JP3844787B2 - Magnesium fluoride hydrate sol and its production method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a magnesium fluoride hydrate sol suitably used for a coating agent for an antireflection film such as a lens and a cathode ray tube or an image display surface of a liquid crystal display device, and a production method thereof.
[0002]
[Prior art]
In general, an antireflection treatment is performed on a lens, a cathode ray tube, and an image display surface of a liquid crystal display device in order to reduce reflection of external light such as sunlight and electric light and to increase light transmission. The antireflection treatment is performed by a vacuum deposition method or a coating method, and magnesium fluoride or silica having a low refractive index is used for the outermost layer. In particular, it is known that magnesium fluoride sol and fine powder are effective as an antireflection coating agent microfiller. However, magnesium fluoride particles have poor dispersibility and have the disadvantage that the desired transparency cannot be obtained unless the primary particle size is significantly reduced. Further, since the primary particle diameter is remarkably reduced, productivity is deteriorated.
[0003]
The following is reported about the manufacturing method of magnesium fluoride sol and fine powder.
Japanese Patent Laid-Open No. 63-124332 proposes a method of producing a dispersion of acidic magnesium fluoride colloidal particles by adding an aqueous hydrofluoric acid solution to a mixed aqueous solution of magnesium acetate and polyvinyl alcohol. The dispersion of colloidal particles obtained by this method has the disadvantage of gelling immediately after preparation at a pH of 2 and a concentration of 5% or more.
[0004]
Japanese Patent Application Laid-Open No. 64-41149 proposes a method for preventing reflection by applying a sol solution composed of fine particles of magnesium fluoride having a particle diameter of 100 to 200 angstroms to a screen panel of a cathode ray tube. However, it does not describe a method for producing this sol solution.
JP-A-2-26824 discloses an aqueous and organomagnesium fluoride sol having a light transmittance of 50% or more, a film-forming body obtained by coating and drying the sol on a substrate surface, and an aqueous magnesium salt solution and an aqueous fluoride solution. A method for producing an aqueous magnesium fluoride sol is proposed, in which a gel-like precipitate is formed by the simultaneous addition method and the obtained reaction solution is heated and aged, and then the electrolyte in the solution is removed. Has been. Magnesium fluoride colloidal particles obtained by this method have a remarkably small particle size of 100 to 120 angstroms. However, it has been reported that the sol obtained by adding a potassium fluoride aqueous solution to a magnesium chloride aqueous solution has a colloidal particle of 100 to 300 angstrom, milky white opaque, and a transmittance of 20% or less.
[0005]
The magnesium fluoride colloidal particles in the magnesium fluoride sol obtained by the above method are all anhydrous magnesium fluoride salts, and there is no description regarding magnesium fluoride hydrates.
On the other hand, regarding the presence of magnesium fluoride hydrate, Melor's “A Comprehensive Treasure on Inorganic and Theoretical Chemistry”, which is a classic of inorganic chemistry, and “Gmelins Handbook der Anganisten”.
There is no report on "Chemie". There is no document describing magnesium fluoride hydrate sol.
[0006]
[Problems to be solved by the invention]
The anhydrous colloidal particles of magnesium fluoride itself have a small binding force, and therefore an organic or inorganic binder is required when used as an antireflection coating agent. In this case, if the primary particle size is small, a large amount of binder is required, and the intended refractive index cannot be obtained.
[0007]
A fluoride sol having a refractive index lower than that of the anhydrous magnesium fluoride salt and a method for easily producing the sol are desired.
It is an object of the present invention to provide a novel magnesium fluoride hydrate sol used for an antireflection film for reducing external light reflection or increasing light transmittance, and a method for easily producing the sol. And
[0008]
[Means for Solving the Problems]
The present _invention, organo MgF 2 · _nH 2 O (where, n is the 0.25 to 0.5) having a composition of, made primary particle diameter of colloidal particles of magnesium fluoride hydrate is 10~100nm It is a sol. The magnesium fluoride hydrate sol of the present invention is a sol in which colloidal particles of magnesium fluoride hydrate are dispersed in an organic solvent .
[0009]
Method for producing a magnesium fluoride hydrate aqueous sol of the present invention, (a): 0.1 to fluoride aqueous magnesium salt solution, so as to be F / Mg molar ratio of 1.9 to 2.0 A step of adding a colloidal particle aggregate of magnesium fluoride hydrate in 10 hours ; (b) : in the aggregate slurry of magnesium fluoride hydrate colloidal particles obtained by step (a) Removing the by-product salt.
