JP2008174868A - Method for producing sheet-formed article, and sheet-formed article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a sheet-formed article excellent in appearance and touch feeling, and also considering environment, and to provide the sheet-formed article. <P>SOLUTION: This method for producing the sheet-formed article includes the following steps (1) to (3) in this order. (1) The step of forming a non-woven fabric by using an ultra-fine fiber-forming fiber consisting of the combination of two kinds or more of polymeric materials having different solubilities to hot water or an aqueous alkaline solution. (2) The step of impregnating the nonwoven fabric with an aqueous dispersion of a self-emulsifiable polyurethane containing a film-forming silicone. (3) The step of expressing the ultra-fine fibers by treating the nonwoven fabric impregnated with the aqueous self-emulsifiable polyurethane dispersion with the hot water or aqueous alkaline solution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a sheet-like material that is excellent in appearance and texture and is environmentally friendly, and to a sheet-like material.

  A sheet-like material mainly composed of ultrafine fibers and polyurethane has excellent characteristics not found in natural leather, and is widely used in various applications.

  In producing such a sheet-like material, after impregnating a nonwoven fabric made of ultrafine fibers with an organic solvent solution of polyurethane, the fiber sheet-like material is immersed in water or an organic solvent aqueous solution which is a non-solvent of polyurethane. A process of wet coagulating polyurethane is generally employed. As such an organic solvent, a water-miscible organic solvent such as N, N'-dimethylformamide is used as an organic solvent for polyurethane.

  In addition, as a manufacturing method of the ultrafine fiber that constitutes the nonwoven fabric, a method of directly spinning the ultrafine fiber, or a nonwoven fabric made of ultrafine fiber generating fiber such as peelable composite fiber or sea-island composite fiber is produced to produce ultrafine fiber. The method of letting it be mentioned. Here, when the direct spinning method and the method using the ultrafine fiber generating fiber are compared, the ultrafine fiber having the fineness can be obtained in the latter than in the former, so that the surface quality and tactile sensation of the sheet-like material are likely to be good. However, an organic solvent such as toluene or trichlorethylene is used in the ultrafine treatment of the ultrafine fiber generating fiber.

  That is, the conventional method for producing a sheet-like material mainly uses a method of using an organic solvent in a polyurethane solvent or fiber ultrafine treatment. However, since organic solvents are highly harmful to the human body and the environment, there has been a strong demand for methods that do not use organic solvents in the production of sheet-like materials.

  In recent years, with regard to the use of polyurethane as an organic solvent from such a background, a polyurethane water dispersion in which polyurethane is dispersed in water is used instead of the conventional organic solvent type polyurethane. A method for making fibers finer using hot water or an aqueous alkaline solution by using a hot water soluble component or an alkaline aqueous solution soluble component as an elution component has been studied.

  Here, when the polyurethane liquid is impregnated into a nonwoven fabric and solidified, in the case of polyurethane of an organic solvent solution, when wet coagulation is performed by solidifying the polyurethane by immersing it in water or an organic solvent aqueous solution which is a non-solvent of polyurethane, The structure of the part is a porous structure. In general, in the case of a polyurethane water dispersion, solidification methods include dry heat coagulation, wet heat coagulation, and hot water coagulation. It becomes a pore structure. Further, when the moisture of the polyurethane water dispersion moves to the outermost surface of the sheet-like material during drying by heating, a so-called migration phenomenon occurs in which the polyurethane is concentrated near the outermost surface. Accordingly, it is known that the texture of the sheet-like material obtained when water-dispersible polyurethane is used becomes very hard, and studies aiming at softening of the texture are underway.

  For example, in Patent Document 1, a heat-sensitive gelling polyurethane emulsion is imparted to a fiber material substrate that has not been subjected to a water-repellent treatment, and a flexible leather-like sheet material is obtained by adding a flexible water-repellent agent in advance to the emulsion liquid. It is described to obtain. However, the silicone oil used as a flexible water repellent is a technology that improves the sliding between fibers and polyurethane, so that the softening effect is naturally not obtained unless silicone oil is attached as the final form. Is. Therefore, there is a problem that the softening effect greatly decreases or disappears when silicone oil is removed due to factors such as washing, dyeing, handling in water such as washing, friction, etc. after applying silicone oil. .

  Moreover, in patent document 2, the softening technique by provision of the heat-sensitive gelling polyurethane emulsion to the nonwoven fabric treated with the softening agent is described. Since silicone oil is used as a flexible water repellent, it is softened when the silicone oil is removed due to factors such as handling in water such as washing, dyeing and washing, and friction, as in the case of Patent Document 1. This is a technology that has a problem that the effect greatly decreases or disappears.

Thus, in consideration of the environment, a sheet-like material obtained by a process not using an organic solvent has not yet been obtained which has a soft texture and a good appearance.
JP 2006-200115 A JP 2000-17581 A

  In view of the background of such a conventional technique, the present invention provides a sheet-like material manufacturing method and sheet-like material which are excellent in appearance and texture and are environmentally friendly.

That is, the method for producing a sheet-like material according to the present invention is “a method for producing a sheet-like material, wherein the following steps (1) to (3) are performed in this order.
(1) The process of creating a nonwoven fabric using the ultra fine fiber generation type | mold fiber which consists of a combination of 2 or more types of polymeric substances from which solubility with respect to hot water or aqueous alkali solution differs.
(2) A step of impregnating a nonwoven fabric with a self-emulsifying polyurethane aqueous dispersion containing a film-forming silicone.
(3) A step of treating the nonwoven fabric impregnated with the self-emulsifying polyurethane aqueous dispersion with hot water or an alkaline aqueous solution to develop ultrafine fibers. It is.

  The sheet-like material of the present invention is “a sheet-like material characterized in that a self-emulsifying polyurethane and a film-forming silicone are contained in a nonwoven fabric made of ultrafine fibers”.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a sheet-like material excellent in the external appearance and the texture, and considering the environment, and a sheet-like material can be obtained.

  The manufacturing method of the sheet-like thing of this invention goes through (1)-(3) in order.

  (1) The process of creating a nonwoven fabric using the ultra fine fiber generation type | mold fiber which consists of a combination of 2 or more types of polymeric materials from which solubility with respect to hot water or aqueous alkali solution differs.

