Anisotropic heat-insulating breathable composite film and dislocation lamination process thereof

Abstract

The composite film is formed by laminating and compounding at least two layers of polymer porous films with anisotropic microporous structures, and the adjacent film layers are stacked after rotating by 45-135 degrees around the axis perpendicular to the film surface, the micropore channels of the upper and lower film layers form a non-through structure in a three-dimensional space, and decoupling of a heat flow transmission direction and a gas diffusion direction is realized. The interlayer dislocation degree is controlled by regulating and controlling the rotation angle, an efficient thermal resistance barrier is formed in the thickness direction, and meanwhile a gas diffusion channel is kept in the plane direction. The composite film has excellent heat insulation performance and air permeability, the heat conductivity coefficient can be as low as 0.028 W / (m.K), the water vapor transmission rate is kept at 980 g / (m.24 h) or above, the preparation process is simple and controllable, and the composite film can be widely applied to the fields of automobile interiors, building heat preservation, garment materials and the like.

Description

An anisotropic thermal insulation and breathable composite membrane and its misaligned lamination process Technical Field

[0001] This invention relates to the field of polymer porous membrane materials technology, and more specifically, to an anisotropic heat-insulating and breathable composite membrane and its misaligned lamination process. Background Technology

[0002] With the rapid development of the automotive industry, building energy conservation, and functional clothing, the demand for membrane materials that combine excellent thermal insulation and good breathability is increasing. For example, in automotive interiors, seat and headliner materials need to block the high temperatures of summer from entering the vehicle while allowing moisture emitted by the body to escape, thus improving passenger comfort. In building insulation, breathable wall membranes need to prevent heat loss while allowing water vapor to diffuse, preventing condensation and mold growth on the walls. In functional clothing fabrics, it is necessary to maintain body temperature in cold environments while allowing sweat to escape, keeping the wearer feeling dry.

[0003] However, thermal insulation and breathability are often contradictory in material design. Traditional thermal insulation materials typically suppress heat conduction by reducing material density and increasing porosity. However, high porosity often leads to enhanced convective heat transfer, and gas molecules can easily penetrate directly, making it difficult to simultaneously achieve low thermal conductivity and high water vapor permeability. Conversely, microporous membranes designed to improve breathability often have poor thermal insulation performance due to their interconnected pores and low thermal resistance.

[0004] To address the aforementioned issues, various improvement schemes have been proposed in existing technologies. A common approach is to employ a multi-layered composite structure, improving thermal insulation performance by increasing material thickness or adding barrier layers with different functions. However, this method often sacrifices breathability, and the increased thickness leads to bulkier materials and reduced flexibility. Another approach is to prepare foam materials or aerogels with isotropic microporous structures. While this can reduce the thermal conductivity to a lower level, the closed or semi-closed microporous structure makes it difficult for water vapor to pass through, failing to meet breathability requirements. Furthermore, while constructing a dense layer on the surface of the membrane material using physical or chemical methods can partially block heat radiation, it also hinders the diffusion of gas molecules.

[0005] In the field of multilayer membrane composite technology, researchers have attempted to control the mass transfer pathway by stacking membrane layers with different pore sizes. However, conventional stacking methods are mostly parallel or random stacking, and the micropore channels between layers often form a continuous structure, allowing heat to still be transferred along a relatively direct path, resulting in limited improvement in thermal insulation performance. At the same time, the bonding method of the interlayer interfaces also affects the overall performance of the composite membrane. If the adhesive layer is too thick or improperly coated, it can easily clog the micropores, leading to a significant decrease in air permeability.

[0006] Therefore, developing a composite membrane material that can significantly improve thermal insulation performance while maintaining high air permeability has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In order to overcome the above-mentioned defects of the prior art, embodiments of the present invention provide an anisotropic heat-insulating and breathable composite membrane and its misaligned lamination process.

[0008] To achieve the above objectives, the innovative aspects of this invention are as follows: the composite membrane is composed of at least two layers of polymer porous membrane stacked together;

[0009] Polymer porous membranes have anisotropic microporous structures, and the anisotropy is manifested in the gradient distribution of pore size from one side surface of the membrane to the other side surface;

[0010] At least two layers of polymer porous membrane are stacked in a specific orientation relationship, so that the micropore channels of adjacent membrane layers form a non-interconnected structure in three-dimensional space;

[0011] The composite membrane is configured to decouple the heat transfer direction from the gas diffusion direction, i.e., to form a thermal resistance barrier that inhibits heat conduction in the thickness direction, while maintaining diffusion channels for gas molecules in the planar direction.

