JP2007308341A - Method for producing surface-coated hexaboride particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing surface-coated hexaboride particles having improved water resistance. <P>SOLUTION: The method for producing surface-coated hexaboride particles where a coating layer of silica is formed on the surface of each hexaboride particle using a hydrolyzable silane compound comprises: a first stage where an organometallic compound having a dispersion function of hexaboride particles and a polymerization promotion function of a hydrolyzable silane compound are added to the dispersion liquid of particles obtained by dispersing hexaboride particles into an organic solvent, and stirring and mixing are performed, so as to adsorb the organometallic compound on the surface of each particle; a second stage where water and a hydrolyzable silane compound are added to the dispersion liquid of the hexaboride particles on which the organometallic compound is adsorbed, and stirring and mixing are performed, so as to coat the surface of each hexaboride particle on which the organometallic compound is adsorbed with the hydrolyzable silane compound; and a third stage where the solvent is removed from the dispersion liquid of the hexaboride particles each coated with the silane compound, thereafter, the hexaboride particles are heated and fired at the thermal decomposition temperature of the organometallic compound or above, and further, the obtained powdery body is pulverized. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing surface-coated hexaboride particles having significantly improved water resistance.

Coating films containing hexaboride particles represented by LaB _{6 and the} like, various resin kneaded substrates, laminated glass, etc. have high light transmittance and low reflectance in the visible light region, and in the near infrared region. Since it has the characteristic that the transmittance | permeability of light is low, it is utilized as a solar radiation shielding material in recent years (refer patent document 1).

  By the way, it is known that the above hexaboride microparticles are decomposed and deteriorated (formation of oxides and hydroxides) by water vapor and water in the air, and the loss of solar radiation shielding effect due to deterioration, especially with finer particles. The ratio is large. The solar shading material is basically used outdoors because of its characteristics, and high weather resistance is often required. In some optical members (films, resin sheets, etc.) containing the hexaboride fine particles, the surface of the hexaboride particles is decomposed by the water vapor or water in the air gradually penetrating into the matrix to decompose the surface. There was a problem that the transmittance in the 2600 nm region increased with time, and the solar radiation shielding performance gradually deteriorated.

  Then, the method of coat | covering the surface of hexaboride particle | grains using surface treatment agents, such as alkoxysilane, for the purpose of improving the water resistance of hexaboride particle | grains is proposed (refer patent document 2).

  However, when the average primary particle diameter of hexaboride particles is as fine as 200 nm or less, in the conventional method described in Patent Document 2, when the concentration of alkoxysilane or the like is increased together with the hexaboride fine particles, In the condensation reaction process, the hexaboride fine particles are likely to aggregate and the surface treatment is performed on the agglomeration of the hexaboride particles. Therefore, after the surface treatment, mechanical dispersion treatment such as a medium stirring mill is performed. In this case, hexaboride fine particles with exposed surfaces that do not have a silica coating layer are formed when the fine particles forming the cluster structure are dissociated through the silica component. It was difficult to impart sufficient transparency and water resistance.

  On the other hand, in order to improve the dispersion stability of hexaboride particles in the coating solution for solar radiation shielding film in which hexaboride particles are dispersed, hexaboride using hydrolyzable silane compounds such as silicate and acidic silicate liquid A method for forming a silica coating layer on the particle surface has also been developed (Patent Document 3).

  In addition, in the method described in Patent Document 3, a film of zirconium oxide or the like is formed in advance on the surface of the hexaboride particles so as to promote the formation of a silica coating layer on the surface of the hexaboride particles. Also proposed is a method of coating a hydrolyzable silane compound such as an acidic silicic acid solution.

  However, since the method described in Patent Document 3 is intended to improve the dispersion stability of hexaboride particles in the coating solution for solar radiation shielding film, the solvent removal and the drying / Because of the surface treatment method that does not go through the firing process, the mechanical strength and chemical stability of the surface treatment coating are remarkably low, and the water resistance of the surface treatment powder obtained has the problem that it is hardly improved compared to the untreated powder. It was.

  Further, there is a method in which inorganic fine particles are dispersed using an anionic, cationic, nonionic surfactant, ester, fatty acid, resin acid, etc., and a silane compound is added thereto to bind to the particle surface. Because of the strong influence of hydrophobic groups such as long-chain alkyl groups and fluorine-containing alkyl groups in these molecules, the surface treatment agent silane compound cannot be efficiently hydrolyzed, and a sufficient amount of particles on the particle surface There was a problem that functional chemical species could not be combined.

Moreover, in order to put the wet surface treatment method, which is costly for concentration and solvent removal, to a practical level, it is necessary to set the hexaboride concentration in the treatment liquid as high as possible. A technique for uniformly treating individual particles while maintaining the fine particles of the fine particles in a monodispersed state has not been developed yet.
JP 2000-169765 A JP 2003-277045 A JP 2004-204173 A

  The present invention has been made paying attention to such problems, and the object is to provide a method for producing surface-coated hexaboride particles with significantly improved water resistance.

  Therefore, as a result of continual research conducted by the inventor in order to solve the above problems, the organoborate particles are adsorbed on the surface of the hexaboride particles dispersed in the organic solvent to keep the hexaboride particles in a highly dispersed state. In addition, after the surface of the hexaboride particles on which the organometallic compound is adsorbed is coated with a hydrolyzable silane compound, and the solvent is removed from the dispersion of the hexaboride particles, the conditions above the pyrolysis temperature of the organometallic compound When the above-described hexaboride particles were heated and fired, uniform and sufficient surface coating treatment was possible for each hexaboride particle. As a result, surface-coated hexaboride particles having excellent water resistance and chemical stability were obtained. I found out that I could get it. The present invention has been completed by such technical discovery.

That is, the invention according to claim 1
Assuming a method for producing surface-coated hexaboride particles in which a silica coating layer is formed on the surface of the hexaboride particles using a hydrolyzable silane compound,
An organometallic compound having a function of dispersing hexaboride particles and a function of promoting polymerization of the hydrolyzable silane compound is added to a dispersion of hexaboride particles in which hexaboride particles are dispersed in an organic solvent; and A first step of stirring and mixing to adsorb the organometallic compound to the surface of the hexaboride particles;
Water and a hydrolyzable silane compound are added to the dispersion of hexaboride particles adsorbed with the organometallic compound, and the surface of the hexaboride particles adsorbed with the organometallic compound is mixed by stirring and mixed. A second step of coating with a degradable silane compound;
After removing the solvent from the dispersion of hexaboride particles coated with the silane compound, the hexaboride particles are heated and fired under conditions equal to or higher than the thermal decomposition temperature of the organometallic compound, and the obtained powder is A third step of grinding,
It is characterized by comprising.

