A thermoplastic melt blown foaming method, melt blown foaming composite

Abstract

The application provides a thermoplastic melt-blown foaming method and a melt-blown foaming composite material. The thermoplastic melt-blown foaming method comprises the following steps: mixing a thermoplastic material with thermal expansion microspheres to obtain a mixture; heating and melting the mixture and continuously conveying the mixture to a melt-blown nozzle to obtain a molten mixture; spraying the molten mixture from the melt-blown nozzle and depositing the molten mixture on a carrier under the action of an auxiliary airflow to form a preformed embryo after cooling; performing thermal foaming treatment on the preformed embryo to obtain a thermal foaming embryo with a primary cell skeleton formed by thermal expansion of the thermal expansion microspheres; and performing supercritical high-pressure fluid treatment on the thermal foaming embryo and releasing pressure after the treatment to obtain a foaming product with secondary micropores. The melt-blown foaming method can improve the problems of limited pore source of traditional melt-blown materials and insufficient cushioning and rebound performance.

Description

Technical Field

[0001] This invention relates to the field of thermoplastic material meltblown foaming technology, specifically to a thermoplastic material meltblown foaming method and a meltblown foamed composite material. Background Technology

[0002] Existing thermoplastic polyurethane meltblowing methods typically utilize high-pressure gas flow to draw molten thermoplastic polyurethane into microfibers, which are then stacked on a carrier or receiving surface to form a porous network structure. This type of structure can achieve a certain degree of lightweighting and flexibility, but its porosity primarily originates from the gaps between the fibers rather than from the foaming pores formed within the material itself. Therefore, under pressure, this type of material mainly relies on the compression of the fiber network and the compaction of the gaps between fibers for cushioning, lacking a large number of uniformly sized pores to participate in elastic compression and recovery. Consequently, its cushioning and resilience performance is inferior to that of conventional thermoplastic polyurethane foam materials. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned defects or problems in the prior art and to provide a method for meltblown foaming of thermoplastic materials and a meltblown foamed composite material. This meltblown foaming method can improve the cushioning and rebound performance of meltblown foamed materials.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for melt-blown foaming of thermoplastic materials includes: S10, mixing thermoplastic materials with thermally expandable microspheres to obtain a mixture; S20, heating and melting the mixture, and continuously conveying the molten material to a melting nozzle to obtain a molten mixture; S30, spraying the molten mixture from the melting nozzle and depositing it on a carrier under the action of an auxiliary airflow, and cooling it to form a preform; S40, performing thermal foaming treatment on the preform to obtain a thermally foamed preform with a primary cell skeleton formed by the expansion of the thermally expandable microspheres; S50, treating the thermally foamed preform with a supercritical high-pressure fluid, and depressurizing after the supercritical high-pressure fluid treatment to obtain a foamed product with secondary micropores.

[0005] In the above preparation method, this invention addresses the problem that the pores of existing thermoplastic meltblown layers mainly originate from fiber packing voids and the material itself lacks foaming pores. In S10, the thermoplastic material is mixed with thermally expandable microspheres, so that the meltblown deposition layer pre-contains foaming units capable of forming foaming pores in the material itself. Therefore, the pore source of the meltblown layer is not limited to fiber gaps or melt deposition gaps, but can further form a foaming structure within the thermoplastic material through the expansion of the thermally expandable microspheres. This provides a foundation for improving the problem that traditional meltblown materials mainly rely on the compaction of fiber webs for buffering.

[0006] However, thermally expandable microspheres cannot be simply and directly added to the meltblown system to complete foaming. Meltblown deposition requires thermoplastic materials to form a fluid molten mixture at a high temperature and continuously convey it to the meltblown nozzle; however, thermally expandable microspheres tend to expand when heated. If they expand significantly before meltblowing or at the moment of ejection, it can easily affect melt delivery, spraying stability, and the thickness and contour of the deposited layer. Therefore, in S20 and S30 of this invention, the mixture is first heated and melted, continuously conveyed, meltblown deposited, and cooled and shaped, so that the meltblown step mainly undertakes the functions of deposition shaping and preform construction, while the main expansion time of the thermally expandable microspheres is postponed until after the preform is formed.

[0007] Building upon this, the present invention performs thermal foaming treatment on the preform in S40, causing the thermally expandable microspheres to expand within the already deposited thermoplastic material layer, forming a primary cell framework. This primary cell framework transforms the meltblown deposition layer from a porous structure formed solely by fiber accumulation voids or deposition gaps into a structure with bulk material foaming characteristics, thereby providing a buffer and rebound basis for the foamed product to compress and recover under pressure through the cells.

[0008] Furthermore, relying solely on thermal expansion microspheres for foaming may still result in cells that are too large in size, not finely distributed, and have limited expansion ratio. Therefore, this invention involves treating the thermally foamed preform with supercritical high-pressure fluid in step S50 and then depressurizing it. This allows the supercritical fluid to enter the interior of the thermally foamed preform based on the aforementioned primary cell framework, forming secondary micropores during the depressurization process. The primary cell framework provides a channel and interface for the supercritical fluid to enter the thick material, while the secondary micropores further refine the cell structure and improve cell uniformity.

