Light-colored photoluminescent materials

Abstract

The invention relates to a photoluminescent material comprising, by weight, 19.3% to 54.3% of a polymer matrix, 45% to 80% of a photoluminescent compound, 0.5% to 15% of zirconia, 0.2% to 7% of a fluorescent whitening agent and optionally comprising 0% to 5% of alumina, 0% to 0.3% of porous silica, and a dye system and additives, wherein the total percentage of the dye system and the additive is 0% to 15%. The invention also relates to an article coated with the photoluminescent material or an article prepared as a whole from the photoluminescent material.

Description

Technical Field

[0001] The present invention relates to a light-colored photoluminescent material with optimized luminescent properties. Background Art

[0002] Strontium aluminate phosphorescent pigments doped with europium and dysprosium (Eu 2+ , Dy 3+ :SrAl2O4) are commonly used to prepare photoluminescent materials. These pigments that emit green or blue usually have a light yellow hue, making it difficult to obtain a specific light color. Adding dopants such as calcium to the lattice can whiten the pigment, but this has a significant impact on the luminescent properties.

[0003] It has been noted that certain compounds used in photoluminescent materials, including coloring pigments, have a quenching effect on the luminescent properties, and the brightness of the phosphorescent material is the result of the physico-chemical interactions between various compounds in the photoluminescent material.

[0004] Therefore, it is difficult to optimize both the coloring and luminescent properties simultaneously. To develop formulations, the inventors experimented with inorganic compounds to whiten the luminescent material, such as TiO2, CaCO3, ZnO, BaSO4, SiO2, and Al2O3. These inorganic compounds were added to an epoxy polymer matrix filled with 60 wt% phosphorescent pigment, which is of the type of strontium aluminate doped with europium and dysprosium (Eu 2+ , Dy 3+ :SrAl2O4). This experiment showed that these inorganic compounds have an adverse effect on the luminescent properties. Therefore, an optimization must always be sought between the color that must be perceived in daylight and the photoluminescent properties. Summary of the Invention

[0005] The present invention includes novel formulations for white and more generally for light colors, which allow for obtaining a beautiful light color in daylight and at the same time having excellent luminescent properties.

[0006] To this end, the present invention proposes adding zirconia (ZrO2), more particularly stabilized zirconia, and even more particularly zirconia stabilized with 4 or 5 mol% yttrium oxide, adding a fluorescent whitening agent, and optionally adding alumina (Al2O3). This combination provides the best balance between whiteness and luminescent properties, thereby resisting the light yellow characteristic of pigments derived from rare earth element-doped alkaline earth metal aluminates. This color can then optionally be adjusted to a lighter shade by adding a dye system.

[0007] More specifically, the present invention relates to a photoluminescent material comprising, by weight, 19.3% to 54.3% of a polymer matrix, 45% to 80% of a photoluminescent compound, 0.5% to 15% of zirconia, 0.2% to 7% of a fluorescent whitening agent, and optionally 0% to 2.5% of alumina, 0% to 0.3% of porous silica, and a dye system and additives, wherein the total percentage of the dye system and additives is 0% to 15%.

[0008] Fluorescent whitening agents can be used to obtain a bright white. This is because they can absorb in the near-UV visible spectral range and re-emit in the blue light range. In particular, fluorescent whitening agents counteract the yellowish tint of phosphorescent pigments.

[0009] If Al2O3 is added, the formulation can be whitened more significantly. Merely adding Al2O3 would quench the luminescence too quickly. Al2O3 must be used in combination with zirconia to avoid this problem.

[0010] Optionally, the photoluminescent material further comprises porous silica derived from algae to improve the luminescence performance. The porous silica is derived from diatom skeletons. They are microalgae, which are single-celled organisms with silica skeletons. More specifically, according to the latest biological research, diatoms, as a type of single-celled alga that makes up plankton, are composed of silica nanocells that are very effective in absorbing sunlight, even in the dark depths of the ocean, so they can carry out photosynthesis effectively. Adding a limited percentage of porous silica to the photoluminescent material can improve the luminescence performance, and the content is less than or equal to 1% by mass.

[0011] The present invention also relates to an article prepared integrally from the photoluminescent material or an article coated with the photoluminescent material. Detailed Description

[0012] The present invention relates to a photoluminescent material comprising zirconia (ZrO2). The material can be used to prepare articles integrally or to coat articles. The articles can be, for example, watch parts. More specifically, the articles can be external parts selected from the non-limiting list including watch middle parts, back covers, bezels, crowns, push-pieces, bracelet links, bracelets, tongue buckles, clasps, dials, flanges, date discs, hands, and dial graduations.

[0013] The photoluminescent material comprises (consists of) a polymer matrix, a photoluminescent compound, zirconia, a fluorescent whitening agent and optionally alumina (Al2O3), porous silica and a dye system and additives.

[0014] The zirconia is in the form of stabilized zirconia, such as zirconia stabilized with 4 mol% or 5 mol% yttrium oxide; the zirconia is present in a weight percentage of 0.5% to 15% based on the total weight of the photoluminescent material, and this percentage depends on the color to be obtained. Preferably, the zirconia is present in a percentage of 1% to 10%. Generally, the particle size of the zirconia is submicron, with a D50 of about 500 nm.

