KR20210148490A - High reflective particles having multiple coating layers and a method for preparation thereof - Google Patents

Abstract

The present invention relates to high reflective particles with a multiple coating structure that exhibits high reflectance by including a spherical TiO_2 core, a SiO_2 shell coated on the surface of the TiO_2 core, and a TiO_2 nanosheet coating layer coated on the surface of the SiO_2 shell, and a preparation method therefor.

Description

High reflective particles having multiple coating layers and a method for manufacturing the same

The present invention relates to highly reflective particles having a multi-coated structure and a method for manufacturing the same, and more particularly, to achieve high reflectance by having a multi-coating structure in which titanium dioxide/silica core-shell particles are coated with titanium dioxide nanosheets. It relates to highly reflective particles and a method for manufacturing the same.

Titanium oxide has a high reflectance of sunlight due to its high refractive index. For this reason, it is widely used in fields such as solar cells, catalysts, and sensors that require high reflectivity, and various studies are being conducted to achieve higher reflectivity.

For example, Korean Patent Laid-Open Publication No. 10-2020-0025501 discloses a highly reflective material having high infrared reflectance and shielding effect by including titanium dioxide particles having a spherical controlled shape and particle size.

Japanese Patent Application Publication No. 6163097 discloses that, by including core-shell silica/titanium dioxide particles whose surfaces are treated with alkoxysilane, the dispersibility of particles is increased, separation/sedimentation is difficult, and even with a thin film thickness Disclosed is a light scattering paint composition capable of achieving high light scattering ability.

In addition, Korean Patent No. 1444028 discloses a method for manufacturing nanoparticles having a core-shell-shell structure of silica/titanium dioxide/silica in order to improve the surface area and light scattering properties.

However, the techniques disclosed in the above patent documents still have room to further improve the reflective properties, and therefore, it is required to manufacture a highly reflective material having a higher reflectance in a more efficient manner.

(Patent Document 1) Korean Patent Publication No. 10-2020-0025501

(Patent Document 2) Japanese Patent Publication No. 6163097

(Patent Document 3) Korean Patent Publication No. 1444028

An object of the present invention is to provide highly reflective particles capable of realizing high reflectance by forming a multi-coating structure of _{TiO 2} and SiO _{2 having a large refractive index difference.}

Another object of the present invention is to provide a method for producing highly reflective particles capable of efficiently producing the above-described highly reflective particles.

In order to achieve the above object, the highly reflective particles of the multi-coated structure according to the present invention are:

spherical TiO ₂ core;

_{SiO 2} shell coated on the surface of the TiO _{2 core;} and

It may include _{a TiO 2} coating layer formed by coating _{TiO 2} in the form of a nanosheet grown vertically on the surface of the SiO _{2 shell.}

The TiO ₂ core may have a rutile crystal phase.

The highly reflective particles of the multi-coated structure may have a solar reflectance of 80% or more.

The method for producing highly reflective particles having a multi-coated structure according to the present invention comprises:

1) a first step of preparing _{spherical TiO 2 particles;}

2) a second step of obtaining _{TiO 2} core/SiO ₂ shell particles by first coating _{SiO 2} on the surface of the spherical TiO _{2 ;} and

3) a third step of coating _{TiO 2} in the form of vertically grown nanosheets on the surface of _{the SiO 2 shell.}

In the first step, the production of _{spherical TiO 2 particles may include reacting the TiOCl 2} aqueous solution at 50 to 90° C. for 10 to 20 hours.

The TiOCl ₂ aqueous solution may have a concentration of 5 to 9 wt%.

In the second step, the first coating may include reacting by adding a Si precursor compound to _{a TiO 2} dispersion obtained by dispersing _{spherical TiO 2 particles in a polymer solution.}

In the polymer solution, the polymer is polyvinylpyrrolidone (PVP), poly(4-vinylpyrrolidone) (P4VP), poly(2-vinylpyrrolidone) (P2VP), and polyvinyl alcohol (PVA) can be selected from

The Si precursor compound may be an alkoxysilane.

