A foamable bead and a method for preparing the same, a bead foamed material and a method for preparing the same

Abstract

The application provides a foamable bead and a preparation method thereof, a bead foamed material and a preparation method thereof, and belongs to the technical field of bead foamed materials. The ethylene-based copolymer elastomer is used as a long-chain branched or low-crystallinity component, is physically entangled with linear or low-branched foamed polymer molecular chains, significantly improves the melt strength and strain hardening behavior of the blending system at a processing temperature, ensures that the bubble wall in the foaming stage is not easy to break when encountering rapid stretching, and is beneficial to forming a uniform closed cell structure; in the steam melting and bonding process, the viscosity and creep resistance of the melted layer on the surface of the bead are enhanced, so that a firm and dense welding interface between the beads can be realized at a lower steam pressure.

Description

Technical Field

[0001] This invention belongs to the field of bead foaming material technology, specifically relating to a foamable bead and its preparation method, and bead foaming material and its preparation method. Background Technology

[0002] Bead foaming is a process that physically expands polymer beads into foam materials. Combined with molds, it can produce parts with complex geometries and features extremely low density and high lightweight. Polypropylene (PP), polyethylene (PE), and polylactic acid (PLA) are widely used in the field of bead foam materials due to their good processability, mechanical strength, and recyclability.

[0003] Taking PP as an example, it possesses excellent properties such as good processability, heat resistance, recyclability, and high mechanical strength, making it the world's second most widely used plastic. PP foam materials also have lightweight, cushioning, and heat and sound insulation properties, especially bead-foamed PP, which has seen rapid development in recent years and is widely used in industries such as automotive, packaging, toys, home furnishings, and construction.

[0004] The preparation of bead-based foam materials includes three main stages: granulation, foaming, and compression molding. In the granulation stage, the foaming polymer and additives are melt-mixed to obtain expandable beads. In the foaming stage, the expandable beads are foamed using a batch foaming method to obtain pre-foamed beads. In the compression molding stage, the pre-foamed beads are placed in a mold, and high-pressure steam is used to melt the surface of the pre-foamed beads and bond them together to obtain the foamed product. Traditional bead-based foaming systems have significant limitations: insufficient polymer melt strength, easy rupture of cell walls during foaming leading to cell collapse or clogging, and difficulty in forming uniform and large-sized cell structures (foaming ratio less than 10 times). This cannot meet the requirements of bead-based foam materials for cell structure and mechanical properties.

[0005] Furthermore, during the compression molding stage, in order to ensure that the foamed products have sufficient mechanical strength, especially tensile properties, a relatively high steam pressure (above 0.28 MPa) is usually required to ensure sufficient melt bonding. This molding step is the main energy-consuming link in the production of bead foam materials. Excessive steam pressure leads to high requirements for molding equipment, high energy consumption, and increased costs.

[0006] Currently, the industry improves the cell structure by optimizing the foaming process or adding nucleating agents. However, in order to improve the mechanical properties of bead foam materials, a higher steam pressure is still required during the molding stage to ensure that the pre-foamed beads are fully melted and bonded. Summary of the Invention

[0007] The purpose of this invention is to provide expandable beads and a method for preparing the same, as well as a foamed bead material and a method for preparing the same. The expandable beads provided by this invention have uniform, high-expansion-ratio foaming properties, and require low steam pressure during compression molding.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides foamable beads, comprising, by weight parts: 80-95 parts of foaming polymer, 5-20 parts of ethylene copolymer elastomer, and 2-10 parts of additives; wherein the foaming polymer is a linear or low-branched polymer, and the low-branched polymer is a polymer in which the branched units account for less than 0.1% of the polymer molecular weight.

[0009] Preferably, the foaming polymer includes one or more of polypropylene, polyethylene, and polylactic acid.

[0010] Preferably, the ethylene copolymer elastomer includes one or more of polyolefin elastomer (POE), ethylene propylene diene monomer (EPDM) rubber, ethylene propylene diene monomer (EPDM) rubber, ethylene-acrylate copolymer, ethylene-acrylic acid copolymer, and ethylene-vinyl acetate copolymer.

[0011] Preferably, the additives include 0.01-0.05 parts of zinc borate, 0.1-0.2 parts of antioxidant, 0.1-0.5 parts of ethylene bis-stearamide (EBS), and 1-5 parts of antistatic agent.