Next, the invention according to claim 2
Based on the manufacturing method of the surface-coated hexaboride particles according to claim 1,
The hexaboride particles are one or more elements selected from Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sr, and Ca. It is a hexaboride of (X),
The invention according to claim 3
The hexaboride particles are characterized by being lanthanum boride.

The invention according to claim 4
Based on the method for producing surface-coated hexaboride particles according to any one of claims 1 to 3,
The average primary particle diameter of hexaboride particles is 10 nm to 1 μm,
The invention according to claim 5
Based on the manufacturing method of the surface-coated hexaboride particles according to claim 1,
The mixed solution of the second step is characterized in that the amount of hexaboride particles is 1 to 50% by weight,
The invention according to claim 6
Based on the method for producing surface-coated hexaboride particles according to any one of claims 1 to 5,
The organometallic compound is selected from aluminum alcoholate or a polymer thereof, cyclic aluminum oligomer, alkoxy group-containing aluminum chelate, zirconium alcoholate or polymer thereof, zirconium chelate compound, titanium alcoholate or polymer thereof, or titanium chelate compound. One type or two or more types.

Next, the invention according to claim 7 provides:
Based on the manufacturing method of the surface-coated hexaboride particles according to any one of claims 1 to 6,
The addition amount of the organometallic compound is 0.05 to 300 parts by weight in terms of metal element with respect to 100 parts by weight of the hexaboride particles,
The invention according to claim 8 provides:
Based on the manufacturing method of the surface-coated hexaboride particles according to claim 1,
The hydrolyzable silane compound is a tetrafunctional silane represented by the general formula (I): Si (OR ¹ ) ₄ (wherein R ¹ is the same or different monovalent hydrocarbon group having 1 to 6 carbon atoms). A compound or a partial hydrolysis product thereof,
The invention according to claim 9 is:
Based on the method for producing surface-coated hexaboride particles according to any one of claims 1 to 8,
The ratio of the hydrolyzable silane compound to hexaboride particles is 0.01 to 100 parts by weight with respect to 1 part by weight of hexaboride particles in terms of silicon dioxide contained,
The invention according to claim 10 provides
Based on the manufacturing method of the surface-coated hexaboride particles according to claim 1,
The organic solvent is an alcohol solvent represented by the general formula (II): R ² OH (where R ² is a monovalent hydrocarbon group having 1 to 6 carbon atoms).

According to the method for producing surface-coated hexaboride particles according to the present invention,
Since the organometallic compound having a dispersing function in the first step is adsorbed on the surface of the hexaboride particles without being hydrolyzed, the dispersibility of the hexaboride particles in the organic solvent is improved by the dispersing action of the organometallic compound. Thus, it becomes possible to keep the high concentration hexaboride particles in a monodispersed state.

  In addition, by adding water and a hydrolyzable silane compound to the dispersion of hexaboride particles to which the organometallic compound is adsorbed in the second step, the organometallic compound having a polymerization promoting function is hydrolyzed. It becomes possible to uniformly coat the monodispersed hexaboride particle surfaces while self-condensing the hydrolyzable silane compound.

  Then, after the solvent is removed from the hexaboride particle dispersion in the third step, the hexaboride particles are heated and fired under a condition equal to or higher than the thermal decomposition temperature of the organometallic compound, and the obtained powder is By being pulverized, it is possible to produce surface-coated hexaboride particles having excellent water resistance and chemical stability.

Hereinafter, embodiments of the present invention will be described in detail.
1. Hexaboride Particles The hexaboride particles applied in the present invention include Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sr, and Ca. And hexaboride of one or more kinds of elements (X) selected from the above. The particle size of the hexaboride particles is appropriately set within the range of 10 nm to 1 μm depending on the intended use. For example, when applied to an optical selective transmission film (meaning the above-mentioned film that transmits light in the visible light region and shields light in the near infrared region), it is necessary to consider scattering by particles. When importance is attached to transparency, the particle size of hexaboride particles is 200 nm or less, preferably 100 nm or less. The reason for this is that if the particle size of the fine particles exceeds 200 nm, the light in the visible light region of 380 nm to 780 nm is scattered by geometrical scattering or Mie scattering to become a frosted glass, and clear transparency cannot be achieved. Because. When the particle diameter is 200 nm or less, the scattering is reduced and a Rayleigh scattering region is obtained. In the Rayleigh scattering region, the scattered light decreases in inverse proportion to the sixth power of the particle diameter, so that the scattering is reduced and the transparency is improved as the particle diameter decreases. Further, when the thickness is 100 nm or less, the scattered light is preferably very small. However, depending on the application, there is a field where such transparency is not required, and the field is appropriately set within a range of 10 nm to 1 μm.

  By the way, when trying to form a silica coating layer on the surface of fine hexaboride particles using a surface treatment agent such as alkoxysilane or a hydrolyzable silane compound such as silicate or acidic silicate liquid, Because it becomes difficult to disperse in the solvent due to the polar or hydrogen bond of reactive groups such as silanol groups on the particle surface, it causes severe aggregation of the particles and it is difficult to uniformly treat the individual particles. Become.

In addition, when a surfactant, polymer dispersant, or the like is used as the dispersant, the hydrolysis efficiency of the silane compound, which is the surface treatment agent, decreases due to the influence of hydrophobic groups in these molecules. It was difficult to bind a sufficient amount of functional species.
2. Accordingly, in the present invention, the hexaboride particle dispersion in which hexaboride particles are dispersed in an organic solvent has a function of dispersing the hexaboride particles and a function of promoting the polymerization of the hydrolyzable silane compound. The organometallic compound is added and mixed by stirring to adsorb the organometallic compound to the surface of the hexaboride particles, thereby maintaining the borosilane fine particles in a highly dispersed state, and then adding a silane compound as a surface treatment agent. It can be efficiently hydrolyzed, resulting in a uniform and sufficient amount of silica coating on the individual particles.

