METHOD FOR MOLDING CNF AND MOLDED PRODUCT OF CNF OBTAINED BY THE MOLDING METHOD

Abstract

A porous body is placed in a rectangular parallelepipedal casing made of a stainless steel to prepare a mold form. A CNF-containing slurry is charged into the mold form, and another porous body is placed on the CNF-containing slurry. If the CNF-containing slurry are enwrapped in a nylon mesh, leakage of the CNF-containing slurry from a gap between the mold form and the porous body or clogging of the porous bodies can be inhibited. The upper and lower porous bodies are heated while applying a load to the CNF-containing slurry for a desired period of time to effect hot pressing, thereby obtaining a desired molded product. This provides a method for molding CNFs which enables a CNF molded product having a three-dimensional configuration to be obtained at a high productivity, and the CNF molded product obtained by the method for molding CNFs.

Claims

1. A method for condensing a slurry containing cellulose nanofibers (a CNF-containing slurry), which comprises: applying a load to the CNF-containing slurry using one or more vapor-permeable means which permits vapor to permeate.

2. A method for molding CNFs, which comprises: charging a CNF-containing slurry into a mold form at least partly composed of a vapor-permeable means; and applying a load to the CNF-containing slurry using the vapor-permeable means of said mold form and/or other vapor-permeable means than that of said mold form in conjunction with condensation of the CNF-containing slurry.

3. A CNF molded product prepared by the method according to claim 1, which has a uniform phase formed by drying a CNF-containing slurry charged into a mold form substantially at a time.

4. A method for molding CNFs, which comprises steps of: charging a CNF-containing slurry into a mold form at least partly composed of a vapor-permeable means; applying a load to the CNF-containing slurry using the vapor-permeable means of the mold form and/or other vapor-permeable means than that of the mold form, while heating the CNF-containing slurry and/or putting the CNF-containing slurry under reduced pressure; and repeating a step of additionally charging the CNF-containing slurry into said mold form and the step of the load application in conjunction with the heating and/or the exposure to reduced pressure.

5. The method for molding CNFs according to claim 2, which further comprises: providing a CNF molded product to be obtained with one or more portions of CNFs imparted with different properties.

6. A CNF molded product obtained by the molding method according to claim 5, wherein two or more partial CNF phases having different properties are non-junctionally integrated.

7. A CNF molded product prepared by the method according to claim 2, which has a uniform phase formed by drying a CNF-containing slurry charged into a mold form substantially at a time.

8. The method for molding CNFs according to claim 4, which further comprises: providing a CNF molded product to be obtained with one or more portions of CNFs imparted with different properties.

9. A CNF molded product obtained by the molding method according to claim 8, wherein two or more partial CNF phases having different properties are non-junctionally integrated.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 shows illustrative views of an embodiment of the present invention.

[0027] FIG. 2 shows illustrative views of another embodiment of the present invention.

[0028] FIG. 3 shows illustrative views of various embodiments of the present invention.

[0029] FIG. 4 shows illustrative views of still another embodiment of the present invention.

[0030] FIG. 5 shows illustrative views of a further embodiment of the present invention.

[0031] As shown in FIG. 1, a porous body 1a made of ceramic, a resin or the like is placed in a rectangular parallelepipedal casing 2 made of a stainless steel of which upper side is open to prepare a mold form 3. A CNF-containing slurry 4 is charged into the mold form 3, and a porous body 1b also made of ceramic, a resin or the like is placed on the CNF-containing slurry 4. If leakage of the CNF-containing slurry 4 from a gap between the mold form 3 and the upper porous body 1b or clogging of the porous bodies 1a, 1b occurs, such problems can be inhibited by enwrapping the CNF-containing slurry 4 in a mesh or a membrane 5. The upper and lower porous bodies 1a, 1b are heated and/or put under reduced pressure while applying a load to the CNF-containing slurry for a desired period of time to effect hot pressing, thereby obtaining a desired molded product 6. Incidentally, the casing 2 may be made of the same material as the porous bodies 1a, 1b instead of the stainless steel. Since the porous bodies 1a, 1b contain plenty of air therein, time reduction is realized by preliminarily heating the porous bodies 1a, 1b.