  (2) A step of impregnating a nonwoven fabric with a self-emulsifying polyurethane aqueous dispersion containing a film-forming silicone.

  (3) A step of treating the nonwoven fabric impregnated with the self-emulsifying polyurethane aqueous dispersion with hot water or an alkaline aqueous solution to develop ultrafine fibers.

  By carrying out in the order of (1) to (3), a gap is formed between the self-emulsifying polyurethane and the ultrafine fiber, between the ultrafine fiber and the ultrafine fiber, or between the self emulsification type polyurethane and the ultrafine fiber, and between the ultrafine fiber and the ultrafine fiber. It can be produced and a very flexible sheet can be obtained. In particular, it is preferable that the ultrafine fiber generating fiber is a sea-island type composite fiber because a self-emulsifying polyurethane and the ultrafine fiber form a structure that is not substantially in close contact with each other, so that a more flexible sheet can be obtained. When the order of the steps is not in the order of (1) to (3), for example, in the order of (1), (3), and (2), there is no void between the self-emulsifying polyurethane and the ultrafine fibers, and it is substantially adhered. In order to form the structure, the texture of the sheet-like material becomes very hard.

  The term “substantially not adhered” means that the self-emulsifying polyurethane is not adhered to the ultrafine fibers when a scanning electron microscope (SEM) photograph of the cross section of the sheet-like material is observed at a magnification of 300 times. It means that it can be confirmed that a void exists between the self-emulsifying polyurethane and the ultrafine fiber. There may be a partial contact, but basically there is a gap.

  In addition, the sheet-like material referred to here has an excellent surface appearance such as suede like natural leather, nubuck, silver surface, etc., and preferably has a smooth appearance such as suede or nubuck. With good touch and excellent lighting effects.

  In the present invention, “sheet” refers to a non-woven fabric impregnated with a self-emulsifying aqueous dispersion containing a film-forming silicone, and then a sheet-like product in which the fibers of the sheet are extremely thinned. That's it.

  First, step (1) will be described.

  As a means for obtaining ultrafine fibers constituting the nonwoven fabric, ultrafine fiber generating fibers are used. A nonwoven fabric in which ultrafine fibers are entangled can be obtained by performing ultrafine fiber after entanglement of ultrafine fiber generating fibers in advance.

  For ultrafine fiber-generating fibers, two or more types of thermoplastic polymer components having different solubility in hot water or alkaline aqueous solution are used as sea components and island components, and sea components are dissolved and removed using hot water or alkaline aqueous solution. The sea-island type composite fiber with the island component as ultrafine fiber and the two-component thermoplastic polymer component are arranged in the fiber cross section alternately in a radial or multilayer form, and each component is separated and divided into ultrafine fibers. A peelable composite fiber or the like can be employed. Above all, the sea-island type composite fiber can provide an appropriate gap between island components, that is, between the ultrafine fibers inside the fiber bundle by removing the sea component, so from the viewpoint of flexibility and texture of the base material. preferable.

  For the sea-island type composite fiber, a sea-island type composite base is used, and a polymer inter-array system in which the two components of the sea and the island are mutually aligned and spun, and the mixed spinning in which the two components of the sea and the island are mixed and spun Although a system etc. can be used, the sea island type composite fiber by a polymer array system is more preferable at the point from which the ultrafine fiber of uniform fineness is obtained.

  The difference in solubility in hot water or alkaline aqueous solution in the present invention means that the dissolution rate is different by 20 times or more, more preferably 40 times or more under the condition that the ultrafine fiber is developed. If it is less than 20 times, it is difficult to control the fineness of the thermoplastic polymer component having low solubility when developing the ultrafine fiber, which is not preferable.

  The dissolution rate in hot water or an aqueous alkali solution was obtained with a treatment time of 1 hour in accordance with the chemical resistance test (test solution: 90 ° C. hot water or sodium hydroxide 10%) of JIS K6911 (1995). It can be calculated from the weight ratio.

  As a sea component of the sea-island type composite fiber having high solubility in hot water or an aqueous alkali solution, polyvinyl alcohol or a copolymer containing polyvinyl alcohol as a main component from the viewpoint of the dissolution rate in hot water or an aqueous alkali solution and spinning stability. Polyesters such as polyethylene terephthalate and polybutylene terephthalate are mixed with 5 to 12 mol% of sodium 5-sulfoisophthalate, polyethylene glycol, sodium dodecylbenzenesulfonate, bisphenol A compound, isophthalic acid, adipic acid, dodecadioic acid, cyclohexyl carboxylic acid and the like. Polymerized copolyester, polylactic acid, or the like can be used. In particular, from the viewpoint of heat resistance, solubility in hot water or alkaline aqueous solution, polyvinyl alcohol, a copolymer containing polyvinyl alcohol as a main component, a polyethylene terephthalate copolymer obtained by copolymerizing 5-12 mol% of sodium 5-sulfoisophthalate, It is preferable to use polylactic acid. These copolymers may be not only binary but also ternary or higher multi-component copolymers.

  The island component of the sea-island type composite fiber having low solubility in hot water or an aqueous alkali solution becomes the ultrafine fiber constituting the nonwoven fabric constituting the sheet-like material of the present invention.

  Examples of the ultrafine fibers constituting the nonwoven fabric constituting the sheet-like material of the present invention include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyesters such as polyethylene-2,6-naphthalenedicarboxylate, 6-nylon, 66- Various synthetic fibers such as polyamide such as nylon, acrylic, polyethylene, and polypropylene can be used. Of these, polyester fibers such as polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate are preferably used from the viewpoints of strength, dimensional stability, light resistance, and dyeability.

  The nonwoven fabric may be configured by mixing ultrafine fibers of different materials, and a woven fabric or a knitted fabric may be inserted into the nonwoven fabric for the purpose of improving the strength. In addition, the average single fiber fineness of the fiber which comprises a textile fabric or a knitted fabric does not have limitation in particular, 0.001 dtex or more and 1 dtex or less ultrafine fiber may be sufficient.

  The average single fiber fineness of the ultrafine fibers constituting the nonwoven fabric is preferably 0.001 dtex or more and 0.5 dtex or less from the viewpoint of sheet flexibility and napped quality. More preferably, it is 0.3 dtex or less, More preferably, it is 0.2 dtex or less. On the other hand, it is preferably 0.005 dtex or more from the viewpoints of color developability after dyeing, dispersibility of fibers during raising treatment such as grinding with sandpaper, and ease of spreading.

