Polyester non-woven fabric for reverse osmosis membrane as well as preparation method and application of polyester non-woven fabric

Abstract

The invention relates to a polyester non-woven fabric for a reverse osmosis membrane as well as a preparation method and application of the polyester non-woven fabric, and belongs to the technical field of reverse osmosis membrane supports. The preparation method comprises the following steps: S1, preparing polyester non-woven fabric raw cloth: defibering and stirring polyester main body fibers and polyester adhesive fibers, and then carrying out inclined wire wet forming, squeezing and drying to obtain the polyester non-woven fabric raw cloth; s2, five-stage continuous process treatment: sequentially carrying out pre-hot pressing, hot pressing, longitudinal stretching, transverse stretching and cooling shaping on the polyester non-woven fabric raw cloth to obtain the polyester non-woven fabric for the reverse osmosis membrane. The polyester non-woven fabric is applied to the field of reverse osmosis membranes. The polyester non-woven fabric has good air permeability while the strength is guaranteed, and the whole polyester non-woven fabric has high surface smoothness, high porosity, high mechanical strength and good pressure resistance. The contradiction that when a traditional polyester non-woven fabric serves as a reverse osmosis membrane supporting base material, the surface flatness and the high porosity are difficult to consider at the same time is solved.

Description

Technical Field

[0001] This invention relates to a polyester nonwoven fabric for reverse osmosis membranes, its preparation method and application, belonging to the field of reverse osmosis membrane support technology. Background Technology

[0002] Reverse osmosis technology is currently a relatively advanced and widely used core technology for advanced water treatment and seawater desalination. Its core component, the reverse osmosis membrane, typically employs a composite membrane structure, consisting of an ultra-thin and dense polyamide active separation layer supported on a porous substrate. The performance of this porous support substrate directly determines the final separation performance, mechanical strength, and long-term operational reliability of the reverse osmosis membrane.

[0003] Currently, commercially available reverse osmosis membranes generally use polyester nonwoven fabric as the porous support substrate. However, as reverse osmosis technology develops to meet higher requirements, the traditional single polyester nonwoven fabric substrate is gradually revealing its inherent technical limitations: First, there is an irreconcilable contradiction between surface smoothness and pore structure in polyester nonwoven fabrics. Achieving a smooth surface through high temperature and pressure inevitably leads to the collapse of the pore structure, a decrease in porosity, and a denser material. Conversely, maintaining ideal high porosity requires sufficient pressure, resulting in a loose fiber network, increased surface fuzz, and deterioration of smoothness. This contradiction makes it difficult for traditional substrates to simultaneously meet the dual requirements of high-performance reverse osmosis membranes for both surface quality and permeability.

[0004] Secondly, the substrate lacks sufficient mechanical strength and dimensional stability. In high-pressure applications, traditional polyester nonwoven fabrics, due to their limited fiber modulus, are prone to creep and compression densification under long-term operation, resulting in thinner substrates, narrower water flow channels, and increased system pressure drop, causing irreversible reduction in water production flux.

[0005] Furthermore, traditional reinforcement methods have significant drawbacks. Increasing the basis weight of the substrate or using coarser fibers to improve strength often further sacrifices porosity and surface smoothness. On the other hand, simple mixing or post-lamination composite methods that introduce other high-performance fibers often face problems such as weak interfacial bonding and complex processes.

[0006] Therefore, there is an urgent need in this field to develop a new type of polyester nonwoven fabric for reverse osmosis membranes that can fundamentally solve the inherent contradiction between surface smoothness and pore structure, while taking into account excellent mechanical strength and dimensional stability, thus providing a reliable foundation for the preparation of next-generation high-performance reverse osmosis membranes. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a polyester nonwoven fabric for reverse osmosis membranes, its preparation method, and its application. It resolves the contradiction between surface smoothness and high porosity when traditional polyester nonwoven fabrics are used as supporting substrates for reverse osmosis membranes. The polyester nonwoven fabric has better mechanical strength and dimensional stability.

[0008] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing polyester nonwoven fabric for reverse osmosis membranes, wherein the preparation method is as follows: S1. Preparation of polyester nonwoven fabric: The polyester base fiber and polyester bonding fiber are loosened and stirred, and then subjected to inclined wire wet forming, pressing and drying to obtain polyester nonwoven fabric. S2, Five-stage continuous process: The polyester nonwoven fabric is subjected to preheating and pressing, hot pressing, longitudinal stretching, transverse stretching and cooling and shaping in sequence to obtain the polyester nonwoven fabric for reverse osmosis membrane.