  In addition, when the organometallic compound is added to a dispersion of hexaboride particles in which hexaboride particles are dispersed in water instead of an organic solvent, the organometallic compound is hydrolyzed after the addition and the organometallic compound itself becomes Because of vigorous aggregation and gelation, the silane compound as the surface treatment agent cannot be efficiently hydrolyzed afterwards while maintaining the hexaboride fine particles in a highly dispersed state.

  Therefore, in the present invention, it is necessary to add an organometallic compound to a dispersion of hexaboride particles in which hexaboride particles are dispersed in an organic solvent.

  Here, the organometallic compound applied in the first step is not particularly limited, but is compatible with the organic solvent, has high affinity and adsorption power with the hexaboride particle surface, and disperses the hexaboride particles. It must be excellent in function and excellent in the function of accelerating the polymerization of the hydrolyzable silane compound, and the coating must be strong and suppress the permeation of water vapor and water.

  From the above viewpoints, aluminum alcoholate or polymer thereof, cyclic aluminum oligomer, alkoxy group-containing aluminum chelate, zirconium alcoholate or polymer thereof, zirconium chelate compound, titanium alcoholate or polymer thereof, or titanium chelate compound are selected. Organometallic compounds are suitable.

  Examples of aluminum-based organometallic compounds include aluminum alcoholates such as aluminum ethylate, aluminum isopropylate, aluminum sec-butyrate, mono-sec-butoxyaluminum diisopropylate, or polymers thereof, and cyclic aluminum oligomers such as cyclic aluminum oxide octylate. , Ethyl acetoacetate aluminum diisopropylate, aluminum tris (ethyl acetoacetate), octyl acetoacetate aluminum diisopropylate, stearyl acetoacetium diisopropylate, aluminum monoacetylacetonate bis (ethyl acetoacetate), aluminum tris (acetylacetonate) ) Aluminum alcoholate as aprotic solvent, petroleum-based It is dissolved in an agent, hydrocarbon solvent, ester solvent, ketone solvent, ether solvent, amide solvent, etc., and β-diketone, β-ketoester, mono- or polyhydric alcohol, fatty acid, etc. are added to this solution. An alkoxy group-containing aluminum chelate compound obtained by heating and refluxing and obtained by a ligand substitution reaction can be exemplified.

  Examples of the zirconia-based organometallic compound include zirconium alcoholates such as zirconium ethylate and zirconium butyrate or polymers thereof, zirconium tributoxy systemate, zirconium tetraacetylacetonate, zirconium tributoxyacetylacetonate, zirconium dibutoxybis. Zirconium chelate compounds such as (acetylacetonate), zirconium tributoxyethyl acetoacetate, and zirconium butoxyacetylacetonate bis (ethylacetoacetate) can be exemplified.

  Examples of titanium-based organometallic compounds include titanium alcoholates such as methyl titanate, ethyl titanate, isopropyl titanate, butyl titanate, and 2-ethylhexyl titanate, and their polymers, titanium acetylacetonate, titanium tetraacetylacetonate, and titanium octylene. Examples of the titanium chelate compound include glycolate, titanium ethyl acetoacetate, titanium lactate, and titanium triethanolamate.

  These organometallic compounds are highly reactive to the inorganic surface, easily adsorbed on the surface of the hexaboride fine particles, and the organic chains in the molecules are oriented on the outside of the fine particle surface, so that the hexaboride fine particles in the organic solvent are aligned. Dispersibility can be remarkably improved. Also, hydrolysis and polycondensation reactions are faster than those of silane compounds, and the organometallic compound itself acts as a crosslinking agent for the silane monomer or oligomer, and promotes the polymerization of the hydrolyzable silane compound added in the second step. Therefore, unlike the surfactants and polymer dispersants described above, the formation of the silica film is not hindered.

  In addition, most of the hexaboride particles have poor reactivity with the silane compound, and simply attaching the silane compound to the hexaboride particles results in weak adhesion to the particle surface, and when a certain level of shear force is applied. In some cases, the silane compound may be detached. However, by adsorbing the organometallic compound described above on the surface of the hexaboride particles, the affinity between the hexaboride particles and the silane compound is improved, and the silane compound can be more firmly attached to the hexaboride particles.

  As described above, the method of adsorbing the organometallic compound to the hexaboride particles is performed by adding the organometallic compound to the dispersion of hexaboride particles in which the hexaboride particles are dispersed in an organic solvent, and stirring and mixing. A wet method is employed. When performing this wet method, agglomerates of fine particles are previously pulverized in an organic solvent using a ball mill, sand mill, ultrasonic homogenizer, etc., and an organometallic compound is added to the uniformly dispersed slurry. The surface treatment agent is preferably applied to the particle surface or the surface treatment agent is added simultaneously during the crushing treatment.

The organic solvent in the first step is a silane compound represented by the general formula (I): Si (OR ¹ ) ₄ (wherein R ¹ is the same or different monovalent hydrocarbon group having 1 to 6 carbon atoms). Or as long as it dissolves the partially hydrolyzed product and water, there is no particular limitation, and alcohols, cellosolves, ketones, ethers and the like can be mentioned, but alcohols are preferable. Examples of alcohols include alcohol solvents represented by the general formula (II): R ² OH (where R ² is a monovalent hydrocarbon group having 1 to 6 carbon atoms), and specifically, methanol, ethanol , Isopropanol, butanol and the like. Note that, depending on the number of carbon atoms of the alcohol used here, the hydrolysis rate of the organometallic compound and silica described later varies, so that the type of alcohol can be conveniently selected by controlling the generated solid content such as the target coating amount.

