Solvent-free quantum dot ink and manufacturing method therefor

Abstract

The present invention relates to a solvent-free quantum dot ink. Specifically, the present invention relates to a solvent-free quantum dot ink, which comprises: a quantum dot containing a first ligand or an organic material on the surface thereof; and a photopolymerizable monomer, wherein the surface of the quantum dot is bonded to or substituted with a second ligand and a third ligand.

Description

Solvent-free quantum dot ink and method for producing the same

[0001] The present invention relates to a solvent-free quantum dot ink and a method for producing the same.

[0002] Quantum dots (DOs) are semiconductor nanocrystals that can produce various colors by emitting light of different wavelengths depending on particle size without changing the type of material. They also have the advantage of higher color purity and light stability than existing light-emitting materials, and are attracting attention as a next-generation light-emitting element.

[0003] In particular, quantum dots, which have become a new trend in the display field, can be applied to various displays and electronic devices in addition to TVs and LEDs. Quantum dots, represented by CdSe and Inp, are rapidly developing in terms of luminous efficiency (Quantum Yield), and synthesis methods with luminous efficiency close to 100% are being introduced. Based on this, TVs using quantum dot sheets are currently being commercialized. The next step is to develop a quantum dot TV that is a self-luminous version rather than a filtering method in the color filter layer by incorporating quantum dots into the color filter layer of existing LED TVs (excluding pigments and dyes). The key to the development of such quantum dot TVs is focusing on how well the luminous efficiency of quantum dots can be maintained throughout the process of forming pixels and the manufacturing process.

[0004] Meanwhile, materials for color filters require high sensitivity, adhesion to substrates, chemical resistance, and heat resistance. Conventionally, color filters used in displays are typically formed through a patterning process that uses photosensitive resist ink to form a desired pattern through an exposure process using a photomask, followed by a development process to dissolve and remove unexposed areas.

[0005] Recently, in order to address the increasing cost and sophistication of materials used in pixels, methods that minimize material use by using materials only in the desired area rather than patterning using conventional spin coating or slit coating are gaining attention. The most representative method is the inkjet method, which prevents unnecessary material waste because it uses materials only in the desired pixels. However, since the quantum dot ink used in the inkjet method requires a viscosity of 100 cP or less, preferably 50 cP or less, a solvent is included to implement low viscosity. However, because the quantum dot ink includes a solvent, there are cases in which the thickness variation after curing becomes severe, there are limitations in increasing the film thickness, and there are concerns about environmental pollution due to the use of organic solvents.

[0006] Therefore, there is a need for the development of quantum dot inks that have low viscosity and excellent optical properties without containing solvents.

[0007] In order to solve the above problems, the present invention aims to provide a solvent-free quantum dot ink.

[0008] Specifically, the purpose is to provide a solvent-free quantum dot ink having low viscosity, excellent optical properties, and high storage stability.

[0009] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0010] According to one aspect of the present invention for achieving the above-described purpose, the present invention relates to a solvent-free quantum dot ink, wherein the solvent-free quantum dot ink comprises a quantum dot having a first ligand or an organic substance on the surface and a photopolymerizable monomer, and the surface of the quantum dot is bonded to or substituted with a second ligand and a third ligand exhibiting hydrophilicity.

[0011] Preferably, the second ligand may be a thiol-based ligand, and the third ligand may be a carboxylic acid-based ligand.

[0012] Preferably, the surface of the quantum dot comprises a first ligand, a second ligand, and a third ligand, wherein the second ligand and the third ligand may be additionally bonded to the surface of the quantum dot.

[0013] Preferably, the quantum dot emits green light or red light, and the substitution rate of the second ligand and the third ligand bound to or substituted on the surface of the green emitting quantum dot and the red emitting quantum dot can be analyzed by a gas chromatograph-mass spectrometer (GC-MS).

[0014] Preferably, the substitution rate of the second ligand substituted on the surface of the green light-emitting quantum dot may be 19% to 24%, and the substitution rate of the third ligand may be 18% to 33%.

[0015] Preferably, the substitution rate of the second ligand substituted on the surface of the red-emitting quantum dot may be 16% to 34%, and the substitution rate of the third ligand may be 24% to 35%.

[0016] According to another aspect of the present invention for achieving the above-described object, a solvent-free quantum dot ink comprising a green light-emitting quantum dot including a first ligand or an organic material on the surface and a photopolymerizable monomer, wherein the surface of the green light-emitting quantum dot is bonded or substituted with a second ligand and a third ligand exhibiting hydrophilicity, and the substitution rates of the substituted second ligand and the third ligand are simultaneously satisfied, the substitution rate of the second ligand is 19% to 24%, and the substitution rate of the third ligand is 18% to 33%, and the substitution rate is analyzed by a gas chromatograph-mass spectrometer (GC-MS).

[0017] According to another aspect of the present invention for achieving the above-described object, a solvent-free quantum dot ink comprising a red-emitting quantum dot including a first ligand or an organic material on the surface and a photopolymerizable monomer, wherein the surface of the red-emitting quantum dot is bonded or substituted with a second ligand and a third ligand exhibiting hydrophilicity, and the substitution rates of the substituted second ligand and the third ligand are simultaneously satisfied, the substitution rate of the second ligand is 16% to 34%, and the substitution rate of the third ligand is 24% to 35%, and the substitution rate is analyzed by a gas chromatograph-mass spectrometer (GC-MS).

