Method for producing light needles by replicating microstructures

Abstract

Method for manufacturing a luminous watch hand (80), according to which, on the one hand, in a first group of operations (1000), at least one light guide (30) or a strip of light guides (35) is manufactured separately by replicating microstructures initially made on a master (1), and on the other hand, in a second group of operations (2000), at least one hand body (50) or a strip of hand body (55) is manufactured separately, which is assembled with said at least one light guide (30) or said strip of light guides (35) by a gluing operation (600) and an assembly operation (700), before finishing said luminous hand (80) by a final cutting operation (800).

Description

Technical field of the invention

[0001] The invention relates to a method for manufacturing luminous watch hands.

[0002] The invention also relates to needles manufactured according to this process.

[0003] The invention relates to the field of watchmaking hand manufacturing, and in particular luminous hands. Technological background

[0004] Documents EP3845974 A1 and WO 2022 / 122199 A1 describe the operating principle of fluorescence-illuminated needles and methods of manufacturing such needles, the main components of which are a metal sheet, a low refractive index layer whose function is to optically isolate the metal surface, a medium refractive index layer whose function is to guide the fluorescent light to the edges of the needle, and the deposition of fluorescent pigments which are excited by a remote primary source, for example an LED or similar.

[0005] Document WO 2022 / 122199 A1 describes in particular a manufacturing process based on the deposition of various resins onto a pre-cut metal sheet. This process is difficult to implement because it proves challenging to keep a liquid resin contained within an opening, in this case, the pre-cut metal sheet. The use of a sacrificial film to seal the opening all around the needle is also particularly delicate. Furthermore, with such a process, the needle tip attachment must be cut beyond the resin that acts as a light guide to allow light extraction all around the needle. The attachment therefore remains visible. Summary of the invention

[0006] The invention aims to develop an industrializable process for the manufacture of luminous needles.

[0007] For this purpose, the invention relates to a method for manufacturing luminous watch hands according to claim 1.

[0008] The invention also relates to needles made according to this process.

[0009] The invention relates to the field of watchmaking display, and in particular to watch hands, more particularly luminous hands. Brief description of the figures

[0010] The goals, advantages, and characteristics will be better understood by reading the detailed description that follows and the attached drawings where: THE figures 1 to 5illustrate, schematically, the steps of the process according to the invention, in several sequence variations, in which a first group of operations for manufacturing a light guide and a second group of operations for manufacturing needle bodies are carried out in parallel, followed by a third group of assembly operations and then a fourth group of finishing operations: ∘ the figure 1 concerns the individual manufacturing of light guides, and the individual manufacturing of needle bodies, and the gluing of the needle body during the third group of assembly operations; ∘ the figure 2 concerns the individual manufacturing of light guides, and the individual manufacturing of needle bodies, and the gluing of the light guide during the third group of assembly operations; ∘ the figure 3concerns the strip manufacturing of light guides, and the unit manufacturing of needle bodies, and the gluing of the needle body during the third group of assembly operations; ∘ the figure 4 concerns the strip manufacturing of light guides, and the unit manufacturing of needle bodies, and the gluing of the needle body during the third group of assembly operations; ∘ the figure 5 concerns the fabrication of light guides from strips, and the fabrication of needle bodies from strips, and the gluing of the needle body during the third group of assembly operations; figures 6 and 7 represent, schematically and in plan view, two examples of light needles made according to the invention, coupled with groups of three LEDs each. Detailed description of the invention

[0011] The method according to the invention aims to manufacture watch hands, in particular watch hands, the edge of which can be illuminated by optical coupling of light in a light guide, so that the hand can be luminous.

[0012] In particular, this process aims to enable a monolithic assembly of a needle body, especially metallic, an optical guidance system, means of coupling light in the optical guide and of diffusing light outside the guide.

[0013] The invention notably uses the techniques described in document EP3845974A1, incorporated herein by reference.

[0014] This process relies on the replication of microstructures.

