CN114144553A

CN114144553A - Composite fiber of cellulose fiber and inorganic particle and method for producing same

Info

Publication number: CN114144553A
Application number: CN202080053008.8A
Authority: CN
Inventors: 长谷川绚香; 渊濑萌
Original assignee: Nippon Paper Industries Co Ltd
Current assignee: Nippon Paper Industries Co Ltd
Priority date: 2019-09-06
Filing date: 2020-09-04
Publication date: 2022-03-04
Also published as: JP7123178B2; WO2021045198A1; US20220290373A1; JP2022133416A; EP4026946A4; EP4026946A1; JPWO2021045198A1

Abstract

The present invention addresses the problem of providing a composite fiber in which the surface of a cellulose fiber is firmly covered with a large number of inorganic particles. In the present invention, (D50-D10)/D50 calculated from the particle size distribution of the following (a) or (b) is used as an index, whereby an excellent composite fiber of a cellulose fiber and inorganic particles can be produced. (a) A filtrate obtained by filtering an aqueous suspension of composite fibers having a solid content of 0.1% with a 60-mesh (250 μm mesh) sieve, and (b) a fraction corresponding to an outflow (L) of 18.51 to 19.50 and an outflow time (sec) of 37.4 to 48.0 in the case of classifying an aqueous suspension of composite fibers having a solid content of 0.3% using a fiber classification analyzer under conditions of a flow rate of 5.7L/min, a water temperature of 25. + -. 1 ℃ and a total outflow of 22L.

Description

Composite fiber of cellulose fiber and inorganic particle and method for producing same

Technical Field

The present invention relates to a composite fiber of cellulose fibers and inorganic particles and a method for producing the same.

Background

Fibers represented by wood fibers exhibit various properties based on functional groups on the surface thereof, and the like, but the surface may be modified depending on the application, and techniques for modifying the surface of fibers have been developed so far.

For example, patent document 1 describes a technique of depositing inorganic particles on fibers such as cellulose fibers, and discloses a composite in which crystalline calcium carbonate is mechanically bonded to the fibers. Patent document 2 describes a technique for producing a composite of pulp and calcium carbonate by precipitating calcium carbonate in a pulp suspension by a carbon dioxide method.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. H06-158585

Patent document 2: U.S. Pat. No. 5679220

Disclosure of Invention

Conventional composite fibers obtained by coating the fiber surface of cellulose with inorganic particles may have insufficient bonding strength between the cellulose fibers and the inorganic particles, a small amount of inorganic particles may be coated on the cellulose fibers, or the inorganic particles may fall off from the cellulose fibers. In view of the above circumstances, an object of the present invention is to provide a composite fiber in which the surface of a cellulose fiber is firmly coated with a large number of inorganic particles.

The present invention includes the following inventions, but is not limited thereto.

[1] A method of making a composite fiber of cellulosic fibers and inorganic particles, comprising:

a step of synthesizing inorganic particles in a solution containing cellulose fibers to obtain composite fibers, and

the particle size distribution of the following (a) or (b) was measured to calculate (D50-D10)/D50.

(a) The filtrate obtained by filtering an aqueous suspension of composite fibers having a solid content of 0.1% through a 60-mesh (250 μm-mesh) sieve,

(b) when an aqueous suspension of composite fibers having a solid content concentration of 0.3% is fractionated using a fiber fractionation analyzer under conditions of a flow rate of 5.7L/min, a water temperature of 25. + -. 1 ℃ and a total discharge amount of 22L, fractions corresponding to a discharge amount (L) of 18.51 to 19.50 and a discharge time (sec) of 37.4 to 48.0 are obtained.

[2] The method according to [1], wherein the aqueous suspension of the conjugate fiber is adjusted so that (D50-D10)/D50 becomes 0.85 or less.

[3] The method according to [1] or [2], wherein the composite fiber has an average fiber diameter of 500nm or more.

[4] The method according to any one of [1] to [3], wherein the inorganic particles include: metal salts of calcium, magnesium, barium or aluminum, metal particles comprising titanium, copper or zinc, or silicates.

[5] A method for producing a composite fiber sheet, comprising a step of forming a sheet from a composite fiber obtained by any one of the methods [1] to [4 ].

[6] A composite fiber comprising a cellulose fiber and inorganic particles, wherein the value of (D50-D10)/D50 calculated from the particle size distribution of the following (a) or (b) is 0.85 or less.

(a) The filtrate obtained when the aqueous suspension of composite fibers having a solid content of 0.1% was filtered through a 60-mesh (250 μm-mesh) sieve,

[7] A composite fiber comprising a cellulose fiber and inorganic particles which have been treated with an aqueous suspension of a composite fiber having a solid content of 0.1% by means of a 60-mesh (250 μm mesh) sieve and passed through the sieve, wherein the value of (D50-D10)/D50, calculated from the particle size distribution of the filtrate passed through the sieve, is 0.85 or less.

[8] A composite fiber comprising an aqueous suspension of composite fiber having a solid content of 0.3% is fractionated using a fiber fractionation analyzer under conditions of a flow rate of 5.7L/min, a water temperature of 25 + -1 ℃ and a total discharge amount of 22L, and the value of (D50-D10)/D50 calculated from the particle size distribution of a cellulose fiber and inorganic particles obtained from a fraction corresponding to a discharge amount (L) of 18.51 to 19.50 and a discharge time (sec) of 37.4 to 48.0 is 0.85 or less.

[9] A method for analyzing a composite fiber of a cellulose fiber and inorganic particles, comprising the step of measuring the particle size distribution of the following (a) or (b) to calculate (D50-D10)/D50.

According to the present invention, a composite fiber can be obtained in which the surface of a cellulose fiber is firmly coated with a large number of inorganic particles and which can improve the production efficiency in the post-process such as dehydration and sheeting.

Since the inorganic particles and the cellulose fibers are strongly bonded to each other as compared with conventional composite fibers, the inorganic particles are less likely to fall off during dehydration, sheeting, and the like (the retention of inorganic particles in a subsequent step is excellent), and the drainability is good because free particles having a small particle diameter are small. The improvement of the dewatering property and the water-filtering property is not only related to the improvement of the productivity (dewatering speed, paper-making speed) of various products but also related to the improvement of the functionality of products made of composite fibers, etc. since the functional inorganic particles are not easily dropped.

Drawings

FIG. 1 is an electron micrograph (magnification: 3000 times) of sample 1.

FIG. 2 is an electron micrograph (magnification: 3000 times) of sample 2.

FIG. 3 is an electron micrograph (magnification: 3000 times) of sample 3.

FIG. 4 is an electron micrograph (magnification: 3000 times) of sample 4.

FIG. 5 is an electron micrograph (magnification: 3000 times) of sample 5.

FIG. 6 is an electron micrograph (magnification: 3000 times) of sample 6.

FIG. 7 is an electron micrograph (magnification: 3000 times) of sample 7.

FIG. 8 is an electron micrograph (magnification: 3000 times) of sample 8.

FIG. 9 is an electron micrograph (magnification: 3000 times) of sample 9.

FIG. 10 is an electron micrograph (left: 3000 times, right: 10000 times) of sample 10.

FIG. 11 is an electron micrograph (left: 3000 times, right: 10000 times) of sample 11.

FIG. 12 is an electron micrograph (left: 3000 times, right: 10000 times) of sample 12.

FIG. 13 is an electron micrograph (magnification: 3000 times) of sample A.

FIG. 14 is an electron micrograph (magnification: 3000 times) of sample B.

FIG. 15 is an electron micrograph (magnification: 3000 magnification) of sample C1.

FIG. 16 is an electron micrograph (magnification: 3000 magnification) of sample C2.

FIG. 17 is an electron micrograph (magnification: 3000 magnification) of sample D1.

FIG. 18 is an electron micrograph (magnification: 3000 magnification) of sample D2.

Detailed Description

The present invention relates to a composite fiber (composite) in which the surface of a cellulose fiber is firmly covered with inorganic particles. In a preferred embodiment, 15% or more of the fiber surface of the composite fiber of the present invention is coated with inorganic particles.

The composite fiber of the present invention does not simply contain fibers and inorganic particles mixed together, but the fibers and the inorganic particles are bonded to each other by hydrogen bonds or the like, and therefore, the inorganic particles are rarely detached from the fibers. The bonding strength between the fibers and the inorganic particles in the composite can be generally evaluated by a value such as ash retention (% i.e., ash of sheet divided by ash of composite before dissociation × 100). Specifically, the composite may be dispersed in water to adjust the solid content concentration to 0.2%, according to JIS P8220-1: 2012 for 5 minutes, according to JIS P8222: 1998 was flaked using a 150-mesh screen, and the ash retention at this time was used for evaluation. However, in the present invention, by classifying the composite fibers, it is possible to evaluate good composite fibers having a strong bond to composite fibers whose bond strength cannot be sufficiently evaluated by a conventional method.

In the present invention, composite fibers of cellulose fibers and inorganic particles can be appropriately evaluated by analyzing the particle size distribution of the following (a) or (b).

(a) The filtrate was obtained by filtering an aqueous suspension of composite fibers having a solid content of 0.1% through a 60-mesh (250 μm-mesh) sieve.

Specifically, the numerical value of (D50-D10)/D50 calculated from the volume-based particle size distribution of the above (a) or (b) can be used as an index. Here, D10 and D50 are particle diameters determined from a volume-based particle size distribution, D10 is a cumulative 10% particle diameter, and D50 is a cumulative 50% particle diameter. A smaller value of (D50-D10)/D50 means a narrower particle size distribution of the sample, indicating that the inorganic substance is firmly fixed to the fiber surface. In a preferred embodiment, the numerical value of (D50-D10)/D50 is 0.85 or less.

Synthesis of composite fibers

In the present invention, the composite fiber can be synthesized by synthesizing inorganic particles in a solution containing a fiber such as a cellulose fiber. This is because the fiber surface becomes an appropriate place for precipitation of inorganic particles, and composite fibers are easily synthesized. As a method for synthesizing the composite fiber, for example, a solution containing the fiber and the precursor of the inorganic particle may be stirred and mixed in an open-type reaction tank to synthesize a composite, or an aqueous suspension containing the fiber and the precursor of the inorganic particle may be sprayed into a reaction vessel to synthesize the composite fiber. As will be described later, when an aqueous suspension of a precursor of an inorganic substance is injected into a reaction vessel, cavitation bubbles are generated, and inorganic particles are synthesized in the presence thereof. The inorganic particles can be synthesized on the cellulose fibers by known reactions.

