JP6256644B1 - Method for producing nanofiber composite - Google Patents

Abstract

Provided is a method for producing a nanofiber composite, which can efficiently mass-produce a nanofiber composite including nanofibers and a crosslinkable resin and having an excellent resin reinforcing effect by nanofibers. A nanofiber composite comprising a first step of mixing a nanofiber, a water-soluble or water-dispersible synthetic resin, a water-soluble dispersant, and an aqueous solvent in a single stage under a mechanical defibrating process. Production method. According to this manufacturing method, it is easy to scale up the production scale, and the component dispersibility is equal to or higher than that of the nanofiber composite obtained by the conventional two-stage method regardless of the laboratory level or the production level. The nanofiber composite can be stably manufactured at an extremely low cost. [Selection figure] None

Description

  The present invention relates to a method for producing a nanofiber composite comprising nanofibers and a crosslinkable resin.

  Nanofibers derived from natural products such as cellulose nanofibers, cellulose nanocrystals, and chitosan nanofibers have been attracting much attention in recent years because they have almost the same resin reinforcement effect as glass fibers that are currently used as resin reinforcements. Collecting. However, at present, one of the technical problems is to uniformly and finely disperse nanofibers in a synthetic resin. For this reason, the mass production of the nanofiber composite containing the nanofiber and the synthetic resin and sufficiently exhibiting the resin reinforcing effect of the nanofiber has not been achieved.

  Conventionally, nanofiber composites are prepared by, for example, mixing a nanofiber dispersion prepared in advance with a resin by a dry process such as a biaxial kneader after solvent removal, or stirring the nanofiber dispersion and the resin solution in a wet state. And by mixing. The nanofiber dispersion can be obtained, for example, by binding a dispersant such as a surfactant to the unmodified nanofibers and dispersing the resultant together with a dispersion medium using a dispersing device such as a homogenizer.

  Patent Document 1 discloses a cellulose nanofiber dispersion liquid that contains cellulose nanofibers, an anionic dispersant, and a dispersion medium, and in which cellulose nanofibers are uniformly dispersed in the dispersion medium by high-pressure jetting. A nanocellulose composite is obtained by mixing the cellulose fiber dispersion and a resin. .

  Patent Document 2 includes a cellulose nanofiber, a dispersant (X), and a dispersion medium, and the dispersant (X) is composed of a resin affinity segment and a cellulose affinity segment, and has a block copolymer structure or a gradient copolymer. Disclosed is a cellulose nanofiber dispersion (Y) having a structure. Moreover, in patent document 2, the cellulose nanofiber composite body is manufactured by mixing the cellulose nanofiber dispersion (Y) prepared beforehand, resin, and a dispersing agent (X).

  Patent Document 3 discloses a coating liquid for forming a gas barrier layer, which is a nanofiber composite containing a cellulose nanofiber dispersion, a water-soluble polymer compound, an inorganic layered compound, and a water repellent. The coating liquid is prepared by adding and mixing a water-soluble polymer compound, an inorganic layered compound, and a water repellent to a cellulose nanofiber dispersion liquid prepared in advance.

JP 2012-51991 A JP 2014-162880 A JP 2014-218579 A

  The cited references 1 to 3 described above all relate to a method for producing a nanofiber composite by a two-stage process in which a nanofiber dispersion is first prepared and the obtained dispersion and a resin are mixed. However, in these techniques, a nanofiber composite in which nanofibers are uniformly dispersed in a resin cannot be obtained, and the effect of improving the properties of the composite by nanofibers may be insufficient.

  An object of the present invention is a method for producing a nanofiber composite, which comprises nanofiber and a water-soluble or water-dispersible synthetic resin, and can efficiently mass-produce a nanofiber composite excellent in resin reinforcement effect by nanofiber. Is to provide.

This invention provides the manufacturing method of the nanofiber composite_body | complex of the following [1]-[ 9 ].

[1 ] including a first step in which nanofibers, a water-soluble or water-dispersible synthetic resin, a water-soluble dispersant, and an aqueous solvent are mixed in a single stage under mechanical defibrating treatment, and the synthetic resin is water-soluble or water-soluble a crosslinkable resin having a dispersibility, combined use of crosslinkable resins and reactive crosslinking agent thereto, a manufacturing method of the nano-fiber composite.
[ 2 ] including a first step in which nanofibers, a water-soluble or water-dispersible synthetic resin, a water-soluble dispersant, and an aqueous solvent are mixed in one step under a mechanical defibration process, and the synthetic resin is water-soluble or water-soluble it is a self-crosslinking resin having a dispersion method of the nano fiber composites.
[ 3 ] The method for producing a nanofiber composite according to [1 ] or [2] , further including a second step of performing a crosslinking treatment on the mixture obtained in the first step.
[ 4 ] A third product is obtained by molding while removing the aqueous solvent from the mixture obtained in the first step, or by molding a solid content obtained by removing the aqueous solvent from the mixture obtained in the first step. The method for producing a nanofiber composite according to the above [1 ] or [2] , further comprising a step and a fourth step of subjecting the molded product obtained in the third step to a crosslinking treatment.
[ 5 ] The nanofiber composite according to any one of [1] to [ 4 ], wherein the nanofiber is at least one selected from the group consisting of unmodified cellulose nanofiber, cellulose nanocrystal, and chitosan nanofiber. Production method.
[ 6 ] The method for producing a nanofiber composite according to any one of [1] to [ 5 ], wherein the synthetic resin is used in the form of a solution or a dispersion.
[ 7 ] The method for producing a nanofiber composite according to any one of [1] to [ 6 ], wherein the dispersant is an anionic dispersant.
[ 8 ] The anionic dispersant is a compound having at least one functional group selected from a phosphoric acid group, a carboxy group, a sulfonic acid group, a metal ester group thereof, and an imidazoline group, and acryloyloxyethyl phosphorylcholine (co-polymer). ) The method for producing a nanofiber composite according to [ 7 ] above, which is at least one selected from the group consisting of polymers.
[ 9 ] The method for producing a nanofiber composite according to [3] or [4] above, wherein the crosslinking treatment is chemical crosslinking or physical crosslinking.

  According to the method for producing a nanofiber composite of the present invention, a nanofiber composite including a nanofiber and a water-soluble or water-dispersible synthetic resin and having an excellent resin reinforcing effect by the nanofiber can be efficiently mass-produced. .

  The inventors of the present invention have made extensive studies to solve the above-described problems of the prior art. As a result, in the conventional two-stage process including the step of obtaining the nanofiber dispersion and the process of mixing the nanofiber dispersion and the resin, particularly in the two-stage process during mass production, the nanofiber is introduced into the resin. It has been found that there is a case where the uniform dispersion of the resin and the resin reinforcement by the nanofibers are insufficient. Of course, it is well known that even if nanofibers, resin, and aqueous solvent are mixed in a single step, uniform dispersion of nanofibers in the resin cannot be obtained.

  As a result of further research in view of the current situation, the present inventors have found that when mixing nanofibers, water-soluble or water-dispersible synthetic resins, water-soluble dispersants, aqueous solvents, and the like in one step, It has been unexpectedly found that nanofibers can be dispersed almost uniformly in a synthetic resin, and a nanofiber composite with a uniform quality can be stably obtained by mixing while performing a defibrating process. The reason why such a nanofiber composite is obtained is not sufficiently clear at present, but by performing mechanical defibration treatment in the presence of nanofiber and synthetic resin, the so-called synthetic resin can obtain a uniform dispersion. It may be functioning as media.

  That is, in the present invention, a single nanofiber composite in which nanofibers and water-soluble or water-dispersible synthetic resin are substantially uniformly dispersed is equivalent to or more than that obtained in the conventional two-stage process. It can be manufactured in a process. Furthermore, in the present invention, a molded article of a nanofiber composite having excellent characteristics such as mechanical properties, heat resistance, chemical resistance, abrasion resistance, scratch resistance, water absorption, water retention, gas barrier properties, and self-healing properties is obtained. Can be mass-produced efficiently on an industrial basis. In addition, according to the production method of the present invention, a nanofiber composite including nanofibers having a very small fiber diameter, for example, a fiber diameter of about 4 to 10 nm, is further entangled between a plurality of nanofibers. can get. It is speculated that inclusion of nanofibers having a very small fiber diameter contributes to improving the above-mentioned properties of the nanofiber composite.

  The mechanical defibrating treatment is a technique usually used when pulverizing or reducing the raw material such as cellulose into nanofibers, and is not a technique used when mixing the nanofiber dispersion and the resin.

  The method for producing a nanofiber composite of the present invention (hereinafter sometimes abbreviated as “the production method of the present invention”) is a nanofiber, a synthetic resin having water solubility or water dispersibility under mechanical defibration treatment, A water-soluble dispersant, other additives, an aqueous solvent, and the like are mixed in a single stage. More specifically, the mixing in one stage means that these components are simultaneously put into one mixing container and mixed. Simultaneously charging includes a case where these components are continuously added in succession without agitation or with agitation. Here, the mixing container may be a device capable of performing a mechanical defibrating process. Details of each component are as follows.

