JP6959290B2 - Monoclinic zirconia nanoparticles and their manufacturing methods - Google Patents

Description

The present invention relates to novel monoclinic zirconia nanoparticles and a method for producing the same.

High-refractive index materials are used in various optical components such as lenses, optical filters, and antireflection materials. Taking a lens as an example, a lens having a high refractive index makes it possible to reduce the thickness and weight of the lens, increase the resolution, and the like, which is advantageous as a product.

As a high-refractive-index material, in addition to transparent inorganic materials such as glass and ceramics, a composite material in which high-refractive-index particles are dispersed using a transparent resin as a matrix is known. In that respect, the composite material as described above is advantageous.

As the high refractive index particles dispersed in the composite material, for example, inorganic oxide particles such as titania, zirconia, and alumina are adopted. In particular, titania, zirconia and the like have a high refractive index (2.00 or more), but they also need to have high transparency in order to be used as an optical material. That is, finer and more stable inorganic oxide particles are required.

Here, as a raw material form for producing a composite material, the inorganic oxide particles are usually provided as a dispersion liquid dispersed in a solvent. Therefore, in the dispersion liquid, it is required that individual particles can exhibit a highly dispersed state without agglutination. From this point of view, various studies and proposals have recently been made in order to develop inorganic oxide particles or dispersions thereof having better dispersibility.

For example, zirconium oxide nanoparticles coated with two or more dressings and containing tetragonal zirconium oxide; at least one of the dressings is represented by the following formula (I).
R ^1- COOH ・ ・ ・ (I)
[In the formula, R ¹ represents a branched chain hydrocarbon group having 6 or more carbon atoms. ]
At least one coating agent other than the coating agent represented by the formula (I) is selected from the group consisting of a hydroxyl group, an amino group, a thiol group, a carboxyl group, an epoxy group, and an alkoxy group. those having a vinyl group or a phenyl group; a plurality having one of a silane coupling agent; or, as R ² -COOH · · · of the following formula (II) (II)
[In the formula, R ² represents a linear hydrocarbon group having 6 or more carbon atoms. ]
Zirconium oxide nanoparticles are known (Patent Document 1).

Further, for example, a zirconia transparent dispersion liquid characterized by containing tetragonal zirconia particles having a dispersed particle size of 1 nm or more and 20 nm or less is known (Patent Document 2).

Further, in the method for producing an inorganic fine particle dispersion solution in which inorganic fine particles having an average particle size of 1 nm or more and 30 nm or less are dispersed in a solvent, inorganic fine particles having an average particle size of 1 nm or more and 30 nm or less are aggregated in the solvent. The mixed solution existing in the above state is stirred by using beads having an average particle size of 15 μm or more and 30 μm or less, and at the same time, ultrasonic waves are applied to disperse the inorganic fine particles. A method for producing a solution has been proposed (Patent Document 3).

Patent No. 5030694 JP-A-2007-99931 JP-A-2010-23031

However, the nanoparticles of zirconia in these prior art dispersions include not only monoclinic zirconia but also tetragonal phase zirconia. Since the tetragonal phase of zirconia is a metastable phase, there is a risk of phase transition to the monoclinic phase over time for some reason. The phase transition to the monoclinic phase causes a volume change (particularly volume contraction), which adversely affects the physical properties of the coating film formed by the dispersion liquid. More specifically, after a coating film is formed by zirconia nanoparticles containing a tetragonal phase, when the tetragonal phase in the film undergoes a phase transition to a monoclinic phase over time, the coating film is distorted due to volume change. As a result of the occurrence of such factors, the physical characteristics may be deteriorated.

From this point of view, zirconia nanoparticles containing less or substantially no tetragonal zirconia are ideal, but such zirconia nanoparticles have not yet been developed.

Therefore, a main object of the present invention is to provide nanoparticles of zirconia that are less or substantially free of tetragonal zirconia.

As a result of diligent research in view of the problems of the prior art, the present inventor has found that nanoparticles produced by a specific method using a specific zirconia powder as a starting material can achieve the above object, and the present invention. Has been completed.

