Method for manufacturing a wet nonwoven fabric

Abstract

To provide a method of manufacturing a wet-type nonwoven fabric with a cylinder paper machine or an inclined wire paper machine, wherein fiber dropout in a press part and a Yankee drier is suppressed and the formation of paper dust and pinholes is suppressed.SOLUTION: A method of manufacturing a wet-type nonwoven fabric according to the present invention is a method of manufacturing a wet-type nonwoven fabric containing a polyester fiber as its main constituent, including a step of obtaining a fiber raw material slurry by feeding the polyester fiber to water with a pulper and dispersing with a disperser, a step of obtaining a fiber slurry by adding water to the fiber raw material slurry for dilution, a step of adding a nonionic surfactant with an HLB value of 3.0-8.5 to the fiber slurry in a vat and / or in a tank before a vat during sheet making with a cylinder paper machine in a manner that the concentration of the nonionic surfactant in the fiber slurry becomes 5-14 ppm, and a step of obtaining a wet-type nonwoven fabric by sheet-forming the fiber slurry with the cylinder paper machine to form a wet sheet, followed by drying the wet sheet.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a wet nonwoven fabric. Specifically, it relates to a method for manufacturing a wet nonwoven fabric suitable as a support for a semipermeable membrane having a separation function such as an ultrafiltration membrane, a microfiltration membrane, a reverse osmosis (RO) membrane, etc.

Background Art

[0002] In recent years, the applications of semipermeable membranes have been continuously increasing in the removal of impurities in drinking water / industrial water, desalination of seawater, removal of miscellaneous bacteria in food or wastewater treatment, or the biochemical field. Currently, Europe, America, China, South Korea, etc. are the main markets, but in the future, it is expected to spread to water treatment for the purpose of solving water shortages and improving sanitation in the Middle East, and the production volume and usage amount of semipermeable membranes at home and abroad are also continuously increasing.

[0003] Generally, a semipermeable membrane is manufactured by a method of coating and fixing a polymer solution as a raw material of the semipermeable membrane on a support such as a nonwoven fabric or a woven fabric. There is also a method of forming a support layer by previously coating a polymer solution on the support and then forming a semipermeable membrane.

[0004] Therefore, when a polymer solution is coated on a nonwoven fabric or the like serving as a support, it is required that no defects such as membrane defects or pinholes occur due to back leakage on the non-coated surface or fuzzing of the support.

[0005] As materials for semipermeable membranes, various polymers such as regenerated cellulose, cellulose derivatives, polyvinyl alcohol, polysulfone, and polyamide are selected according to the application. However, the membrane itself has low strength and cannot withstand the high pressure of 1 to 10 MPa when used alone for ultrafiltration or reverse osmosis. Therefore, it is necessary to form a membrane on a support such as a nonwoven fabric with high strength and high liquid permeability.

[0006] In order to obtain the required liquid permeability, tensile strength, wet strength, and durability for the support, a non-woven fabric is generally used, which is formed by wet or dry forming of synthetic fibers such as polyester and polyolefin into a sheet shape and then heat-pressed to melt-bond the synthetic fibers together.

[0007] As a method for manufacturing a non-woven fabric as a support for a semi-permeable membrane, a method has been proposed in which the dispersibility is improved by blending a surfactant during fiber dispersion to produce a fiber sheet with excellent texture (see, for example, Patent Document 1).

[0008] Also, a semi-permeable membrane support has been proposed in which water and a polyoxyalkylene alkyl ether type surfactant are added to a pulper in a dispersion tank for wet papermaking to disperse synthetic fibers and then papermaking is carried out (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] The nonwoven fabrics of Patent Document 1 or Patent Document 2 both add a surfactant during fiber dispersion in a pulper. Although these improve fiber dispersibility in the pulper, the fiber dispersibility in the vat in a cylinder paper machine and in the stock inlet in an inclined wire paper machine is not always satisfactory. That is, in a cylinder paper machine, the fiber raw material slurry dispersed in the pulper is carried into the vat, but the fiber raw material slurry in this vat is diluted with water and thus thins to, for example, 1 / 50 of the dispersion concentration in the pulper. Similarly, in an inclined wire paper machine, the fiber raw material slurry in the stock inlet thins to 1 / 50 of the dispersion concentration in the pulper. In such a diluted fiber slurry, since the fiber concentration decreases, the fibers seem to be sufficiently dispersed, but since the surfactant concentration also decreases, the surfactant easily detaches from the fiber surface. When the surfactant detaches from the fiber surface, the fiber surface becomes hydrophobic, and as a result, the wet paper on the wire becomes bulky. When the wet paper on the wire becomes bulky, fiber dropout from the wet paper easily occurs in the press part or the Yankee dryer, and also the strength of the nonwoven fabric sheet decreases, so there is a risk of paper dust dropout onto the roll and pinholes occurring during rewinding and heat-press treatment in the winder, which is a process after papermaking. To solve this, if the amount of surfactant added in the pulper is increased so that the surfactant concentration in the vat becomes sufficient, then the surfactant concentration in the pulper becomes excessive this time, and troubles such as foaming easily occur.

