JP7808486B2 - Cellulose nanofiber-containing thermoplastic elastomer composition and method for producing same - Google Patents

Description

This invention relates to a thermoplastic elastomer composition containing dispersed cellulose nanofibers and a method for producing the same.

Polyurethane resin compositions are a type of plastic that excels in elasticity, tensile strength, and abrasion resistance, and are used in a wide variety of applications. Their applications are diverse, including as raw materials for adhesives and paints, highly elastic fibers for sports equipment, and urethane foam for cushions and sponges. They are essentially made from polyurethane, which is polymerized from polyol and polyisocyanate, but numerous attempts have been made to improve their physical properties by adding various additives.

Patent Document 1 proposes a urethane resin composition obtained by adding cellulose nanofibers, which are made by defibrating cellulose in a polyol and then reacting these with polyisocyanate. It is stated that the presence of cellulose nanofibers gives this composition excellent strength.

Patent Document 2 proposes a urethane elastomer molded product containing a urethane prepolymer, a curing agent containing a polyamine compound, and micronized cellulose. It is stated that the addition of the polyamine compound and micronized cellulose results in excellent storage modulus and creep properties.

Patent Document 3 proposes a polyurethane resin composition that improves the dispersibility of cellulose nanofibers in polyurethane, thereby improving strength, heat resistance, and water resistance. The procedures proposed include mixing an aqueous dispersion of polyurethane resin with an aqueous dispersion of cellulose nanofibers, and mixing an organic solvent dispersion of an isocyanate-terminated urethane prepolymer with an aqueous dispersion of cellulose nanofibers to produce a polyurethane resin.

Patent Document 4 proposes using a urethane resin for the coating layer that bonds multiple substrate layers together in a resin diaphragm used in a loudspeaker, and combining this urethane resin with a reinforcing material. It has been shown that using bamboo nanofibers as the reinforcing material improves the elastic modulus and also improves the bonding strength with the urethane resin.

Patent Document 5 proposes a functional film that uses a polyurethane elastomer as a thermoplastic elastomer, with a thickness of 10 to 100 μm and thickness variations adjusted to within 2 μm. It is suggested that this functional film can be used as a vibration-damping material, such as a support member for the vibration system of a speaker, as well as for acoustic applications such as acoustic vibration materials and sound-absorbing materials.

Patent Document 6 proposes an aqueous paint containing cellulose nanofibers and relatively large cellulose fibers. It has been shown that the presence of relatively large cellulose fibers in this aqueous paint creates appropriate unevenness on the coating film surface, thereby improving slipperiness.

JP 2013-194162 A JP 2015-086308 A JP 2017-128664 A Patent No. 6240893 Patent No. 6692182 Patent No. 6866134

In recent years, there has been a growing demand for smartphone speakers to have high-precision sound quality. However, smartphone speakers are placed in environments with greater temperature and humidity changes than stationary speakers, and their smaller diameters require greater precision and finer adjustments. For this reason, there is a growing demand for diaphragms made of a material that causes even less change in sound quality than the polyurethane elastomer described in Patent Document 5.

In addition to acoustic diaphragms, there are also cases where materials with high stability of properties, less susceptible to changes in temperature and humidity, as well as materials with excellent slip properties and transparency are required.

The objective of this invention is to create a thermoplastic elastomer composition whose properties change little with temperature changes. Furthermore, the objective of this invention is to create a material that combines smoothness and transparency.

The present invention solves the above-mentioned problems by providing a cellulose nanofiber-containing thermoplastic elastomer composition comprising a cellulose nanofiber, wherein the cellulose nanofiber is nonionic and has a number-average fiber diameter of 2 nm to 50 nm, the content of the cellulose nanofiber relative to the thermoplastic elastomer is 0.5 mass % to 15 mass %, and the cellulose nanofiber is uniformly dispersed in the composition.

Thermoplastic elastomers that use polyurethane as the thermoplastic elastomer and blend cellulose nanofibers have long been known. However, simply adding cellulose nanofibers can cause the cellulose nanofibers to aggregate or be unevenly distributed, resulting in uneven properties across the entire material. When processed into films, this unevenness can result in regions with different behavior in response to temperature changes, slipperiness, and transparency. Focusing on this issue, the cellulose nanofiber-containing thermoplastic elastomer composition of the present invention uniformly disperses nonionic cellulose nanofibers with a number-average fiber diameter of 2 nm to 50 nm in a content of 0.5% by mass to 15% by mass relative to the thermoplastic elastomer throughout the composition, thereby suppressing the unevenness of the cellulose nanofibers that affect the physical properties of the thermoplastic elastomer and achieving further stability in properties with temperature changes while simultaneously achieving both slipperiness and transparency.

The following production method can be carried out as a procedure for obtaining a cellulose nanofiber-containing thermoplastic elastomer composition in which cellulose nanofibers are dispersed as described above.
A cellulose nanofiber composition containing a polyol compound consisting of a polyol, a polyol derivative, or both, cellulose nanofibers, and water is mixed with a first organic solvent to prepare a cellulose nanofiber dispersion in which cellulose nanofibers are dispersed in the liquid, and the cellulose nanofiber dispersion is mixed with a thermoplastic elastomer solution or dispersion in which a thermoplastic elastomer is dissolved or dispersed in a second organic solvent, and the dispersion medium is evaporated from the mixed liquid after mixing.

When the cellulose nanofiber-containing thermoplastic elastomer composition is produced, it can be molded into a film to obtain a functional film made from the cellulose nanofiber-containing thermoplastic elastomer composition. When this functional film is used, for example, as the diaphragm of a smartphone speaker, the change in sound quality that occurs with temperature changes in the smartphone's operating temperature range is smaller than with conventional films made only of thermoplastic elastomer that do not contain cellulose nanofiber. Furthermore, when used as a protective film for smartphone LCD panels, it has good slip properties without compromising transparency, resulting in excellent visibility and operability of the LCD panel display, and is also easy to apply.

Furthermore, this manufacturing method can employ an embodiment in which the cellulose nanofiber composition has a moisture content of 1% by mass or more and 10% by mass or less, and the mass mixing ratio of the cellulose nanofiber to the polyol compound is 1:2 to 1:20.

Furthermore, this manufacturing method can employ an embodiment in which the cellulose nanofiber composition is prepared by adding the polyol compound as a dispersant to a cellulose nanofiber aqueous suspension containing cellulose nanofibers, and then evaporating the water.

The cellulose nanofiber-containing thermoplastic elastomer composition of this invention ensures high dispersibility, and by combining dispersed cellulose nanofibers, it is possible to suppress changes in physical properties due to temperature changes, and to provide stable properties to precision articles used in environments exposed to large temperature changes.

In addition to the above properties, the cellulose nanofiber-containing thermoplastic elastomer composition of the present invention also has other excellent features. The cellulose nanofibers contained therein create fine irregularities on the surface, which reduces the coefficient of friction and provides high slipperiness when formed into a film or sheet. Another advantage is that this slipperiness can be achieved without compromising transparency. When conventional thermoplastic elastomer films or sheets are treated with surface processing to create irregularities and reduce the contact area in an attempt to impart slipperiness, transparency is often compromised, making it difficult to achieve both slipperiness and transparency. In contrast, the cellulose nanofiber-containing thermoplastic elastomer composition of the present invention has a fiber diameter that is sufficiently smaller than the wavelength of visible light, so it does not scatter visible light and is less likely to impair transparency even when incorporated into a resin. The fine irregularities on the surface when formed into a film or sheet can be evaluated, for example, by surface roughness as specified in JIS B 6101.

