WO2022158544A1 - 湿式不織布シート - Google Patents
湿式不織布シート Download PDFInfo
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- WO2022158544A1 WO2022158544A1 PCT/JP2022/002066 JP2022002066W WO2022158544A1 WO 2022158544 A1 WO2022158544 A1 WO 2022158544A1 JP 2022002066 W JP2022002066 W JP 2022002066W WO 2022158544 A1 WO2022158544 A1 WO 2022158544A1
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- fiber
- fibers
- fiber diameter
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- sheet
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Images
Classifications
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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
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- 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
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- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
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- 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
- D04H1/43828—Composite fibres sheath-core
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- 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
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- 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
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- 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
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- 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
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- 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 composed of at least three types of thermoplastic fibers with different fiber diameters.
- Non-woven fabric sheets made of ultra-fine fibers that easily exhibit their properties are being considered for use in a wide range of fields, from living environments to industrial materials, as materials that can express high functionality.
- Ultrafine fibers can be processed into nonwoven fabric sheets with a very dense structure by taking advantage of the morphological characteristics unique to fiber materials such as thinness and longness.
- a dense structure for example, exhibits high filtration performance by subdividing the fluid flowing inside the sheet, or easily exhibits functionality such as easy retention of the included functional agent for a long period of time.
- each of the ultrafine fibers that make up the sheet has unique characteristics that cannot be obtained with general general-purpose fibers or microfibers, the so-called nanosize effect, and the effect of increasing the specific surface area, which is the surface area per unit weight. It is possible to exhibit characteristics such as excellent adsorption performance due to Therefore, a nonwoven fabric sheet obtained by processing ultrafine fibers is expected as a highly functional nonwoven fabric sheet.
- wet-laid nonwoven fabric sheet fibers with a large fiber diameter substantially bear the mechanical properties as the skeleton of the sheet.
- As a scaffolding it exists in a so-called bridge-like manner and plays a role in forming a microscopic space.
- wet-laid non-woven fabric sheets are expected to be used for high-performance filter media, sound-absorbing materials that can control the wavelength of sound absorption, battery separators, etc., as sheets that combine the characteristics derived from ultrafine fibers and mechanical properties.
- the most important factor in achieving three-dimensional homogeneous dispersion in wet papermaking is to use a fiber dispersion in which each fiber is homogeneously dispersed.
- Patent Document 1 proposes a wet-laid nonwoven fabric using liquid crystalline polymer fibers, at least some of which are fibrillated to have a fiber diameter of 1 ⁇ m or less.
- Patent Document 2 proposes a wet-laid nonwoven fabric containing fibers with a fiber diameter of 3.0 ⁇ m or less by using splittable conjugate fibers and splitting them after wet papermaking.
- Patent Document 3 proposes a wet-laid nonwoven fabric suitable for filters that is composed of two or more types of fibers including ultrafine fibers with a fiber length that does not easily cause aggregation, and that has excellent collection efficiency.
- Patent Document 1 by generating fibrillated fibers of 1 ⁇ m or less in a liquid crystalline polymer fiber in a dispersion liquid to form a wet-laid nonwoven fabric, the fibrillated fibers can be mixed with each other or with other fibers without dispersing the single ultrafine fibers in water.
- the technical point is to make a wet-laid nonwoven fabric having a dense structure by entanglement.
- Patent Literature 2 discloses a technique related to a wet-laid nonwoven fabric in which a special splittable conjugate fiber is used to form a wet-laid nonwoven fabric, and through the process of applying heat treatment and physical impact, the conjugate fiber is split to generate ultrafine fibers and form a dense structure. It is
- the fibers exist as composite fibers in the state of the fiber dispersion, it is possible to avoid agglomeration of the ultrafine fibers in the aqueous medium.
- the fibers present in the wet-laid nonwoven fabric are in a state of being intricately entangled, it is difficult to evenly split all of the splittable conjugate fibers, and as a result, the homogeneity of the fine spaces within the sheet cannot be controlled. Sometimes.
- Patent Document 3 as a fiber form that is difficult to cause aggregation in water dispersion of ultrafine fibers in the first place, ultrafine fibers with a small ratio (L / D) of fiber length (L) to fiber diameter (D) are applied and wet
- L / D ratio of fiber length
- D fiber diameter
- the present invention provides a wet-laid nonwoven fabric sheet that forms three-dimensionally homogeneous microspaces by arranging ultrafine fibers in a state in which the ultrafine fibers are uniformly dispersed on the surface of the sheet and also in the cross-sectional direction. for the purpose.
- the present invention includes the following 1 to 6.
- a wet laid nonwoven fabric sheet comprising at least three types of thermoplastic fibers with different fiber diameters, wherein the fiber diameter R of the fiber with the largest fiber diameter and the fiber diameter r of the fiber with the smallest fiber diameter are A wet laid nonwoven fabric sheet having a fiber diameter ratio (R/r) of 30 ⁇ R/r ⁇ 150, an average pore size of 0.10 to 15 ⁇ m, and a maximum frequency of pore size distribution of 70% or more.
- R/r fiber diameter ratio
- the wet laid nonwoven fabric sheet according to any one of 1 to 3 above which has a basis weight of 10 to 500 g/m 2 . 5.
- a textile product comprising at least a part of the wet laid nonwoven fabric sheet according to any one of 1 to 5 above.
- the ultrafine fibers are uniformly dispersed on the surface of the sheet and also in the cross-sectional direction, so that it is possible to form three-dimensionally homogeneous microspaces.
- adsorption performance derived from the specific surface area of ultrafine fibers can be exhibited in any way. .
- Such wet-laid non-woven fabric sheets are expected to be developed into high-performance filter media, next-generation sound absorbing materials, battery separators, and the like.
- FIG. 1 is a schematic diagram of an example of the fiber diameter distribution of fibers constituting a wet-laid nonwoven fabric sheet according to an embodiment of the present invention.
- FIG. 2 is a diagram showing an example of the pore size distribution in a wet-laid nonwoven fabric sheet, in which (a) is a diagram showing an example of the pore size distribution of a sheet in which fine spaces are homogeneously present, and (b) is a diagram showing an example of the pore size distribution of a sheet in which fine spaces are not present.
- FIG. 4 is a diagram showing an example of pore size distribution when homogeneously formed;
- the wet-laid non-woven fabric sheet according to the embodiment of the present invention is a wet-laid non-woven fabric sheet comprising at least three types of thermoplastic fibers having different fiber diameters.
- the fiber diameter ratio (R/r) to the fiber diameter r of the fiber having the smallest diameter is 30 ⁇ R/r ⁇ 150, the average pore size is 0.10 to 15 ⁇ m, and the maximum frequency of the pore size distribution is 70% or more. are required to be
- thermoplastic fibers having different fiber diameters refers to the fibers observed on the surface of the wet-laid nonwoven fabric sheet, when represented in a graph with the horizontal axis as the fiber diameter and the vertical axis as the number of fibers. , a state of having three or more fiber diameter distributions.
- a group of fibers having a fiber diameter falling within each distribution range (distribution width) is one type, and the presence of three or more of this fiber diameter distribution means three or more types of different fiber diameters as referred to in the present invention.
- the fiber diameter distribution width referred to here means a range of ⁇ 30% of the peak value having the largest number of existence in each fiber diameter distribution.
- FIG. 1 is a diagram illustrating a case where there are three fiber diameter distributions.
- the fiber diameter distribution 1 shows the fiber diameter distribution of the fiber with the largest fiber diameter (fiber with the fiber diameter R)
- the fiber diameter distribution 2 shows the fiber diameter distribution of the fiber with the intermediate fiber diameter
- the fiber A diameter distribution 3 indicates the fiber diameter distribution of the fiber having the smallest fiber diameter (fiber having a fiber diameter r).
