US20160068749A1

US20160068749A1 - Composite, composition containing the same, and apparatus

Info

Publication number: US20160068749A1
Application number: US14/442,083
Authority: US
Inventors: Doo Hyo Kwon; Jeong Og Choi; Oh Kwan Kwon
Original assignee: LMS Co Ltd
Current assignee: LMS Co Ltd
Priority date: 2012-11-09
Filing date: 2013-11-07
Publication date: 2016-03-10
Also published as: US9884992B2; KR20140060449A; KR20140060218A; KR101503290B1; KR101426448B1; US20150301257A1; KR20140060215A; KR20140060222A; KR101525770B1; KR101575143B1; KR101426449B1; KR101396871B1; KR20140144167A; US20150285444A1; KR20140060216A

Abstract

A composite includes at least one quantum dot, and a wax-based compound that covers a surface of the quantum dot. The composite has remarkable quantum efficiency, a small variation in emission peak even when dispersed in a resin, good dispersion stability, good ultraviolet light stability and good heat/moisture stability.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 10-2012-0126925 filed on Nov. 9, 2012 and Korean Patent Application No. 10-2013-0079501 filed on Jul. 8, 2013, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which are incorporated by reference in their entirety.

BACKGROUND

1. Field of the Invention
The present invention relates to a composite, a composition containing the same, and an apparatus including the same, and more particularly, to a composite having improved dispersibility and emission properties, a composition containing the same, and an apparatus including the same.
2. Discussion of Related Art
A quantum dot is a material having a crystalline structure with several to tens nanometer size, and is constituted by hundreds to thousands atoms. Since the quantum dot is very small, a quantum confinement effect is exhibited. The quantum confinement effect is a phenomenon in which a band gap of a material is increased when the material is reduced to a nanosize or less. Accordingly, when light having a wavelength with energy larger than the band gap of the quantum dot enters the quantum dot, the quantum dot absorbs the light to become an excited state, and becomes a ground state while emitting light having a specific wavelength. The wavelength of the emitted light has a value corresponding to the band gap. Since emission properties due to the quantum confinement effect are varied according to a size and a composition of the quantum dot, the quantum dot is various used in various kinds of light emitting diodes and electronic devices by adjusting the size and composition thereof.
In general, when a plurality of quantum dots are dispersed in a solvent or a resin, the quantum dots may be easily aggregated to decrease quantum efficiency. In addition, a quantum dot formed of a metal is very vulnerable to moisture, and thus may be easily oxidized by moisture in air, decreasing quantum efficiency. As described above, since the quantum dot has low dispersibility with respect to a solvent or a resin and low stability with respect to moisture, heat or light, the quantum dot cannot be easily stored.
In addition, even when a light emitting diode is manufactured using the quantum dot in order to improve color reproducibility, since the stability of the quantum dot with respect to moisture, heat or light is low, the quantum dot may be easily damaged as a use time of the light emitting diode is increased. That is, as the quantum dot is applied to the light emitting diode, the lifespan of the light emitting diode is reduced.

SUMMARY OF THE INVENTION

The present invention is directed to provide a composite capable of improving dispersibility, stability with respect to heat, light and moisture, and quantum efficiency.
The present invention is also directed to provide a composition including the composite.
The present invention is also directed to provide an apparatus including a coating layer or film formed of the composition.
A composite according to an embodiment of the present invention includes at least one quantum dot, and wax-based compound that covers a surface of the quantum dot.
In the embodiment, the wax-based compound may encapsulate the quantum dot. Here, the wax-based compound may encapsulate the one quantum dot. Unlike this, as two or more quantum dots may be disposed to be spaced apart from each other in an aggregating agent formed by the wax-based compound, the quantum dots may be encapsulated by the wax-based compound.
In the embodiment, a molecular weight of the wax-based compound may be 1,000 or more and 20,000 or less.
In the embodiment, a melting point of the wax-based compound may be 80° C. or more and 200° C. or less.
In the embodiment, the wax-based compound may include a polyethylene-based wax, a polypropylene-based wax or an amide-based wax.
In the embodiment, the wax-based compound may have an acid value of 1 mg KOH/g to 200 mg KOH/g.
In the embodiment, the wax-based compound may have a density of 0.95 g/cm3 or more.
A composition according to an embodiment of the present invention includes a solvent and a composite. The composite may be dispersed in the solvent, and may include at least one quantum dot, and wax-based compound that covers the quantum dot.
A composition according to another embodiment of the present invention includes a resin and a composite. The composite is dispersed in the resin, and includes at least one quantum dot and wax-based compound that covers the quantum dot. Here, the resin may include a silicon-based resin, an epoxy-based resin or an acryl-based resin.
A coating layer or film according to an embodiment of the present invention is manufactured using the composition.
According to the present invention, even when the plurality of composites including quantum dots covered with the wax-based compound are dispersed in the solvent or resin, the composites can be uniformly dispersed in the solvent or resin without aggregation thereof. In addition, the composites can be maintained in a uniformly dispersed state for a long time.
In addition, as the wax-based compound protects the quantum dot, it is possible to prevent the quantum dot from being damaged due to moisture, light, heat, or the like, and improve stability of the composite with respect to environments such as a temperature, humidity, ultraviolet light, and so on.
Further, the wax-based compound can constitute one composite such that the plurality of quantum dots can be respectively encapsulated without aggregation thereof.
Accordingly, the composite having better quantum efficiency than each of the quantum dots can be manufactured to be used in various fields. In particular, it is possible to prevent a decrease in lifespan thereof while improving color reproducibility, color rendering index, and so on, using the composites according to the present invention in the light emitting diode or the electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:

FIGS. 1 a and 1 b are conceptual views for describing a composite according to an embodiment of the present invention;

FIG. 1 c is a conceptual view for describing a composite according to another embodiment of the present invention;

FIG. 2 is a flow chart for describing a method of manufacturing a composite according to an embodiment of the present invention and a composition including the same; and