[0018] According to another aspect of the present invention for achieving the above-described object, a method for producing a solvent-free quantum dot ink is provided, comprising a quantum dot production step of producing a quantum dot including a first ligand or an organic material on the surface, a surface modification step of modifying the surface of the quantum dot produced in the quantum dot production step, and a step of dispersing the quantum dot whose surface has been modified in the surface modification step in a photopolymerizable monomer.

[0019] Preferably, the surface modification step is to modify the first ligand or organic material on the quantum dot surface with a second ligand and a third ligand, wherein the second ligand is a thiol-based ligand and the third ligand is a carboxylic acid-based ligand, and the second ligand and the third ligand may be introduced simultaneously for modification, or the second ligand and the third ligand may be introduced sequentially for modification.

[0020] Preferably, the second ligand and the third ligand may be additionally bound to the surface of the quantum dot.

[0021] Preferably, the quantum dot emits green light or red light, and the substitution rate of the second ligand and the third ligand bound to or substituted on the surface of the green-emitting quantum dot and the red-emitting quantum dot can be analyzed by a gas chromatograph-mass spectrometer (GC-MS).

[0022] Preferably, the substitution rate of the second ligand and the substitution rate of the third ligand bonded or substituted to the green light-emitting quantum dot and the red light-emitting quantum dot must be satisfied simultaneously, and the substitution rate of the second ligand substituted on the surface of the green light-emitting quantum dot may be 19% to 24%, the substitution rate of the third ligand may be 18% to 33%, and the substitution rate of the second ligand substituted on the surface of the red light-emitting quantum dot may be 16% to 34%, and the substitution rate of the third ligand may be 24% to 35%.

[0023] According to the present invention, which is achieved as described above, there is an effect of providing a solvent-free quantum dot ink.

[0024] Specifically, the quantum dot ink of the present invention has a low viscosity, and thus has the effect of providing a solvent-free quantum dot ink having excellent printing jetting properties, excellent optical properties, and high storage stability.

[0025] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

[0026] FIG. 1 is an image of jetting a green luminescent solvent-free quantum dot ink according to one embodiment (a: Example 1; b: Example 2; c: Example 3; d: Example 4; e: Example 5).

[0027] Figure 2 is an image of jetting a green luminescent solvent-free quantum dot ink according to a comparative example (a: Comparative Example 1; b: Comparative Example 2).

[0028] FIG. 3 is an image of jetting a red luminescent solvent-free quantum dot ink according to one embodiment (a: Example 6; b: Example 7; c: Example 8; d: Example 9; e: Example 10).

[0029] Figure 4 is an image of jetting a red luminescent solvent-free quantum dot ink according to Comparative Example 3.

[0030] The purpose and technical configuration of the present invention and the resulting operation and effects will be more clearly understood through a detailed description based on the drawings attached to the specification of the present invention.

[0031] The terminology used herein is merely used to describe specific embodiments and is not intended to limit the present invention. For example, the term "including" a component in this specification does not exclude other components unless specifically stated otherwise, but rather means that other components may be included. Furthermore, it will be apparent to those skilled in the art that the embodiments are merely illustrative and intended to illustrate the present invention more specifically, and the scope of the present invention is not limited by these embodiments. In addition, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs, and in case of conflict, the description in this specification, including the definitions, shall prevail.

[0032] Below, the solvent-free quantum dot ink and the method for manufacturing the solvent-free quantum dot ink according to the present invention are described in detail.

[0033] The solvent-free quantum dot ink according to the present invention is a solvent-free ink, and is a quantum dot ink applicable to inkjet printing because it has low viscosity even though it does not contain a solvent.

[0034] Specifically, the solvent-free quantum dot ink according to the present invention can be configured to include a quantum dot including a first ligand on a surface and a photopolymerizable monomer.

[0035] The above quantum dots (QDs) are nano-sized semiconductor materials that can have different energy band gaps depending on their size and composition, and thus can emit light of various emission wavelengths. These quantum dots can have a homogeneous single-layer structure, a multi-layer structure such as a core-shell shape, a gradient structure, or a mixed structure thereof. In this case, if the shell is multi-layered, each layer can contain different components.

[0036] The above quantum dot (QD) can be freely selected from a group II-VI compound, a group III-V compound, a group IV-VI compound, a group IV element, a group IV compound, and a combination thereof. When the quantum dot is in a core-shell form, the core and the shell can each be freely composed of the components exemplified below.

[0037] For example, the Group II-VI compound is a binary compound selected from the group consisting of CdO, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, MgSe, MgS and mixtures thereof; a ternary compound selected from the group consisting of CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS and mixtures thereof; and may be selected from the group consisting of four-element compounds selected from the group consisting of CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe and mixtures thereof.

[0038] As another example, the Group III-V compound may be selected from the group consisting of binary compounds selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; ternary compounds selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, and mixtures thereof; and quaternary compounds selected from the group consisting of GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and mixtures thereof.

[0039] As another example, the group IV-VI compound may be selected from the group consisting of binary compounds selected from the group consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe and mixtures thereof; ternary compounds selected from the group consisting of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe and mixtures thereof; and quaternary compounds selected from the group consisting of SnPbSSe, SnPbSeTe, SnPbSTe and mixtures thereof.

