JP2003112925A - Magnetite crystal nanoparticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nanoparticles which essentially consist of magnetite crystals, and have ferromagnetism, and have excellent dispersibility into organic media in a wide area. SOLUTION: The magnetite crystal nanoparticles consist of magnetite crystals in which surface modifier molecules having a molecular weight of <=1,000 are bonded, and having a number average grain diameter of 1 to 20 nm. The standard deviation of the grain diameter of the magnetite crystals is <=20% of the number average grain diameter.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to magnetite crystalline nanoparticles. More specifically, the present invention relates to nanoparticles mainly composed of magnetite (Fe ₃ O ₄ ) nanocrystals. Since the magnetite crystal nanoparticles of the present invention have ferromagnetism (ferrimagnetism), uniform thin film forming property, excellent dispersibility in an organic medium such as resin, and a narrow particle size distribution, for example, a uniform and high recording density can be obtained. It can be used as a material of a characteristic magnetic recording medium.

[0002]

2. Description of the Related Art Fine particles of iron oxide crystals having ferromagnetism or ferrimagnetism (hereinafter collectively referred to as "ferromagnetism" in the present invention) are used for magnetic recording media, magnetic toners and the like which utilize the ferromagnetism. It is important as a raw material. Magnetite nanocrystals, which are iron oxides having ferromagnetism, are known.

M. A. Correa-Duarte et al .;
Langmuir, 14 volumes, 6430-6435 (19).
98), a technique of applying sodium silicate to silica coating on magnetite crystals having an average particle diameter of about 12 nm is reported, but this method cannot disperse only magnetite crystals in an organic medium. Met. The standard deviation of the particle size distribution of the obtained magnetite crystals is the average particle size because it depends on the method of synthesizing magnetite crystals in which hydrochloric acid (aqueous solution) of iron (II) sulfate and iron (III) chloride is added to ammonium hydroxide aqueous solution with stirring. Of 25
%, And those having a narrower particle size distribution have been required for applications such as magnetic recording.

L. Shen et al .; Langmuir, 15
Vol., 447-453 (1999), a fatty acid having about 10 carbon atoms is bound as a surface coating molecule to give an average particle size of 7-1.
Magnetite crystals having a size of about 0 nm have been reported.
However, since this technique is based on a synthetic method using a mixed solution of divalent and trivalent iron cations as a raw material as in the above report, the particle size distribution was similarly large. .

A. A. Mamedov et al .; Langmu
ir, 16 volumes, 5530-5533 (2000),
Magnetite crystals having an average particle size of about 8 to 10 nm have been reported, but they are obtained in a state in which aggregation is suppressed as a composition using a crosslinked special organic ionic polymer called polydiallyldimethylammonium bromide as a medium. However, it was impossible to disperse magnetite crystals in a wide range of organic media by this technique. Further, the particle size distribution was similarly large because of the method of synthesizing magnetite crystals using the mixed solution of divalent and trivalent iron cations as the same as the above report.

On the other hand, a surfactant (for example, dodecylbenzenesulfonic acid) is bound to the surface of the primary particles of iron oxide crystals to impart dispersibility to an organic medium (for example, an organic solvent such as xylene), and then the interface. For example, a method of improving crystallinity while maintaining the dispersibility of the iron oxide crystals in an organic medium by heating under a temperature condition (for example, 220 ° C. or lower) at which thermal decomposition of the activator does not substantially proceed is described, for example. Seijiro Ito et al .; Coloring material, Vol. 55, No. 5, 22-26 (1982).
Has been reported to. However, although α-hematite (α-Fe ₂ O ₃ ) crystals can be prepared by this method, it was not possible to obtain magnetite crystals that are iron oxides having ferromagnetism.

Recently, a method of injecting a thermally decomposable raw material into a melt of an organic compound at a high temperature of about 300 ° C. or higher to cause crystal growth is used, and ferromagnetic iron oxides such as γ-hematite (γ-Fe) are used.
Preparation of nanoparticles in which the organic compound is bound to the surface of primary particles of ( ₂ O ₃ ) crystal to obtain organic solvent dispersibility is described in J. Rock
Enberger et al .; Am. Chem. Soc. ，
121, 11595-11596 (1999). However, with this method, it was not possible to obtain a magnetite crystal which is a ferromagnetic iron oxide having a better chemical stability than γ-hematite.

As can be seen from the above-mentioned prior art, no nanoparticles mainly composed of magnetite crystals having a narrow particle size distribution have been known.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide nanoparticles mainly composed of magnetite crystals having ferromagnetism and excellent dispersibility in a wide range of organic media.

[0010]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in order to achieve the above object, as a result, a fat-soluble molecule (in the present invention, a “surface-modifying molecule”) having a binding property on the particle surface of iron oxides. Said) or an organic solution containing it which is immiscible with water is brought into contact with a hydrosol of hydrated iron oxide primary particles (that is, a dispersion having water as a solvent), whereby the hydration at the interface between both phases is carried out. The binding reaction of the surface-modifying molecule to the iron oxide primary particles is promoted to impart the organic medium dispersibility to the primary particles to extract into the organic phase, and then the primary particles dispersed in the melt of the organic compound are By heating, it was found that it is possible to convert the hydrated iron oxide into magnetite crystals while maintaining the dispersibility in an organic medium, and it was confirmed that the magnetite crystal nanoparticles thus obtained have ferromagnetism. The present invention It has been reached.

