More efficient photoluminescent materials

Abstract

The present invention relates to a photoluminescent material comprising, by weight, a polymer matrix in a percentage of 19.99% to 54.99%, a photoluminescent compound in a percentage of 45% to 80%, porous silica in a percentage of 0.01% to 1% and optionally comprising a dye system and an additive wherein the total percentage of the dye system and the additive is 0% to 15%. The invention also relates to articles prepared from or coated with the photoluminescent material.

Description

Technical Field

[0001] The present invention relates to a photoluminescent material having improved luminescent properties. Background Art

[0002] Phosphorescent materials made from mixtures of transparent or translucent materials and photoluminescent pigments are known, the photoluminescent pigments being prepared from inorganic oxides doped with rare earth elements. Examples include mixtures of borosilicate and 50% strontium aluminate doped with europium or dysprosium (Eu 2+ , Dy 3+ :SrAl2O4), or mixtures of acrylic resins and 50% strontium aluminate doped with europium or dysprosium. The light decay of these materials is exponential at the beginning. If we start with a brightness of several tens of Cd / m 2 and place the material in the dark after saturating it with light energy, the brightness after 10 minutes in the dark will be less than 1 Cd / m 2 . Then, the light decay slowly approaches an asymptote at a few mCd / m 2 , which explains why these materials can maintain visible luminescence persistence in the dark for up to 12 hours. Good passive readability of diving equipment requires these luminescent materials, so progress in luminescent properties is still highly desirable.

[0003] Since phosphorescent pigments are sensitive to humidity, it is currently desirable to prepare photoluminescent decorative elements to encapsulate the pigments in a transparent material, thereby obtaining a photoluminescent material. For aesthetic reasons, especially the perception of daylight, these photoluminescent materials can also be dyed using a dye system, which is a mixture of pigments and additives.

[0004] It has been recognized that compounds used in photoluminescent materials, including coloring pigments, have a quenching effect on luminescent properties, and the brightness of phosphorescent materials is the result of physicochemical interactions between various compounds in the photoluminescent material. Summary of the Invention

[0005] The present invention includes the development of a novel formulation for a photoluminescent material that can limit the quenching effect associated with the compounds added to the formulation.

[0006] To this end, it is proposed to add a porous silica type dopant derived from algae to the formulation. The porous silica comes from diatom skeletons. They are microalgae, which are single-celled organisms with a silica skeleton. In fact, 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 effectively carry out photosynthesis.

[0007] According to the present invention, adding a limited percentage of porous silica to a photoluminescent material can significantly improve the luminescence performance, and this content is less than or equal to 1% by mass.

[0008] More specifically, the present invention relates to an article prepared from a photoluminescent material, which photoluminescent material contains, by weight, a polymer matrix in a percentage of 19.99% to 54.99%, a photoluminescent compound in a percentage of 45% to 80%, porous silica in a percentage of 0.01% to 1%, and optionally contains a dye system and additives, wherein the total percentage of the dye system and additives is 0% to 15%. Detailed Description

[0009] The present invention relates to a photoluminescent material containing porous silica. The present invention also relates to an article coated with or prepared from such a photoluminescent material. The article can be, for example, a watch part. More specifically, the article can be a part selected from a non-limiting list, which non-limiting list includes a watch middle part, a watch back cover, a bezel, a crown, a button, a bracelet link, a bracelet, a tongue buckle, a clasp, a dial, a flange, a date disc, a pointer, and a dial scale.

[0010] The photoluminescent material comprises (consists of) a polymer matrix, a photoluminescent compound, porous silica, and optionally contains a dye system and additives.