[0032] A CNF-containing slurry 4 is charged into a mold form 3 and a porous body 1b is placed on the CNF-containing slurry 4 as in the above preparation method. The resultant is heated and/or put under reduced pressure while applying a load to the CNF-containing slurry to effect evaporation to a desired concentration. Then, the porous body 1b is removed and an additional CNF-containing slurry is charged into the mold form 3 in an amount of about 10% of the weight of the initially charged CNF-containing slurry. After the porous body 1b is placed on the additional CNF-containing slurry, heating and/or exposure to reduced pressure is performed under a load to effect evaporation to a desired concentration. Moreover, a further additional CNF-containing slurry is charged into the mold form in an amount of about 10% of the weight of the initially charged CNF-containing slurry, and heating and/or exposure to reduced pressure is performed under a load to effect evaporation to a desired concentration. By repeating this procedure, a molded product 6 having a desired thickness can be prepared. In this connection, in order to obtain good adhesion between the previously charged CNFs and subsequently added CNFs, it is preferred to maintain somewhat wet state of the previously charged CNFs. Accordingly, the concentration of the previously charged CNF-containing slurry is set to be lower than that of the subsequently charged CNF-containing slurry, in other words, the concentration of the subsequently charged CNF-containing slurry is gradually increased to thereby prepare a molded product 6 having a desired thickness efficiently.

[0033] As described above, by laminating CNF layers step by step, a molded product 6 having a desired thickness can be prepared.

[0034] When it is intended to impart some properties to the surface of the molded product 6, for example, when it is intended to render the surface hydrophobic, hydrophobized CNFs 4 which have been imparted with hydrophobicity may be used only in the surface region to render the surface of the molded product 6 hydrophobic.

[0035] Alternatively (According to an alternative embodiment), in order to maintain CNFs in somewhat wet state, a water may be absorbed or drained from a CNF-containing slurry without either heating or exposure to reduced pressure to concentrate CNF-containing slurry to a desired concentration, and then, the CNF-containing slurry may be heated and/or put under reduced pressure while applying a load to the CNF-containing slurry.

[0036] FIG. 2 shows illustrative views of another embodiment of the present invention. A cylindrical porous body 1a made of ceramic, a resin or the like is placed in a cylindrical casing 2 made of a stainless steel of which upper side is open to prepare a mold form 3. A CNF-containing slurry 4 is charged into the mold form 3, and cylindrical porous body 1b also made of ceramic, a resin or the like is placed on the CNF-containing slurry 4 to thereby prepare a cylindrical molded body 6.

[0037] The cylindrical casing 2 may be made of the same material as the porous body 1a instead of the stainless steel.

[0038] [CNF-Containing Slurry]

[0039] In the present invention, as CNF, those derived from a polysaccharide including a natural plant fiber such as a wood fiber, a bamboo fiber, a sugar cane fiber, a seed hair fiber, a leaf fiber or the like may be mentioned. These CNFs may be used alone or in combination.

[0040] The CNFs used in the present invention have an average thickness of 4 to 200 nm and an average length of 0.1 μm or more and can be prepared by fibrillating a polysaccharide by means of jets of highly pressurized water.

[0041] The fibrillation of a polysaccharide is performed by causing high-pressure jets (about 50 to 400 MPa) of aqueous polysaccharide slurry containing 0.5 to 10% by weight of the polysaccharide to collide with each other.

[0042] However, methods for preparing a CNF used in the present invention are not restricted to the above-described method, a CNF used in the present invention may be prepared by other methods, for example, chemical methods such as an acid hydrolysis method and a TEMPO-mediated oxidation method, and physical methods such as a grinder method and a high-pressure homogenizer method.

