Material for thermoforming and molded product thereof

Abstract

To provide a material for thermoforming that contains microfibrous cellulose exhibiting thermoformability.SOLUTION: A material for thermoforming according to an embodiment contains 50 mass% or more of an onium salt-type anion-modified microfibrous cellulose having a number average fiber width of 2-1000 nm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a material for thermoforming and a formed body obtained by thermoforming the same.

Background Art

[0002] In recent years, from the perspective of sustainability, cellulose fibers, which are biomass abundantly present in nature, particularly microfibrillar cellulose (also referred to as cellulose nanofibers) as a new form of their utilization, have attracted attention.

[0003] For example, Patent Document 1 discloses a microfibrillar cellulose fiber composite in which a cationic surfactant is adsorbed on microfibrillar cellulose fibers having a carboxy group, and a quaternary ammonium compound is chemisorbed on the carboxy group at the C6 position of the cellulose constituent unit as the cationic surfactant. Patent Document 1 also discloses a composite material obtained by mixing the microfibrillar cellulose fiber composite as a reinforcing material with a moldable resin, and that the resin content in the composite material is 40 to 99.99% by mass based on the total mass of the composite material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Cellulose fibers inherently do not have thermoformability. Therefore, they cannot be thermoformed unless added to a resin such as a thermoplastic resin. Conventionally, as described above, it has been known to add microfibrillar cellulose having a carboxy group as a reinforcing material to a resin, but it has not been known that specific anion-modified microfibrillar cellulose has thermoformability.

[0006] An embodiment of the present invention aims to provide a novel thermoformable material containing microfibrillar cellulose having thermoformability and a molded article thereof. **Means for Solving the Problems**

[0007] The present invention includes the following embodiments. [1] A thermoformable material containing 50% by mass or more of an onium salt type anion-modified microfibrillar cellulose having a number average fiber width of 2 to 1000 nm. [2] The thermoformable material according to [1], wherein the melting point of the modifier for converting the anionic group of the anion-modified microfibrillar cellulose into an onium salt is 150°C or lower. [3] The thermoformable material according to [1] or [2], wherein the onium salt of the anion-modified microfibrillar cellulose is a quaternary onium salt. [4] The thermoformable material according to any one of [1] to [3], wherein the anion-modified microfibrillar cellulose has an amount of anionic groups measured with all anionic groups in the acid form of 0.5 to 3.0 mmol / g. [5] A molded article obtained by thermoforming the thermoformable material according to any one of [1] to [4]. **Advantages of the Invention**

[0008] According to the embodiment of the present invention, it is possible to provide a novel thermoformable material containing microfibrillar cellulose having thermoformability and a molded article thereof. **Modes for Carrying Out the Invention**

[0009] The thermoformable material according to the present embodiment contains an onium salt type anion-modified microfibrillar cellulose having a number average fiber width of 2 to 1000 nm. The anion-modified microfibrillar cellulose is a microfibrillar cellulose into which an anionic group has been introduced.

[0010] Microfibrillar cellulose is obtained by refining cellulose fibers to the nanolevel and is also referred to as cellulose nanofiber. The number-average fiber width of microfibrillar cellulose is 2 to 1000 nm, preferably 2 to 500 nm, more preferably 2 to 300 nm, still more preferably 2 to 100 nm, still more preferably 3 to 50 nm, and still more preferably 3 to 20 nm.

[0011] The number-average fiber length of microfibrillar 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 microfibrillar cellulose is not particularly limited and may be, for example, 10 to 1000 or 50 to 700.

[0012] The number-average fiber width of microfibrillar cellulose can be determined by observing it using an atomic force microscope (AFM). From the AFM image, at least 120 microfibrillar cellulose fibers are selected, the fiber width is measured, and the number-average fiber width is obtained by calculating the arithmetic mean. For the number-average fiber length as well, at least 120 microfibrillar cellulose fibers are selected in the same way, the fiber length is measured, and it is determined by 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 way.

[0013] Examples of the anionic groups of the anionic modified microfibrillar cellulose include at least one selected from the group consisting of carboxy groups, phosphate groups, sulfate groups, sulfonic acid groups, nitric acid groups, and boric acid groups. Among these, at least one selected from the group consisting of carboxy groups, phosphate groups, and sulfate groups is preferable. These anionic groups may be directly bonded to the glucose unit which is a constituent unit of the cellulose molecule, or may be indirectly bonded. When indirectly bonded, an alkylene group having 1 to 4 carbon atoms may be present between the glucose unit and the anionic group. The anionic group may be bonded to one or more of all the glucose units constituting the cellulose molecule, or may be bonded to one or more of a part of the glucose units constituting the cellulose molecule.

