JP2589348B2 - Magnesium fluoride sol and its manufacturing method - Google Patents

Description

The present invention relates to a magnesium fluoride sol suitable as a coating agent for lenses and interference filters, a method for producing the sol, and an article dried by applying the sol.

[Prior Art] There are very few known documents describing magnesium fluoride sol, and a method of producing a white translucent aqueous magnesium fluoride sol by adding a sodium fluoride aqueous solution to a slightly magnesium chloride aqueous solution is disclosed in B.И. . Bolicina, C.
Γ. Moculsin Zh.Prikl.Khim., 47 , 1521 (1974).

Magnesium fluoride is widely used for forming an antireflection film on a lens or an interference filter because of its low refractive index. However, when coating magnesium fluoride on lenses and filters, most of them currently have to rely on the vacuum deposition method, so not only is the coating costly, but also the substrate such as a lens whose surface is extremely curved, There was a problem that a uniform coating film could not be formed on the surface. As one of the methods for solving this problem, Japanese Patent Application Laid-Open No. 59-213643 discloses
A method has been proposed in which a solution of a fluorine-containing magnesium compound is adhered to a substrate and then heat-treated to form a magnesium fluoride film on the surface of the substrate. However, since this method requires a high-temperature heat treatment step, it has a drawback that cannot be adopted depending on the type of the substrate.

Therefore, if magnesium fluoride can be provided in the form of an aqueous sol or an organosol, such a sol can be easily applied to a substrate and can volatilize the dispersion medium at a relatively low temperature. Very convenient for formation.

[Problems to be Solved by the Invention] Until now, magnesium fluoride in the form of a sol is not commercially available, and there is no technical literature describing its physical and chemical properties. That is, it is only known that an aqueous magnesium fluoride sol can be obtained by adding an aqueous solution of sodium fluoride to an aqueous solution of magnesium chloride as a conventional technique relating to a magnesium fluoride sol.

However, the aqueous sol produced by this method has a low light transmittance, and the organosol in which the dispersion medium is replaced with an organic solvent also has a low light transmittance, so that this is applied to a substrate to form a film. Then, there is a problem that the transparency of the base is reduced.

Accordingly, a first object of the present invention is to provide an aqueous magnesium fluoride sol having a light transmittance higher than that of a conventional example, and a method for producing the same.

Another object of the present invention is to provide an organosol in which a dispersion medium of a highly transparent aqueous magnesium fluoride sol is replaced with an organic solvent.

Still another object of the present invention is to provide a film-formed body obtained by applying and drying an organomagnesium fluoride sol on the surface of a substrate such as a lens or plastics.

[Means for Solving the Problems] According to the findings obtained by the present inventors, surprisingly,
A magnesium salt aqueous solution and a fluoride aqueous solution are reacted by a simultaneous addition method to form a gel precipitate, and the obtained reaction solution is heated and aged, and then the electrolyte in the solution is removed. A magnesium sol can be obtained. Then, by replacing the dispersion medium of the aqueous sol with an organic solvent, an organosol substantially equivalent to the aqueous sol can be obtained.

Therefore, the aqueous sol and the organosol of magnesium fluoride according to the present invention are each characterized by having a light transmittance of 50% or more. Here, the light transmittance means a 1 cm thick magnesium fluoride sol (MgF ₂ concentration 5 wt.%, Assuming that the transmittance of light having a wavelength of 500 nm in 1 cm thick water is 100.
%) Indicates the relative value of the transmittance of light of the same wavelength. Also,
The aqueous magnesium fluoride sol refers to a magnesium fluoride sol using water as a dispersion medium, and the organomagnesium fluoride sol refers to a magnesium fluoride sol using an organic solvent as a dispersion medium.

[Detailed Description of the Invention] In preparing the aqueous magnesium fluoride sol of the present invention, it is important that a magnesium salt aqueous solution and a fluoride aqueous solution are reacted by a simultaneous addition method. A sol having a light transmittance of 50% or more cannot be obtained by a method of adding an aqueous solution or a method of adding a magnesium salt aqueous solution to a fluoride aqueous solution which is the reverse of the method.

Magnesium chloride,
Aqueous solutions of magnesium salts exemplified by nitrates, sulfates, acetates and the like can be used. As the fluoride aqueous solution, aqueous solutions of potassium, sodium, ammonium and hydrogen fluoride of fluorine can be used. is there.