However, it is desirable that the cellulose nanofibers used in this invention are not substituted with chemically modifying substituents. If substituents are introduced into the cellulose nanofibers, they will not be able to be uniformly dispersed in the resin due to interactions between the cellulose nanofibers, making it difficult to suppress changes in physical properties due to temperature changes, and may not achieve sufficient slip properties and transparency.

The present invention is described in detail below. This invention relates to a cellulose nanofiber-containing thermoplastic elastomer composition comprising a cellulose nanofiber-containing thermoplastic elastomer composition, wherein the cellulose nanofibers are nonionic and have a number-average fiber diameter of 2 nm to 50 nm, the content of the cellulose nanofibers relative to the thermoplastic elastomer is 0.5% by mass to 15% by mass, and the cellulose nanofibers are uniformly dispersed in the composition.

The cellulose nanofibers (hereinafter abbreviated as "CNF") used in this invention are cellulose that has been processed to produce fine fibers. They may include not only cellulose whose molecular structure remains unchanged, but also cellulose whose molecular structure has been partially chemically modified, or cellulose that has been chemically modified and then regenerated into cellulose.

Examples of chemically modified cellulose include TEMPO-oxidized cellulose (oxidized with TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)), carboxymethylated carboxymethyl cellulose, phosphoric acid esterified cellulose, and xanthated cellulose (caused by adding carbon disulfide to alkali-treated cellulose to introduce xanthate groups (-OCSS ^- M ⁺ ). Chemically modifying cellulose materials such as pulp makes it easier to convert them into nanofibers than directly defibrating the cellulose material. This chemically modified and defibrated CNF is called "chemically modified CNF." Furthermore, among chemically modified celluloses, phosphated cellulose and xanthated cellulose are preferred because they can be easily regenerated and restored to cellulose. CNF obtained by performing a regeneration process to return the molecular structure of chemically modified cellulose to cellulose is called "regenerated CNF."

In the following description of this invention, the term "CNF" refers not only to CNF obtained by simply defibrating cellulose materials, but also to the above-mentioned chemically modified CNF and regenerated CNF. Furthermore, regenerated CNF may include not only CNF in which hydroxyl groups have been temporarily modified to other functional groups such as xanthate groups, but in which all of the hydroxyl groups have been returned to their original hydroxyl groups, but also CNF in which some of the functional groups remain. Furthermore, these CNF may be purified before use if necessary.

CNF is preferably non-ionic, such as chemically unmodified cellulose or regenerated CNF. Ionic, chemically modified cellulose such as xanthated cellulose or TEMPO-oxidized cellulose is not preferred, but cellulose that has been chemically modified with ionic modifications such as xanthated cellulose can be used suitably if it has been sufficiently regenerated back into cellulose. Ionic nanofibers tend to aggregate in organic solvents, as described below, making it difficult to ensure sufficient dispersibility, but non-ionic nanofibers are less likely to aggregate in organic solvents, making it easier to ensure dispersibility.

The CNF preferably contains, as its primary component, fine fibers with a fiber diameter of 2 nm to 50 nm. Here, "primary component" means that 50% or more of the fibers present fall within the above fiber diameter range. However, as long as it does not interfere with the production or use of the composition, fine fibers with diameters outside the above range may also be present. The number-average fiber diameter of the CNF is preferably 2 nm or more, and preferably 3 nm or more. While the present invention can be implemented with a diameter smaller than this, achieving a diameter of less than 2 nm requires a great deal of energy, is not very practical in terms of work efficiency, and is disadvantageous when improving slipperiness is desired. On the other hand, the number-average fiber diameter of the CNF is preferably 50 nm or less. If the diameter exceeds 50 nm, the fibers will be too large and will be insufficiently dispersible, potentially resulting in significant variations in the physical properties of the resulting film, etc.

In addition, the CNF-containing thermoplastic elastomer composition of the present invention contains CNF whose fiber diameter is within the above-mentioned range and is sufficiently finer than the wavelength of visible light, so that visible light is hardly scattered even when CNF is contained. As a result, transparency is not easily impaired even when CNF is contained within the content range described below, and the beneficial effects of containing CNF can be exerted while maintaining transparency.

The CNF-containing thermoplastic elastomer composition of this invention is prepared by dispersing the above-mentioned CNF in a thermoplastic elastomer under specified conditions.

The thermoplastic elastomer used in this invention can be selected from common thermoplastic elastomers depending on the purpose. Examples include polyurethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, olefin-based elastomers, and styrene-based elastomers. These elastomers may be used alone or in combination of two or more types.

The polyurethane elastomer may be, for example, a polyurethane elastomer obtained by polymerizing a polyol and a polyisocyanate. Examples of polyols used in this polymerization include ester polyols, ether polyols, and polycarbonate polyols. Examples of ester polyols include polyethylene adipate (PEA), polybutylene adipate (PBA), polyhexamethylene adipate (PHA), poly 3-methylpentane adipate (PMPA), and polycaprolactone (PCL). Examples of ether polyols include polyethylene glycol (PEG), polypropylene glycol (PPG), and polytetramethylene ether glycol (PTMG). Examples of polycarbonate polyols include polyhexamethylene carbonate diol (PHC) and co-condensates of polyhexamethylene carbonate with other ester polyols or ether polyols.

On the other hand, the polyisocyanate used here is a compound having two or more isocyanate groups in one molecule, such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), or an isocyanate-terminated polyurethane prepolymer, which is an intermediate product obtained by reacting a polyol with excess polyisocyanate.

These polyurethane elastomers made from polyols and polyisocyanates may be used alone or in combination of two or more types.

Examples of the polyester-based elastomer include polyester ether types that use polybutylene terephthalate (PBT) for the hard segment and polytetramethylene ether glycol (PTMG) for the soft segment, and polyester ester types that use polybutylene terephthalate (PBT) for the hard segment and polybutylene adipate (PBA) for the soft segment. Any of these resins may be used alone or in combination of two or more.

Examples of the above-mentioned olefin-based elastomers include those in which the hard segment is a mixture of an olefin resin such as polyethylene (PE) or polypropylene (PP), and the soft segment is a mixture of rubber such as ethylene propylene rubber (EPM) or ethylene propylene diene rubber (EPDM). Any of these resins may be used alone, or two or more types may be combined.

Examples of the styrene-based elastomer include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-butadiene rubber (SBR), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-butadiene (SB), and styrene block copolymer (SBC). Any of these resins may be used alone or in combination of two or more.

Examples of the polyamide-based elastomers include polyether ester types that use nylon 6, nylon 11, or nylon 12 for the hard segment and polyethylene glycol (PEG), polypropylene glycol (PPG), or polytetramethylene ether glycol (PTMG) for the soft segment, and polyether amide types that use polypropylene diamine or polybutylene diamine for the soft segment. Any of these resins may be used alone or in combination of two or more.

Of these, polyurethane-based elastomers are particularly suitable when the CNF-containing thermoplastic elastomer composition of this invention is used in functional films for speaker diaphragms. This is because, when used in speaker diaphragms, elastomers with minimal change in storage modulus at temperatures between -10 and 80°C are preferred.

