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

Abstract

To provide a thermoplastic elastomer composition that has its properties not to change with temperature changes and also has excellent slipperiness and transparency.SOLUTION: A thermoplastic elastomer composition contains cellulose nanofiber. The cellulose nanofiber is nonionic one and has a number average fiber diameter of 2 nm or more and 50 nm or less, with its content in the composition being 0.5 mass% or more and 15 mass% or less. In the composition, the cellulose nanofiber is uniformly dispersed.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermoplastic elastomer composition having dispersed therein cellulose nanofibers and a method for producing the same. [Background technology]

[0002] Polyurethane resin compositions are a type of plastic that excels in elasticity, tensile strength, and abrasion resistance, and are used in a variety of applications. Their applications are diverse, including raw materials for adhesives and paints, highly elastic fibers for sports equipment, and polyurethane foams for cushions and sponges. While polyurethane is essentially made by polymerizing polyol and polyisocyanate, numerous attempts have been made to improve its physical properties by adding various additives.

[0003] Patent Document 1 proposes a urethane resin composition obtained by reacting cellulose nanofibers, which are made by defibrating cellulose in a polyol, with polyisocyanate. It is stated that the presence of cellulose nanofibers gives this composition excellent strength.

[0004] Patent Document 2 proposes a urethane elastomer molded article containing a urethane prepolymer, a curing agent containing a polyamine compound, and finely divided cellulose. It is shown that the addition of the polyamine compound and finely divided cellulose results in excellent storage modulus and creep properties.

[0005] Patent Document 3 proposes a polyurethane resin composition that improves the dispersibility of cellulose nanofibers in polyurethane to improve 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.

[0006] 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 binding strength with the urethane resin.

[0007] Patent Document 5 proposes a functional film in which a polyurethane elastomer is used as a thermoplastic elastomer, and the thickness is adjusted to 10 to 100 μm with thickness variations of 2 μm or less. It is disclosed that this functional film can be used for vibration damping materials such as support members for the vibration system of speakers, as well as acoustic applications such as acoustic vibration materials and sound absorption materials.

[0008] 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. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-194162 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-086308 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-128664 [Patent Document 4] Patent No. 6240893 [Patent Document 5] Patent No. 6692182 [Patent Document 6] Patent No. 6866134 Summary of the Invention [Problem to be solved by the invention]

[0010] In recent years, smartphone speakers have come to require high-precision sound quality. However, smartphone speakers are exposed to more drastic changes in temperature and humidity than stationary speakers, and their smaller diameters require greater precision and finer adjustments. For this reason, there is a demand for diaphragms made of a material that exhibits even less change in sound quality than the polyurethane elastomer described in Patent Document 5.

[0011] Furthermore, in applications other than acoustic diaphragms, there are also cases where materials with high stability of properties, that are less susceptible to changes in physical properties due to temperature and humidity changes, and materials with excellent slip properties and transparency are required.

[0012] Therefore, an object of the present invention is to realize a thermoplastic elastomer composition that exhibits minimal changes in properties with temperature changes, and a material that combines smoothness and transparency. [Means for solving the problem]

[0013] 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, has a number average fiber diameter of 2 nm or more and 50 nm or less, the content of the cellulose nanofiber relative to the thermoplastic elastomer is 0.5 mass % or more and 15 mass % or less, and the cellulose nanofiber is uniformly dispersed in the composition.

[0014] Thermoplastic elastomers containing polyurethane and cellulose nanofibers have been known for some time. However, simply adding cellulose nanofibers can result in uneven properties of the material as a whole due to aggregation and uneven distribution of the cellulose nanofibers. When processed into films, this uneven distribution 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 to 50 nm in a content of 0.5 to 15% by mass relative to the thermoplastic elastomer. This suppresses the uneven distribution of cellulose nanofibers that affects the physical properties of the thermoplastic elastomer, thereby achieving further improved stability of properties against temperature changes and achieving both slipperiness and transparency.

[0015] 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.

[0016] 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 as a diaphragm for a smartphone speaker, for example, the change in sound quality that occurs with temperature changes in the smartphone's operating temperature range is smaller than that of a conventional film made only of a thermoplastic elastomer that does not contain cellulose nanofiber. When used as a protective film for a smartphone LCD panel, the film has good slip properties without compromising transparency, resulting in excellent visibility and operability of the LCD panel display, and is also easy to apply.

[0017] Furthermore, in this manufacturing method, an embodiment can be adopted 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.

[0018] Furthermore, in this manufacturing method, an embodiment can be adopted in which the cellulose nanofiber composition is obtained by adding the polyol compound as a dispersant to a cellulose nanofiber aqueous suspension containing cellulose nanofibers, and then evaporating the water. [Effects of the Invention]

[0019] The cellulose nanofiber-containing thermoplastic elastomer composition of the present invention ensures high dispersibility, and the dispersed cellulose nanofibers combine to suppress changes in physical properties due to temperature changes, thereby providing stable properties to precision articles used in environments exposed to large temperature changes.