According to the method of the present invention, the aqueous magnesium salt solution and the aqueous fluoride solution are mixed by a simultaneous addition method. Here, the simultaneous addition method means that a magnesium salt aqueous solution and a fluoride aqueous solution are always mixed while maintaining a stoichiometric amount to generate magnesium fluoride, and the two aqueous solutions are mixed in an arbitrary single container. In the case of mixing while slowly pouring, the amount of magnesium salt and fluoride supplied to the container,
It is always maintained at the stoichiometric amount to produce magnesium fluoride.

In carrying out the simultaneous addition method, it is general that a magnesium salt aqueous solution and a fluoride aqueous solution are gradually poured into an appropriate vessel covered with water and reacted at a temperature in the range of 0 to 50 ° C. In this case, the concentration of the gelatinous precipitate is generated within the container, such that the range of 0.1-5 wt% as MgF _2, it is preferable to adjust the concentration of each raw material aqueous solution, the laying water. If the concentration of the gel precipitate formed in the container is higher than 5 wt%, the light transmittance of the finally obtained sol decreases, and if the concentration is too low, dehydration and concentration of the sol require costs.

The solution containing the gel-like precipitate is dehydrated and concentrated, if necessary, so that the concentration of the gel-like precipitate contained therein is 1 to 5 wt%.
And then heat aging. Heat aging is 60 ~
The reaction is carried out at a temperature of 220 DEG C., preferably 90 DEG to 200 DEG C., for a period of 2 to 168 hours, whereby the primary particles of the gel-like precipitate are reduced to 20 to 50 DEG
From 100 to 120Å. Since this gel is contaminated with electrolytes and is agglomerated and gelled, the gel is dehydrated and concentrated while removing the electrolyte with an ultrafiltration membrane to reduce the specific conductivity of the sol
200 × 10 ⁻⁶ Ω ⁻¹ cm ⁻¹ or less, preferably 20 × 10 ⁻⁶ Ω ⁻¹ cm
^By lowering the value to ^-1 or less, a stable aqueous magnesium fluoride sol aimed at by the present invention can be obtained at a concentration of approximately 10 to 20% by weight.

The conversion from the aqueous sol to the organosol is carried out by replacing the dispersion medium of the magnesium fluoride colloidal particles with water and an organic solvent as usual, and in this case, the organic solvent includes methanol, ethanol, pyropanol, butanol. , Acetone, monoethylene glycol and the like can be used.

[Examples] Example 1 An aqueous solution A was prepared by dissolving 508.3 g of magnesium chloride (MgCl ₂ .6H ₂ O) in 12.5 ion-exchange water, and 470.7 g of potassium fluoride (KF.2H ₂ O) was added. An aqueous solution B was prepared by dissolving in 12.5 ion-exchanged water.

Next, spread 25 ion-exchanged water in a 50-volume container, and add the total amount of both the above-mentioned A and B aqueous solutions at a supply rate of 0.5 / sec to each while stirring vigorously.
A gel precipitate formed. The concentration of the precipitate in the liquid was 0.3 wt% as magnesium fluoride. This solution was concentrated with a ultrafiltration membrane to a liquid volume of 5, and then stirred at 98 ° C.
For 72 hours to form a gel-like liquid. Next, the electrolyte contained in the gel-like liquid was removed by an ultrafiltration membrane, and the amount of the liquid was concentrated to about 1 to obtain a blue-white translucent aqueous magnesium fluoride sol. Table 1 shows the properties of this sol.

Example 2 500 ml of the aqueous magnesium fluoride sol obtained in Example 1 was put into an ultrafiltration apparatus, and while maintaining this liquid amount, the water of the dispersion medium was replaced with methanol using methanol of 3 to replace methanol with the dispersion medium. 500 ml of organomagnesium fluoride sol was obtained.

Next, 800 ml of isopropyl alcohol was added to the methanol sol, and methanol and a small amount of isopropyl alcohol were distilled off under reduced pressure using a rotary evaporator to obtain 500 ml of an organomagnesium fluoride sol using isopropyl alcohol as a dispersion medium. Table 1 shows the properties of this sol.

