Wave-absorbing PVC structural foam and preparation method thereof

Abstract

The invention belongs to the technical field of foam materials, and discloses wave-absorbing PVC (polyvinyl chloride) structural foam and a preparation method thereof, and the wave-absorbing PVC structural foam comprises the following raw material components in parts by weight: 400-600 parts of PVC resin, 300-550 parts of isocyanate, 10-50 parts of a curing agent, 30-80 parts of a foaming agent, 0.1-10 parts of a cross-linking agent, 5-30 parts of a plasticizer and 30-90 parts of an electromagnetic wave absorbent. Modified carbon nanotubes with carboxyl or hydroxyl functional groups and conductive carbon black are added into a PVC structural foam system, the conductive carbon black is coated by utilizing intermolecular force between the modified carbon nanotubes and the conductive carbon black, the dispersity is improved, and a conductive network is formed, so that the problems that the conductive carbon black is poor in dispersity in the PVC structural foam system, and the conductivity of the PVC structural foam system is poor are solved. The problem that the wave-absorbing performance is reduced after the carbon nanotubes are modified is solved, and the forming performance, the mechanical performance and the wave-absorbing performance of the wave-absorbing PVC structural foam are greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of foam materials, and mainly relates to a wave-absorbing PVC structural foam and a preparation method thereof. Background Art

[0002] Radar stealth mainly uses electromagnetic wave absorbing materials (hereinafter referred to as absorbing materials) to convert the incident radar waves into heat energy and dissipate it, thereby eliminating radar echoes. With the development of ultra-low energy consumption, large load, and high mobility of weapons and equipment, the ideal absorbing materials used should meet the requirements of "thin, light, wide, and strong", that is, to achieve strong absorption of electromagnetic waves in a wider frequency band at a smaller thickness and lighter weight.

[0003] According to the molding process, absorbing materials can be divided into coated absorbing materials and structural absorbing materials. Structural absorbing materials combine the absorbing properties of electromagnetic wave absorbers with the mechanical properties and designability of composite materials. In addition, resin-based composite materials with high-strength foam sandwich structures are widely used as load-bearing structures in weapons, equipment, aerospace and other fields due to their low density and high strength. However, PVC foam, one of the high-strength sandwich materials, has poor dispersion in cross-linked PVC structural foam raw materials due to the agglomeration effect of carbon-based absorbing materials, and is not compatible with the cross-linked PVC structural foam system, resulting in large holes, bulging and even cracking in the finished board. Therefore, it is very difficult to prepare PVC structural foam with absorbing function, and its formulation system and molding process are quite difficult. Summary of the invention

[0004] In view of the above problems, the present invention provides an absorbing PVC structural foam and a preparation method thereof. Modified carbon nanotubes with carboxyl or hydroxyl functional groups and conductive carbon black are added to the PVC structural foam system. The intermolecular force between the modified carbon nanotubes and the conductive carbon black is utilized to coat the conductive carbon black, improve the dispersibility, and form a conductive network. The problems of poor dispersibility of the conductive carbon black in the PVC structural foam system and decreased absorbing performance after the carbon nanotubes are modified are solved, and the molding performance, mechanical properties and absorbing performance of the absorbing PVC structural foam are greatly improved.

[0005] The technical solution adopted by the present invention: The present invention provides an absorbing PVC structural foam, including the raw material components measured by weight: 400-600 parts of PVC resin, 300-550 parts of isocyanate, 10-50 parts of curing agent, 30-80 parts of foaming agent, 0.1-10 parts of cross-linking agent, 5-30 parts of plasticizer, and 30-90 parts of electromagnetic wave absorber.

[0006] The isocyanate is one or more of toluene diisocyanate, diphenylmethane diisocyanate, polymethylene polyisocyanate, isophorone diisocyanate and 1,6-hexamethylene diisocyanate.

[0007] The curing agent is an acid anhydride compound, selected from one or more of hexahydrophthalic anhydride, methyl hexahydrophthalic anhydride, maleic anhydride, succinic anhydride, pyromellitic dianhydride and cis-cyclohexane-1,2-dicarboxylic anhydride.

[0008] The foaming agent is an azo foaming agent, which is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, azodicarbonamide and azoaniline.

[0009] Among them, the crosslinking agent is a peroxide crosslinking agent and / or an propylene crosslinking agent, the peroxide crosslinking agent is selected from one or more of tert-butyl hydroperoxide, diisopropylbenzene hydroperoxide, tert-butyl peroxide isopropylbenzene, isopropylbenzene hydroperoxide, diisopropylbenzene peroxide, t-amyl perbenzoate and 2-tetradecanoyl peroxydicarbonate; the propylene crosslinking agent is selected from one or more of methyl acrylate, ethyl acrylate, 2-methyl methacrylate and 2-ethyl methacrylate.

