Preparation method of moisture-permeable and moisture-preserving film

Abstract

The invention discloses a preparation method of a moisture-permeable and moisture-preserving film, belongs to the technical field of functional films, and aims to solve the technical problem of low structural strength of the moisture-permeable and moisture-preserving film. According to the preparation method of the moisture-permeable and moisture-preserving film, a fiber net with the melt-blown density of 65-75 g / m and the molecular weight distribution smaller than 1.8 is formed through PET nascent fiber lapping, the structural strength and the wind pressure resistance of the fiber net are improved, and the structural strength of the finally formed moisture-permeable and moisture-preserving film is improved; the fiber net has electrostatic adsorption capacity after passing through a high-voltage electrostatic field, at the moment, the fiber net is transversely and longitudinally stretched, fibers are not prone to being excessively dispersed in the stretching process, the fibers are directionally arranged, stress concentration points and weak areas of the fiber net film are reduced, and stress of molecular chains or the fibers can be evenly and continuously transmitted under the action of external force; therefore, the structural strength of the moisture-permeable moisturizing film is improved, and the moisture-permeable moisturizing film is not easy to break under the action of external force

Description

Technical Field

[0001] This application relates to the field of functional film technology, and in particular to a method for preparing a moisture-permeable and humidifying film. Background Technology

[0002] Moisture-permeable and moisture-retaining membranes are functional thin-film materials that allow only water vapor to pass through while preventing liquid water from penetrating. They are commonly used in packaging materials and other fields to package items that are sensitive to humidity, such as food and medicine, to prevent them from becoming damp and deteriorating due to excessive humidity.

[0003] In related technologies, the interior of the moisture-permeable and moisturizing membrane forms continuous micropores with a diameter of 0.1 nanometers to 1 nanometer. The pore size of the micropores is larger than the diameter of water vapor molecules (about 0.4 nanometers) and smaller than the diameter of the smallest aggregate unit of liquid water molecules (greater than 100 nanometers), so that water vapor can pass through freely while liquid water is blocked, thus achieving a two-way function of "allowing water vapor to pass through freely" and "blocking liquid water from passing through".

[0004] However, the relevant moisture-permeable and moisturizing membranes suffer from low structural strength. Summary of the Invention

[0005] This application provides a method for preparing a moisture-permeable and moisturizing film, which can solve the technical problem of low structural strength of related moisture-permeable and moisturizing films.

[0006] This application provides a method for preparing a moisture-permeable and humidifying film, comprising:

[0007] Melt PET masterbatch into PET melt;

[0008] Supercritical CO2 is injected into the PET melt to form a CO2-containing melt mixture;

[0009] A CO2-containing melt mixture is stretched to form nascent PET fibers with a microporous structure; wherein the diameter of the nascent PET fibers is less than 15 micrometers.

[0010] The nascent PET fibers are laid into a web and self-adhesive to form a fiber web with a meltblown density of 65g / m²~75g / m² and a molecular weight distribution of less than 1.8.

[0011] The fiber web is passed through a high-voltage electrostatic field, and then the fiber web is stretched laterally and longitudinally to form a directional fiber web membrane with a pore size of less than 2 micrometers and a porosity of more than 95%.

[0012] Polyamide layers are polymerized on the surface and within the pores of the fiber mesh to form a moisture-permeable and humidifying membrane with a pore size of less than 1 nanometer.

[0013] The method for preparing the moisture-permeable and moisturizing membrane according to this application involves injecting supercritical CO2 into the PET melt to form nascent PET fibers with a microporous structure after stretching. This increases the porosity of the final moisture-permeable and moisturizing membrane, thereby improving its moisture permeability. By laying the nascent PET fibers into a web, a fiber web with a melt-blown density of 65 g / m² to 75 g / m² and a molecular weight distribution of less than 1.8 is formed. The small difference in molecular chain length among the fiber webs reduces the possibility of fiber breakage during subsequent stretching, improves the structural strength and wind pressure resistance of the fiber web, and ultimately enhances the structural strength of the final moisture-permeable and moisturizing membrane. After being subjected to a high-voltage electrostatic field, the fiber web acquires electrostatic adsorption capabilities, improving the filtration performance of the moisture-permeable membrane. The fiber web is then stretched bidirectionally in both the transverse and longitudinal directions. During this stretching process, due to electrostatic adsorption, the fibers are less prone to excessive dispersion and are oriented, ultimately forming a dense fiber web membrane with a narrow pore size distribution of less than 2 micrometers and a pore size ratio greater than 95%. This further enhances the structural strength and wind pressure resistance of the fiber web membrane, making it less prone to deformation. Finally, a polyamide layer is polymerized on the surface and within the pores of the fiber web membrane, forming a moisture-permeable membrane that allows water vapor to pass through while blocking liquid water.

[0014] In some embodiments of this application, a polyamide layer is polymerized on the surface and within the pores of the fiber mesh to form a moisture-permeable and humidifying film, specifically including:

[0015] Hot melt adhesive is sprayed onto the fiber web membrane and then hot-pressed to form a composite base film;

[0016] Polyamide layers are polymerized on the surface and in the pores of the composite base film to form a moisture-permeable and humidifying film.

[0017] With this setup, the hot melt adhesive can form a strong bond with PET through in-situ lamination, while providing strong adhesive sites for the subsequent polyamide layer. This improves the structural stability of the polyamide layer, reduces the possibility of delamination and peeling of the polyamide layer, and enhances the filtration effect of the moisture-permeable membrane.

[0018] In some embodiments of this application, after polymerizing the polyamide layer on the surface and within the pores of the fiber mesh, the following is further included:

[0019] Phytic acid is integrated into the surface and pores of the polyamide layer.

[0020] This design allows phytic acid to inhibit the photo-oxidative degradation of the polyamide layer, improving the aging resistance of the moisture-permeable membrane. By integrating phytic acid into the surface and pores of the polyamide layer, the composite membrane gains antibacterial, antifouling, and aging-resistant properties without disrupting the moisture permeability channels.

