JP2013185096A - Cellulose nanofiber film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cellulose nanofiber film having transparency, excellent weather resistance and good toughness while maintaining a characteristic of extremely low thermal expansion.SOLUTION: A cellulose nanofiber film includes a cellulose nanofiber having an average fiber diameter of 2 nm to 200 nm and surface-modified silica fine particles, in which the cellulose nanofiber and the surface modified silica fine particles are bonded.

Description

  The present invention relates to a cellulose nanofiber film.

  BACKGROUND ART Fiber reinforced composite materials whose strength and rigidity are greatly improved by blending various fibrous reinforcing materials with resins are widely used in industrial fields such as electric / electronics, machinery, automobiles, and building materials. As the fibrous reinforcing material blended in the fiber-reinforced composite material, glass fibers having excellent strength and lightness are mainly used. However, in the glass fiber reinforced material, although high rigidity is achieved, the specific gravity is increased, so that there is a limit to weight reduction.

  On the other hand, fiber reinforcement made of organic materials such as polyester fiber, polyamide fiber, and aramid fiber has been studied as a fibrous reinforcement, but fiber reinforcement materials containing these reinforcements are lightweight and thermal recyclable. Although it can be secured, there is a problem that the mechanical reinforcement effect is not sufficient.

  On the other hand, in recent years, highly functional materials using plant-derived materials are attracting attention among biomass materials from the viewpoint of carbon neutrality. There has been proposed a fiber composite material in which cellulose fibers obtained by fibrillating plant fibers are mixed with a resin.

  Patent Document 1 describes a composite film of cellulose and silica fine particles. Since this composite film dissolves cellulose and mixes with silica fine particles, the crystallinity of cellulose is lowered and the thermal expansion is greatly inferior. In addition, since this composite film is not bonded to cellulose and silica fine particles, the silica fine particles on the surface are easily dropped, and when used outdoors, cellulose, which is an organic substance, is exposed on the surface, and thus yellows. Moreover, there exists a fault that a film becomes weak by containing an inorganic particle (silica microparticle).

  Patent Document 2 describes a thermoplastic cellulose ester composition having silica-based inorganic particles and cellulose acetate propionate (hereinafter also referred to as “CAP”) having a substitution degree of esterification of 2.5 to 3. Since esterified cellulose is amorphous, there is no hydrogen bond between celluloses, there is no bond between fibers, and linear expansion is poor. Moreover, since the cellulose and silica fine particle are not couple | bonded with the thermoplastic cellulose-ester composition of patent document 2, the silica fine particle of the surface is easy to drop off, and the cellulose which is organic substance is exposed on the surface at the time of outdoor use. Therefore, yellowing occurs. Moreover, a film becomes weak by containing an inorganic particle (silica microparticle).

  Patent Document 3 describes a composite porous material impregnated with cellulose and silica dissolved in glass fibers. Productivity is poor in the impregnation method described in Patent Document 3, and the composite porous material is poor in transparency because glass fiber is porous, and in toughness when used outdoors.

  Patent Document 4 describes a microfibrillated cellulose produced by a resin impregnation method which is a general composite method of cellulose nanofibers and a resin. The microfibrillated cellulose has poor weather resistance due to the absence of silica fine particles, and also has poor productivity due to the resin impregnation method.

  Thus, there was no cellulose nanofiber film with low thermal linear expansion and excellent weather resistance, good toughness and good transparency while maintaining the crystal structure of the cellulose fiber.

JP 2006-316128 A JP 2004-196932 A JP 2011-80171 A JP 2008-266630 A

  The present invention has been made in view of the above problems, and is to provide a cellulose nanofiber film having transparency, excellent weather resistance, and excellent toughness while maintaining extremely low thermal linear expansion characteristics.

The above object of the present invention is achieved by the following configurations.
1. Cellulose nanofiber film having cellulose nanofiber having an average fiber diameter of 2 nm to 200 nm and surface-modified silica fine particles, cellulose in which the cellulose nanofiber and the surface-modified silica fine particles are bonded Nanofiber film.
2. 2. The cellulose nanofiber film according to 1 above, wherein a part of hydroxyl groups of the cellulose nanofiber is esterified.
3. 3. The cellulose nanofiber film according to 2, wherein the cellulose nanofiber has an esterification substitution degree of 0.5 to 2.5 and a crystallinity of 30 to 90%.
4). The cellulose nanofiber film according to any one of 1 to 3, wherein the surface-modified silica fine particles have a circle-converted average particle diameter of 5 nm to 100 nm.
5. 5. The cellulose nanofiber film according to any one of 1 to 4, wherein the surface-modified silica fine particles are surface-modified with a silane coupling agent.

  The present invention has been made in view of the above problems, and can provide a cellulose nanofiber film having transparency, excellent weather resistance, and excellent toughness while maintaining extremely low thermal linear expansion characteristics.

  As a result of diligent studies by the present inventor, surface-modified silica fine particles were bonded to cellulose nanofibers (hereinafter also referred to as “CNF”), whereby extremely low thermal linear expansion characteristics were obtained compared to CNF alone films. This is because silica particles are bonded to CNF, so silica particles do not fall off even when used outdoors, and the outermost silica particles reflect ultraviolet light without damaging the internal CNF resin component. We believe that the weather resistance has improved. Further, a film containing inorganic fine particles (silica fine particles) has a property of becoming brittle. However, in the present invention, silica fine particles are fixed between CNFs, and there is no deterioration in toughness due to entanglement of fibers. We were able to achieve the challenges.