FIGS. 3 to 5 are cross-sectional views for describing an apparatus according to another embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may be variously modified and may have various shapes, and specific embodiments will be shown in the drawings and described below in detail. However, the present invention is not limited to the specific disclosures but all changes, equivalents and substitutions will be understood to fall within the spirit and the technical scope of the present invention. In the accompanying drawings, dimensions of structures are exaggerated or deemphasized for the purpose of clarity of the present invention.
While terms such as first, second, or the like, may be used to describe various components, the components are not limited by the terms. The terms are used only to distinguish one component from another component. For example, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component without departing from the spirit of the present invention.
The terms used in the application are not intended to limit the present invention but are merely used to describe specific embodiments. A singular form may include a plural referent unless the context specifically indicates otherwise. In the application, when an element is referred to as “comprising,” “including” or “having” something, it does not preclude other features, steps, operations, components, parts and/or combinations, but may further include other features, steps, operations, components, parts and/or combinations unless the context clearly indicates otherwise.
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Although preferred methods, techniques, devices, and materials are described, any methods, techniques, devices, or materials similar or equivalent to those described herein may be used in the practice or testing of the present invention. Structures described herein are to be understood also to refer to functional equivalents of such structures.
FIGS. 1 a and 1 b are conceptual views for describing a composite according to an embodiment of the present invention.
Referring to FIGS. 1 a and 1 b, a composite 101 includes a quantum dot 111 and a wax-based compound 130. In the present invention, “a wax-based compound” is defined as a compound maintained in a solid state at room temperature and having a melting point higher than room temperature. That is, in the present invention, unless defined otherwise, “wax” is in a solid state. “Room temperature” is defined as about 15° C. to about 25° C. The melting point of the wax-based compound 130 may be about 80° C. to about 200° C.
While the two quantum dots 111 are shown in FIGS. 1 a and 1 b to describe a relation between neighboring quantum dots, since the two quantum dots 111 are substantially the same, only one quantum dot will be described, and overlapping description thereof will be omitted.
The quantum dot 111 is a particle having a crystalline structure with several to tens nanometer size, and is constituted by hundreds to thousands atoms. Since the quantum dot 111 has a nanoscale size, a quantum confinement effect is exhibited in the quantum dot 111. The quantum confinement effect is a phenomenon in which a band gap of a particle is discontinuously quantized when a size of the particle is tens nanometer or less, and the band gap is increased as the size of the particle is reduced. Accordingly, when light having larger energy than the band gap enters the quantum dot 111, the quantum dot 111 absorbs the entered light to become an excited state, and the quantum dot in the excited state becomes a ground state to emit light having a specific wavelength corresponding to the band gap. The band gap of the quantum dot 111 may be adjusted by varying a size, a composition, or the like, of the quantum dot 111.
In the present invention, the structure of the quantum dot 111 is not particularly limited. For example, the quantum dot 111 may be a single structure formed of only a core, a core-single shell structure formed of a core and a single-layered shell, or a core-multi-shell structure formed of a core and a multi-layered shell. As an example of a material that forms the core or the shell, a group II-VI compound semiconductor nano crystal such as CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, or the like, a group III-V compound semiconductor nano crystal such as GaN, GaP, GaAs, InP, InAs, or the like, or a mixture thereof. For example, the quantum dot 111 may have a CdSe/ZnS (core/shell) structure having a core including CdSe and a shell including ZnS. As another example, the quantum dot 111 may have an InP/ZnS (core/shell) structure having a core including InP and a shell including ZnS.
Here, the quantum dot 111 may include a ligand SC bonded to a surface of a center particle formed of the above-mentioned compounds. The ligand SC can prevent the neighboring quantum dots 111 from being aggregated and quenched. The ligand SC may include a hydrophobic compound. As an example of the ligand SC, an amine-based compound having an alkyl group or an alkenyl group with 6 to 30 carbon atoms, a carboxylic acid compound having an alkyl group or an alkenyl group with 6 to 30 carbon atoms, or the like, may be provided. The quantum dot 111 shown in FIG. 1 a may include the ligand SC.
The wax-based compound 130 covers the quantum dot 111. The wax-based compound 130 may cover an entire surface of the quantum dot 111 to encapsulate the quantum dot 111. Here, the wax-based compound 130 may form a capsule layer having a predetermined thickness on a surface of the quantum dot 111. As the wax-based compound 130 covers the quantum dot 111, the quantum dot 111 can be prevented from being damaged due to moisture, heat, light, or the like, caused by environments.
A molecular weight (MW) of the wax-based compound 130 may be about 1,000 to 20,000. The molecular weight is a numerical average molecular weight converted by polystyrene. For example, when the molecular weight of the wax-based compound 130 is about 1,000 or less, it is difficult for the wax-based compound 130 to encapsulate the quantum dot 111 because the wax-based compound 130 cannot have a property of wax present in a solid state at room temperature. In addition, when the molecular weight of the wax-based compound 130 exceeds about 20,000, since a size (an average diameter) of recrystallization of the wax-based compound 130 is hundreds μm or more, even when the composite is manufactured using the recrystallization, the wax-based compound 130 cannot be easily dispersed in a solvent or resin. Further, when the molecular weight of the wax-based compound 130 exceeds about 20,000, since the wax-based compound 130 may be liquefied at a temperature of higher than about 200° C., the quantum dot 111 may be damaged in a process of encapsulating the quantum dot 111.
A synthetic wax may be used as the wax-based compound 130. The wax-based compound 130 may be polymer, copolymer or oligomer. The wax-based compound 130 may include a polyethylene-based wax, a polypropylene-based wax or an amide-based wax.
When the wax-based compound 130 is the polyethylene-based wax or the polypropylene-based wax, the wax-based compound 130 may include at least one of monomers shown in the following chemical formulae 1 to 7.
In the chemical formulae 1 to 7, R₁, R₃, R₅and R₇may independently be a single bond or an alkylene group (*—(CH2)_x-*, x is an integer of 1 to 10) with 1 to 10 carbon atoms, R₂, R₄, R₆and R₈may independently be a hydrogen or an alkyl group with 1 to 10 carbon atoms, and R_a, R_b, R_c, R_d, R_e, R_fand R_gmay independently be a hydrogen or an alkyl group with 1 to 3 carbon atoms.
In a specific example, when R₂of the chemical formula 1 is the hydrogen, the monomer of the chemical formula 1 may include a carboxy group, and unlike this, when R₂of the chemical formula 1 is an alkyl group having 1 to 10 carbon atoms, the monomer of the chemical formula 1 may include an ester group.
When R₄of the chemical formula 2 is the hydrogen, the monomer of the chemical formula 2 may include an aldehyde group, and unlike this, when R₄of the chemical formula 2 is an alkyl group having 1 to 10 carbon atoms, the monomer of the chemical formula 2 may include a ketone group.
When R₆of the chemical formula 3 is the hydrogen, the monomer of the chemical formula 3 may include a hydroxy group, and unlike this, when R₆of the chemical formula 3 is an alkyl group having 1 to 10 carbon atoms, the monomer of the chemical formula 3 may include an ether group.
When all of R_a, R_b, R_c, R_d, R_e, R_fand R_gof the chemical formula 1 to 7 are hydrogen, the wax-based compound may be a polyethylene-based wax. For example, the polyethylene-based wax may be a polyethylene wax (a PE wax) including only a monomer of the chemical formula 7 in which R_gis hydrogen. Unlike this, the polyethylene-based wax may be the polyethylene wax further including at least one of oxygen-containing monomers of the chemical formula 1 to 6 in which R_a, R_b, R_c, R_d, R_eand R_fare hydrogen, besides the monomer of the chemical formula 7 in which R_gis hydrogen. For example, the polyethylene-based wax further including the at least one of the oxygen-containing monomers may include an oxidized polyethylene wax (an oxidized PE wax) which is an oxide of the polyethylene, an ethylene-acrylic acid copolymer, an ethylene-vinyl acetate copolymer, an ethylene-maleic anhydride copolymer, and so on.
In addition, when R_a, R_b, R_c, R_d, R_e, R_fand R_gof the chemical formula 1 to 7 are independently a methyl group having 1 carbon atom, the wax-based compound may be the polypropylene-based wax. For example, the polypropylene-based wax may be a polypropylene wax (a PP wax) including only a monomer of the chemical formula 7 in which R_gis a methyl group. Unlike this, the polypropylene-based wax may be a polypropylene wax further including at least one of oxygen-containing monomers of the chemical formulae 1 to 6 in which R_a, R_b, R_c, R_d, R_eand R_fare hydrogen, besides the monomer of the chemical formula 7 in which R_gis a methyl group. For example, the polypropylene-based wax further including the at least one of the oxygen-containing monomers may include a propylene-maleic anhydride copolymer or the like.
A main chain of the amide-based wax includes an amide bond (—CONH—). That is, the Amide-based wax may be a polymer, copolymer or oligomer including a monomer including an amide bond. The monomer of the amide-based wax may have 1 to 10 carbon atoms. The amide-based wax may further include one or more of oxygen-containing monomers among the monomers represented by the chemical formulae 1 to 6.
When the wax-based compound 130 includes at least one oxygen-containing monomer of the monomers represented by the chemical formulae 1 to 6, the quantum dot 111 can be stably encapsulated in comparison with the case in which only the monomer represented by the chemical formula 7 is included. That is, while the PE wax or the PP wax randomly encapsulates the surface of the quantum dot 111, interaction between the wax-based compound 130 and a metal that constitutes the quantum dot 111 is strengthened by polarity of oxygen included in the oxygen-containing monomer. Accordingly, when the wax-based compound 130 includes at least one oxygen-containing monomer of the monomers represented by the chemical formulae 1 to 6, the wax-based compound 130 can stably encapsulate the quantum dot 111. Even in the oxygen-containing monomer, the monomer represented by the chemical formula 1, in particular, the carboxy group is most advantageous to encapsulate the quantum dot 111 because the interaction between the wax-based compound 130 and the quantum dot 111 is strong. Accordingly, the wax-based compound 130 according to the present invention may include at least a carboxy group serving as a substituent.
In addition, in the case in which the wax-based compound 130 including at least one oxygen-containing monomer of the monomers represented by the chemical formulae 1 to 6 is used, in the process of manufacturing the composite 101, when the plurality of quantum dots 111 react with the solution in which the wax-based compound 130 is dissolved, a maximum amount of the quantum dots 111 can be encapsulated by the wax-based compound 130. That is, provided that the amount of the quantum dot 111 added to the solution in which the PE wax or the PP wax is added is “1” and the amount of the encapsulated quantum dot 111 thereby is “A”, the “A” has a value of larger than 0 and smaller than 1. In comparison therewith, provided that the amount of the quantum dot 111 added to the solution in which the wax-based compound 130 including the oxygen-containing monomer is dissolved is “1” and the amount of the encapsulated quantum dot 111 thereby is “B”, the “B” has a value larger than the “A.”
The oxygen-containing wax-based compound serving as the wax-based compound 130 including oxygen-containing monomers represented by the chemical formulae 1 to 6 may be manufactured by oxidizing polyethylene or polypropylene serving as a base material. Unlike this, the oxygen-containing wax-based compound may be manufactured by polymerizing single monomers or copolymerizing two or more different monomers.
For example, since crystallizability of recrystallization formed when the PE wax including ethylene serving as the monomer is recrystallized is good, the PE wax can be easily used for encapsulation of the quantum dot 111 without difficult in control. However, in consideration of interaction between the wax-based compound 130 and the quantum dot 111, even in the polyethylene-based wax, an oxygen-containing PE wax can more stably encapsulate the quantum dot 111 than the PE wax.
