Light-emitting material with improved performance

Description

Technical field of the invention

[0001] The invention relates to a photoluminescent material whose luminescence performance is improved. Technological background

[0002] Phosphorescent materials made from a mixture of transparent or translucent materials with photoluminescent pigments made from rare-earth-doped mineral oxides are already known. Examples include a mixture of borosilicates with 50% Europium- and Dysprosium-doped strontium aluminate (Eu2+, Dy3+:SrAl2O4) or a mixture of acrylic resins with 50% Europium- and Dysprosium-doped strontium aluminate. The luminous decay of these materials is initially exponential. If we start with a luminance of a few tens of Cd / m² for a material placed in darkness after saturation with light energy, the luminance after 10 minutes in the dark will be less than 1 Cd / m². The luminous decay then slowly tends towards an asymptote at a few mCd / m² < explaining that these materials retain a luminous persistence visible in the dark for up to 12 hours.The good readability of diving instruments in a passive manner relies on these luminescent materials, and progress in terms of luminous performance is therefore highly anticipated.

[0003] Because phosphorescent pigments are sensitive to humidity, it is now preferable to encapsulate them in a transparent material to create photoluminescent decorations, thus producing a photoluminescent material. For aesthetic reasons, particularly daytime visibility, these photoluminescent materials can also be colored using a coloring system that mixes pigments and additives.

[0004] It is understood that the compounds used in photoluminescent materials, including color pigments, have a quenching effect on the luminescent properties, the luminance of phosphorescent materials being the result of a physicochemical interaction between the various compounds of the photoluminescent material. US 2021 / 284903 A1 discloses photoluminescent materials. Summary of the invention

[0005] The invention consists of developing a new formulation for photoluminescent materials that limits the "quenching" associated with the compounds added to the formulation.

[0006] To this end, it is proposed to add a porous silica dopant derived from algae to the formulation. This porous silica comes from the skeletons of diatoms. Diatoms are microalgae, which are unicellular organisms with a silica skeleton. Indeed, according to the latest biological research, diatoms, single-celled algae that make up plankton, are composed of silica nanocells that are highly efficient at absorbing daylight, even in the dark depths of the oceans, in order to perform photosynthesis effectively.

[0007] According to the invention, the addition of a limited percentage of porous silica, with contents less than or equal to one percent by mass, in the photoluminescent material makes it possible to significantly improve the luminescence properties.

[0008] More specifically, the invention relates to an article made of a photoluminescent material comprising by weight a polymeric matrix in a percentage between 19.99% and 54.99%, a photoluminescent compound in a percentage between 45% and 80%, porous silica in a percentage between 0.01% and 1% and optionally a dye system and additives with a total percentage for the dye system and additives between 0% and 15%, the porous silica is derived from diatom skeletons. Detailed description of the invention

[0009] The invention relates to a photoluminescent material comprising porous silica derived from diatom skeletons. It also relates to an article coated or made with this photoluminescent material. The article may, for example, be a watch component. More specifically, it may be a casing component chosen from the non-exhaustive list including a case, case back, bezel, crown, pusher, bracelet link, bracelet, pin buckle, clasp, dial, flange, date disc, hands, and dial markers.

[0010] The photoluminescent material comprises (is made up of) a polymer matrix, a photoluminescent compound, porous silica, and possibly a system of dyes and additives.

[0011] Relative to the total weight of the photoluminescent material, porous silica is present in a weight percentage between 0.01% and 1%, preferably between 0.07% and 0.3%, and more preferably between 0.09% and 0.2%. This porous silica is derived from diatom skeletons. Typically, the average pore diameter is around 500 nm. Alternatively, it could be synthetic porous silica. For synthetic silica, the pores typically have an average diameter between 0.1 µm and 3 µm. The polymer matrix is ​​present in a weight percentage between 19.99% and 54.99%, preferably between 29.93% and 49.93%, and more preferably between 29.91% and 49.91%. This can include all polymers that are transparent or semi-transparent in the visible spectrum.For example, it may be one or more of the following polymers: resins from the acrylic family, the polyamide family, the polyolefin family, the epoxy family, the polyurethane family, the fluorinated elastomer family, and silicones. The photoluminescent compound is present in a weight percentage between 45% and 80%, preferably between 50% and 70%. The luminescent compound may be formed from a pigment or from a pigment encapsulated in a shell. The pigment is preferably a rare-earth-doped alkaline earth aluminate derivative. More specifically, the pigment may be Europium-, Dysprosium-doped strontium aluminate with the formula Sr(x)Al(y)O(z): Eu 2+< ,Dy 3+< . In particular, it may be Sr 4 Al 14 O 25 : Eu 2+< ,Dy 3+< or SrAl 2 O 4 : Eu 2+< , Dy 3+< , possibly both present in the photoluminescent compound.Advantageously, pigments can have different particle sizes to allow for optimal distribution within the pigment volume and avoid voids. The presence of different particle sizes also allows for the combination of small particles forming shallow traps on the surface, responsible for high light intensity over short periods, with larger particles forming deeper traps, responsible for light persistence over longer periods.For example, pigments may exhibit a first particle size distribution centered on a diameter D1 between 500 nm and 10 µm, ideally between 500 nm and 5 µm, and a second particle size distribution centered on a diameter D2 between 10 µm and 500 µm, ideally between 10 µm and 20 µm. Particle size analysis is performed using laser grading according to ISO 13320:2020, possibly supplemented by secondary electron scanning electron microscopy (SEM). It should be noted that it is possible to obtain more than two particle size fractions by sieving and then combine them. For example, it is possible to have a first fraction between 500 nm and 5 µm in a weight percentage of 20%, a second fraction between 5 µm and 20 µm in a weight percentage of 60% and a third fraction between 20 µm and 50 µm in a weight percentage of 20%.