  Hereinafter, the present invention, its components, and embodiments for carrying out the present invention will be described in detail.

(1. About cellulose nanofiber)
In the cellulose nanofiber of the present invention, cellulose-derived fibers are defibrated to an average fiber diameter of 2 nm to 200 nm. Furthermore, it is more preferable if the fiber surface is surface-treated by chemical modification or physical modification. Examples of the chemical modification include esterification of cellulose nanofibers.

  Examples of the raw material cellulose fiber used in the present invention include plant-derived pulp, wood, cotton, hemp, bamboo, cotton, kenaf, hemp, jute, banana, coconut, seaweed, tea leaves, and other fibers separated from plant fibers, marine animals Examples include fibers separated from animal fibers produced by sea squirts, and bacterial cellulose produced from acetic acid bacteria. Among these, fibers separated from plant fibers can be preferably used, but fibers obtained from plant fibers such as pulp and cotton are more preferable.

  In the present invention, these fibers are defibrated using a homogenizer, a grinder or the like to obtain a microfibrillated cellulose nanofiber, but as long as the contained cellulose maintains the fiber state. There is no restriction on the fibrillation method. In addition, hard materials such as wood may need to be pulverized with a dry pulverizer as pre-crushing if they cannot be processed directly with a homogenizer.

  As a specific example, a cellulose fiber such as pulp is put into a dispersion container in water so as to be 0.1 to 3% by mass, and this is defibrated with a high-pressure homogenizer to obtain an average fiber diameter of 0.1 to 3%. An aqueous dispersion of cellulose fibers defibrated to about 10 μm microfibrils is obtained. Furthermore, by repeatedly grinding with a grinder or the like, nano-order cellulose fibers having an average fiber diameter of about 2 to 200 nm can be obtained.

  Examples of the grinder used for the grinding treatment include a pure fine mill (manufactured by Kurita Machinery Co., Ltd.). As another method, there is a method using a high-pressure homogenizer in which cellulose fiber dispersion is jetted from a pair of nozzles at a high pressure of about 250 MPa, and the jet fibers collide with each other at a high speed to pulverize the cellulose fibers. Are known. Examples of the apparatus used include “Homogenizer” manufactured by Sanwa Machinery Co., Ltd., “Artemizer System” manufactured by Sugino Machine Co., Ltd., and the like.

  The average fiber diameter of cellulose nanofibers obtained by fibrillation in this manner is preferably 2 nm or more and 200 nm or less, more preferably 2 nm or more and 150 nm or less, and further preferably 2 nm or more and 100 nm or less. .

  In the present invention, if the average fiber diameter of the cellulose nanofiber exceeds 200 nm, the strength of the fiber composite material may be insufficient. Furthermore, when mixed with a transparent resin, the transparency of the resin is adversely affected.

  The length of the nanofiber is not particularly limited, but the average fiber length is preferably 50 nm or more, more preferably 100 nm or more. Within such a range, the entanglement of the fibers is good, the reinforcing effect is high, and the increase in thermal expansion can be suppressed.

  In the present invention, “average fiber diameter” and “average fiber length” are obtained by observing nanofibers using a transmission electron microscope (TEM) (for example, H-1700FA type (manufactured by Hitachi, Ltd.)) at a magnification of 10,000 times. 100 fibers are randomly selected from the obtained images, and the fiber diameter (diameter) and fiber length of each fiber are analyzed using image processing software (for example, WINROOF), and these are calculated as simple number average values. .

(2. Surface-modified silica fine particles)
(2-1. Silica fine particles)
The surface-modified silica fine particles are fine particles obtained by performing surface treatment on the surface of the silica fine particles.

  The average particle diameter in terms of circle of the primary particles of the surface-modified silica fine particles is preferably 1 nm or more and 500 nm or less, and more preferably 1 nm or more and 100 nm or less.

  A circle-converted average particle diameter in the above range is preferable because further improvement in light transmittance is observed.

  The method for measuring the circle-converted average particle diameter of primary particles obtained from the projected area of a transmission electron microscope (TEM) photograph can be obtained from the number average value of the diameters of the silica fine particles. That is, from observation with a transmission electron microscope of silica fine particles, 200 or more random silica fine particles that can be observed as a circle, an ellipse, or a substantially circle or ellipse are randomly observed, the particle diameter of each silica fine particle is obtained, and the number average value thereof Is obtained. Here, the circle-converted average particle diameter according to the present invention is the minimum distance among the distances between the outer edges of the silica fine particles that can be observed as a circle, an ellipse, or a substantially circle or ellipse, between two parallel lines. Point to.

(2-2. Method for preparing silica fine particles)
As a method for producing silica fine particles, a thermal decomposition method (a method for obtaining fine particles by thermally decomposing raw materials. Spray drying method, flame spray method, plasma method, gas phase reaction method, freeze drying method, heated kerosene method, heated petroleum method ), Precipitation method (coprecipitation method), hydrolysis method (aqueous salt method, alkoxide method, sol-gel method), hydrothermal method (precipitation method, crystallization method, hydrothermal decomposition method, hydrothermal oxidation method), etc. . Among these, the thermal decomposition method, the precipitation method, and the hydrolysis method are preferable methods from the viewpoint of producing uniform fine silica particles having a small particle diameter. In preparing the silica fine particles, a plurality of these methods may be combined.