[0020] The cellulose nanofiber-containing thermoplastic elastomer composition of the present invention also has other excellent features in addition to the above properties. 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. Furthermore, this slipperiness can be achieved without impairing transparency. In an attempt to impart slipperiness to a typical thermoplastic elastomer film or sheet by performing surface treatments to create irregularities to reduce the contact area, transparency is often impaired, 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 of a film or sheet can be evaluated, for example, by surface roughness as specified in JIS B 6101.

[0021] However, it is desirable that the cellulose nanofibers used in this invention are not substituted with chemically modifying substituents, because 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 be able to achieve sufficient slip properties and transparency. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention is described in detail below. The present invention relates to a cellulose nanofiber-containing thermoplastic elastomer composition comprising a thermoplastic elastomer composition containing cellulose nanofibers, wherein the cellulose nanofibers are nonionic, have a number average fiber diameter of 2 nm to 50 nm, and contain 0.5% by mass to 15% by mass of the thermoplastic elastomer, and the cellulose nanofibers are uniformly dispersed in the composition.

[0023] 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, and cellulose that has been chemically modified and then regenerated into cellulose.

[0024] Examples of chemically modified cellulose include TEMPO-oxidized cellulose (oxidized with TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical), carboxymethyl cellulose, phosphoric acid esterified cellulose, and alkali-treated cellulose to which carbon disulfide has been added to form xanthate groups (-OCSS). - M + Examples include xanthate cellulose, which has been introduced with cellulose esters. Chemically modifying cellulose materials such as pulp makes it easier to create nanofibers than defibrating the cellulose material as is. CNF that has been chemically modified and defibrated is called "chemically modified CNF." Furthermore, among the chemically modified celluloses, phosphate ester cellulose and xanthate cellulose are preferred because they can be easily regenerated back into cellulose. CNF obtained by regenerating the molecular structure of chemically modified cellulose is called "regenerated CNF."

[0025] In the following description of this invention, the term "CNF" refers not only to CNFs obtained by simply defibrating cellulose materials, but also to the above-mentioned chemically modified CNFs and regenerated CNFs. Furthermore, regenerated CNFs may include not only those in which hydroxyl groups have been modified to other functional groups such as xanthate groups, but also those in which all of the original hydroxyl groups have been restored, but also those in which some of the functional groups remain. Furthermore, these CNFs may be purified before use if necessary.

[0026] CNF is preferably non-chemically unmodified cellulose or non-ionic CNF such as regenerated CNF. Ionic chemically modified cellulose such as xanthated cellulose or TEMPO-oxidized cellulose is not preferred, but even cellulose that has been once chemically modified with ionic cellulose such as xanthated cellulose can be suitably used as long as it has been sufficiently regenerated back into cellulose. Ionic nanofibers tend to aggregate in organic solvents (described below), making it difficult to ensure sufficient dispersibility, but non-ionic nanofibers are less likely to aggregate in organic solvents and therefore more easily dispersible.

[0027] Furthermore, the CNF preferably contains, as its main component, fine fibers with a fiber diameter of 2 nm to 50 nm. Here, "main 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 and use of the composition, fine fibers with a fiber diameter outside the above range may also be present. Furthermore, 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, resulting in insufficient dispersibility, and the resulting film or other physical properties may become significantly uneven.

[0028] In addition, the CNF-containing thermoplastic elastomer composition of the present invention hardly scatters visible light even when CNF is contained, because the fiber diameter of the CNF contained is within the above-mentioned range and is sufficiently smaller than the wavelength of visible light. As a result, transparency is not easily impaired even when CNF is contained within the content range described below, and the advantageous effects of containing CNF can be exerted while maintaining transparency.

[0029] The CNF-containing thermoplastic elastomer composition of the present invention is obtained by dispersing the above-mentioned CNF in a thermoplastic elastomer under predetermined conditions.

[0030] The thermoplastic elastomer used in this invention can be selected from common thermoplastic elastomers depending on the purpose. Examples include polyurethane elastomers, polyester elastomers, polyamide elastomers, olefin elastomers, and styrene elastomers. These elastomers may be used alone or in combination of two or more types.

[0031] Examples of the polyurethane elastomer include polyurethane elastomers obtained by polymerizing polyols and polyisocyanates. 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.

[0032] 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 obtained by reacting a polyol with an excess of polyisocyanate.

[0033] The polyurethane elastomers made of these polyols and polyisocyanates may be used alone or in combination of two or more.

[0034] Examples of the polyester elastomers 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.

[0035] Examples of the olefin-based elastomer include a mixture of an olefin resin such as polyethylene (PE) or polypropylene (PP) for the hard segment and a rubber such as ethylene propylene rubber (EPM) or ethylene propylene diene rubber (EPDM) for the soft segment. Any of these resins may be used alone or in combination of two or more.

[0036] Examples of the styrene elastomer include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-butadiene rubber (SBR), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-butadiene (SB), styrene block copolymer (SBC), etc. Any of these resins may be used alone or in combination of two or more.

