Microporous polyurethane film and preparation method thereof

Abstract

The invention provides a microporous polyurethane film and a preparation method thereof, and the preparation method comprises the following steps: (1) mixing a reinforcing filler, a dispersant and water, and carrying out ultrasonic dispersion to obtain a dispersion liquid; wherein the reinforcing filler is graphene or a carbon nano tube; (2) uniformly mixing polyurethane resin and a solvent, and uniformly stirring and mixing with the dispersion liquid and a functional additive to obtain a composite film liquid; wherein the functional auxiliary agent comprises a pore-foaming agent; and (3) blade-coating a base material with the composite film liquid, drying to obtain a polyurethane base film, and then carrying out two-way stretching on the polyurethane base film to obtain the microporous polyurethane film. The prepared polyurethane film has high moisture permeability, high water pressure resistance and excellent mechanical strength, and can meet the high-performance requirements of multiple scenes such as outdoor sports, medical use and military use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waterproof and moisture-permeable membranes, in particular to a microporous polyurethane film and a preparation method thereof. BACKGROUND

[0002] The number of people participating in outdoor activities nationwide has exceeded 400 million, and the growth of domestic high-performance outdoor clothing continues to be good. The consumer group is becoming younger and more age-inclusive, and consumers are shifting from professional outdoor activities to daily commuting, driving demand for fabrics that combine protection and comfort.

[0003] Clothing such as jackets is mainly prepared by laminating nylon or polyester fabric with a film. Polyurethane (PU) film is of great concern due to its softness, wear resistance, and ease of compounding. In the prior art, non-solvent induced phase separation is generally used to prepare polyurethane film. Although the PU film prepared by this method has a porous and moisture-permeable structure, it often has poor water washing resistance due to insufficient stability of the pore structure, and the pores collapse or the function decays after multiple washes. At the same time, this process has the risk of solvent residue, affecting the safety of wearing and environmental friendliness. In addition, the balance between mechanical strength and high water pressure resistance and high moisture permeability of conventional PU film still faces challenges, making it difficult to meet the demand for durable protection and all-weather comfort of outdoor clothing.

[0004] Therefore, there is an urgent need to provide a microporous polyurethane film and a preparation method thereof. SUMMARY

[0005] The present application provides a microporous polyurethane film and a preparation method thereof, which can solve the problem that existing polyurethane films cannot simultaneously have good air permeability, mechanical strength, water pressure resistance, and high moisture permeability.

[0006] In a first aspect, a preparation method of a microporous polyurethane film is provided, the preparation method comprising the following steps: (1) mixing a reinforcing filler, a dispersant, and water, and then performing ultrasonic dispersion to obtain a dispersion liquid; wherein the reinforcing filler is graphene or a carbon nanotube; (2) mixing polyurethane resin and a solvent, and then stirring and mixing the polyurethane resin and the solvent with the dispersion liquid and a functional additive to obtain a composite film liquid; wherein the functional additive includes a porogen; (3) coating the composite film liquid on a substrate and drying to obtain a polyurethane base film, and then bidirectionally stretching the polyurethane base film to obtain the microporous polyurethane film.

[0007] Preferably, in step (1), the dispersant is sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, or dioctyl sodium sulfosuccinate.

[0008] Preferably, by mass percentage, carbon nanotubes account for 1-3%, dispersant accounts for 0.5-6%, and water accounts for 91-98.5%.

[0009] Preferably, in step (2), the polyurethane resin is a polyether-type polyurethane, and the solvent is at least one of ethanol, propanol, or butanone.

[0010] Preferably, by mass percentage, the polyurethane resin is 25-30%, the solvent is 55-68%, the dispersion is 1-10%, and the functional additives are 1-5%.

[0011] Preferably, in step (2), the functional additives further include defoamers and dispersants; wherein the defoamer is an acrylate copolymer defoamer or a polyether non-silicone modified defoamer.

[0012] Preferably, the pore-forming agent is nano-calcium carbonate, sodium chloride, Al2O3 powder, SiO2 particles, or polyvinylpyrrolidone.

[0013] Preferably, the mass ratio of the pore-forming agent, defoamer, and dispersant in the functional additive is (1~3): 1: 1.