[0015] The method according to the invention is based on the assembly, notably by gluing, of needle bodies with a pre-cut light guide. More specifically, the needle bodies are superimposed on this light guide.

[0016] The light guide can be in the form of a sheet or strip, and can serve as a transport substrate.

[0017] Similarly, a band of needle bodies can serve as a transport substrate.

[0018] Needle bodies can be manufactured in a conventional manner, well known to the person skilled in the art, and are similar to standard needles.

[0019] The light guide consists primarily, but not exclusively, of a thin, transparent plastic substrate with minimal diffusion, onto which a resin is deposited and structured. The plastic substrate can be made of various materials, including but not limited to PET, TAC, PMMA, and PC. PET and TAC offer excellent optical / mechanical compromises.

[0020] The process of depositing and structuring the resin onto the plastic substrate requires choosing a resin with a refractive index close to that of the plastic sheet. More specifically, and without limitation, the resin structuring is done by UV embossing, which can be described as embossing under ultraviolet light, to create areas of light coupling and extraction.

[0021] The glue used to assemble the plastic substrate and the needle body must be transparent, non-diffusing, and have an optical index lower than that of the substrate.

[0022] The process involves different operations, the chronological order of which may differ, as explained below.

[0023] Parallel operations involve the manufacture of light guides on the one hand, and needle bodies on the other.

[0024] A first group of operations 1000 concerns the manufacture of a light guide: either for the manufacture of unitary light guides 30, or for the manufacture of strips 35 of light guides.

[0025] In both cases, the first operation involves creating a master 1, which is a positive model of a micro-relief to be transferred onto the light guides. More specifically, and without limitation, this master 1 is made from a material such as PMMA or similar, which is machined using engraving tools, such as laser engraving (including CO2 laser, picolaser, or femtolaser), micro-milling, thermogravure, or similar methods. On this master 1, the relief of microstructures for coupling and extracting light is created, which will then be reproduced in a replication process. Various microstructures are thus created, some designed to couple / extract light, and others as alignment marks for subsequent manufacturing steps.

[0026] A second operation 200 consists of creating a negative tool 2, such as a pad, based on the master 1, to print microstructures; this negative tool 2 can be made of nickel, silicone, or any suitable material. A plastic substrate 20 is used, onto which a suitable resin is deposited. The substrate 20 can be made of PET or TAC, for example, and have a thickness of 50 to 100 micrometers. The replication of the microstructures is carried out by reproducing the microstructures created on the master 1 onto the plastic substrate 20, using this resin, under the action of the pad 2, which allows the microstructures to be printed into the resin previously deposited on the plastic substrate 20, thus producing at least one raw light guide 30.This replication can be achieved through UV embossing, hot embossing (also known as hot stamping), or any similar process that allows for precise reproduction of microstructure details. This replication process can be performed individually, in sheets (plate-to-plate or roll-to-plate depending on the manufacturing method), or in strips. The UV embossing process is particularly efficient due to its mechanical capabilities, notably the ability to replicate structures up to 30 micrometers deep. The output of this second operation is either a raw light guide 30 in the case of individual production, or a strip of light guides 35, comprising a plurality of raw light guides 30, in the case of strip production.

[0027] A third operation 300 concerns the pre-cutting of the light guide: in order to glue a light guide and a needle together, the raw light guide 30 must be cut at the point where the needle's barrel will be placed. Without this, assembly would not be possible, since the needle's barrel would prevent the entire surface of the needle from making contact. This cut is made using cutting tools 310, including but not limited to a CO2 laser, and must be aligned with the various microstructures present on the raw light guide 30. Preferably, alignment marks have been previously placed on the master 1 and reproduced on the raw light guide 30 for this purpose.

[0028] In the case of manufacturing a strip of light guides 35, it is possible to separate each raw light guide by cutting before, during, or after this third cutting operation 300.