[0037] Examples of the polyamide elastomer include polyether ester types using nylon 6, nylon 11, or nylon 12 for the hard segment and polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene ether glycol (PTMG), or the like for the soft segment, and polyether amide types using polypropylene diamine, polybutylene diamine, or the like for the soft segment. Any of these resins may be used alone or in combination of two or more.

[0038] Among these, polyurethane elastomers are particularly suitable when the CNF-containing thermoplastic elastomer composition of the present invention is used in a functional film for a speaker diaphragm, because when used in a speaker diaphragm, those with little change in storage modulus at -10 to 80°C are preferred.

[0039] The CNF content relative to the thermoplastic elastomer in the CNF-containing thermoplastic elastomer composition of the present invention is preferably 0.5% by mass or more, more preferably 1.0% by mass or more. If the CNF content is less than 0.5% by mass, the stabilization effect of the CNF on the physical properties of the CNF-containing thermoplastic elastomer composition against temperature changes may not be fully exhibited. On the other hand, the CNF content is preferably 15% by mass or less, more preferably 10% by mass or less. If the CNF content exceeds 15% by mass, the CNF tends to be 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.

[0040] 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. While transparency gradually decreases as the CNF content increases, there is almost no decrease in transparency when CNFs within the above-mentioned fiber diameter range are used and the content is 5% by mass or less. 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.

[0041] The CNF-containing thermoplastic elastomer composition of the present invention contains CNFs 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 those made from thermoplastic elastomer compositions that do not contain CNFs. 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 have problems such as the loss of the lubricant or the resulting large irregularities, which can reduce transparency. By molding the CNF-containing thermoplastic elastomer composition of the present invention, transparent films with improved slipperiness can be achieved, 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 impairing the visibility and operability of the LCD screen with fingers. 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.

[0042] In the CNF-containing thermoplastic elastomer composition of the present invention, it is desirable for the CNFs to be uniformly dispersed. Uneven distribution of CNFs in the film can lead to significant variations in temperature-dependent properties. Furthermore, some areas may exhibit reduced transparency. The dispersibility of the CNFs 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 the image using software, for example, the captured image can be binarized using a threshold value that distinguishes between CNF aggregates and non-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.

[0043] Even when the CNF-containing thermoplastic elastomer composition of the present 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, the interaction between the nanofibers can easily result in insufficient uniform dispersion in the resin, making it difficult to ensure sufficient slip properties and transparency.

[0044] When a functional film made of the CNF-containing thermoplastic elastomer composition of the present invention is used for the speaker diaphragm, the thickness is preferably 10 μm or more, and more 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 deviations in physical properties. On the other hand, the thickness is preferably 100 μm or less, and more preferably 40 μm or less. If the thickness exceeds 100 μm, it becomes difficult to suppress the thickness unevenness described below, making production difficult and expensive, so there is little benefit to increasing the thickness beyond 100 μm. When used as a film or sheet taking advantage of its transparency, the thickness is preferably 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 taking advantage of its transparency, a thickness of 10 μm or more is preferred from the standpoint of durability.

[0045] The functional film made of the CNF-containing thermoplastic elastomer composition of the present invention preferably has a thickness tolerance of 2 μm or less, more preferably 1 μm or less. 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 2 μm or less is preferred.

[0046] 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 calculated average value is used. It is not necessary to follow these conditions; for films of different sizes, multiple measurements are taken so that the number of measurement locations per 1m x 1m is 30 or more, and the average value is calculated, which will provide a sufficiently significant thickness value.

[0047] The fine irregularities on the surface of this functional film can be evaluated, for example, by the arithmetic mean roughness, a parameter in the height direction, among the surface roughness indexes 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 fine irregularities on the film surface are small, resulting in insufficient reduction in the coefficient of friction. On the other hand, if it exceeds 0.400 μm, the decrease in transparency becomes significant.

[0048] The stress variation of this functional film can be measured according to JIS K 7127. The film used for the thickness measurement above is measured at five random locations, and the difference between these measurements is taken as the variation value. Stable film rigidity is essential to consistently provide good sound quality. This is generally expressed as elastic modulus, but since stiffness changes as the film becomes thicker, the film must exhibit a stable elongation stress (stress at extension) when stretched. If this stress at extension is stable, the storage modulus will also be stable at temperatures expected in the living environment encountered when the film is installed in a smartphone speaker, enabling the film to exhibit excellent acoustic properties.

[0049] The tensile modulus of the functional film made of the CNF-containing thermoplastic elastomer composition of the present invention is adjusted depending on the application. For example, in the case of a film used for the speaker diaphragm, the tensile modulus is preferably 10 MPa or more, and more preferably 35 MPa or more. In practical use, the tensile modulus is preferably 100 MPa or less.

[0050] The thermal expansion coefficient of the functional film made of the CNF-containing thermoplastic elastomer composition of the present 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 become too large, making the film unsuitable for applications requiring stable acoustic properties.

