Method for producing cellulose fiber dispersion

Abstract

To provide a manufacturing method of a cellulose fiber dispersion which is capable of dispersing a blend of cellulose fibers involving a metal ion or metal nanoparticles and a dispersion medium without causing reduction of fiber length and moreover, has excellent dispersibility of non-disintegrated chips.SOLUTION: A manufacturing method includes a dispersion step of dispersing a blend of cellulose fibers involving a metal ion or metal nanoparticles comprising one kind or more of an element selected from a group consisting of Ag, Au, Pt, Pd, Ni, Mn, Fe, Ti, Al, Zn and Cu and a dispersion medium, the blend having a concentration of 1 wt.% or over, by passing through an in-line type agitator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a cellulose fiber dispersion. [Background technology]

[0002] By using metal-loaded cellulose fibers, which are modified cellulose fibers loaded with metal ions or metal particles, as raw materials, it has been possible to impart antiviral, antibacterial, deodorizing, and other functions to manufactured products (e.g., Patent Document 1, etc.).

[0003] However, when manufacturing metal-loaded cellulose fiber, the dehydrated cake obtained in the process of washing and dehydrating the cellulose fiber after the metal loading process is manually diluted and re-dispersed in the washing tank, and clumps (undisintegrated fragments) remain that are not completely dispersed in the dispersion. This leads to defects in the final product, resulting in paper waste, which is a problem.

[0004] Furthermore, when metal-supported cellulose fibers are dispersed using a homogenizer capable of applying high shear force, the dispersibility of undisintegrated fragments is excellent, but there is a problem that the fiber length is shortened due to the shear force. Therefore, when the metal-supported cellulose fiber dispersion dispersed by this method is made into a final product, its strength development function is impaired, and the product physical properties such as tensile strength and breaking strength are inferior to those of products obtained using a dispersion that has not been subjected to a dispersion treatment.

[0005] Therefore, there has been a demand for a method for producing a metal-supported cellulose fiber dispersion that is excellent in dispersibility of undisintegrated fragments without causing a shortening of the fiber length. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-84870 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the present invention aims to provide a method for producing a cellulose fiber dispersion that can disperse a mixture of metal-supported cellulose fibers and a dispersion medium without causing shortening of the fiber length, and that has excellent dispersibility of undisintegrated fragments. [Means for solving the problem]

[0008] As a result of extensive research into achieving this object, the present inventors have found that using a specific stirring device for dispersion is extremely effective, and have completed the present invention.

[0009] The present invention provides the following: (1) A method for producing a cellulose fiber dispersion, comprising a dispersing step of dispersing a mixture of cellulose fibers containing one or more metal ions or metal nanoparticles selected from the group consisting of Ag, Au, Pt, Pd, Ni, Mn, Fe, Ti, Al, Zn, and Cu, and a dispersing medium, the mixture having a concentration of 1 wt % or more, by passing the mixture through an in-line stirring device. (2) The method for producing a cellulose fiber dispersion according to (1), further comprising a pre-dispersion step of pre-dispersing the mixture in a stirrer before the dispersion step. (3) The method for producing a cellulose fiber dispersion according to (1) or (2), wherein the metal ions or metal nanoparticles contain either Ag or Cu. (4) The method for producing a cellulose fiber dispersion according to any one of (1) to (3), characterized in that the inline stirring device has a first stirring section and a second stirring section, the first stirring section having a turbine and a first stator, and the second stirring section having a rotor and a second stator. [Effects of the Invention]

[0010] According to the present invention, a mixture of cellulose fibers containing metal ions or metal nanoparticles and a dispersion medium can be dispersed without causing shortening of the fiber length, and further, a method for producing a cellulose fiber dispersion with excellent dispersibility of undisaggregated fragments can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing the internal structure of a homomic line mill that can be used in the manufacturing method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below with reference to the drawings. In the present invention, "to" includes both end values. That is, "X to Y" includes both end values ​​X and Y.

[0013] The present invention is a method for producing a cellulose fiber dispersion, which comprises a dispersion step of dispersing a mixture of cellulose fibers containing one or more metal ions or metal nanoparticles selected from the group consisting of Ag, Au, Pt, Pd, Ni, Mn, Fe, Ti, Al, Zn, and Cu (hereinafter, sometimes simply referred to as "metal-supported cellulose fibers") and a dispersion medium, the mixture having a concentration of 1 wt % or more, by passing it through an in-line stirrer.

[0014] (Dispersion process) In the dispersion step of the present invention, a mixture of cellulose fibers containing metal ions or metal nanoparticles and a dispersion medium, the mixture having a concentration of 1 wt % or more, is dispersed by passing it through an in-line stirrer.

[0015] (cellulose fiber) The cellulose fibers used in the present invention are fibers made from cellulose. The average fiber diameter of the cellulose fibers is not particularly limited, but is about 1 nm to 10 μm. The average fiber length of the cellulose fibers is not particularly limited, but is about 0.1 to 5 mm. In the present invention, the average fiber diameter and average fiber length of the cellulose fibers can be measured using an image analysis type fiber analyzer, for example, a Fiber Tester manufactured by ABB Corporation or a Fractionator manufactured by Valmet Co., Ltd.

