A high-density flame-retardant and heat-resistant shielding material and its preparation method

Abstract

The present invention discloses a high-density flame-retardant and heat-resistant shielding material and a preparation method thereof, wherein the high-density flame-retardant and heat-resistant shielding material is composed of the following components: 7-12wt% phenolic resin composite powder, 0.5-5wt% boron carbide powder, 85-92wt% tungsten powder, 0.5-2wt% reinforcing agent and 0.05-0.2wt% lubricant; wherein the phenolic resin composite powder is a mixture of ordinary phenolic resin and boron phenolic resin obtained by the following method: ordinary phenolic resin and boron phenolic resin are dissolved in alcohol or acetone and stirred and mixed. The high-density flame-retardant and heat-resistant shielding material prepared by the present invention has a density higher than 7.0g / cm 3 Its oxygen index reaches 48, vertical combustion reaches V0 level, and it has the characteristics of high strength and low expansion. It also has good neutron and gamma radiation shielding effects, which can meet the radiation protection requirements of specific high temperature areas of nuclear reactors.

Description

Technical Field

[0001] The present invention relates to the technical field of shielding materials, in particular to a high-density flame-retardant and heat-resistant shielding material and a preparation method thereof. Background Art

[0002] In the reactor compartment area, some shielded areas are characterized by high temperature, strong radiation, small space and high safety. The local ambient temperature is as high as 250°C. In addition, the space in this area is small and the radiation dose rate is large. Ordinary polymer materials such as lead-boron polyethylene are difficult to meet the use requirements in terms of heat resistance, flame retardancy and radiation resistance.

[0003] In order to ensure the safety of the nuclear reactor shielding system, a composite shielding material with excellent temperature resistance, flame retardancy and mechanical properties, and capable of shielding neutrons and gamma rays, is needed. This shielding material can be directly used in the high-temperature area of ​​the shielding area, which can significantly simplify the shielding structure and improve the safety of the shielding system.

[0004] Commonly used lead-boron polyethylene materials have good shielding properties, but due to the limitations of the polyethylene substrate, the maximum operating temperature generally does not exceed 130°C, and the flame retardant performance is poor. The invention patent application CN201310294900.7 "A heat-resistant composite shielding material and its preparation method" mentions that the heat deformation temperature can be increased to 120°C when polypropylene is used as the substrate, while the heat deformation temperature of the lead-boron polyethylene material is only 82°C. However, the patent still does not solve the flame retardant problem of polypropylene, and the heat resistance and mechanical properties of polypropylene cannot meet the requirements of the use environment. Invention patent ZL202110191196.7 "Castable epoxy-based heat-resistant shielding material and its preparation method and application" uses epoxy resin as the substrate, adds neutron-proof additives and flame retardant additives, and its heat resistance is increased to 120-150°C, and the oxygen index is increased to 27, but the system has a low density and poor γ shielding performance, and its heat resistance still does not meet the requirements of the use environment. Invention patent CN201310092036.2 "A high temperature resistant shielding material with comprehensive neutron and gamma shielding effect" mentions the use of epoxy resin, boron carbide and tungsten powder to make a heat resistant shielding material with a temperature resistance of 150°C, but epoxy resin is a flammable material with an oxygen index of about 18, so the flame retardant performance of the heat resistant shielding material is poor and cannot meet the use requirements. Invention patent CN202110887236.1 "A high flame retardant, high bonding strength high temperature resistant shielding putty" mentions the use of epoxy resin to add alicyclic amine curing agent, with aluminum hydroxide flame retardant, boron carbide, tungsten powder shielding aids to prepare a shielding putty material with an oxygen index of up to 34 and a density of 3.4g / cm3. If the density is increased to 4.95g / cm3, its oxygen index drops to 26, and due to the limitations of the epoxy resin system, its long-term use temperature does not exceed 160°C. Invention patent CN201410474504.7 "Polyphenylene sulfide / tungsten powder shielding composite material and preparation method thereof" mentions that the shielding material prepared by using polyphenylene sulfide as the base material and adding 85%-97% tungsten powder has good heat resistance and flame retardancy, but polyphenylene sulfide material is very brittle, and it is difficult to change its brittleness by simply adding tungsten powder, and it is difficult to meet the actual engineering needs. In summary, the existing shielding materials cannot meet the requirements of the existing use environment in terms of temperature resistance and flame retardancy.

