Granules containing composite fibers of fibers and inorganic particles

Abstract

To provide highly flowable granules comprising a complex fiber of a fiber with inorganic particles.SOLUTION: Granules comprising a complex fiber of a fiber with inorganic particles are provided herein. The inventive granules have a particle size of 0.1 to 10 mm and a water content of less than 60%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to granules containing composite fibers of fibers and inorganic particles, and a method for producing the same. [Background technology]

[0002] Composite fibers with various properties have been developed by attaching inorganic particles to the fiber surface. For example, it is known that inorganic particles can be attached to the fiber surface by synthesizing inorganic substances in the presence of fibers.

[0003] For example, composite fibers of calcium carbonate and fiber (Patent Document 1), composite fibers of magnesium carbonate and fiber (Patent Document 2), composite fibers of calcium phosphate and fiber (Patent Document 3), composite fibers of hydrotalcite and fiber (Patent Document 4), and composite fibers of silica / alumina and fiber (Patent Document 5) are known.

[0004] Additionally, composite fibers in which most of the fiber surface is covered with inorganic particles (Patent Document 6) and composite fibers in which inorganic particles are attached to the fiber surface to improve flame retardancy (Patent Document 7) have also been reported. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication WO2015 / 152283 [Patent Document 2] International Publication No. WO2017 / 043580 [Patent Document 3] International Publication WO2017 / 043585 [Patent Document 4] International Publication WO2018 / 030521 [Patent Document 5] International Publication WO2019 / 163659 [Patent Document 6] International Publication WO2017 / 057154 [Patent Document 7] International Publication WO2019 / 159943 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide granules that contain composite fibers of fibers and inorganic particles and have excellent flowability. [Means for solving the problem]

[0007] As a result of extensive research into the above-mentioned problems, the present inventors have found that excellent granules can be obtained by controlling the moisture content before and during granulation, and have thus completed the present invention.

[0008] That is, the present invention includes the following aspects, but is not limited thereto. [1] Granules containing composite fibers of fibers and inorganic particles, with a particle size of 0.1 to 10 mm and a moisture content of less than 60%. [2] The granules according to [1], having an angle of repose of 30 to 58°. [3] Granules according to [1] or [2], wherein the inorganic particles comprise metal salts of calcium, magnesium, barium or aluminum, metal particles containing titanium, copper or zinc, or silicates. [4] The granules according to any one of [1] to [3], wherein the inorganic particles are hydrotalcite. [5] Granules according to any one of [1] to [4], wherein the weight ratio of inorganic particles in the granules is 10% or more. [6] The granules according to any one of [1] to [5], wherein the fibers are cellulose fibers. [7] Granules according to any one of [1] to [6], in which 15% or more of the fiber surface is covered with inorganic particles. [8] A method for producing granules according to any one of [1] to [7], comprising the steps of synthesizing inorganic particles in a liquid containing fibers to obtain composite fibers, and granulating the composite fibers into granules having a particle size of 0.1 to 10 mm. [9] The method according to [8], wherein the composite fiber is granulated while being dried in the granulation step.

[10] The method according to [8], wherein the moisture content of the composite fiber is reduced to less than 60% before granulation.

[11] The method according to [8], in which the composite fibers are pulverized and then granulated. [Effects of the Invention]

[0009] According to the present invention, granules can be obtained by processing composite fibers of fibers and inorganic particles into a granular form. The obtained granules have excellent fluidity and dispersibility, so they can be easily blended into other products to impart functionality to the other products according to the characteristics of the inorganic particles. In particular, when inorganic particles with a high deodorizing effect are used, granules with a high deodorizing effect can be obtained. Furthermore, by using composite fibers of fibers and inorganic particles as the raw material for the granules, functionality according to the characteristics of the inorganic particles can be imparted while reducing the amount of inorganic particles blended. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of the production apparatus used in Experiment 1 (P: pump). [Figure 2] 1 is an electron microscope photograph of sample a (magnification: 3000 times). [Figure 3] 1 is an electron microscope photograph of sample b (magnification: 3000 times). [Figure 4] 1 is an electron microscope photograph of sample c (magnification: 3000 times). [Figure 5] 1 is an electron microscope photograph of sample d (magnification: 3000 times). [Figure 6] 1 is an electron microscope photograph of sample f (magnification: 3000 times). [Figure 7] 1 is a photograph of the appearance of Sample 1 in Experiment 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention relates to granules containing composite fibers of fibers and inorganic particles. Granules generally refer to particles with a particle size larger than that of powder, with a particle size of 0.1 mm or greater. The composite fiber granules of the present invention can be obtained, for example, by solidifying powder and molding it into slightly larger particles. The moisture content (solid content) may be adjusted, if necessary, by drying or adding water. Composite fibers of fibers and inorganic particles may be obtained with a high moisture content. In such cases, the composite fibers may be dried and molded into slightly larger particles to produce the granules. Unlike powders, granules are less likely to generate dust or to coagulate when water is added, preventing dissolution. Furthermore, compared to composite fibers in the form of aqueous suspensions or pulp, granules have the advantage of being more easily dispersible in other products.

[0012] There are no particular limitations on the dryer used to dry the composite fiber of synthesized fibers and inorganic particles, but for example, a flash dryer, band dryer, spray dryer, vacuum dryer, low-temperature dryer, rotary dryer, plowshare mixer, oven, etc. can be suitably used. Among these, the use of a device that can perform drying and granulation in parallel, such as a plowshare mixer, is preferred because it makes it easier to produce granules of the desired particle size from the composite fiber. In addition, in the present invention, the composite fiber may be micronized before being granulated.

[0013] Water can be added dropwise through dedicated piping or an attached line as needed.The liquid to be added can be water (industrial water, tap water, distilled water, ultrapure water), a solution of metal ions, a dispersion of starch or CMC, or a solution containing anionic, cationic, or nonionic chemicals, and can be adjusted as needed depending on the application.

[0014] In the present invention, the particle size of the granules is 0.1 mm or more and 10 mm or less. The particle size of the granules is preferably 0.2 mm or more and 4 mm or less, more preferably 0.3 mm or more and 3 mm or less, and the particle size of the granules can also be 0.5 mm or more and 2 mm or less. If the particle size is too small, the granules tend to scatter, and if the particle size is too large, they are difficult to disperse when blended with other raw materials.

[0015] The moisture content (moisture concentration) before granulation can be, for example, 0 to 80%, preferably 2 to 70%, more preferably 4 to 60%, and particularly preferably 6 to 50%. If the moisture content before granulation is too high, drying will take a long time, reducing efficiency, while if the moisture content before granulation is too low, it may be difficult to uniformly disperse the raw materials depending on the granule processing equipment, so a moderate moisture content is more suitable for granule production.

[0016] The moisture content of the granules according to the present invention is less than 60%, and in a preferred embodiment, the moisture content of the granules is less than 45%, and may be less than 30%. By reducing the moisture content of the granules, the flowability of the granules can be improved.

[0017] The granules according to the present invention have excellent fluidity and are easy to handle. In a preferred embodiment, the angle of repose of the granules according to the present invention is 30 to 58°, more preferably 32 to 50°, and particularly preferably 34 to 40°. Granules with a small angle of repose can be obtained by reducing the moisture content of the granules or adjusting the particle size of the granules.

[0018] Synthesis of composite fibers In the present invention, composite fibers can be synthesized by synthesizing inorganic particles in a solution containing fibers such as cellulose fibers. This is because the fiber surface is a suitable site for the precipitation of inorganic particles, facilitating the synthesis of composite fibers. Composite fibers can be synthesized, for example, by stirring and mixing a solution containing fibers and inorganic particle precursors in an open reaction vessel to synthesize a composite, or by injecting an aqueous suspension containing fibers and inorganic particle precursors into a reaction vessel. As described below, cavitation bubbles can be generated when an aqueous suspension of inorganic precursors is injected into a reaction vessel, and inorganic particles can be synthesized in the presence of these bubbles. The inorganic particles can be synthesized on cellulose fibers by known reactions.

[0019] It is generally known that inorganic particles are generated through a process that involves a cluster state (where a small number of atoms and molecules are gathered, and then repeated aggregation and dispersal occurs), followed by nucleation (where the cluster transitions to a stable aggregate state, and once the critical size is reached, the captured atoms and molecules no longer disperse), and finally growth (where new atoms and molecules gather around the nuclei, resulting in larger particles). It is said that the higher the raw material concentration and reaction temperature, the more likely nucleation occurs. The composite fiber of the present invention can be obtained by efficiently bonding nuclei to the fibers and promoting particle growth by adjusting the raw material concentration, the degree of beating (specific surface area) of the pulp, the viscosity of the fiber-containing solution, the concentration and addition speed of the additive chemicals, the reaction temperature, and the stirring speed. This allows for efficient bonding of nuclei to the fibers and promotes particle growth, resulting in composite fibers in which the surfaces of cellulose fibers are tightly coated with inorganic particles.

[0020] In the present invention, the liquid may be injected under conditions that generate cavitation bubbles in the reaction vessel, or under conditions that do not generate cavitation bubbles. In either case, the reaction vessel is preferably a pressure vessel. Note that the pressure vessel in the present invention refers to a vessel to which a pressure of 0.005 MPa or more can be applied. When the conditions do not generate cavitation bubbles, the pressure inside the pressure vessel is preferably 0.005 MPa or more and 0.9 MPa or less in static pressure.