[0016] The cellulose raw material is not particularly limited as long as it contains cellulose, and examples thereof include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (e.g., unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), bleached kraft pulp (BKP), unbleached softwood sulfite pulp (NUSP), bleached softwood sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.)), animals (e.g., ascidians), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), and microbial products. The cellulose raw material may be any one of these or a combination of two or more thereof. However, cellulose raw materials (e.g., cellulose fibers) derived from plants or microorganisms are preferred, and cellulose raw materials (e.g., cellulose fibers) derived from plants are more preferred.

[0017] The number-average fiber diameter and number-average fiber length of the cellulose raw material used in the present invention are not particularly limited, and any number-average fiber diameter and number-average fiber length can be used as needed. Two or more types of cellulose fibers with different number-average fiber diameters and number-average fiber lengths can be mixed in any ratio. For example, softwood kraft pulp (NBKP), a common type of pulp, has a number-average fiber diameter of about 30 to 60 μm and a number-average fiber length of about 3 to 5 mm, while hardwood bleached kraft pulp (LBKP) has a number-average fiber diameter of about 10 to 30 μm and a number-average fiber length of about 1 to 2 mm.

[0018] Cellulose has three hydroxyl groups per glucose unit and can be chemically modified in various ways. In the present invention, from the viewpoint of introducing metal ions or metal nanoparticles into at least a portion of the cellulose fiber, it is preferable that the cellulose fiber is chemically modified so as to introduce carboxyl groups or carboxylate groups into at least a portion of the cellulose fiber.

[0019] Here, the carboxyl group refers to a group represented by -COOH, and the carboxylate group refers to a group represented by -COO - The counter ion of the carboxylate group is not particularly limited. As will be described later, when metal nanoparticles are formed via an ionic bond with a carboxylate group, this metal ion serves as the counter. A carboxyl group or a carboxylate group is also collectively referred to as an "acid group."

[0020] The acid group content can be measured by the method disclosed in paragraph 0021 of JP 2008-001728 A. Specifically, 60 mL of a 0.5 to 1 wt % slurry is prepared using a precisely weighed dried cellulose sample, and the pH is adjusted to approximately 2.5 with a 0.1 mol / L aqueous hydrochloric acid solution. A 0.05 mol / L aqueous sodium hydroxide solution is then added dropwise, and electrical conductivity is measured. Measurements are continued until the pH reaches approximately 11. The amount of acid groups, X1, is calculated using the following formula from the amount of sodium hydroxide (V) consumed until the electrical conductivity changes slowly to indicate the stage of neutralization of the weak acid. X1 (mmol / g) = V (mL) × 0.05 / weight of cellulose fiber (g)

[0021] The amount of acid groups in the cellulose fibers is not particularly limited, but is preferably 0.2 to 2.2 mmol / g. If the amount of acid groups is less than 0.2 mmol / g, the amount of metal particles present on the surface of the cellulose fibers will be insufficient when metal ions or metal nanoparticles are supported on the cellulose fibers. On the other hand, if the amount of acid groups exceeds 2.2 mmol / g, aggregation of the metal particles may occur.

[0022] The modification method for introducing carboxyl groups or carboxylate groups is not particularly limited as long as the modified cellulose fiber contains carboxyl groups or carboxylate groups, and examples include oxidation (carboxylation), etherification, phosphorylation, esterification, silane coupling, fluorination, and cationization. Among these, oxidation (carboxylation) and etherification are preferred, with oxidation (carboxylation) being particularly preferred. These methods will be described in detail below.

[0023] (chemical modification) (oxidation) In the present invention, the method for oxidizing cellulose fibers is not particularly limited, and known methods can be used. One example is a method in which a cellulose raw material is oxidized in water using an oxidizing agent in the presence of a substance selected from the group consisting of N-oxyl compounds, bromides, iodides, or mixtures thereof. This method selectively oxidizes the primary hydroxyl group at C6 of the glucopyranose ring on the cellulose surface, generating a group selected from the group consisting of an aldehyde group, a carboxyl group, and a carboxylate group. The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by weight or less.

[0024] An N-oxyl compound refers to a compound that can generate a nitroxy radical. An example of a nitroxy radical is 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). Any compound that promotes the target oxidation reaction can be used as the N-oxyl compound.

[0025] The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose fibers. For example, it is preferably 0.01 mmol or more, more preferably 0.02 mmol or more, per 1 g of bone-dry cellulose. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, and even more preferably 0.5 mmol or less. Therefore, the amount of the N-oxyl compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.02 to 0.5 mmol, per 1 g of bone-dry cellulose.

[0026] Bromides are compounds containing bromine, such as alkali metal bromides that can dissociate and ionize in water, such as sodium bromide. Iodides are compounds containing iodine, such as alkali metal iodides. The amount of bromide or iodide used may be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is preferably 0.1 mmol or more, more preferably 0.5 mmol or more, per 1 g of bone-dry cellulose. The upper limit is preferably 100 mmol or less, more preferably 10 mmol or less, and even more preferably 5 mmol or less. Therefore, the total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol, per 1 g of bone-dry cellulose.

