Preparation process and application of efficient electromagnetic shielding foaming polyolefin material

Abstract

The invention relates to the field of foam preparation, in particular to the field of efficient electromagnetic shielding foaming polyolefin materials. The preparation method comprises the following steps: (1) extruding and blending macromolecular resin, a conductive filler, a foaming agent, a cross-linking agent or an irradiation cross-linking agent, a foaming active agent, a foam hole control agent and an antioxidant to obtain pre-foamed cotton; (2) performing high-temperature foaming on the pre-foam to obtain foam; and (3) carrying out thermal lamination on the conductive foams with different foam structures to obtain multi-layer foam with gradient change of foam sizes, namely the light and efficient electromagnetic shielding foam. The foaming active agent is one or two of ZnO and Znst2, the foam hole control agent is one or more of CaCO3, silicon dioxide and mica sheets, the particle size is 500-5000 meshes, and the mass fraction is 0-2. The electromagnetic radiation shielding performance of the foam is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of foam preparation, and in particular to the field of high-efficiency electromagnetic shielding foamed polyolefin material. Background Art

[0002] With the vigorous development of my country's electronic science industry, a large number of electronic wireless information technologies have been widely used in medical care, transportation, communications, etc., which has facilitated people's lives and work. However, with the large-scale application of wireless information technology, it has also brought a large amount of inevitable electromagnetic interference. These electromagnetic radiations of different wavelengths and frequencies can not only easily degrade the accuracy and life of electronic equipment, causing huge economic losses, but also cause polarization resonance in the human body, thereby causing organ, nerve and body diseases. Therefore, it is urgent to take action to effectively solve electromagnetic radiation pollution.

[0003] Currently, the primary solution to electromagnetic radiation pollution is electromagnetic shielding technology, which uses shielding to block or weaken electromagnetic radiation transmission. Metal materials are representative electromagnetic shielding materials, and their excellent electrical conductivity effectively weakens electromagnetic radiation. However, metal materials have unavoidable disadvantages: high density, complex processing, and corrosion resistance, which greatly limit their wide-scale application in industrial production and real life. At the same time, metal materials have high reflectivity, which easily causes secondary pollution in actual use environments, greatly reducing their electromagnetic shielding effectiveness. Therefore, the development of lightweight conductive polymer composite electromagnetic shielding materials has become a new trend. Low-density, flexible, corrosion-resistant, and easy-to-process conductive polymer composite materials, as new electromagnetic shielding materials, can not only reflect electromagnetic radiation but also absorb lossy electromagnetic radiation, effectively reducing secondary pollution caused by electromagnetic radiation.

[0004] CN201810819636.7 discloses a conductive foam suitable for electromagnetic shielding, which is a foam that bonds a metal film to the foam, resulting in an electromagnetic shielding foam suitable for electronic devices. CN201320705759.0 discloses a foam-based electromagnetic shielding tape, which is composed of a conductive foam base layer and an adhesive layer coated on one or both sides of the conductive foam, effectively reducing electromagnetic interference in electronic devices. The above patents all explain that conductive polymer composites can block electromagnetic radiation, but they still require the addition of metal materials, making them unable to become truly lightweight electromagnetic shielding materials. Therefore, how to improve the electromagnetic shielding effectiveness of polymer composites remains a major challenge.

[0005] Therefore, the present invention focuses on environmentally friendly porous foam. Through reasonable design and regulation of the foam structure, the electromagnetic shielding mechanism of reflected radiation and absorbed loss radiation is efficiently combined, aiming to invent a lightweight and efficient electromagnetic shielding foam. Summary of the Invention

[0006] The first technical purpose of the present invention is to provide a preparation process of a high-efficiency electromagnetic shielding foamed polyolefin material.

[0007] The second technical purpose of the present invention is to provide an application of a high-efficiency electromagnetic shielding foamed polyolefin material, specifically in the field of electromagnetic shielding.

[0008] The present invention mainly regulates the structure of the foam and effectively combines the reflected radiation and the absorbed loss radiation mechanism, thereby providing a high-efficiency electromagnetic shielding foamed polyolefin material and a preparation method thereof.

[0009] The first technical purpose of the present invention is achieved through the following technical solutions: A preparation process of a high-efficiency electromagnetic shielding foamed polyolefin material, comprising the following steps: Step (1): extruding and blending a polymer resin with a conductive filler, a foaming agent, a cross-linking agent or a radiation cross-linking agent, a foaming active agent, a cell control agent and an antioxidant to obtain a pre-foam; Step (2) foaming the pre-foam at high temperature to obtain foam; Step (3) heat-bonding the conductive foams with different pore structures to obtain a multi-layer foam with gradient pore size changes, which is a lightweight and high-efficiency electromagnetic shielding foam.