[0012] Furthermore, the aforementioned specific orientation relationship involves stacking adjacent film layers after rotating them around an axis perpendicular to the film surface at a certain angle, with the rotation angle being 45°-135°.

[0013] Furthermore, the rotation angle is 90°±10°, so that the main orientation direction of the micropores of adjacent film layers is perpendicular to each other. When the heat flow is transferred along the thickness direction, it must repeatedly cross the solid-gas interface inside the film layer, forming a labyrinthine thermal resistance path.

[0014] Furthermore, the polymer porous membrane is a polyethersulfone membrane, and the microporous structure is formed by phase inversion, with a gradient distribution from the side with smaller pore size to the side with larger pore size; the side with smaller pore size is a dense skin layer, the side with larger pore size is a finger-like pore layer, and there is a sponge-like transition layer between the dense skin layer and the finger-like pore layer.

[0015] Furthermore, an adhesive layer is provided between adjacent membrane layers. The adhesive layer is a low-viscosity, high-permeability polymer solution with a viscosity of 50-500 mPa·s at 25°C. It is applied by spraying, dipping, or scraping, with a coating amount of 1-10 g / m².

[0016] The adhesive layer fills the interfacial gap between the two membranes through capillary action. The thickness of the adhesive layer is 0.1-5μm and does not block the microporous structure inside the membrane.

[0017] Furthermore, the composite membrane is composed of 2-10 layers of polymer porous membrane stacked together, with a total thickness of 50-500μm, a porosity of 50%-85%, and an average pore size of 10nm-100nm or 1μm-5μm.

[0018] Furthermore, the composite membrane has a thermal conductivity of 0.020-0.045 W / (m·K) in the thickness direction and a water vapor transmission rate of 500-2000 g / (m²·24h), making it suitable for applications in automotive interiors, building insulation, or clothing fabrics.

[0019] This invention provides a staggered lamination process for an anisotropic heat-insulating and breathable composite membrane, comprising the following steps:

[0020] (1) At least two polymer porous membranes with anisotropic microporous structures are prepared by phase inversion method, wherein the pore size of the polymer porous membranes is gradient distributed from one side surface to the other side surface;

[0021] (2) Lay the first polymer porous membrane flat on the substrate;

[0022] (3) Rotate the second polymer porous membrane around its geometric central axis by 45°-135° and then cover it on the first membrane;

[0023] (4) Apply an adhesive layer between the two membranes, apply a pressure of 0.05-0.5MPa, and hot press the membranes together at 60-120℃ to fix the two membranes together.

[0024] (5) Repeat steps (2)-(4) 1-8 times to stack more layers of film in sequence to form a composite film with a total number of 2-10 layers.

[0025] Furthermore, the process parameters for the phase inversion method in step (1) are as follows: PES concentration is 15-25wt%, solvent is one or more of dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) or dimethylformamide (DMF), coagulation bath is water or a mixture of water and solvent, coagulation bath temperature is 20-60℃, casting solution coating thickness is 50-500μm, and residence time in coagulation bath is 5-30 minutes;

[0026] By adjusting process parameters, the pore size distribution, porosity, and anisotropy of the monolayer membrane can be controlled, thereby adjusting the interlayer misalignment of the final composite membrane.

[0027] Furthermore, the interlayer misalignment was determined by image analysis and defined as the ratio of the overlapping area of ​​the micropores projected in the thickness direction of the two membranes to the total pore area.

[0028] When the rotation angle is 90°±10°, the interlayer misalignment is ≤15%.

[0029] The technical effects and advantages of this invention are as follows:

