Photoluminescent coating for vehicles

The present invention provides a method and composition for illuminating a contoured surface, such as a vehicle having a receiving surface extending from a structural member. A method includes providing a heterogeneous mixture including a semiconductor nanocrystal complex and a dispersion media, with the complex generally including a middle layer extending between a core and an outer layer. The mixture may be applied to receiving surface which receives illumination having sufficient characteristics for illuminating the contoured surface, and added during the polymer processing. In addition, a vehicle illumination composition is provided in which a heterogeneous mixture of a semiconductor nanocrystal complex is immersed within a dispersion media, wherein the complex may further include a semiconductor nanocrystal core separated from an outer layer by a middle layer, and the heterogeneous mixture illuminates the contoured surface.

FIELD OF THE INVENTION

This invention relates to coating of vehicles. More specifically, the present invention relates to an illuminating semiconductor nanocrystal coating for vehicles.

BACKGROUND OF THE INVENTION

At night, in low light conditions, it is often difficult to visualize approaching vehicles with limited ambient light associated with the approaching vehicle. In addition, some vehicles are not illuminated because they are parked with their lights turned off. One attempt to address these difficulties is with installing reflective lenses in the approaching vehicle, which, at least in part, reflect some of the light back towards the traveling vehicle, allowing the traveling vehicle to at least partially visualize the approaching vehicle. Other attempts include illuminating kits which require electrical circuitry to increase the visibility of approaching cars. Some of these attempts are utilized during the vehicle manufacturing process and some are after market items installed on the vehicle after the manufacturing process has been completed. Present limitations are addressed by the current invention, which is directed to a vehicle illumination layer.

Several automotive pigments including effect pigments, gloss or lustrous pigments are used to produce unique coloristic effects. Generally, these effect pigments have limited effect as they are generally governed by the optical properties related to reflection and/or interference phenomenon. Generally, finishes containing a visual effect pigment produce a “flop effect” whereby the coloristic characteristics of the surface change depending on the viewing angle. In general, when a change in the viewing angle results in a change in lightness, the effect is referred to as lightness flop, and when the changes are in hue, the effect is referred to as color flop. However, these effects are limited to situations with sufficient available ambient light to produce the coloristic effect and are only modified based upon a change in viewing angle. In situations with a constant viewing angle or with limited ambient light, these effects are not as visually noticeable. In addition, a change in color does not necessarily provide illumination for the associated vehicle. Therefore, there is a need to provide a special visual layer which provides an illumination effect in low light situations.

The present invention relates to the surprising discovery that by applying a semiconductor nanocrystal complex, stably coupled to tertiary molecules, an emission of light of a desired frequency is provided which allows for higher visibility of coated surfaces during low light level situations.

SUMMARY OF THE INVENTION

The present invention reduces the difficulties and disadvantages of the prior art by providing a method and composition for illuminating a contoured surface having a receiving surface extending from a structural member, the method comprising the steps of providing a heterogeneous mixture including a semiconductor nanocrystal complex and a dispersion media, said semiconductor nanocrystal complex including a core, a middle layer and an outer layer, said middle layer extending therebetween, applying the heterogeneous mixture to the receiving surface and illuminating the heterogeneous mixture with an illumination source sufficient to cause said contoured surface to luminesce. The present invention also contemplates a vehicle illumination composition comprising a heterogeneous mixture having a semiconductor nanocrystal complex immersed within a dispersion media, said semiconductor nanocrystal complex further including a semiconductor nanocrystal core separated from an outer layer by a middle layer, said middle layer extending therebetween, whereby said heterogeneous mixture causes a contoured surface to luminesce.

DETAILED DESCRIPTION OF THE INVENTION

In general, the present invention relates to a heterogeneous mixture of a semiconductor nanocrystal complex and a dispersion media applied to the surface of an object, the mixture being excitable by a selected illumination source.FIG. 1illustrates an embodiment of the method and composition in which an illuminating heterogeneous mixture (generally referred to by the reference numeral10) is applied to a three dimensionally contoured object2having a receiving surface4positioned adjacent to a structural member6associated with the contoured object2, such as an automotive body. Upon receipt of an illumination source, such as but not exclusively limited to, a vehicle headlight, the contoured object2is adapted for selective illumination. In carrying out the invention, the heterogeneous mixture10may be applied to the contoured object2as a liquid, a solid or an aerosol.