- the fiber diameter is obtained as follows. That is, an image is taken of the surface of the wet-laid nonwoven fabric sheet with a scanning electron microscope (SEM) at a magnification that allows observation of 150 to 3000 fibers. The fiber diameter of 150 fibers randomly selected from the photographed image is measured. For 150 fibers randomly extracted from each image, the fiber width in the direction perpendicular to the fiber axis is measured as the fiber diameter from the two-dimensionally photographed image. Fiber diameter values are measured in microns to two decimal places. The above operation is performed for 10 similarly photographed images, and the number of fiber diameter distributions described above is specified from the evaluation results of the 10 images. Then, for the fibers falling within the distribution width of each fiber diameter distribution, the value obtained by rounding the simple number average value of the fiber diameter to the first decimal place and calculating the fiber diameter of the fiber in each fiber diameter distribution and
- the fibers having the largest fiber diameter serve as the skeleton of the sheet and provide mechanical properties, and play a role in ensuring the handleability and moldability of the sheet.
- fibers with the smallest fiber diameter that is, fibers such as ultrafine fibers with extremely low rigidity, are arranged in a bridging manner using other fibers as a scaffold, forming a fine space. At the same time, it plays a role in exhibiting functionality such as adsorption performance derived from the specific surface area.
- other fibers refers to fibers having intermediate fiber diameters 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 serve as scaffolds so that the fibers with the fiber diameter r do not drop out of the sheet, and allow the fibers with the fiber diameter r to stably exist inside the sheet. From the above viewpoints, it is essential that the wet-laid nonwoven fabric sheet in the present invention is composed of at least three types of fibers having different fiber diameters.
- thermoplastic fibers thermoplastic polymers
- various polymers may be selected depending on the application.
- polyethylene terephthalate examples include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, It can be selected from melt-moldable polymers such as polyamides, polylactic acids, thermoplastic polyurethanes, polyphenylene sulfides, and copolymers thereof. For example, it may be selected in consideration of the compatibility with the environment to be applied, and finally required mechanical properties, heat resistance, chemical resistance, and the like. These polymers include inorganic substances such as titanium oxide, silica, barium oxide, carbon black, colorants such as dyes and pigments, flame retardants, fluorescent brighteners, antioxidants, or Various additives such as ultraviolet absorbers may be included.
- fibers with a fiber diameter r for achieving the wet-laid nonwoven fabric sheet according to the embodiment of the present invention enable three-dimensionally homogeneous existence inside the sheet.
- polyester fibers are particularly preferable among the above polymers. The reasons are detailed below.
- the factor that hinders the homogenous dispersion of ultrafine fibers in an aqueous medium is the attractive force acting between the ultrafine fibers, and in the prior art, methods such as placing restrictions on the shape of the ultrafine fibers have been adopted. It was something. However, such a method may not be a fundamental solution for achieving uniform dispersion of ultrafine fibers.
- the ultrafine fibers have a certain amount of carboxyl groups, they are negatively charged in the aqueous medium, and the electrical repulsive force works, so the dispersibility and dispersion stability of the ultrafine fibers in the medium are dramatically improved. can be substantially improved.
- the ultrafine fibers used in the wet-laid nonwoven fabric sheet according to the embodiment of the present invention have a carboxyl terminal group content of 40 eq/ton or more.
- carboxyl terminal group content 40 eq/ton or more.
- the ultrafine fibers are preferably composed of a polymer with a large elastic modulus, that is, a polymer with excellent rigidity, and from this viewpoint as well, polyester is preferable.
- polyester fibers as the ultrafine fibers, it is possible to suppress plastic deformation when deformation due to external force is applied. As a result, the effect of suppressing unnecessary entanglement between fibers is obtained in the manufacturing process and the high-order processing process of the wet-laid nonwoven fabric sheet according to the embodiment of the present invention, and the sheet processing can be performed while maintaining the dispersibility of the fibers. It is possible to obtain a sheet in which ultrafine fibers are uniformly arranged three-dimensionally.
- polyester refers to polyesters such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, and copolymers thereof, and examples of preferred polymers in the practice of the present invention are given below. can be done.
- the fibers with the fiber diameter R and the fibers with an intermediate fiber diameter are also polyester fibers.
- the fiber diameter R of the fiber with the largest fiber diameter and the fiber diameter r of the fiber with the smallest fiber diameter It is a requirement that the fiber diameter ratio (R / r) with is in the range of 30 ⁇ R / r ⁇ 150.
- the fiber diameter ratio R/r here is extremely small, the function of each fiber depending on the fiber diameter may be insufficient. For example, if the fiber diameter R is small, the rigidity of the sheet tends to be insufficient, which may lead to deterioration of the sheet's handleability and molding processability. Sometimes. For this reason, the lower limit of the fiber diameter ratio R/r is set at 30. On the other hand, if the fiber diameter ratio R/r is extremely large, the function of each fiber according to the fiber diameter is satisfactory, but when the water is drained in the wet papermaking process, the fibers accumulate on the drainage surface. This may result in a non-homogeneous sheet structure. Therefore, the upper limit of the fiber diameter ratio R/r is set to 150.
- the fiber diameter ratio R/r needs to be within the range described above. More preferably, the fiber diameter ratio R/r satisfies 30 ⁇ R/r ⁇ 100. Within such a range, the fine space formed by the ultrafine fibers has a more effective three-dimensional homogeneity.
- the present invention is a wet-laid nonwoven fabric sheet intended for use as a high-performance material that appeals to filtration and adsorption utilizing the specific surface area produced by ultrafine fibers and the fine space within the sheet. It is important that the maximum frequency of the pore size distribution is greater than or equal to 70%.
- the pore size here refers to the value calculated by the bubble point method.
- the bubble point method for example, measurement by a porous material automatic pore measuring system Perm-Porometer (manufactured by PMI) can be used.
- Perm-Porometer manufactured by PMI
- the wet-laid nonwoven fabric sheet is immersed in a liquid with a known surface tension value, and gas is supplied from the upper side of the sheet while increasing the pressure. Measure the pore size from the relationship.
- the pore size can be calculated under the following conditions using a porous material automatic pore measurement system Perm-Porometer (manufactured by PMI).
- the diameter of the measurement sample is 25 mm, and the average flow rate obtained by automatic calculation is used as the average pore size by measuring the pore size distribution using Galwick (surface tension: 16 mN / m) as a measurement liquid with a known surface tension, and the second decimal point is used as the average pore size.
- the pore size frequency the value obtained by automatic calculation is converted into a percentage, expressed as a percentage, and the value obtained by rounding off to the first decimal place is used.
- FIG. 2(a) shows an example of the pore size distribution (vertical axis: frequency, horizontal axis: pore size) of a wet-laid nonwoven sheet forming homogeneous microspaces
- FIG. An example of the pore size distribution when forming is shown.
- the pore size distribution will be sharp, and the frequency of specific pore sizes will be significantly increased (FIG. 2(a)).
- the fine space is heterogeneous, the pore size distribution will be broad ((b) in FIG. 2). From these facts, the homogeneity of the fine space can be evaluated.
- the average pore size in the embodiment of the present invention is the average size of the through-holes formed in the wet-laid nonwoven fabric sheet, and serves as an index of the denseness of the fine spaces in the sheet.
- the maximum frequency of the pore size distribution is an index of the homogeneity of the microspaces within the sheet. That is, when the average pore size is relatively small and the maximum frequency of the pore size distribution is relatively high, it means that the sheet has densified microspaces that are homogeneously present, and the average pore size and the maximum frequency of the pore size distribution are as described above.
- the fluid flows uniformly into the entire sheet without disturbing the flow of the fluid passing through the wet-laid nonwoven fabric sheet.