That is, the present invention relates to the following zirconia-based nanoparticles and a method for producing the same.
1. 1. Zirconia fine particles having a D50 of 20 nm or less in the particle size distribution.
(1) The zirconia fine particles contain a zirconia monoclinic phase and
(2) In the range of 2θ = 29.74 to 30.74 degrees in the diffraction pattern by powder X-ray diffraction analysis of the zirconia fine particles, there is substantially no diffraction peak.
Monoclinic zirconia nanoparticles characterized by this.
2. The monoclinic zirconia-based nanoparticles according to claim 1, wherein the content of the zirconia monoclinic phase is 90% by volume or more.
3. 3. Item 2. The monoclinic zirconia-based nanoparticles according to Item 1 or 2, wherein the particle size distribution of the powder composed of zirconia fine particles is single peak, and D90 in the particle size distribution is 30 nm or less.
4. A dispersion liquid in which the monoclinic zirconia nanoparticles according to any one of Items 1 to 3 are dispersed in a solvent.
5. Item 4. The dispersion liquid according to Item 4, further comprising a silane coupling agent and a phosphoric acid ester-based dispersant.
6. The method for producing monoclinic zirconia nanoparticles according to claim 1 from zirconia powder.
(1) The zirconia powder has a) D50 of 900 nm or less in the particle size distribution, b) a zirconia monoclinic phase content of 90 to 95% by volume, and a zirconia tetragonal phase content. 5 to 10% by volume,
(2) The step of subjecting the zirconia powder to the bead mill treatment in the presence of beads having a D50 of 40 μm or less in the particle size distribution is included.
A method for producing monoclinic zirconia nanoparticles.
7. Item 6. The production method according to Item 6, wherein the bead mill treatment is a wet bead mill treatment performed in the presence of a solvent.
8. Item 7. The production method according to Item 7, wherein the solvent contains a silane coupling agent and a phosphoric acid ester-based dispersant.
9. Item 6. The production method according to Item 6, wherein the beads are at least one of metal beads and ceramic beads.
10. Item 6. The production method according to Item 6, wherein particles having a substantially spherical shape are used as the beads.
11. Item 6. The production method according to Item 6, wherein the zirconia powder has a BET specific surface area of 70 m ^{2 / g or more.}

According to the present invention, it is possible to provide nanoparticles of zirconia containing less or substantially no tetragonal zirconia. More specifically, nanoparticles (monoclinic zirconia particles) containing less or substantially no tetragonal zirconia (quasi-stable tetragonal crystals) and containing monoclinic zirconia can be provided.

Since such special nanoparticles effectively suppress or prevent volume fluctuations associated with the phase transition that tetragonal zirconia can induce, they were obtained by using a dispersion liquid dispersed in the liquid phase. The coating film can also exhibit high reliability.

Further, in the production method of the present invention, zirconia particles containing tetragonal zirconia are used as a starting material, and the zirconia particles are subjected to bead milling in the presence of specific fine beads, so that tetragonal zirconia is less or substantially not contained. Moreover, nanoparticles made of substantially monoclinic zirconia can be produced reliably and efficiently.

Moreover, the nanoparticles obtained by the production method of the present invention can obtain a dispersed state at a fine nano level. The reason is not clear, but it is presumed that it is realized by the following mechanism of action. That is, in the production method of the present invention, zirconia containing both a rectangular phase and a monoclinic phase is used as a starting material, but even if agglomerated particles are contained therein, the square phase is formed during the production process. It is considered that strain due to volume change is generated in the agglomerated particles during the phase transition to the monoclinic phase, and the agglomeration is released by the strain, and as a result, the particles become finer and exhibit high dispersibility.

As described above, since the zirconia nanoparticles of the present invention are stable and have high dispersibility, they are suitably used as raw materials for various optical parts such as lenses, optical filters, and antireflection materials. Can be done.

It is a figure which shows the result of the X-ray diffraction analysis of the zirconia nanoparticles obtained in Example 1. It is a figure which shows the Raman spectrum of the Raman spectroscopic analysis of the zirconia nanoparticles obtained in Example 1. The intensity profile obtained from the electron diffraction of the zirconia nanoparticles obtained in Example 1 is shown. It is a figure which shows the particle size distribution of the zirconia nanoparticles obtained in Example 1. A graph showing the relationship between the peak ratios of D90 and [tetragonal phase (T phase) / monoclinic phase (M phase)] in the particle size distribution of the zirconia nanoparticles obtained in Example 1 and the treatment time. Is. It is a figure (enlarged view) which shows the result of the X-ray diffraction analysis of each zirconia-based nanoparticle obtained using zirconia beads of a different particle diameter. The schematic diagram of the bead mill apparatus used in Example 1 is shown. The schematic diagram of the agitator used in the bead mill apparatus used in Example 1 is shown.