(2-3. Surface modification step)
Examples of the surface modification method include a wet heating method, a wet filtration method, a dry stirring method, an integral blend method, and a granulation method. For example, when surface modification is performed on the surface of uniform silica fine particles having an average particle diameter in terms of a circle of 100 nm or less, a dry method is used from the viewpoint of suppressing the aggregation of particles and the surface adsorbent adsorbing uniformly on the particles. A wet stirring method is preferred over a stirring method.

  As the solvent for the wet stirring method, hexane and heptane are preferable as the nonpolar solvent, and the polar solvent is toluene, methanol, ethanol, acetone, water, acetonitrile, pyridine, dimethylformamide (DMF), methyl ethyl ketone (MEK) MIBK 1,4. -Dioxane, in addition to these ethers or ketones are preferred.

  Examples of the surface modification method for the surface of the silica fine particles include surface treatment with a coupling agent and the like.

  The reagent used for the surface modification on the surface of the silica fine particles may be any one that binds to cellulose nanofibers, and examples thereof include a silane coupling agent. These are not particularly limited, and can be appropriately selected. Further, two or more various surface modifications may be performed simultaneously or at different times.

  Specifically, for example, as a surface modifier for silica fine particles, silane coupling agents: vinyltriacetoxysilane, vinyltris (methoxyethoxy) silane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, etc. Applicable.

  In addition, for example, vinyl trimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, methacryloxypropylmethyldimethoxysilane, etc. Silane coupling agents having epoxy groups such as sidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane, and glycidoxypropylmethyldimethoxysilane, mercapto groups such as mercaptopropyltrimethoxysilane and mercaptopropyltriethoxysilane Coupling agent, 3-aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, 3- (2-aminoethyl) amino Propyl methyl dimethoxy silane, amino silane, a silane coupling agent having a terminal amino group such as 3-phenyl-aminopropyl trimethoxy silane. Among these, those having an epoxy group or an amino group at the terminal are preferably used. One or two or more of these functional groups may be introduced.

  These surface modifiers may be appropriately diluted with hexane, toluene, methanol, ethanol, acetone, water or the like.

  The ratio of the surface modifier is not particularly limited, but the ratio of the surface modifier is preferably 10% by mass or more and 99% by mass or less, and 30% by mass or more and 98% by mass with respect to the silica fine particles after the surface treatment. It is more preferable that the amount is not more than mass%.

(3. About esterification of cellulose nanofiber)
The esterification of cellulose nanofibers in the present invention means that a part of hydroxyl groups (—OH) at the 2-position, 3-position and / or 6-position of the glucose unit of cellulose constituting the cellulose nanofiber is chemically modified to have 1 to 1 carbon atoms. Those substituted with an acyl group of 8 are preferred.

  In the esterified cellulose nanofiber of the present invention, the hydroxyl group on the surface of the cellulose nanofiber is substituted with an acyl group, and the crystalline nanofiber component is the core and the amorphous modified cellulose ester component (acyl group) The component) is considered to be a fiber having a core-shell-shaped cross section.

  The average fiber diameter and the average fiber length of the esterified cellulose nanofiber are the same as the definition of the average fiber diameter and the average fiber length of the cellulose nanofiber described above.

  The acyl group having 1 to 8 carbon atoms is not particularly limited. Formyl group, acetyl group, propionyl group, isopropionyl group, butanoyl group (butyryl group), isobutanoyl group (isobutyryl group), valeryl group, isovaleryl group, 2-methylvaleryl group Group, 3-methylvaleryl group, 4-methylvaleryl group, t-butylacetyl group, pivaloyl group, caproyl group, 2-ethylhexanoyl group, 2-methylhexanoyl group, heptanoyl group, octanoyl group, benzoyl group and the like. . Among these, an acyl group having 2 to 4 carbon atoms is preferable, an acetyl group, a propionyl group, and a butanoyl group are more preferable, and a propionyl group is particularly preferable. Since the propinate component has better fluidity and the like than other acyl group components, transparency and smoothness can be improved. In addition, the hydroxyl group of cellulose nanofiber may be substituted with a single kind of acyl group, or may be substituted with a plurality of acyl groups.

  Moreover, the cellulose nanofiber in this invention can make the surface layer of a fiber amorphous (resinization) by substituting a part of the hydroxyl group of a cellulose nanofiber with an acyl group, and the entanglement of the cellulose nanofiber component While maintaining the above, flexibility can be imparted to the crystalline cellulose nanofiber.

  Thereby, even when it is not mixed with the matrix resin, it is excellent in molding processability and enables uniform film formation. Furthermore, transparency and surface smoothness can be improved by making the surface layer of the fiber amorphous (resinized).

  The substitution degree of the acyl group of cellulose nanofiber is preferably 0.5 to 2.5. If the degree of substitution is 0.5 or more, the resin component (acyl component) on the fiber surface is increased, the film forming property and transparency are improved, and defects can be further reduced, which is preferable. A degree of substitution of 2.5 or less is preferred because the crystalline nanofiber portion (core portion) increases, the entanglement of the nanofibers increases, and the thermal linear expansion is excellent. More preferably, the substitution degree is 0.5 to 2.0. In the present invention, the symbol “to” means a numerical value between the above and the following.

  Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups (—OH) at the 2nd, 3rd and 6th positions. “Acyl group substitution degree of cellulose nanofiber” means the average number of acyl groups per glucose unit, and any one of 2-, 3-, and 6-hydroxyl groups of 1-glucose unit is substituted with an acyl group. The ratio is shown. That is, when all of the hydroxyl groups at the 2nd, 3rd and 6th positions are substituted with acyl groups, the degree of substitution (maximum degree of substitution) is 3.0. The acyl group may be substituted on average at the 2-position, 3-position, and 6-position of the glucose unit, or may be substituted with a distribution.

  The degree of substitution is determined by the method prescribed in ASTM-D817-96 (2010).

  The crystallinity of the esterified cellulose nanofiber is preferably 30 to 90%. If the degree of crystallinity is 30% or more, the deterioration of the thermal linear expansion characteristics of the nanofiber and the accompanying deterioration of the thermal linear expansion characteristics of the film can be suppressed. On the other hand, if it is 90% or less, the fall of film forming property, transparency, and surface smoothness can be suppressed. More preferably, the crystallinity is 50 to 90%, and further preferably 40 to 80%.

  The degree of crystallinity can be calculated by the method described below.

[Calculation method of crystallinity]
The X-ray diffraction intensity was measured, and the crystallinity CrI was calculated based on the following mathematical formula (1). Here, I ₈ indicates the 2θ = 8 ° diffraction peak intensity, and I ₁₈ indicates the 2θ = 18 ° diffraction peak intensity.

  Although the diffraction peak intensity differs depending on the resin, it can be calculated by subtracting the baseline intensity from the peak intensity of each spectrum.

(4. Mixing of surface-modified silica and cellulose nanofiber)
(4-1. Mixing step)
In the kneading step, a manufacturing method for producing a cellulose nanofiber film by adding and kneading surface-modified silica fine particles to esterified cellulose nanofibers, and esterified cellulose nanofibers and surface-modified silica fine particles dissolved in a solvent A production method in which a film is prepared by mixing and then removing the organic solvent is a preferred embodiment.

  In kneading, an organic solvent can be used. In that case, it is preferable to deaerate after kneading to remove the organic solvent from the esterified cellulose nanofibers.

  Examples of the apparatus that can be used for kneading include a closed kneading apparatus such as a lab plast mill, a Brabender, a Banbury mixer, a kneader, and a roll, or a batch kneading apparatus. Moreover, it can also manufacture using a continuous kneading apparatus like a single screw extruder, a twin screw extruder, etc.

  When a kneading machine is used as a treatment mode of the kneading step, esterified cellulose nanofibers and surface-modified silica fine particles may be added and kneaded all at once, or may be divided and added in stages. In this case, in a kneading apparatus such as an extruder, it is possible to add the components to be added step by step from the middle of the cylinder. In the kneading process, it is preferable to add a light-resistant stabilizer in the later step as much as possible. Therefore, at least a part of the light-resistant stabilizer is added after the surface-modified silica fine particles are added.

  When compounding the esterified cellulose nanofiber and the surface-modified silica fine particles by kneading, the surface-modified silica fine particles can be added in a powdered or aggregated state. Alternatively, the surface-modified silica fine particles can be added in a state dispersed in a liquid. When the surface-modified silica fine particles are added in a state dispersed in a liquid, it is preferable to perform deaeration after kneading.

  In the case where the surface-modified silica fine particles are added in a state of being dispersed in the liquid, it is preferable to add the aggregated particles by dispersing them in the primary particles in advance. Various dispersing machines can be used for dispersion, but a bead mill is particularly preferable. There are various kinds of beads, but those having a small size are preferable, and those having a diameter of 0.001 to 0.1 mm are particularly preferable.

  In the case of film formation by the solvent casting method, a method of adding esterified cellulose nanofibers to the surface-modified silica fine particle dispersion and removing the solvent is preferable.

(5. Film formation method)
The reactive groups on the surface of the surface-modified silica fine particles can react with and bind to the hydroxyl groups of cellulose by heating after film formation. As heating temperature, it is 60 to 200 degreeC, Preferably it is 70 to 140 degreeC. The heating time is preferably about 5 seconds to 24 hours, more preferably about 10 seconds to 2 hours.

  The film forming method may be a melt film forming method or a solvent casting method. In the case of melt film formation, pellets may be created once using a kneader, and then put into the kneader again to form a melt film. Dehydration by Nippon Steel's TEX twin-screw extruder and multistage vent method Alternatively, the film may be formed at once using a kneader capable of melt film formation.

  In the case of melt film formation, it is preferable to remove the solvent in advance from the solution of the esterified cellulose nanofiber and the surface-modified silica fine particles, and the removal of the solvent is preferably performed under reduced pressure conditions in consideration of the efficiency. The solvent removal temperature can be appropriately selected in consideration of the boiling point of the solvent, reduced pressure conditions, and the like. In the solvent removal step, it is preferable to finish the step in as short a time as possible considering that the esterified cellulose nanofibers are slightly settled due to the above-described density difference. For this reason, the method of spreading a liquid mixture thinly and widely and removing a solvent in a short time is advantageous. Moreover, when there is little solvent amount, since a liquid mixture becomes a gel form and it becomes difficult to produce the density nonuniformity after stirring, it is preferable.

