TRANSPARENT DISPLAY

Abstract

Described herein is a transparent or translucent substrate at least partially coated with a quantum dot coating such that the coating is invisible in a first non-excited state of the coating and the coating is visible in a second excited state of the coating. Also described herein is a laminate, a glazing unit and a sunroof comprising the described coated substrate. A method of preparing the coated substrate is also described.

Claims

1. A quantum dot coated substrate, comprising: a transparent or translucent substrate; and a quantum dot coating applied to at least part of the substrate, the quantum dot coating defining a first non-excited state and a second excited state, the absorbance of the quantum dot coating in the visible region of the electromagnetic spectrum matching the absorbance of the substrate when the coating is in the first non-excited state and the absorbance of the quantum dot coating in the visible region of the electromagnetic spectrum differing from the absorbance of the substrate when the coating is in the second excited state, such that the coating is invisible in the first non-excited state and the coating is visible in the second excited state, wherein the quantum dots are coated at a density of from about 1.Math.10.sup.13 to about 1.Math.10.sup.19 quantum dot particles/cm.sup.2; and the quantum dot coating is configured to shift from the first non-excited state to the second excited state upon exposure to an excitation source.

2. The quantum dot coated substrate according to claim 1, wherein the quantum dots comprise cadmium-containing quantum dots and/or cadmium free quantum dots.

3. The quantum dot coated substrate according to claim 1, wherein the excitation source comprises a light source in the region of 190-500 nm.

4. The quantum dot coated substrate according to claim 1, wherein the excitation source is an LED light source.

5. The quantum dot coated substrate according to claim 1, wherein the excitation source comprises a light source disposed at a side face of the substrate.

6. The quantum dot coated substrate according to claim 5, wherein the excitation source comprises a lighting module of UK patent application No. 1700141.3.

7. The quantum dot coated substrate according to claim 1, wherein the transparent or translucent substrate is selected from the group consisting of: polyvinyl butyral (PVB); ethylene-vinyl acetate (EVA); and thermoplastic polyurethane (TPU).

8. The quantum dot coated substrate according to claim 1, wherein the coated substrate is overlain by a further substrate or disposed between two or more further substrates.

9. A laminate comprising a quantum dot coated substrate according to claim 1 disposed between two or more further substrates.

10. The quantum dot coated substrate according to claim 8, wherein the further substrate or substrates comprise transparent or translucent plastic and/or glass material.

11. A method of preparing a quantum dot coated substrate according to claim 1, said method comprising: providing a quantum dot formulation; and applying the quantum dot formulation to at least part of the substrate to obtain a coated substrate, wherein the quantum dot formulation comprises quantum dots and a solvent, the formulation having a quantum dot concentration from about 5 mM to about 100 mM of quantum dot core.

12. The method according to claim 11, wherein the formulation has a quantum dot concentration from about 5 mM to about 40 mM of quantum dot core.

13. The method according to claim 11, wherein the quantum dot formulation comprises quantum dots and one or more other components selected from the group comprising: (i) a solvent; (ii) an organic solvent; (iii) turpentine, toluene and/or hexane; (iv) acetone; (v) petroleum ether; (vi) a resin; (vii) a printer ink; (viii) a glazing medium; (ix) charcoal fixative; (x) clear painting medium; and (xi) an oil (for example clarified linseed oil).

14. The method according to claim 11, wherein the quantum dot formulation is applied to discrete locations of the substrate in the form of a pattern.

15. The method according to claim 11, wherein the method comprises a step of forming a laminate by disposing the coated substrate between two or more additional substrates, at least one of the two or more additional substrates being a transparent or translucent substrate, wherein the coated surface of the substrate is disposed such that it faces the at least one transparent or translucent additional substrate.

16. The method according to claim 15, wherein the method comprises the step of subjecting the laminate to heat treatment at temperatures of between about 100 C. and about 200 C. for about 20 minutes to about 30 minutes.

17. The method according to claim 15, wherein the method comprises the step of subjecting the laminate to a vacuum treatment.

18. The method according to claim 15, wherein the method further comprises the step of subjecting the laminate to pressures of between about 0.1 N/cm.sup.2 to about 1 N/cm.sup.2.

19. The method according to claim 18, wherein the method comprises heating the laminate at 130 C. for 30 minutes while under pressure.

20. A glazing unit comprising a quantum dot coated substrate according to claim 1.

21. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0126] FIG. 1: Transmittance spectra of three laminates comprising a quantum dot coating on PVB sandwiched between two pieces of glass.

[0127] FIG. 2: Plot of weight versus temperature obtained from thermogravimetric analysis (TGA) of three quantum dot solutions in dry compressed air to determine the concentration of the solutions.

[0128] FIG. 3: Vinyl mask employed for applying a pattern of a quantum dot coating on a substrate.

[0129] FIG. 4: Quantum dot coating comprising UV resistant transparent resin disposed on a transparent substrate, the coating being shown in a first, non-excited state (FIG. 4a) and in a second, excited state (FIG. 4b).