In general, it is known that the generation of inorganic particles proceeds from a cluster state (where aggregation and dispersion are repeated at a stage where the number of aggregated atoms and molecules is small) to a nucleus (where the cluster is changed to a stable aggregate state and the atoms and molecules trapped when the size of the particles becomes equal to or larger than a critical size are not dispersed) and then grow (where new atoms and molecules are aggregated in the nucleus to enlarge the particle size), and it is considered that the nucleus generation is more likely to occur as the concentration of the raw material and the reaction temperature are higher. The composite fiber of the present invention can obtain a composite fiber in which the surface of cellulose fibers is firmly coated with inorganic particles by effectively binding the core to the fibers and promoting the particle growth mainly by adjusting the raw material concentration, the beating degree (specific surface area) of pulp, the viscosity of the solution containing the fibers, the concentration and addition rate of the additive agent, the reaction temperature, and the stirring rate.

In the present invention, the liquid may be ejected under conditions such that cavitation bubbles are generated in the reaction vessel, or may be ejected under conditions such that cavitation bubbles are not generated. In either case, the reaction vessel is preferably a pressure vessel. The pressure vessel of the present invention is a vessel capable of applying a pressure of 0.005MPa or more. Under such a condition that cavitation bubbles are not generated, the pressure in the pressure vessel is preferably 0.005MPa to 0.9MPa in terms of static pressure.

(cavitation bubbles)

When the composite fiber of the present invention is synthesized, inorganic particles can be precipitated in the presence of cavitation bubbles. In the present invention, cavitation refers to a physical phenomenon in which bubbles are generated and disappear in a short time due to a pressure difference in a fluid flow, and is also referred to as a cavitation phenomenon. Bubbles (cavitation bubbles) generated by cavitation are generated by using, as nuclei, "bubble nuclei" of 100 μm or less present in a liquid when the pressure in the fluid becomes lower than the saturated vapor pressure in a very short time.

In the present invention, cavitation bubbles can be generated in the reaction vessel by a known method. For example, cavitation bubbles may be generated by jetting a fluid at a high pressure, cavitation may be generated by stirring the fluid at a high speed, cavitation may be generated by explosion in the fluid, and cavitation may be generated by ultrasonic vibration (vibration-type cavitation).

In the present invention, cavitation may be generated by using a reaction solution such as a raw material as it is as a jet liquid, or cavitation bubbles may be generated by jetting a certain fluid into a reaction vessel. The fluid that forms a jet flow by a liquid jet flow may be any of a liquid, a gas, a solid such as powder or pulp, and may be a mixture thereof, as long as it is in a fluid state. If further required, another fluid such as carbon dioxide may be added to the above fluid as a new fluid. The fluid and the new fluid may be uniformly mixed and ejected, or may be ejected separately.

The liquid jet is a jet of liquid or solid particles, or a fluid in which gas is dispersed or mixed in liquid, and refers to a liquid jet including pulp, raw material slurry of inorganic particles, and bubbles. The gas referred to herein may also include bubbles generated by cavitation.

Cavitation occurs when a liquid is accelerated and the local pressure becomes lower than the vapor pressure of the liquid, so the flow rate and pressure are of particular importance. Accordingly, the Number of basic dimensionless numbers or Cavitation numbers (Cavitation Number) σ indicating the Cavitation state is preferably 0.001 to 0.5, more 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 small because the pressure difference from the surroundings is low when cavitation bubbles collapse, and if it is more than 0.5, cavitation is less likely to occur because of the pressure difference of the flow.

When cavitation is generated by injecting the injection liquid through the nozzle or orifice tube, the pressure of the injection liquid (upstream pressure) is preferably 0.01 to 30MPa, more preferably 0.7 to 20MPa, and still more preferably 2 to 15 MPa. If the upstream pressure is less than 0.01MPa, a pressure difference is not easily generated between the upstream pressure and the downstream pressure, and the effect is small. In addition, if the pressure is higher than 30MPa, a special pump and a pressure vessel are required, and energy consumption increases, which is disadvantageous in terms of cost. On the other hand, the pressure in the container (downstream side pressure) is preferably 0.005MPa to 0.9MPa in terms of static pressure.

Further, the ratio of the pressure in the container to the pressure of the ejection liquid is preferably in the range of 0.001 to 0.5.

In the present invention, inorganic particles may be synthesized by spraying the ejection liquid under such a condition that cavitation bubbles are not generated. Specifically, the pressure of the injection liquid (upstream pressure) is set to 2MPa or less, preferably 1MPa or less, and the pressure of the injection liquid (downstream pressure) is opened, more preferably 0.05MPa or less.

The velocity of the jet of the ejection liquid is preferably in the range of 1 m/sec to 200 m/sec, and more preferably in the range of 20 m/sec to 100 m/sec. When the velocity of the jet is less than 1 m/sec, the effect is weak because the pressure drop is small and cavitation is not easily generated. On the other hand, if the amount is more than 200 m/sec, high pressure is required, and a special apparatus is required, which is disadvantageous in terms of cost.

The cavitation generation site in the present invention may be generated in a reaction vessel for synthesizing inorganic particles. In addition, can be a single treatment, also can be according to the required times of circulation. Multiple generation mechanisms can also be used to process in parallel or in series.

The spraying of the liquid for generating cavitation may be carried out in a vessel open to the atmosphere, but is preferably carried out in a pressure vessel for controlling cavitation.

In the case where cavitation is generated by liquid jetting, the solid content concentration of the reaction solution is preferably 30% by weight or less, more preferably 20% by weight or less. This is because, if the concentration is such as this, the cavitation bubbles are likely to act uniformly in the reaction system. In addition, the solid content concentration of the aqueous suspension of slaked lime as the reaction solution is preferably 0.1% by weight or more from the viewpoint of reaction efficiency.

In the present invention, for example, in the case of a composite of synthetic calcium carbonate and cellulose fiber, the pH of the reaction solution is on the alkaline side at the start of the reaction, but becomes neutral as the carbonation reaction proceeds. Therefore, the reaction can be controlled by monitoring the pH of the reaction solution.

In the present invention, by increasing the ejection pressure of the liquid, the flow velocity of the ejection liquid increases, and the pressure decreases, whereby more powerful cavitation can be generated. Further, by pressurizing the pressure in the reaction vessel, the pressure in the region where cavitation bubbles collapse becomes high, and the pressure difference between the bubbles and the surroundings becomes large, so that the bubbles collapse violently and the impact force can be increased. Further, dissolution and dispersion of the introduced carbon dioxide can be promoted. The reaction temperature is preferably from 0 ℃ to 90 ℃ and particularly preferably from 10 ℃ to 60 ℃. In general, the impact force is considered to be the largest at the intermediate point between the melting point and the boiling point, and therefore, in the case of an aqueous solution, it is preferable to be about 50 ℃.

In the production of the composite fiber of the present invention, various known auxiliaries may be further added. For example, a chelating agent may be added, 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, saccharides such as sucrose, and polyhydric alcohols such as sorbitol. Further, as the surface treatment agent, saturated fatty acids such as palmitic acid and stearic acid, unsaturated fatty acids such as oleic acid and linoleic acid, resin acids such as alicyclic carboxylic acid and abietic acid, salts, esters and ethers thereof, alcohol-based active agents, sorbitan fatty acid esters, amide-based, amine-based surfactants, polyoxyalkylene alkyl ethers, polyoxyethylene nonylphenyl ether, sodium α -olefin sulfonate, long-chain alkyl amino acids, amine oxide, alkylamine, quaternary ammonium salts, aminocarboxylic acids, phosphonic acids, polycarboxylic acids, condensed phosphoric acid, and the like may be added. Further, a dispersant may be used as needed. Examples of the dispersant include sodium polyacrylate, sucrose fatty acid ester, glycerin fatty acid ester, acrylic acid-maleic acid copolymer ammonium salt, methacrylic acid-naphthyloxy polyethylene glycol acrylate copolymer, methacrylic acid-polyethylene glycol monomethacrylate copolymer ammonium salt, and polyethylene glycol monoacrylate. They may be used alone or in combination of plural kinds. The timing of addition may be before or after the synthesis reaction. Such an additive may be added in an amount of preferably 0.001 to 20%, more preferably 0.1 to 10%, based on the inorganic particles.

In the present invention, the reaction may be a batch reaction or a continuous reaction. In general, it is preferable to perform a batch reaction step from the viewpoint of convenience in discharging a residue after the reaction. The scale of the reaction is not particularly limited, and the reaction may be carried out on a scale of 100L or less, or may be carried out on a scale exceeding 100L. The size of the reaction vessel may be, for example, about 10L to 100L, or about 100L to 1000L.

The reaction can be controlled by the conductivity of the reaction solution and the reaction time, specifically, by adjusting the time during which the reactant stays in the reaction vessel. In the present invention, the reaction may be controlled by stirring the reaction solution in the reaction tank or by performing a multistage reaction.

In the present invention, since the conjugate fiber as a reaction product is obtained in the form of a suspension, it may be stored in a storage tank or subjected to treatments such as concentration, dehydration, pulverization, classification, aging, and dispersion, as necessary. These may be determined by a known process as appropriate in consideration of the use, energy efficiency, and the like. For example, the concentration and dehydration treatment is carried out using a centrifugal dehydrator, a sedimentation concentrator, or the like. Examples of the centrifugal dehydrator include a decanter and a screw decanter. When a filter or dehydrator is used, the type thereof is not particularly limited, and a general filter or dehydrator can be used, and for example, a press type dehydrator such as a filter press, a drum filter, a belt press, a tube press, or a vacuum drum dehydrator such as an Oliver filter can be suitably used to prepare a calcium carbonate cake. Examples of the pulverization method include a ball mill, a sand mill, an impact mill, a high-pressure homogenizer, a low-pressure homogenizer, a DYNO mill, an ultrasonic mill, a KANDA mill, an attritor, a mortar mill, a vibration mill, a chopper, a jet mill, a disintegrator, a beater, a short-shaft extruder, a twin-shaft extruder, an ultrasonic mixer, a home-use juicer, and the like. Examples of the classification method include a screen such as a wire mesh, an external or internal slit or circular screen, a vibrating screen, a heavy foreign matter cleaner, a light foreign matter cleaner, a reverse cleaner, and a sieve tester. Examples of the dispersing method include a high-speed disperser and a low-speed kneader.

The composite fiber of the present invention may be blended with a filler or a pigment in a suspension state without completely dehydrating the composite fiber, but may be dried to be a powder. The dryer in this case is also not particularly limited, and for example, an air dryer, a belt dryer, a spray dryer, or the like can be suitably used.

The composite fiber of the present invention can be modified by a known method. For example, in a certain embodiment, the surface thereof may be hydrophobized to improve the miscibility with a resin or the like.

In the present invention, water is used for preparation of the suspension, and as the water, ordinary tap water, industrial water, underground water, well water, and the like can be used, and ion-exchanged water, distilled water, ultrapure water, industrial wastewater, water obtained when the reaction solution is separated and dehydrated, and the like can be suitably used.

In the present invention, the reaction solution in the reaction tank may be circulated and used. By circulating the reaction solution in this manner and promoting the stirring of the solution, the reaction efficiency can be easily improved and a desired composite of inorganic particles and fibers can be obtained.

