Flame-retardant lead-boron polyvinyl shielding material and preparation method thereof

Abstract

The invention discloses a flame-retardant lead boron polyvinyl shielding material and a preparation method thereof, and the flame-retardant lead boron polyvinyl shielding material is composed of the following components: 2.0 to 5.5 wt% of high density polyethylene, 3.5 to 10 wt% of ethylene-vinyl acetate resin, 0.5 to 8.0 wt% of boron carbide powder, 70 to 80 wt% of lead powder, 9.5 to 15 wt% of a flame retardant, 0.1 to 0.2 wt% of an antioxidant, 0.2 to 0.3 wt% of a coupling agent, and 0.1 to 0.2 wt% of a lubricant. According to the invention, polyethylene is adopted for blending modification, so that the compatibility of resin and a flame retardant is improved, the oxygen index performance is greatly improved under the action of a reasonable proportion, the flame retardant property of the shielding material is remarkably improved, and meanwhile, the shielding property and the mechanical property of the shielding material are considered.

Description

Technical Field

[0001] The invention relates to the technical field of shielding materials, in particular to a flame retardant lead-boron polyethylene-based shielding material and a preparation method thereof. Background Art

[0002] Lead-boron polyethylene is a composite shielding material prepared by adding lead powder, boron carbide powder and processing aids to polyethylene. The polyethylene in the lead-boron polyethylene material has a high hydrogen content, and the hydrogen element has a good weakening ability for fast neutrons; the boron content in boron carbide is high, and the boron element has a large cross-section for absorbing thermal neutrons; the lead element has a good shielding effect on gamma radiation; therefore, lead-boron polyethylene has excellent fast neutron, thermal neutron and gamma radiation shielding effects at the same time. Compared with traditional metal materials, lead-boron polyethylene helps to simplify the shielding structure, reduce the weight of the shielding body, and reduce the volume of the shielding body. It has been widely used in the shielding protection design of nuclear technology devices.

[0003] However, the base material polyethylene of lead-boron polyethylene is a flammable material, and the oxygen index of lead-boron polyethylene itself is only 18, which brings safety hazards to engineering applications. Therefore, on the basis of not reducing the shielding performance, flame retardant modification of lead-boron polyethylene and improving the flame retardant performance are the solutions to improve its safety. However, a large amount of lead powder is added to lead-boron polyethylene, and the process difficulty of adding flame retardants is significantly increased, and the improvement of flame retardant performance is very limited. As mentioned in the invention patent CN200510116946.5, "A lead-boron polyethylene composite shielding material and its preparation method", adding 2 parts by weight of flame retardants, including magnesium hydroxide, aluminum hydroxide, and phosphorus pentoxide, the oxygen index reaches 22, while the oxygen index without flame retardants is only 19. Invention patent CN101033313A "A flame-retardant lead-boron polyethylene composite material" mentions the use of 2.8-3.8 parts by weight of a composite flame retardant, which is 10-20% zinc borate, 60-70% microcapsule-coated red phosphorus and 10-20% phenolic resin, and the flame retardant performance meets the requirements of FV-1 in GB4609-84. The above two patents achieve a certain degree of flame retardant performance by adding a small amount of flame retardant, but their flame retardant performance still cannot meet the actual engineering needs. For example, the oxygen index of flame retardant materials is required to be greater than 28, and some engineering fields require materials to reach the flame retardant level, and the oxygen index must be greater than 32.

[0004] The flame retardant modification of existing lead-boron polyethylene is carried out by adding a certain amount of flame retardant to increase the oxygen index or vertical combustion level. However, due to the flammable properties of polyethylene itself and the inhibitory effect of shielding aids on flame retardants, the simple addition of flame retardants to improve the flame retardant effect is limited. At the same time, adding a large amount of flame retardants has an adverse effect on the shielding performance. Summary of the invention

