Wet process microporous membrane based on direct coating of base cloth and preparation method thereof

Abstract

The present application relates to the technical field of wet micro-porous membrane, in particular to a wet micro-porous membrane based on direct coating of base cloth and a preparation method thereof. The wet micro-porous membrane comprises the following steps: introducing hydrophilic modified carbon particles in a specific proportion into a bio-based polyurethane slurry as phase separation induced crystal nucleus; making the elastic base cloth run flat under a micro-tension state through linkage of a first constant tension unit and a second constant tension unit; immersing the base cloth into a coagulation tank after direct coating of the slurry on the surface of the base cloth in situ, and using directional aggregation of water molecules to the surface of the carbon particles to induce formation of a micro-porous structure; then performing low-stress high-temperature anchoring drying at 160-170 DEG C; and finally winding and separating the membrane. The present application realizes the synergy of micro-induction pore formation of the material and mechanical pressure release in the whole process, and the prepared micro-porous membrane integrates ultra-high moisture permeability, high water pressure resistance, super-soft hand feeling and low-carbon environmental protection.

Description

Technical Field

[0001] This invention relates to the field of wet-process microporous membrane technology, and more specifically, to wet-process microporous membranes based on direct coating of substrate and their preparation method. Background Technology

[0002] With the continuous expansion of applications in outdoor functional apparel, extreme cold protection, and urban commuting, the market demand for textile coating products with multiple functional advantages such as windproofness, breathability, waterproofness, moisture permeability, and dry comfort is increasing. Wet-process microporous membranes, as one of the core technologies of functional textile coatings, work by coating a polyurethane slurry onto the surface of a base fabric, followed by DMF (dimethylformamide) replacement in an aqueous coagulation tank. Phase separation occurs through the bidirectional diffusion of the solvent and water, thereby forming an interconnected microporous structure within the coating.

[0003] Currently, existing wet-process microporous membranes in the industry mainly rely on traditional petrochemical-based polyurethane materials. For example, patent publication number CN106178971A discloses a traditional wet-process film formation process. With the development of green manufacturing, the industry has begun to explore the introduction of biomass conversion materials (such as bio-based microporous series that use bio-based materials as the main carrier raw materials) to endow products with low-carbon, environmentally friendly, and renewable attributes.

[0004] However, when existing technologies attempt to directly apply polyurethane synthesized from biomass conversion precursors to traditional wet-coating processes for base fabrics, serious drawbacks are revealed, failing to simultaneously achieve ultra-high moisture permeability, high water pressure, and the soft hand feel of elastic fabrics. Specifically:

[0005] First, the phase separation kinetics are unbalanced and the pore-forming induction sites are missing. The polarity of biomass conversion resin is different from that of traditional petrochemical-based resins. During the conventional DMF replacement process, the solvent diffusion rate is easily out of control. More importantly, the pure polyurethane slurry system lacks effective microscopic pore-forming induction nuclei, which causes water molecules to aggregate randomly after entering the coating. This easily forms a dense, non-porous skin layer or causes the collapse of internal macropores, directly resulting in low water pressure permeability of the product.

[0006] Secondly, in order to overcome the aforementioned phase separation problem, the traditional approach is to simply extend the replacement time or increase the curing temperature. However, this results in extremely poor flexibility of the cross-linked film layer, severely restricting the elastic deformation space of the elastic fabric. Consequently, the elasticity is poor and the hand feel is hard after coating. At the same time, in the traditional winding and film separation operations, due to the lack of tension linkage control for the characteristics of biomass coatings, the phenomenon of micropores being stretched and closed by stress is very likely to occur.

[0007] Therefore, there is an urgent need in this field for a special method to overcome the rheological and stress defects of biomass conversion materials in wet molding, so as to stably prepare an environmentally friendly membrane composite product with ultra-high moisture permeability, ultra-high water pressure, ultra-soft feel and multiple functions. Summary of the Invention

[0008] The purpose of this invention is to provide a wet-process microporous membrane based on direct coating of substrate and its preparation method. By introducing hydrophilic modified carbon microparticles into bio-based slurry as phase separation nuclei, and by coordinating dilution concentration and temperature parameters, and by supplementing constant tension control throughout the process, microscopic modification and mechanical-thermal control of the material are achieved, thereby solving the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides a method for preparing a wet-process microporous membrane based on direct coating of a substrate, comprising the following steps:

[0010] S1. Preparation of Phase Separation Induced Bio-based Slurry: Mix 100 parts by weight of bio-based polyurethane resin, 30-40 parts by diluent, 0.5-2.0 parts by weight of hydrophilic modified carbon microparticles, and 3 parts by weight of crosslinking agent until homogeneous. After degassing, the coating slurry is obtained. Trace amounts of hydrophilic modified carbon microparticles are uniformly dispersed in the slurry, serving as microscopic nucleation sites during subsequent coagulation and replacement. A diluent concentration of 30-40% precisely matches the rheological properties of the bio-based macromolecules, preventing sedimentation of the modified microparticles.