[0040] As another example, the group IV element may be selected from the group consisting of Si, Ge, and mixtures thereof. The group IV compound may be a binary compound selected from the group consisting of SiC, SiGe, and mixtures thereof.

[0041] The aforementioned binary, ternary, or quaternary compounds may exist within the particle at a uniform concentration, or may exist within the same particle with partially different concentration distributions. Furthermore, a quantum dot may have a core / shell structure, with one quantum dot surrounding another. The interface between the core and shell may have a gradient, with the concentration of the element within the shell decreasing toward the center.

[0042] The shape of the above quantum dots is not particularly limited as long as it is a shape commonly used in the field. For example, nanoparticles, nanotubes, nanowires, nanofibers, nanoplatelets, etc. in the shape of spherical, rod-shaped, pyramidal, disc-shaped, multi-armed, or cubic nanoparticles can be used.

[0043] In addition, the size of the quantum dots is not particularly limited and can be appropriately adjusted within a conventional range known in the art. For example, the average particle diameter (D) of the quantum dots 50 ) can be about 2 nm to 10 nm. When the particle size of the quantum dot is restricted to a range of about 2 nm to 10 nm, light of a desired color can be emitted. For example, when the particle size of the quantum dot core / shell containing InP is about 5 nm to 6 nm, light with a wavelength of about 520 nm to 550 nm can be emitted, and when the particle size of the quantum dot core / shell containing InP is about 7 nm to 8 nm, light with a wavelength of about 620 nm to 640 nm can be emitted.

[0044] In addition, the quantum dots may have a full width of half maximum (FWHM) of an emission wavelength spectrum of about 40 nm or less, and color purity and color reproducibility may be improved within this range. In addition, since light emitted by these quantum dots is emitted in all directions, a wide viewing angle may be improved.

[0045] The above first ligand is formed on the surface during the formation of quantum dots and has hydrophobic properties. Therefore, there may be a barrier to the dispersion of the photopolymerizable monomer included in the solvent-free quantum dot ink.

[0046] Accordingly, it is desirable to modify the quantum dot including the first ligand or organic material on the surface and substitute it with the second ligand and the third ligand.

[0047] For example, it is preferable that the second ligand include a thiol-based ligand. The thiol-based ligand has excellent binding affinity with the quantum dot surface and has the effect of improving the dispersibility of the quantum dot in the photopolymerizable monomer. However, if only a thiol-based ligand is included, problems such as the generation of a harmful odor or an increase in viscosity, which reduces storage stability, may occur, making it unsuitable for use as a composition for inkjet ink.

[0048] In addition, it is preferable that the third ligand includes a carboxylic acid-based ligand that does not include a thiol group, and by substituting the third ligand with the second ligand, there is an effect of improving the dispersibility for the photopolymerizable monomer.

[0049] At this time, the second ligand and the third ligand become hydrophilic. That is, the present invention modifies the surface of a quantum dot, which is hydrophobic due to the first ligand or an organic material, by replacing it with the second ligand and the third ligand, thereby making the surface hydrophilic. In this way, by modifying the surface of the quantum dot to become hydrophilic, the miscibility of the quantum dot with the photopolymerizable monomer can be improved.

[0050] At this time, when replacing the surface of the quantum dot including the first ligand or organic material on the surface with the second ligand and the third ligand, the second ligand is additionally bonded to the surface of the quantum dot without detaching the first ligand, and the third ligand detaches the first ligand on the surface of the quantum dot and is replaced in that position.

[0051] Specifically, in the case of the first ligand, the elimination occurs in an acidic atmosphere, and an acidic atmosphere is created during the substitution with the third ligand containing a carboxylic acid group in contrast to the second ligand containing a thiol group.

[0052] Accordingly, during substitution with the second ligand, the first ligand is not removed much, but during substitution with the third ligand, the first ligand is removed and the third ligand is substituted in its place.

[0053] In addition, the second ligand has a stronger binding force than the third ligand, so the amount of the second ligand that is removed during substitution with the third ligand is small, and only the first ligand is removed and the third ligand is substituted in its place.

[0054] Meanwhile, the quantum dot emits green or red light depending on the emission color, and it is preferable that the second ligand and the third ligand substituted in the quantum dot simultaneously satisfy the substitution rate depending on the emission color of the quantum dot.

[0055] That is, it is preferable to simultaneously satisfy the substitution rate of the second ligand and the substitution rate of the third ligand bound to or substituted on the surface of the green light-emitting quantum dot, and to simultaneously satisfy the substitution rate of the second ligand and the substitution rate of the third ligand bound to or substituted on the surface of the red light-emitting quantum dot. At this time, by simultaneously satisfying the substitution rate of the second ligand and the substitution rate of the third ligand according to the light-emitting color, there is an effect of lowering the viscosity of the ink to 26 cP or less, and improving the processability without generating mist during the jetting process. Meanwhile, the substitution rates that the green light-emitting quantum dot and the red light-emitting quantum dot must simultaneously satisfy may be different.

[0056] Specifically, the substitution rates of the second ligand and the third ligand bonded or substituted on the surface of the green luminescent quantum dot are simultaneously satisfied, and it is preferable that the substitution rate of the second ligand is 19% to 24% and the substitution rate of the third ligand is 18% to 33%.

[0057] In addition, it is preferable that the substitution rates of the second ligand and the third ligand substituted on the surface of the red-emitting quantum dot are simultaneously satisfied, and that the substitution rate of the second ligand is 16% to 34%, and the substitution rate of the third ligand is 24% to 35%.