In the CNF-containing thermoplastic elastomer composition of the present invention, the CNF content relative to the thermoplastic elastomer is preferably 0.5% by mass or more, and more preferably 1.0% by mass or more. If the CNF content is less than 0.5% by mass, the stabilizing effect of the CNF on the physical properties of the CNF-containing thermoplastic elastomer composition against temperature changes may not be fully exerted. On the other hand, the CNF content is preferably 15% by mass or less, and more preferably 10% by mass or less. If the CNF content exceeds 15% by mass, the CNF may become unevenly distributed in the film, which may make it difficult to ensure the required mechanical properties of the film, such as elongation and tensile strength.

Furthermore, the CNF-containing thermoplastic elastomer composition of the present invention can ensure sufficient transparency when the CNF content is 5% by mass or less. Transparency gradually decreases as the CNF content increases, but if CNF within the above fiber diameter range is used and the content is 5% by mass or less, there is almost no decrease in transparency. On the other hand, from the perspective of the effect of reducing the friction coefficient, the CNF content is preferably 0.5% by mass or more, and more preferably 1% by mass or more.

The CNF-containing thermoplastic elastomer composition of the present invention contains CNF at the above-mentioned content, which creates fine irregularities on the surface, reducing the contact area and the coefficient of friction. In other words, films made from the CNF-containing thermoplastic elastomer composition of the present invention have superior slipperiness compared to films made from thermoplastic elastomer compositions without CNF. To improve the slipperiness of conventional thermoplastic elastomer compositions, lubricants are typically incorporated into the film during production or applied together with a binder. However, these methods often result in problems such as loss of the lubricant or significant irregularities, which can reduce transparency. By molding the CNF-containing thermoplastic elastomer composition of the present invention, transparent films can be produced that exhibit improved slipperiness while minimizing the loss of transparency, as described above. This allows for use as a protective material for protecting areas requiring transparency in addition to the speaker diaphragm described above. Specific applications include, for example, as a protective film for the LCD panel of a smartphone that performs slide operations on the surface, providing surface protection for the LCD screen without compromising visibility or finger operability. It can also be used as a protective film for areas that are frequently touched by people's fingers, such as switches on vending machines, and provides a high level of protection without interfering with the visibility of the content displayed underneath.

In the CNF-containing thermoplastic elastomer composition of this invention, it is desirable for the CNF to be uniformly dispersed. Uneven CNF distribution within the film can lead to significant variations in temperature-related properties. Furthermore, some areas may experience reduced transparency. The degree of CNF dispersion can be evaluated, for example, by measuring the amount of CNF aggregates in the CNF-containing thermoplastic elastomer composition. Specifically, the CNF-containing thermoplastic elastomer composition can be molded into a film and observed with a digital microscope through a polarizing filter. The area ratio of CNF aggregates in an image can be used. When processing with software, the captured image can be binarized using a threshold value that distinguishes between CNF aggregates and non-CNF aggregates. The colored areas in the image are then considered to be CNF aggregates, and the area ratio of the colored areas to the entire image is calculated and evaluated. From the perspective of dispersibility, this area ratio is preferably 5.0% or less, and more preferably 1.0% or less.

Even when the CNF-containing thermoplastic elastomer composition of this invention is used as a film or sheet that takes advantage of its transparency, it is preferable that the CNF contained does not contain cellulose whose molecular structure has been chemically modified. When recycled CNF is used, it is preferable that it is fully recycled. If a substituent is introduced into the cellulose, interactions between the nanofibers can easily result in insufficient uniform dispersion in the resin, making it difficult to ensure sufficient slip properties and transparency.

When a functional film made from the CNF-containing thermoplastic elastomer composition of this invention is used for the speaker diaphragm, the thickness should be 10 μm or more, and preferably 15 μm or more. A thickness of less than 10 μm can cause durability problems, and even if the above-mentioned dispersibility is ensured, the influence of the CNF fiber diameter cannot be ignored, which may result in significant bias in physical properties. On the other hand, the thickness should be 100 μm or less, and preferably 40 μm or less. If the thickness exceeds 100 μm, it becomes difficult to suppress thickness unevenness (described below), making manufacturing difficult and expensive, so there is little benefit to increasing the thickness beyond 100 μm. When used as a film or sheet that takes advantage of its transparency, the thickness should be 100 μm or less. If the thickness exceeds 100 μm, the loss of transparency due to the film itself cannot be ignored. On the other hand, even when used as a film or sheet that takes advantage of its transparency, a thickness of 10 μm or more is preferable from the standpoint of durability.

The tolerance (thickness variation) of the functional film made from the CNF-containing thermoplastic elastomer composition of this invention is preferably within 2 μm, and more preferably within 1 μm. If the tolerance exceeds 2 μm, it becomes difficult to suppress stress fluctuations, and when used as a speaker diaphragm or vibration-damping material, it may not be possible to provide the speaker with sufficiently good sound quality. However, when used as a film or sheet that takes advantage of its transparency, a tolerance outside this range is sufficient for use. However, when the object to be attached is an optical device such as a liquid crystal or organic electroluminescent device, a large tolerance may cause the displayed image to be distorted, so a tolerance of within 2 μm is preferable.

The thickness of this functional film can be measured in accordance with JIS Z 1702. Under these conditions, the obtained 1m x 1m film is measured at 30 random locations and the average value calculated is used. It is not necessary to follow these conditions; for films of different sizes, multiple measurements can be taken so that the number of measurement locations per 1m x 1m is 30 or more, and the average value can be calculated to obtain a sufficiently significant thickness value.

Fine irregularities on the surface of this functional film can be evaluated, for example, by the arithmetic mean roughness, a height-direction parameter among the surface roughness indicators specified in JIS B 6101. When used as a film or sheet that takes advantage of its transparency, the arithmetic mean roughness is preferably 0.080 μm or more and 0.400 μm or less, and more preferably 0.100 μm or more and 0.250 μm or less. If it is less than 0.080 μm, the film surface will have few fine irregularities, resulting in an insufficient reduction in the coefficient of friction. On the other hand, if it exceeds 0.400 μm, the decrease in transparency will become significant.

The stress variation of this functional film can be measured in accordance with JIS K 7127. The variation value is the difference between values measured at five random locations on the film used for the thickness measurement above. Stable film rigidity is required to consistently provide good sound quality. This is generally expressed as elastic modulus, but since rigidity changes as the film becomes thicker, stability of the elongation stress (stress at extension) when the above-mentioned film is stretched is required. If this stress at extension is stable, the storage modulus will also be stable at temperatures expected in the living environment that the film will encounter when installed in a smartphone speaker, allowing for excellent acoustic properties to be exhibited.

The tensile modulus of a functional film made from the CNF-containing thermoplastic elastomer composition of this invention is adjusted depending on the application. For example, in the case of a film used for the above-mentioned speaker diaphragm, the tensile modulus should be 10 MPa or more, and preferably 35 MPa or more. Furthermore, for practical purposes, the tensile modulus should be 100 MPa or less.

The thermal expansion coefficient of a functional film made from the CNF-containing thermoplastic elastomer composition of this invention is preferably 4.0% or less, and more preferably 3.5% or less, in an environment of 40°C. If the thermal expansion coefficient exceeds 4.0%, the changes in physical properties due to temperature will be too great, making it unsuitable for applications requiring stable acoustic properties.

