JP2009185417A - Cellulose nano-fiber nonwoven sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material which is a nonwoven sheet using cellulose nano-fibers, and having performances of gradually degrading under the natural environment and finally disappearing after use without causing air pollution when incinerated after the use with less effects on the environment, and having a soft touch feeling and a good touch on skin. <P>SOLUTION: The nonwoven sheet comprises the cellulose nano-fibers as main fibers. The main fibers are mutually heat-bonded by softening or melting a binder component of the binder fibers. The binder component is a polymer obtained by copolymerizing a polyalkylene succinate with at most 10 mol% of lactic acid. The binder fibers are preferably core-sheath type conjugated fibers in which a polylactic acid is arranged in a core part and a polymer that is prepared by copolymerizing the polyalkylene succinate with at most 10 mol% of the lactic acid is arranged in a sheath part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-woven sheet having a soft texture and using cellulose nanofibers.

Cellulose nanofibers are so-called nanofibers with a diameter of about 4 nm that form the basic skeleton of all plant cells, and have a storage capacity of about 1 trillion tons on the earth. In recent years, a technique has been established in which pulp that has been subjected to enzyme treatment and delignification is ground with a biaxial kneader or grinder to obtain uniform cellulose nanofibers (for example, Patent Document 1). This cellulose nanofiber itself has the same high strength as para-aramid fiber, and has a low thermal expansion coefficient comparable to that of quartz glass, so it has been commercialized as a phenolic resin reinforcing material for automobile exterior materials and machine element parts. Yes.
JP 2008-1728 A

  The present inventor considered not using the cellulose nanofiber as a resin reinforcing material but applying it as a constituent material of a fabric. In consideration of the environmental load, it was considered to impart biodegradability to the fabric.

  An object of the present invention is a fabric using cellulose nanofibers, which has an environmental load reducing effect, has a performance of gradually decomposing in a natural environment and finally disappearing after use, and incineration after use It is an object of the present invention to provide a fabric that is free from air pollution and has little environmental impact.

  As a result of studying the present inventors to achieve the above-mentioned problems, by using a binder fiber having a polyalkylene succinate, cellulose nanofibers are thermally bonded together to form a sheet, thereby maintaining practical strength, and The present inventors have found that it has a soft texture and have reached the present invention.

  That is, the present invention is a non-woven sheet having cellulose nanofibers as main fibers, and the main fibers are thermally bonded to each other by softening or melting the binder component of the binder fibers, and the binder component becomes polyalkylene succinate. The gist of the nonwoven sheet of cellulose nanofibers is a polymer obtained by copolymerizing at most 10 mol% of lactic acid.

  Hereinafter, the present invention will be described in detail.

  The nonwoven sheet of the present invention is composed mainly of cellulose nanofibers. Cellulose nanofibers are nano-sized in diameter and are fibers of about 2 to 150 nm. For example, cellulose nanofibers having a substantially uniform diameter and fiber length, which are obtained by grinding a pulp that has been subjected to enzyme treatment and delignification with a twin-screw kneader or a grinder, can be used. The fiber length is generally about a few microns.

  The nonwoven sheet of the present invention is obtained by thermally bonding cellulose nanofibers by melting or softening a binder component of binder fibers.

  The binder fiber used in the present invention is composed of a polymer in which at most 10 mol% of lactic acid is copolymerized with polyalkylene succinate. As polyalkylene succinate, ethylene succinate, butylene succinate, propylene succinate and the like are used as repeating units, and alkylene diols such as ethylene glycol, butanediol, propanediol and succinic acid are polymerized. In the present invention, “fiber” is used as a binder for bonding cellulose nanofibers, which are main fibers, because cellulose nanofibers are in fiber form, so it is not preferable to use the same fiber form as a binder. This is because in the production of the woven sheet, it is easy to disperse uniformly with the cellulose nanofibers which are the main fibers. This is because, by uniformly dispersing, the obtained nonwoven sheet has a uniform strength and good quality. In the present invention, the reason why the above polyalkylene succinate is used as a binder component is that the polymer is not hard and has good flexibility, so that the obtained non-woven sheet is also excellent in flexibility. is there. In the present invention, the above repeating unit includes cyclic lactones such as ε-caprolactone, α-hydroxybutyric acid, α-hydroxyisobutyric acid, α-hydroxyvaleric acid and the like within a range not impairing the object of the present invention. α-Oxyacids, glycols such as diethylene glycol and 1,6-hexanediol, and dicarboxylic acids such as adipic acid, sebacic acid and malic acid may be copolymerized, but if the copolymerization rate is too high, the melting point will be lowered. Accordingly, the copolymerization amount is set to a range of 30 mol% or less.

