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

Abstract

To provide a wet type nonwoven fabric and a manufacturing method of the same having excellent membrane forming property and stable workability even when being heated to 100°C or higher at membrane production work and the like when being used as a semipermeable membrane support.SOLUTION: A wet type nonwoven fabric for a semipermeable membrane support is the wet type nonwoven fabric for the semipermeable membrane support including synthetic fibers. A linear coefficient of expansion in a flow direction is -20×10-6 to -200×10-6 / K and a linear coefficient of expansion in a width direction is 40×10-6 to 150×10-6 / K at the temperature of the wet type nonwoven fabric of 30°C-150°C.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a wet-laid nonwoven fabric for a semipermeable membrane support and a method for producing the same. [Background technology]

[0002] In recent years, membrane technology has been applied in many water treatments. For example, microfiltration membranes and ultrafiltration membranes are used for water treatment at water purification plants, and reverse osmosis membranes are used for desalinizing seawater. In addition, reverse osmosis membranes and nanofiltration membranes are used for treating water for semiconductor manufacturing, boiler water, medical water, pure water for laboratories, etc. Furthermore, the membrane separation activated sludge process using microfiltration membranes and ultrafiltration membranes is also applied to the treatment of sewage wastewater.

[0003] The semipermeable membranes used in these separations are roughly classified into flat membranes and hollow fiber membranes based on their shape. Among these separation membranes, flat membranes, which are mainly made of synthetic polymers, are generally used in combination with a semipermeable membrane support such as a nonwoven fabric, because the flat membranes, which have a separation function, are inferior in mechanical strength when used alone.

[0004] In general, a semipermeable membrane having a separation function and a semipermeable membrane support are integrated by a method of casting and fixing a solution of a polymer, which is a raw material of the membrane having a separation function, on a semipermeable membrane support such as a nonwoven fabric. In addition, in the case of a semipermeable membrane such as a reverse osmosis membrane, the integration is performed by a method of casting a solution of a polymer on a semipermeable membrane support such as a nonwoven fabric to form a support layer, and then forming a semipermeable membrane on the support layer.

[0005] Therefore, a nonwoven fabric used as a semipermeable membrane support is required to have excellent membrane formability so that when a polymer solution is cast, it does not strike through due to excessive penetration, the membrane material does not peel off, and defects such as non-uniformity of the membrane and pinholes do not occur due to fluffing of the nonwoven fabric, etc. Furthermore, in order to stably produce semipermeable membranes with a high yield, a nonwoven fabric used as a support in the semipermeable membrane production process is also required to have high stability against heat and tension applied to the nonwoven fabric during production processes such as casting a polymer solution to form a membrane.

[0006] Furthermore, in the case of semipermeable membranes such as reverse osmosis membranes which are often used under high pressure, the nonwoven fabric used as the support is particularly required to have high mechanical strength.

[0007] Several techniques are known for nonwoven fabrics as semipermeable membrane supports and their manufacturing methods. For example, a semipermeable membrane support has been proposed that is made of a main fiber made of polyester fiber and a binder fiber, and is manufactured by heating and pressurizing the nonwoven fabric after papermaking, and that has a tensile strength ratio of 2:1 to 1:1 in the papermaking flow direction and width direction, and that has a surface roughness of the front and back sides of the support that is 15% or more larger than the back side roughness, so that the support can be conveyed with rolls without bending in the width direction even when a semipermeable membrane liquid is applied thereto, and can be treated in a coagulation washing tank without any problems (see, for example, Patent Document 1).

[0008] Also, in a semipermeable membrane supporting material made of a nonwoven fabric, a semipermeable membrane supporting material made of a nonwoven fabric in which the fibers arranged on one of the front and back surfaces are more horizontally oriented than the fibers arranged on the other surface has been proposed (see, for example, Patent Document 2). Also, in order to prevent the nonwoven fabric used as a semipermeable membrane supporting material from curling into a cylindrical shape due to membrane shrinkage after the semipermeable membrane is formed, a semipermeable membrane supporting material has been proposed in which the center of the sheet is curved convexly (see, for example, Patent Document 3).

[0009] Also proposed is a method for producing a semipermeable membrane supporting material in which the "-transverse shrinkage rate / longitudinal shrinkage rate" in thermal shrinkage of the semipermeable membrane supporting material is -0.10 to 0.30 when the material is bathed in water at 90°C for 10 minutes has been proposed (see, for example, Patent Document 4). Also proposed is a semipermeable membrane supporting material having a two-layer structure, characterized in that the average heat shrinkage rate of the main fiber in the layer on the non-membrane-forming side is 1.3 to 3.0 times the average heat shrinkage rate of the main fiber in the layer on the membrane-forming side of the semipermeable membrane (see, for example, Patent Document 5).

[0010] These documents contain proposals and descriptions regarding the membrane formability and processability during semipermeable membrane production, and also mention the suppression of deformation of the support when the semipermeable membrane or the like solidifies and shrinks on the semipermeable membrane support. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2002-095937 A [Patent Document 2] JP 2011-161344 A [Patent Document 3] JP 2012-135713 A [Patent Document 4] JP 2013-188738 A [Patent Document 5] JP 2021-146248 A Summary of the Invention [Problem to be solved by the invention]

[0012] However, the prior art documents 1 to 5 do not disclose the effect of heat on the nonwoven fabric, which is the semipermeable membrane support, during the semipermeable membrane manufacturing process, and there are cases where problems such as curling of the nonwoven fabric, wrinkles, and deformation of the semipermeable membrane occur when the semipermeable membrane is dried at a temperature of 100°C or higher.

[0013] Therefore, an object of the present disclosure is to provide a wetlaid nonwoven fabric that has excellent film-forming properties and stable processability, even when exposed to heat of 100°C or higher during film formation processing when used as a semipermeable membrane support, and a method for producing the same. [Means for solving the problem]

[0014] As a result of intensive research, the present inventors have found that the above-mentioned problems can be solved by setting the linear expansion coefficient in the machine direction and the linear expansion coefficient in the width direction of a wetlaid nonwoven fabric for semipermeable membrane supports containing synthetic fibers within a predetermined range, respectively, and have completed the present invention. That is, the wetlaid nonwoven fabric for semipermeable membrane supports according to the present invention is a wetlaid nonwoven fabric for semipermeable membrane supports containing synthetic fibers, and the linear expansion coefficient in the machine direction of the wetlaid nonwoven fabric at 30°C to 150°C is -20×10 -6~-200×10 -6 / K, and the linear expansion coefficient in the width direction is 40×10 -6 ~150×10 -6 / K.