The ratio of the storage modulus at -10°C and 60°C (-10°C/60°C) of a functional film made from the CNF-containing thermoplastic elastomer composition of this invention is preferably 1 or more and 15 or less, and more preferably 1 or more and 13 or less. Because the storage modulus of a thermoplastic elastomer decreases as the temperature rises, it is not realistic to achieve a ratio of less than 1, even when CNF is added. On the other hand, if the ratio exceeds 15, the changes in physical properties will be too great, making it unsuitable, especially when stable acoustic properties are required.

The haze, an index of transparency for functional films made from the CNF-containing thermoplastic elastomer composition of this invention, is preferably 20% or less, and more preferably 15% or less, when used in applications where transparency is important. If the haze exceeds 20%, when used as a protective film for switches, etc., it will be difficult to see the content displayed underneath, making it impossible to ensure visibility.

Furthermore, when the functional film made from the CNF-containing thermoplastic elastomer composition of this invention is used in applications that utilize its slipperiness, the coefficient of friction, which is an index of slipperiness, is preferably 5 or less, and more preferably 3 or less, as a dynamic friction coefficient. If the dynamic friction coefficient exceeds 5, it becomes difficult to perform sliding operations on the surface when used as a protective film for the LCD panel of a smartphone or the like.

When producing the CNF-containing thermoplastic elastomer composition of this invention, it is necessary to properly disperse the CNF so that it achieves the above-mentioned dispersibility. An example procedure for achieving this is described below.

First, a CNF composition containing CNF, water, and a polyol compound is prepared (S1). In practice, it is difficult for CNF to maintain dispersibility on its own, so CNF is often handled as a CNF aqueous dispersion in which CNF is dispersed in water or a polar solvent containing water. The CNF composition can be prepared by mixing the CNF aqueous dispersion with a polyol compound.

The polyol compounds used here include polyols such as diols, glycerin, and triethylene glycol, their derivatives, and/or polyol derivatives. However, when used as the functional film described above, if remaining in the functional film causes problems, it is particularly preferable to use diol compounds among these compounds because of their ease of removal. It is also possible to obtain a CNF composition even if other polar solvents are mixed with this polyol compound. However, since other polar solvents may evaporate at unintended times or, conversely, require a separate step for their removal, it is preferable to use as few polar solvents as possible other than the polyol compound.

Here, a polyol is a compound that has multiple hydroxyl groups in its molecule. Furthermore, a polyol derivative is a compound in which one or more of the hydroxyl groups have been modified to provide a functional group. Modification methods include, for example, etherification and esterification reactions. Specific examples include alkyl ethers of polyols and alkyl esters of polyols.

Examples of the polyol compound that can be used include diols such as diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexylene glycol, and 3-methyl-1,3-butylene glycol; diol derivatives such as dipropylene glycol monopropyl ether, diethylene glycol ethyl ether acetate, diethylene glycol monoethyl ether, tripropylene glycol methyl ether, and dipropylene glycol methyl ether acetate; and glycerin. These may be used alone or in combination.

Of the above, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, dipropylene glycol monopropyl ether, diethylene glycol ethyl ether acetate, 1,4-butylene glycol, and 1,6-hexylene glycol maintain good dispersibility even when the CNF composition after mixing is dried to remove most of the water, and when it is subsequently made into a cellulose nanofiber dispersion (CNF dispersion) as described below. Furthermore, they are particularly preferred because they are easily removed when the necessary heating is performed.

The mass mixing ratio of the CNF to the polyol compound in the CNF composition is preferably 1:2 to 1:20. Depending on the type of polyol compound, if the CNF content is greater than 1:2, there may not be enough polyol compound to maintain dispersibility, which may result in poor redispersion of the CNF composition in water or the polyol compound. On the other hand, if the polyol compound content is greater than 1:20, dispersion is possible, but increasing the polyol compound content beyond this point does little to improve redispersibility, and evaporating it as part of the dispersion medium may take a long time when preparing a CNF-containing thermoplastic elastomer composition. Furthermore, even after removing the water, the mass of the CNF composition remains large due to the mass of the polyol compound, thereby reducing the benefits of using the CNF composition.

The moisture content of the CNF composition is preferably 10% by mass or less, and more preferably 7% by mass or less. Since water increases the mass and volume of the CNF composition during storage and transportation, it is desirable to have as little water as possible. However, it is difficult to dry the CNF composition to less than 1% by mass, so a moisture content of 1% by mass or more is more realistic.

The CNF composition is produced by first adding the polyol compound as a dispersant to an aqueous CNF suspension and mixing. The mixture is then dried to evaporate the water, reducing the water content and obtaining the CNF composition. While drying can be achieved by leaving the mixture at room temperature, heating is desirable to shorten production time. A drying temperature of 50°C or higher is preferred, with 60°C or higher being more preferred. Below 50°C, the evaporation rate from the mixture is too slow, resulting in excessive time required for production of the CNF composition. Meanwhile, a drying temperature of 110°C or lower is preferred, with 90°C or lower being more preferred. Above 110°C, the polyol compound evaporates, making redispersion of the CNF difficult. While this depends on the polyol compound selected, keeping the temperature below 90°C can also suppress evaporation of the polyol compound. The drying method for obtaining the CNF composition can be known, such as hot air drying, spray drying, or vacuum drying, or a combination of two or more of these methods. Specific drying equipment includes drum dryers, disc dryers, vacuum versions of these, conical dryers, and spray dryers.

The water content of the above CNF composition is significantly reduced compared to the state of the aqueous suspension after defibration of the CNF, making it easy to store and transport. On the other hand, it has the property of easily ensuring dispersibility, and by using this CNF composition and redispersing it in water, organic solvents, etc., high dispersibility of the CNF can be achieved.

Next, this CNF composition is mixed with a first organic solvent to prepare a CNF dispersion in which the CNF is suitably dispersed in this organic solvent (S2). Dimethylformamide, dimethyl sulfoxide, dimethylacetamide, etc. can be used as this first organic solvent. Of these, dimethylformamide is most preferred because its solubility and solution viscosity for thermoplastic elastomers (TPEs) are suitable for film formation.

The CNF content in this CNF dispersion is preferably 0.1% by mass or more, and more preferably 0.2% by mass or more. If the CNF content is less than 0.1% by mass, the load required to ultimately remove the dispersion medium will be too large. On the other hand, it is preferably 2.0% by mass or less, and more preferably 1.5% by mass or less. If the CNF content exceeds 2.0% by mass, it may be difficult to achieve adequate dispersion in the next step S4.

Furthermore, the water content of the CNF dispersion is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less. If the water content exceeds 1.0% by mass, the thermoplastic elastomer, such as the polyurethane-based elastomer, may react with moisture, affecting its physical properties. Therefore, it is desirable to have as low a water content as possible.

Furthermore, it is preferable that the CNFs in this CNF dispersion do not settle even when centrifuged. The settling properties of CNFs can be evaluated, for example, by centrifuging the CNF dispersion (1400 G, 3 minutes) using a centrifuge (Avanti J-251, manufactured by Beckman Coulter). However, a dispersion containing 0.3% CNF by mass is prepared in advance, and the light transmittance at a wavelength of 660 nm with an optical path length of 10 mm is measured using an ultraviolet-visible spectrophotometer (V-730, manufactured by JASCO Corporation). If this value is 7.0% or higher, no CNF settling is observed, and this value can be used as a useful guide for preliminary evaluation.

