Wet nonwoven fabric for semipermeable membrane support and method for manufacturing the same

Abstract

The purpose of this disclosure is to provide a wet nonwoven fabric for semipermeable membrane supports with a basis weight of 60 g / m². 2 The objective is to provide a wet nonwoven fabric for semipermeable membrane supports and a method for manufacturing the same, which can suppress the occurrence of wavy curl at the dry edge portion during the semipermeable membrane manufacturing process, even in the following cases. [Solution] The wet nonwoven fabric for semipermeable membrane support according to this disclosure is a wet nonwoven fabric for semipermeable membrane support consisting only of polyester fibers as the fiber component, and the basis weight of the wet nonwoven fabric is 30 to 60 g / m². 2 The wet-laid nonwoven fabric has a first surface which is the coated surface of the semipermeable membrane, and a second surface which is the back surface of the first surface and is the uncoated surface of the semipermeable membrane. The surface of the first surface has a low crystallinity region of less than 20% where the crystallinity of the polyester fibers is less than 20%, and the surface of the second surface has a low crystallinity region of 20% to 50%, and the surface of the second surface has 10 to 40% more low crystallinity regions than the surface of the first surface.

Description

[Technical Field]

[0001] The present invention relates to a wet nonwoven fabric for semipermeable membrane supports and a method for producing the same. [Background technology]

[0002] In recent years, membrane technology has been applied to water treatment in many cases. For example, microfiltration membranes or ultrafiltration membranes are used for water treatment in water treatment plants, and reverse osmosis membranes are used for seawater desalination. In addition, reverse osmosis membranes or nanofiltration membranes are used for treating water for semiconductor manufacturing, boiler water, medical water, and laboratory pure water. Furthermore, membrane separation activated sludge methods using microfiltration membranes or ultrafiltration membranes are also applied to the treatment of wastewater.

[0003] The semipermeable membranes used for these separations, also called separation membranes, are broadly classified into flat membranes and hollow fiber membranes based on their shape. Of these separation membranes, flat membranes, which are mainly formed from synthetic polymers, have poor mechanical strength as standalone membranes with separation capabilities, and are therefore often used in conjunction with semipermeable membrane supports such as nonwoven fabrics.

[0004] Generally, a semipermeable membrane and a semipermeable membrane support are integrated by casting and fixing a solution of a polymer, which is the raw material for the semipermeable membrane having separation function, onto a semipermeable membrane support such as a nonwoven fabric to form the semipermeable membrane. In the case of semipermeable membranes such as reverse osmosis membranes, the two are integrated by casting a solution of a polymer onto a semipermeable membrane support such as a nonwoven fabric to form a porous support layer, and then forming the semipermeable membrane, such as a reverse osmosis membrane, on this support layer. The support layer is also called a limiting filtration membrane (UF membrane).

[0005] Therefore, nonwoven fabrics used as semipermeable membrane supports are required to have excellent film-forming properties, such as preventing polymer solutions from seeping through, delamination of the membrane material, and the occurrence of defects such as non-uniformity or pinholes due to fuzzing of the nonwoven fabric when the polymer solution is cast. Furthermore, in order to stably produce semipermeable membranes with a high yield, the nonwoven fabrics used as supports in the semipermeable membrane manufacturing process are required to have high stability against heat and tension applied to the nonwoven fabric during manufacturing processes such as casting polymer solutions to form the membrane. In addition, in the case of semipermeable membranes such as reverse osmosis membranes, which are often used under high pressure, high mechanical strength is required for the nonwoven fabrics used as supports.

[0006] Wet-laid nonwoven fabrics as semipermeable membrane supports and methods for producing the same are well known. For example, a semipermeable membrane support has been proposed characterized by the presence of polyester fibers with a crystallinity of 30% or more in an area of ​​40% to 80% by mass on the surface and back surfaces of the wet-laid nonwoven fabric (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-101145 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] When applying a polymer solution (hereinafter sometimes referred to as the semipermeable membrane solution) that serves as the raw material for a semipermeable membrane to a nonwoven fabric for a semipermeable membrane support by casting it, intentionally leaving uncoated areas (hereinafter referred to as dry edges) on both selvage edges prevents the semipermeable membrane solution from seeping out from the edges of the support and causing roll contamination on the underside. For this reason, it is common practice to create dry edges during the semipermeable membrane manufacturing process. Conventionally, the basis weight of wet-laid nonwoven fabric for semipermeable membrane supports has been 70 g / m². 2The above is generally the case, and no problems have occurred, particularly in the dry edge area during the semipermeable membrane manufacturing process. However, the basis weight of the wet nonwoven fabric for the semipermeable membrane support was 60 g / m². 2 In the following cases, when drying in a hot air dryer or similar device during the semipermeable membrane manufacturing process, a peculiar curl (hereinafter referred to as "wavy curl") sometimes occurs at both edges of the sheet where the dry edge is located, resulting in a wavy appearance in the width direction. When winding the wavy curl onto a roll, folds are more likely to occur at the wavy curled portion, and these folds can become the starting point for wrinkles, potentially leading to problems such as a decrease in the yield of the final product or a decrease in filtration efficiency. However, in conventional technology, the basis weight of the wet nonwoven fabric for the semipermeable membrane support is 60 g / m². 2 There was no mention of the wavy curl that may occur at the dry edge of the semipermeable film manufacturing process in the following cases, nor were there any suggestions or descriptions to suppress the wavy curl.

[0009] Therefore, the purpose of this disclosure is to provide a wet nonwoven fabric for semipermeable membrane supports with a basis weight of 60 g / m². 2 The objective is to provide a wet nonwoven fabric for semipermeable membrane supports and a method for manufacturing the same, which can suppress the occurrence of wavy curl at the dry edge portion during the semipermeable membrane manufacturing process, even in the following cases. [Means for solving the problem]

[0010] As a result of diligent research, the inventors have found that the above problem can be solved by adjusting the crystallinity of the polyester fibers in a wet-laid nonwoven fabric for semipermeable membrane supports, in which a three-dimensional network is formed by polyester fibers, so that the crystallinity of the polyester fibers is higher on the coated surface than on the uncoated surface, and by controlling the distribution of polyester fibers on each surface to a predetermined crystallinity range, thereby completing the present invention. That is, the wet-laid nonwoven fabric for semipermeable membrane supports according to the present invention is a wet-laid nonwoven fabric for semipermeable membrane supports consisting only of polyester fibers as the fiber component, and the basis weight of the wet-laid nonwoven fabric is 30 to 60 g / m². 2and the wet nonwoven fabric has a first surface that becomes the coating surface of the semipermeable membrane and a second surface that is the back surface of the first surface and becomes the non-coated surface of the semipermeable membrane. On the surface of the first surface, a low crystallinity region where the crystallinity of the polyester fiber is less than 20% exists in a range of 20% or less. On the surface of the second surface, the low crystallinity region exists in a range of 20% or more and 50% or less, and on the surface of the second surface, 10 to 40% more of the low crystallinity region exists than on the surface of the first surface. By adjusting the crystallinity of the polyester fibers on the first surface side and the second surface side to the above range, the basis weight is 30 to 60 g / m 2 In the wet nonwoven fabric for a semipermeable membrane support, it is possible to impart an unprecedented characteristic effect.

[0011] In the wet nonwoven fabric for a semipermeable membrane support according to the present invention, in the wet nonwoven fabric, the ratio of the low crystallinity region on the surface of the second surface defined by the following (Equation 1) and the low crystallinity region on the surface of the first surface is 2.0 or more and 10.0 or less, and the ratio of the high crystallinity region on the surface of the second surface defined by the following (Equation 2) and the high crystallinity region on the surface of the first surface is 0.1 or more and 0.9 or less, and on the surface of the second surface, it is preferable that the high crystallinity region exists within a range of 0% or more and 20% or less. (Equation 1) Ratio (%) of the low crystallinity region on the surface of the second surface / Ratio (%) of the low crystallinity region on the surface of the first surface (Equation 2) Ratio (%) of the high crystallinity region where the crystallinity of the polyester fiber on the surface of the second surface is 30% or more / Ratio (%) of the high crystallinity region on the surface of the first surface

[0012] In the wet nonwoven fabric for a semipermeable membrane support according to the present invention, the polyester fiber includes a main fiber and a binder fiber, and it is preferable that the mass of the binder fiber with respect to the total mass of the main fiber and the binder fiber is 20% by mass or more and 60% by mass or less. A balance is achieved between ease of operation and the physical properties of the finished product, and it is possible to suppress excessive cost increases.

[0013] In the wet nonwoven fabric for semipermeable membrane support according to the present invention, it is preferable that the wet nonwoven fabric contains only polyethylene terephthalate fibers as the fiber component. Polyethylene terephthalate fibers are suitably used due to their heat resistance, chemical resistance, low cost, and the wide variety of properties such as fiber diameter, length, and cross-sectional shape.

[0014] In the wet nonwoven fabric for semipermeable membrane support according to the present invention, it is preferable that the main fibers are stretched polyethylene terephthalate fibers and the binder fibers are unstretched polyethylene terephthalate fibers.

[0015] The wet nonwoven fabric for semipermeable membrane support according to the present invention includes a configuration in which the surface of the first surface has a medium crystallinity region in the range of 40 to 95% where the crystallinity of the polyester fibers is 20% or more and less than 30%, and the surface of the second surface has a medium crystallinity region in the range of 40 to 80%.