[0015] In the wetlaid nonwoven fabric for semipermeable membrane supporting material according to the present invention, the ratio of linear expansion coefficients defined by (Mathematical formula 1) is preferably 0.3 to 3.3. Even if the fabric is subjected to heat of 100°C or more during film formation, curling due to shrinkage of the membrane is unlikely to occur, and stable processing with high yields is possible. (Equation 1) {Linear expansion coefficient in the width direction at 30°C to 150°C × (-1)} / (Linear expansion coefficient in the machine direction at 30°C to 150°C)

[0016] In the wetlaid nonwoven fabric for semipermeable membrane supporting material according to the present invention, the pressure loss is preferably 250 Pa or more and 1400 Pa or less. Even if the fabric is subjected to heat of 100° C. or more during membrane production, curling due to membrane shrinkage is unlikely to occur, and stable processing with high yield is possible.

[0017] In the wetlaid nonwoven fabric for semipermeable membrane support according to the present invention, the aspect ratio of the tensile strength in the machine direction (machine direction) to the width direction (width), calculated as (tensile strength in machine direction (machine direction) / tensile strength in width direction (width)), is preferably 3.0 or more. The linear expansion coefficient on the machine direction side tends to be low and the linear expansion coefficient on the width direction side tends to be high, making it easy to adjust the linear expansion coefficient to the range required by the present invention.

[0018] In the wet-laid nonwoven fabric for semipermeable membrane support according to the present invention, the basis weight is 30 to 100 g / m 2 The lower the basis weight of the wetlaid nonwoven fabric for semipermeable membrane support, the greater the curling caused by shrinkage of the semipermeable membrane during the drying step after application of the semipermeable membrane, and the more likely the curling will be to occur, but even when the wetlaid nonwoven fabric for semipermeable membrane support has a low basis weight, curling due to shrinkage of the membrane is unlikely to occur when the fabric is subjected to heat of 100°C or more during membrane production, and stable processing with a high yield is possible.

[0019] In the wetlaid nonwoven fabric for semipermeable membrane support according to the present invention, the synthetic fiber preferably contains polyester fiber. Polyester fiber is preferably used because of its heat resistance, chemical resistance, low cost, and a wide variety of properties such as fiber diameter, length, and cross-sectional shape.

[0020] In the wetlaid nonwoven fabric for a semipermeable membrane supporting material according to the present invention, it is preferable that the synthetic fibers contain only polyester fibers.

[0021] In the wetlaid nonwoven fabric for semipermeable membrane support according to the present invention, the synthetic fibers preferably contain a polyester subject fiber and an unstretched polyester binder fiber. The combination of the polyester subject fiber and the unstretched polyester binder fiber is likely to exhibit strength by heat and pressure treatment.

[0022] In the wetlaid nonwoven fabric for semipermeable membrane support according to the present invention, the synthetic fibers preferably contain subject fibers and binder fibers, and the mass ratio of subject fibers to binder fibers is preferably in the range of 85:15 to 40:60, which provides a good balance between ease of operation and strength of the finished product, and also prevents the pressure loss from increasing. Effect of the Invention

[0023] According to the present disclosure, it is possible to provide a wetlaid nonwoven fabric and a method for producing the same that have excellent film-formability and stable processability even when exposed to heat of 100° C. or more during film formation processing when used as a semipermeable membrane support, etc. For example, when used as a semipermeable membrane support for a reverse osmosis membrane or the like, curling is suppressed even when exposed to heat of 100° C. or more during the process of providing a semipermeable membrane, and defects such as wrinkles and membrane deformation are unlikely to occur, resulting in a nonwoven fabric with excellent film-formability and processability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will now be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. Various modifications of the embodiments may be made as long as the effects of the present invention are achieved.

[0025] The wet nonwoven fabric for semipermeable membrane supports according to the present embodiment is a wet nonwoven fabric for semipermeable membrane supports containing synthetic fibers, and the wet nonwoven fabric has a linear expansion coefficient in the machine direction at 30° C. to 150° C. of −20×10 -6 ~-200×10 -6 / K, and the linear expansion coefficient in the width direction is 40×10 -6 ~150×10 -6 / K. In addition, the flow direction and width direction of the wetlaid nonwoven fabric for semipermeable membrane supporting material according to this embodiment are defined as the winding direction, i.e., the longitudinal direction, of the wetlaid nonwoven fabric for semipermeable membrane supporting material in the form of a wound product, and the width direction, i.e., the transverse direction. In this embodiment, the flow direction may be referred to as the flow direction (vertical) and the width direction may be referred to as the width direction (horizontal).

[0026] The wet nonwoven fabric for semipermeable membrane support according to this embodiment is a nonwoven fabric containing synthetic fibers. The synthetic fibers include both main fibers and binder fibers. The raw material of the synthetic fibers is not particularly limited, and various synthetic resins can be used. It is preferable to select a synthetic fiber having a melting point higher than the temperature at which the fiber is actually heated during the production of the semipermeable membrane, and examples of the fibers include fibers spun from synthetic resins such as polyethylene, polypropylene, polyester, polyacrylate, polyurethane, polyolefin, polyvinyl chloride, polyvinylidene chloride, polyethylene fluoride, polyaramid, polyimide, polyacrylonitrile, nylon, and vinylon. In addition, fibers made from regenerated cellulose such as rayon, cellulose acetate, cellulose nitrile, and natural products such as polylactic acid, polybutyric acid, and polysuccinic acid, which have been actively researched in recent years for biochemical applications, are also included in the category of synthetic fibers referred to in the present invention. Among the above synthetic fibers, polyester fibers are preferably used because of their heat resistance, chemical resistance, low price, and a wide variety of properties such as fiber diameter, length, and cross-sectional shape. Therefore, the wetlaid nonwoven fabric for semipermeable membrane supporting material according to this embodiment preferably contains polyester fiber as a fiber component at 90% by mass or more, more preferably at 95% by mass or more, and further preferably uses only polyester fiber.