That is, the gist of the present invention lies in the following five points. 1. A magnetite crystal having a number average particle size of 1 to 20 nm, which is bound to a surface-modifying molecule having a molecular weight of 1,000 or less, and the standard deviation of the particle size of the magnetite crystal is 20% or less of the number average particle size. Magnetite crystalline nanoparticles characterized by: 2. A polymer composition containing the magnetite crystal nanoparticles. 3. A coating liquid composition containing the magnetite crystal nanoparticles. 4. A thin film-shaped compact containing the magnetite crystal nanoparticles. 5. A magnetic recording medium using the above-mentioned thin film shaped body.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. [Magnetite Crystal Nanoparticles] The magnetite crystal nanoparticles of the present invention are composed of magnetite crystals having a number average particle diameter of 1 to 20 nm, to which surface-modifying molecules described later are bound. Such magnetite crystal nanoparticles have good dispersibility in an organic medium such as a resin or an organic solvent due to the effect of the surface modification molecule. The magnetite crystal is any semiconductor or conductor (such as transition metal or carbon).
Alternatively, it may have an outer shell (shell) having a composition of an insulator (such as silica), and particularly other magnetic materials (such as metal oxides such as γ-hematite and chromium oxide, and transitions such as cobalt and iron). Having a metal, or a composite material of these metal oxides and a transition metal, etc.) as a shell may result in magnetic nanoparticles having excellent magnetic properties.

In the present invention, the magnetite crystal can be identified by observing a diffraction peak attributed to a known magnetite crystal by an X-ray diffraction spectrum. If the number average particle diameter is less than 1 nm, the magnetite crystal properties (for example, ferromagnetism) may not be sufficiently exhibited. Therefore, the lower limit value is preferably 2 nm, more preferably 3 nm. On the other hand, when the number average particle diameter exceeds 20 nm, the dispersibility in an organic medium may be extremely reduced. Therefore, the upper limit is preferably 15
nm, more preferably 10 nm, most preferably 7 nm
Is. The most preferable range of the number average particle diameter is 3 to 7 n.
m.

The standard deviation of the particle size of the magnetite crystals is preferably 20% or less of the number average particle size from the viewpoint of homogeneity of the polymer composition and the thin film-shaped product described later. The standard deviation is more preferably 15% or less, further preferably 10% or less. The number average particle diameter and the standard deviation are determined by using the numerical values measured from a transmission electron microscope (TEM) observation image of the given magnetite crystal nanoparticles. That is, the diameter of a circle having the same area as the observed particle image is defined as the particle size of the particle image. The number average particle diameter is calculated, for example, by a known statistical processing method of image data using the thus determined particle diameter. The number of particle images used for the statistical processing (the number of statistically processed data) is as small as possible. It is naturally desirable that the number is large, and in the present invention, the number of randomly selected particle images in terms of reproducibility is at least 50, preferably 80 or more, more preferably 100 or more.

The content of the surface-modifying molecule in the magnetite crystal nanoparticles depends on the molecular weight of the molecule, but is usually 5 to 70% by weight. From the viewpoint of using the minimum weight of the surface-modifying molecule, the upper limit of the content thereof is preferably 50% by weight, more preferably 40% by weight, while the lower limit thereof is preferably in terms of the dispersibility of magnetite crystal nanoparticles. It is 10% by weight, more preferably 15% by weight. The content of such surface-modifying molecules is determined by thermogravimetric analysis by heating given magnetite crystalline nanoparticles at 600 ° C. for 90 minutes or more in a nitrogen atmosphere.

[Surface modifying molecule] The surface modifying molecule in the present invention is an organic compound having a binding property with a magnetite crystal. There is no limitation on the mode of bonding with the magnetite crystal, but it is usually by a chemical bond such as a covalent bond, an ionic bond, a coordinate bond, and a hydrogen bond. In the present invention, the chemical structure of the surface-modifying molecule that produces such a bond is referred to as a bond-forming functional group.

The molecular weight of the above surface modification molecule is 1000 or less. This is a necessary condition for imparting efficient organic medium dispersibility by avoiding unnecessary high molecular weight and using the minimum amount of organic substance. Since it is desirable to suppress the weight loss due to heating and avoid unnecessary high molecular weight in the method for producing magnetite crystal nanoparticles of the present invention described below,
The range of the molecular weight is usually 150 to 1000, preferably 170 to 700, and more preferably 190 to 500.

The above-mentioned bond-forming functional groups are not particularly limited, but amino groups, carboxyl groups, carboxylic acid amide groups (CON
H ₂ ), sulfonic acid group, phosphonic acid group [P (O) (O
H) ₂ ] or a phosphinic acid group [P (O) OH] is preferable, and among them, an amino group and a phosphonic acid group are more preferable, and an amino group is most preferable. The amino group is preferably a primary amino group or a secondary amino group.

In the above-mentioned surface-modifying molecule, the proportion of the hydrocarbon group (for example, an alkyl group, an alkylene group, a hydrocarbon aromatic ring or the like, preferably having 3 to 18 carbon atoms) in its molecular structure is 40% by weight. % Is desirable in order to exhibit sufficient lipophilicity in the method for producing nanoparticles of the present invention described later, and this value is preferably 50% by weight or more, more preferably 60% by weight or more. Preferred hydrocarbon groups include n-propyl group, isopropyl group, n-butyl group, isobutyl group, n-pentyl group,
An alkyl group having 3 to 18 carbon atoms such as cyclopentyl group, n-hexyl group, cyclohexyl group, octyl group, decyl group, dodecyl group, hexadecyl group, octadecyl group,
Examples thereof include a hydrocarbon group containing an aromatic hydrocarbon group such as a phenyl group, a benzyl group, a naphthyl group, and a naphthylmethyl group. Among them, an n-butyl group, an n-hexyl group, an octyl group, a decyl group, a dodecyl group, etc. Is more preferably a linear alkyl group having 4 to 12 carbon atoms.