  In addition, the average single fiber fineness of the ultrafine fibers constituting the nonwoven fabric is a magnification of a scanning electron microscope (SEM) photograph of the surface of the sheet (or nonwoven fabric) when the cross section of the ultrafine fibers is circular or an ellipse close to a circle. It is calculated by photographing at 2000 times, selecting 100 ultrafine fibers at random, measuring the fiber diameter, converting the specific gravity of the raw material polymer into fineness, and calculating the average value of the 100 fibers. On the other hand, when the ultrafine fiber constituting the nonwoven fabric has an irregular cross section, the outer peripheral circular diameter of the irregular cross section is calculated as the fiber diameter in the same manner. Furthermore, when a circular cross section and an irregular cross section are mixed, or when those having greatly different finenesses are mixed, 100 are selected and calculated so that each has the same number.

  Regarding the uniformity of the fineness of the ultrafine fibers constituting the nonwoven fabric, the fineness CV in the fiber bundle is preferably 10% or less. Here, the fineness CV is a percentage (%) value obtained by dividing the fineness standard deviation of the fibers constituting the fiber bundle by the average fineness within the bundle, and indicates that the smaller the value, the more uniform. . By setting the fineness CV to 10% or less, the appearance of napping on the surface of the sheet-like material becomes graceful, and the dyeing can be made uniform and good. The fineness CV when the cross section of the ultrafine fiber is not a circle or an ellipse close to a circle is obtained by the same method as the calculation of the average single fiber fineness.

  The cross-sectional shape of the ultrafine fiber may be a round cross-section, but may be a polygonal shape such as an ellipse, a flat shape, or a triangle, or an irregular cross-section such as a sector shape or a cross shape.

  The nonwoven fabric constituting the sheet-like material of the present invention may be either a short fiber nonwoven fabric or a long fiber nonwoven fabric, but a short fiber nonwoven fabric is preferred when emphasis is placed on texture and quality.

  It is preferable that the ultrafine fiber-generating fiber is crimped and cut into a predetermined length to obtain a nonwoven fabric raw cotton. A usual method can be used for crimping and cutting.

  In the case of a short fiber nonwoven fabric, the fiber length is preferably 25 mm or more and 90 mm or less in consideration of wear resistance due to entanglement.

  The obtained raw cotton is made into a web with a cross wrapper or the like, and then the fibers are entangled to make a nonwoven fabric.

  As a method for obtaining a nonwoven fabric by entanglement of fibers, usual methods such as needle punching and water jet punching can be used.

  The obtained non-woven fabric may be subjected to a shrinking treatment by hot water or steam treatment or a compression treatment such as hot pressing in order to improve the fineness of the fibers.

  Further, the non-woven fabric may be obtained by half-cutting (dividing into two sheets) or dividing into several sheets in the thickness direction of the non-woven fabric before applying the self-emulsifying polyurethane water dispersion.

  Next, process (2) is demonstrated.

  In applying the self-emulsifying type polyurethane water dispersion to the nonwoven fabric, the nonwoven fabric is impregnated with the polyurethane water dispersion or applied to dry heat solidification, and the nonwoven fabric is impregnated with the polyurethane water dispersion and then wet heat solidified. There are a method of heat drying, a method of wet coagulation in hot water and heat drying, and a combination thereof, but there is no particular limitation.

  If the drying temperature is too low, the drying time will be long, and if it is too high, it may cause thermal degradation of the self-emulsifying polyurethane, so that it is preferably 80 ° C. or higher and 180 ° C. or lower. More preferably, it is 90 ° C or higher and 160 ° C or lower.

  The polyurethane water dispersion used in the production of the present invention is a polyurethane water dispersion which is dispersed in water as an emulsion, and is a self-emulsifying polyurethane water dispersion which does not contain an emulsifier such as a surfactant.

  When a forced emulsification type polyurethane aqueous dispersion containing an emulsifier such as a surfactant is used, the surface of the obtained sheet-like material is sticky due to the emulsifier, so a washing step is required, and the processing step Will increase the cost. In addition, in the forced emulsification type polyurethane water dispersion, the water resistance of the polyurethane film formed into a film is lowered due to the presence of the emulsifier, and therefore, in the dyeing of the sheet-like material containing polyurethane, the polyurethane is not dropped into the dyeing liquid. It is easy to generate and is not preferable.

  The polyurethane water dispersion used in the present invention is a self-emulsifying polyurethane water dispersion, but the self-emulsifying polyurethane water dispersion is a polyurethane in which water is stably dispersed without using an emulsifier such as a surfactant. It is an aqueous dispersion and has a hydrophilic so-called internal emulsifier in the self-emulsifying polyurethane molecular structure.

  The self-emulsifying polyurethane is usually handled in a state of being dispersed in water, and can be obtained from the manufacturer in this state. This is because once dried, it cannot be dispersed in water again.

  The self-emulsifying polyurethane aqueous dispersion used in the present invention may contain a water-soluble organic solvent in an amount of 40% by weight or less with respect to the aqueous dispersion in order to improve storage stability and film forming property. The content of the organic solvent is preferably 1% by weight or less because of concerns such as the release of the organic solvent into the atmosphere by heating during film formation and the remaining organic solvent in the final product.

  The self-emulsifying polyurethane is not particularly limited as long as it is an aqueous dispersion dispersed in water, but is mainly composed of an internal emulsifier, a polyol, a polyisocyanate, and a chain extender.

  Internal emulsifiers are any of cationic systems such as quaternary amine salts, anionic systems such as sulfonates and carboxylates, nonionic systems such as polyethylene glycol, combinations of cationic systems and nonionic systems, and combinations of anionic systems and nonionic systems. However, the cationic internal emulsifier is inferior in light resistance such as yellowing, and the anionic internal emulsifier is preferably a nonionic internal emulsifier because it may cause a harmful effect due to the neutralizing agent.

