JP5913070B2 - Nonwoven fabric for semipermeable membrane support and method for producing the same - Google Patents

Description

  The present invention relates to a non-woven fabric, and more particularly, in the production of a semipermeable membrane having a separation function such as an ultrafiltration membrane, a microfiltration membrane, and a reverse osmosis (RO) membrane, and serves as a support for film formation. The present invention relates to a non-woven fabric for a semipermeable membrane support and a method for producing the same.

  Semipermeable membranes are widely used in the removal of impurities in beverage / industrial water, desalination of seawater, removal of germs in food, wastewater treatment, biochemistry, and the like.

  For the semipermeable membrane, various polymers such as cellulose resin, polyvinyl alcohol resin, polysulfone resin, polyamide resin, polyimide resin, polyacrylonitrile resin, polyester resin, and fluorine resin can be selected according to the application. Is done. However, the semipermeable membrane itself has a low strength and cannot withstand a high pressure of 1 to 10 MPa or more when used alone for ultrafiltration or reverse osmosis. Therefore, it is used in a form in which a semipermeable membrane is formed by applying a semipermeable membrane resin solution to one side of a support such as a nonwoven fabric or a woven fabric having high strength and high liquid permeability. Industrially, many manufacturing apparatuses that continuously coat on one side of a long support such as winding are taken.

  However, since the resin shrinks when the resin is cured after the resin liquid of the semipermeable membrane is applied to the support, the support on which the semipermeable membrane is formed is the machine direction (MD) of the manufacturing apparatus. The so-called “MD curl” that is curved in the width direction is easily generated. This MD curl causes quality problems such as affecting the workability such as causing trouble on the apparatus and stopping when processing the semipermeable membrane into a module, or causing leakage in the product module.

  In order to solve this problem, the nonwoven fabric is composed of a main fiber composed of fine synthetic resin fibers and a binder fiber, and is manufactured by heat-pressing after papermaking, and has a tensile strength ratio of 2 in the paper flow direction and in the width direction. : A semipermeable membrane support of 1: 1 to 1: 1 has been proposed (see, for example, Patent Document 1).

  In addition, in the separation membrane support made of non-woven fabric, a separation membrane support is proposed in which the fibers arranged on the membrane-forming surface side of the separation membrane are transverse to the fibers arranged on the non-membrane-forming surface side of the separation membrane (For example, see Patent Document 2). Furthermore, in the separation membrane support made of nonwoven fabric, the nonwoven fabric has a boiling water shrinkage of 0.1 to 5.0% in the width direction (lateral direction) of the nonwoven fabric, and is heated to a temperature of 60 to 200 ° C. A manufacturing method including a step of widening 1.01 to 1.05 times in the direction (lateral direction) has been proposed (see, for example, Patent Document 3).

  A thermocompression-bonded nonwoven fabric obtained by thermocompression bonding of a nonwoven fabric web mainly composed of a polyester main fiber made of drawn yarn and an undrawn yarn or a polyester binder fiber having a low melting point lower than that of the main fiber, A polyester thermocompression-bonding nonwoven fabric useful in the field of water filter supports, in which the main fiber is a molten liquid crystalline wholly aromatic polyester fiber having a melting point of 290 ° C. or higher, and the polyester binder fiber is a molten liquid crystalline fully aromatic polyester fiber having a melting point of 290 ° C. or lower. It has been proposed (see, for example, Patent Document 4).

  Moreover, the surface layer used as the coating surface of resin, an intermediate | middle layer, and a back layer are comprised by the laminated nonwoven fabric integrated by thermocompression bonding, and the surface layer is a thermoplastic resin long fiber layer whose fiber diameter is 7-30 micrometers, intermediate | middle There has been proposed a separation membrane support in which a layer is a layer made of melt blown fibers having a fiber diameter of 5 μm or less, and a back layer is a thermoplastic resin long fiber layer having a fiber diameter of 7 to 20 μm (see, for example, Patent Document 5). ).

  In addition, in a sheet-like material having a multilayer structure including an upper layer and a lower layer, the upper layer is a nonwoven fabric containing main fibers made of synthetic fibers, and the lower layer is a pulp sheet containing pulp for papermaking, and used as a separation membrane support. A sheet-like material has been proposed (see, for example, Patent Document 6).

JP 2002-95937 A JP 2011-161344 A JP 2011-212602 A JP 2004-100047 A WO2006 / 068100 JP 2009-178915 A

  In the technique of Patent Document 1, it is not easy to control the tensile strength ratio with a paper machine, and even if this method is performed, MD curl often occurs and has a problem.

  In addition, the techniques of Patent Document 2 and Patent Document 3 require a special device to achieve this, and there is a problem that the MD curl problem cannot be easily solved.

  Furthermore, Patent Documents 4 to 6 propose improvements in strength and dimensional stability of the support, prevention of back-through during film formation, and improvement in integrity with the coating resin, but MD in curing the coating film. No curl solution is shown.

  As a non-woven fabric for a semipermeable membrane support, an easy solution for improving MD curl at the time of curing a coating film is required. The subject of this invention is providing the nonwoven fabric for semipermeable membrane support bodies with favorable MD curl at the time of coating and hardening | curing a semipermeable membrane coating liquid to a support body, and its manufacturing method.

The nonwoven fabric for semipermeable membrane support according to the present invention is a nonwoven fabric in which the fiber to be blended is an organic synthetic fiber, and the nonwoven fabric for semipermeable membrane support that supports the semipermeable membrane on one surface of the nonwoven fabric. The non-woven fabric that has a one-layer structure before being hot-pressed, the organic synthetic fiber includes a main fiber, the main fiber is a polyester main fiber, and the semipermeable membrane is applied. In the thickness direction, when the organic layer of the intermediate layer portion is separated from the coated surface portion on the side where the semipermeable membrane is to be provided, the intermediate layer portion, and the non-coated surface portion on the side opposite to the surface on which the semipermeable membrane is provided. The degree of thermal melting of the synthetic fiber is lower than the degree of thermal melting of the organic synthetic fiber at the coated surface portion and the non-coated surface portion, and two layers of the nonwoven fabric to be coated with the semipermeable membrane in the thickness direction To the semi-permeable membrane coated side layer and the semi-permeable membrane non-coated side layer When digits, semi-permeable membrane Ri total der 35 wt% to 70 wt% with respect to the coated surface side layer is a semi-permeable membrane coated surface side layer and a semi-permeable membrane non coated surface side layer, wherein The semipermeable membrane can be applied to any surface of the nonwoven fabric . Due to the one-layer structure, when heat-pressing with a heat calender, the way of heat transmission is uniform, so it is easy to control the peeling position according to the processing conditions.