[0030] 1. This invention achieves effective decoupling of heat conduction and gas diffusion paths by constructing a non-through-hole microporous structure between layers, enabling the composite membrane to possess both excellent thermal insulation and air permeability. Specifically, this invention uses a polymer porous membrane with an anisotropic pore size gradient, and stacks adjacent membrane layers by rotating them 90°±10° around an axis perpendicular to the membrane surface, so that the main orientation of the micropores in the upper and lower membrane layers is perpendicular to each other, forming a labyrinthine thermal resistance path in the thickness direction. As shown in Examples 2 and 4 of the specific embodiments, when the rotation angle is 90°, the interlayer misalignment of the double-layer composite membrane is reduced to 8.2%, and the thermal conductivity in the thickness direction is as low as 0.028 W / (m·K), which is more than 67% lower than that of a single-layer membrane (thermal conductivity 0.086 W / (m·K)); at the same time, the water vapor transmission rate is still maintained above 1250 g / (m²·24h), meeting the air permeability requirements. Example 3 further demonstrates that by employing a four-layer alternating stacking structure, the thermal conductivity can be further reduced to 0.022 W / (m·K), approaching the thermal conductivity level of air. Compared with the 0° parallel stacking in the comparative example (thermal conductivity 0.058-0.062 W / (m·K)), the thermal insulation performance of the composite film of the present invention is significantly improved, fully demonstrating the superiority of its structural design.

[0031] 2. This invention achieves precise adjustment of the composite film's thermal insulation performance by regulating the rotation angle and interlayer misalignment. It can optimize the balance between thermal insulation and breathability over a wide range to meet the needs of different application scenarios. As shown in Example 4 and Figure 4 in the specific implementation, when the rotation angle increases from 0° to 90°, the interlayer misalignment monotonically decreases from 42.5% to 8.2%, and the thermal conductivity simultaneously decreases from 0.058 W / (m·K) to 0.028 W / (m·K). When the angle continues to increase to 180°, the performance returns to a level close to 0°. This pattern indicates that the thermal insulation performance of the composite film can be precisely controlled by simply adjusting the interlayer rotation angle, and the interlayer misalignment can serve as a key indicator for evaluating and controlling the thermal insulation effect. Meanwhile, Examples 5 and 6 further demonstrate that by adjusting the thickness of the adhesive layer (0.1-2μm) and the concentration of PES (15-25wt%), the air permeability and mechanical properties of the composite membrane can be optimized while maintaining the interlayer misalignment structure, so that the product can flexibly adapt to the different requirements of heat insulation and air permeability in different fields such as automotive interiors, building insulation, and clothing fabrics. Attached Figure Description

[0032] Figure 1 is a schematic diagram of the pore size gradient structure of the porous membrane of the present invention;

[0033] Figure 2 is a schematic diagram of the structure of the double-layer composite film of the present invention, which is rotated and stacked at 90°.

[0034] Figure 3 is a schematic diagram of the definition of interlayer misalignment in this invention, wherein the dark area represents the overlapping part of the projection of the micropores of the two membranes in the thickness direction;

[0035] Figure 4 shows the relationship between interlayer misalignment and thermal conductivity under different rotation angles of the present invention.

[0036] Numbers in the diagram

[0037] Porous membrane 1, dense cortex 11, finger-like pore layer 12, sponge-like transition layer 13, micropores 14, membrane layer A100, membrane layer B200, first micropore 141, second micropore 142, interlayer misalignment region 300. Detailed Implementation

[0038] 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 only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Terminology Definition

[0040] In this invention, "opposite" stacking refers to the two membranes having their different side surfaces facing each other, i.e., the upper surface of the first layer is in contact with the lower surface of the second layer; "backward" stacking refers to the two membranes having their same side surfaces facing each other, i.e., the upper surface of the first layer is in contact with the upper surface of the second layer.

[0041] Raw materials used in the examples

[0042] PES (polyethersulfone): BASF, intrinsic viscosity 0.65 dL / g

[0043] DMAc dimethylacetamide: analytical grade, Sinopharm Group

[0044] Epoxidized soybean oil: Industrial grade, used for formulating adhesive layers.

[0045] All other reagents were commercially available analytical grade.

[0046] Performance testing methods

[0047] Thermal conductivity: determined using a HotDisk thermal constant analyzer according to ISO 22007-2 standard.

[0048] Water vapor transmission rate: Cup method was used, according to GB / T1037-2021 standard, at a temperature of 38℃ and a relative humidity of 90%.

[0049] Porosity: Measured by weighing, according to the formula: Porosity = (1 - ρmembrane / ρPES) × 100%

[0050] Pore ​​size distribution: measured using a capillary orifice meter.