[0021] (cavitation bubbles) When synthesizing the composite fiber according to the present invention, inorganic particles can be precipitated in the presence of cavitation bubbles. In the present invention, cavitation is a physical phenomenon in which bubbles appear and disappear in a short period of time due to a pressure difference in a fluid flow, and is also called a cavitation phenomenon. Bubbles generated by cavitation (cavitation bubbles) are generated from tiny "bubble nuclei" of 100 microns or less that exist in the liquid when the pressure in the fluid becomes lower than the saturated vapor pressure for a very short period of time.

[0022] In the present invention, cavitation bubbles can be generated in a reaction vessel by known methods, such as injecting a fluid at high pressure, stirring the fluid at high speed, causing an explosion in the fluid, or using an ultrasonic vibrator (vibratory cavitation).

[0023] In the present invention, cavitation can be generated by using a reaction solution such as a raw material as the liquid to be injected, or by injecting some kind of fluid into a reaction vessel to generate cavitation bubbles. The fluid that forms the liquid jet may be any liquid, gas, or solid such as powder or pulp, as long as it is in a flowing state, or may be a mixture of these. Furthermore, if necessary, another fluid, such as carbon dioxide gas, can be added to the above fluid as a new fluid. The above fluid and the new fluid may be injected after being uniformly mixed, or they may be injected separately.

[0024] A liquid jet is a jet of liquid or fluid in which solid particles or gas are dispersed or mixed within a liquid, and refers to a liquid jet containing raw material slurry of pulp or inorganic particles or air bubbles. The air referred to here may include air bubbles caused by cavitation.

[0025] Cavitation occurs when a liquid is accelerated and the local pressure becomes lower than the vapor pressure of the liquid, so flow velocity and pressure are particularly important. For this reason, the cavitation number σ, a basic dimensionless number that represents the cavitation state, is desirably 0.001 to 0.5, preferably 0.003 to 0.2, and particularly preferably 0.01 to 0.1. If the cavitation number σ is less than 0.001, the effect is reduced because the pressure difference with the surroundings when the cavitation bubbles collapse is low, while if it is greater than 0.5, the pressure difference in the flow is low, making it difficult for cavitation to occur.

[0026] Furthermore, when generating cavitation by injecting the injection liquid through a nozzle or orifice pipe, the pressure of the injection liquid (upstream pressure) is desirably 0.01 MPa or more and 30 MPa or less, preferably 0.7 MPa or more and 20 MPa or less, and more preferably 2 MPa or more and 15 MPa or less. If the upstream pressure is less than 0.01 MPa, it is difficult to create a pressure difference with the downstream pressure, and the effect is small. Furthermore, if it is higher than 30 MPa, a special pump and pressure vessel are required, which increases energy consumption and is therefore cost-inefficient. On the other hand, the pressure inside the vessel (downstream pressure) is preferably 0.005 MPa or more and 0.9 MPa or less in static pressure. Furthermore, the ratio of the pressure inside the vessel to the pressure of the injection liquid is preferably in the range of 0.001 to 0.5.

[0027] In the present invention, inorganic particles can be synthesized by injecting the injection liquid under conditions that do not generate cavitation bubbles. Specifically, the pressure of the injection liquid (upstream pressure) is set to 2 MPa or less, preferably 1 MPa or less, and the pressure of the injection liquid (downstream pressure) is released, more preferably to 0.05 MPa or less.

[0028] The jet speed of the injected liquid is preferably in the range of 1 m / s to 200 m / s, and more preferably in the range of 20 m / s to 100 m / s. If the jet speed is less than 1 m / s, the pressure drop is low and cavitation is unlikely to occur, so the effect is weak. On the other hand, if the jet speed is more than 200 m / s, high pressure is required, and special equipment is needed, which is cost-inefficient.

[0029] In the present invention, cavitation may be generated within a reaction vessel where inorganic particles are synthesized. While a single-pass process is possible, it can also be circulated as many times as necessary. Furthermore, multiple cavitation generating means can be used in parallel or sequentially.

[0030] The liquid injection for generating cavitation may be performed in a vessel open to the atmosphere, but is preferably performed in a pressure vessel to control the cavitation.

[0031] When cavitation is generated by liquid injection, the solids concentration of the reaction solution is preferably 30% by weight or less, more preferably 20% by weight or less. This is because such a concentration makes it easier for cavitation bubbles to act uniformly on the reaction system. Furthermore, from the standpoint of reaction efficiency, it is preferable that the solids concentration of the aqueous suspension of slaked lime, which is the reaction solution, is 0.1% by weight or more.

[0032] In the present invention, for example, when synthesizing a composite of calcium carbonate and cellulose fiber, the pH of the reaction solution is basic at the start of the reaction but changes to neutral as the carbonation reaction progresses. Therefore, the reaction can be controlled by monitoring the pH of the reaction solution.

[0033] In the present invention, increasing the liquid injection pressure increases the flow rate of the injected liquid, which in turn reduces the pressure, resulting in more powerful cavitation. Furthermore, increasing the pressure inside the reaction vessel increases the pressure in the region where the cavitation bubbles collapse, increasing the pressure difference between the bubbles and the surrounding area, causing the bubbles to collapse violently and increasing the impact force. This also promotes the dissolution and dispersion of the introduced carbon dioxide gas. The reaction temperature is preferably between 0°C and 90°C, and more preferably between 10°C and 60°C. Since the impact force is generally thought to be greatest midway between the melting point and the boiling point, a temperature of around 50°C is suitable for aqueous solutions. However, even at temperatures below this range, the vapor pressure does not affect the reaction, and high effectiveness can be achieved within the above range.

[0034] When producing the composite fiber of the present invention, various known auxiliary agents can be further added, for example, a chelating agent, and specific examples thereof include polyhydroxycarboxylic acids such as citric acid, malic acid, and tartaric acid, dicarboxylic acids such as oxalic acid, sugar acids such as gluconic acid, aminopolycarboxylic acids such as iminodiacetic acid and ethylenediaminetetraacetic acid, and alkali metal salts thereof, alkali metal salts of polyphosphoric acids such as hexametaphosphoric acid and tripolyphosphoric acid, amino acids such as glutamic acid and aspartic acid, and alkali metal salts thereof, ketones such as acetylacetone, methyl acetoacetate, and allyl acetoacetate, sugars such as sucrose, and polyols such as sorbitol. Surface treatment agents that can be added include saturated fatty acids such as palmitic acid and stearic acid, unsaturated fatty acids such as oleic acid and linoleic acid, alicyclic carboxylic acids, resin acids such as abietic acid, their salts, esters, and ethers, alcohol-based surfactants, sorbitan fatty acid esters, amide-based and amine-based surfactants, polyoxyalkylene alkyl ethers, polyoxyethylene nonylphenyl ether, sodium alpha-olefin sulfonate, long-chain alkyl amino acids, amine oxides, alkylamines, quaternary ammonium salts, aminocarboxylic acids, phosphonic acids, polycarboxylic acids, and condensed phosphoric acids. Dispersants can also be used if necessary. Examples of dispersants include sodium polyacrylate, sucrose fatty acid esters, glycerin fatty acid esters, acrylic acid-maleic acid copolymer ammonium salts, methacrylic acid-naphthoxy polyethylene glycol acrylate copolymers, methacrylic acid-polyethylene glycol monomethacrylate copolymer ammonium salts, and polyethylene glycol monoacrylate. These can be used alone or in combination. They can be added either before or after the synthesis reaction. Such additives can be added in an amount of preferably 0.001 to 20%, more preferably 0.1 to 10%, based on the inorganic particles. Furthermore, in the present invention, the reaction can be a batch reaction or a continuous reaction. Generally, a batch reaction is preferred for the convenience of discharging the residue after the reaction.The scale of the reaction is not particularly limited, and the reaction may be carried out on a scale of 100 L or less, or on a scale of more than 100 L. The size of the reaction vessel may be, for example, about 10 L to 100 L, or about 100 L to 1000 L.

[0035] The reaction can also be controlled by adjusting the conductivity of the reaction solution or the reaction time, specifically by adjusting the residence time of the reactants in the reaction vessel. In addition, in the present invention, the reaction can also be controlled by stirring the reaction solution in the reaction vessel or by carrying out a multi-stage reaction.

[0036] In the present invention, the composite fiber, which is the reaction product, is obtained as a suspension, and can be stored in a storage tank or subjected to treatments such as concentration, dehydration, pulverization, classification, aging, and dispersion, as necessary. These can be performed using known processes and can be appropriately determined taking into account the intended use, energy efficiency, and the like. For example, concentration and dehydration treatments are performed using a centrifugal dehydrator, a sedimentation concentrator, or the like. Examples of centrifugal dehydrators include a decanter and a screw decanter. When a filter or dehydrator is used, there are no particular limitations on the type, and common types can be used. However, calcium carbonate cake can be produced by suitably using, for example, a pressure dehydrator such as a filter press, a drum filter, a belt press, or a tube press, or a vacuum drum dehydrator such as an Oliver filter. Grinding methods include ball mills, sand grinder mills, impact mills, high-pressure homogenizers, low-pressure homogenizers, Dyno-mills, ultrasonic mills, Kanda grinders, attritors, stone mills, vibration mills, cutter mills, jet mills, disintegrators, beaters, single-screw extruders, twin-screw extruders, ultrasonic agitators, and household juicer mixers. Classification methods include mesh sieves, outward or inward slit or round-hole screens, vibrating screens, heavy foreign matter cleaners, light foreign matter cleaners, reverse cleaners, and sieving testers. Dispersion methods include high-speed dispersers and low-speed kneaders.