The amount of the organometallic compound added is preferably 0.05 to 300 parts by weight in terms of metal element with respect to 100 parts by weight of hexaboride particles. More preferably, the range of 0.3 to 150 parts by weight is more suitable. When the organometallic compound is less than 0.05 parts by weight, the effect of covering the surface is small, and the effect of improving the water resistance may not be sufficient, or the dispersion effect may not be sufficient. Further, if the amount of adsorption to hexaboride particles exceeds 300 parts by weight and becomes a certain level or more, the dispersion effect in the treatment liquid becomes saturated, which is disadvantageous in terms of cost, and when removing the solvent, the organometallic compound and Fine particles are easily granulated through a silica compound as a surface treatment agent. Therefore, depending on the application, good transparency may not be obtained, and a considerable amount of organometallic compound used and treatment time are required, which is disadvantageous in terms of cost. Therefore, the upper limit is preferably 300 parts by weight from an industrial viewpoint.
3. Hydrolyzable silane compound Water, an organic solvent, and a hydrolyzable silane compound are added to a dispersion of hexaboride particles adsorbed with the above organometallic compound, and the mixture is stirred and mixed to form hexaboron on which the organometallic compound is adsorbed. The amount of hexaboride particles in the second step of coating the surface of the fluoride particles with the hydrolyzable silane compound is preferably 1% by weight to 50% by weight in the mixed solution. If it is less than 1% by weight, it is industrially disadvantageous because of costs for concentration and solvent removal. If it exceeds 50% by weight, the primary particle diameter of the hexaboride particles is as small as 200 nm or less. Vigorous aggregation occurs and is difficult to disperse in the solvent.

  In addition, when adding water, an organic solvent, and a hydrolysable silane compound to the dispersion of hexaboride particles on which the organometallic compound is adsorbed, the organic solvent in the first step may be substituted for the organic solvent. . Therefore, the organic solvent is not necessarily added to the dispersion of hexaboride particles on which the organometallic compound is adsorbed in the second step.

The hydrolyzable silane compound used in the present invention is not particularly limited. For example, the general formula (I): Si (OR ¹ ) ₄ (wherein R ¹ is the same or different and has 1 to 6 carbon atoms. A tetrafunctional silane compound represented by (monovalent hydrocarbon group) or a partial hydrolysis product thereof. Specific examples of the tetrafunctional silane compound represented by the general formula (I): Si (OR ¹ ) ₄ include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, and tetrabutoxysilane. Can be mentioned. Specific examples of the partial hydrolysis product of the tetrafunctional silane compound represented by the general formula (I): Si (OR ¹ ) ₄ include methyl silicate and ethyl silicate.

  Next, the amount of the hydrolyzable silane compound added to the hexaboride particles is in principle arbitrary, but if possible, it is 0 per 1 part by weight of hexaboride particles in terms of silicon dioxide contained in the hydrolyzable silane compound. 0.01 to 100 parts by weight is desirable. If the amount is less than 0.01 parts by weight, the effect of covering the surface of the hexaboride particles may be small and the effect of improving the water resistance may not be sufficient. If the amount exceeds 100 parts by weight, the improvement in water resistance by the surface coating is not observed. This is because the covering effect may be small.

Next, the organic solvent of the second step are added as necessary, general formula ^{(I): Si (OR 1} ) 4 ( where, ^{R 1} is the same or different 1 to 6 carbon atoms mono- There is no particular limitation as long as it dissolves the silane compound represented by (hydrocarbon group) or a partially hydrolyzed product thereof and water, and examples thereof include alcohols, cellosolves, ketones, and ethers. Kind is good. Examples of alcohols include alcohol solvents represented by the general formula (II): R ² OH (where R ² is a monovalent hydrocarbon group having 1 to 6 carbon atoms), and specifically, methanol, ethanol , Isopropanol, butanol and the like. However, since the hydrolysis rate of the silane compound varies depending on the number of carbon atoms of the alcohol, as in the case of the organometallic compound described above, the type of alcohol can be conveniently selected by controlling the generated silica, such as the target coating amount. Moreover, it is preferable that the quantity of the water used at this time is 0.5-5 equivalent with respect to the number-of-moles of the alkoxy group of the silane compound shown by general formula (I) or its partial hydrolysis product.

  The hydrolysis / condensation of the tetrafunctional silane compound represented by the above general formula (I) is carried out by the hexaboride particle dispersion prepared in advance as described above and the organic solvent represented by the above general formula (II). This is carried out by a known method in which a tetrafunctional silane compound represented by the general formula (I) is dropped into a reaction medium composed of water.

  By adding a silane compound to the reaction medium and bringing the reaction medium and the silane compound into contact with each other, the silane compound is allowed to undergo a hydrolysis reaction, and a polymerization reaction of silicic acid in the reaction medium generated thereby can proceed. Then, by the progress of the polymerization reaction of silicic acid, silica is produced with the hexaboride particles on which the organometallic compound has been adsorbed in advance as a nucleus, and a silica film having a thickness of 3 to 100 nm, preferably 5 to 50 nm is formed by the growth. Hexaboride particles are obtained.

The hydrolysis reaction can be carried out under reduced pressure, normal pressure, or pressurized pressure, but is preferably carried out at a temperature not higher than the boiling point of the reaction mixture and with sufficient stirring. This hydrolysis reaction is continued until the silane compound disappears from the reaction mixture formed by adding the silane compound to the reaction medium, and can usually be completed in about 1 to 24 hours.
4). Solvent removal, baking by heating, and pulverization Next, in the third step, the solvent of the treatment liquid is removed. Examples of the method for removing the solvent in the treatment liquid include well-known methods such as a filter press method, a ultrafiltration method, and a centrifugal separation method in addition to the evaporation method, but are not limited to these methods.

  The reaction mixture from which the silane compound has disappeared is preferably further heated and aged at the boiling point of the solvent or the like remaining in the reaction mixture, preferably at 60 to 100 ° C. for 2 hours or more. The heat aging performed after the completion of the reaction eliminates ungrown particles remaining in the reaction mixture and suppresses the formation of condensed clusters formed by localization of silica components and hexaboride particles during solvent removal and drying. It is effective for.

  In the surface-coated hexaboride particles of the present invention, the surface-treated film formed on the surface of the hexaboride particles is densified by heat-calcining under the decomposition temperature or higher of the organometallic compound, and moisture permeation is achieved. Can be more effectively suppressed. The heat treatment temperature is determined by the heat resistance temperature of the hexaboride and the heating atmosphere in addition to the thermal decomposition temperature of the organometallic compound. Since hexaboride is oxidized from about 600 ° C. in an oxygen-existing atmosphere, particularly in the air, heat treatment is preferably performed at a temperature not lower than the thermal decomposition temperature of each organometallic compound and not higher than 600 ° C. In an inert gas atmosphere in which oxygen is not present, the upper limit of the heating temperature is the decomposition temperature of hexaboride, but when the temperature is 1000 ° C. or higher, the surface treatment agent (oxide: silica is coated on the surface of hexaboride particles). The change in density of the main component is actually reduced (that is, the effect of densification by heat treatment is reduced), and the effect on moisture resistance and water resistance tends to be saturated. Therefore, the upper limit is preferably about 1000 ° C. from an industrial viewpoint.