[0014] Preferably, in step (3), the substrate is one of nonwoven fabric, spunbond fabric, release paper, kraft paper, wood pulp fabric or cotton fabric.

[0015] Preferably, in step (3), a three-stage gradient heating method is used for drying; wherein, The first stage of drying is at a temperature of 60~80℃ for 3~5 minutes; The second stage of drying is carried out at a temperature of 80~110℃ for 8~15 minutes. The third stage of drying is carried out at a temperature of 120~150℃ for 10~20 minutes.

[0016] Preferably, in step (3), the temperature of the biaxial stretching is 110~120℃, the longitudinal and transverse stretching ratios are 5~8 times, and the setting temperature is 160~180℃.

[0017] Secondly, embodiments of the present invention also provide a microporous polyurethane film, which is prepared by the preparation method described in any one of the first aspects above.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: In this invention, graphene or carbon nanotubes are first ultrasonically dispersed using a dispersant and water to ensure uniform and stable dispersion. Then, polyurethane resin is mixed with the dispersion and a functional additive containing a pore-forming agent to form a composite film liquid. During subsequent stretching, the pore-forming agent forms an interface with the polyurethane matrix, creating micron-sized primary pores. Simultaneously, the addition of graphene or carbon nanotubes further regulates the pore size and distribution. A polyurethane base film is prepared using a blade coating method, and then biaxially stretched to form a polyurethane film with a microporous structure. During biaxial stretching, the interwoven three-dimensional network formed by the graphene or carbon nanotubes not only acts as a rigid framework to support the microporous structure and fix the micropore morphology, but also enhances the mechanical properties of the film through the π-π stacking effect, preventing the pores from disappearing or deforming after the removal of external force (stretching force), thus ensuring uniform micropore shaping. Meanwhile, by precisely controlling the stretching and setting temperatures, billions of uniformly distributed and shape-stable micron-sized pores are formed inside the film under the synergistic effect of the three-dimensional network structure formed by graphene or carbon nanotubes. This overcomes the drawbacks of uneven pore structure or difficulty in setting caused by traditional unidirectional stretching or non-stretching. Ultimately, the resulting polyurethane film possesses high moisture permeability, high water pressure resistance, and excellent mechanical strength, meeting the high-performance requirements of various scenarios such as outdoor sports, medical, and military applications. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. 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.

[0020] Figure 1 This is a scanning electron microscope image of a microporous polyurethane film provided in Embodiment 1 of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 some embodiments of the present invention, but not all 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.

[0022] This invention provides a method for preparing a microporous polyurethane film, the method comprising the following steps: (1) The reinforcing filler, dispersant and water are mixed and then ultrasonically dispersed to obtain a dispersion; wherein the reinforcing filler is graphene or carbon nanotubes; (2) After mixing polyurethane resin and solvent, stir and mix with dispersion and functional additives to obtain composite film liquid; wherein, the functional additives include pore-forming agents; (3) The composite film liquid is coated onto the substrate and dried to obtain a polyurethane base film. Then, the polyurethane base film is biaxially stretched to obtain the microporous polyurethane film.

[0023] In this embodiment of the invention, graphene or carbon nanotubes are first ultrasonically dispersed using a dispersant and water to ensure uniform and stable dispersion. Then, polyurethane resin is mixed with the dispersion and a functional additive containing a pore-forming agent to form a composite film liquid. During subsequent stretching, the pore-forming agent forms an interface with the polyurethane matrix, creating micron-sized primary pores. Simultaneously, the addition of graphene or carbon nanotubes further regulates the pore size and distribution. A polyurethane base film is prepared using a blade coating method, and then biaxially stretched to form a polyurethane film with a microporous structure. During biaxial stretching, the interwoven three-dimensional network formed by the graphene or carbon nanotubes not only acts as a rigid framework to support the microporous structure and fix the micropore morphology, but also enhances the mechanical properties of the film through the π-π stacking effect, preventing the disappearance or deformation of pores caused by the removal of the stretching force, thus ensuring uniform micropore shaping. Meanwhile, by precisely controlling the stretching and setting temperatures, billions of uniformly distributed and shape-stable micron-sized pores are formed inside the film under the synergistic effect of the three-dimensional network structure formed by graphene or carbon nanotubes. This overcomes the drawbacks of uneven pore structure or difficulty in setting caused by traditional unidirectional stretching or non-stretching. Ultimately, the resulting polyurethane film possesses high moisture permeability, high water pressure resistance, and excellent mechanical strength, meeting the high-performance requirements of various scenarios such as outdoor sports, medical, and military applications.

