COMPOSITE SYSTEM COMPRISING A MATRIX AND SCATTERING ELEMENTS, PROCESS FOR PREPARING IT AND USE THEREOF

Abstract

A composite system for light diffusion comprises a matrix of a material that is transparent to light; the matrix contains a dispersion of scattering elements having a core that is a nanocluster of inorganic nanoparticles, and a shell comprising silane compounds and dispersing agents; the nanocluster having average dimensions in the range of 20 nm to 300 nm.

Claims

1. A composite system, comprising a matrix wherein a plurality of scattering elements is dispersed, wherein said matrix is of a material that per se is transparent and does not absorb light, said scattering elements have a core, said core having a refractive index that is different from the refractive index of the matrix to provide a scattering of at least a portion of the light transmitted through said system, characterized in that said core comprises a nanocluster of inorganic nanoparticles, said nanocluster having average dimensions in the range of 20 nm to 300 nm, and wherein said scattering elements further comprise at least a silane compound and at least a dispersing agent that provide at least part of a shell for said nanocluster core.

2. A composite system according to claim 1, wherein said matrix is a polymer matrix.

3. A composite system according to claim 2, wherein said scattering elements are free from a shell made of the same polymer of the polymer matrix.

4. A composite system according to claim 1 or 2, wherein said inorganic material is selected from TiO.sub.2, SiO.sub.2, ZnO, ZrO.sub.2, Fe.sub.2O.sub.3, Al.sub.2O.sub.3, Sb.sub.2SnO.sub.5, Bi.sub.2O.sub.3, CeO.sub.2, preferably from ZnO and TiO.sub.2.

5. A composite system according to any claims 1 to 3, wherein the average dimension of said nanoclusters is comprised in the range of 20 nm to 300 nm, preferably in the range of 50 nm to 200 nm, more preferably in the range of 80 nm to 130 nm.

6. A composite system according to claim 5, comprising scattering elements having a core comprising a single nanoparticle and having a shell including at least one silane compound and at least one dispersing agent that provide at least part of a shell for said single nanoparticle core.

7. A composite system according to any previous claim, wherein said at least one silane compound is selected from Triacetoxy(methyl)silane, Di-Tert-butoxydiacet-oxysilane, Phenyltriethoxysilane, (3-Aminopropyl)tris(trimethylsiloxy)silane, N-(n-butyl)-3-amino-propyltrimehoxysilane, N-[3-(Trimethoxysilyl)propyl]aniline, Bis (3-triethoxysilylpropyl) amine, -Aminopropyltriethoxysilane, 2-(Allyldimethylsilyl)pyridine, 3-(Trimethoxysilyl)propyl-methacrylate, Viniltrimethoxysilane, Triphenyl(vinyl)silane, Tris(2-methoxyethoxy)(vinyl)silane, -Glycidoxypropyltrimethoxysilane, 3-(Triethoxysilyl)propyl isocyanate, or a mixture thereof.

8. A composite system according to any previous claim, wherein the number of scattering elements within a volume element delimited by a portion of so the panel, foil or film surface having an area of 1 m.sup.2, is N, wherein NN.sub.min, preferably 2N.sub.minN13N.sub.min, more preferably N is in the range 3N.sub.min to 10N.sub.min, most preferably N6N.sub.min and wherein: $N_{\min }=.Math.\frac{{10}^{-29}}{D^6}.Math.{.Math.\frac{m^2+2}{m^2-1}.Math.}^2$ where is a dimensional constant equal to 1 meter.sup.6, N.sub.min is expressed as a number/meter.sup.2, the effective diameter D, which is given by the scattering element diameter times the matrix refractive index, is expressed in meters and wherein m is equal to the ratio of the refractive index of the nanoparticle core to the refractive index of the matrix material.

9. A composite system according to any claims 2 to 8, wherein said matrix is a paint, preferably an anti-scratch paint.

10. A composite system according to claim 9, wherein said paint is coupled with a reflecting element, preferably with a mirroring surface.

11. A composite system according to any claims 2 to 10, wherein said polymer matrix is an adhesive material, preferably a film, for glass lamination,

12. A composite system according to claim 11, wherein said polymer matrix is selected from EVA, PVB and mixtures thereof.

13. A process for preparing a composite system that is a matrix/nanocluster composite system, wherein a plurality of scattering elements is dispersed in a matrix, preferably a polymer matrix, wherein the material used for preparing matrix is a material that per se is transparent and does not absorb light, characterized in comprising the following steps: a. selecting at least one inorganic material made of nanoparticles, said nanoparticles having average dimensions in the range of 10-150 nanometers; b. mixing said material, at least one solvent and at least one dispersing agent, to obtain a dispersion of nanoclusters having average dimensions in the range of 20 to 300 nanometers; c. adding at least one silane compound to the dispersion obtained in step b) to give a dispersion of scattering elements having an inorganic core that is a nanocluster as per point b) and at least part of a silane shell; d. optionally filtering the dispersion obtained in step c) in order to select the dispersed scattering elements having the desired average dimension; e. dispersing said dispersed scattering elements into the systems from which said matrix will be obtained; whereby said matrix/nanocluster composite system provides a scattering of at least a portion of the light transmitted through said composite system or through a product containing said system.

