A method of making a microcellular foam injection molded article having a surface decoration of a composite microcellular membrane structure that mimics an eggshell membrane and the product

Abstract

The present application relates to a kind of imitation eggshell membrane structure composite microporous membrane surface decoration's microporous foaming injection molding product manufacturing method and product.Prepare microporous membrane as outer layer material, melt-blown nonwoven fabric as inner layer material;Inner and outer layer are stacked, and imitation eggshell membrane structure composite microporous membrane is prepared using heat treatment and hot pressing molding;Composite microporous membrane is embedded in mold and implements microporous foaming injection molding of composite microporous membrane surface decoration, and product is prepared.In molding, by the selective permeability of outer layer microporous membrane and the penetration of foaming melt and inner layer nonwoven fabric reticular fiber, membrane-base interface gas escape channel is established, gas trapped in membrane-base interface is effectively discharged, and close interface interlocking structure is formed, solve the common internal surface decoration microporous foaming molding plastic piece membrane-base interface produces bulge, separation defect and low bonding strength problem.By the present application, lightweight plastic product with high apparent quality and high bonding strength is prepared at low cost and high efficiency, and has wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of injection molding, specifically relating to a method for manufacturing microporous foam injection molded products with a composite microporous membrane surface decoration imitating an eggshell membrane structure, and the products thereof. Background Technology

[0002] Microcellular foam injection molding (MIM) originated in the 1980s. It involves injecting a homogeneous system of supercritical fluid and polymer melt into a mold cavity, where it foams to produce lightweight polymer products with numerous micron-sized pores. Compared to conventional injection molding (CIM), it offers advantages such as weight reduction, cost savings, and excellent dimensional stability. However, during the molding process, the pores within the foamed melt front are subjected to a fountain effect and strong shear during filling, causing deformation, rupture, and aggregation at the mold wall. This results in surface defects such as bubble marks and silver streaks on the product, severely limiting the application of this process.

[0003] In-mold decoration microporous foaming (IMD / MIM) is a method proposed in recent years to solve the appearance quality defects of MIM-molded plastic parts. This technology embeds a decorative coating into the mold cavity, injects foamed melt, and bonds it to the coating. The coating masks appearance defects such as bubble marks and silver streaks caused by MIM molding. The resulting products have advantages such as good appearance quality, light weight, low cost, and environmental friendliness. However, in the IMD / MIM process, due to the barrier and sealing effect of conventional coatings, broken bubbles accumulated at the interface between the surface coating and the polymer matrix cannot be effectively expelled. This easily leads to low bond strength defects such as detachment and bulging at the film-matrix interface, seriously hindering the application of this process in high-end polymer products. Therefore, achieving high-performance, high-strength bonding between the surface coating and the polymer matrix is ​​key to obtaining high-quality IMD / MIM plastic parts.

[0004] Eggshell membrane (ESM) is a unique multilayered micron-scale network fiber structure biocomposite membrane. It possesses selective permeability, allowing only small molecules to pass through, and the biological characteristic of tightly interlocking and anchoring with the eggshell through biomineralization. Currently, its biomimetic structure has attracted attention in the study of interfacial mass transfer and interfacial adhesion in composite materials. Essentially, it utilizes the biomimetic strategy of the ESM's multilayered micron-scale network fiber structure to achieve gas mass transfer and effective adhesion anchoring at the composite material interface. This aligns perfectly with the technical requirements of the IMD / MIM process, which suffers from gas trapping and low adhesion strength defects at the membrane-substrate interface. Therefore, drawing inspiration from the eggshell membrane structure, preparing a biomimetic composite microporous membrane to facilitate gas removal at the membrane-substrate interface in the IMD / MIM process and further improve adhesion strength offers a potential possibility for producing lightweight polymer products with high-strength adhesion and high apparent quality using this process, and there is an urgent need for such a method. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a manufacturing method and product for a microporous foam injection-molded product with a composite microporous membrane surface decoration imitating an eggshell membrane structure. Inspired by the selective permeability of the eggshell membrane structure and the biological mechanism of tight interlocking and anchoring with the eggshell through biomineralization, a multi-layer fiber structure is used to construct an inner and outer double-layer composite structure of the composite microporous membrane imitating an eggshell membrane structure. This structure replaces conventional film coating for in-mold surface decoration microporous foam composite molding. During the molding process, by utilizing the selective permeability of the constructed outer microporous membrane and the penetration and bonding process between the foamed melt and the inner nonwoven fabric mesh fiber, a gas escape channel is established at the membrane-substrate interface, effectively venting the gas trapped at the membrane-substrate interface and forming a tight interlocking interface structure. This solves the problems of bulging, delamination defects, and low bonding strength at the membrane-substrate interface of conventional in-mold surface decoration microporous foam molded plastic parts.