  Next, the powdery body obtained by heating and firing is pulverized, and the surface-coated hexaboride particle diameter after pulverization is appropriately set within a range of 10 nm to 10 μm depending on the application purpose to be used. When the surface-coated hexaboride particles are applied to, for example, an optically selective transmission film (the above-described film that transmits light in the visible light region and shields light in the near infrared region), it is necessary to consider scattering by the particles. There is. When transparency is emphasized, the particle diameter is 200 nm or less, preferably 100 nm or less. This is because if the particle diameter is larger than 200 nm, the light in the visible light region of 380 nm to 780 nm is scattered by geometric scattering or Mie scattering to become frosted glass, and clear transparency cannot be achieved. When the particle diameter is 200 nm or less, the scattering is reduced and a Rayleigh scattering region is obtained. In the Rayleigh scattering region, the scattered light decreases in inverse proportion to the sixth power of the particle diameter, so that the scattering is reduced and the transparency is improved as the particle diameter decreases. Further, when the thickness is 100 nm or less, the scattered light is preferably very small. However, depending on the application purpose used, there is a field where such transparency is not required, and as described above, it is appropriately set within the range of 10 nm to 10 μm.

Examples of the method applied to the pulverization treatment include a wet pulverization method using a medium stirring mill such as an ultrasonic homogenizer and a ball mill (bead mill), a dry pulverization method using a jet mill, a hammer mill, and a rough machine. It is not limited to such as. In addition, when wet pulverization is performed, or when dispersion in liquid is performed after dry pulverization, use of a polymer dispersant in the mill base is effective for uniformly dispersing and holding fine particles in the liquid. .
5). Method of using surface-coated hexaboride particles The hexaboride particles coated with a surface treatment agent (oxide: mainly composed of silica) can be used, for example, in the form of particles as a raw material for solar shading products, or in a liquid medium or Used in a state dispersed in a solid medium.

  When the surface-coated hexaboride particles are used in a state of being dispersed in a liquid medium, the medium may be, for example, an organic solvent such as alcohol, a liquid medium such as water, or an organic solvent containing resin or water. A liquid medium is mentioned. In order to obtain a dispersion in which the surface-coated hexaboride particles are dispersed in a liquid medium, the surface-coated hexaboride particles obtained by the above-described wet method or the like are mixed with an organic solvent such as alcohol or a liquid medium such as water, Alternatively, there may be mentioned a method of adding to a liquid medium such as an organic solvent containing water or a resin and using a polymer dispersant as required.

  Further, the surface-coated hexaboride particles are applied as they are to form, for example, a sunscreen product, or the sunscreen product or the like is dispersed or dispersed in a solid medium such as resin or glass. May constitute raw materials for solar shading products.

  In the former case, for example, a dispersion in which the above surface-coated hexaboride particles are dispersed as they are in an organic solvent such as alcohol or a liquid medium such as water or using a polymer dispersant is appropriately applied to the surface of the substrate. Then, the liquid medium such as the organic solvent or water is removed by heat treatment, and a solar shading product or the like in which the surface-coated hexaboride particles are directly laminated on the surface of the substrate is exemplified. The hexaboride particles that can be used in this way are cases where the above-described polymer dispersant alone has thermal adhesiveness to the substrate (the silica layer of the surface-coated hexaboride particles is bonded). Because it does not have sex). Therefore, when the adhesion of the polymer dispersant is weak or when the polymer dispersant is not applied, the hexaboride particles are laminated on the surface of the substrate, and then a binder component such as a resin is included. You may obtain the solar shading product etc. which apply | coated the coating liquid and remove the solvent component in a coating liquid, and were resin-coated.

  On the other hand, in the latter case, a dispersion in which the surface-coated hexaboride particles are dispersed in a liquid medium such as an organic solvent containing water or the like is appropriately applied to the surface of the substrate, and the organic solvent or water or the like is applied. A dispersion in which hexaboride particles are dispersed in a solid medium (resin or glass coating in which surface-coated hexaboride particles are dispersed) can be easily prepared by evaporating the solvent and curing the resin. . In addition, as a resin component, it can select according to a use, and ultraviolet curable resin, thermosetting resin, normal temperature curable resin, a thermoplastic resin etc. are mentioned. In the case of using a dispersion to which a liquid medium not containing a resin or the like is applied, after laminating hexaboride particles on the surface of the substrate, a liquid medium containing a resin or the like is applied. As described above, a similar dispersion can be obtained.

  Further, as described above, the surface-coated hexaboride particles are dispersed in a liquid medium such as an organic solvent containing resin or the like or water, and are appropriately applied to the surface of the substrate as described above to form a film to protect the solar radiation. Or a dispersion in which surface-coated hexaboride particles are dispersed in a liquid medium such as an organic solvent containing a resin or water or the like. You may apply as a raw material for a solar radiation shielding product. That is, a powdery dispersion in which hexaboride particles are dispersed in a solid medium may be dispersed again in a liquid medium and used as a dispersion for solar shading products, as will be described later. Or kneaded into a resin. Incidentally, the particle size of the pulverized powdery dispersion is appropriately set within the range of 100 nm to 10 μm depending on the application purpose to be used.

  In addition, the dispersion in which hexaboride particles are dispersed in a solid medium is not limited to the above-described hexaboride particle dispersion or powder dispersion on the surface of the base material. The form which comprises a 0.1 micrometer-50 mm film or board may be sufficient. Then, when kneaded into a resin and molded into a film or board, it is possible to knead the hexaboride particles coated with a surface treatment agent and having a particle size suitable for the purpose directly into the resin, and Mixing a dispersion in which hexaboride particles are dispersed in a liquid medium and a resin, or adding a powdered dispersion in which hexaboride particles are dispersed in a solid medium to the liquid medium and mixing with the resin Is also possible.

