Patent Description:
Document <CIT> discloses the use of InP dots, functionalized with an acrylate derivative of succinic acid, for the preparation of an ink composition. In this case, <NUM>,<NUM>-hexanedioldimethacrylate (HDDMA) is used as the bifunctional unit. These quantum dots have an emission range in the green region of the spectrum. There is no information about the quantum yield for the layer after curing.

Document <CIT> describes an ink composition, wherein the composition contains a quantum dot and/or quantum dot dye, preferably about <NUM>% by weight of the composition. The composition may include, among others: particularly preferably HDDA (relative to QD) or TPGDA (relative to dye). The documents does not describe the effect of the polymerization mixture on quantum yield before and after polymerization.

Document <CIT> discloses an ink composition containing core/shell or core/shell/shell dots. The ink compositions contain a mixture of two mers in various combinations, with the minimum content of quantum dots being <NUM>% by weight.

<CIT> discloses a nanocomposite composition that can be applied by a printing or spin coating process. The obtained layer, after hardening, is characterized by uniform thickness, good charge transport and luminous efficiency. There is no comparison of the QY values before and after the ink polymerization process. Quantum dots are core/shell type dots, stabilized with oleylamine. The content of the quantum dots in the composition is <NUM>% by mass. Additionally, <CIT> might be cited.

Many examples of curable compositions comprising quantum dots have been disclosed in the prior art describing. However, there is no information about compositions that have high quantum yields in colloidal form and after curing. The high quantum yield is a particularly important parameter due to its application in optoelectronics.

The aim of the invention was to develop a UV-curable ink composition, containing red-emitting quantum dots, which exhibits high stability of quantum yield in colloidal form and after UV-curing (as a film). In addition, the aim is to obtain a composition that, after curing, is resistant to visible light for a long time and does not lose its optical properties. The obtained film forms a flexible and non-cracking layer, which can be used in the light emitting devices.

In the first aspect, the invention relates to a UV-curable ink composition comprising:.

Preferably, the composition further comprises up to <NUM> wt. % of phenylbis(<NUM>,<NUM>,<NUM>-trimethylbenzoyl)phosphine oxide.

Preferably, the composition further comprises up to <NUM> wt. % of isobornyl acrylate.

Preferably, the core of a red-emitting quantum dots comprises cadmium or indium.

Preferably, the core of a red-emitting quantum dots is selected from the group consisting of CdSe, CdTe, CuInS and InP.

Preferably, the red-emitting quantum dots have an organic ligand on their surfaces, preferably <NUM>-ethyl-<NUM>-hexanethiol and mono-<NUM>-(methacryloyloxy)ethyl succinate.

Preferably, the photoluminescence quantum yield of the composition comprising cadmium quantum dots is at least <NUM>%.

Preferably, the photoluminescence quantum yield of the composition comprising indium quantum dots is at least <NUM>%.

Preferably, the viscosity of the composition is at <NUM> in the range from <NUM> to <NUM> cP.

Preferably, the surface tension of the composition is at <NUM>° C in the range from <NUM> to <NUM> mN/m.

Preferably, the composition absorb light having a maximum luminous peak wavelength is in the range from <NUM> to <NUM> nanometers.

Another aspect of the invention is a method for producing the UV-curable ink composition, the method comprising:.

Another aspect of the invention is a method for depositing a UV-curable ink composition, in which the ink composition is depositing in a straight line, onto a first substrate to form a film, and then the film is covered by a second substrate of the same size.

Preferably, the film is cured under a UV lamp for up to <NUM> minutes.

Preferably, the substrate is selected from the group consisting of glass and paper and also is selected from the group consisting polymers, such as polyethylene terephthalate, polyethylene glycol, polycarbonate, polystyrene and polyester.

Another aspect of the invention is a film that shows a maximum emission at the wavelength in the range from <NUM> to <NUM> and a decrease of a spectral irradiance is lower than <NUM>% over a period of <NUM> hours.

Another aspect of the invention is a use of the UV-curable ink composition in a light emitting device, in particular in a light-emitting diode.