[0006] To achieve the above objectives, according to the present invention, a method for manufacturing a microporous foamed injection molded article decorated with a composite microporous membrane is provided, characterized in that the manufacturing method includes the following steps:

[0007] Step S1: Preparation of the outer microporous membrane, including: Step S1.1 and Step S1.2.

[0008] Step S1.1: Select thermoplastic powder A and lubricant as raw materials;

[0009] Step S1.2: The thermoplastic powder A is mixed with a lubricant to form a mixed powder. The mixed powder is then subjected to preforming, extrusion, sintering and biaxial stretching to prepare a microporous membrane with selective permeability.

[0010] Step S2: Preparation of the inner nonwoven fabric, including: Step S2.1 and Step S2.2.

[0011] Step S2.1: Select thermoplastic granules B as raw material;

[0012] Step S2.2: After melting thermoplastic particles B, nonwoven fabric with a mesh fiber structure is prepared by melt-blowing process, thereby completing the preparation of nonwoven fabric.

[0013] Step S3: Preparation of the composite microporous membrane with an eggshell-like membrane structure and construction of its inner and outer double-layer composite structure, including: Step S3.1 and Step S3.2.

[0014] Step S3.1: Stack the microporous membrane prepared in step S1 and the meltblown nonwoven fabric prepared in step S2 to form a layered structure, and perform heat treatment on the layered structure to achieve a steady-state heat distribution.

[0015] Step S3.2: The overall layered structure that has reached a steady-state heat distribution is hot-pressed to form the inner and outer layers together. After the overall layered structure with the inner and outer layers together is naturally cooled to room temperature, the preparation of the composite microporous membrane with the eggshell membrane structure is completed, thereby completing the construction of the inner and outer double-layer composite structure of the composite microporous membrane.

[0016] Step S4: Microporous foaming injection molding of composite microporous membrane surface decoration with eggshell membrane structure, including: steps S4.1, S4.2, S4.3, S4.4, S4.5, S4.6, and S4.7.

[0017] Step S4.1: Position and adsorb the composite microporous membrane with eggshell-like membrane structure prepared in step S3 into the mold cavity, with its outer layer in contact with the cavity wall;

[0018] Step S4.2: Close the mold;

[0019] Step S4.3: Add the polymer raw material to the feed cylinder;

[0020] Step S4.4: Inject the supercritical fluid into the feed cylinder;

[0021] Step S4.5: The polymer raw material and supercritical fluid are fully heated and stirred by the heater installed on the outside of the injection molding machine barrel and the screw installed inside the injection molding machine barrel, so that the polymer melt and supercritical fluid form a homogeneous foamed mixed melt system.

[0022] Step S4.6: Inject the homogeneous foamed mixed melt system into the mold, so that the foamed melt and the composite microporous membrane with the eggshell-like membrane structure are tightly bonded in the mold cavity, and perform microporous foaming injection molding for in-mold surface decoration.

[0023] Step S4.7: After cooling, curing and shaping, the mold is opened and the product is taken out, thereby producing a microporous foam injection molded product with a composite microporous membrane surface decoration with an eggshell-like membrane structure.

[0024] More preferably, the thermoplastic powder A is polytetrafluoroethylene (PTFE) powder, the thermoplastic particles B are polypropylene (PP) particles or polyethylene terephthalate (PET) particles, and the lubricant is preferably paraffin oil.

[0025] More preferably, in step S1, the mass fraction of the mixed powder is between 95% and 98% thermoplastic powder A and 2% and 5% lubricant.

[0026] More preferably, in step S1, the sintering process temperature is 320℃~350℃, and the material temperature of the biaxial stretching process is 100℃~300℃.

[0027] More preferably, in step S1, the pore size of the outer microporous membrane is less than 5 μm.

[0028] More preferably, in step S2, the inner meltblown nonwoven fabric is a plain weave, twill weave, or mesh meltblown fabric.

[0029] More preferably, in step S3, the temperature of the heat treatment process is 10°C below the melting point of the thermoplastic particles B, and the heat treatment time is 5 min to 10 min; the temperature of the hot pressing process is 10°C to 20°C below the melting point of the thermoplastic particles B, and the hot pressing time is 3 min to 5 min.

[0030] More preferably, in step S4, the polymer material for the microporous foam injection molding of the composite microporous membrane surface decoration of the eggshell-like membrane structure can be a thermoplastic polymer, a thermosetting polymer, or a copolymer of multiple polymers, and the supercritical gas is preferably nitrogen (N2) or carbon dioxide (CO2).

[0031] More preferably, in step S4, the injection temperature of the microporous foam injection molding of the composite microporous membrane surface decoration of the eggshell membrane structure is 10°C to 30°C higher than the melting point of the injection polymer material and not more than 30°C higher than the melting point of the thermoplastic particles B, and the injection pressure is 50MPa to 300MPa.