[0027] The semipermeable membrane support wet nonwoven fabric according to the present embodiment may be a nonwoven fabric containing fibers other than synthetic fibers, such as paper pulp, or inorganic fibers such as glass fibers, silica fibers, and alumina fibers, within the range in which the effects of the present invention are achieved, but a wet nonwoven fabric made of synthetic fibers is more preferable. When containing fibers other than synthetic fibers, the content of synthetic fibers relative to the total fibers in the nonwoven fabric is preferably 90% by mass or more, more preferably 95% by mass or more. On the other hand, the content of fibers other than synthetic fibers relative to the total fibers in the nonwoven fabric is preferably 10% by mass or less, more preferably 5% by mass or less. In addition, the semipermeable membrane support according to the present embodiment can also be blended with additives, such as water-soluble polymeric thickeners, pH adjusters, chelating agents, dispersants, defoamers, water repellents, wetting agents, preservatives, and antistatic agents, within the range in which the effects of the present invention are achieved during wet papermaking. For example, the content of additives relative to 100% by mass of fiber content in the raw material slurry is preferably 20% by mass or less, more preferably 15% by mass or less. Furthermore, the wetlaid nonwoven fabric for semipermeable membrane supporting material according to this embodiment can also contain inorganic fillers such as calcium carbonate, talc, kaolin, and diatomaceous earth, if necessary.

[0028] In this embodiment, fibers that are not intended for melt adhesion at low temperatures are called main fibers. The shape of the main fiber is not particularly limited, but if a fiber with a small fiber diameter is used, the pore size of the completed sheet will be smaller, and if a fiber with a large fiber diameter is used, the strength of the sheet will be increased. If a fiber with a short fiber is used, the dispersibility in water will be improved, and if a fiber with a long fiber is used, the strength of the sheet will be increased. Therefore, it is necessary to select an appropriate shape in consideration of the strength, pore size, sheet uniformity, etc. required for the support, and in this embodiment, a fiber with a thickness of 0.3 to 5.0 decitex, more preferably 0.5 to 3.0 decitex, and a length of 1 to 8 mm, more preferably 3 to 7 mm is preferably used. In addition, the cross-sectional shape of the fiber can be appropriately selected as necessary, and is not limited in this embodiment.

[0029] In this embodiment, it is preferable to mix binder fibers in order to obtain sufficient sheet strength during the sheet forming process and winding process. The binder fiber generally refers to a fiber having a lower melting point than the main fiber, and has the effect of melting and adhering the surface by heating in the drying process after papermaking, and imparting tensile strength to the sheet that enables operation. The melting point of the binder fiber is preferably lower than that of the main fiber. Since the tensile strength of the binder fiber itself is inferior to that of the main fiber, the blending ratio of the main fiber and the binder fiber needs to be a blending ratio that balances ease of operation and strength of the finished product. In addition, if the blending ratio of the binder fiber is too high, the pressure loss tends to increase and the cost tends to be high. In this embodiment, the main fiber:binder fiber range is preferably 85:15 to 40:60, and more preferably 70:30 to 55:45, but is not particularly limited. The binder fiber may be of a type in which all the resins constituting the fiber have a low melting point, a type having a double structure with an inner and outer side, a structure called a core-sheath structure, and only the surface is fused, or an unstretched fiber type, and any of these may be used in the present embodiment. Among them, a combination of a polyester main fiber and a polyester unstretched fiber as a binder fiber is preferably used because it is easy to develop strength by heat and pressure treatment. The binder fiber is preferably of the same or similar resin composition as the main fiber, but a different resin composition is also possible depending on the required characteristics. It is also possible to use a vinylon binder fiber that has the property of dissolving under moist heat conditions. The thickness, length, cross-sectional shape, etc. may be selected according to the purpose, as with the main fiber. In the present embodiment, the binder fiber used is preferably of a thickness of 0.3 to 5.0 decitex, more preferably 0.5 to 3.0 decitex, and a length of 1 to 8 mm, more preferably 3 to 7 mm. When the binder fibers are made into a nonwoven fabric, the thickness and length of the binder fibers that melt as a whole may change, whereas the length of the binder fibers having a core-sheath structure remains the same but the thickness may change.

[0030] In this embodiment, the fibers are dispersed in water, and then the fibers are layered on a papermaking wire, and the water is removed from below the wire to form a sheet, which is a so-called wet papermaking method. The type of papermaking machine used here is not particularly limited, and for example, a sheet-fed papermaking machine, or a continuous papermaking machine such as a fourdrinier papermaking machine, a short-wire papermaking machine, a cylinder papermaking machine, an inclined wire papermaking machine, a gap former, or a delta former can be used. In this case, in order to obtain a wet-laid nonwoven fabric for a semipermeable membrane support with few defects, it is desirable to form the sheet as uniformly and with good texture as possible. When a sheet of two or more layers is to be obtained, it is necessary to use a multilayer papermaking machine that combines these papermaking machines. For example, an inclined / cylinder papermaking machine or a cylinder / cylinder papermaking machine is preferably used, and a multilayer papermaking machine with a cylinder type combination is particularly preferably used because it can make the space compact. The nonwoven fabric sheet may be one layer or two or more layers, but two or more layers are preferred because they can be made into a sheet more uniformly and with good texture. In the case of two or more layers, the fiber blend in each layer may be different as necessary.

[0031] In this embodiment, it is preferable to adjust the fiber orientation during wet papermaking so that the fiber is oriented in the flow direction as much as possible. This makes it easier to adjust the linear expansion coefficient to the range required by the present invention in the heating and pressurizing step described later.

[0032] The paper-made sheet contains a large amount of moisture of 80% or more by mass, so it is dehydrated to 30 to 70% by mass. There are two dehydration methods: suction and pressing between two rolls to squeeze out the moisture. The latter press dehydration method is preferred because it can be done more uniformly.

[0033] The remaining water in the dehydrated sheet is dried in a drying zone. The drying method is not particularly limited, but hot air drying, infrared drying, multi-cylinder dryer drying, Yankee dryer drying, etc. are preferably used. The drying temperature is preferably 100 to 160°C, more preferably 105 to 140°C.

[0034] The wet nonwoven fabric produced by the above-mentioned method may be used as a semipermeable membrane support as it is, but in many cases, the strength as a semipermeable membrane support is insufficient. Therefore, in order to obtain sufficient strength as a semipermeable membrane support, the fibers are heat-fused and the strength is increased by heating and pressurizing at a temperature near the melting point of the main fiber or near the melting point of the binder fiber. Various heating and pressurizing devices are used for this treatment, but a thermal calendar device is generally effective. For example, a method using a metal roll nip calendar that can be treated at a temperature of 160°C or higher, or a soft nip calendar of a metal roll / resin roll can be used if the resin roll has high heat resistance. The temperature conditions, pressurizing conditions, and sheet tension at this time affect the performance of the completed support, but any conditions can be adopted as long as they do not impair the requirements of the present invention. The temperature conditions are generally preferably in the range of 150°C to 260°C, more preferably 180°C to 240°C, but depending on the type of fiber used, lower or higher temperatures may be desirable. The temperature varies depending on the type of fiber used, but if the processing temperature becomes too high for the fiber used, the nonwoven fabric may stick to the roll, and when peeled off from the roll, the nonwoven fabric may be pulled, which may result in a lower density of the nonwoven fabric or a lower pressure loss. The linear pressure is preferably in the range of 30 to 260 kN / m, but is not limited thereto. The sheet tension during the heating and pressurizing treatment is preferably in the range of 0.03 to 0.25 kN / m before and after the heating and pressurizing roll, but is not limited thereto. In addition, in order to achieve uniform performance throughout the web, it is desirable to perform the treatment with a temperature profile and linear pressure profile as uniform as possible. The roll diameter of the thermal calendar device is appropriately selected depending on parameters such as the substrate to be heated and pressurized, the nip pressure, and the speed.

