EP4283038A1 - Nassgelegte vliesstofffolie - Google Patents

Nassgelegte vliesstofffolie Download PDF

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Publication number
EP4283038A1
EP4283038A1 EP22742663.2A EP22742663A EP4283038A1 EP 4283038 A1 EP4283038 A1 EP 4283038A1 EP 22742663 A EP22742663 A EP 22742663A EP 4283038 A1 EP4283038 A1 EP 4283038A1
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EP
European Patent Office
Prior art keywords
fiber
fiber diameter
fibers
wet
nonwoven fabric
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22742663.2A
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English (en)
French (fr)
Inventor
Kosuke Hamada
Norio Suzuki
Masato Masuda
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Toray Industries Inc
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Toray Industries Inc
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Publication of EP4283038A1 publication Critical patent/EP4283038A1/de
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
    • D21H13/10—Organic non-cellulose fibres
    • D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H13/24—Polyesters
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
    • D04H1/4382—Stretched reticular film fibres; Composite fibres; Mixed fibres; Ultrafine fibres; Fibres for artificial leather
    • D04H1/43835—Mixed fibres, e.g. at least two chemically different fibres or fibre blends
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
    • D04H1/4382—Stretched reticular film fibres; Composite fibres; Mixed fibres; Ultrafine fibres; Fibres for artificial leather
    • D04H1/43825—Composite fibres
    • D04H1/4383—Composite fibres sea-island
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
    • D04H1/4382—Stretched reticular film fibres; Composite fibres; Mixed fibres; Ultrafine fibres; Fibres for artificial leather
    • D04H1/43838—Ultrafine fibres, e.g. microfibres
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
    • D04H1/4391—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece characterised by the shape of the fibres
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
    • D04H1/541—Composite fibres, e.g. sheath-core, sea-island or side-by-side; Mixed fibres
    • D04H1/5412—Composite fibres, e.g. sheath-core, sea-island or side-by-side; Mixed fibres sheath-core
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
    • D04H1/542—Adhesive fibres
    • D04H1/55—Polyesters
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
    • D04H1/72—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged
    • D04H1/732—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged by fluid current, e.g. air-lay
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H15/00—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution
    • D21H15/02—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution characterised by configuration

Definitions

  • the present invention relates to a wet-laid nonwoven fabric sheet including at least three types of thermoplastic fibers having different fiber diameters.
  • Ultrafine fibers in particular, nanofibers having an extremely narrow fiber diameter of 1,000 nm or less, can be processed into a nonwoven fabric sheet having a very dense structure by utilizing morphological features of thin and long fiber materials.
  • a dense structure for example, exhibits high filtration performance by subdividing a fluid flowing in the sheet, or easily exhibits functionality such as easy retention of a functional agent or the like contained therein for a long period of time.
  • each of the ultrafine fibers constituting the sheet may exhibit specific properties that cannot be obtained by general general-purpose fibers or microfibers, that is, excellent adsorption performance and the like due to a so-called nano-size effect and an effect of increasing a specific surface area which is a surface area per weight. Therefore, the nonwoven fabric sheet obtained by processing ultrafine fibers is expected as a highly functional nonwoven fabric sheet.
  • such a wet-laid nonwoven fabric sheet fibers having a large fiber diameter substantially have mechanical properties as a skeleton of the sheet and ensure the handleability and the molding processability of the sheet, and the ultrafine fibers are present in a so-called crosslinked shape using other fibers having a large fiber diameter as a scaffold to play a role of forming a fine space.
  • a wet-laid nonwoven fabric sheet is expected to be developed for applications to a high-performance filter medium, a sound absorption material capable of controlling a sound absorption wavelength, a battery separator, and the like as a sheet satisfying both characteristics derived from ultrafine fibers and mechanical properties.
  • a fine space formed by such ultrafine fibers has more characteristic effect as the denseness and the homogeneity thereof are higher. Therefore, the presence of the fibers constituting the sheet, in particular, the ultrafine fibers, in a three-dimensionally excellent dispersion state is indispensable as a new material that appeals further performance.
  • the dispersibility is improved by applying a dispersant to a fiber surface, but it is difficult to obtain a sufficient dispersibility improvement effect by adding a small amount of the dispersant.
  • Patent Literature 1 proposes a wet-laid nonwoven fabric using liquid-crystalline polymer fibers at least partially fibrillated to a fiber diameter of 1 ⁇ m or less.
  • Patent Literature 2 proposes a wet-laid nonwoven fabric containing fibers having a fiber diameter of 3.0 ⁇ m or less obtained by using split conjugate fibers and splitting the fibers after wet-laid paper making.
  • Patent Literature 3 proposes a wet-laid nonwoven fabric which is made of two or more types of fibers including ultrafine fibers having a fiber length that is less likely to cause aggregation and which is suitable for a filter having excellent trapping efficiency.
  • Patent Literature 1 it is a technical point that fibrillated fibers of 1 ⁇ m or less are generated in a dispersion liquid of liquid-crystalline polymer fibers to form a wet-laid nonwoven fabric, thereby forming a wet-laid nonwoven fabric having a dense structure due to entanglement among the fibrillated fibers or with other fibers without water-dispersing single ultrafine fibers.
  • Such a method is a technique that is also implemented in pulp fibers or the like, but in order to fibrillate the fibers, it is necessary to repeatedly perform a high shear treatment on the fiber dispersion liquid at a high pressure, and as a result, the entanglement of the fibrillated fibers may be unnecessarily promoted, and the denseness and the homogeneity of the fine space may not be controlled.
  • Patent Literature 2 discloses a technique relating to a wet-laid nonwoven fabric in which special split conjugate fibers are used to form a wet-laid nonwoven fabric, followed by being subjected to a heat treatment or a step of applying a physical impact, thereby generating ultrafine fibers by splitting the conjugate fibers and forming a dense structure.
  • the conjugate fibers are surely present in the state of a fiber dispersion liquid, aggregation of the ultrafine fibers in an aqueous medium can be avoided.
  • the fibers present in the wet-laid nonwoven fabric are present in a complicatedly entangled state, it is difficult to evenly divide all of the split conjugate fibers, and as a result, the homogeneity of the fine space in the sheet may not be controlled.
  • Patent Literature 3 it is a technical concept that as a fiber form in which aggregation of ultrafine fibers in water dispersion is unlikely to occur, ultrafine fibers in which a ratio (L/D) of a fiber length (L) to a fiber diameter (D) is reduced are applied to form a wet-laid nonwoven fabric. Therefore, it is an object to prevent aggregation due to unnecessary entanglement among the ultrafine fibers and to uniformize pores appearing on a surface of the wet-laid nonwoven fabric.