1. 1. Zirconia nanoparticles The monoclinic zirconia nanoparticles of the present invention (nanoparticles of the present invention) are zirconia fine particles having a D50 of 20 nm or less in the particle size distribution.
(1) The zirconia fine particles contain a monoclinic phase and
(2) At 2θ = 29.74 to 30.74 degrees of the diffraction pattern in the powder X-ray diffraction analysis of the zirconia fine particles, there is substantially no diffraction peak.
It is characterized by that.

The nanoparticles of the present invention are crystalline zirconia particles and contain a monoclinic phase as a crystal phase. The content of the zirconia monoclinic phase is usually preferably 90% by volume or more, and more preferably 95 to 100% by volume. That is, the nanoparticles of the present invention may contain components other than tetragonal zirconia (for example, other crystal phase, amorphous phase, etc.) as long as the effects of the present invention are not impaired.

Regarding the crystal phase of the nanoparticles of the present invention, there is substantially no diffraction peak at 2θ = 29.74 to 30.74 degrees of the diffraction pattern in the powder X-ray diffraction analysis of the zirconia fine particles. That is, one of the features of the nanoparticles of the present invention is that the diffraction peak (101 plane) of tetragonal zirconia is 2θ = 30.24 degrees, and the diffraction peak of tetragonal zirconia is not recognized on the diffraction pattern. Unless such a diffraction peak is observed, the inclusion of a very small amount of tetragonal zirconia is permitted in the present invention. When the diffraction peak exists, it is not only the case where the peak exists only in the range of 2θ = 29.74 to 30.74 degrees, but also the case where the peak exists in the range of 2θ = 29.74 to 30.74 degrees and its range. It also includes the case where there is a broad peak that straddles the outside.

Further, the present invention nanoparticles, in analysis by Raman spectroscopy, it is preferable that the peak wave number 202 cm ^-1 and 267cm ^-1 is also not confirmed. Furthermore, it is preferable that the nanoparticles of the present invention do not have a peak of 111t derived from tetragonal crystals in the intensity profile obtained from electron diffraction.

Although the nanoparticles of the present invention are nanoparticles at the nano level, they have the above-mentioned crystal structure, and thus it is considered that they contribute to high stability and high dispersibility.

The nanoparticles of the present invention have a D50 (average particle size) of 20 nm or less, preferably 15 nm or less in the particle size distribution. The lower limit is not limited, but usually it may be about 1 nm. Having such an average particle size can contribute to high transparency.

The particle size distribution of the nanoparticles of the present invention is not limited, but it is particularly preferable that the nanoparticles have a single peak and the D90 in the particle size distribution is 30 nm or less (particularly 25 nm or less). As a result, even higher stability and transparency can be exhibited in the dispersion liquid described later and the coating film thereof.

The nanoparticles of the present invention preferably have a relatively high specific surface area (BET method). More specifically, it is desirable that the specific surface area is usually 70 m ² / g or more, more preferably 80 m ² / g or more. The upper limit of the specific surface area is not limited, but usually it may be about ^{200 m 2 / g.}

The nanoparticles of the present invention are basically _{composed of zirconia (ZrO 2} ), but other components may be attached or complexed with other components as long as the effects of the present invention are not impaired. .. For example, when the nanoparticles of the present invention are produced by the production method described later, additives (for example, dispersant, coupling agent, etc.) added in the production process are attached to or composited with the zirconia particles. Is also good.

The nanoparticles of the present invention may be in any form such as a dry powder or a dispersion liquid, and in particular, the form of the dispersion liquid in which the monoclinic zirconia-based nanoparticles (powder) of the present invention are dispersed in a solvent. It is preferable to be provided in. The solvent in this case is not particularly limited, and is, for example, an alcohol solvent such as methanol, ethanol, isopropanol and butanol, a ketone solvent such as ketone, acetone, methyl ethyl ketone, methyl propyl ketone and methyl isobutyl ketone, isopropyl ether and methyl cellosolve. Etc., and glycol ester solvents such as propylene glycol monomethyl ether acetate and ethylene glycol monoethyl ether acetate can be mentioned.

Further, various additives can be added to the above dispersion liquid as needed. For example, additives such as dispersants, coupling agents, and dispersion aids can be used.

The amount of dispersion (solid content) of the nanoparticles of the present invention in the dispersion is not particularly limited, and can be appropriately set according to, for example, the type of solvent used, the desired viscosity, and the like. In the present invention, it is particularly preferable to set the dispersion amount in the range of 1 to 50% by weight in the dispersion liquid.