Separately, the thermoplastic elastomer is dissolved or dispersed in a second organic solvent to prepare a thermoplastic elastomer solution or dispersion (S3). As with the first organic solvent, the second organic solvent can be dimethylformamide, dimethyl sulfoxide, dimethylacetamide, or the like. Among these, dimethylformamide is most preferred because its solubility and solution viscosity for the thermoplastic elastomer (TPE) make it suitable for film formation.

The content of the thermoplastic elastomer in this thermoplastic elastomer solution or dispersion is preferably 1.0% by mass or more, and more preferably 5.0% by mass or more. If the content is less than 1.0% by mass, the load required to finally remove the solvent increases, and the viscosity of the thermoplastic elastomer solution or dispersion is too low, making it more likely that unevenness in the film thickness will occur. On the other hand, it is preferably 20% by mass or less, and more preferably 10% by mass or less. If the content exceeds 20% by mass, it may become difficult to quickly disperse the CNF in the next step S4.

Next, the CNF dispersion is mixed with a thermoplastic elastomer solution or dispersion to obtain a mixed liquid (S4). At this time, since the CNF is sufficiently dispersed in the CNF dispersion, a mixed liquid is obtained in which the CNF is suitably dispersed in the thermoplastic elastomer composition contained in the thermoplastic elastomer solution or dispersion.

The mixing ratio of the CNF dispersion to the thermoplastic elastomer solution or dispersion is preferably 1:2 to 5:1, and more preferably 1:1 to 3:1, by mass, of the respective liquids. If there is too little CNF, the effect of stabilizing the physical properties of the CNF-containing thermoplastic elastomer composition against temperature changes will be reduced, and the effect of adding it will be diminished. On the other hand, if there is too much CNF, it will be difficult to stir the mixture and the distribution will be prone to bias, making it difficult to ensure the dispersibility of the CNF dispersed in the film.

In addition to the above-mentioned CNF dispersion and thermoplastic elastomer solution or dispersion, additives such as colorants, antioxidants, and antistatic agents may also be used in this mixed liquid, as appropriate, depending on the purpose.

The dispersion medium is removed from this mixture to obtain a CNF-containing thermoplastic elastomer composition. The dispersion medium to be removed here includes the first organic solvent, the second organic solvent, the polyol compound, and the water contained in the CNF composition, as well as other polar solvents, if any.

A preferred procedure for obtaining a functional film from the CNF-containing thermoplastic elastomer composition thus obtained is, for example, a coating method. The coating method involves applying the above-mentioned mixed liquid to a uniform thickness (coating amount) and then removing the dispersion medium by evaporation, thereby obtaining a film consisting only of the solute. Compared to the extrusion method, the coating method is preferable because it is less likely to result in uneven thickness and makes it easier to obtain a film of uniform thickness. It also makes it easier to ensure the dispersion of CNF within the CNF-containing thermoplastic elastomer composition that constitutes the film.

When forming the above mixture into a film using the coating method, maintaining a constant temperature of 10 to 40°C and a viscosity of 100 to 50,000 mPa·s makes it easier to achieve a uniform thickness for the final functional film. If the temperature is too low or too high, the viscosity of the above mixture will change, increasing the risk that thickness variations will not be able to be controlled within the specified range.

When carrying out the coating method, the concentration of the thermoplastic elastomer composition in the mixed liquid is preferably 5% by mass or more, and more preferably 10% by mass or more. If it is less than 5% by mass, the viscosity will be too low and the film will be prone to uneven thickness. On the other hand, it is preferably 50% by mass or less, and more preferably 20% by mass or less. If it exceeds 50% by mass, the viscosity will be too high and the film will be prone to uneven thickness.

When carrying out the coating method, the viscosity of the mixed solution is preferably 100 mPa·s or more, and more preferably 500 mPa·s or more. If it is less than 100 mPa·s, there is a risk that the film will be prone to uneven thickness. On the other hand, it is preferably 50,000 mPa·s or less, and more preferably 3,000 mPa·s or less. If it exceeds 50,000 mPa·s, it will again be difficult to keep thickness unevenness within the desired range. Viscosity can be measured in accordance with JIS Z 7117-1.

The solid content and coating thickness of the above mixture will vary depending on the performance and scale of the manufacturing equipment used, and it is not possible to determine a specific range.

To ensure a uniform thickness for the functional film obtained when using the above coating method, experimentally, an applicator or doctor blade can be used to apply a constant amount of solution, but industrially, it is desirable to keep the liquid pressure of the above-mentioned mixed liquid as constant as possible. For example, this can be achieved by keeping the liquid level constant in a comma coater, or by keeping the liquid supply rate constant in a die coater.

When carrying out the above coating method, the coating amount (thickness) is also determined by the width of the gap, such as the gap between the backup roll and knife roll in a roll knife coater. Therefore, the thickness of the functional film formed using the above mixed solution is measured separately in advance to confirm that it is within the desired range of the present invention. After that, the coating thickness of the above mixed solution to be applied is measured and adjusted to the set constant coating thickness.

Examples of coaters used for the above coating include gravure coaters, reverse roll coaters, kiss coaters, roll knife coaters, and die coaters. Of these, roll knife coaters and die coaters are preferred because they allow for relatively easy control of the coating thickness. A uniform coating thickness can be achieved by keeping the gap between the backup roll and knife roll constant in the case of a roll knife coater, or by keeping the gap at the die opening and the internal die pressure constant in the case of a die coater.

After applying the mixed solution using the coating method, the heating temperature and time for removing the solvent are selected appropriately depending on the type and amount of the dispersant used, such as the first organic solvent, second organic solvent, and polyol compound. However, in many cases, a heating temperature of 50°C or higher is preferred, as this facilitates evaporation of the dispersant. On the other hand, temperatures that are too high can pose a risk of fire or can easily denature the resin, etc., that should remain after the dispersant has evaporated. For this reason, a temperature within a range that allows for acceptable changes in the resin's physical properties is preferred. Depending on the type of thermoplastic elastomer, a temperature of 200°C or lower is preferred, with 150°C or lower being more preferred. Furthermore, a temperature of 120°C or lower can be used with a wider range of resins. Furthermore, a long heating time is detrimental to work efficiency and can easily denature the resin, etc., so it is best to keep the heating time as short as possible while still allowing the dispersant to evaporate sufficiently, preferably within one hour.

An embodiment of the present invention will be described below.
First, we will explain the manufacturing procedure of xanthated CNF, which is chemically modified CNF obtained by defibrating chemically modified cellulose. The following materials were used.
Kraft pulp (manufactured by Nippon Paper Industries Co., Ltd.: NBKP, α-cellulose content: 90% by mass, average degree of polymerization of α-cellulose: 1000) hereinafter referred to as "NBKP".

<Alkali treatment>
NBKP was weighed so that the pulp solids (pulp solids excluding water in the pulp; the same applies hereinafter) was 100 g. This was placed in a 3 L beaker, and 2500 g of an 8.5 mass% aqueous sodium hydroxide solution was added and stirred at room temperature for 3 hours to perform an alkali treatment. The alkali-treated pulp was subjected to solid-liquid separation using a centrifugal dehydrator (manufactured by Kokusan Co., Ltd., H-110A, filter cloth 400 mesh) to obtain a dehydrated alkali cellulose. The sodium hydroxide content of this dehydrated alkali cellulose was 7.5 mass% and the pulp solids content was 27.4 mass%.