[0037] The composite fiber of the present invention can be blended with a filler or pigment in the form of a suspension without being completely dehydrated, or can be dried to form a powder. In this case, there are no particular restrictions on the dryer, and for example, a flash dryer, a band dryer, a spray dryer, or the like can be suitably used.

[0038] The composite fiber of the present invention can be modified by known methods. For example, in one embodiment, the surface can be made hydrophobic to enhance compatibility with resins, etc.

[0039] In the present invention, water is used for preparing the suspension, etc., and as this water, ordinary tap water, industrial water, groundwater, well water, etc. can be used. In addition, ion-exchanged water, distilled water, ultrapure water, industrial wastewater, and water obtained during separation and dehydration of the reaction solution can also be suitably used.

[0040] In the present invention, the reaction solution in the reaction tank can be circulated. By circulating the reaction solution in this way and promoting stirring of the solution, the reaction efficiency can be increased and the desired composite of inorganic particles and fibers can be easily obtained.

[0041] inorganic particles In the present invention, the inorganic particles to be composited with the fibers are not particularly limited, but are preferably inorganic particles that are insoluble or poorly soluble in water. Since the synthesis of inorganic particles may be performed in an aqueous system and the fiber composite may be used in an aqueous system, it is preferable that the inorganic particles be insoluble or poorly soluble in water.

[0042] The inorganic particles referred to here are compounds of metal elements or nonmetal elements. Compounds of metal elements are compounds of metal cations (e.g., Na + , Ca 2+ , Mg 2+ , Al 3+ , Ba 2+ ) and anions (e.g., O 2- , O.H. - , CO3 2- , PO4 3- , SO42- , NO3-, Si2O3 2- , SiO3 2- , Cl - , F - , S 2- The term "inorganic salt" refers to what is generally called an inorganic salt, formed by ionic bonding of elements such as inorganic salts (e.g., silicic acid (SiO2)). Compounds of non-metallic elements include silicic acid (SiO2). In the present invention, it is preferred that at least a portion of the inorganic particles are metal salts of calcium, magnesium, or barium, or that at least a portion of the inorganic particles are metal salts of silicic acid or aluminum, or metal particles containing titanium, copper, silver, iron, manganese, cerium, or zinc.

[0043] These inorganic particles can be synthesized by known methods, including either a gas-liquid method or a liquid-liquid method. One example of a gas-liquid method is the carbon dioxide method, which can synthesize magnesium carbonate by reacting magnesium hydroxide with carbon dioxide. Liquid-liquid methods include neutralizing an acid (e.g., hydrochloric acid, sulfuric acid, etc.) with a base (e.g., sodium hydroxide, potassium hydroxide, etc.), reacting an inorganic salt with an acid or base, or reacting inorganic salts with each other. For example, barium sulfate can be obtained by reacting barium hydroxide with sulfuric acid, aluminum hydroxide can be obtained by reacting aluminum sulfate with sodium hydroxide, or calcium carbonate with aluminum sulfate can be used to obtain composite inorganic particles of calcium and aluminum. Furthermore, when synthesizing inorganic particles in this manner, any metal or nonmetal compound can be present in the reaction solution. In this case, the metal or nonmetal compound can be efficiently incorporated into the inorganic particles and composited. For example, when synthesizing calcium phosphate by adding phosphoric acid to calcium carbonate, adding titanium dioxide to the reaction solution can produce composite particles of calcium phosphate and titanium.

[0044] (Calcium carbonate) When calcium carbonate is synthesized, it can be synthesized by, for example, the carbon dioxide gas method, the soluble salt reaction method, the lime-soda method, the soda method, etc., and in a preferred embodiment, calcium carbonate is synthesized by the carbon dioxide gas method.

[0045] Generally, when producing calcium carbonate by the carbon dioxide gas method, lime is used as the calcium source, and calcium carbonate is synthesized through a slaking step in which water is added to quicklime (CaO) to obtain slaked lime (Ca(OH)2), and a carbonation step in which carbon dioxide (CO2) is blown into the slaked lime to obtain calcium carbonate (CaCO3). In this process, a suspension of slaked lime prepared by adding water to quicklime may be passed through a screen to remove low-solubility lime particles contained in the suspension. Alternatively, slaked lime may be used directly as the calcium source. In the present invention, when calcium carbonate is synthesized by the carbon dioxide gas method, the carbonation reaction may be carried out in the presence of cavitation bubbles.

[0046] When calcium carbonate is synthesized by the carbon dioxide gas method, the solids concentration of the aqueous suspension of slaked lime is preferably 0.1 to 40% by weight, more preferably 0.5 to 30% by weight, and even more preferably about 1 to 20% by weight. A low solids concentration results in low reaction efficiency and high production costs, while a too high solids concentration results in poor fluidity and reduced reaction efficiency. In the present invention, calcium carbonate is synthesized in the presence of cavitation bubbles, so that even if a suspension (slurry) with a high solids concentration is used, the reaction liquid and carbon dioxide gas can be suitably mixed.

[0047] The aqueous suspension containing slaked lime can be one commonly used for synthesizing calcium carbonate. For example, it can be prepared by mixing slaked lime with water or by slaking quicklime (calcium oxide) with water. The slaking conditions are not particularly limited, but for example, the CaO concentration can be 0.05% by weight or more, preferably 1% by weight or more, and the temperature can be 20 to 100°C, preferably 30 to 100°C. The average residence time in the slaking reaction tank (slaker) is also not particularly limited, but can be, for example, 5 minutes to 5 hours, and preferably 2 hours or less. Naturally, the slaker may be either a batch or continuous type. In the present invention, the carbonation reaction tank (carbonator) and the slaking reaction tank (slaker) may be separate, or a single reaction tank may be used as both the carbonation reaction tank and the slaking reaction tank.

[0048] In calcium carbonate synthesis, the nucleation reaction proceeds more easily with higher concentrations of raw materials (Ca ions and CO ions) in the reaction solution and higher temperatures. However, in the production of composite fibers, these conditions make it difficult for nuclei to adhere to the cellulose fibers, leading to the synthesis of free inorganic particles in the suspension. Therefore, to produce composite fibers with strongly bonded calcium carbonate, it is necessary to appropriately control the nucleation reaction. Specifically, this can be achieved by optimizing the Ca ion and pulp concentrations and slowing the CO 2 supply rate per hour. For example, the Ca ion concentration in the reaction vessel is preferably 0.01 mol / L or higher but less than 0.20 mol / L. If the concentration is less than 0.01 mol / L, the reaction proceeds slowly, while if it is 0.20 mol / L or higher, the synthesis of free inorganic particles in the suspension is favorable. The pulp concentration is preferably 0.5% or higher but less than 4.0%. If the concentration is less than 0.5%, the reaction proceeds slowly due to reduced collision of raw materials with the fibers, while if it is 4.0% or higher, poor mixing prevents the production of a uniform composite. The amount of CO2 supplied per hour is preferably 0.001 mol / min or more and less than 0.060 mol / min per 1 L of reaction solution. If the amount is less than 0.001 mol / min, the reaction will not proceed smoothly, and if the amount is more than 0.060 mol / min, inorganic particles will be easily synthesized free in the suspension.

[0049] (Magnesium carbonate) When synthesizing magnesium carbonate, known methods can be used. For example, magnesium bicarbonate can be synthesized from magnesium hydroxide and carbon dioxide, and then basic magnesium carbonate can be synthesized from the magnesium bicarbonate via normal magnesium carbonate. Although magnesium carbonate can be obtained as magnesium bicarbonate, normal magnesium carbonate, basic magnesium carbonate, etc. depending on the synthesis method, it is particularly preferable that the magnesium carbonate used in the fiber composite of the present invention be basic magnesium carbonate. This is because magnesium bicarbonate has relatively low stability, and normal magnesium carbonate, which is a columnar (needle) crystal, may be difficult to adhere to fibers. On the other hand, by chemically reacting magnesium carbonate in the presence of fibers to produce basic magnesium carbonate, a fiber composite of magnesium carbonate and fibers can be obtained in which the fiber surface is coated with scales or the like.

[0050] In the present invention, the reaction solution in the reaction tank can be circulated. By circulating the reaction solution in this way and increasing the contact between the reaction solution and carbon dioxide gas, the reaction efficiency can be improved and the desired inorganic particles can be easily obtained.

[0051] In the present invention, a gas such as carbon dioxide (carbonic acid gas) can be blown into a reaction vessel and mixed with the reaction liquid. According to the present invention, carbon dioxide gas can be supplied to the reaction liquid without a gas supply device such as a fan or blower, and the reaction can be carried out efficiently because the carbon dioxide gas is broken down into fine particles by cavitation bubbles.