[0010]
The magnesium salt used in the present invention is a water-soluble salt, and examples thereof include magnesium chloride, magnesium nitrate, magnesium sulfate, magnesium sulfamate, magnesium acetate, magnesium formate, etc., alone or in combination of two or more. Can be used.
The fluoride used in the present invention is a water-soluble salt. For example, sodium fluoride, potassium fluoride, cesium fluoride, rubidium fluoride, ammonium fluoride, guanidine fluoride, and quaternary fluoride. Examples thereof include ammonium, acidic ammonium fluoride, and hydrogen fluoride, and these can be used alone or in combination of two or more.
[0011]
In the method for producing a magnesium fluoride hydrate sol of the present invention, a magnesium salt aqueous solution and a fluoride aqueous solution are mixed by mixing a magnesium salt aqueous solution with a fluoride aqueous solution, and a fluorine / magnesium ratio of 1.9 in F / Mg molar ratio. It is important to add so that it will be -2.0. A method of simultaneously adding an aqueous magnesium salt solution and an aqueous fluoride solution while maintaining the stoichiometric amount of the magnesium salt and fluoride to produce magnesium fluoride, or an aqueous magnesium salt solution in an aqueous fluoride solution In the method of adding, the target magnesium fluoride hydrate sol cannot be efficiently produced.
[0012]
The addition and mixing of the aqueous fluoride solution to the aqueous magnesium salt solution in the step (a) of the present invention is performed at a temperature of 0 to 100 ° C. using an apparatus such as a Satake-type stirrer, a Faudler-type stirrer, a disper, or a homogenizer. The time required for this addition can be 0.1 to 10 hours under stirring.
(A) the concentration of magnesium fluoride hydrate produced in the process is preferably prepared so as MgF ₂ 0.1 to 10 wt%.
[0013]
(A) Aggregates of colloidal particles of magnesium fluoride hydrate having a primary particle size of 10 to 100 nm are generated by the step, and become a slurry. The slurry is settled to precipitate and separate the aggregates of colloidal particles of magnesium fluoride hydrate. The formation of this aggregate is due to the high concentration of salts formed as a by-product of the step (a), that is, magnesium salts and fluorides, that is, salts formed by the respective counter ions of magnesium ions and fluorine ions. Yes.
[0014]
Step (b) in the present invention is a step of removing byproduct salts from the aggregate slurry of colloidal particles of magnesium fluoride hydrate obtained in step (a).
As a method for removing by-product salts, a membrane filtration washing method such as an ultrafiltration membrane or a reverse osmosis membrane, an ion exchange method, a static separation method, etc. can be used, but a membrane using an ultrafiltration membrane can be used. A filtration washing method is most preferred. Moreover, the membrane filtration washing | cleaning method and another method can be used together as needed. In particular, by-product salts can be effectively removed by using a tube type ultrafiltration membrane. Although depending on the material of the membrane, ultrafiltration is usually performed at 0 to 80 ° C., and it is necessary to perform continuous or intermittent water injection in order to sufficiently remove salts. The filtration time is not particularly limited, but is usually 1 to 50 hours.
[0015]
By removing by-product salts by ultrafiltration, the aggregate of colloidal particles of magnesium fluoride hydrate is reduced, and an aqueous magnesium fluoride hydrate sol can be obtained. The magnesium fluoride hydrate aqueous sol obtained in the step (b) has a primary particle diameter of 10 to 100 nm as observed with an electron microscope. After ultrafiltration, an aqueous sol with good transparency can be obtained by performing cation and anion exchange. The magnesium fluoride hydrate aqueous sol obtained in the step (b) of the present invention has a magnesium fluoride hydrate concentration of 2 to 20% by weight. The magnesium fluoride hydrate aqueous sol obtained by the step (b) of the present invention has a light transmittance of 50 or less at 5% by weight as MgF ₂ . This light transmittance is the relative value of the transmittance of light of the same wavelength in a magnesium fluoride hydrate sol having a thickness of 1 cm, where the transmittance of light having a wavelength of 500 nm in water having a thickness of 1 cm is 100. .