[0011] S2. Graded Constant Tension Fabric Feeding and Flattening: The fabric feeding system is activated to ensure the elastic base fabric runs flat. The first constant tension unit maintains a stable basic operating tension of the elastic base fabric. After being processed by opening and bending rollers, the elastic base fabric enters the second constant tension unit to maintain a constant tension in the subsequent coating operation. The first and second constant tension units create a low-stress processing environment, preventing irreversible mechanical stretching of the elastic base fabric before coating.

[0012] S3. In-situ induced direct coating: The coating slurry prepared in S1 is uniformly coated onto the surface of the elastic base fabric using a coating system; the coating system uses a straight knife or a hook knife, and the coating thickness is controlled between 0.1mm and 5.0mm.

[0013] S4. Directional nucleus phase separation and replacement: The elastic base fabric after direct coating is immersed in the coagulation tank for solvent replacement. After the water molecules in the coagulation tank enter the coating, they preferentially gather on the surface of the hydrophilic modified carbon microparticles. The carbon microparticles act as nuclei to induce directional phase separation of the surrounding bio-based polyurethane, forming a microporous structure with carbon microparticles as nodes and internal interconnection.

[0014] S5. Stress Relief and High-Temperature Drying: The solidified elastic base fabric enters the drying system and undergoes drying and cross-linking curing at a drying temperature of 160℃-170℃. Under the low-stress state constructed by the front-end graded constant tension system, the high temperature of 160-170℃ promotes the rapid cross-linking of the crosslinking agent, which not only instantly locks the microporous skeleton formed by phase separation, but also anchors carbon particles on the micropore walls, ensuring that the film layer shrinks synchronously with the deformation of the elastic base fabric.

[0015] S6. Winding and Separation: After being smoothly wound up by the post-winding system, the film is sent to the separation machine for peeling and separation according to product requirements to obtain an independent wet-process microporous finished film, or the base fabric can be retained and used directly as a layered composite fabric.

[0016] Secondly, this invention provides a wet-process microporous membrane based on direct coating of a substrate, prepared by the above-mentioned method. The wet-process microporous membrane uses a bio-based polyurethane material as a framework, and its interior has a highly interconnected phase inversion microporous structure with hydrophilic modified carbon microparticles as nodes.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] In this wet-process microporous membrane based on direct coating of substrate and its preparation method, hydrophilic modified carbon microparticles are introduced into the bio-based slurry and used as micro-phase separation nuclei in the solvent replacement process. Water molecules are oriented to form a highly interconnected and uniform microporous structure, which effectively overcomes the defects of disordered pore formation and easy pore collapse of traditional pure bio-based polyurethane, and significantly improves the moisture permeability and water pressure resistance of the membrane.

[0019] Secondly, this invention eliminates tensile stress during the coating process through the mechanical synergy of the first and second constant tension units. Combined with a specific curing temperature of 160-170℃, the cross-linked microporous membrane layer can seamlessly adhere to the elastic deformation of the base fabric. The uniformly distributed microporous structure at the microscopic level effectively buffers the deformation stress of the fabric, solving the persistent problem of stiffness and loss of elasticity in elastic fabrics after coating due to direct coating processes.

[0020] Meanwhile, the present invention uses biomass conversion materials as the matrix, which endows the product with low-carbon and environmentally friendly properties. The introduction of carbon microparticles further enhances the functionality of the product. The resulting product has advantages such as windproof, waterproof, breathable and cold-resistant properties. It can be widely used for high-energy protection in urban commuting, outdoor extreme cold, hiking and rock climbing scenarios, whether it is formed as a film alone or as a layered fabric. Attached Figure Description

[0021] Figure 1 This is an overall flowchart of Embodiment 1 of the present invention. Detailed Implementation

[0022] The technical solutions in 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.

[0023] Unless otherwise specified, the raw materials used in the embodiments of this invention are all commercially available conventional raw materials; the process equipment used, unless otherwise specified, are all conventional equipment in the art. Wherein:

[0024] Bio-based polyurethane resin is a polyurethane DMF solution containing plant-based polyol segments, with a solid content of 30%-35%.