[0016] The wet nonwoven fabric for semipermeable membrane support according to the present invention preferably has a curl height of 0 mm or more and less than 25 mm at the dry edge portion, as measured under the following condition 1. (Condition 1) A 15% by mass solution of polysulfone resin dimethylformamide is applied to the first surface of the wet nonwoven fabric for semipermeable membrane support, which has been cut to a width of 220 mm and a length of 300 mm. Uncoated areas of 10 mm each are provided as dry edges on both edges in the longitudinal direction, and the coating width is 200 mm and the thickness is 150 μm when wet. The coating layer is then solidified by immersion in water, and then a polyfunctional amine aqueous solution is sprayed onto it. Next, excess polyfunctional amine aqueous solution remaining on the surface of the solidified film is removed, and then a polyfunctional acid halogen is sprayed onto it to form a semipermeable film with a thickness of 20 nm. A fastener is attached to one end in the longitudinal direction of the semipermeable membrane sheet to make it a fixed end, and the other end is left as a free, unfixed end. The semipermeable membrane sheet is suspended in a hot air circulation dryer with the fixed end facing upwards and heated at 140°C for 5 minutes. When the heated semipermeable membrane sheet is removed from the hot air circulation dryer and placed horizontally on a smooth surface with the semipermeable membrane facing upwards, the height of both edges of the non-fixed end relative to the surface on the surface is defined as the curl height.

[0017] The present invention relates to a method for manufacturing a wet nonwoven fabric for a semipermeable membrane support, comprising: a base paper manufacturing step of making a base paper by papermaking and drying a fiber slurry containing the fiber components to obtain a wet nonwoven fabric of base paper (hereinafter sometimes referred to as an intermediate sheet); and a heating and pressing step of heating and pressing the base paper, wherein the heating and pressing step is a step of heating and pressing both the first surface and the second surface at least once on the surface of the metal roll using a metal roll at 160°C to 260°C, wherein the number of times the first surface is heated and pressed with the metal roll is equal to or greater than the number of times the second surface is heated and pressed with the metal roll, and the total temperature of the metal roll used to heat and press the first surface is 10°C or higher than the total temperature of the metal roll used to heat and press the second surface. By heating and pressing both the first surface and the second surface of the sheet with a metal roll, a nonwoven fabric of stable quality can be obtained. Furthermore, by ensuring that the number of times the first side is heated and pressurized with a metal roll is greater than or equal to the number of times the second side is heated and pressurized with a metal roll, or by ensuring that the total temperature of the metal rolls used to heat and pressurize the first side is 10°C or more higher than the total temperature of the metal rolls used to heat and pressurize the second side, a difference in the degree of crystallinity of the polyester fibers between the first and second sides tends to be created. By adjusting the degree of crystallinity of the polyester fibers between the first and second sides to the aforementioned range, a basis weight of 30-60 g / m² can be achieved. 2 This allows for the imparting of unprecedented and distinctive effects to wet nonwoven fabrics for semipermeable membrane supports.

[0018] In the method for manufacturing a wet nonwoven fabric for a semipermeable membrane support according to the present invention, the heating and pressing treatment step is a step of performing heating and pressing treatment once or more between two metal rolls, and it is preferable that the temperature of the first metal roll in contact with the first surface is 5°C or higher than the temperature of the second metal roll in contact with the second surface, and the temperature of the first metal roll is 180°C or higher and 240°C or lower, and the temperature of the second metal roll is 160°C or higher and 220°C or lower. By performing heating and pressing treatment with metal rolls / metal rolls with a temperature difference, it becomes easier to obtain a nonwoven fabric of stable quality, and it also becomes easier to adjust the degree of crystallinity of the polyester fibers on the first surface side and the second surface side.

[0019] In the method for manufacturing a semipermeable membrane wet nonwoven fabric according to the present invention, when the number of heating and pressurizing treatment steps is two or more, a cooling step is further included between each heating and pressurizing treatment step, and it is preferable that the cooling step is at least one selected from the following steps between each heating and pressurizing treatment step: passing the intermediate sheet through a transport path for cooling; contacting the surface of the intermediate sheet that will become the second surface with a transport roll with high thermal conductivity; contacting the surface of the intermediate sheet that will become the second surface with a cooling roll; and cooling the surface of the intermediate sheet that will become the second surface with a non-contact cooling device. This makes it easier to adjust the degree of crystallinity of the polyester fibers in the resulting nonwoven fabric. [Effects of the Invention]

[0020] According to this disclosure, in a wet nonwoven fabric for a semipermeable membrane support, the basis weight of the nonwoven fabric is 60 g / m². 2 Even in the following cases, a wet nonwoven fabric for a semipermeable membrane support and a method for manufacturing the same can be provided that can suppress the occurrence of wavy curl at the dry edge portion during the semipermeable membrane manufacturing process. [Modes for carrying out the invention]

[0021] Next, embodiments of the present invention will be shown and described in detail, but the present invention is not construed as being limited to these descriptions. As long as the effects of the present invention are achieved, the embodiments may be variously modified.

[0022] The wet nonwoven fabric for a semipermeable membrane support according to the present embodiment is a wet nonwoven fabric composed only of polyester fibers as a fiber component, and the basis weight of the wet nonwoven fabric is 30 to 60 g / m 2 and the wet nonwoven fabric has a first surface that becomes the coating surface of the semipermeable membrane and a second surface that is the back surface of the first surface and becomes the non-coating surface of the semipermeable membrane. On the surface of the first surface, a low crystallinity region where the crystallinity of the polyester fiber is less than 20% exists in a range of 20% or less, and on the surface of the second surface, the low crystallinity region exists in a range of 20% or more and 50% or less, and on the surface of the second surface, there is 10 to 40% more low crystallinity region than on the surface of the first surface. In the wet nonwoven fabric for a semipermeable membrane support with a basis weight of 30 to 60 g / m composed of polyester fibers as a fiber component 2 the generation of a wavy and peculiar curl that may occur in the drying part of the semipermeable membrane manufacturing process is suppressed, and defects such as wrinkling or membrane deformation are unlikely to occur, and a nonwoven fabric having excellent film-forming properties and processability can be obtained.

[0023] The wet-laid nonwoven fabric for semipermeable membrane support according to this embodiment is a nonwoven fabric whose fiber component consists solely of polyester fibers. The polyester fibers are fibers made using a condensation polymer synthesized by dehydrating and condensing a polycarboxylic acid and a polyalcohol to form an ester bond. Examples include polyethylene terephthalate fibers (PET fibers), polytrimethylene terephthalate fibers, polybutylene terephthalate fibers, polyethylene naphthalate fibers, or polybutylene naphthalate fibers. Only one type of polyester fiber may be used, or two or more types may be used in combination. However, in the wet-laid nonwoven fabric for semipermeable membrane support according to this embodiment, it is preferable that the wet-laid nonwoven fabric contains only polyethylene terephthalate fibers as its fiber component. By containing only polyethylene terephthalate fibers as the fiber component, it is suitably used due to its heat resistance, chemical resistance, low cost, and the wide variety of properties such as fiber diameter, length, and cross-sectional shape.

[0024] In this embodiment, either only the main fiber may be used as the polyester fiber, or the main fiber and binder fiber may be used, but it is more preferable to use the main fiber and binder fiber as the polyester fiber.

[0025] In the wet nonwoven fabric for semipermeable membrane support according to this embodiment, the polyester fibers include main fibers and binder fibers, and it is preferable that the mass of the binder fibers relative to the total mass of the main fibers and binder fibers is 20% to 60% by mass (main fibers:binder fibers = 80:20 to 40:60), more preferably 25% to 50% by mass (main fibers:binder fibers = 75:25 to 50:50), and even more preferably 30% to 45% by mass (main fibers:binder fibers = 70:30 to 55:45). This balances ease of operation with the physical properties of the finished product and helps to prevent costs from becoming too high.

[0026] The main fibers are those that form the three-dimensional network-like framework of the semipermeable membrane support without melting and bonding during the heat and pressure treatment in the manufacturing process of the wet nonwoven fabric for the semipermeable membrane support. Due to their high melting point, it is preferable to use stretched polyester fibers as the main fibers. The shape of the main fibers is not particularly limited; however, using fibers with a smaller diameter results in smaller pore diameters in the finished sheet, while using fibers with a larger diameter increases the sheet's strength. Furthermore, using fibers with a shorter length improves dispersibility in water, while using fibers with a longer length increases the sheet's strength. Therefore, it is preferable to select an appropriate shape considering the required strength, pore diameter, and sheet uniformity of the support. In this embodiment, the thickness of the main fibers is preferably 0.3 to 5.0 decitex, and more preferably 0.5 to 3.0 decitex. The length of the main fibers is preferably 1 to 8 mm, and more preferably 3 to 7 mm. The cross-sectional shape of the main fibers can be appropriately selected as needed and is not limited in this embodiment.

[0027] Binder fibers are fibers intended to achieve melt adhesion by incorporating a process of raising the temperature to above the softening point or melting temperature (melting point) into the manufacturing process of the wet nonwoven fabric for the semipermeable membrane support. They play a role in melt-bonding the fibers together and reinforcing the three-dimensional framework of the nonwoven fabric. For example, the binder fibers can be softened or melted in the drying process after the papermaking of the wet nonwoven fabric for the semipermeable membrane support or in the subsequent heat and pressure treatment process. Therefore, it is preferable that the melting point of the binder fibers is below the melting point of the main fibers. Binder fibers include types where all the resins constituting the fibers have a low melting point (all-melting type), a double structure of the inner and outer sides, a structure called the so-called core-sheath structure, a type where only the surface fuses (core-sheath type), or an unstretched fiber type, etc., and any of them can be used in the present embodiment. It is preferable to use unstretched polyester fibers having a primary crystallization temperature of 115 to 130°C and a melting point of 230 to 260°C. Since the unstretched polyester fibers are unstretched and crystallization has not progressed, they can be softened even at a temperature lower than the melting point and exhibit an adhesion effect. A combination of stretched polyester fibers as the main fibers and unstretched polyester fibers as the binder fibers is preferably used because it is easy to develop strength through heat and pressure treatment. The thickness, length, cross-sectional shape, etc. of the binder fibers can be selected according to the purpose, similar to the main fibers. In the present embodiment, the thickness of the binder fibers used is preferably 0.3 to 5.0 decitex, and more preferably 0.5 to 3.0 decitex. The length of the binder fibers is preferably 1 to 8 mm, and more preferably 3 to 7 mm. Incidentally, when the binder fibers are made into a nonwoven fabric, the thickness and length of the all-melting type binder fibers or the unstretched fiber type binder fibers may change, and in the case of the core-sheath type binder fibers, the length may not change, but the thickness may change.