[0010] Preferably, the foaming active agent is one or both of ZnO and Znst2, and the cell control agent is one or more of CaCO3, silica and mica flakes, with a particle size of 500-5000 mesh and a mass fraction of 0-2 parts.

[0011] The advantage of adopting the present invention is that the present invention independently develops a foaming active agent and a cell control agent, effectively controls the structure and size of the foam cells, and provides a new idea for the diversity of the foam structure.

[0012] Preferably, the polymer resin in step (1) is one or more of PE, LDPE, PP, PLA and PBS, with a mass fraction of 50-80 parts.

[0013] More preferably, the present invention selects polymer resin PP as one of the raw materials.

[0014] The advantages of using this invention lie in that polypropylene (PP), one of the five most common plastics, is a semi-crystalline thermoplastic formed by polymerizing the monomer propylene. PP is widely used in both industry and daily life. It is a thermoplastic synthetic resin with excellent performance. It is a colorless, translucent, lightweight, general-purpose thermoplastic plastic with excellent chemical and heat resistance, electrical insulation, high mechanical strength, and excellent high-wear processing properties. It is widely used in the production of clothing, fiber products such as blankets, medical devices, automobiles, bicycles, spare parts, pipelines, chemical containers, and food and pharmaceutical packaging. Choosing PP as one of the raw materials can produce products with better performance.

[0015] Preferably, the foaming agent in step (1) is azodicarbonamide, with a mass fraction of 3-10 parts.

[0016] Preferably, the cross-linking agent in step (1) is dicumyl peroxide, with a mass fraction of 0-0.1 parts.

[0017] The present invention has the advantages that dicumyl peroxide, also known as DCP, has the advantages of high cross-linking efficiency and low price, thus having cost advantages.

[0018] Preferably, the antioxidant in step (1) is antioxidant 1010, with a mass fraction of 0.1-1 parts.

[0019] The advantages of the present invention are that Antioxidant 1010 is a phenolic antioxidant, one of the most advanced antioxidants. It exhibits excellent antioxidant properties against polypropylene and polyethylene, effectively extending the shelf life of products. It also exhibits low volatility, excellent extraction resistance, high thermal stability, long-lasting effectiveness, and is non-staining, non-polluting, and non-toxic. Furthermore, Antioxidant 1010 is a high-molecular-weight hindered phenolic antioxidant with very low volatility, low migration resistance, and extraction resistance. Antioxidant 1010 effectively prevents thermal oxidative degradation of polymer materials during long-term aging and is also a highly effective processing stabilizer, improving the discoloration resistance of polymer materials under high-temperature processing conditions.