[0025] Hydrophilic modified carbon microparticles are nanoscale carbon particles that have undergone surface hydroxylation treatment, with an average particle size of 50-100 nm and a specific surface area ≥800 m². 2 / g.

[0026] The elastic base fabric is a standard four-way elastic nylon / spandex interwoven fabric.

[0027] Example 1: This embodiment of the invention provides a method for preparing a wet-process microporous membrane based on direct coating of a substrate. See [link to relevant documentation]. Figure 1 This includes the following steps:

[0028] S1. Preparation of slurry: According to the weight ratio, accurately weigh 100 parts of bio-based polyurethane resin, 30 parts of DMF diluent, 1.0 part of hydrophilic modified carbon microparticles and 3 parts of isocyanate crosslinking agent. Place the above components in a disperser and stir at high speed of 800-1000 rpm for 30 minutes. Then transfer the mixed slurry to a vacuum degassing kettle and degas at a vacuum degree of -0.08 to -0.09 MPa for 20 minutes to obtain a bubble-free and uniformly dispersed coating slurry.

[0029] S2, Graded Constant Tension Fabric Feeding: Four-way stretch fabric is used as the base fabric and fed into the coating production line. The fabric feeding system is started, and the initial operating tension of the base fabric is set and maintained in the range of 50-80N by the servo motor control of the first constant tension unit to ensure that the base fabric is flat and spread out. After the base fabric is opened and bent by rollers, it enters the second constant tension unit, which precisely lowers and keeps the tension in the coating operation area at a micro-tension state of 10-20N.

[0030] S3, In-situ Direct Coating: Using a straight blade coating system, the degassed slurry from S1 is evenly coated onto the surface of the elastic base fabric under slight tension. The coating speed is set to 10 meters per minute, and the blade gap is adjusted to control the wet film coating thickness at 0.15 mm.

[0031] S4. Displacement coagulation: The coated base fabric is continuously introduced into the water-based coagulation tank. The mass concentration ratio of water / DMF in the coagulation tank is set to 85:15. The temperature of the coagulation liquid is controlled at 25-30℃. The residence time of the base fabric in the coagulation tank is 3-5 minutes. Water molecules preferentially aggregate to the surface of hydrophilic modified carbon microparticles, inducing bio-based macromolecules to undergo directional phase separation and form a microporous structure.

[0032] S5. High-temperature anchoring and drying: After sufficient solidification and replacement, the base fabric enters the drying system consisting of a setting machine. The rolling pressure is set to 4 kg to remove free surface moisture. Then, it undergoes continuous drying treatment in a high-temperature oven at 160℃ for 1.5-2 minutes to allow the crosslinking agent to fully crosslink and cure.

[0033] S6. Winding and Separation: The guide rollers of the post-winding system smoothly wind up the film under extremely low tension. Then, the film layer is separated from the base fabric by controlling the peeling tension through the film separator to obtain an independent wet-process microporous finished film.

[0034] Example 2: A method for preparing a wet-process microporous membrane based on direct coating of a substrate, comprising the following steps:

[0035] S1. Preparation of slurry: Weigh 100 parts of bio-based polyurethane resin, 40 parts of DMF diluent, 1.5 parts of hydrophilic modified carbon microparticles and 3 parts of crosslinking agent, and stir and vacuum degassing under the same conditions as in Example 1.

[0036] S2-S4, Fabric feeding, direct coating and solidification: The process steps and parameter settings are the same as in Example 1.

[0037] S5. High-temperature anchoring drying: Set the rolling mill pressure to 6 kg, set the oven drying temperature to 170°C, and the other conditions are the same as in Example 1.

[0038] S6. Rewinding and Separating: In this embodiment, the composite layer is not separated into layers; it is directly rewound to form the finished layered composite fabric.

[0039] Example 3: A method for preparing a wet-process microporous membrane based on direct coating of a substrate, comprising the following steps:

[0040] S1. Preparation of slurry: Weigh 100 parts of bio-based polyurethane resin, 35 parts of DMF diluent, 0.5 parts of hydrophilic modified carbon microparticles and 3 parts of crosslinking agent, and stir and vacuum degassing under the same conditions as in Example 1.

[0041] S2-S4, Fabric feeding, direct coating and solidification: The process steps and parameter settings are the same as in Example 1.

[0042] S5. High-temperature anchoring drying: Set the rolling mill pressure to 5 kg, set the oven drying temperature to 165°C, and the other conditions are the same as in Example 1.

[0043] S6. Winding and separating the film: Same as in Example 1, to obtain independent finished films.