[0058] At this time, the substitution rate is analyzed using a mass spectrometer, and it is preferable to use a gas chromatograph-mass spectrometer (GC-MS) as the mass spectrometer. The gas chromatograph-mass spectrometer (GC-MS) is an analysis technique that combines a gas chromatograph and a mass spectrometer, and can obtain information utilizing the separation and quantitative properties of a gas chromatograph and information on the structure of a compound by mass spectrometry.

[0059] In the present invention, the substitution rate refers to the content ratio of the second ligand and the third ligand present on the surface of a quantum dot when the surface of the quantum dot including the first ligand or organic material on the surface is modified with the second ligand and the third ligand.

[0060] That is, the substitution rate refers to the ratio of the second ligand and the third ligand among 100% of the total organic matter content detected when the modified quantum dot is analyzed by a gas chromatography mass spectrometer (GC-MS).

[0061] The above photopolymerizable monomer controls the overall crosslinking density of the polymer matrix, i.e., the formulation in which quantum dots are dispersed, thereby expressing the structure and various physical properties of the matrix, and can improve flexibility and adhesiveness and adhesion with other materials.

[0062] Accordingly, the photopolymerizable monomer may include a (meth)acrylate monomer, and any monomer commonly used in the field may be used without any special restrictions.

[0063] For example, the (meth)acrylate monomer may include at least one of a (meth)acrylic group, a vinyl group, and an allyl group.

[0064] Specifically, 1,6-hexanedioldiacrylate, 1,6-cyclohexanediol diacrylate, 2,2-dimethyl-1,3-propanediol diacylate, diethylene glycol diacrylate, dipropylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane trimethacrylate, isobonyl acrylate, isobonyl methacrylate, tetrahydrofuryl Examples thereof include tetrahydrofuryl acrylate, acryloyl morpholine, 2-phenoxyethyl acrylate, tripropyleneglycol diacrylate, trimethylolpropane triacrylate, pentaerythritol mono(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, dipentaerythritol hexaacrylate, and dipentaerythritol hexamethacrylate. These may be used alone or in combination of two or more.

[0065] Hereinafter, a method for manufacturing a solvent-free quantum dot ink of the present invention will be described.

[0066] The method for producing a solvent-free quantum dot ink according to the present invention preferably includes a quantum dot production step of producing a quantum dot including a first ligand or an organic substance on the surface, a surface modification step of modifying the surface of the quantum dot produced in the quantum dot production step, and a dispersion step of dispersing the quantum dot whose surface has been modified in the surface modification step in a photopolymerizable monomer.

[0067] The above surface modification step is to modify the first ligand or organic material on the quantum dot surface with a second ligand and a third ligand. At this time, the second ligand is preferably a thiol-based ligand, and the third ligand is preferably a carboxylic acid-based ligand.

[0068]

[0069] For example, the second ligand may be represented by the chemical formula 1 below, and the third ligand may be represented by the chemical formula 2 below.

[0070] [Chemical Formula 1]

[0071]

[0072] [Chemical Formula 2]

[0073]

[0074] The above surface modification step may simultaneously or sequentially introduce the second ligand and the third ligand into the quantum dot manufactured through the above quantum dot manufacturing step.

[0075] Specifically, the surface is modified by introducing a second ligand and a third ligand to a quantum dot having a first ligand or an organic material on the surface, and it is preferable to modify the surface by introducing the second ligand and the third ligand simultaneously or by introducing the second ligand and the third ligand sequentially. In this case, as the surface is modified, the second ligand is additionally bonded to the surface of the quantum dot, and the third ligand can detach and replace the first ligand or the organic material on the surface of the quantum dot.

[0076] Meanwhile, in order to improve the dispersibility for the photopolymerizable monomer, satisfy low viscosity, and secure jetting properties when manufacturing ink using quantum dots whose surface has been modified through the surface modification step, the second ligand and the third ligand must satisfy the substitution ratio.

[0077] At this time, the quantum dot emits green or red light depending on the emission color, and it is preferable that the substitution rate of the second ligand and the substitution rate of the third ligand bonded to or substituted with the green emitting quantum dot and the red emitting quantum dot are simultaneously satisfied.

[0078] Specifically, in the case of the green luminescent quantum dot, the substitution rate of the second ligand substituted on the surface is 19% to 24%, and the substitution rate of the third ligand is 18% to 33%. It is preferable to satisfy the above substitution rates simultaneously in order to apply the solvent-free quantum dot ink.

[0079] In addition, in the case of red-emitting quantum dots, the substitution rate of the second ligand substituted on the surface is 16% to 34%, and the substitution rate of the third ligand is 24% to 35%, and it is desirable to satisfy the above substitution rates simultaneously in order to apply them to the solvent-free quantum dot ink.

[0080] At this time, it is preferable to analyze using a gas chromatograph-mass spectrometer (GC-MS) to measure the substitution rate of the second ligand and the third ligand bound to or substituted on the surface of the green light-emitting quantum dot and the red light-emitting quantum dot.

[0081]

[0082] Hereinafter, the present invention will be described in detail through examples, manufacturing examples, and comparative examples. However, the following examples and experimental examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0083]

[0084] Manufacturing Example 1. Quantum Dot (QD) Synthesis

[0085] In a 200 ml flask, zinc acetate and oleic acid are dissolved in 1-octadecene, heated to 120°C under vacuum, and then cooled to room temperature to obtain a zinc oleate solution.