[0032] According to another aspect of the present invention, a final product manufactured using the above-described manufacturing method is provided, which has a three-layer structure: a polymer foam matrix, an outer selectively permeable microporous membrane, and an inner mesh fiber meltblown nonwoven fabric. The structural composition relationship between the final product manufactured by the present invention and the process product manufactured by the manufacturing method described herein is as follows: the final product manufactured by the present invention is obtained in step S4 by the eggshell-like membrane structure composite microporous membrane prepared in step S3 and the polymer foam melt (which becomes the polymer foam matrix after cooling and setting) described in step S4; the eggshell-like membrane structure composite microporous membrane prepared in step S3 is obtained in step S3 by the selectively permeable microporous membrane prepared in step S1 and the inner mesh fiber meltblown nonwoven fabric prepared in step S2. Overall, compared with the prior art, the above-described technical solution conceived by the present invention can achieve the following beneficial effects:

[0033] 1. This invention enhances the surface protection of microporous foam injection molded products. By utilizing the selective permeability of the outer microporous membrane and the permeation and bonding between the foamed melt and the inner nonwoven fabric mesh fiber, a gas escape channel is established at the membrane-substrate interface. This solves the molding defects such as bulging and delamination that are prone to occur in conventional microporous foam surface decoration processes, reduces the product defect rate, improves product quality, and increases production efficiency.

[0034] 2. This invention solves the problem of low film-substrate interface bonding strength in plastic parts produced by conventional microporous foaming molding of internal surface decoration. Through the penetration, anchoring, curing and cooling of the inner layer fiber in the composite microporous membrane double-layer composite structure by the foaming melt during the injection molding process, an interlocking and anchored strong bonding structure is formed, which greatly improves the bonding strength of the interface between the coating and the polymer foam matrix.

[0035] 3. Inspired by the selective permeability of eggshell membrane structure, which only allows small gas molecules to pass through, and the biological mechanism of tight interlocking and anchoring with the eggshell through biomineralization, this invention uses a combination of heat treatment and hot pressing to prepare a composite microporous membrane with an eggshell-like structure. The porosity and pore size of the composite microporous membrane with an eggshell-like structure are adjusted by controlling the sintering time, stretching temperature, and heat treatment time. The thickness of the composite microporous membrane with an eggshell-like structure is adjusted by controlling the distance between the pressure plates during hot pressing. This preparation process and equipment are simple, and the prepared composite microporous membrane with an eggshell-like structure retains the flexibility of nonwoven fabric and has good tensile strength. Attached Figure Description

[0036] Figure 1 This is a flowchart of a manufacturing method constructed according to a preferred embodiment of the present invention;

[0037] Figure 2 The inspiration for this invention comes from a field emission scanning electron microscope image of a selectively permeable inner shell membrane in an eggshell that allows only small gas molecules to pass through.

[0038] Figure 3 This is a field emission scanning electron microscope image of the outer shell membrane in an eggshell that is interlocked and anchored with the eggshell, which is the source of inspiration for this invention.

[0039] Figure 4 The images show the process products and final product manufactured according to the manufacturing method of preferred embodiment 1 of the present invention.

[0040] Figure 5 This is a field emission scanning electron microscope image of the outer microporous membrane of the eggshell-like membrane structure composite microporous membrane prepared according to preferred embodiment 1 of the present invention;

[0041] Figure 6 This is a field emission scanning electron microscope image of the inner meltblown nonwoven fabric of the eggshell-like membrane structure composite microporous membrane prepared according to preferred embodiment 1 of the present invention.

[0042] Figure 7 This is a schematic diagram of the apparatus used to manufacture composite microporous membrane surface decoration microporous foam injection molded plastic parts with an eggshell-like membrane structure according to a preferred embodiment of the present invention.

[0043] Figure 8 This is a cross-sectional field emission scanning electron microscope image of the article manufactured according to preferred embodiment 1 of the present invention;

[0044] Figure 9 The image shows the bond strength curve of an article manufactured according to the preferred embodiment 1 of the present invention and a microporous foamed plastic part with a conventional inner surface decoration, after a peel test according to standard: ISO 8510.

[0045] Figure 10 This is a cross-sectional field emission scanning electron microscope image of the article obtained according to preferred embodiment 2 of the present invention;

[0046] Figure 11 The image shows the bond strength curve of an article manufactured according to preferred embodiment 2 of the present invention and a microporous foamed plastic part with a conventional internal surface decoration, after a peel test according to standard: ISO 8510.

