Description

HOLLOW MAGNESIUM FLUORIDE PARTICLE, PREPARATION METHOD THEREOF AND ANTIREFLECTION

COATING SOLUTION USING THE SAME

Technical Field

[1] The present invention relates to a hollow magnesium fluoride particle and a preparation method thereof, and, more particularly, to a hollow magnesium fluoride particle, which can be used for a coating agent for an antireflection film, a preparation method thereof, and an antireflection coating solution using the same. Background Art

[2] Generally, the display screens of image display devices, such as lenses, transparent plastic, plastic films, cathode ray tubes, liquid crystal displays, and the like, are an- tireflection-treated in order to decrease the reflection of outside light, such as sunlight, lamplight, or the like, and to increase the transmissivity of light.

[3] The antireflection treatment of a display screen is performed using a vacuum deposition method or a coating method. A coating film, which is composed of silica, magnesium fluoride, or the like, is formed on the outermost layer of the display screen.

[4] Generally, in the case of silica (SiO ) for antireflection treatment, hollow silica particle sols have been developed in order to realize a low refractive index. In the case of magnesium fluoride, the target for the magnesium fluoride is fabricated, and the target is coated using a vacuum deposition method, and thus the coated target is commonly used as an antireflection film of optical lenses etc.

[5] Japanese Unexamined Patent Application Publication Nos. Sho 02-026824, Hei

07-069621, and 2000-169133 disclose various magnesium fluoride sols to be used as coating material for an antireflection film and production methods thereof.

[6] However, since the magnesium fluoride sols disclosed to date require organic or inorganic binders because they have low cohesivity, silica-magnesium fluoride composite hydrate colloidal sols, which have both low refractivity of magnesium fluoride and high cohesivity of silica sol, are being used. Here, there is a problem in that, since the refractive index of the silica-magnesium fluoride composite hydrate colloidal sols is the sum of the refractive index of silica and the refractive index of magnesium fluoride, low refractivity of magnesium fluoride itself cannot be realized. Further, in the case where antireflection films are produced using these silica- magnesium fluoride composite hydrate colloidal sols, there is a problem in that, although the strength of the antireflection film is improved, the refractive index of magnesium fluoride itself is offset, thus decreasing the antireflectivity thereof.

Disclosure of Invention Technical Problem

[7] Accordingly, the present invention has been made to overcome the above problems, and an object of the present invention is to provide a hollow magnesium fluoride particle having low refractivity and a method of preparing the same.

[8] Another object of the present invention is to provide an antireflection coating solution using the hollow magnesium fluoride particle. Technical Solution

[9] In order to accomplish the above objects, an aspect of the present invention provides a hollow magnesium fluoride particle, comprising a magnesium fluoride coating film on an outer surface of the particle.

[10] Another aspect of the present invention provides a method of preparing a hollow magnesium fluoride particle, including the steps of (a-1) obtaining a fluoride raw material solution by diluting an aqueous fluoride solution with an organic solvent; (b-1) obtaining a silica particle-dispersed solution by dispersing a silica particle in an organic solvent; (c-1) obtaining a magnesium raw material solution by mixing magnesium raw material with an organic solvent; (d-1) obtaining a magnesium fluoride particle, comprising a silica core and a magnesium fluoride coating film formed on the surface of the silica core, by mixing the fluoride raw material solution obtained in the step (a-1) and the silica particle-dispersed liquid obtained in the step (b-1) with the magnesium raw material solution obtained in the step (c-1) and then stirring the mixed solution; and (e-1) removing the silica core from the result.

[11] A further aspect of the present invention provides a method of preparing a hollow magnesium fluoride particle, comprising the steps of (a-2) obtaining a fluoride raw material solution by diluting an aqueous fluoride solution with an organic solvent; (b-2) obtaining a magnesium raw material solution by mixing magnesium raw material with an organic solvent; (c-2) obtaining a magnesium fluoride colloidal particle by mixing and reacting the fluoride raw material solution obtained in the step (a-2) with the magnesium raw material solution obtained in the step (b-2); (d-2) obtaining a silica particle-dispersed solution by dispersing a silica particle in an organic solvent; (e-2) obtaining a magnesium fluoride particle comprising a silica core and a magnesium fluoride coating film formed on the surface of the silica core by mixing and reacting the silica particle-dispersed solution obtained in the step (d-2) with a dispersion solution obtained by dispersing the magnesium fluoride colloidal particle obtained in the step (c-2); and (f-2) removing the silica core from the result.

