Multi-layer co-extrusion flame-retardant polyolefin foam particle wave-absorbing material and preparation method thereof

Abstract

The invention provides a multi-layer co-extrusion flame-retardant polyolefin foam particle wave-absorbing material and a preparation method thereof.According to the method, polyolefin resin with different properties is compounded, and polyolefin resin A is highly filled with flame retardant filler to form a flame-retardant polyolefin layer serving as a particle inner layer; polyolefin resin B is filled with a conductive agent to form a conductive polyolefin layer serving as a particle outer layer, the compounded polyolefin resin particles are foamed under the foaming condition of the polyolefin resin B, polyolefin resin wave-absorbing foam particles with the inner layers not foamed or slightly foamed and the outer layers foamed are prepared, and then the wave-absorbing material is prepared through a foam forming process. Therefore, the flame retardance, the environmental protection property and the economic value of the thermoplastic foam wave-absorbing material are improved, the production efficiency is improved, and the thermoplastic foam wave-absorbing material has a good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of polyolefin foam absorbing materials, and in particular to a multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material and a preparation method thereof. Background Art

[0002] In the application field of absorbing materials, most polyolefin foam absorbing materials have the advantages of low water absorption, high hardness, odorless and environmentally friendly, and stable performance in long-term use. They are the main replacement products of sponge absorbing materials in the future. However, when used in electromagnetic wave darkrooms, poor flame retardancy is a major disadvantage of polyolefin foam absorbing materials.

[0003] The more common polyolefin foam absorbing materials include polystyrene foam absorbing materials, polypropylene or polyethylene foam absorbing materials. The polystyrene in the polystyrene foam absorbing materials uses pentane as a foaming agent, which has a strong pungent odor at high temperatures, and its mechanical properties are poor, the damage rate is high during use, and the heat resistance is usually worse than that of polypropylene or polyethylene. Therefore, the mechanical properties and heat resistance of polypropylene or polyethylene foam foamed with carbon dioxide are higher than those of polystyrene foam.

[0004] The foamed polypropylene or polyethylene foam absorbing material currently on the market is prepared by mixing polypropylene resin or polyethylene resin, absorbing agent and flame retardant, granulating, and foaming with carbon dioxide to form a polymer absorbing material. Under the premise of ensuring the absorbing performance, more absorbing agent needs to be added, and the proportion of flame retardant added should be reduced accordingly, so the flame retardant performance will be affected. The oxygen index of the finally prepared polypropylene or polyethylene foam absorbing material cannot meet the requirement of "Technical Specification for Electromagnetic Wave Anechoic Chamber Engineering GB50826-2012" that the oxygen index of absorbing materials for darkrooms must be greater than 28.

[0005] In the prior art, adhesives are usually mixed with flame retardants to prepare polypropylene or polyethylene absorbing foam particles, so that the absorbing flame retardant coating is coated on the surface of the polymer foam particles. However, in the production process, an organic solvent needs to be added to dissolve the adhesive. When using general organic solvents, on the one hand, there may be considerable safety hazards. On the other hand, they are not environmentally friendly and have a certain impact on the physical and mental health of operators. In addition, the process is complicated and requires extrusion, granulation, foaming, coating and molding. Since the volume of the polymer is large after foaming, the operation difficulty increases, which often results in low production efficiency.

[0006] Usually, the microwave-absorbing flame-retardant coating will not add a lot of volume to the foam particles after coating. Without considering the weight of the microwave-absorbing flame-retardant coating, according to calculation, when a 2-cubic-meter mixing barrel is used to mix polypropylene or polyethylene microwave-absorbing foam particles and microwave-absorbing flame-retardant coating, the mixing and drying time for 1 barrel is about 1 hour. Since the 2-cubic-meter mixing barrel can only use 50%-70% of the space, only about 40-56kg of foam particles with a density of 40kg / cubic meter can be produced in 1 hour. Only 24-hour continuous production can produce about 1120kg of foam particles. Generally speaking, the average amount of microwave-absorbing materials used in microwave darkrooms is about 15kg per square meter. A large microwave darkroom of 10,000 square meters requires about 150 tons of microwave-absorbing materials. Even if it is produced 24 hours a day, it takes 133 days to produce 150 tons of materials. However, many customers of large darkrooms have very strict requirements on the construction period. The production efficiency mentioned above cannot meet the large-scale market applications and needs. Summary of the invention

[0007] In view of the above-mentioned insufficient production capacity in the prior art, the inventors have developed a production process for preparing polyolefin foam particle absorbing materials with high flame retardancy and high economic value through continuous exploration and research. The process utilizes polyolefin resins with different properties to compound each other, highly fills the flame retardant filler in polyolefin resin A as the inner layer of the particles, and fills the conductive agent in polyolefin resin B as the outer layer of the particles. The compounded polyolefin small particles are placed in a reactor and foamed under the foaming conditions of polyolefin resin B to obtain polyolefin resin absorbing foam particles with non-foamed or slightly foamed inner layer and normal foaming outer layer, and then the polyolefin resin foam absorbing material is obtained through a foam molding process. Since each absorbing foam particle uniformly contains a large proportion of flame retardant B, each area of ​​the molded absorbing material can be evenly distributed, thereby further improving the flame retardancy, environmental protection and economic value of the thermoplastic foam absorbing material while also improving the production efficiency.