[0047] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0048] P1-Microporous foam injection molded product with eggshell-like membrane structure composite microporous membrane surface decoration; P21-Polymer foam matrix; P22-Eggshell-like membrane structure composite microporous membrane; P121-Inner layer mesh fiber meltblown nonwoven fabric; P122-Outer layer selectively permeable microporous membrane; 1-High-pressure gas tank; 2-Gas compression device; 3-Mold locking device; 4-Moving mold; 5-Eggshell-like membrane structure biomimetic composite microporous membrane; 6-Fixed mold; 7-Heating device; 8-Air inlet valve; 9-Barrel; 10-Hopper. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0050] A method for manufacturing microporous foam injection-molded products with a composite microporous membrane surface decoration imitating an eggshell membrane structure is inspired by the selective permeability of the eggshell membrane structure, which only allows small gas molecules to pass through, and the biological mechanism of tight interlocking and anchoring with the eggshell through biomineralization. Borrowing the structural characteristics of the eggshell membrane, a composite microporous membrane with a selective permeability and interlocking anchoring with the polymer foam matrix is ​​constructed using a microporous membrane as the outer layer and meltblown nonwoven fabric as the inner layer. This results in a double-layer composite structure with inner and outer layers. This composite microporous membrane with an eggshell membrane structure is used for microporous foam surface decoration composite molding. During the molding process, the selective permeability of the outer microporous membrane, which only allows small gas molecules to pass through, and the permeation and bonding between the foam melt and the inner nonwoven fabric mesh fibers establish gas escape channels at the membrane-substrate interface. This effectively releases the gas trapped at the membrane-substrate interface and forms a tight interlocking structure, solving the problems of bulging, delamination defects, and low bonding strength at the membrane-substrate interface in conventional microporous foam molded plastic parts with surface decoration.

[0051] To achieve the above objectives, in combination Figure 1 The manufacturing method of a microporous foam injection molded product with a composite microporous membrane surface decoration imitating an eggshell membrane structure, as described in this invention, can be achieved through the following technical solution:

[0052] Step S1: Preparation of outer microporous membrane. Figure 2 The image shows a field emission scanning electron microscope (FESEM) image of a selectively permeable inner shell membrane that allows only small gas molecules to pass through. With its structure and function as the target, thermoplastic powder and lubricant are mixed to form a mixed powder. The mixed powder is then subjected to preforming, extrusion, sintering and biaxial stretching in sequence to prepare a selectively permeable microporous membrane that allows only small gas molecules to pass through, thus completing the preparation of the outer microporous membrane.

[0053] The thermoplastic powder is preferably polytetrafluoroethylene (PTFE) powder, and the lubricant is preferably paraffin oil. The mass fraction ratio is between 95% and 98% of the thermoplastic powder and 2% and 5% of the lubricant. This ratio helps to reduce the surface energy of PTFE during processing and improve its fluidity and processing performance.

[0054] The sintering process temperature is 320℃~350℃, and the material temperature of the biaxial stretching process is 100℃~300℃. The resulting microporous membrane has a pore size of less than 5μm.

[0055] Step S2: Preparation of inner layer meltblown nonwoven fabric. Figure 3 The image shows a field emission scanning electron microscope image of the outer shell membrane that interlocks and anchors with the eggshell. With its structure and function as the target, thermoplastic particles are melted and nonwoven fabric with a mesh fiber structure is prepared by melt-blowing process to complete the preparation of the inner nonwoven fabric.

[0056] The thermoplastic granules are preferably polypropylene (PP) granules or polyethylene terephthalate (PET) granules, and the meltblown nonwoven fabric is plain weave, twill weave or mesh meltblown fabric.

[0057] Step S3: Preparation of the eggshell-like composite microporous membrane and construction of its inner and outer double-layer composite structure. The outer microporous membrane and the inner nonwoven fabric are stacked to form a layered structure, then placed in a muffle furnace for heat treatment to achieve a stable heat distribution. Next, a hot flat press is used to hot-press the membrane, compositing the inner and outer layers. The composite microporous membrane is then allowed to cool naturally to room temperature, completing the preparation of the eggshell-like composite microporous membrane and thus constructing its inner and outer double-layer composite structure.

[0058] The temperature of the heat treatment process is 10°C below the melting point of the thermoplastic granules, and the heat treatment time is 5 min to 10 min. The temperature of the hot pressing process is 10°C to 20°C below the melting point of the thermoplastic granules, and the hot pressing time is 3 min to 5 min.

[0059] Step S4: Microporous foam injection molding with eggshell-like composite microporous membrane surface decoration. The obtained eggshell-like composite microporous membrane is positioned in the mold cavity, with its outer layer in contact with the cavity wall. Then, a homogeneous foaming melt, a uniform mixture of supercritical fluid and polymer melt, is injected, causing the foaming melt to adhere tightly to the eggshell-like composite microporous membrane in the mold cavity. After cooling, curing, and shaping, a microporous foam injection molded product with an eggshell-like composite microporous membrane surface decoration is obtained.

[0060] Figure 4 This embodiment describes the process product and final product manufactured according to the manufacturing method of the present invention. The microporous foam injection-molded product with a surface decoration of the eggshell-like membrane structure composite microporous membrane is the final product P1 manufactured by the method of the present invention. It has a three-layer structure: a polymer foam matrix P21, an outer selectively permeable microporous membrane P122, and an inner mesh fiber meltblown nonwoven fabric P121. The structural composition relationship between the final product P1 manufactured by the present invention and the process product manufactured by the manufacturing method of the present invention is as follows: The final product P1 manufactured by the present invention is obtained in step S4 by the eggshell-like membrane structure composite microporous membrane P22 prepared in step S3 and the polymer foam melt (which becomes the polymer foam matrix P21 after cooling and setting) described in step S4; the eggshell-like membrane structure composite microporous membrane P22 prepared in step S3 is obtained in step S3 by the selectively permeable microporous membrane P122 prepared in step S1 and the inner mesh fiber meltblown nonwoven fabric P121 prepared in step S2.