[0052] In the present invention, there is no particular limitation on the carbon dioxide concentration of the carbon dioxide-containing gas, but a higher carbon dioxide concentration is preferable. Furthermore, there is no limitation on the amount of carbon dioxide gas introduced into the injector, and it can be selected appropriately.

[0053] The carbon dioxide-containing gas of the present invention may be substantially pure carbon dioxide gas or a mixture with other gases. For example, in addition to carbon dioxide gas, a gas containing an inert gas such as air or nitrogen can be used as the carbon dioxide-containing gas. In addition to carbon dioxide gas (carbonic acid gas), the carbon dioxide-containing gas can also be suitably exhaust gas emitted from incinerators in paper mills, coal boilers, heavy oil boilers, etc. In addition, the carbon dioxide reaction can also be carried out using carbon dioxide generated from the lime calcination process.

[0054] In the synthesis of magnesium carbonate, the nucleation reaction proceeds more easily with higher concentrations of raw materials (Mg ions, CO ions) in the reaction solution and higher temperatures. However, when producing composite fibers, these conditions make it difficult for nuclei to adhere to the cellulose fibers, leading to the synthesis of inorganic particles free in the suspension. Therefore, to produce composite fibers with strongly bonded magnesium carbonate, it is necessary to appropriately control the nucleation reaction. Specifically, this can be achieved by optimizing the Mg ion and pulp concentrations and slowing the CO supply rate per hour. For example, the Mg ion concentration in the reaction vessel is preferably 0.0001 mol / L or more but less than 0.20 mol / L. If the concentration is less than 0.0001 mol / L, the reaction proceeds slowly, while if it is 0.20 mol / L or more, the synthesis of inorganic particles free in the suspension is facilitated. The pulp concentration is preferably 0.5% or more but less than 4.0%. If the concentration is less than 0.5%, the raw materials collide with the fibers less frequently, making the reaction difficult to proceed, while if it is 4.0% or more, poor mixing makes it impossible to obtain a uniform composite. The CO2 supply rate per hour should be between 0.001 mol / min and 0.060 mol / min per liter of reaction solution. If it is less than 0.001 mol / min, the reaction will proceed slowly, and if it is more than 0.060 mol / min, inorganic particles will be easily synthesized that are free in the suspension.

[0055] (barium sulfate) When synthesized, barium sulfate (BaSO4) is an ionic crystalline compound composed of barium ions and sulfate ions. It is often in the form of plates or columns and is poorly soluble in water. Pure barium sulfate is a colorless crystal, but when impurities such as iron, manganese, strontium, and calcium are present, it becomes yellowish-brown or black-gray and translucent. It is obtained as a natural mineral, but can also be synthesized through chemical reactions. In particular, products synthesized through chemical reactions are used in medicine (as X-ray contrast agents), and its chemical stability is widely used in paints, plastics, storage batteries, and other applications.

[0056] In the present invention, a composite of barium sulfate and fiber can be produced by synthesizing barium sulfate in a solution in the presence of fiber. For example, methods include reacting an acid (such as sulfuric acid) with a base by neutralization, reacting an inorganic salt with an acid or base, or reacting inorganic salts with each other. For example, barium sulfate can be obtained by reacting barium hydroxide with sulfuric acid or aluminum sulfate, or barium sulfate can be precipitated by adding barium chloride to an aqueous solution containing a sulfate.

[0057] In the synthesis of barium sulfate, the nucleation reaction proceeds more easily with higher concentrations of raw materials (Ba ions, SO4 ions) in the solution and higher temperatures. However, when producing composite fibers, these conditions make it difficult for nuclei to adhere to the cellulose fibers, leading to the synthesis of inorganic particles free in the suspension. Therefore, to produce composite fibers with strongly bonded barium sulfate, it is necessary to appropriately control the nucleation reaction. Specifically, this can be achieved by optimizing the Ba ion and pulp concentrations and slowing the supply rate of SO4 ions per hour. For example, the Ba ion concentration in the reaction vessel is preferably 0.01 mol / L or more but less than 0.20 mol / L. If it is less than 0.01 mol / L, the reaction proceeds slowly, while if it is 0.20 mol / L or more, it is easy to synthesize inorganic particles free in the suspension. The pulp concentration is preferably 0.5% or more but less than 4.0%. If the concentration is less than 0.5%, the raw materials collide with the fibers less frequently, making the reaction difficult to proceed, while if it is 4.0% or more, poor mixing makes it impossible to obtain a uniform composite. The supply rate of SO4 ions per hour should be between 0.005 mol / min and 0.080 mol / min per liter of reaction solution. If it is less than 0.001 mol / min, the reaction will proceed slowly, and if it is more than 0.080 mol / min, inorganic particles will be easily synthesized free in the suspension.

[0058] (hydrotalcite) Hydrotalcite can be synthesized by known methods. For example, fibers are immersed in a reaction vessel with a carbonate aqueous solution containing carbonate ions that form the intermediate layer and an alkaline solution (such as sodium hydroxide), followed by the addition of an acid solution (a metal salt aqueous solution containing divalent and trivalent metal ions that form the base layer). The temperature, pH, and other parameters are controlled to synthesize hydrotalcite by a coprecipitation reaction. Alternatively, hydrotalcite can be synthesized by immersing fibers in an acid solution (a metal salt aqueous solution containing divalent and trivalent metal ions that form the base layer) in a reaction vessel, followed by the dropwise addition of a carbonate aqueous solution containing carbonate ions that form the intermediate layer and an alkaline solution (such as sodium hydroxide), followed by the coprecipitation reaction by controlling the temperature, pH, and other parameters. While the reaction is typically carried out at atmospheric pressure, there is also a method of obtaining hydrotalcite by a hydrothermal reaction using an autoclave or the like (see JP-A-60-6619).

[0059] In the present invention, various chlorides, sulfides, nitrates, and sulfates of magnesium, zinc, barium, calcium, iron, copper, cobalt, nickel, and manganese can be used as sources of divalent metal ions constituting the basic layer, and various chlorides, sulfides, nitrates, and sulfates of aluminum, iron, chromium, and gallium can be used as sources of trivalent metal ions constituting the basic layer.

[0060] In the present invention, carbonate ions, nitrate ions, chloride ions, sulfate ions, phosphate ions, etc. can be used as interlayer anions. When carbonate ions are used as interlayer anions, sodium carbonate is used as a supply source. However, sodium carbonate can be replaced with a gas containing carbon dioxide (carbonic acid gas), which may be substantially pure carbon dioxide gas or a mixture with other gases. For example, exhaust gases emitted from incinerators, coal boilers, heavy oil boilers, etc. in paper mills can be suitably used as carbon dioxide-containing gases. Alternatively, the carbon dioxide generated during the lime calcination process can be used to carry out the carbonation reaction.

[0061] In the synthesis of hydrotalcite, the higher the concentration of raw materials (metal ions, CO3 ions, etc., that constitute the base layer) in the solution and the higher the temperature, the more likely the nucleation reaction will proceed. However, under these conditions, when producing composite fibers, the nuclei are less likely to be attached to the cellulose fibers, and inorganic particles are more likely to be synthesized free in the suspension. Therefore, to produce composite fibers with strongly bonded hydrotalcite, it is necessary to appropriately control the nucleation reaction. Specifically, this can be achieved by optimizing the CO3 ion and pulp concentrations and slowing the supply rate of metal ions per hour. For example, the CO3 ion concentration in the reaction vessel is preferably 0.01 mol / L or more but less than 0.80 mol / L. If it is less than 0.01 mol / L, the reaction will proceed slowly, while if it is 0.80 mol / L or more, inorganic particles are more likely to be synthesized free in the suspension. The pulp concentration is preferably 0.5% or more but less than 4.0%. If the concentration is less than 0.5%, the raw materials collide with the fibers less frequently, slowing the reaction. If the concentration is more than 4.0%, poor mixing prevents a uniform composite from being obtained. The supply rate of metal ions per hour depends on the type of metal. For example, in the case of Mg ions, a rate of 0.001 mol / min or more but less than 0.010 mol / min per 1 L of reaction solution is desirable, with 0.001 mol / min or more but less than 0.005 mol / min being even more desirable. If the supply rate is less than 0.001 mol / min, the reaction will proceed slowly. If the supply rate is more than 0.010 mol / min, inorganic particles will be easily released from the suspension.

[0062] (alumina / silica) Alumina and / or silica can be synthesized by known methods. When one or more inorganic acids or aluminum salts are used as starting materials for the reaction, an alkali silicate is added to synthesize the alumina and / or silica. Synthesis can also be performed by using an alkali silicate as a starting material and adding one or more inorganic acids or aluminum salts. However, using an inorganic acid and / or aluminum salt as a starting material results in better adhesion of the product to the fibers. The inorganic acid is not particularly limited, and examples include sulfuric acid, hydrochloric acid, and nitric acid. Among these, sulfuric acid is particularly preferred from the standpoints of cost and handling. Examples of aluminum salts include aluminum sulfate, aluminum chloride, polyaluminum chloride, alum, and potassium alum, with aluminum sulfate being particularly preferred. Examples of alkali silicates include sodium silicate and potassium silicate, with sodium silicate being preferred due to its ease of availability. Any molar ratio of silicic acid to alkali is acceptable, but the commonly available No. 3 silicic acid has a molar ratio of SiO2:Na2O=3 to 3.4:1, which can be suitably used.