Inorganic particles

In the present invention, the inorganic particles to be combined with the fibers are not particularly limited, and are preferably insoluble or poorly soluble in water. Since inorganic particles may be synthesized in an aqueous system and a fiber composite may be used in an aqueous system, it is preferable that the inorganic particles are insoluble or poorly soluble in water.

The inorganic particles referred to herein mean compounds of metallic elements or nonmetallic elements. The compound of the metal element means a cation of the metal (e.g., Na)⁺、Ca²⁺、Mg²⁺、Al³⁺、Ba²⁺Etc.) with anions (e.g., O)^2－、OH^－、CO₃ ^2－、PO₄ ^3－、SO₄ ^2－、NO₃－、Si₂O₃ ^2－、SiO₃ ^2－、Cl^－、F^－、S^2－Etc.) are bonded by ionic bonding and are generally referred to as inorganic salts. The compound of nonmetallic element is silicic acid (SiO)₂) And the like. In the present invention, it is preferable that at least a part of the inorganic particles is a metal salt of calcium, magnesium, or barium, or at least a part of the inorganic particles is a metal salt of silicic acid or aluminum, or a metal particle containing titanium, copper, silver, iron, manganese, cerium, or zinc.

The method for synthesizing these inorganic particles may be a known method, and may be either a gas-liquid method or a liquid-liquid method. As an example of the gas-liquid method, there is a carbon dioxide method, and for example, magnesium carbonate can be synthesized by reacting magnesium hydroxide with carbon dioxide. Examples of the liquid-liquid method include a method in which an acid (hydrochloric acid, sulfuric acid, or the like) and a base (sodium hydroxide, potassium hydroxide, or the like) are reacted by neutralization, or an inorganic salt is reacted with an acid or a base, or inorganic salts are reacted 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 can be obtained by reacting calcium sulfate with aluminum sulfate to obtain inorganic particles in which calcium and aluminum are combined. In addition, when the inorganic particles are synthesized in this manner, any metal or nonmetal compound may coexist in the reaction solution, and in this case, the metal or nonmetal compound can be efficiently introduced into the inorganic particles to be composited therewith. For example, when calcium phosphate is synthesized by adding phosphoric acid to calcium carbonate, composite particles of calcium phosphate and titanium can be obtained by allowing titanium dioxide to coexist in the reaction solution.

(calcium carbonate)

In the case of the synthetic calcium carbonate, the calcium carbonate can be synthesized by, for example, a carbon dioxide method, a soluble salt reaction method, a lime-caustic soda method, a caustic soda method, or the like, and in a preferred embodiment, the calcium carbonate is synthesized by a carbon dioxide method.

In general, in the case of producing calcium carbonate by the carbon dioxide method, lime (lime) is used as a calcium source and water is added to quicklime CaO to obtain slaked lime ca (oh)₂And blowing carbon dioxide CO into slaked lime₂To obtain calcium carbonate CaCO₃To synthesize calcium carbonate. At this time, the low-solubility lime particles contained in the suspension of slaked lime prepared by adding water to quick lime may be removed by passing the suspension through a sieve. In addition, slaked lime may be used as the calcium source. In the present invention, in the case of synthesizing calcium carbonate by the carbon dioxide method, the carbonation reaction may be carried out in the presence of cavitation bubbles.

In the case of synthesizing calcium carbonate by the carbon dioxide method, the solid content 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 still more preferably about 1 to 20% by weight. If the solid content concentration is low, the reaction efficiency is low and the production cost is high, and if the solid content concentration is too high, the fluidity is poor and the reaction efficiency is low. In the present invention, calcium carbonate is synthesized in the presence of cavitation bubbles, and therefore, even if a suspension (slurry) having a high solid content concentration is used, the reaction solution and carbon dioxide can be appropriately mixed.

As the aqueous suspension containing hydrated lime, an aqueous suspension generally used in calcium carbonate synthesis can be used, and for example, hydrated lime can be mixed with water to prepare it, or quicklime (calcium oxide) can be digested with water (digestion) to prepare it. The conditions for digestion are not particularly limited, and for example, the CaO concentration may be 0.05 wt% or more, preferably 1 wt% or more, and the temperature may be 20 to 100 ℃, preferably 30 to 100 ℃. The average residence time in the digestion reaction tank (digester) is also not particularly limited, and may be, for example, 5 minutes to 5 hours, preferably within 2 hours. Of course, the digester may be either batch or continuous. In the present invention, the carbonation reaction tank (carbonator) and the digestion reaction tank (digester) may be separated from each other, or one reaction tank may be used as the carbonation reaction tank and the digestion reaction tank.

In the synthesis of calcium carbonate, raw materials (Ca ion, CO) in the reaction solution₃Ion) is more highly concentrated and is more highly heated, the nucleation reaction is more easily progressed, but in the case of producing a composite fiber, it is difficult to fix the nucleus to the cellulose fiber under such conditions, and inorganic particles free in the suspension are easily synthesized. Therefore, in order to manufacture composite fibers in which calcium carbonate is firmly bonded, it is necessary to appropriately control the nucleation reaction. In particular, by rationalizing the Ca ion and pulp concentration and making CO₂This can be achieved by a gentle supply amount per unit time. For example, the concentration of Ca ions in the reaction vessel is preferably 0.01mol/L or more and less than 0.20 mol/L. If the amount is less than 0.01mol/L, the reaction does not proceed easily, and if the amount is 0.20mol/L or more, inorganic particles free in the suspension are easily synthesized. The pulp concentration is preferably 0.5% or more and less than 4.0%. If the amount is less than 0.5%, the frequency of collision between the raw material and the fibers is reduced, and therefore the reaction does not proceed easily, whereas if the amount is 4.0% or more, a uniform composite cannot be obtained due to poor stirring. CO 2₂The amount of (2) is preferably 0.001mol/min to less than 0.060mol/min per 1L of the reaction solution. If the amount is less than 0.001mol/min, the reaction does not proceed easily, and if the amount is 0.060mol/min or more, inorganic particles free in the suspension are easily synthesized.

(magnesium carbonate)

In the case of synthesizing magnesium carbonate, a known method can be used for the synthesis of magnesium carbonate. For example, magnesium bicarbonate can be synthesized from magnesium hydroxide and carbon dioxide, and basic magnesium carbonate can be synthesized from magnesium bicarbonate via magnesium orthocarbonate. Magnesium carbonate magnesium bicarbonate, normal magnesium carbonate, basic magnesium carbonate, and the like can be obtained by a synthetic method, and basic magnesium carbonate is particularly preferable as the magnesium carbonate of the fiber composite of the present invention. This is because magnesium bicarbonate has low stability, and magnesium orthocarbonate in the form of columnar (needle-like) crystals is sometimes not easily fixed to fibers. On the other hand, a fiber composite of magnesium carbonate and fibers with the fiber surface coated with scales or the like can be obtained by carrying out a chemical reaction in the presence of fibers until basic magnesium carbonate is produced.

In the present invention, the reaction solution in the reaction tank may be circulated and used. By circulating the reaction solution in this manner, the contact between the reaction solution and carbon dioxide is increased, and the reaction efficiency is easily improved to obtain desired inorganic particles.

In the present invention, a gas such as carbon dioxide (carbon dioxide gas) may be blown into the reaction container and mixed with the reaction solution. According to the present invention, carbon dioxide can be supplied to the reaction solution without a gas supply device such as a fan or a blower, and the cavitation bubbles can be used to reduce the carbon dioxide to fine particles, thereby enabling efficient reaction.

In the present invention, the carbon dioxide concentration of the carbon dioxide-containing gas is not particularly limited, and a high carbon dioxide concentration is preferred. The amount of carbon dioxide introduced into the syringe is not limited and can be appropriately selected.

The carbon dioxide-containing gas of the present invention may be substantially pure carbon dioxide gas or may be a mixture with other gases. For example, a gas containing an inert gas such as air or nitrogen may be used as the gas containing carbon dioxide in addition to carbon dioxide gas. Further, as the gas containing carbon dioxide, in addition to carbon dioxide gas (carbon dioxide), exhaust gas discharged from an incinerator of a paper mill, a coal-fired boiler, a heavy oil boiler, or the like can be suitably used as the gas containing carbon dioxide. In addition, the carbonation reaction may be performed using carbon dioxide generated from the lime calcination process.

In the synthesis of magnesium carbonate, raw materials (Mg ions, CO) in the reaction solution₃Ions) are present in the higher the concentration is,further, the nucleation reaction is more likely to proceed under high temperature conditions, but in the case of producing a composite fiber, it is difficult to fix the core to the cellulose fiber under such conditions, and inorganic particles free in the suspension are easily synthesized. Therefore, in order to produce a composite fiber in which magnesium carbonate is strongly bonded, it is necessary to appropriately control the nucleation reaction. In particular, by rationalising Mg ions and pulp concentration and CO₂This can be achieved by a gentle supply amount per unit time. For example, the Mg ion concentration in the reaction vessel is preferably 0.0001mol/L or more and less than 0.20 mol/L. If the amount is less than 0.0001mol/L, the reaction does not proceed easily, and if the amount is 0.20mol/L or more, inorganic particles free in the suspension are easily synthesized. The pulp concentration is preferably 0.5% or more and less than 4.0%. If the amount is less than 0.5%, the frequency of collision between the raw material and the fibers is reduced, and therefore the reaction does not proceed easily, whereas if the amount is 4.0% or more, a uniform composite cannot be obtained due to poor stirring. CO 2₂The amount of (2) is preferably 0.001mol/min to less than 0.060mol/min per 1L of the reaction solution. If the amount is less than 0.001mol/min, the reaction does not proceed easily, and if the amount is 0.060mol/min or more, inorganic particles free in the suspension are easily synthesized.

(barium sulfate)

In the case of the synthesis of barium sulfate, it is prepared from barium sulfate (BaSO)₄) The ionic crystalline compound represented by barium ions and sulfate ions is often in the form of a plate or column, and is hardly soluble in water. Pure barium sulfate is colorless crystals, but if it contains impurities such as iron, manganese, strontium, and calcium, it is yellowish brown or dark gray, and becomes translucent. It is also available in the form of natural minerals, but it can also be synthesized by chemical reactions. In particular, a synthetic product obtained by a chemical reaction is widely used for medical purposes (X-ray contrast agent) and also for paints, plastics, secondary batteries, and the like, using its chemically stable property.

In the present invention, a composite of barium sulfate and fibers can be produced by synthesizing barium sulfate in a solution in the presence of fibers. For example, there can be mentioned a method in which an acid (sulfuric acid or the like) and a base are reacted by neutralization, or an inorganic salt is reacted with an acid or a base, or inorganic salts are reacted with each other. For example, barium sulfate may be obtained by reacting barium hydroxide with sulfuric acid or aluminum sulfate, or barium chloride may be added to an aqueous solution containing a sulfate to precipitate barium sulfate.