  The nonwoven fabric for semipermeable membrane support according to the present invention is preferably a wet nonwoven fabric. According to such a configuration, the air permeability of the middle layer of the nonwoven fabric tends to increase, and the adhesion (anchor effect) of the semipermeable membrane to the support tends to increase.

The method for producing a nonwoven fabric for semipermeable membrane support according to the present invention is a nonwoven fabric in which the fibers to be blended are organic synthetic fibers, and the semipermeable membrane support that supports the semipermeable membrane on one surface of the nonwoven fabric In the method for producing a nonwoven fabric for paper, a process of making a fiber slurry containing the organic synthetic fiber to obtain a wet paper having a single layer structure, a process of drying the wet paper with a dryer to obtain a continuous winding base paper, A surface temperature difference is provided between the top roll and the bottom roll of the calender device, and the wet paper is completely dried when the wet paper is dried with the dryer on a roll set at a low temperature. And a step of contacting the surface side receiving a larger amount of heat from the dryer to obtain a nonwoven fabric by subjecting the base paper to hot-pressure processing, wherein the organic synthetic fiber includes a main fiber, and the main fiber includes Polyester-based fiber The non-coated nonwoven fabric to be coated with the semipermeable membrane is coated in the thickness direction on the side opposite to the surface on which the semipermeable membrane is provided, the coating surface portion on the side where the semipermeable membrane is provided, and the surface on which the semipermeable membrane is provided. When separated from the work surface part, the degree of thermal melting of the organic synthetic fiber of the middle layer part is lower than the degree of heat melting of the organic synthetic fiber of the coated surface part and the non-coated surface part, and the hot pressing process is performed. relationship between the amount of heat applied to the heat and the back to give the surface of the base paper meets the condition 1 in performing, and wherein the either side of the nonwoven fabric may applying the semipermeable membrane.
(Condition 1) When the nonwoven fabric is separated into two layers in the thickness direction and divided into a semipermeable membrane coated surface side layer and a semipermeable membrane non-coated surface side layer, the semipermeable membrane coated surface side layer is It is 35 mass% or more and 70 mass% or less with respect to the sum total of a semipermeable membrane coating surface side layer and this semipermeable membrane non-coating surface side layer.

  When the nonwoven fabric is peeled into two layers, the peeled portion has a physical strength (hereinafter sometimes simply referred to as “strength”) when compared in the thickness direction of the nonwoven fabric for semipermeable membrane support. It is a weak site (hereinafter, this site will be referred to as “middle layer site”). Comparing the degree of thermal melting between the fibers on the front and back surfaces of the nonwoven fabric and the degree of thermal melting between the fibers in the middle layer part, the degree of thermal melting between the fibers in the middle layer part is lower, and "semi-molten state" It has become. Thus, since the middle layer portion is in a semi-molten state, the gap between fibers is larger than the portions on the front and back surfaces of the nonwoven fabric, so that the semipermeable membrane coating solution is likely to penetrate. As a result, when the semipermeable membrane coating solution is applied to the nonwoven fabric, much of the coating solution that has penetrated into the nonwoven fabric layer remains in the middle layer portion. As a result, when the coating liquid is cured, the shrinkage of the semipermeable membrane on the surface of the coating surface is synchronized with the shrinkage of the semipermeable membrane in the nonwoven fabric layer as the support, thereby preventing MD curl. In this way, it has become possible to produce an unconventional nonwoven fabric for a semipermeable membrane support.

  Hereinafter, the present invention will be described in detail with reference to embodiments, but the present invention is not construed as being limited to these descriptions. As long as the effect of the present invention is exhibited, the embodiment may be variously modified.

The nonwoven fabric for semipermeable membrane support according to the present embodiment is a nonwoven fabric in which the fiber to be blended is an organic synthetic fiber, and the nonwoven fabric for semipermeable membrane support that supports the semipermeable membrane on one surface of the nonwoven fabric In the above, the nonwoven fabric before the hot pressing process has a one-layer structure, the organic synthetic fiber includes a main fiber, the main fiber is a polyester main fiber, and the semipermeable membrane is applied. When the nonwoven fabric is separated from the non-coated surface portion on the opposite side of the coated surface portion, the middle layer portion, and the surface on which the semipermeable membrane is to be provided in the thickness direction, the middle layer portion The degree of thermal melting of the organic synthetic fiber is lower than the degree of thermal melting of the organic synthetic fiber at the coated surface portion and the non-coated surface portion, and the nonwoven fabric to be coated with the semipermeable membrane is 2 in the thickness direction. Semi-permeable membrane coated surface side layer and semipermeable membrane non-coated surface side layer To when divided, semi-permeable membrane coated surface side layer Ri total der 35 wt% to 70 wt% with respect to the semi-permeable membrane coated surface side layer and a semi-permeable membrane non coated surface side layer The semipermeable membrane can be applied to any surface of the nonwoven fabric . That is, the mass ratio of the semipermeable membrane coated surface side layer and the semipermeable membrane non-coated surface side layer is in the range of 35:65 to 70:30.

  Organic synthetic fibers, which are the main constituent elements of the nonwoven fabric serving as a semipermeable membrane support, are divided into main fibers and binder fibers.

