JP7356675B2 - Magnetic material-containing composite particles, method for producing magnetic material-containing composite particles, and dry powder - Google Patents

Description

The present invention relates to magnetic material-containing composite particles, a method for producing magnetic material-containing composite particles, and dry powder.

In recent years, active efforts have been made to miniaturize cellulose fibers in wood until at least one side of their structure is on the order of nanometers, and to use them as new functional materials.

For example, as shown in Patent Document 1, it is disclosed that micronized cellulose fibers, that is, cellulose nanofibers (hereinafter also referred to as CNFs), can be obtained by repeatedly subjecting wood cellulose to mechanical treatment using a blender or a grinder. There is. It has been reported that CNF obtained by this method has a minor axis diameter ranging from 10 to 50 nm and a major axis diameter ranging from 1 μm to 10 mm. This CNF is one-fifth lighter than steel, more than five times stronger, and has a huge specific surface area of more than 250 m ² /g, so it is expected to be used as a filler for reinforcing resins and as an adsorbent. ing.

In addition, active attempts are being made to produce CNF by chemically treating the cellulose fibers in wood so that they can be easily made fine, and then using a low-energy mechanical treatment using a household mixer to make the fibers fine. The method of the above chemical treatment is not particularly limited, but a method of introducing anionic functional groups into cellulose fibers to facilitate micronization is preferred. By introducing anionic functional groups into the cellulose fibers, the solvent can easily penetrate between the cellulose microfibril structures due to the osmotic pressure effect, and the energy required to refine the cellulose raw material can be significantly reduced. The method for introducing the anionic functional group is not particularly limited, but for example, Non-Patent Document 1 discloses a method of selectively phosphoricating the surface of cellulose fine fibers using phosphoric esterifying treatment. ing. Further, Patent Document 2 discloses a method of carboxymethylating cellulose by reacting it with monochloroacetic acid or sodium monochloroacetate in a highly concentrated alkaline aqueous solution. Alternatively, carboxylic groups may be introduced by directly reacting cellulose with a carboxylic acid anhydride compound such as maleic acid or phthalic acid gasified in an autoclave.

In addition, a method of selectively oxidizing the surface of cellulose fine fibers using 2,2,6,6-tetramethylpiperidinyl-1-oxy radical (TEMPO), which is a relatively stable N-oxyl compound, as a catalyst. has also been reported (for example, see Patent Document 3). The oxidation reaction using TEMPO as a catalyst (TEMPO oxidation reaction) is an environmentally friendly chemical modification that proceeds in water at room temperature and pressure, and when applied to cellulose in wood, the reaction occurs inside the crystal. It is possible to selectively convert only the alcoholic primary carbons of the cellulose molecular chains on the crystal surface into carboxy groups without proceeding.

Cellulose single nanofibers (hereinafter also referred to as CSNF), which are dispersed into individual cellulose microfibril units in a solvent, are produced by the osmotic pressure effect accompanying the ionization of carboxy groups selectively introduced to the crystal surface by TEMPO oxidation. ). CSNF exhibits high dispersion stability derived from the carboxy groups on the surface. Wood-derived CSNF obtained from wood by the TEMPO oxidation reaction is a structure with a high aspect ratio of around 3 nm in short axis diameter and several tens of nm to several μm in long axis diameter, and its aqueous dispersion and molded body is reported to have high transparency. Further, Patent Document 4 reports that a laminated film obtained by coating and drying a CSNF dispersion has gas barrier properties.

Here, a problem facing the practical use of CNF is that the solid content concentration of the resulting CNF dispersion is as low as about 0.1 to 5%. For example, when attempting to transport a finely divided cellulose dispersion, transporting a large amount of solvent is equivalent to transporting a large amount of solvent, leading to an increase in transport costs, which significantly impairs business viability. Further, when used as an additive for reinforcing resins, there are problems such as deterioration of addition efficiency due to low solid content and difficulty in compounding if water as a solvent is not compatible with the resin. Furthermore, when handled in a hydrated state, there is a risk that the hydrated CNF dispersion will rot, so measures such as refrigerated storage and preservative treatment are required, which may increase costs.

However, if the solvent of the micronized cellulose dispersion is simply removed by heat drying, the micronized cellulose will aggregate, become keratinized, or form a film, making it difficult for it to function stably as an additive. Put it away. Furthermore, since the solid content concentration of CNF is low, the solvent removal step itself by drying requires a large amount of energy, which is another factor that impairs business viability.
As described above, handling CNF in the form of a dispersion liquid itself is a cause of impairing business viability, and therefore, it is strongly desired to provide a new handling mode that allows CNF to be handled easily.

As exemplified above, various studies have been made regarding the development of high-performance members that impart new functionality to micronized cellulose, including CNF or CSNF, which are carbon neutral materials.
On the other hand, various microparticles and microcapsules have been put into practical use as functional materials in various fields. Generally, microparticles are micro-sized particles formed from various polymers, and are used, for example, as fillers, spacers, abrasives, and the like.

Among them, microparticles with magnetic materials encapsulated in polymer particles take advantage of the magnetic responsiveness of magnetic materials, and can be used as diagnostic drug carriers, cell separation carriers, cell culture carriers, nucleic acid separation and purification carriers, protein separation and purification carriers, immobilized enzyme carriers, It is used in drug delivery carriers, magnetic toners, magnetic inks, magnetic paints, etc. Methods for producing microparticles containing magnetic materials inside the particles include methods using suspension polymerization (Patent Document 5), methods using emulsion polymerization (Patent Document 6), and methods using mini-emulsion polymerization (Patent Document 7). )It has been known. Normally, in both production methods, polymerization is carried out using a surfactant, but by using a surfactant, it is possible to avoid problems caused by foaming during each process such as stirring operation, transfer, addition of auxiliary agents, and coating. Depending on the purpose of use, the surfactant on the surface of the microparticles may cause problems, so the surfactant must be removed, leading to a decrease in production efficiency. Furthermore, from an environmental perspective, the load on wastewater due to the outflow of surfactants from the system is also a problem. In addition, the particles obtained by these production methods have poor redispersibility, and once dried, agglomeration of particles occurs, and it is difficult to redisperse the agglomerated particles.

Thus, it is strongly desired to provide a new handling mode that allows easy handling of microparticles that have magnetic responsiveness and have good redispersibility even when dried.

Japanese Patent Application Publication No. 2010-216021 International Publication No. 2014/088072 Japanese Patent Application Publication No. 2008-001728 International Publication No. 2013/042654 JP2012-082328A Japanese Patent Application Publication No. 2006-088131 Japanese Patent Application Publication No. 2004-099844

Noguchi Y, Homma I, Matsubara Y. Complete nanofibrillation of cellulose prepared by phosphorylation. Cellulose. 2017;24:1295.10.1007/s10570-017-1191-3

The present invention has been made in view of the above circumstances, and provides magnetic material-containing composite particles that have magnetic responsiveness and good redispersibility even when dried, a method for producing the magnetic material-containing composite particles, and a method for producing the magnetic material-containing composite particles. The purpose of the present invention is to provide a dry powder containing composite particles containing a magnetic material.

A magnetic material-containing composite particle according to one aspect of the present invention has a core particle containing at least one type of polymer and a magnetic material, and a coating layer made of finely divided cellulose, and comprises a core particle and a finely divided cellulose. These are composite particles in which at least a portion of cellulose is bonded and inseparable.

Further, the method for producing magnetic material-containing composite particles according to one aspect of the present invention includes a first step of defibrating a cellulose raw material in a solvent to obtain a dispersion of finely divided cellulose, and at least one type of polymerizable monomer or a second step of mixing a polymer-containing liquid and a magnetic material to obtain a magnetic material-containing liquid; mixing the dispersion liquid and the magnetic material-containing liquid, and containing the magnetic material-containing liquid in the dispersion liquid; a third step of covering at least a part of the surface of the magnetic material-containing droplet with the finely divided cellulose to stabilize the magnetic material-containing droplet as an emulsion; By solidifying the magnetic material-containing droplets to form core particles in a state covered with micronized cellulose, at least a portion of the surface of the core particles is covered with the micronized cellulose, and the core particles and a fourth step of making the micronized cellulose inseparable.

The dry powder according to one aspect of the present invention includes the above-described magnetic material-encapsulating composite particles and has a solid content of 80% or more.

According to one aspect of the present invention, magnetic material-containing composite particles having magnetic responsiveness and good redispersibility even when dried, a method for producing the magnetic material-containing composite particles, and the magnetic material-containing composite particles It is possible to provide a dry powder containing.

FIG. 1 is a schematic diagram of composite particles according to an embodiment of the present invention. 1 is a schematic diagram of an O/W emulsion using CNF according to an embodiment of the present invention, and a magnetic material-containing composite particle obtained by solidifying a polymerizable monomer or polymer containing a magnetic material inside the emulsion. 1 is a measurement result of a spectral transmission spectrum of an aqueous dispersion of finely divided cellulose obtained in Example 1. These are the results of steady viscoelasticity measurement of the aqueous dispersion of finely divided cellulose obtained in Example 1 using a rheometer. FIG. 2 is a diagram (SEM image) showing the results of observing the magnetic material-containing composite particles obtained in Example 1 using a scanning electron microscope (SEM). 1 is a diagram (SEM image) showing the results of observing the magnetic material-containing composite particles obtained in Example 1 at high magnification using a scanning electron microscope (SEM).

Embodiments of the present invention will be described below with reference to the drawings. However, in each of the figures described below, mutually corresponding parts are given the same reference numerals, and descriptions of overlapping parts will be omitted as appropriate. Further, this embodiment is an example of a configuration for embodying the technical idea of the present invention, and the material, shape, structure, arrangement, dimensions, etc. of each part are not specified as described below. The technical idea of the present invention can be modified in various ways within the technical scope defined by the claims.

<Composite particles containing magnetic material>
First, the magnetic material-containing composite particles 5 according to the embodiment of the present invention will be explained.
FIG. 1 shows a core particle 3 containing at least one type of polymer and a magnetic material 4 having a coating layer 2 made of finely divided cellulose (hereinafter also referred to as cellulose nanofiber "CNF") 1 on the surface of the core particle 3 containing a magnetic material. 5 is a schematic diagram of composite particles 5. FIG. The term "finely divided cellulose" as used herein means fibrous cellulose having a number average short axis diameter of 1 nm or more and 1000 nm or less.