[0024] According to some preferred embodiments, in step (1), the dispersant is sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or sodium dioctyl sulfosuccinate; by mass percentage, carbon nanotubes are 1-3% (e.g., 1%, 2% or 3%), dispersant is 0.5-6% (e.g., 0.5%, 1%, 2%, 3%, 4%, 5% or 6%), and water is 91-98.5% (e.g., 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 98.5%).

[0025] In this embodiment of the invention, graphene or carbon nanotubes (multi-walled carbon nanotubes) are mixed with water and the above-mentioned dispersants. First, the mixture is dispersed under ultrasonic treatment for 30-40 minutes to initially de-agglomerate the graphene or carbon nanotubes and achieve nanoscale dispersion. Then, a magnetic stirrer is used to continuously stir for 1-2 hours to further promote the homogenization and stabilization of the solution, thereby ensuring uniform and stable dispersion of the graphene or carbon nanotubes. This facilitates the subsequent construction of an interwoven three-dimensional network structure of graphene or carbon nanotubes in a polyurethane matrix. It should be noted that the reinforcing filler in this embodiment of the invention is preferably carbon nanotubes.

[0026] According to some preferred embodiments, in step (2), the polyurethane resin is a polyether-type polyurethane, and the solvent is at least one of ethanol, propanol, or butanone; by mass percentage, the polyurethane resin is 25-30% (e.g., 25%, 26%, 28%, or 30%), the solvent is 55-68% (e.g., 55%, 58%, 60%, 62%, 65%, or 68%), the dispersion is 1-10% (e.g., 1%, 2%, 3%, 5%, 8%, or 10%), and the functional additive is 1-5% (e.g., 1%, 2%, 3%, 4%, or 5%); the pore-forming agent is nano-calcium carbonate, sodium chloride, Al2O3 powder, SiO2 particles, or polyvinylpyrrolidone.

[0027] In this embodiment of the invention, the above-mentioned solvent is mixed with polyether-type polyurethane, and then the mixture is stirred and mixed with dispersion and functional additives to form a uniform composite film liquid. The functional additives include specific types of pore-forming agents, dispersants, and defoamers. During the subsequent film formation process, carbon nanotubes guide the orderly arrangement of polyurethane hard segments through π-π stacking and interweave in the polyurethane matrix to form an interconnected network, thereby strengthening the strength of the polyurethane matrix itself. At the same time, nano-calcium carbonate can form an interface with the polyurethane matrix to form micron-sized pores, working together with carbon nanotubes to regulate the pore size and distribution, so that the polyurethane film forms a hierarchical multi-level moisture-permeable channel. In the subsequent biaxial stretching process, the three-dimensional network formed by the interconnection of graphene or carbon nanotubes can play the role of a rigid skeleton, not only effectively supporting the porous structure and preventing its collapse, but also the reinforced interface formed by π-π stacking can enhance the mechanical properties of the film, avoiding deformation or closure caused by the removal of external force (tensile force), which is conducive to preparing a polyurethane film with a uniform, stable and mechanically excellent microporous structure.

[0028] Experiments of this invention have confirmed that by synergistically controlling the content of each component in the composite film liquid, it is beneficial to maximize the air permeability, moisture permeability, mechanical strength, and water pressure resistance of the polyurethane film. If the content of polyurethane resin is too high, it will significantly increase the viscosity of the casting liquid, resulting in poor flowability during coating and difficulty in forming a uniform film layer. If the content of carbon nanotubes is too low, it will not be conducive to ensuring good mechanical strength of the film, and the microporous structure is prone to deformation during subsequent stretching, making it difficult to shape. If the content of carbon nanotubes is too high, it is easy to generate agglomeration in the polyurethane matrix, affecting the uniformity and mechanical integrity of the film. The content of pore-forming agent affects the pore structure of the polyurethane film. If the content of pore-forming agent is too low, the porosity of the film will be too low, resulting in a significant decrease in moisture permeability and air permeability. If the content of pore-forming agent is too high, it will lead to significant differences in pore size, increasing internal defects in the film (such as pores and cracks).