  A polyester fiber is used as the main fiber. Polyester fibers are suitably used because of their heat resistance, chemical resistance, fiber diameter and variety of properties. Here, in this embodiment, among organic synthetic fibers, an organic synthetic fiber having a normal melting point that is not intended for fusion bonding at a low temperature, for example, a melting point of 140 to 300 ° C. is referred to as “main fiber”. Depending on the shape of the main fiber, if a fiber having a small fiber diameter is used, the hole diameter of the completed sheet becomes smaller, and if a fiber having a large fiber diameter is used, the strength of the sheet increases. If short fibers are used, dispersibility in water in the wet papermaking process is improved, and if long fibers are used, the strength of the sheet is increased. In the present embodiment, the synthetic fiber has a thickness of 0.05 to 5.0 dtex, preferably 0.1 to 3.0 dtex, a length of 1 to 8 mm, preferably a length of 3 to 6 mm. Preferably used. Further, the shape of the cross section of the fiber can be appropriately selected as necessary, and is not limited in the present embodiment.

  The binder fiber is mixed with the main fiber for the purpose of improving the strength properties of the product and maintaining a sufficient sheet strength during the sheet forming process and the winding process. Here, the “binder fiber” refers to an organic synthetic fiber whose entire fiber or fiber surface (sheath portion) has a melting point of about 20 ° C. or lower than the main fiber by about 20 ° C., and is heated by a drying process or a hot pressing process after papermaking. Thus, the surface of the fiber or the entire fiber is melt-bonded and has an effect of imparting physical strength to the sheet.

  The binder fiber has a low melting point of all the constituent resins, and a type called a core-sheath structure having a double structure inside and outside, and a type in which only the surface is fused, both of which are used in this embodiment. Is possible. Preferably, an unstretched polyester fiber having a melting point of about 200 to 230 ° C. is used. The thickness, length, cross-sectional shape, and the like can be selected according to the purpose as in the case of the main fiber. For example, in this embodiment, the thickness of the binder fiber is in the range of 0.1 to 5.0 dtex, preferably 0.5 to 3.0 dtex, 1 to 8 mm in length, preferably 3 to 6 mm in length. Those are preferably used. The binder fiber preferably has a resin composition that is the same as or close to that of the main fiber, but a different resin composition is possible depending on the required characteristics. In addition, a vinylon binder fiber having a property of dissolving under wet heat conditions is also preferably used.

  In this embodiment, the case where only a main fiber is mix | blended as an organic synthetic fiber and the case where both a main fiber and a binder fiber are mix | blended are included. In this embodiment, the ratio (mass ratio) of the blend amount of the main fiber and the binder fiber is preferably in the range of main fiber: binder fiber = 100: 0 to 50:50. It is possible to melt and bond the main fibers to each other by hot pressing the sheet containing only the synthetic fibers that are the main fibers without mixing the binder fibers. Since it is not intended for adhesion, it is necessary to increase the heating temperature at the time of the hot pressing process to near the melting point of the main fiber. When the binder fiber is blended with the main fiber, the fibers can be melt-bonded at a temperature lower than the melting point of the main fiber. However, if the ratio of the binder fiber exceeds 50%, the physical strength of the sheet is lowered because the physical strength of the binder fiber itself is weaker than the physical strength of the main fiber.

  The fiber to be blended is an organic synthetic fiber. At this time, an inorganic filler such as calcium carbonate, talc, or kaolin may be blended in addition to the organic synthetic fiber as necessary.

  As the nonwoven fabric for a semipermeable membrane support, for example, a wet nonwoven fabric produced by a wet papermaking method is used. Alternatively, a dry nonwoven fabric is also possible. Among these, in this embodiment, the wet nonwoven fabric has a greater effect than the dry nonwoven fabric. This is because wet nonwoven fabrics, which are mainly composed of short cut organic synthetic fibers, are easier to improve than semi-permeable fabrics, compared to dry nonwoven fabrics, which are mainly composed of continuous organic fibers. This is because the adhesion (anchor effect) of the membrane to the nonwoven fabric is likely to increase.

The manufacturing method of the nonwoven fabric for semipermeable membrane supports in the case of using a wet nonwoven fabric is, for example, as follows. (1) a process of making a fiber slurry containing organic synthetic fibers to obtain a wet paper having a single layer structure, (2) a process of drying the wet paper with a dryer to obtain a continuous winding base paper, and (3) a thermal calendar device. The surface temperature difference between the top roll and the bottom roll is set to a low temperature, and the wet paper is completely dried when the wet paper is dried with a dryer. And a step of bringing a base paper into contact with the heat-treated surface side and subjecting the base paper to a hot pressing process to obtain a nonwoven fabric. The organic synthetic fiber includes a main fiber, the main fiber is a polyester main fiber, and a non-woven fabric to be coated with the semipermeable membrane is provided with a semipermeable membrane in a thickness direction; When it is separated from the non-coated surface portion on the side opposite to the coating surface portion, the middle layer portion, and the surface on which the semipermeable membrane is provided, the degree of thermal melting of the organic synthetic fiber in the middle layer portion is the coating surface portion and the above It is assumed that the relationship between the amount of heat applied to the surface of the base paper and the amount of heat applied to the back surface satisfies Condition 1 below the degree of heat melting of the organic synthetic fiber on the non-coated surface portion.
(Condition 1) When the nonwoven fabric is separated into two layers in the thickness direction and divided into a semipermeable membrane coated surface side layer and a semipermeable membrane non-coated surface side layer, the semipermeable membrane coated surface side layer is It is 35 mass% or more and 70 mass% or less with respect to the sum total of a semipermeable membrane coating surface side layer and this semipermeable membrane non-coating surface side layer.

  The effect of the present invention is manifested in the non-woven fabric before the hot pressing process, whether it is a single layer structure or a multilayer structure in which two or more layers are stacked. As long as the effect of the present invention is not impaired, the multilayered nonwoven fabric may have the same raw material configuration or different raw materials in all layers. It is also possible to change the fiber diameter and fiber length of the organic synthetic fiber even with the same raw material. However, when heat-pressing with a heat calender, the heat transfer is uniform, and the peel position can be easily controlled according to the processing conditions, so a single-layer structure is preferred. In the case of a multilayer structure of two or more layers, the way in which heat is transferred may change at the fault portion where the layers are in contact with each other, and the separation position may not be controlled successfully. Therefore, in the present invention, the non-woven fabric before the hot pressing process has a single layer structure.