[0035] In the multiple heat and pressure treatment, the same heat and pressure device may be repeatedly used for the first and second or subsequent treatments, or multiple heat and pressure devices may be used for continuous treatment, or a calender device having multiple heat calender rolls arranged in the height direction may be used. It is preferable that the treatment temperature for the first and second or subsequent treatments is the same as or higher than the first treatment.

[0036] When the treatment temperature of the second or subsequent treatments is made higher than that of the first treatment, the treatment temperature of the second or subsequent heating and pressurizing treatments is preferably at least 10° C. higher than the first heating and pressurizing treatment temperature, and more preferably at least 13° C. higher. However, the upper limit of the temperature difference is preferably up to 70° C.

[0037] A semipermeable membrane coating liquid is applied to a nonwoven fabric to provide a semipermeable membrane, but in order to improve the coating suitability, it is also necessary to control the breathability of the nonwoven fabric after heating and pressurizing treatment. In this embodiment, the breathability is expressed by pressure loss. The unit is Pa. In this embodiment, the pressure loss of the wet nonwoven fabric is in the range of 250 Pa to 1400 Pa, more preferably 500 Pa to 1100 Pa, so that a semipermeable membrane does not curl in the width direction due to shrinkage of the semipermeable membrane, has a uniform semipermeable membrane surface, does not penetrate through the semipermeable membrane solution, and has good adhesion between the support and the semipermeable membrane. If the pressure is less than 250 Pa, the semipermeable membrane coating liquid penetrates too much into the nonwoven fabric, so that curling due to shrinkage of the semipermeable membrane tends not to occur, but the surface of the semipermeable membrane may become uneven or the semipermeable membrane coating liquid may penetrate through the semipermeable membrane. On the other hand, if the pressure loss is greater than 1400 Pa, the semipermeable membrane coating liquid is less likely to penetrate into the nonwoven sheet, and the formed semipermeable membrane is more likely to be present on the support surface, and when heated at 100°C or higher during the membrane formation process, the semipermeable membrane may shrink and curl in the width direction. In addition, since the semipermeable membrane coating liquid is less likely to penetrate into the nonwoven sheet, the adhesion of the semipermeable membrane to the surface of the wet nonwoven fabric may deteriorate, and the coating layer may easily peel off from the base sheet. In this embodiment, the adhesion between the wet nonwoven fabric, which is the base sheet, and the semipermeable membrane is preferably 0.8 N / 50 mm or more in peel strength, more preferably 1.0 N / 50 mm or more, and even more preferably 1.2 N / 50 mm or more. If the peel strength is less than 0.8 N / 50 mm, the semipermeable membrane may easily peel off from the support nonwoven fabric, which may not be practical.

[0038] In this embodiment, the tensile strength tends to be low, particularly in the case of a wet nonwoven fabric for semipermeable membrane support having a low basis weight and a thin thickness, but the tensile strength in the flow direction (vertical) is preferably 4.0 kN / m or more, more preferably 5.0 kN / m or more, and even more preferably 6.0 kN / m or more. The tensile strength in the width direction (horizontal) is preferably 0.6 kN / m or more, more preferably 0.7 kN / m or more, and even more preferably 0.8 kN / m or more. Although it varies depending on the type of semipermeable membrane applied on the nonwoven fabric and the conditions of use, if the tensile strength in the flow direction (vertical) is less than 4.0 kN / m or the tensile strength in the width direction (horizontal) is less than 0.6 kN / m, the strength may be insufficient when used as a wet nonwoven fabric for semipermeable membrane support. In addition, the aspect ratio of the tensile strength in the machine direction (machine direction) and the width direction (width direction) of the wet nonwoven fabric for semipermeable membrane support, calculated by (tensile strength in the machine direction (machine direction) / tensile strength in the width direction (width direction)), is 3.0 or more, more preferably 4.5 or more, so that the linear expansion coefficient in the machine direction tends to be low and the linear expansion coefficient in the width direction tends to be high, and it becomes easy to adjust the linear expansion coefficient to the range required by the present invention. It is preferable to adjust the fiber orientation during wet papermaking and orient it in the machine direction as much as possible. In the conventional technology, when the aspect ratio of the tensile strength is high, there is a risk of curling, wrinkles in the machine direction, and deformation of the membrane during the semipermeable membrane coating process. However, by adjusting the linear expansion coefficient to the range required by the present invention, even if the aspect ratio of the tensile strength is 3.0 or more, these problems are suppressed.

[0039] In this embodiment, the density of the nonwoven fabric is 0.6 to 1.0 g / cm 3 The range of 0.75 to 0.95 g / cm is preferable. 3 More preferably, the range is 1.0 g / cm 3 If the density exceeds 0.6 g / cm, the pore size of the support becomes too small and it may be difficult to obtain sufficient water permeability. 3 If it is less than this, the pore size may become too large, which may cause the coating liquid to easily strike through. 2 It is preferable that the thickness is 30 to 60 g / m 2 More preferably, it is 40 to 60 g / m2 The lower the basis weight of the support, the greater the tendency for curling due to shrinkage of the semipermeable membrane during the drying process after application of the semipermeable membrane, and the more likely curling and warping to occur. 2 In the case of a low basis weight wet-laid nonwoven fabric for semipermeable membrane support, it was difficult to suppress curling due to shrinkage of the semipermeable membrane when heated at a high temperature of 100°C or higher. 2 Even in the case of a low-weight wet-laid nonwoven fabric for semipermeable membrane support, when heated at a high temperature of 100°C or higher, it exhibits an excellent effect of suppressing curling due to shrinkage of the semipermeable membrane, and has good processability and enables stable production. 2 The low basis weight wet-laid nonwoven fabric for semipermeable membrane support tends to have a low cost per area of ​​nonwoven fabric, and is considered to have the advantage that when a module is produced with a completed semipermeable membrane, the area of ​​the semipermeable membrane can be increased even with the same module size, or the size of the module can be reduced even with the same semipermeable membrane area. 2 If the thickness is less than 100 g / m, the thickness is too thin and there is a risk that strike-through may occur easily, and curling due to shrinkage of the semipermeable membrane may become large. 2 If the thickness exceeds this range, the strength of the nonwoven fabric tends to be strong, and curling due to shrinkage of the semipermeable membrane and penetration of the semipermeable membrane solution to the back side tend to be suppressed, but there is a drawback in that the nonwoven fabric becomes too thick and the cost tends to increase.