[0043] FIG. 3 shows other embodiments of the present invention. FIG. 3(a) shows such an embodiment that a CNF-containing slurry 4 is held between upper and lower porous bodies 1b, 1a and a load is placed on the upper porous body 1b. In this embodiment, steam is caused to escape laterally from the porous bodies 1a, 1b. FIG. 3(b) shows such an embodiment that a CNF-containing slurry 4 is held between upper and lower porous bodies 1b, 1a as in the embodiment in FIG. 3(a), and loads are placed on marginal portions of the upper porous body 1a to permit steam to escape from the upper surface of the upper porous body 1b as well as the sides of the porous bodies 1a, 1b. FIG. 3(c) shows such an embodiment that loads are placed on marginal portions of the upper porous body 1b as in the embodiment in FIG. 3(b), and a plurality of through holes 7 as permeation aids are provided in the upper porous body 1b to permit steam to escape also from the through holes 7, thereby streamlining discharge of steam. FIG. 3(d) shows such an embodiment that a plurality of slits 8 are provided in the upper porous body 1b to permit steam to escape also from the slits 8, thereby streamlining discharge of steam. FIG. 3(e) shows such an embodiment that CNF-containing slurry 4 is vertically held between right and left porous bodies 1a, 1b and loads are laterally applied to the right and left porous bodies 1a, 1b. In this embodiment, steam is permitted to escape upward in the vertical direction from the porous bodies 1a, 1b to streamline discharge of steam.

[0044] FIG. 4 shows a further embodiment of the present invention. Molding is carried out under such a condition that CNF-containing slurry 4 is interposed between an upper porous body 1b as a male mold and a lower porous body 1b as a female mold, thereby preparing a molded product 6 having a glass shape.

[0045] FIG. 5 shows a still further embodiment of the present invention. In this embodiment, molding is carried out under such a condition that CNF-containing slurry 4 is interposed between an upper porous body 1b as a male mold and a lower porous body 1b as a female mold with a core of a desired shape, for example, a 100-yen coin in the case shown in FIG. 5 disposed between the lower porous body 1b and the CNF-containing slurry 4, thereby preparing a molded product 6 to which the design of the 100-yen coin is transferred.

EXAMPLES

Example 1

[0046] A CNF-containing slurry 4 enwrapped in a nylon mesh 5 was charged into a mold form 3 composed mainly of a porous body 1a made of a resin (ultrahigh molecular weight polyethylene (UHMWPE), heatproof temperature: 110° C., average pore diameter: 15 μm, porosity: 30 to 50%) and a rectangular parallelepipedal casing 2 made of a stainless steel and having a wall thickness of about 4 mm, and a porous body 1b made of the same material as the porous body 1a was placed on the CNF-containing slurry 4. The upper and lower porous bodies 1b, 1a were heated to 110° C. for a desired period of time to effect hot pressing while applying a load to the CNF-containing slurry. Molding conditions of the hot pressing are shown in Table 1.

TABLE-US-00001 TABLE 1 Concen- tration of Type Starting Basis Thick- Drying of Material Weight Size ness Load Time Wood Fibrillation % g/m.sup.2 cm mm kg h Hard- 100 MPa × 13.6 1230 5 × 9 about 1   200 1.5 wood 10 passes 1110 5 × 9 about 1   400 3   Soft- 180 MPa × 12    550 5 × 9 about 0.5 400 2.5 wood 50 passes 2270 5 × 9 about 2   800 4  