[0027] The oxidizing agent is not particularly limited, but examples include halogens, hypohalous acids, perhalogen acids, their salts, halogen oxides, and peroxides. Among these, hypohalous acids or their salts are preferred due to their low cost and low environmental impact, hypochlorous acid or its salts are more preferred, and sodium hypochlorite is even more preferred. The amount of oxidizing agent used is preferably 0.5 mmol or more, more preferably 1 mmol or more, and even more preferably 3 mmol or more, per 1 g of bone-dry cellulose. The upper limit is preferably 500 mmol or less, more preferably 50 mmol or less, and even more preferably 25 mmol or less. Therefore, the amount of oxidizing agent used is preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol, per 1 g of bone-dry cellulose. When an N-oxyl compound is used, the amount of oxidizing agent used is preferably 1 mol or more per 1 mol of N-oxyl compound. The upper limit is preferably 40 mol. Therefore, the amount of the oxidizing agent used is preferably 1 to 40 mol per 1 mol of the N-oxyl compound.

[0028] Conditions such as pH and temperature during the oxidation reaction are not particularly limited. Generally, the oxidation reaction proceeds efficiently even under relatively mild conditions. The reaction temperature is preferably 4°C or higher, more preferably 15°C or higher. The upper limit is preferably 40°C or lower, more preferably 30°C or lower. Therefore, the temperature is preferably 4 to 40°C, and may be approximately 15 to 30°C, i.e., room temperature. The pH of the reaction solution is preferably 8 or higher, more preferably 10 or higher. The upper limit is preferably 12 or lower, more preferably 11 or lower. Therefore, the pH of the reaction solution is preferably 8 to 12, more preferably approximately 10 to 11. Generally, as the oxidation reaction proceeds, carboxyl groups are generated in the cellulose, and the pH of the reaction solution tends to decrease. Therefore, to efficiently proceed with the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution within the above range. Water is preferred as the reaction medium during the oxidation because of its ease of handling and the low occurrence of side reactions.

[0029] The reaction time for oxidation can be set appropriately depending on the degree of progress of the oxidation, and is usually 0.5 hours or more. The upper limit is usually 6 hours or less, preferably 4 hours or less. Therefore, the reaction time for oxidation is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.

[0030] The oxidation may be carried out in two or more separate reaction stages. For example, the oxidized cellulose obtained by filtration after the completion of the first reaction stage can be oxidized again under the same or different reaction conditions, thereby enabling efficient oxidation without reaction inhibition by sodium chloride produced as a by-product in the first reaction stage.

[0031] Another example of a carboxylation (oxidation) method is a method of oxidation by ozone treatment. This oxidation reaction oxidizes at least the hydroxyl groups at positions 2 and 6 of the glucopyranose ring that constitutes cellulose, and decomposes the cellulose chain. Ozone treatment is usually carried out by contacting the cellulose raw material with a gas containing ozone. The ozone concentration in the gas is 50 g / m 3 The upper limit is 250 g / m or more. 3 Preferably, it is 220 g / m or less. 3 Therefore, the ozone concentration in the gas is preferably 50 to 250 g / m or less. 3 It is preferable that the thickness is 50 to 220 g / m 3The amount of ozone added is preferably 0.1% by weight or more, and more preferably 5% by weight or more, relative to 100% by weight of the solids content of the cellulose raw material. The upper limit is usually 30% by weight or less. Therefore, the amount of ozone added is preferably 0.1 to 30% by weight, and more preferably 5 to 30% by weight, relative to 100% by weight of the solids content of the cellulose raw material. The ozone treatment temperature is usually 0°C or higher, and preferably 20°C or higher. The upper limit is usually 50°C or less. Therefore, the ozone treatment temperature is preferably 0 to 50°C, and more preferably 20 to 50°C. The ozone treatment time is usually 1 minute or more, and preferably 30 minutes or more. The upper limit is usually 360 minutes or less. Therefore, the ozone treatment time is usually about 1 to 360 minutes, and preferably about 30 to 360 minutes. When the ozone treatment conditions are within the above-mentioned ranges, excessive oxidation and decomposition of cellulose can be prevented, resulting in a good yield of oxidized cellulose.

[0032] The product obtained after the ozone treatment may be further subjected to a post-oxidation treatment using an oxidizing agent. The oxidizing agent used in the post-oxidation treatment is not particularly limited, but examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite; oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. Examples of methods for the post-oxidation treatment include dissolving these oxidizing agents in water or a polar organic solvent such as alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the oxidizing agent solution.

[0033] The amounts of carboxyl groups, carboxylate groups, and aldehyde groups contained in the oxidized cellulose fibers can be adjusted by controlling the oxidation conditions, such as the amount of oxidizing agent added and the reaction time.

[0034] (Etherification) For the etherification, any method that results in a carboxyl group or a carboxylate group in the functional group after the reaction can be used, and known methods can be used, so long as it allows for the introduction of metal ions into the cellulose fibers in a subsequent step. Examples include carboxyalkyl etherification such as carboxymethyl (etherification), carboxyethyl (etherification), carboxypropyl (etherification), and carboxybutyl (etherification), as well as carboxyphenyl (etherification). Among these, the carboxymethylation method is described below as an example.