In the synthesis of barium sulfate, the raw materials (Ba ions, SO) in the solution₄Ion) is more highly concentrated and is more highly heated, the nucleation reaction is more easily progressed, but in the case of producing a composite fiber, it is difficult to fix the nucleus to the cellulose fiber under such conditions, and inorganic particles free in the suspension are easily synthesized. Therefore, in order to manufacture a composite fiber in which barium sulfate is firmly bonded, it is necessary to appropriately control the nucleation reaction. In particular, by rationalising Ba ions and pulp concentration and making SO₄This can be achieved by a gradual supply of ions per unit time. For example, the concentration of Ba ions in the reaction vessel is preferably 0.01mol/L or more and less than 0.20 mol/L. If the amount is less than 0.01mol/L, the reaction does not proceed easily, and if the amount is 0.20mol/L or more, inorganic particles free in the suspension are easily synthesized. The pulp concentration is preferably 0.5% or more and less than 4.0%. If the amount is less than 0.5%, the frequency of collision between the raw material and the fibers is reduced, and therefore the reaction does not proceed easily, whereas if the amount is 4.0% or more, a uniform composite cannot be obtained due to poor stirring. SO (SO)₄The amount of ions supplied per unit time is preferably 0.005mol/min to less than 0.080mol/min per 1L of the reaction solution. If the amount is less than 0.001mol/min, the reaction does not proceed easily, and if the amount is 0.080mol/min or more, inorganic particles free in the suspension are easily synthesized.

(hydrotalcite)

In the case of synthesizing hydrotalcite, a known method can be used for the synthesis of hydrotalcite. For example, hydrotalcite is synthesized by immersing fibers in an aqueous carbonate solution containing carbonate ions constituting the intermediate layer and an alkali solution (sodium hydroxide or the like) in a reaction vessel, then adding an acid solution (an aqueous metal salt solution containing divalent metal ions and trivalent metal ions constituting the base layer), controlling the temperature, pH, and the like, and performing a coprecipitation reaction. Further, hydrotalcite may be synthesized by immersing fibers in an acid solution (aqueous metal salt solution containing divalent metal ions and trivalent metal ions constituting the base layer) in a reaction vessel, then adding dropwise an aqueous carbonate solution containing carbonate ions constituting the intermediate layer and an alkali solution (sodium hydroxide or the like), controlling the temperature, pH, or the like, and performing a coprecipitation reaction. In general, the reaction is carried out under normal pressure, but in addition to this, there is a method of obtaining the reaction by hydrothermal reaction using an autoclave or the like (Japanese patent laid-open No. 60-6619).

In the present invention, as a supply source of the divalent metal ions constituting the base layer, various chlorides, sulfides, nitrates, and sulfates of magnesium, zinc, barium, calcium, iron, copper, cobalt, nickel, and manganese can be used. As a source of the trivalent metal ion constituting the base layer, various chlorides, sulfides, nitrates, and sulfates of aluminum, iron, chromium, and gallium can be used.

In the present invention, as the interlayer anion, a carbonate ion, a nitrate ion, a chloride ion, a sulfate ion, a phosphate ion, or the like can be used. In the case of carbonate ions as interlayer anions, sodium carbonate is used as a supply source. However, the sodium carbonate may be replaced with a gas containing carbon dioxide (carbon dioxide gas), or may be a substantially pure carbon dioxide gas or a mixture with another gas. For example, exhaust gas discharged from an incinerator of a paper mill, a coal-fired boiler, a heavy oil boiler, or the like can be suitably used as the carbon dioxide-containing gas. In addition, the carbonation reaction may be performed using carbon dioxide generated from the lime calcination process.

In the synthesis of hydrotalcite, raw materials in solution (metal ions, CO constituting the basic layer)₃Ions, etc.) at a higher concentration and at a higher temperature, the nucleation reaction proceeds more easily, but under such conditions, in the case of producing a conjugate fiber, it is difficult to fix the core to the cellulose fiber, and inorganic particles free in the suspension are easily synthesized. Therefore, in order to produce composite fibers in which hydrotalcite is strongly bonded, it is necessary to appropriately control the nucleation reaction. In particular, by CO₃Rationalizing ion and pulp concentration and making the supply of metal ions per unit timeGentle, this can be achieved. For example, CO in the reaction vessel₃The ion concentration is preferably 0.01mol/L or more and less than 0.80 mol/L. If the amount is less than 0.01mol/L, the reaction does not proceed easily, and if the amount is 0.80mol/L or more, inorganic particles free in the suspension are easily synthesized. The pulp concentration is preferably 0.5% or more and less than 4.0%. If the amount is less than 0.5%, the frequency of collision between the raw material and the fibers is reduced, and therefore the reaction does not proceed easily, whereas if the amount is 4.0% or more, a uniform composite cannot be obtained due to poor stirring. The amount of the metal ion supplied per unit time also depends on the type of the metal, and for example, in the case of Mg ion, it is preferably 0.001mol/min or more and less than 0.010mol/min, and more preferably 0.001mol/min or more and less than 0.005mol/min per 1L of the reaction solution. If the amount is less than 0.001mol/min, the reaction does not proceed easily, and if the amount is 0.010mol/min or more, inorganic particles free in the suspension are easily synthesized.

(alumina/silica)

In the case of synthesizing alumina and/or silica, a known method can be used for the synthesis method of alumina and/or silica. When at least one of an inorganic acid and an aluminum salt is used as a starting material for the reaction, a silicate salt is added to the reaction mixture to synthesize the compound. The fiber can be synthesized by using a silicate salt as a starting material and adding at least one of an inorganic acid and an aluminum salt, but when an inorganic acid and/or an aluminum salt is used as a starting material, the fixation of the product to the fiber is good. The inorganic acid is not particularly limited, and for example, sulfuric acid, hydrochloric acid, nitric acid, or the like can be used. Among these, sulfuric acid is particularly preferable from the viewpoint of cost and handling. Examples of the aluminum salt include aluminum sulfate, aluminum chloride, polyaluminum chloride, alum, potassium alum, and among them, aluminum sulfate can be suitably used. Examples of the alkali silicate salt include sodium silicate and potassium silicate, and sodium silicate is preferred because it is easily available. The molar ratio of silicic acid to alkali can be any, and the product circulated as silicic acid number 3 is generally SiO₂：Na₂O is 3-3.4: sodium silicate is used in a molar ratio of about 1, and the product can be used appropriately.

In the present invention, in the production of a composite fiber in which silica and/or alumina are adhered to the surface of the fiber, it is preferable to synthesize silica and/or alumina on the fiber while maintaining the pH of the reaction solution containing the fiber at 4.6 or less. The reason why the composite fiber having a fiber surface coated well is obtained is not completely understood in detail, but it is considered that the ionization rate to trivalent aluminum ions is increased by maintaining the pH at a low level, and thus a composite fiber having a high coating rate and a high fixation rate can be obtained.

In the synthesis of silica and/or alumina, the nucleation reaction is more likely to proceed under the conditions of higher concentration of the raw materials (silicate ions and aluminum ions) in the reaction solution and higher temperature, but in the case of producing a composite fiber, it is difficult to fix the core to the cellulose fiber under such conditions, and inorganic particles free in the suspension are easily synthesized. Therefore, in order to manufacture composite fibers in which silica and/or alumina are firmly bonded, it is necessary to appropriately control the nucleation reaction. Specifically, this can be achieved by rationalizing the pulp concentration and by making the supply amount per unit time of silicate ions and aluminum ions to be added gentle. For example, the pulp concentration is preferably 0.5% or more and less than 4.0%. If the amount is less than 0.5%, the frequency of collision between the raw material and the fibers is reduced, and therefore the reaction does not proceed easily, whereas if the amount is 4.0% or more, a uniform composite cannot be obtained due to poor stirring. The amount of silicate ions and aluminum ions to be added per unit time is, for example, preferably 0.001mol/min or more, more preferably 0.01mol/min or more, and further preferably less than 0.5mol/min, more preferably less than 0.050mol/min per 1L of the reaction solution in the case of aluminum ions. If the amount is less than 0.001mol/min, the reaction does not proceed easily, and if the amount is 0.050mol/min or more, inorganic particles free in the suspension are easily synthesized.

As a preferable aspect, the average primary particle size of the inorganic particles in the composite fiber of the present invention may be, for example, 1.5 μm or less, but the average primary particle size may be 1200nm or less and 900nm or less, and further, the average primary particle size may be 200nm or less and 150nm or less. The inorganic particles may have an average primary particle diameter of 10nm or more. The average primary particle size can be measured by electron micrograph.

(aluminum hydroxide)

The aluminum hydroxide is prepared from Al (OH)₃The ionic crystalline compound represented by the formula (I) is mostly in the form of particles and is hardly soluble in water. The synthetic products obtained by the chemical reaction are used as pharmaceuticals and adsorbents, and also as flame retardants and noncombustible agents by utilizing the property of releasing water when heated.

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. For example, a method of reacting an acid (sulfuric acid or the like) with a base by neutralization, or reacting an inorganic salt with an acid or a base, or reacting inorganic salts with each other can be mentioned. For example, aluminum hydroxide may be obtained by reacting sodium hydroxide with aluminum sulfate, or aluminum hydroxide may be precipitated by adding aluminum chloride to an aqueous solution containing an alkali salt.

In the synthesis of aluminum hydroxide, the nucleation reaction is more likely to proceed under conditions of higher concentration of raw materials (Al ions and OH ions) in the solution and higher temperature, but in the case of producing a composite fiber, it is difficult to fix the nuclei to the cellulose fiber under such conditions, and inorganic particles free in the suspension are easily synthesized. Therefore, in order to produce a composite fiber in which aluminum hydroxide is firmly bonded, it is necessary to appropriately control the nucleation reaction. Specifically, this can be achieved by rationalizing the OH ion and pulp concentration and making the supply amount of Al ions per unit time gentle. For example, the OH ion concentration in the reaction vessel is preferably 0.01mol/L or more and less than 0.50 mol/L. If the amount is less than 0.01mol/L, the reaction does not proceed easily, and if the amount is 0.50mol/L or more, inorganic particles free in the suspension are easily synthesized. The pulp concentration is preferably 0.5% or more and less than 4.0%. If the amount is less than 0.5%, the frequency of collision between the raw material and the fibers is reduced, and therefore the reaction does not proceed easily, whereas if the amount is 4.0% or more, a uniform composite cannot be obtained due to poor stirring. The amount of Al ions supplied per unit time is preferably 0.001mol/min to less than 0.050mol/min per 1L of the reaction solution. If the amount is less than 0.001mol/min, the reaction does not proceed easily, and if the amount is 0.050mol/min or more, inorganic particles free in the suspension are easily synthesized.