[0008] Specifically, the technical solution adopted by the present invention is:

[0009] The present invention provides a multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material, characterized in that: the single foam particle is a layered structure, including a flame-retardant polyolefin layer and a conductive polyolefin layer, wherein the flame-retardant polyolefin layer is an inner layer and the conductive polyolefin layer is an outer layer; or the flame-retardant polyolefin layer is an intermediate layer and the conductive polyolefin layer is an inner layer and an outer layer; or the flame-retardant polyolefin layer is an outer layer and the conductive polyolefin layer is an inner layer. Preferably, the flame-retardant polyolefin layer is an inner layer and the conductive polyolefin layer is an outer layer.

[0010] Furthermore, in the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material of the present invention, the flame-retardant polyolefin comprises, by weight: 20-80 parts of polyolefin resin A, 20-80 parts of flame retardant A, 0-15 parts of conductive masterbatch, 0-20 parts of functional additive masterbatch A, which are mixed and then formed into flame-retardant polyolefin masterbatch A particles by an extruder. Preferably, the conductive masterbatch is 0.1-15 parts, and the functional additive masterbatch is 0.1-20 parts.

[0011] Furthermore, in the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material described in the present invention, the flame retardant A is selected from one or more of organic flame retardants, inorganic flame retardants, ammonium salt flame retardants, silicone flame retardants, and halogen flame retardants.

[0012] Preferably, the organic flame retardant in the flame retardant A is selected from one or more of pentaerythritol phosphate, triphenyl phosphate, resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), trimethyl phosphate, triethyl phosphate, trihexyl phosphate, triphenyl phosphate, monoammonium phosphate, diammonium phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, diethyl ethyl phosphonate, dimethyl phosphate, alkane diaryl phosphonate, 2-ethylhexyl diphenyl phosphate, and dimer aryl phosphate; the inorganic flame retardant is selected from one or more of One or more selected from magnesium hydroxide, red phosphorus, coated red phosphorus, aluminum dihydrogen phosphate, expanded graphite, aluminum hydroxide, borate, aluminum oxalate, zinc sulfide, and zinc borate; the ammonium salt flame retardant is selected from one or more selected from ammonium polyphosphate, ammonium sulfate, and melamine polyphosphate; the organosilicon flame retardant is selected from one or more selected from organic silicone and polysiloxane; the halogen flame retardant is selected from one or more selected from tetrabromobisphenol A, decabromodiphenyl ethane, octabromodiphenyl ether, chlorinated paraffin, brominated polystyrene, tribromophenol, brominated epoxy flame retardant, and chlorinated polyolefin resin.

[0013] On the other hand, in the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material described in the present invention, the conductive polyolefin includes, by weight: 2-98 parts of polyolefin resin B, 1-20 parts of flame retardant masterbatch B, 0.1-95 parts of conductive masterbatch, and 1-20 parts of functional additive masterbatch B.

[0014] Furthermore, in the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material described in the present invention, the flame retardant masterbatch B includes a polyolefin resin and a flame retardant B, the polyolefin resin is selected from one or more of polypropylene, polyethylene, ethylene acrylic acid copolymer, and chlorinated polyolefin resin; the flame retardant B is selected from one or more of organic flame retardants, inorganic flame retardants, ammonium salt flame retardants, silicone flame retardants, and halogen flame retardants, and after mixing, the flame retardant masterbatch B particles are obtained by an extruder.

[0015] Preferably, the organic flame retardant in the flame retardant B is selected from one or more of pentaerythritol phosphate, triphenyl phosphate, resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), trimethyl phosphate, triethyl phosphate, trihexyl phosphate, triphenyl phosphate, monoammonium phosphate, diammonium phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, diethyl ethyl phosphonate, dimethyl phosphate, alkane diaryl phosphonate, 2-ethylhexyl diphenyl phosphate, and dimer aryl phosphate; the inorganic flame retardant is selected from One or more selected from magnesium hydroxide, red phosphorus, coated red phosphorus, aluminum dihydrogen phosphate, expanded graphite, aluminum hydroxide, borate, aluminum oxalate, zinc sulfide, and zinc borate; the ammonium salt flame retardant is selected from one or more selected from ammonium polyphosphate, ammonium sulfate, and melamine polyphosphate; the organosilicon flame retardant is selected from one or more selected from organic silicone and polysiloxane; the halogen flame retardant is selected from one or more selected from tetrabromobisphenol A, decabromodiphenyl ethane, octabromodiphenyl ether, chlorinated paraffin, brominated polystyrene, tribromophenol, brominated epoxy flame retardant, and chlorinated polyolefin resin.

[0016] Furthermore, in the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material of the present invention, the flame retardant B accounts for 1-20% of the total mass of the conductive polyolefin, preferably 2-15%, preferably 3-10%, and more preferably 5-8%, by mass percentage.