[0009] Therefore, by sequentially coordinating S10 to S50, the present invention retains the advantages of meltblown technology for continuous deposition and carrier forming, while enabling the meltblown layer to obtain a foamed structure in the material body, thereby improving the problem of insufficient buffering and rebound performance of traditional meltblown materials due to limited pore sources.

[0010] In at least one embodiment of the thermoplastic material meltblown foaming method, preferably, the thermoplastic material includes thermoplastic polyurethane, wherein the thermoplastic polyurethane is one or more of polyester-type thermoplastic polyurethane, polyether-type thermoplastic polyurethane, and polycarbonate-type thermoplastic polyurethane; the thermally expandable microspheres include a thermoplastic shell and a low-boiling-point hydrocarbon core material, wherein the low-boiling-point hydrocarbon core material is one or more of isobutane and pentane.

[0011] In the above preparation method, thermoplastic polyurethane has good elasticity, abrasion resistance, melt processability, and resilience, making it suitable for forming foam layers for cushioning and support in footwear. The thermally expandable microspheres, using a thermoplastic shell and a low-boiling-point hydrocarbon core, can form a primary cell framework within the thermoplastic material during thermal foaming through core material vaporization and shell expansion, providing a foundation for subsequent secondary micropore formation.

[0012] In at least one embodiment of the thermoplastic material meltblown foaming method, preferably, in step S10, 90wt% to 98wt% of the thermoplastic material and 2wt% to 10wt% of the thermally expanded microspheres are dry-mixed, master-granulated, or metered-mixed based on the total mass of the thermoplastic material and the thermally expanded microspheres.

[0013] In the above preparation method, the content of thermoplastic material and thermally expandable microspheres is limited to the aforementioned range, which ensures that a sufficient number of thermally expandable microspheres in the preform participate in subsequent thermal foaming while maintaining the melt continuity and deposition formability of the thermoplastic material. Dry mixing, masterbatch mixing, or online metering mixing can all achieve the metered combination of thermoplastic material and thermally expandable microspheres, allowing the thermally expandable microspheres to be distributed in the molten mixture and then deposited onto the carrier together with the molten mixture.

[0014] In at least one embodiment of the thermoplastic material meltblown foaming method, preferably, in step S20, the heating and melting temperature is 160°C to 190°C, and the melt index of the melt mixture is 180 g / 10 min to 220 g / 10 min; the melt mixture remains in a continuous melt state from the completion of heating and melting until it is sprayed out by the melt nozzle.

[0015] In the above preparation method, the heating and melting temperature and melt index are limited to a range suitable for melt-blown deposition, so that the molten mixture can be continuously conveyed to the melting nozzle and ejected from the nozzle after heating and melting. The molten mixture remains in a continuous melt state before ejection, which is beneficial for the melt-blown deposition process to form a continuous or semi-continuous preform, providing a material basis with a predetermined thickness and profile for the subsequent thermal foaming to form the primary cell skeleton.

[0016] In at least one embodiment of the thermoplastic meltblown foaming method, preferably, in step S30, the distance between the meltblown nozzle and the carrier is 50mm to 150mm, the pressure of the auxiliary airflow is 0.2MPa to 1MPa, and the temperature of the auxiliary airflow is room temperature to 240°C.

[0017] In the above preparation method, the distance between the melting nozzle and the carrier, the auxiliary gas flow pressure, and the auxiliary gas flow temperature jointly affect the stretching, spreading, cooling, and deposition thickness of the molten mixture from ejection to deposition. Limiting these parameters within the appropriate range is beneficial for forming a preform with controllable thickness and shape, allowing subsequent thermal foaming and supercritical high-pressure fluid treatment to be carried out in the already deposited material layer.

[0018] In at least one embodiment of the thermoplastic material meltblown foaming method, preferably, in step S30, the auxiliary gas flow is air, nitrogen, carbon dioxide or a mixture thereof; the molten mixture is deposited on the carrier in the form of melt spray, melt jet, short fibrous melt or semi-continuous melt.

[0019] In the above preparation method, the auxiliary gas flow can be selected from air, nitrogen, carbon dioxide, or a mixture thereof, depending on the process requirements, to adapt to different deposition environments and material systems. The molten mixture is deposited on the carrier in the form of molten spray, melt jet, short fibrous melt, or semi-continuous melt. Therefore, the above meltblown deposition is not limited to the traditional microfiber stacking network, but allows the formation of a melt-blown deposition layer that can support the subsequent bulk foaming of the material, thus providing a process basis for the transformation of the meltblown deposition layer from a fiber-stacking porous structure to a bulk foaming structure.

[0020] In at least one embodiment of the thermoplastic material meltblown foaming method, preferably, in step S30, the carrier is a porous substrate; before step S30, the porous substrate is preheated to 60°C to 80°C, and the molten mixture enters the pores of the porous substrate during deposition.