  In the present specification, the nanofiber refers to a fibrous material having a fiber diameter in the nano order regardless of its length. The nanofiber used in the present invention is not particularly limited as long as the fiber diameter is nano-order, but is preferably a fibrous substance having a fiber diameter of 1 to 500 nm, more preferably a fiber diameter of 100 nm or less, and an aspect ratio (fiber length / fiber diameter). ) Is a fibrous material of 100 or less.

  The material of the nanofiber is not particularly limited, and examples thereof include synthetic resins, natural polymer compounds, and carbon materials. Nanofibers made of a synthetic resin can be produced, for example, by melt spinning, super-stretching, electrospinning, melt blowing, or the like. Nanofibers made of a natural polymer compound can be produced, for example, by subjecting a raw material containing a natural polymer compound to a mechanical defibrating treatment or treating the raw material with an oxidation catalyst. Nanofibers (carbon nanofibers, carbon nanotubes, etc.) made of a carbon material can be produced, for example, by vapor phase growth, arc discharge, or the like.

  Among the nanofibers described above, in the production method of the present invention, a nanofiber made of a natural polymer compound can be suitably used, and has a functional group on the surface that can crosslink with a crosslinkable group of a crosslinkable resin described later. From these, cellulose nanofibers, cellulose nanocrystals, chitosan nanofibers and the like can be used more suitably.

  The cellulose nanofiber used in the production method of the present invention has a fiber diameter of, for example, plant-derived pulp (cellulose aggregate) by chemical defibration using an oxidation catalyst or mechanical defibration by a strong shear force. The nanofibers of 3 to 100 nm are unraveled. In addition, the raw material of cellulose nanofibers, such as a cellulose, for example, when a plurality of hydroxyl groups on the surface form hydrogen bonds in one cellulose nanofiber, and the hydroxyl group on the surface of one cellulose nanofiber and another cellulose The hydroxyl group on the surface of the nanofiber may form a hydrogen bond, thereby containing an aggregate. Such agglomerates can be easily unwound by a mechanical defibrating process described later.

  Among cellulose nanofibers, chemical treatment (different from chemical defibration) is not performed, and the hydroxyl group derived from cellulose at the molecular chain and / or at the end of the molecular chain is not hydrophobically modified or blocked with a functional group other than the hydroxyl group. Unmodified cellulose nanofibers that are not used can be preferably used. Since unmodified cellulose nanofibers are very small in nanometer order, when they are dispersed in water at a low concentration, it is not recognized by the naked eye that unmodified cellulose nanofibers are dispersed in water. A transparent dispersion. Further, when unmodified cellulose nanofibers are dispersed in water at a high concentration, an opaque dispersion liquid is obtained. Here, the dispersion includes various forms such as an emulsion, a slurry, a gel, and a paste.

  In the present invention, the unmodified cellulose nanofiber is preferably used in the form of an aqueous dispersion from the viewpoint of the dispersibility of the unmodified cellulose nanofiber in the obtained nanofiber composite. The content of the unmodified cellulose nanofiber in the aqueous dispersion is not particularly limited, but is preferably 0.001 to 10% by weight of the total amount of the aqueous dispersion, and more preferably 0.1 to 5% by weight of the total amount of the aqueous dispersion. It is.

  The fiber diameter, fiber length, and aspect ratio of the unmodified cellulose nanofiber are not particularly limited, but the fiber diameter is preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less, particularly preferably 3 to 40 nm. The length is preferably 10 to 1000 μm, more preferably 100 to 500 μm, and the aspect ratio (fiber length / fiber diameter) is about 1000 to 15000, preferably about 2000 to 10,000. The fiber diameter and fiber length here are obtained as an arithmetic average value of the measured values obtained by measuring the fiber diameter and fiber length of an arbitrary number (for example, 20) of unmodified cellulose nanofibers by observation with an electron microscope. . Thus, the fiber diameter and fiber length of unmodified cellulose nanofibers can be obtained by observation using an electron microscope.

Note that the elastic modulus and strength of unmodified cellulose nanofibers composed of extended chain crystals reach 140 GPa and 3 GPa, respectively, which are equal to typical high-strength fibers and aramid fibers, and are more elastic than glass fibers. Moreover, the linear thermal expansion coefficient is 1.0 × 10 ⁻⁷ / ° C., which is as small as quartz glass.

  The cellulose used for the production of unmodified cellulose nanofibers is preferably used as an aqueous dispersion. The shape of cellulose is arbitrary shapes, such as a fiber form and a granular form, for example. As the cellulose, microfibrillated cellulose from which lignin and hemicellulose have been removed is preferable. Commercially available cellulose may also be used. When microfibrillated cellulose is processed with a medialess disperser, hydrogen bonds derived from hydroxyl groups present on the fiber surface are unraveled and thinned while maintaining the length of the microfibrillated cellulose. It is also possible to cut the fiber or reduce the molecular weight.

  Cellulose nanocrystals are fibrous crystals obtained by subjecting cellulose fibers constituting cellulose or cellulose nanofibers to chemical treatment such as acid hydrolysis using an acid such as sulfuric acid, and the fiber diameter is about 10 to 50 nm. The fiber length is about 100 to 1000 nm (preferably 150 to 500 nm). Cellulose nanocrystals are also called cellulose nanowhiskers.

  Chitosan nanofibers preferably have a fiber diameter of 1 to 100 nm, more preferably 1 to 50 nm, still more preferably 3 to 30 nm, particularly preferably 3 to 20 nm, and an aspect ratio of preferably 100 or more, more preferably 100 to 100 nm. 10,000, more preferably 100-2000. Chitosan nanofibers can be obtained, for example, by subjecting a chitin-containing raw material to deproteinization treatment and deashing treatment, further deacetylation treatment, and then defibration treatment. Deproteinization treatment, decalcification treatment, and defibration treatment can be performed according to a known method. The deproteinization treatment and the deacetylation treatment can be performed simultaneously. Chitosan nanofibers can also be obtained by subjecting a commercially available chitin powder subjected to deproteinization treatment and deashing treatment to deacetylation treatment by an alkali treatment method or the like.

  In the production method of the present invention, as nanofibers, in addition to the above-mentioned various nanofibers, cellulose nanofibers (bacterial cellulose nanofibers) produced by microorganisms such as acetic acid bacteria, and cellulose nanofibers obtained by electrospinning Fibers and chitin nanofibers can also be used. In the production method of the present invention, the nanofibers can be used alone or in combination of two or more.

  Next, the synthetic resin used in the production method of the present invention has water solubility or water dispersibility. The water-soluble synthetic resin is a synthetic resin that can be dissolved in an aqueous solvent. A water-dispersible synthetic resin is a forced emulsification type synthetic resin that can be dispersed in an aqueous solvent with an emulsifier or the like, and a hydrophilic group introduced into the side chain and / or terminal of the main chain skeleton into the aqueous solvent. It contains a self-emulsifying type synthetic resin that can be dispersed.

  Specific examples of such synthetic resins include water-soluble or water-dispersible crosslinkable resins, water-soluble or water-dispersible self-crosslinkable resins, and the like. The crosslinkable resin is a synthetic resin having at least one selected from a crosslinkable group and a crosslinkable structure, for example, reacting with a crosslinking agent to form a crosslink structure, preferably a crosslinkable group and a crosslinkable structure. A synthetic resin having at least one selected from the group consisting of water-soluble or water-dispersible. Although it does not specifically limit as a crosslinkable group here, For example, an epoxy group, a hydroxyl group, an isocyanate group, an amino group, an amide group, a carboxyl group, an ether group (for example, fluoroethylene ether group etc.), a hydrosilyl group etc. are mentioned. The crosslinkable resin can have one or more crosslinkable groups. These crosslinkable groups may be bonded to the main chain skeleton of the synthetic resin as at least a part of the side chain, or may be bonded to the terminal of the main chain skeleton.

  Moreover, although it does not specifically limit as a crosslinkable structure, For example, a pyrrolidone structure, a siloxane structure, an oxetane structure etc. are mentioned. The crosslinkable resin can have one or more crosslinkable structures. These crosslinkable structures may form a part of the main chain skeleton of the synthetic resin, or may be bonded to the side chain and / or the terminal of the main chain skeleton of the synthetic resin.

  The crosslinkable resin may have a hydrophilic group in order to exhibit water solubility or water dispersibility, and is not particularly limited as a hydrophilic group. For example, a hydroxy group, an amino group, a carboxyl group, A sulfone group, an ether group, etc. are mentioned. The hydrophilic group may be bonded as a part of the side chain to the main chain skeleton of the synthetic resin, or may be bonded to the terminal of the main chain skeleton. Among these hydrophilic groups, a synthetic resin having a hydroxy group, an amino group, a carboxyl group, an ether group or the like becomes a crosslinkable resin having water dispersibility or water solubility.