  • such a method of providing a limitation on the form of the ultrafine fibers may not be a fundamental solution to implement homogeneous dispersion of the ultrafine fibers, and may not be able to stably form a homogeneous fine space implemented by three-dimensionally and homogeneously dispersing the ultrafine fibers.
  • an object of the present invention is to provide a wet-laid nonwoven fabric sheet in which ultrafine fibers are arranged in a state of being homogeneously dispersed even on a surface of the sheet and in a cross-sectional direction thereof, thereby forming a three-dimensionally homogeneous fine space.
  • a wet-laid nonwoven fabric sheet including: at least three types of thermoplastic fibers having different fiber diameters, in which the wet-laid nonwoven fabric sheet has a fiber diameter ratio (R/r) of a fiber diameter R of a fiber having a maximum fiber diameter to a fiber diameter r of a fiber having a minimum fiber diameter of 30 ⁇ R/r ⁇ 150, an average pore size of 0.10 ⁇ m to 15 ⁇ m, and a maximum frequency of a pore size distribution of 70% or more.2.
  • a textile product at least partially including the wet-laid nonwoven fabric sheet according to any one of 1 to 5.
  • the ultrafine fibers are arranged in a state of being homogeneously dispersed even on a surface of the sheet and in a cross-sectional direction thereof, it is possible to form a three-dimensionally homogeneous fine space.
  • the adsorption performance derived from the specific surface area of the ultrafine fibers and the like can be satisfactorily exhibited in addition to the high functionality due to the three-dimensional and homogeneous formation of the fine space.
  • Such a wet-laid nonwoven fabric sheet is expected to be developed into a high-performance filter medium, a next generation sound absorption material, a battery separator, and the like.
  • a wet-laid nonwoven fabric sheet is a wet-laid nonwoven fabric sheet including at least three types of thermoplastic fibers having different fiber diameters, in which it is required that a fiber diameter ratio (R/r) of a fiber diameter R of a fiber having a maximum fiber diameter to a fiber diameter r of a fiber having a minimum fiber diameter is 30 ⁇ R/r ⁇ 150, an average pore size is 0.10 ⁇ m to 15 ⁇ m, and a maximum frequency of a pore size distribution is 70% or more.
  • a fiber diameter ratio (R/r) of a fiber diameter R of a fiber having a maximum fiber diameter to a fiber diameter r of a fiber having a minimum fiber diameter is 30 ⁇ R/r ⁇ 150
  • an average pore size is 0.10 ⁇ m to 15 ⁇ m
  • a maximum frequency of a pore size distribution is 70% or more.
  • thermoplastic fibers having different fiber diameters refers to a state in which fibers observed on a surface of the wet-laid nonwoven fabric sheet have three or more fiber diameter distributions in a graph in which a horizontal axis represents the fiber diameter and a vertical axis represents the number.
  • a group of fibers having a fiber diameter within a range of each distribution is regarded as one type, and presence of three or more fiber diameter distributions means that three or more types of fibers having different fiber diameters in the present invention are mixed.
  • the distribution width of the fiber diameter as used herein means a range of ⁇ 30% of a peak value having the largest presence number in each fiber diameter distribution.
  • the fiber group may be distinguished by setting a range of ⁇ 10% of the peak value as the distribution width.
  • the fiber diameter distribution is preferably discontinuous and independent, as shown in FIG. 1.
  • FIG. 1 is a diagram showing the case where three fiber diameter distributions are present.
  • a fiber diameter distribution 1 indicates a fiber diameter distribution of a fiber (fiber having a fiber diameter R) having a maximum fiber diameter
  • a fiber diameter distribution 2 indicates a fiber diameter distribution of a fiber having an intermediate fiber diameter
  • a fiber diameter distribution 3 indicates a fiber diameter distribution of a fiber (fiber having a fiber diameter r) having a minimum fiber diameter.
  • the fiber diameter is determined as follows. That is, an image of a surface of the wet-laid nonwoven fabric sheet is captured at a magnification at which 150 to 3,000 fibers can be observed with a scanning electron microscope (SEM). The fiber diameters of 150 fibers randomly extracted from the captured image are measured. For 150 fibers randomly extracted from each image, a fiber width in a direction perpendicular to a fiber axis is measured as the fiber diameter from the two-dimensionally captured image. Regarding a value of the fiber diameter, the measurement is performed up to a second decimal place in units of ⁇ m. The above operation is performed for 10 images captured in the same manner, and the number of the above-described fiber diameter distributions is specified from evaluation results of the 10 images.
  • a value obtained up to a first decimal place by rounding off a second decimal place of a simple number average value of the fiber diameters with respect to the fibers that fall within the distribution width of each fiber diameter distribution is set as the fiber diameter of the fiber in each fiber diameter distribution.
  • the fiber (fiber having the fiber diameter R) having the maximum fiber diameter has mechanical properties as the skeleton of the sheet, and plays a role of ensuring the handleability and the molding processability of the sheet.
  • fibers (fibers having the fiber diameter r) having the minimum fiber diameter that is, fibers such as ultrafine fibers having extremely low rigidity, are arranged in a crosslinked manner using other fibers as a scaffold, form a fine space, and play a role of exhibiting functionality such as adsorption performance derived from the specific surface area.
  • other fibers refers to the fibers having an intermediate fiber diameter other than the fibers having the maximum and minimum fiber diameters among at least three types of fibers constituting the present invention.
  • the other fibers play a role of a scaffold to prevent the fibers having the fiber diameter r from falling off from the sheet, and cause the fibers having the fiber diameter r to be stably present inside the sheet. From the above viewpoints, it is essential that the wet-laid nonwoven fabric sheet according to the present invention includes at least three types of fibers having different fiber diameters.
  • the fibers constituting the wet-laid nonwoven fabric sheet according to the embodiment of the present invention need to be fibers (thermoplastic fibers) using a thermoplastic polymer excellent in mechanical properties and dimensional stability.
  • the thermoplastic polymer may be selected from various polymers depending on the intended use, and for example, may be selected from polymers that may be melt molded such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polylactic acid, thermoplastic polyurethane, and polyphenylene sulfide, and copolymers thereof.
  • the thermoplastic polymer may be selected in consideration of compatibility with an applied environment, and mechanical properties, heat resistance, chemical resistance, and the like that are finally required.
  • the polymers may contain inorganic materials such as titanium oxide, silica, and barium oxide, colorants such as carbon black, a dye, and a pigment, various additives such as a flame retardant, a fluorescence brightening agent, an antioxidant, and an ultraviolet absorbing agent as long as the object of the present invention is not impaired.
  • the fibers (hereinafter, also simply referred to as "ultrafine fibers") having the fiber diameter r for implementing the wet-laid nonwoven fabric sheet according to the embodiment of the present invention are particularly preferably polyester fibers among the polymers described above, in consideration of ensuring dispersibility in an aqueous medium, which is important for enabling three-dimensionally homogeneous presence in the sheet. The reason will be described in detail below.
