Material for thermoforming and molded product thereof

Abstract

Provided is a material for thermoforming that contains microfibrous cellulose exhibiting thermoformability. A material for thermoforming according to an embodiment of the present invention contains 50 mass % or more of an onium salt-type anion-modified microfibrous cellulose having a number average fiber width of 2-1000 nm.

Description

Thermoforming material and molded body thereof

[0001] The present invention relates to a thermoforming material and a molded article obtained by thermoforming the same.

[0002] In recent years, from the perspective of sustainability, cellulose fibers, which are naturally occurring biomass in large quantities, and in particular fine fibrous cellulose (also called cellulose nanofibers) as a new form of utilization of cellulose fibers, have been attracting attention.

[0003] For example, Patent Document 1 discloses a fine cellulose fiber composite in which a cationic surfactant is adsorbed onto fine cellulose fibers having carboxy groups, and a quaternary ammonium compound as the cationic surfactant is chemically adsorbed to the carboxy group at the C6 position of the cellulose structural unit. Patent Document 1 also discloses a composite material in which the fine cellulose fiber composite is used as a reinforcing material and mixed with a moldable resin, and the resin content in the composite material is 40 to 99.99 mass% based on the total mass of the composite material.

[0004] JP 2011-140738 A

[0005] Cellulose fibers are inherently not thermoformable. Therefore, they cannot be thermoformed unless they are added to resins such as thermoplastic resins. As mentioned above, it has been known to add carboxyl-containing microfibrous cellulose to resins as a reinforcing material, but it has not been known that specific anion-modified microfibrous cellulose has thermoformability.

[0006] An object of an embodiment of the present invention is to provide a novel thermoforming material containing fine fibrous cellulose having thermoformability, and a molded article thereof.

[0007] The present invention includes the following embodiments. [1] A thermoforming material comprising 50% by mass or more of onium salt-type anion-modified fine fibrous cellulose having a number-average fiber width of 2 to 1,000 nm. [2] The thermoforming material according to [1], wherein the melting point of a modifier for converting anionic groups of the anion-modified fine fibrous cellulose into onium salts is 150°C or lower. [3] The thermoforming material according to [1] or [2], wherein the onium salt of the anion-modified fine fibrous cellulose is a quaternary onium salt. [4] The thermoforming material according to any one of [1] to [3], wherein the anion-modified fine fibrous cellulose has an amount of anionic groups of 0.5 to 3.0 mmol / g, measured after all the anionic groups are in the acid form. [5] A molded product obtained by thermoforming the thermoforming material according to any one of [1] to [4].

[0008] According to an embodiment of the present invention, it is possible to provide a novel thermoforming material containing fine fibrous cellulose having thermoformability, and a molded article thereof.

[0009] The thermoforming material according to this embodiment contains an onium salt-type anion-modified fine fibrous cellulose having a number-average fiber width of 2 to 1,000 nm. The anion-modified fine fibrous cellulose is fine fibrous cellulose into which an anionic group has been introduced.

[0010] Fine fibrous cellulose is cellulose fiber refined to the nano level and is also called cellulose nanofiber. The number average fiber width of fine fibrous cellulose is 2 to 1000 nm, preferably 2 to 500 nm, more preferably 2 to 300 nm, more preferably 2 to 100 nm, more preferably 3 to 50 nm, and more preferably 3 to 20 nm.

[0011] The number average fiber length of the fine fibrous cellulose is not particularly limited and may be, for example, 500 nm to 10 μm, 700 to 5000 nm, 800 to 3000 nm, or 1000 to 2000 nm. The average aspect ratio of the fine fibrous cellulose is not particularly limited and may be, for example, 10 to 1000 or 50 to 700.

[0012] The number-average fiber width of fine fibrous cellulose can be determined by observation using an atomic force microscope (AFM). The number-average fiber width is obtained by selecting at least 120 fine fibrous cellulose fibers from an AFM image, measuring their fiber widths, and calculating the arithmetic mean. The number-average fiber length is also determined by similarly selecting at least 120 fine fibrous cellulose fibers, measuring their fiber lengths, and calculating the arithmetic mean. The average aspect ratio is determined by the ratio of the number-average fiber length to the number-average fiber width calculated in this manner.