[0020] Preferably, the extrusion in step (1) is performed using a special single-screw extruder, and the operating temperature of the single-screw extruder is adjusted to: 100-140°C in zone 1, 110-150°C in zone 2, 110-150°C in zone 3, 100-140°C in zone 4, and the mold temperature is 110-150°C; Preferably, the specially made single-screw extruder is a single-screw cooling system device for preparing foaming materials, comprising a single-screw extruder and a cooling device, the single-screw extruder is connected to the cooling device through a connecting assembly, six sets of universal wheels are provided at the bottom end of the cooling device, a water trough is provided at the top left side of the cooling device, a cooling assembly is provided in the water trough, a drainage trough is provided at the top middle side of the cooling device, a drain assembly and a feeding assembly are provided in the drainage trough, a chamber is provided at the rear end of the cooling device, an air-drying assembly is provided at the top left side of the cooling device, and a water circulation assembly is provided inside the chamber; it is characterized in that the cooling assembly comprises a first support plate, two groups of second support plates, two groups of third support plates and two groups of first rotating rods, the bottom end of the water trough is connected to the first support plate, the top end of the first support plate is connected to the two groups of second support plates, the bottom end of the water trough is connected to the two groups of third support plates, the inner ends of the two groups of second support plates and the two groups of third support plates are respectively connected to the front end and rear end bearings of the first rotating rod, and the outer walls of the two groups of first rotating rods are provided with first rubber rollers; The drain assembly includes two groups of fourth support plates, a fifth support plate, three groups of threaded rods, a first lifting plate, a second sponge and a friction block. The bottom end of the drain trough is connected to the two groups of fourth support plates, the top ends of the two groups of fourth support plates are connected to the fifth support plate, a sixth support plate is provided in the middle of the two groups of fourth support plates, the top end of the sixth support plate is provided with a first sponge, and the top end of the fifth support plate is provided with three groups of first through-threaded holes, the three groups of first through-threaded holes are respectively threadedly connected to the threaded rods, the bottom ends of the three groups of threaded rods are connected to the first lifting plate, the bottom end of the first lifting plate is connected to the second sponge, and the top ends of the three groups of threaded rods are respectively connected to the friction blocks; The feeding assembly includes two groups of first fixed plates, a second fixed plate, a second threaded rod, a second lifting plate, a card sliding block, a stepping motor, a rotating rod and a rotating wheel, the top of the cooling device is connected to the two groups of first fixed plates, the top of the two groups of first fixed plates are connected to the second fixed plate, the top of the second fixed plate is provided with a second through-thread hole, the second through-thread hole is threadedly connected to the second threaded rod, the bottom end of the second threaded rod is connected to the second lifting plate, the front end and the rear end of the second lifting plate are respectively connected to the card sliding block; the inner ends of the two groups of first fixed plates are respectively provided with a card sliding groove, the two groups of card sliding grooves are respectively slidably clamped with the card sliding block, the inner end of the second lifting plate is provided with a third rotating rod connected with a bearing, the front end of the cooling device is connected to the stepping motor, the output end bearing seal of the stepping motor is inserted into the drainage groove, the output end of the stepping motor is connected to the rotating rod, the rear end of the rotating rod is connected to the drainage groove bearing, a second rubber roller is provided on the outer walls of the rotating rod and the third rotating rod, and the top of the second threaded rod is connected to the rotating wheel; The air drying component includes a support frame and a reduction motor. The top right side of the cooling device is connected to the support frame. A vent is provided at the top of the support frame. A fixing ring is provided in the vent. A cross is provided on the inner wall of the fixing ring. The top of the cross is connected to the reduction motor. The output end bearing seal of the reduction motor passes through the bottom end of the cross. The output end of the reduction motor is provided with three sets of fan blades. The water circulation component includes a water tank, a water pump, a first pipe, a second pipe and a drain pipe. The bottom end of the chamber is connected to the water tank, the bottom end of the chamber is connected to the water pump, the output end of the water pump is connected to the first pipe, the input end of the water pump is connected to the second pipe, the second pipe is sealed and inserted into the water tank, the first pipe is sealed and inserted into the water tank, the left end of the drain pipe is sealed and inserted into the water tank, and the right end of the drain pipe is sealed and inserted into the water tank; the connection component includes two groups of support blocks and four groups of screws. The front and rear ends of the single-screw extruder are each provided with two groups of mounting threaded holes. The left end of the cooling equipment is connected to the two groups of support blocks. The front ends of the two groups of support blocks are each provided with two groups of mounting through holes. The four groups of screws are threadedly connected to the mounting threaded holes through the mounting through holes.

[0021] The advantage of adopting the present invention is that compared with the prior art, the beneficial effects of the present invention are as follows: first, the single-screw extruder is connected to the cooling equipment through a connecting component, and then when preparing the foaming material, water is first filled into the water tank through the water circulation component, and then the semi-melted strips first fall into the water tank through the first rotating rod, and then the workers put the cooled plastic strips on the rotating rod on the third support plate, and then pass through the drain component and feed the material to the air-drying component through the feeding component, so as to improve the cooling effect and perform fully automatic cooling and drying, thereby reducing the workload of workers and enhancing practicality.

[0022] Preferably, the pre-foaming high temperature in step (2) is 180-250°C.

[0023] Preferably, the foam prepared in step (3) has a pore size range of 10 μm-1 mm and a thickness range of 0.1 mm-10 mm; the multi-layer foam has 2-10 layers.