[0005] Compared with lead-boron shielding materials, tungsten-boron shielding materials have better neutron shielding performance at the same density, and their environmental friendliness is significantly better than that of lead-containing shielding materials. Summary of the invention

[0006] To this end, the technical problem to be solved by the present invention is to provide a high-density flame-retardant and heat-resistant shielding material with a temperature resistance exceeding 250°C and excellent flame retardant performance and a preparation method thereof. The density of the prepared high-density flame-retardant and heat-resistant shielding material is higher than 7.0g / cm 3Its oxygen index reaches 48, vertical combustion reaches V0 level, and it has the characteristics of high strength and low expansion. It also has good neutron and gamma radiation shielding effects, which can meet the radiation protection requirements of specific high-temperature areas of nuclear reactors.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A high-density flame-retardant and heat-resistant shielding material consists of the following components: 7-12wt% of phenolic resin composite powder, 0.5-5wt% of boron carbide powder, 85-92wt% of tungsten powder, 0.5-2wt% of reinforcing agent and 0.05-0.2wt% of lubricant; wherein the phenolic resin composite powder is a mixture of ordinary phenolic resin and boron phenolic resin prepared by the following method: ordinary phenolic resin and boron phenolic resin are dissolved in anhydrous alcohol or anhydrous acetone and stirred and mixed.

[0009] In the high-density flame-retardant and heat-resistant shielding material, in the phenolic resin composite powder, the weight ratio of ordinary phenolic resin to boron phenolic resin is 1:1-4.

[0010] The reinforcing agent of the high-density flame-retardant and heat-resistant shielding material is glass fiber powder.

[0011] The fiber length of the glass fiber powder in the high-density flame-retardant and heat-resistant shielding material is 0.1 to 5 mm.

[0012] The lubricant of the high-density flame-retardant and heat-resistant shielding material is calcium stearate and / or zinc stearate.

[0013] The density of the high-density flame-retardant and heat-resistant shielding material is 7.0-9.5 g / cm 3 .

[0014] The high-density flame-retardant and heat-resistant shielding material has a tungsten powder particle size of 300 to 1000 meshes and a purity greater than or equal to 99.9wt%.

[0015] In the high-density flame-retardant and heat-resistant shielding material, the particle size of the boron carbide powder is less than or equal to 100 μm.

[0016] The preparation method of the flame retardant lead-boron modified polyethylene composite material comprises the following steps:

[0017] Step 1) The weighed ordinary phenolic resin, boron phenolic resin, tungsten powder, boron carbide powder, reinforcing agent and lubricant are mixed to prepare a mixed wet material by the following steps:

[0018] Step 1-1) Ordinary phenolic resin and boron phenolic resin are weighed and dissolved in anhydrous alcohol or anhydrous acetone, and stirred and mixed at a speed of 20 to 40 r / min for 30 to 60 min;

[0019] Step 1-2) Add boron carbide powder, lubricant and reinforcing agent and continue to stir and mix at a speed of 20 to 40 r / min for 15 to 30 min;

[0020] Step 1-3) Add tungsten powder and continue stirring and mixing at a speed of 30 to 50 r / min and a stirring time of 1.5 to 3 h to obtain a mixed wet material;

[0021] Step 2) preparing a mixed dry powder: placing the mixed wet material obtained in step 1) in an oven for air drying, and then crushing the dried material with a crusher to obtain a mixed dry powder, which is then sealed and stored for later use;

[0022] Step 3) Molding: Weigh the mixed dry powder obtained in step 2) and put it into a mold for pressing to obtain a high-density flame-retardant and heat-resistant shielding material. The pressing temperature is 150-195°C, the pressing time is 40-90 minutes, and the pressing pressure is 10-20 MPa.