[0009] Furthermore, in step S1, the sum of the weight parts of the polyester main fiber and the polyester bonding fiber is 100 parts, the amount of polyester main fiber added is 60-85 parts, and the amount of polyester bonding fiber added is 15-40 parts.

[0010] Furthermore, the polyester main fiber has a fineness of 0.5-0.8D, a length of 5-6mm, and a melting point temperature of 258-262℃. The polyester bonded fiber has a fineness of 1.2-2.0D and a length of 3-6mm; the polyester bonded fiber is a core-sheath structure polyester fiber with a sheath melting point of 100-130℃ and a core melting point of 258-262℃.

[0011] Furthermore, the five-stage continuous process in step S2 is completed continuously on an integrated production line consisting of five functional units, each arranged horizontally along the material travel direction, wherein: The first unit consists of two vertically arranged rollers, forming the first roller gap; The second unit consists of two vertically arranged rollers, forming a second roller gap; The third unit consists of two vertically arranged rollers, forming a third roller gap; The fourth unit is a transverse tensioning device; The fifth unit consists of two vertically arranged rollers, forming the fourth roller gap; In step S1, the polyester nonwoven fabric moves horizontally through the first group of units, the second group of units, the third group of units, the fourth group of units, and the fifth group of units.

[0012] Furthermore, during the preheating pressing process, the temperature is 180℃-200℃, the linear pressure is 150N / mm-300N / mm, and the linear velocity is 5.0-15.0 m / min.

[0013] Furthermore, during the hot pressing process, the temperature is 230℃-250℃, the linear pressure is 150N / mm-250N / mm, and the linear velocity of the hot pressing is the same as that of the preheating pressing.

[0014] Furthermore, during the longitudinal stretching process, the linear velocity of the inlet roller is 5.0-15.0 m / min, the linear velocity of the outlet roller is 5.3-17.3 m / min, and the ratio of the linear velocity of the outlet roller to the linear velocity of the inlet roller is 1.05-1.15. During the longitudinal stretching process, the temperature is 200℃-220℃ and the linear pressure is 40N / mm-80N / mm.

[0015] Furthermore, during the transverse stretching process, the temperature is 180℃-210℃, and the ratio of the tenter frame's outlet width to its inlet width is 1.10-1.25; the linear velocity during the transverse stretching process is the same as the linear velocity of the outlet roller during the longitudinal stretching process. During the cooling and shaping process, the surface temperature of the cooling roller is controlled to be less than 80°C, and the linear speed of the cooling and shaping is the same as the linear speed of the transverse stretching.

[0016] The present invention also discloses a polyester nonwoven fabric for reverse osmosis membranes, wherein the polyester nonwoven fabric is prepared by the preparation method described in the present invention.

[0017] The present invention also discloses an application of polyester nonwoven fabric for reverse osmosis membranes, wherein the polyester nonwoven fabric is used in the field of reverse osmosis membranes.

[0018] The beneficial effects of this invention are:

[0019] (1) Achieved a synergistic improvement in surface smoothness and high porosity: This invention successfully overcomes the technical bottleneck of traditional polyester nonwoven fabrics, which struggle to balance surface smoothness and high porosity, through a unique five-stage continuous process: a synergistic process of "hot pressing followed by biaxial stretching." First, hot pressing is performed at specific temperatures and pressures, utilizing the melt-bonding effect of the core-sheath structure to initially construct a smooth surface foundation. Then, under precisely controlled parameters, longitudinal and transverse stretching is performed, actively creating a uniform and interconnected microporous network within the material. This sequential process ensures that the product achieves extremely high surface smoothness (laying the foundation for forming a defect-free polyamide separation layer, thus achieving a high desalination rate) while simultaneously possessing high porosity (providing efficient channels for water molecules, ensuring high water flux), thus solving the dual demanding requirements of high-performance reverse osmosis membranes for substrate surface quality and permeability.

[0020] (2) Significantly enhanced mechanical strength and dimensional stability, extending membrane life: This invention utilizes a precisely controlled biaxial stretching process in both the longitudinal and transverse directions to induce a high degree of orientation of polyester macromolecular chains and fibers along the stress direction, forming a regular fiber network topology. This results in the construction of an anisotropic, high-strength skeleton at both the molecular and fiber scales. This orientation structure significantly enhances the material's elastic modulus and tensile strength, endowing the substrate with excellent creep resistance.

[0021] The subsequent cooling and shaping process, carried out under tensile tension, is essentially a dynamic crystallization and stress relaxation process. This process "freezes" the orientation state structure induced by stretching, significantly reducing the internal stress of the product, thereby achieving extremely low thermal shrinkage and excellent dimensional stability.