[0024] In summary, the present invention has the following beneficial effects: The present invention independently developed a foaming active agent and a cell control agent, which effectively regulated the structure and size of the foam cells, providing a new idea for the diversity of the foam structure; The present invention effectively combines the electromagnetic shielding mechanisms of reflected radiation and absorbed radiation loss to produce a lightweight, highly efficient electromagnetic shielding foam: conductive fillers are introduced into the foam to produce a conductive foam, that is, a foam with radiation reflection function. To further enhance the electromagnetic shielding effect of the foam, a reasonable multi-layer gradient design is performed on the foam cells, which increases the propagation path and internal attenuation of electromagnetic radiation in the foam cells, that is, increases the absorption and loss of electromagnetic radiation, and effectively improves the electromagnetic radiation shielding performance of the foam. The high-efficiency electromagnetic shielding foam in the present invention mainly absorbs and loses electromagnetic radiation, effectively reducing the secondary pollution of electromagnetic radiation, thereby reducing the total amount of electromagnetic radiation in the space and its negative impact on people; The high-efficiency electromagnetic shielding foam of the present invention has low density, light weight, and is easy to prepare, and is suitable for industrial production and practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a schematic diagram of the connection structure of a single-screw extruder for preparing a foam material according to the present invention; FIG2 is a schematic diagram of the connection structure between the first support plate and the water tank of the single-screw extruder for preparing the foam material of the present invention; FIG3 is a schematic diagram of the connection structure between the second threaded rod and the rotating wheel of the single-screw extruder for preparing the foam material of the present invention; 4 is a schematic diagram of the connection structure between the friction block and the first threaded rod of the single-screw extruder for preparing the foam material of the present invention; 5 is a schematic diagram of the cross and reduction motor structure of a single-screw extruder for preparing a foam material according to the present invention; FIG6 is a schematic diagram of the enlarged structure of a single-screw extruder for preparing a foam material according to the present invention; Markings in the accompanying drawings: 1, single screw extruder; 2, cooling equipment; 3, first support plate; 4, second support plate; 5, third support plate; 6, first rotating rod; 7, first rubber roller; 8, fourth support plate; 9, fifth support plate; 10, sixth support plate; 11, first sponge; 12, threaded rod; 13, first lifting plate; 14, second sponge; 15, friction block; 16, first fixed plate; 17, second fixed plate; 18, second threaded rod; 19, second lifting plate; 20, card Install the slider; 21. The third rotating rod; 22. The second rubber roller; 23. The stepping motor; 24. The rotating rod; 25. The water guide platform; 26. The rotating wheel; 27. The support frame; 28. The fixing ring; 29. The cross; 30. The water tank; 31. The drain trough; 32. The chamber; 33. The reduction motor; 34. The fan blade; 35. The dustproof net; 36. The water tank; 37. The water pump; 38. The first pipe; 39. The second pipe; 40. The drain pipe; 41. The support block; 42. The screw; 43. The universal wheel. DETAILED DESCRIPTION

[0026] The following specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the embodiments as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by patent law.

[0027] The present invention will be described in detail below with reference to the accompanying drawings using embodiments.

[0028] Example 1

[0029] 70 parts of polymer resin LDPE, 15 parts of conductive filler graphene, 5 parts of foaming agent azodicarbonamide, 0.06 parts of cross-linking agent diisopropyl peroxide, 1 part of foaming active agent ZnO and 21 parts of Znst, 7.74 parts of cell control agent CaCO3 (2000 mesh), and 0.2 parts of antioxidant 1010 were extruded and blended to obtain pre-foam. The pre-foam was foamed at 230°C to obtain 2mm thick foam A with a cell size of about 0.5mm and a density of 89kg / m 3 57.9 parts of polymer resin LDPE, 20 parts of conductive filler graphene, 10 parts of foaming agent azodicarbonamide, 0.1 parts of cross-linking agent diisopropylbenzene peroxide, 1 part of foaming active agent ZnO and 20.5 parts of Znst, 10 parts of cell control agent CaCO3 (5000 mesh), and 0.5 parts of antioxidant were extruded and blended to obtain pre-foam. The pre-foam was foamed at 220°C to obtain 5mm thick foam B with a cell size of about 0.5mm and a density of 55kg / m 3 ; Foam A and foam B are thermally bonded to obtain a double-layer electromagnetic shielding foam, the electromagnetic shielding efficiency of which can reach 33.8dB, and the electromagnetic radiation reflectivity of the material surface is as low as 0.5.

[0030] Example 2

[0031] 8.9 parts of polymer resin PP6, 25 parts of conductive filler carbon nanotubes, 3 parts of foaming agent azodicarbonamide, 3M radiation cross-linking agent, 2 parts of foaming active agent ZnO, 3 parts of cell control agent CaCO3 (500 mesh), and 0.1 parts of antioxidant 1010 were extruded and blended to obtain pre-foam. The pre-foam was foamed at 200°C to obtain 4mm thick foam A with a cell of about 1mm and a density of 100kg / m 3 ; 6.8 parts of polymer resin PP5, 25 parts of conductive filler carbon nanotubes, 5 parts of foaming agent azodicarbonamide, 4M radiation crosslinking agent, 1 part of foaming active agent ZnO and 22 parts of Znst, 10 parts of cell control agent CaCO3 (2000 mesh), and 0.2 parts of antioxidant were extruded and blended to obtain pre-foam. The pre-foam was foamed at 230°C to obtain 5mm thick foam B with a cell size of about 0.1mm and a density of 66kg / m 3; 0.8 parts of polymer resin PP4, 25 parts of conductive filler carbon nanotubes, 10 parts of foaming agent azodicarbonamide, 3M radiation crosslinking agent, 2 parts of foaming active agent ZnO and 22 parts of Znst, 20 parts of cell control agent CaCO3 (5000 mesh), and 0.2 parts of antioxidant were extruded and blended to obtain pre-foam. The foam was foamed at 230°C to obtain 5mm thick foam C with a cell size of about 20μm and a density of 50kg / m 3 .