[0035] The carboxymethylation method is not particularly limited, and known methods can be used. For example, a method can be used in which the cellulose raw material as the starting material is mercerized and then etherified. A solvent is usually used during the carboxymethylation reaction. Examples of the solvent include water, alcohol (e.g., lower alcohol), and mixed solvents thereof. Examples of lower alcohols include methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, and tertiary butanol. The mixing ratio of the lower alcohol in the mixed solvent is usually 60% by weight or more or 95% by weight or less, preferably 60 to 95% by weight. The amount of solvent is usually 3 times by weight relative to the cellulose raw material. The upper limit is not particularly limited, but is 20 times by weight. Therefore, the amount of solvent is preferably 3 to 20 times by weight.

[0036] Mercerization is typically carried out by mixing the raw material with a mercerizing agent. Examples of mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of mercerizing agent used is preferably 0.5 moles or more, more preferably 1.0 moles or more, and even more preferably 1.5 moles or more, per mole of the anhydrous glucose residue of the raw material. The upper limit is typically 20 moles or less, preferably 10 moles or less, and more preferably 5 moles or less; therefore, 0.5 to 20 moles are preferred, more preferably 1.0 to 10 moles, and even more preferably 1.5 to 5 moles.

[0037] The reaction temperature for mercerization is usually 0°C or higher, preferably 10°C or higher. The upper limit is usually 70°C or lower, preferably 60°C or lower. Therefore, the reaction temperature is usually 0 to 70°C, preferably 10 to 60°C. The reaction time is usually 15 minutes or longer, preferably 30 minutes or longer. The upper limit is usually 8 hours or shorter, preferably 7 hours or shorter. Therefore, the reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

[0038] The etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of the carboxymethylating agent include sodium monochloroacetate. The amount of the carboxymethylating agent added is usually 0.05 times or more by mole, more preferably 0.5 times or more by mole, and even more preferably 0.8 times or more by mole, per glucose residue of the cellulose raw material. The upper limit is usually 10.0 times or less by mole, preferably 5 times or less by mole, and more preferably 3 times or less by mole. Therefore, it is preferably 0.05 to 10.0 times by mole, more preferably 0.5 to 5 times by mole, and even more preferably 0.8 to 3 times by mole. The reaction temperature is usually 30°C or higher, preferably 40°C or higher, and the upper limit is usually 90°C or lower, preferably 80°C or lower. Therefore, the reaction temperature is usually 30 to 90°C, preferably 40 to 80°C. The reaction time is usually 30 minutes or more, preferably 1 hour or more. The upper limit is usually 10 hours or less, preferably 4 hours or less. Therefore, the reaction time is usually 30 minutes to 10 hours, and preferably 1 hour to 4 hours. If necessary, the reaction solution may be stirred during the carboxymethylation reaction.

[0039] When a cellulose raw material is modified by carboxymethylation, the degree of carboxymethyl substitution per anhydroglucose unit in the resulting carboxymethylated cellulose fiber is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.10 or more. The upper limit is preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.35 or less. Therefore, the degree of carboxymethyl substitution is preferably 0.01 to 0.50, more preferably 0.05 to 0.40, and even more preferably 0.10 to 0.30.

[0040] The degree of carboxymethyl substitution per glucose unit of carboxymethylated cellulose fiber can be measured, for example, by the following method: 1) Accurately weigh out approximately 2.0 g of carboxymethylated cellulose (bone dry) and place it in a 300 mL Erlenmeyer flask with a stopper. 2) Add 100 mL of concentrated nitric acid (special grade) to 1000 mL of methanol, add 100 mL of the resulting nitric acid-methanol solution, and shake for 3 hours to convert the carboxymethyl cellulose salt (carboxymethylated cellulose) into hydrogen-type carboxymethyl cellulose. 3) Accurately weigh out 1.5 to 2.0 g of hydrogen-type carboxymethyl cellulose (bone dry) and place it in a 300 mL Erlenmeyer flask with a stopper. 4) Wet the hydrogen-type carboxymethyl cellulose with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake for 3 hours at room temperature. 5) Using phenolphthalein as an indicator, back-titrate the excess NaOH with 0.1 N H2SO4. 6) Calculate the degree of carboxymethyl substitution (DS) using the following formula: A = [(100 × F' - (0.1N H2SO4) (mL) × F) × 0.1] / (bone-dry weight of hydrogen-form carboxymethyl cellulose (g)) DS=0.162×A / (1-0.058×A) A: The amount of 1N NaOH (mL) required to neutralize 1 g of hydrogen-type carboxymethyl cellulose F': Factor of 0.1N NaOH F: Factor of 0.1N H2SO4

[0041] (Cellulose fibers containing metal ions or metal nanoparticles) In the present invention, in order to achieve a high deodorizing effect in the final product, cellulose fibers are used that contain one or more metal ions or metal nanoparticles selected from the group consisting of Ag, Au, Pt, Pd, Ni, Mn, Fe, Ti, Al, Zn, and Cu. In order to impart antibacterial, antiviral, and antiallergenic properties in addition to the deodorizing effect, it is preferable to use one or more ions selected from the group consisting of Ag and Cu. By blending the cellulose fiber dispersion containing the metal ions or metal nanoparticles of the present invention with, for example, paper, nonwoven fabric, film, various resins, and the like, various products having the above-mentioned effects can be produced.