2. Method for Producing Monoclinic Zirconia Nanoparticles The method for producing nanoparticles of the present invention is not particularly limited, but can be suitably produced by, for example, the following production method. That is, it is a method for producing nanoparticles of the present invention from zirconia powder.
(1) The zirconia powder has a) D50 of 900 nm or less in the particle size distribution, b) a zirconia monoclinic phase content of 90 to 95% by volume, and a zirconia tetragonal phase content. 5 to 10% by volume,
(2) The step (bead milling step) of subjecting the zirconia powder to the bead milling treatment in the presence of beads having a D50 of 40 μm or less in the particle size distribution is included.
It is possible to preferably adopt a manufacturing method characterized by the above.

Starting Material In the production method of the present invention, assuming that zirconia powder is used as the starting material, the zirconia powder has a) D50 of 900 nm or less in the particle size distribution and b) the content of the zirconia monoclinic phase. A powder having a content of 90 to 95% by volume and a zirconia tetragonal phase content of 5 to 10% by volume is used.

As the zirconia powder, one having a D50 of 900 nm or less is used. In particular, it is desirable that the D50 is 800 nm or less. The lower limit of D50 in this case is not limited, but is usually about 300 nm, particularly 400 nm. Therefore, as a starting material, zirconia powder containing agglomerated particles of zirconia can be used. For example, zirconia powder having a D50 (average particle size of secondary particles) of 400 to 700 nm in the particle size distribution can be preferably used as a starting material. The primary particle size of the zirconia powder used as the starting material is also not limited, but usually, the zirconia powder in the range of about 1 to 50 nm, particularly 5 to 30 nm can be used. In other words, for example, zirconia powder having a secondary particle size (D50) in the range of 5 times or more, particularly 10 times or more the zirconia crystallite diameter can also be used.

As the zirconia powder as a starting material, one composed of crystalline zirconia particles can be used, and in particular, the content of the zirconia monoclinic phase is 90 to 95% by volume, and the content of the zirconia tetragonal phase. Use zirconia powder with a content of 5-10% by volume. As described above, by using the raw material containing a certain amount of the zirconia tetragonal phase, stable and finer zirconia fine particles can be obtained.

Further, the specific surface area of the zirconia powder as a starting material is not limited, but it is particularly desirable to use a powder having a ^{specific surface area of 70 m 2} / g or more, more preferably 80 m ^{2 / g or more.} By using the zirconia powder having such a specific surface area, nanoparticles having high dispersibility can be obtained more reliably. Although the upper limit of the specific surface area is not limited, it is usually ^{about 200 m 2} / g, and particularly preferably 150 m ² / g.

As the zirconia powder itself having such a crystal structure, physical properties, etc., known or commercially available ones can be used. In addition, zirconia powder synthesized by a known production method can also be used. For example, zirconia synthesized by a liquid phase method such as a hydrolysis method, a coprecipitation method, a neutralization method, or an alkoxide method can be preferably used. In particular, as a hydrolysis method, zirconia powder or the like obtained by synthesizing a hydrated zirconia sol by hydrolyzing a zirconium salt and then calcining the sol can be preferably used as a starting material. As described above, the present invention is a cost-effective method in that a known or commercially available general zirconia powder can be used as a raw material without using a special raw material. That is, in the production method of the present invention, using such a zirconia powder containing a zirconia monoclinic phase and a zirconia tetragonal phase as a starting material, diffraction is performed at 2θ = 29.74 to 30.74 degrees of the diffraction pattern. Monoclinic zirconia nanoparticles with virtually no peaks can be obtained reliably and efficiently.

Bead mill treatment step In the bead mill treatment step, the zirconia powder is subjected to the bead mill treatment in the presence of beads having a D50 of 40 μm or less in the particle size distribution.

The beads used as a medium (crushing medium) may have a D50 of 40 μm or less in the particle size distribution, preferably 35 μm or less, more preferably 32 μm or less, and most preferably 30 μm or less. If the D50 exceeds 40 μm, stable and highly dispersible nanoparticles may not be obtained. The lower limit of D50 is not limited, but is usually about 1 μm, particularly preferably about 10 μm, and more preferably about 20 μm. In the present invention, by using such relatively fine beads, fine monoclinic zirconia nanoparticles can be prepared more efficiently and reliably.

The composition of the beads is not particularly limited, and the same material as the beads used in known bead mills and the like can be adopted. For example, oxide-based beads such as zirconia, alumina, and silica, metal-based beads such as nickel, copper, tungsten, and steel, and inorganic material-based beads such as non-oxide beads such as titanium nitride and silicon nitride are preferably used. Can be done. In particular, it is preferable to use zirconia beads from the viewpoint of reducing / preventing impurities from being mixed in and mixing efficiency.