[0061] The manufacturing method proposed in this invention has clear steps, low operational difficulty, and the manufacturing equipment involved is common in the industry, making it highly operable. The microporous foam injection-molded product with eggshell-like membrane structure composite microporous membrane surface decoration prepared by the manufacturing method proposed in this invention retains the advantages of conventional coated products such as lightweight and stronger impact resistance, while having better appearance quality and higher membrane-substrate interface adhesion strength. The invention will be further illustrated below with specific embodiments.

[0062] Example 1

[0063] Step S1: Preparation of the outer microporous membrane, including: Step S1.1 and Step S1.2.

[0064] Step S1.1: Select PTFE powder and paraffin oil as materials for preparing the outer microporous membrane. Mix PTFE powder and paraffin oil lubricant at a mass ratio of 95% and 5% to form a mixed powder.

[0065] Step S1.2: The mixed powder is pressed into a preform at room temperature, and the preform is extruded into a strip film through an extruder. The extruded film is placed in a muffle furnace for sintering to eliminate the paraffin oil lubricant and promote the crystallization of PTFE segments. The sintering temperature is 340℃ and the sintering time is 10min. After cooling to room temperature, it is placed on a stretching machine and biaxially stretched at 150℃ with a stretching ratio of 5. After cooling to room temperature, the preparation of the outer microporous membrane is completed.

[0066] Figure 5 The PTFE outer microporous membrane prepared in this embodiment has an average pore size of less than 3 μm and a uniform pore distribution. In addition, the low surface energy and high hydrophobicity of PTFE give the membrane itself the ability to be breathable, waterproof and antifouling, and it has excellent selective permeability. It is an excellent choice as the outer layer of a composite microporous membrane with an eggshell-like membrane structure, and can effectively construct a gas escape channel at the membrane-substrate interface during the microporous foaming injection molding process.

[0067] Step S2: Preparation of inner layer meltblown nonwoven fabric, including: Step S2.1 and Step S2.2.

[0068] Step S2.1: Select PP as the material for preparing the inner layer of meltblown nonwoven fabric;

[0069] Step S2.2: PP granules are heated and melted in a screw extruder at a melting temperature of 220℃. The molten PP is extruded through the nozzle of the meltblown die head with a nozzle diameter of 0.3mm. At the nozzle outlet, the molten PP filaments are rapidly stretched into fine fibers by high-speed hot air at 240℃. The PP fibers are bundled onto the web forming device to form a web structure. The PP fiber web is then subjected to deep heat preservation by a smooth roller at a rolling temperature of 140℃. After natural cooling, the preparation of the inner nonwoven fabric is completed.

[0070] Figure 6 This is a field emission scanning electron microscope (FESEM) image of the inner layer meltblown nonwoven fabric of the eggshell-like membrane composite microporous membrane prepared in this embodiment. Its structure is similar to the outer membrane of an eggshell membrane, with an average pore size greater than 50 μm and uniform pore distribution. This allows the polymer melt in the injection filling stage to efficiently penetrate into the membrane and effectively encapsulate the membrane fibers. It is an excellent choice as the inner layer of the eggshell-like membrane composite microporous membrane and can effectively construct the interlocking anchoring structure of the membrane-substrate interface during the microporous foaming injection molding process.

[0071] Step S3: Preparation of the composite microporous membrane with an eggshell-like membrane structure and construction of its inner and outer double-layer composite structure, including: Step S3.1 and Step S3.2.

[0072] Step S3.1: Stack the microporous membrane prepared in step 1 and the meltblown nonwoven fabric prepared in step 2 to form a layered structure, and place it in a muffle furnace for heat treatment to achieve a steady-state heat distribution. The heat treatment temperature is 160℃ and the heat treatment time is 10min.

[0073] Step S3.2: The microporous membrane with steady-state heat distribution and meltblown nonwoven fabric are hot-pressed in a hot press to form a composite inner and outer layer. The hot pressing temperature is 150℃, the hot pressing time is 8min, and the gap between the hot pressing plates is 0.2mm. After the composite microporous membrane cools naturally to room temperature, the preparation of the composite microporous membrane is completed, thus completing the construction of the inner and outer double-layer composite structure of the composite microporous membrane.

[0074] Step S4: Microporous foaming injection molding of composite microporous membrane surface decoration with eggshell membrane structure, including: steps S4.1, S4.2, S4.3, S4.4, S4.5, S4.6, and S4.7.