[0013] Examples of the anionic group of the anion-modified fine fibrous cellulose include at least one selected from the group consisting of a carboxyl group, a phosphate group, a sulfate group, a sulfonate group, a nitrate group, and a borate group. Among these, at least one selected from the group consisting of a carboxyl group, a phosphate group, and a sulfate group is preferred. These anionic groups may be directly or indirectly bonded to glucose units, which are structural units of the cellulose molecule. When indirectly bonded, for example, an alkylene group having 1 to 4 carbon atoms may be present between the glucose unit and the anionic group. One or more anionic groups may be bonded to all glucose units constituting the cellulose molecule, or one or more anionic groups may be bonded to a portion of the glucose units constituting the cellulose molecule.

[0014] In one embodiment, examples of anion-modified fine fibrous cellulose include oxidized cellulose nanofibers obtained by oxidizing the hydroxyl groups of glucose units in cellulose molecules, and carboxymethylated cellulose nanofibers obtained by carboxymethylating the hydroxyl groups of glucose units in cellulose molecules. Examples of oxidized cellulose nanofibers include those in which the hydroxyl group at the C6 position of the glucose unit in the cellulose molecule is selectively oxidized to a carboxyl group. Oxidized cellulose nanofibers are obtained by oxidizing natural cellulose such as wood pulp using a co-oxidant in the presence of an N-oxyl compound and subjecting the cellulose to a defibration (fine fiber) treatment. As the N-oxyl compound, a compound having a nitroxy radical, which is commonly used as an oxidation catalyst, is used, such as a piperidine nitroxyoxy radical. 2,2,6,6-tetramethylpiperidinoxy radical (TEMPO) or 4-acetamido-TEMPO is particularly preferred. In a preferred embodiment, the anion-modified fine fibrous cellulose is a TEMPO-oxidized cellulose nanofiber obtained by oxidizing using TEMPO.

[0015] In this embodiment, an onium salt-type anion-modified fine fibrous cellulose is used. The onium salt-type anion-modified fine fibrous cellulose is anion-modified fine fibrous cellulose in which an onium salt is introduced into the anionic group of the anion-modified fine fibrous cellulose, that is, the anionic group has an onium ion as a counter ion. By introducing an onium salt in this manner, thermoformability (also referred to as heat softening property) can be imparted to the anion-modified fine fibrous cellulose, making it possible to thermoform it even without containing a resin such as a thermoplastic resin.

[0016] The term "onium salt" as used herein refers to a broad onium salt that encompasses not only salts containing onium ions generated by protonation of hydrides, but also salts containing cations in which some or all of the protons of the onium ion have been replaced with alkyl groups, arene groups, or the like. Examples of onium salts include ammonium salts, phosphonium salts, sulfonium salts, and oxonium salts. Among these, ammonium salts and phosphonium salts are preferred. Any one of these may be used alone, or two or more may be used in combination. Here, the arene group refers to a monovalent hydrocarbon group having an aromatic ring, and examples thereof include an aryl group and an aralkyl group.

[0017] Examples of ammonium salts include quaternary ammonium salts (e.g., tetraalkylammonium salts such as tetramethylammonium salt, tetrabutylammonium salt, tetraoctylammonium salt, hexadecyltrimethylammonium salt, methyltrioctylammonium salt, tetradecylammonium salt, trimethyldodecylammonium salt, trimethyltetradecylammonium salt, trimethyloctadecylammonium salt, tributyldodecylammonium salt, trioctylmethylammonium salt, tetradodecylammonium salt, octyldimethylethylammonium salt, dodecyldimethylethylammonium salt, and didecyldimethylammonium salt), benzyltributylammonium salt, benzyltripropylammonium salt, benzyltriethylammonium salt, benzyltrimethylammonium salt, benzyldimethyldodecylammonium salt, and benzyldimethyltetradecylammonium salt). ammonium salts containing an arene group such as benzyldimethyloctadecylammonium salt; heterocyclic quaternary ammonium salts such as 1-ethyl-3-methylimidazolium salt, dodecylpyridinium salt, 1-allyl-3-methylimidazolium salt, 1-butylpyridinium salt, and 1-butyl-4-methylpyridinium salt); tertiary ammonium salts (for example, trialkylammonium salts such as trioctylammonium salt and trihexylammonium salt); secondary ammonium salts (for example, dialkylammonium salts such as dioctylammonium salt, dibutylammonium salt, dihexylammonium salt, didodecylammonium salt, and distearylammonium salt); primary ammonium salts (for example, alkylammonium salts such as dodecylammonium salt, oleylammonium salt, and stearylammonium salt; and alkanolammonium salts such as diethylene glycolammonium salt).