[0028] In the wet nonwoven fabric for the semipermeable membrane support according to the present embodiment, the main fibers are preferably stretched polyethylene terephthalate fibers, and the binder fibers are preferably unstretched polyethylene terephthalate fibers.

[0029] Of the polyester fibers mentioned above, the main fibers undergo some degree of resin crystallization during manufacturing due to stretching, and the degree of crystallinity measured by Raman spectroscopy is approximately 15%. On the other hand, the binder fibers are amorphous, easily softened or melted, and a melt-bonding effect can be obtained, with a degree of crystallinity measured by Raman spectroscopy being approximately 0%. In addition to stretching during the fiber manufacturing process, the degree of crystallinity of polyester fibers can be increased by heating, pressurizing, and increasing sheet tension during the heating and pressurizing process in the wet nonwoven fabric manufacturing process for semipermeable membrane supports, as described later. As the degree of crystallinity of polyester fibers increases, the strength, density, and rigidity tend to increase, but the shrinkage of the fiber itself tends to decrease. In the present invention, it is important to adjust the temperature conditions of the metal rolls so that the degree of crystallinity of the polyester fibers is higher on the coated surface (first surface) than on the uncoated surface (second surface) of the sheet by differentiating the processing temperature conditions of the metal rolls on the coated surface (first surface) and the uncoated surface (second surface) of the sheet during the heating and pressing process described later, thereby controlling the polyester fibers present on the surface of each surface to a predetermined degree of crystallinity distribution range.

[0030] The method for manufacturing a wet nonwoven fabric for a semipermeable membrane support according to this embodiment is a method for manufacturing a wet nonwoven fabric for a semipermeable membrane support according to this embodiment, comprising a base paper manufacturing step of making paper from a fiber slurry containing fiber components and drying it to obtain a base paper, and a heating and pressing treatment step of heating and pressing the base paper, wherein the heating and pressing treatment step is a step of heating and pressing both the first surface and the second surface at least once on the surface of a metal roll with a temperature of 160°C or more and 260°C or less, and the number of times the first surface is heated and pressed with the metal roll is equal to or greater than the number of times the second surface is heated and pressed with the metal roll, and the total temperature of the metal rolls used to heat and press the first surface is 10°C or more higher than the total temperature of the metal rolls used to heat and press the second surface.

[0031] The base paper manufacturing process includes a papermaking process, a dewatering process, and a drying process. In this embodiment, a so-called wet papermaking method is used, in which polyester fibers are dispersed in water, the fibers are laminated on a papermaking wire, and the sheets are formed by dewatering from below the wire. The type of papermaking machine used at this time is not particularly limited and may be, for example, a sheet-fed papermaking machine or a continuous papermaking machine. For continuous papermaking machines, for example, a long-wire papermaking machine, a short-wire papermaking machine, a cylinder-wire papermaking machine, an inclined wire papermaking machine, a gap former, a delta former, etc., can be used. At this time, in order to obtain a wet nonwoven fabric for a semipermeable membrane support with few defects, it is desirable to form the sheets as uniformly and with good formation as possible. When obtaining sheets of two or more layers, a multi-layer papermaking machine that combines these papermaking machines can be used. For example, inclined / inclined paper machines, inclined / cylinder-type paper machines, and cylinder-type / cylinder-type paper machines are suitably used, and multilayer paper machines combined with cylinder-type machines are particularly suitable because they allow for a more compact space. Furthermore, when using an inclined paper machine, it is possible to obtain sheets with two or more layers by using a multilayer headbox. The resulting nonwoven fabric may be one layer or two or more layers, and is not particularly limited, but a nonwoven fabric with two or more layers is preferable because it can be formed into a sheet more uniformly and with better formation. In addition, a multilayer nonwoven fabric can be made by heat-sealing two or more wet nonwoven fabrics in the heat-pressure process described later.

[0032] In this embodiment, the ratio of binder fibers to the total mass of main fibers and binder fibers is preferably 20% to 60% by mass (main fibers:binder fibers = 80:20 to 40:60), more preferably 25% to 50% by mass (main fibers:binder fibers = 75:25 to 50:50), and even more preferably 30% to 45% by mass (main fibers:binder fibers = 70:30 to 55:45). If the binder fiber content is less than 20% by mass, the strength of the wet-laid nonwoven fabric may be weak, making it difficult to obtain a stable base paper. On the other hand, if the binder fiber content exceeds 60% by mass, it tends to become difficult to produce a good form during papermaking, and costs tend to be higher. When the nonwoven fabric has two or more layers, the fiber composition in each layer may be the same, but it is also possible to use different fiber compositions in each layer as needed. When different fiber compositions are used for each layer, it is more preferable that the binder fiber composition ratio of the second side (the uncoated side) layer is higher than that of the first side (the coated side) layer. This is because, as the second side of the semipermeable membrane support wet nonwoven fabric, which is completed after the heat and pressurization process described later, contains more binder fibers, the crystallinity of the second side tends to be slightly lower than that of the first side, making it easier to adjust the crystallinity. However, even in this case, the fiber composition for each layer and the sheet as a whole is preferably in the range of main fiber:binder fiber = 80:20 to 40:60, more preferably in the range of 75:25 to 50:50, and even more preferably in the range of 70:30 to 55:45.

[0033] In this embodiment, the surface of the first side may be the wire surface used during wet papermaking or the felt surface. In the heating and pressing process described later, it is important to adjust the crystallinity of the polyester fibers so that it is higher on the first side surface than on the second side surface, and to control the crystallinity of the polyester fibers present on each surface to a predetermined crystallinity distribution range.

[0034] The nonwoven fabric for semipermeable membrane support according to this embodiment may also contain additives, such as water-soluble polymer viscosities, pH adjusters, chelating agents, dispersants, defoaming agents, water repellents, wetting agents, preservatives, and antistatic agents, within the range that achieves the effects of the present invention during wet papermaking. For example, the content of additives relative to 100% by mass of fiber components in the raw material slurry is preferably 20% by mass or less, and more preferably 15% by mass or less.

[0035] The paper-making sheets contain a large amount of moisture, more than 80% by mass, so they are dewatered to 30-70% by mass. Dewatering methods include suction and pressing between two rolls to squeeze out the moisture. The latter, press dewatering method, is preferred because it can produce a more uniform result. It is also possible to use both suction and press dewatering methods in combination.

[0036] The remaining moisture in the dewatered sheet is dried in a drying zone. The drying method is not particularly limited, but hot air drying, infrared drying, multi-cylinder dryer drying, and Yankee dryer drying are preferably used. The drying temperature is preferably 100 to 160°C, and more preferably 105 to 140°C. Regardless of the drying method used, either side of the wet nonwoven fabric may be adopted as the first side, and it is important to control the degree of crystallinity of the polyester fibers in the heating and pressing process described later.

[0037] The wet-laid nonwoven fabric (hereinafter sometimes referred to as the intermediate sheet) produced through the aforementioned base paper manufacturing process exhibits adhesion due to the softening of some binder fibers, but as is, it lacks sufficient strength as a semipermeable membrane support and has poor suitability for coating semipermeable membranes. Therefore, in this embodiment, in order to obtain sufficient strength as a semipermeable membrane support, the intermediate sheet is subjected to a heat and pressure treatment process to obtain the wet-laid nonwoven fabric for semipermeable membrane support according to this embodiment. Various heat and pressure devices can be used for this treatment, but a thermal calender is generally effective. The wet-laid nonwoven fabric produced by the aforementioned method may be treated directly in the thermal calender without being wound onto a roll, or it can be wound onto a roll once and then treated separately in the thermal calender. When treating with a thermal calender, it is also possible to preheat the sheet using the aforementioned drying equipment or the thermal calender's preheating equipment before heat and pressure treatment, or to heat and pressure treatment with the sheet held in a heat roll of the thermal calender, or to adjust the temperature of the nonwoven fabric by providing a cooling process before heat and pressure treatment. In that case, it is necessary to adjust the heating and pressing conditions according to the situation to adjust the degree of crystallinity of the polyester fibers on the first and second surfaces, but any heating and pressing conditions can be used as long as they do not impair the requirements of the present invention.

[0038] In the method for manufacturing a semipermeable wet nonwoven fabric according to this embodiment, when the number of heating and pressurizing treatment steps is two or more, it is preferable to further have a cooling step between each heating and pressurizing treatment step, and the cooling step is preferably at least one selected from the following steps: passing an intermediate sheet through a transport path for cooling between each heating and pressurizing treatment step; bringing a transport roll with high thermal conductivity into contact with the second surface of the intermediate sheet; bringing a cooling roll into contact with the second surface of the intermediate sheet; and cooling the second surface of the intermediate sheet with a non-contact cooling device. This makes it easier to adjust the degree of crystallinity of the polyester fibers in the resulting nonwoven fabric.

[0039] In this embodiment, when the heating and pressing treatment is performed two or more times, it is preferable to perform a cooling step between each heating and pressing treatment. Also, if the wet nonwoven fabric produced through the base paper manufacturing process is not wound onto a roll once, and the residual heat remains while the first heating and pressing treatment is performed, a cooling step may be performed before the first heating and pressing treatment. In the cooling step, it is sufficient to lower the surface temperature of the nonwoven fabric to a lower temperature than before the cooling step, thereby adjusting the degree of crystallinity of the polyester fibers in the final nonwoven fabric to a desired range, and the surface temperature of the nonwoven fabric in the cooling step is not particularly limited. Furthermore, there are no limitations on the method of adjusting the temperature of the nonwoven fabric by providing a cooling step when processing with a thermal calender. For example, methods include increasing the transport distance between each heating and pressing treatment step, installing transport rolls that act as heat conductors for cooling, installing cooling rolls such as water-cooled or air-cooled types, and installing non-contact cooling devices such as air showers. The conveyor rolls, which act as heat conductors for cooling, can be any rolls with a surface made of a highly thermally conductive material, and are not particularly limited in their material, but their material may be, for example, carbon, silicone, or metal. The diameter of the conveyor rolls is not particularly limited, but it is preferable that the diameter of the conveyor rolls in contact with the second surface is greater than or equal to the diameter of the conveyor rolls in contact with the first surface, as increasing the roll diameter makes it easier to obtain a cooling effect by the conveyor rolls. The number of times the conveyor rolls contact the second surface is preferably greater than or equal to the number of times they contact the first surface. By performing the cooling process, the surface temperature of the wet nonwoven fabric can be controlled, making it easier to adjust the degree of crystallinity of the polyester fibers on the first surface and the second surface to a desired range. In particular, methods of installing conveyor rolls, cooling rolls, or air showers are more preferable because they allow for easier adjustment of the degree of crystallinity of the polyester fibers, as they can lower the surface temperature only on the second surface.

