Nonwoven Fabric, and Method for Producing Same

Abstract

An object of the present invention is to provide a nonwoven fabric that makes it difficult to diffuse liquid in a plane direction and can absorb and transmit liquid in a spot manner, that is, a nonwoven fabric excellent in so-called spot absorbability. The nonwoven fabric according to the present invention is formed by mixing an artificial protein fiber and a hydrophobic synthetic fiber.

Claims

1. A nonwoven fabric having a region formed by mixing an artificial protein fiber containing an artificial fibroin and a hydrophobic synthetic fiber.

2. The nonwoven fabric according to claim 1, wherein the artificial protein fiber containing an artificial fibroin and the hydrophobic synthetic fiber are mixed in an entire region.

3. The nonwoven fabric according to claim 1, wherein the artificial protein fiber containing an artificial fibroin and the hydrophobic synthetic fiber are uniformly mixed.

4. The nonwoven fabric according to claim 1, wherein the artificial fibroin is a modified spider silk fibroin.

5. The nonwoven fabric according to claim 1, wherein the artificial fibroin has an average hydropathy index of −1.0 or more.

6. The nonwoven fabric according to claim 5, wherein the artificial fibroin has an average hydropathy index of more than 0.0.

7. The nonwoven fabric according to claim 1, comprising the artificial protein fiber in an amount of 10 to 90% by mass.

8. The nonwoven fabric according to claim 1, wherein the hydrophobic synthetic fiber has an official moisture regain of less than 2%.

9. The nonwoven fabric according to claim 1, wherein the hydrophobic synthetic fiber is at least one fiber selected from the group consisting of a polyethylene terephthalate fiber, a polypropylene fiber, and a polylactic acid fiber.

10. A method for producing a nonwoven fabric, comprising mixing an artificial protein fiber containing an artificial fibroin and a hydrophobic synthetic fiber.

11. The method for producing a nonwoven fabric according to claim 10, wherein a water flow is applied to a fibrous web formed by mixing an artificial protein fiber containing an artificial fibroin and a hydrophobic synthetic fiber to entangle the artificial protein fiber and the hydrophobic synthetic fiber with each other, thereby further promoting mixing.

Description

EXAMPLES

[0042] Hereinafter, the present invention will be described more specifically based on Examples and the like. Note that the present invention is not limited to the following Examples.

[0043] (1) Production of Modified Fibroin

[0044] (Synthesis of Nucleic Acid Encoding Modified Fibroin and Construction of Expression Vector)

[0045] A modified fibroin 1 having the amino acid sequence set forth in in SEQ ID NO: 40 (average hydropathy index: 0.466) and a modified fibroin 2 having the amino acid sequence set forth in in SEQ ID NO: 15 (average hydropathy index:−0.801) were designed.

[0046] Each of nucleic acids encoding the designed two types of modified fibroins was synthesized. In each of the nucleic acids, an Ndel site was added to a 5′ terminal and an EcoRI site was added downstream of a stop codon. Each of the five types of nucleic acids was cloned with a cloning vector (pUC118). Thereafter, each of the nucleic acids was cleaved at Ndel and EcoRI by a restriction enzyme treatment and then recombined with a protein expression vector pET-22b(+) to obtain an expression vector.

[0047] (Expression of Modified Fibroin)

[0048] Escherichia coli BLR (DE3) was transformed with each of the obtained expression vectors. The transformed Escherichia coli was cultured for 15 hours in a 2 mL LB culture medium containing ampicillin. The culture solution was added to a 100 mL seed culture medium containing ampicillin (Table 2) such that OD600 reached 0.005. The culture solution was maintained at a temperature of 30° C. and subjected to flask culture (for about 15 hours) until OD600 reached 5, thereby obtaining a seed culture solution.

TABLE-US-00002 TABLE 2 Seed culture medium Reagent Concentration (g/L) Glucose 5.0 KH.sub.2PO.sub.4 4.0 K.sub.2HPO.sub.4 9.3 Yeast Extract 6.0 Ampicillin 0.1

[0049] The seed culture solution was added to a jar fermenter to which a 500 mL growing medium (Table 3 below) had been added such that OD600 reached 0.05. The culture solution was maintained at a temperature of 37° C. and cultured while being controlled so as to have a pH of 6.9 constantly. In addition, a dissolved oxygen concentration in the culture solution was maintained at 20% of a saturated dissolved oxygen concentration.