Another aspect of the invention is a light emitting device comprising the UV-curable ink composition wherein LED emission wavelength is <NUM> or <NUM>.

The advantage of the invention is the high stability of the quantum yield (QY) and the maximum of the photoluminescence (PL) over a very long time, both in the case of the composition in colloidal form and after UV-curing. In addition, the UV-cured ink films (layers) are flexible and resistant to visible light for a long time and do not lose their optical properties at room temperature and at elevated temperature - <NUM>. The cured layer is characterized by a quantum yield of min. <NUM>% - in the case of cadmium quantum dots, and at least <NUM>% in the case of indium quantum dots and maintain the stability of color emission. Moreover, stability of Full Width at Half Maximum (FWHM) emission parameter in a very long time, in the composition in colloidal form and in the case of UV-cured layers as well.

Another advantage of the invention is the repeatability of the composition preparation method as well as its universality. The composition, according to the invention can be prepared from various types of dots, not limited to cadmium or indium. Moreover, each step of the synthesis can be easily scaled-up, which is important from the point of view of industrial application.

The invention is presented on the drawing, in which:.

The invention is presented in non-limiting examples:
The synthesis of CdSe quantum dots was performed according to the procedure described in X. Peng, DOI <NUM>/s12274-<NUM>-<NUM>-<NUM>. The CdSe cores were coated with an inorganic CdS shell by a reaction carried out according to a modified procedure originally proposed by Bawendi [<NPL>].

The quantum dots based on InP - personalized High Efficiency Indium Phosphide Zinc Sulfide (InP/ZnS) Quantum Dots (HEINP) - are commercially available from NNCrystal US Corporation.

<NUM>-ethyl-<NUM>-hexanethiol, mono-<NUM>-(methacryloyloxy)ethyl succinate, PGMEA, <NUM>-hydroxycyclohexyl phenyl ketone, diphenyl(<NUM>,<NUM>,<NUM>-trimethylbenzoyl)phosphine oxide, phenylbis(<NUM>,<NUM>,<NUM>-trimethylbenzoyl)phosphine oxide, <NUM>,<NUM>-hexanediol diacrylate, tri(propylene glycol) diacrylate are commercially available.

Photoluminescence (PL) spectra were measured to determine the position and broadening (FWHM - Full Width at Half Maximum) of PL peak and quantum yield (QY) of PL. Absorbance spectra (ABS) were measured for Ink S1 as well as films which allows to determine the optical density of polymerized films.

Absorbance was measured on PerkinElmer LAMBDA <NUM> UV-Vis. Photoluminescence spectra and Photoluminescence Quantum Yield were measured on PerkinElmer FL <NUM> Fluorescence Spectrophotometer. Excitation wavelength for PL and QY was set at <NUM>.

The procedure can be divided into two steps. In the first step <NUM>,<NUM> mmol of <NUM>-ethyl-<NUM>-hexanethiolwas added to the reaction vessel (centrifuge tube <NUM>) and then <NUM>,<NUM> mmol of toluene was added using automatic pipette. <NUM> of QDs (concentration <NUM>/ml) was then transferred to the reaction vessel. Toluene or hexane may be used as a solvent for QDs. The reaction vessel was capped and placed a in a thermal shaker for <NUM> hours at <NUM> rpm and <NUM>.

The second step of the procedure will begin after centrifugation. In the meantime, the quantum dots from the reaction mixture precipitated. Thus, acetonitrile should be added to the reaction vessel in a volume ratio of <NUM>:<NUM> (QDs:acetonitrile). Afterwards, the reaction vessel could be placed in a centrifuge for <NUM> minutes at <NUM> rpm. After centrifugation, when complete precipitation occurs, the pellet can be separated from the supernatant by decanting the supernatant. Then the pellet should be carefully dried and dispersed in more less <NUM>,<NUM> mmol of toluene. The second step of the ligand exchange procedure should be repeated twice.

The procedure described above is scalable.