[0011] In view of such problems, an object of the present disclosure is to provide a method for manufacturing a wet nonwoven fabric that is less likely to cause fiber dropout in the press part or the Yankee dryer and has less paper dust dropout and pinhole generation during manufacturing with a cylinder paper machine and an inclined wire paper machine. can be suppressed.

Means for Solving the Problems

[0012] The manufacturing method of the wet nonwoven fabric according to the present invention is a method for manufacturing a wet nonwoven fabric mainly composed of polyester fibers, comprising the steps of: putting the polyester fibers into water with a pulper and dispersing them with a disperser to obtain a fiber raw material slurry; adding water to the fiber raw material slurry to dilute it and obtain a fiber slurry; adding a nonionic surfactant with an HLB value of 3.0 to 8.5 to the fiber slurry in the vat and / or the tank before the vat during the papermaking process of a cylinder paper machine so that the concentration in the fiber slurry is 5 to 14 ppm; forming a wet paper by papermaking the fiber slurry with the cylinder paper machine and drying the wet paper to obtain a wet nonwoven fabric. The pre-bat tank is arranged on the downstream side of the pulper, and is a tank or pipe immediately before the fiber slurry obtained by adding water to the fiber raw material slurry and diluting it flows into the bat. It is characterized by this.

[0013] In the manufacturing method of the wet nonwoven fabric according to the present invention, it is preferable that the surface tension of the dispersion medium of the fiber slurry in the vat and / or the tank before the vat is 28 to 50 mN / m. According to such a configuration, a wet nonwoven fabric with better texture can be obtained.

[0014] In the manufacturing method of the wet nonwoven fabric according to the present invention, it is preferable to have a step of performing a heat and pressure treatment on the wet nonwoven fabric papermade by the cylinder paper machine at least once. According to such a configuration, sufficient strength can be obtained as a semipermeable membrane support.

[0015] The manufacturing method of the wet nonwoven fabric according to the present invention is a method for manufacturing a wet nonwoven fabric mainly composed of polyester fibers, comprising the steps of: putting the polyester fibers into water with a pulper and dispersing them with a disperser to obtain a fiber raw material slurry; adding water to the fiber raw material slurry to dilute it and obtain a fiber slurry; adding a nonionic surfactant with an HLB value of 3.0 to 8.5 to the fiber slurry in the stock inlet and / or the tank before the stock inlet during the papermaking process of an inclined wire paper machine so that the concentration in the fiber slurry is 5 to 14 ppm; forming a wet paper by papermaking the fiber slurry with the inclined wire paper machine and drying the wet paper to obtain a wet nonwoven fabric. The pre-stock inlet tank is arranged on the downstream side of the pulper, and is a tank or pipe immediately before the fiber slurry obtained by adding water to the fiber raw material slurry and diluting it flows into the stock inlet. It is characterized by this.

[0016] In the method for manufacturing a wet nonwoven fabric according to the present invention, it is preferable that the surface tension of the dispersion medium of the fiber slurry in the stock inlet and / or in the pre-tank before the stock inlet is 28 to 50 mN / m. According to such a configuration, a wet nonwoven fabric with better texture can be obtained.

[0017] In the method for manufacturing a wet nonwoven fabric according to the present invention, it is preferable to have a step of performing a heat and pressure treatment on the wet nonwoven fabric formed by the inclined wire papermaking machine at least once. According to such a configuration, sufficient strength can be obtained as a semipermeable membrane support.