Specific surface-modifying molecules include 1-amino-n-butane (or n-butylamine), 1-amino-n-hexane, 1-amino-n-octane, 1-amino-n-decane, Ω-aminoalkanes such as 1-amino-n-dodecane and 1-amino-n-hexadecane, di-
n-butylamine, di-n-octylamine, di-n-
Secondary alkylamines such as dodecylamine, aniline,
Amines having a phenyl group such as aminophenylmethane (or benzylamine), n-butanoic acid, n-hexanoic acid, n-octanoic acid, n-decanoic acid, n-dodecanoic acid,
Fatty acids such as n-hexadecanoic acid and oleic acid, n-butanoic acid amide, n-hexanoic acid amide, n-octanoic acid amide, n-decanoic acid amide, n-dodecanoic acid amide,
Fatty acid amides such as n-hexadecanoic acid amide and oleic acid amide, carboxylic acid amides having a phenyl group such as benzoic acid amide and cinnamic acid amide, p-toluenesulfonic acid, benzenesulfonic acid, n-butanesulfonic acid, trifluoride Sulfonic acids such as romethanesulfonic acid, aliphatic phosphonic acids such as n-butylphosphonic acid, n-hexylphosphonic acid, n-octylphosphonic acid, n-decylphosphonic acid, n-dodecylphosphonic acid and n-hexadecylphosphonic acid Examples include phosphonic acids having a phenyl group such as benzenephosphonic acid.

[Hydrated iron oxide hydrosol] The magnetite crystal nanoparticles of the present invention are preferably produced by using a hydrated iron oxide hydrosol as a raw material. The hydrated iron oxide hydrosol is a hydrated iron oxide crystal and / or
Or its precursor (hereinafter simply referred to as "hydrated iron oxide particles")
Means a dispersion liquid in which is dispersed. The hydrated iron oxide particles mentioned here are, for example, goethite crystals, acagonite crystals, or iron oxides having a hydroxyl group whose composition is indefinite, and do not settle by gravity in the hydrosol.

The above-mentioned aqueous solvent is homogeneous, and the content of water in the aqueous solvent is usually 7 in terms of phase separation from the organic phase described later.
0 wt% or more is necessary, preferably 80 wt% or more,
More preferably, it is 90% by weight or more. Examples of the water-miscible organic solvent that may be mixed with the aqueous solvent include alcohols having 3 or less carbon atoms such as methanol, ethanol, n-propanol and isopropyl alcohol, and carbon numbers such as ethylene glycol, propylene glycol and butylene glycol. Examples thereof include glycols of 4 or less and polyhydric alcohols such as glycerin and pentaerythritol.

The content of the hydrated iron oxide particles in the hydrated iron oxide hydrosol is not limited, but is usually 0.001 to
10% by weight, and the upper limit thereof is preferably 5% by weight, more preferably 2% by weight in view of dispersibility of the hydrated iron oxide particles in a hydrosol, while the lower limit thereof is in view of productivity. Is preferably 0.01% by weight, more preferably 0.1
% By weight.

PH of the above hydrosol (hydrogen ion concentration)
Is not limited as long as it does not extremely impair the extractability of the hydrated iron oxide particles into the organic phase in the method for producing nanoparticles of the present invention described below, but is usually 1 to 8, the bond-forming functionality contained in the surface-modifying molecule. It is preferably 2 to 7 in terms of reactivity with the group and stability of the bond formed. Hereinafter, a method for producing the hydrated iron oxide hydrosol will be described.

The hydrated iron oxide hydrosol used in the production of the nanoparticles of the present invention can be obtained by, for example, the sol production method described in the above-mentioned document by Ito et al., That is, an iron salt in an aqueous solvent or an alcohol solvent. An example is a method of producing hydrated iron oxide particles by the hydrolysis of and the accompanying condensation reaction, but the hydrated iron oxide prepared by other methods (for example, known gas phase methods and other liquid phase methods). The particles may be used as a raw material and dispersed in an aqueous solvent to form a hydrosol. The most preferably used of these is the above-mentioned sol generation method. As the raw material in the sol generation method,
A trivalent iron salt such as iron (III) chloride or iron (III) nitrate is preferably used.

[Method for producing magnetite crystal nanoparticles]
As the method for producing magnetite crystalline nanoparticles of the present invention, the hydrated iron oxide particles having the fat-soluble amines bound thereto by contacting the organic phase containing the fat-soluble amines with the hydrated iron oxide hydrosol are used. The first step of extracting into a phase,
In addition, a method including a second step of heating the extracted hydrated iron oxide particles in a molten organic compound in a temperature range of 200 to 400 ° C. as an essential step is preferable.

(1) First Step The fat-soluble amine used here is one of the surface-modifying molecules. That is, it is possible to form a liquid phase which is immiscible with water when the bond-forming functional group is an amino group and is mixed with water. A hydrocarbon group having 3 to 18 carbon atoms is preferably contained in the molecular structure. Specific examples thereof are the same as those of the ω-aminoalkanes and secondary alkylamines in the specific examples of the surface modification molecule. is there.