[0075] Step S4.1: As Figure 7 The composite microporous membrane 5 is adsorbed and fixed onto the moving mold 4 of the injection mold by an electrostatic generator, and its outer layer is in direct contact with the mold cavity wall.

[0076] Step S4.2: Close the mold;

[0077] Step S4.3: Select PP as the polymer matrix material and add PP granules into the hopper 10 of the injection molding machine;

[0078] Step S4.4: Nitrogen (N2) from high-pressure gas cylinder 1 is pressurized by gas compression device 2 and injected into the injection molding machine barrel at a pressure of 23 MPa through supercritical fluid dispensing valve 8, with the injection ratio set to 0.4%.

[0079] Step S4.5: Under the heating and stirring action of the screw inside the heating device 7 and the barrel 8, the polymer melt and supercritical gas are mixed into a homogeneous system and heated to 210°C by the heater;

[0080] Step S4.6: Injection molding stage, the PP / N2 mixed melt is injected into the mold cavity at an injection pressure of 130 MPa and an injection speed of 60 cm. 3 / S, mold temperature is 20℃, cooling time is 30S, no pressure holding stage;

[0081] Step S4.7: After cooling, curing, and shaping, the mold is opened and the product is removed, resulting in a PP microporous foamed product decorated with a composite microporous membrane with an eggshell-like membrane structure. The PP microporous foamed product decorated with the composite microporous membrane with an eggshell-like membrane structure has good surface quality and no low-adhesion defects such as bulging or detachment. Gas escape at the membrane-substrate interface during injection molding is achieved by constructing gas escape channels through the composite microporous membrane with an eggshell-like membrane structure.

[0082] Cross-sectional observations were performed on the PP microporous foamed products decorated with a composite microporous membrane that mimics an eggshell membrane structure. Figure 8 The image shows a cross-sectional field emission scanning electron microscope image of the product, in which a large number of membrane fibers of the composite microporous membrane are wrapped by the matrix, proving that the membrane-substrate interface of the plastic part achieves effective interlocking anchoring.

[0083] The interfacial bonding strength of PP microporous foam products with eggshell-like membrane structure composite microporous membrane coating decoration was compared with that of conventional PP microporous foam products with PP coating decoration. According to the standard ISO 8510, a rectangular planar peel test area of ​​25mm×95mm was selected. The plastic part was placed on the rolling platform perpendicular to the direction of equipment movement. One end of the coating was manually peeled off 10mm before the test and fixed to the fixture. The product was subjected to a 90° peel test with a peel rate of 25mm / min, a fixture lifting height of 90mm, and an effective peel distance of 85mm.

[0084] Figure 9 The figure shows the peel force curves for the peel test. Throughout the peeling process, the peel force of the PP microporous foam products coated with the composite microporous membrane was significantly higher than that of the conventional PP microporous foam products coated with the film. The maximum peel forces were 66.72 N and 22.78 N, respectively, indicating that the bonding performance was improved by 292.9%. This effectively proves the effectiveness of the interlocking structure of the membrane-substrate interface in the PP microporous foam products coated with the composite microporous membrane, and further demonstrates that the eggshell-like membrane structure composite microporous membrane can effectively enhance the interfacial bonding strength of the products while improving the appearance quality of IMD / MIM products.

[0085] Example 2

[0086] Step S1: Preparation of the outer microporous membrane, including: Step S1.1 and Step S1.2.

[0087] Step S1.1: Select PTFE powder and paraffin oil as materials for preparing the outer microporous membrane. Mix PTFE powder and paraffin oil lubricant at a mass ratio of 98% and 2% to form a mixed powder.

[0088] Step S1.2: The mixed powder is pressed into a preform at room temperature, and the preform is extruded into a strip film through an extruder. The extruded film is placed in a muffle furnace for sintering to eliminate the lubricant and promote the crystallization of PTFE segments. The sintering temperature is 330℃ and the sintering time is 10min. After cooling to room temperature, it is placed on a stretching machine and biaxially stretched at 160℃ with a stretching ratio of 8. After cooling to room temperature, the preparation of the outer microporous membrane is completed.

[0089] Step S2: Preparation of inner layer meltblown nonwoven fabric, including: Step S2.1 and Step S2.2.

[0090] Step S2.1: Select PET as the material for preparing the inner layer of meltblown nonwoven fabric;

[0091] Step S2.2: PET granules are heated and melted in a screw extruder at a melting temperature of 260°C. The molten PET is extruded through the nozzle of a meltblown die with a nozzle diameter of 0.3 mm. At the nozzle outlet, the molten PET filaments are rapidly stretched into fine fibers by high-speed hot air at 270°C. The PET fibers are bundled onto a web forming device to form a web structure. The PET fiber web is then subjected to deep heat preservation using a smooth roller at a rolling temperature of 220°C. After natural cooling, the preparation of the inner nonwoven fabric is completed.

[0092] Step S3: Preparation of a biomimetic composite microporous membrane with an eggshell membrane structure, including: Step S3.1 and Step S3.2.