[0021] In the above preparation method, when the carrier is a porous substrate, the preheated porous substrate can reduce the temperature drop when the molten mixture contacts the carrier, allowing the molten mixture to enter the pores of the porous substrate during deposition. After cooling and subsequent foaming, a pore interlocking relationship can be formed between the thermoplastic foam layer and the porous substrate, thereby combining the meltblown foam layer and the carrier substrate into a composite structure, reducing the dependence of the separate bonding process on interface bonding.

[0022] In at least one embodiment of the thermoplastic material meltblown foaming method, preferably, in step S40, the temperature of the thermal foaming treatment is 120°C to 150°C, the time is 5 min to 10 min, the foaming ratio of the thermally foamed preform is 3 to 6 times, and the density is 0.20 g / cm³ to 0.35 g / cm³.

[0023] In the above preparation method, under the aforementioned thermal foaming temperature and time, the thermally expandable microspheres in the preform can expand and form a primary cell framework in the thermoplastic material, giving the thermally foamed preform a foaming ratio of 3 to 6 times and a density of 0.20 g / cm³ to 0.35 g / cm³. This primary cell framework not only provides a preliminary lightweight and cushioning structure, but also provides channels and interfaces for the subsequent entry of supercritical high-pressure fluid into the thermally foamed preform and the formation of secondary micropores.

[0024] In at least one embodiment of the thermoplastic material meltblown foaming method, preferably, in step S50, the supercritical high-pressure fluid is carbon dioxide, nitrogen, or a mixture of carbon dioxide and nitrogen; the temperature of the supercritical high-pressure fluid treatment is 100℃~140℃, the pressure is 20MPa~25MPa, and the time is 8min~20min; the pressure relief is to reduce the treatment pressure to atmospheric pressure.

[0025] In the above preparation method, the supercritical high-pressure fluid can enter the thermally expanded foam preform under the aforementioned temperature, pressure, and time conditions, and form secondary micropores during the depressurization process. Since the thermally expanded foam preform already possesses a primary cell framework formed by the expansion of thermally expanded microspheres, the supercritical high-pressure fluid can further act on the thermoplastic matrix and cell wall regions based on this primary cell framework, thereby enabling the foamed product to obtain a secondary microporous structure on the basis of the primary cell framework. This secondary microporous structure can improve the problem of excessively large or unevenly distributed cells during individual thermal foaming, giving the foamed product a finer cell structure and a better cushioning and rebound foundation.

[0026] The present invention also provides a meltblown foamed composite material, which is prepared by the meltblown foaming method of thermoplastic material described in any one of the above claims, and the meltblown foamed composite material includes a carrier substrate and a thermoplastic foam layer meltblownly deposited on the carrier substrate.

[0027] In the aforementioned meltblown foamed composite material, the thermoplastic foam layer is formed on the carrier substrate through meltblown deposition, and then subjected to thermal foaming and supercritical high-pressure fluid treatment to form a foamed structure. Therefore, this meltblown foamed composite material possesses both the shape adaptability provided by meltblown deposition and the lightweight and cushioning resilience properties provided by the internal pore structure of the thermoplastic foam layer. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments are briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1This is a schematic flowchart of the thermoplastic material meltblown foaming method according to an embodiment of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] In the claims, description and accompanying drawings of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0032] Reference Figure 1 The present invention relates to a method for meltblown foaming of thermoplastic materials, which mainly includes the following steps: S10, mix thermoplastic material with thermally expanded microspheres to obtain a mixture; S20, the mixture is heated and melted, and the heated and melted material is continuously conveyed to the melting nozzle to obtain a molten mixture; S30, the molten mixture is ejected from the melting nozzle and deposited on the carrier under the action of auxiliary airflow, and cooled to form a preform; S40, the preform is subjected to thermal foaming treatment to obtain a thermally foamed preform having a primary pore skeleton formed by the expansion of the thermally expanded microspheres. S50, the thermally foamed embryo is subjected to supercritical high-pressure fluid treatment, and the pressure is released after the supercritical high-pressure fluid treatment to obtain a foamed product with secondary micropores.

[0033] The following is a detailed explanation of each of the above steps.

[0034] In step S10, the thermoplastic material is mixed with thermally expanded microspheres to obtain a mixture. The thermoplastic material can be a thermoplastic elastomer capable of melt processing and suitable for melt-blown deposition, preferably thermoplastic polyurethane. The thermally expanded microspheres can be thermally expanded microspheres with a thermoplastic shell and a low-boiling-point hydrocarbon core. During mixing, the thermoplastic material can be dried first, and then the thermally expanded microspheres can be added according to a predetermined mass ratio. The mixture can be formed by dry mixing, masterbatch mixing, or online metering mixing. Dry mixing can be carried out in a low-speed mixer to allow the thermally expanded microspheres to adhere to and distribute between the thermoplastic material particles. Masterbatch mixing can be carried out by first preparing a microsphere-containing masterbatch from a portion of the thermoplastic material and thermally expanded microspheres, and then mixing it with the remaining thermoplastic material. Online metering mixing can be achieved by feeding the thermoplastic material and thermally expanded microspheres through a main feeder and a side feeder, respectively, so that the two are metered and combined before entering the heating and melting process.