<Xanthate treatment>
The dehydrated alkali cellulose prepared above was weighed to a pulp solids content of 100 g and placed in an eggplant-shaped flask. 35 g of carbon disulfide (35% by mass relative to the pulp solids content) was added to the eggplant-shaped flask, and the sulfurization reaction was allowed to proceed at room temperature for 4.5 hours to perform a xanthation treatment, thereby obtaining xanthated cellulose.

<Xanthate substitution degree measurement>
The degree of xanthate substitution for the xanthated cellulose was measured by the Breedee method and found to be 0.312. The degree of xanthate substitution is the average number of hydroxyl groups substituted with xanthate groups per glucose unit of cellulose. The measurement of the degree of xanthate substitution by the Breedee method was carried out as follows. 1.5 g of xanthated cellulose was weighed as a solid content in a 100 mL beaker, and 40 mL of saturated ammonium chloride aqueous solution cooled to 5 ° C. was added. The xanthated cellulose sample was crushed with a glass rod and mixed well, left for 15 minutes, and then filtered with GFP filter paper (GS-25 manufactured by ADVANTEC Co., Ltd.) and thoroughly washed with saturated ammonium chloride aqueous solution. The sample was placed in a 500 mL tall beaker together with the GFP filter paper, and 50 mL of 0.5 mol / L aqueous sodium hydroxide solution cooled to 5 ° C. was added and stirred. The stirred solution was left for 15 minutes and then neutralized with a 1.5 mol/L aqueous acetic acid solution. Phenolphthalein indicator was used as the indicator. After neutralization, 250 mL of distilled water was added and stirred well, and 10 mL of a 1.5 mol/L aqueous acetic acid solution and 10 mL of a 0.05 mol/L aqueous iodine solution were added using a volumetric pipette. This solution was titrated with a 0.05 mol/L aqueous sodium thiosulfate solution. A 1% by mass aqueous starch solution was used as the indicator. The degree of xanthate substitution was calculated from the titration amount of the aqueous sodium thiosulfate solution and the cellulose content in the sample using the following formula (1). The cellulose content in the xanthated cellulose sample was determined by adding water to the xanthated cellulose to disperse it, adding hydrochloric acid to perform a regeneration treatment, filtering the cellulose after the regeneration treatment, thoroughly washing it, and then drying it to measure the mass of the cellulose alone.

Xanthate substitution degree = (0.05 x 10 x 2 - 0.05 x sodium thiosulfate titration (mL)) ÷ 1000 ÷ (cellulose content in sample (g) / 162.1) ... (1)

<Defibrillation processing>
The xanthated cellulose produced by the above xanthation treatment was weighed into a 5 L beaker with a handle so that the pulp solids content was 100 g, and distilled water was added and dispersed to a pulp solids concentration of 5% by mass. This dispersion was centrifuged using the centrifugal dehydrator, and distilled water was added and thoroughly washed to remove impurities, alkali, unreacted carbon disulfide, etc. All of the washed xanthated cellulose was recovered, and distilled water was added to obtain a 20 kg aqueous suspension with a cellulose concentration (hereinafter referred to as "cellulose concentration") of 0.5% by mass. This aqueous suspension was defibrated using a high-pressure homogenizer (manufactured by Sanwa Engineering Co., Ltd., H20 type) at a flow rate of 2.5 L / min and a pressure of 40 MPa for a total of 5 passes to obtain xanthated CNF.

<Degree of CNF defibration>
Distilled water was added to the aqueous suspension of xanthated CNF (cellulose concentration 0.5% by mass) to dilute the cellulose concentration to 0.1% by mass. This diluted aqueous suspension was centrifuged at 12,000 G for 10 minutes using a centrifuge (Avanti J-25I, manufactured by Beckman Coulter) to settle the undefibrated material. The supernatant was separated and transferred to an Erlenmeyer flask, and distilled water was added to the settled undefibrated material and centrifuged again to wash the undefibrated material. The undefibrated material was transferred to a crucible and dried, and the mass of the undefibrated material was measured. The production rate of nanofibers produced was calculated from the mass of the undefibrated material and the cellulose content in the xanthated cellulose using the following formula (2), which was 99.0% by mass.

Nanofiber production rate (mass%) = (cellulose content in xanthate cellulose - mass of undefibrated material) ÷ (cellulose content in xanthate cellulose) × 100... (2)

<Measurement of CNF fiber diameter>
An aqueous suspension of xanthated CNF diluted with water to a cellulose concentration of 0.1% by mass was placed in a centrifuge tube and centrifuged at 12,000 G for 10 minutes using the centrifuge. The supernatant was then collected. This supernatant was further diluted with distilled water, applied to a support membrane, stained with uranyl acetate, and dried on the support membrane to obtain a dried specimen. A transmission electron microscope (TEM: JEOL Ltd., JEM-1400) was used to observe this dried specimen at an accelerating voltage of 120 kV. 50 nanofibers were selected from the 50,000x image obtained in this way, and the fiber diameter was measured. The fiber diameter was 3.0 nm to 7.4 nm, and the number average fiber diameter, which is the average of these measurements, was 6.1 nm.

<Recycling and redispersion processing>
To 16.4 kg of the aqueous suspension of xanthated CNF obtained by the above procedure (cellulose concentration 0.5% by mass), 360 ml of 1 mol / L aqueous sulfuric acid solution (sulfuric acid amount 4.4 mmol / g - cellulose content) was added, and the mixture was stirred with an agitator for 1 hour to perform a regeneration treatment. After completion of the treatment, the mixture was neutralized to pH 7 with a 1 mol / L aqueous sodium hydroxide solution to obtain a regenerated CNF aqueous suspension. When the degree of xanthate substitution of this regenerated CNF was measured, it was found to be less than 0.001, which is the lower limit of measurement, and it was confirmed that the xanthate groups had almost completely been released by the acid treatment and had returned to hydroxyl groups.

The aqueous suspension of regenerated CNF obtained above was thoroughly washed by adding distilled water while being centrifuged using the centrifugal dehydrator. All of the washed regenerated CNF was collected, and distilled water was added to make 8 kg of an aqueous suspension with a CNF concentration of 1.0% by mass. This aqueous suspension was redispersed using the high-pressure homogenizer at a flow rate of 2.5 L/min and a pressure of 40 MPa, passing it three times in total. After processing, the fiber diameter of the redispersed regenerated CNF was measured, and the fiber diameter was found to be 3.0 nm to 7.4 nm, with a number-average fiber diameter of 6.0 nm.

<Procedure for producing CNF composition>
Next, the production of the CNF composition will be described.
The following polyol compounds were used:
Triethylene glycol (TEG: polyol: manufactured by Nacalai Tesque, Inc.: triethylene glycol)
1,3-butylene glycol (1,3-BG: polyol: manufactured by Kanto Chemical Co., Ltd.: 1,3-butanediol)
Glycerin (Gly: polyol: manufactured by Nacalai Tesque, Inc.: glycerin)
Diethylene glycol ethyl ether acetate (DGMEA: polyol derivative: manufactured by Tokyo Chemical Industry Co., Ltd.: diethylene glycol monoethyl ether acetate)

Further, the following was used as the thermoplastic elastomer (TPE) solution or dispersion (S3).
T-78F (a solution of adipate-based polyurethane TPE dissolved in an organic solvent such as DMF with a solid content of 20% by mass: manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.)
U-289HS (a solution of polycaprolactone-based polyurethane TPE dissolved in an organic solvent such as DMF with a solid content of 20% by mass: manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.)