[0093] Step S3.1: After stacking the microporous membrane as the outer layer and the nonwoven fabric as the inner layer to form a layered structure, place it in a muffle furnace for heat treatment to achieve a steady-state heat distribution. The heat treatment temperature is 230℃ and the heat treatment time is 10min.

[0094] Step S3.2: The microporous membrane with steady-state heat distribution and meltblown nonwoven fabric are hot-pressed in a hot flat press to form a composite inner and outer layer. The hot pressing temperature is 220℃, the hot pressing time is 10min, and the gap between the hot pressing plates is 0.2mm. After the composite microporous membrane cools naturally to room temperature, the preparation of the composite microporous membrane is completed.

[0095] Step S4: Microporous foaming injection molding of composite microporous membrane surface decoration with eggshell membrane structure, including: steps S4.1, S4.2, S4.3, S4.4, S4.5, S4.6, and S4.7.

[0096] Step S4.1: As Figure 6 The composite microporous membrane 5 is adsorbed and fixed onto the moving mold 4 of the injection mold by an electrostatic generator, and its outer layer is in direct contact with the mold cavity wall.

[0097] Step S4.2: Close the mold;

[0098] Step S4.3: Select PET as the polymer matrix material and add PET granules into the hopper 10 of the injection molding machine;

[0099] Step S4.4: Nitrogen (N2) from high-pressure gas cylinder 1 is pressurized by gas compression device 2 and injected into the injection molding machine barrel at a pressure of 20MPa through supercritical fluid dispensing valve 8, with the injection ratio set to 0.6%.

[0100] Step S4.5: Under the heating and stirring action of the screw inside the heating device 7 and the barrel 8, the polymer melt and supercritical gas are mixed into a homogeneous system and heated to 250°C by the heater;

[0101] Step S4.6: Injection molding stage, the PET / N2 mixed melt is injected into the mold cavity at an injection pressure of 150 MPa and an injection speed of 120 cm. 3 / S, mold temperature is 20℃, cooling time is 30S, no pressure holding stage;

[0102] Step S4.7: After cooling, curing and shaping, the mold is opened and the product is taken out to obtain a PET microporous foamed product decorated with a composite microporous membrane with an eggshell-like membrane structure.

[0103] The PET microporous foamed products decorated with the imitation eggshell membrane structure composite microporous membrane have good surface quality and no low adhesion defects such as bulging or detachment. The gas escape channel constructed by the fabricated imitation eggshell membrane structure composite microporous membrane realizes gas escape at the membrane-substrate interface during injection molding.

[0104] Cross-sectional observations were performed on the PET microporous foamed products decorated with a composite microporous membrane structure resembling an eggshell. Figure 10 The cross-sectional field emission scanning electron microscope image of the product is similar to that of Example 1, in which the inner membrane PET fiber of the composite microporous membrane is interwoven with the matrix, proving that the membrane-matrix interface of the plastic part achieves effective interlocking anchoring.

[0105] A comparative test of the interfacial bonding strength was conducted on the PET microporous foam products with eggshell-like membrane structure composite microporous membrane coating and the PET microporous foam products with conventional PET coating. The products were subjected to a 90° peel test according to the same test conditions as in Example 1, in accordance with ISO 8510 standard.

[0106] Figure 11 The peel force curves for the peel test are similar to those in Example 1. Throughout the peeling process, the peel force of the PET microporous foam product with composite microporous membrane coating decoration is higher than that of the conventional PET microporous foam product with PET coating decoration. The maximum peel forces are 64.42 N and 23.36 N, respectively. This indicates that the bonding performance is improved by 275.8%, which effectively proves the effectiveness of the interlocking structure of the membrane-substrate interface of the PET microporous foam product with composite microporous membrane coating decoration. It also further proves that the eggshell-like membrane structure composite microporous membrane can effectively enhance the interfacial bonding strength of the product while improving the appearance quality of IMD / MIM products.

[0107] Obviously, the above description is merely a preferred embodiment of the present invention and is not intended to limit the implementation or the content of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible embodiments. Any obvious variations derived therefrom, or any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention, are all included within the scope of protection of the present invention.