[0018] Examples of the phosphonium salt include quaternary phosphonium salts (for example, tetraalkylphosphonium salts such as tributylmethylphosphonium salt, tributyldodecylphosphonium salt, tributyltetradecylphosphonium salt, tributylhexadecylphosphonium salt, trihexyl(tetradecyl)phosphonium salt, tetraethylphosphonium salt, tetrabutylphosphonium salt, and tetraoctylphosphonium salt; and phosphonium salts containing an arene group such as tetraphenylphosphonium salt, benzyltriphenylphosphonium salt, methyltriphenylphosphonium salt, ethyltriphenylphosphonium salt, butyltriphenylphosphonium salt, and tetradecyltriphenylphosphonium salt).

[0019] The onium salts listed above may be used alone or in combination of two or more.

[0020] As the onium salt, a modifying agent for converting an anionic group into an onium salt preferably has a melting point of 150°C or less. A modifying agent having a melting point of 150°C or less can further improve thermoformability. The modifying agent more preferably has a melting point of 100°C or less, more preferably 50°C or less, and even more preferably is liquid at room temperature (25°C). The lower limit of the melting point is not particularly limited, and may be, for example, -50°C.

[0021] Here, the modifying agent refers to a compound that forms an onium salt together with an acid-type anionic group. However, when the modifying agent is a quaternary onium salt, the "melting point" refers to the melting point measured for an acetate salt in which the anion that forms a salt with the onium ion is replaced with an acetate ion. The melting point is determined as the temperature at which the modifying agent melts when the temperature of the modifying agent is gradually increased using a melting point measuring device, as described in detail in the Examples section.

[0022] The onium salt is preferably a quaternary onium salt in order to further improve thermoformability. As the quaternary onium salt, for example, the above-mentioned quaternary ammonium salts and / or quaternary phosphonium salts are preferably used, and more preferably at least one selected from the group consisting of tetraalkylammonium salts, aralkyltrialkylammonium salts, and tetraalkylphosphonium salts is used.

[0023] The anion-modified fine fibrous cellulose preferably has an anionic group amount of 0.5 to 3.0 mmol / g, more preferably 1.0 to 2.8 mmol / g, and even more preferably 1.5 to 2.5 mmol / g, measured after converting all anionic groups to the acid form. Because the anion-modified fine fibrous cellulose according to the embodiment is an onium salt type as described above, all anionic groups are converted to the acid form before measurement of the amount of anionic groups. The amount of anionic groups is the amount of anionic groups (mmol) per dry mass of the acid-form anion-modified fine fibrous cellulose, and can be measured by known methods, specifically, by the method described in the Examples section. In this specification, the term "dry mass" refers to the mass after drying at 140°C until the mass change rate per minute is 0.05% or less.

[0024] In the onium salt-type anion-modified fine fibrous cellulose according to this embodiment, the anionic group may be only an onium salt, or may contain other salts together with the onium salt. The other salts are not particularly limited, and examples thereof include alkali metal salts such as sodium salts and potassium salts, and alkaline earth metal salts such as magnesium salts and calcium salts. In addition, the anionic groups do not all have to be salt-type (for example, in the case of a carboxyl group, -COOX (where X is a cation that forms a salt with a carboxylic acid)), and may be acid-type (where the counter ion is H ＋ and is also called H-type. For example, in the case of a carboxy group, it may contain —COOH.

[0025] In one embodiment, in the onium salt-type anion-modified fine fibrous cellulose, it is preferred that 45 mol % or more of the anionic groups are onium salts. That is, it is preferred that 45 mol % or more of the anionic groups have onium ions as counterions. The onium salt introduction rate is preferably 50 mol % or more of the anionic groups, more preferably 70 mol % or more, more preferably 80 mol % or more, more preferably 90 mol % or more, and even more preferably 100 mol %. For example, when the anionic group is a carboxy group, the onium salt introduction rate is calculated using FT-IR from the absorption peak area derived from the onium salt and the absorption peak area derived from the acid-type anionic group. In this case, when a metal salt is contained as another salt, the metal content is also measured using an ICP atomic emission spectrometer to calculate the onium salt introduction rate. When the anionic group is a phosphate group or a sulfate group, the onium salt introduction rate is calculated by measuring the nitrogen content using a total nitrogen analyzer.