  The polyalkylene succinate serving as the binder component is copolymerized with at most 10 mol% of lactic acid. This is because, by setting the copolymerization ratio of lactic acid to at most 10 mol%, the inherent flexibility of the polyalkylene succinate can be maintained without being impaired. When the amount of lactic acid to be copolymerized exceeds 10 mol%, the inherent flexibility of the polyalkylene succinate is impaired, so the binder fiber becomes hard and lacks flexibility, and the nonwoven sheet using this fiber as a binder has a texture. Becomes hard.

  In the present invention, the melting point of a polymer obtained by copolymerizing at most 10 mol% of lactic acid with a polyalkylene succinate as a binder component is preferably 90 ° C. or higher. When the melting point is less than 90 ° C., adhesion tends to occur at the time of spinning or stretching, and the operability tends to be inferior. The upper limit of the melting point of the binder component is preferably set to 140 ° C. or lower in consideration of the heat treatment temperature for functioning as a binder. When the melting point exceeds 140 ° C., it is necessary to set a high heat treatment temperature when softening or melting the binder component, and in this heat treatment step, decomposition of cellulose may start.

  According to the method described in ASTM D 1238, the binder component preferably has a MFR measured at a temperature of 190 ° C. and a load of 20.2 N (2160 gf) of 5 to 80 g / 10 minutes, and preferably 20 to 40 g / 10. More preferably, it is minutes. When the MFR is less than 5 g / 10 min, not only melt extrusion becomes difficult, but the mechanical strength of the fiber tends to decrease. On the other hand, even if the MFR exceeds 80 g / 10 min, it is difficult to obtain a good fiber by melt extrusion.

  The form of the binder fiber used in the present invention may be a single-phase form composed only of the binder component described above or a composite form in which the binder component occupies a part of the fiber surface. In the case of adopting a composite form, a polymer having a biodegradability is also adopted as the polymer combined with the binder component. In the present invention, a core-sheath type composite fiber in which a polylactic acid is disposed in the core part and a polymer obtained by copolymerizing at most 10 mol% of lactic acid in polyalkylene succinate is disposed in the sheath part as the binder fiber. When polylactic acid and polyalkylene succinate are combined, the compatibility of the polyalkylene succinate with the core is greatly improved by using a copolymer obtained by copolymerizing lactic acid. When the compatibility between the polymer of the core and the sheath is low, the binder component of the melted sheath exhibits a behavior such that the interface with the core is small, and flows and aggregates in an island shape. As a result, the binder component tends to exist locally. By adding lactic acid, which is a component common to the polylactic acid in the core, to the polyalkylene succinate, which is the binder component, the compatibility between the binder component in the sheath and the polylactic acid in the core is improved, as described above. Therefore, since the binder component is present over the entire surface of the sheet, the adhesive strength is not uneven and the strength of the nonwoven sheet itself can be improved. When the binder fiber is a core-sheath composite fiber, the core / sheath ratio between the core and the sheath is preferably 30/70 to 70/30 in terms of the volume ratio of the core / sheath in terms of operability and cost. is there.

  In the present invention, the lactic acid copolymerized with the polyalkylene succinate may be L-lactic acid or D-lactic acid. Moreover, although lactic acid is based on what is copolymerized by a monomer unit, a part of oligomer unit (about 2-10 pieces) may be included in the range which does not impair the effect of this invention. .