[0023] In the above preparation method, in step 3), the specific pressing operation is:

[0024] Step 3-1) pre-pressing for 10 to 20 minutes, the pre-pressing pressure is 3 to 5 MPa, and the pre-pressing temperature is 115 to 130°C;

[0025] Step 3-2) two-stage formal pressing: the first stage of formal pressing has a pressing time of 10 to 30 minutes, a pressure of 10 to 15 MPa, and a temperature of 150 to 165° C.; the second stage of formal pressing has a pressing time of 30 to 60 minutes, a pressure of 15 to 20 MPa, and a temperature of 180 to 195° C.;

[0026] Step 3-3) Cool the mold to 80-90°C with cooling water, maintain the pressure at 18-20MPa, then remove the mold and place it on a natural horizontal surface, and place it for at least 24h before processing.

[0027] The technical solution of the present invention achieves the following beneficial technical effects:

[0028] 1. The flame retardant and heat resistant shielding material of the present invention has an oxygen index of 48, vertical combustion reaches V0 level, and has the characteristics of high strength and low expansion. It has good neutron and gamma radiation shielding effect while ensuring high density, meeting the radiation protection requirements of specific high temperature areas of nuclear reactors.

[0029] 2. The present invention adopts a mixed system of two phenolic resins, combined with a glass fiber reinforcement, which gives the material good mechanical properties while ensuring excellent flame retardant and shielding properties, thereby improving safety and reliability in use.

[0030] 3. The present invention adopts a wet mixing process to fully and evenly mix the resin, additives and shielding filler, thereby achieving good mechanical properties when a large amount of functional filler is added, and greatly reducing dust pollution in the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a ×500 electron microscope image of the high-density flame-retardant and heat-resistant shielding material prepared in Example 2. DETAILED DESCRIPTION

[0032] Example 1

[0033] The high-density flame-retardant and heat-resistant shielding material in this embodiment is composed of 2.4 parts by weight of ordinary phenolic resin PF-304, 9.6 parts by weight of boron phenolic resin THC400, 0.5 parts by weight of boron carbide powder with a particle size of 200 mesh, 86.5 parts by weight of tungsten powder with a particle size of 1000 mesh and a purity greater than or equal to 99.9wt%, 0.95 parts by weight of glass fiber powder and 0.05 parts by weight of calcium stearate CV510, wherein the glass fiber length in the glass fiber powder is 0.15 mm.

[0034] The high-density flame-retardant and heat-resistant shielding material in this embodiment is prepared by the following steps:

[0035] Step 1) mixing: ordinary phenolic resin PF-304 and boron phenolic resin THC400 are weighed and dissolved in anhydrous alcohol, and then stirred and mixed at a speed of 20r / min for 30min; then weighed boron carbide powder, calcium stearate CV510 and glass fiber powder are added, and stirring is continued for 30min at a speed of 30r / min; then weighed tungsten powder is added, and stirring is continued for 2h at a speed of 30r / min to obtain a mixed wet material; when the materials are stirred and mixed in anhydrous alcohol, the system temperature should be controlled not to exceed 50°C, specifically, the system temperature can be cooled by passing cooling water to ensure that the system temperature does not exceed 50°C;

[0036] Step 2) Place the mixed wet material obtained in step 1) in a 50°C oven for 4 hours with air blowing and dry until completely dried, then crush the dried material with a crusher and seal it for later use to obtain a mixed dry powder;

[0037] Step 3) weigh the mixed dry powder obtained in step 2) and put it into a preheated mold, pre-press 3-5MPa for 15min, and the mold temperature is 115°C; the mold temperature is raised to 150°C, the pressure is raised to 15MPa, and the molding time is 30min; the mold temperature is raised to 190°C, the pressure is raised to 20MPa, and the pressure is maintained for 30min; cooling water is passed to cool to 80-90°C and demold, and the pressure is maintained at 20MPa during the cooling period, and then the mold is placed on a natural horizontal surface, and placed for at least 24h before processing.

[0038] Example 2

[0039] The high-density flame-retardant and heat-resistant shielding material in this embodiment is composed of 4.0 parts by weight of ordinary phenolic resin PF-2123, 4.0 parts by weight of boron phenolic resin FB88, 5.0 parts by weight of boron carbide powder with a particle size of 325 mesh, 86.0 parts by weight of tungsten powder with a particle size of 200 mesh and a purity greater than or equal to 99.9wt%, 0.9 parts by weight of glass fiber powder and 0.1 parts by weight of zinc stearate AV302, wherein the glass fiber length in the glass fiber powder is 2mm. The electron microscope image of the high-density flame-retardant and heat-resistant shielding material prepared in this embodiment is as follows Figure 1 As shown, the rod-shaped object is glass fiber, the particles with larger particle size are boron carbide, the particles with smaller particle size are tungsten powder, and the continuous phase is a mixture of ordinary phenolic resin PF-2123 and boron phenolic resin BF88.