[0005] To this end, the technical problem to be solved by the present invention is to provide a flame retardant lead-boron polyethylene-based shielding material and a preparation method thereof, adopt polyethylene blending modification to improve the compatibility with flame retardants, achieve a significant improvement in oxygen index performance under the effect of reasonable ratio, significantly improve the flame retardant properties of the shielding material, and at the same time take into account the shielding properties and mechanical properties of the shielding material.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A flame retardant lead-boron polyethylene-based shielding material consists of the following components: 2.0-5.5wt% of high-density polyethylene, 3.5-10wt% of ethylene-vinyl acetate resin, 0.5-8.0wt% of boron carbide powder, 70-80wt% of lead powder, 9.5-15wt% of flame retardant, 0.1-0.2wt% of antioxidant, 0.2-0.3wt% of coupling agent and 0.1-0.2wt% of lubricant.

[0008] In the flame-retardant lead-boron polyethylene-based shielding material, the particle size of the boron carbide powder is less than or equal to 100 μm.

[0009] The flame-retardant lead-boron polyethylene-based shielding material has a lead powder particle size of 100 to 300 meshes and a lead powder purity greater than or equal to 99.5wt%.

[0010] The flame retardant lead-boron polyethylene-based shielding material, the antioxidant is one or more of antioxidant 1010, antioxidant 7910, antioxidant FD958 and antioxidant FD658, the antioxidant particle size is 200 mesh; the weight of the antioxidant is 0.1-0.5% of the sum of the weight of high-density polyethylene and the weight of ethylene-vinyl acetate resin.

[0011] The flame retardant lead-boron polyethylene-based shielding material has a flame retardant of magnesium hydroxide and / or aluminum hydroxide, a flame retardant particle size of 200 to 1000 meshes, and a flame retardant weight ratio of the sum of the high-density polyethylene weight and the ethylene-vinyl acetate resin weight of 1:1 to 1.5:1.

[0012] The lubricant of the flame-retardant lead-boron polyethylene-based shielding material is calcium stearate and / or zinc stearate, and the weight of the lubricant is 0.1-0.5% of the sum of the weight of high-density polyethylene and the weight of ethylene-vinyl acetate resin.

[0013] In the flame-retardant lead-boron polyethylene-based shielding material, the weight ratio of ethylene-vinyl acetate resin to high-density polyethylene is 1:5 to 5:1.

[0014] In the flame-retardant lead-boron polyethylene-based shielding material, the weight ratio of ethylene-vinyl acetate resin to high-density polyethylene is 1:1 to 5:1.

[0015] The coupling agent of the flame-retardant lead-boron polyethylene-based shielding material is a phthalate coupling agent and / or a silane coupling agent.

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

[0017] Step 1) mixing: high-density polyethylene and ethylene-vinyl acetate resin are placed in a mixing device and mixed at a mixing temperature of 150-165° C. for 10-15 minutes; after the high-density polyethylene is completely melted, weighed antioxidants, lubricants, coupling agents and boron carbide powder are added in sequence, and the flame retardant is added after the mixing is continued for 5-10 minutes, and the lead powder is added after the mixing is continued for 10-20 minutes, and then the mixing is continued for 5-10 minutes to obtain a mixed material; wherein the lead powder is added in 2-3 batches;

[0018] Step 2) Molding: The mixed material obtained in step 2) is weighed and placed into a mold for pressing to obtain a flame retardant lead-boron polyethylene-based shielding material; the specific operation of the pressing process is as follows:

[0019] Step 2-1) pre-pressing for 5 to 10 minutes, the pre-pressing pressure is 3 to 5 MPa, and the pre-pressing temperature is 130 to 150°C;

[0020] Step 2-2) Formal pressing: The pressing time of the formal pressing is 10 to 30 minutes, the pressure is 15 to 20 MPa, and the temperature is 150 to 170° C.;

[0021] Step 2-3) cooling water to 50-60°C, and maintaining the pressure at 15-20MPa;

[0022] Step 3) After the mold temperature drops to 50-60° C., the flame-retardant lead-boron polyethylene-based shielding material obtained in step 2) is placed on a natural horizontal surface for standby use, and the standing time is greater than or equal to 24 hours.