[0014] In one embodiment, examples of the anionic modified microfibrillar cellulose include oxidized cellulose nanofibers obtained by oxidizing the hydroxyl groups of the glucose units in the cellulose molecule, and carboxymethylated cellulose nanofibers obtained by carboxymethylating the hydroxyl groups of the glucose units in the cellulose molecule. Examples of the 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 and modified to a carboxy group. The oxidized cellulose nanofibers can be obtained by oxidizing natural cellulose such as wood pulp in the presence of an N-oxyl compound using a co-oxidant and then performing a fibrillation (miniaturization) treatment. As the N-oxyl compound, a compound having a nitroxyl radical generally used as an oxidation catalyst is used, for example, piperidine nitroxyl radical, and particularly 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) or 4-acetamido-TEMPO is preferable. The anionic modified microfibrillar cellulose according to a preferred embodiment is TEMPO-oxidized cellulose nanofibers oxidized using TEMPO.

[0015] In this embodiment, an onium salt type anion-modified microfibrous cellulose is used. The onium salt type anion-modified microfibrous cellulose is obtained by introducing an onium salt into the anionic group of the anion-modified microfibrous cellulose, that is, the anionic group has an onium ion as a counter ion. By introducing the onium salt in this way, thermoformability (also referred to as thermoplastic softening characteristics) can be imparted to the anion-modified microfibrous cellulose, and thermoforming becomes possible even without containing a resin such as a thermoplastic resin.

[0016] The "onium salt" referred to here is a broad sense onium salt that includes not only a salt containing an onium ion generated by protonation of a hydride, but also a salt containing a cation in which some or all of the protons of the onium ion are substituted with an alkyl group, an arene group, or the like. Examples of the onium salt include ammonium salt, phosphonium salt, sulfonium salt, oxonium salt, and the like. Among these, ammonium salt and phosphonium salt are preferable. Any one of these may be used, or two or more of them may be used in combination. Here, the arene group refers to a monovalent hydrocarbon group having an aromatic ring, and examples 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, didodecyldimethylammonium salt, etc., ammonium salts containing an arene group such as benzyltributylammonium salt, benzyltripropylammonium salt, benzyltriethylammonium salt, benzyltrimethylammonium salt, benzyldimethyldodecylammonium salt, benzyldimethyltetradecylammonium salt, benzyldimethyloctadecylammonium salt, etc., heterocyclic quaternary ammonium salts such as 1-ethyl-3-methylimidazolium salt, dodecylpyridinium salt, 1-allyl-3-methylimidazolium salt, 1-butylpyridinium salt, 1-butyl-4-methylpyridinium salt), tertiary ammonium salts (e.g., trialkylammonium salts such as trioctylammonium salt, trihexylammonium salt), secondary ammonium salts (e.g., dialkylammonium salts such as dioctylammonium salt, dibutylammonium salt, dihexylammonium salt, didodecylammonium salt, distearylammonium salt), and primary ammonium salts (e.g., alkylammonium salts such as dodecylammonium salt, oleylammonium salt, stearylammonium salt, alkanolammonium salts such as diethylene glycol ammonium salt).

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

[0019] In addition, any one of the above-listed onium salts may be used, or two or more of them may be used in combination.

[0020] As the onium salt, those having a melting point of the modifier for forming the anionic group into the onium salt of 150°C or lower are preferred. By having a melting point of the modifier of 150°C or lower, the thermoformability can be further improved. The melting point of the modifier is more preferably 100°C or lower, still more preferably 50°C or lower, and even more preferably 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 modifier refers to a compound that forms an onium salt together with an acid-type anionic group. However, when the modifier is a quaternary onium salt, the "melting point" is the melting point measured for the acetate in which the anion forming the salt with the onium ion is replaced with an acetate ion. The melting point is determined as the temperature at which the modifier melts by gradually raising the temperature of the modifier using a melting point measuring device, and specifically, it is as described in the column of the examples.