[0021] In some embodiments of this application, the purity of supercritical CO2 is greater than or equal to 99.5%.

[0022] This design reduces the likelihood of the micropores becoming clogged.

[0023] In some embodiments of this application, when the fiber web is stretched laterally and longitudinally, it is stretched to 3.0 to 3.5 times its original length in the transverse direction and to 3.0 to 3.5 times its original length in the longitudinal direction. The conveying speed of the fiber web during stretching is 8 m / min to 12 m / min.

[0024] With this setup, when the conveying speed of the fiber web during stretching is 8 m / min to 12 m / min, the conveying speed can match the stretching ratio in the longitudinal and transverse directions, which improves the uniformity of the fiber web during stretching and makes the stretched fiber web less prone to breakage and deformation.

[0025] In some embodiments of this application, before melting the PET masterbatch into PET melt, the method further includes:

[0026] PET chips are subjected to solid-phase polymerization in a high-temperature vacuum environment to form high-viscosity PET chips;

[0027] Nucleating agents are added to high-viscosity PET chips to prepare PET masterbatches containing nucleating agents.

[0028] With this setup, the crystallization temperature of PET masterbatch containing nucleating agents drops to 100-110℃. Even during rapid cooling, PET molecular chains can quickly aggregate and crystallize towards the nucleating agent, forming highly crystalline fibers. The molecular chains of highly crystalline fibers are more regularly arranged, resulting in a fiber strength increase of over 30%. Aging resistance and chemical resistance are significantly optimized, reducing the likelihood of pore collapse due to fiber breakage during use of the moisture-permeable and moisture-retaining membrane.

[0029] In some embodiments of this application, the temperature of the high-temperature vacuum environment is 170°C to 190°C and the vacuum degree is less than or equal to 10 Pa.

[0030] With this setup, when the temperature is between 170℃ and 190℃, the terminal groups of the PET molecular chains exhibit strong reactivity, which can both increase the viscosity after the reaction and reduce the possibility of softening and clumping of the chips. When the vacuum level in the high-temperature vacuum environment is less than or equal to 10 Pa, water molecules formed during polymerization can be removed in time, the condensation reaction dominates, the molecular chains mainly grow, the difference between long and short molecular chains is small, and the molecular weight distribution can be controlled within 1.6-1.8, forming PET chips with a narrow molecular weight distribution. The long molecular chains increase the melt viscosity, making the fibers more uniformly stressed during subsequent stretching, resulting in higher fiber strength and less fraying of the fiber web, thus improving the overall structural stability of the moisture-permeable and moisture-retaining membrane.

[0031] In some embodiments of this application, the nucleating agent is sodium benzoate and hydrophilic nano-SiO2;

[0032] The total weight is the sum of the weights of the high-viscosity PET chips, sodium benzoate, and hydrophilic nano-SiO2.

[0033] Sodium benzoate accounts for less than 0.1% of the total weight, and hydrophilic nano-SiO2 accounts for less than 0.05% of the total weight.

[0034] This configuration ensures that sodium benzoate accounts for less than 0.1% of the total weight, thereby increasing the viscosity of the PET melt during subsequent stretching and making it easier to stretch. The hydrophilic nano-SiO2 accounts for less than 0.05% of the total weight, reducing the possibility of hydrophilic nano-SiO2 agglomeration and clogging of the moisture permeability channels.

[0035] In some embodiments of this application, the particle size of the hydrophilic nano-SiO2 is 25 nm to 35 nm.

[0036] With this configuration, the specific surface area of ​​hydrophilic nano-SiO2 is about 300 m² / g, balancing high activity with low risk of agglomeration. The surface hydroxyl density is moderate, about 4-5 hydroxyl groups / nm², which can be uniformly dispersed in PET melt without obvious agglomeration, and can give full play to the nano-effect.

[0037] In some embodiments of this application, PET masterbatch is melted into PET melt, wherein the melting temperature is 258°C to 262°C.

[0038] This configuration allows PET to melt fully, reducing the particle content of the PET melt. It also reduces the likelihood of thermal degradation of the PET molecular chains, increasing the strength of the PET molecular chains and thus improving the strength of the final fiber. Attached Figure Description

[0039] To more clearly illustrate the implementation methods in the embodiments of this application or related technologies, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings.

[0040] Figure 1 The flowchart illustrating the preparation method of the moisture-permeable and moisturizing film according to an embodiment of this application is shown. Figure 1 ;

[0041] Figure 2 The flowchart illustrating the preparation method of the moisture-permeable and moisturizing film according to an embodiment of this application is shown. Figure 2 ;

[0042] Figure 3 The flowchart illustrating the preparation method of the moisture-permeable and moisturizing film according to an embodiment of this application is shown. Figure 3 ;

[0043] Figure 4 The flowchart illustrating the preparation method of the moisture-permeable and moisturizing film according to an embodiment of this application is shown. Figure 4 ;

[0044] Figure 5 The flowchart illustrating the preparation method of the moisture-permeable and moisturizing film according to an embodiment of this application is shown. Figure 5 ;

[0045] Figure 6 The flowchart illustrating the preparation method of the moisture-permeable and moisturizing film according to an embodiment of this application is shown. Figure 6 ;

[0046] Figure 7 A schematic diagram of the structure of the moisture-permeable and moisturizing membrane according to an embodiment of this application is shown;

[0047] Figure 8 This illustration shows a schematic diagram of the structure of the moisture-permeable and moisture-retaining membrane applied to the top cover of a storage drawer in a refrigeration device according to an embodiment of this application;

[0048] Figure 9 It shows Figure 8 Sectional view along the middle AA direction;

[0049] Figure 10 It shows Figure 9 A magnified view of a portion of point P in the middle. Detailed Implementation

[0050] To make the objectives and implementation methods of this application clearer, the exemplary implementation methods of this application will be clearly and completely described below with reference to the accompanying drawings of the exemplary embodiments of this application. Obviously, the exemplary embodiments described are only some embodiments of this application, and not all embodiments.