The reaction may be carried out at 40 to 60° C. for 2 to 5 hours.

In the third step, the _{coating of TiO 2} in the nanosheet form is performed by adding a Ti precursor compound to the dispersion of _{the TiO 2} core-SiO ₂ shell particles obtained in the second step _{through a hydrothermal reaction to the TiO 2} core- SiO ₂ It may include coating and sintering at the same time as vertically growing _{TiO 2} in the form of nanosheets on the surface of the shell particles.

The Ti precursor compound may be selected from titanium butoxide (TBT), titanium isopropoxide (TTIP), and titanium tetrachloride (TiCl ₄ ).

When the Ti precursor compound is added, diethylenetriamine may be further added.

The hydrothermal reaction may be performed at 180 to 250° C. for 15 to 30 hours, and the sintering may be performed at 600 to 1000° C. for 20 minutes to 1 hour.

According to the present invention, it is possible to provide highly reflective particles having high reflectance at all wavelengths including visible light, infrared light, and near infrared light.

In addition, according to the present invention, it is possible to provide a method for manufacturing highly reflective particles capable of efficiently manufacturing the highly reflective particles.

1 is a conceptual diagram illustrating the structure and effects of multi-coated highly reflective particles according to the present invention.
2 is a view showing an SEM image of _{TiO 2} core particles according to a preparation example of the present invention.
3 is a schematic diagram of the synthesis of multi-coated highly reflective particles according to an embodiment of the present invention and a diagram showing an SEM image of the result of each synthesis step.
4 is a view showing a TEM image of the multi-coated highly reflective particles according to an embodiment of the present invention.
5 is a view showing the results of XRD analysis of the results of Preparation Examples and Examples of the present invention.

Advantages and features of the present invention, and methods of achieving them, will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the embodiments of the present invention allow the disclosure of the present invention to be complete, and in the technical field to which the present invention pertains It is provided to fully inform those of ordinary skill in the scope of the invention, and the present invention is only defined by the scope of the claims.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used with the meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in a commonly used dictionary are not to be interpreted ideally or excessively unless clearly defined in particular.

The highly reflective particles according to the present invention are:

spherical TiO ₂ core;

_{SiO 2} shell coated on the surface of the TiO _{2 core;} and

It may include _{a TiO 2} coating layer formed by coating _{TiO 2} in the form of a nanosheet grown vertically on the surface of the SiO _{2 shell.}

The TiO ₂ core may have a rutile crystal phase. By controlling the crystal phase of the core to be a rutile crystal phase, the reflectance can be controlled to be high, and particles having a high reflectance can be obtained. In the case of rutile particles, the refractive index is higher than that of anatase particles, so it has advantageous properties for reflecting sunlight. In addition, it has superior photostability than anatase particles having photocatalytic properties, so that the material has excellent stability when exposed to sunlight.

In the reflective particle of the present invention, the outermost coating layer, the TiO ₂ coating layer, is formed by coating _{TiO 2} in the form of a vertically grown nanosheet _{, and by the TiO 2} coating layer of the nanosheet structure, light incident at various angles is more efficiently can be reflected/scattered, and due to the expansion of the specific surface area, the reflective particles of the present invention can be easily applied to catalysts or sensors.

If the formation of the conventional thin-film form of a TiO ₂ coating as an outermost coating layer, does not become a do not induce surface scattering effect of light optimized as the outermost coating layer structure, and even if forming a nano-sheet form of the TiO ₂ coating layer nanosheets If is coated parallel to the surface instead of growing vertically, it has _{a structure similar to that of a thin-film TiO 2} coating layer, and has a reflective effect due to the difference in refractive index, but cannot reflect/scatter light in multiple directions, so it is optimized as the outermost layer. Compared to that, according to the present invention, _{by forming a coating layer of TiO 2 in} the form of a vertically grown nanosheet as the outermost coating layer, a nanosheet structure grown vertically on the surface with a reflection effect due to a difference in refractive index by By reflecting/scattering light in various angles, it is possible to further enhance the reflection effect.