Cellulose fiber

The composite fiber used in the present invention is obtained by combining a cellulose fiber and inorganic particles. As the cellulose fiber constituting the composite, natural cellulose fiber, regenerated fiber (semi-synthetic fiber) such as rayon or lyocell, synthetic fiber, or the like may be used without limitation, as well as natural cellulose fiber. Examples of the raw material of the cellulose fiber include pulp fiber (wood pulp, non-wood pulp), cellulose nanofiber, bacterial cellulose, cellulose derived from animals such as ascidians, algae, and the like, and the wood pulp may be produced by pulping the wood raw material. Examples of the wood material include needle-leaved trees such as red pine, black pine, fir, spruce, red pine, larch, japanese fir, hemlock, japanese cedar, japanese cypress, larch, white fir, scale spruce, cypress, douglas fir, canadian hemlock, white fir, spruce, balsam fir, cedar, pine, southern pine, radiata pine, and mixtures thereof, and broad-leaved trees such as japanese beech, birch, japanese alder, oak, red-leaf nanmu, chestnut, white birch, black poplar, water chestnut, sweet poplar, red tree, eucalyptus, acacia, and mixtures thereof.

The method for pulping natural materials such as wood materials (wood materials) is not particularly limited, and examples thereof include pulping methods generally used in the paper industry. Wood pulp can be classified by a pulping method, and examples thereof include chemical pulp obtained by cooking by a method such as a kraft method, sulfite method, soda method, polysulfide method, or the like; mechanical pulp obtained by pulping with mechanical force of a refiner, a grinder, or the like; semichemical pulp obtained by pulping with mechanical force after pretreatment with a chemical agent; waste paper pulp; deinked pulp, and the like. The wood pulp may be unbleached (before bleaching) or bleached (after bleaching).

Examples of the pulp derived from non-wood include cotton, hemp, sisal, abaca, flax, straw, bamboo, bagasse, kenaf, sugarcane, corn, rice stem, broussonetia papyrifera (grape flat), and daphne.

The pulp fiber may be either unbaked or beaten, and may be selected depending on the physical properties of the composite sheet, and beating is preferably performed. This is expected to improve the sheet strength and promote the fixation of the inorganic particles.

These cellulose raw materials may be further processed to be used as chemically modified cellulose such as powdered cellulose and oxidized cellulose, and cellulose nanofibers: CNF (microfibrillated cellulose: MFC, TEMPO oxidized CNF, phosphated CNF, carboxymethylated CNF, mechanically crushed CNF, etc.). As the powdery cellulose used in the present invention, for example, crystalline cellulose powder having a uniform particle size distribution in a rod shape produced by a method such as refining, drying, pulverizing and sieving an undecomposed residue obtained by hydrolyzing selected pulp with an acid may be used, and commercially available products such as KC FLOCK (manufactured by japan paper products), CEOLUS (manufactured by asahi chemicals), Avicel (manufactured by FMC corporation) and the like may be used. The polymerization degree of cellulose in the powdered cellulose is preferably about 100 to 1500, the crystallinity of the powdered cellulose measured by X-ray diffraction method is preferably 70 to 90%, and the volume average particle diameter measured by a laser diffraction particle size distribution measuring apparatus is preferably 500nm to 100 μm.

The oxidized cellulose used in the present invention can be obtained, for example, by oxidizing in water using an oxidizing agent in the presence of a compound selected from an N-oxyl compound and a bromide, an iodide or a mixture thereof. As the cellulose nanofibers, the above-described cellulose raw material can be subjected to a method of defibering. As the defibration method, for example, the following methods can be used: an aqueous suspension of chemically modified cellulose such as cellulose or oxidized cellulose is mechanically ground or beaten by a refiner, a high-pressure homogenizer, a grinder, a single-or multi-shaft mixer, a bead mill or the like to thereby defibrate the cellulose. The above methods may also be combined with 1 or more to produce cellulose nanofibers. The fiber diameter of the produced cellulose nanofibers can be confirmed by electron microscope observation or the like, and is preferably in the range of 5nm to 300nm, for example. In the production of the cellulose nanofibers, an arbitrary compound may be further added before and/or after the cellulose is defibrinated and/or refined to react with the cellulose nanofibers to produce hydroxyl group-modified cellulose. Examples of the modified functional group include acetyl group, ester group, ether group, ketone group, formyl group, benzoyl group, acetal, hemiacetal, oxime, isonitrile, allene, thiol group, urea group, cyano group, nitro group, azo group, aryl group, aralkyl group, amino group, amide group, imide group, acryloyl group, methacryloyl group, propionyl group, propioyl group, butyryl group, 2-butyryl group, pentanoyl group, hexanoyl group, heptanoyl group, octanoyl group, nonanoyl group, decanoyl group, undecanoyl group, dodecanoyl group, myristoyl group, palmitoyl group, stearoyl group, pivaloyl group, benzoyl group, naphthoyl group, nicotinoyl group, isonicotinoyl group, furoyl group, cinnamoyl group and other acyl groups, 2-methacryloyloxyethylisocyanato group and other isocyanato group, such as methyl group, ethyl group, propyl group, 2-propyl group, butyl group, 2-butyl group, tert-butyl group, pentyl group, hexyl group, oxime group, isonicotinoyl group, octanoyl group, and other isocyanato group, Alkyl groups such as heptyl, octyl, nonyl, decyl, undecyl, dodecyl, myristyl, palmityl, and stearyl, ethylene oxide, oxetanyl, oxy, thiiranyl, and thietanyl. The hydrogen in these substituents may be substituted with a functional group such as a hydroxyl group or a carboxyl group. In addition, a part of the alkyl group may be an unsaturated bond. The compound for introducing these functional groups is not particularly limited, and examples thereof include a compound having a group derived from phosphoric acid, a compound having a group derived from carboxylic acid, a compound having a group derived from sulfuric acid, a compound having a group derived from sulfonic acid, a compound having an alkyl group, and a compound having a group derived from amine. The compound having a phosphate group is not particularly limited, and examples thereof include phosphoric acid, lithium dihydrogen phosphate as a lithium salt of phosphoric acid, dilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, and lithium polyphosphate. Further examples of the sodium salt of phosphoric acid include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, and sodium polyphosphate. Further examples of the potassium salt of phosphoric acid include potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate. Further, ammonium salts of phosphoric acid such as monoammonium phosphate, diammonium phosphate, triammonium phosphate, ammonium pyrophosphate and ammonium polyphosphate may be mentioned. Among these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are preferable, sodium dihydrogen phosphate, and disodium hydrogen phosphate are more preferable, and there is no particular limitation, from the viewpoint of high efficiency of introduction of phosphoric acid groups and easy industrial application. The compound having a carboxyl group is not particularly limited, and examples thereof 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. The acid anhydride of the compound having a carboxyl group is not particularly limited, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. The derivative of the compound having a carboxyl group is not particularly limited, and an imide compound of an acid anhydride of the compound having a carboxyl group and a derivative of an acid anhydride of the compound having a carboxyl group are exemplified. The imide compound of the acid anhydride of the compound having a carboxyl group is not particularly limited, and examples thereof include imide compounds of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide. The acid anhydride derivative of the compound having a carboxyl group is not particularly limited. Examples thereof include compounds in which at least a part of hydrogen atoms of an acid anhydride of a compound having a carboxyl group such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, etc. is substituted with a substituent (e.g., an alkyl group, a phenyl group, etc.). Among the compounds having a group derived from a carboxylic acid, maleic anhydride, succinic anhydride, and phthalic anhydride are preferable from the viewpoint of easy industrial application and easy vaporization, and are not particularly limited. In addition, the cellulose nanofibers can be modified in such a manner that the modified compound is physically adsorbed to the cellulose nanofibers, even without chemical bonding. Examples of the physisorbed compound include surfactants, and any of anionic, cationic, and nonionic compounds can be used. In the case where the modification is performed before the cellulose is defibered and/or pulverized, these functional groups may be eliminated after the defibering and/or pulverization to restore the original hydroxyl groups. By performing the modification as described above, the cellulose nanofibers can be accelerated to be defibered, or when cellulose nanofibers are used, the cellulose nanofibers can be easily mixed with various substances.

The fibers shown above may be used alone or in combination of two or more. For example, fibrous materials recovered from the drainage of a paper mill may also be supplied to the carbonation reaction of the present invention. By supplying such a substance to the reaction tank, various composite particles can be synthesized, and fibrous particles and the like can be synthesized in shape.

In the present invention, in addition to the fibers, a substance that is incorporated into inorganic particles as a product to form composite particles may be used. In the present invention, fibers typified by pulp fibers are used, but in addition to these, composite particles further incorporating inorganic particles can be produced by synthesizing the inorganic particles in a solution containing the inorganic particles, organic particles, polymers, and the like.

The fiber length of the composite fiber is not particularly limited, and for example, the average fiber length may be about 0.1 μm to 15mm, or 1 μm to 12mm, 100 μm to 10mm, or 400 μm to 8 mm. In the present invention, the average fiber length is preferably 400 μm or more (0.4mm or more).

The average fiber diameter of the fibers to be combined is not particularly limited, and for example, the average fiber diameter may be about 1nm to 100 μm, or may be 500nm to 100 μm, 1 μm to 90 μm, 3 μm to 50 μm, or 5 μm to 30 μm. Among them, in the present invention, it is preferable that the average fiber diameter is 500nm or more because the production efficiency in the subsequent step can be improved.

The average fiber length and the average fiber diameter of the fibers can be measured by a fiber length measuring device. An example of the fiber length measuring device is a Valmet Fractor (manufactured by Valmet).

The composite fiber is preferably used in such an amount that 15% or more of the fiber surface is coated with inorganic particles, and for example, the weight ratio of the fiber to the inorganic particles may be 5/95 to 95/5, or 10/90 to 90/10, 20/80 to 80/20, 30/70 to 70/30, or 40/60 to 60/40.

In a preferred embodiment of the composite fiber of the present invention, 15% or more of the fiber surface is coated with the inorganic particles, and if the cellulose fiber surface is coated at such an area ratio, the characteristics caused by the inorganic particles are remarkably generated, while the characteristics caused by the fiber surface are reduced.

The composite fiber of the present invention can be used in various shapes, for example, in the form of powder, granule, mold, aqueous suspension, paste, sheet, plate, block, or other shapes. Further, the composite fiber may be used as a main component to form a molded article such as a mold, a pellet, or a pellet together with other materials. The dryer used for drying to obtain powder is not particularly limited, and for example, an air flow dryer, a belt dryer, a spray dryer, or the like can be suitably used.

The composite fiber of the present invention can be used for various applications, and for example, can be widely used for paper, fiber, cellulose-based composite material, filter material, paint, plastic or other resin, rubber, elastomer, ceramic, glass, tire, building material (asphalt, asbestos, cement, plate material, concrete, brick, tile, plywood, fiberboard, ceiling material, wall material, flooring material, roofing material, etc.), furniture, various carriers (catalyst carrier, medical carrier, pesticide carrier, microorganism carrier, etc.), adsorbent (for removing impurities, deodorization, dehumidification, etc.), antibacterial material, antiviral material, anti-wrinkle agent, clay, abrasive material, friction material, modifier, repair material, heat insulating material, heat-resistant material, heat-dissipating material, moisture-proof material, waterproof material, water-proof material, light-screening material, sealing agent, shielding material, heat-resistant material, heat-dissipating material, moisture-proof material, waterproof material, water-screening material, water-proof material, water-blocking material, water-proof material, and the like, Insect-proofing agents, adhesives, medical materials, paste materials, discoloration inhibitors, electromagnetic wave absorbers, insulators, sound insulators, interior materials, vibration insulators, semiconductor sealing materials, radiation-shielding materials, and materials. In addition, the composition can be used for various fillers, coating agents, and the like in the above-mentioned applications. Among them, adsorbents, antibacterial materials, antiviral agents, friction materials, radiation shielding materials, flame retardant materials, building materials, and heat insulating materials are preferable.