  That is, when an anionic internal emulsifier is used, a neutralizing agent is required. For example, the neutralizing agent is a tertiary amine such as ammonia, triethylamine, triethanolamine, triisopropanolamine, trimethylamine, or dimethylethanolamine. In some cases, amines are generated and volatilized by the heat generated during film formation and drying, and released outside the system. Therefore, it is indispensable to introduce an apparatus for recovering volatile amines in order to suppress atmospheric emissions and work environment deterioration. In addition, if the amine does not volatilize by heating and remains in the final product sheet, it may be discharged to the environment when the product is incinerated. However, a nonionic internal emulsifier uses a neutralizing agent. Therefore, it is not necessary to introduce an amine recovery device, and there is no fear of remaining amine in the sheet. In addition, when the neutralizing agent is an alkali metal such as sodium hydroxide, potassium hydroxide or calcium hydroxide, or a hydroxide of an alkaline earth metal, the self-emulsifying polyurethane part exhibits alkalinity when wet. However, since the nonionic internal emulsifier does not use a neutralizing agent, there is no need to worry about degradation due to hydrolysis of the self-emulsifying polyurethane.

  As the polyol, a polycarbonate-based diol, a polyester-based diol, a polyether-based diol, a silicone-based diol, a fluorine-based diol, or a copolymer combining these may be used. Of these, polycarbonate diols and polyether diols are preferably used from the viewpoint of hydrolysis resistance, and polycarbonate diols are more preferable from the viewpoints of light resistance and heat resistance.

  The polycarbonate-based diol can be produced by an ester exchange reaction between an alkylene glycol and a carbonate ester, or a reaction between phosgene or chloroformate ester and an alkylene glycol. Examples of the alkylene glycol include linear chains such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, and 1,10-decanediol. Alkylene glycol, branched alkylene glycol such as neopentyl glycol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 2-methyl-1,8-octanediol, 1,4 -Alicyclic diols such as cyclohexanediol, aromatic diols such as bisphenol A, glycerin, trimethylolpropane, pentaerythritol and the like. Either a polycarbonate diol obtained from a single alkylene glycol or a copolymerized polycarbonate diol obtained from two or more types of alkylene glycols may be used.

  Examples of the polyisocyanate include aliphatic systems such as hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and xylylene diisocyanate, and aromatic systems such as diphenylmethane diisocyanate and tolylene diisocyanate, and these may be used in combination. Of these, aliphatic systems such as hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate are preferable from the viewpoint of light resistance.

  As the chain extender, use is made of amines such as ethylenediamine, hexamethylenediamine and methylenebisaniline, diols such as ethylene glycol, neopentyl glycol and tetraethylene glycol, and polyamines obtained by reacting polyisocyanate with water. be able to.

  In addition, if the self-emulsifying polyurethane present in the interior space of the sheet has a cross-linked structure, the durability such as hydrolysis resistance of the self-emulsifying polyurethane can be dramatically improved. In order to introduce a structure, a compound having a plurality of reactive groups (referred to as an external cross-linking agent) may be added to the self-emulsifying polyurethane aqueous dispersion and used. May be used, and an internal crosslinking agent having a crosslinked structure at the time of film formation may be used. Among these, it is preferable to use an internal crosslinking agent in view of the liquid stability of the self-emulsifying polyurethane aqueous dispersion.

  The external crosslinking agent is not particularly limited as long as it is a compound having a plurality of reactive groups. For example, melamine resin, oxazoline compound, epoxy compound, carbodiimide compound, isocyanate compound, silanol compound, etc. Is mentioned.

  The internal cross-linking agent is not particularly limited as long as it can be introduced into the self-emulsifying polyurethane molecular structure. The reactive group to be introduced is, for example, an oxazoline group, an epoxy group, a carbodiimide group, an isocyanate group, a silanol group, or a silanol group generated during film formation. And hydrolyzable silicon groups that can be used. Especially, it is preferable that it is a hydrolyzable silicon group which can produce | generate a silanol group or a silanol group at the time of film forming from the liquid stability of a self-emulsification type polyurethane water dispersion. By introducing the silanol group into the self-emulsifying polyurethane molecular structure, the self-emulsifying polyurethane existing in the internal space of the nonwoven fabric has a crosslinked structure due to siloxane bonds.

  Silanol groups in silanol group-containing self-emulsifying polyurethane water dispersions are stable in water because they have sufficient water around them, so they do not reach the stage where silanol groups react with each other to form siloxane bonds. To do.

  The silanol group contained in the silanol group-containing self-emulsifying polyurethane may be bonded to at least one or both of the both ends of the silanol group-containing self-emulsifying polyurethane molecule, or both. Since it affects the water resistance, physical properties, etc. of the self-emulsifying polyurethane after film formation, it is preferable to contain a silanol group in the middle part of the silanol group-containing self-emulsifying polyurethane molecule.

  A compound used for introducing a silanol group into a self-emulsifying polyurethane molecular structure is a compound containing an active hydrogen group capable of reacting with at least one isocyanate group and a hydrolyzable silicon group in one molecule. It is.

  The hydrolyzable silicon group means a group in which a hydrolyzable group that is hydrolyzed by moisture is bonded to a silicon atom. Specific examples of the hydrolyzable group include a hydrogen atom, a halogen atom, and an alkoxy group. And generally used groups such as an acyloxy group, a ketoximate group, an amino group, an amide group, an aminooxy group, a mercapto group, and an alkenyloxy group. Among these, an alkoxy group that has low hydrolyzability and is relatively easy to handle is preferable. The hydrolyzable group is bonded to one silicon atom in the range of 1 to 3, but from the viewpoint of reactivity of the hydrolyzable silyl group, water resistance, etc., those having 2 to 3 bonds are preferable. .

  Examples of the active hydrogen group capable of reacting with an isocyanate group include a mercapto group, a hydroxyl group, and an amino group.

  Hydrolyzable silicon group-containing compounds having a mercapto group as an active hydrogen group and an alkoxy group as a hydrolyzable group include, for example, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-mercaptopropylmethyl. Examples of the hydrolyzable silicon group-containing compound having an amino group as an active hydrogen group and an alkoxy group as a hydrolyzable group include dimethoxysilane and γ-mercaptopropylmethyldiethoxysilane. Aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropyltriethoxysilane, γ- (2-aminoethyl) aminopropyldimethoxysilane, γ- (2-aminoethyl) aminopropyldiethoxysilane, γ-aminopropyltrimethoxysilane .gamma.-aminopropyltriethoxysilane, .gamma.-aminopropyl dimethoxysilane, .gamma.-aminopropyl diethoxy silane and the like. Among these, from the viewpoint of weather resistance and hydrolysis resistance, it is preferable to introduce a hydrolyzable silicon group into the middle part of the self-emulsifying polyurethane molecule, and further a hydrolyzable silicon group-containing compound having two or more active hydrogen groups Is preferred.