[0010] Wherein, the plasticizer is an epoxy plasticizer, which is selected from one or more of epoxy triglyceride, epoxy soybean oil, ethylene oxide, epoxy resin and epoxy animal oil.

[0011] The electromagnetic wave absorber is a carbon-based absorbing material, the electromagnetic wave absorber is conductive carbon black and modified carbon nanotubes, and the modified carbon nanotubes are carboxyl functional group-modified carbon nanotubes or hydroxyl-modified carbon nanotubes.

[0012] The preparation method of the wave-absorbing PVC structural foam comprises the following steps: Step 1, weigh the corresponding component materials according to the weight proportions, then add isocyanate, curing agent, plasticizer, crosslinking agent, electromagnetic wave absorber, and foaming agent into a high-speed stirrer, with a stirring frequency of 25 to 75 Hz and a dispersion rate of 800 to 2000 RPM, and mix at 20 to 30° C. for 10 to 30 minutes; Step 2: Add PVC resin into a high-speed stirrer with a stirring frequency of 25 to 75 Hz and mix at 20 to 30° C. for 10 to 25 minutes; Step 3, evacuate the high-speed stirrer, and stir at 20-30° C. for 5-20 min at a stirring frequency of 20-50 Hz, until no obvious bubbles are present, to obtain a premix; Step 4, inject the above premix into the mold, place the mold in a hot press, pressurize to 11-14 MPa, heat to 120-150°C and keep warm for 15-25 minutes, heat to 160-180°C and keep warm for 35-45 minutes; cool to 20-30°C and keep for 15-25 minutes, then quickly reduce the pressure from 11-14 MPa to below 1.2 MPa, and keep the pressure until ejection; Step 5: Open the mold and take out the embryo, place the embryo in a closed environment with a temperature of 80-98° C. and 100% saturated steam, and expand it to a desired density to obtain an expanded block; Step 6: Place the expansion block in an environment with a temperature of 70-90° C. and 100% saturated steam for 5-10 days to obtain the wave-absorbing PVC structural foam.

[0013] The electromagnetic wave absorber used in absorbing PVC foam is mainly conductive carbon black. However, due to the adsorption and electrostatic forces between the conductive carbon black particles, and the influence of flow state, temperature and humidity, etc., during the production process, the contact and collision between the carbon black particles will cause the carbon black to agglomerate. The agglomeration phenomenon will cause the dispersion of the conductive carbon black to decrease, increase the resistance to fluidity, and make the processing and application process more difficult. In addition, conductive carbon black is not compatible with the cross-linked PVC structural foam system, which will also reduce the dispersion of conductive carbon black in the raw materials, resulting in large holes, bulging and cracking in the finished board.

[0014] Carbon nanotubes are lightweight, high-strength, and have excellent electrical and thermal conductivity. They also have unique properties such as small size effect and surface effect. They have good compatibility and wide absorption bandwidth. However, they have strong van der Waals attraction and are more likely to entangle or agglomerate into bundles, which is not conducive to practical applications. In order to further expand the application field of carbon nanotubes, carbon nanotubes are usually modified by directly introducing small molecule compounds and active functional groups on the side walls of carbon nanotubes by means of grafting and oxidation to improve the activity of carbon nanotubes, thereby increasing their dispersion and compatibility in solutions and polymers. However, this method seriously destroys the sp2 structure of the functionalized sites of carbon nanotubes, making the conductivity worse. When used as an absorbing material, the absorbing effect is not good.

[0015] The present invention aims at the problem that the conductive carbon black has poor dispersibility in the raw material of PVC structural foam and the wave absorption performance decreases after the carbon nanotube is modified. The present invention adds modified carbon nanotubes with carboxyl or hydroxyl functional groups and conductive carbon black to the PVC structural foam system, utilizes the intermolecular force between the modified carbon nanotubes and the conductive carbon black, coats the conductive carbon black, improves the dispersibility of the conductive carbon black, and makes it evenly distributed in the PVC matrix. The modified carbon nanotubes themselves also participate in the cross-linking network of the PVC matrix. The modified carbon nanotubes and the conductive carbon black are both conductive, and a conductive network is formed through synergistic action to enhance the wave absorption performance of the PVC structural foam material. In addition, the modified carbon nanotubes participate in the reaction of the PVC raw material system, and improve the molding performance and mechanical properties of the wave-absorbing PVC structural foam.