[0063] In the present invention, when producing composite fibers having silica and / or alumina attached to the fiber surface, it is preferable to synthesize silica and / or alumina on the fibers while maintaining the pH of the reaction solution containing the fibers at 4.6 or less. Although the details of why composite fibers with well-coated fiber surfaces can be obtained in this manner are not fully understood, it is thought that maintaining a low pH increases the ionization rate to trivalent aluminum ions, resulting in composite fibers with high coverage and fixation rates.

[0064] In the synthesis of silica and / or alumina, the nucleation reaction proceeds more easily with higher concentrations of raw materials (silicate ions, aluminum ions) in the reaction solution and higher temperatures. However, when producing composite fibers, these conditions make it difficult for nuclei to adhere to the cellulose fibers, leading to the synthesis of free inorganic particles in the suspension. Therefore, to produce composite fibers with strongly bonded silica and / or alumina, it is necessary to appropriately control the nucleation reaction. Specifically, this can be achieved by optimizing the pulp concentration and slowing the amount of added silicate ions and aluminum ions per hour. For example, a pulp concentration of 0.5% or more but less than 4.0% is preferred. At concentrations below 0.5%, the raw materials collide less frequently with the fibers, slowing the reaction. At concentrations above 4.0%, poor mixing prevents the production of a uniform composite. The supply rate of added silicate ions and aluminum ions per hour, for example, in the case of aluminum ions, is preferably 0.001 mol / min or more per 1 L of reaction solution, more preferably 0.01 mol / min or more, and is preferably less than 0.5 mol / min, more preferably less than 0.050 mol / min. If the rate is less than 0.001 mol / min, the reaction does not proceed easily, and if the rate is 0.050 mol / min or more, inorganic particles are likely to be synthesized free in the suspension.

[0065] In one preferred embodiment, the average primary particle diameter of the inorganic particles in the composite fiber of the present invention can be, for example, 1.5 μm or less, but the average primary particle diameter can also be 1200 nm or less, 900 nm or less, or even 200 nm or less, or 150 nm or less. The average primary particle diameter of the inorganic particles can also be 10 nm or more. The average primary particle diameter can be measured using an electron microscope photograph.

[0066] (aluminum hydroxide) Aluminum hydroxide is an ionic crystalline compound composed of aluminum ions and hydroxide ions, represented by Al(OH)3, and is often in granular form. It is poorly soluble in water. Products synthesized by chemical reactions are used in pharmaceuticals and adsorbents, and are also used as flame retardants and non-combustible agents, taking advantage of their property of releasing water when heated.

[0067] In the present invention, a composite of aluminum hydroxide and fibers can be produced by synthesizing aluminum hydroxide in a solution in the presence of fibers. Examples of methods include reacting an acid (such as sulfuric acid) with a base by neutralization, reacting an inorganic salt with an acid or base, or reacting inorganic salts with each other. For example, aluminum hydroxide can be obtained by reacting sodium hydroxide with aluminum sulfate, or aluminum hydroxide can be precipitated by adding aluminum chloride to an aqueous solution containing an alkali salt.

[0068] In the synthesis of aluminum hydroxide, the nucleation reaction proceeds more easily with higher concentrations of raw materials (Al ions, OH ions) in the solution and higher temperatures. However, in the production of composite fibers, these conditions make it difficult for nuclei to adhere to the cellulose fibers, leading to the synthesis of inorganic particles free in the suspension. Therefore, to produce composite fibers with strongly bonded aluminum hydroxide, it is necessary to appropriately control the nucleation reaction. Specifically, this can be achieved by optimizing the OH ion and pulp concentrations and slowing the supply of Al ions per hour. For example, the OH ion concentration in the reaction vessel is preferably 0.01 mol / L or more but less than 0.50 mol / L. If the concentration is less than 0.01 mol / L, the reaction proceeds slowly, while if the concentration is 0.50 mol / L or more, the synthesis of inorganic particles free in the suspension is favorable. The pulp concentration is preferably 0.5% or more but less than 4.0%. If the concentration is less than 0.5%, the reaction proceeds slowly due to reduced collision of raw materials with the fibers, while if the concentration is 4.0% or more, poor mixing prevents the production of a uniform composite. The supply rate of Al ions per hour is preferably 0.001 mol / min or more and less than 0.050 mol / min per 1 L of reaction solution. If it is less than 0.001 mol / min, the reaction will not proceed smoothly, and if it is 0.050 mol / min or more, inorganic particles will be easily synthesized free in the suspension.

[0069] fiber The composite fiber used in the present invention is a composite of fibers such as cellulose fibers and inorganic particles. Examples of cellulose fibers that constitute the composite include, without limitation, natural cellulose fibers, as well as regenerated fibers (semi-synthetic fibers) such as rayon and lyocell, and synthetic fibers. Examples of raw materials for cellulose fibers include pulp fibers (wood pulp and non-wood pulp), cellulose nanofibers, bacterial cellulose, animal-derived cellulose such as sea squirts, and algae. Wood pulp can be produced by pulping wood raw materials. Examples of wood raw materials include conifers such as red pine, black pine, Abies sachalinensis, Siberian spruce, red pine, larch, fir, hemlock, cedar, cypress, larch, Shirabe, spruce, hiba, Douglas fir, hemlock, white fir, spruce, balsam fir, cedar, pine, Merkusima pine, and radiata pine, as well as mixtures thereof; and hardwoods such as beech, birch, alder, oak, tabu, chinquapin, white birch, cottonwood, poplar, ash, mud willow, eucalyptus, mangrove, lauan, and acacia, as well as mixtures thereof.

[0070] The method for pulping natural materials such as wood raw materials (woody raw materials) is not particularly limited, and examples include pulping methods commonly used in the papermaking industry. Wood pulp can be classified by pulping method, and examples include chemical pulp obtained by cooking using methods such as the Kraft method, sulfite method, soda method, and polysulfide method; mechanical pulp obtained by pulping using mechanical forces such as a refiner or grinder; semi-chemical pulp obtained by chemical pretreatment followed by mechanical pulping; recycled paper pulp; and deinked pulp. Wood pulp may be in an unbleached state (before bleaching) or in a bleached state (after bleaching).

[0071] Examples of non-wood pulp include cotton, hemp, sisal, Manila hemp, flax, straw, bamboo, bagasse, kenaf, sugarcane, corn, rice straw, paper mulberry, and mitsumata.

[0072] The pulp fibers may be either unbeaten or beaten, and the choice may be made depending on the physical properties of the composite sheet, but beating is preferred, as this is expected to improve the sheet strength and promote the fixation of inorganic particles.

[0073] These cellulose raw materials can also be further processed to produce powdered cellulose, chemically modified cellulose such as oxidized cellulose, and cellulose nanofibers (CNF) (microfibrillated cellulose (MFC), TEMPO-oxidized CNF, phosphate-esterified CNF, carboxymethylated CNF, mechanically pulverized CNF, etc.). The powdered cellulose used in the present invention may be, for example, a cylindrical crystalline cellulose powder with a consistent particle size distribution, produced by purifying and drying the undecomposed residue obtained after acid hydrolysis of selected pulp, followed by grinding and sieving. Alternatively, commercially available products such as KC Floc (Nippon Paper Industries Co., Ltd.), Ceolus (Asahi Kasei Chemicals Corporation), and Avicel (FMC) may also be used. The degree of polymerization of the cellulose in the powdered cellulose is preferably approximately 100 to 1500, the crystallinity of the powdered cellulose measured by X-ray diffraction is preferably 70 to 90%, and the volume average particle size measured by a laser diffraction particle size analyzer is preferably 500 nm or more and 100 μm or less.