  The crosslinkable resin used in the present invention is not particularly limited as long as it has a crosslinkable group and / or a crosslinked structure. For example, epoxy resin, phenol resin, polyvinyl alcohol resin, polyvinyl butyral resin, urethane resin, polyvinyl pyrrolidone resin, polyvinyl polypyrrolidone resin, melamine resin, polyethylene imine resin, polyester resin, (meth) acrylic resin, acrylate resin, polysiloxane resin Oxetane resins, polyacrylonitrile resins, fluoroethylene / vinyl ether alternating copolymers, and the like. Crosslinkable resin can be used individually by 1 type or in combination of 2 or more types. The molecular weight of the crosslinkable resin is not particularly limited. For example, in order to improve the mechanical properties, rigidity, and other properties of the finally obtained nanocellulose composite and the molded product, the weight average molecular weight is used. Is preferably 2000 or more.

  In the present invention, when a crosslinkable resin is used as the water-soluble or water-dispersible synthetic resin, a crosslinkable group and / or a crosslinkable structure capable of reacting with the crosslinkable structure is used in combination with the crosslinkable resin. It is preferable. The crosslinking agent will be described later.

  The self-crosslinking resin is a synthetic resin capable of forming a crosslinked structure in its own molecule without using a crosslinking agent. The self-crosslinking resin is not particularly limited as long as it has water solubility or water dispersibility. For example, polyvinyl toluene, t-butyl acrylate / glycidyl acrylate copolymer, carboxyl group-containing vinyl monomer / sulfonic acid Examples thereof include a group-containing vinyl monomer copolymer. The self-crosslinkable resin can be imparted with water dispersibility in the same manner as the crosslinkable resin. Moreover, the crosslinking agent mentioned later can also be used with self-crosslinking resin.

  In the present invention, the synthetic resin is preferably used in the form of a solution or a dispersion. When the synthetic resin is water-soluble, the synthetic resin solution is preferably a solution in which the synthetic resin is dissolved in an aqueous solvent. Examples of the aqueous solvent include water, an organic solvent soluble in water, a mixed solvent of water and an organic solvent soluble in water, and the like. When the synthetic resin is water-dispersible, the synthetic resin dispersion is an emulsion such as a forced emulsification type emulsion or a self-emulsification type emulsion or a slurry using the same aqueous solvent as the dispersion medium. Is preferred. The forced emulsification type emulsion is obtained by dispersing a synthetic resin in an aqueous solvent using a surfactant or other emulsifier. The self-emulsifying emulsion is obtained by dispersing a synthetic resin in an aqueous solvent by introducing hydrophilic groups as side chains and / or terminal groups into the main chain skeleton of the synthetic resin. Among aqueous solvents, water, a mixed solvent of water and a water-soluble solvent are preferable, and water is more preferable.

  Examples of the water-soluble solvent include monovalent or polyhydric alcohols (monohydric alcohols include, for example, lower alcohols having 1 to 4 carbon atoms), amides, ketones, keto alcohols, and cyclic ethers. , Glycols, lower alkyl ethers of polyhydric alcohols, polyalkylene glycols, glycerin, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, glycerin, ethylene glycol, Diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1, 2,6-hexanetriol Polyols such as trimethylolpropane and pentaerythritol, polyhydric alcohol alkyl ethers such as diethylene glycol monobutyl ether and tetraethylene glycol monomethyl ether, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether, and many Polyhydric alcohol aralkyl ethers, lactams such as 2-pyrrolidone, N-methyl-2-pyrrolidone, ε-caprolactam, 1,3-dimethylimidazolidinone acetone, N-methyl-2-pyrrolidone, m-butyrolactone, glycerol Oxyalkylene adduct, propylene glycol monomethyl ether acetate, dimethyl sulfoxide, diacetone alcohol, dimethylformamide, pro And pyrene glycol monomethyl ether. A water-soluble solvent can be used individually by 1 type or in combination of 2 or more types.

  As the water, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water can be used. In addition, use of water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is preferable because generation of mold or bacteria during long-term storage can be prevented.

  Further, when the crosslinkable resin is used as a solution or dispersion, the concentration of the crosslinkable resin is not particularly limited, but the uniform dispersion of the nanofiber and the crosslinkable resin in the obtained nanofiber composite, the solution of the crosslinkable resin or From the viewpoint of handleability of the dispersion, etc., the total amount of the solution or dispersion of the crosslinkable resin is preferably 1 to 50% by weight, more preferably 5 to 45% by weight, and still more preferably 10 to 40% by weight.

The dispersant used in the production method of the present invention is a water-soluble dispersant, preferably a dispersant capable of ionic bonding with a functional group such as a hydroxyl group that the nanofiber has on the surface, more preferably nanofiber. The dispersant is capable of ionic bonding with a functional group such as a hydroxyl group on the surface and can enhance the dispersion stability of the nanofiber in the nanofiber composite by electrostatic repulsion. The dispersant is not particularly limited as long as it is water-soluble as described above, but an anionic dispersant can be preferably used. Examples of the anionic dispersant include a compound having at least one functional group selected from a phosphoric acid group, a —COOH group, a —SO ₃ H group, a metal ester group thereof, and an imidazoline group, and acryloyloxyethyl. Examples include phosphorylcholine (co) polymers. An anionic dispersing agent can be used individually by 1 type or in combination of 2 or more types.

  Specific examples of the anionic dispersant are not particularly limited. For example, polyacrylic acid and its salt, polymethacrylic acid and its salt, polyacrylic acid copolymer and its salt, polyitaconic acid and its salt, olefin-derived monomer And a copolymer containing a monomer derived from an unsaturated carboxylic acid (salt) (for example, JP-A-2015-196790), a polymaleic acid copolymer and its salt, polystyrene sulfonic acid and its salt, sulfonic acid group-bonded polyester, etc. A heterocyclic anionic dispersant such as a carboxylic acid anionic dispersant, an alkyl imidazoline compound (for example, JP-A-2015-934, JP-A-2014-118521, etc.), an acid value and an amine value An anionic dispersant (for example, Tokukai 2010-186124), pyrophosphoric acid, polyphosphoric acid, Phosphoric anionic dispersants such as repolyphosphoric acid, tetrapolyphosphoric acid, metaphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid, hexametaphosphoric acid, phosphonic acid, and salts thereof, sulfonic acid, dodecylbenzenesulfonic acid, lignin sulfonic acid, these Examples thereof include sulfonic acid anionic dispersants such as salts, and other anionic dispersants such as orthosilicic acid, metasilicic acid, humic acid, tannic acid, dodecylsulfuric acid, and salts thereof. Among these, phosphoric acid, polyphosphoric acid, phosphate, polyphosphate, polyacrylic acid, polyacrylic acid copolymer, polyacrylic acid salt, polyacrylic acid copolymer salt and the like are preferable.

  Further, as an anionic dispersant, a copolymer obtained by copolymerizing acrylic acid or methacrylic acid with another monomer can be used. Other monomers include, for example, α-hydroxyacrylic acid, crotonic acid, maleic acid, itaconic acid, fumaric acid and other unsaturated carboxylic acids and their salts, 2-acrylamido-2-methylpropanesulfonic acid, ( Examples thereof include unsaturated sulfonic acids such as (meth) allylsulfonic acid and styrenesulfonic acid, and salts thereof.

  Although it does not specifically limit as a cation which comprises the salt of an above-mentioned anionic dispersing agent, For example, alkaline-earth metals, such as sodium, potassium, lithium, alkaline earth metals, such as calcium, magnesium, ammonium group, etc. are mentioned. From the viewpoint of solubility in water, sodium, potassium, ammonium group and the like are more preferable, and potassium is most preferable.

  In the present invention, a commercially available anionic dispersant may be used. Specific examples of commercially available products include Aron A-6114 (trade name, carboxylic acid-based dispersant, manufactured by Toagosei Co., Ltd.), Aron A-6012. (Trade name, sulfonic acid dispersant, manufactured by Toa Gosei Co., Ltd.), Demol NL (trade name, sulfonic acid dispersant, manufactured by Kao Corp.), SD-10 (trade name, polyacrylic acid dispersant) And Toa Gosei Co., Ltd.).

  In addition, as the anionic dispersant used in the present invention, a (meth) acryloyloxyethyl phosphorylcholine (co) polymer may be used. The (meth) acryloyloxyethyl phosphorylcholine (co) polymer can improve the dispersion stability of each component in the nanofiber composite obtained by the present invention, in particular, the dispersion stability of the nanofibers. And can be suitably used as a dispersant when the nanocellulose composite of the present invention is used for medical use, food use and the like. Here, (meth) acryloyloxyethyl phosphorylcholine includes methacryloyloxyethyl phosphorylcholine and acryloyloxyethyl phosphorylcholine. These are produced according to conventional methods. For example, 2-bromoethyl phosphoryl dichloride, 2-hydroxyethyl phosphoryl dichloride and 2-hydroxyethyl methacrylate are reacted to obtain 2-methacryloyloxyethyl-2'-bromoethyl phosphate, which is further dissolved in trimethylamine and methanol solution. It can obtain by making it react.