[0016] The beneficial effects of the present invention are as follows: the present invention adds modified carbon nanotubes with carboxyl or hydroxyl functional groups and conductive carbon black into the PVC structural foam system, utilizes the intermolecular force between the modified carbon nanotubes and the conductive carbon black, coats the conductive carbon black, improves the dispersibility, and forms a conductive network, thereby greatly improving the molding performance, mechanical properties and wave absorbing performance of the wave absorbing PVC structural foam, and fills the manufacturing gap of the domestic wave absorbing PVC structural foam. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The reflectivity test diagrams of Examples 1-3 and Comparative Examples 1-2 of the present invention; Figure 2 This is a physical picture of the foam material of Examples 1-3 of the present invention; Figure 3 This is a physical picture of the foam material of Comparative Example 1-2 of the present invention. DETAILED DESCRIPTION

[0018] The embodiments of the present invention are described in detail, but they cannot be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art can make several modifications and improvements without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

[0019] The present invention can be further described in detail with reference to the following examples, but the present invention is not limited to these examples. The raw materials used in the following examples and comparative examples of the present invention are all commercially available products.

[0020] Embodiment 1:

[0021] The wave-absorbing PVC structural foam and preparation method thereof include the following components in parts by weight and preparation steps: Step 1, weigh 260 parts of isophorone diisocyanate, 250 parts of 1,6-hexamethylene diisocyanate, 40 parts of pyromellitic anhydride, 60 parts of azobisisoheptonitrile, 8 parts of methyl acrylate, 25 parts of epoxyglycerol trisester, 30 parts of modified carbon nanotubes, and 45 parts of conductive carbon black, and then mix the above materials in a high-speed stirrer with a stirring frequency of 35 Hz and a dispersion rate of 800 RPM, and mix at 20°C for 20 minutes; Step 2: Weigh 600 parts of PVC resin, add it into a high-speed stirrer, stir at 65 Hz, and mix at 25°C for 15 minutes; Step 3: Vacuum the high-speed stirrer and stir at 25°C for 15 minutes at a stirring frequency of 50 Hz until no obvious bubbles are present to obtain a premix; Step 4: Inject the premix into a mold, place the mold in a hot press, pressurize to 13 MPa, raise the temperature to 145°C and keep it for 20 minutes, raise the temperature to 175°C and keep it for 40 minutes; cool to 25°C and keep it for 20 minutes, then quickly reduce the pressure from 13 MPa to 0.9 MPa, and keep the pressure until ejection.

[0022] Step 5: Open the mold and take out the embryo, place the embryo in a closed environment with a temperature of 90-95° C. and 100% saturated steam, and expand it to a desired density to obtain an expanded block; Step 6: Place the expansion block in an environment with a temperature of 85-90° C. and 100% saturated steam for 10 days to obtain the wave-absorbing PVC structural foam.

[0023] Embodiment 2:

[0024] The wave-absorbing PVC structural foam and preparation method thereof include the following components in parts by weight and preparation steps: Step 1, weigh 270 parts of toluene diisocyanate, 280 parts of 1,6-hexamethylene diisocyanate, 50 parts of cis-cyclohexane-1,2-dicarboxylic anhydride, 80 parts of azoaniline, 5 parts of tert-butyl hydroperoxide, 5 parts of methyl 2-methacrylate, 30 parts of ethylene oxide, 25 parts of modified carbon nanotubes, and 65 parts of conductive carbon black, and then mix the above materials in a high-speed stirrer with a stirring frequency of 75 Hz and a dispersion rate of 2000 RPM, and mix at 30°C for 30 minutes; Step 2: Weigh 550 parts of PVC resin, add it into a high-speed stirrer, stir at 75 Hz, and mix at 30°C for 25 minutes; Step 3: Vacuum the high-speed stirrer and stir at 30°C for 20 minutes at a stirring frequency of 40 Hz until no obvious bubbles are present to obtain a premix; Step 4: Inject the premix into a mold, place the mold in a hot press, pressurize to 14 MPa, raise the temperature to 150°C and keep it for 20 minutes, raise the temperature to 180°C and keep it for 45 minutes; cool to 30°C and keep it for 25 minutes, then quickly reduce the pressure from 14 MPa to 1.2 MPa, and keep the pressure until ejection.