[0040] In the wet-laid nonwoven fabric for semipermeable membrane supports according to the present embodiment, it is important to control the linear expansion coefficient of the wet-laid nonwoven fabric for semipermeable membrane supports in which a three-dimensional network is formed by fibers, and it is important that the linear expansion coefficient in the machine direction shrinks to a certain degree and the linear expansion coefficient in the width direction expands to a certain degree. Specifically, the linear expansion coefficient in the machine direction at 30° C. to 150° C. is −20×10 -6 ~-200×10 -6 / K, preferably -40×10 -6 ~-195×10 -6 / K, and more preferably -60×10 -6 ~-190×10 -6On the other hand, the linear expansion coefficient in the width direction from 30°C to 150°C is 40×10 -6 ~150×10 -6 / K, preferably 60×10 -6 ~140×10 -6 / K, and more preferably 80×10 -6 ~130×10 -6 / K. The linear expansion coefficient in the flow direction from 30°C to 150°C is -20×10 -6 If it is larger than -200×10 -6 If the linear expansion coefficient in the width direction is less than 150×10 / K, it may be difficult to balance the linear expansion coefficient in the width direction. -6 If the shrinkage is greater than 40×10 / K, it may be difficult to balance with the shrinkage in the flow direction. -6If it is smaller than / K, the expansion in the width direction may be insufficient. The linear expansion coefficient represents the change rate of the length of an object that expands or shrinks due to a temperature change, and is the rate of deformation per 1°C of temperature change. The measurement method is performed in accordance with JISK7197. When the linear expansion coefficients in the machine direction and the width direction of the semipermeable membrane support wet nonwoven fabric are within the above range, when the semipermeable membrane support wet nonwoven fabric is heated at 100°C or higher in the semipermeable membrane drying process, a shrinkage stress occurs in the machine direction of the sheet inside the wet nonwoven fabric as a support, and at the same time, an expansion stress occurs in the width direction of the sheet. This is presumably because the balance between the machine direction and the width direction stress is achieved inside the wet nonwoven fabric as a support, and the semipermeable membrane shrinkage-induced curling can be suppressed. In addition, the ratio of the linear expansion coefficients defined by (Mathematical formula 1), i.e., "-machine direction linear expansion coefficient / machine direction linear expansion coefficient", is preferably within the range of 0.3 to 3.3, more preferably within the range of 0.5 to 2.0. If it exceeds 3.3, the expansion stress in the width direction becomes too large relative to the shrinkage stress in the machine direction of the wetlaid nonwoven fabric for a support when heated, resulting in large distortion and the risk of not being able to suppress curling due to shrinkage of the semipermeable membrane when heated.If it is less than 0.3, the shrinkage stress in the machine direction becomes too large relative to the expansion stress in the width direction of the wetlaid nonwoven fabric for a support when heated, resulting in the risk of not being able to suppress curling due to shrinkage of the semipermeable membrane when heated. (Equation 1) {Linear expansion coefficient in the width direction at 30°C to 150°C × (-1)} / (Linear expansion coefficient in the machine direction at 30°C to 150°C)

[0041] The method for adjusting the linear expansion coefficient of the wet nonwoven fabric for semipermeable membrane support includes adjusting the blending of fibers used in papermaking, the orientation of fibers, the number of heating and pressurizing roll processes during the heating and pressurizing treatment process, the line speed, the roll temperature, the roll linear pressure, cooling after the heating and pressurizing treatment, and the sheet tension at the outlet side of the heating and pressurizing roll, and the like, and the linear expansion coefficient can be adjusted by combining these. Regarding the blending of fibers, by increasing the ratio of binder fibers in the blending of main fibers and binder fibers, the linear expansion coefficient in the machine direction tends to be lower and the linear expansion coefficient in the width direction tends to be higher. In addition, blending main fibers that shrink more due to heat tends to lower the linear expansion coefficient in the machine direction and to increase the linear expansion coefficient in the width direction. In addition, it is also effective to combine multiple different types of fibers to control the linear expansion coefficient. Regarding the orientation of fibers, by making a paper so that the fibers are oriented in the machine direction when viewed as a whole sheet, the linear expansion coefficient in the machine direction tends to be lower and the linear expansion coefficient in the width direction tends to be higher. Specifically, by making the tensile strength aspect ratio in the flow direction (length) and width direction (width) of the finally completed wet nonwoven fabric for semipermeable membrane support 3.0 or more, more preferably 4.5 or more, the linear expansion coefficient in the flow direction tends to be low and the linear expansion coefficient in the width direction tends to be high, and the linear expansion coefficient in the flow direction and width direction tends to be adjusted within the range. Regarding the conditions during the heating and pressurizing process, by applying sufficient heat to the inside of the support, such as by cooling slowly after the heat processing treatment, the crystallization of the crystalline resin fiber is promoted, and the thermal dimensional stability is improved and the linear expansion coefficient tends to approach zero. In addition, the crystallization of the crystalline resin fiber can be promoted by increasing the sheet tension on the outlet side during the heating and pressurizing process, but when the sheet tension is increased and the heating and pressurizing process is performed, the fibers that have not crystallized are pulled in the flow direction and fixed in a state where they are gathered in the width direction, so that when the completed support is heated to 100 ° C or more in the semipermeable membrane coating process, the fibers of the support shrink or expand in the direction returning to the state before heating and pressurizing. Specifically, by performing a heating and pressurizing process with high sheet tension on the outlet side, the linear expansion coefficient in the machine direction tends to be low and the linear expansion coefficient in the width direction tends to be high.In addition, the crystallization of the crystalline resin fiber can be promoted by performing heating and pressurizing treatment multiple times, increasing the roll temperature, increasing the linear pressure, slowing the line speed, etc., but these methods are more susceptible to the influence of the sheet tension of the exit roll. Specifically, by performing heating and pressurizing treatment multiple times, increasing the roll temperature, increasing the linear pressure, or performing heating and pressurizing treatment at a slower line speed, the linear expansion coefficient in the machine direction tends to decrease and the linear expansion coefficient in the width direction tends to increase. The linear expansion coefficients in the machine direction and width direction can be adjusted by combining the above methods.

