raw 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. Composite materials. Both processing and molding methods rely on molds, and the diversity of shapes of special-shaped components determines the need to process different types of molds, which not only increases manufacturing costs, but also cannot immediately meet the rapid manufacturing needs of radiation shielding materials.

[0003] 3D printing technology has the advantages of 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 γ shielding and neutron shielding materials by direct writing 3D printing (Radiation Physics and Chemistry, 2021, 188: 109616), but it is limited to the preparation of regular shaped materials such as flat plates. Special-shaped components such as arc pipes and multiple right angles are more widely used in practical applications. Radiation shielding materials with suspended structures are required to compact and integrate them for protection. However, during the printing process of suspended structure materials, the polymer slurry is not easy to maintain its shape after deposition, causing structural collapse. Therefore, the 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, with photocurable materials 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 technology based on photocuring or fused deposition, rigid polymer materials are solidified and formed synchronously 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 properties are required. In 3D printing radiation shielding material technology based on DIW, flexible polymer materials cannot be formed immediately after extrusion deposition, and further heating treatment is required to solidify them. 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 requirements on the thermal and mechanical properties of the support material itself and its matching with the thermal / mechanical properties of the main material. Especially in the 3D printing of radiation shielding materials, in order to improve the radiation shielding effect of the material, it is necessary to add radiation shielding functional fillers to the base material, which also affects the performance of the main material and increases the difficulty of technical implementation. Therefore, how to use 3D printing to prepare suspended structure silicone rubber radiation shielding composite materials is still a technical problem that needs to be solved urgently 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, a wax block is used as a support and a direct writing 3D printing method is adopted to prepare a suspended structure flexible radiation shielding composite material that meets the requirements of practical applications.

[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, comprising the following steps:

[0008] 1) According to 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. According to the attenuation coefficient calculation formula and the ray intensity attenuation calculation formula, the radiation shielding filler content, ratio and radiation shielding material thickness (preferably 2 mm) are determined.

[0009] 2) Designing the shape of the silicone rubber radiation shielding composite material to be a geometric shape complementary to the target protection object, and the material thickness is the same as 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 a slicing software (such as Simplify3D) for discretization, and converting it into a code recognizable by a 3D printer to obtain 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 the 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: According to the parameters obtained in step 1), first, add the radiation shielding filler that has been sieved (110 mesh) 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 batches, stir and mix evenly, and obtain a mixed solution II; finally, add a curing agent that matches 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 for centrifugation, and remove bubbles generated during the loading process.

[0012] 4) Load the wax block into a metal barrel and heat it uniformly from room temperature to 100°C through an electric heating device to completely melt the wax block and maintain it for 30 minutes; then cool it uniformly to 40°C and maintain it to condense the wax material and deposit it 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 a large number of 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 and then cools and condenses the wax blocks, which can form a dense whole 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 best temperature to ensure that it can be 3D printed and compatible with the slurry.

[0014] 5) Start the 3D printing process using the multi-material 3D printer: connect the air compressor to the 3D printer after pressurization, load the barrel on the 3D printer, and level and calibrate the 3D printer; select the slicing file in step 2) and print the silicone rubber radiation shielding composite material and the wax support material at the same time; after printing, place it in an oven for heating and curing 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 by mass, with 100 phr of the mass 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 and 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, which has rheological properties that meet the requirements of direct writing 3D printing after temperature treatment based on this application, and the compression strength is higher than the dead weight of the composite material of this application, and the melting temperature is not 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 wax support was introduced into direct writing 3D printing to achieve precise molding of suspended structure silicone rubber radiation shielding composite materials. The shielding material has good conformability and reduces redundant shielding, thus achieving lightweight, small volume and high shielding effectiveness.

[0023] (2) The wax support used can be recovered 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) The present application adopts specific fillers and proportions, 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 Flow chart of a method for preparing a suspended structure of a 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 supports; 2-print silicone rubber radiation shielding materials; 3-repeatedly print wax supports and shielding materials layer by layer; 4-3D print layer by layer to the desired geometric shape; 5-heat and remove the wax supports 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 and forming.

[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 technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0035] The liquid silicone rubber used in the embodiment is Dow Corning Sylgard 184 two-component silicone rubber (containing base rubber and curing agent, the main component is polydimethylsiloxane, and its supporting curing agent is dimethylvinylated and trimethylated siloxane "Dimethylvinylated and Trimethylated Silica", CAS: 68988-89-6), purchased from Dow Chemical Company; the wax block is 80# microcrystalline wax, purchased from Shanghai Chenjun Industrial Co., Ltd.; hydrophilic fumed silica (specific surface area of ​​150m 2 / g), bismuth oxide was purchased from Shanghai Aladdin Co., Ltd.; boron carbide was purchased from Naiyat Alloy Co., Ltd.; the 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 arc-shaped pipeline protection. The preparation process is as follows: Figure 1 As shown, the following steps are included:

[0038] 1) The target protection object of this embodiment is an arc-shaped pipeline, the radiation type is thermal neutrons, and the protection requirement is determined to be that the thermal neutron shielding rate reaches more than 80%; combined with the use environment, it is further determined that the thickness of the composite material is 2 mm, the type of shielding filler is boron carbide, and the addition amount is 100 phr (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 a wax support material shape of Figure 3 As shown, Figure 3 In the figure, A is a schematic diagram of the shape of the external support silicone rubber radiation shielding composite material, and B is a schematic diagram of the shape of the internal support silicone rubber radiation shielding composite material, and both A and B are solid structures. The three-dimensional geometric model of the composite material and the wax support is established using the geometric modeling software SolidWorks, and then imported into the Simplify3D software for slicing to obtain a slice file that can be recognized by the 3D printer.