[0026] Anion-modified fine fibrous cellulose is obtained by the process of chemically modifying unmodified cellulose fibers and the process of defibrating the cellulose fibers, as described above. Defibration of the cellulose fibers may be carried out after or before the introduction of anionic groups (and further onium salts). Defibration treatment can be carried out by treating a dispersion of cellulose fibers using, for example, a homomixer, a high-pressure homogenizer, an ultrasonic dispersion processor, a beater, a disk refiner, a conical refiner, a double-disc refiner, a grinder, or the like under high-speed rotation.

[0027] The anion-modified fine fibrous cellulose preferably has a cellulose type I crystal structure. The cellulose type I crystal structure is the crystalline form of natural cellulose, and the anion-modified fine fibrous cellulose is water-insoluble due to the cellulose type I crystal structure. The presence of a cellulose type I crystal structure can be identified by the presence of typical peaks at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, in a diffraction profile obtained by wide-angle X-ray diffraction image measurement.

[0028] The thermoforming material according to this embodiment contains 50% by mass or more of the above-mentioned onium salt-type anion-modified fine fibrous cellulose, preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. It may also contain 100% by mass, i.e., consist solely of onium salt-type anion-modified fine fibrous cellulose.

[0029] The thermoforming material is a material used in thermoforming. "Thermoforming" refers to a molding method in which a material is softened by heating, molded into a predetermined shape, and then hardened by cooling. Examples include heat press molding, vacuum molding, and pressure molding. Note that "softening" here does not necessarily mean that the anion-modified microfibrous cellulose melts, but rather refers to the fibers becoming more fluid upon heating. It is believed that the fibers adhere to each other upon thermoforming, solidify in that state upon cooling, and maintain a certain shape. Because the thermoforming material is primarily composed of anion-modified microfibrous cellulose, it may be fibrous (i.e., a thermoforming fibrous material). "Fibrous" refers to a material having a fibrous form, and may be a collection of fibers, such as a fiber sheet like paper or nonwoven fabric, a cotton-like material, or a powder formed by agglomeration of microfibrous cellulose. The thickness of the fiber sheet is not particularly limited and may be, for example, 0.1 to 1000 μm or 1 to 100 μm. In this specification, the terms "sheet" and "sheet-like" are concepts that encompass "film" and "film-like", respectively.

[0030] The thermoforming material may contain additives as optional components in addition to the anion-modified fine fibrous cellulose. Examples of additives include colorants such as pigments and dyes, water-resistant agents, flame retardants, plasticizers, antioxidants, light stabilizers, fillers, and antistatic agents. As described above, the anion-modified fine fibrous cellulose according to this embodiment has thermoformability, and therefore can be thermoformed using the anion-modified fine fibrous cellulose alone. Therefore, although thermoforming materials containing resins such as thermoplastic resins are not excluded, in one embodiment, the thermoforming material preferably does not contain resin, and can be subjected to thermoforming directly without the addition of resin.

[0031] A molded article can be obtained by thermoforming the thermoforming material. As described above, thermoforming refers to softening the thermoforming material by heating, molding it into a predetermined shape, and then hardening it by cooling. Examples of such methods include heat press molding, vacuum molding, and pressure molding. The shape of the molded article is not particularly limited, and various shapes such as sheet-like, plate-like, and three-dimensional structures can be mentioned. Specific examples of molded articles include sheets, packaging materials, tableware (cups, plates, etc.), and containers (bottles, trays, etc.).

[0032] When a fiber sheet made of the thermoforming material is stacked on top of another and at least a portion of the stack is heat-press molded, the fiber sheets can be bonded together at the thermoformed portions, making heat sealing possible. Therefore, a heat-sealable fiber sheet can be provided, and a heat-sealed molded product can be obtained.

[0033] Examples will be described in detail below along with comparative examples, but the present invention is not limited to these examples.

[0034] The methods for measuring the various physical properties in the examples and comparative examples are as follows.