[0015] The polymer matrix is present in a weight percentage of 19.3% to 54.3%, preferably 28.5% to 48.5%. It should be noted that the upper limit of the polymer matrix is calculated for the photoluminescent material without alumina, without porous silica and without a dye system and additives. In the presence of any of these compounds, the upper limit will be reduced accordingly so that the total amount of compounds in the photoluminescent material does not exceed 100%. As for the polymer matrix, it can be any polymer that is transparent or translucent in the visible range. For example, it can 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 fluorosilicone family and silicone.

[0016] The photoluminescent compound is present in a weight percentage of 45% to 80%, preferably 50% to 70%. The photoluminescent compound can consist of a pigment or a pigment encapsulated in a transparent shell. The pigment is preferably an alkaline earth metal aluminate derivative doped with rare earth elements. More specifically, the pigment can be strontium aluminate doped with europium and dysprosium, which has the formula Sr(x)Al(y)O(z):Eu 2+ ,Dy 3+ . In particular, it can be Sr4Al 14 O 25 :Eu 2+ ,Dy 3+ or SrAl2O4:Eu 2+ ,Dy 3+, optionally both are present in the photoluminescent compound. Advantageously, the pigments can have different particle sizes to allow for an optimal distribution of the pigments within the volume and to avoid free space. The presence of different particle sizes within the volume also enables the incorporation of small and large particles, where the small particles form superficial traps responsible for high light intensity in the short term and the large particles form deeper traps responsible for the remaining light intensity in the long term. For example, the pigments can have a first particle size range with a diameter D1 of about 500 nm to 10 μm, desirably 500 nm to 5 μm, and a second particle size range with a diameter D2 of about 10 μm to 500 μm, desirably 10 μm to 20 μm, the particle sizes being measured by laser particle size analysis according to ISO13320:2020, optionally equipped with SEM analysis using secondary electron imaging. It should be noted that more than two particle size fractions can be screened and then combined. For example, it can have a first fraction of 500 nm to 5 μm at 20 wt%, a second fraction of 5 μm to 20 μm at 60 wt%, and a third fraction of 20 μm to 50 μm at 20 wt%.

[0017] The pigments can optionally be encapsulated in a transparent organic or inorganic shell. The organic shell can generally be selected from those polymers mentioned with respect to the polymer matrix. The inorganic shell can be, for example, a silica (SiO2) shell, which is obtained, for example, by the sol-gel method. Other examples of inorganic shells include zirconia (ZrO2) and alumina (Al2O3), etc.

[0018] The photoluminescent material also contains a fluorescent whitening agent to impart white color to the material. The fluorescent whitening agent is present in a weight percentage of 0.2% to 7%, preferably 0.5% to 5%. The fluorescent whitening agent used is a synthetic organic molecule derived from a stilbene compound containing a sulfonate group, which absorbs in the range of 300 nm to 400 nm and re-emits in the blue-violet range. They are mainly used in materials as whitening agents. Examples include distyryl biphenyl (DSBP) and diamino stilbene derivatives.

[0019] Optionally, the photoluminescent material can contain alumina (Al2O3) in a weight percentage of 0% to 5%, preferably 0% to 2.5%, depending on the desired whiteness. Advantageously, the photoluminescent material contains 0.5% to 5% of Al2O3, more advantageously 0.5% to 3% of Al2O3.

[0020] The photoluminescent material optionally further contains a total of 0 wt% to 15 wt%, preferably 0.5 wt% to 8 wt% of a dye system and additives. Preferably, the material contains 0.5 wt% to 5 wt% of the dye system. The dye system preferably comprises organic dyes that do not absorb within the emission wavelength range of the photoluminescent pigment. These organic dyes can be fluorescent pigments or dyes, which absorb more in the UV range and emit in the visible spectrum. Examples include organic fluorescent pigments or dyes, such as those from or . They can also be translucent pigments or dyes that have low absorption in the emission wavelength of the phosphorescent pigment. Examples include translucent pigments or dyes from Clariant. Other additives can be added, such as metallic and pearlescent effect pigments, UV-resistant additives for protecting the polymer matrix, dispersants such as silanes for promoting the dispersion of additives, and silica-based nanofillers for adapting the viscosity parameters of the mixture, etc.

[0021] Optionally, the photoluminescent material can contain porous silica derived from diatom skeletons. Generally, the average pore diameter can be about 500 μm. Optionally, it can be synthetic porous silica. Regarding synthetic silica, the pores generally have an average diameter of 0.1 μm to 3 μm. The porous silica is present in a weight percentage of 0% to 0.3%, preferably 0.01% to 1%, more preferably 0.07% to 0.3%, and even more preferably 0.09% to 0.2%.