[0035] In step S10, based on the total mass of the thermoplastic material and the thermally expanded microspheres, the content of the thermoplastic material can be 90wt% to 98wt%, and the content of the thermally expanded microspheres can be 2wt% to 10wt%. If the amount of thermally expanded microspheres is too low, the number of foaming units forming the primary cell skeleton in the preform will be insufficient; if the amount of thermally expanded microspheres is too high, the melt continuity and deposition stability of the mixture during subsequent heating, melting, and meltblowing deposition processes will be easily affected. Limiting the thermally expanded microspheres to the above range is beneficial in maintaining the meltblownability of the thermoplastic material while enabling the subsequent thermal foaming process to form a primary cell skeleton distributed within the thermoplastic material.

[0036] In step S20, the mixture obtained in step S10 is heated and melted, and the molten material is continuously conveyed to the melting nozzle to obtain a molten mixture. Heating and melting can be performed using single-screw extrusion, twin-screw extrusion, plunger-type melt conveying, or other processing methods capable of continuously outputting molten material. The heating and melting temperature can be 160℃~190℃, preferably with a melt index of 180g / 10min~220g / 10min. When the melt index is within this range, the molten mixture can continuously reach the melting nozzle and be carried out under the action of auxiliary airflow, while simultaneously forming a continuous or semi-continuous deposition layer on the carrier.

[0037] In step S20, the mixture transforms from a solid particle or masterbatch state into a molten mixture, with the thermally expanded microspheres entering the molten mixture along with the thermoplastic material. The molten mixture remains in a continuous melt state from the point of heating and melting until it is ejected from the melt nozzle. This continuous melt state allows the material to pass stably through the melt nozzle and enables the melt-blown deposition process to primarily perform deposition shaping and preform construction. During this stage, the thermally expanded microspheres are conveyed to the melt nozzle with the molten mixture, and subsequently expand to form the primary cell framework during the thermal foaming process in step S40.

[0038] In step S30, the molten mixture obtained in step S20 is ejected from the melting nozzle and deposited onto the carrier under the action of the auxiliary gas flow, then cooled to form a preform. The melting nozzle can be a slit-type melting nozzle, an array of multi-hole melting nozzles, or other melting nozzles capable of outputting the molten mixture. The distance between the melting nozzle and the carrier can be 50 mm to 150 mm. The pressure of the auxiliary gas flow can be 0.2 MPa to 1 MPa, and the temperature of the auxiliary gas flow can be from room temperature to 240°C. The auxiliary gas flow can be air, nitrogen, carbon dioxide, or a mixture thereof. A lower temperature of the auxiliary gas flow is beneficial for the rapid cooling and shaping of the deposited material; preheating the auxiliary gas flow can reduce the rate of temperature drop of the molten mixture during the ejection process, resulting in better spreadability and continuity of the deposited layer.

[0039] In step S30, the molten mixture can be deposited on the carrier in the form of molten spray, melt jet, short fibrous melt, or semi-continuous melt. These deposition forms all pertain to the material form during melt-blown deposition, enabling the formation of a preform suitable for subsequent foaming on the carrier. The carrier can be a mold carrier detached after molding, or a carrier substrate retained in the foamed product. When the carrier is a porous substrate, it can be preheated to 60°C–80°C before step S30, allowing the molten mixture to be deposited on its surface. Preheating the porous substrate reduces the temperature drop of the molten mixture upon contact with the carrier, allowing it to enter the pores of the porous substrate during deposition. After cooling, the molten mixture forms a preform on the surface and within the pores of the porous substrate.

[0040] In step S40, the preform obtained in step S30 is subjected to thermal foaming treatment to obtain a thermally foamed preform with a primary cell skeleton formed by the expansion of thermally expanded microspheres. The thermal foaming treatment can be performed using hot air heating, oven heating, infrared heating, a heating tunnel, or other methods that ensure uniform heating of the preform. The temperature of the thermal foaming treatment can be 120℃~150℃, and the time can be 5min~10min. Within this temperature and time range, the low-boiling-point hydrocarbon core material of the thermally expanded microspheres vaporizes upon heating, and the thermoplastic shell expands, forming a primary cell skeleton inside the preform. After step S40, the expansion ratio of the thermally foamed preform can be 3 to 6 times, and the density can be 0.20g / cm³~0.35g / cm³.

[0041] The primary cell skeleton obtained in step S40 is distributed in the thermoplastic material, transforming the preform from a meltblown deposition layer into a thermally foamed preform with bulk material cells. This primary cell skeleton reduces the density of the thermally foamed preform and provides an internal interface for fluid entry and action in subsequent supercritical high-pressure fluid processing. When the carrier is a porous substrate, step S40 also causes the thermoplastic material entering the pores of the porous substrate to expand and solidify along with the foaming layer, thereby forming an interlocking bond between the thermoplastic foaming layer and the carrier substrate.