[0023] The technical solution of the present invention achieves the following beneficial technical effects:

[0024] 1. After EVA and HDPE are blended, the polar groups of EVA resin promote the dispersion of additives such as lead powder, boron carbide powder, and magnesium hydroxide in the resin matrix, making the dispersion more uniform.

[0025] 2. EVA, high-density polyethylene and flame retardants magnesium hydroxide / aluminum hydroxide show good composite flame retardant effect at the appropriate addition ratio. The flame retardant properties are significantly improved while ensuring the mechanical properties, and the oxygen index is as high as 38. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a ×500 electron microscope image of the flame-retardant lead-boron polyethylene-based shielding material prepared in Example 3. DETAILED DESCRIPTION

[0027] Example 1

[0028] In this embodiment, the flame-retardant lead-boron polyethylene-based shielding material is composed of 70 parts by weight of lead powder with a particle size of 200 mesh and a purity greater than or equal to 99.5wt%, 4.0 parts by weight of high-density polyethylene 5000S, 10.0 parts by weight of ethylene-vinyl acetate resin 5110J, 0.5 parts by weight of boron carbide powder with a particle size of 325 mesh, 15 parts by weight of aluminum hydroxide ZM W-QYHL-1, 0.2 parts by weight of antioxidant 7910, 0.1 parts by weight of calcium stearate CV500 and 0.2 parts by weight of coupling agent LD122.

[0029] The flame retardant lead-boron polyethylene-based shielding material in this embodiment is prepared by the following steps:

[0030] Step 1) high-density polyethylene and ethylene-vinyl acetate resin are melted in a mixing device, and boron carbide, antioxidant, calcium stearate CV500 and coupling agent LD122 are added in sequence during stirring, and mixed for 5 minutes, with the stirring rotor speed of 20r / min;

[0031] Step 2) adding aluminum hydroxide to mix, stirring the rotor at a speed of 25 r / min, and mixing for 10 min;

[0032] Step 3) Add lead powder and mix, stir the rotor at a speed of 15 r / min, mix for 7 minutes, and then remove from the mold and place in a mold;

[0033] Step 4) Pre-press for 5 minutes at a pressure of 4 MPa and a temperature of 135°C; then heat to 155°C, increase the pressure to 15 MPa, and mold for 20 minutes; pass cooling water until the mold temperature drops to 50-60°C before demolding, with the pressure maintained at 15 MPa; leave the demolded sample on a horizontal platform for 24 hours before use.

[0034] Example 2

[0035] The flame-retardant lead-boron polyethylene-based shielding material in this embodiment is composed of 70.0 parts by weight of lead powder with a particle size of 200 mesh and a purity greater than or equal to 99.5wt%, 4.0 parts by weight of high-density polyethylene 6100M, 6.6 parts by weight of ethylene-vinyl acetate resin 7470M, 8.0 parts by weight of boron carbide powder with a particle size of 200 mesh, 11.0 parts by weight of magnesium hydroxide ZW W-QYHM-MH-1, 0.1 parts by weight of antioxidant 1010, 0.1 parts by weight of zinc stearate AV350S and 0.2 parts by weight of coupling agent LD560.

[0036] The flame retardant lead-boron polyethylene-based shielding material in this embodiment is prepared by the following steps:

[0037] Step 1) high-density polyethylene and ethylene-vinyl acetate resin are melted in a mixing device, and boron carbide, antioxidant, zinc stearate AV350S and coupling agent LD560 are added in sequence during stirring, and the mixture is mixed for 10 minutes at a stirring rotor speed of 15 r / min;

[0038] Step 2) adding magnesium hydroxide to mix, stirring the rotor at a speed of 20 r / min, and mixing for 8 minutes;

[0039] Step 3) Add lead powder and mix, stir the rotor at a speed of 15 r / min, mix for 5 minutes, and then remove from the mold and place in a mold;

[0040] Step 4) Pre-press for 8 minutes at a pressure of 5 MPa and a temperature of 140°C; then heat to 160°C, increase the pressure to 18 MPa, and mold for 15 minutes; pass cooling water, and demold when the mold temperature drops to 50-60°C, and maintain the pressure at 18 MPa; leave the demolded sample on a horizontal platform for 36 hours before use.