[0040] 3) Use a planetary stirring degassing machine to mix the materials at a speed of 5000 rpm: first, add 100 phr of boron carbide (3 μm) sieved through a 110-mesh sieve to 100 phr of liquid silicone rubber base (Dow Corning 184 base), stir for 1 min until the mixture is uniform, and obtain a mixed solution I; then add a 150 m3 / s silica gel with a specific surface area of ​​150 m3 / s to the mixed solution I in four portions; 2 / g of hydrophilic fumed silica (5phr added each time, totaling 20phr), stirred for 3min until mixed evenly to obtain a mixed solution II; finally, 10phr of a curing agent was added to the mixed solution II, stirred for 1min until mixed evenly to obtain a mixed solution III; the mixed solution III was transferred to a printing barrel, placed in a centrifuge and centrifuged at 4000rpm for 5min to remove bubbles generated during the loading process.

[0041] 4) Load the wax block of 80# microcrystalline wax into a stainless steel barrel (outer diameter 25 mm, inner diameter 23 mm), attach an electric heating film with temperature feedback regulation function to the surface of the stainless steel barrel, heat to 100°C and keep for 30 minutes to completely melt the wax block into liquid and sink to the bottom; then cool to 40°C and keep for 30 minutes 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 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 pipeline switch and the air valve connected to the barrel, and the support material and the rubber material are printed at the same time; after printing, it is placed in an 80℃ oven for curing for 1h, and the wax support is removed to obtain a curved tube-type radiation protection silicone rubber that highly conforms to the designed shape, as shown Figure 5 As shown in the figure, 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 wax-supported 3D-printed suspended structure silicone rubber radiation shielding composite material for low-energy gamma-ray shielding and applied to surface multi-right-angle equipment protection, comprising 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 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; the three-dimensional geometric model of the composite material and wax support is established using the geometric modeling software SolidWorks, and then imported into the Simplify3D software for slicing to obtain a slicing file that can be recognized by the 3D printer.

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

[0049] 4) Load the wax block of 80# microcrystalline wax into a stainless steel barrel (outer diameter 25 mm, inner diameter 23 mm), attach an electric heating film with temperature feedback regulation function to the surface of the stainless steel barrel, heat to 100°C and keep for 30 minutes to completely melt the wax block into liquid and sink to the bottom; then cool to 40°C and keep for 30 minutes to allow the wax material to condense and deposit at the bottom of the barrel.

[0050] 5) Use Figure 4 The multi-head printer (EFL BP6602 extrusion 3D printer) shown in the figure is used for 3D printing; the air compressor is connected to the printer after the pressure reaches 0.6MPa, 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 pipeline switch and the air valve connected to the barrel, and the support material and the rubber material are printed at the same time; after printing, it is placed in an 80°C oven for curing for 1h, and the wax support is removed to obtain a multi-rectangular radiation protection silicone rubber that is highly consistent with 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, causing serious deformation of the silicone rubber radiation shielding composite material structure.

[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 3D printing nozzle clogging 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 of 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 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, since the wax support melted prematurely and could not play a supporting role, the structure of the silicone rubber radiation shielding composite material collapsed severely.

[0068] It can be seen from the embodiments and comparative examples that the preparation of silicone rubber radiation shielding composite materials with suspended structures by wax-supported 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.), and a silicone rubber radiation shielding composite material with a suspended structure that meets the requirements can only be obtained under specific parameter conditions.

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 according to the shielding requirements; design the shape of the silicone rubber radiation shielding composite material into a geometric shape complementary to the target protection object, and add wax support to the hollow structure or suspended structure of the silicone rubber radiation shielding composite material; A three-dimensional geometric model of the silicone rubber radiation shielding composite material and the wax support is established using geometric modeling software, and then imported into the slicing software for processing to obtain a slicing file that can be recognized by the 3D printer; 2) Place the liquid silicone rubber base in a planetary stirring degassing machine, add radiation shielding filler, stir and mix evenly to obtain a mixed solution I; then add hydrophilic fumed silica to the mixed solution I in portions, stir and mix evenly to obtain a mixed solution II; finally, add a curing agent to the mixed solution II, stir and mix evenly to obtain a mixed solution III; transfer the mixed solution III to the barrel of a 3D printer, and place it in a centrifuge for centrifugation; 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℃ and keep it for 30min; then cool to 40℃ and keep it; 4) Connect the air compressor to the 3D printer after pressurizing it, load the barrel on the 3D printer, select the slice file in step 2), and print the silicone rubber radiation shielding composite material and wax support material at the same time; 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 a 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 4000-5000 rpm.

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 material 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 refers to centrifugation 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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