[0042] The cellulose fibers and the metal compound may be contacted by mixing a pre-prepared cellulose fiber dispersion with an aqueous solution of the metal compound, or by applying a cellulose fiber-containing dispersion to a substrate to form a film, and then dripping the aqueous solution of the metal compound onto the film to impregnate it. The film may remain fixed on the substrate, or may be peeled off from the substrate. It is believed that these methods allow metal ions derived from the metal compound to form ionic bonds or coordinate with carboxylate groups, thereby adding the metal ions to the cellulose fibers.

[0043] The metal compound aqueous solution is an aqueous solution of a metal salt. Examples of the metal salt include complexes (complex ions), halides, nitrates, sulfates, and acetates.

[0044] The concentration of the aqueous metal compound solution is not particularly limited, but is preferably in the range of 10 to 80% by weight, more preferably 30 to 60% by weight, relative to 100 parts by weight of cellulose fibers.

[0045] The time for contacting the metal compound may be adjusted as appropriate. The temperature during contact is not particularly limited, but is preferably in the range of 2 to 50°C. The pH of the liquid during contact is also not particularly limited, but a low pH makes it difficult for metal ions to bind to carboxyl groups, so a pH of 7 to 13 is preferred, and a pH of 8 to 12 is particularly preferred.

[0046] The presence of metal ions in oxidized cellulose fibers can be confirmed by scanning electron microscope images and ICP atomic emission spectrometry of a strong acid extract. In other words, the presence of metal ions cannot be confirmed by scanning electron microscope images, whereas the presence of metal can be confirmed by ICP atomic emission spectrometry. In contrast, for example, if the metal is reduced from an ion and exists as metal particles, the metal particles can be confirmed by scanning electron microscope images, allowing the presence or absence of metal ions to be determined. The presence or absence of metal ions can also be determined by scanning electron microscope images and element mapping. In other words, while metal ions cannot be confirmed by scanning electron microscope images, the presence of metal ions can be confirmed by element mapping. In the present invention, if necessary, metal nanoparticles may be partially formed on the surface of the cellulose fibers by reducing the metal compound bound to the obtained metal ion-containing cellulose fibers.

[0047] The mechanism is thought to be as follows: Metal compounds or ions derived from metal compounds that were bonded to acid groups in a reduction reaction are reduced to form metals. At this time, the metals produced are supported on the surface of the oxidized cellulose fibers. Similarly, neighboring metals produced combine with each other, causing the particles to grow and form nanoparticles. Meanwhile, metal compounds present near the cellulose fibers but not bonded to acid groups are also reduced to form metals. These metals quickly combine with the metal on the surface of the cellulose fibers to form metal nanoparticles.

[0048] The reduction reaction may be carried out by a known method, but is preferably carried out while reducing the metal compound without cleaving the bond between the metal compound and the acid group. Examples of such reduction methods include gas-phase reduction using hydrogen and liquid-phase reduction using a reducing agent such as an aqueous solution of sodium borohydride. Conditions such as time and temperature during gas-phase reduction can be adjusted as appropriate; for example, the reaction may be carried out at 50 to 60°C for approximately 1 to 3 hours. The gas-phase reduction reaction is preferably carried out in a state where the oxidized cellulose fibers do not contain water or solvent. In the reduction reaction, the film may remain fixed on the substrate or may be peeled from the substrate. In the case of liquid-phase reduction, a film is obtained from the dispersion and can be subjected to the reduction reaction with or without drying. Alternatively, the dispersion can be subjected to the liquid-phase reduction reaction without drying. The reaction temperature during liquid-phase reduction is preferably 4 to 40°C, more preferably room temperature.

[0049] The metal nanoparticles are supported on the surface of the cellulose fibers via the acid groups present on the surface of the cellulose fibers as contact points. That is, the metal nanoparticles are fixed to the surface of the cellulose fibers via the acid groups present on the surface of the cellulose fibers. The chemical bond involved in the fixation is preferably a coordinate bond, a hydrogen bond, or an ionic bond. The state of the bond can be analyzed by X-ray photoelectron spectroscopy or infrared spectroscopy.

[0050] The average particle size of the metal nanoparticles is determined from a transmission electron microscope image or X-ray diffraction. In the present invention, the average particle size of the metal nanoparticles is preferably in the range of 1 to 50 nm when determined from a transmission electron microscope image. Specifically, the average particle size is determined by preparing a transmission electron microscope image of cellulose fibers, determining the circle-equivalent diameters of the primary particles of multiple metal nanoparticles from the image, and averaging these values. In the step of supporting the metal ions or metal nanoparticles, the content of the metal ions relative to the cellulose fibers is preferably in the range of 10 to 60 mg / g.

[0051] The cellulose fibers containing metal ions or metal nanoparticles obtained as described above are preferably washed with a sufficient amount of water and filtered at least once before being subjected to the dispersion step of the present invention, in order to remove unreacted metal salts.

[0052] (dispersion medium) In the present invention, the dispersion medium may be water, a water-soluble organic solvent, or a mixture thereof, and since the cellulose raw material is hydrophilic, water is preferably used because it is easy to achieve a good dispersion state during dispersion. Furthermore, when the dispersion is cellulose fibers carrying metal ions or metal nanoparticles, the dispersion medium may be the same as or different from the solvent of this dispersion.