[0041] Example 3

[0042] The flame-retardant lead-boron polyethylene-based shielding material in this embodiment is composed of 71.5 parts by weight of lead powder with a particle size of 200 mesh and a purity greater than or equal to 99.5wt%, 2.0 parts by weight of high-density polyethylene 6100M, 8 parts by weight of ethylene-vinyl acetate resin 7360M, 5.0 parts by weight of boron carbide powder with a particle size of 200 mesh, 13 parts by weight of aluminum hydroxide FA-100, 0.1 parts by weight of antioxidant FD958, 0.2 parts by weight of calcium stearate G135 and 0.2 parts by weight of coupling agent KH570. The ×500 electron microscope image of the flame-retardant lead-boron polyethylene-based shielding material prepared in this embodiment is as follows: Figure 1 shown.

[0043] The flame retardant lead-boron polyethylene-based shielding material in this embodiment is prepared by the following steps:

[0044] Step 1) high-density polyethylene and ethylene-vinyl acetate resin are melted in a mixing device, and boron carbide, antioxidant, calcium stearate G135 and coupling agent are added in sequence during stirring, and mixed for 8 minutes, with the stirring rotor speed of 20r / min;

[0045] 2) adding aluminum hydroxide to mix, stirring the rotor at a speed of 20 r / min, and mixing for 10 min;

[0046] 3) Add lead powder and mix, stir the rotor at a speed of 15 r / min, mix for 5 minutes, and then remove from the mold and place in a mold;

[0047] 4) Pre-press for 6 minutes at a pressure of 5 MPa and a temperature of 150°C; then heat to 170°C, increase the pressure to 15 MPa, and mold for 25 minutes; pass cooling water until the mold temperature drops to 50-60°C before demolding, with the pressure maintained at 15 MPa; let the demolded sample stand on a horizontal platform for 24 hours before use.

[0048] Example 4

[0049] The flame-retardant lead-boron polyethylene-based shielding material in this embodiment is composed of 75 parts by weight of lead powder with a particle size of 300 mesh and a purity greater than or equal to 99.5wt%, 5.5 parts by weight of high-density polyethylene 5000S, 6.0 parts by weight of ethylene-vinyl acetate resin 7100M, 2.0 parts by weight of boron carbide powder with a particle size of 280 mesh, 11.0 parts by weight of magnesium hydroxide ZM X-GCCX-2, 0.2 parts by weight of antioxidant 1010, 0.1 parts by weight of calcium stearate CV500S, and 0.2 parts by weight of coupling agent KH550.

[0050] The flame retardant lead-boron polyethylene-based shielding material in this embodiment is prepared by the following steps:

[0051] Step 1) high-density polyethylene and ethylene-vinyl acetate resin are melted in a mixing device, and boron carbide, antioxidant 1010, calcium stearate CV500S and coupling agent KH550 are added in sequence during stirring, and mixed for 3 minutes at a stirring rotor speed of 25 r / min;

[0052] Step 2) adding magnesium hydroxide to mix, stirring the rotor at a speed of 20 r / min, and mixing for 10 min;

[0053] Step 3) Add lead powder and mix, stir the rotor at a speed of 15 r / min, mix for 5 minutes, and then remove from the mold and place in a mold;

[0054] Step 4) Pre-press for 10 min at a pressure of 5 MPa and a temperature of 145°C; then heat to 165°C, increase the pressure to 15 MPa, and mold for 20 min; pass cooling water until the mold temperature drops to 50-60°C before demolding, with the pressure maintained at 15 MPa; leave the demolded sample on a horizontal platform for 24 h before use.