The organic phase containing such fat-soluble amines (hereinafter referred to as "extracted organic phase") may dissolve a small amount of water by contact with hydrated iron oxide hydrosol. It is either a melt of the same class or an organic solvent in which it is dissolved (hereinafter referred to as a “fat-soluble amine solution”). A mechanism for the action of the fat-soluble amines at such a two-phase system interface is a kind of phase transfer catalysis, that is, an interface where the bond-forming functional group of the fat-soluble amines is bound to the surface of the hydrated iron oxide particles present in the hydrosol phase. It is considered that a reaction may occur, and as the interfacial reaction proceeds, the lipophilicity of the hydrated iron oxide particles increases and moves to the extracted organic phase.

The volume ratio of the hydrated iron oxide hydrosol phase to the extracted organic phase in the first step is usually in the range of about 99: 1 to 1:99 depending on the content of the hydrated iron oxide particles in the hydrosol. This volume ratio is preferably 90:10 to 10:90, and more preferably 8 in terms of increasing the interface area.
It is 0:20 to 20:80. The extracted organic phase may contain an organic solvent, but the content of the fat-soluble amines in the extracted organic phase is such that the surface of the hydrated iron oxide particles to be extracted is coated with a fat-soluble amine. You need a sufficient amount to do this. Specifically, the weight percentage in the extracted organic phase is usually 1 to 100%, preferably 10 to 10 in terms of extraction power.
It is 0%, more preferably 20 to 100%.

The organic solvent that may be contained in the above extracted organic phase is not limited as long as it can form a phase that is not uniformly miscible with water. Specifically, pentane, hexane, heptane, octane, isooctane. Alkanes such as methylene chloride, chloroform, dichloroethane and other halogenated hydrocarbons, benzene, toluene, xylene and other aromatic hydrocarbons, chlorobenzene, dichlorobenzene, bromobenzene and other halogenated hydrocarbons, diethyl ether, Examples include ethers such as dibutyl ether, esters such as methyl acetate, ethyl acetate and butyl acetate, and higher alcohols such as hexanol and octanol. Of these, alkanes such as hexane, heptane, octane and isooctane, toluene and Aromatic hydrocarbons such as xylene, chlorobenze Halogenated hydrocarbons such as are preferable in terms of chemical stability, volatility is not too high, and boiling point that is easy to remove and non-hydrophilicity. Among them, aromatic hydrocarbons such as toluene and xylene, and halogenated hydrocarbons such as chlorobenzene are preferable. Hydrocarbons are more preferable in terms of dissolving power.

The extraction temperature in the first step is usually 0 to 1.
The temperature is 00 ° C., and the lower limit is preferably 10 ° C., more preferably 20 ° C. from the viewpoint of the solubility of the extracted organic phase, and the upper limit is set for the purpose of suppressing volatile iron oxide hydrosol and solvent volatilization of the extracted organic phase. Value is preferably 90 ° C, more preferably 80 ° C
Is. On the other hand, there is no limitation on the extraction time in the first step, but it is usually 0.5 to 1500 minutes, and in view of the extraction yield, the lower limit value is preferably 1 minute, more preferably 10 minutes. In this respect, the upper limit is preferably 1000 minutes,
More preferably, it is 500 minutes.

It may be preferable to carry out the first step in an atmosphere of an inert gas such as nitrogen or argon for the purpose of preventing denaturation of hydrated iron oxide particles or organic matter by oxidation, etc. May be. (3) Second Step This step is a step in which the hydrated iron oxide particles extracted in the first step are heated in a molten organic compound in a temperature range of 200 to 400 ° C. The purpose of this step is to convert the hydrated iron oxide particles into magnetite crystals by the above heating while retaining the fat-soluble amines bound to the surface in the first step. As a secondary effect, the number average particle size of the generated magnetite crystals may increase.

The molten organic compound (hereinafter referred to as “molten compound”) as used herein has a melting point of less than 200 ° C.,
It is an organic compound which satisfies the three conditions of having a boiling point of 200 to 400 ° C. at atmospheric pressure and substantially not causing thermal decomposition in a dry argon atmosphere in this temperature range. Examples of the molten compound include organic compounds that are the surface-modifying molecules such as the fat-soluble amines and satisfy the above three conditions (amines having 12 or more carbon atoms such as hexadecylamine and carbon numbers such as stearic acid). 12
The above carboxylic acids, phosphonic acids having 12 or more carbon atoms such as tetradecylphosphonic acid) or 12 to 12 carbon atoms
Examples are alkanes of 20 and the like. Of these, amines having 14 or more carbon atoms and alkanes having 16 to 20 carbon atoms are preferably used, and among them, hexadecylamine is the most preferable in that it maintains the dispersibility of the magnetite crystals formed. If necessary, two or more kinds of molten compounds satisfying the above three conditions may be mixed and used.

The above heating temperature has an effect of promoting the generation and growth of magnetite crystals, and the lower limit value thereof is preferably 230 ° C., more preferably 260 ° C. in view of the effect.
On the other hand, the upper limit is preferably 360 ° C., more preferably 330 ° C. in order to suppress the thermal decomposition of the organic compound (surface modification molecule or molten compound) used. Further, it is preferable to perform such heating in an atmosphere of an inert gas such as nitrogen or argon. This is to prevent denaturation such as oxidative deterioration of the organic compound due to heating. The inert gas atmosphere here means that the oxygen gas concentration is usually less than 1%,
It means an atmosphere of the above-mentioned inert gas which is preferably less than 0.1%, more preferably less than 0.05%. Also,
It may be shielded from light (for example, by using a metal reactor or a brown glass reactor) to suppress undesired photoreaction.