  As a method for producing a wet nonwoven fabric, a so-called wet papermaking method is used in which organic synthetic fibers as raw materials are dispersed in water, then the fibers are laminated on a papermaking wire and dehydrated from below the wire to form a sheet. Among these, the wet nonwoven fabric by the wet papermaking method is particularly preferable because the network of constituent fibers tends to be more uniform than the dry nonwoven fabric. The type of paper machine used in the wet papermaking method is not limited in the present embodiment. For example, if a sheet-fed paper machine or a continuous paper machine, a long net type paper machine, a short net type paper machine, a circular net type paper machine is used. An inclined wire type paper machine, a gap former, a delta former or the like can be used.

  Since the paper sheet contains a large amount of water, it is dried in a drying zone. The drying method at this time is not particularly limited, but hot air drying, infrared drying, multi-cylinder cylinder dryer drying, drying with a Yankee dryer, and the like are preferably used. As drying temperature, 100-160 degreeC is desirable and 105-140 degreeC is more desirable.

  Although the wet nonwoven fabric and the dry nonwoven fabric manufactured by the above-mentioned method may be used for a semipermeable membrane support as they are, 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 can be thermally welded to increase the strength by hot pressing at a temperature near the melting point of the main fiber or near the melting point of the binder fiber. Done. For this treatment, various types of hot-pressing devices are used, but in general, a thermal calendar device is effective. For example, a method using a metal roll nip calender that can be processed at a temperature of 160 ° C. or higher, or a metal nip / resin roll soft nip calender can be used if the resin roll has high heat resistance.

  The temperature condition of the hot pressing process is generally preferably in the range of 160 ° C. to 260 ° C., more preferably in the range of 180 ° C. to 240 ° C., but depending on the type of synthetic fiber used, a lower temperature or higher Temperature may be desirable. For example, when the binder fiber is blended with the main fiber, the fiber is melt-bonded to increase the strength by hot pressing at a temperature near the melting point of the binder fiber. The linear pressure is preferably in the range of 50 to 250 kN / m, more preferably in the range of 100 to 200 kN / m, but not limited thereto. Further, in order to achieve uniform performance throughout the web, it is desirable to process with a temperature profile and linear pressure profile that are as uniform as possible. The roll diameter of the thermal calender device is appropriately selected depending on parameters such as the base material to be subjected to the hot press processing, the nip pressure, and the speed. When the binder fiber is not blended and only the main fiber is used, the hot pressing process is performed at a temperature near the melting point of the main fiber.

  For the multiple times of the hot pressing process, the same hot pressing apparatus may be used repeatedly in the first process and the second and subsequent processes, and a method of continuously processing by arranging a plurality of hot pressing apparatuses, A calendar device in which thermal calendar rolls are arranged in multiple stages in the height direction is also possible. The treatment temperature after the first treatment and the second treatment is preferably set to the same temperature as the first treatment or more after the second treatment.

  When the treatment temperature after the second treatment is higher than the treatment temperature of the first treatment, it is preferable that the second or later hot-pressing temperature is higher by 10 ° C. or more than the first hot-pressing temperature, and 13 ° C. It is more preferable to make it higher, and it is more preferable to make it higher by 15 ° C. or more. However, the upper limit of the temperature difference is preferably up to 70 ° C.

  The method for obtaining the semi-molten state of the middle layer part of the nonwoven fabric for semipermeable membrane support of the present embodiment is not limited to the following method, but as one method, organic synthesis in the production of the support (nonwoven fabric) Utilization of the relationship between the melting temperature and the line speed in the fiber thermal melting step is mentioned. If the line speed is relatively slow, heat is conducted to the inside in the nonwoven fabric thickness direction, and the coated surface portion, the middle layer portion, and the non-coated surface portion are uniformly heat-sealed. When the line exceeds a certain speed, heat becomes difficult to conduct to the inside of the nonwoven fabric, and heat fusion at the middle layer portion does not proceed and a semi-molten state is obtained. However, when the line speed is further increased, the thermal melting in the middle layer portion does not proceed further, and the state becomes almost unmelted. As a result, the coating liquid permeates into the nonwoven fabric too much to deteriorate the formation of the semipermeable membrane, or causes problems such as peeling of the nonwoven fabric itself at the middle layer portion. Strict process control should be performed for the semi-molten state of the middle layer. Examples of the heat-melting process include the drying zone of the papermaking process described above, hot-pressing processing, etc., and are particularly important because various conditions of the hot-pressing processing are greatly affected.

  In order to make the peeled portion of the middle layer portion of the nonwoven fabric for semipermeable membrane support of the present embodiment within the scope of the present invention, heat is uniformly applied from the coated surface portion side and the non-coated surface portion side of the nonwoven fabric for semipermeable membrane support. It is necessary to perform the hot pressing while considering the balance. When a large amount of heat is applied to the coated surface part side, thermal fusion of this part proceeds, and the intermediate layer part in a semi-molten state is deflected to the non-coated surface part side. Conversely, when a large amount of heat is applied to the non-coated surface portion side, the middle layer portion is deflected to the coated surface portion side. In particular, in the case of a thermal calendar device, it is important to manage the roll temperature that contacts the coated surface portion side and the non-coated surface portion side of the nonwoven fabric.

  However, in many cases, wet nonwoven fabrics before being subjected to hot-pressure processing are subjected to non-uniform heat treatment in the drying process, so even if the uniform heat treatment is performed in the hot-pressure processing, the peeling position is not necessarily within the scope of the present invention. Does not enter.