[0022] As the onium salt, it is preferable that it is a quaternary onium salt in order to further improve the thermoformability. As the quaternary onium salt, for example, the above-mentioned quaternary ammonium salt and / or quaternary phosphonium salt 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] It is preferable that the amount of anionic groups measured with all anionic groups in the acid form in the anionic-modified microfibrous cellulose is 0.5 to 3.0 mmol / g, more preferably 1.0 to 2.8 mmol / g, and still more preferably 1.5 to 2.5 mmol / g. Since the anionic-modified microfibrous cellulose according to the embodiment as described above is in the onium salt form, when measuring the amount of anionic groups, measurement is performed after converting all anionic groups into the acid form. The amount of anionic groups is the amount of substance (mmol) of anionic groups per dry mass of the acid-form anionic-modified microfibrous cellulose, and can be measured by a known method. Specifically, it can be measured by the method described in the Examples section. In this specification, the "dry mass" refers to the mass after drying at 140°C until the mass change rate per minute becomes 0.05% or less.

[0024] In the onium salt type anionic-modified microfibrous cellulose according to this embodiment, the anionic groups may be only the onium salt, or may contain other salts together with the onium salt. The other salts are not particularly limited, and examples include alkali metal salts such as sodium salts and potassium salts, and alkaline earth metal salts such as magnesium salts and calcium salts. Also, not all of the anionic groups have to be in the salt form (for example, in the case of a carboxy group, -COOX where X is a cation forming a salt with a carboxylic acid), and may contain an acid form (the counter ion is H + which is also referred to as the H form. For example, in the case of a carboxy group, -COOH) together with the salt form containing the onium salt.

[0025] In one embodiment, it is preferable that 45 mol% or more of the anionic groups of the onium salt type anion-modified microfibrillar cellulose are onium salts. That is, it is preferable that 45 mol% or more of the anionic groups have onium ions as counterions. The introduction rate of the onium salt 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 still more preferably 100 mol%. The introduction rate of the onium salt is calculated, for example, when the anionic group is a carboxy group, from the absorption peak area derived from the onium salt and the absorption peak area derived from the anionic group in the acid form using FT-IR. In that case, when a metal salt is included as another salt, it is calculated by also measuring the metal content using an ICP emission spectroscopic analyzer. When the anionic group is a phosphate group or a sulfate group, the introduction rate of the onium salt is calculated by measuring the nitrogen content with a total nitrogen analyzer.

[0026] As described above, the anion-modified microfibrillar cellulose is obtained by a step of chemically modifying the unmodified cellulose fiber and a step of defibrating the cellulose fiber. The defibrillation of the cellulose fiber may be carried out after introducing an anionic group (more specifically, an onium salt), or may be carried out before the introduction. The defibrillation treatment can be carried out, for example, by treating a dispersion of cellulose fibers using a homomixer under high-speed rotation, a high-pressure homogenizer, an ultrasonic dispersion processor, a beater, a disk-type refiner, a conical-type refiner, a double-disk-type refiner, a grinder, or the like.

[0027] The anion-modified microfibrillar cellulose preferably has a cellulose I-type crystal structure. The cellulose I-type crystal structure is the crystal form of natural cellulose, and by having the I-type crystal structure, the anion-modified microfibrillar cellulose has water insolubility. Having the cellulose I-type crystal structure can be identified from the fact that in the diffraction profile obtained by wide-angle X-ray diffraction image measurement, there are typical peaks at two positions near 2θ = 14° to 17° and near 2θ = 22° to 23°.

[0028] The material for thermoforming according to this embodiment contains 50% by mass or more of the above-mentioned onium salt type anion-modified microfibrillar cellulose, preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may consist of 100% by mass, that is, only the onium salt type anion-modified microfibrillar cellulose.

[0029] The material for thermoforming is a material used for thermoforming. "Thermoforming" refers to a forming method in which a material is softened by heating, formed into a predetermined shape, and then hardened by cooling. Examples include hot press forming, vacuum forming, and pressure air forming. Here, the term "softening" does not necessarily mean that the anion-modified microfibrillar cellulose melts, but rather means that the fibers become more fluid when heated. It is considered that the fibers adhere to each other during thermoforming and solidify in that state upon cooling, maintaining a certain shape. Since the material for thermoforming is mainly composed of anion-modified microfibrillar cellulose, it may be in the form of fibers (i.e., a fibrous material for thermoforming). "Fibrous" means having the form of fibers, and it may be a collection of fibers, such as a fiber sheet like paper or non-woven fabric, a cotton-like form, or a powdery form formed by aggregation of microfibrillar 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" respectively include the concepts of "film" and "film-like".