  Generally, when kneading into a resin, it is heated and mixed at a temperature near the melting point of the resin (around 200 to 300 ° C.). Furthermore, it is possible to form a film or a board by each method after mixing with resin and pelletizing. For example, it can be formed by an extrusion molding method, an inflation molding method, a solution casting method, a casting method, or the like. The thickness of the film or board at this time may be set as appropriate depending on the purpose of use, and the amount of filler relative to the resin (that is, the amount of hexaboride particles added) depends on the thickness of the base material, required optical characteristics, machine Although it is variable depending on the characteristics, it is generally preferably 50% by weight or less based on the resin.

In addition, the resin used as a base of the film or board is not particularly limited and can be selected according to the use. However, in consideration of weather resistance, a fluororesin is effective. Furthermore, compared to fluororesins, low-cost, highly transparent and versatile resins include PET resins, acrylic resins, polyamide resins, vinyl chloride resins, polycarbonate resins, olefin resins, epoxy resins, polyimide resins, etc. It is done.
6). Optical filter to which a dispersion of surface-coated hexaboride particles is applied When an optical filter is constructed by applying the surface-coated hexaboride particles according to the present invention (ie, the surface-coated hexaboride particles according to the present invention are solid media) In the case where the article using the dispersion dispersed in is an optical filter), it is possible to reflect and absorb light in the vicinity of 1000 nm and to transmit light at 380 nm to 780 nm. Such a characteristic is derived from the electronic structure peculiar to hexaboride. In particular, since there is plasmon resonance of free electrons near 1000 nm, light in this region is broadly absorbed and reflected.

  Furthermore, since there is little absorption in the visible light region of 380 nm to 780 nm, it is suitable not only for the use of the optical filter but also for other uses that transmit the visible light region and shield near infrared rays. For example, as an article using the surface-coated hexaboride particles or the surface-coated hexaboride particle dispersion according to the present invention, when applied to a window material of a house or a car, a greenhouse, or the like, a near infrared ray near 1000 nm of solar rays And has a merit that a high heat insulating effect is obtained and at the same time visibility is secured.

In addition, the usage-amount of the hexaboride particle | grains with respect to articles, such as the said optical filter and window material, can be suitably changed with the characteristic calculated | required. In the case of an adiabatic optical filter that transmits the visible light region and shields near infrared rays, for example, in LaB ₆ , an effective heat insulation effect can be obtained when the filler amount per 1 m ² is 0.01 g or more. Although the upper limit depends on the optical characteristics to be obtained, it is possible to absorb and shield about 50% of the heat energy of solar rays at 0.1 g per m ² , and the heat insulation efficiency per unit weight is high.

  EXAMPLES Next, although an Example demonstrates this invention concretely, the technical scope of this invention is not limited to the content of the following Examples.

  “Visible light transmittance” in the examples is an integrated value of transmitted light amounts obtained by normalizing the light transmission amount in the wavelength region of 380 nm to 780 nm with the visibility of the human eye, and the brightness perceived by the human eye. It means a value. In the examples, the measurement is performed by a method according to JISA 5759 (however, the measurement is performed only with a film without being attached to glass).

  The “haze value” of the film was measured based on JIS K7105.

  In addition, the “average dispersed particle size” was measured by a measuring apparatus using a dynamic light scattering method [ELS-800 manufactured by Otsuka Electronics Co., Ltd.], and was taken as an average value.

  Further, the water resistance evaluation method is such that, when immersed in warm water at 65 ° C. for 7 days, a sample with a visible light transmittance of 55% to 65% has a good increase in transmittance of 5 points or less. Those exceeding the point were considered to have poor water resistance.

  In addition, the optical property value (visible light transmittance, haze value) of the film here indicates a value including a base film (100 μm thick PET film, trade name Tetron HLEW manufactured by Teijin DuPont Films Ltd.) The visible light transmittance of the film itself is 90%, and the haze value is 1.9%.

520 g of lanthanum hexaboride particles (LaB _6, manufactured by Sumitomo Metal Mining Co., Ltd.) were mixed with 3480 g of isopropyl alcohol (IPA) with stirring, and this was dispersed with a medium stirring mill to prepare a dispersion A having an average dispersed particle size of 100 nm. .

  Next, 200 g of the above dispersion A, 20 g of ethyl acetoacetate aluminum diisopropylate (trade name aluminum chelate ALCH, manufactured by Kawaken Fine Chemical Co., Ltd.) and 540 g of IPA were mixed and stirred, and then dispersed using an ultrasonic homogenizer.

Next, while stirring this, 100 g of water was added dropwise over 1 hour, and while stirring, 140 g of tetraethoxysilane (Tama Chemical Co., Ltd., ethyl ethyl silicate, SiO ₂ equivalent 28.8 wt%) was added. After dropwise addition over 2 hours and stirring at 20 ° C. for 15 hours, this solution was heated and aged at 70 ° C. for 2 hours.

Next, this liquid is vacuum-dried to evaporate the solvent, and the powder obtained by heating and baking at 500 ° C. for 1 hour is dry-pulverized to obtain about 5% by weight based on the lanthanum hexaboride fine particles. Surface-coated lanthanum hexaboride fine particles coated with about 2 times the weight of Al ₂ O ₃ and about 2 times the weight of SiO ₂ were obtained.

The Al ₂ O ₃ / SiO ₂ surface-coated lanthanum hexaboride fine particles (8 g), the organic dispersant (8 g) and toluene (84 g) were mixed and dispersed to prepare a dispersion having an average dispersed particle size of 100 nm.

  Next, 2 g of this dispersion and 2 g of an ultraviolet curable resin (trade name UV3701 manufactured by Toagosei Co., Ltd.) were mixed to obtain a coating solution.

  Then, a PET film having a thickness of 100 μm was used as the base material, and the coating solution was formed on the PET film (base material) using a bar coater. This was dried at 70 ° C. for 1 minute to evaporate the solvent, and then irradiated with ultraviolet rays using a high-pressure mercury lamp to cure the film. At this time, the visible light transmittance of the cured film was 59.3%, and the haze was 2.0%.

  Next, after immersing the base material on which the cured film was formed in 65 ° C. warm water for 7 days and measuring the visible light transmittance, the visible light transmittance was 60.5%, and the increase in transmittance was It was 1.2 points. Therefore, it was confirmed that the water resistance of the coating film on the surface-coated lanthanum hexaboride fine particles contained in the cured film was good.