The composite of the present invention can be used for paper-making applications, and examples thereof include printing paper, newspaper, ink-jet paper, paper for PPC, kraft paper, fine paper, coated paper, micro-coated paper, wrapping paper, tissue paper, color fine paper, cast paper, carbonless paper, paper for labels, thermal paper, various paper patterns, water-soluble paper, release paper, craft paper, base paper for wallpaper, flame-retardant paper (non-combustible paper), laminate base paper, printed electronic paper, battery separator, cushion paper, drawing paper, impregnated paper, ODP paper, construction paper, paper for cosmetics, envelope paper, tape paper, heat-exchange paper, chemical fiber paper, sterilized paper, water-resistant paper, oil-resistant paper, heat-resistant paper, photocatalytic paper, cosmetic paper (oil-absorbing paper, etc.), various toilet paper (toilet paper, facial tissue, wiping paper, diaper, physiological product, etc.), tobacco paper, cardboard paper (mounting paper, paper for paper, paper for cosmetics, paper, etc.), tobacco, paper for paper, paper for paper, paper for use, paper for use, paper for use, paper for example, paper for paper, paper for use, paper for paper, paper for use, paper for paper, paper for use, paper for paper, paper for use, paper for paper, paper for paper, paper for paper, paper for, Core base paper, white board paper, etc.), paper tray base paper, cup base paper, baking paper, sandpaper, synthetic paper, etc. That is, according to the present invention, since a composite of inorganic particles and fibers having a small primary particle diameter and a narrow particle size distribution can be obtained, it is possible to exhibit characteristics different from those of conventional inorganic fillers having a particle diameter of more than 2 μm. Further, unlike the case where only inorganic particles are simply blended in fibers, when inorganic particles and fibers are combined in advance, a sheet in which the inorganic particles are not only easily retained in the sheet but also uniformly dispersed without aggregation can be obtained. In a preferred embodiment, the inorganic particles are not only fixed to the outer surface and the inner side of the lumen of the fiber but also generated on the inner side of the microfiber, and this is confirmed by the observation result of an electron microscope.

When the composite fiber of the present invention is used, particles and various fibers, which are generally called inorganic filler and organic filler, can be used in combination. Examples of the inorganic filler 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, lamellar kaolin), talc, zinc oxide, zinc stearate, titanium dioxide, silica (white carbon, silica/calcium carbonate complex, silica/titanium dioxide complex) produced from sodium silicate and an inorganic acid, clay, bentonite, diatomaceous earth, calcium sulfate, zeolite, an inorganic filler used by regenerating ash obtained in the deinking step, and an inorganic filler that forms a complex with silica and calcium carbonate in the regeneration step. As the calcium carbonate-silica composite, amorphous silica such as white carbon may be used in combination with calcium carbonate and/or light calcium carbonate-silica composite. Examples of the organic filler include urea resin, polystyrene resin, phenol resin, fine hollow particles, acrylamide composite, wood-derived substances (fine fibers, microfiber fibers, and powdered kenaf), modified insoluble starch, and ungelatinized starch. As the fibers, natural fibers such as cellulose can be used, and synthetic fibers artificially synthesized from raw materials such as petroleum, regenerated fibers (semi-synthetic fibers) such as rayon and lyocell, inorganic fibers, and the like can be used without limitation. Examples of natural fibers include protein fibers such as wool, silk, and collagen fibers, complex carbohydrate fibers such as chitin-chitosan fibers and alginic acid fibers, and the like. Examples of the cellulose-based raw material include pulp fibers (wood pulp, non-wood pulp), bacterial cellulose, cellulose derived from animals such as ascidians, and algae, and the wood pulp can be produced by pulping a wood raw material. Examples of the wood material include needle-leaved trees such as red pine, black pine, fir, spruce, red pine, larch, japanese fir, hemlock, japanese cedar, japanese cypress, larch, white fir, scale spruce, cypress, douglas fir, canadian hemlock, white fir, spruce, balsam fir, cedar, pine, southern pine, radiata pine, and mixtures thereof, and broad-leaved trees such as japanese beech, birch, japanese alder, oak, red-leaf nanmu, chestnut, white birch, black poplar, water chestnut, sweet poplar, red tree, eucalyptus, acacia, and mixtures thereof. The method for pulping the wood material is not particularly limited, and a pulping method generally used in the paper industry can be exemplified. Wood pulp can be classified by a pulping method, and examples thereof include chemical pulp obtained by cooking by a method such as a kraft method, sulfite method, soda method, polysulfide method, or the like; mechanical pulp obtained by pulping with mechanical force of a refiner, a grinder, or the like; semichemical pulp obtained by pulping with mechanical force after pretreatment with a chemical agent; waste paper pulp; deinked pulp, and the like. The wood pulp may be unbleached (before bleaching) or bleached (after bleaching). Examples of the pulp derived from non-wood include cotton, hemp, sisal, abaca, flax, straw, bamboo, bagasse, kenaf, sugarcane, corn, rice stem, broussonetia papyrifera (grape flat), and daphne. The wood pulp and the non-wood pulp may be any of unbleached and beaten. These cellulose raw materials may be further processed to obtain chemically modified cellulose such as powdered cellulose and oxidized cellulose, and cellulose nanofibers: CNF (microfibrillated cellulose: MFC, TEMPO oxidized CNF, phosphated CNF, carboxymethylated CNF, mechanically pulverized CNF) was used. Examples of the synthetic fibers include polyester, polyamide, polyolefin, and acrylic fibers, examples of the semisynthetic fibers include rayon and acetate fibers, and examples of the inorganic fibers include glass fibers, carbon fibers, and various metal fibers. The above components may be used alone or in combination of 2 or more.

The average particle diameter, shape, and the like of the inorganic particles constituting the composite fiber of the present invention can be confirmed by observation with an electron microscope. Further, by adjusting the conditions for synthesizing the inorganic particles, inorganic particles having various sizes and shapes can be combined with the fibers.

Morphology of composite fiber

In the present invention, the composite fiber can be molded into various molded articles (bodies). For example, if the composite fiber of the present invention is formed into a sheet, a sheet with high ash content can be easily obtained. Further, the obtained sheet may be laminated to form a multilayer sheet.

Examples of paper machines (papermaking machines) used for sheet production include fourdrinier wire machines, cylinder wire machines, gap wire machines, hybrid machines, multi-layer paper machines, and known papermaking machines combining these machines. The press line pressure in the paper machine and the calendering line pressure in the case of calendering at the subsequent stage can be determined within a range not affecting the workability and the performance of the composite sheet. The sheet thus formed may be impregnated or coated with starch, various polymers, pigments, or a mixture thereof.

Wet and/or dry paper strength agents (paper strength agents) may be added during sheeting. This can improve the strength of the composite sheet. Examples of the paper strength agent include resins such as urea-formaldehyde resin, melamine-formaldehyde resin, polyamide, polyamine, epichlorohydrin resin, plant rubber, latex, polyethyleneimine, glyoxal, gum, mannogalactan polyethyleneimine, polyacrylamide resin, polyvinylamine, and polyvinyl alcohol; a composite polymer or a copolymer polymer comprising 2 or more selected from the above resins; starch and processed starch; carboxymethyl cellulose, guar gum, urea resins, and the like. The amount of the paper strength agent added is not particularly limited.

In addition, a high molecular polymer or an inorganic substance may be added to facilitate the fixation of the filler to the fiber or to increase the retention of the filler or the fiber. For example, as the coagulant, cationic polymers such as polyethyleneimine, modified polyethyleneimine containing a tertiary amino group and/or a quaternary ammonium group, polyalkylenimine, dicyandiamide polymer, polyamine/epichlorohydrin polymer, dialkyl diallyl quaternary ammonium monomer, dialkyl amino alkyl acrylate, dialkyl amino alkyl methacrylate, dialkyl amino alkyl acrylamide, and a polymer of dialkyl amino alkyl methacrylamide and acrylamide, a polymer composed of a monoamine and an epihalohydrin, polyvinylamine, a polymer having a vinylamine moiety, and a mixture thereof can be used, in addition to these, a cation-rich zwitterionic polymer obtained by copolymerizing an anionic group such as a carboxyl group or a sulfone group in the molecule of the polymer, a mixture of a cationic polymer and an anionic or zwitterionic polymer, or the like can be used. As the retention aid, a cationic, anionic or amphoteric polyacrylamide-based material can be used. In addition, other than this, a so-called two-polymer retention system using at least one kind of cationic and anionic polymer in combination, or a multi-component retention system using at least one kind of anionic bentonite, colloidal silica, polysilicic acid or polysilicate microgel, inorganic microparticles such as aluminum modified products thereof, and one or more kinds of acrylamide, and a so-called organic microparticle having a particle size of 100 μm or less, which is obtained by crosslinking polymerization, may be used. In particular, the polyacrylamide-based substance used alone or in combination can provide a good retention rate when it has a weight average molecular weight of 200 kilodaltons or more as measured by an ultimate viscosity method, and can provide a very high retention rate when it is the above acrylamide-based substance of preferably 500 kilodaltons or more, more preferably 1000 kilodaltons or more and less than 3000 kilodaltons. The form of the polyacrylamide-based material may be emulsion type or solution type. The specific composition is not particularly limited as long as the composition contains an acrylamide monomer unit as a structural unit, and examples thereof include a copolymer of acrylamide and a quaternary ammonium salt of an acrylic acid ester, and an ammonium salt obtained by copolymerizing acrylamide and an acrylic acid ester and then performing quaternization. The cationic charge density of the cationic polyacrylamide-based substance is not particularly limited.

In addition, depending on the purpose, there may be mentioned a drainage improver, an internal sizing agent, a pH adjuster, a defoaming agent, an asphalt control agent, a slime control agent, a bulking agent, inorganic particles (so-called fillers) such as calcium carbonate, kaolin, talc, silica and the like. The amount of each additive is not particularly limited.