The wax-based compound 130 may have an acid value of about 1 mg KOH/g to about 200 mg KOH/g. In the present invention, the “acid value” of the wax-based compound 130 is a number of mg of potassium hydroxide (KOH) required for neutralization of the wax-based compound 130 of 1 g. When the wax-based compound 130 includes a carboxy group, the wax-based compound 130 may have an acid value of about 1 mg KOH/g or more. That is, as the acid value is increased, the carboxy group included in the wax-based compound 130 is increased. When the acid value of the wax-based compound 130 is less than about 1 mg KOH/g, since an amount of the carboxy group that interacts with the quantum dot 111 is very small, interaction between the wax-based compound 130 and the quantum dot 111 is similar to that of the case in which the PE wax or the PP wax is used. In addition, when the acid value of the wax-based compound 130 exceeds about 200 mg KOH/g, the ligand SC may be deteriorated due to the carboxy group to oxidize the surface of the quantum dot 111. Even when the quantum dot 111 is encapsulated due to oxidation of the quantum dot 111, quantum efficiency may be decreased. Accordingly, the wax-based compound 130 may have an acid value of about 1 mg KOH/g to about 200 mg KOH/g. More preferably, the wax-based compound 130 may have an acid value of about 5 mg KOH/g to about 50 mg KOH/g.
The acid value of the wax-based compound 130 may be measured according to ASTM 1386. For example, after the wax-based compound 130 of about 2 g is quantified as a sample and inserted into a triangular flask. Next, 40 ml of xylene is added to the sample, the temperature is increased, and when the sample-containing solution becomes transparent, and 2 to 3 drops of a phenolphthalein solution are added. Then, the acid value can be finally calculated when a KOH solution of about 0.1N is dropped and a color of the solution is maintained for about 10 seconds. The acid value can be calculated according to the following equation.
Acid value=(A×N×56.1)/B [Equation 1]
In Equation 1, “A” represents an amount (unit: ml) of KOH used for dropping the sample, “N” represents a normal concentration (unit: N) of KOH, and “B” represents an amount (unit: g) of the sample.
Meanwhile, the wax-based compound 130 may have a high density of about 0.95 g/cm3 or more. When the wax-based compound 130 has a high density, since a melting point of the wax-based compound 130 is relatively higher than a low density wax having a low density of less than about 0.95 g/cm3, heat resistance of the composite 101 including the wax-based compound 130 can be improved. In addition, when the wax-based compound 130 has a high density, since crystallizability of the recrystallization of the wax-based compound 130 is better than the low density wax, the quantum dot 111 can be stably encapsulated.
For example, the PE wax may be classified into a high density PE wax (HDPE wax) and a low density PE wax (LDPE wax) according to the above-mentioned criteria. That is, the HDPE wax has a density of about 0.95 g/cm3 or more. For example, the density of the HDPE wax may be about 1.20 g/cm3 or less. The HDPE wax may have a melting point of about 120° C. to about 200° C. The LDPE wax may have a density of less than about 0.95 g/cm3. The melting point of the LDPE wax may be about 80° C. to about 110° C. Accordingly, when the PE wax is used as the wax-based compound 130, the HDPE wax can encapsulate the quantum dot 111 more stably and uniformly than the LDPE wax.
Contents of the monomers included in the wax-based compound 130 and represented by the chemical formulae 1 to 7 may be varied according to the molecular weight of the wax-based compound 130 and the acid value of the wax-based compound 130.
Referring to FIGS. 1 a and 1 b again, a diameter d1 of the composite 101 may be about 10 nm to 50 nm. The diameter d1 of the composite 101 may be defined as a value (a hydrodynamic diameter) measured by a dynamic light scattering (DLS) method of calculating a diffusion coefficient using a Stokes-Einstein equation.
FIG. 1 c is a conceptual view for describing a composite according to another embodiment of the present invention.
Referring to FIG. 1 c, a composite 102 includes at least two quantum dots 112 and 114 and a wax-based compound 130.
In the quantum dots 112 and 114 included in the composite 102, for the purpose of convenience, a first quantum dot is designated by reference numeral 112, and a second quantum dot is designated by reference numeral 114. Since each of the first and second quantum dots 112 and 114 is substantially the same as the quantum dot 111 described with reference to FIGS. 1 a and 1 b, detailed overlapping description thereof will be omitted.
As the wax-based compound 130 covers the first and second quantum dots 112 and 114, the first and second quantum dots 112 and 114 can be prevented from being aggregated. That is, the wax-based compound 130 can form one aggregation particle such that the first and second quantum dots 112 and 114 can be individually encapsulated while being not aggregated. The aggregation particle in which the first and second quantum dots 112 and 114 are disposed may be defined as “one composite 102.” In the composite 102, the first and second quantum dots 112 and 114 are disposed in the one aggregation particle formed of the wax-based compound 130. For example, the number of quantum dots disposed in the one aggregation particle may be tens to tens of millions.
A diameter d2 of the composite 102 may be about 5 nm to about 50 μm. In consideration of dispersibility with respect to the resin (to be described below), the diameter d2 of the composite 102 may be about 0.5 μm to about 10 μm. The diameter d2 of the composite 102 may be varied according to a recrystallization speed (a cooling speed) in the process of manufacturing the composite 102.
Since the wax-based compound 130 is substantially the same as the wax-based compound described with reference to FIGS. 1 a and 1 b, detailed overlapping description thereof will be omitted.
In the process of manufacturing the quantum dot covered by the wax-based compound 130, the composite 101 described with reference to FIGS. 1 a and 1 b may be formed, or the composite 102 described with reference to FIG. 1 c may be formed. In the process, the composite 101 described with reference to FIGS. 1 a and 1 b and the composite 102 described with reference to FIG. 1 c may be simultaneously manufactured.
Hereinafter, a method of manufacturing the composites 101 and 102 and the composition including the composites 101 and 102 according to the present invention will be described in detail with reference to FIG. 2.
FIG. 2 is a flow chart for describing a method of manufacturing a composite according to an embodiment of the present invention.
Referring to FIG. 2, a wax powder is added to an organic solvent (step S210).
The organic solvent may include toluene. The wax powder is a solid material formed of a wax-based compound, the wax-based compound that constitutes the wax powder is substantially the same as those described with reference to FIGS. 1 a to 1 c, and thus, detailed overlapping description thereof will be omitted. Instead of the wax powder, a solid wax pellet may be added to the organic solvent.
Next, the wax powder is dissolved (step S220).
The wax powder or the wax pellet can be dissolved by heating the organic solvent. The organic solvent is heated to a temperature higher than the melting point of the wax powder or the wax pellet. For example, the organic solvent may be heated to about 200° C. to 220° C. Accordingly, the wax solution in which the wax powder is dissolved in the organic solvent can be manufactured.
Next, the quantum dots are mixed with the wax solution (step S230).
When the quantum dots are mixed with the wax solution, the quantum dots are dispersed in the wax solution. Here, the quantum dots can be easily dispersed in the wax solution by the ligand of the quantum dots without aggregation. Since the quantum dot is substantially the same as the quantum dot described with reference to FIGS. 1 a to 1 c, detailed overlapping description thereof will be omitted.
Next, the wax solution in which the quantum dots are dispersed is cooled (step S240).
The temperature of the wax solution in which the quantum dots are dispersed can be cooled to room temperature to recrystallize the dissolved wax-based compound. The wax solution in which the quantum dots are dispersed can adjust a recrystallization speed (a cooling speed) by slowly or rapidly cooling the wax solution to room temperature. Here, when the recrystallization speed is high, i.e., when the temperature of the wax solution is rapidly lowered, a size of the aggregation particle formed by the wax-based compound can be reduced. On the other hand, when the temperature of the wax solution is gradually lowered, the size of the aggregation particle can be increased.
The recrystallized wax-based compound can encapsulate the quantum dots. Here, according to the recrystallization speed, as described with reference to FIGS. 1 a and 1 b, the wax-based compound can encapsulate one quantum dot to form the composite 101, and as shown in FIG. 1 c, the wax-based compound can encapsulate the plurality of quantum dots to form the composite 102.
Accordingly, the composites 101 and 102 according to the present invention can be manufactured.
The composites 101 and 102 according to the present invention may be stored and used in a powder phase by removing the organic solvent. On the other hand, the composites 101 and 102 may be stored and used while being dispersed in the organic solvent. The composites 101 and 102 may be stably stored and used in a powder phase without being affected by moisture or may be uniformly dispersed, stored and used without aggregation of the composites 101 and 102 in the organic solvent by the wax-based compound 130 that encapsulate the quantum dots 111, 112 and 114.
In another embodiment, the composition including the composites 101 and 102 may include a resin. The resin may be in a liquid phase. On the other hand, even when the resin is a solid phase as it is, the resin can be dissolved in the solvent. Here, the composites 101 and 102 can be dispersed in the solution including the resin and the solvent. At least one of the composite 101 shown in FIGS. 1 a and 1 b and the composite 102 shown in FIG. 1 c may be included in the composition including the resin. As a specific example of the resin, a vinyl siloxane-based resin, an epoxy siloxane resin, polydimethylsiloxane (PDMS), thermoplastic silicone vulcanizate (TPSiV), thermoplastic silicone polycarbonate-urethane (TSPCU), or the like, may be provided. The composition may further include a cross-linking agent, a catalyst, an initiator, and so on, in addition to the resin.
For example, the composition may include about 0.001 parts by weight to 10 parts by weight of the composites 101 and 102, about 5 parts by weight to about 60 parts by weight of hydride siloxane serving as the cross-linking agent, and about 0.01 parts by weight to about 0.5 parts by weight of platinum catalyst, with respect to 100 parts by weight of vinyl siloxane-based compound serving as the resin.
On the other hand, the composition including the composites 101 and 102 may include at least one monomer and initiator. The monomer may include an acrylate-based compound, an epoxy-based compound, a siloxane-based compound, and so on. Each of these may be solely used or two or more of these may be combined and used. At least one of the composite 101 shown in FIGS. 1 a and 1 b and the composite 102 shown in FIG. 1 c may be included in the composition. When the composition includes the monomer, the monomers may be polymerized to form a cured material, and the composites 101 and 102 may be dispersed in the cured material.
The present invention provides a coating layer or a film formed of the composition. The coating layer or film may be formed by cross-linking the resin of the composition or drying the composition. For example, the composition may be cured using light or heat. In the case of the light curing, ultraviolet light may be used. On the other hand, the coating layer or film may be formed by polymerizing the monomer of the composition. The method of forming the coating layer or film is not particularly limited.
The coating layer or film may have a shape in which the composites 101 and 102 are dispersed in a matrix structure formed by the resin.
In addition, the present invention provides an apparatus including the coating layer or film. The scope of the apparatus is not particularly limited, and for example, the apparatus may be a lighting device, or a display device.
According to the present invention as described above, even when a plurality of composites 101 and 102 including the quantum dots 111, 112 and 114 covered by the wax-based compound 130 are dispersed in the solvent or resin, the composites 101 and 102 can be uniformly dispersed in the solvent or resin without aggregation. In addition, the composites 101 and 102 may be maintained in a uniformly dispersed state for a long time.
In addition, as the wax-based compound 130 protects the quantum dots 111, 112 and 114, the quantum dot can be prevented from being damaged due to moisture, light, heat, and so on, and stability of the composites 101 and 102 with respect to environments can be improved.
Further, the wax-based compound 130 may constitute one composite 101 or 102 such that the plurality of quantum dots 111 can be respectively encapsulated without aggregation. Accordingly, the composite having better quantum efficiency than each of the quantum dots can be manufactured and used in various fields.