[0032] Foam A, foam B and foam C are thermally bonded to obtain a three-layer electromagnetic shielding foam. The electromagnetic shielding efficiency of the foam can reach 43dB, and the electromagnetic radiation reflectivity of the material surface is as low as 0.4.

[0033] Preferably, a single screw extruder is used, such as Figures 1 to 6 As shown, a single-screw cooling system device for preparing a foaming material of the present invention includes a single-screw extruder 1 and a cooling device 2. The single-screw extruder 1 is connected to the cooling device 2 through a connecting component. The bottom end of the cooling device 2 is provided with six groups of universal wheels 43. A water tank 30 is provided at the top left side of the cooling device 2. A cooling component is provided in the water tank 30. A drainage tank 31 is provided at the top middle part of the cooling device 2. A drainage component and a feeding component are provided in the drainage tank 31. A chamber 32 is provided at the rear end of the cooling device 2. An air-drying component is provided at the top left side of the cooling device 2. A water circulation component is provided inside the chamber 32. The cooling component includes a first support plate 3, two groups of second support plates 4, two groups of third support plates 5 and two groups of first rotating rods 6. The bottom end of the water tank 30 is connected to the first support plate 3. The top end of the first support plate 3 is connected to the two groups of second support plates 4, the bottom end of the water tank 30 is connected to the two groups of third support plates 5, the inner ends of the two groups of second support plates 4 and the two groups of third support plates 5 are respectively connected to the front end and rear end bearings of the first rotating rod 6, and the outer walls of the two groups of first rotating rods 6 are provided with first rubber rollers 7; first, the single-screw extruder is connected to the cooling equipment through a connecting assembly, and then when preparing the foaming material, water is first filled into the water tank through the water circulation assembly, and then the semi-melted strips first fall into the water tank through the first rotating rod, and then the workers put the cooled plastic strips on the rotating rod on the third support plate, and then pass through the drain assembly and feed the material to the air-drying assembly through the feeding assembly, so as to improve the cooling effect and perform fully automatic cooling and drying, thereby reducing the workload of workers and thus enhancing practicality.

[0034] As a preferred embodiment of the above, the drain assembly includes two groups of fourth support plates 8, a fifth support plate 9, three groups of threaded rods 12, a first lifting plate 13, a second sponge 14 and a friction block 15. The bottom end of the drain trough 31 is connected to the two groups of fourth support plates 8, and the top end of the two groups of fourth support plates 8 is connected to the fifth support plate 9. The middle part of the two groups of fourth support plates 8 is provided with a sixth support plate 10, and the top end of the sixth support plate 10 is provided with a first sponge 11. The top end of the fifth support plate 9 is provided with three groups of first through-threaded holes, and the three groups of first through-threaded holes are respectively connected to the threaded rod 1 2 threaded connection, the bottom ends of the three groups of threaded rods 12 are connected to the first lifting plate 13, the bottom end of the first lifting plate 13 is connected to the second sponge 14, and the top ends of the three groups of threaded rods 12 are respectively connected to the friction blocks 15; when the plastic strip is cooled, the plastic strip is passed between the first sponge and the second sponge, and then the plastic strip is passed through the feeding assembly, and then the first lifting plate is moved downward by rotating the three groups of first threaded rods, so that the first sponge and the second sponge wrap the plastic strip and drain the water on the plastic strip, thereby accelerating the drying of the plastic, thereby enhancing practicality.

[0035] As a preferred embodiment of the above, the feeding assembly includes two groups of first fixed plates 16, second fixed plates 17, second threaded rods 18, second lifting plates 19, a card-mounted slider 20, a stepping motor 23, a rotating rod 24 and a rotating wheel 26. The top of the cooling device 2 is connected to the two groups of first fixed plates 16, and the top of the two groups of first fixed plates 16 is connected to the second fixed plate 17. The top of the second fixed plate 17 is provided with a second through-threaded hole, and the second through-threaded hole is threadedly connected to the second threaded rod 18. The bottom end of the second threaded rod 18 is connected to the second lifting plate 19. The front end and rear end of the second lifting plate 19 are respectively connected to the card-mounted slider 20. The inner ends of the two groups of first fixed plates 16 are respectively provided with card-mounted slide grooves. The two groups of card-mounted slide grooves They are respectively slidably clamped with the clamping slider 20, and the inner end of the second lifting plate 19 is provided with a third rotating rod 21 connected with a bearing. The front end of the cooling device 2 is connected to the stepping motor 23, and the output end bearing seal of the stepping motor 23 is inserted into the drainage groove 31. The output end of the stepping motor 23 is connected to the rotating rod 24, and the rear end of the rotating rod 24 is connected to the drainage groove 31 bearing. The outer walls of the rotating rod 24 and the third rotating rod 21 are both provided with a second rubber roller 22, and the top of the second threaded rod 18 is connected to the rotating wheel 26; the rotating rod can be driven to rotate by the stepping motor, thereby driving the second rubber roller to rotate, and then driving the plastic strip held between the two second rubber rollers to move to the right for drying, thereby enhancing practicality.