TABLE-US-00003 TABLE 3 Growing medium Reagent Concentration (g/L) Glucose 12.0 KH.sub.2PO.sub.4 9.0 MgSO.sub.4•7H.sub.2O 2.4 Yeast Extract 15 FeSO.sub.4•7H.sub.2O 0.04 MnSO.sub.4•5H.sub.2O 0.04 CaCl.sub.2•2H.sub.2O 0.04 ADEKA NOL (ADEKA, LG-295S) 0.1 (mL/L)

[0050] Immediately after glucose in the growing medium was completely consumed, a feed solution (455 g/1 L of glucose, 120 g/1 L of Yeast Extract) was added thereto at a speed of 1 mL/min. The culture solution was maintained at a temperature of 37° C. and cultured while being controlled so as to have a pH of 6.9 constantly. Culture was performed for 20 hours while the dissolved oxygen concentration in the culture solution was maintained at 20% of the saturated dissolved oxygen concentration. Thereafter, 1 M isopropyl-β-thiogalactopyranoside (IPTG) was added to the culture solution such that a final concentration was 1 mM to induce expression of a target modified fibroin. When 20 hours had elapsed after the addition of IPTG, the culture solution was centrifuged, and bacterial cells were collected. SDS-PAGE was performed using bacterial cells prepared from the culture solutions before the addition of IPTG and after the addition of IPTG. Expression of the target modified fibroin which depended on the addition of IPTG was confirmed by appearance of a band having a size corresponding to the target modified fibroin.

[0051] (Purification of Modified Fibroin)

[0052] The bacterial cells collected two hours after the addition of IPTG were washed with a 20 mM Tris-HCl buffer (pH 7.4). The washed bacterial cells were suspended in a 20 mM Tris-HCl buffer (pH 7.4) containing about 1 mM PMSF, and the cells were disrupted with a high-pressure homogenizer (GEA Niro Soavi). The disrupted cells were centrifuged to obtain a precipitate. The obtained precipitate was washed with a 20 mM Tris-HCl buffer (pH 7.4) until the precipitate obtained a high purity. The washed precipitate was suspended in an 8 M guanidine buffer (8 M guanidine hydrochloride, 10 mM sodium dihydrogen phosphate, 20 mM NaCl, 1 mM Tris-HCl, pH 7.0) such that the precipitate had a concentration of 100 mg/mL, and dissolved therein by being stirred with a stirrer at 60° C. for 30 minutes. After the precipitate was dissolved, the resulting solution was dialyzed with water using a dialysis tube (cellulose tube 36/32 manufactured by Sanko Junyaku Co., Ltd.). A white aggregated protein obtained after dialysis was collected by centrifugation. Water was removed from the collected aggregated protein by a freeze-dryer to obtain freeze-dried powders of two types of modified fibroins 1 and 2 having different amino acid sequences.

[0053] (2) Production of Artificial Protein Fiber

[0054] (Preparation of Dope Solution)

[0055] Dimethyl sulfoxide (DMSO) in which LiCl was dissolved so as to have a concentration of 4.0% by mass was prepared as a solvent, and the freeze-dried powders of the modified fibroins 1 and 2 were added thereto so as to have a concentration of 18% by mass or 24% by mass, and dissolved therein for three hours using a shaker. Thereafter, insoluble matters and foams were removed to obtain two types of modified fibroin solutions.

[0056] (Spinning)

[0057] The obtained two types of modified fibroin solutions were used as dope solutions (spinning dopes), and dry-wet spinning and drawing were performed using a known dry-wet apparatus to produce two types of artificial protein fibers containing the two types of modified fibroins, respectively. Then, these artificial protein fibers 1 and 2 were each wound around a bobbin. Out of these two types of artificial protein fibers, an artificial protein fiber containing the modified fibroin 1 is referred to as an artificial protein fiber 1, and an artificial protein fiber containing the modified fibroin 2 is referred to as an artificial protein fiber

2. Conditions of dry-wet spinning are as described below.

[0058] Temperature of coagulation liquid (methanol): 5 to 10° C.

[0059] Draw ratio: 4.52 times

[0060] Drying temperature: 80° C.

[0061] Next, the artificial protein fibers 1 and 2 obtained as described above and wound around the bobbins were pulled out from the bobbins, respectively. A plurality of the artificial protein fibers 1 was bundled, and a plurality of the artificial protein fibers 2 was bundled. The obtained bundles were each cut into a length of 50 mm with a tabletop fiber cutter to prepare a large number of artificial protein short fibers 1 and a large number of artificial protein short fibers 2. Thereafter, these two types of artificial protein 1 and artificial protein short fibers 2 were each immersed in water at 40° C. for one minute to be crimped, and then dried at 40° C. for 18 hours to obtain a large number of crimped artificial protein short fibers 1 and a large number of crimped artificial protein fibers 2. These two types of artificial protein short fibers 1 and 2 each had a fineness of about 1.4 to 1.8 dtex.