Example 1

After 20 mg of a wax-based compound was mixed with toluene 1 ml, a temperature thereof was increased to about 130° C., and the wax-based compound was dissolved to manufacturing a wax solution. About 20 mg of a solution in which Nanodot-HE-606 (trade name, QD solution Co. Ltd., Korea) serving as a CdSe-based red quantum dot was dispersed in toluene 1 ml was mixed with the wax solution, and then, the solution was cooled to room temperature. Next, the toluene was removed using an evaporator, and then, a composite according to Example 1 in a powder phase was manufactured.
Licowax PED 136 wax (trade name, Clariant AG, Swiss) having an acid value of about 50 mg KOH/g serving as an oxidized high density polyethylene wax (oxidized HDPE wax) was used as the wax-based compound.

Example 2

Except for the kind of the wax-based compound, a composite according to Example 2 of the present invention was manufactured through substantially the same method as the method of manufacturing the composite in Example 1. In manufacture of the composite according to Embodiment 2, Licowax PED 191 wax (trade name, Clariant AG, Swiss) was used as an oxidized high density polyethylene wax (oxidized HDPE Wax) having an acid value of about 7 mg KOH/g.

Example 3

Except for the kind of the wax-based compound, a composite according to Example 3 of the present invention was manufactured through substantially the same method as the method of manufacturing the composite in Example 1. In manufacture of the composite according to Example 3, L-C 301E wax (trade name, Lion Chemtech Co. Ltd., Korea) was used as an oxidized low density polyethylene wax (oxidized LDPE wax) having an acid value of about 16 mg KOH/g.

Example 4

Except for the kind of the wax-based compound, a composite according to Example 4 of the present invention was manufactured through the same method as the method of manufacturing the composite in Example 1. In manufacture of the composite according to Example 4, Escor™ 5000 ExCo wax (trade name, ExxonMobil Chemical Corporation, US) was used as an ethylene acrylic acid copolymer having an acid value of about 75 mg KOH/g.

Example 5

Except for the kind of the wax-based compound, a composite according to Example 5 of the present invention was manufactured through substantially the same method as the method of manufacturing the composite in Example 1. In manufacture of the composite according to Example 5, EVATANE 18-150 wax (trade name, ARKEMA SA., France) was used as an ethylene vinyl acetate copolymer.