[0022] This high-modulus, high-stability structure enables the substrate to effectively resist the compression densification and plastic deformation caused by long-term high-pressure loads in reverse osmosis applications. It fundamentally suppresses the problems of narrowing of permeate channels and increased system pressure drop caused by the collapse of the support layer structure, ensuring the long-term stability of reverse osmosis membrane permeate flux and significantly extending the service life of membrane elements.

[0023] (3) High integration of production processes and good consistency of product performance: This invention integrates five key processes—preheating and pressing, hot pressing, longitudinal stretching, transverse stretching, and cooling and shaping—into a continuous production line. Each unit is precisely and independently driven and controlled via servo motors or vector-controlled variable frequency motors. This highly integrated and automated production model not only significantly improves production efficiency and achieves continuous output from raw materials to finished products, but more importantly, it ensures the uniformity and stability of various product performance indicators, reduces batch variations, and provides a solid guarantee for large-scale, high-quality, and repeatable industrial production. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0026] A method for preparing polyester nonwoven fabric for reverse osmosis membranes, wherein the preparation method comprises: S1. Preparation of polyester nonwoven fabric: The polyester base fiber and polyester bonding fiber are loosened and stirred, and then subjected to inclined wire wet forming, pressing and drying to obtain polyester nonwoven fabric. S2, Five-stage continuous process: The polyester nonwoven fabric is subjected to preheating and pressing, hot pressing, longitudinal stretching, transverse stretching and cooling and shaping in sequence to obtain the polyester nonwoven fabric for reverse osmosis membrane.

[0027] Specifically, in step S1, the sum of the weight parts of the polyester main fiber and the polyester bonding fiber is 100 parts, the amount of polyester main fiber added is 60-85 parts, and the amount of polyester bonding fiber added is 15-40 parts.

[0028] Specifically, the polyester main fiber has a fineness of 0.5-0.8D, a length of 5-6mm, and a melting point temperature of 258-262℃. The polyester bonded fiber has a fineness of 1.2-2.0D and a length of 3-6mm; the polyester bonded fiber is a core-sheath structure polyester fiber with a sheath melting point of 100-130℃ and a core melting point of 258-262℃.

[0029] Specifically, the five-stage continuous process in step S2 is completed continuously on an integrated production line consisting of five functional units, with each functional unit arranged horizontally along the material travel direction, wherein: The first unit (preheating press) contains two vertically arranged rollers, forming the first roller gap; The second unit (hot pressing) contains two vertically arranged rollers, forming a second roller gap; The third unit (longitudinal tension) contains two vertically arranged rollers, forming a third roller gap; The fourth unit (lateral tension) is a lateral tensioning device; The fifth unit (cooling and shaping) contains two vertically arranged rollers, forming the fourth roller gap; In step S1, the polyester nonwoven fabric moves horizontally through the first group of units, the second group of units, the third group of units, the fourth group of units, and the fifth group of units.

[0030] Specifically, the five-stage continuous process is as follows: (1) Preheating and pressing: The polyester nonwoven fabric from step S1 is passed through the first roller gap of the first unit and pre-composite under conditions of 180℃-200℃ and linear pressure of 150N / mm-300N / mm; the linear speed of the first unit is controlled at 5.0-15.0 m / min. The two rollers in the first unit are made of stainless steel.

[0031] (2) Hot pressing: The polyester nonwoven fabric, after preliminary hot pressing, is introduced into the second roller gap of the second unit and further hot-pressed and laminated under conditions of 230℃-250℃ and linear pressure of 150N / mm-250N / mm. The linear speed of the second unit is the same as that of the first unit. In the second unit, the upper roller is a stainless steel roller and the lower roller is a nylon roller (the surface of the stainless steel roller in contact with the coated surface of the polyester nonwoven fabric).

[0032] (3) Longitudinal stretching: The hot-pressed polyester nonwoven fabric is introduced into the third roller gap of the third unit; the inlet linear velocity of the third unit is controlled at 5.0-15.0 m / min, and the outlet linear velocity is controlled at 5.3-17.3 m / min; longitudinal stretching is applied to the polyester nonwoven fabric by controlling the ratio of the linear velocity (V2) of the outlet roller to the linear velocity (V1) of the inlet roller in the third unit; the linear velocity ratio V2 / V1 is controlled at 1.05-1.15; the temperature of the third roller gap is maintained at 200℃-220℃, and the linear pressure is 40N / mm-80N / mm. The upper roller in the third unit is a nylon roller, and the lower roller is a stainless steel roller.