Examples 1 to 6
To the aqueous suspension of regenerated CNF obtained in the above <Regeneration and re-dispersion treatment>, 1,3-butylene glycol, a polyol, was added in an amount 10 times the mass of the regenerated CNF. 30 g of a mixture with a CNF concentration of 0.7 mass% and a polyol concentration of 7.0 mass% was dried at 60°C for 15 hours using a hot air dryer to obtain a CNF composition (S1).
This CNF composition was mixed with N-dimethylformamide (DMF) (Kanto Chemical Co., Ltd.) and stirred for 10 minutes at 10,000 rpm using a rotary homogenizer (AM-7, manufactured by Nippon Seiki Seisakusho Co., Ltd.) to prepare a CNF dispersion in which the recycled CNF was dispersed in DMF (S2). For Example 1, the fiber diameter was measured from an image of the DMF dispersion of the recycled CNF (CNF dispersion) using a transmission electron microscope (TEM: JEM-1400, manufactured by JEOL Ltd.). The fiber diameter ranged from 3.2 nm to 7.4 nm, with an average fiber diameter of 6.1 nm, confirming that the recycled CNF was well dispersed in DMF.
The DMF dispersion of recycled CNF (CNF dispersion) was mixed with T-78F manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd. as a thermoplastic elastomer (TPE) solution or dispersion (S3) to obtain the recycled CNF content (mass %: indicated as "%" in the table) shown in Table 1 per 100 parts by mass of TPE, and the mixture was stirred at 8000 rpm for 15 minutes using a rotary homogenizer to obtain a mixture (S4). The mixture containing the recycled CNF and TPE was degassed for 3 minutes at 3000 rpm using a centrifuge (Avanti J-251 manufactured by Beckman Coulter, Inc.). The degassed recycled CNF-blended TPE solution was cast onto an OPP film (40 μm thick) using a Baker applicator (manufactured by Tester Sangyo Co., Ltd.) to a thickness of 380 μm, and then dried at 120°C for 5 minutes using a hot air dryer to produce a 250 mm x 200 mm TPE film containing recycled CNF (CNF-containing thermoplastic elastomer composition).

Table 1 shows the recycled CNF (referred to as "RCNF" in the table) content of each example and the results of each of the measurements below.

<Thickness measurement>
In accordance with JIS Z1702, the thickness of the obtained TPE film was measured at six random locations (120 locations per 1 m × 1 m) using a film thickness measuring device "Dial Gauge 0.001 mm" manufactured by Ozaki Manufacturing Co., Ltd., and the average of the measured values was taken as the thickness.

<CNF Dispersibility Evaluation>
The obtained TPE film was observed with a digital microscope through a polarizing filter, and the image was binarized to calculate the colored areas, which were considered to be CNF aggregation areas. The area ratio of the colored areas to the entire image was used as an index of CNF dispersibility. This is shown as a percentage in Table 1.

<Measurement of tensile strength>
In accordance with JIS K7127, rectangular test pieces measuring 20 mm wide x 100 mm long were punched out from the obtained TPE film, and a tensile test (n=3) was carried out using an Autograph AG-500NX manufactured by Shimadzu Corporation under conditions of a gripping width of 30 mm and a tensile speed of 300 mm/min, and the tensile modulus was calculated from the average of the measured values.

<Measurement of dynamic viscoelasticity>
In accordance with JIS K7244-4, rectangular test specimens measuring 5 mm wide x 10 mm long were punched out from the resulting TPE film, and the storage modulus was measured using a dynamic viscoelasticity measuring device Q850 manufactured by TA Instruments Japan Co., Ltd. under the following conditions: temperature range -20°C to 80°C, 3°C/min, span 10 mm, strain 2%, and frequency 10 Hz. From the results, the storage modulus values at -10°C and 60°C were designated as E1 and E2, respectively, and the storage modulus ratio (E1/E2) was calculated. In addition, the increase rate of the storage modulus measured at 30°C (F1) relative to that of a TPE film containing no CNF (F2) ((F1-F2)/F2 x 100) was calculated as the storage modulus increase rate.

<Measurement of thermal expansion coefficient>
A rectangular test piece measuring 5 mm wide x 8 mm long was punched out from the obtained TPE film, and the strain was measured using a thermomechanical analyzer Q400SR manufactured by TA Instruments Japan Co., Ltd. in a tensile mode (test piece width 5 mm, grip width 8 mm, load 0.01 N, temperature increase/decrease rate 3°C/min) while heating from room temperature to 80°C and while cooling from 80°C to room temperature, and the strain at 40°C while cooling was taken as the thermal expansion coefficient.

(Examples 7 and 8)
A TPE film containing recycled CNF was produced in the same manner as in Example 2 or 4, except that U-289HS manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd. was used as the TPE dispersion (S3). The measurement results of Examples 7 and 8 are shown in Table 2.

By incorporating CNF into U-289HS, which has a low storage modulus ratio and thermal expansion coefficient (Examples 7-8), the tensile modulus was increased while maintaining a low storage modulus ratio and thermal expansion coefficient, and the storage modulus increase ratio was also improved.

Examples 9 to 11
TPE films containing recycled CNF were produced in the same manner as in Example 3, except that triethylene glycol (TEG: Example 9), glycerin (Gly: Example 10), or diethylene glycol ethyl ether acetate (DGMEA: Example 11) was used instead of 1,3-butylene glycol (1,3-BG) as the polyol. The measurement results for Examples 9 to 11 are shown in Table 2.

Examples 12 to 14
CNF-containing TPE films were produced in the same manner as in Examples 2 to 4, except that CNF produced by mechanical defibration (BiNFi-S: product number WFo10005: manufactured by Sugino Machine Co., Ltd.: average fiber diameter 31 nm) was used instead of recycled CNF. The measurement results for Examples 12 to 14 are shown in Table 2.

(Comparative Examples 1 and 2)
A TPE film was produced in the same manner as in Examples 1 and 7, except that recycled CNF was not used. The measurement results of Comparative Example 1 are shown in Table 3.

(Comparative Examples 3 and 4)
TPE films were produced in the same manner as in Examples 2 and 4, except that TEMPO-oxidized CNF (prepared in accordance with the examples of Japanese Patent No. 6,668,558: average oxidation degree 2 mmol/g; average fiber diameter 6.3 nm) was used instead of recycled CNF. The measurement results for Comparative Examples 3 and 4 are shown in Table 3.

(Comparative Example 5)
A TPE film was produced in the same manner as in Example 1, except that the amount of recycled CNF added was 20 parts by mass per 100 parts by mass of TPE. The measurement results of Comparative Example 5 are shown in Table 3.

(Comparative Example 6)
A TPE film was produced in the same manner as in Example 3, except that microfibrous cellulose (Cerish: product number KY100S, manufactured by Daicel Miraize Co., Ltd.: average fiber diameter 198 nm) pulverized by physical treatment was used instead of the recycled CNF. The measurement results of Comparative Example 6 are shown in Table 3.