Example 6

Except for the kind of the wax-based compound, a composite according to Example 6 of the present invention was manufactured through substantially the same method as the method of manufacturing the composite according to Example 1. In manufacture of the composite according to Example 6, Licomont AR 504 wax (trade name, Clariant AG, Swiss) was used as a polypropylene wax having an acid value of about 40 mg KOH/g to about 45 mg KOH/g.

Example 7

Except for the kind of the wax-based compound, a composite according to Example 7 was manufactured through substantially the same method as the method of manufacturing the composite according to Example 1. In manufacture of the composite according to Example 7, L-C 104N wax (trade name, Lion Chemtech Co. Ltd., Korea) was used as a non-oxidized high density polyethylene wax (non-oxidized HDPE wax) having an acid value of 0 mg KOH/g.

Example 8

Except for the kind of the wax-based compound, a composite according to Example 8 was manufactured through substantially the same method as the method of manufacturing the composite according to Example 1. In manufacture of the composite according to Example 8, Escor™ 5100 ExCo wax (trade name, ExxonMobil Chemical Corporation, US) was used as an ethylene acrylic acid copolymer having an acid value of about 180 mg KOH/g.

Comparative Example 1

Nanodot-HE-606 (trade name, QD solution Co. Ltd., Korea) was prepared as a CdSe-based red quantum dot.

Experiment Example 1

Composite Property Estimation 1

The composites according to Examples 1 to 8 of the present invention were mixed with toluene to manufacture measurement samples 1 to 8.
In the measurement sample 1, quantum efficiency (quantum yield, QY) and emission wavelength of Example 1 of the present invention were measured using C9920-02 (trade name, HAMAMATSU Photonics K. K., Japan) serving as an absolute quantum efficiency measurement device.
Using the same method, in the measurement samples 2 to 8, quantum efficiency and an emission wavelength of the composites according to Examples 2 to 8 of the present invention were measured. The results are shown in Table 1.
In addition, the quantum dot according to Comparative example 1 was mixed with toluene to manufacture a comparative sample 1. Quantum efficiency and an emission wavelength of the quantum dot according to Comparative example 1 were measured using the comparative sample 1. The results are shown in Table 1.

TABLE 1

	Quantum	Emission
Classification	efficiency	wavelength
(in toluene)	(QY, %)	(nm)

Measurement sample 1	83.8	606.4
Measurement sample 2	83.1	606.7
Measurement sample 3	83.0	606.5
Measurement sample 4	82.7	606.3
Measurement sample 5	82.9	606.1
Measurement sample 6	82.6	606.9
Measurement sample 7	82.9	606.3
Measurement sample 8	82.5	606.8
Comparative sample 1	82.3	606.0

Referring to the results of the measurement samples 1 to 6 of Table 1, it will be appreciated that quantum efficiency of the composites according to Examples 1 to 6, which were dispersed in toluene, were 83.8%, 83.1%, 83.0%, 82.7%, 82.9% and 82.6%. In addition, like the results of the measurement samples 7 and 8, it will be appreciated that quantum efficiency of the composites according to Examples 7 and 8, which were dispersed in toluene, were 82.9% and 82.5%.
On the other hand, it will be appreciated that quantum efficiency of the quantum dot according to Comparative example 1, which was dispersed in toluene, was 82.3%.
According to the results of the quantum efficiency according to Examples 1 to 8 and Comparative example 1 of the present invention, it will be appreciated that the quantum efficiency of the composites according to Examples 1 to 8 of the present invention, which were dispersed in toluene, were higher than the quantum efficiency of the quantum dot of Comparative example 1. That is, it will be appreciated that, even when the composite is manufactured using the quantum dot, the quantum efficiency of the composite is not decreased to be lower than the quantum efficiency of the quantum dot.
In addition, it will be appreciated that, in a state in which the composition is dispersed in the toluene like the measurement samples 1 to 6, the emission wavelengths of the composites according to Examples 1 to 6 are 606.4 nm, 606.7 nm, 606.5 nm, 606.3 nm, 606.1 nm and 606.9 nm, and the emission wavelengths of the composites according to Examples 7 and 8 are 606.3 nm and 606.8 nm.
Meanwhile, it will be appreciated that the emission wavelength of the quantum dot according to Comparative example 1 is 606.0 nm.
Accordingly, it will be appreciated that, when encapsulated by the wax-based compound like Examples 1 to 8 of the present invention, the emission wavelength of the composite dispersed in the toluene is larger than the emission wavelength of the quantum dot. However, it will be appreciated that, while the emission wavelength of the composite according to the present invention is larger than the emission wavelength of the quantum dot and a difference therebetween is about 1 nm or less, the emission wavelength of the composite in the state dispersed in the toluene is substantially the same as the emission wavelength of the quantum dot. That is, it will be appreciated that, even when the quantum dot is encapsulated by the wax-based compound, there is little shaft in the emission wavelength in comparison with the emission wavelength of the quantum dot.

Experiment Example 2

Composite Property Estimation 2

The composites according to Examples 1 to 8 of the present invention were mixed with a B kit in OE-6630 A/B kit (trade name, Dow Corning Silicon Corporation, US) serving as a siloxane resin to a concentration having an optical density (OD) of 0.1 to manufacture measurement samples 9 to 16.
In addition, the quantum dot according to Comparative example 1 was mixed with OE-6630 to a concentration having the OD of 0.1 to manufacture a comparative sample 2.
In the measurement sample 9 to 16 and the comparative sample 2, quantum efficiency and an emission wavelength were measured using C9920-02 (trade name, HAMAMATSU Photonics K. K., Japan) serving as an absolute quantum efficiency measurement device. The results are shown in Table 2.

TABLE 2

	Quantum	Emission
Classification	efficiency	wavelength
(in OE-6630)	(%)	(nm)

Measurement sample 9	87.3	609.5
Measurement sample 10	86.5	609.7
Measurement sample 11	84.9	610.6
Measurement sample 12	85.7	610.3
Measurement sample 13	83.5	611.1
Measurement sample 14	82.9	612.4
Measurement sample 15	75.0	614.3
Measurement sample 16	74.6	612.6
Comparative sample 2	73.2	614.5