  The content of silicon atoms, which is a measure of the amount of crosslinking due to siloxane bonds, increases the durability of the self-emulsifying polyurethane, such as hydrolysis resistance, as the crosslinking structure due to siloxane bonds increases. Since flexibility is lowered, it is preferably more than 0% by weight and 1% by weight or less based on the weight of the self-emulsifying polyurethane.

  The concentration of the self-emulsifying polyurethane aqueous dispersion (content of the self-emulsifying polyurethane relative to the self-emulsifying polyurethane aqueous dispersion) is 10% by weight or more and 50% by weight from the viewpoint of storage stability of the self-emulsifying polyurethane aqueous dispersion. The following is preferred.

  The self-emulsifying polyurethane aqueous dispersion preferably has a thermal gelation temperature. By having a heat-sensitive gelation temperature, it is possible to suppress the polyurethane migration phenomenon when the nonwoven fabric is impregnated and dried. However, if the thermal gelation temperature is too low, there is a high possibility of gelation in the storage of the polyurethane water dispersion, and if it is too high, the migration phenomenon cannot be suppressed. preferable.

  The self-emulsifying polyurethane aqueous dispersion preferably has a heat-sensitive gelation property alone, but for the purpose of imparting the heat-sensitive gelation property to the self-emulsifying polyurethane water dispersion or lowering the heat-sensitive gelation temperature, Inorganic salts such as calcium, sodium sulfate and potassium sulfate may be added.

  The self-emulsifying polyurethane aqueous dispersion is composed of 3 to 30% by weight of polyethylene glycol with respect to the total weight of the self-emulsifying polyurethane in order to facilitate thermal gelation with the self-emulsifying polyurethane alone or with an inorganic salt. You may have. In particular, in the case of a self-emulsifying type polyurethane that is self-emulsified with a nonionic internal emulsifier, if it is too little, it becomes difficult to self-emulsify, and if it is too much, physical properties such as water resistance and strength of the polyurethane film are likely to deteriorate. Therefore, the content of polyethylene glycol with respect to the total weight of the polyurethane is more preferably 5% by weight or more and 20% by weight or less.

  The film is made flexible by adding a film-forming silicone emulsion to the self-emulsifying polyurethane aqueous dispersion in the present invention.

  The film-forming silicone is a silicone that becomes a three-dimensional cross-linked structure by heating and cannot be re-dispersed in water. The film-forming property allows the sheet to be washed and dyed after the film-forming silicone is applied. Even if there are external factors such as handling in water such as washing and friction, silicone does not fall off the sheet, and the flexibility of the sheet can be expressed. Although details will be described later, in the production method of the present invention, the sheet is impregnated with a self-emulsifying polyurethane aqueous dispersion containing a film-forming silicone emulsion, and then the sheet is treated with hot water and / or an alkaline aqueous solution to produce fibers. However, since the silicone has a film-forming property, even in the production method of the present invention, the flexibility of the sheet can be expressed. In the present invention, “the film-forming silicone remains in the sheet even after the fiber ultrafine treatment” is a comparison between the actual measured value and the theoretical calculated value of the sheet after the ultrafine treatment, and the difference is 30 %.

  In addition, the sheet flexibility is based on the method A (45 ° cantilever method) described in JIS L1096-8.19.1 (2005 edition), and 5 x 2 cm x 15 cm test pieces are prepared in the vertical and horizontal directions. It can be evaluated by placing it on a horizontal platform having a slope of 45 ° C., sliding the test piece, reading the scale when the central point of one end of the test piece is in contact with the slope, and determining the average value of the five pieces.

  The amount of the film-forming silicone emulsion added to the self-emulsifying polyurethane aqueous dispersion is not particularly limited as long as the sheet can be softened. However, if the amount is too small, sufficient flexibility cannot be achieved. Since it becomes worse, it is preferable that the film-forming silicone solid content is 0.5 wt% or more and 30 wt% or less with respect to the self-emulsifying polyurethane solid content.

  When the nonwoven fabric is impregnated with the self-emulsifying type polyurethane aqueous dispersion to which the film-forming silicone emulsion is added, the content of solid content (self-emulsifying type polyurethane and film-forming silicone) with respect to the weight of the nonwoven fabric is 20% by weight to 200% by weight. It is preferable that By making it 20% by weight or more, it is possible to obtain sheet strength and prevent the fibers from falling off, and by making it 200% by weight or less, it is possible to prevent the texture from becoming unnecessarily hard and to be flexible. A texture and good nap quality can be obtained. More preferably, it is 30 wt% or more and 180 wt% or less.

  The film-forming silicone is not particularly limited as long as it can be formed by heating, but is preferably an amino-modified silicone because a softer texture can be obtained.

  Self-emulsifying type polyurethane water dispersions include pigments such as carbon black, dyes, fungicides, anti-oxidants such as antioxidants and UV absorbers, flame retardants, penetrants and lubricants, silica, titanium oxide, etc. Anti-blocking agents, antistatic agents, antibacterial agents, deodorants, silicone oil and other antifoaming agents, cellulose and other fillers, polyurethane coagulation modifiers, and the like may be added.

  Finally, step (3) will be described.

  The method for producing a sheet-like product of the present invention is to develop a sheet of ultrafine fiber-generating fibers impregnated with a self-emulsifying polyurethane aqueous dispersion with hot water and / or an alkaline aqueous solution to develop ultrafine fibers. .

  The hot water as used in the present invention preferably means water at 60 ° C. or higher, but more preferably at 80 ° C. or higher because the fiber can be made ultrafine in a shorter time at a higher temperature.

  The alkaline aqueous solution is not particularly limited, and an aqueous solution such as sodium hydroxide or potassium hydroxide, an ammonia salt, or the like can be used.

  The concentration of the aqueous alkali solution is not particularly limited as long as ultrafine fibers can be expressed, but is preferably 0.05 mol / L or more and 10 mol / L or less.