[0051] 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 the present 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 increases, it is not realistic to make the ratio less than 1 even when CNF is added. On the other hand, if the ratio exceeds 15, the change in physical properties becomes too great, making it unsuitable, especially when stable acoustic properties are required.

[0052] The haze, which is an index of transparency of the functional film made of the CNF-containing thermoplastic elastomer composition of this invention, is preferably 20% or less, 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 becomes difficult to see the content displayed below the applied area, and visibility cannot be ensured.

[0053] Furthermore, when the functional film made of the CNF-containing thermoplastic elastomer composition of the present invention is used in an application that makes use of the smoothness, the coefficient of friction, which is an index of the smoothness, is preferably 5 or less, and more preferably 3 or less, as a dynamic friction coefficient. If the dynamic friction coefficient exceeds 5, when the film is used as a protective film for a liquid crystal panel of a smartphone or the like, it becomes difficult to perform sliding operations on the surface.

[0054] When producing the CNF-containing thermoplastic elastomer composition of the present invention, it is necessary to properly disperse the CNF so that the above-mentioned dispersibility is achieved. An example of a procedure for achieving this will be described below.

[0055] 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.

[0056] 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, if remaining in the functional film causes problems, diol compounds are particularly preferred from the viewpoint of ease of removal. It should be noted that a CNF composition can be obtained even if other polar solvents are mixed with this polyol compound. However, since other polar solvents may evaporate at unintended times or require a separate step for removal, it is preferable to use as few polar solvents as possible other than the polyol compound.

[0057] Here, a polyol is a compound having multiple hydroxyl groups in the molecule. A polyol derivative is a compound in which one or more of the hydroxyl groups are modified to provide a functional group. Examples of the modification method include etherification and esterification. Specific examples include alkyl ethers of polyols and alkyl esters of polyols.

[0058] 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.

[0059] Among 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 are particularly preferred because they can 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 easily removed when the necessary heating is performed.

[0060] The mass mixture 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 be insufficient polyol compound to maintain dispersibility, potentially resulting 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 itself is sufficient, but further increases in the polyol compound content do little to improve redispersibility, and the polyol compound may take a long time to evaporate as part of the dispersion medium when preparing a CNF-containing thermoplastic elastomer composition. Furthermore, even after removing water, the mass of the CNF composition remains large due to the mass of the polyol compound, reducing the benefits of using the CNF composition.

[0061] The water content of the CNF composition is preferably 10% by mass or less, and more preferably 7% by mass or less. Because water increases the mass and volume of the CNF composition during storage and transportation, it is desirable to keep the water content as low as possible. However, it is difficult to dry the CNF composition to less than 1% by mass, and a water content of 1% by mass or more is more realistic.

[0062] The CNF composition is produced by first adding the polyol compound as a dispersant to an aqueous suspension of CNF and mixing the mixture. The mixture is then dried to evaporate the water content and reduce the water content, yielding the CNF composition. While drying can be achieved by leaving the mixture at room temperature, heating is preferred 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 methods such as hot air drying, spray drying, or vacuum drying, or a combination of two or more of these. Specific examples of drying equipment include drum dryers, disk dryers, vacuum dryers of these, conical dryers, and spray dryers.

[0063] The water content of the CNF composition is significantly reduced compared to the state of the aqueous suspension after defibration of the CNF, making it easy to store, transport, etc. On the other hand, the CNF composition has the property of easily ensuring dispersibility, and high dispersibility of the CNF can be achieved by using this CNF composition to redisperse it in water, an organic solvent, etc.

[0064] Next, this CNF composition is mixed with a first organic solvent to prepare a CNF dispersion in which the CNFs are suitably dispersed in the organic solvent (S2). Examples of suitable organic solvents for this purpose include dimethylformamide, dimethyl sulfoxide, and dimethylacetamide. Among these, dimethylformamide is the most preferred because its solubility and solution viscosity for thermoplastic elastomers (TPEs) are suitable for film formation.

[0065] 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 finally 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 content exceeds 2.0% by mass, it may be difficult to adequately disperse the CNF in the next step S4.

[0066] 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 elastomer may react with water, which may affect the physical properties. Therefore, it is desirable to have as low a water content as possible.

[0067] Furthermore, it is preferable that the CNFs in this CNF dispersion do not undergo sedimentation even when centrifuged. The sedimentation properties of CNFs can be evaluated, for example, by centrifuging this CNF dispersion using a centrifuge (Avanti J-251, manufactured by Beckman Coulter) at 1400 G for 3 minutes. However, a dispersion containing 0.3 mass% CNF is prepared in advance, and the light transmittance at a wavelength of 660 nm with a path length of 10 mm is measured using an ultraviolet-visible spectrophotometer (V-730, manufactured by JASCO Corporation). If the light transmittance is 7.0% or higher, no sedimentation of CNFs is observed, and this value can be used as a useful guide for preliminary evaluation.