The procedure can be divided into two steps. In the first step <NUM>,<NUM> mmol of mono-<NUM>-(methacryloyloxy)ethyl succinate was added to the reaction vessel (centrifuge tube <NUM>). PGMEA and toluene should be added to the reaction vessel using an automatic pipette: PGMEA and toluene in a volume ratio of <NUM>:<NUM>:<NUM> (PGMEA/toluene/QDs). <NUM> of QDs (concentration <NUM>/ml) was then transferred to the reaction vessel. Toluene or hexane may be used as a solvent for QDs. The reaction vessel was capped and placed a in a thermal shaker for <NUM> hours at <NUM> rpm and <NUM>.

The second step of the procedure will begin after centrifugation. In the meantime, the quantum dots from the reaction mixture precipitated. Thus, octane should be added in a volume ratio of <NUM>:<NUM> (QDs:octane). Afterwards, the reaction vessel could be placed in a centrifuge for <NUM> minutes at <NUM> rpm. After centrifugation, when complete precipitation occurs, the pellet can be separated from the supernatant by decanting the supernatant. Then the pellet should be carefully dried and dispersed in the mixture of HDDA:TPGDA in a volume ratio of <NUM>:<NUM> (total sample volume: <NUM>). The reaction vessel was once again capped and placed a in a thermal shaker for more or less <NUM> hours at <NUM> rpm and <NUM>. The colloid should be filtered using a PAsyringe filter (<NUM>) and transferred into a previously prepared vessel. The procedure described above is scalable.

To prepare UV curable ink, <NUM>,<NUM> mmol of <NUM>-hydroxycyclohexyl phenyl ketone, <NUM>,<NUM> mmol of diphenyl(<NUM>,<NUM>,<NUM>-trimethylbenzoyl)phosphine oxide and <NUM>,<NUM> mmol of phenylbis(<NUM>,<NUM>,<NUM>-trimethylbenzoyl)phosphine oxide were dissolved in <NUM>,<NUM> mmol of <NUM>,<NUM>-hexanediol diacrylate and <NUM>,<NUM> mmol of tri(propylene glycol) diacrylate. The ingredients were mixed using vortex mixer for about <NUM> minutes at room temperature. Then, <NUM>,<NUM> ul (concentration about <NUM>/ml) of QDs dispersion from the previous procedure (Example <NUM>) was added to the mixture. In the last step, <NUM>,<NUM> mmol of isobornyl acrylate and <NUM>,<NUM> mmol of <NUM>-hydroxy-2metylpropiophenone were added to the mixture. The mixture was stirred for more or less <NUM> at <NUM> and <NUM> rpm until complete dissolution of solid compounds. The UV-curable ink is ready to use. The procedure described above is scalable.

<NUM> ul of UV-curable ink was deposited on the substrate by using automatic pipette in a straight line. The substrate may be glass or a polymer (e.g. PET film) and measures approximately <NUM> x <NUM>. A second substrate of the same size is then carefully covered from above to uniformly distribute the ink over the entire surface of the substrate. Be careful not to create air bubbles. As a result, a thin UV-curable ink layer is created between two substrates of the same size. The resulting layer should be placed under a UV lamp (wavelength <NUM>/<NUM>) for <NUM> minutes.

The test were performed at room temperature, samples were unprotected from visible light:.

Claim 1:
A UV-curable ink composition comprising:
- Red-emitting quantum dots in the range from <NUM> to <NUM> wt.% based on the total amount of the composition,
- <NUM>,<NUM>-hexanediol diacrylate in the range from <NUM> to <NUM> wt.% based on the total amount of the composition,
- tri(propylene glycol) diacrylate in the range from <NUM> to <NUM> wt.% based on the total amount of the composition,
- <NUM>-hydroxy-<NUM>-methylpropiophenone in the range from <NUM> to <NUM> wt.% based on the total amount of the composition,
- <NUM>-hydroxycyclohexyl phenyl ketone in the range from <NUM> to <NUM> wt.% based on the total amount of the composition,
- diphenyl(<NUM>,<NUM>,<NUM>-trimethylbenzoyl)phosphine oxide in the range from <NUM> to <NUM>% wt.% based on the total amount of the composition,