The magnetic material-containing composite particles 5 contain core particles 3 that are particles containing at least one type of polymer and a magnetic material 4, and have a coating layer 2 made of micronized cellulose 1 on the surface of the core particles 3. have. The core particles 3 and the finely divided cellulose 1 are bonded to each other and are inseparable composite particles.
Furthermore, at least a portion of the magnetic material 4 may be exposed from the surface of the core particle 3.
Here, the content ratio of the magnetic material 4 is preferably in the range of 1% by mass or more and 90% by mass or less with respect to the mass of the entire core particle 3, for example. If the content ratio of the magnetic material 4 is within the above numerical range, it is possible to have magnetic responsiveness and maintain good redispersibility even when the magnetic material-containing composite particles 5 are dried. Note that if the content ratio of the magnetic material 4 is less than 1% by mass with respect to the mass of the entire core particle 3, magnetic responsiveness may not be confirmed. Furthermore, if the content ratio of the magnetic material 4 is more than 90% by mass with respect to the total mass of the core particles 3, redispersibility tends to decrease.

The method for producing the magnetic material-containing composite particles 5 is not particularly limited, but for example, an O/W emulsion using the micronized cellulose 1 is formed, and droplets inside the emulsion are solidified to form solid core particles. By doing so, it is possible to obtain magnetic material-containing composite particles 5 in which the core particles 3 and the finely divided cellulose 1 are bonded and inseparable. By using the micronized cellulose 1, droplets can be formed without using additives such as surfactants, and magnetic material-containing composite particles 5 with high dispersibility can be obtained.

"Indivisible" here means, for example, that the dispersion containing the magnetic material-containing composite particles 5 is centrifuged to remove the supernatant, and then a solvent is added and redispersed to refine the magnetic material-containing composite particles 5.・Even after repeated washing operations or repeated washing operations with a solvent by filtration washing using a membrane filter, the micronized cellulose 1 and the core particles 3 do not separate, and the core particles formed by the micronized cellulose 1 do not separate. This means that the coating state of No. 3 is maintained. The coating state can be confirmed, for example, by observing the surface of the magnetic material-containing composite particles 5 using a scanning electron microscope. Although the bonding mechanism between the fine cellulose 1 and the core particles 3 in the magnetic material-containing composite particles 5 is not certain, the O/W type emulsion in which the magnetic material-containing composite particles 5 are stabilized by the fine cellulose 1 is used as a template. Since the droplets are solidified with the finely divided cellulose 1 in contact with the droplets inside the emulsion, in the magnetic material-containing composite particles 5 obtained after solidification, the particles present on the surface of the core particles 3 It is expected that at least a portion of the micronized cellulose 1 will be incorporated into the core particles 3. For the above reasons, it is presumed that the micronized cellulose 1 is physically immobilized on the core particles 3 after solidification, and eventually the core particles 3 and the micronized cellulose 1 become inseparable.
Here, the O/W emulsion is also called an oil-in-water emulsion, in which water is the continuous phase and oil is dispersed therein as oil droplets (oil particles). .

In addition, since the magnetic material-containing composite particles 5 are produced using an O/W type emulsion stabilized by the micronized cellulose 1 as a template, the shape of the magnetic material-containing composite particles 5 is a true spherical shape derived from the O/W type emulsion. It is characterized by the following. Specifically, the coating layer 2 made of micronized cellulose 1 is formed on the surface of the spherical core particle 3 with a relatively uniform thickness. The average thickness of the coating layer 2 can be determined by, for example, cutting a magnetic material-containing composite particle 5 fixed with an embedding resin using a microtome and observing it with a scanning electron microscope. It can be calculated by measuring the thickness of the coating layer 2 at 100 random locations on the image and taking the average value. Further, the magnetic material-containing composite particles 5 are characterized in that they are uniformly coated with a coating layer 2 having a relatively uniform thickness, and specifically, the coefficient of variation of the thickness of the coating layer 2 mentioned above is 0. It is preferably 5 or less, more preferably 0.4 or less. If the coefficient of variation of the thickness of the coating layer 2 containing the micronized cellulose 1 exceeds 0.5, for example, it may be difficult to collect the magnetic material-containing composite particles 5.

The thickness of the coating layer 2 is preferably in the range of 3 nm or more and 1000 nm or less, more preferably 3 nm or more and 30 nm or less. When the thickness of the coating layer 2 is within the above numerical range, it has magnetic responsiveness and can maintain good redispersibility even when the magnetic material-containing composite particles 5 are dried. Note that if the thickness of the coating layer 2 is less than 3 nm, the redispersibility tends to decrease. Furthermore, when the thickness of the coating layer 2 exceeds 1000 nm, the magnetic responsiveness tends to decrease.

Furthermore, it is preferable that the micronized cellulose 1 has a fiber shape derived from a microfibril structure. Specifically, the micronized cellulose 1 is fibrous, and has a number average minor axis diameter of 1 nm or more and 1000 nm or less, a number average major axis diameter of 50 nm or more, and a number average major axis diameter of 1 nm or more and 1000 nm or less, and a number average major axis diameter of 50 nm or more. It is preferable that it is 5 times or more. Moreover, it is preferable that the crystal structure of the micronized cellulose 1 is cellulose I type.

<Method for manufacturing composite particles containing magnetic material>
FIG. 2 shows an example of a method for manufacturing the magnetic material-encapsulating composite particles 5 of this embodiment. The method for producing magnetic material-containing composite particles 5 according to the present embodiment includes a step (first step) of defibrating a cellulose raw material in a solvent to obtain a dispersion 7 of finely divided cellulose 1; A step of mixing a liquid containing a monomer or polymer with a magnetic material to obtain a magnetic material-containing liquid (second step), and forming droplets (droplets of magnetic material-containing liquid) 6 in a dispersion 7 of micronized cellulose 1. A step (third step) of covering at least a part of the surface of the droplet 6 with the finely divided cellulose 1 to stabilize the droplet 6 as an emulsion; and a state in which at least a part of the surface of the droplet 6 is covered with the finely divided cellulose 1. By solidifying the droplets 6 to form the core particles 3, at least a part of the surface of the core particles 3 is covered with the micronized cellulose 1, and the core particles 3 and the micronized cellulose 1 are made inseparable. By including the step (fourth step) in the manufacturing process, the magnetic material-containing composite particles 5 can be obtained.

The magnetic material-containing composite particles 5 obtained by the above manufacturing method are obtained as a dispersion in a solvent. Further, by removing the solvent, it is obtained as a dry solid. The method for removing the solvent is not particularly limited, and for example, excess solvent may be removed by centrifugation or filtration, and a dry solid may be obtained by further heat-drying in an oven. At this time, the obtained dry solid does not become film-like or aggregate-like, but is obtained as a fine-textured powder. Although the reason for this is not clear, it is known that when the solvent is removed from a finely divided cellulose dispersion, the finely divided cellulose particles are strongly aggregated and formed into a film. On the other hand, in the case of a dispersion containing magnetic material-containing composite particles 5, since the micronized cellulose 1 is a truly spherical composite particle with the micronized cellulose 1 immobilized on the surface, the micronized cellulose 1 does not aggregate with each other even if the solvent is removed. It is thought that the dry solid is obtained as a fine-textured powder because there is no contact between the composite particles and only points between the composite particles. In addition, since there is no aggregation of the magnetic material-containing composite particles 5, it is easy to re-disperse the magnetic material-containing composite particles 5 obtained as a dry powder in a solvent, and even after redispersion, the magnetic material-containing composite particles 5 The dispersion stability derived from micronized cellulose 1 bonded to the surface of 5 is shown.

The dry powder of the magnetic material-containing composite particles 5 is a dry solid that contains almost no solvent and can be redispersed in a solvent. Specifically, the dry powder of the magnetic material-containing composite particles 5 is The fraction can be 80% or more, further 90% or more, and even 95% or more. Since most of the solvent can be removed, favorable effects can be obtained from the viewpoints of, for example, reduction in transportation costs, prevention of spoilage, improvement in addition rate, and improvement in kneading efficiency with resin. Note that when the solid content is increased to 80% or more by drying treatment, the micronized cellulose 1 easily absorbs moisture, so there is a possibility that the solid content may decrease over time by adsorbing moisture in the air. However, considering the technical concept of the present invention, which is characterized in that the magnetic material-containing composite particles 5 can be easily obtained as a dry powder and can be further redispersed, it is considered that the dry powder containing the magnetic material-containing composite particles 5 is Any dry solid produced by a method for producing a dry solid that includes a step of increasing the solid content to 80% or more is defined as falling within the technical scope of the present invention.

Each step will be explained in detail below.

(1st step)
The first step is to obtain a finely divided cellulose dispersion by defibrating the cellulose raw material in a solvent. First, various cellulose raw materials are dispersed in a solvent to form a suspension. The concentration of the cellulose raw material in the suspension is preferably 0.1% or more and less than 10%. If the concentration of the cellulose raw material in the suspension is less than 0.1%, it is not preferable because there is a tendency for too much solvent to impair productivity. Furthermore, if the concentration of the cellulose raw material in the suspension exceeds 10%, the suspension will rapidly thicken as the cellulose raw material is defibrated, making uniform defibration processing difficult, which is not preferable. . The solvent used for preparing the suspension preferably contains 50% or more of water. When the proportion of water in the suspension is less than 50%, dispersion of the finely divided cellulose 1 tends to be inhibited in the step of defibrating the cellulose raw material in a solvent to obtain a finely divided cellulose dispersion, which will be described later. . Moreover, as the solvent contained other than water, a hydrophilic solvent is preferable. There are no particular limitations on the hydrophilic solvent, but alcohols such as methanol, ethanol, and isopropanol; and cyclic ethers such as tetrahydrofuran are preferred. If necessary, for example, the pH of the suspension may be adjusted in order to improve the dispersibility of cellulose and the finely divided cellulose 1 to be produced. Examples of alkaline aqueous solutions used for pH adjustment include sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, Examples include organic alkalis such as an aqueous solution of benzyltrimethylammonium hydroxide. An aqueous sodium hydroxide solution is preferred from the viewpoint of cost.

Subsequently, the suspension is subjected to a physical defibration treatment to refine the cellulose raw material. Physical defibration treatment methods are not particularly limited, but include, for example, high-pressure homogenizers, ultra-high-pressure homogenizers, ball mills, roll mills, cutter mills, planetary mills, jet mills, attritors, grinders, juicer mixers, homomixers, and ultrasonic homogenizers. , nanogenizers, and mechanical treatments such as underwater counter-impact. By performing such a physical defibration treatment, the cellulose in the suspension is finely divided, and a dispersion of cellulose (micronized cellulose) 1 in which at least one side of the structure is finely divided into nanometers is obtained. can be obtained. Further, the number average minor axis diameter and the number average major axis diameter of the micronized cellulose 1 obtained can be adjusted by the time and number of times of the physical defibration treatment at this time.