Upon receipt of the illumination source, the contoured object illuminates as the photons from the illuminating source energize the semiconductor nanocrystal complex, allowing the structural members6associated with the received heterogeneous mixture10to become visible. Depending on the application of the heterogeneous mixture10, the entire contoured object2may illuminate, portions of the contoured object2may illuminate or different portions may have different illumination characteristics for enhanced visibility of the contoured object2.

A cross-section of the heterogeneous mixture10associated with the three dimensional contoured object2is illustrated inFIG. 2. Although illustrated as three regions, the structural member6, an intermediary or receiving surface4and an overlying surface12, the cross-section may vary depending on the number of intermediary layers4. Generally, the receiving surface4is adapted to receive the overlying surface12. Alternatively, the overlying surface12, which generally represents the heterogeneous mixture10, may be applied as plural adjacent layers adapted for illuminating the three dimensional contoured object2.

Generally, the semiconductor nanocrystal complex20of the present invention is illustrated inFIG. 3and includes a semiconductor nanocrystal core22, a middle layer24and a outer layer26. As illustrated, the semiconductor nanocrystal core22is generally coated by the middle layer24. At the surface of the semiconductor nanocrystal core22, surface defects can result in traps for electron or holes that degrade the electrical and optical properties of the semiconductor nanocrystal. The surface of the middle layer24, associated with the semiconductor nanocrystal core22, provides an abrupt jump in electron energy potential which helps contain the electrons and holes. This results in greater luminescent efficiency.

Generally, the middle layer24provides a covering having semiconductors with a higher band gap energy than the semiconductor nanocrystal core22. In addition, the middle layer24may provide a good conduction and valence band offset with respect to the semiconductor nanocrystal core22. The conduction band of the middle layer24is desirably higher and the valance band is desirably lower than those of the semiconductor nanocrystal core22. Thus, the band gap energy of the middle layer24is generally higher than that of the semiconductor nanocrystal core22.

The heterogeneous mixture10, as shown inFIG. 2, includes plural clusters14of semiconductor nanocrystals which range from a few angstroms to a few micrometers in diameter and can become luminescent if subjected to light of a complementary wavelength. The emitted light may depend, at least in part, on the utilized semiconducting material and its parameters, however, it is preferred that the emitted light be within the visible spectrum.

The present invention comprises coating a semiconductor nanocrystal (also known as a “semiconductor nanoparticle” or a “quantum dot”) with a layer of a surface molecule, which has an affinity for the surface of the semiconductor nanocrystal and affinity to the disruption media on the other end to be further used in coating, painting of the surfaces three-dimensional contoured object2and/or as an additive in manufacturing of the polymeric parts. Generally, semiconductor nanocrystals are spherical nanoscale crystalline materials (although oblate and oblique spheroids can be grown as well as rods and other shapes) having a diameter between 1 nm and 20 nm and typically, but not exclusively, composed of II-IV, III-V and IV-VI binary semiconductors.

In accordance with the present invention, the semiconductor nanocrystal core22generally includes a first semiconductor30that has a selected composition and diameter that enables light emission at a predetermined wavelength and optionally a second semiconductor32that has a lattice constant complementary to the semiconductor nanocrystal core22. Non-limiting examples of first and second semiconductors30,32include ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, GgTe (II-VI materials); PbS, PbSe, PbTe (IV-VI materials); AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb (III-V materials).

Generally, the semiconductor nanocrystal complex20associated with the semiconductor nanocrystal core22may be 12 to 150 Å in diameter, depending on the desired wavelength of the emitted light. However, the deviation in size of the semiconductor nanocrystal complex20should be generally around 5% or less to provide the desired size and color dependant properties. As previously described, the middle layer, or shell,24generally provides semiconductors of a higher band gap to trap electrons escaping through the surface due to faults on the surface of the core. The middle layer24may include up to seven monolayers of various semiconducting materials.