Claims

1. A method for producing a microcellular foam injection-molded article having a composite microporous membrane surface decoration of an eggshell membrane structure, characterized by, The manufacturing method includes the following main steps: Step S1: Preparation of the outer microporous membrane, including: Step S1.1 and Step S1.2; Step S1.1: Select thermoplastic powder A and lubricant as raw materials; Step S1.2: The thermoplastic powder A is mixed with a lubricant to form a mixed powder. The mixed powder is then subjected to preforming, extrusion, sintering and biaxial stretching to prepare a microporous membrane with selective permeability. Step S2: Preparation of the inner nonwoven fabric, including: Step S2.1 and Step S2.2; Step S2.1: Select thermoplastic granules B as raw material; Step S2.2: After melting thermoplastic particles B, nonwoven fabric with a mesh fiber structure is prepared by melt-blowing process, thereby completing the preparation of nonwoven fabric; Step S3: Preparation of the composite microporous membrane with an eggshell-like membrane structure and construction of its inner and outer double-layer composite structure, including: Step S3.1 and Step S3.2; Step S3.1: Stack the microporous membrane prepared in step S1 and the meltblown nonwoven fabric prepared in step S2 to form a layered structure, and perform heat treatment on the layered structure to achieve a steady-state heat distribution. Step S3.2: The overall layered structure that has reached a steady-state heat distribution is hot-pressed to form the inner and outer layers together. After the overall layered structure with the inner and outer layers together is naturally cooled to room temperature, the preparation of the composite microporous membrane with the eggshell membrane structure is completed, thereby completing the construction of the inner and outer double-layer composite structure of the composite microporous membrane. Step S4: Microporous foaming injection molding of composite microporous membrane surface decoration with eggshell membrane structure, including: steps S4.1, S4.2, S4.3, S4.4, S4.5, S4.6, and S4.7; Step S4.1: Position and adsorb the composite microporous membrane with eggshell-like membrane structure prepared in step S3 into the mold cavity, with its outer layer in contact with the cavity wall; Step S4.2: Close the mold; Step S4.3: Add the polymer raw material to the feed cylinder; Step S4.4: Inject the supercritical fluid into the feed cylinder; Step S4.5: The polymer raw material and supercritical fluid are fully heated and stirred by the heater installed on the outside of the injection molding machine barrel and the screw installed inside the injection molding machine barrel, so that the polymer melt and supercritical fluid form a homogeneous foamed mixed melt system. Step S4.6: Inject the homogeneous foamed mixed melt system into the mold, so that the foamed melt and the composite microporous membrane with the eggshell-like membrane structure are tightly bonded in the mold cavity, and perform microporous foaming injection molding for in-mold surface decoration. Step S4.7: After cooling, curing and shaping, the mold is opened and the product is taken out, thereby producing a microporous foam injection molded product with a composite microporous membrane surface decoration with an eggshell-like membrane structure.

2. A method of making a microcellular foam injection molded article having a composite microporous membrane surface finish that simulates an eggshell membrane structure according to claim 1, wherein, The thermoplastic powder A is polytetrafluoroethylene (PTFE) powder, the thermoplastic particles B are polypropylene (PP) particles or polyethylene terephthalate (PET) particles, and the lubricant is paraffin oil.

3. A method of making a microcellular foam injection molded article having a composite microporous membrane surface finish that simulates an eggshell membrane structure according to claim 1, wherein, In step S1, the mass fraction of the mixed powder is between 95% and 98% thermoplastic powder A and 2% and 5% lubricant.

4. A method of making a microcellular foam injection molded article having a composite microporous membrane surface finish that simulates an eggshell membrane structure according to claim 1, wherein, In step S1, the outer microporous membrane has a pore size of less than 5 μm.

5. A method of making a microcellular foam injection molded article having a composite microporous membrane surface finish that simulates an eggshell membrane structure according to claim 1, wherein, In step S1, the sintering process temperature is 320 ℃~350 ℃, and the material temperature of the biaxial stretching process is 100 ℃~300 ℃.

6. A method of making a microcellular foam injection molded article having a composite microporous membrane surface finish that simulates an eggshell membrane structure according to claim 1, wherein, In step S2, the inner meltblown nonwoven fabric is a plain weave, twill weave, or mesh meltblown fabric.

7. A method of making a microcellular foam injection molded article having a composite microporous membrane surface finish that simulates an eggshell membrane structure according to claim 1, wherein, In step S3, the temperature of the heat treatment process is 10°C below the melting point of the thermoplastic particles B, and the heat treatment time is 5 min to 10 min. The temperature of the hot pressing process is 10°C to 20°C below the melting point of the thermoplastic particles B, and the hot pressing time is 3 min to 5 min.

8. A method of making a microcellular foam injection molded article having a composite microporous membrane surface finish that simulates an eggshell membrane structure according to claim 1, wherein, In step S4, the polymer material for the microporous foam injection molding of the composite microporous membrane surface decoration of the eggshell-like membrane structure is a thermoplastic polymer, a thermosetting polymer, or a copolymer of multiple polymers, and the supercritical gas is nitrogen (N2) or carbon dioxide (CO2).

9. A method of making a microcellular foam injection molded article having a composite microporous membrane surface finish that simulates an eggshell membrane structure according to claim 1, wherein, In step S4, the injection temperature of the microporous foam injection molding of the composite microporous membrane surface decoration of the eggshell membrane structure is 10 ℃ to 30 ℃ higher than the melting point of the injection polymer material and not more than 30 ℃ higher than the melting point of the thermoplastic particles B, and the injection pressure is 50 MPa to 300 MPa.

10. A product formed by the manufacturing method according to any one of claims 1-9.

Images