[0086] In a reaction flask, indium acetate and lauric acid are heated to 120°C under vacuum together with the zinc oleate. The molar ratio of indium to lauric acid is 1:3. After 1 hour, the atmosphere in the reactor is changed to nitrogen. While the temperature in the reaction flask is raised to 250°C, a mixed solution of tris(trimethylsilyl)phosphine (TMS3P) and trioctylphosphine and optionally the zinc oleate solution are rapidly injected into the reactor. During the reaction, the indium oleate solution, the TMS3P mixed solution, and the zinc oleate are sequentially injected into the reaction flask. The total reaction time is 30 minutes.

[0087] Prepare a Se / TOP solution by dispersing Se in TOP at 120°C. Prepare a S / TOP solution by dispersing S in TOP. Prepare an aluminum chloride-TOP adduct (hereinafter referred to as AlCl3-TOP) by dispersing and stirring aluminum chloride in TOP at 100°C.

[0088] Zinc acetate and oleic acid are dissolved in trioctylamine in a 300 mL reactor and vacuum treated at 120°C for 10 minutes to obtain a zinc precursor. After replacing the inside of the flask with nitrogen (N2), the temperature is increased to 280°C and maintained for a predetermined period of time.

[0089] The manufactured InZnP core and the manufactured Se / TOP are added at a predetermined ratio, and then heated to a high temperature of 300°C or higher to react, thereby forming a ZnSe-containing layer.

[0090] At the point where the Se precursor is exhausted, S / TOP and 0.07 mmol of ZnCl2 are simultaneously injected. The reaction lasts for a total of 1 hour to form a ZnS-containing layer containing zinc sulfide. Accordingly, green-emitting quantum dots and red-emitting quantum dots were manufactured, respectively.

[0091]

[0092] Manufacturing Example 2. Synthesis of thiol ligands

[0093] Thioglycolic acid 0.271 mol, poly(ethylene glycol)methyl ether 550 (number average molecular weight 550) 0.276 mol, and p-toluene sulfonic acid monohydrate 0.027 mol are mixed in 350 ml of cyclohexane and reacted at 80°C for 18 hours in a nitrogen environment.

[0094] After the reaction is complete, remove cyclohexane and dissolve in chloroform. Neutralize with an aqueous NaHCO3 solution, filter with MgSO4, remove the remaining solvent, and obtain PEG 550-thioglycolate (hereinafter referred to as PEG550-T).

[0095] Zn-PEG550-T is prepared by reacting ZnCl2 and PEG550-T in a molar ratio of 1:3.

[0096]

[0097] Example 1. Surface modification of quantum dots

[0098] The green light-emitting quantum dots synthesized through Manufacturing Example 1 are separated using ethanol and acetone, and then dispersed in cyclohexyl acetate at a concentration of 20 wt%. While maintaining the temperature of 100 g of the dispersion at 60°C, 30 g of a solution in which Zn-PEG550-T is diluted in cyclohexyl acetate at 20 wt% and 100 g of a solution in which Mono(2-acryloyloxyethyl) succinate (hereinafter referred to as MAES) is diluted at 20 wt% are added, stirred for 3 hours, and then cooled to room temperature to terminate the reaction.

[0099]

[0100] Example 2. Surface modification of quantum dots

[0101] Surface modification was performed in the same manner as in Example 1, except that 15 g of a solution containing Zn-PEG550-T diluted at 20 wt% in cyclohexyl acetate was used.

[0102]

[0103] Example 3. Surface modification of quantum dots

[0104] Surface modification was performed in the same manner as in Example 1, except that 45 g of a solution containing Zn-PEG550-T diluted at 20 wt% in cyclohexyl acetate was used.

[0105]

[0106] Example 4. Surface modification of quantum dots

[0107] Surface modification was performed in the same manner as in Example 1, except that 50 g of a solution containing MAES diluted to 20 wt% was used.

[0108]

[0109] Example 5. Surface modification of quantum dots

[0110] Surface modification was performed in the same manner as in Example 1, except that 150 g of a solution containing 20 wt% MAES was used.

[0111]

[0112] Example 6. Surface modification of quantum dots

[0113] The surface was modified in the same manner as in Example 1, except that the red-emitting quantum dots synthesized through Manufacturing Example 1 were used.

[0114]

[0115] Example 7. Surface modification of quantum dots

[0116] The surface was modified in the same manner as in Example 2, except that the red-emitting quantum dots synthesized through Manufacturing Example 1 were used.

[0117]

[0118] Example 8. Surface modification of quantum dots

[0119] Surface modification was performed in the same manner as in Example 3, except that the red-emitting quantum dots synthesized through Manufacturing Example 1 were used.

[0120]

[0121] Example 9. Surface modification of quantum dots

[0122] The surface was modified in the same manner as in Example 4, except that the red-emitting quantum dots synthesized through Manufacturing Example 1 were used.

[0123]

[0124] Example 10. Surface modification of quantum dots

[0125] The surface was modified in the same manner as in Example 5, except that the red-emitting quantum dots synthesized through Manufacturing Example 1 were used.

[0126]

[0127] Comparative Example 1. Surface modification of quantum dots

[0128] Surface modification was performed in the same manner as in Example 1, except that a solution diluted to 20 wt% of MAES was not used.