[0042] In step S50, the thermally foamed preform obtained in step S40 is subjected to supercritical high-pressure fluid treatment, and the pressure is released after the supercritical high-pressure fluid treatment to obtain a foamed product with secondary micropores. The supercritical high-pressure fluid can be carbon dioxide, nitrogen, or a mixture of carbon dioxide and nitrogen. The temperature of the supercritical high-pressure fluid treatment can be 100℃~140℃, the pressure can be 20MPa~25MPa, and the time can be 8min~20min. After the treatment is completed, the treatment pressure is reduced to atmospheric pressure. The pressure release process can be carried out in one step or in stages, as long as the fluid entering the interior of the thermally foamed preform forms secondary micropores during the pressure reduction process.

[0043] In step S50, supercritical high-pressure fluid enters the interior of the thermally foamed preform and further forms secondary micropores based on the primary cell skeleton, cell wall region, and thermoplastic matrix formed in step S40. Compared with direct supercritical high-pressure fluid treatment of dense meltblown deposited layers, the primary cell skeleton in the thermally foamed preform provides a channel and interface for the supercritical high-pressure fluid to enter the material interior, making it easier for secondary micropores to form in the thickness direction. After the treatment in step S50, the foamed product has both a primary cell skeleton and secondary micropores, making it suitable for use as a thermoplastic foamed product or meltblown foamed composite material requiring buffering and rebound performance.

[0044] In the above preparation method, this invention addresses the problem that the pores of existing thermoplastic meltblown layers mainly originate from fiber packing voids and the material itself lacks foaming pores. In S10, the thermoplastic material is mixed with thermally expandable microspheres, so that the meltblown deposition layer pre-contains foaming units capable of forming foaming pores in the material itself. Therefore, the pore source of the meltblown layer is not limited to fiber gaps or melt deposition gaps, but can further form a foaming structure within the thermoplastic material through the expansion of the thermally expandable microspheres. This provides a foundation for improving the problem that traditional meltblown materials mainly rely on the compaction of fiber webs for buffering.

[0045] However, thermally expandable microspheres cannot be simply and directly added to the meltblown system to complete foaming. Meltblown deposition requires thermoplastic materials to form a fluid molten mixture at a high temperature and continuously convey it to the meltblown nozzle; however, thermally expandable microspheres tend to expand when heated. If they expand significantly before meltblowing or at the moment of ejection, it can easily affect melt delivery, spraying stability, and the thickness and contour of the deposited layer. Therefore, in S20 and S30 of this invention, the mixture is first heated and melted, continuously conveyed, meltblown deposited, and cooled and shaped, so that the meltblown step mainly undertakes the functions of deposition shaping and preform construction, while the main expansion time of the thermally expandable microspheres is postponed until after the preform is formed.

[0046] Building upon this, the present invention performs thermal foaming treatment on the preform in S40, causing the thermally expandable microspheres to expand within the already deposited thermoplastic material layer, forming a primary cell framework. This primary cell framework transforms the meltblown deposition layer from a porous structure formed solely by fiber accumulation voids or deposition gaps into a structure with bulk material foaming characteristics, thereby providing a buffer and rebound basis for the foamed product to compress and recover under pressure through the cells.

[0047] Furthermore, relying solely on thermal expansion microspheres for foaming may still result in cells that are too large in size, not finely distributed, and have limited expansion ratio. Therefore, this invention involves treating the thermally foamed preform with supercritical high-pressure fluid in step S50 and then depressurizing it. This allows the supercritical fluid to enter the interior of the thermally foamed preform based on the aforementioned primary cell framework, forming secondary micropores during the depressurization process. The primary cell framework provides a channel and interface for the supercritical fluid to enter the thick material, while the secondary micropores further refine the cell structure and improve cell uniformity.

[0048] Therefore, by sequentially coordinating S10 to S50, the present invention retains the advantages of meltblown technology for continuous deposition and carrier forming, while enabling the meltblown layer to obtain a foamed structure in the material body, thereby improving the problem of insufficient buffering and rebound performance of traditional meltblown materials due to limited pore sources.

[0049] Furthermore, specific embodiments of the present invention also relate to a meltblown foamed composite material, which can be obtained by the above-described thermoplastic material meltblown foaming method. The meltblown foamed composite material includes a carrier substrate and a thermoplastic foamed layer meltblownly deposited on the carrier substrate. The thermoplastic foamed layer is formed from a melt mixture of thermoplastic material containing thermally expanded microspheres through meltblown deposition, thermal foaming treatment, and supercritical high-pressure fluid treatment. Thus, the thermoplastic foamed layer has a primary cell framework formed by the expansion of thermally expanded microspheres, and secondary micropores formed after supercritical high-pressure fluid treatment and depressurization.

[0050] When the carrier substrate is a porous substrate, the thermoplastic foam layer at least partially enters the pores of the carrier substrate during meltblown deposition, and forms a composite structure with the carrier substrate after cooling, thermal foaming treatment, and supercritical high-pressure fluid treatment. The meltblown foam composite material can be used as a shoe upper support layer, insole, midsole cushioning sheet, partial cushioning component of the sole, or other thermoplastic composite components requiring cushioning and rebound performance.