[0040] The high-density flame-retardant and heat-resistant shielding material in this embodiment is prepared by the following steps:

[0041] Step 1) mixing: ordinary phenolic resin PF-2123 and boron phenolic resin BF88 are weighed and dissolved in anhydrous alcohol, and then stirred and mixed at a speed of 30r / min for 1h; then weighed boron carbide powder, zinc stearate AV302 and glass fiber powder are added, and stirring is continued for 30min at a speed of 20r / min; then weighed tungsten powder is added, and stirring is continued for 1.5h at a speed of 30r / min to obtain a mixed wet material; when the materials are stirred and mixed in anhydrous alcohol, the system temperature should be controlled not to exceed 50°C, specifically, the system temperature can be cooled by passing cooling water to ensure that the system temperature does not exceed 50°C;

[0042] Step 2) Place the mixed wet material obtained in step 1) in a 40°C oven for 6 hours with air blowing and dry until completely dried, then crush the dried material with a crusher and seal it for later use to obtain a mixed dry powder;

[0043] Step 3) weigh the mixed dry powder obtained in step 2) and put it into a preheated mold, pre-press 3-5MPa for 15min, and the mold temperature is 115°C; the mold temperature is raised to 150°C, the pressure is raised to 15MPa, and the molding time is 30min; the mold temperature is raised to 190°C, the pressure is raised to 20MPa, and the pressure is maintained for 30min; cooling water is passed to cool to 80-90°C and demold, and the pressure is maintained at 20MPa during the cooling period, and then the mold is placed on a natural horizontal surface, and placed for at least 24h before processing.

[0044] Example 3

[0045] The high-density flame-retardant and heat-resistant shielding material in this embodiment is composed of 3.2 parts by weight of phenolic resin PF-304, 4.8 parts by weight of boron phenolic resin THC390, 2.8 parts by weight of boron carbide powder with a particle size of 325 mesh, 87.0 parts by weight of tungsten powder with a particle size of 800 mesh and a purity greater than or equal to 99.9wt%, 2.0 parts by weight of glass fiber powder and 0.2 parts by weight of zinc stearate AV302, wherein the glass fiber length in the glass fiber powder is 0.5 mm.

[0046] The high-density flame-retardant and heat-resistant shielding material in this embodiment is prepared by the following steps:

[0047] Step 1) mixing: ordinary phenolic resin PF-304 and boron phenolic resin THC390 are weighed and dissolved in anhydrous acetone, and then stirred and mixed at a speed of 20r / min for 45min; then weighed boron carbide powder, zinc stearate AV302 and glass fiber powder are added, and stirring is continued for 15min at a speed of 30r / min; then weighed tungsten powder is added, and stirring is continued for 3h at a speed of 30r / min to obtain a mixed wet material; when the materials are stirred and mixed in anhydrous acetone, the system temperature should be controlled not to exceed 50°C, specifically, the system temperature can be cooled by passing cooling water to ensure that the system temperature does not exceed 50°C;

[0048] Step 2) Place the mixed wet material obtained in step 1) in a 40°C oven for 6 hours with air blowing and dry until completely dried, then crush the dried material with a crusher and seal it for later use to obtain a mixed dry powder;

[0049] Step 3) weigh the mixed dry powder obtained in step 2) and put it into a preheated mold, pre-press 3-5MPa for 10min, and the mold temperature is 120°C; the mold temperature is raised to 160°C, the pressure is raised to 12MPa, and the molding time is 15min; the mold temperature is raised to 190°C, the pressure is raised to 18MPa, and the pressure is maintained for 40min; cooling water is passed to cool to 80-90°C and demold, and the pressure is maintained at 18MPa during the cooling period, and then the mold is placed on a natural horizontal surface, and placed for at least 24h before processing.