As described above, a dispersion of cellulose 1 (micronized cellulose dispersion) in which at least one side of the structure is micronized to the order of nanometers is obtained. The obtained dispersion can be used as it is or after dilution, concentration, etc., as a stabilizer for the O/W emulsion described below.

Normally, the micronized cellulose 1 has a fiber shape derived from a microfibril structure, so the micronized cellulose 1 used in the manufacturing method of this embodiment preferably has a fiber shape within the range shown below. That is, the shape of the micronized cellulose 1 is preferably fibrous. Further, the fibrous micronized cellulose 1 may have a number average short axis diameter of 1 nm or more and 1000 nm or less, preferably 2 nm or more and 500 nm or less. Here, if the number average minor axis diameter is less than 1 nm, it is impossible to obtain a highly crystalline, rigid, finely divided cellulose fiber structure, and it is difficult to stabilize the emulsion and perform a polymerization reaction using the emulsion as a template. There is a tendency to On the other hand, if the number average short axis diameter exceeds 1000 nm, the size becomes too large to stabilize the emulsion, and it tends to be difficult to control the size and shape of the resulting composite particles. . Further, there is no particular restriction on the number average major axis diameter, but it is preferably at least 5 times the number average minor axis diameter. If the number average major axis diameter is less than five times the number average minor axis diameter, it is not preferable because it tends to become difficult to sufficiently control the size and shape of the composite particles 5.

In addition, the number average short axis diameter of micronized cellulose fibers is determined as the average value of the short axis diameters (minimum diameter) of 100 fibers measured by transmission electron microscopy and atomic force microscopy, for example. . On the other hand, the number average long axis diameter of micronized cellulose fibers can be determined as the average value of the long axis diameters (maximum diameter) of 100 fibers measured by transmission electron microscopy and atomic force microscopy, for example. .

The type and crystal structure of cellulose that can be used as a raw material for the micronized cellulose 1 is not particularly limited either. Specifically, raw materials consisting of cellulose type I crystals include, in addition to wood-based natural cellulose, non-wood-based natural celluloses such as cotton linters, bamboo, hemp, bagasse, kenaf, bacterial cellulose, ascidian cellulose, and valonia cellulose. can be used. Furthermore, regenerated cellulose typified by rayon fibers and cupra fibers made of cellulose type II crystals can also be used. From the viewpoint of ease of material procurement, it is preferable to use wood-based natural cellulose as the raw material. The wood-based natural cellulose is not particularly limited, and for example, those commonly used in the production of cellulose nanofibers, such as softwood pulp, hardwood pulp, and waste paper pulp, can be used. Softwood pulp is preferred because of its ease of purification and refinement.

Furthermore, the finely divided cellulose raw material is preferably chemically modified. More specifically, it is preferable that an anionic functional group be introduced into the crystal surface of the finely divided cellulose raw material. This is because the introduction of anionic functional groups into the cellulose crystal surface makes it easier for the solvent to penetrate between the cellulose crystals due to the osmotic pressure effect, making it easier for the cellulose raw material to become finer.
The type and method of introduction of the anionic functional group to be introduced into the cellulose crystal surface are not particularly limited, but carboxy groups and phosphoric acid groups are preferred. Carboxy groups are more preferred because they can be easily introduced selectively onto the cellulose crystal surface.

The method for introducing carboxy groups onto the surface of cellulose fibers is not particularly limited. Specifically, for example, carboxymethylation may be performed by reacting cellulose with monochloroacetic acid or sodium monochloroacetate in a highly concentrated alkaline aqueous solution. Alternatively, carboxylic groups may be introduced by directly reacting cellulose with a carboxylic acid anhydride compound such as maleic acid or phthalic acid gasified in an autoclave. Furthermore, co-oxidants are used under relatively mild aqueous conditions in the presence of N-oxyl compounds such as TEMPO, which have high selectivity for the oxidation of alcoholic primary carbon while preserving the structure as much as possible. You may also use the same method. Oxidation using an N-oxyl compound is more preferable in terms of selectivity of the carboxyl group introduction site and reduction of environmental burden.

Here, as the N-oxyl compound, for example, TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy radical), 2,2,6,6-tetramethyl-4-hydroxypiperidine- 1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetamido-2, 2,6,6-tetramethylpiperidine-N-oxyl, and the like. Among them, TEMPO, which has high reactivity, is preferred. The amount of the N-oxyl compound to be used may be a catalytic amount and is not particularly limited. Usually, it is about 0.01 to 5.0% by mass based on the solid content of the wood-based natural cellulose to be oxidized.

Examples of oxidation methods using N-oxyl compounds include a method in which wood-based natural cellulose is dispersed in water and oxidized in the presence of an N-oxyl compound. At this time, it is preferable to use a co-oxidizing agent together with the N-oxyl compound. In this case, in the reaction system, the N-oxyl compound is sequentially oxidized by a co-oxidizing agent to produce an oxoammonium salt, and the cellulose is oxidized by the oxoammonium salt. According to this oxidation treatment, the oxidation reaction proceeds smoothly even under mild conditions, and the efficiency of introducing carboxy groups is improved. When the oxidation treatment is performed under mild conditions, it is easier to maintain the crystal structure of cellulose.

Co-oxidants that can promote the oxidation reaction include, for example, halogens, hypohalous acid, halous acids, perhalogen acids, salts thereof, halogen oxides, nitrogen oxides, peroxides, etc. Any oxidizing agent, if any, can be used. Sodium hypochlorite is preferred because of its ease of availability and reactivity. The amount of the co-oxidant used is not particularly limited and may be an amount that can promote the oxidation reaction. Usually, it is about 1 to 200% by mass based on the solid content of the wood-based natural cellulose to be oxidized.

Furthermore, at least one compound selected from the group consisting of bromides and iodides may be used in combination with the N-oxyl compound and the co-oxidizing agent. This allows the oxidation reaction to proceed smoothly and improves the efficiency of introducing carboxy groups. As such a compound, sodium bromide or lithium bromide is preferable, and sodium bromide is more preferable in terms of cost and stability. The amount of the compound used may be any amount that can promote the oxidation reaction, and is not particularly limited. Usually, it is about 1 to 50% by mass based on the solid content of the wood-based natural cellulose to be oxidized.

The reaction temperature of the oxidation reaction is preferably 4°C or more and 80°C or less, more preferably 10°C or more and 70°C or less. If the reaction temperature of the oxidation reaction is less than 4° C., the reactivity of the reagent tends to decrease and the reaction time tends to become longer. If the reaction temperature of the oxidation reaction exceeds 80°C, side reactions will be promoted and the cellulose sample will be reduced in molecular weight and the highly crystalline, rigid, finely divided cellulose fiber structure will collapse, resulting in the formation of a stabilizer for O/W emulsions. It tends to be difficult to use as a
Further, the reaction time of the oxidation treatment can be appropriately set in consideration of the reaction temperature, the desired amount of carboxy groups, etc., and is usually about 10 minutes to 5 hours, although it is not particularly limited.

The pH of the reaction system during the oxidation reaction is not particularly limited, but is preferably 9 to 11. When the pH is 9 or higher, the reaction can proceed efficiently. If the pH exceeds 11, side reactions may proceed and the decomposition of the cellulose sample may be accelerated. Further, in the oxidation treatment, as the oxidation progresses, the pH in the system decreases due to the production of carboxy groups, so it is preferable to maintain the pH of the reaction system at 9 to 11 during the oxidation treatment. A method for maintaining the pH of the reaction system at 9 to 11 includes, for example, a method of adding an alkaline aqueous solution in response to a decrease in pH.

Examples of the alkaline aqueous solution include sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, and benzyltrimethylammonium hydroxide. Examples include organic alkalis such as aqueous solutions. An aqueous sodium hydroxide solution is preferred from the viewpoint of cost.
The oxidation reaction by the N-oxyl compound can be stopped, for example, by adding alcohol to the reaction system. At this time, it is preferable to maintain the pH of the reaction system within the above range. The alcohol to be added is preferably a low molecular weight alcohol such as methanol, ethanol, or propanol in order to quickly complete the reaction, and ethanol is particularly preferred in view of the safety of by-products produced by the reaction.

The reaction solution after the oxidation treatment may be directly subjected to the micronization process, but in order to remove catalysts such as N-oxyl compounds, impurities, etc., the oxidized cellulose contained in the reaction solution is recovered and washed with a cleaning solution. It is preferable. Oxidized cellulose can be recovered by a known method such as filtration using a glass filter or a nylon mesh with a pore size of 20 μm. Pure water is preferable as the cleaning liquid used for cleaning oxidized cellulose.
When the obtained TEMPO oxidized cellulose is defibrated, cellulose single nanofibers (CSNF) having a uniform fiber width of around 3 nm are obtained. When CSNF is used as a raw material for the micronized cellulose 1 of the composite particles 5, the particle size of the obtained O/W emulsion tends to be uniform due to its uniform structure.

As described above, the CSNF used in this embodiment can be obtained through the steps of oxidizing the cellulose raw material and micronizing it to form a dispersion. Further, the content of carboxyl groups introduced into CSNF is preferably 0.1 mmol/g or more and 5.0 mmol/g or less, more preferably 0.5 mmol/g or more and 2.0 mmol/g or less. Here, if the amount of carboxy groups is less than 0.1 mmol/g, there is a tendency that it becomes difficult to micronize and uniformly disperse cellulose because the solvent entry effect due to osmotic pressure effect does not work between cellulose microfibrils. be. In addition, if the amount of carboxy groups exceeds 5.0 mmol/g, cellulose microfibrils become low-molecular due to side reactions accompanying chemical treatment, making it impossible to obtain a highly crystalline, rigid, finely divided cellulose fiber structure, and O /W type emulsion tends to be difficult to use as a stabilizer.

(Second process)
The second step is a step of mixing a liquid containing at least one type of polymerizable monomer or polymer with a magnetic material to obtain a magnetic material-containing liquid.
The polymerizable monomer or polymer that can be used depends on the method of forming the emulsion to be formed in the next third step. Examples of methods for forming an emulsion include adding a polymerizable monomer containing an initiator to a finely divided cellulose dispersion to form an emulsion, and adding a polymer that is solid at room temperature to a solvent with low compatibility with the finely divided cellulose dispersion. A method of adding the dissolved material to a finely divided cellulose dispersion to form an emulsion, adding a polymer that is solid at room temperature to a finely divided cellulose dispersion, heating it above the temperature at which the polymer has fluidity, melting it, and forming an emulsion. There are several methods, but in any method, it is preferable that the polymerizable monomer or polymer added is not compatible with the finely divided cellulose dispersion. If they are compatible, it becomes difficult to form droplets of the polymerizable monomer or polymer in the finely divided cellulose dispersion, and it tends to be difficult to obtain a composite.