  When the solvent is removed in the solvent removal step, a gel-like resin in which the surface-modified silica fine particles and the esterified cellulose nanofibers are dispersed is obtained. Although it is possible to use this mixture as a molding material without kneading, the elastic modulus and strength of the molded product obtained by using the kneaded material obtained by kneading as the molding material are high. For the kneading step, a method used in the field of kneading a resin can be used. For example, a uniaxial, biaxial or multiaxial kneader, mixing roll, kneader, roll mill, Banbury mixer, screw press, disperser, etc. can be used. Although the kneading temperature varies depending on the resin, it is not lower than the glass transition point and not higher than the melting point of the resin, usually 80 to 220 ° C., preferably 100 to 200 ° C., and the kneading time is usually 1 minute to 3 hours, preferably 5 minutes to 30 minutes. It is.

  When a kneader is used, the reactive group on the surface of the surface-modified silica fine particles reacts with the hydroxyl group of cellulose during kneading and adds a temperature at which bonding is possible. At least the surface-modified silica fine particles are bonded to the cellulose nanofibers.

  In the case of using the melt film forming method or the solvent cast film forming method, the film forming method is preferably a method of coating on a support. Examples of the support include a metal plate such as stainless steel and aluminum, and a glass plate. And a stainless steel plate and a stainless steel belt are particularly preferable.

  Any appropriate method can be adopted as a coating method. Specific examples include a spin coating method, a roll coating method, a flow coating method, an ink jet method, a spray coating method, a printing method, a dip coating method, a casting film forming method, a bar coating method, and a gravure printing method.

  The applied film may be at a temperature at which the solvent can be removed, and the heating temperature is 60 ° C to 200 ° C, preferably 70 ° C to 140 ° C. The drying time after coating is preferably about 5 seconds to 24 hours, more preferably about 10 seconds to 2 hours. When a film is produced by the solvent casting method, the reactive group on the surface of the surface-modified silica fine particles reacts with and bonds to the hydroxyl group of cellulose by applying the above temperature.

  Further, the dried film may be optionally annealed, and the annealing temperature is preferably 60 ° C. to 200 ° C., more preferably 70 ° C. to 160 ° C. The annealing time is preferably about 5 seconds to 24 hours, more preferably about 10 seconds to 2 hours.

  In the examples, the degree of substitution was calculated from the diffraction peak intensity measured by the X-ray diffraction method using the method specified in ASTM-D817-96 (2010) and the crystallinity using the following apparatus.

X-ray generator: RINT TTR2 manufactured by Rigaku Corporation
X-ray source: CuKα
Output: 50kV / 300mA
1st slit: 0.04mm
2nd slit: 0.03 mm
Light receiving slit: 0.1 mm
<Counting and recording device>
2θ / θ: Continuous scan Measurement range: 2θ = 2 to 45 °
Sampling: 0.02 °
Integration time: 1.2 seconds Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<Preparation of CNF dispersion>
(Production Example 1 Production of Cellulose A)
Sulfuric acid bleached pulp obtained from conifers is added to 1.0% by mass in pure water, and cellulose fibers are defibrated using an Excel Auto Homogenizer manufactured by Nippon Seiki Seisakusho Co., Ltd. for 15 minutes at 3000 rpm. did. This aqueous dispersion was designated as cellulose A. The obtained cellulose was defibrated with a transmission electron microscope to an average fiber diameter of 250 nm and confirmed to be microfibrillated.

(Production Example 2 Production of CNF-A)
Cellulose A prepared in Production Example 1 is equivalent to 1 g in dry mass, 0.0125 g of TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and 0.125 g of sodium bromide in 100 ml of water. Then, a 13 mass% aqueous sodium hypochlorite aqueous solution was added to start the reaction so that the amount of sodium hypochlorite was 2.5 mmol. During the reaction, a 0.5 M aqueous sodium hydroxide solution was added dropwise to keep the pH at 10.5. When the change in pH is no longer observed, the reaction is considered to be complete, the reaction product is filtered through a glass filter, washed with a sufficient amount of water and filtered five times, so that the cellulose nanofibers become 0.1% by mass. Diluted with water. Furthermore, it processed with the ultrasonic disperser for 1 hour and obtained CNF-A. It was the average fiber diameter of 4 nm.

(Production Example 3 Production of CNF-B)
Cellulose A prepared in Production Example 1 was treated twice with a grinder made by Masuko Sangyo. It adjusted with water so that a cellulose nanofiber might be 1 mass%, and CNF-B was obtained. The obtained cellulose fiber had an average fiber diameter of 50 nm.

(Production Example 4 Production of CNF-C)
Cellulose A prepared in Production Example 1 was treated once with a Mashiko Sangyo grinder. It adjusted with water so that a cellulose nanofiber might be 1 mass%, and CNF-C was obtained. The obtained cellulose fiber had an average fiber diameter of 150 nm.

<Adjustment of Substituents at Cellulose C2, C3, C6 Position>
(Propionate of hydroxyl group at C2 and C3)
To 500 parts by mass of a propionic anhydride / pyridine (molar ratio 1/1) solution, 10 parts by mass of CNF-B obtained in Production Example 3 dried by lyophilization was added and dispersed, followed by stirring at room temperature for 3 hours. did. Next, the dispersed fiber was filtered, washed three times with 500 parts by mass of water, and then washed twice with 200 parts by mass of ethanol. Further, after washing twice with 500 parts by mass of water, by adjusting with pure water so that the solid content concentration becomes 2% by mass, a cellulose nanofiber having propionated C2 and C3 hydroxyl groups is produced. did. Thus, the cellulose nanofiber which propionated the hydroxyl group of C2, C3 position of CNF-B was made into CNF-B1 (gel form).