[0129]

[0130] Comparative Example 2. Surface modification of quantum dots

[0131] Surface modification was performed in the same manner as in Example 1, except that a solution containing Zn-PEG550-T diluted at 20 wt% in cyclohexyl acetate was not used.

[0132]

[0133] Comparative Example 3. Surface Modification of Quantum Dots

[0134] Red-emitting quantum dots synthesized through Manufacturing Example 1 were used, and the surface was modified in the same manner as in Example 1, except that a solution diluted to 20 wt% of MAES was not used.

[0135]

[0136] Comparative Example 4. Surface Modification of Quantum Dots

[0137] The red-emitting quantum dots synthesized through Manufacturing Example 1 were used, and the surface was modified in the same manner as in Example 1, except that a solution in which Zn-PEG550-T was diluted to 20 wt% in cyclohexyl acetate was not used.

[0138]

[0139] Manufacturing Example 3. Manufacturing of quantum dot ink

[0140] The surface-modified quantum dots manufactured in Example 1 are separated using hexane and acetone, and then dispersed in 1,6-hexandiol diacrylate (hereinafter referred to as HDDA) at 50 wt%. TiO2 powder is dispersed in 1,6-dihexandiol diacrylate at 50 wt% as a dispersing agent, and a TiO2 dispersion is prepared by ensuring that the D90 particle size does not exceed 300 nm.

[0141] Afterwards, QD Ink was manufactured by mixing 80 g of a dispersion of surface-modified quantum dots dispersed at 50 wt% in HDDA, 8 g of TiO2 dispersion, 1 g of TPO-L, and 11 g of additional HDDA.

[0142] The surface-modified quantum dots manufactured through Examples 2 to 10 and Comparative Examples 1 to 4 were also manufactured into ink using the same method.

[0143]

[0144] Table 1 below shows the contents of the second ligand (Zn-PEG550-T) and the third ligand (MAES) included in the surface modification of Examples 1 to 5 and Comparative Examples 1 to 2 using green luminescent quantum dots, and Table 2 shows the results showing the ligand substitution rates of Examples 1 to 5 and Comparative Examples 1 to 2.

[0145] In addition, Table 3 compares the properties, efficiency, and jetting properties of quantum dot inks manufactured with the quantum dots of Examples 1 to 5 and Comparative Examples 1 to 2. At this time, the viscosity of the ink was measured with a rheometer (HAAKE, MARS40) at 25°C, and the optical properties of the ink were measured with an absolute quantum efficiency meter (Otsuka, QE-2100) by coating the ink on glass with a thickness of 10 μm using a spin coater, curing it with nitrogen purge using a curing machine with a wavelength of 395 nm, and heat-treating it at 180°C for 30 minutes to manufacture a cured film.

[0146] In addition, the jetting performance was checked using a drop watcher to ensure that the shape of the drop was good while jetting using a jetting equipment equipped with a KM1024 6pl (pico liter) head, and after continuously jetting 30,000 drops of ink at the same location on the glass, an optical microscope was used to check whether mist was generated around the largest main drop.

[0147]

[0148]

[0149]

[0150]

[0151]

[0152]

[0153]

[0154] Referring to the contents and substitution rates of the second ligand and the third ligand of Examples 1, 2, and 3 in Tables 1 and 2, as the content of the second ligand (Zn-PEG550-T) increased and was substituted, the detection rate (substitution rate) of the second ligand increased, and the detection rates (substitution rates) of the third ligand and the first ligand decreased, and the sum of the detection rates of the second ligand and the third ligand increased.

[0155] In addition, when the second ligand was substituted alone as in Comparative Example 1, the detection amount of the third ligand was not detected, so the detection ratio of the second ligand was high, and it was confirmed that the detection ratio of the first ligand was high.

[0156] Meanwhile, referring to the contents and substitution rates of the second ligand and the third ligand of Examples 1, 4, and 5 of Tables 1 and 2, as the content of the third ligand increased and was substituted, the detection rate (substitution rate) of the third ligand generally showed a similar trend, but the detection rate (substitution rate) of the second ligand gradually increased, and the detection rate of the first ligand decreased.

[0157] In addition, when the third ligand was substituted alone as in Comparative Example 2, the detection rate of the third ligand was high because the detection amount of the second ligand was not present, but the first ligand was not detected at 0%.

[0158] Through this, it was confirmed that in the case of the second ligand, the thiol-based ligand, the first ligand (existing ligand) on the quantum dot surface is additionally substituted without desorbing, but in the case of the third ligand, the carboxylic acid-based ligand, the first ligand (existing ligand) on the quantum dot surface is desorbed and then substituted on the quantum dot surface.

[0159] Referring to Table 3 and Fig. 2, the inks using quantum dots substituted using a single ligand, as in Comparative Examples 1 and 2, had a viscosity of 30 cP or higher, which was not suitable for inkjet processability, and it was confirmed that mist was generated, as disclosed in Table 3 and Fig. 2. This means that inks to be applied to the inkjet process must have a viscosity of 25 cP or lower, and it was confirmed that the inks did not meet the viscosity standard, and the generation of mist made it unsuitable for the process.