The highly reflective particles according to the present invention may have an average particle size of 0.5 to 1.5 μm.

The highly reflective particles according to the present invention have a high refractive material, TiO ₂ , as a core, form a low-refractive material, SiO ₂ shell, on the core, and again, a high refractive material, TiO ₂ By coating, a high refractive material having a different refractive index and The sunlight passing through the material layers in which the low-refractive material is alternately formed is reflected by the difference in refractive index between the layers, thereby maximizing the reflectance.

The highly reflective particles having a multi-coated structure according to the present invention may have a solar reflectance of 80% or more, in particular, a visible light reflectance of 90% or more and a near-infrared reflectance of 85% or more.

The method for preparing multi-coated highly reflective particles according to the present invention comprises:

1) a first step of preparing _{spherical TiO 2 particles;}

2) a second step of obtaining _{TiO 2} core/SiO ₂ shell particles by first coating _{SiO 2} on the surface of the spherical TiO _{2 ;} and

3) a third step of coating _{TiO 2} in the form of vertically grown nanosheets on the surface of _{the SiO 2 shell.}

In a preferred embodiment of the present invention, in the first step, _{the production of spherical TiO 2} particles is a TiOCl ₂ aqueous solution at 50 to 90 ° C., preferably at 60 to 80 ° C. for 5 to 20 hours, preferably It may include reacting for 10 to 15 hours. When the reaction temperature is out of the range, the controlled spherical particles are not formed or the particles are agglomerated, and when the reaction time is less than the reaction time, the spherical particles are not well formed. Since no more large changes are observed, it is undesirable because it may lead to unnecessary waste of energy.

The TiOCl ₂ aqueous solution may have a concentration of 5 to 9 wt%. If the _{concentration of the TiOCl 2} aqueous solution is lower than 5% by weight, spherical particles cannot be formed, and when it is higher than 9% by weight, the shape control fails due to agglomeration between particles, which is not preferable.

In a preferred embodiment of the present invention, in the second step, the first coating may include reacting by adding a Si precursor compound to _{a TiO 2} dispersion obtained by dispersing _{spherical TiO 2 in a polymer solution.}

The polymer solution is a solution in which a polymer is dissolved in an organic solvent, distilled water, or a mixed solvent of an organic solvent and distilled water, and the polymer includes polyvinylpyrrolidone (PVP), poly(4-vinylpyrrolidone) (P4VP). ), poly(2-vinylpyrrolidone) (P2VP), polyvinyl alcohol (PVA), and the like, but is not limited thereto.

Alcohol may be used as the organic solvent, and among them, ethanol is preferable.

Examples of the Si precursor compound include tetraethoxysilane (TEOS), tetramethyl orthosilicate, methyltrimethoxysilane, triethoxyoctylsilane, 3-aminopropyltriethoxysilane, vinyltriethoxysilane, and trimethoxysilyl. and alkoxysilane compounds such as propyl methacrylate and trimethoxysilylpropyl acrylate, but are not limited thereto, and tetraethoxysilane is particularly preferred.

The concentration of the polymer in the polymer solution is 0.1 to 0.5 g/100ml, the concentration of TiO _{2 in the TiO 2} dispersion is 0.1 to 0.5 g/100ml, and the addition amount of the Si precursor compound is 0.1 to 0.1 to _{the TiO 2 dispersion} It is preferable that it is 0.5% (v/v) in terms of being able to achieve a homogeneous coating of _{TiO 2 .} Polymers and Si When the concentration of the precursor is high, _{SiO 2} particles that are not coated on the _{TiO 2} surface may be generated, and when the concentration is low, SiO ₂ may not be sufficiently coated _{on the TiO 2 surface.}

The reaction in the second step may be carried out at 40 to 70 ° C. for 2 to 5 hours, preferably at 40 to 50 ° C. for 3 to 4 hours. If the reaction temperature and reaction time are less than the above ranges, the coating is properly It may not be formed or the coating thickness may not be constant, and when the above range is exceeded, there is no further effect on the coating formation and unnecessary energy wasted.