[0074] The oxidized cellulose used in the present invention can be obtained by oxidizing in water using an oxidizing agent in the presence of, for example, an N-oxyl compound, and a compound selected from the group consisting of bromides, iodides, or mixtures thereof. Cellulose nanofibers can be produced by defibrating the above-mentioned cellulose raw material. Examples of defibration methods include mechanically grinding or beating an aqueous suspension of cellulose or chemically modified cellulose such as oxidized cellulose using a refiner, high-pressure homogenizer, grinder, single- or multi-screw kneader, or bead mill. Cellulose nanofibers may be produced by one or a combination of the above methods. The fiber diameter of the produced cellulose nanofibers can be confirmed by electron microscopy, and is preferably in the range of 5 nm to 300 nm. When producing these cellulose nanofibers, any compound can be added before and / or after defibrating and / or micronizing the cellulose to react with the cellulose nanofibers, thereby modifying the hydroxyl groups. The functional groups to be modified include an acetyl group, an ester group, an ether group, a ketone group, a formyl group, a benzoyl group, an acetal, a hemiacetal, an oxime, an isonitrile, an allene, a thiol group, a urea group, a cyano group, a nitro group, an azo group, an aryl group, an aralkyl group, an amino group, an amido group, an imido group, an acryloyl group, a methacryloyl group, a propionyl group, a propioloyl group, a butyryl group, a 2-butyryl group, a pentanoyl group, a hexanoyl group, a heptanoyl group, an octanoyl group, a nonanoyl group, a decanoyl group, an undecanoyl group, a dodecanoyl group, a myristoyl group, a palmitoyl group, a sucralose ... Examples of the alkyl groups include acyl groups such as a tearoyl group, a pivaloyl group, a benzoyl group, a naphthoyl group, a nicotinoyl group, an isonicotinoyl group, a furoyl group, and a cinnamoyl group; isocyanate groups such as a 2-methacryloyloxyethylisocyanoyl group; alkyl groups such as a methyl group, an ethyl group, a propyl group, a 2-propyl group, a butyl group, a 2-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a myristyl group, a palmityl group, and a stearyl group; and oxirane groups, oxetane groups, oxyl groups, thiirane groups, and thietane groups.Hydrogen in these substituents may be substituted with functional groups such as hydroxyl groups or carboxyl groups. Furthermore, a portion of the alkyl group may be an unsaturated bond. The compounds used to introduce these functional groups are not particularly limited, and examples include compounds having a phosphoric acid-derived group, compounds having a carboxylic acid-derived group, compounds having a sulfuric acid-derived group, compounds having a sulfonic acid-derived group, compounds having an alkyl group, and compounds having an amine-derived group. The compounds having a phosphate group are not particularly limited, and examples thereof include phosphoric acid, and lithium salts of phosphoric acid such as lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, and lithium polyphosphate. Further examples thereof include sodium salts of phosphoric acid such as sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, and sodium polyphosphate. Further examples thereof include potassium salts of phosphoric acid such as potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate. Further examples thereof include ammonium salts of phosphoric acid such as ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium polyphosphate. Among these, from the viewpoint of high efficiency of phosphate group introduction and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, and ammonium salt of phosphoric acid are preferred, with sodium dihydrogen phosphate and disodium hydrogen phosphate being more preferred, but are not particularly limited. Compounds having a carboxyl group are not particularly limited, but include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Acid anhydrides of compounds having a carboxyl group are not particularly limited, but include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Derivatives of compounds having a carboxyl group are not particularly limited, but include imidized products of acid anhydrides of compounds having a carboxyl group, and derivatives of acid anhydrides of compounds having a carboxyl group.The imidized products of acid anhydrides of compounds having carboxyl groups are not particularly limited, and examples include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide. The derivatives of acid anhydrides of compounds having carboxyl groups are also not particularly limited. Examples include acid anhydrides of compounds having carboxyl groups, such as dimethylmaleic anhydride, diethylmaleic anhydride, and diphenylmaleic anhydride, in which at least some of the hydrogen atoms are substituted with substituents (e.g., alkyl groups, phenyl groups, etc.). Among the compounds having a carboxylic acid-derived group, maleic anhydride, succinic anhydride, and phthalic anhydride are preferred because of their ease of industrial application and gasification, but are not particularly limited. Furthermore, cellulose nanofibers may be modified by physically adsorbing the modifying compound to the cellulose nanofibers, even without chemical bonding. Examples of physically adsorbing compounds include surfactants, and any of anionic, cationic, and nonionic surfactants may be used. If the above modification is performed before cellulose is defibrated and / or pulverized, these functional groups can be eliminated after defibration and / or pulverization, restoring the original hydroxyl groups. By applying the above-mentioned modifications, it is possible to promote the defibration of cellulose nanofibers and make it easier to mix the cellulose nanofibers with various substances when using them.

[0075] The fibers described above may be used alone or in combination. For example, fibrous materials recovered from wastewater from a paper mill may be supplied to the carbonation reaction of the present invention. By supplying such materials to the reaction tank, various composite particles can be synthesized, and fibrous particles can also be synthesized.

[0076] In the present invention, in addition to fibers, substances that can be incorporated into the inorganic particles that are the product to produce composite particles can be used. In the present invention, fibers such as pulp fibers are used, but it is also possible to produce composite particles that further incorporate these substances by synthesizing inorganic particles in a solution containing inorganic particles, organic particles, polymers, etc.

[0077] The fiber length of the composite fibers is not particularly limited, but for example, the average fiber length can be about 0.1 μm to 15 mm, or may be 1 μm to 12 mm, 100 μm to 10 mm, 400 μm to 8 mm, etc. Among these, in the present invention, the average fiber length is preferably 400 μm or more (0.4 mm or more).

[0078] The average fiber diameter of the composite fibers is not particularly limited, but may be, for example, about 1 nm to 100 μm, or may be 500 nm to 100 μm, 1 μm to 90 μm, 3 μm to 50 μm, 5 μm to 30 μm, etc. Among these, in the present invention, an average fiber diameter of 500 nm or more is preferred because it can improve production efficiency in subsequent processes.

[0079] The average fiber length and average fiber diameter of the fibers can be measured using a fiber length measuring device, such as a Valmet Fractionator (manufactured by Valmet).

[0080] The fibers to be composited are preferably used in an amount such that 15% or more of the fiber surface is covered with the inorganic particles. For example, the weight ratio of the fibers to the inorganic particles can be 5 / 95 to 95 / 5, or it can also be 10 / 90 to 90 / 10, 20 / 80 to 80 / 20, 30 / 70 to 70 / 30, or 40 / 60 to 60 / 40.

[0081] In a preferred embodiment, the composite fiber according to the present invention has 15% or more of the fiber surface covered with inorganic particles. When the cellulose fiber surface is covered with such an area ratio, the characteristics attributable to the inorganic particles are enhanced, while the characteristics attributable to the fiber surface are diminished.

[0082] The composite fiber according to the present invention can be used in various forms, such as powder, pellets, molds, aqueous suspensions, pastes, sheets, boards, blocks, and other forms. Furthermore, the composite fiber can be used as a main component together with other materials to form molds, particles, pellets, and other shaped articles. There are no particular limitations on the dryer used for drying to form a powder, and suitable dryers include flash dryers, band dryers, and spray dryers.

[0083] The conjugated fiber according to the present invention can be used in a wide variety of applications, including paper, fibers, cellulose-based composite materials, filter materials, paints, plastics and other resins, rubber, elastomers, ceramics, glass, tires, building materials (such as asphalt, asbestos, cement, boards, concrete, bricks, tiles, plywood, fiberboard, ceiling materials, wall materials, flooring materials, and roofing materials), furniture, various carriers (such as catalyst carriers, pharmaceutical carriers, pesticide carriers, and microbial carriers), adsorbents (for impurity removal, deodorization, and dehumidification), antibacterial agents, antiviral agents, wrinkle prevention agents, clay, abrasives, friction materials, modifiers, repair materials, heat insulation materials, heat-resistant materials, heat-dissipating materials, moisture-proof materials, water-repellent materials, water-resistant materials, light-blocking materials, sealants, shielding materials, insect repellents, adhesives, medical materials, paste materials, discoloration prevention agents, radio wave absorbing materials, insulating materials, sound-proofing materials, interior materials, vibration-damping materials, semiconductor encapsulation materials, and radiation-shielding materials. It can also be used as various fillers and coating agents for the above applications. Among these, adsorbents, antibacterial materials, antiviral agents, friction materials, radiation shielding materials, flame retardant materials, building materials, and heat insulating materials are preferred.

[0084] The conjugated fiber of the present invention may be applied to papermaking applications, such as printing paper, newspaper, inkjet paper, PPC paper, kraft paper, fine paper, coated paper, lightly coated paper, wrapping paper, tissue paper, colored fine paper, cast coated paper, non-carbon paper, label paper, thermal paper, various fancy papers, water-soluble paper, release paper, casting paper, wallpaper base paper, flame-retardant paper (non-combustible paper), laminate base paper, printed electronics paper, battery separator, cushion paper, tracing paper, impregnated paper, ODP paper, building paper, decorative paper, envelope paper, tape paper, heat exchange paper, synthetic fiber paper, sterilized paper, waterproof paper, oil-resistant paper, heat-resistant paper, photocatalytic paper, decorative paper (such as grease-blotting paper), various sanitary papers (toilet paper, tissue paper, wipers, diapers, sanitary products, etc.), tobacco paper, paperboard (liner, core base paper, white paperboard, etc.), paper plate base paper, cup base paper, baking paper, abrasive paper, synthetic paper, etc. That is, according to the present invention, a composite of inorganic particles and fibers having a small primary particle size and a narrow particle size distribution can be obtained, thereby exhibiting properties different from those of conventional inorganic fillers having particle sizes of more than 2 μm. Furthermore, unlike when inorganic particles are simply blended with fibers, when inorganic particles are composited with fibers, not only are the inorganic particles more easily retained in a sheet, but also a sheet can be obtained in which the inorganic particles are uniformly dispersed without agglomeration. In a preferred embodiment, electron microscope observation has revealed that the inorganic particles of the present invention are not only fixed on the outer surface and inside the lumens of the fibers, but also formed inside the microfibrils.