[0053] The water-soluble organic solvent is an organic solvent that dissolves in water. Examples include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, and combinations thereof. Among these, lower alcohols having 1 to 4 carbon atoms such as methanol, ethanol, and 2-propanol are preferred, and from the viewpoints of safety and availability, methanol and ethanol are more preferred, and ethanol is even more preferred.

[0054] When a mixed solvent is used, the amount of the water-soluble organic solvent in the mixed solvent is preferably 10% by weight or more, more preferably 50% by weight or more, and even more preferably 70% by weight or more. There is no upper limit to this amount, but it is preferably 95% by weight or less, more preferably 90% by weight or less. Furthermore, the aqueous solvent may contain a water-insoluble organic solvent to the extent that the effects of the invention are not impaired.

[0055] In addition, if the concentration of the mixture of cellulose fibers and dispersion medium used in the present invention is too low, there will be little contact between the fibers, and disintegration will not progress easily.From the perspective of efficiently carrying out the dispersion process, the solids concentration of cellulose fibers relative to the total amount of cellulose fibers and dispersion medium that do not contain metal ions or metal nanoparticles in the mixture is 1 wt% or more, preferably 1.0 to 4.0 wt%, and more preferably 1.0 to 3.0 wt%.

[0056] (In-line type agitator) The in-line stirring device used in the present invention can be any device that can uniformly disperse the above mixture so that no undisintegrated fragments remain, and examples thereof include a homomic line mill and an OHR mixer. It is preferable to use a homomic line mill from the viewpoint of excellent continuous operability.

[0057] The Homomic Line Mill is an agitation device capable of in-line mixing, atomization, and dispersion processing. It draws in the processing liquid through the suction port by utilizing the pressure difference between the suction port and the discharge port created by the high-speed rotation of the turbine. The drawn-in processing liquid is mixed, atomized, agitated, and dispersed by the effects of shear force, crushing, impact, and turbulence generated in the precise, uniform micro-gap between the turbine and the first stator. The processing liquid is further atomized by the coarse crushing and grinding functions between the rotor and the second stator.

[0058] The OHR Mixer is an in-line mixing device that has multiple protrusions on the inner wall of the tube to increase cavitation in the fluid, thereby promoting mixing and stirring.

[0059] In the dispersion step, the operating conditions for passing the mixture through the in-line stirrer are preferably 10 to 1,000 L / min, more preferably 10 to 100 L / min, from the viewpoint of dispersibility of the undisintegrated fragments.

[0060] When a homomic line mill is used as the in-line stirring device, the rotation speed of the turbine and rotor is preferably 1,000 to 10,000 rpm, more preferably 3,000 to 5,000 rpm, from the viewpoint of dispersibility of undisintegrated fragments.

[0061] When an OHR mixer is used as an in-line mixer, a larger inner diameter is preferable in order to prevent shortening of the fiber length. In order to obtain the necessary inner diameter, the inlet diameter is preferably 40A (outer diameter 48.6 mm) or more.

[0062] The number of times the mixture is passed through the in-line stirrer is not particularly limited, but may be once or twice or more.

[0063] An example of using a homomic line mill as an in-line stirring device will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the internal configuration of a homomic line mill. Note that the in-line stirring device that can be used in the present invention is not limited to that shown in Fig. 1.

[0064] The homomic line mill 2 shown in Figure 1 has a pipe 4 through which the mixture passes, a first stirring section 10 equipped with a turbine 6 and a first stator 8 on the upstream side of the pipe 4, and a second stirring section 16 equipped with a rotor 12 and a second stator 14 on the downstream side. The turbine 6 and rotor 12 are attached to a shaft 18, which is connected to a motor (not shown) and driven to rotate. The mixture is introduced through an inlet 20 and discharged through a discharge outlet 22.

[0065] In the method for producing a cellulose fiber dispersion of the present invention, a pre-dispersion step may be further carried out before the dispersion step, in which a mixture of cellulose fibers containing metal ions or metal nanoparticles and a dispersion medium is pre-dispersed using a stirrer.

[0066] (Pre-dispersion process) In the pre-dispersion step, a mixture of cellulose fibers containing one or more metal ions or metal nanoparticles selected from the group consisting of Ag, Au, Pt, Pd, Ni, Mn, Fe, Ti, Al, Zn, and Cu and a dispersion medium is pre-dispersed using a stirrer. By providing the pre-dispersion step, clogging of the sample in the piping of the in-line stirrer during the dispersion step can be suppressed. When providing the pre-dispersion step, the concentration of the mixture after the pre-dispersion step should be 1 wt% or higher. Furthermore, in the pre-dispersion step, cellulose fibers with a high solids concentration may be diluted with a dispersion medium to prepare a mixture with a concentration of 1 wt% or higher.

[0067] When a pre-dispersion step is carried out in the present invention, the cellulose fibers to be subjected to the pre-dispersion step have a solids concentration of 1 wt % or more, preferably 2 wt % to 20 wt %, and more preferably 3 to 15 wt %.