The polymerizable monomer that can be used in the method of adding a mixture of a polymerizable monomer containing an initiator to a finely divided cellulose dispersion to form an emulsion is a polymer monomer that has polymerizable properties in its structure. It is not particularly limited as long as it has a functional group of , is liquid at room temperature, is completely incompatible with water, and can form a polymer (high molecular weight polymer) through a polymerization reaction. The polymerizable monomer has at least one polymerizable functional group. A polymerizable monomer having one polymerizable functional group is also referred to as a monofunctional monomer. Furthermore, a polymerizable monomer having two or more polymerizable functional groups is also referred to as a polyfunctional monomer. The type of polymerizable monomer is not particularly limited, but examples include (meth)acrylic monomers and vinyl monomers. It is also possible to use a polymerizable monomer (eg, ε-caprolactone, etc.) having a cyclic ether structure such as an epoxy group or an oxetane structure.
Note that the expression "(meth)acrylate" includes both "acrylate" and "methacrylate."

Examples of monofunctional (meth)acrylic monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl. (meth)acrylate, t-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl ( meth)acrylate, isodecyl(meth)acrylate, lauryl(meth)acrylate, tridecyl(meth)acrylate, cetyl(meth)acrylate, stearyl(meth)acrylate, benzyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate, 3 -Methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phosphoric acid (meth)acrylate, ethylene oxide modified phosphoric acid (meth)acrylate, phenoxy (meth)acrylate, ethylene oxide modified phenoxy (meth)acrylate, propylene oxide Modified phenoxy (meth)acrylate, nonylphenol (meth)acrylate, ethylene oxide modified nonylphenol (meth)acrylate, propylene oxide modified nonylphenol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl hydrogen phthalate, 2-(meth)acryloyl Oxypropyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl ( meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, adamantyl acrylate with monovalent mono(meth)acrylate derived from 2-adamantane and adamantane diol Examples include adamantane derivative mono(meth)acrylates such as.

Examples of difunctional (meth)acrylic monomers include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, and nonanediol di(meth)acrylate. ) acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate Di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, neopentyl hydroxypivalate di(meth)acrylate, etc. Examples include meth)acrylate.

Examples of trifunctional or higher-functional (meth)acrylic monomers include trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, and tris-2-hydroxy. Tri(meth)acrylates such as ethyl isocyanurate tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, etc. Trifunctional (meth)acrylate compounds, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta( Trifunctional or higher functional (meth)acrylate compounds such as meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane hexa(meth)acrylate, and some of these (meth)acrylates with alkyl groups or ε- Examples include polyfunctional (meth)acrylate compounds substituted with caprolactone.

As monofunctional vinyl monomers, liquids that are incompatible with water at room temperature are preferred, such as vinyl ethers, vinyl esters, aromatic vinyls, and especially styrene and styrene monomers.
Examples of (meth)acrylates among monofunctional vinyl monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, Lauryl (meth)acrylate, alkyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, glycidyl (meth)acrylate, tetrahydrofur Furyl (meth)acrylate, allyl (meth)acrylate, diethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, heptafluorodecyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, ) acrylate, tricyclodecanyl (meth)acrylate, etc.

Examples of monofunctional aromatic vinyl monomers include styrene, such as α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, isopropenyltoluene, isobutyltoluene, and tert-butylstyrene. , vinylnaphthalene, vinylbiphenyl, 1,1-diphenylethylene and the like.
Examples of the polyfunctional vinyl monomer include polyfunctional groups having an unsaturated bond such as divinylbenzene. A liquid that is incompatible with water at room temperature is preferred.

For example, specific examples of polyfunctional vinyl monomers include (1) divinyls such as divinylbenzene, 1,2,4-trivinylbenzene, and 1,3,5-trivinylbenzene, (2) ethylene glycol Dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-propylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexamethylene glycol dimethacrylate, neopentyl glycol dimethacrylate Dimethacrylates such as methacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2-bis(4-methacryloxydiethoxyphenyl)propane, (3) trimethylolpropane trimethacrylate, triethylolethane trimethacrylate, etc. Trimethacrylates, (4) Ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, 1,3-dipropylene glycol diacrylate, 1,4-dibutylene glycol diacrylate, 1,6 -Hexylene glycol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate, 2,2-bis(4-acryloxypropoxyphenyl)propane, 2,2-bis(4-acryloxydiacrylate) diacrylates such as (ethoxyphenyl)propane, (5) triacrylates such as trimethylolpropane triacrylate and triethylolethane triacrylate, (6) tetraacrylates such as tetramethylolmethanetetraacrylate, (7) others, Examples include tetramethylene bis(ethyl fumarate), hexamethylene bis(acrylamide), triallyl cyanurate, and triallyl isocyanurate.

For example, specific examples of functional styrenic monomers include divinylbenzene, trivinylbenzene, divinyltoluene, divinylnaphthalene, divinylxylene, divinylbiphenyl, bis(vinylphenyl)methane, bis(vinylphenyl)ethane, bis(vinylphenyl)ethane, phenyl)propane, bis(vinylphenyl)butane, and the like.
In addition to these, polyether resins, polyester resins, polyurethane resins, epoxy resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiol polyene resins, etc. having at least one polymerizable functional group can be used. Yes, the material is not particularly limited.

The above polymerizable monomers may be used alone or in combination of two or more types.
Further, the polymerizable monomer may contain a polymerization initiator in advance. Examples of common polymerization initiators include radical initiators such as organic peroxides and azo polymerization initiators.
Examples of organic peroxides include peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxycarbonates, and peroxyesters.

Examples of the azo polymerization initiator include ADVN and AIBN.
For example, 2,2-azobis(isobutyronitrile) (AIBN), 2,2-azobis(2-methylbutyronitrile) (AMBN), 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN) , 1,1-azobis(1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2-azobisisobutyrate (MAIB), 4,4-azobis(4-cyanovaleric acid) (ACVA), 1, 1-azobis(1-acetoxy-1-phenylethane), 2,2-azobis(2-methylbutyramide), 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2- Azobis(2-methylamidinopropane) dihydrochloride, 2,2-azobis[2-(2-imidazolin-2-yl)propane], 2,2-azobis[2-methyl-N-(2-hydroxyethyl) propionamide], 2,2-azobis(2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2-azobis(N-butyl-2-methylpropionamide), 2,2 -azobis(N-cyclohexyl-2-methylpropionamide) and the like.

If a polymerizable monomer containing a polymerization initiator is used in the second step, the polymerization initiator will be included in the polymerizable monomer droplets 6 inside the emulsion particles when an emulsion is formed. When polymerizing the monomer inside the emulsion in the fourth step, the polymerization reaction progresses more easily.
The weight ratio of the polymerizable monomer and polymerization initiator that can be used in the second step is not particularly limited, but it is usually 0.1 part by mass or more of the polymerization initiator per 100 parts by mass of the polymerizable monomer. preferable. If the amount of the polymerizable monomer is less than 0.1 part by mass, the polymerization reaction will not proceed sufficiently and the yield of composite particles 5 will tend to decrease, which is not preferable.

The polymerizable monomers mentioned above can be used in the method of dissolving a polymer that is solid at room temperature in a solvent with low compatibility with the finely divided cellulose dispersion and adding it to the finely divided cellulose dispersion to form an emulsion. Examples include polymerized polymers. Moreover, as a solvent for dissolving a polymer that is solid at room temperature, a solvent having low compatibility with the finely divided cellulose dispersion is preferable. When the solubility in water is high, emulsification tends to be difficult because the solvent easily dissolves from the polymer phase into the water phase. If there is no solubility in water, the solvent cannot migrate from the polymer phase, so it tends to be extremely difficult to obtain composite particles. Further, the boiling point of the solvent for dissolving the polymer is preferably 90°C or lower. When the boiling point is higher than 90° C., the micronized cellulose dispersion tends to evaporate before the solvent that dissolves the polymer, making it extremely difficult to obtain composite particles. Specific examples of the solvent for dissolving the polymer include dichloromethane, chloroform, 1,2-dichloroethane, and benzene.

A polymer that is solid at room temperature is added to a finely divided cellulose dispersion and heated above the temperature at which the polymer has fluidity to melt and form an emulsion. Therefore, it has fluidity, and the temperature at which it has fluidity is the melting point or glass transition temperature. The melting point or glass transition temperature of the added polymer is preferably 40°C or higher and 90°C or lower. When the melting point or glass transition temperature of the polymer is less than 40°C, it tends to be difficult to solidify at room temperature, making it extremely difficult to obtain a composite. Furthermore, if the melting point or glass transition temperature of the polymer is 90°C or higher, water, which is the solvent for the finely divided cellulose dispersion that is heated together, vaporizes rather than the polymer melting, making it difficult to form an emulsion. There is a tendency to Therefore, specific examples of polymers that can be used in this embodiment include poly-S-methylheptene, polydecene, polyvinyl palmitate, polyvinyl stearate, cis-1,4-polychloroprene, and cis-1,4-polychloroprene. -1,3 pentadiene, it trans-1,4-poly-1,3 hexadiene, it trans-1,4-poly-1,3 heptadiene, it trans-1,4-poly-1,3 octadiene, polyhexane Examples include methylene oxide, polyoctamethylene oxide, polybutadiene oxide, polytetramethylene sulfide, polypentamethylene sulfide, polyhexamethylene sulfide, polymethylenethiotetramethylene sulfide, polyethylenethiotetramethylene sulfide, polytrimethylene disulfide, and the like.

One of the purposes of encapsulating the magnetic material 4 in the core particles 3 in this embodiment is to use an external magnetic field to disperse, separate, recover, stir, mix, control the flow rate, etc. of the composite particles of this embodiment in various environments. The purpose is to enable the operation of As the magnetic material used for this purpose, it is necessary to use a ferromagnetic material that has spontaneous magnetization. Here, the ferromagnetic material is a magnetic material having spontaneous magnetization, such as ferromagnetism and ferrimagnetism. Such materials include a wide variety of metals, alloys, intermetallic compounds, oxides, and metal compounds. Further, depending on the intended use of the composite particles of this embodiment, a magnetic material with low residual magnetization is required. Magnetic materials exhibiting soft magnetism are generally suitable for such uses. Further, a superparamagnetic material in which a ferromagnetic material is made into nano-order size is also preferable. Further, a superparamagnetic material obtained by making the soft magnetic material described in this embodiment into nano-order size is also preferable.