  In the present invention, a commercially available product of (meth) acryloyloxyethyl phosphorylcholine (co) polymer may be used. Specific examples of commercially available products include lipid HM and lipid BL (both trade names, polymethacryloyloxyethyl phosphorylcholine). ), Lipid PMB (trade name, methacryloyloxyethyl phosphorylcholine / butyl methacrylate copolymer), lipid NR (trade name, methacryloyloxyethyl phosphorylcholine / stearyl methacrylate copolymer), and the like. These are all made by NOF Corporation.

  The cross-linking agent used in the production method of the present invention mainly causes a cross-linking reaction with the cross-linkable group and cross-linking structure possessed by the cross-linkable resin and the functional group possessed on the surface of nanocellulose. As a result of the crosslinking reaction, at least one of the crosslinkable resins, the nanofibers, or between the crosslinkable resin and the nanofibers is crosslinked, and each physical property of the resulting nanofiber composite is improved.

  The cross-linking agent is not particularly limited as long as it has cross-linkability and cross-linking structure possessed by the cross-linkable resin, and reactivity with functional groups possessed on the surface of nanocellulose. For example, polyfunctional monomer, polyfunctionality Resins, organic peroxides, polymerization initiators and the like can be mentioned. These crosslinking agents can be used alone or in combination of two or more. In the present invention, a stabilizer such as an acid catalyst and an antioxidant, a vulcanizing agent, a vulcanization accelerator, a vulcanization accelerating agent, an activity, together with a crosslinking agent, as long as the preferable characteristics of the obtained nanofiber composite are not impaired. Agents, vulcanization retarders, metal soaps, organosilanes, organometallic compounds, resins having unsaturated bonds, and the like can be used in combination.

  Examples of the polyfunctional monomer include polyfunctional acrylic monomers, polyfunctional allyl monomers, and mixed monomers thereof.

  Specific examples of the polyfunctional acrylic monomer include, for example, ethylene oxide-modified bisphenol A di (meth) acrylate, 1,4-butanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, dipentaerythritol hexaacrylate, dipenta Erythritol monohydroxypentaacrylate, caprolactone modified dipentaerythritol hexaacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane triacrylate, EO modified trimethylolpropanetri (Meth) acrylate, PO-modified trimethylolpropane tri (meth) acrylate, tris (acrylo Shiechiru) isocyanurate, tris (methacryloxyethyl) isocyanurate and the like. Among these, from the viewpoint of low skin irritation, tris (acryloxyethyl) isocyanurate (triacrylic ester of tris (2-hydroxyethyl) isocyanuric acid) can be preferably used. Polyfunctional acrylic monomers can be used alone or in combination of two or more.

  Examples of the polyfunctional allyl monomer include triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), diallyl monoglycidyl isocyanurate (DA-MGIC), diallyl phthalate, diallylbenzene phosphonate, and the like. Polyfunctional allylic monomers can be used alone or in combination of two or more

  The polyfunctional monomer can be used in combination with a polymerization initiator as necessary, and an acid catalyst, a stabilizer and the like can be used in combination. The timing of adding the polymerization initiator, catalyst, stabilizer and the like to the nanofiber composite is not particularly limited. For example, the polymerization initiator, the catalyst, and the stabilizer are mixed simultaneously with the nanofiber, the crosslinkable resin, the dispersant, and the aqueous solvent.

  Although the compounding quantity of a polyfunctional monomer is not specifically limited, Preferably it is 0.01 to 10 weight% with respect to the solid content weight of crosslinkable resin, More preferably, it is 0.1 to 5 weight%. When the blending amount of the polyfunctional monomer is less than 0.01% by weight, there is a tendency that the mechanical properties and thermal properties of the nanofiber composite are not significantly improved. When the blending amount of the polyfunctional monomer exceeds 10% by weight, there is a tendency to adversely affect mechanical properties such as elongation and impact strength of the nanofiber composite.

  Specific examples of the polyfunctional resin (polyfunctional polymer) include, for example, epoxy resins, isocyanate resins, cyanate resins, maleimide resins, acrylate resins, methacrylate resins, unsaturated polyester resins, oxetane resins, vinyl ether resins, urea resins, A melamine resin etc. are mentioned. Among these, radiation curable resins such as thermosetting epoxy resins and epoxy (meth) acrylate resins are preferable. The polyfunctional resin has a molecular weight relatively lower than that of the crosslinkable resin. The molecular weight of the polyfunctional resin is preferably less than 1000 as the weight average molecular weight. Like the crosslinkable resin, the polyfunctional resin is preferably a self-emulsifying type modified with a hydrophilic group such as a hydroxyl group or a carboxyl group, or a forced emulsification type that can be dispersed in a dispersion medium by an emulsifier. When these resins are used as the crosslinking agent, it is preferable to use a resin having a different resin type from the crosslinkable resin. The blending amount of the polyfunctional resin is preferably 3 to 20% by weight, more preferably 5 to 15% by weight, based on the solid content weight of the crosslinkable resin.

  The organic peroxide generates free radicals by heating, for example, and thereby crosslinks at least a part between the crosslinkable resins, between the nanofibers, and between the crosslinkable resin and the nanofibers. The organic peroxide falls within the category of the polymerization initiator, but is described separately from the polymerization initiator in this specification. Specific examples of the organic peroxide include, for example, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di- (tert-butylperoxy) hexane, 2,5- Dimethyl-2,5-di (tert-butylperoxy) hexyne-3, 1,3-bis (tert-butylperoxyisopropyl) benzene, 1,1-bis (tert-butylperoxy) -3,3,5 -Trimethylcyclohexane, n-butyl-4,4-bis (tert-butylperoxy) valerate, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butylperoxybenzoate, tert -Butyl peroxyisopropyl carbonate, diacetyl peroxy Id, lauroyl peroxide, tert- butyl cumyl peroxide, benzoyl peroxide, etc. tert- butyl hydroperoxide and the like. An organic peroxide can be used individually by 1 type or in combination of 2 or more types. The compounding amount of the organic peroxide is preferably 0.0001 to 10% by weight, more preferably 0.01 to 5% by weight, and still more preferably 0.1 to 0.1% by weight with respect to the total solid content of the crosslinkable resin and nanofibers. 3% by weight.

  The polymerization initiator generates free radicals by, for example, heating or ionizing radiation irradiation, and thereby crosslinks at least a part between the crosslinkable resins, between the nanofibers, and between the crosslinkable resin and the nanofibers. Specific examples of the polymerization initiator include azo compounds and persulfates. The polymerization initiator may be water-soluble or hydrophobic.

  Specific examples of the polymerization initiator include hydrophobic azo compounds such as azobisisobutyronitrile and 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis [2- (2 -Imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane], 2,2'-azobis [2-methyl-N- (2- Water-soluble azo compounds such as hydroxyethyl) propionamide] and persulfate names such as potassium persulfate, ammonium persulfate, and sodium persulfate. The blending amount of the polymerization initiator is preferably 0.0001 to 5% by weight, more preferably 0.01 to 3% by weight, further preferably 0.1 to 0.1% by weight based on the total solid content of the crosslinkable resin and nanofibers. About 1% by weight.

  In the present invention, an acid catalyst may be used together with the crosslinking agent. The acid catalyst is used, for example, to promote the reaction between the crosslinkable group and / or the crosslinked structure of the crosslinkable resin and the nucleophilic reactive group of the crosslinking agent. Specific examples of the acid catalyst include, for example, organic acids such as p-toluenesulfonic acid, citric acid, acetic acid, and malic acid, inorganic acids such as hydrochloric acid, sulfuric acid, and sulfonic acid, boron trifluoride, zinc chloride, tin chloride, Examples include Lewis acids such as aluminum chloride. An acid catalyst can be used individually by 1 type or in combination of 2 or more types. The amount of the acid catalyst is preferably 0.1 to 8 parts by weight with respect to 100 parts by weight of the solid content of the crosslinkable resin. If the blending amount of the acid catalyst is less than 0.1 parts by weight, the degree of crosslinking may be too low, and if it exceeds 8 parts by weight, the compatibility in the nanofiber composite may be deteriorated.

  As described above, the aqueous solvent used in the production method of the present invention is water, a water-soluble solvent, a mixed solvent of water and a water-soluble solvent, or the like. As the water-soluble solvent, any of the same water-soluble solvents as described above can be used. Water-soluble solvents include water, lower alcohols (methanol, ethanol, propanol, isopropanol), glycols (ethylene glycol, propylene glycol, diethylene glycol). ), Glycerin, acetone, dioxane, tetrahydrofuran, acetonitrile, dimethylformamide, dimethyl sulfoxide, acetamide and the like are preferable. These water-soluble solvents can be used alone or in combination of two or more. A preferable aqueous solvent is water, a mixed solvent of water and a water-soluble solvent, or the like, and water that does not require a special waste liquid treatment facility and hardly pollutes the environment is particularly preferable.

  Further, in the production method of the present invention, when mixing the above-mentioned components in one step or by adding an alkali agent to the obtained nanofiber composite, and adjusting the pH of the nanofiber composite to weak alkali, nanofiber The dispersibility of the nanofibers in the composite can be further improved. It does not specifically limit as an alkali agent, For example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate etc. are mentioned. An alkali agent can be used individually by 1 type or in combination of 2 or more types.