[12] The hollow magnesium fluoride particle according to the present invention has a hollow structure in which a magnesium fluoride coating film is formed on the outer

surface of the particle. Owing to these structural characteristics, the refractive index of the hollow magnesium fluoride particle is 1.2 to 1.35, which is very low. In the case where this hollow magnesium fluoride particle is used for a coating agent for an an- tireflection film, the antireflective function of the antireflection film is greatly improved compared to the case where conventional silica-magnesium fluoride colloidal particles are used therefor.

Advantageous Effects [13] A hollow magnesium fluoride particle according to the present invention can be suitably used for a coating agent for an antireflection film due to its low refractivity, obtained by realizing the inherent refractive property of the magnesium fluoride itself. [14] An antireflection film produced using the hollow magnesium fluoride particle according to the present invention exhibits an excellent antireflective function when the antireflection film is applied to the display screens of image display devices, such as lenses, transparent plastic, plastic films, cathode ray tubes, liquid crystal displays, and the like.

Brief Description of the Drawings [15] The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [16] FIGS. 1 and 2 are flowcharts showing processes of preparing a hollow magnesium fluoride particle according to an embodiment of the present invention; [17] FlG. 3 is a sectional view showing the structure of a hollow magnesium fluoride particle according to an embodiment of the present invention; and [18] FlG. 4 is a sectional view showing the structure of a hollow magnesium fluoride particle according to another embodiment of the present invention.

Best Mode for Carrying Out the Invention [19] Reference should now be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. [20] Hereinafter, methods of preparing a hollow magnesium fluoride particle according to the present invention will be described with reference to FIGS. 1 and 2. [21] The hollow magnesium fluoride particle according to the present invention is prepared through a process of forming magnesium fluoride particles on the surface of a silica particle and then removing the silica particle therefrom. [22] The process of forming magnesium fluoride particles on the surface of a silica particle is performed using the following two methods. [23] The first method of forming magnesium fluoride particles on the surface of a silica

particle is performed in such a manner that a silica particle-dispersed solution, for example, one commercially available from Nissan Chemical Industries, Ltd. (SNOTEX OL), and a fluoride solution are simultaneously dropped into a magnesium raw material solution so that magnesium fluoride particles are deposited on a silica particle, resulting in a silica-magnesium fluoride composite colloidal particle.

[24] The first method of forming magnesium fluoride particles on the surface of a silica particle will be described in detail below with reference to FIG. 3.

[25] First, a fluoride raw material solution is obtained by diluting an aqueous fluoride solution with an organic solvent (Sl 1), and, in addition to this step, a silica particle- dispersed solution is obtained by dispersing silica particles in an organic solvent (S 12).

[26] The organic solvent, which is used to dilute the aqueous fluoride solution and to obtain the silica particle-dispersed solution, includes methanol, ethanol, iso-propanol, butanol, and the like. In this case, after the dilution of the aqueous fluoride solution, the amount of the organic solvent is 90 to 99.9% by weight, and, at the time of the preparation of the silica particle-dispersed solution, the amount thereof is 65 to 77% by weight.

[27] Additionally, a magnesium raw material solution is formed by mixing a magnesium raw material with an organic solvent, and the fluoride raw material solution and silica particle-dispersed solution are dropped into the magnesium raw material solution, and then the magnesium raw material solution, into which the fluoride raw material solution and silica particle-dispersed solution are dropped, is stirred and reacted at a temperature of 30 to 90°C, thus obtaining a magnesium fluoride particle including a silica core and a magnesium fluoride coating film formed on the surface of the silica core (S 13). Here, when the reaction temperature is below 30°C, the productivity of the magnesium fluoride particle is decreased because the reaction rate thereof is low. In contrast, when the reaction temperature is above 90°C, it is difficult to control the size of the magnesium fluoride particle because the reaction rate thereof is excessively high, which is not desirable.

[28] The organic solvent, which is used to form the magnesium raw material solution, includes methanol, ethanol, iso-propanol, butanol, and the like. It is preferred that the amount of the organic solvent be 87 to 95% by weight.

[29] In the preparation of the fluoride raw material solution, silica particle-dispersed solution and magnesium raw material solution, when the amount of the organic solvent is beyond the above range, it is not desirable in the aspect of productivity and particle size control.

[30] Subsequently, a silica particle is removed from the resulting magnesium fluoride particle, in which magnesium fluoride particles are formed on the surface of the silica particle (S 14), thereby completely preparing a hollow magnesium fluoride particle

(S15).