- the wet-laid nonwoven fabric sheet can be expected to effectively exhibit excellent performance such as filtration performance and sound absorption performance.
- the average pore size is 0.10 to 15 ⁇ m, so that the performance according to the purpose of use can be exhibited without hindering the flow of fluid. .
- the impediment to the fluid flow referred to here is due to the extreme increase in pressure loss associated with the miniaturization of the average pore size. Therefore, from the viewpoint of ensuring a stable fluid flow, the lower limit of the average pore size is 0.10 ⁇ m.
- the upper limit of the average pore size is 15 ⁇ m from the viewpoint that the specific performance due to the fine space works effectively.
- the maximum frequency of pore size distribution is within the range described above.
- Such a sheet structure is achieved by forming a complicated space with ultrafine fibers evenly distributed not only in the planar direction of the sheet but also in the thickness direction. Since the fine spaces are uniformly present in this manner, the fluid flows uniformly into the entire sheet, and the filtration performance, sound absorption performance, adsorption performance, etc. can be fully exhibited. Therefore, the maximum frequency of the pore size distribution is 70% or more, preferably 80% or more, 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 a sheet that forms dense and homogeneous microspaces due to the presence of fine fibers responsible for functionality in a well-dispersed state.
- the functionality such as filtration performance and sound absorption performance produced by the sheet structure, adsorption performance etc. derived from the nano-size effect of the ultrafine fibers themselves can be exhibited in any way.
- it is expected to be developed into high-performance filter media, next-generation sound absorbing materials, battery separators, etc.
- the fiber diameter r of the fibers with the smallest fiber diameter is preferably 0.10 to 1.0 ⁇ m.
- the present invention is a wet-laid non-woven fabric sheet aimed at achieving a highly functional material that appeals to filtration and adsorption utilizing the specific surface area, in addition to the dense microspaces due to the presence of ultrafine fibers.
- the fiber diameter r is preferably 0.10 to 1.0 ⁇ m. Within such a range, it is possible to promote densification of the fine spaces in the sheet, and to exhibit the specific surface area effect produced by the ultrafine fibers, and to exhibit excellent performance.
- the practical lower limit of the fiber diameter r is 0.10 ⁇ m in the embodiment of the present invention.
- the upper limit of the fiber diameter r is set to 1.0 ⁇ m as a range in which the effect of the specific surface area with general fibers works predominantly.
- the fiber diameter R of the fiber having the maximum fiber diameter is 3.0 to 50 ⁇ m in that the strength of the sheet can be secured, and the sheet has good handleability and moldability. More preferably, the range is 5.0 to 30 ⁇ m.
- the fiber diameter of the intermediate fiber diameter is preferably 1.0 ⁇ m to 20 ⁇ m. Within such a range, it is likely to act effectively as a scaffold for ultrafine fibers, enabling the formation of three-dimensionally homogeneous microspaces.
- the wet-laid nonwoven fabric sheet according to the embodiment of the present invention preferably has a porosity of 70% or more from the viewpoint that the effect of the fine space can be efficiently exhibited.
- the porosity referred to here is obtained as follows. That is, the porosity is obtained by rounding off the first decimal place of the value calculated from the following formula based on the basis weight and thickness of the wet-laid nonwoven fabric sheet and converting it into an integer value.
- the density of the constituent fibers may be applied, and in the case of polyethylene terephthalate (PET), it was calculated as 1.38 g/cm 3 .
- Porosity (%) 100 - (basis weight) / (thickness x fiber density) x 100
- the weight of the fiber sheet cut into 250 mm ⁇ 250 mm squares is weighed, and the value converted to the weight per unit area (1 m 2 ) is rounded to the first decimal place to obtain an integer value of the wet-laid nonwoven fabric sheet.
- Metsuke 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., probe shape: 10 mm ⁇ , graduation: 0.01 mm, measuring force: 2.5 N or less). The measurement is performed at arbitrary five points per sample, and the average value is rounded off to the third decimal place and the value obtained to the second decimal place is taken as the thickness of the wet-laid nonwoven fabric sheet.
- SM-114 dial thickness gauge
- the porosity is 70% or more.
- the porosity of the wet-laid nonwoven fabric sheet according to the embodiment of the present invention is more preferably 80% or more.
- Such a void ratio inside the sheet can be achieved by appropriately adjusting the sheet thickness and basis weight on the assumption that the fibers that make up the sheet exist in a dispersed state. At this time, if the basis weight of the sheet is extremely reduced, it becomes difficult to form minute spaces of the desired size, and in addition, the strength of the sheet is too low. There is On the other hand, increasing the basis weight of the sheet is preferable in that the through-holes formed by the three-dimensional fine space can be made denser by accumulating more fibers, but if the sheet is excessively increased, The rigidity of the sheet is excessively increased, which may lead to deterioration of the handleability and molding processability of the sheet.
- the wet-laid nonwoven fabric sheet according to the embodiment of the present invention should have a basis weight of 10 to 500 g/m 2 without impairing the intended effect of the present invention and stably making each fiber homogeneous. It is preferable because it becomes an existing sheet.
- the ratio (L/r) of the fiber length L to the fiber diameter r of the fibers having the smallest fiber diameter is preferably 3000-6000.
- the fiber length L referred to here can be obtained as follows. An image of the surface of the wet-laid nonwoven fabric sheet is taken with a microscope at a magnification that allows observation of 10 to 100 fibers with a fiber diameter r that can measure the total length. The fiber length of 10 fibers with a fiber diameter r randomly selected from each photographed image is measured.
- the term "fiber length” as used herein refers to the length of one fiber in the fiber longitudinal direction from a two-dimensionally photographed image, measured in mm to the second decimal place, and rounded off to the nearest whole number. The above operation is performed for 10 images similarly photographed, and the fiber length L is defined as a simple numerical average value of the evaluation results of the 10 images.
- the bridging structure is the key to the formation of the fine space. It is preferable in terms of exhibiting an excellent reinforcing effect because it promotes the formation of
- the larger the fiber length that is, the larger the ratio, the easier it is to form, and the reinforcing effect can be enhanced.
- the ratio is excessively increased, it is assumed that aggregation due to partial entanglement may occur, which may complicate the molding process.
- the upper limit is set to 6000 as a range in which there is no entanglement between fibers and in addition to the specific surface area effect, the reinforcing effect due to the fiber length can be sufficiently exhibited.
- a relatively smaller ratio (L/r) is more advantageous from the viewpoint of handleability in the wet papermaking process.
- the ratio is excessively small, the specific effect exhibited as a sheet may be relatively small, and the lower limit is the range in which the process can be passed without problems such as falling off of fibers during the molding process. is 3000.
- the fibers are appropriately entangled with each other to exert a reinforcing effect, and the sheet strength can be increased.
- the specific tensile strength of the wet laid nonwoven fabric sheet is preferably 5.0 Nm/g or more. From the standpoint of a wet-laid nonwoven fabric sheet having moldability suitable for practical use, the specific tensile strength is preferably 15 Nm/g or less.
- the mixing ratio in the fiber weight of each fiber constituting the wet-laid nonwoven fabric sheet according to the embodiment of the present invention is not particularly limited, but from the viewpoint of ensuring the stable formation of fine spaces and the strength of the wet-laid nonwoven fabric sheet , the fiber diameter r is preferably 2.5 to 30% by weight, and the fiber diameter R is preferably 15 to 85% by weight.
- a wet-laid nonwoven fabric sheet in which fibers are mixed within such a range exhibits good handleability and molding processability, and tends to be a sheet suitable for practical use.
- binder fibers may be mixed as necessary for the purpose of improving sheet strength and suppressing falling-off of constituent fibers.
- a heat-adhesive binder fiber it becomes possible to physically bond the fibers constituting the sheet to each other, and the strength of the sheet can be improved.