As for the shape of the beads, it is usually desirable to use substantially spherical beads. As such spherical beads, known or commercially available beads can be used. In particular, spherical beads prepared by a plasma melting method (thermal plasma melting method) can be preferably used. The plasma melting method itself is a known method, and for example, the method disclosed in Japanese Patent Application Laid-Open No. 2007-4090 can be used. That is, the raw material powder of zirconia (for example, the powder prepared by the pulverization method) is continuously supplied in the gas phase state into the plasma atmosphere formed in the atmospheric pressure, and the surface of the zirconia particles constituting the raw material powder is melted. Spherical zirconia particles can be produced by a method including a step of spheroidizing the particles and then spraying a cooling gas onto the flowing particles to rapidly cool the particles. The spherical zirconia particles obtained by such a method are advantageous in that the particle shape is substantially spherical and the number of coarse particles is relatively small.

The amount of beads used is not limited, but is generally determined by the ratio of the apparent volume of beads to the capacity of the space in which the beads are filled (usually the crushing chamber in a bead mill device) (bead filling rate). The bead filling rate may be appropriately set within the range of 10 to 90% according to the specifications of the bead mill device and the like. Therefore, for example, it can be set in the range of 50 to 70%, and further in the range of 40 to 60%. Further, for example, as shown in Examples described later, when spherical zirconia beads by the thermal plasma melting method are used as beads, the bead filling rate is satisfied and the zirconia powder is 100 parts by weight. The beads may be in the range of 600 to 900 parts by weight.

The bead mill treatment is a method of crushing and dispersing the starting material by a shearing force or an impact force of beads (grounding medium), and can be carried out using, for example, a known or commercially available bead mill device. Therefore, the specifications and types of the bead mill device are not particularly limited. For example, the shape of the agitator provided in the bead mill device is not limited, and may be any of, for example, a disc type, a pin type, a single rotor type, and the like. Further, the crushing chamber (vessel) may be either a vertical type or a horizontal type. Further, the operation method of the bead mill is not limited, and may be any of, for example, a circulation method, a pass method, a batch method, and the like.

The commercially available bead mill device is not limited as long as it can be bead milled under the conditions of the present invention. For example, Super Apex Mill (manufactured by Hiroshima Metal & Machinery Co., Ltd.), Ultra Apex Mill (manufactured by Hiroshima Metal & Machinery Co., Ltd.), Dual Apex Mill (manufactured by Hiroshima Metal & Machinery Co., Ltd.), MSC Mill (manufactured by Nippon Coke Industries Co., Ltd.) ), Nano Getter (manufactured by Ashizawa Finetech Co., Ltd.), MAX Nano Getter (manufactured by Ashizawa Finetech Co., Ltd.), Labstar Mini (manufactured by Ashizawa Finetech Co., Ltd.), JBM Series (JBM-B035, JBM) -C020, JBM-C050, JBM-C200, JBM-C500, JBM-C1000, Waterspout-Combo, JBM-D500, JBM-D1000, JBM-D2000) (all manufactured by JUST NANOTECH CO., Ltd.) are also used. be able to.

The operating conditions in the bead mill device depend on the properties of the zirconia powder used, the type of solvent, the type of beads, etc., on the premise that the conditions according to the production method of the present invention (using a specific starting material and beads) are satisfied. Can be set as appropriate. For example, in the present invention, in a beer mill device provided with an agitator, the peripheral speed of the agitator can usually be set to about 5 to 20 m / sec, particularly 7 to 15 m / sec. The residence time (treatment time) is generally about 5 to 25 minutes (particularly 8 to 20 minutes), but the obtained zirconia fine particles (powder) are substantially zirconia tetragonal crystals on a diffraction chart by X-ray diffraction analysis. As long as sufficient time can be secured so that the phase is not recognized, the above time is not particularly restricted.

Further, the bead mill treatment of the present invention may be either a dry type or a wet type, but it is particularly desirable to employ a wet bead mill treatment. In this case, as the solvent, in addition to water, for example, alcohol solvents such as methanol, ethanol, isopropanol and butanol, ketone solvents such as ketone, acetone, methyl ethyl ketone, methyl propyl ketone and methyl isobutyl ketone, isopropyl ether, methyl cellosolve and the like. Various organic solvents such as an ether solvent, a glycol ester solvent such as propylene glycol monomethyl ether acetate and ethylene glycol monoethyl ether acetate can be used.

Further, in the bead mill treatment, in addition to the solvent, various additives can be blended as needed. For example, various additives such as a dispersant, a coupling agent, a binder, and a dispersion aid can be blended. In particular, in the present invention, it is preferable to contain both the dispersant and the coupling agent in the dispersion liquid for the purpose of obtaining higher dispersibility and the like.