[0033] (4) Lateral stretching: The longitudinally stretched polyester nonwoven fabric is introduced into the lateral stretching device of the fourth unit; this device clamps both sides of the blank with clamps and stretches the polyester nonwoven fabric laterally at a temperature of 180℃-210℃; the linear speed of the fourth unit is the same as the exit speed of the third unit; the lateral stretching is achieved by controlling the ratio of the exit width (W2) to the inlet width (W1) of the tenter frame, and this width ratio W2 / W1 is controlled between 1.10 and 1.25. The two rollers used in this process are stainless steel rollers.

[0034] (5) Cooling and shaping: The biaxially stretched polyester nonwoven fabric is introduced into the fourth roller gap of the fifth unit. This roller is a cooling roller, and the surface temperature is controlled below 80°C. The linear speed of the fifth unit is the same as that of the fourth unit. The microporous structure is shaped while maintaining tension. Among them, the two cooling rollers are stainless steel rollers.

[0035] More specifically, the rollers of the first, second, and third units are heated rollers; the transverse stretching device of the fourth unit is a tracked tenter frame equipped with a heating system; and the rollers of the fifth unit are cooled rollers.

[0036] More specifically, the rollers in the first, second, third, and fifth units are all driven independently by servo motors or vector-controlled variable frequency motors.

[0037] A polyester nonwoven fabric for reverse osmosis membranes is provided, wherein the polyester nonwoven fabric is prepared by the method described in this invention. The polyester nonwoven fabric can maintain strength while also possessing good air permeability, and overall exhibits high surface smoothness, high porosity, high mechanical strength, and good pressure resistance.

[0038] An application of a polyester nonwoven fabric for reverse osmosis membranes, wherein the polyester nonwoven fabric is used in the field of reverse osmosis membranes, particularly as a support substrate for high-performance reverse osmosis membranes.

[0039] Example 1 A method for preparing a polyester nonwoven fabric for reverse osmosis membranes is as follows: S1. Preparation of polyester nonwoven fabric: The polyester base fiber and polyester binder fiber are loosened and stirred, then subjected to inclined wire wet forming, pressing, and drying to obtain the polyester nonwoven fabric base (basis weight 65g / m²). 2 ); The amount of polyester main fiber added is 75 parts by weight, and the amount of polyester bonding fiber added is 25 parts. The polyester main fiber has a fineness of 0.6D, a length of 5mm, and a melting point of 260℃. The polyester bonding fiber has a fineness of 1.5D and a length of 3mm; the polyester bonding fiber is a core-sheath structure polyester fiber with a sheath melting point of 110℃ and a core melting point of 260℃.

[0040] S2, Five-stage continuous process: (1) Preheating and pressing: The polyester nonwoven fabric from step S1 is passed through the first roller gap and pre-composite under the conditions of 190℃ temperature, 200N / mm linear pressure, and 10m / min linear speed. (2) Hot pressing: The polyester nonwoven fabric that has undergone preliminary hot pressing is introduced into the second roller gap and further hot pressing is carried out under the conditions of 240℃ and 200N / mm linear pressure, with a linear speed of 10m / min. (3) Longitudinal stretching: The hot-pressed polyester nonwoven fabric is introduced into the third roller gap; the blank is subjected to longitudinal stretching by controlling the ratio of the linear speed of the exit roller to the inlet roller (stretch ratio V2 / V1 = 1.08), while the temperature of the third roller gap is maintained at 210℃ and the linear pressure is 60N / mm. (4) Transverse stretching: The longitudinally stretched polyester nonwoven fabric is introduced into the transverse stretching device; under the condition of 200℃, the blank is stretched in the transverse direction by controlling the ratio of the exit width to the inlet width of the tenter frame (stretching ratio W2 / W1 = 1.18); (5) Cooling and shaping: The biaxially stretched polyester nonwoven fabric is introduced into the fourth roller gap. This set of rollers is a cooling roller, and the surface temperature is controlled at 60°C. The microporous structure is shaped while maintaining tension to obtain the polyester nonwoven fabric.

[0041] Example 2 A method for preparing a polyester nonwoven fabric for reverse osmosis membranes is as follows: S1. Preparation of polyester nonwoven fabric: The polyester base fiber and polyester binder fiber are loosened and stirred, then subjected to inclined wire wet forming, pressing, and drying to obtain the polyester nonwoven fabric base (basis weight 65g / m²). 2 ); The amount of polyester main fiber added is 60 parts by weight, and the amount of polyester bonding fiber added is 40 parts. The polyester main fiber has a fineness of 0.5D, a length of 6mm, and a melting point temperature of 260℃. The polyester bonding fiber has a fineness of 1.2D and a length of 5mm; the polyester bonding fiber is a core-sheath structure polyester fiber with a sheath melting point of 100℃ and a core melting point of 260℃.