[0018] In the method for manufacturing a wet nonwoven fabric according to the present invention, it is preferable that the wet nonwoven fabric is for a semipermeable membrane support.

Effects of the Invention

[0019] According to the present disclosure, in the manufacture of a wet nonwoven fabric using a cylinder papermaking machine or an inclined wire papermaking machine, a method for manufacturing a wet nonwoven fabric with less fiber shedding in the press part or Yankee dryer and less generation of paper dust and pinholes can be provided.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be shown and described in detail, but the present invention is not construed as being limited to these descriptions. As long as the effects of the present invention are achieved, the embodiments may be variously modified.

[0021] The wet nonwoven fabric according to this embodiment mainly consists of polyester fibers. Here, the main component refers to the component with the highest content among the constituents contained in the wet nonwoven fabric. As the polyester fibers, polyethylene terephthalate fibers, polyethylene naphthalate fibers, polybutylene terephthalate fibers, etc. can be used. In addition to the polyester fibers, within the range that does not impair the effects of the present invention, fibers spun from synthetic resins such as polyethylene, polypropylene, polyacrylate, polyurethane, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyaramid, polyimide, polyacrylonitrile, nylon, etc. can be used. Furthermore, regenerated cellulose such as rayon, cellulose derivatives such as cellulose acetate and nitrocellulose, and fibers sourced from natural products such as polylactic acid, polybutyric acid, and polybutanedioic acid, which have been actively studied for biochemical applications in recent years, can also be used. The wet nonwoven fabric according to this embodiment preferably contains polyester fibers as the fiber component in the range of 90 to 100% by mass, and more preferably in the range of 95 to 100%. In this embodiment, it is preferable to use only polyester fibers, and more preferably only polyethylene terephthalate fibers, due to heat resistance, chemical resistance, low cost, and a wide variety of fiber diameters and properties.

[0022] In this embodiment, the polyester fibers, which are the main components of the wet nonwoven fabric, are divided into main fibers and binder fibers. The polyester fibers not intended for melt bonding at low temperatures are called main fibers. Regarding the shape of the main fibers, if those with a relatively small fiber diameter are used, the pore diameter of the completed sheet will be smaller, and if those with a relatively large fiber diameter are used, the strength of the sheet tends to increase. If fibers with a relatively short length are used, the dispersibility in water during the wet papermaking process will be improved, and if fibers with a relatively long length are used, the strength of the sheet tends to increase. In this embodiment, those with a main fiber thickness in the range of 0.05 to 5.0 decitex, preferably 0.1 to 2.0 decitex, and a length of 1 to 8 mm, preferably 3 to 6 mm, are preferably used. Also, the cross-sectional shape of the main fibers can be appropriately selected as needed and is not limited in this embodiment. The main polyester fibers are those having a melting point of about 220 to 260 °C, preferably 230 to 255 °C.

[0023] The wet nonwoven fabric according to this embodiment can also be blended with inorganic fillers such as calcium carbonate, talc, kaolin, etc. as needed.

[0024] In this embodiment, in order to obtain sufficient sheet strength during the sheeting process and the winding process, it is possible to use binder fibers. Binder fibers generally refer to synthetic fibers whose melting point is about 20°C or 20°C higher than that of the main fibers. During the heating in the drying process after papermaking, the surface is melted and adhered, and it has the effect of imparting to the sheet the tensile strength that enables operation. However, since the tensile strength of the fiber itself is inferior to that of the main fiber, it is necessary to set the blending ratio so as to achieve a balance between ease of operation and the strength of the finished product. In this embodiment, the blending amount of the polyester binder fiber is preferably 20 to 38% by mass, more preferably 25 to 35% by mass, based on the total amount of all polyester fibers (the total amount of the polyester main fiber and the polyester binder fiber). Within this range, heat and pressure treatment can be suitably performed, and an appropriate amount of fiber can be left, so that the quality can be stabilized in the wet state. If the binder fiber is less than 20% by mass, it may not be possible to obtain a stable base paper with weak strength at the stage of manufacturing the wet nonwoven fabric. On the other hand, if the binder fiber exceeds 38% by mass, it can be suitably fused in the heat and pressure process, but since there are many amorphous fibers, it may be difficult to maintain the strength in the wet state.