[0044] Comparative Example 1: The same process steps and parameters as in Example 3 were used, except that hydrophilic modified carbon microparticles were not added in S1.

[0045] Comparative Example 2: The same process steps and parameters as in Example 3 were used, except that in S1, the amount of DMF diluent added was changed to 20 parts.

[0046] Comparative Example 3: The same formula and thermal parameters as Example 3 were used, the only difference being that in S2, the first constant tension unit and the second constant tension unit were turned off, and a conventional traction motor was used to rigidly drag the fabric into the coating area, with the fabric tension in the coating area reaching more than 150N.

[0047] Experimental Example: To verify the advancement of the technical solution of this invention, the performance of the microporous composite membranes (without peeling off the substrate) prepared in Examples 1-3 and Comparative Examples 1-3 was characterized. The results are shown in Table 1. The test methods are as follows:

[0048] Moisture permeability test method: Performed according to JIS L1099B-1 (potassium acetate method). Under constant temperature and humidity conditions (temperature 30±2℃, relative humidity 50±5%), a circular sample with a diameter of 10cm was placed on top of a test cup containing a saturated potassium acetate solution and inverted in a water trough. The test lasted for 24 hours. The moisture permeability of the sample was calculated by weighing the difference in mass of the cup before and after the test (unit: g / m³). 2 • 24h). Take 5 samples from each batch and take the average value.

[0049] Hydrostatic pressure resistance test method: Performed according to ISO 811 standard. Using a hydrostatic pressure tester, a 100cm² area... 2 The sample was fixed on the test fixture, and the water pressure was increased uniformly at a rate of 60 cmH2O / min. The sample surface was closely observed, and the hydrostatic pressure value (unit: mmH2O) was recorded the instant the third water droplet appeared on the sample surface.

[0050] Tensile elastic recovery rate test method:

[0051] Elastic recovery rate: Performed according to FZ / T01034 standard. Using a universal testing machine, the sample was cut into strips of 5cm × 20cm, with a constant elongation of 30% and a tensile speed of 100mm / min. After holding for 3 minutes, the stress was unloaded, and the sample length was measured after resting for 3 minutes to calculate the elastic recovery rate. Hand feel evaluation: Blind touch tests were conducted by 10 textile testing personnel with more than 5 years of experience to comprehensively evaluate the difference in softness compared to the original base fabric.

[0052] Microscopic morphology characterization: The samples of Example 3 and Comparative Example 1 were subjected to brittle fracture treatment in liquid nitrogen. After gold sputtering, the cross-sectional pore structure morphology was observed using a field emission scanning electron microscope (SEM, magnification 5000x-10000x).

[0053] Table 1: Performance Test Data

[0054] Example 1 10500 12000 96% Extremely soft, with no noticeable foreign body sensation. Uniform aperture distribution and continuous channel height Example 2 11200 11500 95% Extremely soft, with no noticeable foreign body sensation. Uniform aperture distribution and continuous channel height Example 3 10800 13000 97% Extremely soft, with no noticeable foreign body sensation. Uniform aperture distribution and continuous channel height Comparative Example 1 4200 8000 90% softer A 2-3μm non-porous dense skin layer exists on the side close to the base fabric. Comparative Example 2 3100 6500 80% Coating hardened Large internal dead holes and phase separation structure collapse Comparative Example 3 10500 12500 38% It became severely hardened, resembling cardboard. The pore size is normal, but there is a large amount of residual stress within the film.

[0055] As shown in the table, the embodiments of the present invention, using 30-40 parts of diluent, successfully induced the directional aggregation of water molecules by utilizing hydrophilic modified carbon microparticles as phase separation nuclei for coagulation and replacement, forming a highly interconnected and structurally stable microporous framework, which was rapidly locked at 160-170℃. This resulted in extremely high levels of moisture permeability and hydrostatic pressure resistance. In contrast, Comparative Example 1, due to the lack of nuclei, suffered from disordered phase separation, forming a dense skin layer that severely blocked the moisture permeability path; Comparative Example 2, due to excessively low dilution concentration, resulted in abnormal slurry rheology, forming large areas of dead pores, and causing the hydrostatic pressure resistance to plummet to 6500 mmH2O.