  • the reason why the homogeneous dispersion of the ultrafine fibers in the aqueous medium is inhibited is an attraction force acting among the ultrafine fibers, and in the related art, a method of providing a limitation on the form of the ultrafine fibers has been adopted. However, such a technique may not be a fundamental solution to implement homogeneous dispersion of the ultrafine fibers.
  • the ultrafine fibers have a certain amount or more of carboxyl groups, so that the ultrafine fibers are negatively charged in the aqueous medium, and an electric repulsive force acts. Therefore, the dispersibility and the dispersion stability of the ultrafine fibers in the medium may be dramatically improved.
  • the ultrafine fiber used in the wet-laid nonwoven fabric sheet according to the embodiment of the present invention preferably has a carboxyl terminal group amount of 40 eq/ton or more. Accordingly, it is easy to ensure extremely high dispersibility regardless of the specification such as the aspect ratio, which is greatly restricted in the related art. That is, in the aqueous medium, electrical repulsive forces derived from a carboxyl group act among an infinite number of ultrafine fibers and repel one another, thereby enabling the ultrafine fibers to continue to float in the aqueous medium without aggregating with one another and ensuring the dispersion stability for a long period of time.
  • the ultrafine fibers are preferably made of a polymer having a high elastic modulus, that is, excellent rigidity, and are preferably polyester from this viewpoint.
  • polyester fibers as the ultrafine fibers
  • plastic deformation when deformation due to an external force is applied can be reduced. Accordingly, in a manufacturing step and a textile processing process of the wet-laid nonwoven fabric sheet according to the embodiment of the present invention, an effect of reducing unnecessary entanglement between fibers is exerted, the sheet may be processed while maintaining the dispersibility of the fibers, and a sheet in which ultrafine fibers are three-dimensionally and homogeneously arranged can be obtained.
  • polyester as used herein is made of a polyester such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, or polytrimethylene terephthalate, or a copolymer thereof, and is exemplified as a preferable example of the polymer in the implementation of the present invention.
  • the fibers having the fiber diameter R and the fibers having the intermediate fiber diameter are also polyester fibers in order not to unnecessarily impair the dispersibility of the ultrafine fibers in a paper making stock solution.
  • the fiber diameter ratio (R/r) between the fiber diameter R of the fiber having the maximum fiber diameter and the fiber diameter r of the fiber having the minimum fiber diameter is required to be in the range of 30 ⁇ R/r ⁇ 150.
  • the function of each fiber in accordance with the fiber diameter may be insufficient.
  • the fiber diameter R is small, the rigidity of the sheet is likely to be insufficient, which may cause a decrease in handleability and molding processability of the sheet, and in the case where the fiber diameter r is large, the specific performance derived from the ultrafine fiber may not be exhibited.
  • a lower limit of the fiber diameter ratio R/r is set to 30.
  • an upper limit of the fiber diameter ratio R/r is set to 150. From the above viewpoints, it is necessary that the fiber diameter ratio R/r is within the above range in the present invention, but in view of the point of more satisfactorily implementing the objective effect of the present invention, the fiber diameter ratio R/r is more preferably 30 ⁇ R/r ⁇ 100. Within such a range, it acts more effectively on the three-dimensional homogeneity of the fine space formed by the ultrafine fibers.
  • the present invention is directed to a wet-laid nonwoven fabric sheet intended for a highly functional material that appeals a specific surface area produced by ultrafine fibers and filtration or adsorption utilizing a fine space in the sheet, and in the embodiment of the present invention, it is important that an average pore size is 0.10 ⁇ m to 15 ⁇ m and a maximum frequency of a pore size distribution is 70% or more.
  • the pore size as used herein refers to a value calculated by a bubble point method.
  • the bubble point method for example, measurement by a porous material automatic pore measurement system Perm-Porometer (manufactured by PMI) can be used.
  • the Perm-Porometer In the measurement by the Perm-Porometer, the wet-laid nonwoven fabric sheet is immersed in a liquid having a known surface tension value and is supplied from an upper side of the sheet while increasing a pressure of a gas, and the pore size is measured based on a relationship between the pressure and the liquid surface tension on the surface of the wet-laid nonwoven fabric sheet.
  • the pore size can be calculated under the following conditions using a porous material automatic pore measurement system Perm-Porometer (manufactured by PMI).
  • An average flow rate diameter obtained by automatic calculation by pore size distribution measurement in which a measurement sample diameter is set to 25 mm and Galwick (surface tension: 16 mN/m) is used as a measurement solution having a known surface tension is set to an average pore size, and a value obtained by rounding off a second decimal place to a first decimal place is used.
  • the pore size frequency is expressed in % by converting the value obtained by the automatic calculation into a percentage, and a value obtained by rounding off a second decimal place to a first decimal place is used.
  • FIG. 2 shows an example of a pore size distribution (vertical axis: frequency, horizontal axis: pore size) of a wet-laid nonwoven fabric sheet in which a homogeneous fine space is formed
  • FIG. 2 shows an example of a pore size distribution when a heterogeneous fine space is formed.
  • the pore size distribution becomes sharp, and the frequency at a specific pore size becomes significantly large ((a) of FIG. 2 ).
  • the pore size distribution is broad ((b) of FIG. 2 ). Accordingly, the homogeneity of the fine space can be evaluated.
  • the average pore size in the embodiment of the present invention is an average size of through-holes formed in the wet-laid nonwoven fabric sheet, and serves as an index of the denseness of the fine space in the sheet.
  • the maximum frequency of the pore size distribution is an index of the homogeneity of the fine space in the sheet. That is, in the case where the average pore size is relatively small and the maximum frequency of the pore size distribution is relatively large, it means that the sheet is a sheet in which a densified fine space is homogeneously present.
  • the fluid uniformly flows into the entire sheet without disturbing the flow of the fluid passing through the wet-laid nonwoven fabric sheet. Accordingly, a wet-laid nonwoven fabric sheet which is expected to effectively exhibit excellent performance such as filtration performance and sound absorption performance is obtained.
  • the average pore size is set to 0.10 ⁇ m to 15 ⁇ m, so that the performance corresponding to the intended use can be exhibited without inhibiting the flow of the fluid.
  • the inhibition of the flow of the fluid as used herein is caused by an extreme increase in pressure loss as the average pore size becomes smaller. Therefore, a lower limit of the average pore size is set to 0.10 ⁇ m from the viewpoint of ensuring a stable fluid flow.
  • an upper limit of the average pore size is 15 ⁇ m from the viewpoint that the specific performance depending on the fine space effectively acts.
  • the maximum frequency of the pore size distribution is within the above range.
  • Such a sheet structure is implemented by forming a complicated space in which ultrafine fibers are uniformly present not only in a planar direction of the sheet but also in a thickness direction thereof.