  Further, CNF-A1 (gel) was used as the cellulose nanofiber obtained by propionating the hydroxyl groups at C2 and C3 using CNF-A in the same manner as CNF-B1. Samples shown in Table 1 were prepared by changing the reaction time and changing the substitution degree and the crystallization degree.

(Solvent substitution)
Sample No. in Table 1 18 and 19 were gradually replaced with a methyl ethyl ketone solvent by a membrane separation method to perform solvent replacement so that the concentration of cellulose nanofibers was 2% by mass.

<Preparation of surface-modified silica fine particles>
(1.1) Production of surface-modified silica fine particles 1 Silica AEROSIL200 (A-200) manufactured by Aerosil Co., Ltd. having an average particle diameter of 12 nm was heated at 200 ° C. for 1 hour in the atmosphere. While stirring 30 g of the powder obtained after heating under dry nitrogen, 12 g of tetraethoxysilane was added to the powder. Thereafter, the powder to which hexamethyldisilazane was added was heated at 200 ° C. for 30 minutes and subsequently cooled to room temperature to obtain silica “surface-modified silica fine particles 1”.

  As a result of TEM observation, the surface-modified silica fine particles 1 had a circle-converted average particle size of 110 nm.

(1.2) Production of surface-modified silica fine particles 2 30 g of tetraethoxysilane was added to a mixed solution of 2700 g of ethanol and 300 g of water and stirred. The acetic acid 15g was added there and it stirred for 10 minutes. 15 g of silica AEROSIL200 (A-200) manufactured by Aerosil Co., Ltd. having an average particle diameter of 12 nm was added to this mixed solution, and the mixture was stirred at room temperature for 1 hour and then stirred at 100 ° C. for 1 hour. The mixed solution was centrifuged at 8000 rpm for 30 minutes, and the settled particles were collected. The collected particles were further washed with 1000 g of ethanol for washing acetic acid and unreacted tetraethoxysilane, and centrifuged again at 8000 rpm for 30 minutes, and the precipitated particles were collected. This operation was repeated three times, and when acetic acid and unreacted tetraethoxysilane were washed well, the recovered particles were dried in an oven at 150 ° C. for 2 hours, and then cooled to room temperature. As a result, “surface-modified silica fine particles 2” were obtained.

  As a result of TEM observation, the surface-modified silica fine particles 2 had a circle-converted average particle size of 20 nm.

(1.3) Preparation of surface-modified silica fine particles 3 As a silane coupling agent having an amino group that reacts with a hydroxyl group of cellulose, 30 g of 3-aminopropyltriethoxysilane is added to a mixed solution of 2700 g of ethanol and 300 g of water and stirred. went. The acetic acid 15g was added there and it stirred for 10 minutes. 15 g of silica AEROSIL200 manufactured by Aerosil Co., Ltd. having an average particle diameter of 12 nm was added to this mixed solution, and the mixture was stirred at room temperature for 1 hour and then stirred at 100 ° C. for 1 hour. The mixed solution was centrifuged at 8000 rpm for 30 minutes, and the settled particles were collected. The collected particles were further washed with 1000 g of ethanol to wash acetic acid and unreacted 3-aminopropyltriethoxysilane, and centrifuged again at 8000 rpm for 30 minutes to collect the precipitated particles. This operation was repeated three times. When acetic acid and unreacted 3-aminopropyltriethoxysilane were washed well, the recovered particles were dried in an oven at 150 ° C. for 2 hours, and then cooled to room temperature. As a result, “surface-modified silica fine particles 3” were obtained.

  As a result of TEM observation, the surface-modified silica fine particles 3 had a circle-converted average particle size of 30 nm.

(1.4) Preparation of surface-modified silica fine particles 4 As a silane coupling agent having an epoxy group that reacts with a hydroxyl group of cellulose, 30 g of 3-glycidyl propyltrimethoxysilane is added to a mixed solution of 2700 g of ethanol and 300 g of water and stirred. Went. The acetic acid 15g was added there and it stirred for 10 minutes. 15 g of silica AEROSIL200 manufactured by Aerosil Co., Ltd. having an average particle diameter of 12 nm was added to this mixed solution, and the mixture was stirred at room temperature for 1 hour and then stirred at 100 ° C. for 1 hour. The mixed solution was centrifuged at 8000 rpm for 30 minutes, and the settled particles were collected. The collected particles were further washed with 1000 g of ethanol to wash acetic acid and unreacted 3-glycidylcyclopyrtrimethoxysilane, and centrifuged again at 8000 rpm for 30 minutes to collect the precipitated particles. This operation was repeated three times, and when acetic acid and unreacted 3-glycidoxypropyltrimethoxysilane were washed well, the recovered particles were dried in an oven at 150 ° C. for 2 hours, and then cooled to room temperature. As a result, “surface-modified silica fine particles 4” were obtained.

  As a result of TEM observation, the surface-modified silica fine particles 4 had a circle-converted average particle size of 50 nm.