[0017] Furthermore, in the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material of the present invention, the polyolefin resin A and the polyolefin resin B are polyolefin resins, preferably one or more of polypropylene resin, polyethylene resin, maleic anhydride grafted polypropylene, ethylene acrylic acid copolymer, and chlorinated polyolefin resin. Preferably, the polyolefin resin A is a polymer that only softens at a certain temperature and does not foam or is difficult to foam. When the polyolefin resin B reaches the melting point, the polyolefin resin A does not reach the melting point or is close to melting; or when the reactor starts to discharge and cool, the polyolefin resin A does not start to crystallize or the crystallization rate is lower than that of the polyolefin resin B.

[0018] Furthermore, in the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material of the present invention, the conductive masterbatch comprises polypropylene resin or polyethylene resin, absorbing powder and / or dispersing lubricant, the absorbing powder is selected from one or more of carbon black, graphite, carbon nanotubes, graphene, and carbon fiber. The dispersing lubricant is selected from one or more of polyethylene wax, polypropylene wax, and polytetrafluoroethylene wax.

[0019] Furthermore, in the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material described in the present invention, the functional additive masterbatch A includes a polyolefin resin and a functional additive, the polyolefin resin is selected from one or more of polypropylene, polyethylene, maleic anhydride grafted polypropylene, ethylene acrylic acid copolymer, and chlorinated polyolefin resin, and the functional additive is selected from one or more of antioxidants, ultraviolet absorbers, antibacterial agents, dispersing lubricants, and molecular weight regulators; the functional additive masterbatch B includes a polyolefin resin and a functional additive, the polyolefin resin is selected from one or more of polypropylene, polyethylene, maleic anhydride grafted polypropylene, ethylene acrylic acid copolymer, and chlorinated polyolefin resin, and the functional additive is selected from one or more of nucleating agents, antioxidants, ultraviolet absorbers, antibacterial agents, and dispersing lubricants.

[0020] Another aspect of the present invention is to provide a method for preparing a multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material, comprising the following steps:

[0021] Step S1: polyolefin resin A, flame retardant A, conductive masterbatch, and functional additive masterbatch A are mixed and then formed into flame retardant masterbatch A particles through an extruder;

[0022] Step S2: adding the flame retardant masterbatch A particles obtained in step S1 into extruder A, and simultaneously adding polyolefin resin B, flame retardant masterbatch B, conductive masterbatch, and functional additive masterbatch B into extruder B, and extruding through a two-layer co-extrusion die head to obtain cylindrical or annular polyolefin resin absorbing small particles with an inner layer of flame retardant polyolefin and an outer layer of conductive polyolefin, or an inner layer of conductive polyolefin and an outer layer of flame retardant polyolefin; or,

[0023] The extruder die is replaced with a three-layer co-extrusion die head to obtain cylindrical or annular polyolefin resin wave-absorbing small particles with a middle layer of flame-retardant polyolefin and inner and outer layers of conductive polyolefin;

[0024] Step S3: adding the polyolefin resin absorbing small particles obtained in step S2 into a reactor, adding water and a dispersant into the high-pressure reactor, stirring, heating and introducing carbon dioxide to pressurize, and continuously heating to the melting point of the conductive polyolefin layer resin, releasing the material to obtain polyolefin absorbing foam particles in which the flame-retardant polyolefin layer is not foamed or slightly foamed and the conductive polyolefin layer is foamed;

[0025] Step S4: forming the polyolefin absorbing foam particles obtained in step S3 into an absorbing material.

[0026] Furthermore, in step S1 of the method for preparing the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material of the present invention, the polyolefin resin A is 20-80 parts, the flame retardant A is 20-80 parts, the conductive masterbatch is 0.1-15 parts, and the functional additive masterbatch A is 0.1-20 parts.

[0027] Furthermore, in step S2 of the method for preparing the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material of the present invention, the polyolefin resin B is 2-98 parts, the flame retardant masterbatch B is 1-20 parts, the conductive masterbatch is 0.1-95 parts, and the functional additive masterbatch B is 1-20 parts.

[0028] Furthermore, in step S2 of the method for preparing the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material of the present invention, the obtained cylindrical or annular polyolefin resin absorbing small particles are 0.5-6 mg.

[0029] Furthermore, in step S3 of the method for preparing the multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material of the present invention, the stirring speed is 300 r / min, heating is continued to the melting point of the conductive polypropylene resin layer of 145° C., and the carbon dioxide pressure is 3.5 MPa.

[0030] The advantages and beneficial effects of the present invention are:

[0031] (1) The process of the present invention is simple, and the absorbing material meeting the highest level of UL94-V0 flame retardant standard is obtained by direct extrusion, granulation, foaming and molding, without the need for a coating process. At the same time, the mechanical properties of the absorbing material are completely unaffected.

[0032] (2) Each of the absorbing foam particles prepared by the present invention uniformly contains a relatively large proportion of the flame retardant B, which works synergistically with the flame retardant A. The flame retardant can be evenly distributed in each area of ​​the molded absorbing material, and the product can have a better flame retardant effect both inside and outside. While improving the flame retardant performance, it will not affect the surface appearance of the absorbing material.

[0033] (3) The process of the present invention is environmentally friendly, does not require solvents in the production process, is harmless to the physical and mental health of workers, has no impact on the air quality of the darkroom, and does not pollute the environment.