The basis weight (weight per unit area: weight per 1 square meter) of the sheet can be suitably adjusted according to the purpose, and for example, when the sheet is used as a building material, the basis weight is 60 to 1200g/m²It is preferable because the strength is high and the drying load during production is low. Further, the weight per unit area of the sheet may be 1200g/m²The amount of the surfactant is, for example, 2000 to 110000g/m²。

Molding methods other than sheet molding may be used, and for example, a method of flowing a raw material into a mold and performing suction dewatering and drying, such as so-called pulp molding, or a method of coating the surface of a molded product of a resin, a metal, or the like, drying, and then peeling the molded product from a base material, and the like can be used to obtain molded products having various shapes. Further, the resin may be mixed and molded like plastic. The plate-like material may be formed by press and hot press molding, which is generally used for forming inorganic boards such as cement and gypsum, or may be formed into a block-like material. Generally, the sheet is bent or wound, but may be formed into a plate shape when further strength is required. The molded article may be a block having a thickness, that is, a block, and may be, for example, a rectangular parallelepiped, a cube, or the like.

In the compounding, drying and molding described above, only 1 type of composite may be used, or 2 or more types of composite may be used in combination. When 2 or more kinds of the composite are used, a mixture of these may be used, or they may be mixed after mixing, drying, molding, and the like.

Thereafter, various organic materials such as polymers and various inorganic materials such as pigments may be added to the composite molded article.

Printing may be performed on the molded article produced from the product of the present invention. The printing method is not particularly limited, and may be performed by a known method such as offset printing, screen printing, gravure printing, micro-gravure printing, flexo printing, letterpress printing, dry printing, form printing, on-demand printing, roll printing, and inkjet printing. Among these, ink jet printing is preferable because it does not require the production of a blanket as in offset printing, and it is relatively easy to increase the size of an ink jet printer, and therefore printing can be performed on a large sheet. In addition, since flexographic printing can be appropriately printed on a molded product having a large surface unevenness, it can be appropriately used even when the molded product is molded into a shape such as a plate, a mold, or a block.

The type of pattern of the print image formed by printing is not particularly limited, and may be arbitrarily selected from, for example, a wood grain pattern, a stone grain pattern, a cloth grain pattern, an abstract pattern, a geometric pattern, a character, a symbol, a combination thereof, or the like, as necessary, or may be a solid color.

Examples

The present invention will be described in more detail by way of specific examples, but the present invention is not limited to the following specific examples. In the present specification, unless otherwise specified, concentrations, parts, and the like are based on weight, and numerical ranges are expressed as including the endpoints thereof.

Experiment 1 Synthesis of Complex

1-1. Composite fiber of Ba sulfate and cellulose fiber

(sample 1, FIG. 1)

After 436g of 1% pulp slurry (LBKP, CSF 450mL, average fiber length: about 0.7mm, average fiber diameter: about 19 μm) and 18.8g of barium hydroxide octahydrate (japanese chemical industry) were mixed by a three-motor (500rpm), aluminum sulfate (stock solution of aluminum sulfate, 25.8g) was added dropwise at 0.4 g/min. After the end of the dropwise addition, the stirring was continued for 30 minutes to obtain sample 1.

(sample 2, FIG. 2)

533g of 1.7% pulp slurry (LBKP, CSF 450mL, average fiber length: about 0.7mm, average fiber diameter: about 19 μm) and 12.4g of barium hydroxide octahydrate (japanese chemical industry) were mixed by a three-motor (667rpm), and then aluminum sulfate (4-fold diluted aqueous solution of aluminum sulfate stock solution, 67.2g) was added dropwise at 1.1 g/min. After the end of the dropwise addition, the stirring was continued for 30 minutes to obtain sample 2.

(sample 3, FIG. 3)

437g of 1% pulp slurry (NBKP, CSF: 425mL, average fiber length: about 1.7mm, average fiber diameter: about 26 μm) and 18.8g of barium hydroxide octahydrate (Japan chemical industry) were mixed by a three-motor (500rpm), and then aluminum sulfate (stock solution of aluminum sulfate, 26.1g) was added dropwise at 0.4 g/min. After the end of the dropwise addition, the stirring was continued for 30 minutes to obtain sample 3.

(sample 4, FIG. 4)

After 436g of 1% pulp slurry (LBKP, CSF 450mL, average fiber length: about 0.7mm, average fiber diameter: about 19 μm) and 18.8g of barium hydroxide octahydrate (japanese chemical industry) were mixed by a three-motor (500rpm), aluminum sulfate (stock solution of aluminum sulfate, 25.8g) was added dropwise at 1.0 g/min. After the end of the dropwise addition, the mixture was directly stirred for 30 minutes to obtain a composite slurry.

(sample 5, FIG. 5, inorganic particles only)

437g of water and barium hydroxide octahydrate (18.8 g in Japan chemical industry) were mixed in a 2L vessel by a three-motor (500rpm), and then aluminum sulfate (stock solution of aluminum sulfate, 25.8g) was added dropwise at 1.0 g/min. After the end of the dropwise addition, the stirring was continued for 30 minutes to obtain a sample of barium sulfate particles.

(sample 6, FIG. 6, mixture of inorganic particles and cellulose fibers)

To 120g of 1% pulp slurry (LBKP, CSF 450mL, average fiber length: about 0.7mm, average fiber diameter: about 19 μm) was mixed 121g of barium sulfate particle slurry (concentration: 3.0%) of sample 6, and then water was added and stirred to obtain a mixed slurry of barium sulfate and cellulose fibers.

(sample 7, FIG. 7)

500g of 1% pulp slurry (LBKP/NBKP. 8/2, average fiber length: about 1.2mm, average fiber diameter: about 14 μm) and 5.82g of barium hydroxide octahydrate (Fuji film and Wako pure chemical industries, Ltd.) were mixed by a three-motor (1000rpm), and then sulfuric acid (Fuji film and Wako pure chemical industries, 2.1g) was added dropwise at 0.8 g/min. After the end of the dropwise addition, the mixture was directly stirred for 30 minutes to obtain a sample of composite slurry.

(sample 8, FIG. 8)

500g of 1% pulp slurry (LBKP/NBKP. 8/2, average fiber length: about 1.2mm, average fiber diameter: about 14 μm) and 5.82g of barium hydroxide octahydrate (Fuji film and Wako pure chemical industries, Ltd.) were mixed by a three-motor (1000rpm), and sulfuric acid (Fuji film and Wako pure chemical industries, Ltd., 2.1g) was added dropwise at 63.0 g/min. After the end of the dropwise addition, the mixture was directly stirred for 30 minutes to obtain a sample of composite slurry.

(sample 9, FIG. 9)

500g of 1% pulp slurry (LBKP/NBKP. 8/2, average fiber length: about 1.2mm, average fiber diameter: about 14 μm) and 5.82g of barium hydroxide octahydrate (Fuji film and Wako pure chemical industries, Ltd.) were mixed by a three-motor (1000rpm), and sulfuric acid (Fuji film and Wako pure chemical industries, 2% aqueous solution 88g) was added dropwise at 8.0 g/min. After the end of the dropwise addition, the mixture was directly stirred for 30 minutes to obtain a sample of composite slurry.

(sample 10, FIG. 10)

1% pulp slurry (LBKP/NBKP. 8/2, CSF 80mL in Canadian Standard freeness, average fiber length: 1.21mm, 500g) and barium hydroxide octahydrate (Wako Junyaku K.K., 5.82g) were mixed with stirring by a three-motor (1000rpm), and then sulfuric acid (Wako Junyaku K.K., 88g in 2% aqueous solution) was added dropwise at 8g/min by a peristaltic pump. After the end of the dropwise addition, the stirring was continued for 30 minutes to obtain a sample. As a result of observation by an electron microscope, it was confirmed that the barium sulfate particles in a plate form were self-fixed to the fiber surface and covered the fiber surface (the primary particle size of the barium sulfate particles: 200 to 1500nm, and the average primary particle size of the barium sulfate particles: 500 nm).

(sample 11, FIG. 11)

1% pulp slurry (LBKP, CSF 500mL, average fiber length: about 0.7mm, 1300g) and barium hydroxide octahydrate (Wako pure chemical industries, Ltd.; 57g) were mixed with stirring by a three-motor (800rpm), and then aluminum sulfate (aluminum sulfate, 77g) was added dropwise at 2g/min by a peristaltic pump. After the end of the dropwise addition, the stirring was continued for 30 minutes to obtain a sample. As a result of observation by an electron microscope, it was confirmed that the barium sulfate particles in a plate form were self-fixed to the fiber surface and covered the fiber surface (the primary particle size of the barium sulfate particles: 20 to 800nm, and the average primary particle size of the barium sulfate particles: 100 nm).

(sample 12, FIG. 12)

In a container (papermaking pulp tank, volume: 4 m)³) In the above-described process, 2% of pulp slurry (LBKP/NBKP: 8/2, CSF: 390mL, average fiber length: about 1.3mm, solid content 25kg) and barium hydroxide octahydrate (japanese chemical industry, 75kg) were mixed and, then, aluminum sulfate (aluminum sulfate, 98kg) was added dropwise at about 500g/min using a peristaltic pump. After the end of the dropwise addition, the stirring was continued for 30 minutes to obtain a sample. As a result of observation with an electron microscope, it was confirmed that barium sulfate in a plate form was self-fixed to and covered the fiber surface (the primary particle diameter of barium sulfate particles: 50 to 1000nm, barium sulfate particles)Average primary particle diameter of (2): 80 nm).

1-2. Composite fiber of Al hydroxide and cellulose fiber

(sample A, FIG. 13)

437g of 1% pulp slurry (LBKP, CSF 450mL, average fiber length: about 0.7mm, average fiber diameter: about 19 μm) and 4.8g of sodium hydroxide (Fuji film and Wako pure chemical industries, Ltd.) were mixed by a three-motor (500rpm), and then aluminum sulfate (stock solution of aluminum sulfate, 25.8g) was added dropwise at 0.8 g/min. After completion of the dropwise addition, the reaction mixture was stirred for 30 minutes, washed with about 3 times the amount of water, and the salt was removed to obtain sample a.

1-3. Composite fiber of silicon dioxide/aluminum oxide and cellulose fiber

(sample B, FIG. 14)

910g of 0.5% pulp slurry (NBKP, CSF: 360mL, average fiber length: about 1.7mm, average fiber diameter: about 18 μm) was put into a 2L-capacity resin container and stirred with a laboratory stirrer (600 rpm). To the aqueous suspension, aluminum sulfate (stock solution of aluminum sulfate) was added dropwise for about 4 minutes until the pH reached 3.8, and then, while maintaining the pH at 4, aluminum sulfate (156 g) and an aqueous sodium silicate solution (fuji film and wako pure chemical industries, concentration 8%, 265g) were added dropwise for about 60 minutes. Peristaltic pumps were used for the dropwise addition, and the reaction temperature was about 25 ℃. Then, only an aqueous sodium silicate solution (fuji film and wako pure chemical industries, concentration 8%, 200g) was added dropwise for about 80 minutes to adjust the pH to 7.3, thereby obtaining a sample of composite slurry.