  • the fine space is homogeneously present in this way, so that the fluid uniformly flows into the entire sheet, and the filtration performance, the sound absorption performance, the adsorption performance, and the like can be satisfactorily exhibited. Therefore, the maximum frequency of the pore size distribution is 70% or more, preferably 80% or more, and more preferably 90% or more.
  • the wet-laid nonwoven fabric sheet according to the embodiment of the present invention which satisfies the above requirements, is directed to a sheet in which a dense and homogeneous fine space is formed by the presence of ultrafine fibers having functionality in a good dispersion state.
  • the adsorption performance derived from the nano-size effect of the ultrafine fibers can be satisfactorily exhibited. Accordingly, it is expected to be developed into a high-performance filter medium, a next generation sound absorption material, a battery separator, and the like.
  • the fiber diameter r of the fiber having the minimum fiber diameter is preferably 0.10 ⁇ m to 1.0 ⁇ m.
  • the present invention is directed to a wet-laid nonwoven fabric sheet for implementing a highly functional material that appeals filtration, adsorption, and the like utilizing a specific surface area, in addition to a dense fine space due to the presence of ultrafine fibers.
  • the fiber diameter r is preferably 0.10 ⁇ m to 1.0 ⁇ m. Within such a range, densification of a fine space in the sheet is promoted, and a specific surface area effect produced by the ultrafine fibers can be predominantly exhibited, and exhibition of excellent performance can be expected.
  • a substantial lower limit of the fiber diameter r is 0.10 ⁇ m in the embodiment of the present invention.
  • an upper limit of the fiber diameter r is set to 1.0 ⁇ m as a range in which the specific surface area effect with respect to general fibers is predominantly exerted.
  • the fiber diameter R of the fiber having the maximum fiber diameter is preferably 3.0 ⁇ m to 50 ⁇ m from the viewpoint of ensuring the strength of the sheet, and more preferably 5.0 ⁇ m to 30 ⁇ m as a range in which the handleability and the molding processability of the sheet are favorably exhibited.
  • the fiber diameter of the fiber having an intermediate fiber diameter is preferably from 1.0 ⁇ m to 20 ⁇ m. Within such a range, it is easy to effectively act as a scaffold of ultrafine fibers, and it is possible to form a three-dimensionally homogeneous fine space.
  • a porosity is preferably 70% or more from the viewpoint of efficiently exhibiting the effect of a fine space.
  • the porosity as used herein is determined as follows. That is, a value obtained by rounding off a first decimal place of a value calculated by the following equation from a basis weight and a thickness of the wet-laid nonwoven fabric sheet to an integer value is defined as the porosity.
  • a fiber density may be a density of the constituent fibers, and is calculated as 1.38 g/cm 3 in the case of polyethylene terephthalate (PET).
  • PET polyethylene terephthalate
  • a weight of a fiber sheet cut out into a 250 mm ⁇ 250 mm square is weighed out, and a first decimal place of a value converted into a weight per unit area (1 m 2 ) is rounded off to an integer value, which is defined as the basis weight of the wet-laid nonwoven fabric sheet.
  • the thickness of the wet-laid nonwoven fabric sheet is measured in units of mm using a dial thickness gauge (SM-114 manufactured by TECLOCK Co., Ltd., probe shape: 10 mm diameter, scale interval: 0.01 mm, measuring force: 2.5 N or less). The measurement is performed at any five positions per one sample, and a value obtained by rounding off a third decimal point of an average thereof to a second decimal point is defined as the thickness of the wet-laid nonwoven fabric sheet.
  • SM-114 manufactured by TECLOCK Co., Ltd.
  • the porosity is preferably 70% or more is exemplified.
  • the porosity of the wet-laid nonwoven fabric sheet according to the embodiment of the present invention is more preferably 80% or more is exemplified.
  • Such a porosity inside the sheet can be implemented by appropriately adjusting the thickness and the basis weight of the sheet on the premise that the fibers constituting the sheet are present in a dispersed state. At this time, in the case where the basis weight of the sheet is extremely decreased, it is difficult to form a fine space having an intended size, and a strength of the sheet becomes too low, which may result in an inappropriate sheet for practical use.
  • the through-holes formed by a three-dimensional fine space can be densified by accumulating more fibers, but in the case where the basis weight is extremely increased, the rigidity of the sheet is excessively increased, and the handleability and the molding processability of the sheet may be deteriorated.
  • the wet-laid nonwoven fabric sheet according to the embodiment of the present invention preferably has a basis weight of 10 g/m 2 to 500 g/m 2 because the fibers are stably and homogeneously present without impairing the objective effect of the present invention.
  • the ratio (L/r) of the fiber length L of the fiber having the minimum fiber diameter to the fiber diameter r of the fiber having the minimum fiber diameter is preferably 3,000 to 6,000.
  • the fiber length L as used herein can be determined as follows. An image of the surface of the wet-laid nonwoven fabric sheet is captured with a microscope at a magnification at which 10 to 100 fibers having the fiber diameter r of which the entire length can be measured can be observed. The fiber lengths of 10 fibers having the fiber diameter r randomly extracted from each captured image are measured.
  • the term "fiber length” as used herein refers to a length of a single fiber in a fiber longitudinal direction from an image captured two-dimensionally, which is measured up to a second decimal place in units of mm, and the decimal place is rounded off. The above operation is performed for 10 images captured in the same manner, and a simple number average value of an evaluation result of the 10 images is defined as the fiber length L.
  • the case where the ratio (L/r) is 3,000 to 6,000 is preferable from the viewpoint of exhibiting an excellent reinforcing effect because the number of contact points among the fibers can be increased, thereby reducing falling-off of the fibers and promoting formation of a crosslinking structure which is important for forming a fine space.
  • the upper limit is set to 6,000 as a range in which the reinforcing effect by the fiber length can be sufficiently exhibited, in addition to the specific surface area effect without the entanglement among the fibers.
  • the ratio (L/r) is relatively smaller, it is more advantageous from the viewpoint of the handleability in the wet-laid paper making step.
  • the ratio is excessively small, the specific effect exhibited as a sheet may be relatively small, and the lower limit is set to 3,000 as a range in which the fiber can pass through the molding step without causing any problem such as falling-off of the fiber.
  • a specific tensile strength of the wet-laid nonwoven fabric sheet is preferably 5.0 Nm/g or more.
  • the specific tensile strength is preferably 15 Nm/g or less.
  • test pieces each having a width of 15 mm and a length of 50 mm were taken and subjected to a tensile test in accordance with JIS P8113:2006 using a tensile tester Tensilon UCT-100 manufactured by ORIENTEC CO., LTD. to measure the tensile strength of the wet-laid nonwoven fabric sheet.