[0029] According to some preferred embodiments, in step (2), the functional additives further include defoamers and dispersants; wherein, the defoamers are acrylate copolymer defoamers (such as FOAMEX 800, BYK-051) and polyether non-silicone modified defoamers; According to some preferred embodiments, the mass ratio of pore-forming agent, defoamer and dispersant in the functional additive is (1~3):1:1 (for example, it can be 1:1:1, 2:1:1 or 3:1:1).

[0030] In this embodiment of the invention, to further ensure the uniform dispersion of graphene or carbon nanotubes in the polyurethane matrix and avoid structural defects caused by agglomeration, specific types of defoamers and dispersants are further introduced into the functional additive system. The defoamer effectively suppresses microbubbles generated during stirring and film formation, preventing them from interfering with the uniform distribution of carbon nanotubes. The dispersant added during this process further maintains the stable dispersion of graphene or carbon nanotubes during mixing and subsequent processes. Simultaneously, by controlling and optimizing the proportions of each component (including pore-forming agents, defoamers, and dispersants) in the functional additives, not only can the pore-forming effect and good mechanical strength of the polyurethane film be guaranteed, but the additives can also work synergistically to ensure that the final polyurethane microporous film achieves an optimal balance in terms of structural uniformity, air and moisture permeability, water pressure resistance, and overall mechanical properties.

[0031] According to some preferred embodiments, in step (3), the substrate is one of non-woven fabric, spunbond fabric, release paper, kraft paper, wood pulp fabric or cotton fabric.

[0032] According to some preferred embodiments, in step (3), a three-stage gradient heating method is used for drying; wherein, the temperature of the first stage drying is 60~80℃ (for example, it can be 60℃, 70℃ or 80℃), and the time is 3~5min (for example, it can be 3min, 4min or 5min); the temperature of the second stage drying is 80~110℃ (for example, it can be 80℃, 90℃, 100℃ or 110℃), and the time is 8~15min (for example, it can be 8min, 9min, 10min, 11min, 12min, 13min, 14min or 15min); the temperature of the third stage drying is 120~150℃ (for example, it can be 120℃, 130℃, 140℃ or 150℃), and the time is 10~20min (for example, it can be 10min, 12min, 14min, 15min, 18min or 20min).

[0033] In this embodiment of the invention, the composite film liquid formed after the above-mentioned mixing is coated onto a clean and flat substrate. The substrate coated with the liquid film is then subjected to gradient heating and drying to obtain a polyurethane-based film. During the drying process, a three-stage gradient heating method is used. By rationally controlling the temperature at each stage, thermal stress can be effectively alleviated, and residual stress inside the film layer can be slowly released. This reduces surface defects and improves the overall strength of the polyurethane film. Specifically, the first stage of drying removes residual solvent and moisture from the surface, promoting the initial orientation and alignment of polyurethane molecular chains to form a uniform and continuous film layer, and reducing deformation of the polyurethane-based film caused by high-temperature shrinkage of the substrate. The second stage of drying promotes the cross-linking reaction of polyurethane molecular chains at a higher temperature, thereby enhancing the mechanical strength of the film layer and preventing pore collapse during subsequent processing or use. The third stage of drying further promotes the complete cross-linking of resin molecular chains, forming a stable three-dimensional network structure, significantly improving the tensile strength and flexural strength of the film. In this way, by controlling the drying temperature in a gradient manner, not only is the internal stress of the membrane layer reduced and the solvent evaporation rate reasonably controlled, but also the overall performance of the polyurethane-based membrane is significantly improved by optimizing the membrane layer structure in stages, ensuring that it has excellent mechanical strength and durability.

[0034] It should be noted that in this embodiment of the invention, after drying, the polyurethane base film formed is separated from the substrate by a peeling roller, and the peeling force is controlled to be 2-6 N / cm.