Typical metal materials are transition metals Fe, Ni, and Co, but alloys with these metals include Fe-V, Fe-Cr, Fe-Ni, Fe-Co, Ni-Co, and Ni-Cu. , Ni-Zn, Ni-V, Ni-Cr, Ni-Mn, Co-Cr, Co-Mn, 50Ni50Co-V, 50Ni50Co-Cr, etc. can also be used. Among these, systems containing Fe or Ni, which have a large saturation magnetic moment, are preferred, and Fe--Ni systems are particularly preferred. Other metal materials include rare earth Gd and its alloys.

Examples of intermetallic compounds include _ZrFe2 , HfFe2, _FeBe2 , _ScFe2 , _YFe2 , CeFe2, _SnFe2 , _GdFe2 , _{DyFe2 , HoFe2} , _{ErFe2 , TmFe2} , _GdCo2 , etc. . In addition, YCo ₅ , LaCo ₅ , CeCo ₅ , SmCo ₅ , Sm ₂ Co ₁₇ , Gd ₂ O ₁₇ , and also Ni ₃ Mn, FeCa, FeNi, Ni ₃ Fe, CrPt ₃ , MnPt ₃ , FePd, FePd ₃ , Fe ₃ Pt, FePt, CoPt, CoPt ₃ , Ni ₃ Pt, and the like.

As the oxide, magnetic oxides having crystal structures such as spinel type, garnet type, perovskite type, magnetoplumbite type, etc. can be used. Examples of spinel types include MnFe ₂ O ₄ , FeFe ₂ O ₄ , CoFe ₂ O ₄ , _{NiFe 2} O ₄ , CuFe 2 O 4 , MgFe ₂ O ₄ , ZnFe _{2 O 4} , Li _0.5 Fe _0.5 Fe ₂ O ₄ , FeMn ₂ O ₄ , FeCo ₂ O ₄ , NiCo ₂ O ₄ , γ-Fe ₂ O ₃ and the like. γ-Fe ₂ O ₃ is iron oxide called maghemite. Unlike α-Fe ₂ O ₃ (red iron), which is known as a pigment, this material is known to have a relatively low density (approximately 3.6 g/cm ³ ) and a large saturation magnetic moment. It is particularly preferable as a magnetic material used for. All of these are known as soft magnetic materials, but among them, Mn-ZnFe ₂ O ₄ and Ni-ZnFe ₂ O ₄ , that is, manganese zinc ferrite, nickel zinc ferrite, etc., have little residual magnetization, and magnetic resin particles This is preferable because the collection and dispersion operation characteristics by the magnetic field are good.

Rare earth iron garnet can be used as the garnet type oxide. _{Y3Fe5O12 , Sm3Fe5O12 , Zn3Fe5O12 , Gd3Fe5O12 , Tb3Fe5O12 , Dy3Fe5O12 , Ho3Fe5O12 , Er _ _ _ _ _ _} It is known that ₃ Fe ₅ O ₁₂ , Tm ₃ Fe ₅ O ₁₂ , Yb ₃ Fe ₅ O ₁₂ , and Lu ₃ Fe ₅ O ₁₂ exhibit ferrimagnetism. Among these, Y, Sm, Yb, Lu, etc. are preferable because they have large saturation magnetization. Among these, Y is particularly preferable because it has a low density (5.17 g/cm ³ ).

Examples of magnetoplumbite type oxides include BaFe ₁₂ O ₁₉ , SrFe ₁₂ O ₁₉ , CaFe ₁₂ O ₁₉ , PbFe ₁₂ O ₁₉ , Ag _0.5 La _0.5 Fe ₁₂ O ₁₉ , Ni _0.5 La _{0. 5} Fe ₁₂ O ₁₉ , Mn ₂ BaFe ₁₆ O ₂₇ , Fe ₂ BaFe _{16 O 27} , Ni ₂ BaFe ₁₆ O ₂₇ , FeZnBaFe ₁₆ O ₂₇ , MnZnBaFe ₁₆ O ₂₇ , Co ₂ Ba _{3 Fe24O41 , Ni2Ba3} Fe ₂₄ O ₄₁ , Cu ₂ Ba ₃ Fe ₂₄ O ₄₁ , Mg ₂ Ba _{3 Fe} 24 O ₄₁ , Co _1.5 Fe _0.5 Ba ₃ Fe ₂₄ O ₄₁ , Mn ₂ Ba ₂ Fe ₁₂ O ₂₂ , Co ₂ Ba ₂ Fe ₁₂ O ₂₂ , Ni ₂ Ba ₂ Fe ₁₂ O ₂₂ , Mg ₂ Ba ₂ Fe ₁₂ O ₂₂ , Zn ₂ Ba ₂ Fe ₁₂ O ₂₂ , Fe _0.5 Zn _1.5 Ba ₂ Fe ₁₂ O ₂₂ , etc. It will be done.
Examples of perovskite-type oxides include RFeO ₃ (R=rare earth ion).

Examples of metal compounds include borides (Co ₃ B, CoB, Fe ₃ B, MnB, FeB, etc.), Al compounds (Fe ₃ Al, Cu ₂ MnAl, etc.), and carbides (Fe ₃ C, Fe ₂ C, Mn ₃ ZnC). , _{Co2Mn2C ,} etc.), silicides ( _Fe3Si , _Fe5Si3 , _{Co2MnSi ,} etc.), nitrides ( _Mn4N , _Fe4N , _Fe8N , _Fe3NiN , _Fe3PtN , Fe ₂ N _0.75 , Mn ₄ N _0.75 C _0.25 , Mn ₄ N _0.5 C _0.5 , Fe ₃ N _1-x C _x , etc.), phosphides, arsenic compounds, Sb compounds , Bi compounds, sulfides, Se compounds, Te compounds, halogen compounds, rare earth elements, etc. can also be used.
On the other hand, as the superparamagnetic material, any material can be used as long as it is a ferromagnetic material obtained in the form of particles with a size of several nanometers to several tens of nanometers. In particular, nanoparticles such as magnetite are preferred.

The magnetic material used in this embodiment preferably has a hydrophobic surface from the viewpoint of affinity and dispersibility with the polymerizable monomer or polymer to be mixed. As a method for hydrophobizing the surface of a magnetic material, there can be mentioned a method in which a compound having in its molecule a part with extremely high affinity for the magnetic material and a hydrophobic part is brought into contact with the magnetic material and bonded thereto. Examples of compounds having such a high affinity part and a hydrophobic part in the molecule include silane compounds typified by silane coupling agents.

Silane compounds represented by silane coupling agents include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and γ-glyside. Oxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl)-γ-aminopropyltrimethoxysilane, dodecyltrimethoxy Examples include silane, hexyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, dodecyltrichlorosilane, hexyltrichlorosilane, methyltrichlorosilane, and phenyltrichlorosilane.

A method for bonding these silane compounds to a magnetic material is, for example, mixing the magnetic material and the silane compound in an inorganic medium such as water or an organic medium such as alcohol, ether, ketone, or ester, and heating the mixture while stirring. After that, the magnetic material is separated by decantation or the like, and the inorganic medium or organic medium is removed by drying under reduced pressure. Alternatively, the magnetic material and the silane compound may be directly mixed and heated to bond them together. In these means, the heating temperature is usually 30 to 100°C and the heating time is about 0.5 to 2 hours.
By performing the hydrophobization treatment on the surface of the magnetic material as described above, the magnetic material is easily encapsulated in the core particles and the micronized cellulose when magnetic material-containing composite particles are produced. By encapsulating the magnetic material in the core particles and the finely divided cellulose, the magnetic material can be protected from the outside, and deterioration of the magnetic material can be prevented.

The size of the magnetic material is preferably an average particle diameter of 0.001 μm or more and 10 μm or less. When the average particle diameter is smaller than 0.001 μm, the magnetic material has poor dispersion stability and tends to self-agglomerate. Moreover, if the average particle diameter is larger than 10 μm, the particles will not be properly encapsulated in the core particles when formed into composite particles. The average particle diameter of the magnetic material can be calculated by performing scanning electron microscopy, measuring the size of the magnetic material in the image at 100 random locations, and taking the average value.
In addition, the magnetic material-containing liquid may contain functional ingredients, and the functional ingredients include fragrances, deodorants, fungicides, fertilizers, pH adjusters, agricultural chemicals, plant vitalizers, plant life extension agents, and insect pests. and animal repellents, soil penetrants, nutritional components, plant hormones, antibacterial substances, etc.

(3rd step)
The third step is a step of covering at least a portion of the surface of the magnetic material-containing liquid in the finely divided cellulose dispersion with finely divided cellulose to stabilize the droplets containing the magnetic material-containing liquid as an emulsion.

Examples of methods for producing an emulsion include adding a polymerizable monomer containing an initiator to a finely divided cellulose dispersion to form an emulsion, and adding a polymer that is solid at room temperature to a finely divided cellulose dispersion because it has low compatibility with the finely divided cellulose dispersion. A method in which a solution dissolved in a solvent is added to a finely divided cellulose dispersion to form an emulsion. A polymer that is solid at room temperature is added to a finely divided cellulose dispersion, and the polymer is heated above the temperature at which the polymer has fluidity to melt and form an emulsion. There is a method in which a finely divided cellulose dispersion is heated above a temperature at which a solid polymer has fluidity and melted, and then the mixture is added to form an emulsion. More specifically, a magnetic material-containing liquid containing a magnetic material 4, at least one type of polymerizable monomer, and a polymerization initiator is added to a finely divided cellulose dispersion to form droplets 6 containing the magnetic material-containing liquid. A step of emulsifying the micronized cellulose dispersion, adding a magnetic material-containing liquid containing the magnetic material 4 and a polymer that is solid at room temperature dissolved in a solvent with low compatibility with the micronized cellulose dispersion. A step of emulsifying the droplets containing the magnetic material-containing liquid by adding the magnetic material-containing liquid containing the magnetic material 4 and a polymer that is solid at room temperature to the finely divided cellulose dispersion; A step of heating and melting the polymer above a temperature at which it has fluidity to emulsify the droplets containing the magnetic material-containing liquid, and adding the magnetic material 4 and the polymer that is solid at room temperature to the fine cellulose dispersion. Adding a magnetic material-containing liquid that has been heated to a temperature above the temperature at which the polymer has fluidity and melting the polymer, and emulsifying the droplets containing the magnetic material-containing liquid. Can be used.

The weight ratio of the finely divided cellulose dispersion and the magnetic material-containing liquid that can be used in the third step is not particularly limited, but the amount of the magnetic material-containing liquid is 1 part by mass or more and 50 parts by mass for 100 parts by mass of finely divided cellulose fibers. It is preferable that the amount is less than 100%. If the magnetic material-containing liquid is less than 1 part by mass, it is not preferable because the yield of the magnetic material-containing composite particles 5 tends to decrease. Moreover, if the magnetic material-containing liquid exceeds 50 parts by mass, it tends to be difficult to uniformly cover the droplets 6 with the micronized cellulose 1, which is not preferable.