[0012] Preferably, the mass of the foamable beads is 0.8~1.2 mg / bead.

[0013] The present invention also provides a method for preparing the foamable beads described in the above technical solution, comprising: mixing raw materials and then sequentially performing melt extrusion and granulation to obtain foamable beads; wherein the extrusion temperature of the melt extrusion is 150~220℃ and the die temperature is 170~190℃.

[0014] This invention also provides a method for preparing bead-based foamed materials, comprising the following steps: The foamable beads described in the above technical solution are mixed with a gaseous foaming agent and saturated, then depressurized and foamed to obtain pre-foamed beads; the saturation temperature is 120~200℃, the saturation gas pressure is 1~4MPa, and the saturation time is 10~40min. The pre-foamed beads are molded to obtain bead foam material; the steam pressure used for the molding is 0.22~0.28MPa.

[0015] Preferably, the heat preservation time for the molding process is 10~60s.

[0016] Preferably, the gaseous foaming agent includes one or more of carbon dioxide, nitrogen, isobutylene, and n-heptane.

[0017] The present invention also provides a beaded foaming material prepared by the preparation method described in the above technical solution.

[0018] This invention provides foamable beads, comprising, by weight parts: 80-95 parts of a foaming polymer, 5-20 parts of an ethylene copolymer elastomer, and 2-10 parts of additives; wherein the foaming polymer is a linear or low-branched polymer, and the low-branched polymer is a polymer in which branched units account for less than 0.1% of the polymer molecular weight. By adding the ethylene copolymer elastomer, this invention can improve the melt strength of the foaming polymer, control the cell nucleation density, and promote the formation of larger and more uniformly distributed cells; furthermore, during the steam-heated melt-bonding stage, the ethylene copolymer elastomer can lower the melting temperature, completing the melt bonding at a lower steam pressure; and by controlling the mass relationship between the foaming polymer and the ethylene copolymer elastomer, the foaming performance and mechanical properties of the material can be guaranteed. The results of the embodiments show that the foamable beads provided by the present invention can prepare pre-foamed beads with a cell diameter of 62μm and uniform size; the pre-foamed beads can be used to obtain bead foaming materials with tensile strength higher than 0.95MPa and fracture strain higher than 12.2% under a steam forming pressure of 0.22~0.28MPa. Attached Figure Description

[0019] Figure 1 This is a cross-sectional SEM image of the bead-foamed material obtained in Example 9 of the present invention; Figure 2 This is a cross-sectional SEM image of the bead-foamed material obtained in Example 11 of the present invention; Figure 3 This is a cross-sectional SEM image of the bead-foamed material obtained in Comparative Example 1 of the present invention. Detailed Implementation

[0020] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0021] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of industrial purity or those with conventional purity in the field of bead foaming materials.

[0022] The present invention provides foamable beads, comprising, by weight parts: 80-95 parts of foaming polymer, 5-20 parts of ethylene copolymer elastomer, and 2-10 parts of additives; wherein the foaming polymer is a linear or low-branched polymer, and the low-branched polymer is a polymer in which the branched units account for less than 0.1% of the polymer molecular weight.

[0023] The expandable beads provided by this invention comprise 80-95 parts, preferably 85-90 parts, of a foaming polymer by weight. The foaming polymer is the main material of the expandable beads, and the presence of the foaming polymer within the above-mentioned weight range ensures the foaming performance of the material.

[0024] In this invention, the foaming polymer is a linear or low-branched polymer, wherein the low-branched polymer is a polymer in which the branched units account for less than 0.1% of the polymer molecular weight.

[0025] In this invention, the foaming polymer preferably includes one or more of polypropylene, polyethylene, and polylactic acid, more preferably polypropylene. Polypropylene, polyethylene, and polylactic acid are common foaming polymers, and using these polymers as foaming polymers is beneficial for further improving foaming stability.