- the binder fiber is contained excessively, the fine space may be clogged by fusion or the fine space may be significantly reduced to impede fluid flow.
- the excessive rigidity of the sheet may cause molding defects.
- the mixing ratio of binder fibers is preferably in the range of 5 to 75% by weight. From the viewpoint of securing the adhesiveness between the fibers in the sheet, the substantial lower limit of the blending ratio of the binder fibers is 5% by weight.
- the binder fiber referred to here is not particularly limited, for example, it is preferably a core-sheath composite fiber in which a polymer having a melting point of 150°C or less is arranged in the sheath. After forming a wet-laid nonwoven fabric sheet, it is subjected to a drying process such as a Yankee dryer or an air-through dryer, or a heat treatment process such as calendering. Rigidity can be increased. At the same time, the remaining core component fibers can play a role of securing sheet strength as fibers with a fiber diameter R and serving as scaffolding as fibers with an intermediate fiber diameter depending on the fiber diameter. From this point of view, the core-sheath composite fiber as described above is preferable.
- the melting point of the core component of the binder fiber is higher than the melting point of the sheath component, and the melting point difference is 20°C or more, the sheath component on the surface of the binder fiber is sufficiently easily melted, and the orientation of the core component is improved. It is more preferable from the viewpoint of being able to obtain sufficient thermal adhesiveness and high rigidity since the width of the decrease can be suppressed.
- Short fibers such as fibers with the largest fiber diameter, fibers with an intermediate fiber diameter, and heat-fusible core-sheath composite fibers (binder fibers) whose sheath component is made of a low-melting polymer are put into water and stirred with a disaggregator.
- a fiber dispersion is prepared by dispersing the fibers uniformly.
- the core-sheath composite fiber which functions as a binder, has a core component that remains in the sheet after heat-sealing, so it plays a role of either a fiber with the largest fiber diameter or a fiber with an intermediate fiber diameter.
- the dispersibility can be adjusted by adjusting the amount of fibers to be added, the amount of the aqueous medium, the stirring time, etc., and it is preferable that the short fibers are uniformly dispersed in the aqueous medium as much as possible.
- a dispersant may be added to improve dispersibility in water, but when the wet-laid nonwoven fabric is post-processed, the amount added should be kept to the minimum necessary so as not to affect the processability. preferably stay.
- a microfiber dispersion liquid in which microfibers are uniformly dispersed in an aqueous medium is prepared.
- This ultrafine fiber dispersion and the fiber dispersion described above are mixed to form a stock solution for papermaking, which is subjected to wet papermaking to obtain a wet-laid nonwoven sheet in which ultrafine fibers are evenly arranged.
- the ultrafine fiber referred to here is preferably composed of polyester having a carboxyl terminal group content of 40 eq/ton or more from the viewpoint of ensuring water dispersibility, and is a sea-island fiber composed of two or more types of polymers having different dissolution rates in solvents.
- a sea-island fiber refers to a fiber having a structure in which island components made of a sparingly soluble polymer are interspersed in a sea component made of a readily soluble polymer.
- sea-island composite spinning by melt spinning is preferable from the viewpoint of increasing productivity, and a method using a sea-island composite spinneret is preferable from the viewpoint of being excellent in controlling the fiber diameter and cross-sectional shape.
- the reason for using the melt spinning method is that it is highly productive and can be manufactured continuously. In continuous production, it is preferable that a so-called sea-island composite cross section can be stably formed. From the viewpoint of the stability of this cross section over time, it is important to consider the combination of polymers that form this cross section. Become. In the present invention, it is preferable to select polymers in such a combination that the melt viscosity ratio ( ⁇ B/ ⁇ A) between the melt density ⁇ A of polymer A and the melt viscosity ⁇ B of polymer B is in the range of 0.1 to 5.0.
- the melt viscosity as used herein refers to the melt viscosity that can be measured with a capillary rheometer after the moisture content of the chip polymer is reduced to 200 ppm or less using a vacuum dryer, and means the melt viscosity at the same shear rate at the spinning temperature. .
- the easily soluble polymer of the sea-island fiber here includes, for example, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polylactic acid, thermoplastic polyurethane, and polyphenylene. It is selected from melt moldable polymers such as sulfides and copolymers thereof.
- the sea component is preferably copolyester, polylactic acid, polyvinyl alcohol, etc., which are readily soluble in aqueous solvents or hot water, and particularly polyethylene glycol and sodium. It is preferable to use a polyester or polylactic acid obtained by copolymerizing sulfoisophthalic acid alone or in combination, from the viewpoint of handleability and easy dissolution in a low-concentration aqueous solvent.
- the easily soluble here means that the dissolution rate ratio (easily soluble polymer/slightly soluble polymer) is 100 or more when the poorly soluble polymer is used as a reference in the solvent used for the dissolution treatment. do.
- the dissolution rate ratio is large, and the dissolution rate ratio is preferably 1000 or more, more preferably 10000 or more. . Within this range, the dissolution treatment can be completed in a short period of time, so that ultrafine fibers suitable for the present invention can be obtained without unnecessarily deteriorating the difficultly soluble component.
- polylactic acid polyester obtained by copolymerizing 3 mol% to 20 mol% of 5-sodium sulfoisophthalic acid, and the above-mentioned 5-
- a polyester copolymerized with sodium sulfoisophthalic acid and polyethylene glycol having a weight average molecular weight of 500 to 3000 in the range of 5 wt % to 15 wt %.
- a suitable combination of polymers for the sea-island fiber is a sea component copolymerized with 3 to 20 mol % of 5-sodium sulfoisophthalic acid and 5 wt of polyethylene glycol having a weight average molecular weight of 500 to 3,000. % to 15 wt %, and one or more selected from the group consisting of polyester and polylactic acid, and the island component is polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and copolymers thereof.
- An example is one or more selected from the group consisting of union.
- the spinning temperature of the sea-island fibers is preferably a temperature at which, among the polymers used, which are determined from the above-described viewpoint, mainly high-melting-point and high-viscosity polymers exhibit fluidity.
- the temperature at which this fluidity is exhibited differs depending on the properties and molecular weight of the polymer, the melting point of the polymer serves as a guideline, and may be set at the melting point +60° C. or lower. At this temperature, the polymer is not thermally decomposed in the spinning head or the spinning pack, the decrease in molecular weight is suppressed, and sea-island fibers can be produced satisfactorily.
- the melted and extruded yarn is cooled and solidified, converged by applying an oil agent, etc., and taken up by a roller with a specified peripheral speed.
- the take-up speed is determined, for example, from the discharge amount and the target fiber diameter.
- the take-up speed is preferably from 100 m/min to 7000 m/min from the viewpoint of stably producing sea-island fibers.
- the spun sea-island fibers are preferably drawn from the viewpoint of improving thermal stability and mechanical properties. The spinning may be followed by drawing.
- the sea-island fibers are bundled into a tow of several tens to several million units, and cut into a desired fiber length using a cutting machine such as a guillotine cutter, a slicing machine, and a cryostat.
- the fiber length L is preferably cut so that the ratio (L/r) to the island component diameter (corresponding to the fiber diameter r) is within the range of 3,000 to 6,000. Within this range, the number of contact points between fibers increases when a wet-laid nonwoven fabric sheet is formed, promoting the formation of a bridging structure, thereby enhancing the reinforcing effect of the sheet.
- the island component diameter referred to here substantially coincides with the fiber diameter of the ultrafine fibers, and is obtained as follows.
- the sea-island composite fiber is embedded in an embedding agent such as epoxy resin, and an image of the cross section is taken with a transmission electron microscope (TEM) at a magnification that allows observation of 150 or more island components.
- TEM transmission electron microscope
- the fiber cross sections of several filaments may be photographed to observe a total of 150 or more island components.