[0130] FIG. 5: Second laminate comprising a transparent quantum dot coating on transparent PVB substrate sandwiched between two pieces of glass in a first, non-excited state (FIG. 5a) and in a second, excited state (FIG. 5b).

[0131] FIG. 6: Another laminate comprising a transparent quantum dot coating on transparent PVB substrate sandwiched between two pieces of glass in a first, non-excited state (FIG. 6a) and in a second, excited state upon edge lighting the laminate with UV light (FIG. 6b).

[0132] FIG. 7: yet another laminate comprising a transparent quantum dot coating on transparent PVB substrate sandwiched between two pieces of glass in a first, non-excited state (FIG. 7a) and in a second, excited state upon optical activation of the quantum dot coating with UV light (FIG. 7b).

DETAILED DESCRIPTION

Preparation of Quantum Dot Solutions/Dispersions

[0133] Stock solutions of quantum dots were prepared by dispersing 0.4 g of CuInS.sub.2/ZnS quantum dots (UbiQD) in 5 mL of solvent (hexane or toluene). After homogenisation, 1 drop of stock solution was diluted in different volumes of solvent (clear turpentine or white spirit). Table 1 shows the dilution ratios employed for each solution:

TABLE-US-00001 TABLE 1 Quantum Dot solutions/dispersions Volume of Volume of Solvent of stock solution Dilution dilution Solution ID stock solution (L) solvent solvent (mL) A Hexane 70 turpentine 0 B Hexane 70 turpentine 0.5 C Hexane 70 turpentine 1 D Hexane 70 turpentine 1.5 E Hexane 70 turpentine 2 F Hexane 70 white spirit 0 G Hexane 70 white spirit 0.5 H Hexane 70 white spirit 1 I Hexane 70 white spirit 1.5 J Hexane 70 white spirit 2 K Toluene 70 turpentine 0 L Toluene 70 turpentine 0.5 M Toluene 70 turpentine 1 N Toluene 70 turpentine 1.5 O Toluene 70 turpentine 2 P Toluene 70 white spirit 0 Q Toluene 70 white spirit 0.5 R Toluene 70 white spirit 1 S Toluene 70 white spirit 1.5 T Toluene 70 white spirit 2

Determination of Concentration of Quantum Dots in Solution/Dispersion by Thermogravimetric Analysis (TGA)

[0134] The concentration of quantum dots was determined by thermogravimetric analysis (Perkin Elmer TGA-4000). The solutions/dispersions of quantum dots were first sonicated for 1 hour to disperse the quantum dots uniformly. 50 L of solution were deposited in a clean ceramic crucible boat.

[0135] The temperature range was ramped from 30 C. to 200 C. with a scan rate of 3 degrees/min and maintained at 200 C. for a hold time of 10 minutes. A continuous flow of dry compressed air (flow rate: 20 mL/min) was applied.

[0136] The change in mass over time was observed and compared between the initial mass and final mass after the scam scan. At 200 C., all solvent and surfactants had evaporated and a precipitate of pure inorganic quantum dot powder (solute) was recovered at the base of crucible. The value of final mass of inorganic solute was then used to calculate concentration parameters in mg/mL.

[0137] Once the concentration of the solutions was determined, calculations to find the density of Core (CuInS.sub.2) and Shell (ZnS) of the quantum dots were performed, in order to determine the weight percentage of CuInS.sub.2 and ZnS in the quantum dots. The molarity with respect to CuInS.sub.2 was then calculated using the following formula:

Molarity (mol/L)=Mass (g)/[Vol (L)Molecular Weight (g/mol)].

[0138] FIG. 2 shows the TGA results obtained for solutions (A, K, L). Laminates prepared with these three solutions provided the best results in the lamination process in terms of transparency of the laminate when the quantum dot coating is not activated and vibrancy of colour of the quantum dot coating when it is activated (see FIGS. 5, 6 and 7).

Preparation of Laminates

[0139] PVB substrates (Solutia RB41 PVB of dimensions 3 cm3 cm0.76 mm) were refrigerated overnight at 0-7 C. A quantum dot coating was deposited on each PVB substrate by either drop casting 50 L of a solution of quantum dots prepared as described above or hand painting a pattern on the PBV substrate using a template of the pattern cut on a vinyl mask (see FIG. 3). The coated substrates were allowed to dry at room temperature for 40 minutes.

[0140] A laminate was formed by sandwiching each PBV substrate between two clean clear glass panels (inner glass: 2.1 mm UltraClear glass; outer glass: 4 mm tinted Ultra dark glass). The side of the PVB substrate coated with the quantum dot coating was disposed facing and adhered to the inner glass. The inner glass is configured to face the inner space of a vehicle or building such that a viewer can observe a pattern displayed by the quantum dot coating from the inside of the vehicle or building. The outer glass is configured to face the outside surface of a vehicle or building.

[0141] The glass-PVB laminate was disposed in a vacuum chamber and vacuum was applied. The glass-PVB laminate was heated in an oven at 22 C. for 1 h under vacuum, the heat was ramped from 22 C. to 98 C. over a period of 3 hours under vacuum and the laminate was maintained at 98 C. for further 3 hours. The heat was ramped from 98 C. to 130 C. over a period of 30 minutes without applying vacuum and the laminate was maintained at 130 C. for 20-30 minutes without applying vacuum to reduce the air content in between the layers of the laminate. The sandwiches were allowed to reach room temperature over 1.5 hours.