[0034] (4) The present invention has high production efficiency. One extruder can produce 6 tons of polyolefin resin absorbing small particles 24 hours a day. One 2.5 cubic high-pressure reactor can foam 6 tons of polyolefin absorbing foam particles 24 hours a day. It only takes 25 days to produce 150 tons of absorbing materials required for a large darkroom of 10,000 square meters, which greatly shortens the project construction period.

[0035] (5) The present invention has high economic value, and the production capacity can be increased by about 4 to 5 times per day compared with the coating process, and no organic solvent is required, which greatly reduces the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a scanning electron microscope (SEM) image of the foam particles prepared in Example 1, the foam particles having an inner layer of flame-retardant polypropylene and an outer layer of conductive polypropylene being cut open.

[0037] Figure 2 This is a physical picture of the foam absorbing particles prepared in Example 1, with the inner layer being flame-retardant polypropylene and the outer layer being conductive polypropylene.

[0038] Figure 3 It is a comparison chart of the reflectivity of the samples prepared by the embodiment and the comparative example. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with the accompanying drawings and preferred specific embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention. The raw materials, masterbatches, reagents, etc. used in the following embodiments are all commercially available or conventionally available.

[0040] As described in the present invention, in the polyolefin resin described in the present invention, the polyolefin is a polyolefin with different melting points obtained by mixing one or more polyolefins. The polyolefin resin includes but is not limited to: polypropylene, polyethylene, maleic anhydride grafted polypropylene, ethylene acrylic acid copolymer resin, chlorinated polyolefin resin, etc.

[0041] As described in the present invention, the flame retardant A in the flame retardant polyolefin of the present invention includes but is not limited to: organic flame retardants, inorganic flame retardants, ammonium salt flame retardants, silicone flame retardants, halogen flame retardants, etc. Specifically, the organic flame retardant includes but is not limited to pentaerythritol phosphate, triphenyl phosphate, resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), trimethyl phosphate, triethyl phosphate, trihexyl phosphate, triphenyl phosphate, monoammonium phosphate, diammonium phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, diethyl ethylphosphonate, dimethyl phosphate, alkane diaryl phosphonate, 2-ethylhexyl diphenyl phosphate, dimer aryl phosphate, etc.; Organic flame retardants are preferably one or more of magnesium hydroxide, red phosphorus, coated red phosphorus, aluminum dihydrogen phosphate, expanded graphite, aluminum hydroxide, borate, aluminum oxalate, zinc sulfide, and zinc borate; ammonium salt flame retardants are preferably ammonium polyphosphate, ammonium sulfate, melamine polyphosphate, etc.; organosilicon flame retardants are preferably organic silicones, polysiloxanes, etc.; halogen flame retardants are preferably tetrabromobisphenol A, decabromodiphenyl ethane, octabromodiphenyl ether, chlorinated paraffin, brominated polystyrene, tribromophenol, brominated epoxy flame retardants, chlorinated polyolefin resins, etc.

[0042] As described in the present invention, the flame retardant B in the conductive polyolefin of the present invention includes but is not limited to: organic flame retardants, inorganic flame retardants, ammonium salt flame retardants, silicone flame retardants, halogen flame retardants, etc. Specifically, the organic flame retardant is preferably pentaerythritol phosphate, triphenyl phosphate, resorcinol bis (diphenyl phosphate), bisphenol A bis (diphenyl phosphate), trimethyl phosphate, triethyl phosphate, trihexyl phosphate, triphenyl phosphate, monoammonium phosphate, diammonium phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, diethyl ethyl phosphonate, dimethyl phosphate, alkane diaryl phosphonate, 2-ethylhexyl diphenyl phosphate, dimer aryl phosphate, etc. ; Inorganic flame retardants are preferably magnesium hydroxide, red phosphorus, coated red phosphorus, aluminum dihydrogen phosphate, expanded graphite, aluminum hydroxide, borates, aluminum oxalate, zinc sulfide, zinc borate, etc.; ammonium salt flame retardants are preferably ammonium polyphosphate, ammonium sulfate, melamine polyphosphate, etc.; organosilicon flame retardants are preferably organic silicones, polysiloxanes, etc.; halogen flame retardants are preferably tetrabromobisphenol A, decabromodiphenyl ethane, octabromodiphenyl ether, chlorinated paraffin, brominated polystyrene, tribromophenol, brominated epoxy flame retardants, chlorinated polyolefin resins, etc.

[0043] As described in the present invention, the functional additive A in the functional additive masterbatch A described in the present invention includes but is not limited to: antioxidants, ultraviolet absorbers, antibacterial agents, dispersing lubricants, molecular weight regulators, etc.; the functional additive B in the functional additive masterbatch B includes but is not limited to: nucleating agents, antioxidants, ultraviolet absorbers, antibacterial agents, dispersing lubricants, etc.; the molecular weight regulator includes but is not limited to: benzoyl peroxide, di-tert-butyl peroxide, methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane, etc.

[0044] As described in the present invention, the absorbing powder in the conductive masterbatch of the present invention includes but is not limited to: carbon black, graphite, carbon nanotubes, graphene, carbon fiber, etc. The dispersing lubricant includes but is not limited to: polyethylene wax, polypropylene wax, polytetrafluoroethylene wax, etc.