[0050] Example 4

[0051] The high-density flame-retardant and heat-resistant shielding material in this embodiment is composed of 2.0 parts by weight of phenolic resin PF-302, 6.0 parts by weight of boron phenolic resin PF-242, 1.0 parts by weight of boron carbide powder with a particle size of 325 mesh, 90.0 parts by weight of tungsten powder with a particle size of 800 mesh and a purity greater than or equal to 99.9wt%, 0.9 parts by weight of glass fiber powder and 0.1 parts by weight of calcium stearate, wherein the glass fiber length in the glass fiber powder is 1.5 mm.

[0052] The high-density flame-retardant and heat-resistant shielding material in this embodiment is prepared by the following steps:

[0053] Step 1) mixing: ordinary phenolic resin PF-302 and boron phenolic resin PF-242 are weighed and dissolved in anhydrous acetone, and then stirred and mixed at a speed of 30r / min for 40min; then weighed boron carbide powder, calcium stearate and glass fiber powder are added, and stirring is continued for 30min at a speed of 30r / min; then weighed tungsten powder is added, and stirring is continued for 2h at a speed of 50r / min to obtain a mixed wet material; when the materials are stirred and mixed in anhydrous acetone, the system temperature should be controlled not to exceed 50°C, specifically, the system temperature can be cooled by passing cooling water to ensure that the system temperature does not exceed 50°C;

[0054] Step 2) Place the mixed wet material obtained in step 1) in a 40°C oven for 4 hours with air blowing and dry until completely dried, then crush the dried material with a crusher and seal it for later use to obtain a mixed dry powder;

[0055] Step 3) weigh the mixed dry powder obtained in step 2) and put it into a preheated mold, pre-press 3-5MPa for 15min, and the mold temperature is 120°C; the mold temperature is raised to 150°C, the pressure is raised to 10MPa, and the molding time is 10min; the mold temperature is raised to 180°C, the pressure is raised to 15MPa, and the pressure is maintained for 30min; cooling water is passed to cool to 80-90°C and demold, and the pressure is maintained at 15MPa during the cooling period, and then the mold is placed on a natural horizontal surface, and placed for at least 24h before processing.

[0056] Example 5

[0057] The high-density flame-retardant and heat-resistant shielding material in this embodiment is composed of 2.4 parts by weight of phenolic resin PF-305, 5.0 parts by weight of boron phenolic resin FB88, 0.75 parts by weight of boron carbide powder with a particle size of 325 mesh, 91.0 parts by weight of tungsten powder with a particle size of 800 mesh and a purity greater than or equal to 99.9wt%, 0.8 parts by weight of glass fiber powder and 0.05 parts by weight of zinc stearate AV332, wherein the glass fiber length in the glass fiber powder is 0.2 mm.

[0058] The high-density flame-retardant and heat-resistant shielding material in this embodiment is prepared by the following steps:

[0059] Step 1) mixing: ordinary phenolic resin PF-305 and boron phenolic resin FB88 are weighed and dissolved in anhydrous alcohol, and then stirred and mixed at a speed of 30r / min for 1h; then weighed boron carbide powder, zinc stearate AV332 and glass fiber powder are added, and stirring is continued for 30min at a speed of 40r / min; then weighed tungsten powder is added, and stirring is continued for 2.5h at a speed of 30r / min to obtain a mixed wet material; when the materials are stirred and mixed in anhydrous alcohol, the system temperature should be controlled not to exceed 50°C, specifically, the system temperature can be cooled by passing cooling water to ensure that the system temperature does not exceed 50°C;

[0060] Step 2) Place the mixed wet material obtained in step 1) in a 50°C oven for 6 hours with air blowing and dry until completely dried, then crush the dried material with a crusher and seal it for later use to obtain a mixed dry powder;

[0061] Step 3) weigh the mixed dry powder obtained in step 2) and put it into a preheated mold, pre-press 3-5MPa for 15min, and the mold temperature is 125°C; the mold temperature is raised to 155°C, the pressure is raised to 12MPa, and the molding time is 10min; the mold temperature is raised to 185°C, the pressure is raised to 18MPa, and the pressure is maintained for 60min; cooling water is passed to cool to 80-90°C and demold, and the pressure is maintained at 18MPa during the cooling period, and then demolded and placed on a natural horizontal surface, and placed for at least greater than or equal to 24h before processing.