[0025] Binder fibers include those that use all of their constituent resins in a molten state, and those that have a so-called core-sheath structure, a double structure of the inner and outer layers, and only the surface is melted. Any of these can be used in the present embodiment. Preferably, polyester undrawn fibers having a melting point of about 200 to 230 °C are used. Also, the thickness, length, cross-sectional shape, etc. can be selected according to the purpose, similar to the main fibers. The binder fibers preferably have the same or a resin composition close to that of the main fibers, but different resin compositions are also possible depending on the required characteristics. Also, vinylon binder fibers having the property of dissolving under wet heat conditions are preferably used. Furthermore, pulp for papermaking having self-adhesiveness by hydrogen bonding can also be used as a binder. Even when blending binder fibers other than polyester binder fibers, it is preferable that the wet nonwoven fabric satisfies the condition of containing polyester fibers as a fiber component in the range of 90% by mass or more and 100% by mass or less.

[0026] As a method for manufacturing a wet nonwoven fabric, a so-called wet papermaking method is used, in which fibers are dispersed in water, then the fibers are laminated on a papermaking wire, and dehydrated from below the wire to form a sheet. In the present embodiment, a cylinder mold papermaking machine or an inclined wire papermaking machine is used as the papermaking machine. An example of the papermaking method using a cylinder mold papermaking machine will be given. First, the fiber raw material slurry dispersed by a pulper or the like is diluted with water to obtain a fiber slurry. The fiber slurry used as the papermaking raw material flows into the vat beyond the making board. Here, the fiber slurry comes into contact with the wire on the surface of the cylinder, is dehydrated by obtaining a vacuum due to the water level difference, and becomes a sheet shape and is conveyed to the top of the cylinder. Then, it is pressed against the felt and dehydrated in the press part, and then conveyed to a drying process such as a Yankee dryer. In the papermaking method using an inclined wire papermaking machine, the fiber raw material slurry dispersed by a pulper or the like, similar to the cylinder mold papermaking machine, is diluted with water to obtain a fiber slurry. The fiber slurry used as the papermaking raw material flows into the stock inlet, is ejected onto the inclined wire from the pond, and the fiber slurry on the wire is dehydrated through the pond and becomes a sheet shape. Then, it is pressed against the felt and dehydrated in the press part, and then conveyed to a drying process such as a Yankee dryer.

[0027] In this embodiment, a nonionic surfactant having an HLB value of 3.0 to 8.5 is added to the fiber slurry in the vat or the stock inlet during papermaking so that the concentration in the fiber slurry in the vat or the stock inlet is 5 to 14 ppm. More specifically, it is added continuously or intermittently so as to be constant within the range of 5 to 14 ppm. In this way, the fiber surface of the polyester fiber in the fiber slurry in the vat or the stock inlet can be sufficiently hydrophilized, and while maintaining good fiber dispersibility, appropriate water filtration properties and water retention properties of the wet paper can be achieved. As a result, the tightening of the wet paper on the wire is improved, so that the fiber dropout from the wet paper in the press part or the Yankee dryer can be prevented. In addition, a wet nonwoven fabric with less pinholes due to paper powder dropout and uneven ground can be obtained.

[0028] In this embodiment, the addition of the aforementioned nonionic surfactant may be carried out in the pre-bathtub tank or the pre-stock inlet tank. As described above, when attempting to add a nonionic surfactant to the fiber raw material slurry in the pulper so as to ensure sufficient dispersion of the fiber slurry in the vat or the stock inlet, the concentration of the nonionic surfactant in the pulper has to be increased, which easily causes problems such as foaming. Apart from this problem, there is another problem. That is, the fiber raw material slurry dispersed in the pulper is fed while being diluted and diluted to a predetermined concentration, for example, 50-fold dilution, in the pre-bathtub tank to become a fiber slurry. At this time, the fiber raw material slurry is subjected to an external force by the pump pressure associated with stirring and liquid feeding while being diluted until it is carried into the vat or the stock inlet. It has been found that when papermaking is carried out using the fiber slurry subjected to this external force, the wet paper on the wire becomes bulky. That is, what is important in the present invention is to prevent the fiber slurry from being subjected to as little external force as possible from after the addition of the nonionic surfactant until it reaches the wire. If it is not subjected to a strong external force such as stirring, for example, the nonionic surfactant may be added in a tank (for example, a mixing box) or a pipe immediately before the fiber slurry flows into the vat. In this embodiment, the tank or pipe immediately before the fiber slurry flows in is referred to as the "pre-bathtub tank" or the "pre-stock inlet tank". In the "pre-bathtub tank" or the "pre-stock inlet tank", the fiber slurry is not stirred and no large external force is applied. In the cylinder machine, the cylinder rotates in the vat. However, since the stirring caused by the rotation of the cylinder is weak, the fiber slurry is less likely to be subjected to an external force and is far less likely to be subjected to an external force compared to the stirring by a disperser.