1-4. Hydrotalcite and cellulose fiber composite fiber

(sample C1, FIG. 15)

As a solution for synthesizing Hydrotalcite (HT), MgSO was prepared₄(Fuji film and Wako pure chemical industries) and Al₂(SO₄)₃(Fuji film and Wako pure chemical industries, Ltd.) was used. MgSO (MgSO)₄In a concentration of 0.6M, Al₂(SO₄)₃The concentration of (3) is 0.1M.

88.6g of sodium hydroxide (Fuji film and Wako pure chemical industries, Ltd.) and 14.8g of sodium carbonate (Fuji film and Wako pure chemical industries, Ltd.) were added to 2250g of 2.0% pulp slurry (NBKP, CSF 270mL, average fiber length: about 1.8mm, average fiber diameter: about 19 μm), mixed by a three-motor (650rpm), and 1362g of an acid solution was added dropwise at 4.7g/min while maintaining the mixture at 50 ℃. After completion of the dropwise addition, the reaction mixture was stirred for 30 minutes, washed with about 3 times the amount of water, and the salts were removed to obtain a sample.

(sample C2, FIG. 16)

To 2281g of 1.6% pulp slurry (NBKP, CSF 690mL, average fiber length: about 1.9mm, average fiber diameter: about 19 μm) were added 88.6g of sodium hydroxide (fuji film and guoki) and 14.8g of sodium carbonate (fuji film and guoki), and mixed by a three-motor (650rpm), followed by dropwise addition of 1322g of an acid solution at 4.6g/min while maintaining the mixture at 50 ℃. After completion of the dropwise addition, the reaction mixture was stirred for 30 minutes, washed with about 3 times the amount of water to remove salts, and then subjected to suction filtration using a filter paper to obtain a sample (solid content concentration: about 35%).

1-5. Composite fiber of calcium carbonate and cellulose fiber

(sample D1, FIG. 17)

Preparing a mixture containing calcium hydroxide (slaked lime: Ca (OH)₂100g, fuji film and plain drug) and powdered cellulose (KC FLOCK (trademark) W-06 MG, manufactured by japan paper, average particle diameter: 6 μm, 100g) of water suspension 10L. This aqueous suspension was placed in a 40L-volume closed apparatus, and cavitation was generated by blowing carbon dioxide into the reaction vessel, thereby synthesizing a composite fiber of calcium carbonate microparticles and fibers by the carbon dioxide method. The reaction temperature was about 15 ℃, carbon dioxide was supplied from a commercially available liquefied gas, the amount of carbon dioxide blown in was 3L/min, and the reaction was stopped at a stage at which the pH of the reaction solution was about 7 (pH before the reaction was about 12.8).

In the synthesis of conjugate fibers, a reaction solution is circulated and sprayed into a reaction vessel, thereby generating cavitation bubbles in the reaction vessel. Specifically, the reaction solution was injected at high pressure through a nozzle (nozzle diameter: 1.5mm) to generate cavitation bubbles. The jet velocity was about 70m/s, the inlet pressure (upstream pressure) was 7MPa, and the outlet pressure (downstream pressure) was 0.3 MPa.

(sample D2, FIG. 18)

A conjugate fiber was synthesized in the same manner as in sample D1, except that the powdery cellulose used was W-100G (manufactured by Japan paper, average particle diameter: 37 μm) and the blowing amount of carbon dioxide was 20L/min.

[ Table 1]

Experiment 2 evaluation of Complex samples

2-1. Evaluation of coating percentage and the like

The obtained complex samples were washed with ethanol, and observed with an electron microscope. As a result, in any of the samples, the inorganic substance was observed to cover the fiber surface and self-fix. The coating ratios of the composite samples are shown in the table, and the coating ratios are all 15% or more.

The obtained slurry of the conjugate fiber (3 g in terms of solid content) was suction-filtered with filter paper, and the residue was oven-dried (105 ℃ C., 2 hours) to measure ash content, thereby measuring the weight ratio of the inorganic particles in the conjugate fiber.

The average fiber length and average fiber diameter of the fibers are reported as the fiber length, as measured by the Valmet Fractinator. When the fiber length is measured, the solid content concentration of the slurry is adjusted to 0.1 to 0.3%, and the water temperature in the apparatus is adjusted to 25 ℃. + -. 1 ℃.

2-2. Evaluation based on screening/automated grading

< screening of composite sample >

In order to remove coarse particles in the synthesized slurry, filtration was performed using a mesh filter. The obtained composite sample (1 g in terms of solid content) was diluted with water so that the solid content concentration became 0.1%, and 0.2 l of the suspension was filtered through a 60-mesh (250 μm-mesh) sieve and washed with 0.6 l of water. Subsequently, the particle size distribution of the filtrate after filtration was measured by a wet method (Mastersizer 3000, malmem corporation).

< automatic Classification of Complex sample >

In addition, in addition to the sieving, as a method for automatically fractionating a sample into a plurality of fractions under certain conditions, a fiber fractionation analyzer (Valmet Fractionator) was used. The apparatus is an apparatus which passes a pulp slurry through a pipe having a length of about 100m at a medium temperature and a constant velocity, separates the pulp slurry from long fibers into fine fibers/fillers according to the hydrodynamic size, and automatically classifies the pulp slurry into 5 fractions (FR 1-3: long/short fibers, FR 4-5: fine fibers/fillers) according to the flow-out time.

Specifically, the composite sample (3 g in terms of solid content) was diluted with water so that the solid content concentration became 0.3%, and the mixture was passed through a fiber fractionation analyzer 3 times for about 250g, and fractions fractionated under the following flow-out conditions were collected (water temperature at the time of fractionation was 25 ± 1 ℃).

[ Table 2]

FR	Outflow (L)	Outflow time (seconds)
			1	16.00～17.55	10.6～27.2
2	17.56～18.05	27.3～32.5
			3	18.06～18.50	32.6～37.3
4	18.51～19.50	37.4～48.0
			5	19.51～20.50	48.1～59.0

The recovered FR4 was left to stand in a bucket for several hours to settle the fiber component, and after removing the supernatant, the particle size distribution was measured by a wet method (Mastersizer 3000, Malvern).

< particle size distribution >

The numerical value of "(D50-D10)/D50" was calculated from D10 (particle diameter at 10% accumulation) and D50 (particle diameter at 50% accumulation) in the volume-based particle size distribution measured in the above manner. The smaller the value, the narrower the particle size distribution of the sample, indicating that the inorganic substance is firmly fixed to the fiber surface.

2-3 evaluation of Retention for flaking

From the obtained composite samples (samples 1 to 12 and sample a) in accordance with JIS P8222: 2015 Using 150 mesh screen to obtain a weight per unit area of 100g/m²Handsheets were produced in the manner described above, and the stock retention was calculated from the basis weight of the obtained sheet.

Good: over 70 percent

And (delta): more than 50 percent and less than 70 percent

X: less than 50 percent

2-4. Evaluation of Water drainability

The composite samples (samples 1 to 12 and sample a) obtained were diluted with water so that the solid content concentration became 0.1%, and the passage time when a slurry prepared so that the solid content of inorganic substances in the total solid content became 0.15g was passed through a membrane filter (0.8 μm) under a reduced pressure of 20mmHg was measured.

Very good: less than 2 minutes

Good: 2 minutes or more and less than 4 minutes

And (delta): 4 minutes or more and less than 6 minutes

X: over 6 minutes

[ Table 3]

It was confirmed from the results that the retention rates of the composite fiber samples 1 to 3 and 9 having a larger D50 in the filtrate after classification were higher than those of the samples 4 to 8 in the case of sheeting. This indicates that more functional inorganic particles can be incorporated into the sheet, and that the sheet is excellent in functional quality in addition to good production efficiency.

In addition, in the evaluation of the water drainability assuming the case of producing the sheet in which the same amount of inorganic particles were blended, it was found that the dewatering speed of the conjugate fiber samples 1 to 3 and 9 was higher than that of the conjugate fiber samples 4, 7, 8, 10 to 12, the inorganic particle-only sample 5, and the mixed sample 6. This is considered because the composite fiber samples 1 to 3 and 9 had fewer fine particles that affect the drainability. If the water drainability is good, the drying process can be shortened and relaxed, so that the productivity can be improved (the frequency of paper breaking is reduced, the paper making speed is increased) when producing sheets, and the effect is great particularly when producing thick sheets.

Claims

1. A method of making a composite fiber of cellulosic fibers and inorganic particles, comprising:

measuring the particle size distribution of the following (a) or (b) to calculate (D50-D10)/D50;

(a) the filtrate obtained by filtering an aqueous suspension of composite fibers having a solid content of 0.1% through a sieve having a mesh size of 60 meshes, i.e., a mesh size of 250 μm,

(b) when an aqueous suspension of composite fibers having a solid content concentration of 0.3% is fractionated using a fiber fractionation analyzer under conditions of a flow rate of 5.7L/min, a water temperature of 25. + -. 1 ℃ and a total discharge amount of 22L, a fraction corresponding to a discharge amount of 18.51 to 19.50L and a discharge time of 37.4 to 48.0 seconds is obtained.

2. The method according to claim 1, wherein the aqueous suspension of composite fibers is adjusted in such a manner that (D50-D10)/D50 becomes 0.85 or less.

3. The method according to claim 1 or 2, wherein the composite fiber has an average fiber diameter of 500nm or more.

4. The method of any of claims 1-3, wherein the inorganic particles comprise: metal salts of calcium, magnesium, barium or aluminum, metal particles comprising titanium, copper or zinc, or silicates.

5. A method for producing a composite fiber sheet, comprising a step of forming a sheet from the composite fiber obtained by the method according to any one of claims 1 to 4.

6. A composite fiber comprising a cellulose fiber and inorganic particles, wherein the numerical value of (D50-D10)/D50 calculated from the particle size distribution of the following (a) or (b) is 0.85 or less,

(a) the filtrate obtained when the aqueous suspension of composite fibers having a solid content of 0.1% was filtered through a sieve having a mesh size of 60 mesh and a mesh size of 250 μm,

7. A composite fiber comprising a cellulose fiber and inorganic particles obtained by treating an aqueous suspension of a composite fiber having a solid content of 0.1% with a 60-mesh sieve having a mesh opening of 250 μm and passing the treated aqueous suspension through the sieve,

the value of (D50-D10)/D50 calculated from the particle size distribution of the filtrate passing through the sieve is 0.85 or less.

8. A composite fiber comprising a cellulose fiber and inorganic particles obtained from a fraction having an outflow rate of 18.51 to 19.50L and an outflow time of 37.4 to 48.0 seconds, wherein an aqueous suspension of the composite fiber having a solid content concentration of 0.3% is fractionated using a fiber fractionation analyzer under conditions of a flow rate of 5.7L/min, a water temperature of 25 + -1 ℃ and a total outflow rate of 22L,

the value of (D50-D10)/D50 calculated from the particle size distribution of the fraction is 0.85 or less.

9. A method for analyzing a composite fiber of a cellulose fiber and inorganic particles, comprising the step of measuring the particle size distribution of (a) or (b) described below to calculate (D50-D10)/D50,