[0030] The thermoformable material may contain an additive as an optional component together with the anionic modified microfibrous cellulose. Examples of the additive include colorants such as pigments and dyes, water resistance agents, flame retardants, plasticizers, antioxidants, light stabilizers, fillers, antistatic agents, and the like. Since the anionic modified microfibrous cellulose according to the present embodiment has thermoformability as described above, it can be thermoformed alone. Therefore, the thermoformable material does not exclude those containing a resin such as a thermoplastic resin, but in one embodiment, it is preferably resin-free and can be directly subjected to thermoforming without adding a resin.

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

[0032] In the case of a fiber sheet made of the thermoformable material, by stacking a plurality of sheets and thermoforming at least a part thereof by hot press molding, it is possible to adhere between the fiber sheets at the thermoformed part, and heat sealing is possible. Therefore, a fiber sheet capable of heat sealing can be provided, and a heat-sealed molded article can be obtained.

Examples

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

[0034] The measurement methods of each physical property in the examples and comparative examples are as follows.

[0035] [Amount of anionic group (amount of carboxy group)] 50 mL of an aqueous suspension of acid-type anionic modified microfibrillar 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 hydrochloric acid aqueous solution. Subsequently, a 0.05 mol / L sodium hydroxide aqueous solution was added dropwise to the aqueous suspension, and electrical conductivity was measured until the pH reached approximately 11. The amount of carboxyl groups was calculated according to the following formula from the amount of sodium hydroxide (V) consumed in the neutralization stage of the weak acid where the change in electrical conductivity was gradual. Amount of carboxyl groups (mmol / g) = V (mL) × [0.05 / mass of acid-type anionic modified microfibrillar cellulose (g)]

[0036] [Amount of anionic groups (phosphate group amount)] For an aqueous suspension prepared by diluting anionic modified microfibrillar cellulose with ion-exchanged water to a content of 0.2% by mass, after treatment with an ion-exchange resin to obtain acid-type anionic modified microfibrillar cellulose, titration with an alkali was performed for measurement. The treatment with the ion-exchange resin was carried out by adding a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) with a volume of 1 / 10 to the aqueous suspension, performing a shaking treatment for 1 hour, and then pouring it onto a mesh with an opening of 90 μm to separate the ion-exchange resin from the aqueous suspension. Also, the titration with an alkali was performed by measuring the change in the value of the electrical conductivity shown by the aqueous suspension while adding 50 μL of a 0.1 mol / L sodium hydroxide aqueous solution to the aqueous suspension after treatment with the ion-exchange resin, once every 30 seconds. 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 (sulfate group amount)] A predetermined amount of acid-type anionic modified microfibrillar cellulose was burned, and the sulfur content contained in the combustion product was measured using a combustion ion chromatograph by a method compliant with IEC 62321 and converted to the amount of sulfate groups for calculation.

[0038] [Measurement of number-average fiber width] The number average fiber width of the anionic modified microfibrillar cellulose was measured as follows. That is, an anionic modified microfibrillar cellulose aqueous dispersion treated by high-pressure dispersion with a solid content of 0.005 to 0.0001% by weight was prepared, and the dispersion was cast on a mica substrate and dried to obtain a sample for observation with an atomic force microscope (AFM). Then, observation was carried out using an atomic force microscope image at any one of magnifications of 5000 times, 10000 times, or 50000 times according to the size of the constituent fibers. At that time, an axis with an arbitrary image width in the vertical and horizontal directions was assumed in the obtained image, and the sample and observation conditions (magnification, etc.) were adjusted so that 20 or more fibers intersected the axis. After obtaining an observation image that satisfies this condition, two random axes in the vertical and horizontal directions were drawn for each image, and the fiber widths of the fibers intersecting the axis were visually read. In this way, images of at least three non-overlapping surface portions were taken with an atomic force microscope, and the values of the fiber widths of the fibers intersecting the two axes were read respectively (therefore, information on at least 20×2×3 = 120 fiber widths 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 a room temperature liquid (amine, phosphine, ammonium salt, phosphonium salt, etc.) was finely pulverized in a mortar and filled into a melting point measuring tube. The melting point measuring tube was set in the depression on the aluminum plate of the melting point measuring device, and a glass cover was placed on it. The temperature of the melting point measuring 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 the modifier of the quaternary onium salt, the acetate in which the anion forming a salt with the onium ion was replaced with an acetate ion was measured.