[0045] Example 1

[0046] A multi-layer co-extruded flame-retardant polypropylene foam particle absorbing material, the preparation method of which comprises the following steps:

[0047] Step S1: by weight, 48 parts of polypropylene resin A, 50 parts of expanded graphite, 1 part of conductive masterbatch, and 1 part of functional additive masterbatch A are mixed and then formed into flame retardant masterbatch A particles through an extruder.

[0048] Step S2: by weight, add 60 parts of the flame retardant masterbatch A obtained in step S1 to extruder A as the inner layer; add 19 parts of polypropylene resin B, 15 parts of flame retardant masterbatch B, 70 parts of conductive masterbatch, and 1 part of functional additive masterbatch B to extruder B as the outer layer. The flame retardant masterbatch B is prepared by mixing 45 parts of polypropylene, 50 parts of coated red phosphorus, and 5 parts of PE wax, and then extruded. According to calculation, the coated red phosphorus in the flame retardant B accounts for 7.5% of the total mass of the conductive polypropylene; 0.5-6mg cylindrical polypropylene resin wave absorbing small particles are obtained by extruding through a two-layer co-extrusion die head, the inner layer of which is flame retardant polypropylene and the outer layer of which is conductive polypropylene.

[0049] Step S3: Add the polypropylene resin absorbing small particles obtained in step S2 into a reactor, add water and 3.5% of the mass of sodium dodecylbenzene sulfonate as a dispersant into the high-pressure reactor, start stirring at a speed of 300 r / min, heat and gradually introduce carbon dioxide, continue heating until the melting point of the outer conductive polypropylene resin layer reaches 145°C, the carbon dioxide pressure reaches 3.5 MPa, release the material and wash to obtain polypropylene foam absorbing particles with a non-foamed inner layer and a foamed outer layer.

[0050] Step S4: molding the polypropylene foam absorbing particles obtained in step S3 to obtain a polypropylene foam absorbing material.

[0051] Note:

[0052] 1. The flame retardant polypropylene layer is a mixture, and the melting point measured by differential scanning calorimetry (DSC) is 150°C; the conductive polypropylene layer is also a mixture, and the melting point measured by DSC is 145°C.

[0053] 2. The functional additive masterbatch A is prepared by mixing 70 parts of polypropylene resin and 30 parts of dispersing lubricant polyethylene (PE) wax through an extruder. The functional additive masterbatch B is prepared by mixing 70 parts of polypropylene resin, 10 parts of nucleating agent zinc borate, 5 parts of BASF antioxidant with model 1010, and 1 part of dispersing lubricant PE wax through an extruder.

[0054] 3. The conductive masterbatch is prepared by mixing in an internal mixer and then extruding in an extruder. The ratio of the conductive masterbatch is 77 parts of polypropylene resin, 3 parts of dispersing lubricant PE wax, and 20 parts of carbon black with a specific surface area greater than 1000.

[0055] Example 2

[0056] A multi-layer co-extruded flame-retardant polypropylene foam particle absorbing material, the preparation method of which comprises the following steps:

[0057] Step S1: By weight, 24 parts of maleic anhydride grafted polypropylene resin and 24 parts of ethylene acrylic acid copolymer, a total of 46 parts as polyolefin resin A, 50 parts of expanded graphite, 1 part of conductive masterbatch, and 3 parts of functional additive masterbatch A are mixed and formed into flame retardant masterbatch A particles through an extruder.

[0058] Step S2: by weight, 14 parts of polypropylene resin B, 15 parts of flame retardant masterbatch B, 70 parts of conductive masterbatch, and 1 part of functional additive masterbatch B are mixed and added to extruder A as an inner layer, wherein the flame retardant masterbatch B has a ratio of 45 parts of polypropylene, 50 parts of coated red phosphorus, and 5 parts of PE wax, and the mixture is prepared by an extruder; 60 parts of the flame retardant masterbatch A particles prepared in step S1 are added to extruder B as an outer layer; and 0.5-6 mg cylindrical polypropylene resin wave-absorbing small particles are obtained by extruding through a two-layer co-extrusion die head, wherein the inner layer is conductive polypropylene and the outer layer is flame retardant polypropylene.

[0059] Step S3: Add the polyolefin resin absorbing small particles obtained in step S2 into a reactor, add water and 3.5% of the mass of sodium dodecylbenzene sulfonate as a dispersant into the high-pressure reactor, start stirring at a speed of 300 r / min, heat and gradually introduce carbon dioxide, continue heating until the melting point of the inner conductive polypropylene resin layer reaches 145°C and the carbon dioxide pressure reaches 3.5 MPa, release the material for washing to obtain polypropylene foam absorbing particles with a foamed inner layer and a non-foamed outer layer.

[0060] Step S4: molding the polypropylene foam absorbing particles obtained in step S3 to obtain a polypropylene foam absorbing material.

[0061] Note:

[0062] 1. The flame retardant polypropylene layer is a mixture, and the melting point measured by DSC is 146°C; the conductive polypropylene layer is also a mixture, and the melting point measured by DSC is 145°C.