  • This operation is repeated five times, and a value obtained by rounding off a third decimal place of the simple average value of the obtained result is defined as the tensile strength of the wet-laid nonwoven fabric sheet, and a value divided by the basis weight is defined as the specific tensile strength.
  • a mixing ratio in a fiber weight of each of the fibers constituting the wet-laid nonwoven fabric sheet according to the embodiment of the present invention is not particularly limited, but it is preferable that the fiber having the fiber diameter r is 2.5 wt% to 30 wt% and the fiber having the fiber diameter R is 15 wt% to 85 wt% from the viewpoint of forming a stable fine space and ensuring the strength of the wet-laid nonwoven fabric sheet.
  • the wet-laid nonwoven fabric sheet in which fibers are mixed within such a range is likely to be a sheet that exhibits good handleability and molding processability, and that is suitable for practical use.
  • binder fibers may be mixed as necessary for the purpose of improving the sheet strength and preventing the constituent fibers from falling off.
  • the fibers constituting the sheet may be physically bonded to one another, and the sheet strength can be improved.
  • the fine space may be blocked by melting or the fine space may be significantly reduced to inhibit the fluid flow.
  • a molding processing defect caused by the rigidity of the sheet that is increased more than necessary may occur.
  • the mixing ratio of the binder fibers is preferably within the range of 5 wt% to 75 wt%. From the viewpoint of ensuring the adhesiveness among fibers in the sheet, a substantial lower limit of a blending ratio of the binder fibers is 5 wt%.
  • the binder fiber as used herein is not particularly limited, but is preferably, for example, a core-sheath conjugate fiber in which a polymer having a melting point of 150°C or lower is arranged in a sheath.
  • the wet-laid nonwoven fabric sheet is subjected to a drying step using a yankee dryer, an air-through dryer, or the like, or a heat treatment step using a calendar or the like, so that a sheath component on the surface of the binder fiber melts and adheres to other fibers, thereby increasing the rigidity of the fiber sheet.
  • fibers of a remaining core component can ensure the sheet strength as the fiber having the fiber diameter R in accordance with the fiber diameter and play a role of a scaffold as the fiber having an intermediate fiber diameter.
  • the core-sheath conjugate fiber as described above is preferable. It is preferable that a melting point of the core component of the binder fiber is higher than a melting point of the sheath component and a difference in melting point therebetween is 20°C or higher from the viewpoint of implementing sufficient thermal adhesiveness and high rigidity because the sheath component on the surface of the binder fiber is likely to be sufficiently melted, and a decrease width in orientation of the core component is reduced.
  • a fiber having a maximum fiber diameter, a fiber having an intermediate fiber diameter, and a short fiber such as a thermally-fusible core-sheath conjugate fiber (binder fiber) of which a sheath component is made of a low-melting-point polymer are put into water, followed by being stirred in a disintegrator to prepare a fiber dispersion liquid in which the fibers are uniformly dispersed.
  • a core component remains in the sheet after thermal fusion, and thus the core-sheath conjugate fiber may be used as a fiber that plays a role of either the fiber having a maximum fiber diameter or the fiber having an intermediate fiber diameter.
  • this preparation step it is possible to adjust the dispersibility by the charged amount of the fibers, the amount of the aqueous medium, the stirring time, and the like, and it is preferable that the short fibers are dispersed as uniformly as possible in the aqueous medium.
  • a dispersant may be added in order to improve the dispersibility in water, but in the case where the wet-laid nonwoven fabric is subjected to post-processing, the addition amount of the dispersant is preferably limited to a necessary minimum limit so as not to affect the processability.
  • an ultrafine fiber dispersion liquid in which ultrafine fibers are uniformly dispersed in an aqueous medium is prepared in accordance with a step to be described later.
  • the ultrafine fiber dispersion liquid and the above-described fiber dispersion liquid are mixed to prepare a paper making stock solution, followed by being subjected to wet-laid paper making to thereby obtain a wet-laid nonwoven fabric sheet in which the ultrafine fibers are uniformly arranged.
  • the ultrafine fibers as used herein are preferably made of polyester having a carboxyl terminal group amount of 40 eq/ton or more from the viewpoint of ensuring the water dispersibility, and can be produced using a sea-island fiber made of two or more types of polymers having different dissolution rates in a solvent.
  • the sea-island fiber refers to a fiber having a structure in which an island component made of a hardly soluble polymer is scattered in a sea component made of an easily soluble polymer.
  • sea-island conjugate spinning by melt spinning is preferable from the viewpoint of improving productivity, and a method using a sea-island conjugate spinneret is preferable from the viewpoint of excellent control on the fiber diameter and the cross-sectional shape.
  • a reason of using a method according to the melt spinning is that the productivity is high and continuous production is possible.
  • a so-called sea-island conjugate cross section can be stably formed.
  • the polymers are preferably selected in a combination such that a melt viscosity ratio ( ⁇ B/ ⁇ A) of a melt viscosity ⁇ B of a polymer B to a melt density ⁇ A of a polymer A is within the range of 0.1 to 5.0.
  • the melt viscosity as used herein refers to a melt viscosity that can be measured by a capillary rheometer using a chip-shaped polymer having a moisture content of 200 ppm or less by a vacuum dryer, and refers to a melt viscosity at the same shear rate at a spinning temperature.
  • the easily soluble polymer of the sea-island fiber as used herein is selected from, for example, melt-formable polymers such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polylactic acid, thermoplastic polyurethane, and polyphenylene sulfide, and copolymers thereof.
  • melt-formable polymers such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polylactic acid, thermoplastic polyurethane, and polyphenylene sulfide, and copolymers thereof.
  • the sea component is preferably a copolymerized polyester, polylactic acid, polyvinyl alcohol, or the like that exhibits easy elution in an aqueous solvent, hot water, or the like from the viewpoint of simplifying an elution step of the sea component, and is particularly preferably polyester or polylactic acid in which polyethylene glycol or sodium sulfoisophthalic acid is copolymerized alone or in combination from the viewpoint of the handleability and easy solubility in an aqueous solvent having a low concentration.
  • easily soluble as used herein means that a dissolution rate ratio (easily soluble polymer/hardly soluble polymer) is 100 or more based on the hardly soluble polymer with respect to the solvent used for the dissolution treatment.
  • the dissolution rate ratio is preferably large, and the dissolution rate ratio is preferably 1,000 or more, more preferably 10,000 or more. Within such a range, the dissolution treatment can be completed in a short period of time, and thus the ultrafine fiber suitable for the present invention can be obtained without unnecessarily deteriorating the hardly soluble component.
  • polylactic acid polyester obtained by copolymerizing 3 mol% to 20 mol% of 5-sodium sulfoisophthalic acid, and polyester obtained by copolymerizing 5 wt% to 15 wt% of polyethylene glycol having a weight-average molecular weight of 500 to 3,000 in addition to the above-described 5-sodium sulfoisophthalic acid are particularly preferable from the viewpoint of the solubility in an aqueous solvent and simplification of waste liquid treatment generated during dissolution.