  For example, a Yankee dryer is often used as a method for drying a wet nonwoven fabric prior to hot-pressure processing. is important. Since the Yankee dryer applies heat only from one side of the paper sheet and dries it, more and more organic synthetic fibers are melted on the Yankee dryer contact surface side of the sheet. As a result, when hot-press processing is performed with two rolls of a metal roll nip calender, even if the roll temperature is the same, the intermediate layer portion in a semi-molten state is more easily deflected to the surface opposite to the Yankee dryer contact surface. In this case, it is preferable to lower the roll temperature on the Yankee dryer contact surface of the sheet and raise the roll temperature on the opposite surface. Although it depends on the line speed of the processing machine, the temperature difference between the top roll and the bottom roll is preferably 5 ° C. or more, more preferably 10 ° C. or more. When the line speed is 30 m / min or more, the temperature difference is preferably larger than 10 ° C. If the temperature difference is too large, the middle layer part tends to be deflected on the contrary, so care must be taken.

  As another example, when a multi-cylinder cylinder dryer is used for the drying method, the wet non-woven fabric is made of paper, although it is relatively unlikely to cause deflection of the middle layer portion because the wet non-woven fabric is alternately contacted and dried. Since the wet synthetic paper is completely dried and the organic synthetic fiber is melted by heat, the both surfaces of the nonwoven fabric are not necessarily melted uniformly. After complete drying, the semi-molten middle layer portion tends to be deflected on the surface side in contact with the cylinder dryer. In this case as well, it is preferable to provide a temperature difference between the top roll and the bottom roll as in the case of the Yankee dryer. The temperature difference between the top roll and the bottom roll is preferably 5 ° C. or more, more preferably 10 ° C. or more. When the line speed is 30 m / min or more, the temperature difference is preferably larger than 10 ° C.

  When using a metal roll / resin roll soft nip calender as the hot pressing process, the first hot pressing process is performed, and the second hot pressing process is performed on the semi-facing surface where the metal roll is contacted for the first time. Process. Also in this case, the peeling position can be within the range of the present invention by increasing the temperature of the metal roll on the opposite surface side where the middle layer portion is deflected. In this case, it is possible to increase either the first or second roll temperature. Also, when the first time metal roll nip calender is combined with the second time metal roll / resin roll soft nip calender, the first time the temperature difference is reduced to within 10 ° C, preferably within 5 ° C, for the second time. It is also possible to bring the metal roll into contact with the opposite surface side where the middle layer portion is deflected by the soft nip calender, so that the peeling position is within the range of the present invention.

  In this embodiment, when the nonwoven fabric to be coated with the semipermeable membrane is peeled into two layers in the thickness direction, the semipermeable membrane coated surface side layer and the semipermeable membrane coated surface side layer and the semipermeable membrane non-coated layer 35 mass% or more and 70 mass% or less with respect to the sum total with a coating surface side layer, ie, the mass ratio of a semipermeable membrane coating surface side layer and a semipermeable membrane non-coating surface side layer is 35: 65-70: 30. Within range. More preferably, it exists in the range of 40: 60-60: 40. When the ratio of the semipermeable membrane coating surface side layer in the mass ratio is less than 35, the semi-molten intermediate layer portion is deflected to the coating surface portion side, so that when the semipermeable membrane coating solution is applied to the nonwoven fabric Since the penetration of the coating liquid into the nonwoven fabric layer is shallow, the shrinkage of the semipermeable membrane on the surface of the coating surface and the shrinkage of the semipermeable membrane in the nonwoven fabric layer occur more on the coated surface side when the coating solution is cured , Curl will occur. Further, if the ratio of the semipermeable membrane coated surface side layer in the mass ratio is larger than 70, the semi-molten intermediate layer portion is deflected to the noncoated surface side, so that the semipermeable membrane coating solution is not coated on the nonwoven sheet. It becomes easy to get through to the side. Here, the relationship between the coated surface portion, the middle layer portion, and the non-coated surface portion, and the semipermeable membrane coated surface side layer and the semipermeable membrane noncoated surface side layer will be described. A coated surface part, a middle layer part, and a non-coated surface part are each area | region classified into 3 area | regions along the thickness direction of a nonwoven fabric. The semipermeable membrane coating surface side layer and the semipermeable membrane non-coating surface side layer are each layer when the nonwoven fabric is peeled into two layers in the thickness direction. And since peeling occurs mainly in the middle layer part, the semipermeable membrane coated surface side layer consists of a part of the coated surface part and the middle layer part, and the semipermeable membrane non-coated surface side layer consists of the non-coated surface part and the middle layer part. It consists of the rest.

  In this embodiment, a nonwoven fabric is peeled into two layers, a semipermeable membrane coating surface side layer and a semipermeable membrane non-coating surface side layer, and the respective mass ratios are determined. Here, as a peeling method of the nonwoven fabric, for example, (1) a method of measuring the weight ratio of each sample peeled into two layers using a sheet splitter (for example, manufactured by Kumagai Riken Kogyo Co., Ltd.), and (2) JAPAN TAPPI Paper pulp test method no. 18-2: 2000 “Paper and paperboard—Internal bond strength test method—Part 2: Internal bond tester method” After measuring the internal bond strength, each sample peeled off in two layers was weighed. (3) JAPAN TAPPI Paper Pulp Test Method No. 18-1: 2000 “Paper and paperboard—Internal bond strength test method—Part 1: Z-axis direction tensile test method” After measuring the internal bond strength, each sample peeled into two layers was weighed. There is a method for obtaining the mass ratio. Although there is a method of peeling it into two layers using a hand, it is preferable to employ any one of the methods (1) to (3) because it is easy to peel unevenly.

  The semi-molten state of the fiber in the middle layer portion can be indicated by, for example, the internal bond strength in the transverse direction of the sheet. Here, the internal bond strength is the above-mentioned JAPAN TAPPI paper pulp test method No. 18-2: 2000 is a numerical value measured by an internal bond tester for evaluating internal bond strength in accordance with “Paper and paperboard—Internal bond strength test method—Part 2: Internal bond tester method”. The test method is to apply a test piece with adhesive tape on both sides of the sample adhesive plate, impact the L-shaped fitting affixed on it with a hammer, and peel off the test piece together with the L-shaped fitting. It is obtained by measuring. The unit is N · m. Since the internal bond strength measures the peel strength at a weak portion in the nonwoven fabric layer, it can serve as an index indicating the degree of high or low in the heat-melted state of the fibers in the middle layer portion of the nonwoven fabric. The internal bond strength in the transverse direction of the sheet is generally because the fiber orientation of the nonwoven fabric tends to be in the longitudinal direction, and the internal bond strength in the transverse direction tends to be lower than the longitudinal direction of the sheet, and the fiber is in a hot melt state. This is because the difference is easily generated.