[0016]
In the present invention, the organosol can be obtained by substituting the water of the magnesium fluoride hydrate aqueous sol with an organic solvent under reduced pressure or normal pressure in a conventional method in the step (c). In the present invention, examples of the organic solvent include methanol, ethanol, isopropanol, n-propanol, DMF, DMAC, ethylene glycol, propyl cellosolve and the like, and these can be used alone or in combination of two or more.
[0017]
The magnesium fluoride hydrate organosol obtained in the step (c) has a magnesium fluoride hydrate concentration of 2 to 20% by weight and a primary particle diameter of 10 to 100 nm as observed by an electron microscope. The light transmittance is 50 or more as measured by the above method.
The magnesium fluoride hydrate sol obtained by the method of the present invention was dried at 110 ° C. and subjected to X-ray diffraction as a powder. The measurement result was measured by ASTM (Index to the X-ray Powder Date). Magnesium fluoride X-ray diffraction pattern no. 6-0290 and the X-ray diffraction peak did not match, confirming the shift of the main peak and the presence of a new small peak.
[0018]
On the other hand, the magnesium fluoride hydrate sol obtained by the method of the present invention was dried at 110 ° C. and subjected to differential thermal analysis (DTA-TG analysis) as a powder. An endothermic peak was observed at 190 ° C., and a weight loss of 6.5 to 13% by weight was measured. Further, it was confirmed by the Karl Fischer method that this weight loss was water.
[0019]
From the above results, the magnesium fluoride hydrate sol dried product of the present invention clearly has water of crystallization, and the composition thereof is MgF ₂ · nH ₂ O, where n is 0.25 to 0.5. Equivalent to. This crystal water shows a tendency to decrease as the reaction temperature in the step (a) increases. As a result of the differential thermal analysis, the dehydration is completed at 400 to 500 ° C. The result of X-ray diffraction of the fired product at 500 ° C. is the above ASTM No. It completely coincided with the X-ray diffraction peak of 6-0290 magnesium fluoride, and the presence of other peaks was not observed.
[0020]
Furthermore, the magnesium fluoride hydrate sol obtained by the method of the present invention was subjected to wet analysis (ICP analysis and ion chromatography analysis) as a powder by drying the sol at 110 ° C. As for the ratio of fluorine to magnesium, the F / Mg molar ratio was 2.0.
From the above results, it was found that the magnesium fluoride hydrate obtained by the method of the present invention was MgF ₂ · nH ₂ O (where n is 0.25 to 0.5).
[0021]
[Action]
In the step (a) of the present invention, the reaction between the magnesium salt aqueous solution and the fluoride aqueous solution is such that the ratio of fluorine to magnesium is 1.9 to 2.0 in terms of F / Mg molar ratio, and may be less than 1.9. Since the amount of unreacted MgCl ₂ increases, it is not efficient. On the other hand, if it is 2.0 or more, the product of the reaction in the step (a) becomes a gel, and when removing salts in the step (b), the viscosity of the slurry becomes high and the productivity is remarkably lowered. The reason for this is not clear, but in the method of the present invention, first, basic magnesium fluoride of Mg (OH) _x F _y · zH ₂ O (x> 0, y <2) is formed, and finally, infinitely It is estimated that it is close to MgF ₂ · zH ₂ O.
[0022]
The temperature of the step (a) is 0 to 100 ° C., and if it is 100 ° C. or higher, dehydration proceeds, which is not preferable.
(A) The time of the process is 0.1 to 10 hours, and may be less than 0.1 hour, but it is not preferable because mixing becomes insufficient. Further, although it may exceed 10 hours, the production time is unnecessarily long.
[0023]
The concentration of magnesium fluoride hydrate in step (a) is 0.1 to 10% by weight as MgF ₂ , and may be less than 0.1% by weight, but is not efficient, and the concentration exceeds 10% by weight. However, it is not preferable because the viscosity of the liquid becomes high and the reaction becomes non-uniform. Most preferred is 0.5 to 2.0% by weight.
(B) The temperature of the process is 0 to 80 ° C., and the higher temperature is effective because the filtration rate increases. However, since the dehydration proceeds when the filtration temperature becomes higher, room temperature to 60 ° C. is more preferable.
[0024]
(B) The process time is 1 to 50 hours and may be 50 hours or more, but the production time is unnecessarily long.
The solvent substitution temperature in the step (c) varies depending on the boiling point of the solvent, but it is preferable to carry out at a temperature as low as possible under reduced pressure so that dehydration of magnesium fluoride hydrate does not occur during substitution.