[0029] The HLB (Hydrophile-Lipophile-Balance) value of a nonionic surfactant is a value representing the degree of affinity of the surfactant for water and oil, and takes values from 0 to 20. The closer it is to 0, the higher the lipophilicity, and the closer it is to 20, the higher the hydrophilicity. In this embodiment, a nonionic surfactant with an HLB value of 3.0 to 8.5, more preferably 3.0 to 5.0, is used. A nonionic surfactant with a low HLB value is compatible with hydrophobic fibers, so the dispersibility of polyester fibers is improved. However, since it has poor hydrophilicity, aggregates formed by micelle aggregation are likely to occur when it comes into contact with water, and undispersed oil is likely to remain. When these aggregates and oil are incorporated into the sheet, there are places where the polyester fibers are difficult to fuse in the heat and pressure treatment process, resulting in defects. Therefore, in the present invention, a nonionic surfactant with an HLB value of 3.0 to 8.5 is used. If the HLB value is within this range, uniform dispersion is possible without problems such as aggregation and undispersion in water. When the HLB value of the nonionic surfactant is less than 3.0, defects are likely to occur. When the HLB value exceeds 8.5, the compatibility with hydrophobic fibers deteriorates, the dispersibility of the fibers decreases, and the wet paper on the wire becomes bulky.

[0030] The nonionic surfactant is not particularly limited, and examples include polyhydric alcohol fatty acid esters such as glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyalkylene fatty acid ester, polyoxyalkylene alkylamide, polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyalkylene-modified silicone, amino-modified silicone, polyether-modified silicone, etc. These nonionic surfactants have the advantage that they are less likely to foam, less likely to cause fiber aggregation, and it is easier to achieve the electrokinetic balance of the fiber slurry, so it is easy to form a fabric structure compared to ionic (anionic, cationic, amphoteric) surfactants.

[0031] In this embodiment, the concentration of the nonionic surfactant in the fiber slurry in the vat or the stock inlet is set to 5 to 14 ppm. By setting it within this range, while maintaining the fiber dispersibility in the fiber slurry in the vat or the stock inlet, it is easy to make the drainage property and water retention property of the wet paper on the wire within an appropriate range. As a result, the fiber shedding at the press part and the Yankee dryer can be reduced, and the generation of paper dust and pinholes can be suppressed. When the concentration of the nonionic surfactant in the fiber slurry in the vat is less than 5 ppm, the fiber dispersibility in the fiber slurry decreases and the amount of water entering between the fibers increases, so that the wet paper on the wire becomes bulky. As a result, fiber shedding occurs at the press part and the Yankee dryer, and paper dust and pinholes are likely to be generated. Conversely, when it exceeds 14 ppm, the drainage on the wire becomes too much and the wet paper becomes bulky. As a result, fiber shedding occurs at the press part and the Yankee dryer, and paper dust and pinholes are likely to be generated.

[0032] In this embodiment, it is preferable that the surface tension of the dispersion medium of the fiber slurry of the nonionic surfactant in the vat or the stock inlet is 28 to 50 mN / m. By setting it within this range, it is easy to make the drainage property and water retention property of the wet paper on the wire within an appropriate range. As a result, the fiber shedding at the press part and the Yankee dryer can be reduced, and the generation of paper dust and pinholes can be suppressed. When the dispersion medium of the fiber slurry of the nonionic surfactant in the vat is less than 28 mN / m, the drainage on the wire becomes too much and the wet paper becomes bulky. As a result, fiber shedding may occur at the press part and the Yankee dryer, and paper dust and pinholes may be likely to be generated. Conversely, when it exceeds 50 mN / m, the fiber dispersibility in the fiber slurry decreases and the amount of water entering between the fibers increases, so that the wet paper on the wire becomes bulky. As a result, fiber shedding may occur at the press part and the Yankee dryer, and the formation may easily collapse and paper dust and pinholes may be likely to be generated.