  Further, in the present invention, weather resistance of antioxidants such as hindered phenols, phosphate esters and phosphites, heat stabilizers, triazine compounds and the like within a range that does not impair the preferable characteristics of the obtained nanofiber composite. Stabilizers such as imparting agents and weather resistance imparting agents, plasticizers, antistatic agents, flame retardants, glass fibers, glass beads, metal powder, silica, inorganic layered compounds such as talc and mica, and other inorganic and organic fillers, Colorants such as pigments and dyes, lubricants, water-repellent agents, antiblocking agents, flexibility improvers, leveling agents, antifoaming agents, metal soaps, organosilanes, organometallic compounds, and the like can be blended. These additives may be mixed simultaneously with each of the above-described components in a single step, or may be added to and mixed with the obtained nanofiber composite.

Among these additives, an antioxidant is preferable. Examples of the antioxidant include phenolic antioxidants, sulfur antioxidants, and amine antioxidants. Among these, phenolic antioxidants are particularly preferable. The blending amount of the antioxidant is usually 0.1 to 10% by weight based on the total solid content of the nanofiber and the crosslinkable resin or the total solid content of the nanofiber, the crosslinkable resin and the dispersant. Preferably it is 0.2 to 5 weight%.

  The production method of the present invention includes the first step, may further include the second step or the third and fourth steps, and may further include a premixing step described later. More specifically, the manufacturing method of one embodiment of the present invention includes first and second steps, and may further include a third step and a premixing step. In addition, the manufacturing method of another embodiment of the present invention includes first, third, and fourth steps, and may further include a premixing step.

  According to the production method of the present invention, a nanofiber composite in which nanofibers are substantially uniformly dispersed in a crosslinkable resin, a molded body composed of a solid content of the nanofiber composite, and at least a part of the solid content of the nanofiber composite. A cross-linked molded body obtained by cross-linking is obtained. In the present invention, a preliminary mixing step may be performed before the first step. Hereinafter, the premixing step, the first step, the second step, the third step, and the fourth step will be described in detail.

[Preliminary mixing process]
In the premixing step, nanofibers, a synthetic resin having water solubility or water dispersibility, a dispersant or other additive, an aqueous solvent, and the like are simply mixed without performing a mechanical defibrating treatment to obtain a premix. The dispersibility of the nanofibers in the synthetic resin in the obtained premix is not sufficient. However, by applying mechanical defibration treatment to the premix in the first step, the dispersibility of the nanofibers in the synthetic resin in the resulting nanofiber composite is more than when only the first step is performed. Will be further improved. In addition, when a synthetic resin is a crosslinkable resin, it is preferable to use a crosslinking agent with a crosslinkable resin.

[First step]
In the first step, nanofibers, a water-soluble or water-dispersible synthetic resin, a dispersant, an aqueous solvent, and other additives as necessary are mixed in one stage under mechanical defibrating treatment. When the synthetic resin is a crosslinkable resin, it is preferable to use a crosslinker together with the crosslinkable resin. In the first step, mechanical defibrating treatment may be applied to the premix obtained in the premixing step. In the present specification, mixing in one stage means that the above-described components are put into the same container at a time and mixed. In the first step, the synthetic resin is preferably used in the form of a solution or a dispersion from the viewpoint of the dispersibility of the nanofibers in the obtained nanofiber composite, and is used in the form of an aqueous solvent solution or an aqueous solvent dispersion. It is more preferable. Moreover, you may use a nanofiber, a dispersing agent, a crosslinking agent, and another additive in the form dissolved or dispersed separately in the aqueous solvent, respectively.

  The mechanical defibrating treatment is carried out using an apparatus capable of applying a shearing force to the premix obtained in the premixing step or the mixture in which the components are charged almost simultaneously in the first step. Examples of such an apparatus include a high-pressure homogenizer, an underwater counter collision, a high-speed rotary disperser, a beadless disperser, and a high-speed stirring medialess disperser. Among these, high-speed agitation type medialess disperser from the viewpoint of not only further improving the dispersibility of nanofibers in synthetic resin, but also obtaining a highly pure nanofiber composite with less contamination of impurities. Is preferred.

  The high-speed agitation type medialess disperser is a disperser that uses a shearing force to perform a dispersion process without using a dispersion medium (for example, beads, sand, balls, or the like). Commercially available medialess dispersers can be used. Examples of the commercially available products include DR-PILOT2000, ULTRA-TURRAX series, Dispax-Reactor series (all trade names, manufactured by IKA), T.C. K. Homomixer, T.W. K. Pipeline homomixer (Brand name, manufactured by Primix Co., Ltd.), High Shear Mixer (Brand name, manufactured by Silverson), Milder, Cavitron (Brand name, manufactured by Taiheiyo Kiko Co., Ltd.), Clare mix (trade name, manufactured by M Technique Co., Ltd.), homomixer, pipeline mixer (trade name, manufactured by Mizuho Industry Co., Ltd.), Jet Pasta (trade name, manufactured by Nihon Spindle Manufacturing Co., Ltd.), Apex Disper The ZERO (trade name, manufactured by Hiroshima Metal & Machinery Co., Ltd.).

  Among the high-speed stirring medialess dispersers, a high-speed stirring medialess disperser of a type including a stator and a rotor is preferable. Specific examples of this type include, for example, a type including a stator and a rotor that rotates inside the stator, and a type in which the stator and the rotor are installed in multiple stages. Among the above-mentioned commercial products, Apex Disperser ZERO is this type. In this type, there is a gap between the stator and the rotor. This gap is defined as the “shear clearance”. By passing the mixture of the above components through the gap between the stator and the rotor while the rotor is rotating, shear force can be applied to the mixture and the nanofiber diameter can be increased. Can be further miniaturized, and nanofibers can be uniformly dispersed in a synthetic resin. In addition, from the viewpoint of uniformly applying a shearing force to the entire mixed liquid of the above components, an inline circulation type high-speed stirring medialess disperser in which the mixed liquid of the components of the character container circulates in the apparatus is preferable.

  When using a high-speed agitation type medialess disperser, the nanofiber diameter can be further refined by setting the shear rate, shear clearance and rotor rotational peripheral speed, particularly the shear clearance and rotor rotational peripheral speed within a predetermined range. Research by the present inventors has revealed that excellent effects such as crystallization, further uniform dispersion of nanofibers in a synthetic resin, and prevention of nanofiber settling in the resulting nanofiber composite can be obtained. .

  The shear rate preferably exceeds 900,000 [1 / sec]. When the shear rate is 900,000 [1 / sec] or less, both the defibration of the nanofiber and the dispersion of the nanofiber into the synthetic resin tend to be insufficient. The shear rate is preferably 2,000,000 [1 / sec] or less, preferably 1,500,000 [1 / sec] or less, and more preferably 1,200,000 [1 / sec] or less.

  The shear clearance is appropriately set according to the shear rate, the viscosity of the mixture of the above components, etc., but the diameter of the nanofiber is made as small as possible, and the dispersibility of the nanofiber in the synthetic resin is further improved. From the viewpoint of improving, it is preferably 100 μm or more, more preferably 150 μm or more, and further preferably 200 μm or more. Moreover, even if the viscosity of the liquid mixture of each of the above components is high, the clearance is preferably 2 mm or less, more preferably 1.5 mm or less from the viewpoint of ensuring high dispersibility while maintaining the rotation speed of the disperser in an appropriate range. Preferably, it is 1.2 mm or less.

  The rotational peripheral speed of the rotor is appropriately set according to the shear rate. From the viewpoint of making the diameter of the nanofiber as small as possible and further improving the dispersibility of the nanofiber in the synthetic resin, it is 18 m / s or more is preferable, 20 m / s or more is more preferable, and 23 m / s or more is more preferable. Further, from the viewpoint of obtaining an optimum nanofiber diameter, the rotational peripheral speed is preferably 60 m / s or less, more preferably 50 m / s or less, and further preferably 45 m / s or less. The rotational peripheral speed is the peripheral speed of the most advanced portion of the rotor.

  In the premixing step and the first step, the amount of each component described above is not particularly limited. For example, the total solid content of the synthetic resin to be blended is 100 parts by weight, and the nanofibers are preferably 0.001 to 10 parts. Parts by weight, more preferably 0.5 to 5 parts by weight, the aqueous solvent is preferably 100 to 10,000 parts by weight, more preferably 150 to 1000 parts by weight, and the dispersant is preferably 0.01 to 0.5 parts by weight. Preferably 0.025 to 0.25 parts by weight may be blended. The amount of the crosslinking agent is as described above.

  In the nanocellulose composite obtained in the first step, the nanofibers and the synthetic resin are dispersed almost uniformly in the aqueous solvent, and the nanofibers precipitate very little over time. Further, in the composite, a dispersant may be ionically bonded to the surface of at least a part of the nanofibers. The ionic conjugate of the nanofiber and the dispersant may remain after the molding and the crosslinking treatment described later. The average fiber diameter of the nanofibers contained in the composite is about 10 to 100 nm, preferably about 10 to 40 nm, and more preferably about 15 to 25 nm. That is, by performing the first step, the fiber diameter of the nanofiber may be smaller after the implementation than before the implementation. In addition, since the nanofiber composite can be obtained by one-stage mixing in the first step, significant labor savings (particularly, significant labor saving during mass production) can be achieved as compared to the conventional two-step process.