  As polylactic acid combined with the binder component, poly L-lactic acid, poly D-lactic acid, poly DL-lactic acid which is a copolymer of L-lactic acid and D-lactic acid, or a mixture of poly L-lactic acid and poly D-lactic acid Any of (stereo complex) may be used. When poly DL-lactic acid which is a copolymer of L-lactic acid and D-lactic acid is used, the copolymerization ratio of D-lactic acid and L-lactic acid (D-lactic acid / L-lactic acid) is 100/0 to 95/5. 5/95 to 0/100 is preferable. Copolymers with a copolymerization ratio outside the above range have a low melting point and a high amorphous property, making it difficult to obtain high-strength fibers. In the present invention, by providing polylactic acid having crystallinity in the core of the binder fiber, the fiber can maintain a practical strength.

  The viscosity of polylactic acid is 5-80 g / 10 min in melt flow rate (hereinafter abbreviated as MFR) measured at a temperature of 210 ° C. and a load of 20.2 N (2160 gf) according to the method described in ASTM D 1238. It is preferable that it is 20-40 g / 10min. When the MFR is less than 5 g / 10 min, not only melt extrusion becomes difficult, but the mechanical strength of the fiber tends to decrease. On the other hand, if the MFR exceeds 80 g / 10 min, it is difficult to obtain a good fiber by melt extrusion.

  Moreover, you may add terminal blockers, such as aliphatic alcohol, a carbodiimide compound, an oxazoline compound, an oxazine compound, an epoxy compound, to polylactic acid for the purpose of improving the durability of a binder fiber. As long as the purpose of the present invention is not impaired, cyclic lactones such as ε-caprolactone, α-hydroxy acids such as α-hydroxybutyric acid, α-hydroxyisobutyric acid and α-hydroxyvaleric acid, ethylene glycol, 1,4-butane Glycols such as diols and dicarboxylic acids such as succinic acid and sebacic acid may be contained in the polylactic acid.

  The fineness of the binder fiber used in the present invention is preferably about 1.0 to 20 dtex, more preferably 1.7 to 10 dtex, in consideration of productivity, operational stability, adhesion performance, and the like.

  The shape of the binder fiber is not limited to a circular cross section, and may be a flat shape, a polygonal shape, a multi-leaf shape, a gourd shape, an alphabet shape, and other various non-circular shapes (an irregular shape).

  In addition, the binder fiber is made of various pigments, dyes, water repellents, water absorbents, flame retardants, stabilizers, antioxidants, UV absorbers, metal particles, crystal nucleating agents, lubricants, plasticizers, antibacterial agents, fragrances, etc. You may mix and add an additive according to the objective.

  The binder fiber used in the present invention can be obtained by the following method. A polymer in which at most 10 mol% of lactic acid is copolymerized with polyalkylene succinate or this and polylactic acid are melted using an ordinary single component spinning device or a compound spinning device (concentric core-sheath type compound spinning device). After spinning, cooling, and applying an oil agent, it is wound up without stretching. The undrawn yarn is focused on a tow of several hundred thousand to two million dtex, drawn at a draw ratio of 2 to 5 times, a draw temperature of 40 to 80 ° C, and subjected to heat treatment at 80 to 130 ° C. Subsequently, after applying mechanical crimping with a push-in type crimper if necessary, applying a finishing oil, drying with a drier, and further using a cutter such as an EC cutter (fiber length of about 5 to 150 mm) Into short fibers to obtain binder fibers.

  The nonwoven sheet of the present invention can be obtained by the following method.

  Disperse in binder fibers and cellulose nanofibers in water so that the solid content concentration is usually about 0.1 to 2%, and if necessary, dispersants such as polyalkylene oxide, polyacrylamide and other surfactants A small amount of an antifoaming agent such as alcohol, higher alcohol, or silicone oil is blended, and then rolled up by a wet papermaking method to obtain a sheet. Next, in order to melt or soften the binder component together with the purpose of removing excess moisture and to function as a binder, the heat treatment temperature is 10 ° C. lower than the melting point of the binder component through a Yankee dryer or a hot air dryer. Heat treatment is performed at a temperature 30 ° C. higher than the melting point to obtain a nonwoven sheet. Note that the set temperature at the time of the heat treatment is appropriately set because it is related to the processing speed (processing time). Also, once the excess moisture is removed with a Yankee dryer or hot air dryer (heat treatment temperature and time are set so that the binder component does not melt or soften), the binder component is melted or softened in a separate process. To obtain a non-woven sheet. As a separate process, it is preferable to pass through a Yankee dryer, a hot air dryer or a heat calendar roll.