[0051] It should be noted that the brief descriptions of terms in this application are only for the convenience of understanding the embodiments described below, and are not intended to limit the embodiments of this application. Unless otherwise stated, these terms should be understood in their ordinary and common meaning.

[0052] The terms "first," "second," "third," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar or related objects or entities, and do not necessarily imply a specific order or sequence, unless otherwise specified. It should be understood that such terms are interchangeable where appropriate.

[0053] The terms “comprising” and “having”, and any variations thereof, are intended to cover but not exclude inclusion, for example, a product or device that includes a range of components is not necessarily limited to all of the components that are clearly listed, but may include other components that are not clearly listed or that are inherent to such product or device.

[0054] As stated in the background section, the moisture-permeable membranes in the related technologies have the problem of low structural strength. The inventors have found that the reason for this problem is that the pores in the related moisture-permeable membranes are irregularly arranged, forming a large number of stress concentration points and weak areas. This makes it impossible to evenly transmit the force on the molecular chains or fibers under the action of external force, which ultimately leads to a reduction in the structural strength of the moisture-permeable membrane, making it prone to breakage under the action of external force.

[0055] To address the aforementioned technical problems, this application provides a moisture-permeable and humidifying membrane. This membrane is formed by laying nascent PET (Polyethylene Terephthalate) fibers to create a meltblown fiber web with a density of 65 g / m² to 75 g / m² and a molecular weight distribution of less than 1.8. The small difference in molecular chain length among the fiber webs reduces the possibility of fiber breakage during subsequent stretching, improves the structural strength and wind pressure resistance of the fiber web, and ultimately enhances the structural strength of the resulting moisture-permeable and humidifying membrane. After being subjected to a high-voltage electrostatic field, the fiber web acquires electrostatic adsorption capabilities, improving the filtration performance of the moisture-permeable membrane. The fiber web is then stretched bidirectionally in both the transverse and longitudinal directions. During this stretching process, due to electrostatic adsorption, the fibers are less prone to excessive dispersion and are oriented, ultimately forming a dense fiber web membrane with a narrow pore size distribution of less than 2 micrometers and a pore size ratio greater than 95%. This further enhances the structural strength and wind pressure resistance of the fiber web membrane, making it less prone to deformation. Finally, a polyamide layer is polymerized on the surface and within the pores of the fiber web membrane, forming a moisture-permeable membrane that allows water vapor to pass through while blocking liquid water.

[0056] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0057] refer to Figure 1 The method for preparing the moisture-permeable and humidifying film provided in this application includes the following steps:

[0058] Step S100: Melt the PET masterbatch into PET melt.

[0059] Moisture-permeable and moisture-retaining membranes can be prepared using PET masterbatch. PET-based moisture-permeable and moisture-retaining membranes have excellent heat and cold resistance. They can maintain stable performance over a wide temperature range and are not prone to deformation or embrittlement due to temperature changes. Their impact strength at -35℃ is greater than 5 kJ / m², which makes the prepared moisture-permeable and moisture-retaining membranes less prone to embrittlement at low temperatures below -20℃, thus improving the structural strength of the membranes.

[0060] PET masterbatch can be melted into PET melt using a screw extruder. The PET masterbatch is added to the screw extruder, whose barrel has a heating function. Through the rotation of the screw and the heating of the barrel, the solid PET masterbatch is gradually melted into PET melt. PET melt has fluidity and a higher viscosity compared to PET masterbatch.

[0061] The heating temperature of the screw extruder, or the temperature at which PET masterbatch is melted, can be between 258℃ and 262℃, for example, 258℃, 259℃, 260℃, 261℃, or 262℃. On the one hand, this allows the PET to melt fully, reducing the particle content of the formed PET melt; on the other hand, it reduces the possibility of thermal degradation of the PET molecular chains, improving the strength of the PET molecular chains, thereby increasing the strength of the final fiber.

[0062] When the temperature of the molten PET masterbatch is below 258°C, some of the PET masterbatch will not be melted, resulting in particles mixed in the formed PET melt.

[0063] When the temperature of molten PET masterbatch exceeds 262℃, the molecular chains of PET will undergo thermal degradation, making them prone to breakage and reducing their strength. This results in discoloration and reduced strength in the final fibers.

[0064] Step S200: Inject supercritical CO2 (Carbon Dioxide) into the PET melt to form a CO2-containing melt mixture.

[0065] The critical temperature of CO2 is 31℃ and the critical pressure is 7.4MPa. When the temperature is ≥31℃ and the pressure is ≥7.4MPa, CO2 will be in a supercritical state. Supercritical CO2 has both high diffusivity and high solubility, and its viscosity is extremely low (only about 1 / 100 of that of conventional hot air).

[0066] When supercritical CO2 is injected into PET melt, it can quickly penetrate into the PET melt due to its high diffusivity. After the supercritical CO2 penetrates into the PET melt, it will reduce the viscosity of the resulting CO2-containing melt mixture, making the PET melt easier to stretch.

[0067] Step S300: Stretch the CO2-containing melt mixture to form nascent PET fibers with a microporous structure; wherein the diameter of the nascent PET fibers is less than 20 micrometers.

[0068] Supercritical CO2 is injected into the PET melt to reduce the viscosity of the CO2-containing melt mixture. The CO2-containing melt mixture is then stretched, resulting in a smaller fiber diameter. Due to the pressure reduction, the supercritical CO2 in the CO2-containing melt mixture returns to a gaseous state and escapes from the fiber interior, forming a microporous structure on the fiber surface. These microporous structures allow water vapor to pass through quickly but block liquid water, achieving the functions of moisture permeability and water retention.

[0069] A CO2-containing melt mixture is stretched to form nascent PET fibers with a microporous structure, the diameter of which is less than 15 micrometers.