[0042] S2, Five-stage continuous process: (1) Preheating and pressing: The polyester nonwoven fabric from step S1 is passed through the first roller gap and preliminarily composited under the conditions of 180℃ temperature, 200N / mm linear pressure, and 5m / min linear speed. (2) Hot pressing: The polyester nonwoven fabric that has undergone preliminary hot pressing is introduced into the second roller gap and further hot pressing is carried out under the conditions of 230℃ and 200N / mm linear pressure, with a linear speed of 5m / min. (3) Longitudinal stretching: The hot-pressed polyester nonwoven fabric is introduced into the third roller gap; the blank is subjected to longitudinal stretching by controlling the ratio of the linear speed of the exit roller to the inlet roller (stretch ratio V2 / V1 = 1.05), while the temperature of the third roller gap is maintained at 200℃ and the linear pressure is 80N / mm. (4) Transverse stretching: The longitudinally stretched polyester nonwoven fabric is introduced into the transverse stretching device; under the condition of a temperature of 190℃, the blank is stretched in the transverse direction by controlling the ratio of the exit width to the inlet width of the tenter frame (stretching ratio W2 / W1 = 1.12); (5) Cooling and shaping: The biaxially stretched polyester nonwoven fabric is introduced into the fourth roller gap. This set of rollers is a cooling roller, and the surface temperature is controlled at 50°C. The microporous structure is shaped while maintaining tension to obtain the polyester nonwoven fabric.

[0043] Example 3 Preparation of a polyester nonwoven fabric for reverse osmosis membranes, wherein the preparation method is as follows: S1. Preparation of polyester nonwoven fabric: The polyester base fiber and polyester binder fiber are loosened and stirred, then subjected to inclined wire wet forming, pressing, and drying to obtain the polyester nonwoven fabric base (basis weight 65g / m²). 2 ); The amount of polyester main fiber added is 85 parts by weight, and the amount of polyester bonding fiber added is 15 parts. The polyester main fiber has a fineness of 0.8D, a length of 5mm, and a melting point temperature of 260℃. The polyester bonding fiber has a fineness of 2D and a length of 6mm; the polyester bonding fiber is a core-sheath structure polyester fiber with a sheath melting point of 130℃ and a core melting point of 260℃.

[0044] S2, Five-stage continuous process: (1) Preheating and pressing: The polyester nonwoven fabric from step S1 is passed through the first roller gap and pre-composite under the conditions of 200℃ temperature, 200N / mm linear pressure, and 15m / min linear speed. (2) Hot pressing: The polyester nonwoven fabric that has undergone preliminary hot pressing is introduced into the second roller gap and further hot pressing is carried out under the conditions of 250℃ and 200N / mm linear pressure, with a linear speed of 15m / min. (3) Longitudinal stretching: The hot-pressed polyester nonwoven fabric is introduced into the third roller gap; the blank is subjected to longitudinal stretching by controlling the ratio of the linear speed of the exit roller to the inlet roller (stretch ratio V2 / V1 = 1.15), while the temperature of the third roller gap is maintained at 220℃ and the linear pressure is 40N / mm. (4) Transverse stretching: The longitudinally stretched polyester nonwoven fabric is introduced into the transverse stretching device; under the condition of a temperature of 210℃, the blank is stretched in the transverse direction by controlling the ratio of the exit width to the inlet width of the tenter frame (stretching ratio W2 / W1 = 1.22); (5) Cooling and shaping: The biaxially stretched polyester nonwoven fabric is introduced into the fourth roller gap. This set of rollers is a cooling roller, and the surface temperature is controlled at 70°C. The microporous structure is shaped while maintaining tension to obtain the polyester nonwoven fabric.

[0045] Comparative Example 1 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the stretch ratio (V2 / V1) was 1.00 during the longitudinal stretching process and the stretch ratio (W2 / W1) was 1.00 during the transverse stretching process.

[0046] Comparative Example 2 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the stretch ratio (V2 / V1) was 1.00 during the longitudinal stretching process of Comparative Example 2.

[0047] Comparative Example 3 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the stretch ratio (V2 / V1) was 1.25 during the longitudinal stretching process of Comparative Example 3.

[0048] Comparative Example 4 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the temperature during the longitudinal stretching process of Comparative Example 4 was 190°C (lower than the temperature conditions specified in this invention).