[0033] In this embodiment, the fiber slurry in the vat or the fiber slurry in the stock inlet is prepared in this way and then paper is made using a paper machine. The wet paper on the wire is dehydrated in the press section and then dried in the drying zone. The drying method at this time is not particularly limited, but hot air drying, infrared drying, drum drying, drying by a Yankee dryer, etc. are preferably used. The drying temperature is preferably 100 to 160°C. As described above, if the wet paper on the wire becomes too bulky, fiber shedding is likely to occur in these press sections and drying zones (especially the Yankee dryer).

[0034] After going through the papermaking process and the drying process, the wet nonwoven fabric has insufficient strength as a semipermeable membrane support as it is, and has poor coatability for the semipermeable membrane. Therefore, in this embodiment, in order to obtain sufficient strength as a semipermeable membrane support, heat and pressure treatment may be performed to increase the strength of the nonwoven fabric. For this treatment, various thermocompression processing devices are used, but generally a heat calender device is effective. The heat and pressure treatment by the thermocompression processing device may be a single treatment or a plurality of treatments.

[0035] The wet nonwoven fabric according to this embodiment has few paper dusts and pinholes, and is particularly suitable as a nonwoven fabric for a semipermeable membrane support.

Examples

[0036] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. Also, "parts" and "%" in the examples indicate "parts by mass" and "mass%" in terms of solid content conversion, respectively, unless otherwise specified.

[0037] <Example 1> (Preparation of Fiber Raw Material Slurry) 210 kg of a commercially available polyester-based fiber (product name: EP133, manufactured by Kuraray Co., Ltd.) with a fineness of 1.45 dtex and a cut length of 5 mm, and 90 kg of a commercially available polyester binder fiber (product name: TR07N, manufactured by Teijin Fibers Limited) with a fineness of 1.2 dtex and a cut length of 5 mm were put into 9700 kg of water in a pulper and dispersed for 10 minutes with a disperser to obtain a fiber raw material slurry with a fiber content concentration of 3%. (Preparation of Fiber Slurry) Water was added to the fiber raw material slurry to dilute the whole, and a fiber slurry with a fiber content concentration of 0.05% was obtained. A nonionic surfactant (product name: Formless P76, polyoxyalkylene fatty acid ester type, manufactured by Meisei Chemical Industry Co., Ltd.) with an HLB value of 3.0 was blended into this fiber slurry at 7 ppm with respect to the fiber slurry. The surface tension of this fiber slurry was 34.2 mN / m. The mixing box is included in the pre-bathtub tank. (Production of Sheet) This fiber slurry was put into the vat of a cylinder mold paper machine. After papermaking the fiber slurry, it was dehydrated in the press part and the sheet was dried with a Yankee dryer having a surface temperature of 120°C, and a wet nonwoven fabric sheet was wound up to a width of 500 mm to obtain a nonwoven fabric roll. (Thermal Pressing Process) Using a hot calendar device with a metal roll / metal roll hard nip, a surface length of the metal roll of 550 mm, a roll diameter of 210 mm (circumference 660 mm), the above nonwoven fabric roll was subjected to heat pressing treatment under the conditions of a roll surface temperature of 220°C, a roll gap of 30 μm, a linear pressure of 50 kN / m, a processing speed of 2 m / min, and a paper passing number of 2 times, to obtain a wet nonwoven fabric with a basis weight of 75.0 g / m 2 , a thickness of 0.090 mm, and a sheet density of 0.83 g / cm 3 .

[0038] <Example 2> A wet nonwoven fabric was obtained in the same manner as in Example 1 except that the nonionic surfactant was changed to polyoxyethylene lauryl ether (product: Emulgen 103, manufactured by Kao Corporation) with an HLB value of 8.1. The surface tension of the fiber slurry was 29.2 mN / m.

[0039] <Example 3> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the nonionic surfactant was changed to a polyether-modified silicone (product: KF-6028, manufactured by Shin-Etsu Silicone Co., Ltd.) having an HLB value of 4.0. The surface tension of the fiber slurry was 49.2 mN / m.