[0070] The diameter of PET nascent fibers can be 10 micrometers, 11 micrometers, 12 micrometers, 13 micrometers, or 14 micrometers, etc. When the diameter of PET nascent fibers is less than 15 micrometers, the specific surface area of ​​PET nascent fibers is larger, and the surface area per unit weight is more than doubled, laying the foundation for the high porosity and moisture permeability of the fiber web formed subsequently.

[0071] In some possible implementations of the embodiments of this application, the purity of supercritical CO2 can be greater than or equal to 99.5% to reduce the possibility of micropore blockage.

[0072] When the purity of supercritical CO2 is less than 99.5%, if it contains impurities such as dust, moisture, and oil, these impurities are forced into the PET melt under high pressure. After cooling, they form solid particles that easily clog the micropores on the fiber surface. The blockage of micropores will reduce the moisture permeability of the formed moisture-permeable and moisturizing film, or even cause it to lose its moisture permeability function.

[0073] Step S400: Lay out PET nascent fibers into a web and self-adhere to form a fiber web with a meltblown density of 65g / m²~75g / m² and a molecular weight distribution of less than 1.8.

[0074] The stretched PET nascent fibers can be laid and shaped in the web-collecting area to form a fiber web.

[0075] The laying and self-adhesive molding of PET nascent fibers can be carried out at a temperature of 200℃. The glass transition temperature of PET is about 70℃. 200℃ is higher than the glass transition temperature but much lower than the melting point of PET. At this temperature, the PET nascent fibers are in a highly elastic state. The contact points between the PET nascent fibers will self-adhere due to slight thermal melting. No additional adhesive is needed, so that the randomly laid PET nascent fibers form a stable fiber web, reducing the possibility of the fiber web fraying.

[0076] Furthermore, oxygen in the air reacts with PET molecular chains at high temperatures, causing thermal oxidative degradation, chain breakage, and an increase in molecular weight distribution. 200℃ is far below the active thermal oxidation temperature of PET, significantly slowing down the oxidation reaction, protecting the integrity of the PET molecular chains, reducing chain breakage, and minimizing the possibility of a wider molecular weight distribution.

[0077] Low-temperature setting at 200℃ reduces the possibility of secondary degradation of molecular chains caused by high temperature, reduces the difference in the length of PET molecular chains in the final fiber web, ensures a sufficient proportion of long chains to guarantee fiber strength, reduces the proportion of short chains to reduce the possibility of fiber fragility and breakage, and the molecular weight distribution of the final fiber web is less than 1.8, resulting in more uniform and stable strength, air permeability and filtration properties of the fiber web.

[0078] Because short chains reduce fiber viscosity, making fibers more prone to breakage during subsequent stretching, PET molecular chains with a molecular weight distribution of less than 1.8 have small differences in length, resulting in stable fiber viscosity. This allows for the continuous stretching of fibers with uniform diameter, reducing the possibility of thick sections and breakage.

[0079] In the description of the embodiments of this application, meltblown density refers to the mass of fibers contained in a unit area of ​​fiber web. A fiber web with a meltblown density of 65g / m² to 75g / m² has a mass of 65g to 75g per unit area, enabling a 20-micron-thick fiber web to withstand 800Pa wind pressure in a 10L container, meaning it does not deform under 800Pa wind pressure, thus improving the structural strength and wind pressure resistance of the fiber web.

[0080] Step S500: The fiber web is passed through a high-voltage electrostatic field, and then the fiber web is stretched laterally and longitudinally to form a directionally arranged fiber web membrane with a pore size of less than 2 micrometers and a pore ratio of more than 95%.

[0081] Although the fiber web formed in step S400 has high porosity, it has the disadvantages of low filtration efficiency and wide pore size distribution.

[0082] The fiber web formed in step S400 relies solely on fibers to block liquid water, which is physical interception. If it is necessary to improve the filtration efficiency, finer fibers or thicker web layers are required, which increases the air resistance of the fiber web and reduces its air permeability.

[0083] The fiber web formed in step S400 has randomly stacked fibers, resulting in uneven pore sizes. Some large pores allow liquid water to pass through easily, while some small pores are prone to clogging, which reduces the air permeability of the fiber web.

[0084] In step S500, after the fiber web flows through a high-voltage electrostatic field, charge polarization and charge capture are generated on the surface or inside of the fiber web, so that the fiber web has a stable static charge for a long time, so that the fiber web has electrostatic adsorption capacity, and the final fiber web can capture tiny liquid water particles through electrostatic force, thereby improving the filtration efficiency of liquid water.

[0085] Along the fiber web's conveying path, a high-voltage electrode plate (connected to 5kV DC high voltage) and a grounding electrode plate can be installed, with the distance between the two plates set to 5cm-10cm, forming a uniform parallel plate high-voltage electrostatic field. The fiber web passes through the space between the two plates at a uniform speed (the conveying speed is matched with the subsequent stretching rate, approximately 10m / min).

[0086] The electric field strength of a 5kV high-voltage electric field exceeds the breakdown field strength of air, causing corona discharge in the air and generating a large number of free electrons and ions. Under the action of the electric field force, the free electrons are adsorbed onto the surface of the fiber web. Since the fiber web is an insulating polymer material, the charge on the fiber web is difficult to dissipate and will be "captured" in "charge traps" (such as molecular chain defects and grain boundaries) on the surface of the fiber web, forming "electrets" (i.e., fiber webs that are permanently charged).

[0087] After the fiber web is charged, the charge on the surface of the fiber web has not yet stabilized. The surface static charge will generate a "weak electrostatic attraction". At this time, the fiber web is stretched in the transverse and longitudinal directions. During the stretching process, the fibers are not easily dispersed excessively and the fibers are oriented. This reduces the stress concentration points and weak areas of the fiber web membrane, so that the force on the molecular chains or fibers under the action of external force can be transmitted evenly and continuously. This improves the structural strength of the moisture-permeable and moisturizing membrane and makes it less likely to break under the action of external force.

[0088] In addition, during stretching, the fibers are oriented, which reduces the possibility of forming large pores and ultimately forms a dense fiber web with a narrow pore size distribution of less than 2 micrometers and a pore ratio of more than 95%, which improves the structural strength and wind pressure resistance of the fiber web.