In a preferred embodiment of the present invention, in the third step, the _{coating of TiO 2} in the nanosheet form is obtained in the second step TiO ₂ Core-SiO ₂ Ti precursor compound is added to the dispersion of shell particles. Thus, through a hydrothermal reaction, the TiO ₂ core-SiO _{2 TiO 2} in the form of a nanosheet is vertically grown on the surface of the shell particles, and at the same time, coating and sintering may be included.

The TiO ₂ core / SiO dispersion of the _second shell particles is the TiO ₂ core / the SiO ₂ shell particles as an alcohol solvent, preferably added to isopropyl alcohol (IPA), and for example, may be prepared by dispersing through the ultrasonic dispersion have. The concentration of the TiO ₂ core / SiO ₂ shell particles in the dispersion of the TiO ₂ core / SiO ₂ shell particles is It may be 0.1-2 g/100ml, and when it is out of the above range, it is not preferable because the coating _{of TiO 2 particles in the form of nanosheets may not be well made.}

The Ti precursor compound may include, but is not limited to, titanium butoxide (TBT), titanium propoxide, titanium tetrachloride (TiCl ₄ ), and the like, and titanium isopropoxide (TTIP) is particularly preferable. .

The Ti precursor compounds, the TiO ₂ may be added in an amount of 0.1 ~ 2 ml / 100ml for the dispersion of the core / SiO ₂ shell particles, for out of the range, the vertical growth of the nano-sheet in the form of TiO ₂ particles and It is not preferable because the coating may not be performed well.

In a preferred embodiment of the present invention, in the third step, _{when the Ti precursor compound is added to the dispersion of TiO 2} core-SiO ₂ shell particles, diethylenetriamine (DETA) may be added and mixed together. The DETA is _{a structure control additive that helps TiO 2} to grow vertically in the form of nanosheets on the surface of the _{TiO 2} core/SiO _{2 shell particle.} The amount of DETA added is preferably 0.5-3 ml/100ml with respect to the dispersion of _{the TiO 2} core/SiO ₂ shell particles in terms of efficient growth _{of TiO 2 in the form of nanosheets.}

The hydrothermal reaction may be performed at 150 to 250° C. for 10 to 25 hours, and the sintering may be performed at 600 to 1000° C. for 30 minutes to 2 hours. If the hydrothermal reaction is performed at a temperature lower than 150° C. or only for a time shorter than 10 hours, the nanosheets do not grow sufficiently, and when the reaction temperature is higher than 250° C. or the reaction time is longer than 25 hours, the nanosheet-shaped particles is not manufactured If the sintering temperature and time are less than the above ranges, impurities cannot be completely removed, and if the sintering temperature and time are above the above ranges, the manufactured particles may be deformed or damaged.

Hereinafter, preferred examples are presented to aid the understanding of the present invention, but the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited to the following examples.

TiO ₂ Preparation of particles

Preparation Example 1 (Comparative Preparation Example)

TiOCl ₂ 40wt% aqueous solution was diluted to 3wt% concentration in water and reacted at 60°C for 15 hours. As the reaction proceeded, the initial transparent yellow solution was changed to an opaque white dispersion as _{TiO 2 particles were generated.} The prepared TiO ₂ particles were separated by a centrifuge, washed several times with water and ethanol, and sintered at 450° C. for 30 minutes to remove unreacted solution and impurities to obtain _{TiO 2 particles having an anatase crystal phase.}

Preparation 2

_{A spherical TiO 2} (TS; TiO ₂ sphere) having a rutile crystal phase was prepared in the same manner as in Preparation Example 1, except that the dilution concentration of the TiOCl _{2 40wt% aqueous solution was changed to 6.5wt% instead of 3wt%.}

Preparation Example 3 (Comparative Preparation Example)

TiOCl _{2 Composite crystalline TiO 2} particles in which anatase and rutile crystalline phases were mixed were prepared in the same manner as in Preparation Example 1, except that the dilution concentration of the 40wt% aqueous solution was set to 11wt% instead of 3wt%.