[0040] [Formability] The sheets as the thermoforming materials obtained in Examples 1 to 15 and Comparative Examples 1 to 2 were cut into pieces of 3 cm in length and 3 cm in width to prepare test pieces. The test pieces were sandwiched in a drawing die and pressed at 100°C and 0.4 MPa using a hot press device. The obtained molded body was observed and evaluated according to the following criteria. A: A molded product without wrinkles or cracks can be obtained with a pressing time of 10 seconds or less. B: A molded product without wrinkles or cracks can be obtained with a pressing time of 11 seconds or more and 60 seconds or less. C: A molded product without wrinkles or cracks can be obtained with a pressing time of 61 seconds or more and 180 seconds or less. D: The sheet is cracked during pressing and no molded product can be obtained.

[0041] [Heat sealability] The sheets as thermoforming materials obtained in Examples 1 to 15 and Comparative Examples 1 to 2 were cut into pieces with a length of 100 mm and a width of 15 mm to prepare test pieces. Two test pieces were stacked, and a range with a length of 10 mm and a width of 15 mm was pressed at 150 °C and 0.1 MPa using a hot press apparatus. Using a tensile testing machine, the two non-pressed ends were grasped and T-peel was performed at a tensile speed of 300 mm / min, and the maximum value was taken as the heat seal strength. The criteria for judging heat sealability are shown below. A: Those with a pressing time of 10 seconds or less and a heat seal strength of 0.1 N / 15 mm or more B: Those with a pressing time of 11 seconds or more and 60 seconds or less and a heat seal strength of 0.1 N / 15 mm or more C: Those with a pressing time of 61 seconds or more and 180 seconds or less and a heat seal strength of 0.1 N / 15 mm or more D: Those with a pressing time of 180 seconds and a heat seal strength of less than 0.1 N / 15 mm, or those that do not adhere.

[0042] [Preparation of anionic modified cellulose fibers A1 to A5] Prior to the preparation of the thermoforming materials of the examples and comparative examples, the acid-type anionic modified cellulose fibers A1 to A5 used therein were prepared according to the following Production Examples 1 to 5. [Production Example 1: Preparation of anionic modified cellulose fiber A1 (TEMPO-oxidized cellulose fiber)] To 2 g of softwood pulp, 150 mL of water, 0.25 g of sodium bromide, and 0.025 g of TEMPO were added, and after thoroughly stirring and dispersing, an aqueous solution of 13 mass% sodium hypochlorite (co-oxidizing agent) was added such that the amount of sodium hypochlorite was 10.0 mmol / g with respect to 1.0 g of the above pulp, and the reaction was started. Since the pH decreased as the reaction proceeded, a 0.5 mol / L aqueous sodium hydroxide solution was added dropwise while maintaining the pH at 10 - 11, and the reaction was carried out until no change in pH was observed (reaction time: 120 minutes). After completion of the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 2.0, and then filtration and washing with water were repeated for purification to obtain cellulose fibers with an oxidized fiber surface. Pure water was added thereto and diluted to a cellulose fiber concentration of 4 mass% to prepare a TEMPO-oxidized cellulose fiber suspension. Thereafter, after adjusting the pH of the slurry to 10 with a 24 mass% aqueous sodium hydroxide solution, sodium borohydride was added at 0.2 mmol / g with respect to the cellulose fibers, and the reaction was started. The reduction treatment was carried out by reacting for 2 hours. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 2.0, and then filtration and washing with water were repeated for purification to obtain anionic modified cellulose fiber A1 in which the carboxy group was in the acid form.

[0043] [Production Example 2: Preparation of Anionic Modified Cellulose Fiber A2 (TEMPO-Oxidized Cellulose Fiber)] An anionic modified cellulose fiber A2 in which the carboxy group was in the acid form was obtained in the same manner as the preparation method of anionic modified cellulose fiber A1, except that the addition amount of the aqueous sodium hypochlorite solution was 6.0 mmol / g with respect to 1.0 g of softwood pulp.

[0044] [Production Example 3: Preparation of Anionic Modified Cellulose Fiber A3 (TEMPO-Oxidized Cellulose Fiber)] An anionic modified cellulose fiber A3 in which the carboxy group was in the acid form was obtained in the same manner as the preparation method of anionic modified cellulose fiber A1, except that the addition amount of the aqueous sodium hypochlorite solution was 4.0 mmol / g with respect to 1.0 g of softwood pulp.