[0035] [Amount of Anionic Groups (Amount of Carboxy Groups)] A 50 mL aqueous suspension of acid-type anion-modified fine fibrous cellulose with a cellulose fiber concentration of 0.1% by mass was prepared, and the pH was adjusted to approximately 2.5 with a 0.1 mol / L aqueous hydrochloric acid solution. Next, a 0.05 mol / L aqueous sodium hydroxide solution was added dropwise to the aqueous suspension, and electrical conductivity measurements were performed until the pH reached approximately 11. The amount of carboxy groups was calculated from the amount of sodium hydroxide (V) consumed in the neutralization stage of the weak acid, where the change in electrical conductivity was gradual, according to the following formula: Amount of Carboxy Groups (mmol / g) = V (mL) × [0.05 / Mass of Acid-Type Anion-Modified Fine Fibrous Cellulose (g)]

[0036] [Amount of Anionic Groups (Amount of Phosphate Groups)] Anion-modified fine fibrous cellulose was diluted with ion-exchange water to a content of 0.2% by mass to prepare an aqueous suspension. The anion-modified fine fibrous cellulose was treated with an ion exchange resin to obtain acidic anion-modified fine fibrous cellulose, and then titrated with alkali to measure the amount. The ion-exchange resin treatment was carried out by adding 1 / 10 by volume of a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the aqueous suspension, shaking for 1 hour, and then pouring the suspension onto a 90 μm mesh to separate the ion-exchange resin from the aqueous suspension. The alkali titration was carried out by adding 50 μL of 0.1 mol / L aqueous sodium hydroxide solution to the aqueous suspension after the ion-exchange resin treatment every 30 seconds, and measuring the change in the electrical conductivity of the aqueous suspension. The amount of phosphate groups (mmol / g) was calculated by dividing the amount of alkali (mmol) required in the region corresponding to the first region in the measurement results by the solid content (g) in the aqueous suspension to be titrated.

[0037] [Amount of Anionic Groups (Amount of Sulfate Groups)] A predetermined amount of acid-type anion-modified fine fibrous cellulose was combusted, and the sulfur content in the combustion product was measured using a combustion ion chromatograph according to a method in accordance with IEC 62321, and the amount was converted into the amount of sulfate groups.

[0038] [Measurement of Number Average Fiber Width] The number average fiber width of anion-modified fine fibrous cellulose was measured as follows. Specifically, an aqueous dispersion of anion-modified fine fibrous cellulose was prepared by high-pressure dispersion treatment to a solids content of 0.005 to 0.0001 wt %. The dispersion was cast on a mica substrate and dried to prepare a sample for observation with an atomic force microscope (AFM). Then, atomic force microscope images were observed at a magnification of 5,000x, 10,000x, or 50,000x depending on the size of the constituent fibers. In this case, an arbitrary axis of image width, either vertical or horizontal, was assumed within the obtained image, and the sample and observation conditions (magnification, etc.) were adjusted so that 20 or more fibers intersected with the axis. After obtaining an observation image satisfying these conditions, two random axes were drawn vertically and horizontally on the image, and the fiber widths of the fibers intersecting the axes were visually read. In this way, at least three non-overlapping images of the surface portion were taken with an atomic force microscope, and the fiber width values ​​of the fibers intersecting on each of the two axes were read (thus, information on the widths of at least 20 fibers x 2 x 3 = 120 fibers was obtained).The number-average fiber width was calculated from the fiber width data obtained in this way.

[0039] [Melting Point of Modifier] A modifier that is not liquid at room temperature (such as an amine, phosphine, ammonium salt, or phosphonium salt) was finely ground in a mortar and packed into a melting point tube. The melting point tube was set in a depression on the aluminum plate of a melting point measurement device, and a glass cover was placed on top of it. The temperature of the melting point measurement device was raised from 25°C at a rate of 5°C / min, and the temperature at which the modifier melted was taken as the melting point. For quaternary onium salt modifiers, measurements were taken of acetate salts in which the anion that forms a salt with the onium ion was replaced with acetate ion.

[0040] [Moldability] Test pieces were prepared by cutting the sheets of thermoforming materials obtained in Examples 1 to 15 and Comparative Examples 1 and 2 into pieces measuring 3 cm length x 3 cm width. The test pieces were sandwiched between a drawing die and pressed at 100°C and 0.4 MPa using a hot press. The obtained molded bodies were observed and evaluated according to the following criteria. A: A molded body without wrinkles or cracks was obtained when the pressing time was 10 seconds or less. B: A molded body without wrinkles or cracks was obtained when the pressing time was 11 to 60 seconds. C: A molded body without wrinkles or cracks was obtained when the pressing time was 61 to 180 seconds. D: The sheet cracked during pressing, and no molded body was obtained.