[0025] Step 5: Open the mold and take out the embryo, place the embryo in a closed environment with a temperature of 95-98° C. and 100% saturated steam, and expand it to a desired density to obtain an expanded block; Step 6: Place the expansion block in an environment with a temperature of 85-90° C. and 100% saturated steam for 10 days to obtain the wave-absorbing PVC structural foam.

[0026] Embodiment 3:

[0027] The wave-absorbing PVC structural foam and preparation method thereof include the following components in parts by weight and preparation steps: Step 1: weigh 300 parts of toluene diisocyanate, 10 parts of maleic anhydride, 30 parts of azobisisobutyronitrile, 0.1 parts of diisopropylbenzene hydroperoxide, 5 parts of epoxidized soybean oil, 15 parts of modified carbon nanotubes, and 15 parts of conductive carbon black, and then mix the above materials in a high-speed stirrer with a stirring frequency of 25 Hz and a dispersion rate of 800 RPM, and mix at 25° C. for 10 minutes; Step 2: Weigh 400 parts of PVC resin, add it into a high-speed stirrer, stir at 25 Hz, and mix at 20°C for 10 minutes; Step 3: Vacuum the high-speed stirrer and stir at 20°C for 5 minutes at a stirring frequency of 20 Hz until no obvious bubbles are present to obtain a premix; Step 4: Inject the premix into a mold, place the mold in a hot press, pressurize to 11 MPa, heat to 120°C and keep warm for 25 minutes, heat to 160°C and keep warm for 35 minutes; cool to 20°C and keep for 15 minutes, then quickly reduce the pressure from 11 MPa to 0.8 MPa, and keep the pressure until ejection.

[0028] Step 5: Open the mold and take out the embryo, place the embryo in a closed environment with a temperature of 80° C. and 100% saturated steam, and expand it to a desired density to obtain an expanded block; Step 6: Place the expansion block in an environment with a temperature of 70° C. and 100% saturated steam for 10 days to obtain the wave-absorbing PVC structural foam.

[0029] Comparative Example 1 Step 1, weigh 300 parts of toluene diisocyanate, 150 parts of polymethylene polyisocyanate, 20 parts of maleic anhydride, 30 parts of azobisisobutyronitrile, 20 parts of azodicarbonamide, 5 parts of diisopropylbenzene hydroperoxide, and 13 parts of epoxidized soybean oil, and then mix the above materials in a high-speed stirrer with a stirring frequency of 35 Hz and a dispersion rate of 800 RPM, and mix at 20°C for 15 minutes; Step 2: Weigh 480 parts of PVC resin, add it into a high-speed stirrer, stir at a frequency of 35 Hz, and mix at 20°C for 15 minutes; Step 3: Vacuum the high-speed stirrer and stir at 20°C for 5 minutes at a stirring frequency of 20 Hz until no obvious bubbles are present to obtain a premix; Step 4: Inject the above premix into the mold, place the mold in a hot press, pressurize to 11 MPa, heat to 135°C and keep warm for 15 minutes, heat to 165°C and keep warm for 35 minutes; cool to 20°C and keep for 15 minutes, then quickly reduce the pressure from 11 MPa to 0.8 MPa, and keep the pressure until ejection.

[0030] Step 5: Open the mold and take out the embryo, place the embryo in a closed environment with a temperature of 80° C. and 100% saturated steam, and expand it to a desired density to obtain an expanded block; Step 6: Place the expansion block in an environment with a temperature of 70° C. and 100% saturated steam for 10 days to obtain PVC structural foam.

[0031] Comparative Example 2 Step 1, weigh 300 parts of toluene diisocyanate, 230 parts of 1,6-hexamethylene diisocyanate, 40 parts of pyromellitic anhydride, 60 parts of azobisisoheptonitrile, 8 parts of methyl acrylate, 25 parts of epoxyglycerol trisester, and 60 parts of conductive carbon black, and then mix the above materials in a high-speed stirrer with a stirring frequency of 35 Hz and a dispersion rate of 800 RPM, and mix at 20°C for 20 minutes; Step 2: Weigh 480 parts of PVC resin, add it into a high-speed stirrer, stir at 65 Hz, and mix at 25°C for 15 minutes; Step 3: Vacuum the high-speed stirrer and stir at 25°C for 15 minutes at a stirring frequency of 50 Hz until no obvious bubbles are present to obtain a premix; Step 4: Inject the premix into a mold, place the mold in a hot press, pressurize to 13 MPa, raise the temperature to 145°C and keep it for 20 minutes, raise the temperature to 175°C and keep it for 40 minutes; cool to 25°C and keep it for 15 minutes, then quickly reduce the pressure from 13 MPa to 0.9 MPa, and keep the pressure until ejection.