[0049] Comparative Example 5 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the temperature during the longitudinal stretching process of Comparative Example 5 was 230°C (higher than the temperature conditions specified in this invention).

[0050] Comparative Example 6 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the pressure during the longitudinal stretching process of Comparative Example 6 was 30 N / mm (lower than the pressure conditions specified in this invention).

[0051] Comparative Example 7 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the pressure during the longitudinal stretching process of Comparative Example 7 was 90 N / mm (higher than the pressure conditions specified in this invention).

[0052] Comparative Example 8 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the stretch ratio (W2 / W1) was 1.05 during the transverse stretching process of Comparative Example 8.

[0053] Comparative Example 9 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the stretch ratio (W2 / W1) was 1.30 during the transverse stretching process of Comparative Example 9.

[0054] Comparative Example 10 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the temperature during the transverse stretching process of Comparative Example 6 was 170°C (lower than the temperature conditions specified in this invention).

[0055] Comparative Example 11 Polyester nonwoven fabric was prepared using the same method as in Example 1, except that the temperature during the transverse stretching process of Comparative Example 7 was 220°C (higher than the temperature conditions specified in this invention).

[0056] The process conditions for the above embodiments and comparative examples are shown in Tables 1, 2 and 3 below.

[0057] Table 1. Process conditions for steps S1 in the examples and comparative examples Table 2. Process conditions for the first two stages in step S2 of the examples and comparative examples. Table 3. Process conditions for the last three stages in step S2 of the examples and comparative examples. The polyester nonwoven fabrics prepared in the above examples and comparative examples were subjected to performance tests, and the test methods involved are as follows: I. Porosity Testing Methods: Step 1: Take a circular plate with a diameter of 4cm, dry the sample in a vacuum drying oven at 90℃ for 4 hours to remove moisture and volatile substances, and quickly take out the sample after cooling. Record the initial dry weight as m1.

[0058] Step 2: Place the sample from Step 1 into a vacuum-capable desiccator. Pour sufficient isopropanol into the desiccator, ensuring the liquid completely submerges the sample. Seal the container, connect the vacuum pump, and begin evacuation. Maintain a pressure above -0.095 MPa for 2 to 4 hours, or until no more bubbles are observed escaping from the sample. Slowly release the vacuum, allowing atmospheric pressure to further force the liquid into the pores.

[0059] Step 3: After impregnation, use tweezers to remove the sample from the isopropanol. Hold the sample vertically above the isopropanol surface briefly (about 2-3 seconds) to allow excess liquid to drip off. Immediately place the sample on a balance and weigh it in its saturated state, recording the weight as m2.

[0060] Step 4: Prepare a beaker, fill it with an appropriate amount of isopropanol, and place it on a balance. Suspend the sample (from Step 3) using a very fine metal wire or nylon thread, ensuring it is completely submerged in the isopropanol in the beaker and does not contact the beaker wall or bottom. After the balance reading stabilizes, record this weight (m³). (Note: This value is negative). Calculate the porosity using the following formula: P (%) = - [ (m2- m1) / m3] × 100%.

[0061] II. Other indicator testing methods: 1. Quantitative testing: Detected according to the method in GB / T 451.2; 2. Thickness: Refer to GB / T 451.3 standard; 3. Tightness = Basis weight / Thickness; 4. Tensile strength: Tested according to the method of GB / T 12914; 5. Internal bond strength: Tested according to the method of GB / T 26203; 6. Air permeability: Tested according to the method of GB / T 24218.15; 7. Surface smoothness: The reference standard is GB / T 456-2002; 8. Pressure resistance: The reference standard is GB / T 32373-2025; The various indicators of the polyester nonwoven fabrics in the above embodiments and comparative examples were tested, and the specific test results are shown in Tables 4 and 5 below.

[0062] Table 4 Performance Test Results Table 5. Other performance test results From the performance data in Tables 4 and 5 above, we can see that: Examples 1-3 show that the polyester nonwoven fabrics prepared by the method described in this invention have excellent tensile strength and interlayer bonding strength, achieve a synergistic improvement in surface smoothness and high porosity, have high initial desalination rate and water flux, and have good pressure resistance (low variability in desalination rate and water flux).

[0063] A comparison of the results of Comparative Example 1 and Example 1 shows that the tensile strength, surface smoothness of the coated surface, interlayer bonding strength, initial water flux, initial desalination rate, and compressive strength of Comparative Example 1 are significantly reduced. This demonstrates that the longitudinal and transverse stretching processes applied to the polyester nonwoven fabric of this invention significantly improve the performance of Example 1 in all aspects.