[0068] Meanwhile, the thermoplastic elastomer is dissolved or dispersed in a second organic solvent to prepare a thermoplastic elastomer solution or dispersion (S3). Similar to the first organic solvent, the second organic solvent can be dimethylformamide, dimethyl sulfoxide, dimethylacetamide, or the like. Among these, dimethylformamide is the most preferred because its solubility and solution viscosity for the thermoplastic elastomer (TPE) are suitable for film formation.

[0069] 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 the film thickness prone to unevenness. 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 be difficult to quickly disperse the CNF in the next step S4.

[0070] Next, the CNF dispersion and the thermoplastic elastomer solution or dispersion are mixed to obtain a mixed solution (S4). At this time, since the CNFs are sufficiently dispersed in the CNF dispersion, a mixed solution in which the CNFs are suitably dispersed in the thermoplastic elastomer composition contained in the thermoplastic elastomer solution or dispersion is obtained.

[0071] The mixing ratio of the CNF dispersion to the thermoplastic elastomer solution or dispersion is preferably 1:2 to 5:1, more preferably 1:1 to 3:1, by mass. If the amount of CNF is too small, the effect of stabilizing the physical properties of the CNF-containing thermoplastic elastomer composition against temperature changes is reduced, resulting in a poor effect of adding the CNF. On the other hand, if the amount of CNF is too large, stirring the mixture becomes difficult and the distribution tends to become uneven, making it difficult to ensure the dispersibility of the CNF in the film.

[0072] In addition to the above-mentioned CNF dispersion and the above-mentioned thermoplastic elastomer solution or dispersion, additives such as colorants, antioxidants, and antistatic agents may be used in this mixed liquid as appropriate depending on the purpose.

[0073] 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.

[0074] 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 solution to a specific thickness (coating amount) and then removing the dispersion medium by evaporation to obtain a film containing only the solute. The coating method is preferable compared to the extrusion method because it is less likely to result in uneven thickness and makes it easier to obtain a film of uniform thickness. Furthermore, it is easier to ensure the dispersion of CNF within the CNF-containing thermoplastic elastomer composition that constitutes the film.

[0075] When forming the above-mentioned mixed solution into a film using the coating method, maintaining the temperature at 10 to 40°C and the viscosity at 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 mixed solution will change, increasing the risk that thickness variations will not be able to be controlled within the specified range.

[0076] The concentration of the thermoplastic elastomer composition in the mixed solution when carrying out the coating method is preferably 5% by mass or more, 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, 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.

[0077] The viscosity of the mixed solution used in the coating method is preferably 100 mPa·s or more, more preferably 500 mPa·s or more. If it is less than 100 mPa·s, the film thickness may become uneven. On the other hand, it is preferably 50,000 mPa·s or less, more preferably 3,000 mPa·s or less. If it exceeds 50,000 mPa·s, it becomes difficult to keep the thickness unevenness within the desired range. Viscosity can be measured in accordance with JIS Z 7117-1.

[0078] The solid content and coating thickness of the above-mentioned mixed solution vary depending on the performance and scale of the manufacturing equipment used, and it is not possible to determine a specific range.

[0079] To achieve a uniform thickness for the functional film obtained when carrying out 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 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.

[0080] The coating amount (thickness) when carrying out the above coating method is also determined by the width of the gap, such as the gap between the backup roll and the knife roll in a roll knife coater. Therefore, the thickness of the functional film formed with the above mixed solution is measured separately in advance to confirm that it is within the desired range of the present invention, and then the coating thickness of the above mixed solution to be applied is measured and adjusted to a set constant coating thickness.

[0081] Examples of coaters used for the above coating include gravure coaters, reverse roll coaters, kiss coaters, roll knife coaters, and die coaters. Among these, roll knife coaters and die coaters are preferred because they allow relatively easy control of the coating thickness. A uniform coating thickness can be achieved by keeping the gap between the backup roll and the knife roll constant in the case of a roll knife coater, or by keeping the gap at the die opening and the die internal pressure constant in the case of a die coater.

[0082] After applying the mixed solution by the coating method, the heating temperature and time for removing the solvent are appropriately selected depending on the type and amount of the dispersion medium, such as the first organic solvent, the second organic solvent, and the polyol compound. However, in many cases, a heating temperature of 50°C or higher is preferred, as this facilitates evaporation of the dispersion medium. On the other hand, if the temperature is too high, there is a risk of fire or the resin, etc. that should remain after the dispersion medium has evaporated, may be easily denatured. Therefore, 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 allows use with a wider range of resins. Furthermore, a long heating time is disadvantageous in terms of work efficiency and may easily denature the resin, etc. Therefore, it is best to keep the heating time as short as possible within the range that allows sufficient evaporation of the dispersion medium, preferably within one hour. [Example]

[0083] An embodiment of the present invention will be described below. First, we will explain the manufacturing procedure for 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".

[0084] <Alkali treatment> NBKP was weighed out so that the pulp solids (pulp solids are the amount excluding water in the pulp; the same applies below) 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. The mixture was 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 (Kokusan Co., Ltd., H-110A, 400 mesh filter cloth) 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 %.