[0085] The composite fibers of the present invention can be used in combination with particles commonly referred to as inorganic and organic fillers, as well as various fibers. Examples of inorganic fillers include calcium carbonate (light calcium carbonate, heavy calcium carbonate), magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay (kaolin, calcined kaolin, delaminated kaolin), talc, zinc oxide, zinc stearate, titanium dioxide, silica produced from sodium silicate and mineral acid (white carbon, silica / calcium carbonate complex, silica / titanium dioxide complex), white clay, bentonite, diatomaceous earth, calcium sulfate, zeolite, inorganic fillers recycled from ash obtained during the deinking process, and inorganic fillers formed as complexes with silica or calcium carbonate during the regeneration process. As calcium carbonate-silica composites, amorphous silica such as white carbon may be used in combination with calcium carbonate and / or light calcium carbonate-silica composites. Examples of organic fillers include urea-formaldehyde resin, polystyrene resin, phenolic resin, microhollow particles, acrylamide complexes, wood-derived materials (microfibers, microfibril fibers, powdered kenaf), modified insolubilized starch, and ungelatinized starch. Fibers include natural fibers such as cellulose, as well as synthetic fibers artificially synthesized from raw materials such as petroleum, regenerated fibers (semi-synthetic fibers) such as rayon and lyocell, and inorganic fibers. Natural fibers include protein-based fibers such as wool, silk, and collagen fibers, and complex carbohydrate fibers such as chitin-chitosan and alginate fibers. Cellulosic raw materials include pulp fibers (wood pulp and non-wood pulp), bacterial cellulose, animal-derived cellulose such as sea squirts, and algae. Wood pulp can be produced by pulping wood raw materials.Examples of wood raw materials include conifers such as red pine, black pine, Abies sachalinensis, Siberian spruce, red pine, larch, fir, hemlock, cedar, Japanese cypress, larch, Shirabe, spruce, hiba, Douglas fir, hemlock, white fir, spruce, balsam fir, cedar, pine, Merkusima pine, and radiata pine, as well as mixtures thereof, and hardwoods such as beech, birch, alder, oak, tabu, chinquapin, white birch, cottonwood, poplar, ash, mud willow, eucalyptus, mangrove, lauan, and acacia, as well as mixtures thereof. The method for pulping the wood raw materials is not particularly limited, and examples include pulping methods commonly used in the papermaking industry. Wood pulp can be classified by the pulping method, and examples include chemical pulp obtained by cooking using methods such as the kraft method, sulfite method, soda method, and polysulfide method; mechanical pulp obtained by mechanical pulping using a refiner or grinder; semi-chemical pulp obtained by mechanical pulping after chemical pretreatment; recycled paper pulp; and deinked pulp. Wood pulp may be unbleached (before bleaching) or bleached (after bleaching). Examples of non-wood-derived pulp include cotton, hemp, sisal, Manila hemp, flax, straw, bamboo, bagasse, kenaf, sugarcane, corn, rice straw, paper mulberry, and mitsumata. Wood pulp and non-wood pulp may be either unbeaten or beaten. These cellulose raw materials can also be further processed to produce powdered cellulose, chemically modified cellulose such as oxidized cellulose, and cellulose nanofibers (CNF) (microfibrillated cellulose (MFC), TEMPO-oxidized CNF, phosphate-esterified CNF, carboxymethylated CNF, and mechanically pulverized CNF). Synthetic fibers include polyester, polyamide, polyolefin, and acrylic fibers; semi-synthetic fibers include rayon and acetate; and inorganic fibers include glass fiber, carbon fiber, and various metal fibers. These may be used alone or in combination of two or more.

[0086] The average particle size, shape, etc. of the inorganic particles constituting the composite fiber of the present invention can be confirmed by observation with an electron microscope. Furthermore, by adjusting the conditions for synthesizing the inorganic particles, inorganic particles of various sizes and shapes can be composited with the fiber. [Example]

[0087] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Furthermore, unless otherwise specified in this specification, concentrations, parts, etc. are by weight, and numerical ranges are stated as including their endpoints.

[0088] Experiment 1: Synthesis and evaluation of composite fibers 1-1. Zinc-based hydrotalcite and fiber composite fiber (samples a and b) Solutions for synthesizing hydrotalcite (Zn-based HT) were prepared. An alkaline solution (solution A) was prepared, consisting of a mixture of Na2CO3 (Fujifilm Wako Pure Chemical Industries) and NaOH (Fujifilm Wako Pure Chemical Industries). An acid solution (solution B) was prepared, consisting of a mixture of ZnSO4 (Fujifilm Wako Pure Chemical Industries) and Al2(SO4)3·16H2O (Fujifilm Wako Pure Chemical Industries). Alkaline solution (solution A, Na2CO3 concentration: 0.05M, NaOH concentration: 0.8M) ·Acid solution (B solution, Zn-based, ZnSO4 concentration: 0.9M, Al2(SO4)3·16H2O concentration: 0.15M)

[0089] Cellulose fibers were used as the composite fibers. Specifically, the pulp fibers were composed of bleached hardwood kraft pulp (LBKP, Nippon Paper Industries, fiber width 20 μm) and bleached softwood kraft pulp (NBKP, Nippon Paper Industries, fiber width 50 μm) in a weight ratio of 8:2, and were refined to a Canadian Standard Freeness of 300 ml using a single disc refiner (SDR).

[0090] An alkaline solution was added to the pulp fibers to prepare an aqueous suspension containing pulp fibers (pulp fiber concentration: 3.0%, pH: approximately 12.8). This aqueous suspension (pulp solids content: 20 kg) was placed in a 1000 L reaction vessel, and while stirring the aqueous suspension, an acid solution was added dropwise to synthesize composite fibers of hydrotalcite microparticles and fibers. Using the apparatus shown in Figure 1, the reaction temperature was 50 °C, and the addition was stopped when the pH of the reaction solution reached approximately 7.5. After the addition was completed, the reaction solution was stirred and aged for 30 minutes. After aging, the sample was dehydrated in a centrifugal dehydrator, and 2 to 10 times the amount of water was added. This dehydration was repeated until the electrical conductivity reached 100 mS / m or less, and the composite fibers were washed.

[0091] 1-2. Barium sulfate and fiber composite fiber (sample c) As with sample a, pulp fibers (LBKP:NBKP=8:2) with a Canadian standard freeness adjusted to 300 ml were used.

[0092] Barium hydroxide octahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) was added to pulp fiber to prepare an aqueous suspension containing pulp fiber (pulp fiber concentration: 3.0%, pH: approximately 12.5). This aqueous suspension (pulp solids content: 20 kg) was placed in a 1000 L reaction vessel. While stirring the aqueous suspension, sulfuric acid (Fujifilm Wako Pure Chemical Industries, prepared as a 2% aqueous solution) was added dropwise to synthesize a composite of barium sulfate microparticles and fiber. Using the apparatus shown in Figure 1, the reaction temperature was 50 °C, and the addition was stopped when the pH of the reaction solution reached approximately 7.5. After the addition was completed, the reaction solution was stirred for 30 minutes and then washed with 10 times the volume of water to remove salt. The composite fiber was then dehydrated in a centrifugal dehydrator, and the dehydration was repeated by adding 2 to 10 times the volume of water until the electrical conductivity reached 100 mS / m or less.

[0093] 1-3. Composite fiber of copper-containing zinc-based hydrotalcite and fiber (sample d) As with sample a, pulp fibers (LBKP:NBKP=8:2) with a Canadian standard freeness adjusted to 300 ml were used.

[0094] To synthesize copper-containing zinc-based hydrotalcite (Cu-containing Zn-based HT), a mixed aqueous solution of Na2CO3 (Fujifilm Wako Pure Chemical Industries, Ltd.) and NaOH (Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared as an alkaline solution (solution A). In addition, a mixed aqueous solution of three chemicals, ZnSO4 (Fujifilm Wako Pure Chemical Industries, Ltd.), CuSO4 (Wako Pure Chemical Industries, Ltd.), and Al2(SO4)3·16H2O (Fujifilm Wako Pure Chemical Industries, Ltd.), was prepared as an acid solution (solution C). Alkaline solution (solution A, Na2CO3 concentration: 0.05M, NaOH concentration: 0.8M) ·Acid solution (C solution, ZnSO4 concentration: 0.75M, CuSO4 concentration: 0.15M, Al2(SO4)3 16H2O concentration: 0.15M) A composite fiber was synthesized in the same manner as sample a, except that the above chemicals were used, and the sample after aging was dehydrated in a centrifugal dehydrator to wash the composite fiber.

[0095] 1-4. Composite fiber of copper-containing zinc-based hydrotalcite and PET fiber (sample e) A composite fiber was synthesized in the same manner as sample d, except that polyethylene terephthalate fiber (PET, fiber diameter: 1.7 decitex, fiber length: 5 mm) was used as the fiber. After aging, the sample was dehydrated in a centrifugal dehydrator and the composite fiber was washed.

[0096] 1-5. Composite fiber of titanium oxide, magnesium hydrotalcite, and fiber (sample f) As with sample a, pulp fibers (LBKP:NBKP=8:2) with a Canadian standard freeness adjusted to 300 ml were used.