The method for producing the emulsion is not particularly limited, but general emulsification treatments such as various homogenizer treatments and mechanical stirring treatments can be used. Specifically, high-pressure homogenizers, ultra-high-pressure homogenizers, all-purpose homogenizers, ball mills, roll mills, Mechanical treatments include cutter mills, planetary mills, jet mills, attritors, grinders, juicer mixers, homomixers, ultrasonic homogenizers, nanogenizers, underwater counter-impingement, and paint shakers. Further, a combination of a plurality of mechanical treatments may be used.

For example, when using an ultrasonic homogenizer, a magnetic material-containing liquid is added to the micronized cellulose dispersion obtained in the first step to form a mixed solvent, and the tip of the ultrasonic homogenizer is inserted into the mixed solvent to perform ultrasonic treatment. Implement. The processing conditions of the ultrasonic homogenizer are not particularly limited, but for example, the frequency is generally 20 kHz or higher, and the output is generally 10 W/cm ² or higher. Although the processing time is not particularly limited, it is usually about 10 seconds to 1 hour.

By the above ultrasonic treatment, the droplets 6 are dispersed in the micronized cellulose dispersion to progress emulsion, and the micronized cellulose 1 is selectively added to the liquid/liquid interface between the droplets 6 and the micronized cellulose dispersion. By adsorption, the droplets 6 are covered with the finely divided cellulose 1, forming a stable structure as an O/W emulsion. An emulsion that is stabilized by adsorption of solid matter at the liquid/liquid interface is academically referred to as a "Pickering emulsion." As mentioned above, the mechanism by which Pickering emulsions are formed by finely divided cellulose fibers is not clear, but cellulose has hydrophilic sites derived from hydroxyl groups and hydrophobic sites derived from hydrocarbon groups in its molecular structure. Since it exhibits amphiphilic properties, it is thought that it adsorbs to the liquid/liquid interface between the hydrophobic monomer and the hydrophilic solvent due to its amphiphilic properties.

The O/W emulsion structure can be confirmed, for example, by optical microscopic observation. The particle size of the O/W emulsion is not particularly limited, but is usually about 0.1 μm to 1000 μm.
In the O/W emulsion structure, the thickness of the finely divided cellulose layer (coating layer 2) formed on the surface layer of the droplet 6 is not particularly limited, but is usually about 3 nm to 1000 nm. The thickness of the micronized cellulose layer (covering layer 2) can be measured using, for example, cryo-TEM.

(4th step)
The fourth step is a step of solidifying the droplets 6 to obtain magnetic material-containing composite particles 5 in which the core particles 3 are coated with the finely divided cellulose 1. More specifically, in the fourth step, the surface of the core particle 3 is solidified to form the core particle 3 with at least a portion of the surface of the droplet 6 covered with the finely divided cellulose 1. This is a step of covering at least a portion of the micronized cellulose 1 with the micronized cellulose 1, and making the core particles 3 and the micronized cellulose 1 inseparable.
When a method of adding a polymerizable monomer containing an initiator to the finely divided cellulose dispersion to form an emulsion is used in the third step, the method of polymerizing the polymerizable monomer is not particularly limited, and the method of polymerizing the polymerizable monomer used is It can be appropriately selected depending on the type and type of polymerization initiator. Examples of methods for polymerizing the above-mentioned polymerizable monomers include suspension polymerization.

The specific suspension polymerization method is not particularly limited either, and any known method can be used. For example, by heating the O/W emulsion produced in the third step, in which droplets 6 containing a magnetic material, a polymerization initiator, and a polymerizable monomer are coated with finely divided cellulose 1 and stabilized, while stirring. It can be implemented. The stirring method is not particularly limited, and any known method can be used, and specifically, a disperser or a stirrer can be used. Alternatively, only heat treatment may be performed without stirring. Further, the temperature conditions during heating can be appropriately set depending on the type of polymerizable monomer and the type of polymerization initiator, but preferably 20 degrees or more and 90 degrees or less. If the temperature during heating is less than 20 degrees, the reaction rate of polymerization tends to decrease, which is undesirable, and if it exceeds 90 degrees, the fine cellulose dispersion tends to evaporate, which is not preferred. The time for the polymerization reaction can be appropriately set depending on the type of polymerizable monomer and the type of polymerization initiator, but is usually about 1 hour to 24 hours. Further, the polymerization reaction may be carried out by ultraviolet irradiation treatment, which is a type of electromagnetic wave. In addition to electromagnetic waves, particle beams such as electron beams may also be used.

In the third step, when a method is used in which a polymer that is solid at room temperature is dissolved in a solvent with low compatibility with the finely divided cellulose dispersion and added to the finely divided cellulose dispersion to form an emulsion, the emulsion is heated, The polymer can be solidified by volatilizing the solvent in which the polymer is dissolved. Temperature conditions during heating can be appropriately set depending on the type of solvent to be dissolved, but are preferably higher than the boiling point of the solvent and lower than 90 degrees. If the heating temperature is lower than the boiling point of the solvent, the movement of the solvent to the aqueous phase will be slow, and if it exceeds 90 degrees, the micronized cellulose dispersion will tend to evaporate, which is not preferable.

In the third step, when a polymer that is solid at room temperature is added to the finely divided cellulose dispersion and heated above the temperature at which the polymer has fluidity to melt and form an emulsion, the emulsion is cooled and the polymer is The polymer can be solidified by lowering the temperature below the fluidity level.
Through the above-described steps, true spherical magnetic material-containing composite particles 5 in which the core particles 3 are covered with the finely divided cellulose 1 can be produced.

In addition, in the state immediately after the completion of the solidification reaction, there is a large amount of water in the dispersion of the magnetic material-containing composite particles 5, and free micronized cellulose 1 that does not contribute to the formation of the coating layer of the magnetic material-containing composite particles 5. It is in a mixed state. Therefore, it is necessary to collect and purify the produced magnetic material-containing composite particles 5, and as a collection and purification method, washing by centrifugation or washing by filtration is preferable. As the washing method using centrifugation, a known method can be used. Specifically, the operation of sedimenting the magnetic material-containing composite particles 5 by centrifugation, removing the supernatant, and redispersing it in a mixed solvent of water and methanol is repeated. Finally, the magnetic material-containing composite particles 5 can be recovered by removing residual solvent from the sediment obtained by centrifugation. Known methods can be used for filtration and cleaning, for example, repeating suction filtration with water and methanol using a PTFE membrane filter with a pore size of 0.1 μm, and finally removing residual solvent from the paste remaining on the membrane filter. Then, the magnetic material-containing composite particles 5 can be recovered.

The method for removing the residual solvent is not particularly limited, and can be carried out, for example, by air drying or heat drying in an oven. The dry solid material containing the magnetic material-containing composite particles 5 obtained in this manner does not form a film or aggregate as described above, but is obtained as a finely textured powder.

In the magnetic material-containing composite particles 5 of this embodiment, functional components may be added to the coating layer 2 and the core particles 3. For example, by reacting the finely divided cellulose 1 forming the coating layer 2 with a compound having a chelate-forming group (iminodiacetic acid, aminomethylphosphonic acid, etc.), it can be used as a metal ion adsorbent. By adding magnetic material-containing composite particles that have the ability to adsorb metal ions to contaminated water such as industrial wastewater, they can be dispersed in the contaminated water and efficiently adsorb metal ions. The encapsulated composite particles 5 can be collected by an external magnetic field and can be used to purify contaminated water.
Further, by reacting an antibody with the micronized cellulose 1, it can be used as an antigen adsorbent. For example, when polyethyleneimine-modified magnetic material-containing composite particles are added to an aqueous bovine serum albumin solution containing E. coli-derived LPS, albumin is not adsorbed because cellulose has non-protein adsorption properties, and E. coli selectively Only the derived LPS can be adsorbed, and the magnetic material-containing composite particles 5 that have adsorbed the target substance can be recovered using an external magnetic field.

(Effects of embodiment)
The magnetic material-containing composite particles 5 according to the present embodiment have magnetic responsiveness, excellent dispersion stability, good redispersibility even after drying, and can be produced by a simple method without using a surfactant. It is a composite particle containing a magnetic material that has a low impact on the environment.
Further, the dry solid material containing the magnetic material-containing composite particles 5 according to the present embodiment is obtained as a fine-textured powder, and there is no aggregation of the particles. Therefore, it is easy to redisperse the magnetic material-containing composite particles 5 obtained as a dry powder in a solvent, and even after redispersion, the fine cellulose 1 bonded to the surface of the magnetic material-containing composite particles 5 remains. Indicates dispersion stability derived from the coating layer.

Further, according to the method for manufacturing magnetic material-containing composite particles 5 according to the present embodiment, it is possible to provide a novel method for manufacturing magnetic material-containing composite particles 5 that can be provided by a simple method.
Moreover, according to the dry solid material containing the composite of finely divided cellulose 1 according to the present embodiment, the dry solid material can be provided in a form that can be redispersed in a solvent.
Moreover, according to the magnetic material-containing composite particles 5 according to the present embodiment, since it is possible to remove most of the solvent, effects such as a reduction in transportation costs and a reduction in the risk of spoilage can be expected.

Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and may include design changes within the scope of the gist of the present invention. Further, the components shown in the first embodiment and the modified example described above can be configured by appropriately combining them.

[Example]
Hereinafter, the present invention will be explained in detail based on Examples, but the technical scope of the present invention is not limited to these Examples. In each of the following examples, "%" indicates mass % (w/w%) unless otherwise specified.

<Example 1>
(First step: Step of obtaining cellulose nanofiber dispersion)
(TEMPO oxidation of wood cellulose)
70 g of softwood kraft pulp was suspended in 3500 g of distilled water, a solution of 0.7 g of TEMPO and 7 g of sodium bromide dissolved in 350 g of distilled water was added, and the mixture was cooled to 20°C. 450 g of an aqueous sodium hypochlorite solution having a concentration of 2 mol/L and a density of 1.15 g/mL was added dropwise thereto to start an oxidation reaction. The temperature in the system was always kept at 20° C., and the pH during the reaction was kept at 10 by adding a 0.5N aqueous sodium hydroxide solution. When the total amount of sodium hydroxide added to the weight of cellulose reached 3.50 mmol/g, about 100 mL of ethanol was added to stop the reaction. Thereafter, filtration and washing with distilled water was repeated using a glass filter to obtain oxidized pulp.