The magnetite crystals produced through the second step are usually present in the form of magnetite crystal nanoparticles having surface-modifying molecules bound to the surface in the second step, and are used for isolation. As a post-treatment, for example, a precipitation operation of the magnetite crystal nanoparticles may be performed by injecting the heated organic phase into a poor solvent (for example, alcohols such as methanol which may contain water).

[Polymer Composition] The polymer composition of the present invention, in which nanoparticles mainly composed of magnetite crystals are dispersed in a suitable polymer medium, is used as a molding material having characteristics such as magnetic properties of the magnetite crystals. It is useful. The polymer medium used here is not limited and may be either thermoplastic or curable (crosslinkable). For example, a polyethylene resin, a polypropylene resin, an α-olefin polymer, a polyolefin resin such as an amorphous polyolefin resin, Vinyl chloride resins such as polyvinyl chloride, fluororesins such as polyperfluoroethylene (Teflon brand name) and polyvinylidene fluoride, polystyrene, styrene-acrylonitrile copolymer (SAN resin), acrylonitrile-butadiene-styrene copolymer Styrene resins such as polymer (ABS resin), styrene-maleic anhydride copolymer, styrene-methyl acrylate copolymer, styrene-butadiene-styrene (SBS) block copolymer, styrene-ethylene / butadiene-styrene ( SEBS) block copolymer, su Len - butadiene - styrene thermoplastic elastomers such as methyl acrylate copolymer, polymethyl methacrylate (PMMA resin), polyacrylonitrile,
Acrylic resin such as polyacrylamide and crosslinkable acrylic resin, aromatic polycarbonate resin such as bisphenol A polycarbonate, nylon 6, nylon 66,
Polyamide resin such as amorphous polyamide, polyethylene terephthalate (PET resin), polybutylene terephthalate (PBT resin), polyethylene naphthalate (PE
Aromatic polyester resin such as N resin, polyoxymethylene (POM) resin, polyphenylene ether (PP
E) resin, polyarylene sulfide resin such as polyphenylene sulfide (PPS resin), polyether ketone (PEK) resin, polyether ether ketone (PEE)
K) resin, liquid crystal polymers, polyethylene oxide (P
EO), polypropylene oxide (PPO), polyalkylene oxides such as ethylene oxide-propylene oxide copolymers, aliphatic polyesters including biodegradable polyesters such as polycaprolactam and poly 3-hydroxybutyrate, polyaspartic acid, etc. , Polyalcohols such as polyvinyl alcohol and ethylene-vinyl alcohol copolymers, polyvinyl esters such as polyvinyl acetate, polyamines such as polyvinylamine and polyallylamine, polyurethanes, epoxy resins, urea resins, alkyds Resin etc. are mentioned.

Among the above-mentioned polymer media, preferred from the viewpoint of versatility are polyolefin resins such as polyethylene and polypropylene, styrene resins such as ABS resins and SB.
Styrenic thermoplastic elastomers such as S, acrylic resins such as PMMA resins, aromatic polycarbonate resins,
An aromatic polyester resin such as a PET resin or a PBT resin is preferable, and an acrylic resin such as a PMMA resin or an aromatic polycarbonate resin is more preferable in terms of easiness of production by solution blending described later. Two or more kinds of these polymer media may be used in combination, if necessary.

The content of the magnetite crystal-based nanoparticles of the present invention in the above polymer composition is usually 0.01 to 80% by weight as a weight percentage of magnetite crystals.
The lower limit is preferably 0.1% by weight, and more preferably 1% by weight in order to make characteristics such as magnetic properties of the magnetite crystal remarkable, while the upper limit of the content is the polymer composition. From the viewpoint of mechanical properties of the product, preferably 70% by weight,
More preferably, it is 60% by weight. The weight percentage is determined by the residue weight% when the given polymer composition is kept in a temperature range of about 570 to 610 ° C. for 90 minutes or more under a nitrogen gas atmosphere.

If desired, any modifier may be added to the polymer composition. Examples of such modifiers include stabilizers such as antioxidants, heat stabilizers, or light absorbers, glass fibers, glass beads, mica, talc, kaolin, clay minerals, carbon fibers, carbon black, graphite, metals. Examples thereof include fillers such as fibers and metal powders, additives such as antistatic agents and plasticizers, and colorants such as pigments and dyes.

[Manufacturing Method of Polymer Composition] The manufacturing method of the polymer composition is not limited. For example, a method of mixing the magnetite crystal nanoparticles of the present invention with an arbitrary polymer medium, or the magnetite crystal is used. A method in which nanoparticles are mixed with polymerizable monomers and then a polymerization reaction of the monomers is allowed to proceed (hereinafter referred to as “monomer mixing method”) is preferably used. As a method of mixing with the former polymer medium,
Melt kneading and solution blending are included.

As the above-mentioned melt-kneading method, resin pellets, powders, flakes and the like of the above-mentioned polymer medium are mixed with the magnetite crystal nanoparticles of the present invention (dry blending), and then a single-screw extruder and a twin-screw extruder are used. Extruder, brabender,
Examples thereof include a method of introducing the mixture into an arbitrary melt-kneading machine such as a roll, a Banbury mixer, a Labo Plastomill, etc., and shearing at a temperature equal to or higher than the softening point of the thermoplastic resin to mix with the molten thermoplastic resin.