[0051] Interlayer misalignment: The cross-section of the composite membrane was imaged using a scanning electron microscope (SEM). Image analysis software (such as ImageJ) was used to calculate the ratio of the overlapping area of ​​the micropores projected along the thickness direction to the total pore area of ​​the two membrane layers, as shown in Figure 3. The dark area represents the overlapping portion. Specifically, a slice of the composite membrane sample along the thickness direction was taken. Five fields of view (each ≥ 100 μm × 100 μm) were randomly selected under the SEM to identify the micropore contours of membrane layers A and B. After projecting them onto the same plane, the overlapping area was calculated. Interlayer misalignment = (overlapping area of ​​projected micropores) / (pore area of ​​membrane layer A + pore area of ​​membrane layer B) × 100%, and the average of five measurements was taken. It was determined that when the rotation angle was 90° ± 10°, the interlayer misalignment was ≤ 15% (e.g., 8.2% at 90° in Example 4).

[0052] Working principle of the invention

[0053] This invention provides an anisotropic heat-insulating and breathable composite membrane. Its core design concept lies in constructing a special three-dimensional structure to decouple heat transfer and gas diffusion paths, thereby simultaneously obtaining excellent heat insulation and breathability performance.

[0054] Specifically, this invention first prepares a polymer porous membrane with an anisotropic microporous structure. As shown in Figure 1, this monolayer polymer porous membrane 1 does not have a uniform pore structure, but rather exhibits a pore size gradient distribution from one surface to the other. This structure is typically prepared by a phase inversion method, forming a composite structure such as a dense skin layer 11, a sponge-like transition layer 13, and a finger-like pore layer 12. This anisotropic structure itself has a certain thermal resistance in the thickness direction.

[0055] The key innovation of this invention lies in stacking at least two layers of the aforementioned anisotropic microporous membranes with a specific orientation relationship. As shown in Figure 2, by rotating the upper membrane (membrane layer B200) relative to the lower membrane (membrane layer A100) around an axis perpendicular to the membrane surface and then stacking them, the main orientations of the micropores in the adjacent membrane layers (the first micropore direction 141 and the second micropore direction 142) are staggered. This staggered stacking method cuts off the micropore channels of the upper and lower membranes in three-dimensional space, preventing the formation of continuous straight channels, thus forming a "non-continuous structure".

[0056] In terms of heat conduction, for heat to be transferred along the thickness direction, it must repeatedly cross the interlayer interfaces and numerous solid-gas interfaces within the film. Due to the misalignment of the micropore channels, the heat flow path is greatly complicated, forming a so-called "labyrinthine thermal resistance path," as shown in the interlayer misalignment region 300 in Figure 2. This creates a highly efficient thermal resistance barrier in the thickness direction, significantly reducing the thermal conductivity of the composite film.

[0057] Regarding gas diffusion, although gas molecules such as water vapor cannot penetrate in a straight line along the thickness direction, they can diffuse along the planar direction of the membrane layer in the interconnected microporous network and eventually find an outlet. Due to the overall high porosity of the composite membrane, the diffusion channels of gas molecules in the planar direction are preserved.

[0058] In summary, this invention, through a clever interlayer misalignment design, decouples the heat transfer direction (mainly along the thickness direction) from the gas diffusion direction (which can be along planar and three-dimensional meandering paths), enabling the composite membrane to simultaneously possess low thermal conductivity and high water vapor permeability, thus solving the technical problem of traditional materials being unable to balance heat insulation and air permeability.

[0059] Example 1: Preparation of a monolayer PES porous membrane

[0060] PES was dissolved in DMAc to prepare a 20 wt% casting solution, which was then degassed under vacuum for 12 hours. The casting solution was then coated onto a glass plate to a thickness of 200 μm and immediately immersed in a deionized water coagulation bath at 25 °C for 10 minutes, after which the membrane detached automatically. The membrane was then removed, thoroughly washed with deionized water, and then vacuum dried at 60 °C for 24 hours to obtain a monolayer PES porous membrane.

[0061] As shown in Figure 1, the prepared monolayer polymer porous membrane 1 has a typical asymmetric structure: a dense skin layer 11 is formed on the side in contact with the coagulation bath, with a small pore size and an average pore size of about 15 nm; a finger-like pore layer 12 is formed on the side in contact with the glass substrate, with a larger pore size and an average pore size of about 1.2 μm; between the dense skin layer 11 and the finger-like pore layer 12 is a sponge-like transition layer 13, with a gradual transition in pore size. This structure achieves a gradient distribution of pore size from one surface to the other, which is the "anisotropic microporous structure" described in this invention. The membrane porosity is 75% and the thickness is about 150 μm.