  The non-woven sheet of the present invention is a non-woven sheet using fibers composed of a single component having a binder component of a polymer obtained by copolymerizing at most 10 mol% of lactic acid with the polyalkylene succinate or other polymer. It is. In the nonwoven sheet of the present invention, since the polyalkylene succinate functioning as a binder is excellent in flexibility, the fused portion of the binder part, which is a melted or softened polymer, does not become too hard and does not have a rough feeling. A feel sheet can be obtained.

  Since the nonwoven sheet of the present invention uses cellulose nanofibers as the main fiber, it is possible to impart performance capable of filtering even unprecedented fine components by the action of cellulose nanofibers. The nonwoven sheet of the present invention is preferably used as a filter cloth.

  Moreover, it is preferable to use a nonwoven sheet as a disposable mask. Even if it directly touches the skin, it has a soft feel and can block pollen and dust.

  Moreover, since the nonwoven sheet contains the binder component, it is possible to perform three-dimensional molding by heat, and three-dimensional molding can be performed in various shapes depending on the application.

  The present invention is a binder fiber comprising a cellulose nanofiber as a main fiber and a polymer obtained by copolymerizing at most 10 mol% of lactic acid with a polyalkylene succinate, and the polymer melts or softens. Therefore, the cellulose nanofiber is a non-woven sheet formed by thermal bonding, and therefore, when incinerated after use, it is a material that has no air pollution and little environmental impact. In addition, it is a non-woven sheet that has practical strength but soft texture and good touch. It can be suitably used as a filter cloth and is also suitable as a disposable mask.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples. In addition, the measuring methods, such as a characteristic value in an Example, are as follows. Moreover, the measuring method of MFR is as having mentioned above.

(1) Melting point (° C.): Temperature that gives an extreme value in the obtained melting endothermic curve, measured using a differential scanning calorimeter DSC-2 manufactured by Perkin Elma Co., Ltd. under a temperature rising rate of 20 ° C./min. Was the melting point.

(2) Single yarn fineness (dtex): measured by the method of JIS L-1015 7-5-1A.

(3) Tensile strength of nonwoven sheet (cN / 25 mm width): A nonwoven fabric was cut into strips having a width of 25 mm and a length of 150 mm to prepare a sample. This sample was stretched and cut using a UTM-4 type Tensilon manufactured by Orientec Corp. under the conditions of a grip interval of 100 mm and a tensile speed of 100 mm / min, and the maximum strength was read. In the present invention, a tensile strength of 1000 cN or more is assumed to have a practical strength.

 (4) Texture of non-woven sheet: The non-woven sheet was subjected to a sensory evaluation of the softness of the texture by a hand test by 10 panelists. When 9 or more out of 10 people evaluate that the texture is soft, ○, when 5 to 8 people evaluate that the texture is soft, △, and 4 or less who also evaluate that the texture is soft When it was, it was set as x.

Example 1
Polybutylene succinate (MFR 24 g / 10 min, melting point 112 ° C.) was melt-spun at a spinning temperature of 230 ° C. and a spinning speed of 800 m / min. A drawn yarn was obtained. Next, the obtained undrawn yarn was drawn at a drawing temperature of 60 ° C. and a draw ratio of 3.50 times, and then dried at 70 ° C. after applying a hydrophilic oil for wet papermaking, cut to a fiber length of 5 mm, and fineness A binder fiber having a diameter of 1.5 dtex was obtained.

When 40% by mass of the obtained binder fiber and 60% by mass of cellulose nanofiber were mixed and dispersed in water at a paper stock concentration of 0.1% and a surfactant concentration of 0.02%, they were uniformly dispersed. When this was subjected to wet paper making using a 25 cm square square sheet machine, a sheet with good texture was obtained. The obtained sheet was dried through a Yankee dryer at 110 ° C. to remove excess moisture, and further subjected to thermocompression treatment through a hot flat roller at 110 ° C. to obtain a nonwoven sheet having a basis weight of 35 g / m ² . The resulting nonwoven sheet had a tensile strength of 2240 cN / 25 mm and a texture of ◯.