As the method of the above solution blending, the polymer medium and the magnetite crystal nanoparticles of the present invention are mixed with a suitable common solvent (typically, aromatic hydrocarbon such as toluene, nitrogen-containing aroma such as pyridine). Group compounds, THF and 1,3
-Cyclic ethers such as dioxane, alkyl halides such as methylene chloride and chloroform, amide-based aprotic polar solvents such as DMF and NMP, or hexafluoroisopropanol), and thoroughly mixed in such a solution Then, a method of removing the solvent by distillation or drying, or a method of putting the solution in a poor solvent such as methanol or ethanol to precipitate the resin composition can be mentioned.

The polymerizable monomers used in the monomer mixing method are styrene, α-methylstyrene, p-
Chlorostyrene, p-methylstyrene, p-chloromethylstyrene, p-hydroxystyrene, p-acetoxystyrene, vinylnaphthalene, 2-vinylpyridine, 4
-Aromatic vinyl compounds such as vinyl pyridine, methyl acrylate, ethyl acrylate, butyl acrylate, benzyl acrylate, phenyl acrylate, adamantyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate. , Benzyl methacrylate, phenyl methacrylate, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile and other acrylic acid and methacrylic acid derivatives,
Vinyl esters such as vinyl acetate, radically polymerizable monomers such as N-vinyl compounds such as N-vinylpyrrolidone and N-vinyloxazoline, cyclic ethers such as THF, propylene oxide and epichlorohydrin, and ε-caprolactam. Cyclic amides, ε-caprolactone, γ
Examples thereof include ring-opening-polymerizable monomers such as cyclic esters such as butyrolactone, and metal alkoxides used for hydrolysis condensation (so-called sol-gel method) such as tetraethoxysilane. Of these, aromatic vinyl compounds such as styrene and p-chloromethylstyrene, and acrylic acid and methacrylic acid derivatives such as ethyl acrylate, methyl methacrylate, and acrylonitrile are preferable from the viewpoint of polymerizability and versatility.

If desired, a crosslinkable polyvalent monomer may be added to such polymerizable monomers. Examples thereof include divinylbenzene as a radically polymerizable crosslinker,
Examples thereof include aromatic vinyl compounds such as trivinylbenzene and divinylpyridine, bisacryloyloxyethane, tetrakis (meth) acrylic acid ester of pentaerythritol, and tris (meth) acrylic acid ester of pentaerythritol.

In the monomer mixing method, for example, when radical polymerization of radically polymerizable monomers is carried out, a radical initiator is usually added. There is no limitation on the radical initiator that can be used here. For example, a radical decomposable radical initiator that is soluble in the radical polymerizable monomer, such as azobisisobutyronitrile (AI
Typical examples are azo compounds such as BN), peroxides such as benzoyl peroxide and t-butyl peroxide, and water-soluble radical generators such as sodium persulfate, potassium persulfate, lithium persulfate and ammonium persulfate. Persulfate and the like may be used. Further, a photodegradable radical initiator such as α-aminoacetophenone or 2-benzyl-
2-dimethylamino-1- (4-morpholinophenyl)
In addition to aminoacetophenones such as -butan-1-one, benzyl dimethyl ketals, glyoxy esters and the like can be used.

In the above method for producing a polymer composition,
The magnetite crystal nanoparticles of the present invention may be used as a so-called masterbatch in which a suitable organic substance is contained in a high concentration in advance. As the medium organic substance in the masterbatch, the above-mentioned arbitrary thermoplastic resins, waxes, solvents, or the above-mentioned arbitrary polymerizable monomers (including crosslinkable polyvalent monomers) and the like are used. The masterbatch may be prepared by any known method such as the above-mentioned melt-kneading or solution blending.

In the step of producing the above-mentioned arbitrary resin composition, in order to suppress the oxidation reaction due to heat or light when mixing the raw materials, an inert gas atmosphere (eg, dry nitrogen or argon) or a light-shielding condition is preferable. There is. [Coating Liquid Composition] Since the coating liquid composition containing magnetite crystal nanoparticles of the present invention gives a thin film-shaped molded product by coating, such a thin film-shaped molded product is used, for example, as a magnetic recording medium. The coating liquid composition of the present invention is a solvent and / or
Alternatively, it is a liquid containing polymerizable monomers and the magnetite crystal nanoparticles of the present invention as essential components, and the content of the magnetite crystal nanoparticles is usually 1 to 95% by weight based on the whole coating liquid composition, and magnetite. For the purpose of improving the content of crystalline nanoparticles, the lower limit is preferably 5% by weight, more preferably 10% by weight, while the upper limit is preferably 80% by weight, more preferably 70% by weight from the viewpoint of the coating property of the liquid. %.