[31] Meanwhile, the second method of forming a magnesium fluoride particle on the surface of a silica particle is performed in such a manner that magnesium fluoride particles having a primary particle size of 1 to 10 nm are prepared and then the magnesium fluoride particles are applied on the surface of a silica particle having a primary particle size of 5 to 50 nm, thereby forming a composite colloidal particle.

[32] The second method of forming magnesium fluoride particles on the surface of a silica particle will be described in detail below with reference to FlG. 2.

[33] A fluoride raw material solution was obtained by diluting an aqueous fluoride solution with an organic solvent (S21), and a magnesium raw material solution is obtained by mixing a magnesium raw material with an organic solvent (S22).

[34] Further, magnesium fluoride colloidal particles, having a primary particle size of 1 to

IOnm, and preferably 2 to 5 nm, was obtained by mixing the fluoride raw material solution with the magnesium raw material solution and then stirring the mixed solution at a temperature of 30 to 90°C (S23). In this case, when the primary particle size of the magnesium fluoride colloidal particle is below 1 nm, the productivity of the magnesium fluoride colloidal particle is decreased because the reaction rate thereof must be kept low. In contrast, when the primary particle size of the magnesium fluoride colloidal particle is above 10 nm, the bonding force of the magnesium fluoride colloidal particle to a base material is insufficient, which is not desirable.

[35] A silica particle-dispersed solution, including 1 to 10% by weight of silica particles, is obtained by mixing silica particles with an organic solvent (S24), and the silica particle-dispersed solution is mixed with a dispersion solution obtained by dispersing 2 to 20% by weight of the magnesium fluoride colloidal particles in an organic solvent.

[36] A magnesium fluoride particle including a silica core and a magnesium fluoride coating film formed on the surface of the silica core is obtained by reacting the result at a temperature of 30 to 60°C (S25).

[37] The kinds and amounts of the solvents, which are used to obtain the fluoride raw material solution, magnesium raw material solution, and silica particle-dispersed solution in the second process, may be the same as those of the solvents, which are used in the first process.

[38] Subsequently, a silica particle component is removed from the result, in which magnesium fluoride particles are formed on the surface of the silica particle (S26), thereby completely preparing a hollow magnesium fluoride particle (S27).

[39] Methods for removing the silica particle component are not particularly limited, but, as an example, the silica particle component is removed by dissolving it using an alkaline component. Specifically, the alkaline component may be 0.5 to 20% by weight of an aqueous sodium hydroxide solution.

[40] The amount of the alkaline component is adjusted such that the pH of the result, in which magnesium fluoride particles are formed on the surface of the silica particle and a mixture containing the alkaline component, is in the range of 9 to 12.

[41] The result of the above processes is ultrafiltered using methanol and ethanol, and is then washed, and thus impurities are removed therefrom. Then, residual liquid is aged for a predetermined time, thereby obtaining a hollow magnesium fluoride particle according to the present invention.

[42] The aging process is performed to compact the surface of the hollow magnesium fluoride particle, and includes a procedure of stirring the residual liquid at a tern perature ranging from 50 to 190°C, preferably at a temperature of about 100°C, for 24 hours.

[43] The silica particle, which is used as a starting material in the above processes, has a primary particle size of 5 to 50 nm, which is commercially available.

[44] In the present invention, the fluoride raw material may include, but is not limited to, sodium fluoride, potassium fluoride, ammonium fluoride, hydrogen fluoride, and the like, and the amount thereof is 0.1 to 10% by weight. In this case, when the amount of the fluoride raw material is below 0.1% by weight, fluorides are insufficiently deposited on the surface of a silica particle. In contrast, when the amount of the fluoride raw material is above 10% by weight, surface coating efficiency is decreased due to the fluorides that are not deposited on the surface of the silica particle according to the excess supply of fluorides, which is not desirable.

[45] The magnesium raw material, which is used in the present invention, includes, but is not limited to, magnesium chloride, magnesium nitrate, magnesium sulfate, magnesium alkoxide, and the like, and the magnesium alkoxide includes, but is not limited to, magnesium methoxide, magnesium ethoxide, magnesium butoxide, and the like. The amount of the magnesium raw material is 0.1 to 10% by weight. Here, when the amount of the magnesium raw material is below 0.1% by weight, magnesium fluoride is not sufficiently deposited on the surface of the silica particles. In contrast, when the amount of the magnesium raw material is above 10% by weight, surface coating efficiency is decreased due to the magnesium fluoride that is not deposited on the surface of the silica particle according to the excess supply of magnesium, which is not desirable.