[0036] As a preference of the above embodiment, a water guide platform 25 is further included, a drain outlet is provided at the right end of the drain trough 31, and the left end of the drain outlet is connected to the water guide platform 25; the water drained from the two groups of sponges can be guided by the water guide platform, thereby enhancing practicality.

[0037] As a preferred embodiment of the above, the air-drying component includes a support frame 27 and a reduction motor 33. The top right side of the cooling device 2 is connected to the support frame 27. A vent is provided at the top of the support frame 27. A fixing ring 28 is provided in the vent. A cross 29 is provided on the inner wall of the fixing ring 28. The top of the cross 29 is connected to the reduction motor 33. The output end bearing seal of the reduction motor 33 passes through the bottom end of the cross 29. The output end of the reduction motor 33 is provided with three groups of fan blades 34. The three groups of fan blades can be driven to rotate by reducing the motor to dry the plastic strips, thereby enhancing practicality.

[0038] As a preference of the above embodiment, a dustproof net 35 is provided on the top of the fixing ring 28; the dustproof net can prevent dust from contacting the motor and the fan blades, thereby enhancing practicality.

[0039] As a preferred embodiment of the above, the water circulation component includes a water tank 36, a water pump 37, a first pipe 38, a second pipe 39 and a drain pipe 40. The bottom end of the chamber 32 is connected to the water tank 36, the bottom end of the chamber 32 is connected to the water pump 37, the output end of the water pump 37 is connected to the first pipe 38, the input end of the water pump 37 is connected to the second pipe 39, the second pipe 39 is sealed and inserted into the water tank 36, the first pipe 38 is sealed and inserted into the water tank 30, the left end of the drain pipe 40 is sealed and inserted into the water tank 30, and the right end of the drain pipe 40 is sealed and inserted into the water tank 36; the water in the water tank can be injected into the water tank through the water pump, and the drain pipe in the water tank will discharge the excess water into the water tank, thereby forming a water circulation between the water tank and the water tank, and keeping the water in the water tank at a lower temperature, thereby accelerating the cooling of the plastic strip, thereby enhancing practicality.

[0040] As a preferred embodiment of the above embodiment, the connecting assembly includes two groups of support blocks 41 and four groups of screws 42. The front and rear ends of the single-screw extruder 1 are each provided with two groups of mounting threaded holes. The left end of the cooling device 2 is connected to the two groups of support blocks 41. The front ends of the two groups of support blocks 41 are each provided with two groups of mounting through holes. The four groups of screws 42 are respectively threadedly connected to the mounting threaded holes through the mounting through holes. The cooling device and the single-screw extruder can be fixedly connected by two groups of support blocks and four groups of screws, thereby enhancing practicality.

[0041] The present invention provides a single-screw cooling system device for preparing foamed materials. Its working principle is that when it is working, the single-screw extruder is first connected to the cooling device through two groups of support blocks and four groups of screws. Then, when preparing the foamed material, the water in the water tank is first injected into the water tank through a water pump, and then the reducing motor and the stepping motor are started. Then, the semi-melted strips first fall into the water tank through the first rotating rod. Then, the workers put the cooled plastic strips on the rotating rod on the third support plate, and then pass through between the two groups of sponges and between the two groups of rubber rollers driven to rotate by the stepping motor, so as to feed the plastic strips to the right side of the cooling device. When the plastic strips move to the right, the rotating fan blades are driven by the reduction motor for rapid drying. Then, the workers cut the dried plastic strips into pieces, and then collect the shredded plastic.

[0042] Among them, electromagnetic shielding effectiveness is usually expressed in decibels (dB). The higher the decibel value, the better the shielding effectiveness of the material against electromagnetic waves. The calculation formula for electromagnetic shielding effectiveness is as follows: Electromagnetic shielding effectiveness (dB) =

[0043] Wherein, I0 represents the electromagnetic radiation intensity without shielding material, and I represents the electromagnetic radiation intensity with shielding material.

[0044] Comparative Example 1 Pre-foam was prepared by blending 90 parts of polymer resin PP, 10 parts of foaming agent azodicarbonamide and radiation cross-linked 3M. The pre-foam was foamed at 230°C to obtain a 4mm thick foam with a pore size of about 2mm. The foam had no electromagnetic shielding effect.