[0085] <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 carried out at room temperature for 4.5 hours to perform a xanthation treatment, thereby obtaining xanthated cellulose.

[0086] <Xanthate substitution degree measurement> The degree of xanthate substitution for the xanthated cellulose was measured by the Bredee 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 degree of xanthate substitution by the Bredee method was measured as follows: 1.5 g of xanthated cellulose (solid content) was weighed into 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 thoroughly. After leaving it for 15 minutes, it was filtered through GFP filter paper (GS-25, manufactured by ADVANTEC) and thoroughly washed with saturated ammonium chloride aqueous solution. The sample, along with the GFP filter paper, was placed in a 500 mL tall beaker, and 50 mL of 0.5 mol / L sodium hydroxide aqueous solution cooled to 5°C was added and stirred. The stirred solution was left for 15 minutes and then neutralized with 1.5 mol / L acetic acid aqueous solution. Phenolphthalein indicator was used as the indicator. After neutralization, 250 mL of distilled water was added and stirred thoroughly. 10 mL of 1.5 mol / L acetic acid solution and 10 mL of 0.05 mol / L iodine solution were added using a volumetric pipette. This solution was titrated with 0.05 mol / L sodium thiosulfate solution. A 1% by mass starch solution was used as the indicator. The degree of xanthate substitution was calculated using the following formula (1) based on the titration amount of the sodium thiosulfate solution and the cellulose content in the sample. The cellulose content in the xanthated cellulose sample was determined by dispersing the xanthated cellulose in water, adding hydrochloric acid to regenerate the cellulose, filtering the regenerated cellulose, thoroughly washing it, and then drying it to measure the mass of the cellulose alone.

[0087] Degree of xanthate substitution = (0.05 × 10 × 2 - 0.05 × sodium thiosulfate titration volume (mL)) ÷ 1000 ÷ (cellulose content (g) in sample / 162.1)......(1)

[0088] <Defibration treatment> Weighed the xanthated cellulose produced by the above xanthation treatment into a 5 L beaker with a pulp solid content of 100 g, added distilled water to make the pulp solid content concentration 5% by mass, and dispersed it. While centrifuging this dispersion using the above centrifuge, distilled water was added and thoroughly washed to remove impurities, alkali, unreacted carbon disulfide, etc. All the washed xanthated cellulose was recovered, distilled water was added, and a 20 kg aqueous suspension with a cellulose concentration (hereinafter referred to as "cellulose concentration") of 0.5% by mass contained in the xanthated cellulose was prepared. This aqueous suspension was passed through a high-pressure homogenizer (model H20, manufactured by Sanwa Engineering Co., Ltd.) 5 times at a flow rate of 2.5 L / min and a pressure of 40 MPa for defibration treatment to obtain xanthated CNF.

[0089] <Degree of defibration of CNF> Distilled water was added to the aqueous suspension (cellulose concentration 0.5% by mass) of the above xanthated CNF 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 (manufactured by Beckman Coulter, Avanti J-25I) to precipitate the undefibrated matter. The supernatant was separated and transferred to an Erlenmeyer flask, distilled water was added to the precipitated undefibrated matter, and centrifugation was performed again to wash the undefibrated matter. The undefibrated matter was transferred to a crucible and dried to constant weight, and the mass of the undefibrated matter was measured. From the mass of the undefibrated matter and the cellulose content in the xanthated cellulose, the production rate of nanofibers generated from the following formula (2) was determined to be 99.0% by mass.

[0090] Production rate of nanofibers (% by mass) = (cellulose content in xanthated cellulose - mass of undefibrated matter) ÷ (cellulose content in xanthated cellulose) × 100......(2)

[0091] <Measurement of the Fiber Diameter of CNF> A water suspension of zanthated CNF diluted with water to a cellulose concentration of 0.1 mass% was placed in a centrifuge tube, centrifuged at 12,000 G for 10 minutes using the above centrifuge, and the centrifugal supernatant was collected. This centrifugal supernatant was further diluted with distilled water, applied onto a support membrane, stained with uranyl acetate, and dried on the support membrane to obtain a dried specimen. Observation of this dried specimen was performed at an acceleration voltage of 120 kV using a transmission electron microscope (TEM: manufactured by JEOL Ltd., JEM-1400). Fifty nanofibers were selected from the thus obtained image at 50,000 times magnification, and the fiber diameter was measured. As a result, the fiber diameter was from 3.0 nm to 7.4 nm, and the number-average fiber diameter, which is the average of these measured values, was 6.1 nm.

[0092] <Regeneration Treatment and Redispersion Treatment> To 16.4 kg of the water suspension of zanthated CNF (cellulose concentration: 0.5 mass%) obtained by the above procedure, 360 ml of 1 mol / L sulfuric acid aqueous solution (amount of sulfuric acid: 4.4 mmol / g-cellulose content) was added, and stirring was performed for 1 hour with an agitator to conduct a regeneration treatment. After the treatment was completed, it was neutralized to pH 7 with 1 mol / L sodium hydroxide aqueous solution to obtain a regenerated CNF water suspension. When the degree of zanthate substitution of this regenerated CNF was measured, it was less than 0.001, which is the lower limit of measurement. Thus, it was confirmed that the zanthate groups were almost completely eliminated by the acid treatment and returned to hydroxyl groups.