[0035] According to some preferred embodiments, in step (3), the temperature of the biaxial stretching is 110~120℃ (for example, it can be 110℃, 115℃, 118℃ or 120℃), the longitudinal and transverse stretching ratios are 5~8 times (for example, it can be 5 times, 6 times, 7 times or 8 times), and the setting temperature is 160~180℃ (for example, it can be 160℃, 165℃, 170℃, 175℃ or 180℃).

[0036] In this embodiment of the invention, by precisely controlling the stretching temperature, setting temperature, and stretching ratio during the biaxial stretching process, it is beneficial to achieve directional regulation and effective fixation of the microporous structure of the polyurethane-based film. Simultaneously, combined with the rigid framework formed by the graphene or carbon nanotube network in the polyurethane-based film, and the synergistic regulation of the aforementioned stretching parameters, not only are problems such as pore collapse, merging, or disappearance caused by improper stretching in traditional processes avoided, but the film also maintains excellent mechanical strength, dimensional stability, and water pressure resistance while achieving high moisture permeability. Furthermore, the aforementioned biaxial stretching and gradient drying process parameters are clearly defined, and the equipment compatibility is strong, making it suitable for existing dry-stretched film production lines.

[0037] This invention also provides a microporous polyurethane film, prepared using any of the above-described preparation methods.

[0038] To more clearly illustrate the technical solution and advantages of the present invention, the following describes in detail a microporous polyurethane film and its preparation method through several embodiments.

[0039] Example 1: (1) 1 wt% carbon nanotubes, 0.6 wt% dispersant (sodium dodecyl sulfate) and 98.4 wt% deionized water were poured into an Erlenmeyer flask and mixed. The mixture was then placed in an ultrasonic cleaner for ultrasonic dispersion for 30 min. After that, a magnetic stirrer was used to continue stirring and mixing for 1 h to obtain a dispersion. (2) Mix 26wt% polyurethane resin (polyether polyurethane) and 68wt% solvent (volume ratio 1:1.5) Ethanol After adding methyl ethyl ketone (MEK) to the reaction vessel and mixing well, add 1 wt% dispersion and 5 wt% functional additives and stir to obtain composite film liquid; wherein, the functional additives include pore-forming agent (calcium carbonate powder), defoamer (BYK-051 polyacrylate) and dispersant (sodium dodecyl sulfate) in a mass ratio of 3:1:1. (3) The composite film liquid is coated onto the substrate (release paper) with a doctor blade, and the thickness is controlled to be 150 μm. The substrate coated with the composite film liquid is transported by a conveyor belt and dried in three ovens. The polyurethane base film is separated from the substrate by a peeling roller with a peeling force of 4 N / cm to obtain the polyurethane base film. The drying temperature in the first stage is 70℃ and the time is 5 min; the drying temperature in the second stage is 90℃ and the time is 15 min; the drying temperature in the third stage is 130℃ and the time is 15 min. A polyurethane-based film was subjected to biaxial stretching at a temperature of 180℃, with a stretching ratio of 5 times in both the longitudinal and transverse directions, and a setting temperature of 190℃ to obtain a microporous polyurethane film.

[0040] Example 2: (1) 2wt% carbon nanotubes, 1.2wt% dispersant (sodium dodecyl sulfate) and 96.8wt% deionized water were poured into an Erlenmeyer flask and mixed. The mixture was then placed in an ultrasonic cleaner for ultrasonic dispersion for 30 min. After that, a magnetic stirrer was used to continue stirring and mixing for 1 h to obtain a dispersion. (2) 26wt% polyurethane resin (polyether polyurethane) and 67wt% solvent (ethanol and butanone in a volume ratio of 1:1.5) were added to the reactor and mixed. Then, 3wt% dispersion and 4wt% functional additives were added and stirred to obtain a composite film liquid. The functional additives included a pore-forming agent (calcium carbonate powder), an antifoaming agent (BYK-051 polyacrylate), and a dispersant (sodium dodecyl sulfate) in a mass ratio of 3:1:1. (3) The composite film liquid is coated onto the substrate (release paper) with a doctor blade, and the thickness is controlled to be 150 μm. The substrate coated with the composite film liquid is transported by a conveyor belt and dried in three ovens. The polyurethane base film is separated from the substrate by a peeling roller with a peeling force of 5 N / cm to obtain the polyurethane base film. The drying temperature in the first stage is 60℃ and the time is 5 min; the drying temperature in the second stage is 100℃ and the time is 15 min; the drying temperature in the third stage is 120℃ and the time is 15 min. A polyurethane-based film was subjected to biaxial stretching at a temperature of 170℃, with a stretching ratio of 5 times in both the longitudinal and transverse directions, and a setting temperature of 190℃ to obtain a microporous polyurethane film.

