METHOD FOR MANUFACTURING A LUMINOUS WATCH COMPONENT

Description

Technical field of the invention

[0001] The invention relates to a method for manufacturing a luminescent watch component. The present invention also relates to such a watch component obtained from the manufacturing method. Technological background

[0002] The use of photoluminescent materials is quite widespread on the market and for various applications, such as hands or indexes.

[0003] Phosphorescence technology is commonly used in the watchmaking industry through various decoration methods to illuminate hands, dials and other components.

[0004] Fluorescence technology is also used for the decoration of internal casing components via pad printing or spraying using fluorescent pigments to decorate the watch in several colors.

[0005] On the other hand, dials and hands are usually made of a metallic material and then, after several finishing steps, decorated with either phosphorescent or fluorescent ink. Document US 2020 / 201260 A1 discloses the production of a luminescent watch component by extruding a mixture composed of a phosphorescent pigment and a thermoplastic resin.

[0006] This design has several drawbacks: the limitation of luminous performances, the thicknesses of phosphorescent and fluorescent inks are limited to a hundred microns with current decoration processes; a complexity of decoration processes, a white undercoat is sometimes necessary before the phosphorescent decoration in order to have an opaque decoration and to maximize performances; completely opaque components limiting the design. Summary of the invention

[0007] The invention aims to provide a method for manufacturing a luminescent watch component which does not suffer from the drawbacks described above.

[0008] The present invention relates to a method of manufacturing a luminescent watch component for a portable object comprising the following steps: making a premix of a phosphorescent pigment at a level of 10 to 40% by mass, a fluorescent pigment at a level of 1 to 4% by mass and a plasticizer at a maximum level of 10% by mass; mixing a polymer base with said premix and extruding the mixture obtained a first time to obtain a homogeneous polymer mixture; extruding the polymer mixture a second time on a single-screw extrusion machine equipped with a die allowing the production of calendered strips with a thickness of at least 0.3 mm; cutting the strip to obtain the desired luminescent watch component;

[0009] According to other advantageous variants of the invention: the polymer base is a thermoplastic polymer base; the polymer base is transparent to wavelengths of the near-ultraviolet spectrum and to wavelengths of the visible spectrum; the thermoplastic polymer base is chosen from polycarbonate, PMMA, etc. the extruded strip is cooled to room temperature; the first extrusion is carried out via a twin-screw extruder; the second extrusion is carried out via a single-screw extruder; the strip obtained during the second extrusion is in the form of a strip in two parts, a first part called the upper part is formed by the luminescent mixture obtained at the end of the first extrusion, and the second part called the lower part is formed by a strip of white polymer material. Detailed description of the invention

[0010] The present invention relates to a method of manufacturing a luminescent watch component for a portable object.

[0011] Luminescent means that the component is photoluminescent, fluorescent, phosphorescent, or a combination.

[0012] Phosphorescent means an element having the property of being able to absorb light and re-emit it at a longer wavelength. The emission persists for a certain time after the light excitation has ceased. The ink contains at least one photoluminescent agent to confer the photoluminescence properties to the ink. Preferably, the luminescent agent is a fluorescent agent. It is advantageously chosen from inorganic fluorophores and organo-lanthanide complexes. Alternatively, the fluorescent agent may also be chosen from organic fluorophores. It may be, for example, fluorescein, europium 1,3-diphenyl-1,3-propanedionate-1,10-phenantroline, doped gadolinium oxysulfide, doped barium and magnesium aluminate, doped lithium aluminate, doped strontium molybdate.

[0013] Fluorescent means an element that has the property of being able to absorb light and re-emit it at a longer wavelength. Emission ceases when light excitation ceases.

[0014] The various stages of the manufacturing process according to the invention will now be described.

[0015] During a first step, a pre-mixture of a phosphorescent pigment at a level of 10 to 40% by mass, a plasticizer and a fluorescent pigment at a level of 4% by mass is carried out in order to obtain a sufficiently visible daytime color without compromising on phosphorescent performance. The quantity of luminescent particles is chosen so as to be sufficient to be able to distinguish the decorated watch component and make it easily and immediately visible in the dark. The plasticizers are present at a maximum level of 10% by mass to adjust the malleability of the polymer base thereafter and thus make it less brittle during handling and machining. This pre-mixture makes it possible to coat the pigments, to prevent their abrasion and to facilitate their incorporation into the polymer base for the rest of the process. Polyethylenes, paraffins, or polydimethoxysilanes are commonly used as plasticizers.

[0016] The daytime fluorescent pigment is added at a rate of 1 to 4% by mass, which makes it possible to modify the visible color during the day because these fluorescent pigments are colored. Daytime fluorescent pigments are the equivalent of "Daylight fluorescent pigment", these pigments have a daytime color unlike "UV Light fluorescent pigment" which are neutral in color under daylight but excited by UV light. They also make it possible to strengthen and modify the phosphorescent effect via an energy conversion. For example, if we use a blue emission phosphorescent pigment "Light Blue", and we add pink fluorescent pigment, then the final night emission color will be pinkish / purple. It is therefore possible, depending on the mixtures made, to match the fluorescent color visible during the day with the phosphorescent color visible at night.