[0062] Example 2: Preparation of a double-layer 90° rotational composite membrane

[0063] Two PES porous membranes prepared according to Example 1 were cut into 10cm × 10cm squares. The first membrane was laid flat on a polytetrafluoroethylene plate with its upper surface facing upwards. The second membrane was rotated 90° clockwise around its geometric center and placed over the first membrane, so that the upper surface of the second membrane was in contact with the upper surface of the first membrane (i.e., "opposite" stacking). As shown in Figure 2, the main orientation directions of the micropores of the two membranes are perpendicular to each other, forming an interlaced stacked structure.

[0064] An adhesive layer, consisting of an epoxidized soybean oil solution (diluted with ethanol to a viscosity of 200 mPa·s at 25°C), was uniformly sprayed between the two films at a coating weight of 5 g / m², corresponding to an adhesive layer thickness of approximately 1.0 μm. Then, a polytetrafluoroethylene (PTFE) film was applied, and the layers were hot-pressed at 80°C for 10 minutes under a pressure of 0.2 MPa. After cooling, the layers were peeled off to obtain a double-layer composite film with a total thickness of approximately 305 μm.

[0065] Figure 2 is a schematic diagram of the structure of the double-layer composite membrane of the present invention, rotated and stacked at 90°. As shown in Figure 2, to clearly illustrate the spatial relationship between the two membranes, this figure is drawn as an isometric side view. The double-layer composite membrane includes a first polymer porous membrane (membrane layer A) 100 and a second polymer porous membrane (membrane layer B) 200. The first polymer porous membrane 100 has a first micropore orientation 141 (as shown by the short horizontal line in the figure), defined as the first direction; the second polymer porous membrane 200 has a second micropore orientation 142 (as shown by the short vertical line in the figure), defined as the second direction. In this preferred embodiment, the second polymer porous membrane 200 is rotated 90° around its geometric central axis and then covers the first polymer porous membrane 100, such that the first direction and the second direction are perpendicular to each other. The area shown by the dashed box in the figure is the overlapping area of ​​the two membranes, that is, the interlayer misalignment area 300. In this area, because the micropore orientations 141 of the two membranes are perpendicular to each other and their spatial positions are misaligned, the "non-through structure" described in the present invention is formed.

[0066] Example 3: Preparation of a four-layer alternating rotation composite membrane

[0067] Four PES porous membranes were prepared according to the method in Example 1. They were then laminated sequentially using the lamination method in Example 2: first membrane (top surface facing up) → second membrane (rotated 90°, bottom surface facing up, i.e., stacked "back-to-back") → third membrane (rotated 90°, top surface facing up) → fourth membrane (rotated 90°, bottom surface facing up). An adhesive layer was sprayed between each layer at a coating amount of 5 g / m², and the hot-pressing conditions were the same as in Example 2. The final four-layer composite membrane had a total thickness of approximately 480 μm.

[0068] Example 4: Effect of different rotation angles on the performance of composite membranes

[0069] Following the method in Example 2, bilayer composite films with rotation angles of 0° (aligned stacking), 45°, 90°, 135°, and 180° were prepared respectively, with other conditions remaining unchanged.

[0070] Figure 4 shows the relationship between interlayer misalignment and thermal conductivity at different rotation angles according to the present invention. Referring to Figure 4, it shows the relationship between interlayer misalignment and thermal conductivity at different rotation angles. In the figure, the horizontal axis (X-axis) represents the rotation angle between the two films, ranging from 0° to 180°; the left vertical axis (left Y-axis) represents the interlayer misalignment (%), and the right vertical axis (right Y-axis) represents the thermal conductivity (W / (m·K)) in the thickness direction of the composite film. The solid line in the figure represents the change in interlayer misalignment with the rotation angle, and the dashed line represents the change in thermal conductivity with the rotation angle.

[0071] As can be clearly seen from Figure 4, in general, as the rotation angle increases from 0° to 90°, both the interlayer misalignment and thermal conductivity show a monotonically decreasing trend; when the rotation angle exceeds 90° and continues to increase to 180°, both monotonically increase again, and the overall distribution is a symmetrical V-shape.