  The internal bond strength in the lateral direction of the sheet is preferably within a range of 0.4 to 0.8 N · m, and more preferably within a range of 0.5 to 0.75 N · m. If it is greater than 0.8 N · m, the heat-fusibility of the fibers in the middle layer portion of the nonwoven fabric becomes high and the middle layer portion becomes dense, so that the semipermeable membrane coating solution does not easily penetrate into the middle layer portion and curls are likely to occur. If it is less than 0.4 N · m, the heat melting property of the fibers in the middle layer portion of the nonwoven fabric becomes low and the middle layer portion becomes sparse, so that the semipermeable membrane coating solution penetrates too much into the middle layer portion and the coating layer surface properties (thickness (Uniformity) may be deteriorated or the resin may be exposed.

  In order to improve the applicability of the semipermeable membrane coating solution to the nonwoven fabric, it is also necessary to control the breathability of the nonwoven fabric after being subjected to the hot pressing process. In this embodiment, air permeability is indicated by pressure loss. The unit is Pa. The pressure loss at the surface wind speed of 5.3 cm / second of the wet nonwoven fabric is preferably 50 Pa or more and 3000 Pa or less, more preferably 80 Pa or more and 1500 Pa or less. If it is less than 50 Pa, the semipermeable membrane coating solution will permeate the nonwoven fabric too much and the surface of the semipermeable membrane coating layer will become non-uniform or cause back-through. On the other hand, when the pressure loss is greater than 3000 Pa, the semipermeable membrane coating solution hardly penetrates into the wet nonwoven fabric sheet, and therefore the biting of the semipermeable membrane coating layer on the surface of the wet nonwoven fabric becomes worse.

In order to improve the applicability of the semipermeable membrane coating solution to the nonwoven fabric, it is also necessary to increase the sheet density of the nonwoven fabric serving as the substrate. The sheet density is preferably 0.5 g / cm ³ or more, more preferably 0.6 g / cm ³ or more, and most preferably 0.7 g / cm ³ or more. If it is less than 0.5 g / cm ³ , the semipermeable membrane coating solution will permeate the nonwoven fabric too much and the surface of the semipermeable membrane coating layer will become non-uniform or cause back-through. The upper limit of the sheet density is, for example, 1.0 g / cm ³ .

The basis weight of the nonwoven fabric is preferably ^{30~200g / m 2, 50~150g / m} 2 is more preferable. When the basis weight of the nonwoven fabric is larger than 200 g / m ² , when the manufactured semipermeable membrane is made into a module, it is too thick and the area per module is reduced and the filtration performance is lowered, and is less than 30 g / m ^2. There is a risk that the back-through of the semipermeable membrane coating solution may occur in the film forming process because the thickness is too thin. Moreover, 30-400 micrometers is preferable and, as for the thickness of a nonwoven fabric, 55-300 micrometers is more preferable. When the thickness of the non-woven fabric exceeds 400 μm, when the produced semipermeable membrane is made into a module, it is too thick, the area per module is reduced and the filtration performance is lowered, and when it is less than 30 μm, the thickness is too thin. There is a risk that the back-through of the semipermeable membrane coating solution may occur in the membrane process.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Example 1
<Preparation of fiber raw material slurry>
22 kg of commercially available polyester-based fiber (trade name: EP133, manufactured by Kuraray Co., Ltd.) with a thickness of 1.45 dtex and a cut length of 5 mm, and a commercially available polyester binder fiber (product name with a thickness of 1.2 dtex and a cut length of 5 mm) : TR07N (manufactured by Teijin Fibers Ltd.) was introduced into water and dispersed with a disperser for 5 minutes to obtain a fiber raw material slurry having a fiber concentration of 1% by mass.
<Preparation of fiber slurry>
The fiber raw material slurry 1 was diluted with water to obtain a fiber slurry having a fiber content of 0.03% by mass.
<Production of sheet>
The fiber slurry was put into a head box of a short net type paper machine to make the fiber slurry, and then dried with a Yankee dryer having a surface temperature of 120 ° C. to obtain a continuous wound base paper.
<Hot-pressure processing>
Using a heat calender device with a metal roll / metal roll hard nip with a surface length of 1170 mm and a roll diameter of 450 mm, the above-mentioned winding base paper is roll surface temperature top roll / bottom roll: 190 ° C./180° C., clearance between rolls Under the conditions of 70 μm, linear pressure of 100 kN / m, and line speed of 17 m / min, hot-pressure processing was performed so that the Yankee dryer contact surface of the base paper was in contact with the bottom roll to obtain a nonwoven fabric for a semipermeable membrane support.

(Example 2)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
In Example 1, the roll base paper was roll surface temperature top roll / bottom roll: 192 ° C./178° C., and the hot paper was processed so that the Yankee dryer contact surface of the base paper was in contact with the bottom roll. In the same manner as above, a nonwoven fabric for a semipermeable membrane support was obtained.

(Example 3)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
In Example 1, the roll base paper was roll surface temperature top roll / bottom roll: 195 ° C./175° C., and the hot press processing was performed so that the Yankee dryer contact surface of the base paper was in contact with the bottom roll. In the same manner as above, a nonwoven fabric for a semipermeable membrane support was obtained.

Example 4
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
In Example 1, the roll base paper was roll surface temperature top roll / bottom roll: 200 ° C./170° C., and the hot press processing was performed so that the Yankee dryer contact surface of the base paper was in contact with the bottom roll. In the same manner as above, a nonwoven fabric for a semipermeable membrane support was obtained.

(Example 5)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
Of Example 1, the roll base paper is roll surface temperature top roll / bottom roll: 195 ° C./175° C., the line speed is 20 m / min, and the hot press processing is performed so that the Yankee dryer contact surface of the base paper contacts the bottom roll. A non-woven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1 except for the treatment.