[0025]
The concentration of the magnesium fluoride hydrate aqueous sol or organosol obtained in the step (b) or (c) is 2 to 20% by weight and may be less than 2% by weight. This is not preferable because it becomes thinner. Further, it may be 20% by weight or more, but in this case, it is not preferable because the sol has a high viscosity and is difficult to handle.
[0026]
In the present invention, the primary particle diameter of colloidal particles of magnesium fluoride hydrate is 10 to 100 nm as observed with an electron microscope, and more than 100 nm is not preferable because it exceeds 100 nm which is an effective thickness as an antireflection film. . Further, the higher the reaction temperature in the step (a), the larger the primary particle size of the magnesium fluoride hydrate colloid particles.
[0027]
In the present invention, magnesium fluoride hydrate has a lower refractive index than the anhydrous salt of magnesium fluoride. By using this magnesium fluoride hydrate sol, a good antireflection effect can be exhibited. .
[0028]
【Example】
Example 1
(A) Process Magnesium chloride (MgCl ₂ · 6H ₂ O, reagent grade, manufactured by Oso Chemical) 2436 g (1125 g as MgCl ₂ ) was dissolved in 40 kg of pure water to prepare 42.4 kg of magnesium chloride aqueous solution. The MgCl ₂ concentration in this aqueous solution was 2.65% by weight.
[0029]
On the other hand, after 685 g of acidic ammonium fluoride (NH ₄ F · HF, reagent grade, manufactured by Morita Chemical) was dissolved in 40 kg of pure water, 730 g of 28% ammonia water (reagent, manufactured by Komune Chemical) was added, and fluorinated. 41.4 kg of aqueous ammonium solution (867 g as NH ₄ F) was prepared. The NH ₄ F concentration in this aqueous solution was 2.09% by weight.
[0030]
The magnesium chloride aqueous solution was charged into a 200 liter container, and the ammonium fluoride aqueous solution was added at room temperature for 30 minutes while stirring vigorously with a disper. 83.8 kg of a slurry of colloidal particles of the product was obtained.
The ratio of fluorine to magnesium in the magnesium chloride and ammonium fluoride was 1.98 in F / Mg molar ratio. The obtained magnesium fluoride hydrate colloidal particle slurry shows a colloidal color close to that of a sol but shows a tendency to settle and settle due to settling. The magnesium fluoride hydrate colloidal particles form aggregates. ing. This slurry had a pH of 7.07, an electric conductivity of 40 ms / cm, and a magnesium fluoride hydrate concentration of 0.87% by weight as MgF ₂ . The by-product salt was ammonium chloride, which was 1.51% by weight in the slurry.
[0031]
(B) Step 8a kg of the magnesium fluoride hydrate colloidal particle slurry obtained in step (a) was added to a tube-type ultrafiltration device [UF (PS-150), manufactured by Mitsubishi Rayon Engineering Co., Ltd.] The filter was washed while adding 270 kg of pure water at the same rate as the ultrafiltration rate. The liquid temperature was 25 ° C. and the filtration washing time was 18.5 hours. The concentration at the time of filtration and washing was 2.5% by weight as MgF ₂ , and after filtration and washing, the solution was concentrated by an ultrafiltration device to obtain 12.74 kg of magnesium fluoride hydrate aqueous sol (I). No sediment was observed, and the solation rate was 100%.
[0032]
The obtained aqueous sol (I) has a specific gravity of 1.042, a pH of 7.10, and a viscosity of 1.8 c. p. The concentration of magnesium fluoride hydrate was 5.9% by weight, the conductivity was 355 μs / cm, and the yield of magnesium fluoride hydrate was 91%. The aqueous sol (I) had a light transmittance of 28.6% (5% by weight as MgF ₂ ). As a result of observation with an electron microscope, the primary particle diameter of colloidal particles of magnesium fluoride hydrate was 20 to 40 nm, and the particle diameter by dynamic light scattering was 336 nm. The particle diameter by the dynamic light scattering method was measured by a commercially available N ₄ apparatus manufactured by Coulter, USA.
[0033]
1 and 2 show X-ray diffraction patterns of the powder obtained by drying the aqueous sol (I) obtained at 110 ° C. and the powder obtained by firing at 500 ° C. The calcined product at 500 ° C. is ASTM No. Although completely consistent with 6-0290, the 110 ° C. dry product was not identical.