[0097] To synthesize magnesium-based hydrotalcite (Mg-based HT), a mixed aqueous solution of MgSO4 (Fujifilm Wako Pure Chemical Industries, Ltd.) and Al2(SO4)3·16H2O (Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared as an alkaline solution (solution A) and an acid solution (solution D). Alkaline solution (solution A, Na2CO3 concentration: 0.15M, NaOH concentration: 2.4M) ·Acid solution (D solution, MgSO4 concentration: 0.9M, Al2(SO4)3·16H2O concentration: 0.15M)

[0098] Pulp fiber was added to an alkaline solution to prepare an aqueous suspension containing pulp fiber (pulp fiber concentration: 2.0%, pH: approximately 12.7). 3.5 kg of titanium dioxide (R-3L, manufactured by Sakai Chemical Industry Co., Ltd.) was added to this aqueous suspension (pulp solids content: 3 kg) and thoroughly stirred. While stirring this aqueous suspension, an acid solution was added dropwise, and the reaction temperature was raised to 50°C. The dropwise addition was stopped when the pH of the reaction solution reached approximately 7. After the dropwise addition was completed, the reaction solution was stirred for 30 minutes and then washed with 10 times the amount of water to remove salts. The composite fiber was then dehydrated in a centrifugal dehydrator, and 2 to 10 times the amount of water was added, and dehydration was repeated until the electrical conductivity reached 100 mS / m or less, thereby washing the composite fiber.

[0099] 1-6. Evaluation of composite fibers The composite fiber samples were evaluated according to the following procedure. (1)Surface coverage The obtained composite fibers were observed under an electron microscope (Sample a: Figure 2, Sample b: Figure 3, Sample c: Figure 4, Sample d: Figure 5, Sample f: Figure 6). In all samples, approximately 70% of the fiber surface was covered with inorganic particles. (2) Moisture content (moisture rate) The sample was dried at 105°C for 2 hours, and the moisture content was calculated from the weight lost by drying. The solid content (concentration) is "100 - moisture content." (3) Weight ratio of fibers to inorganic particles For the sample dried at 105°C for 2 hours, the ash content of the composite fiber was measured based on JIS P 8251:2003, and the weight ratio of the fiber and inorganic particles constituting the composite fiber was calculated.

[0100] [Table 1]

[0101] Experiment 2: Production and evaluation of granules containing composite fibers 2-1. Production of granules containing composite fibers (Sample 1) Granules were produced using sample a as the raw material. Specifically, sample a (moisture content: approximately 70%) was placed in a Plossar mixer (WB type, Pacific Machinery Works) and stirred at room temperature. Next, steam was introduced into the Plossar mixer to raise the temperature inside the device to 80°C or higher, and the mixture was dried while stirring. After drying until the moisture content reached approximately 10%, water was added and the mixture was granulated (finished particle size after granulation: approximately 0.5 mm, moisture content after granulation: approximately 50%). Granules with a particle size of 0.5 mm or less were finally obtained using a 0.5 mesh sieve. (Sample 2) Except for using sample b as the raw material, granulation was carried out in the same manner as sample 1. Granules of 0.5 to 1.0 mm were finally obtained using a 0.5 to 1.0 mesh sieve. (Sample 3) The granules of Sample 2 were air-dried for 72 hours to produce granules with a moisture content of 20%. (Sample 4) Granules were produced in the same manner as Sample 3, except that Sample a was used as the raw material. (Sample 5) Sample b was used as the raw material, and granulation was carried out in the same manner as Sample 2, except that the final particle size after granulation was 1.0 mm. Granules with particle sizes of 1.0 to 3.0 mm were finally obtained using a 1.0 to 3.0 mesh sieve. (Sample 6) The granules of Sample 5 were air dried for 72 hours to produce granules with a moisture content of 20%. (Sample 7) Granules were produced in the same manner as in Sample 5, except that Sample a was used as the raw material. (Sample 8) Sample b was used as the raw material, and granulation was carried out in the same manner as Sample 3, except that the final particle size after granulation was set to 3.0 mm. Granules with particle sizes of 3.0 to 4.0 mm were finally obtained using a 3.0 to 4.0 mesh sieve. (Sample 9) Sample b (moisture content: approximately 70%) was dried until the moisture content was below 10%, and then further refined using a cutter mill to a size of approximately 0.5 mm or less. The processed sample was placed in a rolling granulator (CF-360N, Freund Corporation) and granulated while adding water (finished particle size after granulation: approximately 1.0 mm, moisture content after granulation: approximately 20%). Granules with particle sizes of 1.0 to 3.0 mm were finally obtained using a 1.0 to 3.0 mesh sieve. (Sample 10) It was produced in the same manner as Sample 3, except that Sample c was used as the raw material. (Sample 11) It was produced in the same manner as sample 2, except that sample d was used as the raw material. (Sample 12) It was produced in the same manner as Sample 2, except that Sample e was used as the raw material. (Sample 13) It was produced in the same manner as Sample 2, except that Sample f was used as the raw material. (Sample 14: Comparative Example) The moisture content of sample b was adjusted to about 70% using a Buchner funnel to prepare a sample. (Sample 15: Comparative Example) Water was added to 100 g of powdered cellulose (trade name: W-50, manufactured by Nippon Paper Industries Co., Ltd., average particle size: 40 μm) and mixed with stirring. This wet powder (moisture content: approximately 5%) was then granulated using a tumbling granulator while adding water (finished particle size after granulation: approximately 1 mm, moisture content after granulation: approximately 35%). The resulting granules were sieved to obtain granules with particle sizes of 0.5 to 1.0 mm.

[0102] 2-2. Evaluation of granules The samples were evaluated according to the following evaluation procedures. (1) Moisture content (moisture content), weight percentage of inorganic matter The moisture content (%) was measured in the same manner as in Experiment 1. The weight ratio (%) of the inorganic content was also calculated by measuring the weight ratio of the fibers to the inorganic particles in the same manner as in Experiment 1.

[0103] (2) Angle of repose (fluidity) Using a powder property measuring device (Hosokawa Micron, Powder Tester PT-X type), a powder sample was dropped from the attached metal funnel (φ5 mm) at a vibration scale of 1.5, and the angle of the ridge line formed by the powder was measured using the angle measurement method "Peak Operation" to obtain the angle of repose. If the angle of repose could be measured, it was evaluated as "fluidity present," and if it could not be measured, it was evaluated as "no fluidity." The lower the angle of repose value, the better the fluidity.

[0104] (3) Dispersibility 90 g of sodium chloride and 10 g of sample were added to a plastic bag (170 mm x 240 mm) and mixed manually for 3 minutes. 10 g of the mixture was taken, 200 ml of distilled water was added, and the sodium chloride was dissolved using a stirrer. The treated solution was filtered using filter paper (JIS P3801, for quantitative analysis, Type 5B). The residue on the filter paper was dried under tension at 50°C for 2 hours, and the weight of the granules contained in 10 g of the mixture was measured. The dispersion rate was calculated using the formula "weight of granules after drying / 1 g x 100," with a dispersion rate of 70% or more considered a pass (○) and a dispersion rate of less than 70% considered a fail (×).

[0105] (4) Bulk density The mass of a sample lightly packed into a certain volume was measured, and the value divided by the volume was used as the "bulk density (loose bulk density)." Specifically, the mass of a sample filled into a 1000 mL measuring cylinder up to the 1000 mL mark was measured, and the bulk density (g / cm 3 ) values ​​were calculated.

[0106] (5) Particle size distribution A laser diffraction particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern Panalytical) was used. The cumulative 50% particle size (average particle size) by volume was obtained from the sample (0.3 to 1.0 g) used for the measurement.

[0107] [Table 2]

[0108] As is clear from the above table, the granules of the present invention had better flowability and dispersibility than those not processed into granules.

Claims

1. Granules containing composite fibers of cellulose fibers and inorganic particles, having a particle size of 0.1 to 10 mm and a moisture content of less than 60%, The above granules, wherein the average fiber diameter of the cellulose fibers is 3 to 50 μm, the inorganic particles contain metal salts of calcium, magnesium, barium, or aluminum, metal particles containing titanium, copper, or zinc, or silicates, and the weight ratio of the cellulose fibers to the inorganic particles in the composite fibers is 10 / 90 to 90 / 10.

2. The granules according to claim 1, having an angle of repose of 30 to 58°.

3. Granules described in claim 1 or 2, wherein the inorganic particles contain barium sulfate.

4. The granules according to claim 1 or 2, wherein the inorganic particles are hydrotalcite.

5. The granules according to claim 1 or 2, wherein the weight ratio of inorganic particles in the granules is 10% or more.

6. Granules described in claim 1 or 2, wherein the cellulose fibers are wood pulp fibers.

7. Granules described in claim 1 or 2, in which 15% or more of the surface of the cellulose fibers is covered with inorganic particles.

8. Granules described in claim 1 or 2, wherein the weight ratio of cellulose fibers / inorganic particles is 40 / 60 to 60 / 40, and the weight proportion of inorganic content is 50.1% or more.

9. The granules according to claim 1 or 2, having a bulk density of 0.58 g / cm 3 or more.

10. Granules according to claim 1 or 2, having a particle size of 0.2 to 4 mm.

11. A method for producing granules according to any one of claims 1 to 10, comprising the steps of: A step of synthesizing inorganic particles in a liquid containing cellulose fibers to obtain composite fibers; A step of granulating the composite fibers into granules having a particle size of 0.1 to 10 mm; The above method, comprising:

12. The method according to claim 11, wherein the composite fibers are granulated while being dried in the granulation step.

13. The method according to claim 11, wherein the moisture content of the composite fiber is adjusted to 6 to 50% before granulation.

14. The method according to claim 11, wherein the bicomponent fibers are micronized before being granulated.

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