[0055] Example 5

[0056] The flame-retardant lead-boron polyethylene-based shielding material in this embodiment is composed of 80 parts by weight of lead powder with a particle size of 260 mesh and a purity greater than or equal to 99.5wt%, 3.0 parts by weight of high-density polyethylene 5000S, 6.0 parts by weight of ethylene-vinyl acetate resin 7100M, 1.0 parts by weight of boron carbide powder with a particle size of 260 mesh, 9.6 parts by weight of magnesium hydroxide 1410, 0.1 parts by weight of antioxidant 7910, 0.1 parts by weight of zinc stearate AV320 and 0.2 parts by weight of coupling agent KH550.

[0057] The flame retardant lead-boron polyethylene-based shielding material in this embodiment is prepared by the following steps:

[0058] Step 1) high-density polyethylene and ethylene-vinyl acetate resin are melted in a mixing device, and boron carbide, antioxidant 7910, zinc stearate AV320 and coupling agent KH550 are added in sequence during stirring, and the mixture is mixed for 10 minutes at a stirring rotor speed of 15 r / min;

[0059] Step 2) adding magnesium hydroxide to mix, stirring the rotor at a speed of 20 r / min, and mixing for 12 min;

[0060] Step 3) Add lead powder and mix, stir the rotor at a speed of 15 r / min, mix for 8 minutes, and then remove from the mold and place in a mold;

[0061] Step 4) Pre-press for 6 minutes at a pressure of 3 MPa and a temperature of 140°C; then heat to 160°C, increase the pressure to 18 MPa, and mold for 25 minutes; pass cooling water, and remove the mold when the mold temperature drops to 50-60°C, and maintain the pressure at 18 MPa; leave the removed sample on a horizontal platform for 24 hours before use.

[0062] Example 6

[0063] The flame-retardant lead-boron polyethylene-based shielding material in this embodiment is composed of 80 parts by weight of lead powder with a particle size of 200 mesh and a purity greater than or equal to 99.5wt%, 4.0 parts by weight of high-density polyethylene 7100M powder, 4.0 parts by weight of ethylene-vinyl acetate resin NU3160 powder, 0.5 parts by weight of boron carbide powder with a particle size of 260 mesh, 11.0 parts by weight of magnesium hydroxide, 0.1 parts by weight of antioxidant FD658, 0.1 parts by weight of zinc stearate and 0.2 parts by weight of coupling agent KH550.

[0064] The flame retardant lead-boron polyethylene-based shielding material in this embodiment is prepared by the following steps:

[0065] Step 1) high-density polyethylene and ethylene-vinyl acetate resin are melted in a mixing device, and boron carbide, antioxidant, zinc stearate and coupling agent KH550 are added in sequence during stirring, and mixed for 5 minutes at a stirring rotor speed of 15 r / min;

[0066] Step 2) adding magnesium hydroxide to mix, stirring the rotor at a speed of 25 r / min, and mixing for 8 minutes;

[0067] Step 3) Add lead powder and mix, stir the rotor at a speed of 15 r / min, mix for 8 minutes, and then remove from the mold and place in a mold;

[0068] Step 4) Pre-press for 10 minutes at a pressure of 5 MPa and a temperature of 150°C; then heat to 170°C, increase the pressure to 20 MPa, and mold for 30 minutes; pass cooling water until the mold temperature drops to 50-60°C before demolding, with the pressure maintained at 20 MPa; leave the demolded sample on a horizontal platform for 24 hours before use.

[0069] Performance tests were performed on the flame-retardant lead-boron polyethylene-based shielding materials prepared in Examples 1 to 6 and the lead-boron polyethylene PB202 mentioned in the document "High-efficiency Shielding Material Lead-boron Polyethylene". The test results are shown in Table 1.

[0070] Table 1 Performance test results of flame retardant lead-boron polyethylene-based shielding materials and PB202

[0071]

[0072]

[0073] Among them, samples 1 to 6 are samples obtained from the flame-retardant lead-boron polyethylene-based shielding materials obtained in Examples 1 to 6. It can be seen from the data in Table 1 that compared with the lead-boron polyethylene PB202 mentioned in the document "High-efficiency Shielding Material Lead-boron Polyethylene", the flame-retardant lead-boron polyethylene-based shielding material in the present invention has a significantly improved oxygen index and reaches the flame retardant grade under the condition of similar density and mechanical properties.