(Example 6)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
In Example 1, the roll base paper is roll surface temperature top roll / bottom roll: 195 ° C./185° C., the line speed is 12 m / min, and the hot press processing is performed so that the Yankee dryer contact surface of the base paper contacts the bottom roll. A non-woven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1 except for the treatment.

(Example 7)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
In Example 1, the roll base paper is roll surface temperature top roll / bottom roll: 190 ° C./180° C., the line speed is 8 m / min, and the hot press processing is performed so that the Yankee dryer contact surface of the base paper contacts the bottom roll. A non-woven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1 except for the treatment.

(Example 8)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
Using a heat calender device with a metal roll / metal roll hard nip with a surface length of 1170 mm and a roll diameter of 450 mm, the above-mentioned winding base paper is roll surface temperature top roll / bottom roll: 190 ° C./180° C., clearance between rolls Under the conditions of 70 μm, a linear pressure of 100 kN / m, and a line speed of 30 m / min, a hot pressing process was performed so that the Yankee dryer contact surface of the base paper was in contact with the bottom roll. Next, the roll surface temperature was 195 ° C. using a heat calender device having a metal roll / cotton roll soft nip and a metal roll surface length of 1170 mm, a roll diameter of 450 mm, a cotton roll surface length of 1170 mm, and a roll diameter of 400 mm. The non-woven fabric for semipermeable membrane support is subjected to hot-pressure processing so that the Yankee dryer contact surface of the base paper contacts the cotton roll under the conditions of clearance between rolls of 0 μm, linear pressure of 150 kN / m, and processing speed of 15 m / min. Got.

Example 9
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
In Example 1, continuous winding base paper was obtained in the same manner as in Example 1 except that drying was performed so as to continuously pass four multi-cylinder cylinder dryers having a surface temperature of 110 ° C. as a drying method. The drying was performed so that the surface of the papermaking sheet was alternately in contact with the first and third cylinder dryer surfaces and the back surface was in contact with the second and fourth cylinder dryer surfaces. However, since the papermaking sheet is completely dried after the third cylinder dryer, and the fiber is melted by heat at the 4th, the organic synthetic fiber is further melted at the back side of the sheet.
<Hot-pressure processing>
In Example 1, the roll base paper was roll surface temperature top roll / bottom roll: 195 ° C./175° C., and the back side of the base paper (fourth cylinder dryer contact surface) was hot-pressed so as to be in contact with the bottom roll. Except for the above, a nonwoven fabric for semipermeable membrane support was obtained in the same manner as Example 1.

(Comparative Example 1)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
In Example 1, the roll base paper was roll surface temperature top roll / bottom roll: 185 ° C./185° C., and the hot paper was processed so that the Yankee dryer contact surface of the base paper was in contact with the bottom roll. In the same manner as above, a nonwoven fabric for a semipermeable membrane support was obtained.

(Comparative Example 2)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
In Example 1, the roll base paper was roll surface temperature top roll / bottom roll: 205 ° C./165° C., and the hot paper was processed so that the Yankee dryer contact surface of the base paper was in contact with the bottom roll. In the same manner as above, a nonwoven fabric for a semipermeable membrane support was obtained.

(Comparative Example 3)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 1.
<Hot-pressure processing>
In Example 1, the roll base paper is roll surface temperature top roll / bottom roll: 190 ° C./180° C., the line speed is 30 m / min, and the hot press processing is performed so that the Yankee dryer contact surface of the base paper contacts the bottom roll. A non-woven fabric for a semipermeable membrane support was obtained in the same manner as in Example 1 except for the treatment.

(Comparative Example 4)
<Preparation of fiber raw material slurry>
Same as Example 1.
<Preparation of fiber slurry>
Same as Example 1.
<Production of sheet>
Same as Example 8.
<Hot-pressure processing>
In Example 1, the roll base paper was roll surface temperature top roll / bottom roll: 185 ° C./185° C., and the back side of the base paper (fourth cylinder dryer contact surface) was subjected to hot press processing so as to contact the bottom roll. Except for the above, a nonwoven fabric for semipermeable membrane support was obtained in the same manner as Example 1.

The nonwoven fabrics for semipermeable membrane supports obtained in the examples were evaluated by the following methods.
<Measurement of basis weight>
It was performed according to JIS P 8124: 1998 “Paper and paperboard—basis weight measurement method”. The unit was g / m ² .

<Measurement of thickness and density>
JIS P 8118: 1998 “Paper and paperboard—Test method for thickness and density”. The unit was μm.

<Measurement of pressure loss>
Using a self-manufactured device, the pressure loss was measured with a slight differential pressure gauge (manostar gauge manufactured by Yamamoto Electric Co., Ltd.) when air was passed through a filter medium having an effective area of 100 cm ^{2 at} a surface wind speed of 5.3 cm / sec. The unit was Pa.

<Measurement of lateral internal bond strength of sheet>
Using an internal bond tester manufactured by Kumagai Riki Kogyo Co., Ltd., the JAPAN TAPPI paper pulp test method no. The internal bond strength was measured according to 18-2: 2000 “Paper and paperboard—Internal bond strength test method—Part 2: Internal bond tester method”. The sample size was 25.4 × 25.4 mm, and the average value of 5 points was determined. The unit was N · m. A case where 0.4 to 0.8 N · m was satisfied was regarded as acceptable.

<Formation of semipermeable membrane coating layer>
A sample of A4 size was cut out from the nonwoven fabric for semipermeable membrane support obtained in the Examples, and a 15% by mass solution of polysulfone resin in DMF (dimethylformamide) was applied onto the semipermeable membrane support using a gap applicator. did. The film thickness after drying was 50 μm. Immediately after coating, it was immersed in water for 10 seconds to solidify the coating layer. Subsequently, this was immersed in warm water at 80 ° C. for 2 minutes and then dried with a 40 ° C. dryer to form a semipermeable membrane.

<Resin backthrough>
About the nonwoven fabric sample for support bodies which formed the said semipermeable membrane coating layer, the back-through state of the semipermeable membrane coating liquid of a non-coating surface was evaluated visually. If there is a see-through on the non-coated surface, × (problem is problematic), if there is a sign of see-through △ (practical lower limit level), if there is no see-through, ○ (no problem in practical use) ○ and △ were accepted, and x was rejected.