As the dispersant, for example, any type of dispersant such as nonionic, anionic, and cationic dispersants can be used, but in the present invention, anionic dispersants are particularly preferable. As the anion-based dispersant, a phosphoric acid ester-based dispersant can be particularly preferably used. Commercially available products can also be used as these dispersants.

The amount of the dispersant added is not particularly limited, and is usually set within the range of 0.1 to 100 parts by weight with respect to 100 parts by weight of the zirconia powder, depending on the type of dispersant to be used and the like. .. Therefore, for example, the range is 0.4 to 100 parts by weight with respect to 100 parts by weight of the zirconia powder, and the range is 0.5 to 20 parts by weight with respect to 100 parts by weight of the zirconia powder, and further, for example, the zirconia powder. It can be in the range of 1 to 10 parts by weight with respect to 100 parts by weight.

Examples of the coupling agent include a silane coupling agent and a titanium coupling agent, and in particular, the silane coupling agent can be preferably used in the present invention.
The silane coupling agent is not particularly limited, but preferably a silane coupling agent having at least an acrylic group or a methacrylic group as a functional group can be used.
As an example, the general formula X _3-n (CH ₃ ) _n Si-RY (where n = 1 or 2, R represents an ethylene group or a propylene group, X represents a hydrolyzing group, and Y represents a functional group, respectively. ) Can be mentioned. Examples of the hydrolyzing group X include alkoxy groups such as methoxy group, ethoxy group, and 2-methoxyethoxy. Examples of the functional group Y include a vinyl group, an epoxy group, a slityl group, a ureido group, an acrylic group, a methacryl group, an amino group, an isocyanurate group, an isocyanate group and a mercapto group. In the above general formula, for example, a silane coupling agent in which the above R is an acrylic group or a methacrylic group can be preferably used. Commercially available products can also be used as these silane coupling agents.

The amount of the coupling agent added is not particularly limited, but is generally set within the range of 2 to 200 parts by weight with respect to 100 parts by weight of the zirconia powder, depending on the type of dispersant used, for example. can. Therefore, for example, it is in the range of 5 to 100 parts by weight with respect to 100 parts by weight of zirconia powder, within the range of 5 to 50 parts by weight with respect to 100 parts by weight of zirconia powder, and further with respect to 100 parts by weight of zirconia powder. It can also be in the range of 10 to 20 parts by weight.

After the bead mill treatment is completed, the zirconia-based nanoparticles may be recovered after being separated from the beads according to a conventional method. In this case, when the wet bead mill treatment is carried out, it can be recovered in the form of a dispersion liquid in which zirconia-based nanoparticles are dispersed in the solvent. In this case, if necessary, a part or all of the solvent may be replaced with another solvent, or a dispersant or the like may be further added to the solvent.

3. 3. Use of zirconia-based nanoparticles The zirconia-based nanoparticles of the present invention can be applied to the same applications as known zirconia nanoparticles.

In particular, in order to utilize the features such as high refractive index of the nanoparticles of the present invention, for various applications centering on various optical components such as lenses, optical filters, antireflection materials, hard coat materials, and refractive index adjusting materials. It can be widely used. That is, the nanoparticles of the present invention can be applied as a dispersant (particularly high refractive index particles) in known or commercially available optical components. In this case, the zirconia-based nanoparticles of the present invention can be used alone, or can be used in the form of a composite material containing the zirconia-based nanoparticles of the present invention and a resin component. As the resin component, various synthetic resins used in known composite materials such as polyester resin, polyolefin resin, polyamide resin, and acrylic resin can be used.

Examples will be shown below, and the features of the present invention will be described in more detail. However, the scope of the present invention is not limited to the examples.

Example 1
(1) Preparation of dispersion of zirconia nanoparticles A dispersion of zirconia nanoparticles dispersed in a solvent was prepared as follows. A commercially available product was used as the zirconia powder as a starting material. This commercially available product has a D50 in the particle size distribution in the range of 0.4 to 0.7 μm, a monoclinic phase of 94% by volume and a tetragonal phase of 6% by volume, and a specific surface area of 80 m ² / g. After blending 6 g of this zirconia powder and an additive (0.9 g of a silane coupling agent and 0.3 g of a phosphoric acid ester-based dispersant) in 15 g of methyl ethyl ketone, the obtained mixed solution is used in a bead mill device (batch type bead mill, Daiken). A bead mill treatment was carried out at Chemical Industry Co., Ltd.). The apparatus has a configuration as shown in FIG. 7, and uses one single rotor type agitator shown in FIG. As the beads, 50 g (44% by volume with respect to the volume of the crushing chamber) of zirconia beads (“DZB” manufactured by Daiken Kagaku Kogyo Co., Ltd., D50 in the particle size distribution is 30 μm) spheroidized by a commercially available thermal plasma melting method was used. The peripheral speed of the agitator was 10 m / s, and the processing time was 15 minutes. In this way, a dispersion liquid containing zirconia-based nanoparticles was obtained.