[0022] The method for manufacturing an article from the photoluminescent material as a whole includes mixing one or more polymers for forming a polymer matrix with a preferably a dispersant. This initial mixture is mixed with a photoluminescent pigment, which can optionally have been pre-encapsulated. Then, zirconia, a fluorescent brightener, and any dye system, additives, alumina, and porous silica are added to the second mixture. These mixtures can be prepared from liquid resins using an accelerating mixer or a paddle mixer. The resulting mixture can then be extrusion molded. These mixtures can also be prepared in a twin-screw extruder or a high-speed mixer for producing thermoplastic mixtures and transformed into pellets, which can be reused for injection molding.

[0023] The method for manufacturing an article coated with the photoluminescent material includes depositing a coating on a substrate, which is carried out using techniques such as screen printing, pad printing, or spraying.

[0024] The test for preparing a sample from the photoluminescent material as a whole is carried out as follows: Based on the total weight of the photoluminescent material, 5 wt% of yttria-stabilized zirconia is added to an epoxy resin, where the photoluminescent pigment Eu 2+ ,Dy 3+: The filling content of SrAl2O3 is 60% by weight. These samples were observed under a D65 light source light box. At the same time, parallel tests were carried out with TiO2, ZnO, BaSO4, CaCO3, SiO2, and Al2O3 and the same base material.

[0025] Tests were also carried out with combinations of 5% by weight of yttrium-stabilized zirconia with 0.25%, 2.5%, or 5% by weight of Al2O3.

[0026] Tests were also carried out with 5% by weight of yttrium-stabilized zirconia and 0.2% by weight of porous silica.

[0027] These materials were formed by vacuum casting.

[0028] These tests showed that the use of yttrium-stabilized zirconia achieved the best balance between whiteness and phosphorescence emission intensity, and increased the whiteness level in the presence of Al2O3, depending on the white quality to be achieved in terms of visible color.

[0029] Tests using porous silica showed a 20% improvement in luminescence performance after 10 minutes, where the luminescence performance was detected according to ISO17514-2003.

Claims

1. A photoluminescent material comprising by weight 19.3% to 54.3% of a polymer matrix, 45% to 80% of a photoluminescent compound, 0.5% to 15% of zirconium oxide, 0.2% to 7% of a fluorescent whitening agent and optionally 0% to 5% of aluminum oxide, 0% to 0.3% of porous silica, and a dye system and additives, wherein the total percentage of the dye system and additives is 0% to 15%.

2. The photoluminescent material according to claim 1, characterized in that The polymer matrix is ​​present in a percentage of 28.5% to 48.5%, the photoluminescent compound is present in a percentage of 50% to 70%, zirconium oxide is present in a percentage of 1% to 10%, and the fluorescent whitening agent is present in a percentage of 0.5% to 5%.

3. The photoluminescent material according to any one of the preceding claims, characterized in that Alumina is present in a percentage of 0.5% to 5% Al2O3, preferably 0.5% to 3%.

4. The photoluminescent material according to any one of the preceding claims, characterized in that The porous silica is present in a percentage ranging from 0.01% to 1%, preferably from 0.07% to 0.3% and more preferably from 0.09% to 0.2%.

5. The photoluminescent material according to any one of the preceding claims, characterized in that The porous silica is derived from a diatom skeleton.

6. The photoluminescent material according to any one of the preceding claims, characterized in that The photoluminescent compound comprises a pigment which is an alkaline earth metal aluminate derivative doped with a rare earth element.

7. Photoluminescent material according to the preceding claim, characterized in that The pigment has the formula Sr(x)Al(y)O(z):Eu 2+ ,Dy 3+ Alkaline earth metal aluminate derivatives doped with europium and dysprosium.

8. Photoluminescent material according to the preceding claim, characterized in that The pigment is Sr4Al 14 O 25 :Eu 2+ ,Dy 3+ and / or SrAl2O4:Eu 2+ ,Dy 3 .

9. The photoluminescent material according to any one of claims 6 to 8, characterized in that The photoluminescent compound consists of the pigment encapsulated in an organic transparent shell or an inorganic transparent shell.

10. The photoluminescent material according to any one of the preceding claims, characterized in that The zirconium oxide is stabilized zirconium oxide, preferably stabilized with yttria.

11. The photoluminescent material according to any one of the preceding claims, characterized in that The polymer matrix comprises 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.

12. The photoluminescent material according to claim 9, characterized in that The organic transparent shell comprises one or more resins from the acrylic family, the polyamide family, the polyolefin family, the epoxy family, the polyurethane family, the fluoroelastomer family and silicone, and the inorganic transparent shell comprises silicon dioxide.

13. The photoluminescent material according to any one of claims 6 to 12, characterized in that The photoluminescent compound includes pigments having different particle sizes.

14. Photoluminescent material according to the preceding claim, characterized in that The pigment has at least a first particle size range of 500 nm to 10 μm in diameter D1 and a second particle size range of 10 μm to 500 μm in diameter D2.

15. The photoluminescent material according to any one of the preceding claims, characterized in that The fluorescent whitening agent is a stilbene derivative containing a sulfonic acid group.

16. An article prepared from or coated with a photoluminescent material according to any one of the preceding claims.

17. Article according to the preceding claim, characterised in that This item is a watch part.