[0026] Based on 80-95 parts by weight of the foaming polymer, the foamable beads provided by the present invention include 5-20 parts, preferably 10-15 parts, of ethylene copolymer elastomer. Using ethylene copolymer elastomers as long-chain branched or low-crystallinity components, physical entanglement occurs with linear or low-branched foaming polymer molecular chains, significantly improving the melt strength and strain hardening behavior of the blend system at processing temperatures. This ensures that the cell walls are less prone to rupture under rapid stretching during the foaming stage, facilitating the formation of a uniform closed-cell structure. High melt strength guarantees the stability of these large cells during growth. The ethylene copolymer elastomers exhibit good compatibility with the foaming polymer, uniformly distributed as a submicron-sized dispersed phase within the continuous phase of the foaming polymer. Due to the difference in interfacial tension between the two phases, cells tend to nucleate heterogeneously at the interface rather than homogeneously within the homogeneous matrix phase, effectively controlling cell nucleation density without the need for additional nucleating agents. Furthermore, the ethylene copolymer elastomers possess a higher adsorption capacity and faster diffusion rate for physical foaming agents, allowing bubble nuclei to absorb foaming agents from a larger volume. This promotes the formation of larger and more uniformly distributed cells. During the steam heating and melting bonding stage, the ethylene copolymer elastomer enhances the viscosity and creep resistance of the molten layer on the surface of the pre-foamed beads, enabling a strong and dense welding interface between the pre-foamed beads at lower steam pressures. As a diluent, the ethylene copolymer elastomer penetrates the interlamellae of the foamed polymer, disrupting the regular arrangement of its molecular chains, thus interfering with nucleation and blocking crystallization space. This reduces the overall crystallinity and crystal perfection of the blend system, increasing the proportion of amorphous regions. During steam heating, more amorphous regions can achieve chain segment movement and surface melting at lower temperatures (corresponding to lower steam pressures), significantly reducing the energy barrier required for molding. The uniformly dispersed ethylene copolymer elastomer particles act as soft stress concentration points, inducing a large number of crazes and shear bands in the matrix under external force, consuming a large amount of impact energy. Simultaneously, its low T... gThe properties promote the movement of molecular chain segments at room temperature, changing the fracture mode of the material from brittle fracture to ductile fracture, and significantly improving the elongation at break.

[0027] In this invention, the ethylene copolymer elastomer preferably includes one or more of POE, ethylene propylene diene monomer (EPDM), ethylene propylene diene monomer (EPDM), ethylene-acrylate copolymer, ethylene-acrylic acid copolymer, and ethylene-vinyl acetate copolymer, more preferably ethylene propylene diene monomer (EPDM). These copolymers can act as diluents, penetrating between the lamellar crystals of the foaming polymer to further reduce the melting temperature; they can also adsorb more gaseous foaming agents, further improving foaming stability.

[0028] Based on 80-95 parts by weight of the foaming polymer, the foamable beads provided by this invention include 2-10 parts, preferably 5-8 parts, of additives. The additives can improve foaming performance and enhance foaming stability; when the mass fraction of the additives is within the above range, it ensures that the material has stable foaming performance.

[0029] In this invention, the additives preferably include 0.01-0.05 parts of zinc borate, 0.1-0.2 parts of antioxidant, 0.1-0.5 parts of EBS, and 1-5 parts of antistatic agent; as one embodiment of this invention, the antioxidant can be antioxidant 1010 and antioxidant 168; the antistatic agent can be glyceryl monostearate.

[0030] In this invention, the mass of the expandable beads is preferably 0.8~1.2 mg / bead, more preferably 0.9~1.1 mg / bead; in an embodiment of this invention, the mass of the expandable beads is 1 mg / bead. A mass of expandable beads within the above range is beneficial for stable foaming and further increases the cell diameter.