[0063] 2. The functional additive masterbatch A comprises 70 parts of polypropylene resin, 29.5 parts of dispersing lubricant PE wax, and 0.5% of molecular weight regulator di-tert-butyl peroxide, which are mixed and prepared by an extruder; the functional additive masterbatch B comprises 70 parts of polypropylene resin, 10 parts of nucleating agent zinc borate, 5 parts of BASF antioxidant with model number 1010, and 1 part of dispersing lubricant PE wax, which are mixed and prepared by an extruder.

[0064] Example 3

[0065] A multi-layer co-extruded flame-retardant polypropylene foam particle absorbing material, the preparation method of which comprises the following steps:

[0066] Step S1: By weight, 24 parts of maleic anhydride grafted polypropylene resin and 24 parts of ethylene acrylic acid copolymer, a total of 46 parts, are used as polypropylene resin, 50 parts of expanded graphite, 1 part of conductive masterbatch, and 3 parts of functional additive masterbatch A, and after mixing, flame retardant masterbatch A particles are formed through an extruder.

[0067] Step S2: by weight, 19 parts of polypropylene resin B, 10 parts of flame retardant masterbatch B, 70 parts of conductive masterbatch, and 1 part of functional additive masterbatch B are mixed and added to extruder A as the inner layer and outer layer respectively, wherein the flame retardant masterbatch B has a ratio of 45 parts of polypropylene, 50 parts of coated red phosphorus, and 5 parts of PE wax, and is prepared by extrusion after mixing; 60 parts of the flame retardant masterbatch A particles prepared in step S1 are added to extruder B as the middle layer, and are extruded through a 3-layer co-extrusion die to obtain 0.5-6 mg cylindrical polypropylene resin wave-absorbing small particles, wherein the inner and outer layers are conductive polypropylene and the middle layer is flame retardant polypropylene.

[0068] Step S3: Add the polypropylene resin absorbing small particles obtained in step S2 into a reactor, add water and 3.5% of the mass of sodium dodecylbenzene sulfonate as a dispersant into the high-pressure reactor, start stirring at a speed of 300 r / min, heat and gradually introduce carbon dioxide, continue heating until the melting point of the conductive polypropylene resin of the inner and outer layers is 145° C., release the material for washing to obtain polypropylene foam absorbing particles with foamed inner and outer layers and non-foamed middle layers.

[0069] Step S4: molding the polyolefin foam absorbing particles obtained in step S3 to obtain a polypropylene foam absorbing material.

[0070] Note:

[0071] 1. The flame retardant polypropylene layer is a mixture, and the melting point measured by DSC is 146°C; the conductive polypropylene layer is also a mixture, and the melting point measured by DSC is 145°C.

[0072] 2. The functional additive masterbatch A comprises 70 parts of polypropylene resin, 25 parts of dispersing lubricant PE wax, and 0.5% of molecular weight regulator di-tert-butyl peroxide, which are mixed and prepared by an extruder; the functional additive masterbatch B comprises 70 parts of polypropylene resin, 10 parts of nucleating agent zinc borate, 5 parts of BASF antioxidant of model 1010, and 1 part of dispersing lubricant PE wax, which are mixed and prepared by an extruder.

[0073] Comparative Example 1

[0074] A polypropylene foam particle absorbing material, the preparation method of which comprises the following steps:

[0075] Step S1: By weight, 48 parts of polypropylene resin, 50 parts of coated red phosphorus, and 2 parts of dispersed lubricant PE wax are mixed and formed into flame retardant masterbatch through an extruder.

[0076] Step S2: by weight, 14 parts of polypropylene resin, 70 parts of conductive masterbatch, 15 parts of flame retardant masterbatch prepared in step S1, and 1 part of zinc borate as a nucleating agent are mixed and extruded through a twin-screw extruder to obtain 0.2-3.2 mg of cylindrical polypropylene resin wave absorbing microparticles;

[0077] Step S3: adding the columnar polypropylene resin absorbing microparticles obtained in step S2 into a reactor, adding water and 3.5% by mass of sodium dodecylbenzene sulfonate as a dispersant into the autoclave, starting stirring at a stirring speed of 300 r / min, heating and gradually introducing carbon dioxide, and continuously heating to the melting point of the columnar polypropylene resin absorbing microparticles of 145° C., discharging the material for washing to obtain polypropylene foam absorbing particles;

[0078] Step S4: molding the polypropylene foam absorbing particles obtained in step S3 to obtain a polypropylene foam absorbing material.

[0079] Comparative Example 2

[0080] A polypropylene foam particle absorbing material, the preparation method of which comprises the following steps:

[0081] Step S1: By weight, 48 parts of polypropylene resin, 50 parts of coated red phosphorus, and 2 parts of dispersed lubricant PE wax are mixed and formed into flame retardant masterbatch through an extruder.