[0089] In some possible implementations of the embodiments of this application, when the fiber web is stretched in the transverse and longitudinal directions, the fiber web is stretched to 3.0 to 3.5 times its original length in the transverse direction and to 3.0 to 3.5 times its original length in the longitudinal direction, and the conveying speed of the fiber web during stretching is 8 m / min to 12 m / min.

[0090] The longitudinal direction is the conveying direction of the fiber web, and the transverse direction is the direction perpendicular to the conveying direction.

[0091] The following examples illustrate the fiber web stretching method by stretching the fiber web to 3.0 times its original length in the transverse direction and 3.5 times its original length in the longitudinal direction:

[0092] Longitudinal stretching can be achieved using two sets of traction rollers, one before stretching and one after. The front traction roller (before stretching) rotates at a slower speed, while the rear traction roller (after stretching) rotates at a faster speed, with a speed ratio of 1:3.5. This means the rear roller's speed is 3.5 times that of the front roller, allowing the fiber web to be stretched to 3.5 times its original length in the longitudinal direction. As the fiber web is elongated in the conveying direction (longitudinal direction), the originally randomly arranged fibers become oriented longitudinally, and the longitudinal pores between the fibers are stretched, narrowing, and lengthening.

[0093] Lateral stretching can be performed using a tenter frame. The fiber web is clamped on both sides by chain clamps, and the spacing between the chains on the transverse track gradually increases until the final spacing is 3.0 times the initial spacing, thus stretching the fiber web laterally to 3.0 times its original length. As the fiber web is widened laterally, the fibers further align in a transverse orientation, and the transverse pores between the fibers are stretched to a uniform size, ultimately forming a bidirectional oriented fiber web membrane.

[0094] The conveying speed of the fiber web during stretching is 8 m / min to 12 m / min, for example, 8 m / min, 9 m / min, 10 m / min, 11 m / min, or 12 m / min. When the conveying speed of the fiber web during stretching is 8 m / min to 12 m / min, the conveying speed can match the stretching ratio in the longitudinal and transverse directions, which improves the uniformity of the fiber web during stretching and makes the stretched fiber web less prone to breakage and deformation.

[0095] When the conveying speed of the fiber web during stretching exceeds 12 meters per minute, the fiber web moves too fast, which can easily lead to uneven stretching and localized breakage.

[0096] When the conveying speed of the fiber web during stretching is less than 8 meters per minute, the moving speed of the fiber web is too slow, and the fiber web is prone to overheating and deformation due to the long residence time.

[0097] Step S600: Polymerize a polyamide layer on the surface and within the pores of the fiber mesh to form a moisture-permeable and humidifying membrane with a pore size of less than 1 nanometer.

[0098] After a polyamide layer is polymerized on the surface and within the pores of the fiber membrane, continuous moisture-permeable channels with a pore size of less than 1 nanometer are formed. Water vapor molecules, with a diameter of approximately 0.4 nanometers, can diffuse freely through these channels, driven by the humidity difference across the moisture-permeable membrane. Liquid water molecules, due to surface tension, form a water film with a minimum aggregate unit diameter greater than 100 nanometers, making it impossible for them to pass through the smaller 1-nanometer moisture-permeable channels. Therefore, the resulting moisture-permeable membrane allows only water vapor to pass through, while liquid water is difficult to pass through.

[0099] Step S600 may specifically include:

[0100] Step S601: Immerse the fiber membrane in an aqueous solution of 1.5wt% polyethyleneimine + 0.5wt% piperazine for 60 seconds.

[0101] Step S601 allows the aqueous monomer (polyethyleneimine + piperazine) to be uniformly adsorbed on the surface and pores of the fiber membrane, providing a sufficient source of amino groups for subsequent reaction with the oil-phase monomer.

[0102] Step S602: Transfer the fiber membrane to a 0.1 wt% isoparaffinic solvent solution of 1,3,5-pyromellitic chloride for 60 seconds.

[0103] Step S602 allows the oil-phase monomer (1,3,5-pyromellitic acid chloride) to react with the aqueous-phase monomer on the surface of the fiber membrane at the interface to generate a polyamide layer.

[0104] Step S603: Heat-treat the fiber membrane at 70°C for 5 minutes.

[0105] Heat treatment can be carried out in a forced-air oven with a wind speed of 1m / s-2m / s to improve the temperature uniformity inside the oven and reduce the possibility of cracking of the polyamide layer due to local overheating.

[0106] Heat treatment at 70℃ can evaporate the residual isoparaffin solvent and moisture on the surface of the base film, avoiding swelling of the polyamide film caused by residual isoparaffin solvent, which would affect its compactness.

[0107] A temperature of 70℃ can activate unreacted amino and acyl chloride groups, further increasing the crosslinking degree of the polyamide layer, thereby improving the structural stability of the moisture-permeable membrane.

[0108] During the heat treatment process, the polyamide molecular chains will shrink slightly to form nanoscale moisture-permeable channels with a pore size ≤1nm. These channels only allow small water vapor molecules (about 0.4nm in diameter) to pass through, while blocking liquid water (>100nm in diameter), thus giving the formed moisture-permeable and humidifying film waterproof and moisture-permeable functions.