[0040] <Example 4> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the blending amount of the nonionic surfactant was changed to 5 ppm with respect to the fiber slurry. The surface tension of the fiber slurry was 45.1 mN / m.

[0041] <Example 5> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the blending amount of the nonionic surfactant was changed to 14 ppm with respect to the fiber slurry. The surface tension of the fiber slurry was 27.8 mN / m.

[0042] <Example 6> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the paper machine was changed to an inclined wire paper machine and the fiber slurry was changed to be charged into the stock inlet.

[0043] <Example 7> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the addition location of the nonionic surfactant was changed to inside the vat. The surface tension of this fiber slurry was 34.0 mN / m.

[0044] <Comparative Example 1> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the nonionic surfactant was changed to be unblended. The surface tension of the fiber slurry was 59.5 mN / m.

[0045] <Comparative Example 2> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the nonionic surfactant was changed to a polyoxyethylene alkyl ether (product: Emulgen 404, manufactured by Kao Corporation) having an HLB value of 8.8. The surface tension of the fiber slurry was 52.0 mN / m.

[0046] <Comparative Example 3> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the nonionic surfactant was changed to a sorbitan fatty acid ester type with an HLB value of 1.8 (product: Nonion OP-85R, manufactured by NOF Corporation). The surface tension of the fiber slurry was 26.0 mN / m.

[0047] <Comparative Example 4> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the blending amount of the nonionic surfactant was changed to 3 ppm with respect to the fiber slurry. The surface tension of the fiber slurry was 58.3 mN / m.

[0048] <Comparative Example 5> A wet nonwoven fabric was obtained in the same manner as in Example 1, except that the nonionic surfactant was changed to a polyoxyethylene alkyl ether with an HLB value of 11.5 (product: DKS NL-60, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and the blending amount was changed to 15 ppm with respect to the fiber slurry. The surface tension of the fiber slurry was 25.5 mN / m.

[0049] <Comparative Example 6> The addition location of the nonionic surfactant was changed to the pulper, and 420 ppm of the nonionic surfactant was blended with 10000 kg of the fiber raw material slurry with a fiber content concentration of 3% (the concentration in the diluted fiber slurry was 7 ppm). A wet nonwoven fabric was obtained in the same manner as in Example 1, except that it was dispersed in the pulper together with the polyester fiber. The surface tension of the fiber slurry with a fiber content concentration of 0.05% after dilution was 51.0 mN / m.

[0050] The following evaluations were carried out for the examples and comparative examples, and the results are shown in Table 1 together with the outline of the nonwoven fabric manufacturing method.

[0051] (Fiber shedding evaluation) In the sheet production process of each example and comparative example, the presence or absence of shedding to the felt in the press part was observed and visually evaluated. The evaluation was considered qualified if it was Δ or more. <Evaluation criteria> ○: Good level without shedding to the felt △: There is a slight drop-off onto the felt, but it is at a level where there are no practical problems. ×: There is a lot of drop-off onto the felt.

[0052] (Paper dust evaluation) The wet nonwoven fabric before heat and pressure treatment obtained in each example and comparative example was cut into pieces with a width of 25 mm and a length of 250 mm, and using a Kagaku-Shinbun friction fastness tester (manufactured by Tester Sangyo Co., Ltd.), it was evaluated with a weight of 200 g and 10 reciprocations with reference to the JIS L0849 test method for color fastness to rubbing. The evaluation was re-categorized based on the following criteria due to the drop-off of paper dust from the nonwoven fabric. Evaluations with △ or above were considered qualified. <Evaluation criteria> ○: There is a slight drop-off of fibers, but it is at a level that is practically good. △: There is fiber drop-off, but it is at a level where there are no practical problems. ×: There is a lot of fiber drop-off.

[0053] (Pinhole evaluation) Light was projected from one side of the wet nonwoven fabric after heat and pressure treatment obtained in each example and comparative example, and the leakage condition was visually evaluated. Evaluations with △ or above were considered qualified. <Evaluation criteria> ○: There is a slight light leakage, but since the aperture diameter of the pinholes is small, it is at a level that is practically good. △: There is light leakage, but it is at a level where there are no practical problems. ×: The light leakage is large and the aperture diameter of the pinholes is large. Since the coating liquid penetrates too much, it is at a level that causes practical problems.