[0082] Step S2: by weight, 14 parts of polypropylene resin, 70 parts of conductive masterbatch, 15 parts of flame retardant masterbatch prepared in step S1, and 1 part of zinc borate as a nucleating agent are mixed and extruded through a twin-screw extruder to obtain 0.2-3.2 mg of cylindrical polypropylene resin wave absorbing microparticles;

[0083] Step S3: adding the columnar polypropylene resin absorbing microparticles obtained in step S2 into a reactor, adding water and 3.5% by mass of sodium dodecylbenzene sulfonate as a dispersant into the autoclave, starting stirring at a stirring speed of 300 r / min, heating and gradually introducing carbon dioxide, and continuously heating to the melting point of the columnar polypropylene resin absorbing microparticles of 145° C., discharging the material for washing to obtain polypropylene foam absorbing particles;

[0084] Step S4: by weight, 50 parts of 50% acrylic resin, 5 parts of carbon black, 80 parts of expanded graphite flame retardant, and 100 parts of ammonia solvent are added in a dispersing mixer and mixed for 20 minutes until uniform to obtain a flame retardant coating;

[0085] Step S5: adding 30 parts of the flame retardant coating obtained in step S4 and 60 parts of the polypropylene foam absorbing particles obtained in step S3 into a stirring barrel, mixing them for 20 minutes, and then adding them into a drying device and drying them at 50-80° C. for 20 minutes to obtain polypropylene foam absorbing particles coated with a flame retardant coating;

[0086] Step S6: molding the polypropylene foam absorbing particles coated with the flame retardant coating obtained in step S5 to obtain a polypropylene foam absorbing material.

[0087] The absorbing materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were tested. The size of the test samples was 600*600*50 mm. The test results are shown in Table 1 and Attached Figure 3 shown.

[0088] Table 1

[0089]

[0090] in conclusion:

[0091] As shown in Table 1, the absorbing material prepared in Comparative Example 1 cannot meet the flame retardant requirements of absorbing materials used in microwave darkrooms. The absorbing material in Comparative Example 2 is coated with a flame retardant coating on the basis of Comparative Example 1, but since the expanded graphite used as a flame retardant has conductivity, the surface resistance of the absorbing material prepared in Comparative Example 2 becomes low and cannot meet the resistance requirements of some absorbing materials.

[0092] From Table 1 and Figure 3 It can also be seen that the 30M-2000M reflectivity resonance peak of the absorbing materials prepared in the embodiment and the comparative example has changed. The absorbent contained in the materials prepared in the comparative example 1 and the comparative example 2 is the same, wherein the comparative example 2 is coated with a layer of flame retardant containing expanded graphite, so that the resistance of the prepared absorbing material becomes smaller, so the resonance peak shifts to the low frequency, and the high-frequency reflectivity becomes smaller. In addition, due to the poor compatibility of polypropylene with the adhesive acrylic resin, after the polypropylene foam particles are wrapped and then pressed into a product using a foam molding machine, the obtained polypropylene foam absorbing material has poor mechanical properties, the product is very brittle, very easy to damage, and has a high defect rate, which is not conducive to the transportation of finished products and the subsequent installation of materials.

[0093] The saturated materials prepared in Examples 1 to 3 of the present invention can reach or even exceed the national standards in terms of flame retardancy, volume resistance and electromagnetic parameters. Figure 1 The microstructure of the inner layer of flame-retardant polypropylene at the center of the whole foam particle prepared in Example 1 is shown, and a large number of expanded graphite sheets are compounded inside the flame-retardant polypropylene. Figure 2The stacking state of the foam particles prepared in Example 1 and the physical picture of a part of the microwave-absorbing foam particles cut open are shown. It can be seen that the inner flame-retardant polypropylene layer is filled with a large amount of expanded graphite flame retardant. Due to the small proportion of conductive carbon black added, the inner layer is gray; the outer layer is a conductive polypropylene layer, which can be seen to be very black. In addition, since the melting point of the flame-retardant polypropylene layer is higher than that of the conductive polypropylene layer, the flame-retardant polypropylene layer is thicker than that of the conductive polypropylene layer. Figure 2 The complete single foam particle on the lower right side clearly shows that the inner layer of flame-retardant polypropylene has a small expansion and shrinkage phenomenon. Therefore, the flame-retardant polypropylene layer will not occupy a large volume of the entire absorbing foam particle, and has no effect on the mechanical properties and absorbing properties of the final foam absorbing material.

[0094] On the other hand, Example 1 uses an extruder and a reactor to directly prepare flame-retardant polypropylene absorbing foam particles, without the need for a coating process. According to calculations, a 2.5 cubic reactor can foam 6 tons of flame-retardant polypropylene absorbing foam particles per day. According to the method of Comparative Example 2, the particles prepared in Comparative Example 1 need to be foamed and then an adhesive coating process is used to prepare flame-retardant polypropylene foam particles. According to calculations, Comparative Example 2 uses a 2.5 cubic mixing barrel, which can produce 60 kg of foam particles per hour, and can only produce 1440 kg of flame-retardant polypropylene absorbing foam particles per day. According to calculations, the solvent accounts for about 30% of the mass of the overall absorbing foam particles. After drying, the solvent evaporates and is a lossy material. The material cost is about 10% higher than that of Example 1.

[0095] The present invention has high production efficiency. One extruder can produce 6 tons of polyolefin resin absorbing small particles 24 hours a day. One 2.5 cubic high-pressure reactor can foam 6 tons of polyolefin absorbing foam particles 24 hours a day. It only takes 25 days to produce 150 tons of absorbing materials required for a large darkroom of 10,000 square meters, which greatly shortens the project period. Compared with comparative example 2, the production efficiency is improved by 416%, indicating that the present invention has achieved excellent technical effects.