[0093] While centrifugally dehydrating the water suspension of the regenerated CNF obtained above using the above centrifugal dehydrator, distilled water was added and thoroughly washed. All of the washed regenerated CNF was collected, and distilled water was added to obtain 8 kg of a water suspension with a CNF concentration of 1.0 mass%. This water suspension was redispersed by passing it through a high-pressure homogenizer three times at a flow rate of 2.5 L / min and a pressure of 40 MPa. After the treatment, when the fiber diameter of the redispersion of the regenerated CNF was measured, the fiber diameter was from 3.0 nm to 7.4 nm, and the number-average fiber diameter was 6.0 nm.

[0094] <Manufacturing Procedure of CNF Composition> Next, the manufacturing of the CNF composition will be described. The following polyol compounds were used: Triethylene glycol (TEG: Polyol: Nacalai Tesque, Inc.: Triethylene glycol) 1,3-Butylene glycol (1,3-BG: Polyol: Kanto Chemical Co., Ltd.: 1,3-butanediol) Glycerin (Gly: Polyol: Nacalai Tesque, Inc.: Glycerin) Diethylene glycol ethyl ether acetate (DGMEA: polyol derivative: manufactured by Tokyo Chemical Industry Co., Ltd.: diethylene glycol monoethyl ether acetate)

[0095] 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.)

[0096] Examples 1 to 6 To the aqueous suspension of regenerated CNF obtained in the above <Regeneration and redispersion treatment>, the polyol 1,3-butylene glycol 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 in a hot air dryer at 60°C for 15 hours to obtain a CNF composition (S1). This CNF composition was mixed with N-dimethylformamide (DMF) (Kanto Chemical Co., Ltd.) and stirred at 10,000 rpm for 10 minutes using a rotary homogenizer (AM-7, Nippon Seiki Seisakusho Co., Ltd.) to prepare a CNF dispersion in which the regenerated CNF was dispersed in DMF (S2). For Example 1, the fiber diameter was measured from an image of the DMF dispersion of this regenerated CNF (CNF dispersion) using a transmission electron microscope (TEM: JEOL Ltd., JEM-1400). The fiber diameter ranged from 3.2 nm to 7.4 nm, with an average fiber diameter of 6.1 nm, confirming that the regenerated CNF was well dispersed in DMF. The DMF dispersion of the recycled CNF (CNF dispersion) was mixed with a thermoplastic elastomer (TPE) solution or dispersion (S3) made by Dainichiseika Color & Chemicals Mfg. Co., Ltd. (T-78F) 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 resulting mixture containing recycled CNF and TPE was degassed for 3 minutes using a centrifuge (Avanti J-251 made by Beckman Coulter, Inc.) at 3000 rpm. The degassed recycled CNF mixed TPE solution was cast onto an OPP film (40 μm thick) using a Baker applicator (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).

[0097] Table 1 shows the content of recycled CNF (referred to as "RCNF" in the table) in each of the examples and the results of the following measurements.

[0098] [Table 1]

[0099] <Thickness measurement> In accordance with JIS Z1702, in the obtained TPE film, six random locations (converted to 120 locations per 1 m × 1 m) were measured using a film thickness measuring machine "Dial Gauge 0.001 mm" manufactured by Ozaki Seisakusho Co., Ltd., and the average of the measured values was taken as the thickness.

[0100] <CNF Dispersibility Evaluation> The obtained TPE film was observed with a digital microscope through a polarizing filter, and the image was binarized. The colored part calculated was taken as the agglomerated part of CNF, and the area ratio of the colored part occupying the entire image was used as an index of CNF dispersibility. It is shown as a percentage in Table 1.

[0101] <Measurement of Tensile Strength> In accordance with JIS K7127, a strip-shaped test piece with a width of 20 mm × a length of 100 mm was punched out from the obtained TPE film, and a tensile test (n = 3) was conducted using an autograph AG-500NX manufactured by Shimadzu Corporation under the conditions of a grip width of 30 mm and a tensile speed of 300 mm / min. The tensile elastic modulus was obtained from the average of the measured values.

[0102] <Measurement of Dynamic Viscoelasticity> In accordance with JIS K7244-4, a strip-shaped test piece with a width of 5 mm × a length of 10 mm was punched out from the obtained TPE film, and the storage elastic modulus was measured using a dynamic viscoelasticity measuring device Q850 manufactured by TA Instruments Japan Co., Ltd. under the conditions of a temperature range of -20°C → 80°C, 3°C / min, a span of 10 mm, a strain of 2%, and a frequency of 10 Hz. From the results, the values of the storage elastic modulus at -10°C and 60°C were taken as E1 and E2 respectively, and the storage elastic modulus ratio (E1 / E2) was calculated. Also, in the measured value (F1) of the storage elastic modulus at 30°C, the increase rate ((F1 - F2) / F2 × 100) with respect to that (F2) of the TPE film not containing CNF was calculated as the storage elastic modulus increase rate.