The measurement result of differential thermal analysis of the powder obtained by drying the obtained aqueous sol (I) at 110 ° C. showed an endothermic peak at 184 ° C., and the weight loss was 11.5% by weight (FIG. 3). Accordingly, when the composition of magnesium fluoride hydrate is MgF ₂ · xH ₂ O, x = 0.455, which is MgF ₂ · 1 / 2H ₂ O.
[0034]
A column filled with a cation exchange resin (Amberlite IR-120B) after adding 150 g of pure water to 500 g of aqueous sol (I) and diluted to a MgF ₂ concentration of 4% by weight, and an anion exchange resin (Amberlite IRA- The aqueous sol obtained by passing through a column packed with 410) was concentrated by a rotary evaporator to obtain 183 g of an aqueous sol (II). The obtained aqueous sol (II) has a specific gravity of 1.110, a pH of 8.18, and a viscosity of 19 c. p. The concentration of magnesium fluoride hydrate was 16.1 wt% and the conductivity was 437 μs / cm. The aqueous sol (II) had a light transmittance of 33.9% (5% by weight as MgF ₂ ). As a result of observation with an electron microscope, the primary particle diameter of colloidal particles of magnesium fluoride hydrate was 10 to 20 nm, and the dynamic light scattering particle diameter was 190 nm.
[0035]
Example 2
(B) Magnesium fluoride hydrate aqueous sol (I) obtained in step (I) (concentration of magnesium fluoride hydrate is 5.9% by weight) (726 g) was reduced by a rotary evaporator as step (c). Solvent substitution was performed while continuously charging about 9 liters of isopropyl alcohol at a liquid temperature of 20 to 40 ° C. to obtain 411 g of magnesium fluoride hydrate isopropyl alcohol sol. The substitution time was 9.5 hours, and the magnesium fluoride hydrate concentration at the time of substitution was 10 to 20% by weight.
[0036]
The obtained magnesium fluoride hydrate isopropyl alcohol sol has a specific gravity of 0.844, a pH of 6.83 when diluted to 1 + 1 with water, and a viscosity of 5.6 c. p. The concentration of magnesium fluoride hydrate was 8.9% by weight and the water content was 0.56% by weight. The light transmittance of this organosol (5% by weight as MgF ₂ ) was 94.8%. As a result of observation with an electron microscope, the primary particle size of colloidal particles of magnesium fluoride hydrate was the same as that of the aqueous sol (I), 20 to 40 nm, and the dynamic light scattering particle size was 274 nm. Moreover, the measurement result of the differential thermal analysis of the powder dried at 110 ° C. of the obtained organosol showed an endothermic peak at 170 ° C., and the weight loss was 11.5%, which was the same as that of the aqueous sol (I). Further, the refractive index of the powder of this organosol dried at 110 ° C. was measured by a liquid immersion method. As a result, the refractive index was 1.385.
[0037]
Both the obtained aqueous sol (II) and organosol were stable with no abnormalities such as separation and thickening observed even after standing at room temperature for 6 months or longer. The aqueous sol (I) showed a tendency to separate slightly upon standing.
Example 3
208 g of ethyl silicate 28 (manufactured by Colcoat Co.) was dissolved in 600 g of isopropyl alcohol, and a mixture of 300 g of isopropyl alcohol, 1 g of oxalic acid and 90 g of water was added to this solution at room temperature with stirring for 30 minutes and then refluxed at 78 ° C. Under heating for 2 hours, an ethyl silicate-based thinning agent (SiO ₂ concentration 5 wt%) was prepared.
[0038]
To 160 g of this ethylsilicate-based thinning agent, 254 g of magnesium fluoride hydrate isopropyl alcohol sol (concentration of magnesium fluoride hydrate) obtained in step (c) was added with stirring, 414 g of an antireflection coating agent was obtained. This coating agent had a solid content 7.4%, SiO ₂ in magnesium fluoride hydrate and ethyl silicate type thin-film agent, the weight ratio of (magnesium fluoride hydrate) / (SiO ₂₎ 2.83 Met. This coating agent was diluted about 3 times with isopropyl alcohol, applied to a glass plate (soda lime) with a bar coater, and dried at 110 ° C. for 30 minutes to form an antireflection coating film. The film thickness was about 0.1 μm. As a result of measuring the transmittance of this glass plate at a wavelength of 550 nm, the untreated glass plate was 91.61, whereas the glass plate treated with the antireflection film was 93.92, which was antireflective. The effect was recognized.