- the contrast of the island component can be made clear.
- the island component diameters of 150 island components randomly extracted from each image of the cross section of the fiber are measured.
- island component diameter means the diameter of a perfect circle circumscribing a cross-section perpendicular to the fiber axis from a two-dimensionally photographed image.
- the sea-island fibers after the above cut processing are immersed in a solvent capable of dissolving the readily soluble component (sea component) to remove the easily soluble component. do it.
- the easily soluble component is one or more selected from the group consisting of copolymerized polyethylene terephthalate obtained by copolymerizing 5-sodium sulfoisophthalic acid, polyethylene glycol, etc., and polylactic acid, an alkaline aqueous solution such as an aqueous sodium hydroxide solution is added. can be used.
- the bath ratio of the sea-island fibers to the alkaline aqueous solution is preferably 1/10000 to 1/5, more preferably 1/5000 to 1/10. is. Within this range, it is possible to prevent the ultrafine fibers from unnecessarily entangling with each other when the sea component is dissolved.
- the alkali concentration of the alkaline aqueous solution is preferably 0.1 to 5% by weight, more preferably 0.5 to 3% by weight.
- the dissolution of the sea component can be completed in a short time, and a fiber dispersion in which the ultrafine fibers are uniformly dispersed can be obtained without unnecessarily deteriorating the island component.
- the temperature of the alkaline aqueous solution is not particularly limited, it is preferable to set the temperature to 50° C. or higher, for example, because the dissolution of the sea component can be accelerated.
- the ultrafine fiber is separated by filtering, washed with water, and freeze-dried. It is also possible to re-disperse it in an aqueous medium and form a sheet.
- the ultrafine fiber dispersion may contain a dispersant as necessary.
- dispersants include natural polymers, synthetic polymers, organic compounds and inorganic compounds.
- additives that suppress aggregation between fibers include cationic compounds, nonionic compounds, anionic compounds, etc. Among them, when aiming to improve dispersibility, electrical From the viewpoint of repulsive force, it is preferable to use an anionic compound.
- the amount of these dispersants added is preferably 0.001 to 10 equivalents to the ultrafine fibers, and within this range, the dispersibility of the ultrafine fibers is ensured without impairing the processability of wet papermaking. It's easy to do.
- the ultrafine fiber dispersion prepared in this way is mixed with the fiber dispersion prepared above, diluted to a constant concentration, and then dehydrated on an inclined wire, cylinder mesh, or the like to form a wet-laid nonwoven fabric sheet. do.
- Apparatuses used for papermaking include a cylinder paper machine, a fourdrinier paper machine, an inclined short-mesh paper machine, and a paper machine combining these machines. In the papermaking process, in addition to the dispersibility of the fibers in the stock solution, the papermaking speed, the amount of the fibers, and the amount of the aqueous medium are adjusted to control the accumulation of the fibers during drainage. can be made.
- the fiber length of the constituent fibers is preferably 30.0 mm or less.
- a wet-laid nonwoven fabric sheet having practical homogeneity can be formed as a highly functional sheet. If the fiber length exceeds 30.0 mm, the fibers will be strongly entangled with each other during dispersion in an aqueous medium, forming a mass of fibers, which tends to make it difficult to form a homogeneous sheet.
- the sheet formed by wet papermaking is passed through a drying process to remove moisture.
- a drying method a method using hot air ventilation (air-through) or a method of contacting with a heat rotating roll (heat calender roll, etc.) is preferable from the viewpoint of simultaneously drying the sheet and thermally adhering the binder fibers.
- the basis weight and thickness of the wet nonwoven fabric can be changed as appropriate depending on the amount of papermaking stock solution supplied and the papermaking speed in the wet papermaking process.
- the thickness of the wet-laid nonwoven fabric sheet according to the embodiment of the present invention is not particularly limited, it is preferably 0.050 to 2.50 mm. In particular, the thickness is preferably 0.10 mm or more in that the sheet can be formed with excellent moldability.
- a wet-laid nonwoven fabric sheet that satisfies the above requirements can fully demonstrate the adsorption performance derived from the specific surface area of ultrafine fibers. Filtration performance and the like can be improved by being formed homogeneously three-dimensionally. Therefore, the wet-laid nonwoven fabric sheet of the present invention can be expected as a material that can be developed into high-performance filter media, next-generation sound absorbing materials, battery separators, and the like. A textile product containing at least a portion of the wet-laid nonwoven fabric sheet can be suitably used for these uses.
- melt Viscosity of Polymer Chip-shaped polymer was adjusted to a moisture content of 200 ppm or less by a vacuum dryer, and the melt viscosity was measured by changing the strain rate stepwise by Capilograph 1B manufactured by Toyo Seiki Seisakusho Co., Ltd.
- the measurement temperature is the same as the spinning temperature, and the melt viscosity at 1216 s ⁇ 1 is described in Examples and Comparative Examples. It should be noted that the measurement was carried out in a nitrogen atmosphere with a period of 5 minutes from the time the sample was put into the heating furnace until the start of the measurement.
- Fiber diameter The surface of the wet-laid nonwoven fabric sheet is imaged with a scanning electron microscope (SEM) at a magnification that allows observation of 150 to 3000 fibers, and the fiber diameter of 150 fibers randomly extracted from the photographed image is measured. It was measured. The fiber diameter was measured by taking the fiber width in the direction perpendicular to the fiber axis from a two-dimensionally photographed image as the fiber diameter. Regarding the value of the fiber diameter, it was measured in units of ⁇ m to two decimal places. The above operation was performed on 10 images similarly photographed, and the number of fiber diameter distributions was identified from the evaluation results of the 10 images. Then, for the fibers falling within the distribution width of each fiber diameter distribution, the value obtained by rounding the simple number average value of the fiber diameter to the first decimal place and calculating the fiber diameter of the fiber in each fiber diameter distribution and
- Fiber Length An image of the surface of the wet-laid nonwoven fabric sheet is photographed with a microscope at a magnification that allows observation of 10 to 100 fibers of each fiber diameter whose total length can be measured. The fiber length of 10 fibers of each fiber diameter randomly selected from each photographed image was measured.
- the term "fiber length” as used herein refers to the length of one fiber in the fiber longitudinal direction from a two-dimensionally photographed image, measured in mm to the third decimal place, and rounded to the second decimal place. The above operation was performed for 10 images similarly photographed, and a simple numerical average value of the evaluation results of the 10 images was taken as the fiber length.
- Pore size was calculated according to the bubble point method (based on ASTM F-316-86) using a porous material automatic pore measurement system Perm-Porometer (manufactured by PMI).
- the diameter of the measurement sample is 25 mm, and the average flow rate obtained by automatic calculation is used as the average pore size by measuring the pore size distribution using Galwick (surface tension: 16 mN / m) as a measurement liquid with a known surface tension, and the second decimal point is used as the average pore size.
- a value obtained by rounding off to the first decimal place was used.
- the pore size frequency the value obtained by automatic calculation was converted into a percentage, expressed as a percentage, and the value obtained by rounding off to the first decimal place was used.
- the thickness of the wet-laid nonwoven fabric sheet was measured in units of mm using a dial thickness gauge (SM-114, TECLOCK Co., probe shape: 10 mm ⁇ , scale: 0.01 mm, measuring force: 2.5 N or less). The measurement was performed at five random locations for each sample, and the average value was rounded off to the second decimal place to determine the thickness of the wet-laid nonwoven fabric sheet.
- SM-114 dial thickness gauge
- Example 1 Polyethylene terephthalate (PET1, melt viscosity 160 Pa ⁇ s, carboxyl terminal group amount 40 eq/ton) as an island component, and 8.0 mol% of 5-sodium sulfoisophthalic acid and 10 wt% of polyethylene glycol having a molecular weight of 1000 as a sea component were copolymerized.