[0103] <Measurement of Thermal Expansion Rate> Strip-shaped test pieces measuring 5 mm wide x 8 mm long were 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 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. The strain at 40°C while cooling was taken as the thermal expansion coefficient.

[0104] (Examples 7 and 8) A TPE film containing recycled CNF was produced in the same manner as in Examples 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 for Examples 7 and 8 are shown in Table 2.

[0105] [Table 2]

[0106] By incorporating CNF into U-289HS, which has a low storage modulus ratio and thermal expansion coefficient (Examples 7 to 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.

[0107] Examples 9 to 11 TPE films containing recycled CNF were produced using the same procedure as in Example 3, except that triethylene glycol (TEG: Example 9), glycerin (Gly: Example 10), and diethylene glycol ethyl ether acetate (DGMEA: Example 11) were 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.

[0108] 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.

[0109] (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.

[0110] [Table 3]

[0111] (Comparative Examples 3 and 4) TPE films were produced using the same procedures as in Examples 2 and 4, except that TEMPO-oxidized CNF (prepared according to the examples in Japanese Patent No. 6668558: 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.

[0112] (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.

[0113] (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 Miraizu Co., Ltd.: average fiber diameter 198 nm) refined by physical treatment was used instead of the regenerated CNF. The measurement results of Comparative Example 6 are shown in Table 3.

[0114] 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 cellulose was smaller than that of CNF.

[0115] <Verification of smoothness and transparency> Using the above-mentioned manufacturing procedure for regenerated CNF, regenerated CNF was prepared by passing the 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 each were 6.1 nm for RCNF(A), 19.1 nm for RCNF(B), and 35.8 nm for RCNF(C).

[0116] Example 15 A TPE film containing recycled CNF was produced using the same procedure 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.

[0117] <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 for determining haze of 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.

[0118] <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 200g weight so that the top surface of the film, when cast, was facing outward and in contact with the stainless steel plate. The test specimen was attached to a string attached to the upper chuck of an autograph and placed on the stainless steel plate for 30 seconds. The test specimen was then slid on the autograph at a speed of 100mm / min. The static coefficient of friction was calculated from the load at the start of sliding, and the dynamic coefficient of friction was calculated from the load during sliding. The test was conducted at a temperature of 23°C and a humidity of 50%RH.

[0119] <Arithmetic mean roughness measurement method> The measurement device used was an Olympus Corporation LEXT OLS5000 3D measuring laser microscope. 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 1024 x 1024 3D image 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 resulting 3D image, and the arithmetic mean roughness was calculated from the cross-sectional profiles along the lines in accordance with JIS B 0601:2013. To distinguish between the roughness and waviness components, a λc filter was set to 100 μm, 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.

[0120] [Table 4]

[0121] (Examples 16 to 18) TPE films containing recycled CNF were produced using the same procedure 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.

[0122] (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 with a different fiber diameter. The results are shown in Table 4.

[0123] 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.

[0124] (Reference example 1) A TPE film containing recycled CNF was produced using the same procedure as in Example 15, except that the recycled CNF content was increased by 10 times. The results are shown in Table 4.

[0125] (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.

[0126] (Comparative Example 8) A TPE film containing recycled CNF was produced in the same manner as in Example 15, except that the recycled CNF was replaced with the microfibrous cellulose (Cerish: product number KY100S: manufactured by Daicel Miraize Co., Ltd.: average fiber diameter 198 nm) refined by physical treatment used in Comparative Example 6. The results are shown in Table 4.

[0127] (Comparative Example 9) A TPE film containing recycled CNF was produced in the same manner as in Example 17, except that the same TEMPO-oxidized CNF as in Comparative Examples 3 and 4 was used instead of the recycled CNF. The results are shown in Table 4.

[0128] (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 content was 5% or less, the film exhibited excellent slipperiness while suppressing the increase in haze.

[0129] On the other hand, when microfibrous cellulose other than CNF was used (Comparative Example 8), the haze was higher than that of Example 17, which contained the same amount of regenerated CNF, posing a problem in terms of transparency. Also, in Comparative Example 9, which used TOCN instead of regenerated CNF, the haze increased significantly compared to Example 17, which contained the same amount of regenerated CNF, demonstrating that even in chemically modified cellulose nanofibers, transparency is significantly reduced when the cellulose has a substituent.

[0130] In addition, in Examples 17, 19, and 20, which used different regenerated CNF, the haze increased slightly as the fiber diameter increased, but this was within an acceptable range and transparency could be maintained.

Claims

1. 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.

2. A functional film as described in claim 1, having an arithmetic mean roughness as specified in JIS B 6101 of 0.080 μm or more and 0.400 μm or less.

3. 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 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.

4. 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.

5. 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.

Images