Even when microfibrous cellulose was added to a TPE film, the tensile modulus did not improve significantly compared to when the same amount of CNF was added, and the storage modulus ratio remained high, indicating that the effect of adding it was smaller than that of CNF.

<Verification of smoothness and transparency>
In the above-mentioned manufacturing procedure for recycled CNF, recycled CNFs were prepared by passing the material through a high-pressure homogenizer five times, three times, and two times in the above-mentioned "defibration treatment." These were designated RCNF (A), (B), and (C), respectively. The number-average fiber diameters of RCNF (A) were 6.1 nm, RCNF (B) was 19.1 nm, and RCNF (C) was 35.8 nm.

Example 15
A TPE film containing recycled CNF was produced in the same manner as in Example 1, except that RCNF (A) was used as the recycled CNF, TEG was used as the polyol, and U-289HS manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd. was used as the TPE dispersion (S3). The haze and friction coefficient of this film were measured as described below. The results are shown in Table 4.

<Haze measurement method>
Measurements were made using a haze meter HM-65N manufactured by Murakami Color Research Laboratory Co., Ltd., in accordance with JIS K 7136 "Method of determining haze for plastics - transparent materials." In each example, the film obtained by casting was cut into a 50 mm x 50 mm sample. The sample was set so that the upper surface of the film when cast faced the light source, and the haze was measured at any five points, and the average value was taken as the haze of the film.

<Method for measuring friction coefficient>
The static and dynamic coefficients of friction against a stainless steel plate were measured according to ASTM D1894. A test specimen was prepared by wrapping the film around a 200 g weight so that the upper surface of the film, when cast, was facing outward and in contact with the stainless steel plate. The test specimen was tied to a string attached to the upper chuck of an autograph, and the test specimen was placed on the stainless steel plate and held there for 30 seconds. The static and dynamic coefficients of friction were calculated from the load at the start of sliding when the test specimen was slid at a speed of 100 mm/min on the autograph, and the dynamic coefficient of friction was calculated from the load during sliding. The test was carried out at a temperature of 23°C and a humidity of 50% RH.

<Arithmetic mean roughness measurement method>
The measurement device used was a 3D measuring laser microscope LEXT OLS5000 manufactured by Olympus Corporation. A 50x objective lens, MPLAPON50xLEXT (numerical aperture 0.95, working distance 0.35 mm), was used to observe an area of 0.256 mm x 0.256 mm on the top surface of the cast film. A 3D image with an image size of 1024 x 1024 was obtained using a laser with a wavelength of 405 nm and a beam divergence angle of 0.15 to 1.25 rad. Six measurement lines were arbitrarily drawn on the obtained 3D image, and the arithmetic mean roughness was calculated from the cross-sectional profile on the lines in accordance with JIS B 0601:2013. In the calculation, a λc filter was set to 100 μm to distinguish between roughness and waviness components, and only the roughness component was extracted. The same procedure was carried out at five locations per sample, and measurements were taken at 6 lines x 5 locations = 30 locations, and the average value was taken as the arithmetic mean roughness of the sample.

(Examples 16 to 18)
TPE films containing recycled CNF were produced in the same manner as in Example 15, except that the recycled CNF content was doubled (Example 16), tripled (Example 17), and five times (Example 18). The results are shown in Table 4.

(Examples 19 and 20)
TPE films containing recycled CNF were produced in the same manner as in Example 17, except that the recycled CNF used was changed to RCNF (B) and RCNF (C), each having a different fiber diameter. The results are shown in Table 4.

(Example 21)
A TPE film containing recycled CNF was produced in the same manner as in Example 17, except that the TPE dispersion used was changed to T-78F. The results are shown in Table 4.

(Reference example 1)
A TPE film containing recycled CNF was produced in the same manner as in Example 15, except that the content of recycled CNF was increased by 10 times. The results are shown in Table 4.

(Comparative Example 7)
A TPE film was produced in the same manner as in Example 15, except that recycled CNF was not added. The results are shown in Table 4.

(Comparative Example 8)
In Example 15, a TPE film containing recycled CNF was produced in the same manner as in Comparative Example 6, except that the recycled CNF was replaced with microfibrous cellulose (Cerish: product number KY100S, manufactured by Daicel Miraize Co., Ltd.: average fiber diameter 198 nm) refined by physical treatment. The results are shown in Table 4.

(Comparative Example 9)
A TPE film containing recycled CNF was produced in the same manner as in Example 17, except that the recycled CNF was replaced with the same TEMPO-oxidized CNF as in Comparative Examples 3 and 4. The results are shown in Table 4.

(summary)
Compared to Comparative Example 7, which did not contain recycled CNF, as the CNF content increased (Examples 15 to 18, Reference Example 1), the haze increased gradually, while the static and dynamic friction coefficients gradually decreased. However, in Reference Example 1, where the CNF content was 10%, the values of the dynamic and static friction coefficients became sufficiently small, and the slipperiness was excellent, but the haze reached 25%, which was a problem in terms of transparency. When the CNF content was 5% or less, the film exhibited excellent slipperiness while suppressing the increase in haze.

On the other hand, when microfibrous cellulose other than CNF was used (Comparative Example 8), the haze was higher than in Example 17, which contained the same amount of recycled CNF, posing a problem in terms of transparency. Furthermore, in Comparative Example 9, which used TOCN instead of recycled CNF, the haze was significantly higher than in Example 17, which contained the same amount of recycled CNF, demonstrating that even in chemically modified cellulose nanofiber fibers, transparency is significantly reduced when the cellulose has a substituent.

In addition, in Examples 17, 19, and 20, which used different recycled CNF, haze increased slightly as the fiber diameter increased, but this was within an acceptable range and transparency was maintained.

Claims (5)

A thermoplastic elastomer composition containing cellulose nanofibers,
the cellulose nanofibers are nonionic and have a number average fiber diameter of 2 nm or more and 50 nm or less, the content of the cellulose nanofibers relative to the thermoplastic elastomer is 0.5 mass % or more and 15 mass % or less, and the cellulose nanofibers are uniformly dispersed in the composition,
A functional film having a thickness of 10 μm or more and 100 μm or less . The functional film according to claim 1, wherein the arithmetic mean roughness as defined in JIS B 6101 is 0.080 μm or more and 0.400 μm or less. A cellulose nanofiber composition containing a polyol, a polyol derivative, or a polyol compound consisting of both, cellulose nanofibers, and water is mixed with a first organic solvent to prepare a cellulose nanofiber dispersion in which the cellulose nanofibers are dispersed in the liquid;
A thermoplastic elastomer solution or dispersion in which a thermoplastic elastomer is dissolved or dispersed in a second organic solvent is mixed with the cellulose nanofiber dispersion,
This method for producing a thermoplastic elastomer composition containing cellulose nanofibers involves evaporating the dispersion medium from the mixed liquid and molding it. The method for producing a cellulose nanofiber-containing thermoplastic elastomer composition according to claim 3 , wherein the cellulose nanofiber composition has a water content of 1% by mass or more and 10% by mass or less, and the mass mixing ratio of the cellulose nanofiber to the polyol compound is 1:2 to 1:20. The method for producing a cellulose nanofiber-containing thermoplastic elastomer composition according to claim 3 or 4 ,
The shape to be molded is a film.
A method for manufacturing functional films.