- Polyethylene terephthalate (copolymerized PET, melt viscosity 121 Pa s) (melt viscosity ratio: 1.3, dissolution rate ratio: 30,000 or more) is used, and a sea-island composite spinneret (number of islands: 2,000) with circular island components is used.
- the mechanical properties of this sea-island fiber are sufficient for cutting with a strength of 2.4 cN/dtex and an elongation of 36%. did.
- the sea-island fibers were treated with a 1% by weight sodium hydroxide aqueous solution (bath ratio of 1/100) heated to 90° C. to obtain an ultrafine fiber dispersion.
- cut fibers of heat-fusible core-sheath composite fibers (core component fiber diameter: 10 ⁇ m, fiber length: 5.0 mm) were mixed at a rate of 30% by weight, and PET was used as a scaffold for ultrafine fibers.
- the cut fibers (fiber diameter 4 ⁇ m, fiber length 3.0 mm) were adjusted to a mixing ratio of 65% by weight, and uniformly mixed and dispersed with water by a disintegrator to prepare a fiber dispersion.
- the structures of the core component and the sheath component are as follows.
- PET Sheath component polyester (copolyester) with a melting point of 110°C, copolymerized at a ratio of 60 mol% terephthalic acid, 40 mol% isophthalic acid, 85 mol% ethylene glycol, and 15 mol% diethylene glycol
- a stock solution for papermaking was prepared by homogeneously mixing the above-mentioned ultrafine fiber dispersion with this fiber dispersion so that the mixing ratio of the ultrafine fibers was 5% by weight.
- This papermaking stock solution is made into paper using a square sheet machine (250 mm square) manufactured by Kumagai Riki Kogyo Co., Ltd., and dried and heat-treated in a rotary dryer with a roller temperature set to 110 ° C. to form a wet nonwoven fabric sheet. Obtained.
- the obtained wet-laid nonwoven fabric sheet is a sheet in which ultrafine fibers are present in a form of bridging with other fibers having a large fiber diameter as a scaffold, and has a fiber diameter ratio R/r of 50, a basis weight of 25 g/m 2 and a thickness of 0.005 g/m 2 . 09 mm, and the porosity was 79.9%.
- the average pore size calculated by the bubble point method was 4.9 ⁇ m, and the maximum frequency of the pore size distribution was 91.6%.
- the specific tensile strength was 6.7 Nm/g, and due to the reinforcing effect of the entanglement of the ultrafine fibers, the handleability and moldability were good.
- Examples 2 to 5 The procedure of Example 1 was followed, except that wet papermaking was carried out by changing the mixing ratio of the ultrafine fibers stepwise.
- the mixing ratio of the ultrafine fibers was increased, the microspaces formed by the ultrafine fibers were densified, and in addition, the reinforcing effect was improved by promoting entanglement, and the specific tensile strength was also improved. It was something.
- the sheet formed extremely homogeneous microspaces with a maximum pore size distribution frequency of 80% or more due to the fact that papermaking was possible without impairing the dispersibility in an aqueous medium.
- Example 6 Example 3 was followed except that the basis weight of the sheet was set to 150 g/m 2 . Even if the basis weight of the sheet was increased, a three-dimensionally uniform sheet structure was formed, and the wet-laid nonwoven fabric sheet stably formed extremely dense fine spaces with an average pore size of 0.8 ⁇ m.
- Example 7 As fibers with an intermediate fiber diameter, cut fibers with a fiber diameter of 4 ⁇ m and a fiber length of 3.0 mm were mixed at a mixing ratio of 62.5% by weight, and PET cut fibers with a fiber diameter of 0.6 ⁇ m and a fiber length of 0.6 mm were mixed at a mixing ratio of 2.5%.
- Example 1 was followed, except that the sheet was composed of four types of fibers having different fiber diameters, which were mixed at 5% by weight. Even when the sheet was composed of four types of fibers with different fiber diameters, the sheet formed homogeneous microspaces.
- Example 8 was carried out according to Example 1, except that the fiber diameter of the ultrafine fibers was 0.3 ⁇ m.
- Example 9 was carried out according to Example 8, except that the mixing ratio of the ultrafine fibers was changed to 10% by weight.
- Examples 10 to 13 were carried out according to Example 9, except that the basis weight of the sheets was changed to 12.5 g/m 2 , 50 g/m 2 , 100 g/m 2 and 300 g/m 2 . Even when the fiber diameter ratio R/r was reduced as compared with Example 1, the formation of microscopic spaces peculiar to ultrafine fibers was achieved. Furthermore, even if the sheet basis weight was changed stepwise, the sheet stably formed homogeneous fine spaces without greatly impairing the dispersibility of each fiber.
- Example 14 to 16 were carried out according to Example 8, except that the mixing ratios of fibers having a fiber diameter R were changed to 15% by weight, 45% by weight, and 75% by weight, respectively. Even when the mixing ratio of the fibers having the fiber diameter R is increased, the homogeneity of the fine spaces in the sheet is good, and the specific tensile strength is greatly improved by forming the skeleton of the sheet more firmly. Met.
- Example 17 and 18 were carried out according to Example 1, except that the fiber diameter R was changed to 15 ⁇ m and 20 ⁇ m. Even when the fiber diameter R was increased, the wet-laid nonwoven fabric sheet did not hinder the uniform accumulation of fibers in the wet-laid papermaking process and had uniform fine spaces. In addition, since the fibers having the fiber diameter R are responsible for the mechanical properties of the sheet, the specific tensile strength of the obtained sheet was improved compared to that of Example 1.
- Example 19 Example 1 was followed except that polyethylene terephthalate (PET2, melt viscosity 160 Pa ⁇ s, carboxyl terminal group content 52 eq/ton) was used as the island component to produce ultrafine fibers.
- PET2 polyethylene terephthalate
- An extremely homogeneous sheet structure was formed due to the increased dispersibility in an aqueous medium by increasing the amount of carboxyl end groups in the ultrafine fibers.
- Example 1 was followed except that the ultrafine fibers were cut to have a fiber diameter of 0.3 ⁇ m and fiber lengths of 1.2 mm and 1.8 mm. Even when the ratio (L/r) of the fiber length to the fiber diameter of the ultrafine fibers is increased to 4000 and 6000 compared to Example 1, it becomes easier to form fiber aggregates in the aqueous medium. The resulting sheet formed homogeneous microspaces. Furthermore, the specific tensile strength was improved as compared with Example 1 due to the reinforcing effect due to the entanglement of the ultrafine fibers.
- Example 1 Wet-laid nonwoven fabric according to Example 1, except that microfibers obtained by using polyethylene terephthalate (PET3, melt viscosity: 120 Pa s, carboxyl terminal group content: 28 eq/ton) different from that in Example 1 were used as island components. created a sheet.
- the obtained sheet has a broad pore size distribution sheet structure due to the fact that the electrical repulsive force derived from the carboxyl group is not sufficient and the water dispersibility of the ultrafine fibers is greatly impaired. The maximum frequency was small, and the sheet formed non-homogeneous microspaces.
- Comparative Example 2 was carried out according to Example 1, except that the fiber diameter of the ultrafine fibers was 0.6 ⁇ m.
- Comparative Example 3 was carried out according to Comparative Example 2, except that the mixing ratio of the ultrafine fibers was 20% by weight.
- the obtained sheet is a sheet that does not exhibit the effects peculiar to the ultrafine fibers due to the too small fiber diameter ratio R/r, and is inferior in specific tensile strength as compared with Examples 1 and 5. For this reason, it was difficult to achieve both sheet strength and fine space construction.