[0031] This invention uses ethylene copolymer elastomers as long-chain branched or low-crystallinity components, which physically entangle with linear or low-branched foaming polymer molecular chains. This significantly improves the melt strength and strain hardening behavior of the blend system at processing temperatures, ensuring that the cell walls are less prone to breakage during rapid stretching in the foaming stage, thus facilitating the formation of a uniform closed-cell structure. The high melt strength ensures the stability of these large cells during growth. The ethylene copolymer elastomers and foaming polymers exhibit good compatibility, with the elastomers uniformly distributed as submicron-sized dispersed phases within the continuous phase of the foaming polymer. Due to the difference in interfacial tension between the two phases, the cells tend to nucleate heterogeneously at the interface rather than homogeneously within the homogeneous matrix phase, effectively controlling the cell nucleation density without the need for additional nucleating agents. Furthermore, the ethylene copolymer elastomers have a higher adsorption capacity and faster diffusion rate for physical foaming agents, allowing the bubble nuclei to absorb foaming agents from a larger volume. This promotes the formation of larger and more uniformly distributed cells. During the steam-heated melting and bonding molding stage, the ethylene copolymer elastomer enhances the viscosity and creep resistance of the molten layer on the surface of the pre-foamed beads, enabling a strong and dense welding interface between the pre-foamed beads at lower steam pressures. As a diluent, the ethylene copolymer elastomer penetrates the interlamellae of the foamed polymer, disrupting the regular arrangement of its molecular chains, thus interfering with nucleation and blocking crystallization space. This reduces the overall crystallinity and crystal perfection of the blend system, increasing the proportion of amorphous regions. During steam heating, more amorphous regions can achieve chain segment movement and surface melting at lower temperatures (corresponding to lower steam pressures), significantly reducing the energy barrier required for molding. The uniformly dispersed ethylene copolymer elastomer particles act as soft stress concentration points, inducing a large number of crazes and shear bands in the matrix under external force, consuming a large amount of impact energy. Simultaneously, its low T... g The properties promote the movement of molecular chain segments at room temperature, changing the fracture mode of the material from brittle fracture to ductile fracture, and significantly improving the elongation at break.

[0032] The present invention also provides a method for preparing the foamable beads described in the above technical solution, comprising: mixing raw materials and then sequentially performing melt extrusion and granulation to obtain foamable beads; wherein the extrusion temperature of the melt extrusion is 150~220℃ and the die temperature is 170~190℃.

[0033] In this invention, the raw material is the same as the component of the foamable beads described in the above technical solution.

[0034] In this invention, the melt extrusion temperature is 150~220℃, and the die temperature is 170~190℃, preferably 180℃. Melt extrusion parameters within these ranges facilitate thorough mixing of raw materials and improve foaming stability.

[0035] The present invention does not impose any particular limitation on the granulation operation; the desired size of beads can be obtained by using conventional operations in the art.

[0036] The preparation method provided by this invention is simple, easy to control, requires no special equipment, and is conducive to large-scale production.

[0037] This invention also provides a method for preparing bead-based foamed materials, comprising the following steps: The foamable beads described in the above technical solution are mixed with a gaseous foaming agent and saturated, then depressurized and foamed to obtain pre-foamed beads; the saturation temperature is 120~200℃, the saturation gas pressure is 1~4MPa, and the saturation time is 10~40min. The pre-foamed beads are molded to obtain bead foam material; the steam pressure used for the molding is 0.22~0.28MPa.

[0038] The present invention mixes the foamable beads with a gaseous foaming agent to saturate them, and then depressurizes and foams them to obtain pre-foamed beads.

[0039] In this invention, the gaseous foaming agent preferably includes one or more of carbon dioxide, nitrogen, isobutylene, and n-heptane, more preferably carbon dioxide. These gases are all conventional gaseous foaming agents in the art, and using them facilitates stable foaming.

[0040] In this invention, the saturation temperature is 120~200℃, preferably 130~160℃; as one embodiment of this invention, the saturation temperature can be 126℃, 135℃, 140℃, 146℃, 148℃, 150℃, 151℃, 170℃, or 190℃. A saturation temperature within the above range can soften the polymer, allowing the gaseous foaming agent to dissolve and diffuse into the amorphous regions of the polymer, thus providing conditions for foaming.

[0041] In this invention, the saturated gas pressure is 1-4 MPa, preferably 2-3 MPa; in embodiments of this invention, the saturated gas pressure is 2.8 MPa or 3.5 MPa. A saturated gas pressure within the above range allows the gaseous foaming agent to dissolve and diffuse into the amorphous region of the polymer under pressure, providing conditions for foaming.

[0042] In this invention, the saturation time is 10-40 minutes, preferably 20-30 minutes; in an embodiment of this invention, the saturation time is 25 minutes. A saturation time within the above range allows the gaseous foaming agent to dissolve and diffuse into the amorphous region of the polymer under pressure, reaching a saturated state and providing conditions for foaming.

[0043] In an embodiment of the present invention, foamable beads can be placed in a high-pressure reactor, a gaseous foaming agent is continuously introduced, and the mixture is heated until the saturation temperature and pressure are reached, and the mixture is kept at a constant temperature and pressure until saturation is achieved.

[0044] The present invention does not have any particular limitation on the operation of the pressure relief foaming, and conventional pressure relief foaming methods in the art can be used.