[0045] Comparative Example 2 90 parts of polymer resin PE, 20 parts of foaming agent azodicarbonamide, and radiation cross-linked 3M are blended to obtain pre-foam, which is foamed at 230°C to obtain 3mm thick foam with a pore size of about 2.2mm. The foam has no electromagnetic shielding effect.

[0046] It can be seen from the embodiments and comparative examples that the foam made of polymer resin PP has good electromagnetic shielding performance and low electromagnetic radiation reflectivity on the material surface, while the foam made of polymer resin LDPE is slightly worse; the control of the proportion of foaming activator, cell control agent and antioxidant also has a certain influence on it; the radiation cross-linking effect is better in Example 2; and the foam in Example 2 is a three-layer thermal bonding, so the quality of the product is better than the two-layer thermal bonding in Example 1.

[0047] By comparing the embodiment with the comparative example, it can be concluded that the addition of the conductive filler, the foaming activator, the cell control agent and the antioxidant enables the material to have electromagnetic shielding performance, and the multi-layer foam structure also has an impact on it.

Claims

1. A process for preparing a highly efficient electromagnetic shielding foamed polyolefin material, characterized in that The steps include: Step (1): extruding and blending a polymer resin with a conductive filler, a foaming agent, a cross-linking agent or a radiation cross-linking agent, a foaming active agent, a cell control agent and an antioxidant to obtain a pre-foam; Step (2) foaming the pre-foam at high temperature to obtain foam; Step (3) The conductive foams with different pore structures are thermally bonded to obtain a multi-layer foam with gradient pore size, which is a lightweight and highly efficient electromagnetic shielding foam; The foaming active agent is one or two of ZnO and Znst2, and the cell control agent is one or more of CaCO3, silica and mica flakes, with a particle size of 500-5000 mesh and a mass fraction of 0-2 parts.

2. The process for preparing a high-efficiency electromagnetic shielding foamed polyolefin material according to claim 1, characterized in that: The polymer resin described in step (1) is one or more of PE, LDPE, PP, PLA and PBS, with a mass fraction of 50-80 parts.

3. The process for preparing a high-efficiency electromagnetic shielding foamed polyolefin material according to claim 1, characterized in that: The foaming agent described in step (1) is azodicarbonamide, with a mass fraction of 3-10 parts.

4. The process for preparing a high-efficiency electromagnetic shielding foamed polyolefin material according to claim 1, characterized in that: The cross-linking agent described in step (1) is dicumyl peroxide, with a mass fraction of 0-0.1 parts.

5. The process for preparing a high-efficiency electromagnetic shielding foamed polyolefin material according to claim 1, characterized in that: The antioxidant described in step (1) is antioxidant 1010, with a mass fraction of 0.1-1 parts.

6. The process for preparing a high-efficiency electromagnetic shielding foamed polyolefin material according to claim 1, characterized in that: The extrusion in step (1) is performed using a special single-screw extruder, and the operating temperature of the single-screw extruder is adjusted to: 100-140°C in zone 1, 110-150°C in zone 2, 110-150°C in zone 3, 100-140°C in zone 4, and the mold temperature is 110-150°C.