(Create film)
<Melt film forming method (sample No. 1 to No. 17)>
100 parts by mass of the solid content of the cellulose fiber shown in Table 1 was dried at a hot air temperature of 150 ° C. and a dew point of −36 ° C. by a dehumidifying hot air dryer manufactured by Matsui Manufacturing Co., Ltd., and then a plasticizer P-1: 8 masses Part, antioxidant A-1: 1 part by mass, A-2: 0.5 part by mass, silica fine particles shown in Table 1 together with 20 parts by mass in a V-type tumbler for 30 minutes Mixed.

  Subsequently, it supplied at 120 kg / hr to the twin screw extruder manufactured by Technobel. The screw design uses fewer kneading discs to suppress heat generation from resin kneading. The temperature setting of the barrel was 180 ° C. to 250 ° C., and a vent port was provided near the tip to remove volatile matter. A filter, gear pump, and filter are placed downstream of the extruder, extruded from a coat hanger type T-die, dropped between two chrome-plated mirror rolls controlled to 120 ° C, and passed between the three rolls. It was wound up on a winder after slitting. The extrusion amount and the rotation speed of the take-up roll were adjusted so that the thickness of the wound film was 125 μm.

(Plasticizer) P-1: Trimethylolpropane tribenzoate (Antioxidant) A-1: IRGANOX-1010 (manufactured by Ciba Specialty Chemicals)
A-2: Sumilizer GP (Sumitomo Chemical Co., Ltd.)
Subsequently, the following calendar processing was performed.

(Calendar processing)
The obtained film or nonwoven fabric sheet was subjected to a calendar process using a roll press device manufactured by Yuri Roll Co., Ltd. Both the upper and lower parts were metal rolls, the roll temperature was set to 200 ° C., and the calendar process was performed at a linear pressure of 0.5 tons and a traveling speed of 2 m / min.

(Solution Cast (Sample No. 18 to No. 19))
100 parts by mass (solid content) of CNF-A1 obtained in Production Example 3 was diluted to 1% by mass with methyl ethyl ketone (MEK), and 20 parts by mass of surface-modified silica fine particles listed in Table 1 were added and stirred well. .

  This was cast uniformly on a stainless steel belt support at 30 ° C. using a belt casting device with an internal temperature of 35 ° C. Then, after drying the composition that had flowed to the peelable range, the web was peeled from the stainless steel belt support. The residual solvent amount of the web at this time was 80% by mass.

(Extension process)
The web obtained above is dried while roll transporting the 85 ° C. drying zone, and when the residual solvent amount is less than 35% by mass, after preheating, it is stretched in the film transport direction (longitudinal stretching) due to the roll speed difference. Then, it led to the tenter type stretching machine and stretched in the direction perpendicular to the film transport direction (width stretching). The draw ratio was 1.5 times the longitudinal stretch and 1.5 times the width stretch.

  The film sample of Table 1 was obtained according to the said process.

(Sample No. 20, comparative example)
Cellulose copper ammonia stock solution containing 10% by weight of cellulose, 6.5% by weight of NH ₃ , 3.6% by weight of Cu, 2.7 residues with respect to 3.3% by weight of cellulose and 1 residue of glucose of cellulose 14% ammonia water and water glass (about 35% as SiO ₂ ) were mixed and adjusted so that the silica content (100 parts by weight of cellulose and 20 parts by weight of silica) was obtained.

  These silica-containing mixed adjustment solutions were cast on a glass plate, dried at 80 ° C. for 5 minutes, then immersed in water, acetone, tetrahydrofuran, 1-butanol and toluene for 2 minutes at room temperature, then air-dried, Next, after neutralization and regeneration with 2% sulfuric acid, washing and drying were performed to obtain a membrane.

(Sample No. 21, comparative example)
<Acetylated cellulose and silica fine particles>
The following acetylated cellulose was used as a raw material polymer.

C-1: cellulose acetate propionate (acetyl group substitution degree 1.5, propionyl group substitution degree 1.2, molecular weight Mn = 70000, molecular weight Mw = 220,000, Mw / Mn = 3)
<Additive>
The following materials were used as additives.

(Plasticizer)
P-1: Trimethylolpropane tribenzoate (antioxidant)
A-1: IRGANOX-1010 (Ciba Specialty Chemicals)
A-2: Sumilizer GP (Sumitomo Chemical Co., Ltd.)
<Preparation of masterbatch containing cellulose nanofiber>
Acetylated cellulose C-1: 100 parts by mass, plasticizer P-1: 8 parts by mass, antioxidant A-1: 1 part by mass, A-2: 0.5 part by mass,
As porous silica particles, an average particle diameter of 2.8 μm, a pore volume V of 0.9 ml / g, 20 parts by mass were mixed for 30 minutes with a V-type tumbler, It was supplied at 100 kg / hr from one supply port. C-1 was vacuum-dried at 130 ° C. for 12 hours before use. The cellulose nanofiber CNF-C was supplied at 23 kg / hr from the second supply port (on the downstream side of the first supply port) of the kneading extruder. The screw design has more kneading discs so that the kneading effect is strong. The screw rotation speed was 500 rpm, the temperature setting from the barrel to the die was 180 ° C. to 250 ° C., and a vent port was provided near the tip to remove volatile matter. The die was a strand die, and the discharged strand was guided into cooling water, cut with a pelletizer, and formed into a pellet having a diameter of about 3 mm and a length of about 3 mm. This pellet was formed into a film by the melt film forming method.