[0045] As one embodiment of the present invention, after the pressure relief foaming, the resulting product can be dehydrated and dried to obtain pre-foamed beads; the present invention does not particularly limit the specific parameters of the dehydration and drying, as long as the moisture in the pre-foamed beads can be removed.

[0046] After obtaining the pre-foamed beads, the present invention molds the pre-foamed beads to obtain bead foaming material.

[0047] In this invention, the steam pressure used for compression molding is 0.22~0.28 MPa, preferably 0.24~0.28 MPa; as one embodiment of this invention, the steam pressure can be 0.22 MPa, 0.24 MPa, 0.26 MPa, or 0.28 MPa. This invention can achieve melt bonding at relatively low steam pressure and give the material better mechanical properties.

[0048] In this invention, the heat preservation time for molding is preferably 10-60s, more preferably 30-50s; as one embodiment of this invention, the heat preservation time for molding can be 15s, 20s, 25s, 30s, 35s, 45s, or 55s. A heat preservation time within the above range is beneficial for the bonding of the pre-foamed beads.

[0049] As one embodiment of the present invention, the foaming ratio of the foaming material can be 15 to 20 times, specifically 15 times.

[0050] The preparation method provided by this invention can produce beaded foam materials with high tensile properties under relatively low steam pressure.

[0051] The present invention also provides a beaded foaming material prepared by the preparation method described in the above technical solution.

[0052] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0053] Example 1 A type of foamable beads, by mass parts, is composed of the following components: 95 parts linear polypropylene (molecular weight 80,000~150,000), 5 parts ethylene propylene diene monomer (EPDM) rubber (ExxonMobil Vistalon 722, melt index 1 g / 10 min), 0.01 parts zinc borate, 0.08 parts antioxidant 1010, 0.08 parts antioxidant 168, 0.3 parts EBS, and 4.5 parts antistatic agent glyceryl monostearate.

[0054] The preparation method is as follows: after mixing the raw materials, they are sequentially melt-extruded and granulated to obtain beads with a mass of 1 mg / bead; the extrusion temperature of the melt extrusion is 150~220℃, and the die temperature is 180℃.

[0055] Example 2 A type of foamable beads, by mass parts, is composed of the following components: 90 parts of linear polypropylene (molecular weight 80,000~150,000), 10 parts of ethylene propylene diene monomer (EPDM) rubber (ExxonMobil Vistalon 722, melt index 1 g / 10 min), 0.01 parts of zinc borate, 0.08 parts of antioxidant 1010, 0.08 parts of antioxidant 168, 0.3 parts of EBS, and 4.5 parts of antistatic agent glyceryl monostearate.

[0056] The preparation method is as follows: after mixing the raw materials, they are sequentially melt-extruded and granulated to obtain beads with a mass of 1 mg / bead; the extrusion temperature of the melt extrusion is 150~220℃, and the die temperature is 180℃.

[0057] Example 3 A type of foamable beads, by mass parts, is composed of the following components: 85 parts of linear polypropylene (molecular weight 80,000~150,000), 15 parts of ethylene propylene diene monomer (EPDM) rubber (ExxonMobil Vistalon 722, melt index 1 g / 10 min), 0.01 parts of zinc borate, 0.08 parts of antioxidant 1010, 0.08 parts of antioxidant 168, 0.3 parts of EBS, and 4.5 parts of antistatic agent glyceryl monostearate.

[0058] The preparation method is as follows: after mixing the raw materials, they are sequentially melt-extruded and granulated to obtain beads with a mass of 1 mg / bead; the extrusion temperature of the melt extrusion is 150~220℃, and the die temperature is 180℃.

[0059] Example 4 A type of foamable beads, by mass parts, is composed of the following components: 80 parts linear polypropylene (molecular weight 80,000~150,000), 20 parts ethylene propylene diene monomer (EPDM) rubber (ExxonMobil Vistalon 722, melt index 1g / 10min), 0.01 parts zinc borate, 0.08 parts antioxidant 1010, 0.08 parts antioxidant 168, 0.3 parts EBS, and 4.5 parts antistatic agent glyceryl monostearate.

[0060] The preparation method is as follows: after mixing the raw materials, they are sequentially melt-extruded and granulated to obtain beads with a mass of 1 mg / bead; the extrusion temperature of the melt extrusion is 150~220℃, and the die temperature is 180℃.