[0062] Example 6

[0063] The high-density flame-retardant and heat-resistant shielding material in this embodiment is composed of 2.0 parts by weight of phenolic resin PF-306, 5.0 parts by weight of boron phenolic resin PF-242, 0.5 parts by weight of boron carbide powder with a particle size of 325 mesh, 91.95 parts by weight of tungsten powder with a particle size of 800 mesh and a purity greater than or equal to 99.9wt%, 0.5 parts by weight of glass fiber powder and 0.05 parts by weight of calcium stearate CV550, wherein the glass fiber length in the glass fiber powder is 0.15 mm.

[0064] The high-density flame-retardant and heat-resistant shielding material in this embodiment is prepared by the following steps:

[0065] Step 1) mixing: ordinary phenolic resin PF-306 and boron phenolic resin PF-242 are weighed and dissolved in anhydrous acetone, and then stirred and mixed at a speed of 40r / min for 30min; then weighed boron carbide powder, calcium stearate CV550 and glass fiber powder are added, and stirring is continued for 30min at a speed of 40r / min; then weighed tungsten powder is added, and stirring is continued for 3h at a speed of 30r / min to obtain a mixed wet material; when the materials are stirred and mixed in anhydrous acetone, the system temperature should be controlled not to exceed 50°C, specifically, the system temperature can be cooled by passing cooling water to ensure that the system temperature does not exceed 50°C;

[0066] Step 2) Place the mixed wet material obtained in step 1) in a 40°C oven and dry it for 5 hours until it is completely dried. Then, crush the dried material with a crusher and seal it for later use to obtain a mixed dry powder;

[0067] Step 3) weigh the mixed dry powder obtained in step 2) and put it into a preheated mold, pre-press 3-5MPa for 20min, and the mold temperature is 130°C; the mold temperature is raised to 165°C, the pressure is raised to 12MPa, and the molding time is 15min; the mold temperature is raised to 195°C, the pressure is raised to 20MPa, and the pressure is maintained for 60min; cooling water is passed to cool to 80-90°C and demold, and the pressure is maintained at 20MPa during the cooling period, and then the mold is placed on a natural horizontal surface, and placed for at least 24h before processing.

[0068] The performance of the high-density flame-retardant and heat-resistant shielding materials prepared in Examples 1 to 6 was tested. The test results are shown in Table 1.

[0069] Table 1 Performance test results of high-density flame-retardant and heat-resistant shielding materials

[0070] Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 <![CDATA[Density (g / cm 3 )]]> 7.01 7.60 7.90 8.55 9.01 9.50 Tensile strength(MPa) 35.5 30.3 23.1 28.5 31.5 30.2 Bending strength(Mpa) 68.1 49.2 57.1 44.2 41.9 44.2 Oxygen Index LOI 49.1 48.8 48.6 48.5 48.5 49.1 Vertical combustion performance V0 V0 V0 V0 V0 V0 Vicat softening point(℃) 262 265 264 269 271 263 <![CDATA[Coefficient of linear expansion (×10 -6 mm / mm·°C)]]> 20.1 27.7 21.3 21.2 13.3 11.7 <![CDATA[ 252 Cf fast neutron shielding coefficient (4cm)]]> 2.25 2.22 2.24 2.23 2.23 2.22 <![CDATA[ 60 Co photon shielding coefficient (4cm)]]> 2.24 2.35 2.44 2.65 2.76 2.81

[0071] Among them, Samples 1 to 6 are samples made from the high-density flame-retardant and heat-resistant shielding materials obtained in Example 1 to Example 6, respectively. It can be seen from the data recorded in Table 1 that compared with the shielding materials recorded in patent CN110774512A, a method for forming a high-tungsten-content tungsten-boron cross-linked polyethylene composite shielding body, the high-density flame-retardant and heat-resistant shielding material in the present invention has a higher oxygen index, reaching the flame retardant level, and the vertical burning performance reaches V0 level, and the mechanical properties are good. Among them, the highest density of the shielding material recorded in patent CN110774512A, a method for forming a high-tungsten-content tungsten-boron cross-linked polyethylene composite shielding body, is 5.0g / cm 3, Vicat softening point is 130℃, tensile strength is 12.6MPa, and oxygen index is only 18.