  • examples of a suitable combination of polymers of the sea-island fiber include one or more selected from the group consisting of polylactic acid and polyester in which 3 mol% to 20 mol% of 5-sodium sulfoisophthalic acid is copolymerized and 5 wt% to 15 wt% of polyethylene glycol having a weight-average molecular weight of 500 to 3,000 is copolymerized, as sea components, and one or more selected from the group consisting of polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and copolymers thereof, as island components.
  • a spinning temperature of the sea-island fiber is preferably a temperature at which a polymer having a high melting point and a high viscosity mainly exhibits fluidity among the polymers to be used determined from the above-described viewpoints.
  • the temperature at which the polymer exhibits fluidity depends on the properties of the polymer and the molecular weight thereof, but the melting point of the polymer serves as a criterion, and the temperature may be set to the melting point +60°C or lower. At this temperature, the polymer is not thermally decomposed in a spinning head or a spinning pack, a decrease in molecular weight is prevented, and the sea-island fiber can be favorably produced.
  • a melted and discharged yarn is cooled and solidified, is converged by applying an oil agent or the like, and is taken up by a roller whose peripheral speed is regulated.
  • the take-up speed is determined, for example, based on the discharge amount and the target fiber diameter.
  • the take-up speed is preferably 100 m/min to 7,000 m/min from the viewpoint of stably producing the sea-island fiber.
  • the spun sea-island fibers are preferably drawn, and the spun multifilament may be drawn after being once wound, or may be drawn following spinning without being wound.
  • the sea-island fibers are preferably bundled in units of several tens to several millions and subjected to cutting processing to a desired fiber length using a cutting machine such as a guillotine cutter, a slicing machine, or a cryostat.
  • the fiber length L at this time is preferably cut such that the ratio (L/r) with respect to an island component diameter (corresponding to the fiber diameter r) is within the range of 3,000 to 6,000. Within such a range, the number of contact points among fibers increases at the time of forming a wet-laid nonwoven fabric sheet, and formation of a crosslinking structure is promoted, and thus the reinforcing effect of the sheet can be enhanced.
  • the island component diameter as used herein is substantially equal to the fiber diameter of the ultrafine fibers, and is determined as follows.
  • the sea-island conjugate fiber is embedded in an embedding agent such as an epoxy resin, and an image of a cross section thereof is captured at a magnification at which 150 or more island components can be observed with a transmission electron microscope (TEM).
  • TEM transmission electron microscope
  • 150 or more island components are not arranged in one filament, a cross section of fibers of several filaments may be captured to observe 150 or more island components in total.
  • metal dyeing is performed, a contrast of the island components can be made clear.
  • the island component diameter of 150 island components randomly extracted from each captured image of the fiber cross section is measured.
  • the island component diameter as used herein refers to a diameter of a perfect circle circumscribing a cutting surface in a direction perpendicular to a fiber axis from a two-dimensionally captured image.
  • a homogeneous dispersion liquid of ultrafine fibers can be produced by dissolving and removing the sea components from the sea-island fibers obtained as described above.
  • the sea-island fibers after the above-described cutting processing may be immersed in a solvent or the like capable of dissolving the easily soluble component (sea component) to remove the easily soluble component.
  • the easily soluble component is one or more components selected from the group consisting of polylactic acid and copolymerized polyethylene terephthalate obtained by copolymerizing 5-sodium sulfoisophthalic acid, polyethylene glycol, or the like
  • an alkaline aqueous solution such as an aqueous solution of sodium hydroxide can be used.
  • a bath ratio (sea-island fiber weight (g)/alkaline aqueous solution weight (g)) of the sea-island fiber to the alkaline aqueous solution is preferably 1/10,000 to 1/5, more preferably 1/5,000 to 1/10. Within this range, it is possible to prevent the ultrafine fibers from being unnecessarily entangled with one another at the time of dissolving the sea component.
  • an alkali concentration of the alkaline aqueous solution is preferably 0.1 wt% to 5 wt%, more preferably 0.5 wt% to 3 wt%.
  • a temperature of the alkaline aqueous solution is not particularly limited, but is preferably, for example, 50°C or higher because the progress of dissolution of the sea component can be accelerated.
  • a fiber in which an easily soluble component (sea component) is dissolved from a sea-island fiber may be used as it is, or ultrafine fibers may be separated once by filtration or the like, washed with water, freeze-dried, and then dispersed again in an aqueous medium to form a sheet.
  • an acid or an alkali may be added, thereby adjusting the PH of the medium, or the medium may be diluted with water.
  • the ultrafine fiber dispersion liquid may contain a dispersant as necessary.
  • Examples of the type of the dispersant include natural polymers, synthetic polymers, organic compounds, and inorganic compounds.
  • Examples of an additive for preventing aggregation of fibers include a cationic compound, a nonionic compound, and an anionic compound.
  • the addition amount of the dispersant is preferably 0.001 equivalent to 10 equivalent with respect to the ultrafine fibers, and within such a range, the dispersibility of the ultrafine fibers is easily secured without impairing processability of wet-laid paper making.
  • the ultrafine fiber dispersion liquid prepared as described above is mixed with the fiber dispersion liquid prepared as described above, diluted and adjusted to a certain concentration, followed by being dehydrated with a tilted wire, a circular net, or the like to form a wet-laid nonwoven fabric sheet.
  • the device used for paper making include a cylinder paper machine, a fourdrinier paper machine, an inclination type tanmo machine, and a paper machine in which the above machines are combined.
  • the paper making speed, the amount of the fibers, and the amount of the aqueous medium in addition to the dispersibility of the fibers in the paper making stock solution can be adjusted to control the accumulation of the fibers at the time of filtering , thereby producing a three-dimensionally homogeneous sheet.
  • the fiber length of the constituent fibers is preferably 30.0 mm or less. Within such a range, a wet-laid nonwoven fabric sheet having practical homogeneity can be formed as a highly functional sheet. In the case where the fiber length exceeds 30.0 mm, the fibers may be strongly entangled with one another during dispersion in the aqueous medium, a fiber mass may be formed, and it tends to be difficult to form a homogeneous sheet.
  • the sheet formed by wet-laid paper making passes through a drying step in order to remove moisture.
  • a drying method a method using hot air ventilation (air-through) or a method of bringing the sheet into contact with a thermal rotation roll (thermal calendar roll or the like) is preferable from the viewpoint of simultaneously performing the drying of the sheet and the thermal adhesion of the binder fibers.
  • the basis weight and the thickness of the wet-laid nonwoven fabric may be appropriately changed according to a supply amount of the paper making stock solution and the paper making speed in the wet-laid paper making step.