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Abstract
Description
1.繊維径の異なる少なくとも3種類の熱可塑性繊維を含んで構成される湿式不織布シートであって、繊維径が最大である繊維の繊維径Rと、繊維径が最小である繊維の繊維径rとの繊維径比(R/r)が30≦R/r≦150であり、かつ平均ポアサイズが0.10~15μmであり、ポアサイズ分布の最大頻度が70%以上である湿式不織布シート。
2.前記繊維径rが0.10~1.0μmである前記1に記載の湿式不織布シート。
3.空隙率が70%以上である前記1または2に記載の湿式不織布シート。
4.目付が10~500g/m2である前記1~3のいずれか1に記載の湿式不織布シート。
5.前記繊維径が最小である繊維において、前記繊維径rに対する繊維長Lの比(L/r)が3000~6000である前記1~4のいずれか1に記載の湿式不織布シート。
6.前記1~5のいずれか1に記載の湿式不織布シートを少なくとも一部に含む繊維製品。
本発明の湿式不織布シートによれば、微細空間が3次元的に均質に形成されることによる高機能化に加えて、極細繊維の比表面積に由来した吸着性能等を如何なく発揮することができる。かかる湿式不織布シートは、高性能な濾材や次世代吸音素材、電池セパレーターなどへの展開が期待される。
本発明の実施形態に係る湿式不織布シートは、繊維径の異なる少なくとも3種類の熱可塑性繊維を含んで構成される湿式不織布シートであって、繊維径が最大である繊維の繊維径Rと、繊維径が最小である繊維の繊維径rとの繊維径比(R/r)が30≦R/r≦150であり、かつ平均ポアサイズが0.10~15μm、ポアサイズ分布の最大頻度が70%以上であることを要件としている。
空隙率(%)=100-(目付)/(厚さ×繊維密度)×100
この際、250mm×250mm角に切り出した繊維シートの重量を秤量し、単位面積(1m2)当たりの重量に換算した値の小数点第1位を四捨五入して整数値としたものを湿式不織布シートの目付とする。
また、湿式不織布シートの厚みはダイヤルシックネスゲージ(TECLOCK社 SM-114 測定子形状10mmφ、目量0.01mm、測定力2.5N以下)を用いてmm単位で測定する。測定は1サンプルにつき任意の5ヶ所で行い、その平均の小数点3桁目を四捨五入して小数点2桁目まで求めた値を湿式不織布シートの厚みとする。
比引張強さ(Nm/g)=引張強さ(N/m)/目付(g/m2)
幅15mm×長さ50mmの試験片を5枚採取し、オリエンテック社製引張試験機 テンシロン UCT-100型を用い、JIS P8113:2006に準じて引張試験を実施し、湿式不織布シートの引張強さを測定する。この操作を5回繰り返し、得られた結果の単純平均値の小数点第3位を四捨五入した値を湿式不織布シートの引張強さとし、目付で除した値を比引張強さとする。
繊維径が最大の繊維、繊維径が中間の繊維、鞘成分が低融点ポリマーからなる熱融着性の芯鞘複合繊維(バインダー繊維)等の短繊維を水中に投入し、離解機で攪拌して均一になるように分散させた繊維分散液を調製する。この際、バインダーとして働く芯鞘複合繊維は、熱融着後には芯成分がシート内に残存することになるため、繊維径が最大の繊維または繊維径が中間の繊維のいずれかの役割を担う繊維として使用してもよい。この仕込み工程では、繊維仕込み量や水媒体量、攪拌時間等により分散性を調整することが可能であり、できるだけ短繊維が水媒体中で均一に分散している状態が好ましい。また、水への分散性を向上させるために分散剤を添加してもよいが、湿式不織布に後加工を施す場合に、その加工性に影響が出ないよう、その添加量は必要最小限にとどめることが好ましい。
海島複合繊維をエポキシ樹脂などの包埋剤にて包埋し、この横断面を透過型電子顕微鏡(TEM)で150本以上の島成分が観察できる倍率として画像を撮影する。1フィラメントで150本以上の島成分が配置されない場合は、数本フィラメントの繊維断面を撮影し、合計150本以上の島成分が観察されればよい。この際、金属染色を施せば、島成分のコントラストをはっきりさせることができる。繊維断面が撮影された各画像から無作為に抽出した150本の島成分の島成分径を測定する。ここで言う島成分径とは、2次元的に撮影された画像から繊維軸に対して垂直方向の断面を切断面とし、この切断面に外接する真円の径のことを意味する。以上のように得られた海島繊維について、海成分を溶解除去することで、極細繊維の均質分散液を製造することができる。
チップ状のポリマーを真空乾燥機によって、水分率200ppm以下とし、株式会社東洋精機製作所製キャピログラフ1Bによって、歪速度を段階的に変更して、溶融粘度を測定した。なお、測定温度は紡糸温度と同様にし、実施例あるいは比較例には、1216s-1での溶融粘度を記載している。なお、加熱炉にサンプルを投入してから測定開始までを5分とし、窒素雰囲気下で測定を行った。
チップ状のポリマーを真空乾燥機によって、水分率200ppm以下とし、約5mgを秤量し、TAインスツルメント社製示差走査熱量計(DSC)Q2000型を用いて、0℃から300℃まで昇温速度16℃/分で昇温後、300℃で5分間保持してDSC測定を行った。昇温過程中に観測された融解ピークより融点を算出した。測定は1試料につき3回行い、その平均値を融点とした。なお、融解ピークが複数観測された場合には、最も高温側の融解ピークトップを融点とした。
湿式不織布シートの表面を走査型電子顕微鏡(SEM)で150~3000本の繊維が観察できる倍率で画像を撮影し、撮影された画像から無作為に抽出した150本の繊維の繊維径を測定した。繊維径は、2次元的に撮影された画像から繊維軸に対して垂直方向の繊維幅を繊維径として測定した。繊維径の値に関しては、μm単位で小数点第2位まで測定した。以上の操作を、同様に撮影した10画像について行い、10画像の評価結果から、繊維径分布の個数を特定した。そして、各繊維径分布の分布幅に入る繊維について、繊維径の単純な数平均値の小数点第2位を四捨五入して小数点第1位まで求めた値を、各繊維径分布における繊維の繊維径とした。
湿式不織布シートの表面をマイクロスコープにて、全長を測定できる各繊維径の繊維が10~100本観察できる倍率で画像を撮影する。撮影された各画像から無作為に抽出した10本の、各繊維径の繊維の繊維長を測定した。ここで言う繊維長とは、2次元的に撮影された画像から繊維1本の繊維長手方向の長さとし、mm単位で小数点第3位まで測定し、小数点第2位を四捨五入するものである。以上の操作を、同様に撮影した10画像について行い、10画像の評価結果の単純な数平均値を繊維長とした。
多孔質材料自動細孔測定システム Perm-Porometer(PMI社製)を用い、バブルポイント法(ASTMF-316-86に基づく)に従ってポアサイズを算出した。測定サンプル径を25mmとし、表面張力既知の測定液としてGalwick(表面張力:16mN/m)を使用した細孔径分布測定により、自動計算して得られた平均流量径を平均ポアサイズとし、小数点第2位を四捨五入して小数点第1位まで求めた値を用いた。また、ポアサイズ頻度は自動計算により得られた値を百分率で換算して%表示とし、小数点第2位を四捨五入して小数点第1位まで求めた値を用いた。
250mm×250mm角に切り出した繊維シートの重量を秤量し、単位面積(1m2)当たりの重量に換算した値の小数点第1位を四捨五入して整数値としたものを湿式不織布シートの目付とした。
ダイヤルシックネスゲージ(TECLOCK社 SM-114 測定子形状10mmφ、目量0.01mm、測定力2.5N以下)を用いてmm単位で測定し、湿式不織布シートの厚みを測定した。測定は1サンプルにつき無作為の5ヶ所で行い、その平均の小数点第3位を四捨五入して小数点第2位まで求めた値を湿式不織布シートの厚みとした。