14. A process according to claim 13, wherein said matrix/nanocluster composite system provides a Rayleigh or a Rayleigh-type scattering of at least a portion of the light transmitted through said system or through a product containing said system.

15. A process according to claim 14, wherein step b) provides a dispersion including nanoclusters and single nanoparticles, said nanoclusters and nanoparticles having average dimensions in the range of 20 to 300 nanometers.

16. A process according to claim 13 or 15, wherein said matrix is a paint comprising polymer resins and at least a solvent, and wherein said scattering is provided by said polymer matrix/nanocluster composite system after said solvent has evaporated from a layer of paint.

17. A process according to any claims 13 to 16, further comprising the step of acidifying the mixture during step b) and/or the step of concentrating the dispersion obtained in step d).

18. A process according to any claims 13 to 17 wherein said polymer matrix is an adhesive material for glass lamination, preferably selected from EVA, PVB and mixtures thereof.

19. A process of glass lamination, wherein a composite system according to so claim 11 or 12 is used as adhesive material for coupling layers of glass.

Description

EXAMPLE

Phase 1

Selection of the Inorganic Nanoparticles Material

[0111] Nanoparticles of Zinc Oxide were used for the development of the core of the scattering element. Zinc Oxide is available on the market and. In this embodiment Zinc Oxide nanoparticles having nominal diameter<100 nm are used. Nanoparticles are present as aggregates. As discussed above, Zinc Oxide is a preferred inorganic material for the core of the scattering elements, since it has a quite high refractive index and leads to efficient Rayleigh scattering effect.

Phase 2

Wetting of the Inorganic Nanoparticles and Acidification of the Working Environment

[0112] The nanoparticles of phase 1 are added to the solvent. Suitable solvents are the ones mentioned before.

[0113] As different solvents can be used, a proper solvent can be selected according to the matrix medium in which the scattering element's dispersion must be incorporated.

[0114] At least one dispersant is then added to the solvent and nanoparticles mixture.

[0115] Suitable dispersants are the above mentioned ones, marketed, for example, by Byk, Finco, Macri Chemicals and other professional producers.

[0116] The resulting mixture is then sonicated (600 W, 22 kHz continuous) at 40-50 C. for 4 days; at the end of this time the average dimension of the nanoclusters is 80-130 nm.

[0117] After 1.5 days of sonication, the mixture is acidified by adding Acetic Acid in a quantity of 0.05 ml for 100 ml of solvent, in order to further improve the action of the dispersants.

Phase 3

Functionalization With Silane

[0118] The nanoclusters, dispersed as above discussed are functionalized by adding a specific silane compound, selected to obtain the best compatibility with the chemical nature of the final matrix.

[0119] The quantity of silane to be added into the mixture is calculated by using the commonly known formula:

silane (gr.)=nanoparticles (gr.)surface area (m2/gr)/kSWA

[0120] where k=Specific Wetting Area of the used silane

[0121] By adding the silane compound, silane-functionalized nanoclusters of inorganic nanoparticles, which do not further aggregate, are obtained. In other words, the silane freezes the cluster of nanoparticles in the size it was in at the time of its addition.

[0122] Furthermore the silane allows the compatibilization of the inorganic core of the scattering element, with the matrix wherein the silane-coated nanoparticles will be dispersed.

Phase 4

Filtration and Concentration

[0123] The dispersion obtained as discussed above, is filtered through a suitable system with, in this example, a cutoff at 150 nm. This physically removes aggregates and nanoparticles having a non-adequate size in a fast, precise and relatively inexpensive.

[0124] It shall be noted that after centrifuging the dispersion, removing the solvent, and leaving for 2 months the scattering elements to dry, once they are wetted again by addition of solvent to the dry scattering elements, by simple mechanical stirring, the scattering elements return to their original conditions of dispersion, i.e. without showing an increase in diameter of the scattering elements. This has been verified by measuring the size of the scattering elements by means of Dynamic Light Scattering machine.

Phase 5

Preparation of the PMNC

[0125] The dispersion, containing the scattering elements, was weighed and diluted in a commercial solvent borne paint. The transparent dispersion was sonicated for 2 hours to get the scattering elements well dispersed. Spray coating, a standard application technique, is then used to coat a selected substrate material according to the final application. Depending on the thickness of the paint and the concentration of scattering elements used, various gradation of Rayleigh Scattering can be obtained.

[0126] Other techniques may be used, such as extrusion, injection moulding, reaction injection moulding, bulk polymerization compression moulding, transfer moulding, extrusion moulding, rotomoulding, blow moulding, calendering, knife coating, etc.

[0127] The characteristic of having a starting material that can undergo many different treatments is one of the advantages of the present invention.