Example 1 except that 200 g of the above dispersion A and 20 g of zirconium tributoxyacetylacetonate (trade name: ZC-540, manufactured by Matsumoto Kosho Co., Ltd.) and 540 g of IPA were mixed and stirred, and then dispersed using an ultrasonic homogenizer. In the same manner, surface coating with silica was performed to obtain surface-coated lanthanum hexaboride fine particles coated with about 5% by weight of ZrO ₂ and about 2 times weight of SiO ₂ with respect to the lanthanum hexaboride fine particles.

The above-mentioned ZrO ₂ / SiO ₂ surface-coated lanthanum hexaboride fine particles (8 g), an organic dispersant (8 g), and toluene (84 g) were mixed and dispersed to prepare a dispersion having an average dispersed particle size of 100 nm.

  Next, 2 g of this dispersion and 2 g of an ultraviolet curable resin (trade name UV3701 manufactured by Toagosei Co., Ltd.) were mixed to obtain a coating solution.

  Then, a PET film having a thickness of 100 μm was used as the base material, and the coating solution was formed on the PET film (base material) using a bar coater. This was dried at 70 ° C. for 1 minute to evaporate the solvent, and then irradiated with ultraviolet rays using a high-pressure mercury lamp to cure the film. At this time, the visible light transmittance of the cured film was 57.2%, and the haze was 2.5%.

  Next, after immersing the substrate on which the cured film was formed in 65 ° C. warm water for 7 days and measuring the visible light transmittance, the visible light transmittance was 59.1%, and the increase in transmittance was It was 1.9 points. Therefore, it was confirmed that the water resistance of the coating film on the surface-coated lanthanum hexaboride fine particles contained in the cured film was good.

The same procedure as in Example 1 was performed except that 200 g of the dispersion A, 20 g of tetranormal butyl titanate (trade name: TA-25, manufactured by Matsumoto Kosho Co., Ltd.) and 540 g of IPA were mixed and stirred, and then dispersed using an ultrasonic homogenizer. Then, the surface coating treatment with silica was performed to obtain surface-coated lanthanum hexaboride fine particles coated with about 5% by weight of TiO ₂ and about 2 times weight of SiO ₂ with respect to the lanthanum hexaboride fine particles.

The above-mentioned TiO ₂ / SiO ₂ surface-coated lanthanum hexaboride fine particles (8 g), an organic dispersant (8 g), and toluene (84 g) were mixed and dispersed to prepare a dispersion having an average dispersed particle size of 100 nm.

  Next, 2 g of this dispersion and 2 g of an ultraviolet curable resin (trade name UV3701 manufactured by Toagosei Co., Ltd.) were mixed to obtain a coating solution.

  Then, a PET film having a thickness of 100 μm was used as the base material, and the coating solution was formed on the PET film (base material) using a bar coater. This was dried at 70 ° C. for 1 minute to evaporate the solvent, and then irradiated with ultraviolet rays using a high-pressure mercury lamp to cure the film. At this time, the visible light transmittance of the cured film was 64.7%, and the haze was 2.8%.

Next, after immersing the substrate on which the cured film was formed in warm water at 65 ° C. for 7 days and measuring the visible light transmittance, the visible light transmittance was 66.5%, and the increase in transmittance was It was 1.8 points. Therefore, it was confirmed that the water resistance of the coating film on the surface-coated lanthanum hexaboride fine particles contained in the cured film was good.
[Comparative Example 1]
0.4 g of the dispersion A, 1.6 g of toluene, and 2 g of an ultraviolet curable resin (trade name UV3701 manufactured by Toagosei Co., Ltd.) were mixed with stirring to obtain a coating solution.

  Then, a PET film having a thickness of 100 μm was used as the base material, and the coating solution was formed on the PET film (base material) using a bar coater. This was dried at 70 ° C. for 1 minute to evaporate the solvent, and then irradiated with ultraviolet rays using a high-pressure mercury lamp to cure the film. At this time, the visible light transmittance of the cured film was 56.8%, and the haze was 2.0%.

Next, after immersing the base material on which the cured film was formed in 65 ° C. warm water for 7 days and measuring the visible light transmittance, the visible light transmittance was 64.9%, and the increase in transmittance was It was 8.1 points. Therefore, it was confirmed that the water resistance of the lanthanum hexaboride fine particles contained in the cured film was poor.
[Comparative Example 2]
200 g of the above dispersion A, 560 g of IPA and 100 g of water were mixed. While stirring this, 140 g of tetraethoxysilane (Tama Chemical Co., Ltd., ethyl silicate, 28.8% by weight of SiO ₂ equivalent) was added dropwise over 2 hours. Thereafter, the mixture was aged for 15 hours, and this solution was further aged by heating at 70 ° C. for 2 hours.

  Next, this solution is vacuum dried to evaporate the solvent, and then heated and baked at 500 ° C. for 1 hour. The obtained powder is dry-pulverized to form lanthanum hexaboride fine particles coated with silica. Got.

  8 g of this silica-coated lanthanum hexaboride fine particles, 8 g of an organic dispersant and 84 g of toluene were mixed and subjected to dispersion treatment to prepare a dispersion having an average dispersed particle size of 100 nm.

  Next, 2 g of this dispersion and 2 g of an ultraviolet curable resin (trade name UV3701 manufactured by Toagosei Co., Ltd.) were mixed to obtain a coating solution.

  Then, a PET film having a thickness of 100 μm was used as the base material, and the coating solution was formed on the PET film (base material) using a bar coater. This was dried at 70 ° C. for 1 minute to evaporate the solvent, and then irradiated with ultraviolet rays using a high-pressure mercury lamp to cure the film. At this time, the visible light transmittance of the cured film was 55.8%, and the haze was 0%.

Next, after immersing the substrate on which the cured film was formed in 65 ° C. warm water for 7 days and measuring the visible light transmittance, the visible light transmittance was 62.3%, and the increase in transmittance was It was 6.5 points. Therefore, it was confirmed that the water resistance of the coating on the silica-coated lanthanum hexaboride fine particles contained in the cured film was poor.
[Comparative Example 3]
When 520 g of lanthanum hexaboride particles (LaB ₆ manufactured by Sumitomo Metal Mining Co., Ltd.), 3480 g of water and 100 g of tetra n-propoxyzirconium (trade name: ZA-40 manufactured by Matsumoto Kosho Co., Ltd.) were stirred and mixed, the above tetra n -Propoxyzirconium hydrolyzed and aggregated violently, which itself separated and settled. Further, when this mixed solution was subjected to dispersion treatment with a medium stirring mill, a gel-like dispersion was obtained in which the aggregates of tetra-n-propoxyzirconium and the aggregated particles of lanthanum hexaboride were mixed independently.