Referring to Table 2, it will be appreciated that, in a state in which the composition is dispersed in a siloxane resin like measurement samples 9 to 16, the quantum efficiency of the composites according to Examples 1 to 6 are 87.3%, 86.5%, 84.9%, 85.7%, 83.5% and 82.9%, and the quantum efficiency of the composites according to Examples 7 and 8 are 75.0% and 74.6%.
Referring to the results of the comparative sample 2, it will be appreciated that the quantum efficiency of the quantum dot according to Comparative example 1 in a state dispersed in siloxane resin is 73.2%.
According thereto, it will be appreciated that, even when the composite including the quantum dot encapsulated by the wax-based compound is dispersed in a siloxane resin like Examples 1 to 8 of the present invention, higher quantum efficiency can be exhibited in comparison with the quantum dot dispersed in the siloxane resin.
Comparing Table 2 with data of Table 1, it will be appreciated that the quantum efficiency of the measurement sample 9 in a state in which the composite is dispersed in the siloxane resin is 87.3%, and a difference from the quantum efficiency 83.8% of the measurement sample 1 in a state in which the composite is dispersed in toluene is +3.5%. In addition, it will be appreciated that the quantum efficiency of the measurement sample 10 is 86.5%, and a difference from the quantum efficiency 83.1% of the measurement sample 2 is +3.4%. It will be appreciated that differences between the quantum efficiency of the measurement samples 11 to 14 and the quantum efficiency of the measurement samples 3 to 6 are +1.9%, +3%, +0.6% and +0.3%, respectively.
On the other hand, it will be appreciated that, when data of the comparative sample 2 representing the quantum efficiency of the quantum dot dispersed in the siloxane resin is compared with the quantum efficiency of the comparative sample 1, a difference between the quantum efficiency becomes −9.1% as the quantum dots are dispersed in the siloxane resin. That is, it will be appreciated that, when the quantum dots are dispersed in the siloxane resin, the quantum efficiency is decreased in comparison with when dispersed in the toluene.
According to the above-mentioned description, it will be appreciated that, while the quantum efficiency is maintained or increased even when the composites according to Examples 1 to 6 of the present invention are dispersed in the siloxane resin, the quantum efficiency is largely decreased when the quantum dots are dispersed in the siloxane resin. However, it will be appreciated that, when the quantum efficiency of the measurement samples 7 and 8 is compared with the quantum efficiency of the measurement samples 15 and 16, while the quantum efficiency of the samples is increased to be higher than the quantum efficiency of the quantum dot when the quantum dot is encapsulated in the case of the wax in which the wax-based compound is a no-oxygen-containing wax or the acid value of the wax is high, for example, about 180 mg KOH/g, the quantum efficiency may be decreased when mixed with the siloxane resin and used.
Referring to Table 2 again, it will be appreciated that, in the state in which the composition is dispersed in the siloxane resin, the emission wavelengths of the composites according to Examples 1 to 6 are 609.5 nm, 609.7 nm, 610.6 nm, 610.3 nm, 611.6 nm and 612.4 nm, and the emission wavelengths of the composites according to Examples 7 and 8 are 614.3 nm and 612.6 nm. It will be appreciated that the emission wavelength of the quantum dot according to Comparative example 1 is 614.5 nm. Accordingly, it will be appreciated that, in all of the composites according to Examples 1 to 8 of the present invention and the quantum dot according to Comparative example 1, the emission wavelength when dispersed in the siloxane resin is larger than the emission wavelength of the quantum dot dispersed in the toluene, which is about 606.0 nm.
Comparing with data of Table 1, it will be appreciated that the emission wavelength of the measurement sample 9 is 3.1 nm longer than the emission wavelength of the measurement sample 1. In addition, it will be appreciated that the emission wavelengths of the measurement samples 10 to 14 are increased to be larger 3.0 nm, 4.1 nm, 4.0 nm, 5.0 nm and 5.5 nm than the emission wavelengths of the measurement samples 2 to 6, respectively. In addition, it will be appreciated that the emission wavelengths of the measurement samples 15 and 16 are increased to be larger 8 nm and 5.8 nm than the emission wavelengths of the measurement samples 7 and 8, respectively.
Meanwhile, it will be appreciated that, comparing the emission wavelength of the comparative sample 2 with the comparative sample 1, the emission wavelength of the quantum dot is increased by 8.5 nm as dispersed in the siloxane resin.
According to the above-mentioned description, it will be appreciated that, even when dispersed in the siloxane resin, a variation in emission wavelength of the composites according to Examples 1 to 6 of the present invention is smaller than a variation in emission wavelength of the quantum dot according to Comparative example 1. That is, in the process in which the composites or quantum dots are disposed in the siloxane resin, since the composites or quantum dots are aggregated, the emission wavelength is relatively increased when dispersed in the siloxane resin more than the emission wavelength in the toluene serving as a simple dispersion solvent. Nevertheless, it will be appreciated that, when the composites according to the present invention are dispersed in the siloxane resin, a variation in emission wavelength is relatively smaller than the case in which the quantum dots are dispersed in the siloxane resin as they are.
However, since the quantum dot of the composite according to Example 7 is somewhat encapsulated by the wax-based compound, the quantum efficiency in the state in which the composition is dispersed in the toluene is similar to these of the measurement samples 1 to 6. However, it will be appreciated that, since the wax-based compound that constitutes the composite according to Example 7 does not include oxygen, while the quantum efficiency is higher than that of the quantum dot according to Comparative example 1 when the quantum dots having an encapsulation effect are dispersed in the siloxane resin, the quantum efficiency is lower than that of the composites according to Examples 1 to 6. In addition, it will be appreciated that a variation in emission wavelength is increased when the emission wavelength (of the measurement sample 15) in the case in which the composites according to Example 7 are dispersed in the siloxane resin is compared with (the measurement sample 7) the case in which the composition is dispersed in the toluene.
In addition, since the quantum dot of the composite according to Example 8 is encapsulated by the wax-based compound, the quantum efficiency in the state in which the composition is dispersed in the toluene is similar to these of the measurement samples 1 to 6. However, it will be appreciated that, when the ligand on the surface of the quantum dot is broken by the compound that constitutes the composite according to Example 8 and the quantum dot is oxidized to be dispersed in the siloxane resin, while the quantum efficiency is higher than that of the quantum dot according to Comparative example 1, the quantum efficiency is lower than that of the composite according to Examples 1 to 7.

Experiment Example 3

Dispersion Stability Estimation

In the measurement sample 9 to 16 and the comparative sample 2, transmittance (transmittance immediately after dispersion) immediately after manufacture of the measurement samples 9 to 16 and the comparative sample 2 was measured using Cary-4000 (trade name, Agilent Technologies Inc., US) serving as a transmittance measurement device. After one month elapses, the transmittance (transmittance after one month) was measured again to calculate dispersion stability. The results are shown in Table 3.

	TABLE 3

	Classification (in OE-6630)	Dispersion stability (%)

	Measurement sample 9	2
	Measurement sample 10	4
	Measurement sample 11	3
	Measurement sample 12	5
	Measurement sample 13	6
	Measurement sample 14	6
	Measurement sample 15	13
	Measurement sample 16	14
	Comparative sample 2	18

In Experiment example 3, the “transmittance immediately after dispersion” is a value (unit: %) as an average of the transmittance within a range of about 400 nm to about 700 nm serving as a visible light region measured by transmittance measurement equipment immediately after manufacture of the measurement sample or the comparative sample. In addition, the “transmittance measured after one month” is a value (unit: %) calculated as an average of the transmittance within a range of about 400 nm to about 700 nm serving as a visible light region measured by transmittance measurement equipment when one month elapses from leaving at a normal temperature after manufacture of the measurement sample or the comparative sample. Dispersion stability of Table 3 is calculated by calculating a value (%) of a difference between the transmittance (%) immediately after dispersion of the quantum dots and the transmittance (%) after one month. As the transmittance measured after one month is lower, the dispersion stability has a smaller value, and as the transmittance measured after one month is higher, the dispersion stability has a larger value. That is, when the dispersion stability of the measurement sample or the comparative sample is not good, precipitation occurs to increase transmittance, and thus, the dispersion stability has a large value.
Referring to Table 3, it will be appreciated that the dispersion stability of the measurement samples 9 to 16 are 2%, 4%, 3%, 5%, 6%, 6%, 13% and 14%, respectively. On the other hand, it will be appreciated that the dispersion stability of the comparative sample 2 is 18%. That is, it will be appreciated that the dispersion stability of the measurement samples 9 to 16 including the composites according to the embodiments of the present invention is better than that of the comparative sample 2. In addition, it will be appreciated that the state in which the composition is dispersed in the siloxane resin is maintained without precipitation even when time elapses. In particular, it will be appreciated that, in the cases of the measurement samples 15 and 16, while the dispersion stability is better than the comparative sample 2, the dispersion stability is not better than the measurement samples 9 to 14.