[0041] [Heat sealability] The sheets of thermoforming materials obtained in Examples 1 to 15 and Comparative Examples 1 and 2 were cut into 100 mm length x 15 mm width to prepare test pieces. Two test pieces were stacked on top of each other, and an area of ​​10 mm length x 15 mm width was pressed at 150°C and 0.1 MPa using a heat press. Using a tensile tester, both unpressed ends were gripped and T-peel was performed at a tensile speed of 300 mm / min, and the maximum value was recorded as the heat seal strength. The evaluation criteria for heat sealability are as follows: A: Pressing time 10 seconds or less, heat seal strength 0.1 N / 15 mm or more B: Pressing time 11 to 60 seconds, heat seal strength 0.1 N / 15 mm or more C: Pressing time 61 to 180 seconds, heat seal strength 0.1 N / 15 mm or more D: Pressing time 180 seconds, heat seal strength less than 0.1 N / 15 mm, or no adhesion

[0042] [Preparation of Anion-Modified Cellulose Fibers A1 to A5] Prior to the preparation of the thermoforming materials of the Examples and Comparative Examples, the acid-type anion-modified cellulose fibers A1 to A5 used therein were prepared according to the following Preparation Examples 1 to 5. [Preparation Example 1: Preparation of Anion-Modified Cellulose Fiber A1 (TEMPO-Oxidized Cellulose Fiber)] 150 mL of water, 0.25 g of sodium bromide, and 0.025 g of TEMPO were added to 2 g of softwood pulp and thoroughly stirred to disperse the mixture. A 13% by mass aqueous solution of sodium hypochlorite (co-oxidant) was then added so that the sodium hypochlorite content per 1.0 g of pulp was 10.0 mmol / g, and the reaction was initiated. As the reaction progressed, the pH decreased, and 0.5 mol / L aqueous sodium hydroxide solution was added dropwise to maintain the pH at 10-11, and the reaction was continued until no further change in pH was observed (reaction time: 120 minutes). After the reaction was completed, 0.1 mol / L hydrochloric acid was added to adjust the pH to 2.0, followed by repeated filtration and washing with water for purification, yielding cellulose fibers with oxidized fiber surfaces. This was diluted with pure water to a cellulose fiber concentration of 4% by mass to prepare a TEMPO-oxidized cellulose fiber suspension. The pH of the slurry was then adjusted to 10 with a 24% by mass aqueous solution of sodium hydroxide, and sodium borohydride was added at 0.2 mmol / g relative to the cellulose fibers to initiate the reaction. The reaction was allowed to proceed for 2 hours for reduction treatment. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 2.0, followed by repeated filtration and washing with water for purification, yielding anion-modified cellulose fibers A1 in which the carboxy groups were in the acid form.

[0043] [Manufacturing Example 2: Preparation of anion-modified cellulose fiber A2 (TEMPO-oxidized cellulose fiber)] Anion-modified cellulose fiber A2 in which the carboxyl groups are in the acid form was obtained in the same manner as the preparation method for anion-modified cellulose fiber A1, except that the amount of sodium hypochlorite aqueous solution added was 6.0 mmol / g per 1.0 g of softwood pulp.

[0044] [Manufacturing Example 3: Preparation of anion-modified cellulose fiber A3 (TEMPO-oxidized cellulose fiber)] Anion-modified cellulose fiber A3 in which the carboxyl groups are in the acid form was obtained in the same manner as the preparation method for anion-modified cellulose fiber A1, except that the amount of sodium hypochlorite aqueous solution added was 4.0 mmol / g per 1.0 g of softwood pulp.

[0045] [Production Example 4: Preparation of Anion-Modified Cellulose Fiber A4 (Phosphate-Esterified Cellulose Fiber)] A mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of softwood kraft pulp to adjust the total weight to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, to obtain a chemical-impregnated pulp. The obtained chemical-impregnated pulp was then heated in a hot air dryer at 165°C for 200 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphate-esterified cellulose fiber. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 1.0, and the fiber was purified by repeated filtration and washing with water, resulting in anion-modified cellulose fiber A4 in which the fiber surface was phosphated and the phosphate groups were in the acid form.