[0064] A comparison of the results from Comparative Examples 2, 3, and 1 shows that the tensile strength, surface smoothness of the coated surface, interlayer bonding strength, initial water flux, initial desalination rate, and pressure resistance of Comparative Examples 2-3 are significantly reduced. This demonstrates that both excessively high and low longitudinal stretch ratios are detrimental to the overall performance of the product. There is a critical threshold for the longitudinal stretch ratio. When the stretch ratio is outside the range required by this invention, it not only fails to effectively improve the performance of the polyester nonwoven fabric but may also introduce localized defects such as large pores on the substrate surface, resulting in uneven pore structure, increased air permeability (CV value), and consequently, damage to the integrity of the reverse osmosis membrane separation layer, leading to an initial desalination rate lower than that of the unstretched substrate. This proves that the preferred stretch ratio range (1.05-1.15) of this invention is not a conventional or obvious choice in the art, but rather a specific parameter range discovered through inventive effort that enables performance breakthroughs.

[0065] A comparison of the results from Comparative Examples 4, 5, and Example 1 shows that the tensile strength, surface smoothness of the coated surface, interlayer bonding strength, initial water flux, initial desalination rate, and compressive strength of Comparative Examples 4 and 5 are significantly reduced. Meanwhile, the air permeability CV value of Comparative Examples 4-5 is significantly increased, indicating that the pore structure of the polyester nonwoven fabric is non-uniform.

[0066] When the temperature is too low (e.g., <200℃), the material is brittle under tension, which can lead to fiber breakage and microcracks. The resulting product has a rough surface, weak interlayer bonding, and uneven pore structure, ultimately resulting in low desalination rate and water flux, deterioration of mechanical properties, and decreased pressure resistance.

[0067] When the temperature is too high (e.g., >220℃), the material becomes viscous and flows, which can lead to molecular chain disorientation, pore collapse and failure of bonded fibers. As a result, the strength of the product decreases and the pore structure becomes uneven, ultimately resulting in low water flux and desalination rate, deterioration of mechanical properties and decreased pressure resistance.

[0068] A comparison of the results of Comparative Examples 6, 7 and 1 shows that the tensile strength, surface smoothness of the coating, interlayer bonding strength, initial water flux, desalination rate and pressure resistance of Comparative Examples 6 and 7 are significantly reduced.

[0069] This invention discovers that the linear pressure of longitudinal tension is the key to achieving a high-performance balance, and it must be precisely controlled within the range of 40 N / mm to 80 N / mm.

[0070] When the linear pressure is too low (as in Comparative Example 6), effective interlayer bonding and surface leveling cannot be achieved, resulting in weak interlayer bonding strength and a rough surface. This manifests as low tensile strength due to interface damage, and deterioration of the initial desalination rate due to defects in the reverse osmosis membrane separation layer. Simultaneously, the loose structure is easily compressed under pressure, leading to low water flux and desalination rate with accelerated decline (large rate of change).

[0071] Meanwhile, when the longitudinal tensile pressure is too low, it cannot effectively shape and fix the fiber network during the stretching process. This leads to two serious consequences: First, the fibers undergo non-cooperative slippage and tearing during stretching, instead of uniform orientation, directly generating defective pores with significant size variations; second, the bonded fiber melt cannot be uniformly distributed due to the lack of driving pressure, resulting in few and uneven interlayer bonding points, failing to form a stable overall skeleton to maintain the long-term stability of the pore structure. Therefore, excessively low linear pressure is one of the fundamental reasons for uneven pore structure, leading to initial performance degradation and insufficient long-term stability (decreased pressure resistance) of the product.

[0072] When the linear pressure is too high (as in Comparative Example 7), it can cause irreversible crushing damage to the pore structure, resulting in a severe decrease in porosity and uneven pore structure. The most direct manifestation of this is a sharp loss of initial water flux, rendering the product useless. At the same time, excessive compaction can make the material brittle, and reduce its tensile strength and interlayer bonding strength.

[0073] Therefore, within the pressure range defined by this invention, a strong interlayer bond and excellent surface smoothness can be achieved without damaging the pore structure, thereby simultaneously obtaining a high initial desalination rate, high water flux, and excellent long-term operational stability (good pressure resistance).

[0074] A comparison of the results from Comparative Examples 8, 9, and Example 1 shows that the surface smoothness, interlayer bonding strength, initial water flux, desalination rate, and pressure resistance of the coatings in Comparative Examples 8 and 9 are significantly reduced. Simultaneously, the transverse tensile strength of Comparative Example 8 and the tensile strength of Comparative Example 9 are also significantly reduced. The increased air permeability (CV) values ​​of Comparative Examples 8 and 9 indicate an uneven pore structure.