[0032] Step 5: Open the mold and take out the embryo, place the embryo in a closed environment with a temperature of 85° C. and 100% saturated steam, and expand it to a desired density to obtain an expanded block; Step 6: Place the expansion block in an environment with a temperature of 75° C. and 100% saturated steam for 10 days to obtain the wave-absorbing PVC structural foam.

[0033] The PVC structural foam samples prepared in Examples 1-3 and Comparative Examples 1-2 were sampled and tested for performance, as shown in the following table:

Claims

1. A wave-absorbing PVC structural foam, characterized in that: The invention comprises the following raw material components in parts by weight: 400-600 parts of PVC resin, 300-550 parts of isocyanate, 10-50 parts of curing agent, 30-80 parts of foaming agent, 0.1-10 parts of cross-linking agent, 5-30 parts of plasticizer, and 30-90 parts of electromagnetic wave absorber; the preparation method of the electromagnetic wave absorbing PVC structural foam comprises the following steps: Step 1, weigh the corresponding component materials according to the weight proportions, then add isocyanate, curing agent, plasticizer, crosslinking agent, electromagnetic wave absorber, and foaming agent into a high-speed stirrer, with a stirring frequency of 25 to 75 Hz and a dispersion rate of 800 to 2000 RPM, and mix at 20 to 30° C. for 10 to 30 minutes; Step 2: Add PVC resin into a high-speed stirrer with a stirring frequency of 25 to 75 Hz and mix at 20 to 30° C. for 10 to 25 minutes; Step 3, evacuate the high-speed stirrer, and stir at 20-30° C. for 5-20 min at a stirring frequency of 20-50 Hz, until no obvious bubbles are present, to obtain a premix; Step 4, inject the above premix into the mold, place the mold in a hot press, pressurize to 11-14 MPa, heat to 120-150°C and keep warm for 15-25 minutes, heat to 160-180°C and keep warm for 35-45 minutes; cool to 20-30°C and keep for 15-25 minutes, then quickly reduce the pressure from 11-14 MPa to below 1.2 MPa, and keep the pressure until ejection; Step 5: Open the mold and take out the embryo, place the embryo in a closed environment with a temperature of 80-98° C. and 100% saturated steam, and expand it to a desired density to obtain an expanded block; Step 6: Place the expansion block in an environment with a temperature of 70-90° C. and 100% saturated steam for 5-10 days to obtain the wave-absorbing PVC structural foam.

2. The wave-absorbing PVC structural foam according to claim 1, characterized in that: The isocyanate is one or more of toluene diisocyanate, diphenylmethane diisocyanate, polymethylene polyisocyanate, isophorone diisocyanate and 1,6-hexamethylene diisocyanate.

3. The wave-absorbing PVC structural foam according to claim 1, characterized in that: The curing agent is an acid anhydride compound, which is one or more selected from hexahydrophthalic anhydride, maleic anhydride, succinic anhydride, methyl hexahydrophthalic anhydride, pyromellitic dianhydride and cis-cyclohexane-1,2-dicarboxylic anhydride.

4. The wave-absorbing PVC structural foam according to claim 1, characterized in that: The foaming agent is an azo foaming agent, which is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, azodicarbonamide and azoaniline.

5. The wave-absorbing PVC structural foam according to claim 1, characterized in that: The crosslinking agent is a peroxide crosslinking agent and / or an propylene crosslinking agent, the peroxide crosslinking agent is selected from one or more of tert-butyl hydroperoxide, diisopropylbenzene hydroperoxide, tert-butyl peroxide isopropylbenzene, isopropylbenzene hydroperoxide, diisopropylbenzene peroxide, t-amyl perbenzoate and 2-tetradecanoyl peroxydicarbonate; the propylene crosslinking agent is selected from one or more of methyl acrylate, ethyl acrylate, 2-methyl methacrylate and 2-ethyl methacrylate.

6. The wave-absorbing PVC structural foam according to claim 1, characterized in that: The plasticizer is an epoxy plasticizer, which is selected from one or more of epoxy triglyceride, epoxy soybean oil, ethylene oxide, epoxy resin and epoxy animal oil.

7. The wave-absorbing PVC structural foam according to claim 1, characterized in that: The electromagnetic wave absorber is a carbon-based wave absorbing material, which is conductive carbon black and modified carbon nanotubes, and the modified carbon nanotubes are carboxyl functional group-modified carbon nanotubes or hydroxyl-modified carbon nanotubes.

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