[0046] [Production Example 5: Preparation of Anion-Modified Cellulose Fiber A5 (Sulfate-Esterified Cellulose Fiber)] 2 g of softwood kraft pulp, 20 g of sulfamic acid, 50 g of urea, and 100 g of ion-exchanged water were mixed and stirred for 10 minutes using a stirrer. After stirring, the slurry was suction filtered using filter paper (No. 2). Suction filtration was continued until the solution stopped dripping. After suction filtration, the pulp was peeled from the filter paper and placed in a dryer with a thermostatic chamber set to 50°C for 6 hours to react. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 1.0, and the fiber was purified by repeated filtration and washing with water to obtain anion-modified cellulose fiber A5 in which the fiber surface was sulfated and the sulfate groups were in the acid form.

[0047] [Example 1] (Preparation of modifying agent) Tetrabutylammonium bromide (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in ethanol to a concentration of 0.1 N, and then an ion exchange resin (manufactured by Tokyo Chemical Industry Co., Ltd., Amberlite IRN78) in an amount five times the amount of tetrabutylammonium bromide was added, followed by stirring overnight in a shaker. The ion exchange resin was then removed by filtration, yielding a 0.1 N tetrabutylammonium hydroxide ethanol solution.

[0048] (Preparation of anion-modified fine fibrous cellulose) Anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ion-exchanged water, and then a 0.1N tetrabutylammonium hydroxide ethanol solution in an amount equimolar to the amount of carboxy groups in the anion-modified cellulose fiber A1 was added and stirred. Further, by treating three times at a pressure of 150 MPa using a high-pressure homogenizer, anion-modified fine fibrous cellulose B1 with an onium salt introduction rate of 100 mol% was obtained. (Preparation of sheet) The obtained anion-modified fine fibrous cellulose B1 was placed in a Teflon (registered trademark) Petri dish and dried at 40°C for 24 hours to obtain a 30 μm-thick sheet (thermoforming material) of Example 1.

[0049] [Example 2] The modifying agent, anion-modified fine fibrous cellulose, and sheet were prepared in the same manner as in Example 1, except that tetraoctylammonium bromide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of tetrabutylammonium bromide, and the anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ethanol, thereby obtaining the sheet of Example 2.

[0050] [Example 3] A modifying agent, anion-modified fine fibrous cellulose, and a sheet were prepared in the same manner as in Example 1, except that benzyltributylammonium bromide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of tetrabutylammonium bromide, to obtain the sheet of Example 3.

[0051] [Example 4] The modifying agent, anion-modified fine fibrous cellulose, and sheet were prepared in the same manner as in Example 1, except that hexadecyltrimethylammonium bromide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of tetrabutylammonium bromide, and the anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ethanol, thereby obtaining the sheet of Example 4.

[0052] [Example 5] The modifying agent, anion-modified fine fibrous cellulose, and sheet were prepared in the same manner as in Example 1, except that trihexyl(tetradecyl)phosphonium chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of tetrabutylammonium bromide, and the anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ethanol, thereby obtaining the sheet of Example 5.

[0053] [Example 6] The modifying agent, anion-modified fine fibrous cellulose, and sheet were prepared in the same manner as in Example 1, except that tetraoctylphosphonium bromide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of tetrabutylammonium bromide, and the anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ethanol, thereby obtaining the sheet of Example 6.

[0054] [Example 7] (Preparation of anion-modified fine fibrous cellulose) Anion-modified cellulose fiber A1 was diluted with ethanol to 0.5% by mass, and then trioctylamine was added in an amount equimolar to the amount of carboxyl groups in anion-modified cellulose fiber A1, followed by stirring. The mixture was further treated 10 times at a pressure of 150 MPa using a high-pressure homogenizer to obtain anion-modified fine fibrous cellulose B7 having an onium salt introduction rate of 100 mol%.

[0055] (Preparation of Sheet) The obtained anion-modified fine fibrous cellulose B7 was placed in a Teflon (registered trademark) petri dish and dried at 40° C. for 24 hours to obtain a sheet of Example 7 having a thickness of 30 μm.

[0056] Example 8 An anion-modified fine fibrous cellulose and a sheet were prepared in the same manner as in Example 7, except that dioctylamine was used instead of trioctylamine, to obtain the sheet of Example 8.

[0057] Example 9 Preparation of Anion-Modified Fine Fibrous Cellulose Anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ion-exchanged water, and then diethylene glycol amine (i.e., 2-(2-aminoethoxy)ethanol) was added in an amount equimolar to the amount of carboxy groups in the anion-modified cellulose fiber A1 and stirred. Further, the mixture was treated once at a pressure of 150 MPa using a high-pressure homogenizer to obtain anion-modified fine fibrous cellulose B9 having an onium salt introduction rate of 100 mol%.