[0040] The thermal calendering apparatus can employ, for example, a nip calender combining two metal rolls capable of processing at temperatures of 160°C or higher, a soft nip calender combining a resin roll with high heat resistance and a metal roll, or a soft nip calender combining a metal roll and an elastic roll. Resin rolls include, for example, resin rolls made of urethane resin, epoxy resin, silicone resin, polyester resin, or hard rubber, or mixtures thereof. Elastic rolls include, for example, cotton rolls, aramid rolls, or paper rolls. The heating and pressing conditions of the thermal calendering apparatus affect the performance of the finished support, but any conditions can be adopted as long as they do not impair the requirements of the present invention. Furthermore, the number of heating and pressing treatments can be either one treatment or multiple treatments, as long as they do not impair the requirements of the present invention. In this specification, the combination of calender rolls in the thermal calendering apparatus is described in the order of the type of roll in contact with the surface of the first side of the nonwoven fabric and the type of roll in contact with the surface of the second side of the nonwoven fabric, and may be expressed with a / between the two rolls as follows. For example, "metal roll / metal roll" indicates the use of metal rolls on both the first and second surfaces. Similarly, "metal roll / resin roll" indicates the use of a metal roll on the first surface and a resin roll on the second surface, while "resin roll / metal roll" indicates the use of a resin roll on the first surface and a metal roll on the second surface.

[0041] When the heat-pressure treatment is performed in a single pass, it is preferable to use metal rolls / metal rolls. The detailed conditions for metal rolls / metal rolls will be described later, but since different temperature controls can be easily implemented with each metal roll, it is easy to adjust the degree of crystallinity of the polyester fibers on the first and second surfaces, and a nonwoven fabric of stable quality can be obtained. When the heat-pressure treatment is performed in a single pass, if a soft nip calender is used, such as a combination of metal rolls and resin rolls or a combination of metal rolls and elastic rolls, it may be difficult to adjust the degree of crystallinity of the polyester fibers on the first and second surfaces.

[0042] When performing multiple heat and pressure treatments, the same heat and pressure device may be used repeatedly for the first treatment and subsequent treatments. Alternatively, multiple heat and pressure devices can be arranged to perform continuous treatment, or a calendering device with multiple heat calendering rolls arranged in the height direction can be used. Detailed conditions will be described later, but any combination of rolls can be used, such as metal roll / metal roll, metal roll / resin roll, resin roll / metal roll, metal roll / elastic roll, or elastic roll / metal roll. Even when performing multiple heat and pressure treatments, it is preferable to perform the heat and pressure treatment with metal rolls / metal rolls at least once. This makes it easier to adjust the degree of crystallinity of the polyester fibers on the first and second surfaces.

[0043] The temperature conditions for the heat roll are generally preferably in the range of 160°C to 260°C, and more preferably in the range of 180°C to 240°C. Similarly, the temperature conditions for the metal roll used in the heat and pressurization process of this embodiment are also preferably in the range of 160°C to 260°C, and more preferably in the range of 180°C to 240°C. The linear pressure of the heat roll is preferably in the range of 30 to 260 kN / m, and the sheet tension during the heat and pressurization process is preferably in the tension range of 0.03 to 0.25 kN / m before and after the heat and pressurization roll, but this is not an exhaustive range. As a method for adjusting the degree of crystallinity of the polyester fibers, for example, the degree of crystallinity can be increased by increasing the temperature, linear pressure, and sheet tension during the heat and pressurization process. However, in order to adjust the degree of crystallinity of the polyester fibers in the heat and pressurization process so that the first surface surface is higher than the second surface surface, which is a requirement of the present invention, it is difficult to adjust this using only linear pressure and sheet tension. Therefore, as described later, it is important to create a difference in the metal roll temperature between the first and second surfaces of the sheet. Furthermore, in order to achieve uniform performance across the entire web, it is desirable to process the material with the most uniform temperature and linear pressure profiles possible. The roll diameter of the thermal calender is appropriately selected depending on parameters such as the substrate being heated and pressurized, the nip pressure, and the speed. On the heated and pressurized sheet surface, the main fibers generally retain their shape, although they may be slightly deformed by being compressed, while the binder fibers are melted and bonded, making it possible to distinguish between the main fibers and the binder fibers.

[0044] In this embodiment, it is preferable that both the first and second surfaces are subjected to heat and pressure treatment on a metal roll surface at least once. By treating both the first and second surfaces with a metal roll at least once, a nonwoven fabric of stable quality can be obtained. If the heat and pressure treatment process is performed only once, a metal roll / metal roll is used in that process. If the heat and pressure treatment process is performed two or more times, the process of heat and pressure treating the first surface with the surface of a metal roll and the process of heat and pressure treating the second surface with the surface of a metal roll may be performed in the same heat and pressure treatment process, or in different heat and pressure treatment processes. When performed in the same heat and pressure treatment process, for example, a metal roll / metal roll may be used in the first heat and pressure treatment process, and a combination other than metal roll / metal roll or metal roll / metal roll may be used in the second heat and pressure treatment process. Furthermore, if the heating and pressing processes are carried out in different stages, for example, in the first heating and pressing process, the first surface may be heated and pressed using a metal roll / resin roll, and in the second heating and pressing process, the second surface may be heated and pressed using a resin roll / metal roll, with the metal roll surface being used. These are just examples, and the timing of heating and pressing the first or second surface with the metal roll surface is not limited to these.

[0045] Furthermore, it is preferable that the number of times the first side is heated and pressurized with a metal roll is greater than or equal to the number of times the second side is heated and pressurized with a metal roll, and it is more preferable that the number of times the first side is heated and pressurized with a metal roll is greater than the number of times the second side is heated and pressurized with a metal roll. This makes it easier to create a difference in the degree of crystallinity of the polyester fibers on the first side and the second side. The number of times the first side is heated and pressurized may be once or two or more times, but it is more preferable that it is two or more times. This effectively promotes melt bonding and crystallization of the nonwoven fabric, making it easier to develop strength and obtain a nonwoven fabric of stable quality.

[0046] Furthermore, during the heating and pressing treatment, the total temperature of the metal rolls used to heat and pressurize the first side is preferably 10°C or more higher than the total temperature of the metal rolls used to heat and pressurize the second side, more preferably 15°C or more higher, and even more preferably 20°C or more higher. There is no particular limit to the upper limit of the temperature difference between the total temperature of the metal rolls used to heat and pressurize the first side and the total temperature of the metal rolls used to heat and pressurize the second side. However, in this embodiment, since it is possible to heat and pressurize with the metal rolls of the soft nip calender after heating and pressing with the metal rolls / metal rolls, it is preferably 260°C or less, and more preferably 250°C or less. If the temperature difference between the total temperature of the metal rolls used to heat and pressurize the first side and the total temperature of the metal rolls used to heat and pressurize the second side is less than 10°C, it becomes difficult to create a difference in the degree of crystallinity of the polyester fibers between the first side and the second side. If the temperature difference exceeds 260°C, there is a risk that the heating of the first side will become too strong.

[0047] Furthermore, when using a soft nip calender such as a metal roll / resin roll or a metal roll / elastic roll, the temperature of the non-heated rolls, such as the resin roll or elastic roll, is lower than the preferred temperature of 160°C during the heating and pressing process, even when the temperature is stable during the heating and pressing operation, although this depends on the operating speed of the thermal calender. Therefore, in this embodiment, the influence of the temperature of the resin roll or elastic roll on the crystallization of polyester fibers is considered to be small. For this reason, emphasis is placed on the heating and pressing process using metal rolls. As mentioned above, since the influence of the non-heated rolls, such as the resin roll or elastic roll, on the crystallization of polyester fibers is considered to be small, temperature control such as providing a cooling process is not necessary. However, the temperature of the non-heated rolls may be adjusted as needed by changing the operating speed of the thermal calender, circulating the heat transfer medium, bringing a heat transfer medium circulating roll into contact with the non-heated roll, or installing a non-contact cooling device such as an air shower.

[0048] "Number of times the metal roll is heated and pressurized" refers to the number of times the metal roll is heated and pressurized at 160°C or higher. "Total temperature of the metal roll used for heating and pressurizing" is the cumulative temperature when the metal roll is heated and pressurized at 160°C or higher. Normally, the metal roll is not set to a temperature below 160°C for heating and pressurizing. However, if the metal roll temperature is set below 160°C, it will deviate from the preferred temperature for the heating and pressurizing process, and it is thought that this will have a smaller impact on the crystallization of the polyester fibers. For this reason, in this embodiment, heating and pressurizing using a metal roll below 160°C is not included in "Number of times the metal roll is heated and pressurized" nor in "Total temperature of the metal roll used for heating and pressurizing". For example, in a heating and pressing treatment using metal rolls / metal rolls with a temperature setting of 200°C / 100°C, only the 200°C side is treated as a heating and pressing treatment using metal rolls and is included in the "number of times heating and pressing treatment is performed with metal rolls" and the "total temperature of the metal rolls used for heating and pressing treatment." However, the heating and pressing treatment using metal rolls on the 100°C side is not counted in the "number of times heating and pressing treatment is performed with metal rolls," and 100°C is not added to the "total temperature of the metal rolls used for heating and pressing treatment." For example, if metal rolls / metal rolls are used for the first heating and pressing treatment with a temperature setting of 200°C / 160°C, and metal rolls / metal rolls are used for the second heating and pressing treatment with a temperature setting of 240°C / 210°C, then the "number of times heating and pressing treatment is performed with metal rolls" on the first side is 2, and the "total temperature of the metal rolls used for heating and pressing treatment" is 440°C, while the "number of times heating and pressing treatment is performed with metal rolls" on the second side is 2, and the "total temperature of the metal rolls used for heating and pressing treatment" is 370°C. Furthermore, if a metal roll / metal roll is used for the first heating and pressing treatment with a temperature setting of 200°C / 160°C, and a metal roll / metal roll is used for the second heating and pressing treatment with a temperature setting of 240°C / 100°C, then on the first side, the "number of times the metal roll is used for heating and pressing" is 2, and the "total temperature of the metal rolls used for heating and pressing" is 440°C. On the second side, the "number of times the metal roll is used for heating and pressing" is only the first heating treatment with the 160°C metal roll, not including the second heating and pressing treatment with the 100°C metal roll, and the "total temperature of the metal rolls used for heating and pressing" is 160°C.These are just examples, and the timing and temperature for heating and pressurizing the first or second surface on the metal roll surface are not limited to these.