[0075] A comparison of the results of Comparative Examples 10, 11, and 1 shows that the tensile strength, surface smoothness of the coating, interlayer bonding strength, initial water flux, desalination rate, and pressure resistance of Comparative Examples 10 and 11 are significantly reduced. The increased air permeability (CV) values ​​of Comparative Examples 10 and 11 indicate that their pore structure is uneven.

[0076] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing polyester nonwoven fabric for reverse osmosis membranes, characterized in that, The preparation method is as follows: S1. Preparation of polyester nonwoven fabric: The polyester base fiber and polyester bonding fiber are loosened and stirred, and then subjected to inclined wire wet forming, pressing and drying to obtain polyester nonwoven fabric. S2, Five-stage continuous process: The polyester nonwoven fabric is subjected to preheating and pressing, hot pressing, longitudinal stretching, transverse stretching and cooling and shaping in sequence to obtain the polyester nonwoven fabric for reverse osmosis membrane.

2. The method for preparing a polyester nonwoven fabric for a reverse osmosis membrane according to claim 1, characterized in that, In step S1, the total weight of the polyester main fiber and the polyester bonding fiber is 100 parts, the amount of polyester main fiber added is 60-85 parts, and the amount of polyester bonding fiber added is 15-40 parts.

3. The method for preparing a polyester nonwoven fabric for a reverse osmosis membrane according to claim 1, characterized in that, The polyester main fiber has a fineness of 0.5-0.8D, a length of 5-6mm, and a melting point temperature of 258-262℃. The polyester bonded fiber has a fineness of 1.2-2.0D and a length of 3-6mm; the polyester bonded fiber is a core-sheath structure polyester fiber with a sheath melting point of 100-130℃ and a core melting point of 258-262℃.

4. The method for preparing a polyester nonwoven fabric for a reverse osmosis membrane according to claim 1, characterized in that, Step S2, the five-stage continuous process, is completed continuously on an integrated production line consisting of five functional units, each arranged horizontally along the material travel direction, wherein: The first unit consists of two vertically arranged rollers, forming the first roller gap; The second unit consists of two vertically arranged rollers, forming a second roller gap; The third unit consists of two vertically arranged rollers, forming a third roller gap; The fourth unit is a transverse tensioning device; The fifth unit consists of two vertically arranged rollers, forming the fourth roller gap; In step S1, the polyester nonwoven fabric moves horizontally through the first group of units, the second group of units, the third group of units, the fourth group of units, and the fifth group of units.

5. The method for preparing a polyester nonwoven fabric for a reverse osmosis membrane according to claim 1, characterized in that, During the preheating and pressing process, the temperature is 180℃-200℃, the linear pressure is 150N / mm-300N / mm, and the linear velocity is 5.0-15.0 m / min.

6. The method for preparing a polyester nonwoven fabric for a reverse osmosis membrane according to claim 1, characterized in that, During the hot pressing process, the temperature is 230℃-250℃, the linear pressure is 150N / mm-250N / mm, and the linear velocity of the hot pressing is the same as that of the preheating pressing.

7. The method for preparing a polyester nonwoven fabric for a reverse osmosis membrane according to claim 1, characterized in that, During the longitudinal stretching process, the linear velocity of the inlet roller is 5.0-15.0 m / min, the linear velocity of the outlet roller is 5.3-17.3 m / min, and the ratio of the linear velocity of the outlet roller to the linear velocity of the inlet roller is 1.05-1.

15. During the longitudinal stretching process, the temperature is 200℃-220℃ and the linear pressure is 40N / mm-80N / mm.

8. The method for preparing a polyester nonwoven fabric for a reverse osmosis membrane according to claim 1, characterized in that, During the transverse stretching process, the temperature is 180℃-210℃, and the ratio of the tenter frame's outlet width to its inlet width is 1.10-1.25; the linear velocity during the transverse stretching process is the same as the linear velocity of the outlet roller during the longitudinal stretching process. During the cooling and shaping process, the surface temperature of the cooling roller is controlled to be <80℃, and the linear speed of the cooling and shaping is the same as the linear speed of the transverse stretching.

9. A polyester nonwoven fabric for reverse osmosis membranes, characterized in that, The polyester nonwoven fabric is prepared by the preparation method described in any one of claims 1-8.

10. An application of the polyester nonwoven fabric for reverse osmosis membranes according to claim 9, characterized in that, The polyester nonwoven fabric is used in the field of reverse osmosis membranes.

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