7. The process for preparing a high-efficiency electromagnetic shielding foamed polyolefin material according to claim 6, characterized in that: The special single-screw extruder is a single-screw cooling system device for preparing foaming materials, comprising a single-screw extruder (1) and a cooling device (2), wherein the single-screw extruder (1) is connected to the cooling device (2) via a connecting assembly, six sets of universal wheels (43) are provided at the bottom end of the cooling device (2), a water tank (30) is provided at the top left of the cooling device (2), a cooling assembly is provided in the water tank (30), a drainage tank (31) is provided at the top middle of the cooling device (2), a drainage assembly and a feeding assembly are provided in the drainage tank (31), a chamber (32) is provided at the rear end of the cooling device (2), and a fan is provided at the top left of the cooling device (2). A dry component, wherein a water circulation component is provided inside the chamber (32); the cooling component comprises a first support plate (3), two groups of second support plates (4), two groups of third support plates (5) and two groups of first rotating rods (6); the bottom end of the water tank (30) is connected to the first support plate (3), the top end of the first support plate (3) is connected to the two groups of second support plates (4), the bottom end of the water tank (30) is connected to the two groups of third support plates (5), the inner ends of the two groups of second support plates (4) and the two groups of third support plates (5) are respectively connected to the front end and rear end bearings of the first rotating rod (6), and the outer walls of the two groups of first rotating rods (6) are provided with first rubber rollers (7); The drain assembly comprises two groups of fourth support plates (8), a fifth support plate (9), three groups of threaded rods (12), a first lifting plate (13), a second sponge (14) and a friction block (15); the bottom end of the drain groove (31) is connected to the two groups of fourth support plates (8); the top end of the two groups of fourth support plates (8) is connected to the fifth support plate (9); a sixth support plate (10) is provided in the middle of the two groups of fourth support plates (8); the top end of the sixth support plate (10) is provided with a first sponge (11); the top end of the fifth support plate (9) is provided with three groups of first through-threaded holes; the three groups of first through-threaded holes are respectively threadedly connected to the threaded rods (12); the bottom ends of the three groups of threaded rods (12) are connected to the first lifting plate (13); the bottom end of the first lifting plate (13) is connected to the second sponge (14); and the top ends of the three groups of threaded rods (12) are respectively connected to the friction block (15); The feeding assembly includes two groups of first fixed plates (16), a second fixed plate (17), a second threaded rod (18), a second lifting plate (19), a clamping slider (20), a stepping motor (23), a rotating rod (24) and a rotating wheel (26). The top of the cooling device (2) is connected to the two groups of first fixed plates (16), the top of the two groups of first fixed plates (16) is connected to the second fixed plate (17), the top of the second fixed plate (17) is provided with a second through-threaded hole, the second through-threaded hole is threadedly connected to the second threaded rod (18), the bottom end of the second threaded rod (18) is connected to the second lifting plate (19), and the front end and the rear end of the second lifting plate (19) are respectively connected to the clamping slider (20). The inner ends of the two groups of first fixed plates (16) are respectively provided with a card-mounting slide groove, and the two groups of card-mounting slide grooves are respectively slidably carded with the card-mounting slider (20), and the inner end of the second lifting plate (19) is provided with a third rotating rod (21) connected with a bearing, the front end of the cooling device (2) is connected to the stepper motor (23), the output end bearing seal of the stepper motor (23) is inserted into the drainage groove (31), the output end of the stepper motor (23) is connected to the rotating rod (24), the rear end of the rotating rod (24) is connected to the bearing of the drainage groove (31), the outer walls of the rotating rod (24) and the third rotating rod (21) are both provided with a second rubber roller (22), and the top end of the second threaded rod (18) is connected to the rotating wheel (26); The air drying component includes a support frame (27) and a reduction motor (33). The top right side of the cooling device (2) is connected to the support frame (27). The top of the support frame (27) is provided with a vent, and a fixing ring (28) is provided in the vent. The inner wall of the fixing ring (28) is provided with a cross (29). The top of the cross (29) is connected to the reduction motor (33). The output end bearing seal of the reduction motor (33) passes through the bottom end of the cross (29). The output end of the reduction motor (33) is provided with three sets of fan blades (34). The water circulation assembly includes a water tank (36), a water pump (37), a first pipe (38), a second pipe (39) and a drain pipe (40). The bottom end of the chamber (32) is connected to the water tank (36), the bottom end of the chamber (32) is connected to the water pump (37), the output end of the water pump (37) is connected to the first pipe (38), the input end of the water pump (37) is connected to the second pipe (39), the second pipe (39) is sealed and inserted into the water tank (36), the first pipe (38) is sealed and inserted into the water tank (30), and the drain pipe (40) is connected to the first pipe (39). The left end of the water pipe (40) is sealed and inserted into the water tank (30), and the right end of the drain pipe (40) is sealed and inserted into the water tank (36); the connecting assembly includes two groups of support blocks (41) and four groups of screws (42), the front end and the rear end of the single-screw extruder (1) are both provided with two groups of mounting threaded holes, the left end of the cooling device (2) is connected to the two groups of support blocks (41), the front ends of the two groups of support blocks (41) are both provided with two groups of mounting through holes, and the four groups of screws (42) are respectively threadedly connected to the mounting threaded holes through the mounting through holes.

8. The process for preparing a high-efficiency electromagnetic shielding foamed polyolefin material according to claim 1, characterized in that: The pre-foaming high temperature in step (2) is 180-250°C, and the heat bonding is performed.

9. The process for preparing a high-efficiency electromagnetic shielding foamed polyolefin material according to claim 8, characterized in that: The pore size of the foam in step (3) is in the range of 10 μm-1 mm, and the thickness is in the range of 0.1 mm-10 mm; the multi-layer foam has 2-10 layers.

10. A high-efficiency electromagnetic shielding foamed polyolefin material, characterized by: The material is prepared by the preparation process of a high-efficiency electromagnetic shielding foamed polyolefin material according to any one of claims 1 to 9, and is applied in the field of electromagnetic shielding technology.

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