  The treatment with hot water or an alkaline aqueous solution involves immersing a sheet made of ultrafine fiber-generating fibers after application of self-emulsifying polyurethane and performing a constriction liquid. In the case of peelable composite fibers, hot water or an alkaline aqueous solution In the case of sea-island type composite fiber, which is divided by physical force such as treatment and stagnation action, sea components dissolved in hot water or alkaline water are eluted to generate ultrafine fibers, so the method is particularly limited Although there is no treatment, for example, a treatment using a liquid dyeing machine, a refining apparatus or the like, or a combination thereof may be mentioned.

  The temperature and time in the treatment using a liquid dyeing machine are preferably 50 ° C. or higher and 140 ° C. or lower and 5 minutes or longer and 90 minutes or shorter, respectively.

  In addition, for the purpose of improving the generation of ultrafine fibers, heat treatment, steam treatment, treatment with addition of a penetrant such as a surfactant may be performed as appropriate, and treatment with an acidic aqueous solution having a pH of 3 or less is performed in advance. After performing, you may process by alkaline aqueous solution.

  The sheet-like material thus obtained may be a nap-like leather-like sheet-like material having napped fibers on at least one side.

  The raising treatment for forming napping on the surface of the sheet-like material can be performed by a grinding method using a sandpaper or a roll sander. In the method for producing a sheet-like material of the present invention, since the sheet-like material contains a film-forming silicone, the sheet is flexible, and at the same time, raising by surface grinding is easily possible, and the surface quality and feel are very good. It becomes.

  It is preferable to apply an antistatic agent before the raising process, because the grinding powder generated from the sheet-like material by grinding tends to be difficult to deposit on the sandpaper.

  In addition, the sheet-like material may be obtained by half cutting or dividing into several sheets in the sheet thickness direction before performing the raising treatment.

  Further, the sheet-like material may be dyed. As the dyeing method, it is preferable to use a liquid dyeing machine because the sheet-like material can be further softened by dyeing the sheet-like material and simultaneously giving a stagnation effect. As the liquid dyeing machine, a normal liquid dyeing machine can be used.

  If the dyeing temperature is too high, the self-emulsifying polyurethane and the film-forming silicone may deteriorate. Conversely, if the dyeing temperature is too low, the dyeing to the fiber becomes insufficient. 80 degreeC or more and 150 degrees C or less are preferable, and 110 degreeC or more and 130 degrees C or less are more preferable.

  The dye is not particularly limited and may be selected according to the ultrafine fiber constituting the sheet-like material. For example, a polyester-based ultrafine fiber is a disperse dye, and a polyamide-based ultrafine fiber is a dye such as an acid dye or a metal-containing dye, And dyes combining them can be used.

  When dyed with disperse dyes, reduction washing may be performed after dyeing.

  Moreover, it is preferable to use a dyeing assistant during dyeing for the purpose of improving the uniformity and reproducibility of dyeing. Furthermore, finishing agents such as softeners such as silicone, antistatic agents, water repellents, flame retardants, light proofing agents, deodorants, and anti-pilling agents may be applied. But you can.

  The sheet-like material obtained by the manufacturing method of the present invention is an interior material having a very elegant appearance as a skin material for furniture, chairs, wall materials, seats, ceilings, interiors, etc. in vehicle interiors of automobiles, trains, airplanes, etc. , Shirts, jackets, casual shoes, sports shoes, men's shoes, women's shoes, upper and trim of shoes, bags, belts, wallets, etc., clothing materials used for some of them, wiping cloth, polishing cloth, etc. It can be suitably used as an industrial material.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely using an Example, this invention is not limited only to a following example.

[Evaluation methods]
(1) Average single fiber fineness A scanning electron microscope (SEM) photograph of the surface of a non-woven fabric or sheet-like material was taken at a magnification of 2000 times, and 100 fibers having a circular shape or a nearly elliptic shape were randomly selected, and the fiber diameter was selected. It measured and converted into the fineness from the specific gravity of the raw material polymer of fiber, and also calculated by calculating the average value of 100 pieces.

(2) Fineness CV
The cross section inside the non-woven fabric or sheet-like material is observed with a scanning electron microscope (SEM) at a magnification of 2000 times, and from the photograph, the fiber diameter of the ultrafine fibers constituting one bundle of bundle fibers is measured. The value obtained by converting the fiber diameter to the fineness of each single fiber and dividing the fineness standard deviation of the fibers constituting the fiber bundle by the average fineness in the bundle was expressed as a percentage (%). The same measurement was performed on the five bundle fibers, and the average value was defined as the fineness CV.

(3) Sheet-like structure The cross section inside the sheet-like article was observed with a scanning electron microscope (SEM) at a magnification of 300 times, and the adhesion between polyurethane and ultrafine fibers and the structure of the polyurethane portion were judged from the photograph.

(4) Remaining film-forming silicone on sheet-like material The measured weight of the sheet after ultrafine treatment and the theoretical calculation value were compared, and if the difference was within 30%, it was judged that the sheet remained.

(5) Quantification of silicon atom content in self-emulsifying polyurethane molecular structure The elemental analysis of the self-emulsifying polyurethane was conducted three times, and the average value was taken as the silicon atom content.

(6) Confirmation of polyethylene glycol Measured by NMR of self-emulsifying polyurethane, and compared the area of the peak attributed to the reference substance and the peak attributed to polyethylene glycol (for example, the proton of the ethylene chain portion adjacent to the oxygen atom). . The measurement was performed twice and the average value was taken as the content.

(7) Thermal gelation temperature of self-emulsifying polyurethane water dispersion 10 g of a self-emulsifying polyurethane water dispersion with a solid content concentration of 10% by weight is placed in a test tube and heated in a constant temperature hot water bath at 95 ° C. The temperature at which the emulsified polyurethane aqueous dispersion lost its fluidity and gelled and solidified was defined as the thermal gelation temperature.

(8) Amount of organic solvent contained in self-emulsifying polyurethane water dispersion In polyurethane water dispersion having a solid concentration used for impregnation, gas chromatography analysis of dispersion medium (263-50, manufactured by HITACHI, column: depending on the type of organic solvent) Although different, the amount of the organic solvent contained was quantified by using PEG20M in the case of N, N-dimethylformamide.