A schematic diagram of the bead mill device used in Example 1 is shown in FIG. The bead mill device 10 includes a) a crushing chamber (vessel) 13 for accommodating the beads 11 and the object to be treated (including the dispersion medium) 12, b) an agitator 14 arranged in the crushing chamber 13, and c) the agitator 14. The motor 15 for rotating the motor 15, d) the shaft 16 for transmitting the rotational driving force of the motor 15 to the agitator 14, and e) the cooling water jacket 17 for accommodating the cooling water 18 for cooling the outside of the crushing chamber 13. The cooling water 18 flows into the cooling water jacket 17, absorbs heat generated during crushing, is discharged from the cooling water jacket 17, is allowed to cool, and then circulates so as to return to the cooling water jacket 17.

As shown in FIG. 8A, the agitator 13 has a shaft 16 attached to the agitator 14 at a position serving as a central axis. FIG. 8B is a view seen from the direction of arrow A in FIG. 8A. As shown in FIG. 8B, the agitator 14 used in the embodiment is a single rotor type having a substantially wind turbine shape, and the agitator 14 is pulverized by rotating clockwise (in the direction of the arrow).

(2) Evaluation of zirconia-based nanoparticles The crystal structure and particle size of the zirconia-based nanoparticles in the obtained dispersion were investigated.

1) Crystal structure 1-1) X-ray diffraction analysis Powder X-ray diffraction analysis was performed on the powder obtained by drying the dispersion obtained in Example 1. "MiniFlex 600" (manufactured by Rigaku Co., Ltd.) was used as the X-ray diffractometer. The analysis result (displayed as "after processing") is shown in FIG. For comparison, FIG. 1 also shows the results of measuring the zirconia powder (starting material) before the treatment in the same manner. As shown in FIG. 1, in the zirconia-based nanoparticles obtained in Example 1, diffraction peaks (particularly, diffraction peaks due to the zirconia tetragonal phase) in the range of 2θ = 29.74 to 30.74 degrees in the diffraction pattern). Can be seen to have disappeared.

1-2) Raman spectroscopy analysis In addition, the crystallinity of the powder by Raman spectroscopy was also examined. A "laser Raman microscope RAMAN Touch" (manufactured by Nanophoton Corporation) was used as a Raman spectroscope, the excitation wavelength was 532 nm, and the diffraction grating was 2400 gr / mm. The Raman spectrum (indicated as "after processing") is shown in FIG. For comparison, FIG. 2 also shows the results of measuring the zirconia powder (starting material) before the treatment in the same manner. As is apparent from FIG. 2, in the Raman spectrum, the zirconia nanoparticles prepared in Example 1, that the peak of wavenumber 202 cm ^-1 and 267cm ^-1 derived from zirconia tetragonal phase is not observed Recognize.

1-3) Electron diffraction analysis Furthermore, electron diffraction analysis was performed on the powder. Gold fine particles were used as a standard sample for interplanar spacing reference, and length information was obtained from the profile of the standard sample. The positions of the strongest lines of monoclinic and tetragonal crystals, 111m and 111t, were calculated. The intensity profile obtained from the electron diffraction is shown in FIG. The upper figure of FIG. 3 shows the result before the treatment (starting material), and the lower figure of FIG. 3 shows the result of the nanoparticles obtained in Example 1. As is clear from the results of FIG. 3, it can be seen that the 111t peak of the tetragonal crystal is not confirmed in the treated nanoparticles.