[0061] Example 5 A type of foamable beads, by mass parts, is composed of the following components: 90 parts linear polypropylene (molecular weight 80,000~150,000), 10 parts POE (ExxonMobil 6102FL, melt index 1.4 g / 10 min), 0.01 parts zinc borate, 0.08 parts antioxidant 1010, 0.08 parts antioxidant 168, 0.3 parts EBS, and 4.5 parts antistatic agent glyceryl monostearate.

[0062] The preparation method is as follows: after mixing the raw materials, they are sequentially melt-extruded and granulated to obtain beads with a mass of 1 mg / bead; the extrusion temperature of the melt extrusion is 150~220℃, and the die temperature is 180℃.

[0063] Example 6 A type of foamable beads, by mass parts, is composed of the following components: 90 parts of linear polypropylene (molecular weight 80,000~150,000), 10 parts of ethylene-vinyl acetate copolymer (Mitsui EV150, melt index 43 g / 10 min), 0.01 parts of zinc borate, 0.08 parts of antioxidant 1010, 0.08 parts of antioxidant 168, 0.3 parts of EBS, and 4.5 parts of antistatic agent glyceryl monostearate.

[0064] The preparation method is as follows: after mixing the raw materials, they are sequentially melt-extruded and granulated to obtain beads with a mass of 1 mg / bead; the extrusion temperature of the melt extrusion is 150~220℃, and the die temperature is 180℃.

[0065] Example 7 A type of foamable beads, by mass parts, is composed of the following components: 90 parts of polylactic acid (molecular weight 100,000~150,000), 10 parts of ethylene propylene diene monomer (EPDM) rubber (ExxonMobil Vistalon 722, melt index 1g / 10min), 0.01 parts of zinc borate, 0.08 parts of antioxidant 1010, 0.08 parts of antioxidant 168, 0.3 parts of EBS, and 4.5 parts of antistatic agent glyceryl monostearate.

[0066] The preparation method is as follows: after mixing the raw materials, they are sequentially melt-extruded and granulated to obtain beads with a mass of 1 mg / bead; the extrusion temperature of the melt extrusion is 150~220℃, and the die temperature is 180℃.

[0067] Example 8 A method for preparing a beaded foam material, comprising the following steps: The expandable beads from Example 1 were placed in a high-pressure reactor, carbon dioxide was continuously introduced, and the temperature was raised until it reached 150°C and the pressure reached 2.8 MPa. The temperature and pressure were maintained for 20 minutes to achieve saturation. Open the discharge valve of the high-pressure reactor to release pressure and foam, and dehydrate and dry the product to obtain pre-foamed beads; The pre-foamed beads are placed in a molding mold, and 0.28MPa high-pressure steam is introduced to melt and bond them for 30 seconds to obtain a bead foam material with a foaming ratio of 15 times.

[0068] Example 9 A method for preparing a beaded foam material, using the foamable beads provided in Example 2, with the same preparation process and parameters as in Example 8.

[0069] Example 10 A method for preparing a beaded foaming material, using the foamable beads provided in Example 3, with the same preparation process and parameters as in Example 8.

[0070] Example 11 A method for preparing a beaded foaming material, using the foamable beads provided in Example 4, with the same preparation process and parameters as in Example 8.

[0071] Example 12 A method for preparing a beaded foam material, the raw materials, preparation process and parameters are the same as in Example 8, except that 0.26MPa high-pressure steam is introduced.

[0072] Example 13 A method for preparing a beaded foam material, the raw materials, preparation process and parameters are the same as in Example 8, except that 0.24MPa high-pressure steam is introduced.

[0073] Example 14 A method for preparing a beaded foam material, the raw materials, preparation process and parameters are the same as in Example 9, except that 0.26MPa high-pressure steam is introduced.

[0074] Example 15 A method for preparing a beaded foam material, the raw materials, preparation process and parameters are the same as in Example 9, except that 0.24MPa high-pressure steam is introduced.

[0075] Example 16 A method for preparing a beaded foam material, the raw materials, preparation process and parameters are the same as in Example 9, except that 0.22MPa high-pressure steam is introduced.

