Method for producing a solid material containing composite fibers of fibers and inorganic particles

Abstract

To provide a solid matter containing a composite fiber of a fiber and an inorganic particle.SOLUTION: A method includes: a step of synthesizing an inorganic particle in a liquid including a fiber to obtain a composite fiber; a step of dehydrating the composite fiber; and a step of crushing the dehydrated composite fiber by a crusher, so as to produce a solid matter containing the composite fiber of the fiber and the inorganic particle.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for producing a solid material containing composite fibers of fibers and inorganic particles. [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 a method for producing a solid material that contains a composite fiber of fibers and inorganic particles and has excellent transportability and dispersibility. [Means for solving the problem]

[0007] As a result of extensive research into the above-mentioned problems, the inventors discovered that a solid material with excellent transportability and dispersibility can be obtained by combining two different processes, dehydration and pulverization, and thus completed the present invention.

[0008] That is, the present invention includes, but is not limited to, the following aspects. [1] A method for producing a solid material containing composite fibers of fibers and inorganic particles, comprising: A step of synthesizing inorganic particles in a liquid containing fibers to obtain composite fibers; dehydrating the composite fibers; A step of pulverizing the dehydrated composite fiber in a pulverizer; The above method, comprising: [2] The method according to [1], wherein the moisture content of the composite fiber is less than 60% in the step of dehydrating the composite fiber. [3] The method according to [1] or [2], wherein the step of dehydrating the composite fiber is performed by dehydrating the composite fiber in a press or by drying the composite fiber in a dryer. [4] The method according to any one of [1] to [3], wherein in the step of pulverizing the composite fibers with a pulverizer, the composite fibers are pulverized until the average particle size is 10 mm or less. [5] The method according to any one of [1] to [4], wherein the inorganic particles include metal salts of calcium, magnesium, barium, or aluminum, metal particles containing titanium, copper, or zinc, or silicates. [6] The method according to any one of [1] to [5], wherein the inorganic particles are hydrotalcite or barium sulfate. [7] The method according to any one of [1] to [6], wherein the fibers are cellulose fibers. [8] The method according to any one of [1] to [7], wherein 50% or more of the surface of the composite fiber is covered with inorganic particles. [Effects of the Invention]

[0009] According to the present invention, a solid product can be obtained by processing a composite fiber of fibers and inorganic particles. The obtained solid product has excellent transportability and dispersibility, so it can be easily blended into other products and can efficiently impart functionality to the other products according to the characteristics of the inorganic particles. For example, when inorganic particles with a high deodorizing effect are used, a solid product with a high deodorizing effect can be obtained. [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 a photograph of the appearance of Sample 1 in Experiment 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a method for producing a solid material containing composite fibers of fibers and inorganic particles. A solid material generally has a larger particle size than a powder, and refers to a granular material with a particle size of 1 mm or more. The particle size of the solid material is preferably 50 mm or less, and may be 30 mm or less or 20 mm or less. The particle size of the solid material according to the present invention can be evaluated by the length of the longest point (long side). The average particle size of the solid material according to the present invention can be, for example, 1 to 30 mm, or may be 1 to 20 mm or 1 to 10 mm.

[0012] The solid composite fiber of the present invention, consisting of fibers and inorganic particles, is produced by dehydrating and then pulverizing the composite fiber containing water. The solid is less likely to generate dust, as is the case with powders, or to coagulate when water is added, preventing dissolution. Furthermore, compared to composite fibers in the form of aqueous suspensions or pulp, the solid has the advantage of being easily dispersible in other products.

[0013] Methods for dehydrating composite fibers of fibers and inorganic particles include a physical squeezing method and a drying method using a heat source. There are no particular limitations on the press used for pressing, and suitable examples include a filter press, a drum filter, a screw press, a roller press, a belt press, a tube press, etc. Among these, it is preferable to use a device capable of carrying out continuous production, such as a screw press, because this facilitates workability.

[0014] There are no particular limitations on the dryer used for drying, but for example, a flash dryer, band dryer, spray dryer, vacuum dryer, low-temperature dryer, rotary dryer, proshare mixer, oven, etc. can be suitably used.

[0015] There are no particular restrictions on the mill used to mill the dehydrated composite fiber, and suitable examples include a ball mill, sand grinder mill, impact mill, high-pressure homogenizer, low-pressure homogenizer, Dyno-mill, ultrasonic mill, Kanda grinder, attritor, stone mill, vibration mill, cutter mill, jet mill, rotary mill, disintegrator, beater, single-screw extruder, twin-screw extruder, twin-screw mill, ultrasonic agitator, and household juicer mixer. Of these, it is preferable to use a device that can produce a large amount in a short time, such as a cutter mill or rotary mill, because this facilitates workability.