Experiment Example 4

Estimation of Ultraviolet Light Stability and Heat/Moisture Stability −1

The composite according to Embodiment 1 in a powder phase was prepared and first quantum efficiency (QYT1, unit: %) of the composite was measured using C9920-02 (trade name, HAMAMATSU Photonics K. K., Japan) serving as an absolute quantum efficiency measurement device. Then, after ultraviolet light (UV) having a wavelength of 365 nm was radiated at a radiation intensity of about 1 mW/cm2 for 150 hours, i.e. in a severe condition of about 540 J/cm2, second quantum efficiency (QYT2, unit: %) was measured. A difference (
1%) between the first quantum efficiency and the second quantum efficiency was calculated to estimate ultraviolet light stability with respect to the composite according to Embodiment 1. The results are shown in Table 4.
The composites according to Example 2 to Example 8 in a powder phase and the quantum dot according to Comparative example 1 were prepared, and ultraviolet light stability with respect to the composites according to Examples 2 to 8 in the powder phase and the quantum dot according to Comparative example 1 were estimated through substantially the same method as the experiment method of the composite according to Example 1 in the powder phase. The results are shown in Table 4.
In addition, after first quantum efficiency (QYT1, unit: %) was measured with respect to the composites according to Examples 1 to 8 in the powder phase and the quantum dot according to Comparative example 1, they were left in a thermo-hygrostat under the severe condition of a temperature 85° C. and a relative humidity 85%. Next, third quantum efficiency (QYT3, unit: %) with respect to the composites according to Examples 1 to 8 and the quantum dot according to Comparative example 1 was measured. A difference (ΔQY2=QYT1−QYT3, unit: %) between the first quantum efficiency and the third quantum efficiency was calculated to estimate heat/moisture stability with respect to the composites according to Embodiments 1 to 8 and the quantum dot according to Comparative example 1. The results are shown in Table 4.

TABLE 4

	Ultraviolet light	Heat/moisture
	stability	stability
Classification	(ΔQY1, %)	(ΔQY2, %)

Example 1	15	16
Example 2	19	18
Example 3	21	21
Example 4	19	21
Example 5	22	24
Example 6	21	25
Example 7	29	41
Example 8	30	42
Comparative example 1	52	55

Referring to Table 4, it will be appreciated that the ultraviolet light stability of the composites according to Examples 1 to 8 are 15%, 19%, 21%, 19%, 22%, 21%, 29% and 30%, respectively, whereas the ultraviolet light stability of the quantum dot according to Comparative example 1 is 52%. Since a variation in quantum efficiency under the severe condition (a radiation amount of about 540 J/cm2) of the ultraviolet light becomes small as the stability with respect to the ultraviolet light is improved, the ultraviolet light stability has a smaller value. That is, it will be appreciated that the ultraviolet light stability of the composites according to Examples 1 to 8 of the present invention is better than the quantum dot according to Comparative example 1. In addition, it will be appreciated that, even in the composites according to Examples 1 to 8, the ultraviolet light stability of the composites according to Examples 1 to 6 is better than the ultraviolet light stability of the composites according to Examples 7 and 8.
In addition, it will be appreciated that the heat/moisture stability of the composites according to Examples 1 to 8 are 16%, 18%, 21%, 21%, 24%, 25%, 41% and 42%, respectively, whereas the heat/moisture stability of the quantum dot according to Comparative example 1 is 55%. Since a variation in quantum efficiency under the high temperature and high humidity (a temperature 85° C. and a relative humidity 85%) severe condition becomes small as the stability with respect to the temperature and humidity is increased, the heat/moisture stability has a smaller value. That is, it will be appreciated that the heat/moisture stability of the composites according to Examples 1 to 8 of the present invention is better than the quantum dot according to Comparative example 1. In addition, it will be appreciated that, even in the composites according to Examples 1 to 8, the heat/moisture stability of the composites according to Examples 1 to 6 is better than the heat/moisture stability of the composites according to Examples 7 and 8.

Experiment Example 5

Estimation of Ultraviolet Light Stability and Heat/Moisture Stability −2

The composite according to Example 1 was dispersed in OE-6630 B kit of OE-6630 A/B kit (trade name, Dow Corning Silicon Corporation, US), mixed with OE-6630 A kit at a mass ratio of 1:4 (A kit:B kit), and heat-treated in an over at a temperature of about 150° C. for about two hours to manufacturing a first film sample having a thickness of about 200 μm.
Second to eighth film samples were manufactured through substantially the same process as the process of manufacturing the first film sample using the composites according to Examples 2 to 8. In addition, a first comparative film sample was manufactured through substantially the same process as the process of manufacturing the first film sample using the quantum dot according to Comparative example 1.
Ultraviolet light stability and heat/moisture stability were estimated through substantially the same method as the estimation method of Experiment example 4 with respect to the first to eighth film samples and the first comparative film sample. The results are shown in Table 5.

TABLE 5

		Heat/
	Ultraviolet light	moisture
	stability	stability
Classification	(ΔQY1, %)	(ΔQY2, %)

First film sample	3	4
Second film sample	4	7
Third film sample	4	6
Fourth film sample	5	10
Fifth film sample	5	9
Sixth film sample	6	11
Seventh film sample	21	30
Eighth film sample	28	32
First comparative film	38	40
sample

Referring to Table 5, it will be appreciated that, comparing the ultraviolet light stability of the first to eighth film samples with the ultraviolet light stability of the first comparative film sample, the ultraviolet light stability of the film samples including the composites according to Examples 1 to 8 of the present invention is better than the first comparative film sample including the quantum dot.
It will be appreciated that, even in the first to eighth film samples, while the ultraviolet light stability of the seventh and eighth film samples is better than the first comparative film sample but not better than the first to sixth film samples. That is, it will be appreciated that the ultraviolet light stability of the first to sixth film samples is about 6% or less, which is very good.
In addition, it will be appreciated that, comparing the heat/moisture stability of the first to eighth film samples with the heat/moisture stability of the first comparative film sample, the heat/moisture stability of the film samples including the composites according to Examples 1 to 8 of the present invention is better than the first comparative film sample.
It will be appreciated that, even in the first to eighth film samples, the heat/moisture stability of the seventh and eighth film samples is better than the first comparative film sample but not better than the first to sixth film samples. That is, it will be appreciated that the heat/moisture stability of the first to sixth film samples is about 11% or less, which is very good.
According to the above-mentioned description, it will be appreciated that, even when the cured material is manufactured using the siloxane-based resin, the ultraviolet light stability and the heat/moisture stability of the composite according to the present invention is better than the case in which the quantum dot is used as it is.

Experiment Example 6

Estimation of Ultraviolet Light Stability and Heat/Moisture Stability −3

After MB2478 (trade name, Mitsubishi Rayon Co. Ltd, Japan) is dissolved in toluene, the composite according to Example 1 is dispersed and dried at about 80° C. to manufacture a ninth film sample having a thickness of about 200 μm.
Tenth to sixteenth film samples were manufactured through substantially the same process as the process of manufacturing the ninth film sample using the composites according to Examples 2 to 8. In addition, a second comparative film sample was manufactured through substantially the same process as the process of manufacturing the ninth film sample using the quantum dot according to Comparative example 1.
The ultraviolet light stability and the heat/moisture stability were estimated through substantially the same method as the estimation method of Experiment example 4 with respect to the ninth to sixteenth film samples and the second comparative film sample. The results are shown in Table 6.

TABLE 6

		Heat/
	Ultraviolet light	moisture
	stability	stability
Classification	(ΔQY1, %)	(ΔQY2, %)

Ninth film sample	8	5
Tenth film sample	9	7
Eleventh film sample	11	7
Twelfth film sample	14	13
Thirteenth film sample	13	10
Fourteenth film sample	16	12
Fifteenth film sample	27	32
Sixteenth film sample	35	34
Second comparative	48	43
film sample