[0042] Methods for adjusting the pressure loss of the above-mentioned wetlaid nonwoven fabric for semipermeable membrane support include, in addition to the blending of fibers used in papermaking, multiple heating and pressurizing treatments during the heating and pressurizing step, adjustment of line speed, roll temperature, roll linear pressure, etc., and the pressure loss can be adjusted by combining these. Regarding the blending of fibers, blending fibers with narrower fiber diameters tends to increase the pressure loss, while blending fibers with wider fiber diameters tends to decrease the pressure loss. In addition, in the blending of main fibers and binder fibers, increasing the ratio of binder fibers tends to increase the pressure loss. In addition, blending main fibers with a high thermal shrinkage rate tends to make the fibers more likely to be crushed during heating and pressurizing treatment, and as a result, the pressure loss tends to increase. Regarding the conditions during the heating and pressurizing step, the pressure loss tends to increase by applying sufficient heat, such as multiple heating and pressurizing treatments, slowing down the line speed, increasing the roll temperature, and increasing the linear pressure. However, when the roll temperature becomes too high for the fibers used, the nonwoven fabric may stick to the roll, and the pressure loss may tend to decrease when peeling it off from the roll. The pressure loss can be adjusted by combining the above methods.

[0043] As the material of the semipermeable membrane formed on the wet nonwoven fabric for semipermeable membrane support according to the present embodiment, polyarylethersulfone such as polysulfone and polyethersulfone, polyimide, polyvinylidene fluoride, cellulose acetate, etc. are preferably used. Among them, polysulfone is particularly preferably used in terms of chemical, mechanical and thermal stability. The method of forming a semipermeable membrane on a substrate is not particularly limited, but for example, the above-mentioned material is dissolved in a solvent, the obtained solution is applied to the substrate, microphase separation is caused, and then the polymer is solidified to obtain the semipermeable membrane.

[0044] For example, when a polysulfone semipermeable membrane is produced, a DMF (dimethylformamide) solution of polysulfone resin is used as the coating liquid, and water is used as the coagulation liquid. The semipermeable membrane thus obtained can be used as an ultrafiltration membrane as it is, but when used as a reverse osmosis membrane, a layer called an active layer is further provided on its surface. This active layer can be obtained by forming, for example, cellulose acetate, aromatic polyamide, crosslinked polyamic acid, polyurea, etc. as an ultrathin film on a supporting semipermeable membrane by interfacial polymerization. Here, the term "supporting semipermeable membrane" refers to a polysulfone layer (semipermeable membrane) that is a supporting layer of an active layer. For example, when an active layer of a crosslinked polyamide is produced, the method is not particularly limited, but for example, the surface of the supporting semipermeable membrane is immersed in a solution of a polyfunctional amine compound, and then contacted with a solvent solution of an acid halide compound to proceed with interfacial polymerization. The manufacturing process of a composite semipermeable membrane in which an active layer is formed on a supporting semipermeable membrane includes a heating process, and a phenomenon occurs in which the supporting semipermeable membrane or the composite semipermeable membrane shrinks due to drying caused by heating. In particular, in continuous film production, since no tension is applied in the width direction, the film tends to shrink in the width direction. The heating method is not particularly limited, but drying with hot air is preferably used for its simplicity. In drying with hot air, the drying temperature is preferably 70°C or higher. On the other hand, the drying temperature is preferably 150°C or lower, more preferably 130°C or lower, and more preferably 120°C or lower. A higher temperature is preferable because it can shorten the time required for drying, but the more rapid the drying, the more likely the curl due to shrinkage in the width direction of the semipermeable membrane tends to increase, making stable production difficult. In addition, in the case of rapid drying, warping may occur at the edge of the curl due to overdrying. If warping occurs at the edge of the curl, the warped part will bend when wound into a roll, and wrinkles will easily occur from there. In the case of drying at 150° C., the drying is rapid after the semipermeable membrane application, so the curl tends to become large, and wrinkles due to curling tend to occur, but in this embodiment, the curl can be suppressed even in such a drying at 150° C., which contributes to improving productivity. In addition, in this embodiment, even when the drying temperature after the semipermeable membrane application is 100° C. or higher and lower than 150° C., curling and wrinkles due to curling can be suppressed in the same manner.This is because, strictly speaking, the linear expansion coefficient is slightly different in the range of 100° C. or more and less than 150° C., but the drying is not as rapid as under the condition of 150° C., and it is believed that curling can be suppressed by satisfying the requirements of this embodiment. In addition, the lower the basis weight of the support, the greater the curling due to shrinkage of the semipermeable membrane during the drying process after application of the semipermeable membrane, and the more likely curling will occur. However, by satisfying the requirements of the present invention, this can also be suppressed to 30 to 60 g / m. 2 Even in the case of a low-basis-weight wet-laid nonwoven fabric for semipermeable membrane support such as that described above, when the fabric is heated at a high temperature of 100°C or higher, it exhibits an excellent effect of suppressing curling due to shrinkage of the semipermeable membrane, and enables good processability and stable production. EXAMPLES

[0045] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" respectively refer to "parts by mass" and "% by mass" calculated on a solid content basis, unless otherwise specified.

[0046] <Example 1> (Preparation of raw material slurry) 70 kg of polyester subject fiber A (melting point: 250-270°C) having a thickness of 0.6 decitex and a cut length of 5 mm and 30 kg of unstretched polyester binder fiber (melting point: 255°C) having a thickness of 1.2 decitex and a cut length of 5 mm were added to water so that the mass blending ratio of polyester subject fiber to polyester binder fiber was 70:30, and the mixture was dispersed for 5 minutes using a disperser. Further water was then added to obtain a raw material slurry with a fiber concentration of 0.03%.

[0047] (Sheet Creation) The obtained raw material slurry was used to make paper using a cylinder paper machine, and dried in a Yankee dryer at a surface temperature of 120°C to give a basis weight of 50 g / m 2 A nonwoven fabric sheet was obtained with the goal of achieving an aspect ratio of 5.0 in the tensile strength in the machine direction (machine direction) and the width direction (width).

[0048] (heat and pressure treatment) Using a metal roll / metal roll hard nip thermal calendar device equipped with a metal roll having a face length of 1,170 mm and a roll diameter of 450 mm (circumference of 1,413 mm), the aforementioned rolled base paper was heated and pressurized under conditions of a roll surface temperature of 215°C, roll clearance of 30 μm, linear pressure of 150 kN / m, inlet side tension of 0.15 kN / m, outlet side tension of 0.09 kN / m, and line speed of 20 m / min, to obtain a wet nonwoven fabric for a semipermeable membrane support.