[0041] Example 3: (1) 3wt% carbon nanotubes, 1.8wt% dispersant (sodium dodecyl sulfate) and 95.2wt% deionized water were poured into an Erlenmeyer flask and mixed. The mixture was then placed in an ultrasonic cleaner for ultrasonic dispersion for 30 min. After that, a magnetic stirrer was used to continue stirring and mixing for 1 h to obtain a dispersion. (2) 26wt% polyurethane resin (polyether polyurethane) and 68wt% solvent (ethanol and acetone in a volume ratio of 1:3) were added to the reactor and mixed. Then, 2wt% dispersion and 4wt% functional additives were added and stirred to obtain a composite film liquid. The functional additives included a pore-forming agent (calcium carbonate powder), an antifoaming agent (BYK-051 polyacrylate), and a dispersant (sodium dodecyl sulfate) in a mass ratio of 2:1:1. (3) The composite film liquid is coated onto the substrate (release paper) with a doctor blade, and the thickness is controlled to be 180 μm. The substrate coated with the composite film liquid is transported by a conveyor belt and dried in three ovens. The polyurethane base film is separated from the substrate by a peeling roller with a peeling force of 5 N / cm to obtain the polyurethane base film. The drying temperature in the first stage is 80℃ and the time is 5 min; the drying temperature in the second stage is 100℃ and the time is 15 min; the drying temperature in the third stage is 120℃ and the time is 15 min. A polyurethane-based film was biaxially stretched at a temperature of 170°C with a longitudinal and transverse stretch ratio of 5 times, and then set at a temperature of 185°C to obtain a microporous polyurethane film.

[0042] Example 4: Example 4 is basically the same as Example 1, except that in step (2), the content of the dispersion is 8 wt%.

[0043] Example 5: Example 5 is basically the same as Example 1, except that in step (2), the content of the dispersion is 0.1 wt%.

[0044] Example 6: Example 6 is basically the same as Example 1, except that in step (2), no dispersant is added to the functional additives, and only a pore-forming agent (calcium carbonate powder) and an antifoaming agent (BYK-051 polyacrylate) with a mass ratio of 2:1 are included.

[0045] Example 7: Example 7 is basically the same as Example 1, except that: in step (2), no pore-forming agent is added to the functional additives, only defoamer (BYK-051 polyacrylate) and dispersant (sodium dodecyl sulfate) in a mass ratio of 1:1.

[0046] Example 8: Example 8 is basically the same as Example 1, except that in step (3), the polyurethane base film is dried at a constant temperature of 100°C for 60 minutes.

[0047] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that step (1) is removed, and in step (2), 29 wt% polyurethane resin (polyether polyurethane) and 69 wt% solvent (ethanol and butanone in a volume ratio of 1:1) are added to the reaction vessel and mixed, and then 2 wt% functional additives are added and stirred to obtain a composite film liquid; wherein, the functional additives include a pore-forming agent (calcium carbonate powder), a defoamer (BYK-051 polyacrylate) and a dispersant (sodium dodecyl sulfate) in a mass ratio of 2:1:1; and in step (3), the polyurethane film is longitudinally stretched at a stretching temperature of 170°C and a stretching ratio of 3 times to obtain a polyurethane film.

[0048] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that step (1) is removed, and in step (2), 29 wt% polyurethane resin (polyether polyurethane) and 69 wt% solvent (ethanol and butanone in a volume ratio of 1:1) are added to the reaction vessel and mixed, and then 2 wt% functional additives are added and stirred to obtain a composite film liquid; wherein, the functional additives include a pore-forming agent (calcium carbonate powder), a defoamer (BYK-051 polyacrylate) and a dispersant (sodium dodecyl sulfate) in a mass ratio of 2:1:1; and in step (3), the polyurethane film is subjected to biaxial stretching at a stretching temperature of 170°C, a stretching ratio of 5 times, and a setting temperature of 190°C to obtain a polyurethane film.