[0072] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A high-density flame-retardant and heat-resistant shielding material, characterized in that: The invention is composed of the following components: 7-12wt% of phenolic resin composite powder, 0.5-5wt% of boron carbide powder, 85-92wt% of tungsten powder, 0.5-2wt% of reinforcing agent and 0.05-0.2wt% of lubricant; wherein the phenolic resin composite powder is a mixture of ordinary phenolic resin and boron phenolic resin prepared by the following method: ordinary phenolic resin and boron phenolic resin are dissolved in anhydrous alcohol or anhydrous acetone and stirred and mixed.

2. The high-density flame-retardant and heat-resistant shielding material according to claim 1, characterized in that: In the phenolic resin composite powder, the weight ratio of the common phenolic resin to the boron phenolic resin is 1:1-4.

3. The high-density flame-retardant and heat-resistant shielding material according to claim 1, characterized in that: The reinforcing agent is glass fiber powder.

4. The high-density flame-retardant and heat-resistant shielding material according to claim 3, characterized in that: The fiber length in glass fiber powder is 0.1 to 5 mm.

5. The high-density flame-retardant and heat-resistant shielding material according to claim 1, characterized in that: The lubricant is calcium stearate and / or zinc stearate.

6. The high-density flame-retardant and heat-resistant shielding material according to claim 1, characterized in that: The density of high-density flame-retardant and heat-resistant shielding materials is 7.0-9.5 g / cm 3 .

7. The high-density flame-retardant and heat-resistant shielding material according to claim 1, characterized in that: The particle size of the tungsten powder is 300-1000 meshes, and the purity is greater than or equal to 99.9wt%.

8. The high-density flame-retardant and heat-resistant shielding material according to claim 1, characterized in that: The particle size of the boron carbide powder is less than or equal to 100 μm.

9. The method for preparing the flame-retardant lead-boron modified polyethylene composite material according to claim 1, characterized in that: The steps include: Step 1) The weighed ordinary phenolic resin, boron phenolic resin, tungsten powder, boron carbide powder, reinforcing agent and lubricant are mixed to prepare a mixed wet material by the following steps: Step 1-1) Ordinary phenolic resin and boron phenolic resin are weighed and dissolved in anhydrous alcohol or anhydrous acetone, and stirred and mixed at a speed of 20 to 40 r / min for 30 to 60 min; Step 1-2) Add boron carbide powder, lubricant and reinforcing agent and continue to stir and mix at a speed of 20 to 40 r / min for 15 to 30 min; Step 1-3) Add tungsten powder and continue stirring and mixing at a speed of 30 to 50 r / min and a stirring time of 1.5 to 3 h to obtain a mixed wet material; Step 2) preparing a mixed dry powder: placing the mixed wet material obtained in step 1) in an oven for air drying, and then crushing the dried material with a crusher to obtain a mixed dry powder, which is then sealed and stored for later use; Step 3) Molding: Weigh the mixed dry powder obtained in step 2) and put it into a mold for pressing to obtain a high-density flame-retardant and heat-resistant shielding material. The pressing temperature is 150-195°C, the pressing time is 40-90 minutes, and the pressing pressure is 10-20 MPa.

10. The preparation method according to claim 9, characterized in that: In step 3), the specific pressing operation is: Step 3-1) pre-pressing for 10 to 20 minutes, the pre-pressing pressure is 3 to 5 MPa, and the pre-pressing temperature is 115 to 130°C; Step 3-2) two-stage formal pressing: the first stage of formal pressing has a pressing time of 10 to 30 minutes, a pressure of 10 to 15 MPa, and a temperature of 150 to 165° C.; the second stage of formal pressing has a pressing time of 30 to 60 minutes, a pressure of 15 to 20 MPa, and a temperature of 180 to 195° C.; Step 3-3) Cooling water is passed to cool down to 80-90°C, and the pressure is maintained at 18-20 MPa, and then the mold is removed and placed on a natural horizontal surface, and placed for at least 24 hours before processing.

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