[0047] As shown in Table 1, an aqueous slurry of pulp derived from LB (hardwood) was introduced into opposing two nozzles and jetted therefrom toward one point under a high pressure of 100 MPa and thereby caused to collide. (The resultant was re-introduced into the opposing two nozzles.) This cycle was repeated 10 times (10 passes) to obtain a 13.6% CNF-containing aqueous slurry. 1230 g/m.sup.2 of the 13.6% CNF aqueous slurry was weighed and charged into the mold form 3 composed of the porous body 1a and the casing 2, and the porous body 1b was placed on the CNF-containing slurry. The upper and lower porous bodies 1b, 1a were heated to 110° C. while applying a load of 200 kg for 1.5 hours to obtain a CNF molded product having a thickness of about 1 mm. The thus obtained CNF molded product was somewhat warped. It is assumed that the CNF molded product was substantially free from the warp at the time of removal from the mold form 3 but somewhat moistened, and accordingly, underwent the warp afterward due to the insufficient dryness. Accordingly, if the CNFs are dried sufficiently while a load is applied to the CNFs, such deformation of the CNFs due to shrinkage can be prevented. Accordingly, when a CNF molded product was obtained in substantially the same manner as above except that 1110 g/m.sup.2 of the 13.6% CNF-containing aqueous slurry was weighed and charged into a mold form 3 and a load of 400 kg was applied to the CNF-containing aqueous slurry for 3.0 hours, the thus obtained CNF molded product was substantially free from deformation.

[0048] An aqueous slurry of pulp derived from NB (softwood) was introduced into opposing two nozzles and jetted therefrom toward one point under a high pressure of 180 MPa and thereby caused to collide. (The resultant was re-introduced into the opposing two nozzles.) This cycle was repeated 50 times (50 passes) to obtain a 12.0% CNF-containing aqueous slurry. 550 g/m.sup.2 of the 12.0% CNF-containing aqueous slurry was weighed and charged into the mold form 3 composed of the porous body 1a and the casing 2, and the porous body 1b was placed on the CNF-containing aqueous slurry. The upper and lower porous bodies 1b, 1a were heated to 110° C. while applying a load of 400 kg for 2.5 hours to obtain a CNF molded product having a thickness of about 0.5 mm. The thus obtained CNF molded product was also somewhat warped. It is assumed that the drying for 2.5 hours was insufficient and the CNF molded product underwent the warp due to the insufficient dryness. On the other hand, when a CNF molded product was obtained in substantially the same manner as above except that 2270 g/m.sup.2 of the 12.0% CNF-containing aqueous slurry was weighed and charged into a mold form 3 and a load of 800 kg was applied to the CNF-containing aqueous slurry for 4.0 hours, the thus obtained CNF molded product was substantially free from deformation.

Example 2

[0049] In order to maintain CNFs in a partly wet state, water was absorbed from a CNF-containing aqueous slurry by means of Kimtowel (prepared and sold by Nippon Paper Crecia Co., Ltd) without either heating or exposure to reduced pressure to concentrate the CNF-containing aqueous slurry to a desired concentration. Then, the concentrated CNF-containing aqueous slurry was hot pressed (at 90° C. overnight (for 20 hours) under a load of 800 kg) using a mold form 3 somewhat larger than that in Example 1 to prepare a CNF molded product. Molding conditions of the hot pressing are shown in Table 2. Also by this molding process, a CNF molded product with no substantial deformation was obtained.

TABLE-US-00002 TABLE 2 Concen- tration Type of Starting Basis Thick- Drying of Material Weight Size ness Load Time Wood Fibrillation % g/m.sup.2 cm mm kg h Soft- 180 MPa × 12 2990 9.5 × about 3 800 20 wood 50 passes 9.5

[0050] In each of the above Examples, heat resistant temperature of the porous bodies made of the resin was 110° C. However, when vapor permeable bodies made of ceramic, a metal or the like which has a higher heat resistant temperature are used, drying temperature can be increased to thereby realize reduction of drying time.

NOTE ON REFERENCE NUMBERS

[0051] 1 . . . porous body, 2 . . . casing made of a stainless steel, 3 . . . mold form, 4 . . . CNF, 5 . . . nylon mesh, 6 . . . molded product