<Sheet peeling position>
After measuring the above-mentioned sheet transverse internal bond strength, the weight of the coated surface side layer and the non-coated surface layer was measured for each of the peeled samples, and the coated surface side layer: mass of the non-coated surface layer The ratio was determined (the total was 100).

<MD curl after coating>
The sample was sampled from the above-mentioned coated paper to the size of 25 mm in the vertical axis direction (MD) and 38 mm in the horizontal axis direction (CD). For this sample, the distance between both ends in the horizontal axis direction was measured and subtracted from the original length (38 mm) to obtain an MD curl. The larger the value, the greater the curl. The case of 4.0 mm or less was accepted, and the case of exceeding 4.0 mm was rejected.

  The results are shown in Table 1. Examples 1 to 7 use a winding base paper dried from only one side with a Yankee dryer, but the sheet peeling position falls within the scope of the present application by providing a top / bottom temperature difference in the hot pressing process. After application, the MD curl was reduced to a satisfactory level. However, in Example 7, since the line speed was slow, the thermal meltability of the fibers in the middle layer portion of the nonwoven fabric increased, the internal bond strength increased, and the MD curl slightly increased.

  On the other hand, in Comparative Example 1 where there was no top / bottom temperature difference, the sheet peeling position was outside the range of the present invention, and the MD curl was large. Further, in Comparative Example 2, since the temperature difference between the top and the bottom was excessively increased, the sheet peeling position was too close to the non-coated surface side, and the resin was breached.

  Further, in Comparative Example 3, although the top / bottom temperature difference was added, the line speed was too fast, the thermal meltability of the whole nonwoven fabric was deteriorated, the sheet peeling position was too close to the coated surface side, and the MD curl was large. On the other hand, in Example 8 in which soft nip hot pressing was performed in addition to the conditions of Comparative Example 3, the coating surface side was heated with a metal top roll, and as a result, thermal melting of the coating surface side proceeded and the sheet peeling position However, the MD curl decreased as it approached the middle part of the middle layer region.

  In Example 9 and Comparative Example 4, when making the winding base paper, the Yankee dryer was not used and the sheets were dried alternately on both sides with a multi-cylinder cylinder dryer. This is an example in which thermal melting of the back side of the sheet is progressing. In Example 9, as in Examples 1 to 7, the sheet peeling position entered the range of the present application by making the top / bottom temperature difference in the hot pressing process, and the MD curl was reduced. On the other hand, in Comparative Example 4, since there was no top / bottom temperature difference, the sheet peeling position was close to the coated surface side, and the MD curl increased.

Claims (3)

In the nonwoven fabric for semipermeable membrane support, which is a nonwoven fabric in which the fiber to be blended is an organic synthetic fiber, and which supports the semipermeable membrane on one surface of the nonwoven fabric,
The non-woven fabric before hot pressing is a single layer structure,
The organic synthetic fiber includes a main fiber, and the main fiber is a polyester main fiber,
The non-coating surface on the side opposite to the surface on which the non-woven fabric to be coated with the semipermeable membrane is provided in the thickness direction, the coated surface portion on the side where the semipermeable membrane is to be provided, the middle layer portion, and the semipermeable membrane. When divided from the portion, the degree of thermal melting of the organic synthetic fiber of the middle layer portion is lower than the degree of thermal melting of the organic synthetic fiber of the coated surface portion and the non-coated surface portion,
When the non-woven fabric to be coated with the semipermeable membrane is peeled into two layers in the thickness direction and divided into a semipermeable membrane coated surface side layer and a semipermeable membrane non-coated surface side layer, the semipermeable membrane coated surface side layer Ri total der 35 wt% to 70 wt% with respect to the semi-permeable membrane coated surface side layer and a semi-permeable membrane non coated surface side layer,
A non-woven fabric for a semipermeable membrane support, wherein the semipermeable membrane can be applied to any surface of the non-woven fabric.   The non-woven fabric for a semipermeable membrane support according to claim 1, wherein the non-woven fabric is a wet non-woven fabric. In the method for producing a non-woven fabric for a semipermeable membrane support, which is a non-woven fabric in which the fibers to be blended are organic synthetic fibers, and the semipermeable membrane is supported on one surface of the non-woven fabric,
Paper making a fiber slurry containing the organic synthetic fiber to obtain a wet paper having a single layer structure;
Drying the wet paper with a dryer to obtain a continuous winding base paper;
A surface temperature difference is provided between the top roll and the bottom roll of the heat calender device, and the wet paper is completely dried when the wet paper is dried with the dryer on a roll set at a low temperature. And a step of contacting the surface side that received a larger amount of heat from the dryer and subjecting the base paper to hot-pressure processing to obtain a nonwoven fabric,
The organic synthetic fiber includes a main fiber, and the main fiber is a polyester main fiber,
The non-coating surface on the side opposite to the surface on which the non-woven fabric to be coated with the semipermeable membrane is provided in the thickness direction, the coated surface portion on the side where the semipermeable membrane is to be provided, the middle layer portion, and the semipermeable membrane. When divided from the portion, the degree of thermal melting of the organic synthetic fiber of the middle layer portion is lower than the degree of thermal melting of the organic synthetic fiber of the coated surface portion and the non-coated surface portion,
Relationship between the amount of heat applied to the heat and the back to give the surface of the base paper meets the condition 1 in performing the heat pressure processing, and,
A method for producing a non-woven fabric for a semipermeable membrane support, wherein the semipermeable membrane can be applied to any surface of the non-woven fabric.
(Condition 1) When the nonwoven fabric is separated into two layers in the thickness direction and divided into a semipermeable membrane coated surface side layer and a semipermeable membrane non-coated surface side layer, the semipermeable membrane coated surface side layer is It is 35 mass% or more and 70 mass% or less with respect to the sum total of a semipermeable membrane coating surface side layer and this semipermeable membrane non-coating surface side layer.