[0109] The method for preparing the moisture-permeable and moisturizing membrane according to this application involves injecting supercritical CO2 into the PET melt to form nascent PET fibers with a microporous structure after stretching. This increases the porosity of the final moisture-permeable and moisturizing membrane, thereby improving its moisture permeability. By laying the nascent PET fibers into a web, a fiber web with a melt-blown density of 65 g / m² to 75 g / m² and a molecular weight distribution of less than 1.8 is formed. The small difference in molecular chain length among the fiber webs reduces the possibility of fiber breakage during subsequent stretching, improves the structural strength and wind pressure resistance of the fiber web, and ultimately enhances the structural strength of the final moisture-permeable and moisturizing membrane. After being subjected to a high-voltage electrostatic field, the fiber web acquires electrostatic adsorption capabilities, improving the filtration performance of the moisture-permeable membrane. The fiber web is then stretched bidirectionally in both the transverse and longitudinal directions. During this stretching process, due to electrostatic adsorption, the fibers are less prone to excessive dispersion and are oriented, ultimately forming a dense fiber web membrane with a narrow pore size distribution of less than 2 micrometers and a pore size ratio greater than 95%. This further enhances the structural strength and wind pressure resistance of the fiber web membrane, making it less prone to deformation. Finally, a polyamide layer is polymerized on the surface and within the pores of the fiber web membrane, forming a moisture-permeable membrane that allows water vapor to pass through while blocking liquid water.

[0110] In some possible implementations of the embodiments of this application, reference is made to Figure 2 In step S600, the specific steps include:

[0111] Step S610: Spray hot melt adhesive onto the fiber web and hot press to form a composite base film.

[0112] Because PET molecular chains contain strongly polar ester groups but have low surface energy, the surface of the fiber membrane is highly inert and has weak interfacial adhesion to the polyamide layer. If it is directly laminated with the polyamide layer, interlayer gaps are likely to occur, and delamination is likely to occur during use, resulting in the polyamide layer falling off and the filtration effect being reduced.

[0113] Hot melt adhesives can be polyurethane hot melt adhesives or other types of hot melt adhesives. Hot melt adhesives have high viscosity, thermal compatibility with PET, and low-temperature curing ability. After spraying hot melt adhesive onto the fiber web, hot pressing is performed immediately to allow the molten hot melt adhesive to fully contact, diffuse, and initially cure with the PET fiber surface, forming an integrated composite base film. This reduces the possibility of the hot melt adhesive falling off or shifting during subsequent transportation.

[0114] Step S620: Polymerize a polyamide layer on the surface and in the pores of the composite base film to form a moisture-permeable and humidifying film.

[0115] Hot melt adhesive can form a strong bond with PET through in-situ lamination, while providing strong adhesive sites for the subsequent polyamide layer, improving the structural stability of the polyamide layer, reducing the possibility of delamination and peeling of the polyamide layer, and improving the filtration effect of the moisture-permeable and moisturizing membrane.

[0116] In some possible implementations of the embodiments of this application, reference is made to Figure 3 In step S600, after polymerizing the polyamide layer on the surface and within the pores of the fiber mesh, the process further includes:

[0117] Step S630: Integrate phytic acid into the surface and pores of the polyamide layer.

[0118] Because of the strong polarity and antibacterial properties of the phosphate groups in phytic acid, it can inhibit the photo-oxidative degradation of the polyamide layer, thus improving the aging resistance of the moisture-permeable membrane. By integrating phytic acid into the surface and pores of the polyamide layer, the composite membrane possesses antibacterial, anti-fouling, and aging-resistant functions without damaging the moisture permeability channels.

[0119] refer to Figure 4 Phytic acid can be integrated into the surface and pores of the polyamide layer using the following methods:

[0120] Step S631: Immerse the fiber mesh with the polymerized polyamide layer in a 3wt% phytic acid aqueous solution for 120 seconds.

[0121] Phytic acid has a molecular weight of approximately 660 and is a natural macromolecule. A concentration of 3 wt% ensures that it forms saturated adsorption on the polyamide surface, while avoiding excessive concentration that would cause phytic acid to accumulate in the pores and block the moisture permeability channels.

[0122] The ionic reaction between phytic acid and polyamide requires a certain amount of time. 120 seconds can ensure a sufficient reaction. If the time is too short, the phytic acid will not be adsorbed enough, which will weaken the antibacterial, anti-fouling and anti-aging functions of the formed moisture-permeable film.

[0123] In step S632, after drying at a constant temperature of 40℃ for 10 minutes, gradually increase the temperature to 60℃ and dry at a constant temperature for 5 minutes.

[0124] The fiber membrane soaked in phytic acid is first dried at a low temperature to allow the moisture on the surface of the fiber membrane to evaporate slowly, so that the phytic acid is initially fixed on the surface of the polyamide layer under the action of ionic bonds, reducing the possibility of phytic acid migration.

[0125] The temperature is then gradually increased to 60°C to further evaporate the residual moisture inside the fiber membrane, while also making the bond between phytic acid and polyamide stronger and reducing the possibility of phytic acid falling off during subsequent use.

[0126] First, the fiber membrane is dried at a low temperature, and then the temperature is gradually increased to continue drying the fiber membrane. This avoids the possibility of cracking caused by the rapid evaporation of moisture on the surface and inside of the fiber membrane due to direct high-temperature drying.

[0127] In some possible implementations of the embodiments of this application, reference is made to Figure 5 and Figure 6Before step S100, the method further includes:

[0128] Step S110: Solid-state polymerization of PET chips is carried out in a high-temperature vacuum environment to form high-viscosity PET chips.

[0129] The intrinsic viscosity of PET chips is 0.65 dL / g. The PET melt formed by directly melting PET chips has low viscosity and weak strength, and is prone to breakage during subsequent stretching, making it difficult to form a continuous fiber web.

[0130] The ends of PET molecular chains contain hydroxyl (-OH) and carboxyl (-COOH) groups. Under high temperature and vacuum conditions, these end groups undergo solid-state polycondensation. The -OH at the end of the PET molecular chain reacts with the -COOH at the end of another molecular chain in an esterification reaction, removing water molecules (H2O) and forming an ester bond (-COO-). This connects the two molecular chains into a longer molecular chain. The longer PET molecular chains increase the entanglement between the molecular chains, forming highly viscous PET chips. The viscosity of highly viscous PET chips increases to 0.85 dL / g.

[0131] In some possible implementations of the embodiments of this application, the temperature of the high-temperature vacuum environment is 170°C to 190°C and the vacuum degree is less than or equal to 10 Pa.