[0072] The key data points are as follows:

[0073] When the rotation angle is 0°, the interlayer misalignment is 42.5% and the thermal conductivity is 0.058 W / (m·K);

[0074] When the rotation angle is 45°, the interlayer misalignment decreases to 21.3% and the thermal conductivity decreases to 0.041 W / (m·K);

[0075] When the rotation angle is 90°, the interlayer misalignment reaches a minimum of 8.2%, and the thermal conductivity also reaches a minimum of 0.028 W / (m·K).

[0076] When the rotation angle is 135°, the interlayer misalignment increases to 19.8%, and the thermal conductivity increases to 0.039 W / (m·K).

[0077] When the rotation angle is 180°, the interlayer misalignment increases to 43.1%, and the thermal conductivity increases to 0.059 W / (m·K).

[0078] Conclusion Verification: The experimental data in Figure 4 fully demonstrate that the rotation angle has a significant regulatory effect on interlayer misalignment and thermal conductivity. Around 90° (i.e., within the range of 90°±10°), the interlayer misalignment is lowest (≤15%), and the thermal conductivity is also lowest (≤0.030 W / (m·K)). This indicates that this angle range can maximize the misalignment of interlayer micropores, effectively blocking the convection conduction channels of heat along the thickness direction, thereby achieving optimal thermal insulation performance. This result is completely consistent with the preferred angle range of "90°±10°" and the requirement of "interlayer misalignment ≤15%" specified in this invention.

[0079] To further verify the interlayer misalignment within the range of 90°±10°, bilayer composite films with rotation angles of 80° and 100° were also prepared and tested using the same method. The results showed that at 80°, the interlayer misalignment was 10.3% and the thermal conductivity was 0.030 W / (m·K); at 100°, the interlayer misalignment was 9.8% and the thermal conductivity was 0.029 W / (m·K). Both were within the range of ≤15%.

[0080] Example 5: Effect of different adhesive layer thicknesses

[0081] Following the method in Example 2, the adhesive layer coating amount was varied (2, 5, 10 g / m²), corresponding to adhesive layer thicknesses of approximately 0.4, 1.0, and 2.0 μm (measured via SEM cross-section). The test performance is as follows:

[0082] Coating amount (g / m²) Adhesive layer thickness (μm) Interlayer misalignment (%) Thermal conductivity (W / m·K) Water vapor transmission rate (g / m²·24h) 20.4 9.1 0.029 1320 51.0 8.2 0.028 1250 102.0 8.5 0.030 1080 surface

[0083] The results showed that an adhesive layer thickness of 0.1-2 μm (corresponding to a coating amount of 1-10 g / m²) had little impact on thermal conductivity and could effectively bond the two membrane layers without clogging the microporous structure. To further verify the feasibility of the upper limit of the adhesive layer thickness, a sample with a coating amount of 15 g / m² (corresponding to a thickness of approximately 3.0 μm) was prepared. Tests showed that the water vapor transmission rate decreased to 850 g / (m²·24h), and the thermal conductivity increased to 0.032 W / (m·K), indicating that an excessively thick adhesive layer began to affect air permeability. When the coating amount reached 20 g / m² (thickness of approximately 4.0 μm), the water vapor transmission rate further decreased to 620 g / (m²·24h), and some micropores became clogged. Therefore, an adhesive layer thickness of 0.1-5 μm can achieve effective bonding, but to balance air permeability, 0.1-2 μm is preferred.

[0084] Example 6: Effect of different PES concentrations

[0085] Following the method of Example 1, single-layer membranes were prepared by changing the PES concentration (15%, 20%, 25%), and then 90° rotated bilayer composite membranes were prepared according to the method of Example 2. The performance was tested as follows:

[0086] PES concentration (%) Single-layer membrane porosity (%) Single-layer membrane average pore size (μm) Composite membrane thermal conductivity (W / m·K) Composite membrane water vapor transmission rate (g / m²·24h) 1582 1.8 / 0.02 0.026 1450 2075 1.2 / 0.015 0.028 1250 2568 0.8 / 0.01 0.032980 surface

[0087] The results show that PES concentration affects the porosity and pore size of the membrane, thus affecting the performance of the composite membrane. A 15% concentration membrane has high porosity and good air permeability but slightly lower mechanical strength; a 25% concentration membrane has low porosity, slightly poorer thermal insulation but higher strength. The appropriate concentration can be selected according to application requirements. All concentrations are within the 15-25 wt% range defined in this invention.

[0088] Comparative Example 1: Single-layer PES membrane

[0089] The single-layer PES membrane prepared according to Example 1 has a thickness of 150 μm.