[0049] In the method for manufacturing a wet nonwoven fabric for a semipermeable membrane support according to this embodiment, the heat-pressure treatment step is a step in which heat-pressure treatment is performed once or more between two metal rolls, and the temperature of the first metal roll in contact with the first surface of the two metal rolls is 5°C or higher than the temperature of the second metal roll in contact with the second surface of the two metal rolls, and preferably the temperature of the first metal roll is 180°C or higher and 240°C or lower, and the temperature of the second metal roll is 160°C or higher and 220°C or lower. By performing heat-pressure treatment with metal rolls / metal rolls with a temperature difference, it becomes easier to obtain a nonwoven fabric of stable quality, and it also becomes easier to adjust the degree of crystallinity of the polyester fibers on the first surface side and the second surface side.

[0050] In this embodiment, it is preferable to have a temperature difference of 5°C or more between the metal roll that heats and pressurizes the first side of the metal roll and the metal roll that heats and pressurizes the second side of the metal roll during the heat and pressurizing process, more preferably 10°C or more, and even more preferably 15°C or more. If the temperature difference between the metal roll that heats and pressurizes the first side and the metal roll that heats and pressurizes the second side is less than 5°C, it may not be a sufficient temperature difference, making it difficult to adjust the degree of crystallinity of the polyester fibers on the first side and the second side. There is no particular upper limit to the temperature difference between the metal roll that heats and pressurizes the first side and the metal roll that heats and pressurizes the second side, but the temperature of the metal roll that heats and pressurizes the first side of the metal roll is preferably 180°C or more and 240°C or less, and more preferably 190°C or more and 235°C or less. Furthermore, the temperature of the metal roll / metal roll that is subjected to heating and pressurizing treatment on its second side is preferably 160°C to 220°C, and more preferably 180°C to 210°C, in order to obtain the effects of the heating and pressurizing treatment.

[0051] In this embodiment, when the heating and pressing treatment process is performed two or more times, it is preferable that the treatment temperature for the second and subsequent treatments be the same as or higher than the temperature of the first treatment. This effectively promotes the melt bonding and crystallization of the nonwoven fabric fibers. When the treatment temperature for the second and subsequent treatments is higher than the treatment temperature for the first treatment, it is preferable that the treatment temperature for the second and subsequent treatments be 10°C or more higher than the heating and pressing treatment temperature of the first treatment, more preferably 13°C or more higher, and even more preferably 15°C or more higher. However, it is preferable that the upper limit of the temperature difference be 70°C.

[0052] The basis weight of the wet nonwoven fabric for semipermeable membrane support according to this embodiment is 30-60 g / m². 2 The basis weight of the wet nonwoven fabric for semipermeable membrane supports is 40-60 g / m². 2 It is more preferable that this is the case. Conventionally, the basis weight of wet nonwoven fabrics for semipermeable membrane supports is 70 g / m². 2 The above is the general practice, and regarding the aforementioned heating and pressing process, it was common to perform the heating and pressing treatment under temperature conditions such that the degree of crystallinity of the coated side and the uncoated side were roughly the same. The larger the basis weight of the wet nonwoven fabric for semipermeable film support, the less likely wavy curling is to occur at the dry edge during the semipermeable film manufacturing process, so 70g / m² is used. 2 When using the above-mentioned wet nonwoven fabric for semipermeable membrane supports, wavy curling at the dry edge was not a problem. On the other hand, a basis weight of 60 g / m² was not an issue. 2 It has been found that in the following low basis weight wet nonwoven fabrics for semipermeable membrane supports, wavy curling tends to occur at the dry edge during the semipermeable membrane manufacturing process. By satisfying the requirements of the present invention, 30-60 g / m² 2 In low-basis-weight wet-laid nonwoven fabrics for semipermeable membrane supports, this fabric exhibits excellent suppression of wavy curling at the dry edge during the semipermeable membrane manufacturing process, resulting in good processability and stable production, thus providing unprecedented and distinctive effects. Furthermore, it offers a processing capacity of 30-60 g / m². 2Low basis weight wet nonwoven fabrics for semipermeable membrane supports tend to have lower costs per unit area, and offer advantages such as the ability to increase the area of ​​the semipermeable membrane even with the same module size, or to reduce the module size even with the same area of ​​semipermeable membrane, when manufacturing modules with the finished semipermeable membrane. 2 The reason for limiting it to this is as follows: basis weight of 30g / m² 2 Below this level, the strength may be insufficient, and the basis weight should be 60g / m². 2 Beyond a certain point, in addition to the fact that the wavy curl at the dry edge during the semipermeable membrane manufacturing process, which is a challenge of the present invention, tends to occur less frequently, the cost per unit area of ​​the nonwoven fabric tends to increase, and when manufacturing modules with the completed semipermeable membrane, the area of ​​the semipermeable membrane tends to decrease even for the same module size. Furthermore, even with the same area of ​​semipermeable membrane, the size of the module tends to increase.

[0053] 60 g / m² during the semipermeable membrane manufacturing process 2The reason why wavy curl occurs at the dry edge of the following low-basis-weight wet nonwoven fabrics for semipermeable membrane supports is not well understood. However, it is presumed that the dry edge is prone to over-drying, and that the coated side has both semipermeable membrane coated and uncoated portions. During drying, complex shrinkage of the semipermeable membrane occurs, including not only the shrinkage in the XY axis direction of the semipermeable membrane but also the semipermeable membrane portion in the Z axis direction that has penetrated the wet nonwoven fabric, resulting in a unique wavy curl. In this embodiment, we found that by adjusting the heating and pressurizing treatment conditions and adjusting the degree of crystallinity of the polyester fibers on the uncoated and coated surfaces, wavy curl at the dry edge can be suppressed even at low basis weight. Furthermore, by satisfying the requirements of the present invention, it is presumed that during the semipermeable membrane manufacturing process, the polyester fibers on the coated surface of the sheet have a high degree of crystallinity, are dense and rigid, while the polyester fibers tend to shrink and have a progressively lower degree of crystallinity towards the uncoated side of the sheet. In the dry edge portion of the semipermeable film manufacturing process, the combined effect of the shrinkage of the semipermeable film formed by coating the coated side of the wet nonwoven fabric for the support in the XYZ axis direction and the shrinkage of the wet nonwoven fabric for the support in the XYZ axis direction, where the crystallinity distribution of polyester fibers differs from the coated side to the uncoated side, is thought to suppress curling that occurs in the dry edge portion, thereby suppressing the unique wavy curl. For this reason, in the present invention, it is important to adjust the degree of crystallinity by promoting crystallization throughout the fiber components through heat and pressure treatment, and when the fiber components include main fibers and binder fibers, it is preferable to promote crystallization in both the main fibers and binder fibers. In particular, the crystallization of the binder fibers that melt-bond the three-dimensional network formed by polyester fibers is thought to have a greater influence on suppressing wavy curl in the dry edge portion. Here, the X-axis direction is the short-side direction (width direction) in the form of a rolled wet nonwoven fabric for semipermeable membrane support, the Y-axis direction is the long-side direction (flow direction) in the form of a rolled wet nonwoven fabric for semipermeable membrane support, and is perpendicular to the X-axis direction, and the Z-axis direction is perpendicular to the surface of the nonwoven fabric, i.e., the thickness direction of the nonwoven fabric.

[0054] The thickness of the nonwoven fabric is not particularly limited, but is preferably 45 to 70 μm, and more preferably 50 to 65 μm. By setting the thickness within this range, it exhibits an excellent effect of suppressing wavy curl at the dry edge during the semipermeable membrane manufacturing process, enabling good processability and stable production. In addition, the cost per unit area of ​​the nonwoven fabric tends to be lower, and when manufacturing modules with the finished semipermeable membrane, it is possible to increase the area of ​​the semipermeable membrane even for the same module size, or to decrease the size of the module even for the same semipermeable membrane area. If the thickness is less than 45 μm, the strength may be insufficient, or the semipermeable membrane solution may easily seep through to the back. If the thickness exceeds 70 μm, in addition to the tendency for wavy curl at the dry edge during the semipermeable membrane manufacturing process, which is a problem of the present invention, the cost per unit area of ​​the nonwoven fabric tends to increase, and when manufacturing modules with the finished semipermeable membrane, the area of ​​the semipermeable membrane tends to decrease even for the same module size, and the size of the module may tend to increase even for the same semipermeable membrane area.

[0055] In the wet nonwoven fabric for semipermeable membrane support according to this embodiment, the low crystallinity region on the first surface, where the crystallinity of polyester fibers is less than 20%, is preferably 20% or less, and more preferably 15% or less. The presence of a low crystallinity region within a range of 20% or less on the first surface allows for sufficient density and rigidity to suppress wavy curling at the dry edge during the semipermeable membrane manufacturing process. If the low crystallinity region exceeds 20% on the first surface, it indicates that the heat and pressure treatment of the first surface was insufficient, and sufficient density and rigidity to suppress wavy curling at the dry edge during the semipermeable membrane manufacturing process cannot be obtained.