湿式不織布シートの目付および厚さから、下記式より算出した値の小数点第1位を四捨五入して整数値とした値を空隙率とした。
空隙率(%)=100-(目付)/(厚さ×繊維密度)×100
なお、繊維密度は構成される繊維の密度を適用すればよく、PETの場合は1.38g/cm3として算出した。
比引張強さは以下のようにして求めたものである。
比引張強さ(Nm/g)=引張強さ(N/m)/目付(g/m2)
幅15mm×長さ50mmの試験片を5枚採取し、オリエンテック社製引張試験機 テンシロン UCT-100型を用い、JIS P8113:2006に準じて引張試験を実施し、湿式不織布シートの引張強さを測定した。この操作を5回繰り返し、得られた結果の単純平均値の小数点第3位を四捨五入した値を湿式不織布シートの引張強さとし、目付で除した値を比引張強さとした。
島成分として、ポリエチレンテレフタレート(PET1、溶融粘度160Pa・s、カルボキシル末端基量40eq/ton)、海成分として、5-ナトリウムスルホイソフタル酸8.0mol%および分子量1000のポリエチレングリコール10wt%が共重合したポリエチレンテレフタレート(共重合PET、溶融粘度121Pa・s)(溶融粘度比:1.3、溶解速度比:30000以上)を使用し、島成分の形状が丸である海島複合口金(島数2000)を用いて、海成分/島成分の複合比率を50/50として溶融吐出した糸条を冷却固化した。その後、油剤を付与し、紡糸速度1000m/minで巻き取ることで未延伸糸を得た(総吐出量12g/min)。さらに、未延伸糸を85℃と130℃に加熱したローラー間で3.4倍延伸を行い(延伸速度800m/min)、海島繊維を得た。
芯成分:PET
鞘成分:テレフタル酸60mol%、イソフタル酸40mol%、エチレングリコール85mol%、ジエチレングリコール15mol%の割合で共重合した融点110℃のポリエステル(共重合ポリエステル)
極細繊維の混合率を段階的に変更して湿式抄紙したこと以外は、実施例1に従い実施した。
実施例2~5においては、極細繊維の混合率を増大させた場合では、極細繊維により形成される微細空間は緻密化し、加えて絡み合い促進による補強効果の向上も相まって、比引張強さも向上するものであった。さらに、水媒体中での分散性を損なうことなく抄紙が可能であることに起因して、ポアサイズ分布の最大頻度が80%以上と非常に均質な微細空間を形成するシートであった。
シートの目付を150g/m2となるようにしたこと以外は、実施例3に従い実施した。
シートの目付を増大させても、3次元的に均質なシート構造が形成されており、平均ポアサイズが0.8μmと非常に緻密な微細空間を安定的に形成する湿式不織布シートであった。
繊維径が中間の繊維として、繊維径4μm、繊維長3.0mmのカット繊維を混合率62.5重量%、繊維径0.6μm、繊維長0.6mmのPETのカット繊維を混合率2.5重量%で混合し、繊維径の異なる4種類の繊維でシートを構成したこと以外は、実施例1に従い実施した。
繊維径の異なる4種類の繊維でシートを構成した場合でも、均質な微細空間を形成するシートであった。
実施例8においては、極細繊維の繊維径を0.3μmとしたこと以外は、実施例1に従い実施した。
実施例9においては、極細繊維の混合率を10重量%と変更したこと以外は、実施例8に従い実施した。
実施例10~13においては、シートの目付をそれぞれ12.5g/m2、50g/m2、100g/m2、300g/m2と変更したこと以外は、実施例9に従い実施した。
実施例1と比較して繊維径比R/rを減少した場合においても、極細繊維特有の微細空間の形成を達成するものであった。さらに、シート目付を段階的に変更しても、各繊維の分散性を大きく損なうことなく、安定的に均質な微細空間を形成するシートであった。
実施例14~16においては、繊維径Rの繊維の混合率をそれぞれ15重量%、45重量%、75重量%と変更したこと以外は、実施例8に従い実施した。
繊維径Rの繊維の混合率を増大した場合でも、シートの微細空間の均質性は良好なものであり、シートの骨格がより強固に形成されることで、比引張強さは大きく向上するものであった。
実施例17、18においては、繊維径Rを15μm、20μmと変更したこと以外は、実施例1に従い実施した。
繊維径Rを増大させた場合においても、湿式抄紙工程における繊維の均等な集積を阻害することがなく、均質な微細空間を有する湿式不織布シートであった。また、繊維径Rの繊維はシートの力学特性を担うことから、得られたシートの比引張強さは実施例1と対比して向上するものであった。
島成分として、ポリエチレンテレフタレート(PET2、溶融粘度160Pa・s、カルボキシル末端基量52eq/ton)を使用して極細繊維を製造したこと以外は、実施例1に従い実施した。
極細繊維のカルボキシル末端基量を増大させることで水媒体中での分散性がより高まることに起因して、非常に均質なシート構造を形成するものであった。
極細繊維の繊維径を0.3μm、繊維長を1.2mm、1.8mmとなるようにカットしたこと以外は、実施例1に従い実施した。
極細繊維の繊維径に対する繊維長の比(L/r)を4000、6000と、実施例1と対比して増大させた場合においても、水媒体中において繊維凝集体を形成しやすくなるものの、得られるシートは均質な微細空間を形成するものであった。さらに、極細繊維の絡み合いによる補強効果が発揮されることで、実施例1と比較して、比引張強さは向上するものであった。
島成分として実施例1とは異なるポリエチレンテレフタレート(PET3、溶融粘度120Pa・s、カルボキシル末端基量28eq/ton)を使用して得られた極細繊維を用いたこと以外は、実施例1に従い湿式不織布シートを作成した。
得られたシートは、カルボキシル基由来の電気的な反発力が十分でないために極細繊維の水分散性を大きく損なうものであることに起因して、ポアサイズ分布がブロードなシート構造として、ポアサイズ分布の最大頻度が小さく、不均質な微細空間を形成するシートであった。
比較例2においては、極細繊維の繊維径を0.6μmとしたこと以外は、実施例1に従い実施した。
比較例3においては、極細繊維の混合率を20重量%としたこと以外は比較例2に従い実施した。
得られたシートは、繊維径比R/rが小さすぎることに起因して、極細繊維特有の効果を発揮しにくいシートとなり、実施例1および5と比較すると比引張強さにも劣るものであることから、シート強度と微細空間の構築の両立が困難なシートであった。
2:繊維径が中間の繊維の繊維径分布
3:繊維径が最小の繊維(繊維径rの繊維)の繊維径分布
Claims (6)
- 繊維径の異なる少なくとも3種類の熱可塑性繊維を含んで構成される湿式不織布シートであって、繊維径が最大である繊維の繊維径Rと、繊維径が最小である繊維の繊維径rとの繊維径比(R/r)が30≦R/r≦150であり、かつ平均ポアサイズが0.10~15μmであり、ポアサイズ分布の最大頻度が70%以上である湿式不織布シート。
- 前記繊維径rが0.10~1.0μmである請求項1に記載の湿式不織布シート。
- 空隙率が70%以上である請求項1または2に記載の湿式不織布シート。
- 目付が10~500g/m2である請求項1~3のいずれか1項に記載の湿式不織布シート。
- 前記繊維径が最小である繊維において、前記繊維径rに対する繊維長Lの比(L/r)が3000~6000である請求項1~4のいずれか1項に記載の湿式不織布シート。
- 請求項1~5のいずれか1項に記載の湿式不織布シートを少なくとも一部に含む繊維製品。
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