Example 3 In Example 1, the concentration of the gel precipitate formed in a 50-volume container was 0.1 wt.
%, A gel-like precipitate was formed in exactly the same manner as in Example 1, and the solution containing this was concentrated with an ultrafiltration membrane, and then heated and aged at 98 ° C. for 72 hours with stirring to obtain a gel. Liquid. Next, the electrolyte contained in the gel-like liquid was removed by an ultrafiltration membrane, and the liquid amount was concentrated to about 0.3 to obtain a blue-white translucent aqueous magnesium fluoride sol. Table 1 shows the properties of this sol.

Example 4 An aqueous magnesium fluoride sol was obtained in exactly the same manner as in Example 1, except that the heat aging conditions were changed to 98 ° C. and 144 hours. Table 1 shows the properties of this sol.

Example 5 In Example 1, the concentration of the gel precipitate formed in a 50-volume container was 5 wt% as magnesium fluoride.
A gel-like precipitate was formed in exactly the same manner as in Example 1, and the solution containing the same was heated and aged at 98 ° C. for 72 hours without concentration to obtain a gel-like solution. Next, the electrolyte contained in the gel-like liquid was removed by an ultrafiltration membrane, and the liquid amount was concentrated to about 15, thereby obtaining a blue-white translucent aqueous magnesium fluoride sol. Table 1 shows the properties of this sol.

Example 6 In Example 1, an aqueous magnesium fluoride sol was obtained in exactly the same manner as in Example 1 except that the degree of removal was changed when the electrolyte was removed from the gel-like liquid using the ultrafiltration membrane. Was. Table 1 shows the properties of this sol.

Comparative Example 1 A solution prepared by dissolving 508.3 g of magnesium chloride (MgCl ₂ .6H ₂ O) in 25 ion-exchanged water was mixed with potassium fluoride (KF.2H).
₂ O) solution in deionized water of 25 to 470.7g were prepared.

While vigorously stirring the aqueous potassium fluoride solution, an aqueous magnesium chloride solution was added thereto at a feed rate of 1 / second to obtain a milky white liquid containing a gel-like precipitate. This solution was concentrated with an ultrafiltration membrane to a liquid volume of 5, and then heated and aged at 98 ° C. for 72 hours while stirring to obtain a gel-like liquid. Next, the electrolyte in the gel-like liquid was removed by an ultrafiltration membrane, and the liquid was concentrated to obtain a milky white opaque aqueous magnesium fluoride sol. Table 1 shows the properties of this sol.

Comparative Example 2 An aqueous magnesium fluoride sol was prepared in the same manner as in Comparative Example 1, except that an aqueous solution of potassium chloride was added to an aqueous solution of magnesium chloride instead of adding an aqueous solution of magnesium chloride to an aqueous solution of potassium fluoride. Obtained. Table 1 shows the properties of this sol.

Example 7 Each of the sols prepared in Examples 1 to 6 and Comparative Examples 1 and 2 was solvent-substituted with monoethylene glycol, and then diluted with monoethylene glycol so that the MgF ₂ concentration of each sol became 2%. Each diluted sol was uniformly applied to a glass plate which had been sufficiently washed and dried, and dried with warm air to form a coating having a thickness of about 10 μm. The transparency of the obtained coating film is shown at the bottom of Table-1.

[Effect of the Invention] The aqueous magnesium fluoride sol and the organomagnesium fluoride sol of the present invention have a high light transmittance because the particle size distribution of the colloidal particles dispersed therein is in a narrow range of about 100 to 120 °. By applying this to a substrate such as a lens or a filter and drying it, the coating is also highly transparent, so that an antireflection film can be easily formed on the substrate surface using the sol of the present invention.

Claims (4)

(57) [Claims] An aqueous magnesium fluoride sol having a light transmittance of 50% or more. 2. An organomagnesium fluoride sol having a light transmittance of 50% or more. 3. A film-formed body formed by applying and drying the organomagnesium fluoride sol according to claim 2 on a substrate surface. 4. A method in which an aqueous solution of a magnesium salt and an aqueous solution of a fluoride are reacted by a simultaneous addition method to form a gel precipitate, and the obtained reaction solution is heated and aged, and then the electrolyte in the solution is removed. For producing an aqueous magnesium fluoride sol.