[46] A hollow magnesium fluoride particle prepared through the above processes, as shown in FlG. 3, has a magnesium fluoride coating film 11 constituting a shell of the particle and a cavity 10 defined in the magnesium fluoride film 11. The hollow magnesium fluoride particle has an average particle size of 10 to 100 nm, and particularly 20 to 60 nm, and has a refractive index of 1.2 to 1.35. Like this, the hollow magnesium fluoride particle exhibits a low refractive property because it is hollow

inside. Therefore, the hollow magnesium fluoride particle can realize the inherent refractive property of the magnesium fluoride itself, compared to conventional magnesium fluoride particles which include a silica core and a magnesium fluoride coating film on the silica core.

[47] It is preferred that the average inner diameter of the cavity 10 be 5 to 100 nm. In this case, when the average diameter thereof is below 5 nm, the magnitude of the decrease in the refractive index is decreased. In contrast, when the average diameter thereof is above 100 nm, the size of the particle is increased, and thus the coatability of the particle is decreased, which is not desirable.

[48] In the hollow magnesium fluoride particle according to the present invention, it is preferred that the thickness of the magnesium fluoride coating film 11 be 3 to 20 nm. In this case, when the thickness of the magnesium fluoride coating film 11 is below 3 nm, a coating layer can be easily cracked or broken. In contrast, when the thickness thereof is above 20 nm, a silica core component cannot easily be removed, which is not desirable.

[49] Further, in the present invention, the hollow magnesium fluoride particle, as shown in FIG. 4, may further include a silica coating film 12 formed on the inner surface of the magnesium fluoride coating film 11. In this case, silica included in the silica coating film 12 is absorbed into the magnesium fluoride coating film 11, thereby improving the bonding force of the hollow magnesium fluoride particle.

[50] That is, the hollow magnesium fluoride particle further including the silica coating film 12 is advantageous in that the refractive index thereof is low, and simultaneously the considerable bonding force thereof can be maintained to some extent. In this case, it is preferred that the thickness of the silica coating film 12 be in the range from 1 to 5 nm. When the thickness of the silica coating film 12 is below 1 nm, it is difficult to maintain the considerable bonding force thereof. In contrast, when the thickness of the silica coating film 12 is above 5 nm, the refractive index thereof is excessively increased, which is not desirable.

[51] The hollow magnesium fluoride particle according to the present invention can be usefully used for a coating agent for an antireflection film. A process of forming an an- tireflection film using the hollow magnesium fluoride particle will be described below.

[52] The antireflection film can be formed through the processes of preparing an antireflection film formation composition by mixing the hollow magnesium fluoride particle according to the present invention, an organic solvent and a coating formation binder; applying the composition on a base material; drying the base material coated with the composition; and curing the dried base material coated with the composition. Here, a transparent resin film, such as a polyester film, a triacetylcellulose (TAC) film, an acrylic resin film, or a polycarbonate film is used as the base material. The curing

process is performed through a light irradiation process or a heat treatment process.

[53] The coating formation binder includes a hydrolyzable organic silicon compound such as alkoxy silane (for example, triethyl orthosilicate) and a partial hydrolysate, and may further include a thermosetting resin, an ultraviolet-setting resin, and the like.

[54] The composition, coating condition, drying condition, and curing condition of the an- tireflection film formation composition are set at typical levels. The antireflection film formed in such conditions exhibit a very good antireflective function when the antireflection film is applied to the display screens of image display devices, such as lenses, transparent plastic, plastic films, cathode ray tubes, liquid crystal displays, and the like. In particular, the antireflection film is generally used as a low-reflective layer film among the polarizing films of liquid crystal displays. Mode for the Invention

[55] A better understanding of the present invention may be obtained through the following examples, which are set forth to illustrate, but is not to be construed to be the limit of the present invention.

[56] Example 1

[57] A first solution was provided by diluting 38.3g of hydrogen fluoride (49 wt%, reagent grade) with 2.3g of methanol (reagent grade). In addition to the first solution, a second solution was provided by diluting 21 g of a silica particle (20 wt%, primary particle size: 40~50nm, SNOTEXOL), manufactured by Nissan Chemical Industries Ltd., with 145g of methanol.

[58] Subsequently, 30.2g of magnesium methoxide (Mg(OCH ) , 8 wt% solution,

Aldrich) and lOOg of methanol were put in a IL beaker and then diluted. The magnesium methoxide solution was put in a IL beaker, and each of the first solution and second solution was dropped into the magnesium methoxide solution at a rate of 4.81D/min using a quantitative pump while stirring the magnesium methoxide solution at a temperature of 40°C, and then the magnesium methoxide solution was stirred for 120 minutes, thereby preparing a colloidal particle including a silica core and magnesium formed on the silica core.