[0045] [Production Example 4: Preparation of Anionic Modified Cellulose Fiber A4 (Phosphoric Acid Esterified Cellulose Fiber)] To 100 parts by mass (dry mass) of softwood kraft pulp, an aqueous mixed solution of ammonium dihydrogen phosphate and urea was added and adjusted to contain 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. Next, the obtained chemical impregnated pulp was heated in a hot air dryer at 165°C for 200 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining phosphoric acid esterified cellulose fibers. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 1.0, and then filtration and washing with water were repeated for purification to obtain anionic modified cellulose fiber A4 in which the fiber surface was phosphoric acid esterified and the phosphate group was in the acid form.

[0046] [Production Example 5: Preparation of Anionic Modified Cellulose Fiber A5 (Sulfuric Acid 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 using a stirrer for 10 minutes. After stirring, the slurry was suction filtered using filter paper (No. 2). The suction filtration was carried out until the solution stopped dripping. After suction filtration, the pulp was peeled off from the filter paper, and the pulp was placed in a dryer with the temperature of the constant temperature bath set at 50°C and reacted for 6 hours. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 1.0, and then filtration and washing with water were repeated for purification to obtain anionic modified cellulose fiber A5 in which the fiber surface was sulfated and the sulfate group was 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 5 times the amount of ion-exchange resin (manufactured by Tokyo Chemical Industry Co., Ltd., Amberlite IRN78) of tetrabutylammonium bromide was added and stirred overnight using a shaker. Thereafter, the ion-exchange resin was removed by filtration to obtain a 0.1 N tetrabutylammonium hydroxide ethanol solution.

[0048] (Preparation of Anion-Modified Microfibrillar Cellulose) After diluting anion-modified cellulose fiber A1 to 0.5% by mass with ion-exchanged water, a 0.1 N tetrabutylammonium hydroxide ethanol solution in an equimolar amount to the amount of carboxy groups of 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 microfibrillar cellulose B1 with an introduction rate of onium salt of 100 mol% was obtained. (Preparation of Sheet) The obtained anion-modified microfibrillar cellulose B1 was placed in a Teflon (registered trademark) petri dish and dried at 40 °C for 24 hours to obtain a sheet (material for thermoforming) of Example 1 with a thickness of 30 μm.

[0049] [Example 2] The modifier, anion-modified microfibrillar 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 anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ethanol, to obtain a sheet of Example 2.

[0050] [Example 3] The modifier, anion-modified microfibrillar cellulose, and 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 a sheet of Example 3.

[0051] [Example 4] The modifier, anion-modified microfibrillar 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 anion-modified cellulose fiber A1 was diluted to 0.5% by mass with ethanol, to obtain a sheet of Example 4.

[0052] [Example 5] The modifier, anionic modified microfibrillar cellulose, and the 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 anionic modified cellulose fiber A1 was diluted to 0.5% by mass with ethanol, to obtain the sheet of Example 5.

[0053] [Example 6] The modifier, anionic modified microfibrillar cellulose, and the 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 anionic modified cellulose fiber A1 was diluted to 0.5% by mass with ethanol, to obtain the sheet of Example 6.

[0054] [Example 7] (Preparation of anionic modified microfibrillar cellulose) After diluting anionic modified cellulose fiber A1 to 0.5% by mass with ethanol, trioctylamine in an equimolar amount to the amount of carboxy groups of anionic modified cellulose fiber A1 was added and stirred. Further, by treating 10 times at a pressure of 150 MPa using a high-pressure homogenizer, anionic modified microfibrillar cellulose B7 with an onium salt introduction rate of 100 mol% was obtained.

[0055] (Preparation of sheet) The obtained anionic modified microfibrillar cellulose B7 was placed in a Teflon (registered trademark) petri dish and dried at 40 °C for 24 hours to obtain the sheet of Example 7 with a thickness of 30 μm.

[0056] [Example 8] The anionic modified microfibrillar cellulose and the 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 anionic modified microfibrillar cellulose) After diluting anionic modified cellulose fiber A1 to 0.5% by mass with ion-exchanged water, diethylene glycolamine (i.e., 2-(2-aminoethoxy)ethanol) in an equimolar amount to the amount of carboxy groups of anionic modified cellulose fiber A1 was added and stirred. Further, by subjecting it to one treatment at a pressure of 150 MPa using a high-pressure homogenizer, anionic modified microfibrillar cellulose B9 with an onium salt introduction rate of 100 mol% was obtained.