(9) Appearance quality The surface quality of the sheet-like material was evaluated by visual inspection and sensory evaluation as follows.
○: Napped length and fiber dispersion state are good.
Δ: Napped length is good, but fiber dispersion is poor.
X: There is almost no napped and it is inferior.

(10) Flexibility Based on method A (45 ° cantilever method) described in JIS L1096-8.19.1 (2005 edition), 5 test pieces each having a size of 2 × 15 cm are prepared in the vertical direction and the horizontal direction. The sample was placed on a horizontal base having a slope of ° C., and the test piece was slid to read the scale when the center point of one end of the test piece was in contact with the slope, and the average value of the five pieces was obtained.

[Notation of chemical substances]
The meanings of the abbreviations of chemical substances used in each example and comparative example are as follows.
PHC: polyhexamethylene carbonate polyol H12MDI: dicyclohexylmethane diisocyanate HDI: hexamethylene diisocyanate PET: polyethylene terephthalate Ny6: 6-nylon PEG: polyethylene glycol.

[Polyurethane type]
The composition of the polyurethane water dispersion used in Examples and Comparative Examples is as follows. The solid content concentration of each solution was 30% by weight. Furthermore, the characteristics of each polyurethane are shown in Table 1.
(1) Self-emulsifying polyurethane water dispersion I (PU-I)
Polyisocyanate: H12MDI
Polyol: PHC
Internal emulsifier: Diol compound having polyethylene glycol in the side chain Chain extender: Ethylenediamine
Internal cross-linking agent: γ- (2-aminoethyl) aminopropyltrimethoxysilane-containing organic solvent: 0.1% by weight
Silicone: Film-forming amino-modified silicone
“BY22-856EX” (trade name, manufactured by Toray Dow Corning)
(2) Self-emulsifying polyurethane water dispersion II (PU-II)
Polyisocyanate: H12MDI
Polyol: PHC
Internal emulsifier: dimethylolpropionic acid triethylamine salt Chain extender: ethylenediamine Internal cross-linking agent: γ- (2-aminoethyl) aminopropyltrimethoxysilane-containing organic solvent: 0.5% by weight
Silicone: Film-forming amino-modified silicone
“FZ4658” (trade name, manufactured by Toray Dow Corning)
(3) Self-emulsifying polyurethane water dispersion III (PU-III)
Polyisocyanate: HDI
Polyol: PHC
Internal emulsifier: Diol compound having polyethylene glycol in the side chain Chain extender: Ethylene diamine Internal cross-linking agent: None Contained organic solvent: 0.2% by weight
Silicone: Polydimethylsilicone film-forming
"BY22-826EX" (trade name, manufactured by Toray Dow Corning)
(4) Self-emulsifying polyurethane water dispersion IV (PU-IV)
Polyisocyanate: H12MDI
Polyol: PHC
Internal emulsifier: Diol compound having polyethylene glycol in the side chain Chain extender: Ethylenediamine Internal cross-linking agent: γ- (2-aminoethyl) aminopropyltrimethoxysilane-containing organic solvent: 0.1% by weight
Silicone: None (5) Self-emulsifying polyurethane water dispersion V (PU-V)
Polyisocyanate: H12MDI
Polyol: PHC
Internal emulsifier: Diol compound having polyethylene glycol in the side chain Chain extender: Ethylenediamine Internal cross-linking agent: γ- (2-aminoethyl) aminopropyltrimethoxysilane-containing organic solvent: 0.1% by weight
Silicone: Polydimethylsilicone oil
“SM7036EX” (trade name, manufactured by Toray Dow Corning)
(6) Forced emulsification type polyurethane water dispersion VI (PU-VI)
Polyisocyanate: H12MDI
Polyol: PHC
Internal emulsifier: None External emulsifier: Nonionic surfactant Internal cross-linking agent: None Contained organic solvent: 0.8% by weight
Silicone: Film-forming amino-modified silicone
“BY22-856EX” (trade name, manufactured by Toray Dow Corning).

[Example 1]
Polyethylene terephthalate copolymerized with 8 mol% sodium 5-sulfoisophthalate is 45 parts as a sea component and PET is 55 parts as an island component, and 36 islands are included in one filament. Using sea-island fiber staples (fiber length 51 mm) with an average fineness of 2.8 dtex, a web was formed through a card and a cross wrapper, and a nonwoven fabric was formed by needle punching.

  This non-woven fabric was shrunk by treating in hot water at 90 ° C. for 2 minutes and dried at 100 ° C. for 5 minutes. Next, a sheet impregnated with polyurethane aqueous dispersion I (PU-I) and dried with hot air at a drying temperature of 125 ° C. for 10 minutes to give polyurethane to 80% by weight of polyurethane relative to the weight of island components of the nonwoven fabric. Got.

  Next, this sheet was immersed in a 15 g / L aqueous sodium hydroxide solution heated to 90 ° C. and treated for 30 minutes to obtain a sea removal sheet from which sea components of sea-island fibers were removed. By observation with a scanning electron microscope (SEM) on the surface of the sea removal sheet, it was confirmed that the average single fiber fineness was 0.04 dtex and the fineness CV was 7.4%. Moreover, it was confirmed by the scanning electron microscope (SEM) observation of the sheet cross section that the polyurethane and the ultrafine fiber were not in close contact. Furthermore, the actual weight value of the sheet after ultrathinning treatment was compared with the theoretical calculation value, and the difference was 5.6%, so it was confirmed that the film-forming silicone remained on the sheet-like material.

  Then, the sea removal sheet is cut in half in the thickness direction, and the surface opposite to the half-cut surface is brushed by grinding using a 240 mesh endless sandpaper, and then dyed with a disperse dye in a circular dyeing machine. An inventive sheet was obtained.

  The appearance quality and flexibility of the obtained sheet-like material were good.

[Example 2]
A polyethylene-polyvinyl acetate-polyvinyl alcohol copolymer is composed of 45 parts as a sea component and 55 parts as PET as an island component, and 36 circular island components are contained in one filament, and the average fineness is A 2.4 dtex sea-island fiber staple (fiber length 51 mm) was used to form a web through a card and a cross wrapper, and a nonwoven fabric was formed by needle punching.