[0076] Example 17 A method for preparing a beaded foam material, comprising the following steps: The expandable beads from Example 5 were placed in a high-pressure reactor, carbon dioxide was continuously introduced, and the temperature was increased until the temperature reached 148°C and the pressure reached 2.8 MPa. The temperature and pressure were maintained for 20 minutes to achieve saturation. Open the discharge valve of the high-pressure reactor to release pressure and foam, and dehydrate and dry the product to obtain pre-foamed beads; The pre-foamed beads are placed in a molding mold, and 0.28MPa high-pressure steam is introduced to melt and bond them for 30 seconds to obtain a bead foam material with a foaming ratio of 15 times.

[0077] Example 18 A method for preparing a beaded foam material, the raw materials, preparation process and parameters are the same as in Example 17, except that 0.26MPa high-pressure steam is introduced.

[0078] Example 19 A method for preparing a beaded foam material, comprising the following steps: The expandable beads from Example 6 were placed in a high-pressure reactor, carbon dioxide was continuously introduced, and the temperature was increased until the temperature reached 151°C and the pressure reached 2.8 MPa. The temperature and pressure were maintained for 20 minutes to achieve saturation. Open the discharge valve of the high-pressure reactor to release pressure and foam, and dehydrate and dry the product to obtain pre-foamed beads; The pre-foamed beads are placed in a molding mold, and 0.26MPa high-pressure steam is introduced to melt and bond them for 30 seconds to obtain a bead foam material with a foaming ratio of 15 times.

[0079] Example 20 A method for preparing a beaded foam material, comprising the following steps: The expandable beads from Example 7 were placed in a high-pressure reactor, carbon dioxide was continuously introduced, and the temperature was raised until it reached 126°C and the pressure reached 3.5 MPa. The temperature and pressure were maintained for 20 minutes to achieve saturation. Open the discharge valve of the high-pressure reactor to release pressure and foam, and dehydrate and dry the product to obtain pre-foamed beads; The pre-foamed beads are placed in a molding mold, and 0.26MPa high-pressure steam is introduced to melt and bond them for 30 seconds to obtain a bead foam material with a foaming ratio of 15 times.

[0080] Comparative Example 1 A beaded foam material, by mass parts, is composed of the following components: 100 parts linear polypropylene (molecular weight 80,000~150,000), 0.01 parts zinc borate, 0.08 parts antioxidant 1010, 0.08 parts antioxidant 168, 0.3 parts EBS, and 4.5 parts antistatic agent glyceryl monostearate.

[0081] The foamed material was prepared according to the foaming method of Example 8.

[0082] Comparative Example 2 A beaded foam material, by mass parts, is composed of the following components: 100 parts polylactic acid (molecular weight 80,000~150,000), 0.01 parts zinc borate, 0.08 parts antioxidant 1010, 0.08 parts antioxidant 168, 0.3 parts EBS, and 4.5 parts antistatic agent glyceryl monostearate.

[0083] The foamed material was prepared according to the foaming method of Example 20.

[0084] Test Example 1 Cross sections of the bead-foamed materials obtained in Examples 9, 11, and Comparative Example 1 were observed using a scanning electron microscope (SEM) to obtain SEM images, as shown below. Figures 1-3 As shown.

[0085] from Figure 1 , Figure 2 It can be seen that the bead foam materials obtained in Examples 9 and 11 have uniform pores with a pore diameter of approximately 60 μm.

[0086] from Figure 3 It can be seen that the bead foam material obtained in Comparative Example 1 has uneven cell size, with a cell diameter of approximately 10~20μm.

[0087] Test Example 2 SEM images were taken using a scanning electron microscope. The cell diameter of the bead foam materials obtained in Examples 9, 11, 17, 19, 20 and Comparative Examples 1 and 2 was detected using Image-Pro Plus software. The test results are recorded in Table 1.

[0088] Table 1. Test Record of Cell Diameter of Different Beaded Foaming Materials

[0089] Test Example 3 The mechanical properties of the bead foam materials obtained in Examples 8-19 and Comparative Example 1 were tested according to GB / T 9641-2025, and the test results are recorded in Table 2.

[0090] Table 2. Mechanical property test record of different bead foaming materials

[0091] By comparing Examples 8-11 with Comparative Example 1, it can be seen that, under the same conditions of controlling the extruder temperature, reactor foaming temperature, reactor foaming pressure, steam pressure, and holding time, the tensile strength and breaking strain of the 15x polypropylene bead foam material obtained by adding EPDM rubber are both improved. Therefore, adding EPDM rubber can improve the tensile properties of polypropylene bead foam material. However, when the weight ratio of polypropylene to EPDM rubber is 85:15 and 80:20, the tensile strength of the 15x polypropylene bead foam material rapidly decreases to the level without the addition of EPDM rubber, but the breaking strain does not decrease. Therefore, attention should be paid to the amount of EPDM rubber added, as excessive addition will lead to a decrease in the tensile properties of polypropylene bead foam material.