[0058] (Preparation of sheet) The obtained anionic modified microfibrillar 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 with a thickness of 30 μm.

[0059] [Example 10] Except for using anionic modified cellulose fiber A2, modifiers, anionic modified microfibrillar cellulose, and sheets were prepared in the same manner as in Example 2 to obtain a sheet of Example 10.

[0060] [Example 11] Except for using anionic modified cellulose fiber A3, modifiers, anionic modified microfibrillar cellulose, and sheets were prepared in the same manner as in Example 2 to obtain a sheet of Example 11.

[0061] [Example 12] Except for changing the conditions of the high-pressure homogenizer treatment to a pressure of 150 MPa and the number of treatments to 2 times, modifiers, anionic modified microfibrillar cellulose, and sheets were prepared in the same manner as in Example 2 to obtain a sheet of Example 12.

[0062] [Example 13] Except for changing the conditions of the high-pressure homogenizer treatment to a pressure of 150 MPa and the number of treatments to 1 time, modifiers, anionic modified microfibrillar cellulose, and sheets were prepared in the same manner as in Example 2 to obtain a sheet of Example 13.

[0063] [Example 14] Except for using anionic modified cellulose fiber A4, a modifier, anionic modified microfibrillar cellulose, and a sheet were prepared in the same manner as in Example 2 to obtain the sheet of Example 14.

[0064] [Example 15] Except for using anionic modified cellulose fiber A5, a modifier, anionic modified microfibrillar cellulose, and a sheet were prepared in the same manner as in Example 2 to obtain the sheet of Example 15.

[0065] [Comparative Example 1] (Preparation of anionic modified microfibrillar cellulose) Anionic modified cellulose fiber A1 was diluted to 0.5% by mass with ion-exchanged water and then neutralized with a 0.5N aqueous sodium hydroxide solution to adjust the pH (25°C) to 7.0. Further, it was treated three times at a pressure of 100 MPa using a high-pressure homogenizer to obtain anionic modified microfibrillar cellulose C1.

[0066] (Preparation of sheet) The obtained anionic modified microfibrillar cellulose C1 was placed in a Teflon (registered trademark) petri dish and dried at 40°C for 24 hours to obtain a sheet of Comparative Example 1 with a thickness of 30 μm.

[0067] [Comparative Example 2] (Preparation of sheet) The anionic modified microfibrillar cellulose C1 obtained in Comparative Example 1 was placed in a Teflon (registered trademark) petri dish and dried at 40°C for 24 hours. 0.1M hydrochloric acid was added to the dried product and immersed for 24 hours, then washed 5 times with purified water and air-dried to obtain a sheet of Comparative Example 2 with a thickness of 30 μm.

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

[0069]

Table 1

[0070] As shown in Table 1, in Comparative Examples 1 and 2 where no onium salt was introduced, the anionic modified microfibrous cellulose did not have thermoformability, so the formability and heat sealability were poor. On the other hand, in Examples 1 to 15 where an onium salt was introduced, it had formability by thermoforming and heat sealability. The formability and heat sealability were better in those with a lower melting point of the modifier, and furthermore, the quaternary onium salt was superior to the primary to tertiary ones in these performances.

[0071] In addition, various numerical ranges described in the specification can be arbitrarily combined with their upper and lower limit values respectively, and all these combinations are regarded as being described in this specification as preferred numerical ranges. Also, the description of the numerical range of "X to Y" means X or more and Y or less.

[0072] As described above, some embodiments of the present invention have been explained, but 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, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their omissions, replacements, changes, etc. are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Claims

1. A thermoforming material containing 50% by mass or more of an onium salt type anion-modified microfibrillar cellulose having a number average fiber width of 2 to 1000 nm.

2. The thermoforming material according to Claim 1, wherein the melting point of the modifier for converting the anionic group of the anion-modified microfibrillar cellulose into an onium salt is 150°C or lower.

3. The thermoforming material according to Claim 1, wherein the onium salt of the anion-modified microfibrillar cellulose is a quaternary onium salt.

4. The thermoforming material according to Claim 1, wherein the anion-modified microfibrillar cellulose has an amount of anionic groups measured with all anionic groups in acid form of 0.5 to 3.0 mmol / g.

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

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