Next, 140 g of tetraethoxysilane (manufactured by Tama Chemical Co., Ltd., normal ethyl silicate, 28.8% by weight in terms of SiO ₂ ) was added dropwise over 2 hours while stirring the gel dispersion, and for 15 hours at 20 ° C. After stirring for 2 hours, this solution was heated and aged at 70 ° C. for 2 hours. However, silica precipitated on the aggregates of tetra-n-propoxyzirconium and lanthanum hexaboride particles to form coarse clusters, improving water resistance. It was difficult to coat lanthanum hexaboride particles for the purpose.
[Comparative Example 4]
In Comparative Example 3, since it was difficult to coat lanthanum hexaboride particles for the purpose of improving water resistance, isopropyl alcohol (IPA), which is an organic solvent, was added and the same coating treatment was performed.

That is, 520 g of lanthanum hexaboride particles (LaB ₆ manufactured by Sumitomo Metal Mining Co., Ltd.), 960 g of isopropyl alcohol (IPA), 2000 g of water, and 520 g of tetra n-propoxyzirconium (trade name: ZA-40 manufactured by Matsumoto Kosho Co., Ltd.) The mixture was agitated and mixed, and this was dispersed in a medium agitating mill to prepare Dispersion B having an average dispersed particle diameter of 260 nm.

  Next, 200 g of the above dispersion B and 660 g of IPA were mixed and stirred, and then dispersed using an ultrasonic homogenizer.

Next, while stirring this, 140 g of tetraethoxysilane (manufactured by Tama Chemical Co., Ltd., ethyl orthosilicate, 28.8% by weight in terms of SiO ₂ ) was added dropwise over 2 hours and stirred at 20 ° C. for 15 hours. Thereafter, this solution was aged by heating at 70 ° C. for 2 hours.

  Next, 2 g of this liquid and 2 g of an ultraviolet curable resin (trade name UV3701 manufactured by Toagosei Co., Ltd.) were mixed to obtain a coating liquid.

  Then, a PET film having a thickness of 100 μm was used as the base material, and the coating solution was formed on the PET film (base material) using a bar coater. This was dried at 70 ° C. for 1 minute to evaporate the solvent, and then irradiated with ultraviolet rays using a high-pressure mercury lamp to cure the film. At this time, the visible light transmittance of the cured film was 59.3%, and the haze was 13.8%.

  Next, after immersing the base material on which the cured film was formed in warm water at 65 ° C. for 7 days and measuring the visible light transmittance, the visible light transmittance was 67.2%, and the increase in transmittance was It was 7.9 points. Therefore, it was confirmed that the water resistance of the coating on the surface-coated lanthanum hexaboride fine particles contained in the cured film was poor.

  Since the surface-coated hexaboride particles obtained by the production method of the present invention are excellent in water resistance and chemical stability, they are used as a solar radiation shielding material added to coating films, various resin kneaded substrates, laminated glass and the like. Has industrial applicability.

Claims (10)

In the method for producing surface-coated hexaboride particles, in which a silica coating layer is formed on the surface of the hexaboride particles using a hydrolyzable silane compound,
An organometallic compound having a function of dispersing hexaboride particles and a function of promoting polymerization of hydrolyzable silane compounds is added to a dispersion of hexaboride particles in which hexaboride particles are dispersed in an organic solvent, and the mixture is stirred and mixed. A first step of adsorbing the organometallic compound on the surface of the hexaboride particles,
Water and a hydrolyzable silane compound are added to the dispersion of hexaboride particles adsorbed with the organometallic compound, and the surface of the hexaboride particles adsorbed with the organometallic compound is mixed by stirring and mixed. A second step of coating with a degradable silane compound;
After removing the solvent from the dispersion of hexaboride particles coated with the silane compound, the hexaboride particles are heated and fired under conditions equal to or higher than the thermal decomposition temperature of the organometallic compound, and the obtained powder is A third step of grinding,
A method for producing surface-coated hexaboride particles, comprising:   The hexaboride particles are one or more elements selected from Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sr, and Ca. The method for producing surface-coated hexaboride particles according to claim 1, wherein the hexaboride is (X).   The method for producing hexaboride particles according to claim 1, wherein the hexaboride particles are lanthanum boride.   The method for producing surface-coated hexaboride particles according to any one of claims 1 to 3, wherein the hexaboride particles have an average primary particle diameter of 10 nm to 1 µm.   The method for producing surface-coated hexaboride particles according to claim 1, wherein the mixed solution in the second step contains 1 to 50% by weight of hexaboride particles.   The organometallic compound is selected from aluminum alcoholate or a polymer thereof, cyclic aluminum oligomer, alkoxy group-containing aluminum chelate, zirconium alcoholate or polymer thereof, zirconium chelate compound, titanium alcoholate or polymer thereof, or titanium chelate compound. The method for producing surface-coated hexaboride particles according to any one of claims 1 to 5, wherein the method is one or more types.   The addition amount of the organometallic compound is 0.05 to 300 parts by weight in terms of metal element with respect to 100 parts by weight of the hexaboride particles. A method for producing surface-coated hexaboride particles. The hydrolyzable silane compound is a tetrafunctional silane represented by the general formula (I): Si (OR ¹ ) ₄ (wherein R ¹ is the same or different monovalent hydrocarbon group having 1 to 6 carbon atoms). 2. The method for producing surface-coated hexaboride particles according to claim 1, wherein the compound is a compound or a partial hydrolysis product thereof.   The ratio of the hydrolyzable silane compound to hexaboride particles is 0.01 to 100 parts by weight with respect to 1 part by weight of hexaboride particles in terms of silicon dioxide contained. The method for producing hexaboride particles according to any one of the above. The organic solvent is an alcohol solvent represented by the general formula (II): R ² OH (where R ² is a monovalent hydrocarbon group having 1 to 6 carbon atoms). A method for producing surface-coated hexaboride particles.