[0142] After heating the laminates, they were subjected to pressure to minimise the presence of air bubbles in the laminate.

[0143] The laminates providing the greatest colour intensity in the excited state of the coating while maintaining a high degree of transparency in the non-excited state of the coating (measured as % transmittance, as shown in FIG. 1) were those prepared with solutions A (hexane stock solution undiluted), K (toluene stock solution undiluted) or L (dilution of toluene stock solution in 0.5 mL turpentine).

[0144] In order to apply pressure, the laminates were placed between two slabs of marble, concrete, metal or wood and a soft material (e.g. a fabric cloth) was placed in between the slabs and the laminate to prevent cracking the laminate during the application of pressure. However, pressure may be applied in an industrial process by any other suitable means, such as employing a laminating press, for example a hot laminating press that employs platens or rollers to generate pressure.

[0145] The coating of the laminates was excited by coupling a UV lamp (optical excitation source) to the glass panel to which the surface of the PVB coated with the quantum dot coating was adhered. Coupling a UV lamp to the laminate was performed by disposing a UV lamp in contact facing the laminate, for example on a side surface of the laminate to provide edge lighting. When the UV lamp was not switched on, the laminate remained colourless and transparent, and no image was displayed in the laminate (i.e. the coating was invisible to the human eye). When the UV lamp was switched on, the quantum dot coating was excited and emitted light, thus rendering the coating visible, for example displaying a pattern painted or deposited from the quantum dot coating on the PVB coating.

Measurement of Transmittance of Laminates by UV/Vis/NIR

[0146] The optical transparency of the laminates prepared with solutions A, K, and L in visible white light spectrum was measured by UV-Vis spectroscopy using a Perkin Elmer Lambda 750 UV/Vis/NIR spectrometer.

[0147] FIG. 1 shows a transmittance spectrum of the three laminates from 300 to 900 nm. It is observed that the laminate prepared with the most diluted solution showed the greatest transmittance, which is an indication of the highest degree of transparency.

Results

[0148] Table 2 shows the results of concentration of quantum dot solutions and the transmittance of laminates prepared with said solutions.

[0149] The concentration of the stock solutions A and K was comparable and the dilution factor of stock solution K in turpentine to generate solution L was around 1:7.

[0150] The density of quantum dots in each of the slides is provided as an average number of quantum dots per surface area and it is calculated by taking into account the volume employed to drop cast the solution on the substrate (50 L), the molarity of each solution, Avogadro's number and the area of each of the substrates (9 cm.sup.2):

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TABLE-US-00002 TABLE 2 Concentration of quantum dot solutions and transmittance of laminates coated with the solutions Molarity Density of Concen- of Trans- quantum dots Laminate QD tration CuInS.sub.2 mittance in substrate ID solution (mg/mL) (mM) (%) (QD/cm.sup.2) A Hexane stock 22.82 47.04 45 1.57 .Math. 10.sup.17 solution K Toluene stock 21.22 43.76 52 1.46 .Math. 10.sup.17 solution L Toluene stock 3.00 6.16 71 2.06 .Math. 10.sup.16 solution in 0.5 mL turpentine

[0151] FIG. 4 shows a quantum dot coating prepared by mixing Fxpoxy-Epoxy ultra clear UV resistant resin with quantum dots as a proof of concept. The coating was printed on a clear glass substrate using a Formlabs printer. In FIG. 4a it can be observed that the coating is transparent and colourless, and the line present in the wooden surface underneath the glass substrate is visible both through the glass substrate and the quantum dot coating. In FIG. 4b the quantum dot coating is activated by UV optical excitation and as a result the quantum dots in the coating emit blue-violet light. The line on the wooden surface underneath the glass substrate can still be seen through the coating.

[0152] FIGS. 5, 6 and 7 show images of three prototype laminates prepared according to the method described above. As shown in FIGS. 5a, 6a and 7a, the pattern printed on the substrate sandwiched between two pieces of glass in the laminate is not visible when the quantum dot coating of the substrate is in a first, not excited state. The coated substrate is transparent and colourless and objects behind the laminate can be observed through the laminate (see particularly FIG. 6a, in which the foot of the person holding the laminate is visible through the laminate, and FIG. 7a, in which the legs of the person holding the laminate are visible through the laminate and the colour of the trousers is unchanged).

[0153] Upon excitation of the quantum dot coating of the laminate with a UV lamp, the pattern printed using a quantum dot coating as described herein is revealed because the quantum dots absorb the UV light and emit light in a different wavelength (see the red and green emission of the pattern in FIGS. 5b, 6b and 7b). FIG. 6b shows that edge lighting the laminate with a UV lamp by directing the UV light to a side face of the substrate efficiently excites the quantum dot coating in the illuminated region, revealing the printed pattern only in the region illuminated by the UV light.