[0068] The dehydration and drying method for producing cellulose fibers with a high solid content is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include spray drying, squeezing, air drying, hot air drying, freeze drying, spray drying, vacuum drying, etc. The drying apparatus is also not particularly limited, and a continuous tunnel dryer, band dryer, vertical dryer, vertical turbo dryer, multi-stage disk dryer, through-flow dryer, rotary dryer, flash dryer, spray dryer, cylindrical dryer, drum dryer, belt dryer, screw conveyor dryer, rotary dryer with heating tube, vibration transport dryer, batch box dryer, vacuum box dryer, agitator dryer, etc. can be used alone or in combination of two or more.

[0069] (mixer) When a preliminary dispersion step is performed, any agitator that can uniformly disperse cellulose fibers without shortening the fiber length of the cellulose fibers with high shear force (without substantially changing the pulp freeness) can be used as appropriate. For example, a disperser, an agitator, etc. can be used. The conditions for preliminary dispersion using an agitator are not particularly limited, but are, for example, 100 to 1500 rpm and 15 seconds to 30 minutes.

[0070] According to the production method of the present invention, a mixture of cellulose fibers containing metal ions or metal nanoparticles and a dispersion medium can be dispersed without causing a shortening of the fiber length, and a cellulose fiber dispersion with few undisaggregated fragments can be produced. [Example]

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, unless the method for measuring / calculating each value in each example is specifically stated, it was measured / calculated by the method described in the specification.

[0072] (Method for measuring average fiber length) The average fiber length was calculated by automatically analyzing images taken continuously using a Fiber Tester Plus (L&W Fiber Tester Plus, ABB). 20,000 fibers were photographed per sample. The results are shown in Table 1.

[0073] (removal rate) In the examples and comparative examples, 1.0 g of cellulose fiber (bone dry weight) was suspended in 1,000 mL of deionized water for the cellulose fiber aqueous dispersion before and after the dispersion treatment, and the suspension was filtered through a Buchner funnel to form a sheet. A light source was shone from behind the sheet to visualize the unmacerated fragments, and the number of unmacerated fragments was determined by visual observation. The removal rate of unmacerated fragments was calculated using the following formula and is shown in Table 1. Removal rate (%) = 1 - {number of undisaggregated pieces after treatment (pieces / 1.0g sheet) / number of undisaggregated pieces before treatment (pieces / 1.0g sheet)} x 100 A higher removal rate of undisintegrated fragments indicates better dispersibility of the undisintegrated fragments.

[0074] (Continuous operation) In the examples and comparative examples, after the dispersion treatment, the in-line agitator or turbine pump used was opened and inspected. Continuous operability was evaluated according to the following criteria, and the results are shown in Table 1. A: No clogging of the raw materials inside the mixer was observed. B: Blockage of raw materials inside the mixer was confirmed. The degree of blockage was small. C: Blockage of raw materials inside the mixer was confirmed. The degree of blockage was large.

[0075] (Production Example 1) (Production of oxidized cellulose fiber) 500 g (bone-dry) of bleached, unbeaten kraft pulp (85% brightness) derived from softwood was added to 50 L of an aqueous solution containing 3.9 g (0.05 mmol per g of bone-dry cellulose) of TEMPO (Sigma-Aldrich) and 51.4 g (1.0 mmol per g of bone-dry cellulose) of sodium bromide. The mixture was stirred until the pulp was uniformly dispersed. Sodium hypochlorite solution was added to the reaction system to adjust the sodium hypochlorite concentration to 6.0 mmol / g, initiating the oxidation reaction. During the reaction, the pH of the system decreased, but was gradually adjusted to 10 by the addition of 3 M sodium hydroxide solution. The reaction was terminated when the sodium hypochlorite was consumed and the pH no longer changed. The reaction mixture was separated by filtration through a glass filter, and the pulp was thoroughly washed with water to obtain oxidized cellulose fibers (carboxylated cellulose). The pulp yield was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g.

[0076] (Production of metal ion-containing cellulose fibers) Water was added to the resulting oxidized cellulose fibers to prepare a dispersion with a solids concentration of 2%. The pH was then adjusted to 9.0. CuCl2 (Wako Pure Chemical Industries, Ltd.) was then added with stirring to a concentration of 1.0 mmol / g per gram of oxidized cellulose fibers, and the mixture was stirred for an additional 30 minutes to incorporate Cu ions into the oxidized cellulose fibers. Unreacted metal salts were removed by washing with sufficient amounts of water and filtering twice, yielding an aqueous dispersion of Cu ions-containing cellulose fibers with a solids content of 3 wt%. The metal ion content relative to the cellulose fibers was 31.9 mg / g.