[0096] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material, characterized in that: The single foam particle is a layered structure, including a flame retardant polyolefin layer and a conductive polyolefin layer, wherein the flame retardant polyolefin layer is an inner layer and the conductive polyolefin layer is an outer layer; or the flame retardant polyolefin layer is an intermediate layer and the conductive polyolefin layer is an inner layer and an outer layer; or the flame retardant polyolefin layer is an outer layer and the conductive polyolefin layer is an inner layer.

2. The multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material according to claim 1, characterized in that: The flame retardant polyolefin comprises, by weight, 20-80 parts of polyolefin resin A, 20-80 parts of flame retardant A, 0-15 parts of conductive masterbatch, and 0-20 parts of functional auxiliary agent masterbatch A. After mixing, the flame retardant polyolefin masterbatch A particles are formed by an extruder.

3. The multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material according to claim 2, characterized in that: The flame retardant A is selected from one or more of organic flame retardants, inorganic flame retardants, ammonium salt flame retardants, organosilicon flame retardants, and halogen flame retardants.

4. The multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material according to claim 1, characterized in that: In parts by weight, the conductive polyolefin comprises: 2-98 parts of polyolefin resin B, 1-20 parts of flame retardant masterbatch B, 0.1-95 parts of conductive masterbatch, and 1-20 parts of functional additive masterbatch B.

5. The multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material according to claim 4, characterized in that: The flame retardant masterbatch B comprises a polyolefin resin and a flame retardant B, wherein the polyolefin resin is selected from one or more of polypropylene, polyethylene, ethylene acrylic acid copolymer, and chlorinated polyolefin resin; the flame retardant B is selected from one or more of an organic flame retardant, an inorganic flame retardant, an ammonium salt flame retardant, an organosilicon flame retardant, and a halogen flame retardant, and after mixing, flame retardant masterbatch B particles are obtained through an extruder.

6. The multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material according to claim 5, characterized in that: Calculated by mass percentage, the flame retardant B accounts for 1-20% of the total mass of the conductive polyolefin.

7. The multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material according to claim 2 or 4, characterized in that: The polyolefin resin A and the polyolefin resin B are respectively selected from one or more of polypropylene resin, polyethylene resin, maleic anhydride grafted polypropylene, ethylene acrylic acid copolymer, and chlorinated polyolefin resin.

8. The multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material according to claim 2 or 4, characterized in that: The conductive masterbatch comprises polypropylene resin or polyethylene resin, absorbing powder and / or dispersed lubricant, and the absorbing powder is selected from one or more of carbon black, graphite, carbon nanotubes, graphene, and carbon fiber.

9. The multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material according to claim 2 or 4, characterized in that: The functional additive masterbatch A comprises a polyolefin resin and a functional additive A, wherein the polyolefin resin is selected from one or more of polypropylene, polyethylene, maleic anhydride grafted polypropylene, ethylene acrylic acid copolymer, and chlorinated polyolefin resin, and the functional additive A is selected from one or more of an antioxidant, an ultraviolet absorber, an antibacterial agent, a dispersing lubricant, and a molecular weight regulator; the functional additive masterbatch B comprises a polyolefin resin and a functional additive B, wherein the polyolefin resin is selected from one or more of polypropylene, polyethylene, maleic anhydride grafted polypropylene, ethylene acrylic acid copolymer, and chlorinated polyolefin resin, and the functional additive B is selected from one or more of a nucleating agent, an antioxidant, an ultraviolet absorber, an antibacterial agent, and a dispersing lubricant.

10. A method for preparing a multi-layer co-extruded flame-retardant polyolefin foam particle absorbing material, characterized in that: The steps include: Step S1: polyolefin resin A, flame retardant A, conductive masterbatch, and functional additive masterbatch A are mixed and then formed into flame retardant masterbatch A particles through an extruder; Step S2: adding the flame retardant masterbatch A particles obtained in step S1 into extruder A, and simultaneously adding polyolefin resin B, flame retardant masterbatch B, conductive masterbatch, and functional additive masterbatch B into extruder B, and extruding through a two-layer co-extrusion die head to obtain cylindrical or annular polyolefin resin absorbing small particles with an inner layer of flame retardant polyolefin and an outer layer of conductive polyolefin, or an inner layer of conductive polyolefin and an outer layer of flame retardant polyolefin; or, The extruder die is replaced with a three-layer co-extrusion die head to obtain cylindrical or annular polyolefin resin wave-absorbing small particles with a middle layer of flame-retardant polyolefin and inner and outer layers of conductive polyolefin; Step S3: adding the polyolefin resin absorbing small particles obtained in step S2 into a reactor, adding water and a dispersant into the high-pressure reactor, stirring, heating and introducing carbon dioxide to pressurize, and continuously heating to the melting point of the conductive polyolefin layer resin, releasing the material to obtain polyolefin absorbing foam particles in which the flame-retardant polyolefin layer is not foamed or slightly foamed and the conductive polyolefin layer is foamed; Step S4: forming the polyolefin absorbing foam particles obtained in step S3 into an absorbing material.

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