[0132] The temperature of the high-temperature vacuum environment can be 170℃, 180℃, or 190℃, etc. When the temperature is between 170℃ and 190℃, the reaction activity of the terminal groups of the PET molecular chain is stronger, which can increase the viscosity after the reaction and reduce the possibility of softening and clumping of the chips.

[0133] When the temperature in a high-temperature vacuum environment is below 170°C, the low temperature will lead to a decrease in the reaction rate, making it difficult to increase the viscosity of PET chips to the required viscosity value.

[0134] When the temperature in a high-temperature vacuum environment exceeds 190℃, the temperature is too high. Although the reaction rate is accelerated, the slices are prone to softening and clumping.

[0135] When the vacuum level in a high-temperature vacuum environment is less than or equal to 10 Pa, water molecules formed during polymerization can be removed promptly, the condensation reaction dominates, molecular chains primarily grow, the difference between long and short molecular chains is small, and the molecular weight distribution can be controlled within 1.6-1.8, resulting in PET chips with a narrow molecular weight distribution. Longer molecular chains increase melt viscosity, ensuring uniform fiber stress during subsequent stretching, ultimately improving fiber strength and reducing the likelihood of fraying in the fiber web, thus enhancing the overall structural stability of the moisture-permeable and humidifying membrane.

[0136] When the vacuum level in a high-temperature vacuum environment exceeds 10 Pa, insufficient vacuum leads to hydrolysis and degradation, causing long chains to break into short chains. Simultaneously, the polycondensation reaction stagnates, resulting in a system containing both unbroken long chains and a large number of newly generated short chains. This significantly increases the difference in molecular chain length, ultimately resulting in a molecular weight distribution greater than 1.8. This leads to the formation of PET chips with a wide molecular weight distribution, which in turn reduces the strength of the subsequently formed fibers. Short molecular chains reduce melt viscosity, while long molecular chains increase it. This viscosity unevenness causes uneven stress on the fibers during stretching, ultimately resulting in decreased fiber strength. Furthermore, the fiber web is prone to fraying, reducing the overall structural stability of the moisture-permeable and humidifying membrane.

[0137] The solid-state polymerization processing time is between 1.5 hours and 2.5 hours, for example, it can be 1.5 hours, 2 hours, or 2.5 hours, etc.

[0138] The solid-state polymerization treatment time is 1.5 to 2.5 hours, which can increase the viscosity after the reaction and reduce the possibility of softening and clumping of the chips.

[0139] When the solid-state polymerization process takes less than 1.5 hours, the reaction time is too short, making it difficult to increase the viscosity of the PET chips to the required viscosity value.

[0140] When the solid-phase polymerization process takes longer than 2 hours, the reaction time is too long and it can easily cause the slices to soften and clump together.

[0141] Step S120: Add a nucleating agent to high-viscosity PET chips and prepare PET masterbatch containing the nucleating agent.

[0142] PET masterbatch without nucleating agents has a high crystallization temperature (120-130℃) and cannot crystallize during rapid cooling, forming amorphous fibers.

[0143] PET masterbatch containing nucleating agents has a crystallization temperature reduced to 100-110℃. Even during rapid cooling, PET molecular chains can quickly aggregate and crystallize towards the nucleating agent, forming highly crystalline fibers. The molecular chains of highly crystalline fibers are more regularly arranged, resulting in a fiber strength increase of over 30%. Their aging resistance and chemical resistance are significantly optimized, reducing the possibility of pore collapse due to fiber breakage during use of the moisture-permeable and moisturizing membrane.

[0144] In some possible implementations of the embodiments of this application, the nucleating agent can be sodium benzoate and hydrophilic nano-SiO2.

[0145] The total weight is the sum of the weights of the high-viscosity PET chips, sodium benzoate, and hydrophilic nano-SiO2.

[0146] Sodium benzoate accounts for less than 0.1% of the total weight, and hydrophilic nano-SiO2 accounts for less than 0.05% of the total weight.

[0147] Sodium benzoate is an organic nucleating agent. Its molecular structure is compatible with PET molecular chains, allowing it to disperse uniformly in PET melt and form tiny crystal nuclei. PET molecular chains can rapidly aggregate and align themselves around these nuclei without requiring additional energy to form new nuclei, thus lowering the temperature required for crystallization, increasing the crystallization rate, and improving fiber strength.

[0148] Hydrophilic nano-SiO2 serves as an inorganic nucleating agent. With a particle size much smaller than the molecular chains of PET, it can be uniformly dispersed in the PET melt, acting as inorganic crystallization nuclei to further promote PET crystallization. The synergistic effect of hydrophilic nano-SiO2 and sodium benzoate forms a dual nucleation system of "organic nucleus + inorganic nucleus," which exhibits a more significant crystallization-promoting effect than a single nucleating agent, further enhancing fiber strength.

[0149] Calculated by weight ratio, take "99.85% of solid-phase thickened PET chips (intrinsic viscosity 0.85dL / g) + 0.1% sodium benzoate + 0.05% hydrophilic nano SiO2", melt the PET chips at 240℃ using a twin-screw extruder to uniformly disperse the nucleating agent, and then extrude and pelletize them to produce PET masterbatch containing the nucleating agent.

[0150] Sodium benzoate accounts for less than 0.1% of the total weight to increase the viscosity of the PET melt during subsequent stretching, making it easier to stretch.

[0151] When the weight of sodium benzoate accounts for more than 0.1% of the total weight, the sodium benzoate will be in excess, causing the PET melt viscosity to decrease and affecting subsequent stretching.

[0152] The weight of hydrophilic nano-SiO2 accounts for less than 0.05% of the total weight, in order to reduce the possibility of hydrophilic nano-SiO2 agglomeration and blockage of the moisture permeability channels.

[0153] When the weight of hydrophilic nano-SiO2 accounts for more than 0.05% of the total weight, the surface energy of the hydrophilic nano-SiO2 particles is high, they attract and aggregate with each other, easily forming micron-sized particles, which leads to impurities in the fibers and blockage of the moisture permeability channels.