[0029] In parallel with this first group of operations 1000 relating to the manufacture of a light guide, a second group of operations 2000 includes a needle body manufacturing operation 400, either individually for the manufacture of a needle body 50, or in strip form according to a standard process with final die-cutting. In the case of strip production, the separation of the needle bodies 50 can take place immediately after the needle body manufacturing operation 400, in a separation operation 500 using separation means 510, such as die-cutting means or other suitable cutting means. In an alternative, a strip of needle bodies 55 can be retained until a subsequent separation in the process.

[0030] A third group of assembly operations 3000 includes a gluing operation 600 for gluing the raw light guide 30, or the strip of light guides 35, and / or the needle body 50, or the strip of needle bodies 55, prior to the assembly between the light guide and the needle body. For this purpose, an adhesive 6 with a lower refractive index than that of the light guide is selected and deposited on the needle body and / or on the light guide, typically by means of dispensing 610.

[0031] THE Figures 1 , 3 à 5 illustrate the case where gluing is carried out on the needle bodies, unit 50 in Figures 1 And 3 , or in 55 needle body strips figures 4 And 5 The glued product is then respectively a glued needle body 68, or a glued needle body strip 685. figure 2illustrates the case where the light guide is glued, this figure shows a unit light guide 30, which becomes a glued light guide 38 after the gluing operation 600.

[0032] This gluing operation 600 is followed, within the time frame dictated by the properties of the chosen adhesive, by an assembly operation 700, during which the needle body is optically aligned and positioned against the light guide before being bonded by polymerization. More specifically, but not limited to, a UV optical adhesive is chosen due to its rapid polymerization. Advantageously, robotic handling methods 710 are used, such as a robot coupled with optical recognition systems to ensure correct alignment and positioning. The output of this assembly operation 700 is a raw, assembled needle 70, which then requires finishing.

[0033] In the case of strip manufacturing, whether it be a strip of light guides 35 and / or a strip of needle bodies 55, the third group of operations 3000 can be carried out similarly. However, the assembly operation 700 is more complex to implement when assembling a strip of light guides 35 with a strip of needle bodies 55.

[0034] A fourth group of operations 4000 includes a final cutting operation 800, which aims to finish and release each luminous needle 80. This final cutting operation 800 is carried out in particular by laser cutting means such as already mentioned, in particular by femtolaser which gives good results on PET, or cutting by a CO2 laser, or others.

[0035] In the case of a single-unit production, during this final cutting operation (800), the light guide can finally be cut to release the hand. The cut is preferably made approximately 0.1 mm wider than the nominal width of the hand, in order to allow light to escape around the hand and towards the wearer of the watch, thanks to the extraction microstructures designed for this purpose.

[0036] The process described above details the manufacture of needles that will be illuminated around their circumference. It is also possible, in the case of skeleton needles, for the illumination to occur through the needle's openings, or both. The illumination design is not limited to the entire circumference and, depending on the position of the extractors and the final cut, can be on only one side, or only on the needle tip, for example.

[0037] An alternative process can be implemented, comprising similar steps but in a different order. Specifically, the process can include pre-cutting the hands into strips. Advantageously, the cut is made approximately 0.1 mm narrower than the nominal width of the assembled raw hand 70 in order to allow light to escape around the hand towards the wearer of the watch through the extraction microstructures designed for this purpose. Simultaneously, the light guide can be manufactured in strip form, as a light guide strip 35, and the light guide can be cut and bonded. During the assembly operation between the hand body and the light guide, adhesive with a lower refractive index than that of the light guide is applied to the light guide (alternatively to the hand body), typically by dispensing. The light guide is then optically aligned and placed against the hand body to polymerize the adhesive.During the final cutting operation, the needles can be cut into strips to release the assembled needle. Cutting is advantageously done by laser or die.