(Sample No. 22, comparative example)
100 g of an aqueous solution containing 4.6 wt% lithium hydroxide and 15 wt% urea was cooled to −12 ° C., and 2 g of filter paper pulp (pure cellulose: manufactured by Advantech Toyo), average particle size of 2.8 μm, pore volume V When 2 g of porous silica particles of 0.9 ml / g were added and stirred, the cellulose quickly dissolved to obtain a transparent solution.

To the cellulose solution, a glass paper manufactured by Nippon Sheet Glass Co., Ltd. (thickness: 50 μm, fiber diameter: 0.5 μm, density: about 0.14 g / cm ³ , porosity: 90% or more, average pore diameter: 2-5 μm, Maximum pore size: 10-15 μm was dipped, the adhering liquid was removed, then dipped in methanol, washed thoroughly with water to gel the cellulose, and cellulose hydrogel-containing glass paper was obtained.

  The liquid containing the composite gel was replaced with water → ethanol → fluorinated solvent (Zeorolla H, manufactured by Nippon Zeon Co., Ltd.), the gel was immersed in liquid nitrogen and frozen, and freeze dryer DC- manufactured by Yamato Scientific Co., Ltd. It lyophilized | freeze-dried by 800 and the glass paper carrying | support cellulose aerogel was obtained.

(Sample No. 23, comparative example)
CNF-B1 obtained by propionating the hydroxyl groups at C2 and C3 of cellulose nanofiber B obtained in Production Example 3 was hot-pressed at 120 ° C. and 2 MPa for 3 minutes, and a BC sheet having a thickness of about 50 μm (water content: 0) % By weight).

  The BC sheet was immersed in a transparent epoxy resin (“Celloside 2021” manufactured by Daicel Chemical Industries, Ltd.) under reduced pressure (0.08 MPa) for 12 hours to produce a fiber-reinforced composite material. The fiber content of this fiber-reinforced composite material was 50% by mass.

  Further, the fiber reinforced composite resin material was cured according to the curing method of the liquid precursor of the matrix resin to prepare a sample having a diameter of 50 mm and a thickness of 125 μm, and then cut into a film for measurement. The described physical properties were measured.

(Evaluation)
With the measurement methods described below, the light transmittance, thermal linear expansion coefficient, yellowing, and elongation at break of the film were evaluated.

(Film evaluation method)
(1) Measurement of light transmittance (transparency evaluation)
A spectrophotometer UV-2500PC: manufactured by Shimadzu Corporation was used to measure the total transmitted light amount with respect to the incident light amount of visible light. The measurement results at 550 nm are shown in Table 1 below.

(2) Measurement of thermal expansion coefficient (heat resistance evaluation)
About a molded object, temperature was changed within the range of 40-200 degreeC, and the thermal expansion coefficient was measured. SII (Seiko Instruments) EXSTAR6000 TMA / SS6100 was used as a measuring device. The test piece was 2 cm in length and 2 mm in width.

(3) Measurement of elongation at break (toughness evaluation)
Using a variable temperature tensile tester (“Shimadzu Autograph AGS-100D”; manufactured by Shimadzu Corporation), a test piece cut to a width of 10 mm was pulled at 23 ° C., a distance between chucks of 50 mm, and a tensile speed of 50 mm / min. The elongation rate until breakage was determined. After metaharass (ultraviolet ray) forced deterioration test (temperature: 63 ° C., humidity: 50%, irradiation intensity: 100 mW / cm ² , continuous 200 hours input) using an I-super UV tester (SUV-W151) manufactured by Iwasaki Electric Co., Ltd. The results are shown in Table 1 after degradation / before degradation × 100%.

(4) Evaluation of yellowing (weather resistance evaluation)
The yellow discoloration was evaluated by performing a meta-harassment forced deterioration test (temperature: 63 ° C., humidity: 50%, irradiation intensity: 100 mW / cm) using an I-super UV tester (SUV-W151) manufactured by Iwasaki Electric Co., Ltd. ² and continuously 200 hours), the deterioration due to ultraviolet rays was visually confirmed.
Evaluation was made according to the following criteria.

○: Equivalent transparency before deterioration Δ: Slightly yellowish ×: Yellow The evaluation results of Samples 1 to 23 are shown in Table 1.

  As is clear from the table, the composite film of the present invention has good transparency, extremely low thermal linear expansion, good weather resistance, and good toughness.

Claims (5)

In a cellulose nanofiber film having cellulose nanofibers having an average fiber diameter of 2 nm to 200 nm and surface-modified silica fine particles,
A cellulose nanofiber film in which the cellulose nanofiber and the surface-modified silica fine particles are bonded.   The cellulose nanofiber film according to claim 1, wherein a part of hydroxyl groups of the cellulose nanofiber is esterified.   The cellulose nanofiber film according to claim 2, wherein the substitution degree of esterification of the cellulose nanofiber is 0.5 to 2.5, and the crystallinity is 30 to 90%.   The cellulose nanofiber film according to any one of claims 1 to 3, wherein the surface-modified silica fine particles have a circle-converted average particle diameter of 5 nm to 100 nm.   The cellulose nanofiber film according to any one of claims 1 to 4, wherein the surface-modified silica fine particles are surface-modified with a silane coupling agent.