The semiconductor nanocrystal complex20may include the middle layer or alternatively, may omit the middle layer. If present, the middle layer may be crystalline with semiconductor properties. The middle layer24, if present extends between the semiconductor nanocrystal core22and the outer layer26. The outer layer26may be a monolayer or may be comprised of molecules that have two or more functional groups or ends. The first functional group36may be polar, generally having an affinity for the middle layer or the core. The first functional group36generally extends towards and has an affinity for the surface of the semiconductor middle layer24or nanocrystal core22if the middle layer24is absent. The second functional group38generally extends towards and has an affinity for a solvent16associated with a colloid suspension18. The molecules comprising outer layer26may have an additional optional functional group40, that may modify the affinity of the nanocrystal complex20for solvent16.

In use, the semiconductor nanocrystal complex20is suspended within the heterogeneous mixture10or at least adapted for suspension within a heterogeneous mixture10for application as a luminescent layer on the three-dimensional contoured object2. The colloid suspension18may depend, in part, on which modifying agent is associated with the heterogeneous mixture10. Through association with a complementary surfactant, the colloid suspension18may have an affinity for a hydrophobic or a hydrophilic solvent.

Generally, the first end38may include plural functional groups, one being associated with the semiconductor nanocrystal core22or middle layer24and the other with the hydrophobic solvent which may include, but is not limited to, thiols, amines, phosphines, phosphine oxides, and any combinations thereof. Non-exclusive examples of molecules comprising outer layer26may include trioctyl phospine oxide (TOPO), trioctyl phospine (TOP), tributyl phospine (TBP), dodecyl amine, octadecyl amine, hexadecylamine, steric acid, oleic acid, palmitic acid, lauric acid and any combination thereof. Covering the semiconductor nanocrystal core22with the middle layer24may be accomplished through pyrolysis or by the addition of organometallic precursors in a chelating ligand solution or by an exchange reaction using the prerequisite salts in a chelating surface solution, such chelating surfaces typically being lipophilic. Generally, the middle layer24tends to assemble into a coating around the semiconductor nanocrystal core22, forming a surface-coated semiconductor nanocrystal. The addition of outer layer26enables the nanocrystal complex20to be suspended within the hydrophobic solvent.

Alternatively, the outer layer26may be coated with a stabilizing agent such as a surfactant or a diblock polymer, to stabilize the surface-coated semiconductor nanocrystal within an aqueous solution. In addition to stabilizing the surface-coated semiconductor nanocrystal, the stabilizing agent may also isolate nearby semiconductor nanocrystal cores22from each other by spacing them apart and preventing charge transfer across neighboring spaces.

The outer layer26may be associated with the bi-functional agents or other molecules, including a variety of surfactants, and may consist of molecules that have a first outer-end38and a second outer-end40, the first outer-end38having an affinity for the semiconductor nanocrystal. When the present invention is immersed within a dispersion media, such as but not limited to paint or some other surface coloring material, the second outer-end40may be adapted with an affinity for the dispersion media thereby allowing the heterogeneous mixture10, including the surface coloring material, to be selectively applied to the contoured object2.

Generally, the resulting coloristic effect may depend upon the size of the selected semiconductor nanocrystal, which in operation, may be easily adjusted to produce the desired effect. The bi-functional agent associated with the outer layer26may be optimized for dispersion within a pigmented substance like automotive paint, however, other uses may be contemplated including for use within cosmetics, inks and plastics and other materials suited for a coloristic effect produced by the illumination of light. Alternatively, plural semiconductor nanocrystal complex mixtures may be selectively applied to the receiving surface, each mixture producing different coloristic effects produced by semiconductor nanocrystal having varying diameters, providing various effects through-out the surface of the contoured object2.

In operation, the semiconductor nanocrystal complex20may be immersed within a dispersion media to form the heterogeneous mixture10which is then adapted for application to the contoured object2, having a three-dimensionally contoured surface such as an automotive body panel which may or may not have an underlying pigmented surface adapted to receive the heterogeneous mixture10.