[0056] Furthermore, it is preferable that the low crystallinity region on the second surface is within the range of 20% to 50%, and more preferably within the range of 20% to 40%. If the low crystallinity region is within the range of less than 20% on the second surface, it becomes difficult to create a difference in crystallinity between it and the polyester fibers on the first surface, making it difficult to suppress wavy curling at the dry edge during the semipermeable film manufacturing process. If the low crystallinity region is within the range of more than 50% on the second surface, it indicates that the heat and pressure treatment of the second surface was insufficient, which may lead to problems as a support material, such as increased fuzzing on the second surface.

[0057] Furthermore, the low crystallinity region is 10-40% more abundant on the second surface than on the first surface. It is more preferable that the low crystallinity region on the second surface is 15-30% more abundant than on the first surface, and even more preferable that it is 20-28% more abundant. The presence of 10-40% more low crystallinity regions on the second surface than on the first surface makes it easier to obtain the effect of greater shrinkage on the second surface than on the first surface, and an effect of suppressing wavy curl at the dry edge during the semipermeable film manufacturing process is obtained.

[0058] In the wet-laid nonwoven fabric for semipermeable membrane support according to this embodiment, it is preferable that the ratio of the low crystallinity region on the surface of the second surface to the low crystallinity region on the surface of the first surface, as defined in (Equation 1) below, is 2.0 or more and 10.0 or less, and the ratio of the high crystallinity region on the surface of the second surface to the high crystallinity region on the surface of the first surface, as defined in (Equation 2) below, is 0.1 or more and 0.9 or less, and that the high crystallinity region exists on the surface of the second surface within the range of 0% or more and 20% or less. (Equation 1) Ratio of the low crystallinity region on the surface of the second surface (%) / Ratio of the low crystallinity region on the surface of the first surface (%) (Equation 2) Ratio of highly crystallized regions on the surface of the second surface where the crystallinity of polyester fibers is 30% or more (%) / Ratio of the highly crystallized regions on the surface of the first surface (%)

[0059] In the wet nonwoven fabric for semipermeable membrane support according to this embodiment, the ratio of the low crystallinity region between the second surface and the first surface, as defined by (Equation 1), is preferably 2.0 to 10.0, and more preferably 2.3 to 8.0. Furthermore, the ratio of the high crystallinity region, where the polyester fibers have a crystallinity of 30% or more, between the second surface and the first surface, as defined by (Equation 2), is preferably 0.1 to 0.9, and more preferably 0.2 to 0.8. By setting the ratio of the low crystallinity region to the high crystallinity region between the second surface and the first surface within the above ranges, it becomes easier to suppress wavy curling at the dry edge during the semipermeable membrane manufacturing process.

[0060] Furthermore, the high crystallinity region on the second surface is preferably within the range of 0 to 20%, more preferably within the range of 0 to 15%, and even more preferably within the range of 0 to 8%. If the high crystallinity region on the second surface exceeds 20%, the crystallinity of the polyester fibers on the second side becomes too high, making it difficult to create a difference in the distribution amount of the low crystallinity region between the first surface and the second surface, which is a requirement of the present invention. This can make it difficult to suppress wavy curling at the dry edge during the semipermeable film manufacturing process.

[0061] The distribution amount of the medium crystallinity region, where the crystallinity of the polyester fibers is 20% or more and less than 30%, is not particularly limited, but it is preferable that the medium crystallinity region be present in the range of 40-95% on the surface of the first surface, and more preferably in the range of 50-90%. Furthermore, it is preferable that the medium crystallinity region be present in the range of 40-80% on the surface of the second surface, and more preferably in the range of 50-75%. The medium crystallinity region may be present in greater quantities on the second surface than on the first surface, or greater quantities on the first surface than on the second surface, or the same amount may be present on both the first and second surfaces.

[0062] In this invention, the distribution amounts of the low crystallinity region, the medium crystallinity region, and the high crystallinity region can be measured using Raman spectroscopy as follows: Using a Raman microscope, the surface of the first or second surface is observed under the conditions of a field magnification of 100x, a measurement area of ​​75 μm × 75 μm, and a measurement pitch of 5 μm, and the scattering intensity peaks of the polyester fibers are detected. Then, the scattering intensity peaks detected by the Raman microscope are measured at 1096 cm⁻¹. -1 The Raman band is set to It, and the length is 1120cm. -1 Let the Raman band be Ig, and the range is 1720-1740cm. -1 When the full width at half maximum (FWHM) of a peak is taken as the FWHM, the proportion of detected peaks with an It / Ig ratio (hereinafter sometimes referred to as the crystallization ratio) greater than 0 and a FWHM of 21 or more and less than 23 to the total number of detected peaks represents the distribution of the low crystallization region. The proportion of detected peaks with a crystallization ratio greater than 0 and a FWHM of 18 or more and less than 21 to the total number of detected peaks represents the distribution of the medium crystallization region. The proportion of detected peaks with a crystallization ratio of 1.5 or more and a FWHM of less than 18 to the total number of detected peaks represents the distribution of the high crystallization region.

[0063] In this embodiment, the crystallinity of the polyester fibers on the first and second surfaces was measured by Raman spectroscopy. While methods for measuring the crystallinity of polyester fibers include X-ray diffraction, DSC (differential scanning calorimeter), FT-IR (Fourier transform infrared spectroscopy), solid-state NMR (nuclear magnetic resonance), and Raman spectroscopy, Raman spectroscopy is suitable for measuring the crystallinity of polyester fibers on the first and second surfaces because it can selectively measure the crystallinity of polyester fibers present on the sheet surface. As mentioned above, it is important that crystallinity progresses throughout the fiber components through heating and pressurizing treatment, and the crystallinity of binder fibers is considered to have a particularly significant influence. Therefore, when the fiber components include both main fibers and binder fibers, it is preferable to position the binder fibers, which can be confirmed to be fused together, in the center of the field of view when measuring the crystallinity of the sheet surface by Raman spectroscopy. When measuring with the binder fiber positioned in the center of the field of view, other binder fibers may also enter the field of view depending on the fiber composition ratio, in addition to the main fiber or the binder fiber positioned in the center of the field of view. Therefore, the crystallinity was measured by selecting the location of the binder fiber positioned in the center of the field of view. Polyester fibers may have a uniform crystallinity throughout the entire fiber, or there may be parts with mutually different crystallinity within a single fiber. If there are parts with mutually different crystallinity within a single fiber, for example, it may be a form in which there is a part with a crystallinity of less than 20% and a part with a crystallinity of 20% or more within a single fiber.

[0064] In the wet nonwoven fabric for semipermeable membrane support according to this embodiment, the density of the nonwoven fabric is 0.6 to 1.0 g / cm³. 3 Preferably, it is within the range of 0.75 to 0.95 g / cm³. 3 It is more preferable that the density be within the range of 1.0 g / cm³. 3 If the density exceeds 0.6 g / cm³, the pore size of the support becomes too small, which may make it difficult to obtain sufficient water permeability. 3 If the value is less than this, the pore size may become too large, potentially leading to the coating liquid seeping through to the back of the surface.

[0065] The semipermeable membrane to be formed on the wet nonwoven fabric for the semipermeable membrane support according to this embodiment is preferably made of polyaryl ethersulfone such as polysulfone or polyethersulfone, polyimide, polyvinylidene fluoride, or cellulose acetate. Among these, polysulfone is particularly preferred in terms of chemical, mechanical, and thermal stability. The method for forming the semipermeable membrane on the substrate is not particularly limited, but for example, it can be obtained by dissolving the above material in a solvent, applying the resulting solution to the substrate, causing microphase separation, and then solidifying the polymer. In this case, it is preferable to intentionally provide a dry edge area, which is an uncoated area, at the edges of both selvages. By providing a dry edge area, it is possible to prevent backing roll contamination caused by the semipermeable membrane solution overflowing from the edges of both selvages of the support and running to the back.

[0066] For example, when manufacturing a polysulfone semipermeable membrane, a DMF (dimethylformamide) solution of polysulfone resin is used as the coating solution, and water is used as the coagulation solution. The semipermeable membrane obtained in this way can be used as an ultrafiltration membrane as is, but when used as a reverse osmosis membrane, a layer called an active layer is further added to its surface. This active layer is obtained by forming an ultrathin film on the supporting semipermeable membrane by interfacial polymerization of, for example, cellulose acetate, aromatic polyamide, crosslinked polyamic acid, polyurea, etc. Here, "supporting semipermeable membrane" refers to the polysulfone layer (semipermeable membrane) that serves as the support layer for the active layer. For example, when manufacturing a crosslinked polyamide active layer, the method is not particularly limited, but it can be done by immersing the surface of the supporting semipermeable membrane in a solution of a polyfunctional amine compound, and then contacting it with a solvent solution of an acid halide compound to allow interfacial polymerization to proceed. The composite semipermeable membrane with the active layer formed on the supporting semipermeable membrane is heat-dried. The heating method is not particularly limited, but drying by hot air is preferably used due to its simplicity. In drying by hot air, a drying temperature of 70°C or higher is preferred. On the other hand, the drying temperature is preferably 150°C or lower, more preferably 130°C or lower, and even more preferably 120°C or lower, but is not limited to these. Higher temperatures are preferable because they can shorten the drying time, but rapid drying tends to cause over-drying of the dry edge, and wavy curling is more likely to occur due to the shrinkage of the semipermeable membrane forming the dry edge, especially the supporting semipermeable membrane (polysulfone layer). However, by fulfilling the requirements of the present invention, a basis weight of 30-60 g / m² is achieved. 2 This wet nonwoven fabric for semipermeable membrane supports exhibits a distinctive and excellent effect in suppressing the wavy curl that may occur at the dry edge during the semipermeable membrane manufacturing process, resulting in good processability and stable production.