TiO ₂ /SiO ₂ Preparation of core-shell particles (TS/SL)

Preparation 4

In order to improve the reflectance of the _{spherical TiO 2} prepared in Preparation Example 2, _{low refractive index SiO 2} was first coated as follows.

A PVP mixture was prepared by dissolving 0.2 g of polyvinylpyrrolidone (PVP) in a mixture of 50 ml of ethanol and 10 ml of distilled water, and then 0.2 g of spherical TiO ₂ particles (Preparation Example 2) were put into the prepared solution and well dispersed in TiO ₂ dispersions were prepared. It was stirred at room temperature for 24 hours so that PVP could be well bound to _{the TiO 2 particle surface.} 5 ml of aqueous ammonia and 0.2 ml of tetraethylorthosilicate (TEOS) were added, and the reaction was performed at 45° C. for 4 hours to carry out the coating reaction. The prepared TiO ₂ /SiO ₂ core-shell particles were separated by a centrifuge, washed several times using water and ethanol, and then dried.

TiO ₂ /SiO ₂ /TiO ₂ Preparation of double-coated highly reflective particles (TS/SL/TNS)

Example

To improve reflectivity, a secondary coating of high refractive TiO _{2 nanosheets on the surface of TiO 2} /SiO _{2 particles as follows.}

_{0.1 g of TiO 2} /SiO ₂ particles were added to 20 ml of isopropyl alcohol (IPA) and dispersed with an ultrasonic disperser, and 0.2 ml of diethylenetriamine (DETA) and 0.3 ml of titanium isopropoxide (TTIP) were added to the obtained dispersion. and stirred for 30 minutes, the well-mixed mixture was put into an autoclave, and hydrothermal reaction was performed at 200° C. for 20 hours. After the reaction was cooled to room temperature, the precipitate was separated by a centrifuge, washed several times using water and ethanol, dried, and sintered at 700° C. for 30 minutes to remove unreacted solution and impurities.

Particle Analysis Results

_{The SEM analysis result of the TiO 2} particles prepared in Preparation Examples 1 to 3 is shown in FIG. 2 , and the XRD analysis result is shown in FIG. 5 .

2 and 5, when the _{dilution concentration of the TiOCl 2} 40wt% aqueous solution was low, nanoparticles were prepared (Preparation Example 1), and as the dilution concentration increased, they changed to spherical particles (Preparation Example 2), When the concentration was further increased, aggregation of the particles occurred and the structure was not controlled (Preparation Example 3).

By additional experiments, it was confirmed that _{the concentration of the TiOCl 2} 40wt% aqueous solution was controlled to be spherical particles in the rutile crystal phase between about 5wt% and 9wt%, and the optimum concentration was found to be 6.5±1wt%. At a concentration of 5 wt% or less, nanoparticles of anatase crystalline phase were produced, and at a concentration of 9 wt% or more, anatase crystalline phase appeared again, becoming anatase + rutile crystalline phase, and aggregation between particles occurred severely, making it impossible to control the structure.

In addition, SEM, TEM, XRD analysis of the spherical TiO ₂ particles of Preparation Example _{2 and the TiO 2} /SiO ₂ core-shell particles of Preparation Example 4 and the double-coated highly reflective particles of _{TiO 2} /SiO ₂ /TiO _{2 nanosheets of Examples} The results are shown in FIGS. 3 to 5 . It can be seen that all of them have a spherically controlled particle shape, and as a result of TEM analysis of Preparation Example 4, the SiO ₂ coating thickness was found to be about 50 nm, and the TiO ₂ nanosheet coating was formed to have a rod-shaped vertically grown shape. can be checked

Reflectance measurement results

Visible light reflectance and near-infrared reflectance were measured for the particles of Preparation Examples 1 to 4 and Examples, and the results are shown in Table 1 below.