[0016] In the present invention, the particle size of the solid material is 1 mm or more and 30 mm or less. The particle size of the solid material is preferably 3 mm or more and 20 mm or less, more preferably 5 mm or more and 15 mm or less, and the particle size of the solid material can also be 7 mm or more and 12 mm or less. If the particle size is too small, the solid material will easily scatter, and if the particle size is too large, it will be difficult to disperse when blended with other raw materials.

[0017] The moisture content (moisture concentration) of the raw material before processing into a solid product can be, for example, 10 to 95%, preferably 30 to 90%, more preferably 40 to 85%, more preferably 50 to 80%, and particularly preferably 60 to 75%. If the moisture content before processing is too high, dehydration will take a long time and efficiency will decrease, while if the moisture content before processing is too low, it will be difficult to uniformly compress the raw material depending on the device used to process into a solid product. Therefore, a moderate moisture content is more suitable for producing a solid product. In the present invention, the moisture content of the composite fiber when pulverized is preferably 10 to 60%, more preferably 20 to 55%, and may be 30 to 50%. The water content of the solid material according to the present invention is less than 60%, and in a preferred embodiment, the water content of the solid material is less than 50%, and may be less than 40%. By reducing the water content of the solid material, the fluidity of the solid material can be improved.

[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] 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 step is preferred for the convenience of discharging the residue after the reaction. The scale of the reaction is not particularly limited, but the reaction can 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 can be, for example, about 10 L to 100 L, or about 100 L to 1000 L.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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- , SO4 2- , 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.

[0029] 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.

[0030] (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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] (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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] (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.

[0042] 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.

[0043] 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.

[0044] (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, a hydrothermal reaction using an autoclave or the like is also possible (see JP-A-60-6619).

[0045] 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.

[0046] 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.

[0047] 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.

[0048] (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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] (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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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).

[0057] Examples of non-wood pulp include cotton, hemp, sisal, Manila hemp, flax, straw, bamboo, bagasse, kenaf, sugarcane, corn, rice straw, paper mulberry, and mitsumata.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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).

[0064] 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.

[0065] 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).

[0066] 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.

[0067] The composite fiber according to the present invention has at least 15% 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. In addition, in composite fibers, the coverage (area ratio) of fibers with inorganic particles is more preferably 25% or more, and even more preferably 40% or more. Furthermore, according to the method of synthesizing inorganic particles in a fiber-containing solution according to the present invention, the coverage can be 60% or more or 80% or more. The upper limit of the coverage can be appropriately set depending on the application, and is, for example, 100%, 90%, or 80%.

[0068] In a preferred embodiment, when an aqueous suspension of the composite fiber having a solids concentration of 0.1% is filtered through a 60-mesh (250 μm mesh) sieve, the weight ratio B / A of the amount of inorganic matter (B) in the residue remaining on the sieve after filtration to the amount of inorganic matter (A) in the composite fiber before the filtration is 0.3 or more. In particular, B / A is preferably 0.5 or more, more preferably 0.6 or more, and more preferably 0.8 or more. Within this range, the composite fiber is strong and has good adhesion, and the solid product obtained using such composite fiber is also of good quality.

[0069] A composite fiber having a B / A ratio of 0.3 or more can be obtained by adjusting the composite fiber synthesis conditions, the composite fiber concentration, the composite fiber classification treatment, etc., to prepare an aqueous suspension of the composite fiber, as described below.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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]

[0075] 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.

[0076] Experiment 1: Synthesis and evaluation of composite fibers 1-1. Zinc-based hydrotalcite and fiber composite fiber (samples a and b) Copper-zinc hydrotalcite compound (CuZn5Al2(OH) 16 Solutions for synthesizing Al(SO4)3·16H2O 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), CuSO4 (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: 0.6M, CuSO4 concentration: 0.6M, Al2(SO4)3 16H2O concentration: 0.12M) 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).

[0077] An alkaline solution was added to 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. For samples a and b, the amounts of pulp and chemicals (acid and alkali) added were adjusted so that the inorganic content of the final product was 50% and 70%, respectively.

[0078] 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.

[0079] 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. For sample c, the amounts of pulp and chemicals (acid, alkali) added were adjusted so that the inorganic content of the finished product was 70%.

[0080] 1-3. 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). In all of Samples a to c, 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.