(Measurement of carboxy group amount of oxidized pulp)
The solid content of 0.1 g of the oxidized pulp and reoxidized pulp obtained by the above TEMPO oxidation was weighed, dispersed in water at a concentration of 1%, and hydrochloric acid was added to adjust the pH to 2.5. Thereafter, the amount of carboxy groups (mmol/g) was determined by conductivity titration using a 0.5M aqueous sodium hydroxide solution. The result was 1.6 mmol/g.

(Defibration treatment of oxidized pulp)
1 g of the oxidized pulp obtained by the above TEMPO oxidation was dispersed in 99 g of distilled water and micronized using a juicer mixer for 30 minutes to obtain a CSNF aqueous dispersion with a CSNF concentration of 1%. The CSNF dispersion liquid was placed in a quartz cell with an optical path length of 1 cm, and the spectral transmission spectrum was measured using a spectrophotometer (manufactured by Shimadzu Corporation, "UV-3600"). The results are shown in FIG. As is clear from FIG. 3, the CSNF aqueous dispersion exhibited high transparency. Further, the number average minor axis diameter of CSNF contained in the CSNF aqueous dispersion was 3 nm, and the number average major axis diameter was 1110 nm. Furthermore, the results of steady viscoelasticity measurement using a rheometer are shown in FIG. As is clear from FIG. 4, the CSNF dispersion exhibited thixotropic properties.

(Second step: step of producing a mixture of magnetic material, monomer, and polymer)
Next, 1 g of 2,2-azobis-2,4-dimethylvaleronitrile (hereinafter also referred to as ADVN), which is a polymerization initiator, is added to 10 g of divinylbenzene (hereinafter also referred to as DVB), which is a polymerizable monomer. After dissolving, 1 g of iron oxide particles (particle size: 30 nm, hydrophobized) was added and stirred to prepare a magnetic material-containing liquid.

(Third step: step of producing O/W type emulsion)
Next, when the entire amount of the prepared magnetic material-containing liquid was added to 40 g of a CSNF dispersion with a CSNF concentration of 1%, the magnetic material-containing liquid and the CSNF dispersion were separated into two layers.
Next, the shaft of an ultrasonic homogenizer was inserted from the liquid level of the upper layer of the mixed liquid separated into two layers, and ultrasonic homogenizer treatment was performed for 3 minutes at a frequency of 24 kHz and an output of 400 W. The appearance of the mixed solution after treatment with an ultrasonic homogenizer was that of a cloudy emulsion. When a drop of the mixed solution was placed on a slide glass, sealed with a cover glass, and observed under an optical microscope, countless emulsion droplets of about 1 to several μm were formed, indicating that the dispersion was stabilized as an O/W emulsion. was confirmed.

(Fourth step: Step of obtaining magnetic material-containing composite particles 5 coated with CNF by polymerization reaction)
The O/W type emulsion dispersion was placed in a water bath at 70°C and treated for 8 hours while stirring with a stirrer to carry out a polymerization reaction. After 8 hours of treatment, the dispersion was cooled to room temperature. There was no change in the appearance of the dispersion before and after the polymerization reaction. When the obtained dispersion liquid was treated with a centrifugal force of 75,000 g (g is gravitational acceleration) for 5 minutes, a precipitate was obtained. The supernatant was removed by decantation to collect the sediment, which was then washed repeatedly with pure water and methanol using a PTFE membrane filter with a pore size of 0.1 μm. The purified and collected product thus obtained was redispersed at a concentration of 1%, and the particle size was evaluated using a particle size distribution meter (NANOTRAC UPA-EX150, Nikkiso Co., Ltd.), and the average particle size was 2.1 μm. Next, the purified and collected product was air-dried and further vacuum-dried for 24 hours at a room temperature of 25 degrees Celsius to obtain a fine-textured dry powder (magnetic material-containing composite particles 5).

(Shape observation using a scanning electron microscope)
The results of observing the obtained dry powder using a scanning electron microscope are shown in FIGS. 5 and 6. As is clear from FIG. 5, by carrying out the polymerization reaction using the O/W type emulsion droplets as a template, countless true spherical magnetic material-containing composite particles 5 were formed, which was derived from the shape of the emulsion droplets. It was confirmed that there is. Further, as shown in FIG. 6, it was confirmed that the surface was uniformly covered with CNF having a width of several nm. Furthermore, even though the magnetic material-containing composite particles 5 were repeatedly washed by filtration and washing, the surfaces of the magnetic material-containing composite particles 5 were evenly and uniformly covered with the finely divided cellulose 1. It was shown that the core particles 3 inside the material-containing composite particles 5 and CNF, which is the finely divided cellulose 1, may be bonded to each other, and the core particles 3 and the finely divided cellulose 1 are inseparable.

(Evaluation of magnetic response)
Dry powder of magnetic material-containing composite particles 5 was added to pure water at a concentration of 1%, and a permanent magnet was brought close from the outside of the container containing the dispersion liquid, which was redispersed by ultrasonic irradiation, and left to stand for 12 hours. However, the magnetic material-containing composite particles 5 were attracted by the magnet and were separated into pure water and an aggregated portion of the magnetic material-containing composite particles 5.

(Evaluation of redispersibility)
When the dry powder of magnetic material-containing composite particles 5 was added to pure water at a concentration of 1% and redispersed by ultrasonic irradiation, it was easily redispersed and no aggregation was observed. Furthermore, when the particle size was evaluated using a particle size distribution meter, the average particle size was 2.1 μm, the same as before drying, and there was no signal indicating aggregation in the data from the particle size distribution meter.
From the above, it can be seen that the magnetic material-containing composite particles 5 can be obtained as a powder without forming a film upon drying, and have good redispersibility, even though their surfaces are coated with CNF. Shown.

<Example 2>
Example 2 was carried out under the same conditions as in Example 1, except that diethylene glycol diacrylate (trade name FA-222A, Hitachi Chemical, hereinafter also referred to as FA-222A) was used instead of DVB in Example 1. Magnetic material-containing composite particles 5 were produced, and various evaluations were conducted in the same manner.

<Example 3>
Same as Example 1 except that instead of TEMPO oxidation in Example 1, a phosphated CNF dispersion obtained by performing phosphoric acid esterification treatment according to Non-Patent Document 1 cited as a prior art document was used. The magnetic material-containing composite particles 5 according to Example 3 were produced under the following conditions, and various evaluations were performed in the same manner.

<Example 4>
As a polymer forming the core particles 3, 6 g of polystyrene (hereinafter referred to as PS) was dissolved in 4 g of dichloromethane (boiling point: 39.6° C.). The entire amount of the PS/dichloromethane mixed solution was added to 40 g of the CSNF dispersion used in Example 1.
Next, the above mixture was subjected to ultrasonic homogenizer treatment for 3 minutes at a frequency of 24 kHz and an output of 400 W in the same manner as in Example 1 to obtain an O/W emulsion dispersion.

Next, the O/W type emulsion dispersion was placed in a water bath at 70°C and treated for 8 hours while stirring with a stirrer to volatilize dichloromethane. After 8 hours of treatment, the dispersion was treated in the same manner as in Example 1 to obtain a dry powder (magnetic material-containing composite particles 5).
Next, 5 g of the obtained composite particles were added to an aqueous solution prepared by mixing 2 g of limonene in 10 g of methanol with 20 g of water, and mixed for 24 hours while stirring with a magnetic stirrer. The composite particles immersed in the aqueous solution were filtered using a PTFE membrane filter with a pore size of 0.1 μm, and the collected material was air-dried for 48 hours to produce magnetic material-containing composite particles 5 according to Example 4, and various evaluations were similarly conducted. carried out.

<Example 5>
The magnetic material according to Example 5 was produced under the same conditions as Example 4 except that polymethyl methacrylate (hereinafter also referred to as PMMA) was used instead of PS and chloroform was used instead of dichloromethane. Encapsulated composite particles 5 were produced and various evaluations were conducted in the same manner.

<Example 6>
As a polymer forming the core particles 3, 10 g of polyhexamethylene oxide (hereinafter also referred to as PHMO, melting point: 58° C.) was added to 40 g of the CSNF dispersion liquid used in Example 1.
Next, the above mixed solution was heated to 80° C. using a water bath to melt the PHMO, and then subjected to ultrasonic homogenizer treatment for 3 minutes at a frequency of 24 kHz and an output of 400 W as in Example 1. An O/W emulsion dispersion was obtained.
Next, the O/W emulsion dispersion was cooled to room temperature.
Finally, the above dispersion liquid was treated in the same manner as in Example 1 to obtain a dry powder (magnetic material-containing composite particles 5).

<Example 7>
The magnetic material encapsulation according to Example 7 was carried out under the same conditions as in Example 1, except that cobalt oxide particles (particle diameter 50 nm, hydrophobized) were used instead of iron oxide particles as the magnetic material in Example 1. Composite particles 5 were produced and various evaluations were performed in the same manner.

<Example 8>
The magnetic material encapsulation according to Example 8 was carried out under the same conditions as in Example 4, except that cobalt oxide particles (particle diameter 50 nm, hydrophobized) were used instead of iron oxide particles as the magnetic material in Example 4. Composite particles 5 were produced and various evaluations were performed in the same manner.

<Example 9>
The magnetic material encapsulation according to Example 9 was carried out under the same conditions as in Example 6, except that cobalt oxide particles (particle diameter 50 nm, hydrophobized) were used instead of iron oxide particles as the magnetic material in Example 6. Composite particles 5 were produced and various evaluations were performed in the same manner.

<Example 10>
The magnetic material-containing composite according to Example 10 was prepared under the same conditions as in Example 4, except that iron oxide particles with a particle size of 1 nm were used instead of the iron oxide particles with a particle size of 30 nm, which are the magnetic materials in Example 4. Particle 5 was produced and various evaluations were performed in the same manner.

<Example 11>
The magnetic material-containing composite according to Example 11 was produced under the same conditions as in Example 4, except that iron oxide particles with a particle size of 10,000 nm were used instead of the iron oxide particles with a particle size of 30 nm, which are the magnetic materials in Example 4. Particle 5 was produced and various evaluations were performed in the same manner.

<Example 12>
The magnetic material-containing composite according to Example 12 was produced under the same conditions as Example 8, except that cobalt oxide particles with a particle size of 1 nm were used instead of the cobalt oxide particles with a particle size of 30 nm, which were the magnetic material in Example 8. Particle 5 was produced and various evaluations were performed in the same manner.

<Example 13>
The magnetic material-containing composite according to Example 13 was produced under the same conditions as in Example 8, except that cobalt oxide particles with a particle size of 10,000 nm were used instead of the cobalt oxide particles with a particle size of 30 nm, which are the magnetic materials in Example 8. Particle 5 was produced and various evaluations were performed in the same manner.