[0154] In some possible implementations of this application, the particle size of hydrophilic nano-SiO2 can be 25 nm to 35 nm, for example, 25 nm, 30 nm, or 35 nm. The specific surface area of ​​hydrophilic nano-SiO2 is about 300 m² / g, balancing high activity and low risk of agglomeration. The surface hydroxyl group density is moderate, about 4-5 hydroxyl groups / nm², which can be uniformly dispersed in PET melt without obvious agglomeration, and can give full play to the nano-effect.

[0155] When the particle size of hydrophilic nano-SiO2 is less than 25 nanometers, the specific surface area of ​​hydrophilic nano-SiO2 is >400m² / g, the surface energy is extremely high, the van der Waals forces between particles are extremely strong, and irreversible aggregation is prone to occur, forming micron-sized aggregates. It is difficult to disperse uniformly in PET melt, which eventually leads to impurity points in the fiber and blockage of pores.

[0156] When the particle size of hydrophilic nano-SiO2 is greater than 35 nanometers, the specific surface area is less than 200 m² / g, the specific surface area is significantly reduced, the surface hydroxyl density decreases, the nano-effect is greatly weakened, the hydrophilicity is not sufficiently improved, and the assisted nucleation efficiency decreases.

[0157] refer to Figures 7-10 The moisture-permeable and moisturizing membrane 10 of this application embodiment can be applied to the top cover 20 of the storage drawer in refrigeration equipment (such as refrigerators, low-temperature display cabinets, etc.). When the humidity inside the storage drawer is too high, the humidity difference between the two sides of the moisture-permeable and moisturizing membrane 10 is large. Water vapor inside the storage drawer can diffuse to the outside of the storage drawer through the moisture-permeable and moisturizing membrane to reduce the humidity inside the storage drawer, making the humidity inside the storage drawer suitable for the storage of items and extending the shelf life of the items inside the storage drawer.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0159] For ease of explanation, the above description has been provided in conjunction with specific embodiments. However, the above exemplary discussion is not intended to be exhaustive or to limit the embodiments to the specific forms disclosed above. Various modifications and variations can be obtained based on the above teachings. The selection and description of the above embodiments are for the purpose of better explaining the principles and practical applications, thereby enabling those skilled in the art to better utilize the above embodiments and various different variations of embodiments suitable for specific application considerations.

Claims

1. A method for producing a moisture-permeable and moisture-retentive film, characterized by, The application relates to a method for preparing a microporous polyethylene terephthalate (PET) membrane. The method comprises the following steps: melting PET masterbatch into a PET melt; injecting supercritical CO2 into the PET melt to form a melt mixture containing CO2; stretching the melt mixture containing CO2 to form PET primary fibers containing a microporous structure; wherein the diameter of the PET primary fibers is less than 15 microns; laid and self-adhesive forming the PET primary fibers to form a fiber web with a melt-blowing density of 65 g / m2 to 75 g / m2 and a molecular weight distribution of less than 1.8; making the fiber web flow through a high-voltage electrostatic field, and then stretching the fiber web in the transverse and longitudinal directions to form an oriented fiber web film with a pore size of less than 2 microns and a pore ratio of more than 95%; 2. The method for producing a moisture-permeable and moisture-retentive film according to claim 1, characterized by, polymerizing a polyamide layer on the surface and in the pores of the fiber web film to form a moisture-permeable and moisture-retaining film. The method for preparing the moisture-permeable and moisture-retaining film by polymerizing a polyamide layer on the surface and in the pores of the fiber web film comprises the following steps: spraying hot melt adhesive on the fiber web film and hot-pressing to form a composite base film; 3. The method for producing a moisture-permeable and moisture-retentive film according to claim 2, characterized by, polymerizing a polyamide layer on the surface and in the pores of the composite base film to form a moisture-permeable and moisture-retaining film. After the step of polymerizing a polyamide layer on the surface and in the pores of the fiber web film, the method further comprises the following step:

4. The method for producing a moisture-permeable and moisture-retentive film according to any one of claims 1 to 3, characterized by, integrating phytic acid into the surface and pores of the polyamide layer.

5. The method for producing a breathable and moisture-permeable film according to any one of claims 1 to 3, characterized by, The purity of the supercritical CO2 is greater than or equal to 99.5%.

6. The method for producing a breathable and moisture-permeable film according to any one of claims 1 to 3, characterized by, When the fiber web is stretched in the transverse and longitudinal directions, the fiber web is stretched to 3.0 to 3.5 times the original length in the transverse direction and to 3.0 to 3.5 times the original length in the longitudinal direction, and the conveying speed of the fiber web during stretching is 8 to 12 meters per minute. Before the step of melting the PET masterbatch into a PET melt, the method further comprises the following steps: solid-phase polymerizing PET chips in a high-temperature vacuum environment to form high-viscosity PET chips; 7. The method for producing a moisture-permeable and moisture-retentive film according to claim 6, characterized by, adding a nucleating agent to the high-viscosity PET chips to prepare PET masterbatch containing the nucleating agent.

8. The method for producing a moisture-permeable and moisture-retentive film according to claim 6, characterized by, The temperature of the high-temperature vacuum environment is 170 to 190 DEG C, and the vacuum degree is less than or equal to 10 Pa. The nucleating agent is sodium benzoate and hydrophilic nano-SiO2. The sum of the weights of the high-viscosity PET chips, the sodium benzoate and the hydrophilic nano-SiO2 is the total weight.

9. The method for producing a moisture-permeable and moisture-retentive film according to claim 8, characterized by, The weight of the sodium benzoate accounts for less than 0.1% of the total weight, and the weight of the hydrophilic nano-SiO2 accounts for less than 0.05% of the total weight.

10. The method of producing a moisture-permeable and moisture-retentive film according to any one of claims 1 to 3, characterized by, The particle size of the hydrophilic nano-SiO2 is 25 to 35 nanometers. The melting temperature of the PET masterbatch is 258 to 262 DEG C.

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