[0081] [Table 1]

[0082] Experiment 2: Preparation and evaluation of composite fiber-containing solids 2-1. Production of solids containing composite fibers (Sample 1) A solid material was produced using sample a as the raw material. Specifically, sample a (moisture content: approximately 70%) was placed in a screw press (SHX type, Fukoku Kogyo) and dehydrated at a rotation speed of 9 rpm (moisture content: 50%). The dehydrated sample was passed through a single-shaft rotary grinder (Fukoku Kogyo) once to be pulverized (average particle size: 10 mm or less). After that, the coarse particles contained in the pulverized sample at approximately 3% were removed using a 10 mm mesh sieve, and a solid material with a particle size of 1 to 10 mm was finally obtained (Figure 5). (Sample 2) The solids of Sample 1 were air-dried overnight to produce a solid with a moisture content of 20%. (Sample 3) Sample b was used as the raw material, and the treatment was the same as for sample 1. (Sample 4) The solids of Sample 3 were air-dried overnight to produce a solid with a moisture content of 20%. (Sample 4) A solid material was produced in the same manner as in Sample 3, except that Sample a was used as the raw material. (Sample 5) Sample b (moisture content: approximately 70%) was placed in a blower dryer and treated at 105°C for 1 hour (moisture content: approximately 25%). The resulting sample was then pulverized in a single-shaft rotary pulverizer (Fukoku Kogyo) (average particle size: 10 mm or less). Afterwards, coarse particles were removed using a 10 mm mesh sieve, and a solid with a particle size of 1 to 10 mm was finally obtained. (Sample 6) Sample b (moisture content: approximately 70%) was placed in a screw press (SHX type, Fukoku Kogyo) and dehydrated at a rotation speed of 9 rpm (moisture content: 50%). The dehydrated sample was passed through a wet pulp disintegrator (Kumagaya Riki Kogyo Co., Ltd.) once to be pulverized (average particle size: 20 mm or less). Next, coarse particles were removed using a 20 mm mesh sieve, and solids with particle sizes of 5 to 20 mm were finally obtained. (Sample 7) Sample c was used as the raw material, and the manufacturing process was the same as that for Sample 1. (Sample 8: Comparative Example) Sample b (moisture content 70%, no dehydration or drying treatments) was used. (Sample 9: 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 passed through a 1 mm mesh sieve to obtain a solid with a particle size of 0.5 to 1.0 mm. (Sample 10: Comparative Example) A solid was produced from pulp fibers containing 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 an 8:2 weight ratio. The fibers were refined to a Canadian standard freeness of 300 ml using a single-disc refiner (SDR). Specifically, the fibers were fed into a screw press (SHX type, Fukoku Kogyo) and dewatered at a rotation speed of 9 rpm (moisture content: 50%). The resulting sample was crushed in a single-shaft rotary crusher (Fukoku Kogyo) and then sieved through a 10 mm mesh sieve to obtain a solid with a particle size of 1–10 mm.

[0083] 2-2. Evaluation of solids The samples were evaluated based on the following evaluation procedures: The moisture content (moisture content) and the weight ratio of inorganic particles were measured in the same manner as in Experiment 1. (1) Particle size (size of solids) The longest part (long side) of the solid was measured using a ruler and used as the particle size. The average particle size of the solid was calculated by measuring the particle size (length of the long side) of 10 randomly selected solids and averaging the results. (2) Dispersibility in liquids 450 g of sodium chloride and 50 g of sample were added to a plastic bag (170 mm x 240 mm) and mixed manually for 3 minutes. 50 g of the mixture was removed, 1000 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 solids contained in 50 g of the mixture was measured. The dispersion rate was calculated using the formula "weight of solids after drying / 5 g x 100," with a dispersion rate of 70% or more considered optimal (◎), 60% or more considered acceptable (○), and less than 60% considered unacceptable (×). (3) Bulk density (g / cm 3 ) The mass of a sample lightly packed into a certain volume was measured and divided by the volume to obtain the bulk density (loose bulk density). Specifically, the mass was measured when the sample was filled into a 1000 mL measuring cylinder up to the 1000 mL mark. (4) Deodorization test (samples a and b) The deodorizing properties were evaluated using the solid product produced. 1g of solid material was used for the deodorizing test. The deodorizing test was conducted based on the SEK Mark Textile Product Certification Standard (JEC301, Textile Evaluation Technology Council), and targeted hydrogen sulfide, which corresponds to excrement odors and food waste odors.