[0039]
Example 4
Magnesium fluoride hydrate aqueous sol (I) (II) and isopropyl alcohol sol prepared in Examples 1 and 2 were diluted to a MgF ₂ concentration of 3% and applied to a glass plate with a bar coater at 110 ° C. The film was dried to form a magnesium fluoride hydrate film. The film thickness was about 0.1 μm. The transmittance of this glass plate at a wavelength of 550 nm was 93.98, 94.05, and 94.28, respectively, and the transparency and antireflection effect were good.
[0040]
Comparative Example 1
41.4 kg of the ammonium fluoride aqueous solution prepared in Example 1 was charged into a 200 liter container, and 42.4 kg of the magnesium chloride aqueous solution prepared in Example 1 was added over 30 minutes at room temperature while stirring vigorously with a disper. Thereafter, stirring was further continued for 1 hour to obtain 83.8 kg of a slurry of magnesium fluoride colloidal particles.
[0041]
The ratio of fluorine to magnesium in the above ammonium fluoride and magnesium chloride was 1.98 in F / Mg molar ratio.
The obtained slurry of colloidal particles of magnesium fluoride was cloudy, and the magnesium fluoride formed large aggregates. The magnesium fluoride colloidal particle slurry 83.8 kg was filtered and washed using a tube type ultrafiltration device while adding 270 kg of pure water at the same rate as the ultrafiltration rate. The concentration of MgF ₂ was 5.0% by weight, and it was sufficiently washed until the conductivity reached 305 μs / cm. However, most of the aggregates of magnesium fluoride colloidal particles did not sol, and the solation rate was 15%. The solated portion was magnesium fluoride hydrate.
[0042]
【The invention's effect】
The magnesium fluoride hydrate aqueous sol and the magnesium fluoride hydrate organosol of the present invention have a primary particle diameter of 10 to 100 nm as observed by an electron microscope and exhibit good dispersibility. The dried sol has a composition of MgF ₂ · nH ₂ O (where n is 0.25 to 0.5) and has a low refractive index of 1.385. Moreover, although the primary particle diameter is relatively large, the dry film shows good light transmittance. Therefore, this sol can be used alone or in an organic solvent solution of an organic resin such as methyl methacrylate, an organic resin emulsion such as acrylic or acrylic styrene, a water-soluble polymer aqueous solution such as polyvinyl alcohol, or a partially hydrolyzed silane coupling agent. By mixing with other binders such as decomposition solution, partial hydrolysis solution of ethyl silicate, silica sol, glass lens, plastic lens, glass plate, transparent plastic plate, transparent plastic film, cathode ray tube and liquid crystal display device A good anti-reflection coating film can be formed by applying to an image display surface, a color filter or the like.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of a powder obtained by drying the magnesium fluoride hydrate aqueous sol obtained in Example 1 at 110 ° C. FIG.
2 is an X-ray diffraction pattern of a powder obtained by firing the magnesium fluoride hydrate aqueous sol obtained in Example 1 at 500 ° C. FIG.
3 is a differential thermal analysis diagram of a powder obtained by drying the magnesium fluoride hydrate aqueous sol obtained in Example 1 at 110 ° C. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Curve which shows the result of differential thermal analysis (DTA) 2 ... Curve which shows the result of thermogravimetric analysis (TG)

Claims (2)

MgF ₂ · _{nH 2} O (where, n is 0.25 to 0.5) having a composition of, organosol primary particle diameter of colloidal particles of magnesium fluoride hydrate is 10 to 100 nm. The following steps (a), (b) and (c):
(A) An aqueous fluoride solution is added to an aqueous magnesium salt solution for 0.1 to 10 hours so that the F / Mg molar ratio is 1.9 to 2.0, and the colloidal particles of magnesium fluoride hydrate are agglomerated. Producing the aggregate slurry;
(B) a step of removing by-product salts in the aggregate slurry of colloidal particles of magnesium fluoride hydrate obtained in the step (a), and (c) magnesium fluoride water obtained in the step (b) water hydrate aqueous sol according to claim 1 preparation of magnesium fluoride hydrate organosol according step, consisting of replacing the organic solvent by solvent displacement method.

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