[0090] Comparative Example 2: Randomly Stacked Composite Membrane

[0091] The method of Example 2 was followed, but the second film was not rotated and was directly stacked in the same direction (i.e., 0°), with the stacking method being "opposite" stacking, consistent with Example 4-0°, and other conditions remaining unchanged. The thermal conductivity was tested to be 0.058 W / (m·K), and the interlayer misalignment was 42.5%, consistent with the results of Example 4-0°.

[0092] Summary of performance test results

[0093] Sample rotation angle, stacking method, interlayer misalignment (%), thermal conductivity (W / m·K), water vapor transmission rate (g / m²·24h). Example 2: 90° facing each other, 8.2, 0.028, 1250. Example 3: 90° alternating facing / backwards, 6.5, 0.022, 980. Example 4: -0° 0° facing each other, 42.5, 0.058, 1480. Example 4: -45° 45° facing each other, 21.3, 0.041, 1320. Example 4: -90° 90° facing each other, 8.2, 0.028, 1250. Example 4: -135° 135° facing each other, 19.8, 0.039, 1280. Example 4: -180° 180° facing each other, 43.1, 0.059, 1460. Comparative Example 1: --- 0.086, 1600. Comparative Example 2: 0° same direction, 42.5, 0.058, 1520. surface

[0094] Results Analysis

[0095] The relationship between the curves shown in Figure 4 makes it even clearer:

[0096] 1. The single-layer PES membrane (Comparative Example 1) has a thermal conductivity of 0.086 W / (m·K) and a water vapor permeability of 1600 g / (m²·24h), exhibiting high air permeability but only average heat insulation.

[0097] The interlayer misalignment of 2.0° stacking (Comparative Example 2) is as high as 45.2%, but the thermal conductivity only decreases to 0.062 W / (m·K), indicating that simply increasing the thickness without changing the micropore orientation has limited effect on improving thermal insulation.

[0098] 3. 90° rotational stacking (Example 2) reduced interlayer misalignment to 8.2%, significantly decreased thermal conductivity to 0.028 W / (m·K), while maintaining water vapor permeability at 1250 g / (m²·24h), achieving a good balance between thermal insulation and air permeability. Figure 4 shows a clear trough in the curve near 90°, and experimental data verify that the interlayer misalignment is lowest and the reduction in thermal conductivity is greatest within the range of 90°±10°.

[0099] 4. The four layers are stacked alternately at 90° (Example 3) to further reduce the thermal conductivity to 0.022 W / (m·K), which is close to the thermal conductivity of air, but the water vapor permeability is slightly reduced, but still remains at 980 g / (m²·24h), which meets the requirements of automotive interiors.

[0100] Rotation at 5.45° and 135° (Example 4) results in an interlayer misalignment of approximately 20% and a thermal conductivity of 0.039-0.041 W / (m·K), which falls between 0° and 90°, further demonstrating that 90° is the optimal angle.

[0101] A 6.180° rotation is equivalent to two layers of film stacked in opposite directions, with the interlayer misalignment close to 0°, resulting in poor heat insulation.

[0102] Conclusion: Within a rotation angle of 90°±10°, an interlayer misalignment of ≤15% can achieve the best thermal insulation and breathability performance; multilayer composites can further reduce the thermal conductivity, but breathability needs to be balanced; the adhesive layer thickness is controlled at 0.1-2μm (coating amount 1-10g / m²) to effectively bond without clogging micropores.

[0103] Other implementation methods

[0104] The scope of protection of this invention is not limited to the specific embodiments described above. Any equivalent transformation or substitution based on the concept of this invention, such as using other polymer materials (e.g., PVDF, PI, PAN) to prepare anisotropic porous membranes, or using other adhesive layer materials (e.g., polyurethane, acrylate), or adjusting the lamination parameters (pressure 0.05-0.5MPa, temperature 60-120℃), as long as the heat flow and gas diffusion direction are decoupled, falls within the scope of protection of this invention.

[0105] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", and "linkage" should be interpreted broadly, and can be mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.

[0106] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.