[0012] The pigments may optionally be encapsulated in a transparent organic or mineral shell. The organic shell can typically be chosen from the polymers mentioned for the polymer matrix. For a mineral shell, it could, for example, be a silica (SiO₂) shell obtained, for instance, via a sol-gel process. Other examples include zirconium oxide (ZrO₂), aluminum oxide (Al₂O₃), etc. The photoluminescent material optionally contains, in a percentage between 0% and 15%, preferably between 0% and 5%, a system of colorants and additives. The colorant system preferably comprises organic colorants that do not absorb in the emission wavelength ranges of the photoluminescent pigment. These may be fluorescent pigments or dyes whose absorption is primarily in the UV range and whose emission is in the visible spectrum.For example, these could be organic fluorescent pigments or dyes such as those from the Radiant or Aralon® brands. They could also be translucent pigments or dyes that absorb little light in the emission wavelengths of the phosphorescent pigment. For example, these could be translucent pigments or dyes from the Clariant brand. Other additives such as metallic and pearlescent pigments, UV-blocking additives to protect the polymer matrix, a dispersant such as silane to facilitate the dispersion of additives, and a nanometric silica-type filler to adjust the viscosity parameters of the mixture, etc., can be added.

[0013] The process involves mixing the polymer(s) intended to form the polymer matrix, preferably with a dispersant. This initial mixture includes photoluminescent pigments, which may be pre-encapsulated. Next, porous silica is added to this second mixture, along with the optional colorant system and additives. The mixtures can be prepared starting from liquid resins using a speed mixer or a paddle mixer. The resulting mixture can then be shaped by extrusion. Alternatively, the mixtures can be prepared in a twin-screw extruder or a high-speed mixer for the production of thermoplastic compounds and their transformation into granules, which can be reused for injection molding.

[0014] Tests were carried out by adding between 0.09% and 0.2% by weight, relative to the total weight of the photoluminescent material, of porous silica to a two-component epoxy resin with an amide hardener. A loading rate of 50% of photoluminescent pigments formed from Europium-doped strontium aluminate and Dysprosium, relative to the total weight of the photoluminescent material, was also added.

[0015] The material was shaped by casting this mixture. Those skilled in the art can easily adapt this formula to other classes of polymer materials that can be injection molded or extruded. This formula is also readily transferable to polymer dispersions in solvents for application by screen printing, pad printing, spraying, etc.

[0016] Luminescence properties were measured according to ISO 17514-2003 and an improvement of 5% to 7% was observed compared to the same composition without the addition of porous silica.

Claims

1. A photoluminescent material including by weight a polymer matrix in a percentage comprised between 19.99% and 54.99%, a photoluminescent compound in a percentage comprised between 45% and 80%, porous silica in a percentage comprised between 0.01% and 1% and optionally a dye system and additives with a total percentage for the dye system and additives comprised between 0% and 15%, porous silica is derived from diatom skeletons.

2. The photoluminescent material according to claim 1, characterised in that the polymer matrix is present in a percentage comprised between 29.93% and 49.93%, the photoluminescent compound in a percentage comprised between 50% and 70%, and the porous silica in a percentage comprised between 0.07% and 0.3%.

3. The photoluminescent material according to claim 1 or 2, characterised in that the polymer matrix is present in a percentage comprised between 29.91% and 49.91%, the photoluminescent compound in a percentage comprised between 50% and 70%, and the porous silica in a percentage comprised between 0.09% and 0.2%.

4. The photoluminescent material according to one of the preceding claims, characterised in that the photoluminescent compound includes a pigment which is a rare earth-doped alkaline earth aluminate derivative.

5. The photoluminescent material according to the preceding claim, characterised in that the pigment is a Europium, Dysprosium doped alkaline earth aluminate derivative of formula Sr(x)Al(y)O(z): Eu2+, Dy3+.

6. The photoluminescent material according to the preceding claim, characterised in that the pigment is Sr4Al14O25: Eu2+, Dy3+ and / or SrAl2O4: Eu2+, Dy3.

7. The photoluminescent material according to one of claims 5 to 6, characterised in that the photoluminescent compound consists of said pigment encapsulated in a transparent organic or mineral shell.

8. The photoluminescent material according to one of the preceding claims, characterised in that the polymer matrix includes one or more resins from the acrylic family, the polyamide family, the polyolefin family, the epoxy family, the polyurethane family, the fluoroelastomer family and silicones.

9. The photoluminescent material according to claim 7, characterised in that the transparent organic shell includes one or more resins from the acrylic family, the polyamide family, the polyolefin family, the epoxy family, the polyurethane family, the fluoroelastomer family and silicones, and in that the transparent inorganic shell includes silica.

10. The photoluminescent material according to one of claims 4 to 9, characterised in that the photoluminescent compound includes pigments of different particle sizes.

11. The photoluminescent material according to the preceding claim, characterised in that the pigments have at least a first particle size range centred on a diameter D1 comprised between 500 nm and 10 µm and a second particle size range centred on a diameter D2 comprised between 10 µm and 500 µm.

12. An article made of or coated with said photoluminescent material according to one of the preceding claims.

13. The article according to the preceding claim, characterised in that it is a timepiece component.