[0077] (Method for measuring the amount of carboxyl groups) 60 mL of a 0.5 wt % slurry (aqueous dispersion) of oxidized cellulose fiber was prepared, and a 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. After that, a 0.05 N aqueous sodium hydroxide solution was added dropwise, and the electrical conductivity was measured until the pH reached 11. The electrical conductivity was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid, where the change in electrical conductivity was gradual: Amount of carboxyl groups [mmol / g oxidized cellulose] = a [mL] x 0.05 / weight of oxidized cellulose [g]

[0078] Example 1 The aqueous dispersion of Cu ion-containing cellulose fibers obtained in Production Example 1 above, with a solids concentration of 3 wt% and an average fiber length of 1.82 mm, was pumped and passed once through a Homomic Line Mill (LM-V, manufactured by Primix Corporation), an in-line mixer connected to the pump and filled with water, at 3400 rpm and 22.2 L / min, to obtain an aqueous dispersion of Cu ion-containing oxidized cellulose fibers with a solids concentration of 2.43 wt%. The undisintegrated fragment removal rate of the resulting oxidized cellulose fiber aqueous dispersion was determined. The average fiber length was also measured. The in-line mixer was also inspected and its continuous operability was evaluated. The results are shown in Table 1.

[0079] Example 2 The aqueous dispersion of Cu ion-containing cellulose fibers having a solid content of 3 wt % and an average fiber length of 1.53 mm obtained in Production Example 1 above was pumped into an OHR mixer (manufactured by OHR Fluid Engineering Laboratory Co., Ltd., F-20, inlet diameter: 40A (outer diameter: 48.6 mm), outlet cross-sectional area: 415.3 mm), which was an in-line type mixing device filled with water connected to the pump. 2 Dispersion was performed by passing the mixture through a filter at 100 L / min once to obtain a Cu ion-containing oxidized cellulose fiber aqueous dispersion with a solids concentration of 2.66 wt%. The undisintegrated fragment removal rate of the obtained oxidized cellulose fiber aqueous dispersion was determined. The average fiber length was also measured. The in-line mixing equipment used was also inspected and its continuous operability was evaluated. The results are shown in Table 1.

[0080] (Comparative Example 1) The aqueous dispersion of Cu ion-containing cellulose fibers obtained in Production Example 1, which had a solids concentration of 3 wt% and an average fiber length of 1.79 mm, was diluted three times to prepare a slurry with a solids concentration of 0.95 wt%. This slurry was pumped into an OHR mixer (manufactured by OHR Fluid Engineering Laboratory Co., Ltd., F-8, inlet diameter 20A (outer diameter 27.2 mm), outlet cross-sectional area: 50.2 mm), which was an in-line mixing device filled with water and connected to the pump. 2 Dispersion was performed by passing the mixture through a filter at a rate of 8.8 L / min once, yielding an aqueous dispersion of Cu ion-containing oxidized cellulose fibers with a solids concentration of 0.88 wt%. The undisintegrated fragment removal rate of the resulting aqueous dispersion of oxidized cellulose fibers was determined. The average fiber length was also measured. The in-line mixing equipment used was also inspected and its continuous operability was evaluated. The results are shown in Table 1.

[0081] (Comparative Example 2) The aqueous dispersion of Cu ion-containing cellulose fibers obtained in Production Example 1 above, with a solids concentration of 3 wt% and an average fiber length of 1.68 mm, was dispersed by passing it through a turbine pump (NIKUNI, 20NED04Z-V) filled with water at 100 L / min once to obtain an aqueous dispersion of Cu ion-containing oxidized cellulose fibers with a solids concentration of 2.35 wt%. The undisintegrated fragment removal rate of the resulting aqueous dispersion of oxidized cellulose fibers was determined. The average fiber length was also measured. The turbine pump used was also overhauled and its continuous operability was evaluated. The results are shown in Table 1.

[0082] [Table 1]

[0083] As can be seen from Table 1, Examples 1 and 2, which were used for the method of producing a cellulose fiber dispersion, included a dispersion step in which a mixture of cellulose fibers containing one or more metal ions or metal nanoparticles selected from the group consisting of Ag, Au, Pt, Pd, Ni, Mn, Fe, Ti, Al, Zn, and Cu and a dispersion medium, with a concentration of 1 wt % or more, was dispersed by passing the mixture through an in-line stirrer, and had an excellent removal rate of undisintegrated fragments, and the resulting cellulose fiber dispersion had reduced shortening of the fiber length. [Explanation of symbols]

[0084] 2... Homomic line mill, 4... tubular body, 6... turbine, 8... first stator, 10... first stirring section, 12... rotor, 14... second stator, 16... second stirring section, 18... shaft, 20... intake port, 22... discharge port

Claims

1. A method for producing a cellulose fiber dispersion, comprising: The method includes a dispersion step of dispersing a mixture of cellulose fibers and a dispersion medium containing one or more metal ions or metal nanoparticles selected from the group consisting of Ag, Au, Pt, Pd, Ni, Mn, Fe, Ti, Al, Zn, and Cu, the mixture having a concentration of 1 wt % or more, by passing the mixture through an in-line stirrer; The in-line stirring device has a first stirring section and a second stirring section, The first stirring section includes a turbine and a first stator, The second stirring unit includes a rotor and a second stator, The method for producing a cellulose fiber dispersion, wherein the rotation speeds of the turbine and the rotor are 3,000 to 5,000 rpm.

2. The method for producing a cellulose fiber dispersion according to claim 1, further comprising a pre-dispersion step of pre-dispersing the mixture with a stirrer before the dispersion step.

3. 3. The method for producing a cellulose fiber dispersion according to claim 1, wherein the metal ions or metal nanoparticles contain either Ag or Cu.

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