[0058] (Preparation of Sheet) The obtained anion-modified fine fibrous cellulose B9 was placed in a Teflon (registered trademark) petri dish and dried at 40° C. for 24 hours to obtain a sheet of Example 9 having a thickness of 30 μm.

[0059] Example 10 A sheet of Example 10 was obtained by preparing a modifying agent, anion-modified fine fibrous cellulose, and a sheet in the same manner as in Example 2, except that anion-modified cellulose fiber A2 was used.

[0060] Example 11 A sheet of Example 11 was obtained by preparing a modifying agent, an anion-modified fine fibrous cellulose, and a sheet in the same manner as in Example 2, except that anion-modified cellulose fiber A3 was used.

[0061] [Example 12] The modifier, anion-modified fine fibrous cellulose, and sheet were prepared in the same manner as in Example 2, except that the conditions for the high-pressure homogenizer treatment were changed to a pressure of 150 MPa and the number of treatments was changed to two, thereby obtaining the sheet of Example 12.

[0062] [Example 13] A modifier, anion-modified fine fibrous cellulose, and a sheet were prepared in the same manner as in Example 2, except that the conditions for the high-pressure homogenizer treatment were changed to a pressure of 150 MPa and the number of treatments was one, thereby obtaining the sheet of Example 13.

[0063] Example 14 A sheet of Example 14 was obtained by preparing a modifying agent, an anion-modified fine fibrous cellulose, and a sheet in the same manner as in Example 2, except that anion-modified cellulose fiber A4 was used.

[0064] Example 15 A sheet of Example 15 was obtained by preparing a modifying agent, an anion-modified fine fibrous cellulose, and a sheet in the same manner as in Example 2, except that anion-modified cellulose fiber A5 was used.

[0065] Comparative Example 1 Preparation of Anion-Modified Fine Fibrous Cellulose Anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ion-exchanged water and then neutralized with 0.5 N aqueous sodium hydroxide solution to a pH (25° C.) of 7.0. The mixture was further treated three times using a high-pressure homogenizer at a pressure of 100 MPa to obtain anion-modified fine fibrous cellulose C1.

[0066] (Preparation of Sheet) The obtained anion-modified fine fibrous cellulose C1 was placed in a Teflon (registered trademark) dish and dried at 40° C. for 24 hours to obtain a sheet of Comparative Example 1 having a thickness of 30 μm.

[0067] [Comparative Example 2] (Preparation of Sheet) The anion-modified fine fibrous cellulose C1 obtained in Comparative Example 1 was placed in a Teflon (registered trademark) Petri dish and dried for 24 hours at 40° C. 0.1 M hydrochloric acid was added to the dried product, and the product was immersed for 24 hours. After that, the product was washed five times with purified water and air-dried to obtain a sheet of Comparative Example 2 having a thickness of 30 μm.

[0068] The moldability and heat sealability of the sheets prepared above in Examples 1 to 15 and Comparative Examples 1 and 2 were evaluated. The results are shown in Table 1.

[0069]

[0070] As shown in Table 1, in Comparative Examples 1 and 2, in which no onium salt was introduced, the anion-modified fine fibrous cellulose did not have thermoformability, and therefore was poor in moldability and heat-sealability. In contrast, in Examples 1 to 15, in which an onium salt was introduced, the anion-modified fine fibrous cellulose had thermoformability as well as heat-sealability. The lower the melting point of the modifying agent, the better the moldability and heat-sealability. Furthermore, quaternary onium salts were superior to primary to tertiary onium salts in these performances.

[0071] The various numerical ranges described in this specification can be arbitrarily combined with their respective upper and lower limit values, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0072] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. A thermoforming material containing 50% by mass or more of onium salt-type anion-modified fine fibrous cellulose having a number average fiber width of 2 to 1,000 nm.

2. The thermoforming material according to claim 1, wherein the melting point of the modifying agent for converting the anionic groups of the anion-modified fine fibrous cellulose into onium salts is 150°C or lower.

3. The thermoforming material according to claim 1, wherein the onium salt of the anionically modified fine fibrous cellulose is a quaternary onium salt.

4. The thermoforming material according to claim 1, wherein the anion-modified fine fibrous cellulose has an anionic group content of 0.5 to 3.0 mmol / g, as measured after all anionic groups are in the acid form.

5. A molded article obtained by thermoforming the thermoforming material according to any one of claims 1 to 4.

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