[0056] Secondly, the embodiments of the present invention construct a micro-tension processing environment through the first and second constant tension units. Under this state, high-temperature anchoring at 160-170℃ allows the microporous membrane layer to seamlessly adhere to and conform to the elastic deformation of the base fabric, with an elastic recovery rate exceeding 95%, resulting in an extremely soft feel. As a counter-evidence, Comparative Example 3 underwent high-temperature cross-linking under rigid dragging high stress, causing the microporous membrane to completely lock the shrinkage space of the base fabric, resulting in a complete loss of fabric elasticity (recovery rate of only 38%) and a severely deteriorated feel. This fully demonstrates the necessity of the mechanical stress release and high-temperature curing effects in the present invention.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing wet-process microporous membranes based on direct coating of a substrate, characterized in that, Includes the following steps: S1. Preparation of phase separation-induced bio-based slurry: According to the weight ratio, mix 100 parts of bio-based polyurethane resin, 30-40 parts of diluent, 0.5-2.0 parts of hydrophilic modified carbon microparticles and 3 parts of crosslinking agent evenly and degas to obtain coating slurry. S2, Graded Constant Tension Fabric Feeding and Flattening: Start the fabric feeding system to make the elastic base fabric run flat, and maintain the basic running tension of the elastic base fabric through the first constant tension unit; after the elastic base fabric is opened and bent by the roller, it enters the second constant tension unit to maintain the tension of the elastic base fabric in the subsequent coating operation area. S3, In-situ induced direct coating: The coating slurry obtained in S1 is uniformly coated onto the surface of the elastic base fabric under constant tension using a coating system; S4. Directional nucleus phase separation and replacement: The elastic base fabric after direct coating is immersed in a coagulation tank for solvent replacement. Water molecules in the coagulation tank preferentially gather on the surface of the hydrophilic modified carbon microparticles. The hydrophilic modified carbon microparticles act as nuclei to induce directional phase separation of the surrounding bio-based polyurethane, forming a microporous structure. S5. Stress relief and high-temperature drying: The elastic base fabric after solidification and replacement enters the drying system and is dried and cross-linked at a drying temperature of 160℃-170℃, so that the hydrophilic modified carbon microparticles are anchored to the pore wall. S6. Winding and Separation: After being smoothly wound up by the post-winding system, a wet-process microporous composite membrane is obtained.

2. The method for preparing a wet-process microporous membrane based on direct coating of a substrate according to claim 1, characterized in that, In S1, the bio-based polyurethane resin is a polyurethane solution containing plant-based polyol segments, with a solid content of 30%-35%; the hydrophilic modified carbon microparticles are nanoscale carbon particles that have undergone surface hydroxylation treatment, with an average particle size of 50-100 nm and a specific surface area ≥800 m². 2 / g.

3. The method for preparing a wet-process microporous membrane based on direct coating of a substrate according to claim 1, characterized in that, In S1, the specific process of mixing and degassing is as follows: each component is stirred at high speed at 800-1000 rpm for 30 minutes, and then transferred to a vacuum degassing kettle and degassed for 20 minutes under a vacuum of -0.08 to -0.09 MPa.

4. The method for preparing a wet-process microporous membrane based on direct coating of a substrate according to claim 1, characterized in that, In S2, the first constant tension unit sets and maintains the initial operating tension of the elastic base fabric in the range of 50-80N; the second constant tension unit lowers and keeps the tension of the elastic base fabric in the coating operation range at a micro-tension state of 10-20N.

5. The method for preparing a wet-process microporous membrane based on direct coating of a substrate according to claim 1, characterized in that, In S3, the coating system uses a straight blade or a hook blade, the coating speed is set to 10 meters / minute, and the wet film coating thickness is controlled between 0.1mm and 5.0mm.

6. The method for preparing a wet-process microporous membrane based on direct coating of a substrate according to claim 1, characterized in that, In step S4, the coagulation tank is a water-based coagulation tank, the mass concentration ratio of water to the diluent in the tank is 85:15, the temperature of the coagulation liquid is controlled at 25-30℃, and the residence time of the elastic bottom cloth in the coagulation tank is 3-5 minutes.

7. The method for preparing a wet-process microporous membrane based on direct coating of a substrate according to claim 1, characterized in that, In S5, the front end of the drying system is equipped with a shaping machine roller, and the roller pressure is set to 4-6 kg; the residence time of the elastic bottom fabric at the drying temperature is 1.5-2 minutes.

8. A wet-process microporous membrane based on direct coating of a substrate, characterized in that, The wet-process microporous membrane based on direct coating of substrate is prepared by any one of claims 1-7; the wet-process microporous membrane is made of bio-based polyurethane resin cross-linked as a skeleton and has an internally interconnected phase inversion microporous structure.

9. The wet-process microporous membrane based on direct coating of substrate according to claim 8, characterized in that, The microporous structure is induced to form by hydrophilic modified carbon microparticles as phase separation nodes, and the hydrophilic modified carbon microparticles are anchored on the pore walls of the microporous structure.

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