[0054]

Table 1

[0055] As is clear from the results shown in Table 1, in Examples 1 to 7, wet nonwoven fabrics with less fiber shedding and excellent paper dust evaluation could be manufactured, and the heat and pressure treatment was also excellent in pinhole evaluation without any problems. In Comparative Example 1, since no nonionic surfactant was blended, the results were inferior in all of the fiber shedding evaluation, paper dust evaluation, and pinhole evaluation. In Comparative Example 2, since the HLB value of the nonionic surfactant was 8.8, the results were inferior in all of the fiber shedding evaluation, paper dust evaluation, and pinhole evaluation. In Comparative Example 3, since the HLB value of the nonionic surfactant was 1.8, the result was inferior in pinhole evaluation. In Comparative Example 4, since the concentration value of the nonionic surfactant in the fiber slurry was 3 ppm, the results were inferior in all of the fiber shedding evaluation, paper dust evaluation, and pinhole evaluation. In Comparative Example 5, since the concentration value of the nonionic surfactant in the fiber slurry was 15 ppm and the HLB value of the nonionic surfactant was 11.5, the results were inferior in paper dust evaluation and pinhole evaluation. In Comparative Example 6, since the addition location of the nonionic surfactant was the pulper, the results were inferior in all of the fiber shedding evaluation, paper dust evaluation, and pinhole evaluation.

Claims

1. A method for manufacturing a wet nonwoven fabric mainly composed of polyester fibers, comprising: a step of putting the polyester fibers into water in a pulper and dispersing them with a disperser to obtain a fiber raw material slurry; a step of adding water to the fiber raw material slurry to dilute it and obtain a fiber slurry; a step of adding a nonionic surfactant having an HLB value of 3.0 to 8.5 to the fiber slurry in the vat and / or the pre-vat tank during papermaking by a cylinder papermaking machine so that the concentration in the fiber slurry is 5 to 14 ppm; a step of forming a wet paper by papermaking the fiber slurry with the cylinder papermaking machine and drying the wet paper to obtain a wet nonwoven fabric; wherein the pre-vat tank is arranged on the downstream side of the pulper and is a tank or pipe immediately before the fiber slurry obtained by adding water to the fiber raw material slurry and diluting it flows into the vat. A method for manufacturing a wet nonwoven fabric characterized by this.

2. The method for manufacturing a wet nonwoven fabric according to claim 1, wherein the surface tension of the dispersion medium of the fiber slurry in the vat and / or the pre-vat tank is 28 to 50 mN / m.

3. The method for manufacturing a wet nonwoven fabric according to claim 1, characterized by having a step of performing a heat and pressure treatment on the wet nonwoven fabric made by the cylinder papermaking machine at least once.

4. A method for manufacturing a wet nonwoven fabric mainly composed of polyester fibers, comprising: a step of putting the polyester fibers into water in a pulper and dispersing them with a disperser to obtain a fiber raw material slurry; a step of adding water to the fiber raw material slurry to dilute it and obtain a fiber slurry; a step of adding a nonionic surfactant having an HLB value of 3.0 to 8.5 to the fiber slurry in the stock inlet and / or the pre-stock inlet tank during papermaking by an inclined wire papermaking machine so that the concentration in the fiber slurry is 5 to 14 ppm; a step of forming a wet paper by papermaking the fiber slurry with the inclined wire papermaking machine and drying the wet paper to obtain a wet nonwoven fabric; wherein the pre-stock inlet tank is arranged on the downstream side of the pulper and is a tank or pipe immediately before the fiber slurry obtained by adding water to the fiber raw material slurry and diluting it flows into the stock inlet. A method for manufacturing a wet nonwoven fabric characterized by this.

5. The manufacturing method of the wet nonwoven fabric according to claim 4, characterized in that the surface tension of the dispersion medium of the fiber slurry in the stock inlet and / or in the pre-tank before the stock inlet is 28 to 50 mN / m.

6. The manufacturing method of the wet nonwoven fabric according to claim 4, characterized by having a step of performing a heat and pressure treatment on the wet nonwoven fabric formed by the inclined wire paper machine at least once.

7. The manufacturing method of the wet nonwoven fabric according to any one of claims 1 to 6, characterized in that the wet nonwoven fabric is for a semipermeable membrane support.

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