Example 1

[0062] As a hydrophobic synthetic fiber, a polyester fiber (“Tetron T471” manufactured by Toray Industries, Inc.) having a fineness of 1.6 dtex and a fiber length of 51 mm was prepared. This polyester fiber has an official moisture regain of about 0.4%. Subsequently, 50% by mass of the crimped artificial protein short fibers 1 containing the modified fibroin 1 having the amino acid sequence of SEQ ID NO: 40, obtained as described above, and 50% by mass of the polyester fibers were uniformly mixed and then caused to pass through a carding machine to obtain a fibrous web. While this fibrous web was placed on a conveyor and conveyed, a water flow was applied to the fibrous web at a water pressure of 2 MPa. Thereafter, the fibrous web was reversed, and a water flow was applied to the fibrous web at a water pressure of 4 MPa to preliminarily entangle the fibers with each other. Thereafter, the fibrous web was further reversed, and a water flow was applied to the fibrous web at a water pressure of 6 MPa to entangle the fibers with each other. Thereafter, the fibrous web was dried to obtain a nonwoven fabric having a basis weight of 62 g/m.sup.2.

Example 2

[0063] A nonwoven fabric having a basis weight of 72 g/m.sup.2 was obtained in a similar manner to Example 1 except that a polypropylene fiber (“Polypro PN” manufactured by Daiwabo Holdings Co., Ltd.) having a fineness of 1.7 dtex and a fiber length of 44 mm was used instead of the polyester fiber. Note that the polypropylene fiber has an official moisture regain of about 0.0%.

Example 3

[0064] A nonwoven fabric having a basis weight of 69 g/m.sup.2 was obtained in a similar manner to Example 1 except that a polylactic acid fiber (“Terramac PL01” manufactured by Unitika Corporation) having a fineness of 1.7 dtex and a fiber length of 51 mm was used instead of the polyester fiber. Note that the polylactic acid fiber has an official moisture regain of about 0.5%.

Example 4

[0065] A nonwoven fabric having a basis weight of 55 g/m.sup.2 was obtained in a similar manner to Example 1 except that the crimped artificial protein short fiber 2 containing the modified fibroin 2 having the amino acid sequence of SEQ ID NO: 15 was used instead of the crimped artificial protein short fiber 1.

Example 5

[0066] A nonwoven fabric having a basis weight of 55 g/m.sup.2 was obtained in a similar manner to Example 4 except that a polylactic acid fiber (“Terramac PL01” manufactured by Unitika Corporation) having a fineness of 1.7 dtex and a fiber length of 51 mm was used instead of the polyester fiber.

Comparative Example 1

[0067] A nonwoven fabric having a basis weight of 64 g/m.sup.2 was obtained in a similar manner to Example 1 except that a fibrous web formed only of the crimped artificial protein short fiber 1 was used without using the polyester fiber.

Comparative Example 2

[0068] A nonwoven fabric having a basis weight of 57 g/m.sup.2 was obtained in a similar manner to Example 1 except that a polyacrylonitrile fiber (“Vonnel H129” manufactured by Mitsubishi Chemical Corporation), which is a hydrophilic synthetic fiber, having a fineness of 1.0 dtex and a fiber length of 44 mm was used instead of the polyester fiber. Note that the polyacrylonitrile fiber has an official moisture regain of about 2.0%.

Comparative Example 3

[0069] A nonwoven fabric having a basis weight of 64 g/m.sup.2 was obtained in a similar manner to Example 1 except that a rayon fiber (“HOPE NWD” manufactured by Omikenshi Co., Ltd.), which is a hydrophilic synthetic fiber, having a fineness of 1.7 dtex and a fiber length of 40 mm instead of the artificial protein short fiber 1. Note that the rayon fiber has an official moisture regain of about 11.0%.

[0070] The nonwoven fabrics obtained in Example 1 to 5 and Comparative Example 1 to 3 were measured for the following physical properties, and results thereof are as presented in Table 4.

[0071] [Water absorption ability]

[0072] Water absorption ability (%) was measured in accordance with JIS L 1912.

[0073] [Suction Height]

[0074] A suction height (mm) after one minute was measured for an MD direction (a direction in which the fibrous web is conveyed) of the nonwoven fabric and a CD direction (direction orthogonal to the MD direction) thereof in accordance with JIS L 1912.

TABLE-US-00004 TABLE 4 Water Suction height absorption MD CD ability direction direction Example 1 1064 2 1 Example 2 603 6 1 Example 3 613 0 0 Example 4 491 0 0 Example 5 370 0 0 Comparative Example 1 505 47 54 Comparative Example 2 982 40 51 Comparative Example 3 1010 30 25

[0075] As can be seen from the results in Table 4, the nonwoven fabrics according to Examples have lower suction heights in both the MD direction and the CD direction than the nonwoven fabrics according to Comparative Examples. This means that water does not diffuse in a plane direction even when water is dropped onto the nonwoven fabrics according to Examples. Therefore, when each of the nonwoven fabrics according to Examples is used for a surface material of a sanitary material such as a sanitary napkin, it is possible to provide a sanitary material which absorbs and transmits a body fluid well, but does not cause the body fluid to diffuse in a plane direction, and does not easily adhere to the skin.