[0051] To further illustrate the performance and effect of the thermoplastic material meltblown foaming method provided by the present invention, the following embodiments and comparative examples are provided.

[0052] First, the raw materials used in the following embodiments and comparative examples will be described. It should be understood that the raw materials described below are only used to illustrate the source of the raw materials in the embodiments and do not constitute a limitation on the scope of protection of this invention.

[0053] Thermoplastic polyurethane A85: Thermoplastic polyurethane elastomer from Wanhua Chemical Group Co., Ltd., grade WHT-8185, with a hardness of Shore A85, was selected and dried at 80°C for 4 hours before use. It was used as the thermoplastic material in Examples 1, 2 and various comparative examples.

[0054] Thermoplastic polyurethane A95: Thermoplastic polyurethane elastomer from Wanhua Chemical Group Co., Ltd., grade WHT-8195, with a hardness of Shore A95, was selected and dried at 80°C for 4 hours before use, and was used in the thermoplastic material in Example 3.

[0055] Thermally expandable microspheres: Acrylonitrile copolymer shell-coated isobutane-type thermally expandable microspheres, grade 930DU, manufactured by Nouryon Chemicals, were selected; the microspheres were in powder form, with an initial expansion temperature of approximately 120°C to 130°C, suitable for expansion in thermal foaming treatment at 120°C to 150°C, and were used in Examples 1 to 3 and Comparative Example 1.

[0056] Porous substrate: Polyester warp-knitted mesh fabric was selected, supplied by Fujian Huafeng New Material Co., Ltd., with a basis weight of 110g / m² and a thickness of 0.45mm. The pores are continuous along the thickness direction and it is used as the carrier substrate in Examples 1 to 3 and the comparative examples.

[0057] Auxiliary airflow: Compressed air is used as the auxiliary airflow in this embodiment. Nitrogen or carbon dioxide can also be used when an inert processing environment is required.

[0058] Supercritical high-pressure fluid: In the examples, a mixture of carbon dioxide and nitrogen was used, with a volume ratio of 1:2. The same mixture was used in the comparative examples, depending on the specific process settings.

[0059] Example 1 This embodiment prepares a meltblown foamed composite material.

[0060] Take 95 parts by weight of thermoplastic polyurethane A85 and 5 parts by weight of thermally expandable microspheres. First, dry the thermoplastic polyurethane A85 and add it to a low-speed mixer, then add the thermally expandable microspheres and mix for 8 minutes to obtain a mixture.

[0061] The mixture is heated and melted at a temperature of 170°C. The molten material is continuously fed to the melting nozzle to obtain a molten mixture. The melt index of the molten mixture is 200 g / 10 min. The molten mixture remains in a continuous molten state from the completion of heating and melting until it is ejected from the melting nozzle.

[0062] Polyester warp-knitted mesh was used as the carrier substrate and preheated to 70°C before meltblown deposition. The molten mixture was ejected from the melt nozzle, with a distance of 100 mm between the nozzle and the carrier substrate. Air was used as the auxiliary gas flow at a pressure of 0.4 MPa and a temperature of 180°C. The molten mixture was deposited on the carrier substrate in a semi-continuous melt and short-fiber melt mixture form, with some of the molten mixture entering the pores of the carrier substrate. After cooling, a preform with a thickness of approximately 1.0 mm was formed.

[0063] The preform was subjected to thermal foaming treatment at 130℃ for 8 minutes to obtain a thermally foamed preform. The expansion ratio of the thermally foamed preform was 4.4 times, and the density was 0.35 g / cm³.

[0064] The thermally expanded foam preform was subjected to supercritical high-pressure fluid treatment. The supercritical high-pressure fluid was a mixture of carbon dioxide and nitrogen. The treatment temperature was 120°C, the pressure was 25 MPa, and the treatment time was 10 min. After the treatment, the treatment pressure was reduced to atmospheric pressure to obtain a foamed product with secondary micropores. In the foamed product obtained in this embodiment, the thermoplastic foam layer was melt-blown deposited on the carrier substrate and formed a composite structure with the carrier substrate.

[0065] Example 2 98 parts by mass of thermoplastic polyurethane A85 and 2 parts by mass of thermally expanded microspheres were mixed online to obtain a mixture. The heating and melting temperature was 160℃, and the melt index of the molten mixture was 185 g / 10 min. The carrier substrate was preheated to 60℃. The distance between the melting nozzle and the carrier substrate was 150 mm, the auxiliary gas flow was air, the auxiliary gas flow pressure was 0.2 MPa, and the auxiliary gas flow temperature was room temperature. The molten mixture was deposited on the carrier substrate in the form of short fibrous melt and semi-continuous melt, and after cooling, it formed a preform with a thickness of approximately 0.8 mm.

[0066] The preform was subjected to thermal foaming treatment at 120℃ for 10 minutes to obtain a thermally foamed preform. The expansion ratio of the thermally foamed preform was 3.1 times, and the density was 0.35 g / cm³.