2) Particle size A dynamic light scattering type particle size distribution measuring device "Nanotrac Wave EX-150" (manufactured by Microtrac Bell Co., Ltd.) was used for the particle size measurement. For the particle size, D50 and D90 in the cumulative distribution based on the volume were measured. The result is shown in FIG. As is clear from the results of the frequency distribution and the cumulative distribution in FIG. 4, the particle size distribution (frequency distribution) was a single peak, D50 was about 12 nm, and D90 was about 20 nm.
In addition, the relationship between D90, treatment time, and the peak ratio (intensity ratio) of tetragonal / monoclinic crystals in the particle size distribution was investigated. The result is shown in FIG. As shown in FIG. 5, it can be seen that as the zirconia monoclinic phase increases, D90 also becomes smaller so as to be linked. That is, it can be seen that the zirconia tetragonal phase is decreasing and the zirconia monoclinic phase is increasing, so that the amount is larger than the monoclinic phase of 94% by volume in the starting material. In addition, from the results of FIG. 5, it is inferred that the dissolution of zirconia agglomerated particles when the tetragonal crystals present in the starting material undergo a phase transition to monoclinic crystals also contributes to miniaturization, resulting in high dispersibility. can.

Test Example 2
Zirconia nanoparticles (Comparative Sample 1 and Comparative Sample 2) were prepared in the same manner as in Example 1 using zirconia beads having different average particle diameters D50. The crystal phase of the obtained zirconia-based nanoparticles was examined by X-ray diffraction analysis in the same manner as in Example 1. As the zirconia beads, beads having a D50 of 50 μm (used in Comparative Sample 1) and beads having a D50 of 100 μm (used in Comparative Sample 2) were used. The result is shown in FIG. Note that FIG. 6 also shows the analysis results of the zirconia-based nanoparticles obtained in Example 1.
As is clear from the results of FIG. 6, in the zirconia-based nanoparticles of Example 1 (bead diameter D50 used = 30 μm, reference numeral A in FIG. 6), the diffraction peak is in the range of 2θ = 29.74 to 30.74 degrees. Does not exist. On the other hand, Comparative Sample 1 (used bead diameter D50 = 50 μm, reference numeral B in FIG. 6) and comparative sample 2 (used bead diameter D50 = 100 μm, reference numeral B in FIG. 6) prepared with zirconia beads having a D50 of more than 40 μm. In C), it can be seen that a slight diffraction peak appears in the range of 2θ = 29 to 30 degrees (particularly in the range of 2θ = 29.74 to 30.74 degrees).

Test Example 3
A dispersion containing zirconia nanoparticles was prepared in the same manner as in Example 1, and the change in particle size distribution from immediately after the preparation to a certain period was examined. The results are shown in Table 1.

As is clear from the results in Table 1, the dispersion liquid containing the zirconia-based nanoparticles maintains almost the same particle size distribution as the initial (0 days) even after about 6 months from the preparation, and the dispersion stability is improved. It turns out to be excellent.

Test Example 4
A dispersion liquid (dispersion liquid 1) containing zirconia-based nanoparticles was prepared in the same manner as in Example 1. Further, using zirconia beads having different average particle diameters D50, dispersion liquids (comparative dispersion liquid 1 and comparative dispersion liquid 2) containing zirconia-based nanoparticles were prepared in the same manner as in Example 1. As the zirconia beads, beads having a D50 of 100 μm (used in the comparative dispersion 1) and beads having a D50 of 50 μm (used in the comparative dispersion 2) were used. The transmittance and particle size distribution of each of the obtained dispersions were examined. As for the transmittance, the spectral transmittance at a measurement wavelength of 600 nm was measured when the solvent (MEK) was a blank sample (transmittance 100%) and the optical path length was 5 mm. The particle size distribution was measured in the same manner as in Example 1. These results are shown in Table 2.

As is clear from the results in Table 2, the dispersion liquid 1 of the present invention is fine and has excellent dispersibility, so that a high transmittance of 30% or more (particularly 35% or more) can be obtained. On the other hand, it can be seen that the comparative dispersions 1 and 2 have low transmittance because they contain relatively coarse particles.

Claims (5)

Zirconia fine particles having a D50 of 20 nm or less in the particle size distribution.
(1) The zirconia fine particles contain a zirconia monoclinic phase and
(2) In the range of 2θ = 29.74 to 30.74 degrees in the diffraction pattern by powder X-ray diffraction analysis of the zirconia fine particles, there is substantially no diffraction peak.
Monoclinic zirconia nanoparticles characterized by this. The monoclinic zirconia-based nanoparticles according to claim 1, wherein the content of the zirconia monoclinic phase is 90% by volume or more. The monoclinic zirconia-based nanoparticles according to claim 1 or 2, wherein the particle size distribution of the powder composed of zirconia fine particles is single peak, and the D90 in the particle size distribution is 30 nm or less. A dispersion liquid in which the monoclinic zirconia nanoparticles according to any one of claims 1 to 3 are dispersed in a solvent. The dispersion liquid according to claim 4, further comprising a silane coupling agent and a phosphoric acid ester-based dispersant.

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