  Moreover, the zeta potential of the nanocellulose composite obtained in the first step is preferably −20 to −50 mV, more preferably −30 to −45 mV. If the zeta potential is higher than −20 mV, the nanofibers may settle due to non-uniform dispersion. On the other hand, when the zeta potential is less than −50 mV, the nanofiber is cut, and a sufficient crosslinked network structure may not be formed. In the present invention, the zeta potential of the nanocellulose composite after production may be measured, and the value of the zeta potential may be adjusted as necessary. The zeta potential of the nanocellulose composite can be adjusted by, for example, the blending amount and type of the dispersant. A method for measuring the zeta battery will be described later.

[Second step]
In the second step, the nanocellulose composite obtained in the first step is subjected to a crosslinking treatment. When the nanocellulose composite includes a crosslinkable resin and a crosslinker, at least some nanofibers, at least some nanofibers and at least some crosslinkable resins, and at least A nanocellulose cross-linked composite in which a cross-linked structure is formed in one or more of some cross-linkable resins is obtained. When the nanocellulose composite contains a self-crosslinking resin as a synthetic resin, a crosslinked structure is formed in the molecule of the resin, and a crosslinked structure is also formed between the resin and the nanofiber. A cross-linked nanofiber structure is obtained.

  By molding this nanocellulose crosslinked composite in the same manner as in the third step described later, mechanical strength, heat resistance, chemical resistance, abrasion resistance, scratch resistance, water absorption, water retention, gas barrier properties, self A molded article containing a cross-linked structure with improved repairability and the like can be obtained. In the present invention, since an aqueous solvent is used as a dispersion medium, there is an advantage that even if the nanofiber composite is subjected to a crosslinking treatment as it is, the safety is high.

  The crosslinking treatment method is not particularly limited, but a chemical crosslinking method and a physical crosslinking method using a crosslinking agent contained in the nanofiber composite are preferable.

  Specific examples of the chemical crosslinking method include crosslinking by heating. Heating conditions include the component composition of the nanofiber composite, the solid content concentration, the type and blending amount of the crosslinkable resin and the crosslinking agent, the degree of crosslinking set, the values of each physical property set for the resulting nanofiber crosslinked composite, etc. However, the cross-linking is usually formed by heating for a long time at a temperature of about 30 ° C. or higher. From the viewpoint of shortening the time required for crosslinking to save labor as a whole process, and further improving each physical property of the nanocellulose composite after crosslinking, the heating conditions are preferably 30 ° C to 220 ° C. For 1 to 40 minutes at a temperature of 100 ° C. to 180 ° C., more preferably 1 to 20 minutes (preferably 5 to 10 minutes) at 125 ° C. to 140 ° C.

  Specific examples of physical crosslinking include crosslinking by irradiation with ionizing radiation. Crosslinking by irradiation with ionizing radiation has the advantage of being easy to control. Although it does not specifically limit as ionizing radiation, An electron beam, a gamma ray, an X-ray, a charged particle beam, an ultraviolet-ray, a neutron beam etc. are mentioned. Among these, ultraviolet rays, γ rays, electron beams, and the like are preferable from the viewpoints of availability of an apparatus for generating ionizing radiation, ease of control of the crosslinking reaction, safety, and the like.

  The irradiation dose of ionizing radiation depends on the component composition of the nanofiber composite, the solid content concentration, the type and blending amount of the crosslinkable resin and crosslinker, the degree of crosslinking set, and the physical properties set for the resulting nanofiber crosslinkable composite Although it can select suitably according to the value of etc., Preferably it is 10 kGy-1000 kGy, More preferably, it is 10-50 kGy. When the irradiation dose is less than 10 kGy, the degree of cross-linking of the finally obtained molded product is insufficient, and the physical properties of the molded product tend to be lowered. On the other hand, when the irradiation field amount exceeds 1000 kGy, the coloring of the molded product increases, and the physical properties of the molded product tend to decrease due to an increase in molecular chain breakage in regions other than the region where the crosslinked structure is formed. is there.

  The degree of crosslinking is usually 20 to 98%, preferably 60 to 98% as the degree of crosslinking. If the degree of cross-linking is less than 20%, it may not be possible to further improve mechanical strength and heat resistance such as rigidity, creep resistance, and wear resistance of the finally obtained molded product. On the other hand, if the degree of cross-linking exceeds 98%, the physical properties of the molded product may be deteriorated due to an increase in molecular chain breakage and the like other than in the region where the cross-linked structure is formed.

The degree of crosslinking is determined, for example, as a gel fraction (%). An appropriate amount of a sample such as a nanocellulose composite or a nanocellulose crosslinked composite obtained by the production method of the present invention is dried at 100 ° C. for 2 hours and then weighed to obtain an initial dry weight (g). Next, after immersing this in normal temperature sewage for 24 hours, the dissolution residue is filtered with a quantitative filter paper, dried at 100 ° C. for 2 hours, and weighed to determine the insoluble matter weight (g). And a gel fraction (%) is calculated | required from a following formula.
Gel fraction (%) = [(insoluble weight) / (initial dry weight)] × 100

[Third step]
In the third step, the mixture (nanofiber composite) obtained in the first step is molded. That is, a molded product is obtained by molding while removing the aqueous solvent from the mixture obtained in the first step, or by molding a solid content obtained by removing the aqueous solvent from the mixture. Further, as described above, the nanofiber crosslinked composite obtained in the second step may be molded in the same manner.
Here, as a molding method, a known method for obtaining a molded product from a resin solution or a resin dispersion can be used without limitation, but depending on the type of the crosslinkable resin contained in the nanofiber composite, etc. It is preferable to select appropriately.

  As a method of molding while removing the aqueous solvent from the nanofiber composite or nanofiber cross-linked composite, for example, using a nanofiber composite or nanofiber cross-linked composite, film-like molded products are formed on the surfaces of various substrates. A resin coating method is generally used. In the resin coating method, for example, a film-shaped molded article is obtained by applying a nanofiber composite or a nanofiber cross-linked composite to the surface of a substrate and drying by heating. Here, the coating method is not particularly limited, and examples thereof include a spin coater method, a bar coater method, a spray coating method, coating with a brush or a roller, a dipping method, a solution casting method (casting method), and the like.

  As another method of molding while removing the aqueous solvent from the nanofiber composite or nanofiber cross-linked composite, there is a method of obtaining a molded product via a prepreg. That is, a prepreg is prepared by impregnating a nanofiber composite or a nanofiber cross-linked composite into various woven fabrics, knitted fabrics, nonwoven fabrics, cotton canvases, and the like, and heating is performed on one or a plurality of prepregs by press molding. By performing pressurization, heating and pressurization using an autoclave, etc., a molded product can be obtained. Examples of the material for the base material for impregnation include carbon fiber, glass fiber, and vegetable fiber.

  Examples of the solid content molding method obtained by removing the aqueous solvent from the nanofiber composite or nanofiber cross-linked composite include, for example, a plane pressing method, a material jetting method, a binder jetting method, and an optical modeling 3D printing method. Is mentioned.

  In the third step, molding and crosslinking may be performed at the same time. For example, a molding form in which the nanofiber composite is held in a high temperature state (about 120 to 150 ° C.) in a mold such as casting or compression molding, and the resulting molded product is taken out from the mold and then post-heated in a hot air furnace or the like. Molding form for curing, molding form for forming nanofiber composite film on substrate surface, post-curing this in a hot air oven, etc., molding form for post-curing solid material hydrogelated from nanofiber composite as it is For example, molding and chemical crosslinking are performed simultaneously.

[Fourth step]
In a 4th process, a crosslinking process is performed with respect to the uncrosslinked molded article produced using the nano cellulose composite in the 3rd process. The crosslinking treatment can be performed in the same manner as in the second step. By the fourth step, a molded product in which at least a part of each component contained is crosslinked is obtained.

  The nanocellulose composite, nanocellulose cross-linked composite of the present invention obtained in this way, and these molded articles have stable quality even when the production lot changes, mainly uniform dispersion of nanofiber and crosslinkable resin For example, due to mechanical properties such as rigidity, creep resistance, wear resistance, and impact resistance, flexibility, heat resistance, chemical resistance, weather resistance, self-repairability, gas barrier properties, adhesiveness, etc. It tends to be excellent. .

  The nanofiber composite of the present invention is, for example, a weather-resistant, abrasion-resistant, scratch-resistant coating for general mechanical parts, a coating for vehicles and ships, an adhesive or cast film, a coating or adhesive for optical parts, a biological Suitable for medical, nursing and welfare material coating materials, cast films, small mechanical parts or material jetting, binder jetting or stereolithography 3D printer materials including fields that require compatibility It can be used and preferably used for medical, nursing / welfare members including fields requiring biocompatibility.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, the measuring method of each component used in the Example, an apparatus, a fiber diameter, and a zeta potential is as follows.