  • the thickness of the wet-laid nonwoven fabric sheet according to the embodiment of the present invention is not particularly limited, but is preferably 0.050 mm to 2.50 mm. In particular, the thickness is preferably 0.10 mm or more from the viewpoint of being able to obtain excellent sheet molding processability.
  • the wet-laid nonwoven fabric sheet satisfying the above requirements can satisfactorily exhibit the adsorption performance and the like derived from a specific surface area of the ultrafine fibers, and in addition, can implement high filtration performance and the like by three-dimensionally and homogeneously forming a fine space because the respective fibers constituting the sheet are present in a homogeneously dispersed state. Therefore, the wet-laid nonwoven fabric sheet according to the present invention can be expected as a material that can be developed into a high-functional filter medium, a next generation sound absorption material, a battery separator, or the like. A textile product at least partially including the wet-laid nonwoven fabric sheet may be suitably used for such applications.
  • a moisture content of a chip-shaped polymer was set to 200 ppm or less using a vacuum dryer, and melt viscosity was measured by changing a strain rate in a stepwise manner by Capillograph 1B manufactured by Toyo Seiki Seisakusho Co., Ltd.
  • a measurement temperature was the same as a spinning temperature, and in Examples and Comparative Examples, a melt viscosity of 1,216 s -1 is described. The measurement was performed under a nitrogen atmosphere setting the time when a sample was put into a heating furnace to the time when the measurement was started to 5 minutes.
  • a moisture content of a chip-shaped polymer was set to 200 ppm or less using a vacuum dryer, about 5 mg of the chip-shaped polymer was weighed out, and DSC measurement was performed using a differential scanning calorimetry (DSC) Q2000 manufactured by TA Instruments at a heating rate of 16°C/min from 0°C to 300°C and then holding the temperature at 300°C for 5 minutes.
  • DSC differential scanning calorimetry
  • a melting point was calculated from a melting peak observed during the heating process. The measurement was performed three times for each sample, and an average value thereof was defined as the melting point. In the case where a plurality of melting peaks were observed, a melting peak top on the highest temperature side was defined as the melting point.
  • An image of a surface of the wet-laid nonwoven fabric sheet was captured with a scanning electron microscope (SEM) at a magnification at which 150 to 3,000 fibers can be observed, and a fiber diameter of 150 fibers randomly extracted from the captured image was measured.
  • a fiber diameter was measured by using a fiber width in a direction perpendicular to a fiber axis from the two-dimensional image as the fiber diameter.
  • a value of the fiber diameter was measured up to a second decimal place in units of ⁇ m. The above operation was performed for 10 images captured in the same manner, and the number of fiber diameter distributions was specified from evaluation results of the 10 images.
  • fiber length refers to a length of a single fiber in a fiber longitudinal direction from the two-dimensionally captured image, and is measured up to a third decimal place in units of mm, and a second decimal place is rounded off. The above operation was performed for 10 images captured in the same manner, and a simple number average value of evaluation results of the 10 images was defined as the fiber length.
  • a pore size was calculated by a bubble point method (based on ASTM F-316-86) using a porous material automatic pore measurement system Perm-Porometer (manufactured by PMI).
  • An average flow rate diameter obtained by automatic calculation by fine pore size distribution measurement in which a measurement sample diameter was set to 25 mm and Galwick (surface tension: 16 mN/m) was used as a measurement solution having a known surface tension was set to an average pore size, and a value obtained by rounding off a second decimal place to a first decimal place was used.
  • a pore size frequency was expressed in % by converting a value obtained by automatic calculation into a percentage, and a value obtained by rounding off a second decimal place to a first decimal place was used.
  • a weight of a fiber sheet cut out into a 250 mm ⁇ 250 mm square was weighed out, and a first decimal place of a value converted into a weight per unit area (1 m 2 ) was rounded off to an integer value, which was defined as a basis weight of the wet-laid nonwoven fabric sheet.
  • a thickness of the wet-laid nonwoven fabric sheet was measured in units of mm using a dial thickness gauge (SM-114 manufactured by TECLOCK Co., Ltd., probe shape: 10 mm diameter, scale interval: 0.01 mm, measuring force: 2.5 N or less). The measurement was performed at random five points per one sample, and a value obtained by rounding off a third decimal place of an average thereof to a second decimal place was defined as a thickness of the wet-laid nonwoven fabric sheet.
  • SM-114 manufactured by TECLOCK Co., Ltd.
  • a value obtained by rounding off a first decimal place of a value calculated by the following equation based on the basis weight and the thickness of the wet-laid nonwoven fabric sheet to an integer value was defined as the porosity.
  • Porosity % 100 ⁇ basis weight / thickness ⁇ fiber density ⁇ 100
  • the fiber density may be a density of the constituent fibers, and was calculated as 1.38 g/cm 3 in the case of PET.
  • test pieces each having a width of 15 mm and a length of 50 mm were taken and subjected to a tensile test in accordance with JIS P8113:2006 using a tensile tester Tensilon UCT-100 manufactured by ORIENTEC CO., LTD. to measure a tensile strength of the wet-laid nonwoven fabric sheet.
  • This operation was repeated five times, a value obtained by rounding off a third decimal place of a simple average value of the obtained results was defined as the tensile strength of the wet-laid nonwoven fabric sheet, and a value divided by the basis weight was defined as the specific tensile strength.
  • polyethylene terephthalate PET1, melt viscosity: 160 Pa s, carboxyl terminal group amount: 40 eq/ton
  • PET1 melt viscosity: 160 Pa s
  • carboxyl terminal group amount: 40 eq/ton a sea component
  • polyethylene terephthalate copolymerized PET, melt viscosity: 121 Pa s
  • melt viscosity ratio: 1.3, dissolution rate ratio: 30,000 or more obtained by copolymerizing 8.0 mol% of 5-sodium sulfoisophthalic acid and 10 wt% of polyethylene glycol having a molecular weight of 1,000 was used, and a yarn melted and discharged at a sea component/island component composite ratio of 50/50 was cooled and solidified using a sea-island conjugate spinneret (number of islands: 2,000) in which a shape of the island component was a circle.
  • sea-island conjugate spinneret number of islands: 2,000
  • the sea-island fiber had mechanical properties sufficient for cutting processing such as a strength of 2.4 cN/dtex and an elongation of 36%, and cutting processing was performed such that the fiber length was 0.6 mm.
  • the sea-island fiber was treated with a 1 wt% aqueous solution of sodium hydroxide (bath ratio: 1/100) heated to 90°C, thereby obtaining an ultrafine fiber dispersion liquid.