[0067] The product is then subjected to supercritical high-pressure fluid treatment, which is a mixture of carbon dioxide and nitrogen. The treatment temperature is 100℃, the pressure is 20MPa, and the time is 20min. After the treatment, the pressure is reduced to atmospheric pressure to obtain the foamed product.

[0068] Example 3 90 parts by weight of thermoplastic polyurethane A95 and 10 parts by weight of thermally expanded microspheres were mixed by dry mixing for 10 minutes to obtain a mixture. The melting temperature was 190℃, and the melt index of the molten mixture was 218 g / 10 min. The carrier substrate was preheated to 80℃. The distance between the melting nozzle and the carrier substrate was 50 mm, the auxiliary gas flow was air, the auxiliary gas flow pressure was 1.0 MPa, and the auxiliary gas flow temperature was 240℃. The molten mixture was deposited on the carrier substrate in the form of molten spray and melt jet, and after cooling, a preform with a thickness of approximately 1.5 mm was formed.

[0069] The preform was subjected to thermal foaming treatment at 150℃ for 5 minutes to obtain a thermally foamed preform. The expansion ratio of the thermally foamed preform was 5.2 times, and the density was 0.28 g / cm³.

[0070] The product was then subjected to supercritical high-pressure fluid treatment, which consisted of a mixture of carbon dioxide and nitrogen. The treatment temperature was 140°C, the pressure was 20 MPa, and the treatment time was 8 minutes. After the treatment, the pressure was reduced to atmospheric pressure to obtain the foamed product.

[0071] Comparative Example 1 This comparative example is based on Example 1, except that the supercritical high-pressure fluid treatment in step S50 is not performed.

[0072] Specifically, after completing S10, S20, S30 and S40 in accordance with Example 1 to obtain the thermally foamed embryo, supercritical high-pressure fluid treatment and depressurization secondary micro-foaming are no longer performed, and the thermally foamed embryo is directly used as a comparative sample.

[0073] Comparative Example 2 This comparative example is based on Example 1, except that thermally expanding microspheres are not added and supercritical high-pressure fluid treatment is performed directly.

[0074] Specifically, 100 parts by mass of thermoplastic polyurethane A85 were taken without the addition of thermally expandable microspheres. A melt-blown deposited preform was prepared according to the heating, melting, melt-blowing deposition, and cooling conditions in Example 1. This preform was not subjected to thermal foaming with thermally expandable microspheres to form a primary cell framework, but was directly processed and depressurized according to the supercritical high-pressure fluid processing conditions in Example 1 to obtain a comparative sample.

[0075] Comparative Example 3 This comparative example is based on Example 1, except that it adopts the traditional thermoplastic polyurethane meltblown deposition route, without adding thermally expanding microspheres, and without thermal foaming treatment and supercritical high-pressure fluid treatment.

[0076] Specifically, 100 parts by mass of thermoplastic polyurethane A85 were taken and, according to the heating and melting and auxiliary gas flow deposition conditions in Example 1, the molten material was used to form a meltblown fiber stack layer on a carrier substrate. After cooling, a comparative sample was obtained. The porosity of this sample mainly came from the fiber gaps and deposition gaps formed by meltblown deposition.

[0077] Performance testing Performance tests were conducted on the samples obtained from Examples 1 to 3 and Comparative Examples 1 to 3. All test samples were placed in an environment of 23℃±2℃ and 50%±5% relative humidity for 24 hours before testing.

[0078] Apparent density was tested according to GB / T 6343. The test object was a composite sample of thermoplastic foam layer and its carrier substrate cut from the foamed product. The test result was the average of 5 samples.

[0079] The average pore size was determined by observing the sample cross-section using a scanning electron microscope and statistically analyzing the pore size using image analysis software. Three different cross-sectional regions were selected for each sample, with at least 50 pores counted in each region, and the average value was taken. For traditional meltblown fiber stack samples, since the main pores are interfiber spaces, the average pore size was not recorded.

[0080] The ball rebound rate was tested according to GB / T 6670, and the test object was a sample containing a thermoplastic foam layer in the thickness direction. For samples with insufficient thickness, the same sample was stacked until the test clamping and impact requirements were met before testing, and the test result was taken as the average of 5 tests.

[0081] Compression set was tested according to GB / T 6669, with a compression ratio of 50% and a compression time of 22 hours. Thickness changes were recorded after 30 minutes of recovery. The test results were the average of three samples.

[0082] The interfacial peel test used strip samples with a width of 25 mm and a peeling speed of 100 mm / min. The peel force between the carrier substrate and the thermoplastic foam layer was tested, and the failure mode was recorded. If the foam layer tore or the substrate yarn broke during the peeling process, it was recorded as material failure; if the foam layer separated from the carrier substrate at the interface, it was recorded as interfacial peel.

[0083] The test results for each embodiment and comparative example are shown in the table below.

[0084]

[0085] Of these, Comparative Example 2 did not undergo thermal foaming treatment, so the density of the thermally foamed preform was not recorded; Comparative Example 3 did not form foam pores in the material body, so the average pore diameter was not recorded.