[Synthetic resin]
Polyvinyl alcohol (trade name: Poval PVA-205, water-soluble crosslinkable resin, manufactured by Kuraray Co., Ltd.) was used as a 10% by weight aqueous solution. Hereinafter, it may be referred to as “PVA resin”.
Polyvinyl butyral (trade name: ESREC KW-1, water-soluble crosslinkable resin, manufactured by Sekisui Chemical Co., Ltd.) may hereinafter be referred to as {PVB resin}.
Urethane resin (trade name: Superflex 820, self-emulsifying type crosslinkable resin, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) may be hereinafter referred to as “URT resin”.
[Nanofiber]
Unmodified cellulose nanofiber (trade name: BiNFi-s, manufactured by Sugino Machine Co., Ltd.) was used as a 5% by weight aqueous dispersion. Hereinafter, it may be referred to as “unmodified CNF”.
[Water-soluble dispersant]
Polymethacryloyloxyethyl phosphorylcholine (trade name: Lipidure BL, manufactured by NOF Corporation)
[Crosslinking agent]
Both terminal isocyanate type polycarbodiimide (trade name: Carbodilite VS-02, polyfunctional resin, manufactured by Nisshinbo Chemical Co., Ltd.) was used as a 40 wt% aqueous solution. Hereinafter, it may be referred to as “carbodilite”.
Triallyl isocyanurate (polyfunctional allyl monomer, manufactured by Nippon Kasei Co., Ltd., hereinafter sometimes referred to as “TAIC”)
[High-speed stirring medialess disperser]
Apex Disperser ZERO (trade name, manufactured by Hiroshima Meta & Machinery Co., Ltd.)

<Fiber diameter>
The nanofiber composites obtained in Examples and Comparative Examples were observed with a field emission electron microscope (FE-SEM), and an electron micrograph (50000 times) was taken. On the photographed photo, draw two lines intersecting 20 or more nanofibers at any position across the photograph, measure the diameter of all nanofibers intersecting the line, and the measured value obtained The average fiber diameter (nm) was calculated as the arithmetic average value of (n = 20 or more). In addition, based on the measured value of the fiber diameter, the standard deviation of the fiber diameter distribution and the maximum fiber diameter of the nanofiber can be obtained.

<Zeta potential measurement method>
1 ml of the nanofiber composite obtained in Examples and Comparative Examples is placed in a disposable glass test tube, diluted with purified water, and the cellulose nanofiber concentration is adjusted to 0.01% by weight. Subsequently, after the ultrasonic treatment for 30 minutes, it was subjected to the following zeta potential measurement. The equipment used and the measurement conditions are as follows.
Measuring instrument: Zeta potential, particle size measurement system (Otsuka Electronics Co., Ltd.)
Measurement conditions: Standard cell SOP for zeta potential
Measurement temperature: 25.0 ° C
Zeta potential conversion formula: Smolchowski's formula Solvent: Water (Otsuka Electronics Co., Ltd. ELSZ software values are applied as they are for the solvent refractive index, viscosity, and dielectric constant parameters)
System suitability: Latex 262 nm standard solution (0.001%) does not exceed the range of specification values.

<Presence / absence of gelation>
An aqueous dispersion of the resin composition obtained in Examples and Comparative Examples was applied to a glass substrate hydrophilized with oxygen plasma at a speed of 3 m / s, and then naturally dried, 100 mm × 200 mm × thickness 5 μm. The coating film was formed. This coating film was heated at 170 ° C. for 20 minutes to perform chemical crosslinking to obtain a crosslinked coating film (crosslinked body of the coating film). The presence or absence of gelation was determined from the presence or absence of the water-soluble content of the obtained crosslinked coating film.

<Gel fraction>
The gel fraction was determined as the degree of crosslinking. The aqueous dispersions of the resin compositions obtained in Examples and Comparative Examples were dried at 100 ° C. for 2 hours and then weighed to determine the initial dry weight (g). The sample with the initial dry weight weighed was immersed for 24 hours at room temperature, and then the dissolved residue was filtered with a quantitative filter paper, dried at 100 ° C. for 2 hours, and weighed to determine the insoluble matter weight (g). The gel fraction is calculated from the following formula.
Gel fraction (%) = [(insoluble weight) / (initial dry weight)] × 100

<Pencil hardness>
A pencil hardness tester is applied to a coating film obtained by coating the composition obtained by the present invention on a glass substrate hydrophilized with a spin coater to a thickness of 5 μm and then crosslinking (physical crosslinking or chemical crosslinking). (All Good Co., Ltd.) was used and measured according to JIS K5600.
Mitsubishi pencil Hi-uni (hardness 10H-10B) was used for the measurement pencil.

<Abrasion resistance>
Steel wool # 0000 (manufactured by Nippon Steel Wool Co., Ltd.) having a length and width of 10 mm is brought into close contact with the surface of the coating film, and the steel wool is coated under the conditions of a moving distance of 130 mm and a moving speed of about 100 mm / sec under a load of 400 g. Was reciprocated 10 times in the longitudinal direction. Thereafter, the state of the coating film surface was visually observed and evaluated based on the following criteria.
A: There is no scratch.
◯: There are several scratches with a very small scratch width and a dimension of 10 mm or less.
(Triangle | delta): Although the width | variety of a damage | wound is very small, many scratches with a dimension exceeding 10 mm exist in excess of 10 pieces.
X: The width | variety of a damage | wound is large and clear, and abrasion powder is scattered on the surface.

<Dispersibility (CNF dispersion) and dispersion stability (CNF dispersion stability)>
About the aqueous dispersion of the obtained resin composition, the dispersibility (CNF dispersibility) and the dispersion stability (CNF dispersion stability) were examined by visual observation.
Dispersibility (CNF dispersibility) is a visual evaluation result of dispersibility of unmodified cellulose nanofibers and crosslinkable resin in an aqueous dispersion of a resin composition immediately after production. “○” for those in which no non-modified cellulose nanofiber or water-soluble crosslinkable resin is dispersed or agglomerated, although white turbidity is observed even though it is entirely cloudy What was produced was evaluated as “x”.

  Dispersion stability (CNF dispersion stability) is the result of visual evaluation of the dispersibility of unmodified cellulose nanofibers and crosslinkable resins in an aqueous dispersion after standing for 24 hours or more. No evaluation was evaluated as “◯”, and even a slight precipitation of unmodified cellulose nanofibers was evaluated as “x”. Although the aqueous dispersion is cloudy, when the unmodified cellulose nanofiber is precipitated, the degree of whiteness of the portion changes and can be identified as white shades.

Example 1
Hereinafter, the blending amount of the components used as the aqueous solution or the aqueous dispersion is shown as a solid content, but of course water is included. .
20 g of PVA resin, 1 g of a crosslinking agent (carbodilite) (5% by weight based on PVA resin), 0.2 g of unmodified CNF (BiNFi-s) (1% by weight based on PVA resin), and a dispersant (Repidure BL) ) 0.01 g (5% by weight based on unmodified CNF) was blended and premixed with a desktop stirrer to prepare a premix.

  500 ml of the obtained preliminary mixture was set to a shear clearance of 1 mm and a rotational peripheral speed of the rotor of 45 m / s with a high-speed rotation type medialess disperser (Apex Disperser ZERO). The composite nanocellulose composite of the present invention was produced as an aqueous dispersion.

  The obtained nanocellulose composite of Example 1 was a cloudy liquid, and dispersion unevenness and aggregation of unmodified CNF and PVA resin were not observed by visual observation. Further, even when the nanocellulose composite of Example 1 was allowed to stand for 24 hours or longer, precipitation of unmodified CNF was not observed, and the aqueous dispersion was stable. In addition, the nanocellulose composite of Example 1 had a zeta potential of −40.2 mV. Since the absolute value of the zeta potential was large, it was confirmed that unmodified CNF was almost uniformly dispersed in the PVA resin. The fiber diameter of unmodified CNF contained in Example 1 was in the range of 20 to 50 nm, and the average fiber diameter was 18 nm.

  The nanofiber composite of Example 1 was coated on a glass substrate hydrophilized with oxygen plasma with a bar coater at a coating speed of 3 m / min. After the solvent, chemical crosslinking was performed by heating at 170 ° C. for 20 minutes to prepare a coating film as a molded article of the nanocellulose crosslinked composite. The presence or absence of gelation is determined from the presence or absence of water soluble in the coating film, and the pencil hardness of the coating film is measured based on JIS K5600-5-4, and the scratch resistance is examined by the following method. It was. The results are shown in Table 1.

(Comparative Example 1)
In Example 1, except that a dispersant was not added, the same operation as in Example 1 was performed to prepare a nanocellulose composite, to form a coating film and to perform a crosslinking treatment, and thereafter, the same evaluation was performed. The results are shown in Table 1. Further, the zeta potential of the obtained nanocellulose composite was -14.05 mV, and it was confirmed that the uniform dispersibility of unmodified CNF and the like was insufficient. Moreover, after the nanofiber composite obtained was allowed to stand for a while, precipitation of unmodified CNF and the like started, and after standing for 12 hours, most of the blended unmodified CNF was precipitated to about ½ of the liquid volume.