[0160] In addition, referring to Table 2, Table 3 and Figure 1, comparing Examples 1, 2 and 3, it was confirmed that as the substitution rate (content) of the second ligand increased, the viscosity of the ink increased, and in the case of Example 3, it was confirmed that the viscosity of the ink was 30 cP or more, making it unsuitable for application to the inkjet process. In addition, in the case of Example 2, it was confirmed that the viscosity was 25 cP or less, making it suitable for the jetting process, but mist was generated, which could cause problems in the processability.

[0161] In addition, for Examples 1, 4, and 5, it was confirmed that the viscosity was 25 cP or less, making it suitable for application to the inkjet process, and it was confirmed that the processability was good because no mist was generated.

[0162] Through this, it was confirmed that the substitution rate (content) of the second ligand (PEG550-T ligand) and the third ligand (MAES ligand) must be within a certain range when looking at the commonality between the implementation of ink normal viscosity and the occurrence of mist in jetting properties.

[0163] Specifically, the substitution rate of the second ligand for surface modification of green luminescent quantum dots and application as inkjet ink was 19% to 24%, and the substitution rate of the third ligand was 18% to 33%. It was confirmed that ink viscosity and jetting properties could be secured when the above substitution rates were simultaneously satisfied.

[0164] This result shows that the stability of quantum dots, as well as the properties and fairness of quantum dot ink, can be secured through a process of simultaneously removing and replacing existing ligands by using thiol ligands and carboxylic acid ligands simultaneously.

[0165] Table 4 shows the contents of the second ligand (Zn-PEG550-T) and the third ligand (MAES) included in the surface modification of Examples 6 to 10 and Comparative Examples 3 to 4 using red-emitting quantum dots, and Table 5 shows the results showing the ligand substitution rates of Examples 6 to 10 and Comparative Examples 3 to 4. In addition, Table 6 compares the physical properties, efficiency, and jetting properties of quantum dot inks manufactured with the quantum dots of Examples 6 to 10 and Comparative Examples 3 to 4.

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[0173] Referring to the contents and substitution rates of the second ligand and the third ligand of Examples 6, 7, and 8 in Tables 4 and 5, as the content of the second ligand (Zn-PEG550-T) increased and was substituted, the detection rate (substitution rate) of the second ligand increased, and the detection rates (substitution rates) of the third ligand and the first ligand decreased, and the sum of the detection rates of the second ligand and the third ligand increased.

[0174] In addition, as in Comparative Example 3, when the second ligand was substituted alone, there was no detection amount of the third ligand, so the detection ratio of the second ligand was high, and it was confirmed that the detection ratio of the first ligand was high.

[0175] Meanwhile, referring to the contents and substitution rates of the second ligand and the third ligand of Examples 6, 9, and 10 of Tables 4 and 5, as the content of the third ligand is increased and substituted, the detection rate (substitution rate) of the third ligand increases, the detection rate (substitution rate) of the second ligand gradually decreases or is maintained, and the detection rate of the first ligand decreases.

[0176] In addition, when the third ligand was substituted alone as in Comparative Example 4, the detection rate of the third ligand was high because there was no detection amount of the second ligand, but the detection rate of the first ligand was low at 0.8%.

[0177] Through this, it was confirmed that in the case of the second ligand, the thiol-based ligand, the first ligand (existing ligand) on the quantum dot surface is additionally substituted without desorbing, but in the case of the third ligand, the carboxylic acid-based ligand, the first ligand (existing ligand) on the quantum dot surface is desorbed and then substituted on the quantum dot surface.

[0178] Referring to Table 6 and Fig. 4, it was confirmed that inks using quantum dots substituted with a single ligand, such as Comparative Examples 3 and 4, were not suitable for inkjet processability because their viscosity was 26 cP or higher. In particular, Comparative Example 4 showed a rapid increase in viscosity to the extent that viscosity measurement was difficult, and since it was impossible to manufacture a cured film, efficiency, wavelength, and half-maximum width could not be measured, and jetting performance could not be evaluated.

[0179] In addition, referring to Table 5, Table 6 and Figure 3, when the ink was manufactured with the quantum dots of Example 7, the detection amount of the second ligand was lower and the detection amount of the third ligand was higher compared to the ink manufactured with the quantum dots of Example 6, and it was confirmed that the viscosity was 24.8 cP, which is suitable for the jetting process, but it was confirmed that mist was generated during the jetting evaluation, and it was confirmed that this could be a problem in the fairness.

[0180] In addition, in the case of the ink manufactured with the quantum dots of Example 8, the substitution rate (detection amount) of the second ligand was higher than that of the ink manufactured with the quantum dots of Example 6, and the viscosity was somewhat higher at 25.2 cP, but it was confirmed that there was no problem with the jetting property.

[0181] In addition, when ink was manufactured with the quantum dots of Examples 9 and 10, it was confirmed that the substitution rate (detection amount) of the second ligand and the third ligand was lower overall compared to the ink manufactured with the quantum dots of Example 6, and it was confirmed that the viscosity was 26 cP or less, making it suitable for the jetting process, but it was confirmed that mist was generated, which could cause problems in the processability.

[0182] Through this, it was confirmed that the wettability at the interface between the nozzle and ink was suitable only when a certain substitution rate range was maintained.

[0183] That is, through the commonality of the ink normal viscosity implementation and the occurrence of mist in the jetting property, it was confirmed that the red-emitting quantum dots also need to have a certain range of substitution rates (contents) of the second ligand (PEG550-T ligand) and the third ligand (MAES ligand).