<Example 14>
The magnetic material according to Example 14 was prepared under the same conditions as in Example 4, except that iron oxide particles with a particle size of 0.8 nm were used instead of the iron oxide particles with a particle size of 30 nm, which are the magnetic materials in Example 4. Encapsulated composite particles 5 were produced and various evaluations were conducted in the same manner.

<Example 15>
The magnetic material-containing composite according to Example 15 was produced under the same conditions as in Example 4, except that iron oxide particles with a particle size of 10,100 nm were used instead of the iron oxide particles with a particle size of 30 nm, which are the magnetic materials in Example 4. Particle 5 was produced and various evaluations were performed in the same manner.

<Comparative example 1>
An attempt was made to produce magnetic material-containing composite particles 5 according to Comparative Example 1 under the same conditions as in Example 1, except that pure water was used instead of the CSNF dispersion in Example 1.

<Comparative example 2>
An attempt was made to produce magnetic material-containing composite particles 5 according to Comparative Example 2 under the same conditions as in Example 1, except that an aqueous solution of carboxymethyl cellulose (hereinafter also referred to as CMC) was used instead of TEMPO oxidation in Example 1. Ta.

<Comparative example 3>
Magnetic material-containing composite particles 5 according to Comparative Example 3 were prepared under the same conditions as in Example 1, except that an 8% aqueous solution of polyvinyl alcohol (hereinafter also referred to as PVA) was used instead of the CSNF dispersion in Example 1. I tried to make it.

<Comparative example 4>
Preparation of magnetic material-containing composite particles 5 according to Comparative Example 4 under the same conditions as Example 1 except that aluminum oxide (particle size 300 nm) was used instead of iron oxide particles as the magnetic material in Example 1. I tried.

The evaluation results using the above Examples and Comparative Examples are summarized in Table 1 below.

In Table 1, the emulsion stabilizer refers to an additive used to stabilize the O/W emulsion in the second step, and for example, micronized cellulose 1 in this embodiment is equivalent to do.

〔Evaluation criteria〕
In Table 1, the feasibility of the second step was determined as follows.
○: Formation of an O/W type emulsion is possible. ×: Formation of an O/W type emulsion is not possible. Furthermore, whether or not the third step can be performed was determined as follows.
○: True spherical particles were obtained as the emulsion mold in the third step. ×: The above particles were not obtained.

Furthermore, the magnetic responsiveness was determined as follows.
○: The magnetic material-containing composite particles 5 dispersed in the solvent (water) were attracted by a magnet (magnetic force of 0.5 Tesla), and the magnetic material-containing composite particles 5 and the solvent (water) were separated within 12 hours.△: The magnetic material-containing composite particles 5 dispersed in the solvent (water) were attracted by a magnet (magnetic force of 0.5 Tesla), and the magnetic material-containing composite particles 5 and the solvent (water) were separated within 24 hours. The magnetic material-containing composite particles 5 dispersed in water) were not attracted to the magnet (magnetic force of 0.5 Tesla), and the magnetic material-containing composite particles 5 and the solvent (water) did not separate even after 24 hours. In the example, "○" and "△" were considered to be passed.

Furthermore, the redispersibility was determined as follows.
○: The obtained magnetic material-containing composite particles were dispersed in the solvent (water) within 1 minute without agglomeration. △: The obtained magnetic material-containing composite particles were dispersed in the solvent (water) within 5 minutes. ×: The obtained magnetic material-containing composite particles did not disperse in the solvent (water) even after 5 minutes had elapsed, but aggregated. In this example, "○" and "△" were considered acceptable.

Further, dispersion stability was determined as follows.
○: The dispersibility was maintained even after 100 hours had passed after the magnetic material-containing composite particles 5 were dispersed in the solvent (water). △: The magnetic material-containing composite particles 5 were dispersed in the solvent (water). After 50 hours had passed, about 10% of the dispersed magnetic material-containing composite particles 5 had separated. ×: Within 24 hours after dispersing the magnetic material-containing composite particles 5 in a solvent (water). In this example, the solvent (water) and the magnetic material-containing composite particles 5 were almost separated. In this example, "○" and "△" were passed.

Furthermore, the necessity of using a surfactant was determined as follows.
○: A surfactant was used in the manufacturing process of the magnetic material-containing composite particles 5. ×: A surfactant was not used in the manufacturing process of the magnetic material-containing composite particles 5. In this example, "○" was passed. And so.

In addition, the diagonal lines in each cell in the comparative example in Table 1 indicate that the core particles could not be manufactured, and that the process became impossible during each process and the subsequent process was not performed. ing.
As is clear from the evaluation results of Examples 1 to 15 in Table 1, regardless of the type of micronized cellulose 1 (TEMPO-oxidized CNF, phosphate-esterified CNF), the type of magnetic material, or the type of core particles, It was confirmed that magnetic material-containing composite particles having both magnetic responsiveness and redispersibility can be produced and are successful in solving the problems of the present invention.

On the other hand, in Comparative Example 1, it was impossible to perform the second step. Specifically, even if the ultrasonic homogenizer treatment was carried out, the monomer layer and the pure water layer remained separated into two layers, making it impossible to produce an O/W emulsion itself.
Furthermore, in Comparative Example 2, it was possible to form an O/W type emulsion in the second step. This is thought to be because CMC exhibited amphiphilic properties like finely divided cellulose, and therefore functioned as a stabilizer for the emulsion. However, when the polymerization reaction was carried out in the subsequent third step, the emulsion collapsed, making it impossible to obtain composite particles using the O/W emulsion as a template. The reason for this is not certain, but since CMC is water-soluble, it is likely to be weak as a coating layer to maintain the emulsion shape during the polymerization reaction, and therefore the emulsion may collapse during the polymerization reaction. Conceivable.

Furthermore, in Comparative Example 3, polymerization could be performed in the third step and the powder could be recovered, but the obtained powder had poor redispersibility and was in an agglomerated state. When a magnet was brought close to the aggregate, it had magnetic responsiveness.
In addition, in Comparative Example 4, it was possible to polymerize in the third step and recover it as powder, and the obtained powder had good redispersibility, but aluminum oxide is a non-magnetic substance. Therefore, it did not have magnetic responsiveness.

The magnetic material-containing composite particles of this example can provide favorable effects from the viewpoint of industrial implementation, such as contributing to cost reduction from the viewpoint of improving transportation efficiency and preventing spoilage. In addition, this composite particle has magnetic responsiveness, excellent dispersion stability, good redispersibility even after drying, and can be produced by a simple method without using surfactants, making it environmentally friendly. It has a low load and can be applied to diagnostic drug carriers, cell separation carriers, cell culture carriers, nucleic acid separation and purification carriers, protein separation and purification carriers, immobilized enzyme carriers, drug delivery carriers, magnetic toners, magnetic inks, magnetic paints, etc. can.

1 Cellulose nanofiber (micronized cellulose)
2 Covering layer 3 Core particle 4 Magnetic material 5 Magnetic material-containing composite particle 6 Droplet (polymerizable monomer droplet, polymer droplet)
7 Dispersion liquid

Claims (10)

It has a core particle containing at least one type of polymer and a magnetic material, and a coating layer made of finely divided cellulose,
A composite particle in which the core particle and at least a portion of the micronized cellulose are bonded and inseparable ;
A composite particle containing a magnetic material , wherein the polymer is polymethyl methacrylate or polyhexamethylene oxide . The magnetic material-containing composite particle according to claim 1, wherein at least a portion of the magnetic material is exposed from the surface of the core particle. The magnetic material-containing composite particle according to claim 1 or 2, wherein the magnetic material is a soft magnetic material. The magnetic material-containing composite particle according to any one of claims 1 to 3, wherein the magnetic material is a superparamagnetic material. The magnetic material-containing composite particle according to any one of claims 1 to 4, wherein the magnetic material has an average particle diameter of 0.001 μm or more and 10 μm or less. the polymer is polymethyl methacrylate;
The magnetic material-containing composite particle according to any one of claims 1 to 5, wherein the magnetic material is iron oxide . the polymer is polyhexamethylene oxide,
The magnetic material-containing composite particle according to any one of claims 1 to 5, wherein the magnetic material is iron oxide or cobalt oxide. A dry powder comprising the magnetic material-containing composite particles according to any one of claims 1 to 7 , wherein the solid content of the magnetic material-containing composite particles is 80% or more. A first step of defibrating the cellulose raw material in a solvent to obtain a dispersion of finely divided cellulose;
A second step of mixing a liquid containing at least one type of polymerizable monomer or polymer with a magnetic material to obtain a magnetic material-containing liquid;
The dispersion liquid and the magnetic material-containing liquid are mixed, at least a part of the surface of a magnetic material-containing droplet containing the magnetic material-containing liquid in the dispersion liquid is covered with the micronized cellulose, and the magnetic material-containing liquid is mixed with the magnetic material-containing liquid. a third step of stabilizing the droplets as an emulsion;
By solidifying the magnetic material-containing droplet to form a core particle in a state where at least a part of the surface of the magnetic material-containing droplet is covered with the finely divided cellulose, at least a portion of the surface of the core particle is solidified. a fourth step of covering the core particles with the micronized cellulose and making the core particles and the micronized cellulose inseparable ;
The polymer is polymethyl methacrylate or polyhexamethylene oxide,
A method for producing magnetic material -containing composite particles, wherein the polymerizable monomer is a monofunctional vinyl monomer . In the third step,
The magnetic material-containing liquid containing the magnetic material, the at least one polymerizable monomer, and a polymerization initiator is added to the finely divided cellulose dispersion to form droplets containing the magnetic material-containing liquid. emulsification process,
The magnetic material-containing liquid containing the magnetic material and the polymer, which is solid at room temperature, dissolved in a solvent having low compatibility with the finely divided cellulose dispersion, is added to the finely divided cellulose dispersion. emulsifying droplets containing the magnetic material-containing liquid by adding
Adding the magnetic material-containing liquid containing the magnetic material and the polymer that is solid at room temperature to the finely divided cellulose dispersion, and heating and melting the polymer above a temperature at which the polymer has fluidity, emulsifying droplets containing the magnetic material-containing liquid, and
Adding to the dispersion of micronized cellulose is a solution containing the magnetic material, which is obtained by heating and melting a material containing the magnetic material and the polymer that is solid at room temperature above a temperature at which the polymer has fluidity. 10. The method for producing magnetic material-containing composite particles according to claim 9 , further comprising emulsifying droplets containing the magnetic material-containing liquid.

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