(Comparative Example 2)
In Example 1, except that a crosslinking agent was not blended, the same operation as in Example 1 was performed to prepare an unmodified cellulose nanofiber composite, to form a coating film, and to perform a crosslinking treatment, and thereafter, the same evaluation was performed. . The results are shown in Table 1. The resulting nanocellulose composite had a zeta potential of −36.8 mV.

(Comparative Example 3)
Hereinafter, the blending amount of the components used as the aqueous solution or the aqueous dispersion is shown as a solid content, but of course water is included. .
0.25 g of modified CNF (BiNFi-s) and 0.01 g of dispersant (Lipidure BL) are blended, and with a high-speed rotating medialess disperser (Apex Disperser ZERO), the shear clearance is 1 mm and the rotational peripheral speed of the rotor Set to 45 m / s, fibrillation for 10 minutes was performed 5 times to prepare an aqueous dispersion of unmodified CNF. The obtained aqueous dispersion of unmodified CHF, 20 g of PVA resin, and 1 g of a crosslinking agent (carbodilite) were blended and mixed with a table stirrer at 300 rpm for 1 hour to prepare a cloudy liquid nanocellulose composite by a two-stage method.

After visually evaluating the dispersibility of the obtained nanocellulose composite, the presence or absence of sedimentation of unmodified CNF after standing for 24 hours was evaluated. The nanocellulose composite was found to have a zeta potential of −39.67 mV, although dispersion, aggregation and sedimentation of unmodified CNF were hardly observed immediately after production and after standing for 24 hours. The zeta potential was slightly smaller than −40.2 mV, and the dispersibility of each component viewed from the zeta potential was better in Example 1 than in Comparative Example 3.
Moreover, the coating film was formed like Example 1 using the nanofiber composite_body | complex of the comparative example 3, and the physical property was investigated. The results are shown in Table 1.

(Example 2 and Comparative Examples 4 to 6)
In Example 1 and Comparative Examples 1 to 3, TAIC as a cross-linking agent (Nippon Kasei Co., Ltd.) was added in an amount of 5% by weight with respect to the solid content of the PVA resin, and the cross-linking treatment was performed from chemical cross-linking to 1000 UV rays. (MJ / cm ² ) Except for the physical cross-linking to be irradiated, the same operations as in Example 1 and Comparative Examples 1 to 4 were performed to prepare the nanofiber composite, form the coating film, and perform the cross-linking treatment. The same evaluation was performed. The results are shown in Table 1.

(Examples 3 and 4 and Comparative Examples 7 to 12)
In Example 1 and Comparative Examples 1 to 3, except that a 10% by weight aqueous solution of PVB resin was used instead of PVA resin, the same operation as in Example 1 and Comparative Examples 1 to 3 was performed to prepare a nanofiber composite, A coating film was formed and crosslinked, and then the same evaluation was performed. The results are shown in Table 1.

(Examples 5 and 6 and Comparative Examples 13 to 18)
In Example 2 and Comparative Examples 4 to 6, except that a 10 wt% aqueous dispersion of URT resin was used instead of PVA resin, the same operation as in Example 2 and Comparative Examples 4 to 6 was performed, and the nanofiber composite Preparation, formation of a coating film, and crosslinking treatment were performed, and then the same evaluation was performed. The results are shown in Table 1.

<Effect of Example>
The following evaluation is a comparison of coating film characteristics when a coating film is formed from nanofiber composites with different manufacturing methods, and does not evaluate the overall characteristics of the nanofiber composite. That is, in Examples 1 to 6 and Comparative Examples 1 to 18, when the manufacturing method of the nanofiber composite is a one-step method or a two-step method, the characteristics of the coating film formed from the nanofiber composite obtained are compared. Further, the effects of the presence or absence of the addition of a crosslinking agent, the presence or absence of addition of a dispersant, and the presence or absence of crosslinking on the physical properties (pencil hardness, scratch resistance) of the coating film were examined.

From Table 1, unmodified cellulose nanofibers and water-soluble crosslinkable resin while performing mechanical defibrating treatment (giving shearing force) with a high-speed rotating beadless disperser. It was found that the nanocellulose composite in which the dispersant and the crosslinking agent were mixed in one stage had good dispersibility of the unmodified cellulose nanofiber and high dispersion stability. When these were cross-linked, the gel fraction was 90% or more, and it was confirmed that the cross-linking was sufficiently advanced.
Moreover, it was found that all of these crosslinked nanofiber composites have a pencil hardness of 2H or more and very excellent scratch resistance. (Examples 1-6).

  On the other hand, in Comparative Examples 3, 6, 9, 12, 15, and 18, each component was used in the same composition as in Examples 1 to 6, and the unmodified CNF and the dispersant were previously stored in a high-speed rotation type medialess disperser. A nanofiber composite is obtained by a conventional two-stage process in which an unmodified CNF dispersion is prepared by dispersion and a water-soluble crosslinkable resin and a crosslinking agent are mixed therein. Examples 1 to 6 are comparative examples 3 regarding the dispersibility, dispersion stability and sedimentation stability of unmodified CNF, the gel fraction of the cross-linked product, pencil hardness, scratch resistance, etc. in the nanofiber composite. , 6, 9, 12, 15 and 18 or a better value depending on the physical properties, it was confirmed that not only labor saving of the process was achieved.

  From the above, the nanofiber composite obtained by the one-step method of the present invention and the molded product thereof are equivalent to or better than the nanofiber composite obtained by the conventional two-step method and the molded product (gel fraction). , Pencil hardness, scratch resistance).

  Further, in Examples 1 to 6, the nanofiber composites of Comparative Examples 1, 4, 7, 10, 13, and 16 to which no dispersant was added were inferior in dispersibility and dispersion stability of the unmodified CNF, and It was found that the pencil hardness and scratch resistance of the prepared coating film were also inferior to those of Examples 1-6.

  Furthermore, although the nanocellulose composite of the comparative example which does not add a crosslinking agent to Examples 1-6 is equivalent to Examples 1-6, although the dispersibility and dispersion stability of unmodified CNF are equivalent, the coating produced from these The film was inferior in pencil hardness and scratch resistance.

  In Examples 1 to 6 and Comparative Examples 1 to 18, the dispersant is changed from polymethacryloyloxyethyl phosphorylcholine (Lipidure BL) to a sulfonic acid dispersant (Aron A-6012) or a carboxylic acid dispersant (Aron A-6114). Except for changing, the same operation as in Examples 1 to 6 and Comparative Examples 1 to 18 was carried out to prepare a nanofiber composite, and the same applies to the dispersibility and dispersion stability of cellulose nanofiber and the coating film subjected to crosslinking treatment. Was evaluated. Cellulose nanofiber dispersibility, sedimentation stability, presence or absence of gelation, gel fraction, pencil hardness, and scratch resistance were almost the same as those of Examples 1 to 6 and Comparative Examples 1 to 18, respectively.

Claims (9)

A first step of mixing nanofibers, a water-soluble or water-dispersible synthetic resin, a water-soluble dispersant, and an aqueous solvent in one step under a mechanical defibrating process, wherein the synthetic resin is water-soluble or water-dispersible a crosslinkable resin having sex, the combined use of the crosslinkable resin and the reactive crosslinking agent thereto, a manufacturing method of the nano-fiber composite. A first step of mixing nanofibers, a water-soluble or water-dispersible synthetic resin, a water-soluble dispersant, and an aqueous solvent in one step under a mechanical defibrating process, wherein the synthetic resin is water-soluble or water-dispersible is a self-crosslinking resin having sex, method of manufacturing the nano-fiber composite. The method for producing a nanofiber composite according to claim 1 or 2 , further comprising a second step of subjecting the mixture obtained in the first step to a crosslinking treatment. The third step of obtaining a molded product by molding while removing the aqueous solvent from the mixture obtained in the first step, or molding the solid content obtained by removing the aqueous solvent from the mixture, and the third further comprising the molded product obtained in step and a fourth step of performing crosslinking treatment, a manufacturing method of the nanofiber composite according to claim 1 or 2. The nanofiber composite according to any one of claims 1 to 4 , wherein the nanofiber is at least one selected from the group consisting of unmodified cellulose nanofibers, cellulose nanocrystals, and chitosan nanofibers. Method. The method for producing a nanofiber composite according to any one of claims 1 to 5 , wherein the synthetic resin is used in the form of a solution or a dispersion. The method for producing a nanofiber composite according to any one of claims 1 to 6 , wherein the dispersant is an anionic dispersant. The anionic dispersant is a compound having at least one functional group selected from a phosphoric acid group, a carboxy group, a sulfonic acid group, a metal ester group thereof, and an imidazoline group, and acryloyloxyethyl phosphorylcholine (co) heavy. The manufacturing method of the nanofiber composite_body | complex of Claim 7 which is at least 1 sort (s) chosen from the group which consists of coalescence. The method for producing a nanofiber composite according to claim 3 or 4 , wherein the crosslinking treatment is a chemical crosslinking treatment or a physical crosslinking treatment.