[0084] The odor reduction rate (%) was calculated using the following formula, with 70% or more being considered a pass (◯) and less than 70% being considered a fail (×). Odor reduction rate (%) = (Sb - Sm) / Sb × 100 Sb: average value of blank test Sm: average value of the measurements (5) Antibacterial test (samples a and b) The antibacterial properties were evaluated using the produced solid material. The weight of the sheet used for the antibacterial test was 0.4 g. A standard cotton cloth was used as a reference. The antibacterial test was performed using the bacterial liquid absorption method specified in JIS L 1902 (a quantitative test method in which the test inoculum is inoculated directly onto the test specimen). Two types of bacteria were used as test bacteria: Staphylococcus aureus (NBRC 12732) and Escherichia coli (NBRC 3301). The number of viable bacteria after 18 hours of incubation was measured using the pour plate culture method, and the antibacterial activity value was calculated. An antibacterial activity value of 2.0 or higher against both Staphylococcus aureus and Escherichia coli was considered a pass (◯), and any other value was considered a fail (×). (Measurement procedure) 1. Place 0.4 g of the test piece (above solid) in a vial, add 0.2 ml of test bacteria solution (containing 0.05% surfactant (Tween 80)) dropwise, and then close the vial lid. 2. Incubate the vial at 37°C for 18 hours. 3. Add 20 ml of washout solution to wash out the test bacteria from the test piece, and measure the number of viable bacteria in the washout solution using the pour plate culture method or luminescence measurement method. 4. Calculate the antibacterial activity value according to the following formula: An antibacterial activity value of 2.0 or higher means that the bacterial death rate is 99% or higher. Antibacterial activity value = {log(viable bacteria count after incubation of control sample) - log(viable bacteria count immediately after inoculation of control sample)} - {log(viable bacteria count after incubation of test sample) - log(viable bacteria count immediately after inoculation of test sample)} (6) Radiation shielding (sample c) The radiation (X-ray) shielding ability was evaluated based on the "Lead Equivalent Test Method for X-ray Protective Equipment" (JIS Z 4501). Specifically, the transmitted X-ray dose rate was measured using the following procedure, and an X-ray dose reduction rate of 30.0% or more was judged to have radiation shielding ability (Good), and an X-ray dose reduction rate of less than 30.0% was judged to have no radiation shielding ability (Poor). (Measurement procedure) X-rays were irradiated using radiation quality and placement in accordance with the test method of JIS Z 4501, and the transmitted X-ray dose rate was measured. Five measurements were taken for each requested product and each measurement position, and the average value and standard deviation were calculated. The dose reduction rate was calculated from the obtained transmitted dose rate using the following formula. Dose reduction rate (%) = (transmitted dose rate of each sample / transmitted dose rate of blank (no sample)) x 100 (Measurement conditions) X-ray equipment: YXLON International MG-452 (smoothing circuit, focal spot size 5.5 mm, Be window) X-ray tube voltage and current: MG-452 type 100kV 12.5mA Additional filter plate 0.25mm Cu X-ray tube focal point-sample distance: 1500 mm Distance between sample and measuring device: 50 mm Measuring instrument: Ionization chamber exposure dose rate meter, Toyo Medic, RAMTEC-1000D type, A-4 probe used X-ray dose measurement unit: Air impact kerma X-ray beam: narrow beam

[0085] [Table 2]

[0086] As is clear from the above table, when a solid product was produced using the method of the present invention, the resulting solid product had good dispersibility. Furthermore, the solid product of the present invention had better functionality than a solid product produced without using composite fibers of fibers and inorganic particles.

Claims

1. A method for producing a solid material containing composite fibers of fibers and inorganic particles, comprising: a step of synthesizing inorganic particles in a liquid containing fibers to obtain composite fibers in which 15% or more of the fiber surface is covered with inorganic particles; dehydrating the composite fiber until the moisture content is less than 60%; A step of pulverizing the dehydrated composite fiber in a pulverizer to obtain a solid having an average particle size of 1 to 20 mm and a loose bulk density of 0.46 to 0.50 g / cm3; The above method, comprising:

2. The method of claim 1 , wherein the grinder is a cutter mill or a rotary grinder.

3. A method according to claim 1 or 2, wherein the moisture content of the composite fiber before dehydration is 60 to 75%.

4. The method according to any one of claims 1 to 3, wherein the step of dewatering the composite fiber comprises dewatering the composite fiber in a press or by drying the composite fiber in a dryer.

5. The method according to any one of claims 1 to 4, wherein in the step of pulverizing the composite fibers with a pulverizer, the composite fibers are pulverized until the average particle size is 10 mm or less.

6. The method of any one of claims 1 to 5, wherein the inorganic particles comprise metal salts of calcium, magnesium, barium or aluminium, metal particles comprising titanium, copper or zinc, or silicates.

7. The method according to any one of claims 1 to 6, wherein the inorganic particles are hydrotalcite or barium sulfate.

8. The method according to any one of claims 1 to 7, wherein the fibers are cellulose fibers.

9. The method according to any one of claims 1 to 8, wherein 50% or more of the surface of the composite fiber is covered with inorganic particles.

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