[59] Subsequently, in order to remove the silica component from the colloidal particle,

80Og of an aqueous sodium hydroxide solution (10 wt%) was added into the silica- magnesium fluoride colloidal solution, and was stirred at room temperature for 20 hours, and then the silica component was removed therefrom through an ultrafiltering method using ultrapure water.

[60] Subsequently, in order to compact the surface of a hollow magnesium fluoride particle, the hollow magnesium fluoride particle was aged at a temperature of 100°C for 10 hours, and was then substituted with an organic solvent, such as isopropyl

alcohol, propyl alcohol, ethyl cellosolve, methylethylketone, toluene or the like, thereby preparing a hollow magnesium fluoride colloidal particle dispersed in the organic solvent.

[61] The properties of the hollow magnesium fluoride particle obtained in Example 1 are given in Table 1. [62] Table 1 [Table 1] [Table ]

[63] A solution obtained by diluting 19.83g of hydrogen fluoride (49 wt%, reagent grade) with 317 g of methanol (reagent grade) was dropped into a solution obtained by diluting 25Og of magnesium methodixide (Mg(OCH ) ) with 250 g of methanol in a 2L beaker at a rate of 3.25D/min using a quantitative pump while being stirred at a temperature of 40°C, and then the mixed solution was stirred for 120 minutes, thereby preparing a magnesium fluoride colloidal particle having a particle sized of 2 to 5 nm. Subsequently, a colloidal solution obtained by diluting 21 g of a silica particle (20 wt%, primary particle size: 40~50nm, SNOTEXOL), manufactured by Nissan chemicals Corp., with 145g of methanol was provided.

[64] Next, lOOOg (1.0 wt%) of the methanol-dispersed magnesium fluoride colloidal particle solution prepared through the above process was put in a 2L beaker, and was mixed with 40Og of the methanol-dispersed silica particle solution at a room temperature for 24 hours, and then the mixed solution was reacted at a temperature of 40°C for 15 hours in order to increase the bonding force between particles. Subsequently, an unreacted magnesium fluoride particle was removed from the resultant by filtering the resultant, thereby obtaining only a colloidal particle in which a magnesium fluoride particle was adhered on the surface of silica.

[65] Subsequently, a silica component was removed from the obtained silica-magnesium fluoride colloidal particle using the same method as in Example 1, thereby obtaining a organic solvent-substituted hollow magnesium fluoride colloidal particle.

[66] The properties of the hollow magnesium fluoride particle obtained in Example 2 are given in Table 2.

[67] Table 2 [Table 2] [Table ]

[68] [69] As given in Tables 1 and 2, it can be seen that the refractive indexes of the hollow magnesium fluoride particles obtained in Examples 1 and 2 are very low. In this case, it was found that the refractive indexes of the hollow magnesium fluoride particles obtained in Examples 1 and 2 were similar to each other.

[70] Application Example [71] An antireflection coating solution was prepared by mixing lOOg of an ethyl cellosove-dispersed hollow magnesium fluoride solution (concentration: 1.0 wt%) obtained in Example 1 with 100 g of an ultraviolet-setting resin (solid content 40 wt, component: urethane acrylate), manufactured by Finesol Tech Corp. Subsequently, an antireflection film was formed by applying this coating solution on a polyethylene terephthalate (PET) film using a bar coating method, and irradiating it with a high- pressure mercury lamp (80W/cm) for 1 minute and then curing it.

[72] The total transmissivity, haze, reflectivity at a wavelength of 550 nm, refractive index, adhesivity, and pencil hardness of the antireflection film were evaluated and given in Table 3. Here, the adhesivity of the antireflection film was evaluated using the number of quadrangles remaining on the surface of the film with them being not peeled, in which the remaining quadrangles are formed by making 100 speckled- patterned quadrangles on the surface of the film at an interval of 1 mm using a small cutter, attaching a cellophane tape to the surface of the film, and then detaching the cellophane taper from the surface of the film. In this case, 90 or more quadrangles remained. Here, ® is 90 or more remaining quardrangles.

[73] Table 3

[Table 3] [Table ]

[74] As given in Table 3, it can be seen that the antireflection film formed using the hollow magnesium fluoride particle obtained in Example 1 has excellent antireflctivity.

[75] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.