[0038] In summary, the microstructures are sufficient to exploit the luminescence that comes from an external light source such as an LED 90, or LEDs 90, whose light "enters" an input light guide 70 of the luminous needle 80 under the needle head and "exits" at the level of the microstructures of the light guide 30 which are arranged along the length of the needle. figures 6 and 7 illustrate examples of luminous needles, each transmitting the light emitted by three LEDs arranged in a triangle, and where a light coupling zone relates to the input light guide 70, which is either of revolution as on the figure 6 or occasional, as on the figure 7, a peripheral zone is that of the extraction of light by the micro-structures of the light guide 30 all along the needle, and at its end, slightly overhanging relative to the needle body 50. This ensures continuity of light, even if some of the light extraction structures happen to be cut or removed, depending on the precision of the cutting alignment.

[0039] Regarding the materials, the light guide is advantageously a combination of a plastic substrate 20 (support) with a resin in which the various micro-structures are printed, in particular by the preferred method of UV-embossing, which gives very good results, even if hot-embossing of the micro-structures directly into the substrate 20 is also conceivable.

[0040] Both the substrate and the resin must be as transparent as possible to avoid light loss. Using "clear" materials is advantageous because they are readily available in the desired thicknesses. In theory, colored materials (e.g., fluorescent) could be used while maintaining transparency. However, it is essential that the refractive indices of the two materials be as close as possible. The refractive index of the adhesive bonding the guide to the needle must be as low as possible compared to that of the substrate to optically isolate the guide. It is not necessary to insert any particles whatsoever into the light guide.

Claims

1. Method for manufacturing a luminous watch hand (80), characterized in that separately manufacturing, on the one hand in a first group of operations (1000) at least one light guide (30) or a strip of light guides (35) by replication of micro-structures initially produced on a master (1), and on the other hand in a second group of operations (2000) at least one needle body (50) or a strip of needle bodies (55), which is assembled with said at least one light guide (30) or said strip of light guides (35) by a gluing operation (600) and an assembly operation (700), before finishing said light needle (80) by a final cutting operation (800).

2. Method according to claim 1, characterized in that, in said first group of operations (1000), in a first operation (100) said master (1) is produced with engraving means (110), which is a positive model of a micro-relief to be transferred onto said at least one light guide (30) or said strip of light guides (35), said micro-relief comprising micro-structures, some provided for the coupling and extraction of light, and others as alignment marks for other manufacturing steps.

3. Method according to claim 2, characterized in that, in said first group of operations (1000), in a second operation (200) a negative tool (2) is produced on the basis of said master (1), to print micro-structures, a substrate (20) made of plastic material is provided, on which a resin is deposited, and micro-structures are replicated by reproducing the micro-structures created on said master (1) on said plastic substrate (20), by means of said resin, under the action of said negative tool (2) which makes it possible to print said micro-structures in said resin previously deposited on said plastic substrate (20) to produce at least one raw light guide (30) or a strip of light guides (35).

4. Method according to claim 3, characterized in that said substrate (20) is chosen in PET or TAC, with a thickness of 50 to 100 micrometers.

5. Method according to claim 3 or 4, characterized in thatsaid replication of said micro-structures is carried out by UV-embossing or by hot-embossing.

6. Method according to one of claims 3 to 5, characterized in that after said second operation (200), in a third operation (300) the raw light guide is pre-cut at the location where the needle barrel is to be placed, with cutting means (310) or a CO2 laser, and it is aligned with said alignment marks present on the raw light guide.

7. Method according to one of claims 1 to 6, characterized in that during said final cutting operation (800) each said luminous hand (80) is finished and released, with laser cutting means, and the cut is made approximately 0.1 mm wider than the nominal width of the hand, in order to allow the light to escape around the hand and towards the wearer of the watch, thanks to said extraction micro-structures provided for this purpose.

8. Method according to one of claims 1 to 7, characterized in that the said process is implemented by manufacturing a needle to be illuminated on its periphery, on which the said micro-structures are replicated.

9. Method according to one of claims 1 to 8, characterized in that said method is implemented to manufacture a skeleton needle to be illuminated at least through the openings of said needle.

10. Method according to one of claims 1 to 9, characterized in that the said process is implemented to manufacture a needle to be illuminated on one side only, or only on the tip of the needle.

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