As shown in Table 1, the reflectance measuring results, an embodiment particles of TiO ₂ showed a higher reflectance than the TiO ₂ that the particles of Production Example 2 to form a particle with spherical commercially available, to form a secondary coated with TiO ₂ nanosheets It showed the highest reflectance.

Claims (14)

A multi-coated highly reflective particle comprising:
spherical TiO ₂ core;
_{SiO 2} shell coated on the surface of the TiO _{2 core;} and
_{A TiO 2} coating layer formed by coating _{TiO 2} in the form of a nanosheet grown vertically on the surface of the SiO _{2 shell.} According to claim 1,
The TiO ₂ core is a multi-coated highly reflective particle having a rutile crystal phase. According to claim 1,
The multi-coated highly reflective particles are multi-coated highly reflective particles having a solar reflectance of 80% or more. A method for preparing multi-coated highly reflective particles comprising the steps of:
1) a first step of preparing _{spherical TiO 2 particles;}
2) a second step of obtaining _{TiO 2} core- _{SiO 2} shell particles by first coating _{SiO 2} on the surface of the spherical TiO _{2 ;} and
3) A third step of coating _{TiO 2} in the form of vertically grown nanosheets on the surface of _{the SiO 2 shell.} 5. The method of claim 4,
In the first step, the production of the _{spherical TiO 2 particles is a method of producing multi-coated highly reflective particles comprising reacting the TiOCl 2} aqueous solution at 50 to 90° C. for 10 to 20 hours. 6. The method of claim 5,
The TiOCl ₂ aqueous solution is a concentration of 5 to 9% by weight, a method for producing a multi-coated highly reflective particles. 5. The method of claim 4,
In the second step, the first coating is a multi-coating method of producing highly reflective particles comprising reacting by adding a Si precursor compound to _{a TiO 2} dispersion obtained by dispersing _{spherical TiO 2 particles in a polymer solution.} 8. The method of claim 7,
In the polymer solution, the polymer is polyvinylpyrrolidone (PVP), poly(4-vinylpyrrolidone) (P4VP), poly(2-vinylpyrrolidone) (P2VP), and polyvinyl alcohol (PVA) Method for producing multi-coated highly reflective particles selected from. 8. The method of claim 7,
The Si precursor compound is an alkoxysilane method for producing multi-coated highly reflective particles. 8. The method of claim 7,
The reaction is a method for producing multi-coated highly reflective particles that is carried out at 40 to 60 ° C. for 2 to 5 hours. 5. The method of claim 4,
In the third step, the _{coating of TiO 2 in the form of nanosheets is the TiO 2} core- _{SiO 2} obtained in the second step after adding a Ti precursor compound to the powdered solution of the shell particles, and then, through a hydrothermal reaction, the TiO ₂ The core-SiO _{2 TiO 2} in the form of a nanosheet is vertically grown and coated on the surface of the shell particle, A method of making multi-coated highly reflective particles comprising sintering. 12. The method of claim 11,
The Ti precursor compound is titanium butoxide (TBT), titanium isopropoxide (TTIP), and titanium tetrachloride (TiCl ₄ ) Method for preparing multi-coated highly reflective particles. 12. The method of claim 11,
When the Ti precursor compound is added, a method for producing multi-coated highly reflective particles by further adding diethylenetriamine. 12. The method of claim 11,
The hydrothermal reaction is performed at 150 to 250 ° C. for 10 to 25 hours, and the sintering is performed at 600 to 1000 ° C. for 30 minutes to 2 hours.

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