[0067] In this embodiment, the wet nonwoven fabric for semipermeable membrane support preferably has a curl height of 0 mm or more and less than 25 mm at the dry edge portion, as measured under the following condition 1. (Condition 1) A 15% by mass solution of polysulfone resin dimethylformamide is applied to the first surface of the wet nonwoven fabric for semipermeable membrane support, which has been cut to a width of 220 mm and a length of 300 mm. Uncoated areas of 10 mm each are provided as dry edges on both edges in the longitudinal direction, and the coating width is 200 mm and the thickness is 150 μm when wet. The coating layer is then solidified by immersion in water, and then a polyfunctional amine aqueous solution is sprayed onto it. Next, excess polyfunctional amine aqueous solution remaining on the surface of the solidified film is removed, and then a polyfunctional acid halogen is sprayed onto it to form a semipermeable film with a thickness of 20 nm. A fastener is attached to one end in the longitudinal direction of the semipermeable membrane sheet to make it a fixed end, and the other end is left as a free, unfixed end. The semipermeable membrane sheet is suspended in a hot air circulation dryer with the fixed end facing upwards and heated at 140°C for 5 minutes. When the heated semipermeable membrane sheet is removed from the hot air circulation dryer and placed horizontally on a smooth surface with the semipermeable membrane facing upwards, the height of both edges of the non-fixed end relative to the surface on the surface is defined as the curl height. The method for measuring curl height is, in more detail, the "wavy curl evaluation" method described later. [Examples]

[0068] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass," respectively, unless otherwise specified. The number of added parts is the value on a solid content basis.

[0069] <Example 1> (Preparation of fiber raw material slurry) To achieve a mass blending ratio of 70:30 between polyester-based fibers and polyester binder fibers, 70 kg of polyester-based fibers (stretched polyethylene terephthalate fibers, crystallization temperature 230-260°C, melting point 255°C) with a thickness of 0.6 decitex and a cut length of 5 mm, and 30 kg of polyester binder fibers (unstretched polyethylene terephthalate fibers, primary crystallization temperature 115-130°C, secondary crystallization temperature 220-260°C, melting point 255°C) with a thickness of 1.2 decitex and a cut length of 5 mm were added to water, dispersed in a disperser for 5 minutes, and then water was added to obtain a fiber slurry with a fiber concentration of 0.03%.

[0070] (Creating the sheet) The resulting fiber slurry was used to make paper using a cylinder-type paper machine, and then dried in a Yankee dryer at a surface temperature of 120°C, resulting in a basis weight of 50 g / m². 2 With the goal of achieving this, we obtained a roll of nonwoven fabric sheet (intermediate sheet) base paper.

[0071] (Heating and pressurizing treatment) Using the Yankee side of the aforementioned rolled base paper as the second side, a metal roll / metal roll hardnip thermal calender equipped with a metal roll with a face length of 1170 mm and a roll diameter of 450 mm (circumference of 1413 mm) was used to heat and pressurize the rolls under the following conditions: roll surface temperature 235°C / 200°C for the first side roll and 20°C for the second side roll, no clearance between rolls, linear pressure of 150 kN / m, inlet tension of 0.15 kN / m, outlet tension of 0.09 kN / m, and line speed of 20 m / min, to obtain a wet nonwoven fabric for semipermeable membrane support.

[0072] <Example 2> A wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1, except that the mass blending ratio of polyester-based fibers to polyester binder fibers was changed to 55:45, and the surface temperature of the metal rolls during the heat and pressure treatment was changed to 225°C / 200°C for the first side roll and the second side roll.

[0073] <Example 3> A wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1, except that the heating and pressing treatment was performed twice on a metal roll / metal roll, with the metal roll surface temperatures during the first heating and pressing treatment being 200°C / 190°C for the first side roll / second side roll, and the metal roll surface temperatures during the second heating and pressing treatment being 220°C / 210°C for the first side roll / second side roll.

[0074] <Example 4> A wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1, except that the heating and pressing treatment was performed twice using a metal roll / metal roll thermal calender, with the metal roll surface temperatures during the first heating and pressing treatment being 200°C / 195°C for the first side roll and 220°C / 215°C for the second side roll.

[0075] <Example 5> During the heat and pressure treatment, the process was carried out twice in total: once using a metal roll / metal roll thermal calender and once using a metal roll / resin roll thermal calender. In the first heat and pressure treatment using metal rolls / metal rolls, the metal roll surface temperatures were set to 200°C / 190°C for the first side roll and 190°C for the second side roll. In the second heat and pressure treatment using metal rolls / resin rolls, the surface temperature of the metal roll on the first side was set to 215°C. Otherwise, a wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1. The surface temperature of the resin roll on the second side was measured to be 110°C.

[0076] <Example 6> A wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1, except that the heating and pressing treatment was performed twice using a thermal calender. In the first heating and pressing treatment, a resin roll / metal roll was used, with the metal roll surface temperature set to 200°C and the second side treated with the metal roll, and in the second heating and pressing treatment, a metal roll / resin roll was used, with the metal roll surface temperature set to 225°C and the first side treated with the metal roll. The surface temperature of the resin roll was measured to be 100°C during the first heating and pressing treatment and 120°C during the second heating and pressing treatment.

[0077] <Example 7> The mass blending ratio of polyester-based fibers to polyester binder fibers was changed to 80:20. The heat and pressure treatment was performed twice in total: once using a metal roll / metal roll thermal calender and once using a metal roll / resin roll thermal calender. In the first heat and pressure treatment using metal rolls / metal rolls, the metal roll surface temperature was set to 190°C / 180°C for the first side roll and 180°C for the second side roll. In the second heat and pressure treatment using metal rolls / resin rolls, the metal roll surface temperature on the first side was set to 210°C. Otherwise, a wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1. The surface temperature of the resin roll on the second side was measured to be 105°C.

[0078] <Comparative Example 1> A wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1, except that the surface temperature of the metal rolls during the heat and pressurizing treatment was changed to 200°C for the first side metal roll and 200°C for the second side metal roll.

[0079] <Comparative Example 2> A wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1, except that the heating and pressing treatment was performed twice using a metal roll / metal roll thermal calender, with the metal roll surface temperatures during the first heating and pressing treatment set to 190°C / 200°C for the first side roll / second side roll, and the metal roll surface temperatures during the second heating and pressing treatment set to 210°C / 220°C for the first side roll / second side roll.

[0080] <Comparative Example 3> A wet nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1, except that the heating and pressing treatment was performed twice using a metal roll / metal roll thermal calender, with the metal roll surface temperatures during the first heating and pressing treatment being 230°C / 230°C for the first side roll and 230°C / 230°C for the second side roll.

[0081] The following evaluations were performed on the examples and comparative examples, and the results are shown in Tables 1 to 3.

[0082] [Table 1]

[0083] [Table 2]

[0084] [Table 3]

[0085] <Measurement of basis weight> Measurements were taken in accordance with JIS P 8124:1998 "Paper and cardboard - Method for determining basis weight". The unit is g / m². 2 That's what I decided.

[0086] <Measurement of thickness and density> Measurements were taken in accordance with JIS P 8118:1998 "Paper and cardboard - Test methods for thickness and density". The unit was μm.

[0087] (Evaluation of the degree of crystallinity of polyester fibers) The crystallinity of polyester fibers in the wet-laid nonwoven fabric for semipermeable membrane supports was measured using a Raman microscope (XploRA PLUS, HORIBA) on the first and second surfaces of the wet-laid nonwoven fabrics obtained in each example and comparative example. The Raman microscope measurement conditions were a field magnification of 100x, a measurement area of ​​75 μm × 75 μm, and a measurement pitch of 5 μm. The microscope was focused so that binder fibers that could be confirmed to be fused were located in the center of the field of view. The location of the binder fibers located in the center of the field of view was selected, and the scattering intensity peaks were detected at 500 locations, and the average value was taken as the measurement result. There was no particular effect from fiber orientation. The peak detection function used was "GAUSS (area parameter)". For the detected peaks, the ratio of detected peaks with a crystallinity ratio (It / Ig) greater than 0 and a full width at half maximum (FWHM) of 21 or more and less than 23 to the total number of detected peaks was calculated, and this ratio was defined as the distribution amount of the low crystallinity region, where the crystallinity of the measured polyester fiber was less than 20%. Furthermore, the ratio of detected peaks with a crystallinity ratio greater than 0 and a FWHM of 18 or more and less than 21 to the total number of detected peaks was defined as the distribution amount of the medium crystallinity region, where the crystallinity of the measured polyester fiber was 20% or more and less than 30%. The ratio of detected peaks with a crystallinity ratio greater than 0 and a FWHM of less than 18 to the total number of detected peaks was defined as the distribution amount of the high crystallinity region, where the crystallinity of the measured polyester fiber was 30% or more. Note that a higher crystallinity ratio (It / Ig) value indicates a higher degree of crystallinity. In this invention, by targeting detected peaks with a crystallinity ratio (It / Ig) greater than 0, it is possible to measure the degree of crystallinity from the FWHM value even for polyester fibers where crystallination has not progressed.

[0088] (Crystallization ratio of polyester fibers) The scattering intensity peak detected by Raman microscopy was 1096 cm⁻¹. -1 The Raman band is set to It, and the length is 1120cm. -1 The Raman band was defined as Ig, and the crystallization ratio was set to It / Ig. 1080~1130 cm⁻¹ -1 At its peak height (intensity), the 1096 cm² peak height originates from the trans glycol units of PET.-1 The nearby Raman band (It) reflects the crystal structure. On the other hand, 1120 cm -1 The nearby Raman band (Ig) is a gauche-type glycol unit, indicating an amorphous component. Therefore, the ratio of It (crystallized peak) to Ig (amorphous peak) can be used as an indicator of the degree of crystallization, and in this specification, this indicator is referred to as the crystallization ratio.