Referring to Table 6, it will be appreciated that, comparing the ultraviolet light stability of the ninth to sixteenth film samples with the ultraviolet light stability of the second comparative film sample, the ultraviolet light stability of the film samples including the composite according to Examples 1 to 8 of the present invention are 8%, 9%, 11%, 14%, 13%, 16%, 27% and 35%, respectively, which are better than the ultraviolet light stability 48% of the second comparative film sample including the quantum dot.
It will be appreciated that, even in the ninth to sixteenth film samples, the ultraviolet light stability of the fifteenth and sixteenth film samples is better than the second comparative film sample but not better than the ninth to fourteenth film samples. That is, it will be appreciated that the ultraviolet light stability of the ninth to fourteenth film samples is about 16% or less, which is good.
In addition, it will be appreciated that, comparing the heat/moisture stability of the ninth to sixteenth film samples with the heat/moisture stability of the second comparative film sample, the heat/moisture stability of the film samples including the composites according to Embodiments 1 to 8 of the present invention are 5%, 7%, 7%, 13%, 10%, 12%, 32% and 34%, which are better than the heat/moisture stability 43% of the first comparative film sample.
It will be appreciated that, even in the ninth to sixteenth film samples, the heat/moisture stability of the fifteenth and sixteenth film samples is better than the second comparative film sample but not better than the ninth to fourteenth film samples. That is, it will be appreciated that the heat/moisture stability of the ninth to fourteenth film samples is about 13% or less, which is very good.
According to the above-mentioned description, it will be appreciated that, even when the cured material is manufactured using the acryl-based resin, the ultraviolet light stability and the heat/moisture stability of the composite according to the present invention is better than the case in which the quantum dot is used as it is.
Hereinafter, an apparatus according to the present invention will be described in detail with reference to FIGS. 3 to 5. However, the scope of the present invention is not limited thereto.
FIGS. 3 to 5 are cross-sectional views for describing an apparatus according to another embodiment of the present invention.
Referring to FIG. 3, an emission device 501 includes a light-emitting diode (LED) device part 10, and a first cured material layer 310 and a second cured material layer 320 formed on the LED device part 10 and including the composites according to the present invention. The LED device part 10 includes a base part 2, and an LED chip 1 formed in a groove section of the base part 2.
The first cured material layer 310 includes a green composite 311 dispersed in a matrix structure of which a curable resin is formed. The green composite 311 includes a green quantum dot, and the green quantum dot is encapsulated by the wax-based compound. The “matrix structure” is an internal structure of the cured material formed by a chemical reaction of the curable resin of the composition used to form the first cured material layer 310. Since the wax-based compound is substantially the same as those described with reference to FIGS. 1 a, 1 b and 1 c, detailed overlapping description thereof will be omitted.
The second cured material layer 320 includes a red composite 321 dispersed in the matrix structure formed by the curable resin. The red composite 321 includes a red quantum dot, and the red quantum dot is encapsulated by the wax-based compound. The wax-based compound that encapsulates the red quantum dot may be the same as or different from the wax-based compound that encapsulates the green quantum dot.
The green composite 311 may have an emission peak in a green wavelength region of about 520 nm to about 570 nm. In addition, the red composite 321 may have an emission peak in a red wavelength region of about 600 nm to about 680 nm. For example, the red wavelength region may be about 620 nm to about 670 nm.
The LED chip 1 generates blue light. The blue light may have a wavelength of about 400 nm to about 480 nm. For example, the blue wavelength region may be about 400 nm to about 450 nm.
Unlike the stacked structure shown in FIG. 3, the first cured material layer 310 may include the red composite 321 and the second cured material layer 320 may include the green composite 311.
While not shown, unlike the stacked structure shown in FIG. 3, the emission device 501 may have a structure including the cured material layer that covers the LED chip 1 and includes both of the green composite 311 and the red composite 321.
Referring to FIG. 4, an emission device 502 includes the LED device part 10, the first cured material layer 310, the second cured material layer 320, and a fluorescent layer 410 including a fluorescent substance 411. The emission device 502 is substantially the same as the emission device 501 described with reference to FIG. 3 except for the fluorescent layer 410. Accordingly, detailed overlapping description thereof will be omitted.
The fluorescent layer 410 can supplement emission of the green composite 311 of the first cured material layer 310 and/or the red composite 321 of the second cured material layer 320. For example, the fluorescent substance 411 may have an emission peak in a green region of about 520 nm to about 570 nm and/or a red region of about 600 nm to about 680 nm. Unlike this, the fluorescent substance 411 may have an emission peak in a yellow region of about 580 nm to about 600 nm.
Referring to FIG. 5, an emission device 503 includes the LED device part 10 and a cured material layer ML. The cured material layer ML may include all of the green composite 311, the red composite 321 and the fluorescent substance 411 dispersed in the matrix structure formed by the curable resin.
While not shown in the drawing, the emission device may include a first layer including two kinds of compounds among the green composite 311, the red composite 321 and the fluorescent substance 411, and a second layer including the other one kind of compound.
Unlike this, when the LED chip is a light emitting chip configured to generate UV light, the emission device may have a structure in which a first layer including a blue composite, a second layer including a green composite, and a third layer including a red composite are deposited on the light emitting chip. Here, each of the red, green and blue composites includes a quantum dot encapsulated by the wax-based compound. A deposition sequence of the first to third layers may be variously varied.
As the composite according to the present invention having good ultraviolet light stability and heat/moisture stability is used in the emission devices having the above-mentioned various structures, deterioration of the emission device can be minimized, and reduction in lifespan of the emission device due to damage to the quantum dot can be prevented. In addition, the composites according to the present invention can minimize a shift of the emission peak when the composites are dispersed in the resin to form the cured material layer. Accordingly, color properties (spectrum) required for the emission device or the display device can be easily controlled by a user, and color reproducibility can be improved.
As described above, as the composite according to the present invention is used in the emission device, the emission device that satisfies all of color reproducibility and lifespan properties can be manufactured.
While the present invention has been described with reference to the exemplary embodiments, it will be apparent to those skilled in the art that the present invention could be variously modified and changed without departing from the spirit and the scope of the present invention disclosed in the accompanying claims.

Claims

What is claimed is:

1. A composite comprising:

at least one quantum dot; and

a wax-based compound that covers a surface of the quantum dot.

2. The composite according to claim 1, wherein the wax-based compound encapsulates the quantum dot.

3. The composite according to claim 1, wherein the wax-based compound encapsulates the one quantum dot.

4. The composite according to claim 1, wherein two or more quantum dots are disposed to be spaced apart from each other in an aggregation particle formed by the wax-based compound.

5. The composite according to claim 1, wherein a molecular weight of the wax-based compound is 1,000 or more and 20,000 or less.

6. The composite according to claim 1, wherein a melting point of the wax-based compound is 80° C. or more and 200° C. or less.

7. The composite according to claim 1, wherein the wax-based compound comprises a polyethylene-based wax, a polypropylene-based wax or an amide-based wax.

8. The composite according to claim 7, wherein the wax-based compound comprises at least one of monomers represented by the following chemical formulae 1 to 7:

where, in the chemical formulae 1, 2, 3, 4, 5, 6 and 7, R₁, R₃, R₅and R₇independently represent a single bond or an alkylene group (*—(CH2)x-*, x is an integer of 1 to 10) having 1 to 10 carbon atoms, respectively, R₂, R₄, R₆and R₈independently represent a hydrogen or an alkyl group having 1 to 10 carbon atoms, respectively, and R_a, R_b, R_c, R_d, R_e, R_fand R_gindependently represent a hydrogen or an alkyl group having 1 to 3 carbon atoms, respectively.

9. The composite according to claim 1, wherein the wax-based compound has an acid value of 1 mg KOH/g to 200 mg KOH/g.

10. The composite according to claim 9, wherein the wax-based compound comprises a polyethylene-based wax.

11. The composite according to claim 1, wherein the wax-based compound has a density of 0.95 g/cm3 or more.

12. The composite according to claim 11, wherein the wax-based compound comprises a polyethylene-based wax.

13. The composite according to claim 12, wherein the polyethylene-based wax has an acid value of 1 mg KOH/g to 200 mg KOH/g.

14. A composition comprising:

a solvent; and

a composite dispersed in the solvent, the composite including at least one quantum dot and a wax-based compound that covers the quantum dot.

15. A composition comprising:

a resin; and

a composite dispersed in the resin, the composite including at least one quantum dot and a wax-based compound that covers the quantum dot.

16. The composition according to claim 15, wherein the resin comprises at least one of a silicon-based resin, an epoxy-based resin and an acryl-based resin.

17. An apparatus comprising: a coating layer or film formed of the composition according to claim 14.

18. The apparatus according to claim 17, wherein the apparatus is a lighting device or a display device.