  This nonwoven fabric was subjected to a dry heat treatment at 190 ° C. for 2 minutes to be shrunk. Subsequently, the sheet | seat which gave the polyurethane so that the polyurethane weight with respect to the island component weight of a nonwoven fabric might be set to 70 weight% by impregnating the polyurethane water dispersion I (PU-I) and drying with hot air at a drying temperature of 125 ° C. for 10 minutes. Got.

  Next, this sheet was immersed in hot water at 90 ° C. and treated for 30 minutes to obtain a sea-removal sheet from which sea components of sea-island fibers were removed. By observation with a scanning electron microscope (SEM) on the surface of the sea removal sheet, it was confirmed that the average single fiber fineness was 0.06 dtex and the fineness CV was 7.3%. Moreover, it was confirmed by the scanning electron microscope (SEM) observation of the sheet cross section that the polyurethane and the ultrafine fiber were not in close contact. Furthermore, the weight measurement value and the theoretical calculation value of the sheet after the ultra-thinning treatment were compared, and the difference was 6.3%. Therefore, it was confirmed that the film-forming silicone remained on the sheet-like material.

  Then, the sea removal sheet is cut in half in the thickness direction, and the surface opposite to the half-cut surface is brushed by grinding using a 240 mesh endless sandpaper, and then dyed with a disperse dye in a circular dyeing machine. An inventive sheet was obtained.

  The appearance quality and flexibility of the obtained sheet-like material were good.

[Example 3]
A sea island type fiber staple in which polylactic acid is composed of 20 parts of sea component and Ny6 is 80 parts of island component, and 16 circular island components are contained in one filament, and the average fineness is 3.8 dtex. Using (fiber length 51 mm), a web was formed through a card and a cross wrapper, and a nonwoven fabric was formed by needle punching.

  This non-woven fabric was shrunk by treating in hot water at 90 ° C. for 2 minutes and dried at 100 ° C. for 5 minutes. Next, the sheet was impregnated with polyurethane aqueous dispersion II (PU-II) and dried with hot air at a drying temperature of 100 ° C. for 10 minutes to obtain a sheet provided with polyurethane so that the polyurethane weight relative to the nonwoven fabric weight was 85% by weight. .

  Next, this sheet was immersed in an aqueous solution of sodium hydroxide having a concentration of 40 g / L heated to 90 ° C. and treated for 30 minutes to obtain a sea removal sheet from which sea components of sea-island fibers were removed. By observation with a scanning electron microscope (SEM) on the surface of the sea removal sheet, it was confirmed that the average single fiber fineness was 0.2 dtex and the fineness CV was 7.5%. Moreover, it was confirmed by the scanning electron microscope (SEM) observation of the sheet cross section that the polyurethane and the ultrafine fiber were not in close contact. Furthermore, the actual weight value of the sheet after ultrathinning treatment was compared with the theoretical calculation value, and the difference was 7.0%. Therefore, it was confirmed that the film-forming silicone remained on the sheet-like material.

Then, the sea removal sheet is cut in half in the thickness direction, and the surface opposite to the half-cut surface is brushed by grinding using a 240 mesh endless sandpaper, and then dyed with a disperse dye in a circular dyeing machine. An inventive sheet was obtained.
The obtained sheet-like product was good in appearance quality, pilling evaluation, and flexibility.

[Example 4]
Except for using polyurethane aqueous dispersion III (PU-III), the same treatment as in Example 1 was performed to obtain a sheet-like material. The obtained sheet was good in appearance quality and flexibility.

[Comparative Examples 1-3]
Comparative Examples 1 and 2 were processed in the same manner as in Example 1 except that polyurethane water dispersions IV (PU-IV) and V (PU-V) containing no film-forming silicone were used, and were in sheet form. I got a thing.

  The comparative example 3 performed the process similar to Example 1 except having used forced emulsification type polyurethane water dispersion VI (PU-VI), and obtained the sheet-like material.

  All of the obtained sheet-like materials were inferior in appearance quality and flexibility.

Claims (10)

The manufacturing method of the sheet-like thing characterized by passing through the process of following (1)-(3) in this order.
(1) The process of creating a nonwoven fabric using the ultra fine fiber generation type | mold fiber which consists of a combination of 2 or more types of polymeric materials from which solubility with respect to hot water or aqueous alkali solution differs.
(2) A step of impregnating a nonwoven fabric with a self-emulsifying polyurethane aqueous dispersion containing a film-forming silicone.
(3) A step of treating the nonwoven fabric impregnated with the self-emulsifying polyurethane aqueous dispersion with hot water or an alkaline aqueous solution to develop ultrafine fibers. The method for producing a sheet-like material according to claim 1, wherein the film-forming silicone is amino-modified silicone. The content of silicon atoms in the molecular structure of the self-emulsifying polyurethane is more than 0% by weight and 1% by weight or less based on the total weight of the self-emulsifying polyurethane. The manufacturing method of the sheet-like material in any one. The said self-emulsifying type polyurethane has 3 to 30 weight% of polyethylene glycol with respect to the total weight of self-emulsifying type polyurethane, The manufacture of the sheet-like material in any one of Claims 1-3 characterized by the above-mentioned. Method. The method for producing a sheet-like product according to any one of claims 1 to 4, wherein the self-emulsifying polyurethane contains an internal emulsifier, and the internal emulsifier is nonionic. The method for producing a sheet-like material according to any one of claims 1 to 5, wherein the ultrafine fiber generating fiber is a sea-island type composite fiber. The sea component of the sea-island type composite fiber is composed of a copolyester containing terephthalic acid and ethylene glycol as main components and containing 5 to 12 mol% sodium 5-sulfoisophthalate with respect to the total acid component. The manufacturing method of the sheet-like material in any one of Claims 1-6. The method for producing a sheet-like product according to any one of claims 1 to 7, wherein the self-emulsifying polyurethane aqueous dispersion has a thermal gelation temperature of 55 ° C or higher and 90 ° C or lower. The method for producing a sheet-like material according to any one of claims 1 to 8, wherein the content of the organic solvent in the self-emulsifying polyurethane water dispersion is 1% by weight or less. A sheet-like product characterized in that a self-emulsifying polyurethane and a film-forming silicone are contained in a nonwoven fabric composed of ultrafine fibers.