  • a fiber dispersion liquid was prepared by adjusting a mixing ratio of cut fibers of thermally fusible core-sheath conjugate fibers (fiber diameter of core component: 10 ⁇ m, fiber length: 5.0 mm) as a skeleton of the sheet and the binder fiber to 30 wt% and a mixing ratio of cut fibers of PET (fiber diameter: 4 ⁇ m, fiber length: 3.0 mm) serving as a scaffold of ultrafine fibers to 65 wt% and uniformly mixing and dispersing the cut fibers with water by a disintegrator.
  • the core-sheath conjugate fiber configurations of a core component and a sheath component were as follows.
  • the above-described ultrafine fiber dispersion liquid was homogeneously mixed with the fiber dispersion liquid such that the mixing ratio of the ultrafine fibers was 5 wt%, thereby preparing a paper making stock solution.
  • the paper making stock solution was made into paper using a square sheet machine (250 mm square) manufactured by Kumagai Riki Kogyo Co., Ltd, followed by being dried and thermally treated in a rotary dryer in which a roller temperature was set to 110°C to thereby obtain a wet-laid nonwoven fabric sheet.
  • the obtained wet-laid nonwoven fabric sheet was a sheet in which the ultrafine fibers were present in a crosslinked shape using other fibers having a large fiber diameter as a scaffold, and had a fiber diameter ratio R/r of 50, a basis weight of 25 g/m 2 , a thickness of 0.09 mm, and a porosity of 79.9%.
  • the obtained wet-laid nonwoven fabric sheet was a sheet in which an average pore size calculated by a bubble point method was 4.9 ⁇ m, a maximum frequency of the pore size distribution was 91.6%, and a fine dense space was formed very homogeneously.
  • the specific tensile strength thereof was 6.7 Nm/g, and the handleability and the molding processability were favorable by the reinforcing effect due to the entanglement of the ultrafine fibers.
  • Example 1 The procedure of Example 1 was performed except that the mixing ratio of the ultrafine fibers was changed in a stepwise manner to perform wet-laid paper making.
  • the wet-laid nonwoven fabric sheet was a sheet in which the maximum frequency of the pore size distribution was 80% or more and a very homogeneous fine space was formed.
  • Example 3 The procedure of Example 3 was performed except that the basis weight of the sheet was 150 g/m 2 .
  • the sheet was a wet-laid nonwoven fabric sheet in which even when the basis weight of the sheet was increased, a three-dimensionally homogeneous sheet structure was formed, the average pore size was 0.8 ⁇ m, and a very dense fine space was stably formed.
  • Example 1 The procedure of Example 1 was performed except that as the fibers having an intermediate fiber diameter, cut fibers having a fiber diameter of 4 ⁇ m and a fiber length of 3.0 mm were mixed at a mixing ratio of 62.5 wt% and cut fibers of PET having a fiber diameter of 0.6 ⁇ m and a fiber length of 0.6 mm were mixed at a mixing ratio of 2.5 wt% to thereby form a sheet with four types of fibers having different fiber diameters.
  • the sheet was a sheet in which a homogeneous fine space was formed even when the sheet was made of four types of fibers having different fiber diameters.
  • Example 8 was carried out in accordance with Example 1 except that the fiber diameter of the ultrafine fibers was changed to 0.3 ⁇ m.
  • Example 9 was carried out in accordance with Example 8 except that the mixing ratio of the ultrafine fibers was changed to 10 wt%.
  • Examples 10 to 13 were carried out in accordance with Example 9 except that the basis weight of the sheet was changed to 12.5 g/m 2 , 50 g/m 2 , 100 g/m 2 , and 300 g/m 2 , respectively.
  • Examples 14 to 16 were carried out in accordance with Example 8 except that the mixing ratio of the fiber having the fiber diameter R was changed to 15 wt%, 45 wt%, and 75 wt%, respectively.
  • Examples 17 and 18 were carried out in accordance with Example 1 except that the fiber diameter R was changed to 15 ⁇ m and 20 ⁇ m, respectively.
  • the wet-laid nonwoven fabric sheet had a homogeneous fine space without inhibiting uniformly accumulation of the fibers in the wet-laid paper making step.
  • the fiber having the fiber diameter R was responsible for the mechanical properties of the sheet, the specific tensile strength of the obtained sheet was improved as compared with Example 1.
  • Example 1 The procedure of Example 1 was performed except that an ultrafine fiber was produced using polyethylene terephthalate (PET2, melt viscosity: 160 Pa s, carboxyl terminal group amount: 52 eq/ton) as the island component.
  • PET2 polyethylene terephthalate
  • melt viscosity 160 Pa s
  • carboxyl terminal group amount 52 eq/ton
  • Example 1 The procedure of Example 1 was performed except that the ultrafine fiber was cut to have a fiber diameter of 0.3 ⁇ m and fiber lengths of 1.2 mm and 1.8 mm, respectively.
  • a wet-laid nonwoven fabric sheet was prepared in accordance with Example 1 except that an ultrafine fiber obtained using polyethylene terephthalate (PET3, melt viscosity: 120 Pa ⁇ s, carboxyl terminal group amount: 28 eq/ton) different from that of Example 1 as an island component was used.
  • PET3 polyethylene terephthalate
  • melt viscosity 120 Pa ⁇ s
  • carboxyl terminal group amount 28 eq/ton
  • the water dispersibility of the ultrafine fibers was greatly impaired caused by insufficient electrical repulsive force derived from the carboxyl group, as a sheet structure in which the pore size distribution was board, the maximum frequency of the pore size distribution was small and a heterogeneous fine space was formed.
  • Comparative Example 2 was carried out in accordance with Example 1 except that the fiber diameter of the ultrafine fibers was 0.6 ⁇ m.
  • Comparative Example 3 was carried out in accordance with Comparative Example 2 except that the mixing ratio of the ultrafine fibers was 20 wt%.
  • the obtained sheet was a sheet that hardly exhibited the effect specific to the ultrafine fibers due to the extremely small fiber diameter ratio R/r, and was inferior in specific tensile strength to Examples 1 and 5, and thus was a sheet in which it was difficult to implement both the sheet strength and the construction of a fine space.
  • Example 1 Example 2
  • Example 3 Constituent fiber Fiber having fiber diameter R Polymer - PET PET PET PET Fiber diameter R ⁇ m 10.0 10.0 10.0 Fiber length mm 5.0 5.0 5.0 Fiber length/fiber diameter - 500 500 Mixing ratio % 30 30
  • Other fibers Polymer - PET PET PET PET PET Fiber diameter ⁇ m 4.0 4.0 4.0 Fiber length mm 3.0 3.0 3.0 Fiber length/fiber diameter - 750 750
  • Basis weight g/cm 2 25 25 25 25 Thickness mm 0.09 0.10 0.09 Porosity %

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  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Nonwoven Fabrics (AREA)
EP22742663.2A 2021-01-22 2022-01-20 Nassgelegte vliesstofffolie Pending EP4283038A1 (de)

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