[0017] In the next step, a mixture is made with the premix and a polymer base, then a first extrusion of the premix to obtain a homogeneous mixture and to distribute the luminescent particles well in the polymer base and thus avoid clusters of particles which would harm both the visual rendering on the watch component and the performance of the luminescent pigments. The base polymer is thus mixed with the premix based on plasticizer and pigments in order to allow sliding between the chains.

[0018] The polymer base used can be a thermoplastic polymer such as polycarbonate (PC), polyamide (PA), Methylmethacrylate Acrylonitrile Butadiene Styrene (MABS), polyethylene terephthalate glycol (PETg), etc. Advantageously, the polymer base used is both transparent to wavelengths in the near-ultraviolet spectrum and to wavelengths in the visible spectrum, this allows better absorption of light by the pigments.

[0019] Preferably, extrusion is carried out using a twin-screw extruder to obtain a homogeneous mixture and good dispersion of the pigments. At the end of this first extrusion, the material generally comes out in the form of granules, which facilitates transport and storage for the rest of the process.

[0020] The material obtained during the first extrusion is then re-extruded on a single-screw extrusion machine equipped with a die allowing the production of calendered strips with a thickness of at least 0.3 mm. The thickness can of course be varied depending on the watch component that one wishes to obtain at the end. It was noted by the inventors that below a thickness of 0.3 mm, the parts are too fragile and do not hold mechanically. For example, a 0.15 mm hand is too flexible and has inhomogeneous mechanical performance, the hand not supporting its own weight. Thus, in order to guarantee good performance and good hold, a minimum thickness of 0.3 mm is desired.

[0021] According to a variant of the invention, the profile obtained during the second extrusion is in the form of a strip in two parts, a first part called the upper part is formed by the mixture obtained at the end of the first extrusion, and the second part called the lower part is formed by a strip of white polymer material. Such an arrangement makes it possible to obtain a reflective layer under the layer of luminescent material and thus to obtain better performance.

[0022] There is no upper limit on thickness. It is possible to directly determine the thickness of the part and cut the part if it is flat. It is also possible to extrude thicker strips and machine the parts after cutting to also adjust their thickness. For example, for needles, to be able to cut the top of the needle wider and a thinner foot. For cost reasons, the die can be adapted to the larger needle section in order to extrude the needle profile.

[0023] Once the compound is re-extruded, the strip is cut, via stamping or laser cutting for example, to obtain the desired luminescent watch component.

[0024] Finally, a final optional step consists of decorating the resulting watch component by printing or engraving so that only a luminescent part of the component is visible.

[0025] According to the invention, such a method makes it possible to obtain a luminescent dial or hands. Example of realization

[0026] A premix is made by mixing a plasticizing agent at a maximum height of 10% by mass with a photoluminescent pigment at a height of 10 to 40% by mass (particle size D50: 15-20 µm) and a fluorescent pigment is then added at a height of 1 to 4% by mass. The plasticizing agent improves the strength of the material and optimizes the matrix-phosphorescent pigment interactions.

[0027] A polymer base is then mixed into the premix.

[0028] The mixture is homogenized via a first twin-screw extrusion.

[0029] A second extrusion of the compound is then carried out to form a strip with a thickness of at least 0.3 mm.

[0030] Cooling the strip to room temperature.

[0031] Once the strip is formed and cooled, it is cut via laser or stamping to obtain the desired watch parts.

Claims

1. Method for manufacturing a luminescent timepiece component for a portable object, said method being characterised in that it comprises the steps of: - producing a pre-mixture of a phosphorescent pigment in an amount of 10 to 40% by weight, a fluorescent pigment in an amount of 1 to 4% by weight and a plasticiser in a maximum amount of 10% by weight; - mixing a polymer base with said pre-mixture and extruding a first time the mixture obtained to obtain a homogeneous polymer mixture; - extruding a second time the mixture on a single-screw extruder equipped with a die for producing calendered strips of a thickness of at least 0.3 mm; - cutting the strip to obtain the desired luminescent timepiece component.

2. Manufacturing method according to claim 1, characterised in that the polymer base is a thermoplastic polymer base.

3. Manufacturing method according to claim 1 or 2, characterised in that the polymer base is transparent at wavelengths of the near ultra-violet spectrum and at wavelengths of the visible spectrum.

4. Manufacturing method according to claim 1 to 3, wherein the thermoplastic polymer base is selected from polycarbonate, PMMA.

5. Manufacturing method according to claims 1 to 4, wherein the extruded strip is cooled at ambient temperature.

6. Manufacturing method according to claims 1 to 5, wherein the first extrusion is performed via a twin-screw extruder.

7. Manufacturing method according to claims 1 to 6, wherein the strip obtained during the second extrusion is in the form of a strip in two portions, a first portion referred to as upper is formed by the luminescent mixture obtained at the end of the first extrusion, and the second portion referred to as lower portion is formed by a strip made of white polymer material.

8. Manufacturing method according to claims 1 to 7, wherein the luminescent timepiece component formed is a dial or a hand.