[0089] (Half-width) The scattering intensity peaks detected by Raman microscopy were at 1720-1740 cm⁻¹. -1 The full width at half maximum of the peak was defined as the half maximum width. 1720~1740cm -1 The full width at half maximum (FWHM) of the C=O group band is influenced by the planarity of the benzene ring and C=O in PET, and the FWHM (unit: cm) -1 ) and density (unit: g / cm³) 3 A linear correlation function, as shown in (Equation 3), is shown between ( ) and ( ). (Math 3) Δv 1 / 2 = 305 - 209 × p However, Δv1 / 2 represents the band width at half maximum, and p represents the reduced density. Equation (3) allows us to evaluate the degree of crystallinity, which is correlated with density. A smaller full width at half maximum indicates a higher density, i.e., a higher degree of crystallinity. The conversion formula shown in (4) was used to convert from reduced density to degree of crystallinity. (Math. 4) Crystallinity χ(%)=100×(p-1.335) / (1.455-1.335)

[0090] (Wavy curl evaluation) The wet nonwoven fabrics for semipermeable membrane supports obtained in each example and comparative example were cut to a width of 220 mm and a length of 300 mm to prepare sample pieces. A 15% by mass solution of polysulfone resin DMF (dimethylformamide) was applied to the first side of each sample piece using a gap application method, with a coating width of 200 mm and 10 mm on each edge remaining uncoated (dry edge), and the coating layer thickness being wet with a clearance of 150 μm. The sample piece was then immersed in water to solidify the coating layer and form a solidified film. After that, excess moisture remaining on the surface of the solidified film was absorbed with an absorbent sheet, and then a polyfunctional amine aqueous solution was sprayed onto the surface of the solidified film. Next, the excess polyfunctional amine aqueous solution remaining on the surface of the solidified film was removed with a rubber scraper, and then a polyfunctional acid halogen was sprayed to induce interfacial polymerization, forming a semipermeable film with a thickness of 20 nm to obtain a semipermeable film sheet. After removing excess liquid remaining on the surface of the semipermeable membrane sheet by absorbing it with an absorbent sheet, a fastener was attached along the entire width of the upstream end of the semipermeable membrane sheet in the flow direction (machine direction during wet nonwoven fabric manufacturing for semipermeable membrane support) to create a fixed end, and the downstream end in the flow direction was left free as an unfixed end. The sheet was then suspended in a hot air circulation dryer and heated at 140°C for 5 minutes. The heated semipermeable membrane sheet was removed from the hot air circulation dryer and placed horizontally on a smooth table with the semipermeable membrane-forming surface facing upwards. The curl height and undulation state of both selvages of the downstream end, which was dried in a free state without fasteners, were evaluated. The curl height was calculated by measuring the distance from the surface of the table on which the semipermeable membrane sheet was placed to one end of the unfixed end, and the distance from the surface of the table to the other end of the unfixed end, and taking the average of these two measured distances. Furthermore, the degree of waviness was evaluated on a four-point scale: A for good condition with small curl height on both ears and suppressed waviness, and D for conditions with large curls that are unsuitable for practical use or with waviness that makes them unsuitable for practical use. A, B, and C were considered usable levels. Evaluation Criteria A: Curl height less than 0-10mm. The curl is small, and wavy curls are suppressed, which is good (practical level). B: Curl height between 10mm and 15mm. The curl height is slightly higher, but the wavy curl is suppressed, and there are no practical problems (practical level). C: Curl height 15mm or more but less than 25mm. The curl height may increase further, and slight signs of wavy curl may be observed, but this is not a problem as wrinkles will form when rolled up. Note that if signs of wavy curl are observed, the curl angle will be gentle, but the curl will tend to start slightly inward from the edge of the sheet, and the curl height may increase (lower practical limit). D: The curl height is 25mm or more, making it unsuitable for practical use. Alternatively, the curl is wavy, causing the edges to bend and wrinkle when rolled up, making it unsuitable for practical use (unsuitable level).

[0091] As is clear from the results shown in Tables 1 to 3, the wet nonwoven fabric for semipermeable membrane supports obtained in Examples 1 to 7 had a density of 60 g / m². 2 The following basis weights showed an effect in suppressing the wavy curl that may occur at the dry edge during the semipermeable film manufacturing process. In contrast, in Comparative Examples 1 to 3, the crystallinity distribution range of the polyester fibers on the first and second surface sides fell outside the range of the present invention, resulting in wavy curl occurring at the dry edge during the semipermeable film manufacturing process, making them unsuitable for practical use.

Claims

1. A wet nonwoven fabric for semipermeable membrane supports, consisting solely of polyester fibers as the fiber component, The basis weight of the wet-laid nonwoven fabric is 30 to 60 g / m². ２ And, The wet-laid nonwoven fabric has a first surface which is the coated surface of the semipermeable membrane, and a second surface which is the back surface of the first surface and is the uncoated surface of the semipermeable membrane. On the surface of the first surface, there is a low-crystallinity region of less than 20% where the crystallinity of the polyester fibers is less than 20%, On the surface of the second surface, the low crystallinity region exists in a range of 20% to 50%, and A wet-type nonwoven fabric for a semipermeable membrane support, characterized in that the surface of the second surface has 10 to 40% more of the low crystallinity region than the surface of the first surface.

2. In the wet-laid nonwoven fabric, the ratio of the low crystallinity region on the surface of the second surface to the low crystallinity region on the surface of the first surface, as defined in (Equation 1) below, is 2.0 or more and 10.0 or less. The ratio of the high crystallinity region on the surface of the second surface to the high crystallinity region on the surface of the first surface, as defined in (Equation 2) below, is 0.1 or more and 0.9 or less, and The wet nonwoven fabric for semipermeable membrane support according to claim 1, characterized in that the high crystallinity region is present on the surface of the second surface within the range of 0% to 20%. (Equation 1) Ratio of the low crystallinity region on the surface of the second surface (%) / Ratio of the low crystallinity region on the surface of the first surface (%) (Equation 2) Ratio of highly crystallized regions on the surface of the second surface where the crystallinity of polyester fibers is 30% or more (%) / Ratio of the highly crystallized regions on the surface of the first surface (%)

3. The polyester fiber comprises a main fiber and a binder fiber. The wet nonwoven fabric for semipermeable membrane support according to claim 1, characterized in that the mass of the binder fibers is 20% by mass or more and 60% by mass or less relative to the total mass of the main fibers and the binder fibers.

4. The wet nonwoven fabric for semipermeable membrane support according to claim 1, characterized in that the wet nonwoven fabric contains only polyethylene terephthalate fibers as the fiber component.

5. The main fiber is an extended polyethylene terephthalate fiber. The wet nonwoven fabric for semipermeable membrane support according to claim 3, characterized in that the binder fibers are undrawn polyethylene terephthalate fibers.

6. On the surface of the first surface, there is a medium crystallinity region in the range of 40 to 95% where the crystallinity of the polyester fibers is 20% or more and less than 30%. The wet nonwoven fabric for a semipermeable membrane support according to claim 1, characterized in that the medium crystallinity region is present on the surface of the second surface in the range of 40 to 80%.

7. The wet nonwoven fabric for semipermeable membrane support according to claim 1, characterized in that the curl height at the dry edge portion measured under the following condition 1 is 0 mm or more and less than 25 mm. (Condition 1) A 15% by mass solution of polysulfone resin dimethylformamide is applied to the first surface of the wet nonwoven fabric for semipermeable membrane support, which has been cut to a width of 220 mm and a length of 300 mm. Uncoated areas of 10 mm each are provided on both edges in the longitudinal direction as the dry edges, and the coating width is 200 mm and the thickness is 150 μm when wet. The coating layer is then solidified by immersion in water, and then a polyfunctional amine aqueous solution is sprayed onto it. Next, excess polyfunctional amine aqueous solution remaining on the surface of the solidified film is removed, and then a polyfunctional acid halogen is sprayed onto it to form a semipermeable film with a thickness of 20 nm. A fastener is attached to one end in the longitudinal direction of the semipermeable membrane sheet to make it a fixed end, and the other end is left as a free, unfixed end. The semipermeable membrane sheet is suspended in a hot air circulation dryer with the fixed end facing upwards and heated at 140°C for 5 minutes. When the heated semipermeable membrane sheet is removed from the hot air circulation dryer and placed horizontally on a smooth surface with the semipermeable membrane facing upwards, the height of both edges of the non-fixed end relative to the surface on the surface is defined as the curl height.

8. A method for producing a wet nonwoven fabric for a semipermeable membrane support according to any one of claims 1 to 7, The manufacturing method comprises a base paper production step of papermaking and drying a fiber slurry containing the fiber components to obtain an intermediate sheet, The process includes a heating and pressurizing step in which the intermediate sheet is heated and pressurized, The aforementioned heating and pressing treatment step is a step of heating and pressing both the first surface and the second surface at least once on the surface of the metal roll using a metal roll at 160°C to 260°C, and, A method for manufacturing a wet nonwoven fabric for a semipermeable membrane support, characterized in that the number of times the first surface is heated and pressurized with the metal roll is equal to or greater than the number of times the second surface is heated and pressurized with the metal roll, and the total temperature of the metal rolls used to heat and pressurize the first surface is 10°C or higher than the total temperature of the metal rolls used to heat and pressurize the second surface.

9. The aforementioned heating and pressurizing process is a process in which heating and pressurizing is performed one or more times between the two metal rolls, and, The temperature of the first metal roll in contact with the first surface of the two metal rolls is 5°C or higher than the temperature of the second metal roll in contact with the second surface of the two metal rolls, and The method for producing a wet nonwoven fabric for a semipermeable membrane support according to claim 8, characterized in that the temperature of the first metal roll is 180°C or more and 240°C or less, and the temperature of the second metal roll is 160°C or more and 220°C or less.

10. When the number of times the aforementioned heating and pressurizing process is performed is two or more, Each of the aforementioned heating and pressurizing processes further includes a cooling process, The method for manufacturing a wet nonwoven fabric for a semipermeable membrane support according to claim 8, characterized in that the cooling step is at least one selected from the following steps: passing the intermediate sheet through a transport path for cooling between each heating and pressurizing treatment step; bringing a highly thermally conductive transport roll into contact with the second surface of the intermediate sheet; bringing a cooling roll into contact with the second surface of the intermediate sheet; and cooling the second surface of the intermediate sheet with a non-contact cooling device.

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