[0011] Based on the total weight of the photoluminescent material, the porous silica is present in a weight percentage of 0.01% to 1%, preferably 0.07% to 0.3%, more preferably 0.09% to 0.2%. The porous silica is porous silica derived from a diatom skeleton. Generally, the average diameter of the pores can be about 500 nm. The porous silica can also be synthetic porous silica. Regarding synthetic silica, the pores generally have an average diameter of 0.1 μm to 3 μm. The polymer matrix is present in a weight percentage of 19.99% to 54.99%, preferably 29.93% to 49.93%, more preferably 29.91% to 49.91%. This can include all polymers that are transparent or translucent in the visible range. For example, it can be one or more of the following polymers: resins from the acrylic family, polyamide family, polyolefin family, epoxy family, polyurethane family, fluorinated elastomer family, and silicone. 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 a rare earth element-doped alkaline earth metal aluminate derivative. More specifically, the pigment can be strontium aluminate doped with europium or 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+ , and 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 makes it possible to combine small particles and large particles, where the small particles form shallow 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 pigment can have a first particle size range with a diameter D1 of about 500 nm to 10 μm, ideally 500 nm to 5 μm, and a second particle size range with a diameter D2 of about 10 μm to 500 μm, ideally 10 μm to 20 μm. The particle sizes are measured by laser particle size analysis according to ISO 13320:2020 and can be equipped with SEM analysis with 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% by weight, a second fraction of 5 μm to 20 μm at 60% by weight, and a third fraction of 20 μm to 50 μm at 20% by weight.

[0012] The pigments can 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. The photoluminescent material optionally contains 0% to 15%, preferably 0% to 5% of a dye system and additives. The dye system preferably contains organic dyes that do not absorb within the emission wavelength range of the photoluminescent pigment. These organic dyes can be fluorescent pigments or dyes that absorb more in the UV range and emit in the visible spectrum. For example, it can be an organic fluorescent pigment or dye, 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. For example, it can be a translucent pigment or dye 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-type nanofillers for adapting the viscosity parameters of the mixture, etc.

[0013] The method includes mixing one or more polymers for forming the polymer matrix with a dispersant preferably. This first mixture is mixed with the photoluminescent pigment, which can have been pre-encapsulated. Then porous silica is added to this second mixture, and any dye system and additives can be added. These mixtures can be prepared from a liquid resin using an accelerating mixer or a paddle mixer. The resulting mixture can then be formed by extrusion molding. These mixtures can also be prepared in a twin-screw extruder or a high-speed mixer for producing thermoplastic mixtures and turned into pellets, which can be reused for injection molding.

[0014] Tests were carried out by adding 0.09 wt% to 0.2 wt% of porous silica with respect to the total weight of the photoluminescent material to a two-component epoxy resin with an amide hardener. A photoluminescent pigment with a filling rate of 50% with respect to the total weight of the photoluminescent material was added, and this pigment was formed from strontium aluminate doped with europium and dysprosium.

[0015] The material is formed by casting the mixture. A person skilled in the art can easily transform this formulation into other types of polymer materials, which can be injection molded or extruded. This formulation can also be easily transformed into a dispersion of the polymer in a solvent, so as to be applied by techniques such as screen printing, pad printing, spraying, etc.

[0016] The luminescence properties were measured according to the ISO 17514-2003 standard, and an increase of 5% to 7% was observed compared to the same composition without porous silica.

Claims

1. A photoluminescent material comprising by weight 19.99% to 54.99% of a polymer matrix, 45% to 80% of a photoluminescent compound, 0.01% to 1% of porous silica and optionally 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 29.93% to 49.93%, the photoluminescent compound is present in a percentage of 50% to 70%, and the porous silica is present in a percentage of 0.07% to 0.3%.

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

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

5. 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.

6. 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.

7. 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 .

8. The photoluminescent material according to any one of claims 5 to 7, characterized in that The photoluminescent compound consists of the pigment encapsulated in an organic transparent shell or an inorganic transparent shell.

9. 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.

10. The photoluminescent material according to claim 8, 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.

11. The photoluminescent material according to any one of claims 5 to 10, characterized in that The photoluminescent compound includes pigments having different particle sizes.

12. 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.

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

14. Article according to the preceding claim, characterised in that The product is a watch part.