[0049] <Example 2> A wet-laid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Example 1, except that the roll surface temperature during the heating and pressurizing treatment was changed to 225°C.

[0050] <Example 3> A wet-laid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Example 1, except that the roll surface temperature during the heating and pressurizing treatment was changed to 235°C.

[0051] <Example 4> A wetlaid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Example 3, except that the mass blending ratio of the polyester subject fibers to the unstretched polyester binder fibers was 55:45.

[0052] <Example 5> A wetlaid nonwoven fabric for semipermeable membrane supporting material was obtained in the same manner as in Example 3, except that the type of polyester main fiber was changed to a high-strength type polyester main fiber B (melting point: 250 to 270°C) with a thickness of 0.7 decitex and a cut length of 6 mm, and the fibers were oriented during wet papermaking with the aim of achieving an aspect ratio of 3.5 in the tensile strength in the machine direction (length) and width direction (width).

[0053] <Example 6> A wet-laid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Example 5, except that the outlet side tension during the heating and pressurizing treatment was changed to 0.03 kN / m.

[0054] <Example 7> A wetlaid nonwoven fabric for a semipermeable membrane support was obtained in the same manner as in Example 3, except that the type of polyester main fiber was changed to polyester main fiber C (melting point: 250 to 280°C) with a thickness of 0.55 decitex, a cut length of 5 mm, and a high thermal shrinkage rate, the fibers were oriented during wet papermaking with the aim of achieving an aspect ratio of 6.5 in the tensile strength in the machine direction (length) and width direction (width), and the outlet side tension during the heating and pressurizing treatment was changed to 0.25 kN / m.

[0055] <Example 8> A wet-laid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Example 7, except that the roll surface temperature during the heating and pressurizing treatment was changed to 225° C. and the heating and pressurizing treatment was performed twice.

[0056] <Example 9> A wet-laid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Example 4, except that the binder fiber was changed to a core-sheath binder fiber (core: polyester, melting point 250°C, sheath: polyester, melting point 180°C) having a thickness of 2.2 decitex and a cut length of 5 mm, and the roll surface temperature during the heating and pressurizing treatment was changed to 180°C.

[0057] <Example 10> A wet-laid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Example 3, except that the fiber blend ratio was changed so that the mass blend ratio of polyester main fiber, unstretched polyester binder fiber, and papermaking pulp (unbeaten LBKP) was 67:30:3.

[0058] <Comparative Example 1> A wet-laid nonwoven fabric for semipermeable membrane supporting materials was obtained in the same manner as in Example 6, except that the roll surface temperature during the heating and pressurizing treatment was changed to 225°C.

[0059] <Comparative Example 2> A wet-laid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Comparative Example 1, except that the roll surface temperature during the heating and pressurizing treatment was changed to 215° C. and the line speed was changed to 10 m / min.

[0060] <Comparative Example 3> During wet papermaking, the fibers were oriented with the aim of achieving an aspect ratio of tensile strength in the machine direction (length) and width direction (width) of 2.5, and the line pressure during the heating and pressurizing treatment was changed to 50 kN / m and the outlet side tension to 0.03 kN / m, respectively, to obtain a wet nonwoven fabric for a semipermeable membrane support in the same manner as in Example 3.

[0061] <Comparative Example 4> A wet-laid nonwoven fabric for a semipermeable membrane supporting material was obtained in the same manner as in Example 1, except that the line speed during the heating and pressurizing treatment was changed to 5 m / min.

[0062] <Comparative Example 5> A wet-laid nonwoven fabric for semipermeable membrane supporting materials was obtained in the same manner as in Example 6, except that the roll surface temperature during the heating and pressurizing treatment was changed to 240°C.

[0063] The following evaluations were carried out for the Examples and Comparative Examples, and the results are shown in Tables 1 and 2.

[0064] <Measurement of basis weight> The measurement was performed according to JIS P 8124:1998 "Paper and paperboard - Basis weight measurement method". The unit is g / m 2 It was decided.

[0065] <Thickness and density measurement> The test was performed in accordance with JIS P 8118:1998 "Paper and paperboard - Test methods for thickness and density" with the unit being μm.

[0066] <Pressure loss measurement> Using a homemade device, the effective area is 100 cm 2 The pressure loss when the filter medium was ventilated at a surface velocity of 5.3 cm / sec was measured with a micro-differential pressure gauge (Yamamoto Electric Works, Ltd., Manostar Gauge). The unit was Pa.

[0067] <Measurement of tensile strength> The test was conducted according to JIS P8113:2006 "Paper and paperboard - Test method for tensile properties". The tensile test was conducted using an autograph AGS-X (manufactured by Shimadzu Corporation).

[0068] <Measurement of linear expansion coefficient> The linear expansion coefficient was measured by the TMA method in accordance with JIS K7197:1991. A thermomechanical analyzer TMA-50 (manufactured by Shimadzu Corporation) was used for the measurement. A strip with a width of 5 mm was cut out from the wet nonwoven fabric for semipermeable membrane support to prepare a test piece, and the test piece was heated to 180°C with a chuck distance of 11 mm, atmospheric gas air, gas flow rate of 0 mL / min, load of 2.7 gf, and heating rate of 10°C / min. The linear expansion coefficient from 30°C to 150°C was obtained from the obtained TMA curve. The measurement results were positive (plus) when the support dimensions increased (expanded) with an increase in temperature, and negative (minus) when the support dimensions decreased (shrinked) with an increase in temperature.

[0069] <Curl test> The wet nonwoven fabric for semipermeable membrane support obtained in each Example and Comparative Example was cut to a size of 300 mm wide and 400 mm long, and a 16% solution of polysulfone resin in DMF (dimethylformamide) was applied to the wet nonwoven fabric for semipermeable membrane support using a Mayer bar #12 so that the coating layer thickness was 0.04 mm, and then the semipermeable membrane was formed by solidifying the coating layer by immersing it in water. Thereafter, excess water from the wet coating layer was wiped off, and the coating layer was left to stand for 5 minutes and dried. After standing, a polyfunctional amine aqueous solution was sprayed onto the coating layer, and excess liquid was removed with a 350 mm wide rubber squeegee, and then a polyfunctional acid halogen was sprayed and interfacially polymerized. After removing excess liquid after 1 minute, a 300 mm wide fastener was attached to the upstream side in the flow direction, and the downstream side in the flow direction was hung in a hot air circulation dryer while remaining free, and dried under conditions of 150 ° C. x 5 minutes to form a semipermeable membrane. After drying, the sheet was taken out, placed horizontally on a flat table with the semipermeable membrane-forming surface facing up, and dried in a free state without fasteners. The curl height and curl warping of both downstream ends were evaluated. When the curl height was 0 to less than 10 mm, the curl was evaluated as small and good, with a rating of "◎", when the curl height was 10 mm or more but less than 20 mm, curling was observed but there was no curl warping, with a rating of "〇", and when the curl height was 20 mm or more, the edge part was evaluated as possibly bending and wrinkled when wound into a roll, with a rating of "△", and when the curl was tightly rolled into a cylindrical shape or when the curl warping was large but not cylindrical, with a rating of "×", the edge part was evaluated as bending and wrinkled when wound into a roll. "◎" and "〇" were the pass criteria.