[0086] The test results show that Examples 1 to 3 can all form foamed products with primary cell skeleton and secondary micropores. The resulting samples have lower density, finer cells and better buffering and rebound performance, indicating that the process range defined in this application can achieve the expected technical effect.

[0087] Comparative Example 1, which only underwent thermal foaming, showed a larger average pore size, and its rebound rate and compression set were inferior to the previous example, indicating that relying solely on thermally expanded microspheres for foaming still limits pore refinement and compression recovery performance. Comparative Example 2, without the addition of thermally expanded microspheres, underwent direct supercritical high-pressure fluid treatment, resulting in poor foaming degree and pore uniformity, suggesting that the primary pore framework facilitates the entry of supercritical high-pressure fluid into the material interior and the formation of secondary micropores. Comparative Example 3, employing a traditional melt-blown deposition route, did not form bulk foam pores in the material, resulting in lower buffering and rebound performance and lower interfacial bonding effectiveness.

[0088] In summary, this application transforms the fiber-stacking porous structure of the meltblown layer into a bulk foamed structure by forming a preform through meltblown deposition, forming a primary pore skeleton through thermal foaming, and forming secondary micropores through supercritical high-pressure fluid treatment. This improves the problems of limited pore source and insufficient buffering and rebound performance of traditional meltblown materials.

[0089] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A method for melt-blown foaming of thermoplastic materials, characterized in that, include: S10, mix thermoplastic material with thermally expanded microspheres to obtain a mixture; S20, the mixture is heated and melted, and the heated and melted material is continuously conveyed to the melting nozzle to obtain a molten mixture; S30, the molten mixture is ejected from the melting nozzle and deposited on the carrier under the action of auxiliary airflow, and cooled to form a preform; S40, the preform is subjected to thermal foaming treatment to obtain a thermally foamed preform having a primary pore skeleton formed by the expansion of the thermally expanded microspheres. S50, the thermally foamed embryo is subjected to supercritical high-pressure fluid treatment, and the pressure is released after the supercritical high-pressure fluid treatment to obtain a foamed product with secondary micropores.

2. The method for melt-blown foaming of thermoplastic materials as described in claim 1, characterized in that, The thermoplastic material includes thermoplastic polyurethane, which is one or more of polyester-type thermoplastic polyurethane, polyether-type thermoplastic polyurethane, and polycarbonate-type thermoplastic polyurethane; the thermally expandable microspheres include a thermoplastic shell and a low-boiling-point hydrocarbon core material, which is one or more of isobutane and pentane.

3. The method for melt-blown foaming of thermoplastic materials as described in claim 1, characterized in that, In step S10, based on the total mass of the thermoplastic material and the thermally expandable microspheres, 90wt% to 98wt% of the thermoplastic material and 2wt% to 10wt% of the thermally expandable microspheres are dry-mixed, master-granulated, or metered online.

4. The method for melt-blown foaming of thermoplastic materials as described in claim 1, characterized in that, In step S20, the heating and melting temperature is 160℃~190℃, and the melt index of the molten mixture is 180g / 10min~220g / 10min; the molten mixture remains in a continuous melt state from the completion of heating and melting until it is ejected from the melting nozzle.

5. The method for melt-blown foaming of thermoplastic materials as described in claim 1, characterized in that, In step S30, the distance between the melting nozzle and the carrier is 50mm to 150mm, the pressure of the auxiliary gas flow is 0.2MPa to 1MPa, and the temperature of the auxiliary gas flow is from room temperature to 240℃.

6. The method for melt-blown foaming of thermoplastic materials as described in claim 1, characterized in that, In step S30, the auxiliary gas flow is air, nitrogen, carbon dioxide, or a mixture thereof; the molten mixture is deposited on the carrier in the form of molten spray, molten jet, short fibrous melt, or semi-continuous melt.

7. The method for melt-blown foaming of thermoplastic materials as described in claim 1, characterized in that, In step S30, the carrier is a porous substrate; before step S30, the porous substrate is preheated to 60°C to 80°C, and the molten mixture enters the pores of the porous substrate during deposition.

8. The method for melt-blown foaming of thermoplastic materials as described in claim 1, characterized in that, In step S40, the temperature of the thermal foaming treatment is 120℃~150℃, the time is 5min~10min, the foaming ratio of the thermally foamed embryo is 3 to 6 times, and the density is 0.20g / cm³~0.35g / cm³.

9. The method for melt-blown foaming of thermoplastic materials as described in claim 1, characterized in that, In S50, the supercritical high-pressure fluid is carbon dioxide, nitrogen, or a mixture of carbon dioxide and nitrogen; the temperature of the supercritical high-pressure fluid treatment is 100℃~140℃, the pressure is 20MPa~25MPa, and the time is 8min~20min; the pressure relief is to reduce the treatment pressure to atmospheric pressure.

10. A meltblown foamed composite material, characterized in that, The meltblown foamed composite material is prepared by the thermoplastic material meltblown foaming method according to any one of claims 1 to 9, and the meltblown foamed composite material includes a carrier substrate and a thermoplastic foam layer meltblownly deposited on the carrier substrate.

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