[0107] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An anisotropic thermal insulation and breathable composite membrane, characterized in that: The composite membrane is composed of at least two layers of polymer porous membrane stacked together; the polymer porous membrane has an anisotropic microporous structure, the anisotropy being manifested in the gradient distribution of pore size from one side surface of the membrane to the other side surface; the at least two layers of polymer porous membrane are stacked with a specific orientation relationship, so that the microporous channels of adjacent membrane layers form a non-through structure in three-dimensional space; the composite membrane is configured to decouple the heat flow transfer direction from the gas diffusion direction, that is, to form a thermal resistance barrier that inhibits heat conduction in the thickness direction, while maintaining the diffusion channel of gas molecules in the planar direction.

2. The anisotropic heat-insulating and breathable composite membrane according to claim 1, characterized in that: The specific orientation relationship is that adjacent film layers are stacked after being rotated at a certain angle around an axis perpendicular to the film surface, and the rotation angle is 45°-135°.

3. The anisotropic heat-insulating and breathable composite membrane according to claim 2, characterized in that: The rotation angle is 90°±10°, so that the main orientation direction of the micropores of adjacent film layers is perpendicular to each other. When the heat flow is transferred along the thickness direction, it must repeatedly cross the solid-gas interface inside the film layer, forming a labyrinthine thermal resistance path.

4. The anisotropic heat-insulating and breathable composite membrane according to claim 1, characterized in that: The polymer porous membrane is a polyethersulfone membrane, and the microporous structure is formed by phase inversion and has a gradient distribution from the side with smaller pore size to the side with larger pore size. The side with smaller pore size is a dense skin layer, the side with larger pore size is a finger-like pore layer, and there is a sponge-like transition layer between the dense skin layer and the finger-like pore layer.

5. The anisotropic heat-insulating and breathable composite membrane according to claim 1, characterized in that: An adhesive layer is provided between adjacent membrane layers. The adhesive layer is a low-viscosity, high-permeability polymer solution with a viscosity of 50-500 mPa·s at 25°C. It is applied by spraying, dipping, or scraping, with a coating amount of 1-10 g / m². The adhesive layer fills the interfacial gap between the two membrane layers through capillary action. The thickness of the adhesive layer is 0.1-5 μm, and it does not block the microporous structure inside the membrane layers.

6. The anisotropic heat-insulating and breathable composite membrane according to claim 1, characterized in that: The composite membrane is composed of 2-10 layers of polymer porous membrane stacked together, with a total thickness of 50-500μm, a porosity of 50%-85%, and an average pore size of 10nm-100nm or 1μm-5μm.

7. An anisotropic thermal insulation and breathable composite membrane according to any one of claims 1-6, characterized in that: The composite membrane has a thermal conductivity of 0.020-0.045 W / (m·K) in the thickness direction and a water vapor transmission rate of 500-2000 g / (m²·24h), and can be used in automotive interiors, building insulation or clothing fabrics.

8. A staggered lamination process for preparing the anisotropic thermally insulating and breathable composite membrane as described in any one of claims 1-7, characterized in that: Includes the following steps: (1) Prepare at least two polymer porous membranes with anisotropic microporous structures by phase inversion method, wherein the pore size of the polymer porous membranes is gradient distributed from one side surface to the other side surface; (2) Lay the first polymer porous membrane flat on the substrate; (3) Rotate the second polymer porous membrane 45°-135° around its geometric center axis and cover it on the first membrane; (4) Apply an adhesive layer between the two membranes, apply a pressure of 0.05-0.5MPa, and hot press the membranes together at 60-120℃ to fix the two membranes together; (5) Repeat steps (2)-(4) 1-8 times to stack more membranes in sequence to form a composite membrane with a total number of 2-10 layers.

9. The staggered lamination process according to claim 8, characterized in that: The process parameters for the phase inversion method described in step (1) are as follows: PES concentration is 15-25 wt%, solvent is one or more of dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) or dimethylformamide (DMF), coagulation bath is water or a mixture of water and solvent, coagulation bath temperature is 20-60℃, casting solution coating thickness is 50-500 μm, and residence time in coagulation bath is 5-30 minutes. By adjusting the process parameters, the pore size distribution, porosity and anisotropy of the monolayer membrane are controlled, thereby adjusting the interlayer misalignment of the final composite membrane.

10. The staggered lamination process according to claim 8 or 9, characterized in that: The interlayer misalignment is determined by image analysis and is defined as the ratio of the overlapping area of ​​the micropores of the two membranes projected in the thickness direction to the total pore area; when the rotation angle is 90°±10°, the interlayer misalignment is ≤15%.

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