Example 2
In Example 1, the nonwoven sheet was obtained like Example 1 except having used the following core-sheath-type composite binder fiber as a binder fiber. The binder fiber was obtained by the following method.

  Polybutylene having polylactic acid (MFR 21 g / 10 min, copolymerization ratio of D-lactic acid / L lactic acid = 1.3 / 98.7, melting point 170 ° C.) and 3.0 mol% L-lactic acid copolymerized Succinate (MFR 32 g / 10 min, melting point 109 ° C.) is used as the sheath, 560 holes and a circular cross-section core-sheath composite spinneret is used, and the core-sheath ratio is such that the core volume ratio is 50:50. And melt-spun at a spinning temperature of 230 ° C. and a spinning speed of 800 m / min to obtain an unstretched yarn of core-sheath type composite fiber. Next, the obtained undrawn yarn is drawn at a drawing temperature of 60 ° C. and a draw ratio of 3.50 times, and then after applying a hydrophilic oil agent for wet papermaking, after applying a crimp with a push-in type crimping machine. After applying the finishing oil, it was dried at 70 ° C., cut to a fiber length of 5 mm, and a core-sheath type composite binder fiber having a fineness of 2.2 dtex was obtained.

  The obtained nonwoven sheet had a tensile strength of 2450 cN / 25 mm width and a texture of ◯.

Example 3
In Example 2, as the polymer of the binder component of the core-sheath type composite binder fiber, the amount of lactic acid copolymerized with polybutylene succinate is 1.5 mol% (the melting point of the binder component is 112 ° C.). A non-woven sheet was obtained in the same manner as in Example 2 except that.

  The resulting nonwoven sheet had a tensile strength of 1970 cN / 25 mm width and a texture of ◯.

Example 4
In Example 2, as the polymer of the binder component of the core-sheath composite binder fiber, a copolymer of 4.5 mol% of lactic acid copolymerized with polybutylene succinate (melting point of the binder component at 107 ° C.) is used. A non-woven sheet was obtained in the same manner as in Example 2 except that.

  The obtained nonwoven sheet had a tensile strength of 2050 N / 25 mm and a texture of ◯.

Example 5
In Example 2, polyethylene succinate (MFR 29 g / 10 min, melting point 101 ° C.) obtained by copolymerizing 3.0 mol% of L-lactic acid was used as the polymer of the binder component of the core-sheath composite binder fiber. A nonwoven sheet was obtained in the same manner as in Example 2.

  The obtained nonwoven sheet had a tensile strength of 2120 N / 25 mm width and a texture of ◯.

Comparative Example 1
In Example 2, a copolymerization ratio of L-lactic acid / D-lactic acid of 8.8 / 91.2 (MFR = 24/10 minutes, melting point 130 ° C.) was used as the binder component of the core-sheath composite binder fiber. Except for the above, a nonwoven sheet was obtained in the same manner as in Example 2.

  The resulting nonwoven sheet had a tensile strength of 2640 N / 25 mm width and a texture of x.

  In Examples 1 to 5, which are the nonwoven sheets of the present invention, the strength of the nonwoven sheets was sufficiently high, and the texture was very soft. On the other hand, in Comparative Example 1, polylactic acid was used as a binder component. Although the nonwoven sheet had high strength, the nonwoven sheet itself was rigid and hard, and lacked softness.

Claims (4)

It is a non-woven sheet with cellulose nanofibers as the main fiber, and the main fibers are thermally bonded by softening or melting the binder component of the binder fiber. The binder component is polyalkylene succinate and lactic acid is at most 10 mol%. A cellulose nanofiber nonwoven sheet characterized by being a copolymerized polymer. 2. The core-sheath type composite fiber according to claim 1, wherein the binder fiber is a core-sheath type composite fiber in which a polylactic acid is disposed in the core part and a polymer in which at most 10 mol% of lactic acid is copolymerized in the polyalkylene succinate is disposed in the sheath part. Cellulose nanofiber nonwoven sheet. A filter cloth comprising the cellulose nanofiber nonwoven sheet according to claim 1. A disposable mask comprising the cellulose nanofiber nonwoven sheet according to claim 1 or 2.