[0074] 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 flame retardant lead boron polyethylene-based shielding material, characterized in that: The invention is composed of the following components: 2.0-5.5wt% of high-density polyethylene, 3.5-10wt% of ethylene-vinyl acetate resin, 0.5-8.0wt% of boron carbide powder, 70-80wt% of lead powder, 9.5-15wt% of flame retardant, 0.1-0.2wt% of antioxidant, 0.2-0.3wt% of coupling agent and 0.1-0.2wt% of lubricant.

2. The flame retardant lead boron polyethylene-based 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.

3. The flame retardant lead boron polyethylene-based shielding material according to claim 1, characterized in that: The lead powder has a particle size of 100 to 300 meshes, and the purity of the lead powder is greater than or equal to 99.5wt%.

4. The flame retardant lead boron polyethylene-based shielding material according to claim 1, characterized in that: The antioxidant is one or more of antioxidant 1010, antioxidant 7910, antioxidant FD958 and antioxidant FD658, and the particle size of the antioxidant is 200 meshes; the weight of the antioxidant is 0.1-0.5% of the sum of the weight of high-density polyethylene and the weight of ethylene-vinyl acetate resin.

5. The flame retardant lead boron polyethylene-based shielding material according to claim 1, characterized in that: The flame retardant is magnesium hydroxide or / and aluminum hydroxide, and the particle size of the flame retardant is 200-1000 meshes; the weight of the flame retardant is the sum of the weight of high-density polyethylene and the weight of ethylene-vinyl acetate resin, and the ratio is 1:1-1.5:

1.

6. The flame retardant lead boron polyethylene-based shielding material according to claim 1, characterized in that: The lubricant is calcium stearate and / or zinc stearate, and the weight of the lubricant is 0.1-0.5% of the sum of the weight of the high-density polyethylene and the weight of the ethylene-vinyl acetate resin.

7. The flame retardant lead boron polyethylene-based shielding material according to claim 1, characterized in that: The weight ratio of ethylene-vinyl acetate resin to high-density polyethylene is 1:5 to 5:

1.

8. The flame retardant lead boron polyethylene-based shielding material according to claim 1, characterized in that: The weight ratio of ethylene-vinyl acetate resin to high-density polyethylene is 1:1 to 5:

1.

9. The flame retardant lead boron polyethylene-based shielding material according to claim 1, characterized in that: The coupling agent is a phthalate coupling agent and / or a silane coupling agent.

10. The method for preparing the flame retardant lead-boron polyethylene-based shielding material according to claim 1, characterized in that: The steps include: Step 1) mixing: high-density polyethylene and ethylene-vinyl acetate resin are placed in a mixing device and mixed at a mixing temperature of 150-165° C. for 10-15 minutes; after the high-density polyethylene is completely melted, weighed antioxidants, lubricants, coupling agents and boron carbide powder are added in sequence, and the flame retardant is added after the mixing is continued for 5-10 minutes, and the lead powder is added after the mixing is continued for 10-20 minutes, and then the mixing is continued for 5-10 minutes to obtain a mixed material; wherein the lead powder is added in 2-3 batches; Step 2) Molding: The mixed material obtained in step 2) is weighed and placed into a mold for pressing to obtain a flame retardant lead-boron polyethylene-based shielding material; the specific operation of the pressing process is as follows: Step 2-1) pre-pressing for 5 to 10 minutes, the pre-pressing pressure is 3 to 5 MPa, and the pre-pressing temperature is 130 to 150°C; Step 2-2) Formal pressing: The pressing time of the formal pressing is 10 to 30 minutes, the pressure is 15 to 20 MPa, and the temperature is 150 to 170° C.; Step 2-3) cooling water to 50-60°C, and maintaining the pressure at 15-20MPa; Step 3) After the mold temperature drops to 50-60° C., the flame-retardant lead-boron polyethylene-based shielding material obtained in step 2) is placed on a natural horizontal surface for standby use, and the standing time is greater than or equal to 24 hours.

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