The solvent used in such a coating liquid composition is not limited, but for example tetrahydrofuran (abbreviated as TH
F), cycloaliphatic ethers such as 1,4-dioxane and tetrahydropyran, linear aliphatic ethers such as ethyl cellosolve, pentane, hexane, cyclohexane,
Alkanes such as heptane, octane and isooctane, aromatic hydrocarbons such as benzene, toluene and xylene, lower alcohols such as methanol, ethanol, n-propanol, isopropyl alcohol, n-butanol, isobutyl alcohol and t-butyl alcohol. , Esters such as methyl acetate and ethyl acetate, halogenated alkyls such as methylene chloride and chloroform, amide aprotic polar solvents such as N, N-dimethylformamide (abbreviation DMF) and N-methylpyrrolidone (abbreviation NMP) Etc. can be used. You may use these solvents in mixture of multiple types. As the preferred solvent, those which dissolve it preferably can be arbitrarily selected depending on the chemical structure of the surface modification molecule to which the magnetite crystal nanoparticles of the present invention are bound, but from the boiling point and economical efficiency, for example, THF, hexane, cyclohexane, toluene. , Ethanol, n-propanol, isopropyl alcohol, ethyl acetate and the like.

Examples of the polymerizable monomers that can be used as a component of the coating liquid composition are the same as those described in the polymerizable monomers used in the monomer mixing method. The use of such polymerizable monomers is extremely suitable for producing a polymer by polymerization after coating to form a thin film-shaped molded product of the polymer composition, and if necessary, reaction of a radical initiator or the like. Initiators may be added. Also when carrying out the polymerization after coating, a non-polymerizable solvent may be used together.

There is no limitation on the viscosity of the coating liquid composition of the present invention, and the optimum value varies depending on the coating method, temperature conditions and the like, but normally the viscosity at 23 ° C. is 0.5 to 500.
It is adjusted to 0 mPa · sec, preferably 1 to 3000 mPa · sec, more preferably 10 to 1000 mPa · sec. In the case of performing multiple film formation described below, it may be preferable to lower the solution viscosity of the coating solution used for the second time and thereafter for the reason of casting.

Any modifier that may be mixed with the polymer composition may be added to the coating solution composition. [Thin Film Molded Product] The thin film molded product of the present invention contains the magnetite crystal nanoparticles of the present invention and has a thickness (film thickness) of usually 0.01 to 10,000 μm, preferably 0.05 to.
5,000 μm, more preferably 0.1 to 3,000 μm
It is a solid molded body having a size of about m. Such a molded body may be composed of the above-mentioned polymer composition or may be composed only of the magnetite crystal nanoparticles of the present invention without containing a polymer medium, and retains a solid while containing a solvent. You can do it. The solid here means a state in which irreversible self-weight deformation does not occur due to gravity. Therefore, the thin film-shaped molded product of the present invention also includes a hydrogel or an organogel in which the network of polymer chains holds solvent molecules and which can be reversibly deformed.

The above-mentioned film thickness may be the same in the thin film-shaped molded product or may be continuously or discontinuously changed if necessary, but it is possible in a usual application such as a magnetic recording medium. It is desirable to be uniform. Although the content of the magnetite crystal nanoparticles of the present invention in such a thin film shaped body is not limited, it is usually 0.01 to 95% by weight as a weight percentage of magnetite crystals, and the characteristics such as magnetic properties of the magnetite crystal are remarkable. In that respect, the lower limit is preferably 0.1% by weight, more preferably 1% by weight,
On the other hand, the upper limit of the content is preferably 9 from the viewpoint of mechanical properties.
It is 0% by weight, more preferably 80% by weight. When the weight percentage becomes large, a secondary characteristic that the surface hardness of the thin film shaped article of the present invention becomes large may appear. The method for determining the weight percentage is the same as that for the polymer composition.

The above-mentioned thin-film molded body is in the form of a film or a thin plate (that is, a sheet), and is made of a resin, an organic crystal, diamond, glass, ceramics, an inorganic crystal, a metal, a semiconductor, a paper pulp, or a wood depending on the application. It may be formed by closely adhering to a substrate of any material such as. The thin film shaped article of the present invention does not necessarily have to be flat, and is formed on a substrate of any shape such as a spherical shape, an aspherical curved surface shape, a cylindrical shape, a conical shape, or a bottle shape such as a PET bottle. May be. Further, the thin-film molded body made of a flexible substrate such as paper pulp, wood, or resin may be physically deformed by bending, stretching, compressing or the like before or after the molding operation.

If necessary, the thin film-shaped molded product may have a layer for coating the coating surface, for example, a protective layer for preventing mechanical damage to the coating surface due to friction or abrasion, a cause of deterioration of semiconductor crystal particles, a base material or the like. A light absorbing layer that absorbs light having an undesired wavelength, a transmission blocking layer that suppresses or prevents the transmission of reactive low molecules such as water and oxygen gas, an antiglare layer, an antireflection layer,
A multi-layer structure may be provided by providing an optional additional functional layer such as a low refractive index layer or the like, an undercoat layer for improving the adhesion between the base material and the coated surface, an electrode layer or the like.

The method for producing the thin film shaped article of the present invention is not limited, but it is preferably produced by applying the coating liquid composition onto a substrate by a known application method. As the coating method, for example, a spin coating method, a dip coating method, a wetting film method, a spray coating method, a die coating method, a doctor blade method or the like can be used. Further, the substrate, the coating liquid composition, or the atmosphere may be heated if necessary. Furthermore, the atmosphere of the coating step may be a controlled atmosphere such as dry air or dry nitrogen for the purpose of preventing moisture absorption or oxidative deterioration, and a blower may be provided as necessary for the purpose of controlling the evaporation rate of the solvent. You may use together.