[0184] Specifically, the substitution rate of the second ligand suitable for red-emitting quantum dots to be applied as inkjet ink is 16% to 34%, and the substitution rate of the third ligand is 24% to 35%. It can be confirmed that ink viscosity and jetting properties can be secured when the above substitution rates are simultaneously satisfied. This is a result showing that the stability of quantum dots as well as the physical properties and processability of quantum dot ink can be secured through a process of removing and replacing existing ligands simultaneously by using thiol-based ligands and carboxylic acid-based ligands simultaneously.

[0185] According to the present invention, which is achieved as described above, there is an effect of providing a solvent-free quantum dot ink.

[0186] Specifically, it has the effect of providing a solvent-free quantum dot ink with low viscosity, excellent optical properties, and high storage stability.

[0187] The above description is merely an example of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications, changes, and substitutions may be made without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical idea of ​​the present invention, but rather to explain it, and the scope of the technical idea of ​​the present invention is not limited by these embodiments and the accompanying drawings. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

Claims

1. Regarding solvent-free quantum dot ink, The above solvent-free quantum dot ink comprises a quantum dot having a first ligand or organic material on the surface and a photopolymerizable monomer, The surface of the quantum dot is bonded or substituted with a second ligand and a third ligand exhibiting hydrophilicity. Solvent-free quantum dot ink.

2. In paragraph 1, The second ligand is a thiol-based ligand, and the third ligand is a carboxylic acid-based ligand. Solvent-free quantum dot ink.

3. In paragraph 1, The surface of the quantum dot comprises a first ligand, a second ligand, and a third ligand, The second ligand and the third ligand are additionally bonded to the surface of the quantum dot. Solvent-free quantum dot ink.

4. In paragraph 1, The above quantum dots emit green light or red light, The substitution rate of the second ligand and the third ligand bound to or substituted on the surface of the green light-emitting quantum dot and the red light-emitting quantum dot is analyzed by a gas chromatograph-mass spectrometer (GC-MS). Solvent-free quantum dot ink.

5. In paragraph 4, The substitution rate of the second ligand substituted on the surface of the green luminescent quantum dot is 19% to 24%, and the substitution rate of the third ligand is 18% to 33%. Solvent-free quantum dot ink.

6. In paragraph 4, The substitution rate of the second ligand substituted on the surface of the above red-emitting quantum dot is 16% to 34%, and the substitution rate of the third ligand is 24% to 35%. Solvent-free quantum dot ink.

7. In a solvent-free quantum dot ink comprising a green luminescent quantum dot including a first ligand or organic substance on the surface and a photopolymerizable monomer, The surface of the above green luminescent quantum dot is bonded or substituted with a second ligand and a third ligand exhibiting hydrophilicity, and the substitution rates of the substituted second ligand and the third ligand are simultaneously satisfied. The substitution rate of the second ligand is 19% to 24%, and the substitution rate of the third ligand is 18% to 33%. The above substitution rate is analyzed by a gas chromatograph-mass spectrometer (GC-MS). Solvent-free quantum dot ink.

8. In a solvent-free quantum dot ink comprising a red light-emitting quantum dot including a first ligand or organic material on the surface and a photopolymerizable monomer, The surface of the above red-emitting quantum dot is bonded or substituted with a second ligand and a third ligand exhibiting hydrophilicity, and the substitution rates of the substituted second ligand and the third ligand are simultaneously satisfied. The substitution rate of the second ligand is 16% to 34%, and the substitution rate of the third ligand is 24% to 35%. The above substitution rate is analyzed by a gas chromatograph-mass spectrometer (GC-MS). Solvent-free quantum dot ink.

9. A quantum dot manufacturing step for manufacturing a quantum dot including a first ligand or organic material on the surface; A surface modification step for modifying the surface of the quantum dots manufactured in the above quantum dot manufacturing step; and Including a dispersion step of dispersing the surface-modified quantum dots in a photopolymerizable monomer in the surface modification step; Method for manufacturing solvent-free quantum dot ink.

10. In paragraph 9, The above surface modification step is to modify the first ligand or organic material on the quantum dot surface with a second ligand and a third ligand, The second ligand is a thiol-based ligand, and the third ligand is a carboxylic acid-based ligand. Modification is performed by simultaneously introducing the second ligand and the third ligand, or Modification is performed by sequentially introducing the second ligand and the third ligand. Method for manufacturing solvent-free quantum dot ink.

11. In paragraph 10, The second ligand and the third ligand are additionally bonded to the surface of the quantum dot. Solvent-free quantum dot ink.

12. In paragraph 10, The above quantum dots emit green light or red light, The substitution rate of the second ligand and the third ligand bound to or substituted on the surface of the green light-emitting quantum dot and the red light-emitting quantum dot is analyzed by a gas chromatograph-mass spectrometer (GC-MS). Method for manufacturing solvent-free quantum dot ink.

13. In paragraph 12, The substitution rate of the second ligand and the substitution rate of the third ligand bound to or substituted with the green light-emitting quantum dot and the red light-emitting quantum dot must be satisfied simultaneously. The substitution rate of the second ligand substituted on the surface of the green luminescent quantum dot is 19% to 24%, and the substitution rate of the third ligand is 18% to 33%. The substitution rate of the second ligand substituted on the surface of the above red-emitting quantum dot is 16% to 34%, and the substitution rate of the third ligand is 24% to 35%. Method for manufacturing solvent-free quantum dot ink.

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