[0049] The performance of the microporous polyurethane film samples provided in the examples and comparative examples was tested, and the test results are shown in Table 1 below: Porosity: Determined according to GB / T 33052-2016 Method for Determination of Porosity of Microporous Functional Thin Films - Cetane Absorption Method.

[0050] Tensile strength: The test standard is ASTM D638-02; the PU films prepared in the examples and comparative examples are cut into dumbbell-shaped strips, and five standard strips are collected in the transverse direction for each sample. The strips are fixed on the universal testing machine, and the tensile rate is set to 200 mm / min. Data are collected after the test is completed, and the final result is the average value.

[0051] Moisture permeability: determined according to Method A of GB / T 12704.1-2009 "Textiles - Test methods for moisture permeability of fabrics - Part 1: Moisture absorption method".

[0052] Hydrostatic pressure: determined according to GB / T 4744-2013 "Water repellency test of textiles - static hydrostatic pressure method".

[0053] Table 1 Combining Table 1 and Figure 1As can be seen from the above, the microporous polyurethane film prepared in this embodiment has high porosity and uniform structure distribution. It has good moisture permeability and water pressure resistance. Moreover, compared with Comparative Example 1, the mechanical strength of the polyurethane microporous film is increased by 30-40%, which can meet the long-term use requirements of functional clothing fabrics.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a microporous polyurethane film, characterized in that, The preparation method includes the following steps: (1) The reinforcing filler, dispersant and water are mixed and then ultrasonically dispersed to obtain a dispersion; wherein the reinforcing filler is graphene or carbon nanotubes; (2) After mixing polyurethane resin and solvent, stir and mix with dispersion and functional additives to obtain composite film liquid; wherein, the functional additives include pore-forming agents; (3) The composite film liquid is coated onto the substrate and dried to obtain a polyurethane base film. Then, the polyurethane base film is biaxially stretched to obtain the microporous polyurethane film.

2. The preparation method according to claim 1, characterized in that, In step (1), the dispersant is sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or sodium dioctyl sulfosuccinate; By mass percentage, carbon nanotubes account for 1-3%, dispersant for 0.5-6%, and water for 91-98.5%.

3. The preparation method according to claim 1, characterized in that, In step (2), the polyurethane resin is a polyether-type polyurethane, and the solvent is at least one of ethanol, propanol, or butanone; and / or By mass percentage, the polyurethane resin is 25-30%, the solvent is 55-68%, the dispersion is 1-10%, and the functional additives are 1-5%.

4. The preparation method according to claim 1, characterized in that, In step (2), the functional additives also include defoamers and dispersants; wherein the defoamer is an acrylate copolymer defoamer or a polyether non-silicone modified defoamer.

5. The preparation method according to claim 1, characterized in that, In step (2), the pore-forming agent is at least one of nano-calcium carbonate, sodium chloride, Al2O3 powder, SiO2 particles or polyvinylpyrrolidone.

6. The preparation method according to claim 4, characterized in that, In the functional additives, the mass ratio of pore-forming agent, defoamer and dispersant is (1~3):1:

1.

7. The preparation method according to claim 1, characterized in that, In step (3), the substrate is one of non-woven fabric, spunbond fabric, release paper, kraft paper, wood pulp cloth or cotton cloth.

8. The preparation method according to claim 1, characterized in that, In step (3), a three-stage gradient heating method is used for drying; wherein, The first stage of drying is at a temperature of 60~80℃ for 3~5 minutes; The second stage of drying is carried out at a temperature of 80~110℃ for 8~15 minutes. The third stage of drying is carried out at a temperature of 120~150℃ for 10~20 minutes.

9. The preparation method according to claim 1, characterized in that, In step (3), the temperature of the biaxial stretching is 110~120℃, the longitudinal and transverse stretching ratios are 5~8 times, and the setting temperature is 160~180℃.

10. A microporous polyurethane film, characterized in that, It is prepared by any one of the preparation methods according to claims 1 to 9.

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