[0092] By comparing Examples 12 and 13 with Comparative Example 1, it can be seen that when the mass ratio of polypropylene to ethylene propylene diene monomer (EPDM) rubber is 95:5 and the steam pressure is reduced to 0.24 MPa, the tensile properties of the polypropylene bead foam material are similar to those of the polypropylene bead foam material without EPDM rubber. In fields where tensile properties are not strictly required, the addition of EPDM rubber can effectively reduce the steam pressure required for compression molding, save energy, reduce processing costs, and lower the requirements for molding equipment.

[0093] By comparing Examples 14-16 with Comparative Example 1, it can be seen that when the mass ratio of polypropylene to ethylene propylene diene monomer (EPDM) rubber is 90:10 and the steam pressure is reduced to 0.22 MPa, the tensile properties of the polypropylene bead foam material are similar to those of the polypropylene bead foam material without EPDM rubber, but the fracture strain value is twice that of the polypropylene bead foam material with EPDM rubber.

[0094] By comparing Examples 17-19 with Comparative Example 1, it can be seen that adding ethylene copolymer elastomers (such as POE and ethylene-vinyl acetate copolymer) similar to ethylene propylene diene monomer (EPDM) to polypropylene can also improve the tensile properties of polypropylene bead foam and reduce the steam pressure required for compression molding.

[0095] By comparing Example 20 with Comparative Example 2, it can be seen that POE has the same working principle in polylactic acid. It can expand the cell structure of polylactic acid foam material, improve the tensile properties of polylactic acid foam material, reduce the steam pressure required for compression molding, save energy, reduce processing costs and requirements for molding equipment.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A type of expandable beads, comprising, by weight parts: The foaming polymer comprises 80-95 parts, ethylene copolymer elastomer comprises 5-20 parts, and additives comprises 2-10 parts; the foaming polymer is a linear or low-branched polymer, wherein the low-branched polymer is a polymer in which the branched units account for less than 0.1% of the polymer molecular weight.

2. The expandable beads according to claim 1, characterized in that, The foaming polymer includes one or more of polypropylene, polyethylene, and polylactic acid.

3. The expandable beads according to claim 1, characterized in that, The ethylene copolymer elastomers include one or more of the following: polyolefin elastomers, ethylene propylene diene monomer (EPDM) rubber, ethylene propylene diene monomer (EPDM) rubber, ethylene-acrylate copolymers, ethylene-acrylic acid copolymers, and ethylene-vinyl acetate copolymers.

4. The expandable beads according to claim 1, characterized in that, The additives include 0.01-0.05 parts zinc borate, 0.1-0.2 parts antioxidant, 0.1-0.5 parts ethylene bis-stearamide, and 1-5 parts antistatic agent.

5. The expandable beads according to claim 1, characterized in that, The mass of the foamable beads is 0.8~1.2 mg / bead.

6. The method for preparing the foamable beads according to any one of claims 1 to 5, characterized in that, include: The raw materials are mixed and then melt-extruded and granulated in sequence to obtain foamable beads. The extrusion temperature of the melt extrusion is 150~220℃, and the die temperature is 170~190℃.

7. A method for preparing a beaded foam material, comprising the following steps: The expandable beads are mixed with a gaseous foaming agent and saturated, then depressurized and foamed to obtain pre-foamed beads; the saturation temperature is 120~200℃, the saturation gas pressure is 1~4MPa, and the saturation time is 10~40min; the expandable beads are the expandable beads according to any one of claims 1 to 5 or the expandable beads prepared by the preparation method according to claim 6. The pre-foamed beads are molded to obtain bead foam material; the steam pressure used for the molding is 0.22~0.28MPa.

8. The preparation method according to claim 7, characterized in that, The heat preservation time for the molding process is 10~60s.

9. The preparation method according to claim 7, characterized in that, The gaseous foaming agent includes one or more of carbon dioxide, nitrogen, isobutylene, and n-heptane.

10. The beaded foam material prepared by the preparation method according to any one of claims 7 to 9.

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