In any of these coating methods, after one coating film formation is completed, further coating film formation may be further performed thereon, and in this case, it is used in each film formation. The concentration of the coating solution, the solvent composition, or the above-mentioned various film forming temperature conditions may be changed. Further, in each film formation in such a multiple film formation, the composition itself of the constituent components of the thin film shaped product can be changed as necessary to form a multiple composition molded product. In such multiple film formation, the next film formation may be carried out in a state where an arbitrary amount of the solvent in the applied film remains.

[Magnetic Recording Medium] The thin-film molded body can be used as a magnetic recording medium having a thin-film magnetic layer such as a magnetic tape, a floppy (registered trademark) disk, a hard disk, and a magneto-optical disk.

[0058]

EXAMPLES Specific examples of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded. [Measuring device] (1) Transmission electron microscope (TEM): Hitachi, Ltd.
H-9000UHR transmission electron microscope (accelerating voltage 3
00kV, vacuum degree during observation: 7.6 × 10 ^-9 Tor
r). (2) X-ray diffraction (XRD) spectrum: RINT1500 manufactured by Rigaku Corporation (X-ray source: copper Kα ray, wavelength 1.541)
8Å). The measurement was performed in a room whose temperature was adjusted to 23 ° C.

[Synthesis Example of Hydrosol] Synthesis Example 1: Hydrosol iron (III) nitrate nonahydrate (4.03 g) containing hydrated iron oxide was mixed with water (1) at room temperature.
0 mL), and a 2.5 N aqueous solution of sodium hydroxide (10 mL) was added dropwise with stirring over 25 minutes. Further, stirring was continued at room temperature to obtain a hydrosol having a pH of 1.68 and a dark wine red color.

[Production Example of Magnetite Crystal Nanoparticles] Example 1: Nanoparticles mainly composed of magnetite crystals Hydrosol having a wine red color obtained in Synthesis Example 1 (1
Hexadecylamine (1.465 g) dissolved in toluene (15 mL) was added to 2 mL), and the mixture was vigorously stirred at room temperature. The organic phase separated by standing was concentrated and dried in vacuum to obtain a brown solid (1.19 g). This brown solid (512.8 mg) was mixed with hexadecylamine (8.10 g) in a glass container at 100 ° C.
The mixture was vacuum dried with stirring at, and then placed under a dry argon atmosphere at atmospheric pressure. The reaction solution is approximately 1
When heated for a period of time, the liquid color became black, so it was cooled by air, poured into methanol (20 mL) before the reaction liquid solidified, and stirred for 10 minutes to precipitate a solid. The precipitate was separated by centrifugation (3000 rpm), the supernatant was removed, and toluene (3 mL) was added to redissolve the precipitate. Pour the redissolved solution back into methanol (20 mL) 1
A solid was precipitated by stirring for 0 minutes, and the precipitate was centrifuged (3000 rpm) to settle to remove the supernatant.
The purified precipitate thus obtained was vacuum dried to obtain a black powder (32 mg). From the X-ray diffraction spectrum (shown in FIG. 1) of this black powder, it was found that the particles were mainly composed of magnetite nanocrystals. The number average particle diameter was 6 nm and the standard deviation of the particle diameter was about 15% of the number average particle diameter by TEM observation, and a lattice image derived from magnetite crystals was observed. Further, it was also confirmed that this black powder had ferromagnetism because it was attracted to the magnet.

The nanoparticles mainly composed of magnetite crystals obtained in Example 1 can be redissolved in a wide range of organic solvents such as toluene, tetrahydrofuran, acetone, chloroform, etc., and give a transparent solution which is completely cloudless by visual observation. From this, it was considered that hexadecylamine was dispersed in the organic solvent as nanoparticles bound with the surface modification molecule. Also, polymethylmethacrylate was dissolved in the toluene solution of nanoparticles obtained in Example 1 and spin-coated on a glass plate to give a transparent and smooth coating film.
It has been found that the nanoparticles are dispersed in a polymer medium such as an acrylic resin to give the polymer composition of the present invention and a thin film-shaped molded product thereof.

[0062]

The magnetite crystal nanoparticles of the present invention are
Since the magnetite crystals are the main constituent and the surface-modifying molecules are bonded to the surface, they have ferromagnetism and are excellent in dispersibility in a wide range of organic media such as polymer media and solvents. In addition, since a thin film shaped body can be easily formed, for example, as a polymer composition, it can be used as a raw material for a magnetic recording medium.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction spectrum diagram of magnetite crystal nanoparticles obtained in Example 1.

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Claims (7)

[Claims] 1. A magnetite crystal having a number average particle diameter of 1 to 20 nm, which is bound with surface-modifying molecules having a molecular weight of 1000 or less, and the standard deviation of the particle diameter of the magnetite crystal is 20 of the number average particle diameter. % Or less, magnetite crystal nanoparticles. 2. The surface-modifying molecule has a bond-forming functional group of any one of an amino group, a carboxyl group, a carboxylic acid amide group, a sulfonic acid group, a phosphonic acid group, and a phosphinic acid group in its molecular structure. The magnetite crystal nanoparticles according to claim 1. 3. The magnetite crystal nanoparticles according to claim 1 or 2, wherein the surface modification molecule has a hydrocarbon group having 3 to 18 carbon atoms in its molecular structure. 4. A polymer composition containing the magnetite crystal nanoparticles according to claim 1. 5. A coating liquid composition containing the magnetite crystal nanoparticles according to claim 1. 6. A thin-film shaped article containing the magnetite crystal nanoparticles according to claim 1. Description: 7. A magnetic recording medium using the thin film-shaped molded product according to claim 6.