[0070] <Strike-through test> A sample of A4 size was cut from the wet nonwoven fabric for semipermeable membrane support obtained in each Example and Comparative Example, and a 16% by mass solution of polysulfone resin in DMF (dimethylformamide) was applied to the wet nonwoven fabric for semipermeable membrane support using a Mayer bar #12 so that the coating layer thickness was 0.04 mm. The coating layer was then solidified by immersing in water to form a semipermeable membrane. The support was observed from the back side and the degree of run-through of the coating liquid was visually evaluated. When there was no run-through, it was evaluated as good and marked with "◎", when there was no run-through but the penetration of the coating liquid was observed in the thin part of the texture, it was evaluated as a practical level and marked with "〇", when there was run-through when multiple sheets were applied, it was evaluated as possibly not suitable for practical use and marked with "△", and when there was run-through and it was not suitable for practical use, it was marked with "×". Note that "◎" and "〇" were the pass criteria.

[0071] <Semipermeable membrane adhesion test> The peel strength between the semipermeable membrane made of polysulfone resin and the semipermeable membrane support was measured for the semipermeable membrane prepared in the back-bleed test. A 50 mm wide film adhesive tape (Nittoms Strong Packing Tape No. 375 Transparent, Product No. J6071) was attached to the flow direction and width direction of the semipermeable membrane side of the sample, and a sample of 50 mm wide and 120 mm long was cut out from the tape-attached portion to obtain samples in the flow direction and width direction. The sample was conditioned for 24 hours or more under conditions of 23°C and 50% RH. After conditioning, the film adhesive tape and the semipermeable membrane support were peeled off with the semipermeable membrane attached to the film adhesive tape side under conditions of 23°C and 50% RH, and the peel strength was measured at a measurement length of 150 mm, a gripping movement speed of 100 mm / min, and a peeling direction of 180°. The measured values ​​in the flow direction and width direction were averaged to obtain the peel strength. An autograph AGS-X (manufactured by Shimadzu Corporation) was used to measure the peel strength. A peel strength of 1.2N / 50mm or more was evaluated as having high durability and marked with a "◎", 0.8N / 50mm or more but less than 1.2N / 50mm was evaluated as having durability that could withstand practical use and marked with a "〇", 0.60N / 50mm or more but less than 0.8N / 50mm was evaluated as possibly not withstanding practical use and marked with a "△", and less than 0.60N / 50mm was evaluated as unusable and marked with an "×". "◎" and "〇" were the pass criteria.

[0072] [Table 1]

[0073] [Table 2]

[0074] As is clear from the results shown in Tables 1 and 2, the semipermeable membrane support wet nonwoven fabrics obtained in Examples 1 to 10 were excellent in curl evaluation even when dried at 150 ° C. during the formation of the semipermeable membrane in the curl test, and the semipermeable membrane strike-through and adhesion were at a practical level. In contrast, Comparative Examples 1, 2, and 3 were out of the range of linear expansion coefficients, and the balance between the flow direction and the width direction of the linear expansion coefficient was also lost, so the curl evaluation was poor. In Comparative Example 4, the pressure loss was too high, so the semipermeable membrane coating liquid did not easily penetrate into the support, and the semipermeable membrane was formed on the surface of the support, so the curl evaluation due to the shrinkage of the semipermeable membrane was poor, and the adhesion of the semipermeable membrane was also poor. In Comparative Example 5, the pressure loss was too low, so the semipermeable membrane solution struck through in the strike-through test. Therefore, although the curl evaluation and the adhesion of the semipermeable membrane were good, the results were not suitable for practical use.

Claims

1. A wet-laid nonwoven fabric for a semipermeable membrane support containing synthetic fibers, the wet-laid nonwoven fabric having a linear expansion coefficient of -20×10 in the machine direction at 30° C. to 150° C. －６ ~ -200 x 10 －６ / K, and the linear expansion coefficient in the width direction is 40×10 －６ ~150 x 10 －６ 2. A wet-laid nonwoven fabric for semipermeable membrane supports, comprising:

2. 2. The wet-laid nonwoven fabric for semipermeable membrane supporting materials according to claim 1, characterized in that the ratio of linear expansion coefficients defined by (Mathematical formula 1) is 0.3 to 3.

3. (Equation 1) {Linear expansion coefficient in the width direction at 30°C to 150°C × (-1)} / (Linear expansion coefficient in the machine direction at 30°C to 150°C)

3. 3. The wet-laid nonwoven fabric for semipermeable membrane supporting materials according to claim 1 or 2, wherein the pressure loss is 250 Pa or more and 1,400 Pa or less.

4. The wetlaid nonwoven fabric for semipermeable membrane supporting material according to claim 1, characterized in that the aspect ratio of the tensile strength in the machine direction (machine direction) to the tensile strength in the width direction (width), calculated by (tensile strength in machine direction (machine direction) / tensile strength in width direction (width)), is 3.0 or more.

5. Basis weight: 30 to 100 g / m ２ 2. The wet-laid nonwoven fabric for semipermeable membrane supporting materials according to claim 1,

6. The wet-laid nonwoven fabric for semipermeable membrane supporting materials according to claim 1, characterized in that the synthetic fibers contain polyester fibers.

7. The wet-laid nonwoven fabric for semipermeable membrane supports according to claim 1, characterized in that the synthetic fibers contain only polyester fibers.

8. The wet-laid nonwoven fabric for semipermeable membrane supports according to claim 1 , characterized in that the synthetic fibers comprise polyester subject fibers and unstretched polyester binder fibers.

9. The wetlaid nonwoven fabric for semipermeable membrane supporting materials according to claim 1, characterized in that the synthetic fibers include subject fibers and binder fibers, and the mass ratio of subject fibers:binder fibers is in the range of 85:15 to 40:60.

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